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Title: Principles and practice of agricultural analysis. Volume 2 (of 3),
Fertilizers

Author: Harvey Washington Wiley

Release date: December 17, 2023 [eBook #72438]

Language: English

Original publication: Easton: Chemical Publishing Co., 1894

Other information and formats: www.gutenberg.org/ebooks/72438

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*** START OF THE PROJECT GUTENBERG EBOOK PRINCIPLES
AND PRACTICE OF AGRICULTURAL ANALYSIS. VOLUME 2 (OF 3),
FERTILIZERS ***

PRINCIPLES AND PRACTICE
OF
AGRICULTURAL ANALYSIS.
A MANUAL FOR THE ESTIMATION OF
SOILS, FERTILIZERS, AND
AGRICULTURAL PRODUCTS.

FOR THE USE OF ANALYSTS, TEACHERS, AND STUDENTS
OF AGRICULTURAL CHEMISTRY.

VOLUME II.

FERTILIZERS.

BY HARVEY W. WILEY,
Chemist of the U. S. Department of Agriculture.
EASTON, PA.,
Chemical Publishing Co.,
1895.
COPYRIGHT, 1895,
By Harvey W. Wiley.

PREFACE TO VOLUME SECOND.
In this volume an attempt has been made to treat the subject of
fertilizers and fertilizing materials in the manner followed in the first
volume with soils. The general principles of fertilizer manufacture and
application have been presented in so far as they seemed to throw light on
the rational method of examination and analysis. The standard methods of
analysis in use in this and other countries, have been presented with
sufficient fullness for the guidance of the skilled worker, and the
information of the student. To those who make use of a book only for
routine work or for preparation for an examination, this volume, as its
predecessor, will be found to have little attraction. This fact, however, will
not be a cause of regret to the author whose purpose has been, avowedly, to
present to the busy worker and student a broad view of a great subject
which each one does not have the time to search out for himself.
It is a matter of regret, however, that the contents of the volume have
again exceeded all expectations. It was found impracticable to secure any
greater condensation without departing from the purpose, and impairing the
completeness of the work. When work is done with no prospect of financial
compensation, it is gratifying to find it appreciated, and the author will be
content to have this volume meet with as kindly a reception as has been
accorded volume one.

Harvey W. Wiley.
Washington, D. C.,
End of July, 1895.

TABLE OF CONTENTS OF
VOLUME SECOND.
PART FIRST.
PHOSPHATES AND PHOSPHATIC FERTILIZERS.

Introduction, pp. 1-4.—Natural fertilizers; Waste matters as fertilizing
materials; Valuation of fertilizing ingredients.
General Analytical Processes, pp. 4-15.—Taking samples; Fertilizing
minerals; Mixed fertilizers; French methods of taking samples; Sampling
stable manures; Preparation of sample in laboratory; French and German
methods; Drying fertilizer samples; Moisture in acid phosphates.
Analysis of Mineral Phosphates, pp. 15-39.—Constituents to be
determined; Direct estimation of phosphoric acid; Official method;
Preparation of solution; Use of tartaric acid; Determination of water and
organic matters; Carbon dioxid; Soluble and insoluble matter; Silica and
insoluble bodies; Estimation of lime; Ammonium oxalate method;
Immendorff method; Estimation of iron and alumina; The acetate and Hess
methods; Methods of Jones and Crispo; Geological Survey method; Method
of Marioni and Fasselli; Method of Krug and McElroy; Method of Wyatt;
Estimation of magnesia; of sulfuric acid; of fluorin.
General Methods for Phosphoric Acid, pp. 39-57.—Preliminary
considerations; Estimation as stannic phosphate; Water soluble acid; Citrate
insoluble acid; Total phosphoric acid; Norwegian methods; German
experiment station methods; Soluble phosphoric acid; Swedish methods;
Dutch methods; Errors in molybdate method; Color of pyrophosphate;
Solution in sulfuric acid.
The Citrate Method, pp. 57-70.—General principles; Halle method;
Swedish method; Methods adopted at the Brussels Congress; Dutch method
for citrate soluble acid; Comparative accuracy of citrate and molybdate
methods.

Basic Phosphatic Slags, pp. 70-86.—History and manufacture;
Composition; Molecular structure; Solubility; Separation and solution;
Estimation of total acid; Alternate method; Halle method of analysis; Dutch
method; Estimation of citrate soluble acid in basic slags; Wagner’s shaking
and digesting apparatus; Estimation of caustic lime in slags; Detection of
adulteration.
Volumetric Determination of Phosphoric Acid, pp. 86-106.—
Classification of methods; Uranium method; Preparation of sample;
Precipitation of the phosphoric acid by magnesium citrate; Composition of
magnesium citrate solution; Solution of ammonium magnesium phosphate;
Preparation of standard solutions; Verifying standard solutions; Conduct of
the analysis; Phosphoric acid in superphosphates; Determination of soluble
and reverted phosphoric acid; Conclusions.
Titration of the Yellow Precipitate, pp. 106-118.—Pemberton’s method;
Conduct of the analysis; Reactions; Calculation of results; Comparison with
Official method; Titration as a lead compound; Water soluble acid;
Estimation of phosphoric acid in presence of a large excess of iron;
Emmerton method; Method of Dudley and Noyes; The Jones reductor; The
volumetric silver method.
Technical Determination of Phosphoric Acid, pp. 118-125.—
Desirability of methods; Reagents employed; Conduct of the molybdenum
method; Conduct of the citrate method; Treatment of mineral phosphates
and basic slags; Analysis of superphosphates.
Miscellaneous Notes on Phosphates and Phosphatic Fertilizers, pp.
126-150.—Time required for precipitation; Examination of the
pyrophosphate; Iodin in phosphates; Chromium in phosphates; Estimation
of Vanadium; Fluorin in bones; Note on separation of iron and alumina
from phosphoric acid; Ammonium citrate soluble acid; Influence of time
and strength of solvent on solution; Arbitrary Determination of reverted
phosphoric acid; Digestion apparatus of Huston; Huston’s mechanical
stirrer; Citrate method with small percentage of phosphoric acid; Direct
precipitation of the citrate soluble phosphoric acid; Availability of
phosphatic fertilizers; Direct weighing of the molybdenum precipitate.
Chemistry of the Manufacture of Superphosphates, pp. 150-156.—
Reactions with phosphates; with fluorids; with carbonates; with iron and

alumina; with magnesium compounds; Determination of quantity of
sulfuric acid; Phosphoric acid superphosphates; Authorities cited in Part
First.

PART SECOND.
NITROGEN IN FERTILIZERS AND
FERTILIZING MATERIALS.

Kinds of Nitrogen in Fertilizers, pp. 161-169.—Determination of state
of combination; Microscopic examination; Seeds and seed residues; Fish
scrap; Dried blood and tankage; Horn, hoof, and hair; Ammoniacal
nitrogen; Nitrogen in guanos; Nitric nitrogen.
Methods of Analysis, pp. 169-192.—Classification of methods; Official
methods; Combustion in copper oxid; Official volumetric method; Mercury
pump; Combustion furnace; Process of combustion; Method of Johnson and
Jenkins; Calculating results; Reading barometer; Tension of aqueous vapor;
Aqueous tension in solutions of potassium hydroxid; Tables for calculating
results; Soda-lime process; Official French method; The ruffle soda-lime
method; Official ruffle method; Boyer’s ruffle method.
Moist Combustion Process, pp. 192-220.—Historical; Method of
Kjeldahl; Theory of the reactions; Preparation of reagents; Dutch kjeldahl
method; Halle kjeldahl method; Official kjeldahl method; Distillation
apparatus; Patrick’s distilling flask; Modification of the kjeldahl process;
Method of Wilfarth; Method of Asboth; Method of Jodlbaur; Dutch
jodlbaur method; Halle jodlbaur method; Official method for nitric
nitrogen; Method of Scovell; Gunning method; Reactions of the gunning
method; Official gunning method; Gunning method adapted to nitrates.
Determination of Nitrogen in Definite Forms of Combination, pp. 221-
231.—Introductory considerations; Nitrogen as ammonia; Method of
Boussingault; Determination of thiocyanates; Separation of albuminoid
nitrogen; Separation of nitric nitrogen; Separation of ammoniacal nitrogen;
Ulsch method for mixed fertilizers; Method of Schlöesing-Wagner;
Schmitt’s modified method; Krüger’s method.
Sodium Nitrate, pp. 231-247.—Functions of sodium nitrate;
Commercial forms of Chile saltpeter; Percentage of nitrogen in Chile

saltpeter; Adulteration of Chile saltpeter; The Halle zinc-iron method for
estimating nitrogen in Chile saltpeter; French method; Gantter’s volumetric
method; Method of difference; Application of Chile saltpeter to the soil;
Taking samples of soil to determine nitric nitrogen; The nitrifiable solution;
Quantity of Chile saltpeter per acre; Consumption of Chile saltpeter;
Authorities cited in Part Second.

PART THIRD.
Potash in Fertilizing Materials and Fertilizers, pp. 248-266.—
Introduction; Forms of potash; Organic sources of potash; Tobacco stems
and waste; Cottonseed hulls and meal; Wood ashes; Fertilizing value of
ashes; Sugar beet molasses; Residue of wineries; Destruction of organic
matter; Ignition with sulfuric acid; Potash in mineral deposits; Occurrence
and history; Changes in potash salts in situ; Kainit; Carnallit; Polyhalit;
Krugit; Sylvin; Sylvinit; Kieserit; Schönit; Potassium sulfate; Potassium
magnesium carbonate; Potash in factory residues; Quantity of potash salts
used.
Methods of Analysis, pp. 266-289.—Classification of methods; Platinic
chlorid method; Official method; Alternate official method; Solution of
organic compounds; Factors for calculation; Halle potash method; Dutch
method; Swedish method; Method of the German Kali syndicate; Method
for high grade potash salts; Barium oxalate method; de Roode method for
kainit; Calcium chlorid method; Rapid control method; Determination from
metallic platinum; Errors in platinum method; Effect of concentration on
accuracy; Differences in form of crystals of potassium platinochlorid;
Recovery of the platinum waste.
Estimation of Potash as Perchlorate, pp. 289-301.—General principles;
Caspari’s method of preparing perchloric acid; Kreider’s method; Keeping
properties of perchloric acid; The analytical process for determining
potassium as perchlorate; Removal of sulfuric acid; Applicability of the
process; Accuracy of the process; Authorities cited in Part Third.

PART FOURTH.
Miscellaneous Fertilizers, pp. 302-324.—Classification; Forms of lime;
Application of lime; Action of lime; Analysis of lime; Gypsum, or land

plaster; Analysis of gypsum; Common salt; Green vitriol; Stall manures;
Hen manure; Guanos and cave deposits; Official French method for
phosphoric acid in guanos; Leather waste; Wood ashes; Analysis of wood
ashes; Method of analysis used in this laboratory; Official method for
estimating alkalies in wood ashes; Statement of results; Authorities cited in
Part Fourth; Index.

ILLUSTRATIONS TO
VOLUME SECOND.
Page.
Figure 1. Apparatus for crushing mineral fertilizers 5
“ 2. Plate grinder for minerals 6
“ 3. Shaking apparatus for superphosphates 60
“ 4. Shaking machine for ammonium magnesium phosphate 64
“ 5. Rössler ignition furnace 65
“ 6. Wagner’s digestion apparatus for slags 79
“ 7. Jones’ reduction tube 115
“ 8. Huston’s digesting apparatus 142
“ 9. Huston’s mechanical stirrer 145
“ 10. Mercury pump and azotometer 174
“ 11. Moist combustion apparatus of the Halle agricultural laboratory 201
“ 12. Distillation apparatus of Halle agricultural laboratory 203
“ 13. Distilling apparatus 208
“ 14. Schlöesing-Wagner apparatus 229
“ 15. Halle nitric acid apparatus 234
“ 16. Gantter’s nitrogen apparatus 237
“ 17. Geological relations of the potash deposits near Stassfurt 258

VOLUME SECOND.
EXAMINATION OF FERTILIZING MATERIALS,
FERTILIZERS, AND MANURES.

PART FIRST.
PRELIMINARY TREATMENT AND PHOSPHATES.
1. Introduction.—In the first volume the principal plant foods occurring in soils
have been named and the methods of estimating them described. As fertilizers are
classed those materials which are added to soils to supply supposed deficiencies in
plant foods, or to render more available the stores already present. There is little
difference between the terms fertilizer and manure. In common language the former
is applied to goods prepared for the farmer by the manufacturer or mixer, while the
latter is applied to the stores accumulated about the stables or made elsewhere on the
farm. Thus it is common to speak of a barnyard or stall manure and of a commercial
fertilizer.
One of the objects of the analysis of soils, as described in the first volume of this
work, is to determine the character of the fertilizer which should be added to a field
in order to secure its maximum fertility.
One purpose of the present part is to determine the fitness of offered fertilizing
material to supply the deficiencies which may be revealed by a proper study of the
needs of the soil.
2. Natural Fertilizers.—In the succession of geologic epochs which has marked
the natural history of the earth there have been brought together in deposits of
greater or less magnitude the stores of plant food unused by growing crops or which
may once have been part of vegetable and animal organisms. Some of these deposits
have been mentioned in the first volume, paragraphs 11, 12, and 18.
For a full description of the extent and origin of these deposits the reader is
referred to works on economic geology. These deposits are the chief sources of the
commercial fertilizers which are offered to the farmers of to-day and to which the
agricultural analyst is called upon to devote much of his time and labor. The methods
of determining the chemical composition and agricultural value of these deposits, as
practiced by the leading chemists of this country and Europe, will be fully set forth
in the following pages.
3. Waste Matters as Fertilizing Materials.—In addition to the natural products
just mentioned the analyst will be called on also to deal with a great variety of waste
materials which, in the last few years, have been saved from the débris of factories
and abattoirs, and prepared for use on the farm. Among these waste matters may be
mentioned, bones, horns, hoofs, hair, tankage, dried blood, fish scrap, oil cakes,
ashes, sewage, and sewage precipitates, offal of all kinds, leather scraps, and organic
débris in general.

It is important, before beginning an analysis, to know the origin of the substances
to be determined. As has already been pointed out in volume first the process which
would be accurate with a substance of a mineral origin might lead to error if applied
to the same element in organic combination. This is particularly true of phosphorus
and potash. A simple microscopic examination will usually enable the analyst to
determine the nature of the sample. In this manner, in the case of a phosphate, it
would at once be determined whether it was bone, mineral, or basic slag. The odor,
color, and general consistence will also aid in the determination.
4. Valuation of Fertilizing Ingredients.—Perhaps there are no more numerous
and perplexing questions propounded to the analyst than those which relate to the
value of fertilizing materials. There is none harder to answer. As a rule these
questions are asked by the farmer, and refer to the fertilizers put down on his fields.
In such cases the cost of transportation is an important factor in the answer. The
farther the farmer is removed from the place of fertilizer manufacture the greater, as
a rule, will be the cost. Whether the transportation is over land or by water also plays
an important part in the final cost. The discovery of new stores of fertilizing
materials has also much to do with the price. This fact is especially noticeable in this
country, where the price of crude phosphates at the mines has fallen in a few years
from nearly six dollars to three dollars and forty-three cents per ton[1]. This decrease
has been largely due to discoveries of vast beds of phosphatic deposits in Florida,
North Carolina, Tennessee, and Virginia. The state of trade, magnitude of crops, and
the vigor of commerce also affect, in a marked degree, the cost of the raw materials
of commercial fertilizers.
5. Trade Values of Fertilizing Ingredients in Raw Materials and Chemicals.
—The values proposed by the Massachusetts Experiment Station are given below.[2]
Cents per
pound.
Nitrogen in ammonia salts, 19
“ “ nitrates, 14½
Organic nitrogen in dry and fine-ground fish, meat, blood,
and in high-grade mixed fertilizers, 18½
“ “ “ cottonseed meal, linseed meal,
and castor pomace, 15
“ “ “ fine-ground bone and tankage, 16½
“ “ “ fine-ground medium bone and tankage, 15
“ “ “ medium bone and tankage, 12
“ “ “ coarse bone and tankage, 7
“ “ “ hair, horn shavings, and coarse
fish scraps, 7
Phosphoric acid soluble in water, 6

“ “ soluble in ammonium citrate, 5½
“ “ in fine bone and tankage, 5½
“ “ in fine medium bone and tankage, 4½
“ “ in medium bone and tankage, 3
“ “ in coarse bone and tankage, 2
“ “ in fine-ground fish, cottonseed meal,
linseed meal, castor pomace, and wood-ashes,5
“ “ insoluble (in ammonium citrate) in
mixed fertilizers, 2
Potash as high-grade sulfate, and in mixtures
free from muriate, 5
“ “ muriate, 4½
The manurial constituents contained in feed stuffs are valued as follows:
Organic nitrogen, 15
Phosphoric acid, 5
Potash, 5
The organic nitrogen in superphosphates, special manures, and mixed fertilizers
of a high grade is usually valued at the highest figures laid down in the trade values
of fertilizing ingredients in raw materials; namely, eighteen and one-half cents per
pound, it being assumed that the organic nitrogen is derived from the best sources;
viz., animal matter, as meat, blood, bones, or other equally good forms, and not from
leather, shoddy, hair, or any low-priced, inferior form of vegetable matter, unless the
contrary is evident. In such materials the insoluble phosphoric acid is valued at two
cents a pound. These values change as the markets vary.
The scheme of valuation prepared by the Massachusetts station does not include
phosphoric acid in basic slags. By many experimenters the value of the acid in this
combination, tetracalcium phosphate, is fully equal to that in superphosphates
soluble in water and ammonium citrate. It would perhaps be safe to assign that value
to all the phosphoric acid in basic slags soluble in a five per cent citric acid solution.
Untreated fine-ground phosphates, especially of the soft variety, so abundant in
many parts of Florida, have also a high manurial value when applied to soils of an
acid nature or rich in humus. On other soils of a sandy nature, or rich in calcium
carbonate, such a fertilizer would have little value. The analyst in giving an opinion
respecting the commercial value of a fertilizer, must be guided not only by the
source of the material, its fineness or state of decomposition, and its general physical
qualities, but also by the nature of the crop which it is to nourish and the kind of soil
to which it is to be applied.

GENERAL ANALYTICAL PROCESSES.

6. Taking Samples.—It is impracticable to give definite directions for taking
samples of fertilizers which will be applicable to all kinds of material and in all
circumstances. If the chemist himself have charge of the taking of the sample, it will
probably be sufficient to say that it should accurately represent the total mass of
material sampled. Generally the samples which are brought to the chemist have been
taken without his advice or direction and he is simply called upon to make an
analysis of them.

Figure. 1.
Apparatus for Crushing Mineral Fertilizers.

7. Minerals Containing Fertilizing Materials.—When possible, the samples
should be accompanied by a description of the mines where they are procured and a
statement of the geologic conditions in which the deposits were made. As large a
quantity of the material as can be conveniently obtained and transported should be
secured. Where a large quantity of mineral matter is at hand it should first be put
through a crusher. Many forms of crusher, driven by hand and other power, are on
the market. Among these may be mentioned the Alden, Blake, Bisworth, Forster, and
Lipsay machines.[3] They are all constructed essentially on the same principle, the
pieces of mineral being broken into small fragments between two heavy vibrating
steel plates. The general form of these instruments is seen in Fig. 1.
The fragments coming from the crusher can be reduced to a coarse powder by
means of the iron plate and crusher shown in Fig. 2.

Where only a small quantity of mineral is at hand the apparatus just mentioned
may be used at once after breaking the sample into small fragments by means of a
hammer.
Finally the sample, if to be dissolved in an acid or soluble materials only, is
reduced to a powder in an iron mortar until it will pass a sieve with a one or, better,
one-half millimeter circular mesh. The powder thus obtained must be stirred with a
magnet to remove all iron particles that may have been incorporated with the mass
by abrasion of the instruments employed.
If a complete mineral analysis of the sample is to be secured, the material freed
from iron, as above described, is to be rubbed to an impalpable powder in an agate
mortar.

Figure. 2.
Plate Grinder for Minerals.

8. Mixed Fertilizers.—In fertilizing materials in bulk, the first requisite is that
they shall be thoroughly mixed so that a given volume of the material may represent,
practically, definite quantities of the materials sampled. The finer the material is, in
the original state, and the more thoroughly it has been mixed, the better the sample
will be. If the sample be already in sacks it will be sufficient to take portions by
means of the ordinary trier, such as is used for sampling sugar and other substances.
This consists of a long metal implement such as would be formed by a longitudinal
section of a tube. The end is pointed and suited for penetrating into the sack and the
materials contained therein. On withdrawing it, the semi-circular concavity is found

filled with the material sampled. Samples in this way should be taken from various
parts of the sack and these samples well mixed together and a subsample of the
amount necessary to be taken to the laboratory can then be obtained.
9. Method of the French Experiment Stations.—In the method employed by
the French Experiment Stations it is directed that in no case should stones or other
foreign particles be removed from the fertilizer sampled, but they should enter into
the sample taken in, as nearly as possible, the same proportions as they exist in the
whole mass.
In the case of stones or other solid masses which are to be sampled, as many
samples as possible should be taken from all parts of the heap and these should be
reduced to a coarse powder, thoroughly mixed together and sampled.
In case the material is in the form of a paste, if it is homogeneous, it will be
sufficient to mix it well and take the sample directly; but in case there is a tendency
for the pasty mass to separate into two parts, of which the one is a liquid and the
other, more of a solid consistence, it may be well to take samples from each in case
they can not be thoroughly incorporated by stirring.
10. Method of the French Association of Sugar Chemists.—The method
adopted by the French sugar chemists directs that the sample should be taken from
the fertilizer in bulk or from a portion used for industrial purposes.[4] The sample for
analysis is to be taken from the above sample after it has been sent to the laboratory.
The method of taking should be varied according to the condition of the substances
to be analyzed.
The large sample selected from the goods delivered to commerce having been
delivered at the laboratory, the analytical sample is taken as follows:
When the industrial sample, more or less voluminous, reaches the laboratory, the
chemist is to begin by taking a note of the marks, labels, and descriptions found
thereon, and of the nature and state of the package which contains it, and the date of
its arrival. All this information should be entered upon the laboratory book and
afterwards transcribed on the paper containing the results of the analysis, as well as
the name of the person sending it. This having been done, the sample is to be
properly prepared in order that a portion may be taken representing exactly the mean
composition of the whole.
If it is in a state of fine powder, such as ground phosphates and certain other
fertilizers, it is sufficient to pass it two or three times through a sieve with meshes
one millimeter in diameter, taking care to break up the material each time in order to
mix it and to pulverize the fragments which the sieve retains. The whole is
afterwards spread in a thin layer upon a large sheet of paper, and a portion is taken

here and there upon the point of a knife until about twenty grains are removed, and
from this the portion subjected to analysis is afterwards taken.
If the sample comes in fragments, more or less voluminous, such as phosphatic
rocks or coarsely pulverized guanos containing agglomerated particles, it is
necessary first to reduce the whole to powder by rubbing it in a mortar or in a small
drug mill. It is next passed through a sieve of the size mentioned above and that
which remains upon the sieve pulverized anew until all has passed through. This
precaution is very important, since the parts which resist the action of the pestle the
most have often a composition different from those which are easily broken.
When the products to be analyzed contain organic materials, such as horn, flesh,
dry blood, etc., the pulverization is often a long and difficult process, and results in a
certain degree of heating which drives off some of the moisture in such a way that
the pulverized product is at the last drier, and, consequently, richer than the primitive
sample. It is important to take account of this desiccation, and since the pulverization
of a mass so voluminous can not be made without loss, the determination of the total
weight of the sample before and after pulverization does not give exact results.
In such a case it is indispensable to determine the moisture, both before and after
pulverizing, and to calculate the analytical results obtained upon the pulverized
sample back to the original sample.
In order to escape this necessity, as well as the difficulties resulting from the
variations in moisture during transportation, some chemists have thought it better to
always dry the commercial products before submitting them to analysis, and to
report their results in the dry state, accompanied by a determination of the moisture,
leaving thus to the one interested the labor of calculating the richness in the normal
state, that is to say, in the real state in which the merchandise was delivered.
In addition to the fact that this method allows numerous chances of errors, many
substances undergoing important changes in their composition by drying alone, it
has been productive of the most serious consequences. The sellers have placed their
wares on the market with the analysis of the material in a dry state, and a great
number of purchasers have not perceived the fraud concealed under this expression
so innocent in appearance. It is thus that there has been met with in the markets
guano containing twenty-five per cent of water, which was guaranteed to contain
twelve per cent of phosphoric acid, when, in reality, it contained only eight per cent
in the moist state.
11. Barn-Yard Manures.—The sampling of stall and barnyard manures is more
difficult on account of the fact that the materials are not homogeneous and that they
are usually mixed with straw and other débris from the feed trough, and only the
greatest care and patience will enable the operator to secure a fair sample.

In the case of liquid manures the liquid should be thoroughly stirred before the
sample is taken.
Frear points out the difficulty of securing representative samples of stall manure
and describes methods of removing it.[5] The stall manure sampled had been piled in
the cattle-yard for a time and the cattle were allowed to run over the heaps for an
hour or two each day. Pigs were also allowed free access to the heaps in order to
insure a more perfect mixture of the ingredients.
Twenty-nine loads of 3,000 pounds each were taken from the exposed heap and
thirty-four loads of 2,000 pounds each were taken from the covered heap. From each
load were removed two carefully selected portions of ten pounds each, which were
placed in separate covered boxes numbered A and B. When the sampling was
completed these boxes were covered. After being removed to the laboratory the
boxes were weighed and the contents thoroughly mixed. Two samples of twelve
liters volume each, were drawn from each box. One-third of this was chopped in a
large meat chopper and the other two-thirds taken into the laboratory without being
cut. These samples, on entering the laboratory, were weighed and dried at a
temperature of 60°. Smaller samples were then drawn from each of these and ground
in a drug mill for analysis. Duplicate samples taken in this way, while they did not
give absolutely concordant results, showed a near approximation. A more careful
sampling on the line proposed would, in all probability, secure absolutely agreeing
results in duplicate samples.
12. Preparation of Sample in Laboratory.—The method of preparing mineral
fertilizers for analysis has been given under directions for sampling. Many
difficulties attend the proper preparation of other samples, and the best approved
methods of procedure are given below:
According to the directions given by the Association of Official Agricultural
Chemists the sample should be well intermixed, finely ground, and passed through a
sieve having circular perforations one millimeter in diameter.[6] The processes of
grinding and sifting should take place as rapidly as possible so that there may be no
gain or loss of moisture during the operation.
13. Method of the French Agricultural Stations.—The manner of proceeding
recommended by the French stations varies with the fertilizer.[7] If it is not already in
the form of a powder it is necessary to pulverize it as finely as possible by rubbing it
up in a mortar. In certain cases, as with superphosphates, the material should be
passed through a sieve having apertures of one millimeter diameter, all the larger
parts being pulverized until they will pass this sieve.
When the matters are too pasty to be divided in the mortar they should be divided
by means of a knife or a spatula. They should then be incorporated with a known

weight of inert, pulverulent matter such as fine sand, with which they should be
thoroughly mixed and in subsequent calculations the quantity of sand or other inert
matter added must be taken into consideration. Usually a pasty state of a fertilizer is
due to the humidity of the mixture. In this case a considerable volume of the sample
is taken and dried and then reduced to a pulverulent state. In the subsequent
calculations, however, the percentage of moisture lost must be taken into
consideration.
Before drying a sample it is necessary to take into consideration whether or not
the product will be modified by desiccation as would be the case, for instance, with
superphosphates. With these, which are often in a state more or less agglomerated, it
is recommended to introduce into them, in order to divide them, a certain quantity of
calcium sulfate in order to obtain them in a pulverulent state.
In the case of animal débris they should be divided as finely as possible with the
aid of scissors and then passed through a drug mill if dry enough. They are then
mixed by hand and may finally be obtained in a state of considerable homogeneity.
When fertilizers are in a pasty state more or less liquid, they are dried at 100°,
first introducing a little oxalic acid in case they contain any volatile ammoniacal
compounds. The product of desiccation is then passed through a mill. Before treating
in this way it is necessary to be sure that the composition will not be altered by
drying. In the case of a mixture containing superphosphates and nitrate, for instance,
drying would eliminate the nitric acid. In such a case the free phosphoric acid should
be neutralized with a base like lime. In the case of fertilizers containing both nitrates
and volatile ammoniacal compounds the addition of oxalic acid might also set free
nitric acid during the desiccation. In such a case it is necessary to dry two samples;
one with the addition of oxalic acid for the purpose of estimating the ammonia, and
the other without the acid for the purpose of estimating the nitrate. A qualitative
analysis should precede all the operations so as to determine the nature of the
material to be operated on.
14. German Method.—In the method pursued by the German experiment
stations it is directed:[8]
(1) Dry samples of fertilizers must be passed through a sieve and afterwards well
mixed.
(2) With moist fertilizers, which can not be subjected to the above process, the
preparation should consist in a careful and thorough mixing, without sieving.
(3) On the arrival of the samples in the laboratory their weight should be
determined. The half of the sample is prepared for analysis and the other part, to the
amount of a kilo, should be placed in a glass vessel, closed air-tight, and placed in a

cool place for at least a quarter of a year from the time of its reception, in order that
it may be subjected to any subsequent investigations which may be demanded.
(4) In the case of raw phosphates and bone-black the amount of water which they
contain should be determined at from 105° to 110°. Samples which in drying lose
ammonia in any way, should have this ammonia determined.
(5) Samples which are sent to other laboratories for control analyses, should be
sent securely packed in air-tight glass bottles.
(6) The weight of the samples sent should be entered in the certificates of
analysis.
(7) Samples which, on pulverizing, change their content of water, must have the
water content estimated in both the coarse and powdered condition and the results of
the analysis must be calculated to the water content of the original coarse substance.
15. Special Cases.—Many cases arise of such a nature as to make it impossible
to lay down any rule which can be followed with success. As in almost every other
process in agricultural chemistry the analyst in such cases must be guided by his
judgment and experience. Keeping in view the main object, viz., to secure in a few
grams of material a fair representation of large masses he will generally be able to
reach the required result by following the broad principles already outlined. In many
cases the details of the work and the adaptations necessary to success must be left to
his own determination.
16. Drying Samples of Fertilizers.—The determination of the uncombined
moisture in a sample of fertilizer is not an easy task. In some cases, as in powdered
minerals, drying to constant weight at the temperature of boiling water is sufficient.
In organic matters containing volatile nitrogenous compounds, these must first be
fixed by oxalic or sulfuric acid, before the desiccation begins. If any excess of
sulfuric acid be added, however, drying at 100° becomes almost impossible.
Particular precautions must be observed in drying superphosphates. In drying
samples preparatory to grinding for analysis, it is best to stop the process as soon as
the materials can be pulverized. In general, samples should be dried only to
determine water, and the analytical processes should be performed on the undried
portions. It is not necessary, as a rule, to dry samples of fertilizers in an inert
atmosphere, such as hydrogen or carbon dioxid. Drying in vacuo may be practiced
when it is desired to secure a speedy desiccation or one at a low temperature.
17. Official Methods.—The Official Agricultural Chemists direct, in the case of
potash salts, sodium nitrate, and ammonium sulfate, to heat from one to five grams
in a flat platinum or aluminum dish at 130° until the weight is constant.[9] The loss in
weight is taken to represent the water. In all other cases heat two grams, or five
grams if the sample be very coarse, for five hours in a steam-bath.

In the German stations in the case of untreated phosphates and bone-black the
moisture is estimated at from 105° to 110°. Samples which lose ammonia should
have the weight of ammonia given off at that temperature, determined separately.
For purposes of comparison it would be far better to have all contents of
moisture determined at the boiling-point of water. While this varies with the altitude
and barometric pressure yet it is quite certain that the loss on drying to constant
weight at all altitudes is practically the same. Where the atmospheric pressure is
diminished for any cause the water escapes all the more easily. This, practically, is a
complete compensation for the diminished temperature at which water boils.
Where the samples contain no ingredient capable of attacking aluminum, they
can be conveniently dried, in circular dishes of this metal about seven centimeters in
diameter and one centimeter deep, to constant weight, at the temperature of boiling
water.
18. Moisture in Monocalcium Phosphates.—In certain fertilizers, especially
superphosphates, containing the monocalcium salt, the estimation of water is a
matter of extreme difficulty on account of the presence of free acids and of
progressive changes in the sample due to different degrees of heat.
Stoklasa has studied these changes and reaches the following results[10]:
A chemically pure monocalcium phosphate of the following composition, viz.,
CaO 22.36 per cent.
P₂O₅ 56.67 “ “
H₂O 21.53 “ “
was subjected to progressive dryings. The loss of water after ten hours was 1.83 per
cent; after twenty hours, 2.46 per cent; after thirty hours, 5.21 per cent; after forty
hours, 6.32 per cent; after fifty hours, 6.43 per cent. This loss of water remained
constant at 6.43 per cent. This loss represents one molecule of water as compared
with the total molecular magnitude of the mass treated. A calcium phosphate,
therefore, of the following composition, CaH₄(PO₄)₂·H₂O loses, after forty hours,
drying at 100°, its water of crystallization. The calcium phosphate produced by this
method forms opaque crystals which are not hygroscopic and which give, on
analysis, the following numbers:
CaO 24.02 per cent.
P₂O₅ 16.74 “ “
H₂O 15.09 “ “
The temperature can be raised to 105° without marked change. If the temperature
be raised to 200° the decomposition of the molecule is hastened according to the

following formula:
4 CaH₄(PO₄)₂ = Ca₂P₂O₇ + Ca(PO₃)₂ + CaH₂P₂O₇ + 2 H₃PO₄ + 4 H₂O.
The chemical changes during the drying of monocalcium phosphates can be
represented as follows, temperature 200° for one hour:
8[CaH₄(PO₄)₂·H₂O] = 4CaH₄(PO₄)₂ + Ca(PO₃)₂ + Ca₂P₂O₇
+ CaH₂P₂O₇ + 2H₃PO₄ + 12H₂O.
The further drying at 200° produces the following decomposition:
4CaH₄(PO₄)₂ + Ca(PO₃)₂ + Ca₂P₂O₇ + CaH₂P₂O₇ + 2H₃PO₄
= 2Ca(PO₃)₂ + 4CaH₂P₂O₇ + Ca₂P₂O₇ + 2H₃PO₄ + 5H₂O.
2Ca(PO₃)₂ + 4CaH₂P₂O₇ + Ca₂PO₇ + 2H₃PO₄
= 6Ca(PO₃)₂ + 2CaH₂P₂O₇ + 5H₂O.
Finally, pyrophosphate at 210° is completely decomposed into metaphosphate
and water according to the following formula:
6Ca(PO₃)₂ + 2CaH₂P₂O₇ = 8Ca(PO₃)₂ + 2H₂O.
Provided the drying is made at once at 210° the sum of the changes produced as
indicated above, can be represented by the following formula:
8[CaH₄(PO₄)₂·H₂O] = 8Ca(PO₃)₂ + 24H₂O.

COMPLETE ANALYSIS OF
MINERAL PHOSPHATES.

19. Constituents to be Determined.—The most important point in the analysis
of mineral phosphates is to determine their content of phosphoric acid. Of equal
scientific interest, however, and often of great commercial importance is the
determination of the percentage of other acids and bases present. The analyst is often
called on, in the examination of these bodies, to make known the content of water
both free and combined, of organic and volatile matter, of carbon dioxid, sulfur,
chlorin, fluorin, silica, iron, alumina, calcium, manganese, magnesia, and the
alkalies. The estimation of some of these bodies presents problems of considerable
difficulty, and it would be vain to suppose that the best possible methods are now
known. Especially is this the case with the processes which relate to the estimation
of the fluorin, silica, iron, alumina, and lime. The phosphoric acid, however, which is
the chief constituent from a commercial point of view, it is believed, can now be
determined with a high degree of precision. Often the estimation of some of the less

important constituents is of great interest in determining the origin of the deposits,
especially in the case of fluorin. While the merchant is content with knowing the
percentage of phosphoric acid and the manufacturer asks in addition only some
knowledge of the quantity of iron, alumina, and lime the analyst in most cases is
only content with a complete knowledge of the constitution of the sample at his
disposal.
20. Direct Estimation of the Phosphoric Acid.—It often happens, in the case of
a mineral phosphate, that the only determination desired is of the phosphoric acid. In
this instance the analyst may proceed as follows: If the qualitative test shows the
usual amount of phosphoric acid, two grams of the sample passed through a sieve,
with a millimeter mesh, are placed in a beaker and thoroughly moistened with water.
The addition of water is to secure an even action of the hydrochloric acid on the
carbonates present. The beaker is covered with a watch-glass and a little
hydrochloric acid is added from time to time until all effervescence has ceased.
There are then added about thirty cubic centimeters of aqua regia and the mixture
raised to the boiling-point on a sand-bath or over a lamp. The heating is continued
until chlorin is no longer given off and solution is complete. The volume of the
solution is then made up to 200 cubic centimeters without filtering, filtered, and an
aliquot part of the filtrate, usually fifty cubic centimeters, representing half a gram of
the original sample, taken for the determination of the phosphoric acid according to
the method of the Official Agricultural Chemists. The small quantity of insoluble
material does not introduce any appreciable error into the process when the volume
is made up to 200 or 250 cubic centimeters.
21. Method of the Official Agricultural Chemists for Total Phosphoric Acid.
—To the hot solution, for every decigram of phosphorus pentoxid which may be
present, add fifty cubic centimeters of the molybdic solution. Digest at 65° for an
hour, filter, and wash with water or ammonium nitrate solution[11]. Test the filtrate by
renewed digestion with additional molybdate reagent. Dissolve the precipitate on the
filter with ammonia in hot water and wash into a beaker, making the volume of
filtrate and washings not more than 100 cubic centimeters. Nearly neutralize with
hydrochloric acid, cool, and add magnesia mixture from a burette at the rate of about
one drop a second, stirring vigorously, meanwhile. The quantity of magnesia mixture
to be added is not prescribed in the official method but it should always be in excess
of the amount necessary for complete precipitation. For each decigram of
phosphorus pentoxid, from eight to ten cubic centimeters should be used. Fifteen
minutes after the last of the magnesia mixture has been stirred in, thirty cubic
centimeters of ammonia of 0.95 specific gravity are added and the beaker set aside
for two hours or longer. The ammonium magnesium phosphate is separated by
filtration, dried, ignited gently at first, and finally over a blast-lamp and weighed as
magnesium pyrophosphate. The factors for calculating the phosphorus pentoxid and

tricalcium phosphate from the weight of pyrophosphate are given below on the two
bases; viz., hydrogen equals 1, and oxygen equals 16.
H = 1.
Mg₂P₂O₇ × 0.63976 = P₂O₅
Mg₂P₂O₇ × 1.3964 = Ca₃(PO₄)₂
P₂O₅ × 2.1827 = Ca₃(PO₄)₂
O = 16.
Mg₂P₂O₇ × 0.63792 = P₂O₅
Mg₂P₂O₇ × 1.3926 = Ca₃(PO₄)₂
P₂O₅ × 2.1831 = Ca₃(PO₄)₂
22. Preparation of Solutions.—Molybdic Solution.—Dissolve 100 grams of
molybdic acid in 400 grams or 417 cubic centimeters of ammonia, of 0.96 specific
gravity, and pour the solution thus obtained into 1,500 grams or 1,250 cubic
centimeters of nitric acid, of 1.20 specific gravity. Keep the mixture in a warm place
for several days, or until a portion heated to 40° deposits no yellow precipitate of
ammonium phosphomolybdate. Decant the solution from any sediment and preserve
in glass-stoppered vessels.
Magnesia Mixture.—Dissolve twenty-two grams of recently ignited calcined
magnesia in dilute hydrochloric acid, avoiding an excess of the latter. Add a little
calcined magnesia in excess, and boil a few minutes to precipitate iron, alumina, and
phosphoric acid; filter, add 280 grams of ammonium chlorid, 700 cubic centimeters
of ammonia of specific gravity 0.96, and water enough to make a volume of two
liters. Instead of the solution of twenty-two grams of calcined magnesia, 110 grams
of crystallized magnesium chlorid may be used.
Dilute Ammonia for Washing.—One volume of ammonia, of 0.96 specific
gravity, mixed with three volumes of water, or usually one volume of concentrated
ammonia with six volumes of water.
23. Use of Tartaric Acid in Phosphoric Acid Estimation.—In the presence of
iron the molybdate mixture is likely to carry down some ferric oxid with the yellow
precipitate. To prevent this, and also hinder the separation of molybdic acid in the
solution on long standing, tartaric acid has been recommended.
Jüptner has found that the presence of tartaric acid does not interfere with the
separation of the yellow precipitate, as some authorities assert.[12] Even 100 grams of
the acid in one liter of molybdate solution produce no disturbing effect. Molybdate
solution treated with tartaric acid did not show any separation of molybdic acid when
kept for a year at room temperatures. The presence of tartaric acid, therefore, is

highly recommended by him to prevent the danger of obtaining both ferric oxid and
molybdic acid with the yellow precipitate.
24. Water and Organic Matters.—The sample, according to the practice of
Chatard, should be ground fine enough to leave no residue on an eighty mesh sieve,
and should be thoroughly mixed by passing it three times through a forty mesh
sieve[13].
Two grams are weighed into a tared platinum crucible. This, with its lid, is
placed in an air-bath at 105°, and heated for at least three hours. The lid is then put
on, and the crucible is placed in a desiccator and weighed as soon as cold. The loss
in weight is the moisture.
Wyatt recommends that two grams of the fine material be heated in ground
watch-glasses, the edges of which are separated so as to allow the escape of the
moisture.[14] The heating is continued for three hours at 110°, the watch-glasses then
closed and held by the clip, cooled in a desiccator, and weighed. This method is
excellent for very hygroscopic bodies, but where quick-acting balances are used,
scarcely necessary for a powdered mineral.
The residue from the moisture determination is gradually heated to full redness
over a bunsen, and then ignited over the blast-lamp. This operation is repeated after
weighing until a constant weight is obtained. The loss (after deducting the
percentage of carbon dioxid as found in another portion) may be taken as water and
organic matter. This method is sufficient for all practical purposes; but when
minerals containing fluorin are strongly ignited, a part of the fluorin is expelled;
hence, if more accurate determinations are required, the loss of fluorin must be taken
into account. In this laboratory it has been proved that a pure calcium fluorid
undergoes progressive decomposition at a bright red heat with formation of lime.
Wyatt directs that the combined water and organic matters be determined in the
residue from the moisture estimation as follows: The residue is brushed into a
weighed platinum crucible, which is heated over a small bunsen for ten minutes and
then brought to full heat of a blast-lamp for five minutes. After cooling, the total loss
is determined by weighing. After deducting the carbon dioxid determined in a
separate portion, the residual loss is regarded as due to combined moisture and
organic matter.
25. Carbon Dioxid.—Many forms of compact apparatus have been devised for
this estimation, but none of them is satisfactory if accurate results are desired.[15] Not
to mention other objections, many phosphates must be heated nearly to the boiling-
point with dilute acid to effect complete decomposition of the carbonates. The
distillation method described by Gooch[16] is excellent, and when once the apparatus
is set up, its work will be found to be rapid and satisfactory.

Wyatt regards the estimation of carbon dioxid as one of the most important for
factory use. The carbonates present in a sample indicate the loss of an equivalent
amount of acid in the process of conversion into superphosphate.[17]
The apparatus employed for estimating carbon dioxid may be any one of those in
ordinary use for this purpose. The principle of the process depends on the liberation
of the gas with a mineral acid, its proper desiccation, and subsequent absorption by a
caustic alkali, best in solution.
The apparatus of Knorr, described in volume first, page 338, may be
conveniently used. The weight of the sample to be used should be regulated by the
content of carbonate. When this is very high, from one to two grams will be found
sufficient; when low, a larger quantity must be used. Hydrochloric is preferred as the
solvent acid. Those forms of apparatus which are weighed as a whole and the carbon
dioxid determined by reweighing after its expulsion, are not as reliable as the
absorption apparatus mentioned.
26. Soluble and Insoluble Matter.—Five grams of the fine phosphate are put
into a beaker, twenty-five cubic centimeters of nitric acid, (specific gravity 1.20) and
12.5 cubic centimeters of hydrochloric acid (specific gravity 1.12) are added. The
beaker, covered with a watch-glass, is placed upon the water-bath for thirty
minutes[18]. The contents of the beaker are well stirred from time to time, and at the
end of the period the beaker is removed from the bath, filled with cold water, well
stirred, and allowed to settle. The solution is next filtered into a half liter flask, and
the residue is thoroughly washed with cold water, partially dried, and then ignited,
(finishing with the blast-lamp) and brought to constant weight. The figures thus
obtained will, however, be incorrect, because the fluorin liberated during the solution
of the phosphates dissolves a portion of the silica. Hence, the results are too low.
Nevertheless, as the same action would occur in the manufacture of a
superphosphate from the material, the determination may be considered, as a fair
approximation to commercial practice. The ignited residue must be tested for
phosphorus pentoxid.
27. Preparation of the Solution.—The flask containing the filtrate is filled to
the mark with cold water, and the solution is thoroughly mixed by twice pouring into
a dry beaker and returning it to the flask. Cold water is used for washing the residue,
since if hot water be used, the sesquichlorids are apt to become basic and insoluble,
and hence to remain in the residue and on the filter paper. Besides, as the flask is to
be filled to the mark, the contents must be cold before any volumetric measurements
can be made.
28. Silica and Insoluble Bodies.—Wyatt describes the following method for
determining the total insoluble or siliceous matters in a mineral phosphate[19]. Five
grams of the fine sample are placed in a porcelain dish with about thirty cubic

centimeters of aqua regia. The dish is covered with a funnel, placed on a sand-bath
and, after solution is complete, evaporated to dryness with care to prevent sputtering.
When dry the residue is moistened with hydrochloric acid and again dried, rubbing
meanwhile to a fine powder. The heat of the bath is then increased to 125° and
maintained at this temperature for about ten minutes. When cool, the residue is
treated with fifty cubic centimeters of hydrochloric acid for fifteen minutes. The acid
is then diluted and filtered on a gooch, which is washed with hot water until the
filtrate amounts to a quarter of a liter. The residue in the crucible is dried, ignited,
and weighed. This method, unless the solution be subsequently boiled with nitric
acid, may not retain all the phosphoric acid in the ortho form.
It is difficult to estimate the total silica by the ordinary methods of mineral
analysis. This is due to the fact that in an acid solution of a substance containing
silicates and fluorids the whole of the silica or the fluorin, as the case may be may
escape as silicofluorid on evaporation. Again, it is not easy to decompose calcium
phosphate by fusing with sodium carbonate. If an attempt be made to do this,
however, the process should be conducted as follows: A portion of the sample is
ground to an impalpable powder in an agate mortar. From one to two grams of the
substance are mixed with five times its weight of sodium carbonate and fused with
the precautions given in standard works on quantitative analysis. The fused mass is
digested in water, boiled, and filtered, and the residue washed first with boiling water
and afterwards with ammonium carbonate. The filtrate contains all the fluorin as
sodium fluorid and, in addition to this, sodium carbonate, silicate, and aluminate.
Mix the filtrate with ammonium carbonate and heat for some time, replacing the
ammonium carbonate which evaporates. Separate by filtration the silicic acid hydrate
and aluminum hydroxid which are formed and wash them with ammonium
carbonate. To separate the last portions of silica from the filtrate, add a solution of
zinc oxid in ammonia. Evaporate until no more ammonia escapes and separate, by
filtration, the zinc silicate and oxid. Determine the silica in this precipitate by
dissolving in nitric acid, evaporating to dryness, taking up with nitric acid and
separating the undissolved silica by filtration. In the alkaline filtrate the fluorin may
be estimated by the usual method as calcium salt.
29. Estimation of Lime.—One hundred cubic centimeters of the solution
(containing one gram of the original substance) are evaporated in a beaker to about
fifty cubic centimeters; ten cubic centimeters of dilute sulfuric acid (one to five) are
added; and the evaporation is continued on the water-bath until a considerable crop
of crystals of gypsum has formed[20]. The solution is then allowed to cool, when it
generally becomes pasty, owing to the separation of additional gypsum. When it is
cold, 150 cubic centimeters of ninety-five per cent alcohol are slowly added, with
continual stirring, and the whole is allowed to stand for three hours, being stirred
from time to time. After three hours, it is filtered, with the aid of a filter-pump, into a

distillation flask, and the beautifully crystalline precipitate, which does not adhere to
the beaker, is washed with ninety-five per cent alcohol. The filter, with the
precipitate, is gently removed from the funnel and inverted into a platinum crucible,
so that, by squeezing the point of the filter, the precipitate is made to fall into the
crucible, and the paper can be pressed down smoothly upon it. On gentle heating of
the crucible, the remaining alcohol burns off, and when the paper has been
completely destroyed, the heat is raised to the full power of a bunsen for about five
minutes. After cooling in a desiccator the crucible containing the calcium sulfate, is
weighed. The filtration may also be accomplished on asbestos felt.
30. The Ammonium Oxalate Method.—This method has been extensively used
in this country in commercial work, and is best carried out as described by Wyatt.[21]
The total filtrates from the iron and alumina precipitates, secured as described in
paragraph 33, are well mixed and concentrated to a volume of about 100 cubic
centimeters. There are added about twenty cubic centimeters of a saturated solution
of ammonium oxalate, and after stirring, the mixture is allowed to cool and remain at
rest for six hours. The supernatant liquid is poured through a filter, the residue
washed three times by decantation with hot water and brought upon the filter. The
beaker and precipitate are washed at least three times. The precipitate is dried and
ignited at low redness for ten minutes. The temperature is then raised by a blast and
the ignition continued for five minutes longer, or until the lime is obtained as oxid.
The precipitate is likely to contain magnesia. The magnesia is estimated in the
filtrates from the lime determination by first mixing them and concentrating to 100
cubic centimeters, which, after cooling, are made strongly alkaline with ammonia.
After allowing to stand for twelve hours the ammonium magnesium phosphate is
collected and reduced to magnesium pyrophosphate by the usual processes. If one
gram of the original material has been used the pyrophosphate obtained, multiplied
by 0.36, will give the weight of magnesia contained therein.
31. Lime Method of Immendorff.—The tedious processes required to
determine the lime in the presence of iron, alumina, and large quantities of
phosphoric acid are well known to analysts. Immendorff has published a method,
accompanied by the necessary experimental data, based on the comparative
insolubility of calcium oxalate in very dilute solution of hydrochloric acid. He has
shown in the data given that the lime is all precipitated in the conditions named and
that the precipitate, when properly prepared, is not contaminated with weighable
amounts of the other substances found in the original solution[22]. The ease with
which oxalic acid can be determined volumetrically with potassium permanganate
solution aids greatly in the time-saving advantages of the process.
In a hydrochloric acid solution of a mineral phosphate an aliquot part of the
filtrate representing about 250 milligrams of calcium oxid, usually about twenty-five
cubic centimeters, should be taken for the analysis. Ammonia is added in slight

excess and then the acid reaction restored with hydrochloric until shown plainly by
litmus. The solution is then heated and the lime thrown down by adding a solution of
ammonium oxalate in excess. In order to secure a greater dilution of the hydrochloric
acid after the precipitation has been made, water should be added until the volume is
half a liter. Before filtering, the whole should be cooled to room temperature. The
precipitate should be washed first with cold and afterwards with warm water. The
well-washed precipitate is dissolved in hot dilute sulfuric acid and the solution, while
hot, titrated with a standard solution of potassium permanganate set by a solution of
ammonio-ferrous sulfate.
If one cubic centimeter of the permanganate represent 0.005 gram of iron it will
correspond almost exactly to 0.0035 gram of calcium oxid.
Example.—Sample of rather poor mineral phosphate, five
grams in half a liter. Strength of potassium permanganate, one
cubic centimeter equivalent to 0.00697 gram of iron and to
0.003484 gram of calcium oxid.
Twenty-five cubic centimeters of the solution, representing
one quarter of a gram, in which the lime was precipitated as
above described, required 9.6 cubic centimeters of the potassium
permanganate to saturate the oxalic acid. Then
9.6 × 0.003484 = 0.0334464 gram,
or 13.38 per cent of calcium oxid. The method is also applicable
to basic slags.
32. Estimation of Iron and Alumina in Mineral Phosphates.—When mineral
phosphates are to be used for the manufacture of superphosphates by treatment with
sulfuric acid their content of iron and alumina becomes a matter of importance. By
reason of the poor drying qualities of the sulfates of these bases their presence in any
considerable excess of a few per cent becomes exceedingly objectionable. The
accurate estimation of these ingredients is not only then a matter of scientific interest
but one of great commercial significance to the manufacturer.
The conventional methods so long in use depending on the precipitation of the
iron and alumina as phosphates in the presence of acetic acid have been proved to be
somewhat unreliable. Not only does the acetic acid fail to prevent the precipitation of
some of the lime, but it also dissolves more or less of the iron and aluminum
phosphates. The solution of the precipitate and its reprecipitation by the addition of
ammonia, may free the second precipitate from lime, but it increases the error due to
the solubility of the aluminum salt. The methods recently introduced for the
estimation of iron and alumina in presence of excess of lime and phosphoric acid are
not entirely satisfactory, but are the best which can now be offered.

33. The Acetate Method.—The principle of this process is based on the fact that
in a solution containing iron, alumina, lime, and phosphoric acid the iron and
aluminum phosphates can be thrown down in a slightly acid solution by ammonium
acetate while the calcium phosphate remains in solution. The acidity in the older
methods is due to acetic and can be secured by making the solution slightly alkaline
with ammonia and adding acetic to slight acidity. One of the best methods of
conducting the operation is that of C. Glaser[23]. Glaser’s modification of the older
processes is based on the assumption that at 70° the aluminum phosphate is
quantitatively precipitated by ammonium acetate in a dilute hydrochloric acid
solution and that the mixed precipitates of iron and aluminum phosphates obtained at
this temperature are free of lime. The operation is conducted in the following
manner:
The hydrochloric acid solution of the phosphate must contain no free chlorin and
is treated with a few drops of a methyl orange solution. Ammonia is added until
nearly neutral, but the acid reaction is retained as shown by the indicator. A few
cubic centimeters of ammonium acetate are added, which produce a yellow
coloration of the liquid and also a complete precipitation of the iron and aluminum
phosphates when warmed to 70°. At this temperature the precipitation of any
calcium phosphate is avoided. A small quantity of the lime may be carried down
mechanically and therefore the precipitate should be dissolved in hydrochloric acid
and the precipitation again made as above after the addition of some sodium
phosphate. If the original solution contain any free chlorin, as may be the case when
aqua regia is employed as solvent, before beginning the separation, ammonia should
be added in slight excess and the acidity restored by hydrochloric after adding the
indicator. In washing the precipitates, water of not over 70° must be used. As has
been shown by Hess in the work cited in the next paragraph, the statement of C.
Glaser to the effect that the precipitates obtained as above are free of lime has not
been proved to be strictly correct. The process, however, is a distinct improvement
over the older methods and forms the basis of the amended process given below,
which appears to be sufficiently accurate to entitle the acetate method to favorable
consideration.
34. Method of Hess.—Hess has lately made a thorough investigation of the
standard methods of determining the iron and aluminum oxids in the presence of
phosphoric acid and has shown that the assumption that the composition of the
precipitate is represented by the formula Al₂(PO₄)₂ + Fe₂(PO₄)₂ is erroneous[24].
In the washing of the precipitated iron and aluminum phosphates there is a
progressive decomposition of the compound with the production of a basic salt. The
composition of the precipitate at the end is dependent chiefly upon the way in which
the washing takes place. It is quite difficult to always secure a washing in exactly the
same way and the final composition of the precipitate varies with almost every

determination. It is not, therefore, an accurate proceeding to take half the weight of
the precipitate as phosphoric acid or as iron oxid and alumina. In every case it is
necessary to dissolve the precipitate and determine the phosphoric acid in the regular
way. Hess proposes the following method for carrying out the acetate process of
separation:
The mineral phosphate should be dissolved in hydrochloric acid and the solution
made up to such a volume as shall contain in each fifty cubic centimeters, one gram
of the original substance. This quantity of the solution is diluted with two or three
times its volume of water to which a drop of methyl orange solution (1-100) is
added, and ammonia added with constant stirring until the solution is just colored
and still reacts slightly acid. Without taking any account of the precipitate which is
produced by this approximate neutralization of the solution, there are added fifty
cubic centimeters of acid ammonium acetate which in one liter contains 250 grams
of commercial ammonium acetate. The acidity of the solution is due to an excess of
acetic in the commercial salt. The temperature is then carried to 70° and the
precipitate produced immediately separated by filtration, washed four times with
water below 70°, and again dissolved in dilute hydrochloric acid. The dissolved
precipitate is treated with ten cubic centimeters of a ten per cent ammonium
phosphate solution and again almost neutralized as described above, twenty-five
cubic centimeters of the ammonium acetate solution added and warmed to 70°.
The precipitate obtained is once more dissolved and precipitated as above
described, and is then collected upon a filter, washed, ignited, and weighed. The
residue after ignition is dissolved in the crucible by heating with a little concentrated
hydrochloric acid, and washed into a beaker. Any silicic acid present is separated by
filtration, ignited, and weighed, and subtracted from the total weight of the
precipitate. To the filtrate is added ammonia to diminish the acidity, but not sufficient
to produce a precipitate and the clear solution is treated with thirty cubic centimeters
of the ordinary ammoniacal citrate solution and fifteen cubic centimeters of
magnesium mixture, and the precipitation of the ammonium magnesium phosphate
hastened by stirring with a glass rod.
It is advisable to always make the filtrate from the third precipitation slightly
ammoniacal and to boil it for a long time. If the operation have been carried on
correctly, there occurs only a slight precipitate of Ca₃P₂O₈ amounting only to a few
milligrams. In some cases it may be necessary to dissolve the precipitate and
reprecipitate the iron and aluminum phosphates a fourth time.
The whole time required for the triple precipitation, according to Hess, if all the
operations be properly conducted, is from three to four hours. It is therefore possible
by this variation of the acetate method to secure a determination of the iron and
alumina as phosphates in the same time which is occupied by the Glaser-Jones
method when the separation of lime is taken into account.

If the solution of the mineral phosphate employed contain any notable quantity
of organic material, it must be destroyed by boiling with bromin or some other
oxidation agent, before the precipitation by the acetate method is commenced.
The presence of silicic acid need not be taken into special consideration since
this can be detected and determined in the phosphate precipitates after they have
been ignited and weighed. While the determinations of the phosphoric acid in Hess’
method were made by precipitation in the presence of citrate, he found that they
agree perfectly with the previous precipitations with molybdic solution.
35. Method of Glaser.—The principle on which this method rests depends on
the preliminary removal of the lime by conversion into calcium sulfate and its
precipitation in the presence of strong alcohol.[25] It is conducted as follows:
Five grams of the phosphate are dissolved in a mixture of twenty-five cubic
centimeters of nitric acid of 1.2 specific gravity and about 12.5 cubic centimeters of
hydrochloric acid of 1.12 specific gravity, and made up to a volume of half a liter,
and filtered. One hundred cubic centimeters of the filtrate, equivalent to one gram of
the substance, are placed in a quarter liter flask and twenty-five cubic centimeters of
sulfuric acid of 1.84 specific gravity added. The flask is allowed to stand for about
five minutes and meanwhile shaken a few times. About 100 cubic centimeters of
alcohol of ninety-five per cent are then added and the flask filled with alcohol to the
mark and well shaken. A certain degree of concentration takes place and this is
compensated for by lifting the stopper and filling again with alcohol to the mark and
shaking a second time. After allowing to stand for half an hour the contents of the
flask are filtered, 100 cubic centimeters of the filtrate being equal to four-tenths gram
of the substance. This volume, filtered, is evaporated in a platinum dish until the
alcohol is driven off. The alcohol-free residue is heated to boiling in a beaker with
about fifty cubic centimeters of water. Ammonia is added to alkaline reaction, but in
order to avoid strong effervescence it is not added during the boiling. The excess of
ammonia is evaporated, the flask allowed to cool, the contents filtered, precipitate
and filter washed with warm water, ignited, and the phosphates of iron and alumina
weighed. Half of the weight of the precipitate represents the weight of Fe₂O₃ +
Al₂O₃. The estimation, as before indicated, should be carried on without delay, the
whole time required not exceeding from one and a half to two hours.
36. Jones’ Variation.—The method of Glaser described above, as practiced by
the German chemists, has been found by Jones to be inaccurate on account of the
alcohol not being added in sufficient quantity in the precipitation of calcium sulfate
and for the additional reason that the amount of sulfuric acid added is more than is
actually necessary[26]. Jones modifies the method as follows: Ten grams of the
material are dissolved in nitro-hydrochloric acid and the solution made up to 500
cubic centimeters and filtered. Fifty cubic centimeters of this solution, representing

one gram, are evaporated to twenty-five cubic centimeters and, while still hot, ten
cubic centimeters of dilute sulfuric acid (one to five) added. The mixture is then well
stirred and cooled. One hundred and fifty cubic centimeters of ninety-five per cent
alcohol are next added and after stirring, the solution is allowed to stand three hours.
The calcium sulfate is collected on a filter, washed with alcohol, and the filtrate and
washings collected in an erlenmeyer. The washing is completed when the last ten
drops, after dilution with an equal volume of water, are not colored with a drop of
methyl orange.
The moist calcium sulfate is transferred to a platinum crucible, the filter placed
on it, the alcohol burned off, the filter incinerated, and the calcium sulfate ignited
and weighed. The contents of the flask are heated to expel the alcohol, the residue
washed into a beaker, made slightly alkaline with ammonia, and again heated till all
the ammonia is driven off. This treatment is necessary to prevent the precipitate from
being contaminated with magnesia. The precipitate is collected on a filter, washed
four times with hot water, or water containing ammonium nitrate, dried, ignited, and
weighed. One-half of the weight of the precipitate represents the weight of the ferric
and aluminic oxids.
37. Estimation of Iron and Alumina in Phosphates by Crispo’s Method.—
The phosphate of ferric iron is subject to a slight decomposition in presence of both
hot and cold water with a tendency to the production of basic compounds. It is
soluble to a slight extent in hot and cold acetic acid, almost insoluble in ammonium
acetate, and quite insoluble in ammonium chlorid and nitrate. Aluminum phosphate
is likewise soluble, to a slight degree, in acetic acid and ammonium acetate, and
insoluble in ammonium chlorid and nitrate. The method of Crispo for the separation
of iron and alumina in phosphates is based on the above properties.[27] Five grams of
the mineral phosphate are dissolved in fifty cubic centimeters of aqua regia,
composed of forty cubic centimeters of hydrochloric acid of 1.10, and ten of nitric
acid of 1.20 specific gravity, and this solution is diluted to half a liter. To fifty cubic
centimeters of the filtered solution are added two of ammonia (0.96) and fifty of a
half saturated solution of ammonium chlorid, and the whole boiled. The liquid
should remain clear, but if it become cloudy add a little dilute nitric acid, drop by
drop, until the turbidity is removed, and then ten cubic centimeters of a saturated
solution of ammonium acetate, and boil for three minutes, cool, and filter. The
precipitate is washed twice with a ten per cent solution of ammonium chlorid and
redissolved with two cubic centimeters of nitric acid, and the filter washed with hot
water. The phosphoric acid is separated by forty cubic centimeters of molybdate
solution, and the precipitate washed three or four times with a one per cent nitric
acid solution.
To the filtrate are added fifty cubic centimeters of a one-half saturated
ammonium chlorid solution, ammonia is added in slight excess to produce

precipitation and the mixture boiled for a few minutes. After filtering, the precipitate
is washed with hot water three or four times, dissolved in two cubic centimeters of
nitric acid, and the filter washed with hot water. Again, fifty cubic centimeters of half
saturated ammonium chlorid are added and the precipitate thrown down once more
by ammonia in slight excess. The precipitate is washed with hot water and finally
ignited and weighed as iron and aluminum oxids.
According to Crispo, the original Glaser method, with its various modifications,
is not to be considered reliable, and the choice lies between the molybdic method as
usually practiced, and his own for the accurate estimation of iron and alumina.
Manganese disturbs the accuracy of the results unless the directions given are
carefully followed. Manganese phosphate is soluble at all temperatures below fifty.
If then the mixture of the phosphates be allowed to cool before filtering, the iron and
aluminum salts are not contaminated with manganese. This method of Crispo is
somewhat tedious, but it is claimed that these variations of the molybdic method
render it exact in respect of the determination of iron and alumina.
38. Method Employed in Geological Survey.—Chatard gives the following
directions for conducting the Glaser-Jones process[28]: The distillation flask
containing the alcoholic filtrate is connected with its condenser and heated on a
water-bath until no more alcohol comes over. This distillate, if mixed with a little
sodium carbonate and redistilled over quicklime, can be used over and over again, so
that the expense for alcohol is really very slight, while in the use of the Glaser
method, with its large amount of sulfuric acid, all the alcohol is lost.
When the distillation is ended the residue in the flask is washed into a platinum
dish and evaporated to a small bulk on the water-bath. The dark brown color
produced is due to the presence of organic matter and this must be destroyed, as it
prevents the complete precipitation of the phosphate in the subsequent operation.
The organic matter is best destroyed by removing the dish from the bath, adding
a small quantity of pure sodium nitrate, and heating very carefully over the naked
flame, keeping the dish well covered with a watch-glass to avoid spattering. The
mass fuses to a colorless, viscous liquid, becoming glassy when cooled and is readily
soluble in a hot very dilute solution of nitric acid. The solution transferred to a
beaker is made distinctly alkaline with ammonia and carefully neutralized with
acetic acid, diluted with hot water, boiled, and the precipitate allowed to settle, after
which it is separated by filtration.
After the precipitate has been completely transferred to the filter, the washing is
completed with a dilute solution of ammonium nitrate. The precipitate is dried,
ignited, cooled, and weighed.
The determinations should be made in pairs, one portion being used for the
estimation of the phosphoric acid by fusing with a little sodium carbonate, and the

other, after fusion with sodium carbonate, is dissolved with sulfuric acid and the iron
reduced and titrated with potassium permanganate solution. The filtrate from the iron
and alumina determination is evaporated to a small bulk, made strongly ammoniacal
and allowed to stand for some time when the magnesia present separates as
ammonium magnesium phosphate which is determined in the usual way.
If, during the evaporation of the filtrate, any flocculent matter separate, it should
be removed by filtration and examined before precipitating the magnesia.
39. Variation of Marioni and Fasselli.—Glaser’s method has been shown to be
subject to errors by Marioni and Fasselli[29] in the following respects:
1. The precipitation of a small quantity of calcium phosphate with the ferric and
aluminum phosphates.
2. The possible precipitation of basic phosphates if all the iron and alumina are
not combined with phosphoric acid in the mineral.
3. The partial solubility of ferric and aluminum phosphates in dilute acetic acid.
4. The decomposition of ferric orthophosphate into soluble acid phosphate and
insoluble basic salt by boiling.
To avoid these errors the following procedure is proposed: From one to five
grams of the phosphate are boiled in a flask for ten minutes with fifteen cubic
centimeters of strong hydrochloric acid, and afterwards diluted with a double volume
of water. A few crystals of potassium chlorate are added, and several drops of nitric
acid, and the liquid boiled to expel chlorin. It is then filtered and washed until the
volume of the filtered liquid amounts to 150 cubic centimeters. After cooling, a half
gram of ammonium phosphate in solution is added, and two cubic centimeters of
glacial acetic acid, followed by dilute ammonia, drop by drop, until a slight
precipitate persists on stirring. Again the same quantity of acetic acid is added as
above, well shaken, and left for two hours. The precipitate is collected on a filter and
washed with a one per cent ammonium phosphate solution. The precipitate is
dissolved by a minimum quantity of hydrochloric acid and the solution collected in
the same vessel in which the precipitation took place. A second precipitation is
conducted just as described above. The precipitate is washed as above described and
ignited at a dull red heat. Half the weight obtained represents the ferric oxid and
alumina.
40. Method of Ogilvie.—For the separation of alumina from phosphoric acid
Ogilvie recommends that the filtrate from the phosphomolybdate precipitate be
neutralized with ammonia, the precipitate thus formed redissolved in nitric acid,
again precipitated with ammonia, filtered, ignited, and weighed as aluminum oxid.
[30]
If iron be present it will, of course, appear in the product. For use in the

examination of mineral phosphates the method can not have a wide application
without amendment.
41. Method of Krug and McElroy.—Krug and McElroy show that when
sufficient alcohol is added to precipitate all of the calcium sulfate in the Glaser
method, it will also cause a precipitation of a considerable quantity of iron, by means
of which the calcium sulfate will be colored.[31] The presence of potassium and
ammonium salts also affects very notably the precipitation of calcium. The method
employed by them, in order to avoid these sources of error, is as follows:
One hundred cubic centimeters, equivalent to one gram of the substance, in a
nitric acid solution, are placed in a half liter flask and a solution of ammonium
molybdate added until all the phosphoric acid has been precipitated. The addition of
ammonium nitrate will hasten the separation of the ammonium phosphomolybdate.
The liquid should be allowed to stand for twelve hours. The flask is then filled to the
mark, the contents well shaken, filtered through a dry filter, and duplicate samples of
200 cubic centimeters each of the filtrate taken for analysis.
A small quantity of ammonium nitrate is dissolved in the liquid, and ammonia
cautiously added, keeping the solution as cool as possible. The iron and alumina are
precipitated as hydroxids. The mixed hydroxids are collected on a filter, washed with
water, the filtrate and washings being collected in a beaker. The precipitate should be
dissolved with a small quantity of a solution of ammonium nitrate and nitric acid,
again precipitated with ammonia, filtered, washed, ignited, and weighed. This
treatment is for the purpose of excluding all possibility of error from the presence of
molybdic anhydrid. After weighing, the mixed oxids should be fused with sodium
bisulfate, the magma dissolved in water, and the iron determined volumetrically with
potassium permanganate after reduction to the ferrous state.
McElroy has further shown by experiments in this laboratory that even the
molybdate method of separating the iron and alumina from phosphoric acid with the
improvements as first suggested by Krug and himself, may not always give reliable
results.[32] In a solution containing ferrous iron equivalent to 56.4 milligrams of
ferric oxid, were placed enough of a solution of sodium phosphate to correspond to
100 milligrams of phosphorus pentoxid. The precipitate was dissolved by adding
nitric acid, oxidized with bromin water, and the phosphoric acid thrown out with
ammonium molybdate. The precipitate was washed with weak nitric acid and the
combined filtrate and washings neutralized with ammonia. The resultant precipitate
was dissolved in a solution of ammonium nitrate and nitric acid, filtered, and again
precipitated with ammonia. In two instances the quantities of material recovered
after ignition were 56.9 and 57.3 milligrams, respectively, instead of the theoretical
amount, viz., 56.4 milligrams.

When the work was repeated after the addition of 400 milligrams of calcium oxid
the weight of the precipitate recovered was 62.3 and 63.1 milligrams in duplicate
determinations. Similar determinations were made with a known weight, viz., 35.6
milligrams of alumina. The treatment of the mixture was precisely as indicated
above for iron. The quantity of alumina finally obtained was 28.9 and 29.3
milligrams, respectively, in duplicate determinations. When the lime was added,
however, the weights of alumina, recovered, fell to 19.8 and 20.6 milligrams,
respectively. These results show that the molybdate method for the separation of iron
and alumina in the presence of a large excess of lime and phosphoric acid is subject
to widely varying results, but that the error due to the excess of iron in the weighed
product is partly corrected by the one due to deficiency of alumina.
42. Method of Wyatt.—A method largely used in this country, both in private
laboratories and by fertilizer factories, for determining iron and alumina, is described
by Wyatt[33]. It is claimed for this method that, while it may not be strictly accurate,
yet it is rapid and easy, and in the hands of trained analysts yields concordant results.
Fifty cubic centimeters of the first solution of the sample in aqua regia, or an amount
thereof equivalent to one gram of the phosphate, in a beaker, are rendered alkaline by
ammonia. The resulting precipitate is first redissolved by hydrochloric acid, and a
slight alkalinity is again produced with ammonia. Fifty cubic centimeters of strong
acetic acid are next added, the mixture stirred and placed in a cool place and left
until cold. The precipitate is then separated by filtration and washed twice with
boiling water. The vessel holding the filtrate is replaced by the beaker in which the
precipitation was made. The precipitate is dissolved in a little fifty per cent hot
hydrochloric acid and the filter washed with hot water. After rendering slightly
alkaline, as in the first instance, the treatment with acetic acid is repeated as
described. The precipitate is washed this time, twice with cold water containing a
little acetic acid and three times with hot water. The precipitate is dried, ignited, and
weighed as iron and aluminum phosphate. Half of this weight may be taken to
represent the quantity of iron and aluminum oxids.
To separate the iron and alumina the precipitate just described is dissolved in hot
hydrochloric acid, filtered into a 100 cubic centimeter flask, and made up to the
mark by hot wash-water.
The phosphoric acid is determined in one-half of the filtrate and in the remaining
half the iron is reduced with zinc and determined with potassium permanganate in
the usual way. The phosphoric acid and iron having been thus determined the
alumina is estimated by difference. The chief objection to this process is in the
excessive quantity of acetic acid used and the danger of solution of the precipitated
phosphates caused thereby.

43. Estimation of the Lime and Magnesia.—The filtrate and washings from the
first precipitation, (paragraph 41,) of iron and alumina in the method of Krug and
McElroy, above described, are collected and sufficient ammonium oxalate is added
to precipitate the calcium. The precipitated calcium is very fine and should be
collected on a gooch, under pressure. The filtrate and washings from the calcium
precipitate are again collected, and a solution of sodium phosphate added to
precipitate the magnesia. The solution must be kept cool and slightly alkaline with
ammonia during the above operations in order to prevent the separation of molybdic
anhydrid.
44. Estimation of Sulfuric Acid.—As a rule, sulfates are not abundant in
mineral phosphates. In case the samples are pyritiferous, however, considerable
quantities of sulfuric acid may be found after treatment with aqua regia.
The acid is precipitated with barium chlorid, in the usual way, in an aliquot
portion of the filtrate first obtained. The precipitate of barium sulfate is washed with
hot water until clean, dried, ignited, and weighed. If the portion of the filtrate taken
represent half a gram of the original material then the weight of barium sulfate
obtained multiplied by 0.6858 will give the quantity of sulfur trioxid in one gram.
45. Estimation of Fluorin by the Method of Berzelius as Modified by
Chatard.—The method of estimating fluorin as proposed by Berzelius, has been
found quite satisfactory in the laboratory of the Geological Survey, with the
modifications given below.[34]
Two grams of the phosphate are intimately mixed in a large platinum crucible
with three grams of precipitated silica and twelve grams of pure sodium carbonate,
and the mixture is gradually brought to clear fusion over the blast-lamp. When the
fusion is complete the melt is spread over the walls of the crucible, which is then
rapidly cooled (preferably by a blast of air). If this have been properly done, the
mass separates easily from the crucible, and the subsequent leaching is hastened. The
mass, detached from the crucible, is put into a platinum dish into which whatever
remains adhering to the crucible, or its lid, is also washed with hot water. A
reasonable amount of hot water is now put into the dish, which is covered and
digested on the water-bath until the mass is thoroughly disintegrated. To hasten this,
the supernatant liquid may, after awhile, be poured off, the residue being washed into
a small porcelain mortar, ground up, returned to the dish and boiled with fresh water
until no hard grains are left. The total liquid is then filtered, and the residue is
washed with hot water. The filtrate (which should amount to about half a liter) is
nearly neutralized with nitric acid (methyl orange being used as indicator), some
pure sodium bicarbonate is at once added, and the solution (in a platinum dish, if one
large enough is at disposal, otherwise in a beaker) is placed on the water-bath, when
it speedily becomes turbid through separation of silica. As soon as the solution is

warm it is removed from the bath, stirred, allowed to stand for two or three hours,
and then filtered by means of the filter-pump and washed with cold water.
The filtrate is concentrated to about a quarter of a liter and nearly neutralized, as
before, some sodium carbonate is added, and the phosphoric acid is precipitated with
silver nitrate in excess. The precipitate is separated by filtration and washed with hot
water, and the excess of silver in the filtrate is removed with sodium chlorid.
The filtrate from the silver chlorid (after addition of some sodium bicarbonate) is
evaporated to its crystallizing point, then cooled and diluted with cold water; still
more sodium bicarbonate is added, and the whole is allowed to stand, when
additional silica will separate, and this is to be removed by filtration.
This final solution is nearly neutralized, as before; a little sodium carbonate
solution is added; it is heated to boiling and an excess of solution of calcium chlorid
is added. The precipitate of calcium fluorid and carbonate must be boiled for a few
minutes, when it can be easily filtered and washed with hot water. The precipitate is
then washed from the filter into a small platinum dish and evaporated to dryness,
while the filter, after being partially dried and used to wipe off any particles of the
precipitate adhering to the dish in which it was formed, is burned, and the ash is
added to the main precipitate. This, when dry, is ignited, and allowed to cool; dilute
acetic acid is added in excess, and the whole is evaporated to dryness, being kept on
the water-bath until all odor of acetic acid has disappeared. The residue is then
treated with hot water, digested, filtered on a small filter, washed with hot water,
partially dried, put into a crucible, carefully ignited, and weighed as calcium fluorid.
The calcium fluorid is then dissolved in sulfuric acid by gentle heating and agitation,
evaporated to dryness on a radiator, ignited at full red heat, and weighed as calcium
sulfate. From this weight the equivalent weight of calcium fluorid should be
calculated, and this should be very close to that actually found as above, but should
never exceed it. The difference, which is generally about a milligram (sometimes
more), is due to silica precipitated with the fluorid. The percentage of fluorin is,
therefore, always calculated from the weight of the sulfate, and not from that of the
fluorid obtained.
The main improvements in this method are the use of sodium bicarbonate to
separate the silica, and the keeping of the earlier solutions as dilute as possible,
which can not be done, if ammonium carbonate be used for the separation of the
silica. These changes make the fluorin estimation, although still tedious, far more
rapid than before, and the results are very satisfactory.
46. Modification of Wyatt.—By reason of the tediousness of the method of
Chatard given above, Wyatt has sought to shorten the process by the following
modification:[35]

Five grams of the finely ground phosphate are fused in a platinum dish with
fifteen grams of the mixed carbonates of sodium and potassium and three grams of
fine sand. After fusing very thoroughly with a strong heat for a quarter of an hour,
the dish is removed from the fire and cooled. Its contents, dissolved in hot water, are
then put into a half liter flask, and a considerable excess of ammonium carbonate is
added to the liquid. All the soluble silica falls out of solution, and the flask, after
cooling, is made up to the mark with distilled water, well shaken, and then set aside
for twenty-four hours to settle. At the end of this time 200 cubic centimeters are
carefully decanted through a filter; the filter is well washed, and the filtrate, after
being nearly neutralized with hydrochloric acid, is treated with an excess of calcium
chlorid solution.
The precipitate, consisting of phosphate, fluorid, and some calcium carbonate, is
allowed to settle, and is then carefully washed with boiling water, first by
decantation several times, and finally on the filter. After being properly dried in the
gas-oven, calcined, and cooled, the residue is treated with acetic acid, placed upon
the water-bath, and evaporated to complete dryness.
The calcium acetate is now well washed out by several treatments with boiling
water, and the residue is brought upon a filter, dried, calcined, and weighed. The
weight represents the calcium phosphate and fluorid contained in two grams of the
original sample; and if the calcium phosphate in the residue be determined,
according to the usual methods, the difference will be calcium fluorid and may be
thus estimated.
Example.—Assuming the calcined residue of calcium
phosphate and fluorid in two grains of the original sample to
have amounted to one and six-tenths gram and the calcium
phosphate in this quantity to have been determined as 1.540
gram, the calcium fluorid is thus proved to be 0.060 gram, and,
therefore, 2: 0.60::100: x = 3 per cent calcium fluorid which,
multiplied by 0.4897, gives 1.46 per cent of fluorin.
The above method, while shorter, is not to be preferred to the Chatard process
when great accuracy is desired. All the soluble silica may not fall out of the solution
as Wyatt says. Finally the fluorin is calculated from small differences in the weight
of very heavy precipitates and all the error of the process may be found affecting the
numbers for fluorin. For commercial purposes, however, the method is to be
recommended for its comparative brevity.

GENERAL METHODS FOR ESTIMATING
PHOSPHORIC ACID IN FERTILIZERS.

47. Preliminary Considerations.—The chief sources of the phosphoric acid in
commercial fertilizers are the mineral phosphates and bones. In respect of the
analyses of mineral phosphates detailed directions have been given in the preceding
pages. Bones are valuable for fertilizing materials, both because of their content of
phosphoric acid and of their organic nitrogen. The methods of treating bones for
their phosphoric acid will be found in the general methods for fertilizing materials,
and their nitrogen content can be determined by the processes to be described
hereafter. Other fertilizing materials also contain phosphorus, as ashes, tankage, oil
cakes, and other organic products. In general, the methods for determining the
phosphoric acid is the same in all cases, but the means of destroying the organic
matter precedent to the analysis vary in different cases. In most cases a simple
ignition is sufficient, while, if the phosphorus be found in certain organic products,
the oxidation must be accomplished by one of the methods described in the
processes adopted by the official chemists, or by the means described in volume
first, paragraph 378 or 382. In all cases of acid phosphates and superphosphates, the
water and ammonium citrate soluble phosphoric acid is to be determined as well as
the total. In basic slags the amount soluble in ammonium citrate or dilute citric acid
is also to be ascertained.
In all cases where soluble or so-called reverted acid is to be considered, the
analysis must be performed without previous desiccation or ignition. If water content
or loss on ignition are to be considered, the operation to determine them must be
conducted on a separate part of the sample.
The methods of analysis which have been adopted by associations of chemists
should be given the preference in the conduct of the work, although it must be
admitted that they may contain sources of error, and may be in no respect superior to
processes employed by chemists in their private capacity. In this country the methods
adopted by the Association of Official Agricultural Chemists should be followed as
closely as possible. The great merit of other methods, however, must not be denied.
Especially those methods which shorten the time required or diminish the labor and
expense of the analysis are worthy of careful consideration. In factory work, for
instance, it is often far more important for the chemist to be able to rapidly determine
the phosphoric acid in a great number of samples with approximate accuracy than to
confine his work to one with absolute precision. Some of the shorter methods,
moreover, notably the citrate process, appear to be quite, if not altogether, as reliable
as the molybdate method, while in the case of the uranium volumetric process, it
must not be forgotten that it is almost the only one practiced in France. Other
volumetric processes are given in full, as, for instance, the one perfected by
Pemberton, but data are still lacking to justify their strong recommendation. It should
be remembered that this manual is not written for the beginner but rather for the
chemist already acquainted with the principles and practice of general chemical

analysis, and it is, therefore, expected that each analyst will make intelligent use of
the data placed at his disposal.
48. Determination of Phosphoric Acid with Preliminary Precipitation as
Stannic Phosphate.—This method, once much in use and highly recommended, is
now almost unknown among the processes of fertilizer control. It was first proposed
and described by Girard, and rests on the precipitation of the phosphoric acid in a
nitric acid solution by means of metallic tin.[36] The stannic acid formed by the
oxidation of the tin unites with the phosphoric acid held in a free state by the nitric
acid. The precipitation of the phosphoric acid is said to be complete, but a trace of it
has been found in the iron and alumina subsequently separated from the solution.
The precipitate obtained is dissolved in caustic potash, whereby soluble potassium
metastannate and phosphate are obtained. Following is the method of conducting the
analysis as described by Crookes:[37]
The phosphate should be dissolved in nitric acid, and any chlorin present be
expelled by repeated evaporations with the solvent. Finally, to the evaporated mass
the strongest nitric acid is added. Pure tin-foil is added and heat applied. The
phosphoric acid is precipitated by the stannic acid formed. The quantity of tin used
should be from six to eight times as great as that of the phosphoric acid present.
The precipitate is collected on a filter, washed, and dissolved in caustic potash.
The solution is saturated with hydrogen sulfid, and on adding acetic acid in slight
excess the tin sulfid is separated and removed by filtration. The whole of the
phosphoric acid, supposed to be almost free of tin, is now found in the filtrate. The
filtrate is concentrated to small bulk and any tin sulfid present separated by filtering,
and the phosphoric acid finally removed from the ammoniacal filtrate by
precipitation with magnesia mixture. The chief difficulties of this method are to be
found, on the one hand, in the retention of some of the phosphoric acid by the iron
and alumina which may be present, and on the other, in the presence of some tin in
the final magnesium pyrophosphate. If the tin be all removed as sulfid, the latter
source of error will be avoided. It is difficult to secure pure metallic tin, and this is
another disturbing element in the process. It can not be recommended for the work
which agricultural analysts are usually called on to perform.[38]
49. Water-Soluble Phosphoric Acid.—The method of procedure recommended
by the Association of Official Chemists is as follows:[39] Place two grams of the
sample in a nine centimeter filter; wash with successive small portions of cold water,
allowing each portion to pass through before adding more, until the filtrate measures
about 250 cubic centimeters. If the filtrate be turbid, add a little nitric acid. Make up
to any convenient definite volume; mix well; take any convenient portion and
proceed as under total phosphoric acid.

50. Citrate-Insoluble Phosphoric Acid.—Heat 100 cubic centimeters of strictly
neutral ammonium citrate solution of 1.09 specific gravity to 65° in a flask placed in
a bath of warm water, keeping the flask loosely stoppered to prevent evaporation.
When the citrate solution in the flask has reached 65°, drop into it the filter
containing the washed residue from the water-soluble phosphoric acid determination,
close tightly with a smooth rubber stopper, and shake violently until the filter paper
is reduced to a pulp. Place the flask back into the bath and maintain the water in the
bath at such a temperature that the contents of the flask will stand at exactly 65°.
Shake the flask every five minutes. At the expiration of exactly thirty minutes from
the time the filter and residue were introduced, remove the flask from the bath and
immediately filter as rapidly as possible. It has been shown by Sanborn, in this
laboratory, that the filtration is greatly facilitated by adding asbestos pulp. Wash
thoroughly with water at 65°. Transfer the filter and its contents to a crucible, ignite
until all organic matter is destroyed, add from ten to fifteen cubic centimeters of
strong hydrochloric acid, and digest until all phosphate is dissolved; or return the
filter with contents to the digestion flask, add from thirty to thirty-five cubic
centimeters of strong nitric, and from five to ten cubic centimeters of strong
hydrochloric acid, and boil until all the phosphate is dissolved. Dilute the solution to
200 cubic centimeters. If desired, the filter and its contents can be treated according
to methods (1), (2), or (3), under total phosphoric acid. Mix well; filter through a dry
filter; take a definite portion of the filtrate and proceed as under total phosphoric
acid.
In case a determination of citrate-insoluble phosphoric acid be required in non-
acidulated goods it is to be made by treating two grams of the phosphatic material,
without previous washing with water, precisely in the way above described, except
that in case the substance contain much animal matter (bone, fish, etc.), the residue
insoluble in ammonium citrate is to be treated by one of the processes described
below under total phosphoric acid, (1), (2), or (3).
51. Total Phosphoric Acid.—In case of ignition the residual material is to be
dissolved in hydrochloric acid. The following methods of treating the raw material,
using two grams in each case, may be employed: (1) Evaporate with five cubic
centimeters of magnesium nitrate, ignite, and dissolve in hydrochloric acid. (2) Boil
in a Kjeldahl flask graduated to 250 cubic centimeters, with from twenty to thirty
cubic centimeters of strong sulfuric acid, adding from two to four grams of sodium
or potassium nitrate at the beginning of the digestion and a small quantity after the
solution has become nearly colorless; or adding the nitrate in small portions from
time to time. After the solution is colorless, add 150 cubic centimeters of water and
boil for a few minutes, cool, and make up to volume. (3) Digest with strong sulfuric
acid and such other reagents as are used in either the plain or modified Kjeldahl or
Gunning methods for estimating nitrogen. Do not add any potassium permanganate,

but after the solution has become colorless add about 100 cubic centimeters of water
and boil for a few minutes, cool, and make up to a convenient volume; two and five-
tenths grams of substance and a digestion flask graduated to 250 cubic centimeters
are recommended. This method will be found convenient when both the nitrogen and
the total phosphoric acid are to be determined in a fertilizer. In this case, after
diluting the volume and mixing, a part for the estimation of nitrogen, may be
removed with a pipette and the remainder then filtered through a dry filter and a
portion taken for the determination of the total phosphoric acid. (4) Dissolve in thirty
cubic centimeters of concentrated nitric acid and a small quantity of hydrochloric
acid. (5) Add thirty cubic centimeters of concentrated hydrochloric acid, heat, and
add cautiously, in small quantities at a time, about five-tenths gram of finely-
pulverized potassium chlorate. (6) Dissolve in from fifteen to thirty cubic
centimeters of strong hydrochloric and from three to ten cubic centimeters of nitric
acid. This method is recommended for fertilizers containing much iron or aluminum
phosphate. Boil until all phosphates are dissolved and all organic matter is destroyed;
cool and dilute to 200 or 250 cubic centimeters; mix and pass through a dry filter;
take an aliquot part of the filtrate corresponding to a quarter, half, or one gram,
neutralize with ammonia, and clear with a few drops of nitric acid. In case
hydrochloric or sulfuric acid have been used as a solvent, add about fifteen grams of
dry ammonium nitrate.
To the hot solutions, for every decigram of phosphorus pentoxid that is present,
add fifty cubic centimeters of molybdic solution. Digest at about 65° for an hour,
filter, and wash with water or ammonium nitrate solution. Test the filtrate by
renewed digestion and the addition of more molybdic solution. Dissolve the
precipitate on the filter with ammonia and hot water and wash into a beaker to a bulk
of not more than 100 cubic centimeters. Nearly neutralize with hydrochloric acid,
cool, and add magnesia mixture from a burette; add slowly (about one drop per
second), stirring vigorously. After fifteen minutes add thirty cubic centimeters of
ammonia solution of 0.95 density. Let stand for some time; two hours are usually
enough. Filter, wash with dilute ammonia, ignite gently at first and then at white heat
for ten minutes, and weigh. For the quantity of magnesia mixture to be added see
paragraph 21.
52. Citrate-Soluble Phosphoric Acid.—The sum of the water-soluble and
citrate-insoluble subtracted from the total gives the citrate-soluble phosphoric acid.
53. Preparation of Reagents.—(1) Ammonium Citrate Solution.—(a) Mix 370
grams of commercial citric acid with 1,500 cubic centimeters of water, nearly
neutralize with commercial ammonia, cool, add ammonia until exactly neutral
(testing with saturated alcoholic solution of corallin) and bring to a volume of two
liters. Test the specific gravity, which should be 1.09 at 20°, before using.

(b) Alternate Method.—To 370 grams of commercial citric acid add commercial
ammonia, of 0.96 specific gravity, until nearly neutral; reduce the specific gravity to
nearly 1.09 and proceed as follows: Prepare a solution of fused calcium chlorid 200
grams to the liter, and add four volumes of strong alcohol. Make the mixture exactly
neutral, using a small amount of freshly prepared corallin solution as a preliminary
indicator, and test finally by withdrawing a portion, diluting with an equal volume of
water, and testing with cochineal solution. Fifty cubic centimeters of this solution
will precipitate the citric acid from ten cubic centimeters of the citrate solution. To
ten cubic centimeters of the nearly neutral citrate solution add fifty cubic centimeters
of the alcoholic calcium chlorid solution, stir well, filter at once through a folded
filter, dilute with an equal volume of water, and test the reaction with neutral solution
of cochineal. If acid or alkaline, add ammonia or citric acid, as the case may be, to
the citrate solution, mix, and test again as before. Repeat this process until a neutral
reaction of the citrate solution is obtained. At the end the specific gravity must be
1.09 at 20°.
(2) Molybdic Solution.—See paragraph 22.
(3) Ammonium Nitrate Solution.—Dissolve 200 grams of commercial
ammonium nitrate in water and bring to a volume of two liters.
(4) Magnesia Mixture.—See paragraph 22.
(5) Dilute Ammonia for Washing.—See paragraph 22.
(6) Magnesium Nitrate.—Dissolve 320 grams of calcined magnesia in nitric acid,
avoiding an excess of the latter; then add a little calcined magnesia in excess, boil,
filter from the excess of magnesia, ferric oxid, etc., and bring to volume of two liters.
54. Official Methods with Norwegian Fertilizers.—The Director of the
Chemical Control Station of Norway, expresses the opinion, that for Norwegian,
Swedish, Danish, and German conditions, the American methods for the
determination of phosphoric acid, notwithstanding their analytical exactness, are
quite inapplicable.[40] In those countries are found many, in part, poorly pulverized
and badly mixed manures, such as ammonium superphosphate, potassium
superphosphate, and potassium ammonium superphosphate, and these can not
usually be so well pulverized and mixed that one can take out a true average sample
of from two to two and five-tenths grams. Care in the analysis is useless when the
material employed does not represent the average condition of the materials
investigated. Therefore, in the countries named, often from ten to twenty grams, and
almost never less than five grams of substance are taken in the preparation of the
solutions, except for instance, in the determination of nitrogen and reverted
phosphoric acid.

55. The Molybdic Acid Method, as Practiced by Direction of the Union of
the German Experiment Stations.—The method adopted by the German
Experiment Stations is essentially that used at Halle.[41] The samples are brought
into solution in the following way: For the estimation of phosphoric acid in bone-
meal, fish-guano and raw phosphates, and the total phosphoric acid in
superphosphates, five grams of the sample are dissolved in fifty cubic centimeters of
aqua regia, made of three parts of hydrochloric acid of 1.12 specific gravity and one
part of nitric acid of 1.25 specific gravity, or the solution may be made of a mixture
of twenty cubic centimeters of nitric acid of 1.42 specific gravity and fifty cubic
centimeters of sulfuric acid of 1.8 specific gravity. The boiling should continue for
half an hour. The solution is made up to half a liter and filtered. Fifty cubic
centimeters of the filtrate containing the phosphoric acid, with double
superphosphates twenty-five cubic centimeters, are digested with 200 cubic
centimeters of ammonium molybdate solution for three hours at 50° in a water-bath
and, after cooling, filtered, so that as little as possible of the precipitate is collected
upon the filter, which is made of strong paper.
The yellow precipitate is washed by decantation in the flask nine times with
twenty cubic centimeters of molybdic solution diluted with one volume of water and
the filter washed out once with the same quantity of liquid. The funnel, with the
filter, is immediately placed upon the flask and the portion of the precipitate
collected in the filter dissolved in five per cent ammonia, which is easily
accomplished by throwing ammonia upon it from a wash-bottle. Afterwards the filter
is washed with a sufficient quantity of hot water and finally removed. The contents
of the flask are neutralized warm, with hydrochloric acid, the acid being added until
the precipitate first formed, after continued shaking, is again dissolved in the liquid.
The solution is then cooled and treated, drop by drop, with constant stirring, with
twenty cubic centimeters of magnesia mixture. Finally twenty-five cubic centimeters
of dilute ammonia solution are added, the precipitate is not shaken, and, after two
hours, is filtered through a gooch.
For the filtering of the ammonium magnesium phosphate by the molybdic
method, freshly prepared felts are always employed since the remarkably fine
crystalline precipitates will pass through a filter which has once been used. It is
necessary also that special precautions be taken in the ignition. The crucible should
be heated in a platinum cap, which has the purpose of protecting the contents of the
crucible from the access of reducing gases during the ignition. After redness has
been reached the cap can be removed and the crucible transferred to a blast where it
is strongly ignited for ten minutes before weighing. The precipitate should be pure
white.
The molybdic solution is prepared as follows: 150 grams of ammonium
molybdate are dissolved in a liter of water, and after the solution is completely

cooled, poured into a liter of nitric acid of 1.2 specific gravity.
56. Estimation of Soluble Phosphoric Acid.—1. The extraction of the
superphosphates is made as follows: Twenty grams of the superphosphates are
placed in a liter flask with 800 cubic centimeters of water and shaken continuously
for thirty minutes. The flask is then filled with water to the mark and the whole again
thoroughly shaken and filtered. For shaking, a machine is recommended, driven by
hand or water power. The normal rate of the machine is fixed at 150 turns per
minute.
2. The solution of the total superphosphates, obtained as above, must be boiled
with nitric acid before the precipitation of the phosphoric acid in order to convert
any phosphoric acid present as pyrophosphoric into tribasic phosphoric acid. For
each twenty-five cubic centimeters of the superphosphate solution ten cubic
centimeters of concentrated nitric acid are added and the mixture boiled.
3. The precipitation of the phosphoric acid is conducted by the molybdenum
method as usually practiced.
4. For the estimation of iron and alumina in each of the superphosphates the
Glaser method is recommended provisionally.
57. Methods for Phosphoric Acid used in the Norway Stations.[42]—1.
Description of the Method for Total Phosphoric Acid.—For determining the
phosphoric acid in bone-meal, fish-guano, and superphosphates, five grams of the
substance, with twenty cubic centimeters of nitric acid of 1.42 specific gravity, and
fifty cubic centimeters of sulfuric acid of 1.8 specific gravity, are boiled half an hour
in a half liter flask, diluted with water, and after cooling, made up to the mark. Fifty
cubic centimeters of the filtrate are made alkaline with ammonia, then acid with
nitric acid, precipitated with fifty cubic centimeters of molybdic solution for every
one-tenth gram of phosphorus pentoxid present, heated over the water-bath for one
hour, and allowed to stand twelve hours more, when the supernatant liquid is
separated by decantation the precipitate washed thoroughly with dilute molybdate
solution (1: 4) dissolved in warm dilute ammonia, and the filter washed with hot
water. The ammoniacal solution is neutralized with hydrochloric acid, cooled,
mixed, drop by drop, with constant stirring, with from ten to twenty cubic
centimeters of magnesia mixture, and after a quarter of an hour one-third the volume
of ten per cent ammonia is added. This is allowed to stand two hours, is filtered,
washed with five per cent of ammonia until the disappearance of the chlorin
reaction, dried, burned in an open crucible over a bunsen, and finally for a quarter of
an hour, in a covered crucible heated over the blast.
2. Water-Soluble Phosphoric Acid.—To twenty grams of the substance in a liter
flask, are added 800 cubic centimeters of water, and shaken every fifteen minutes for

two hours; the volume made up to the mark and the phosphoric acid in fifty cubic
centimeters of the filtrate, equaling one gram substance, is determined as under total.
3. Reverted Citrate-Soluble Phosphoric Acid.—Two and five-tenths grams
substance are rubbed up with water, then washed upon the filter with about 100
cubic centimeters of water, the residue on the filter washed into a flask with a part of
the measured citrate solution, and digested one hour at 35° to 40° with 200 cubic
centimeters of Petermann’s citrate solution. The water and citrate extracts are made
up to a quarter of a liter each, and the phosphoric acid determined in from twenty-
five to fifty cubic centimeters, according to the quantity present.
Solutions. 1. Molybdate Solution.—375 grams of ammonium molybdate are
dissolved in two and five-tenths liters of water, and the solution poured into two and
five-tenths liters of nitric acid of 1.20 specific gravity.
2. Magnesia Mixture.—275 grams of crystallized magnesium chlorid and 350
grams of ammonium chlorid are dissolved in 3250 cubic centimeters of water and
filled up to five liters with ammonia of 0.96 specific gravity.
3. Petermann’s Solution.—One kilogram of citric acid is dissolved in about two
liters of water and 1350 cubic centimeters of ammonia of 0.925 specific gravity and
filled up with water to 5750 cubic centimeters. The solution then has a specific
gravity of 1.09; 300 cubic centimeters of ammonia of 0.925 specific gravity are now
added.
58. Swedish Official Method for Determination of Phosphoric Acid.[43]—The
Swedish chemists determine phosphoric acid in fertilizers both by the molybdate and
the citrate methods. These methods carefully conducted according to the directions
given below, give very concordant results. In doubtful cases the former method is
taken as the deciding one, it having proved by long practice to give very satisfactory
results.
Reagents for the Molybdate Method.—1. Molybdic Solution.—Prepared by
dissolving 100 grams of finely powdered molybdic acid with heat, in 400 grams of
eight per cent ammonia of 0.967 specific gravity and pouring the solution into 1,500
grams of nitric acid of one and two-tenths specific gravity; or else by dissolving 150
grams ammonium molybdate in one liter of hot water, and pouring the solution into
one liter of nitric acid of 1.2 specific gravity. Prepared in this way, the molybdic
solution will contain, in the former case five per cent, in the latter case from five to
six per cent of molybdic acid, and 100 cubic centimeters of it are required for
precipitating one-tenth gram of phosphorus pentoxid.
2. Magnesia Mixture.—Prepared from 110 grams of crystallized magnesium
chlorid, 140 grams ammonium chlorid, 700 grams of eight per cent ammonia of
0.967 specific gravity and 1,300 grams of distilled water. The mixture is filtered after

a few days, if necessary; ten cubic centimeters of the same are required for
precipitating one-tenth gram of phosphorus pentoxid.
3. Ten per cent ammonia of 0.959 specific gravity.
(a) Water-Soluble Phosphoric Acid.—1. Preparation of the Aqueous Solution.—
Of superphosphates and in general fertilizers containing water-soluble phosphoric
acid, a sample of twenty grams is taken, and water poured over it in a mortar; lumps
are crushed lightly, but completely with the pestle without pulverizing it finer; the
whole mass is then washed into a graduated flask holding one liter, which at once is
filled up to the mark. The volume taken up by the residue insoluble in water, is left
out of consideration in the calculation. The sample is left standing in the flask (which
is occasionally shaken) at the ordinary temperature of the room for two hours, and
the solution is then filtered.
2. The Determination.—Take twenty-five cubic centimeters of the
superphosphate solution thus prepared (when a twenty per cent sample is taken equal
to one-tenth gram phosphorus pentoxid); add a quantity of molybdic solution
sufficient for complete precipitation, leave standing for four hours in a beaker
covered with a watch-glass; decant the solution through a small filter, wash the
precipitate first by decantation, then on filter, with a mixture containing 100 parts
molybdic solution, twenty parts nitric acid of 1.2 specific gravity, and eighty parts
water, until a few drops put into alcohol, to which some dilute sulfuric acid has been
added, does not, any longer, cause turbidity. The molybdic precipitate is now washed
with but little water from the filter into a beaker, and particles adhering to the filter
are dissolved by a hot mixture of one part ammonia and three parts water, which is
allowed to flow into the beaker till the precipitate is, finally, completely dissolved in
it. To the clear solution, add dilute hydrochloric acid while stirring, till the yellow
precipitate formed by the acid is no longer immediately dissolved; then add from six
to eight cubic centimeters of ammonia through the filter. The volume of the solution
is not to exceed seventy-five cubic centimeters. It is now cooled completely and one
cubic centimeter of magnesia mixture is added from a burette for every centigram of
phosphorus pentoxid which it is expected to contain, and finally one-quarter of its
volume of ammonia is added. The precipitate may be filtered after four hours. This is
washed on the filter, preferably by means of suction, with a mixture of one part
ammonia and three parts water till the filtrate is entirely free from chlorin. After
drying, heat the precipitate, first gently, then stronger, and finally with a blast for a
few minutes and then weigh it.
Treated with hydrochloric acid it must leave no insoluble residue (SiO₂), nor
should hydrogen sulfid cause any precipitation in the solution thus formed (MoO₃).
(b) Total Phosphoric Acid.—1. In Superphosphates.—For the determination of
total phosphoric acid, treat a weighed quantity of the superphosphate with nitric acid,

if necessary to bring a difficultly soluble residue into solution, with addition of
hydrochloric acid, or of potassium chlorate, to destroy organic matter present. Dilute
the solution to a definite volume, and determine the phosphoric acid in a measured
quantity of the same, as directed under (a) 2; if hydrochloric acid or potassium
chlorate, be applied in the preparation of the solution, however, not till the measured
quantity has been repeatedly evaporated to dryness with concentrated nitric acid.
2. In Bone-meal.—Destroy organic matter in five grams of the sample by
ignition, dissolve the residue in nitric acid, filter from the insoluble residue, dilute
the filtrate to half a liter, take an aliquot part containing about one-tenth gram
phosphorus pentoxid and determine the phosphoric acid as directed under (a) 2.
3. In Fish-guano (and other fertilizing materials of organic origin).—The organic
matter cannot here be removed by simple ignition, as in this way a loss of
phosphorus may take place; It is therefore destroyed either in the wet way through
nitric acid and potassium chlorate or in the dry way by fusion with a mixture of
potassium nitrate and sodium carbonate, otherwise the procedure is as in (b) 1.
4. In Mineral Phosphates.—Determine the phosphoric acid in a solution obtained
by nitric acid; organic matter is destroyed preferably in the wet way.
5. In Basic Slag.—Dissolve ten grams of powdered slag by treating it with 100
cubic centimeters of fuming hydrochloric acid with heat; wash the solution into a
graduated half liter flask, fill to the mark, shake well, and filter. Determine the
phosphoric acid in twenty-five cubic centimeters of the clear filtrate, according to (a)
2, after having first, however, evaporated the solution to dryness and then at least
three times evaporated the residue to dryness with concentrated nitric acid.
59. Method Employed by the Royal Experiment Station of Holland.—A.
Soluble Phosphoric Acid.[44]—The necessary reagents are:
(1) Molybdate solution, made by dissolving 150 grams of ammonium molybdate
in a liter of water and pouring the solution into a liter of nitric acid of 1.20 specific
gravity.
(2) A ten per cent solution of ammonium nitrate.
(3) Strong and dilute ammonia, the latter being between two and five-tenths and
three per cent of 0.988 specific gravity.
(4) Magnesia mixture made by dissolving 110 grams of crystallized magnesium
chlorid, 140 grams of ammonium chlorid, and 700 cubic centimeters of ammonia of
0.96 specific gravity in water and bringing the solution to two liters.
(5) Ammoniacal citrate solution, made by dissolving 500 grams of citric acid in a
liter of water, and mixing with four liters of ten per cent ammonia of 0.96 specific
gravity.

Manipulation.—Place twenty grams of substance in a mortar together with some
cold distilled water or pure rain water, stir, and decant the water and suspended
matters into a liter flask. After this has been repeated several times, rub up the
residual mass and wash it all into the flask. Fill up to about 900 cubic centimeters
and allow to stand two hours (twenty-four hours in the case of double phosphates
with more than twenty-two per cent of soluble phosphoric acid), shaking repeatedly;
or shaking continuously, for half an hour. Fill up to the liter mark and filter through a
dry filter. Take portions of twenty-five or fifty cubic centimeters for each
determination, add 100 cubic centimeters of molybdate solution for each 100
milligrams of phosphorus pentoxid present, warm to about 80° for an hour, filter, and
wash the precipitate with the ammonium nitrate solution. Add a little molybdate
solution to the filtrate, warm, and, if a fresh precipitate be observed, it is to be added
to the first. The precipitate is to be dissolved in ammonia, and hydrochloric acid
carefully added until the precipitate caused by it only slowly redissolves on stirring.
The phosphoric acid is precipitated from the clear liquid which is still ammoniacal
with magnesia mixture, using ten cubic centimeters for each 100 milligrams of
phosphorus pentoxid present. This is added, drop by drop, and the liquid kept stirred
during the addition. Allow it to stand at least two hours, filter, wash with dilute
ammonia, dry, and ignite. This last is done at first with a very small flame but is
finished with the blast-lamp or in a Rössler furnace. To insure burning to whiteness,
nitric acid may be used, but not more than one or two drops.
B. Total Phosphoric Acid.—(1) For bone and flesh-meal, fish-guano, and similar
fertilizers the reagents necessary are the same as before.
Carefully burn five grams to ash, boil the ash for half an hour with nitric acid of
1.32 specific gravity, dilute with water, and, after cooling, dilute to 500 cubic
centimeters. Filter through a dry filter and take fifty cubic centimeters of the filtrate.
Add 100 cubic centimeters of the molybdate solution for each 100 milligrams of
phosphorus pentoxid present. Treat further as before described.
(2) Phosphates, guanos, bone-black, etc.
One gram of substance, after powdering, and, if necessary, igniting, is covered
with four cubic centimeters of hydrochloric acid of 1.13 specific gravity and a little
water and heated for an hour and a half. Evaporate to dryness without filtration,
making repeated additions of nitric acid until no more vapors of hydrochloric acid
are evolved. Boil the residue with nitric acid, cool, make up to 100 cubic centimeters
with water, and shake. Filter and treat fifty cubic centimeters of the resulting solution
by the molybdate method and proceed further as before described.
60. Sources of Error in the Molybdate Method.—When conducted with proper
care, the gravimetric molybdate method is one of the most exact processes known to
analytical chemistry.

There are, however, some sources of error in the process which should be
avoided as carefully as possible or taken into account.
1. Error Due to Occluded Silica.—When silica passes into solution in the
original sample, and this may be the case especially with mineral phosphates, it may
appear both in the yellow precipitate and in the final magnesium pyrophosphate. In
all such cases the residue, after ignition, should be dissolved in hydrochloric acid,
and any insoluble residue weighed as silica and deducted from the first weight. If the
silica be removed by evaporating the solution of the original material to dryness, and
igniting to destroy organic matter, care must be taken to reconvert all phosphoric
acid into the ortho form by long boiling with nitric acid before precipitation.
Another method of avoiding any trouble from silica consists in using sulfuric and
a little nitric acid as the solvent for the original substance. Silica is not soluble in hot
concentrated sulfuric acid. The volume of the sulfuric should be about ten times that
of the nitric acid used, and the boiling be continued until sulfuric vapors are evolved.
2. Error Due to Arsenic.—Only in rare cases will arsenic be found in phosphatic
fertilizing materials. In case of pyritic phosphates, the iron disulfid may carry
arsenic. The solution in such a case is best accomplished in hydrochloric acid. If
aqua regia be used, all nitric acid should be removed by repeated evaporation with
hydrochloric. The arsenic can then be precipitated in the hot dilute hydrochloric acid
solution by hydrogen sulfid.
3. Error Due to Occluded Magnesia.—The danger of contamination of the
yellow precipitate with magnesium oxid has been pointed out by some authors. The
re-solution of the precipitate followed by a second precipitation is the usual remedy
proposed. Lorenz states that this source of error may be entirely avoided by the
addition of two per cent of citric acid to the phosphomolybdate solution.[45]
4. Error Due to Volatility of Phosphoric Acid.—This source of error has been
made the subject of a special study by Neubauer.[46]
From the results, a table has been constructed, the use of which is recommended
for phosphoric acid determinations. The source of error in this method lies
exclusively in the loss of phosphoric acid by volatilization. The magnesia-covered
crucible lid offers a very good control of this error, and its use is recommended to the
analyst. Of course, the presence of sulfur in the gas used for ignition is liable to
disturb this check.
The following course of procedure in the determination of phosphoric acid can
be recommended to avoid or correct this error:
Separate the phosphoric acid in the form of the yellow precipitate and wash this
latter in the usual way. Too high a heat should not be employed, nor should the
solutions be allowed to stand too long lest excess of molybdic acid separate.

Dissolve the phosphomolybdate in 100 cubic centimeters of cold two and five-tenths
per cent ammonia and add as many cubic centimeters of the usual magnesia mixture
(fifty-five grams magnesium chlorid and seventy grams ammonium chlorid
dissolved in a liter of two and five-tenths per cent ammonia) as there are centigrams
of phosphorus pentoxid present. Addition should not be made faster than ten cubic
centimeters per minute. Stir during the addition. After the precipitation, stir briskly
once more and then allow to stand at least three hours. Wash with two and five-
tenths per cent ammonia till the chlorin reaction disappears, dry the filter, and
introduce into a well-cleaned crucible which has been thoroughly ignited. Place the
lid at an angle, carbonize the filter, and gradually raise the heat, though not higher
than a medium red heat, till the pyrophosphate becomes completely white. When this
happens bring the blast into action and ignite to constant weight. The weight finally
accepted must not change even after half an hour’s ignition. Upon this requirement
especial stress must be laid. Pure magnesium pyrophosphate does not suffer any loss
even after several hours’ ignition nor does a good platinum crucible. To the weighed
amount of pyrophosphate, add the correction given in the table. For example, if the
weight be 250 milligrams, the correction to be added is four and two-tenths
milligrams, and the correct weight is then 254.2 milligrams. Multiplication of the
sum by sixty-four gives the amount of phosphorus pentoxid in the weight taken for
analysis.

Correction for Phosphoric Acid Determination.
Found, Lost, Found, Lost,
Mg₂P₂O₇ milligrams Mg₂P₂O₇ milligrams
in grams. Mg₂P₂O₇ in grams. Mg₂P₂O₇
0.10 0.6 0.24 4.0
0.12 0.8 0.25 4.2
0.14 1.2 0.26 4.6
0.15 1.4 0.27 5.0
0.16 1.6 0.28 5.5
0.17 2.4 0.29 6.1
0.18 2.6 0.30 6.8
0.19 3.2 0.31 7.6
0.20 3.5 0.32 8.6
0.21 3.6 0.33 9.6
0.22 3.8 0.34 10.6
When phosphoric acid is to be estimated as pyrophosphate it must always be first
separated as molybdate, even when the original solution contains no bases capable of

forming insoluble phosphates, as otherwise these corrections will not be applicable.
Using these corrections the estimation of phosphoric acid becomes one of the
most accurate of known analytical methods.
61. The Color of the Magnesium Pyrophosphate.—After the final ignition of
the magnesium pyrophosphate, whether secured by the citrate or the molybdic
method, a black or grayish tint is often noticed. This may be due to traces of organic
matter brought down by the precipitate and especially to a lack of care in the initial
ignition. Many devices have been proposed for the purpose of avoiding this
coloration, although general experiments have shown that there is no appreciable
increase in the weight of the precipitate when colored in this way.
When the precipitation is carried on according to the citrate method,
Neubauer[47] proposes to eliminate this coloration by the use of ammonium sulfate.
About seven cubic centimeters of a saturated solution of ammonium sulfate should
be added to the solution before the precipitation by the magnesium mixture. With
this precaution it is possible to obtain a perfectly white precipitate after five minutes
of ignition. The lively glowing of the precipitate throughout the whole mass at the
time of changing into pyrophosphate, is much more easily observed by this treatment
than when the mass is gray or black. Even should the addition of the ammonium
sulfate solution to one containing a large amount of lime produce a precipitate of
crystalline calcium sulfate, it is of no importance inasmuch as the ammonium citrate
immediately dissolves large quantities of the calcium salt.
In this laboratory a white pyrophosphate is easily obtained by treating the
precipitate on the gooch after washing free of chlorids with a drop or two of
ammonium nitrate. The ignition is commenced very gently at first and afterwards
when the mass is white the blast is used.
If the ignited residue be gray it may sometimes be whitened by moistening with a
drop or two of nitric acid, burning at a very low temperature, followed by the blast.
There is no appreciable difference in weight between a gray and white
pyrophosphate.
62. Determination of Phosphoric Acid and Nitrogen in the Same Solution by
Treatment with Sulfuric Acid and Mercury.—Fertilizing materials which contain
organic nitrogen and phosphoric acid, such as bones, are of such a nature that it is
often difficult to obtain a fair sample of them in quantities suited to the direct
determination; viz., about one gram. Thus it often becomes important to take a much
larger quantity of the material, to bring it into solution and to take an aliquot part
thereof. It may also often happen that it is important to determine the phosphoric
acid in the same sample which has been used for the determination of the nitrogen by
moist combustion with sulfuric acid and mercury. In this connection, however, it is

somewhat difficult to avoid the precipitation of some of the mercury with the
phosphoric acid.
The mercuric sulfate which is produced by the Kjeldahl method is not
precipitated in the presence of ammoniacal solution of ammonium citrate, but there
may be small quantities of mercurous salts present or some finely divided metallic
mercury which may contaminate mechanically the phosphate precipitate. These
disturbing influences may be removed by previous treatment with sodium chlorid. If
from fifty to sixty cubic centimeters of sulfuric acid have been used for the solution
and oxidation and this be made up to half a liter, it will be sufficiently dilute to
permit an almost quantitative separation of the mercurous chlorid produced by
treatment with sodium chlorid.
Neubauer, who has proposed this method, finds that when sodium chlorid is used
previous to the precipitation of the phosphoric acid, a precipitate of ordinary size
contains, at most, only one milligram of mercury, while without the use of sodium
chlorid as much as four milligrams may be found. The details of the method
employed by Neubauer are as follows:
Ten grams of the fertilizing material are placed in a half liter flask with from fifty
to sixty cubic centimeters of strong sulfuric acid, two grams of mercury, and a little
paraffin to prevent foaming. The oxidation is carried on as usual in the Kjeldahl
method. The liquid, after cooling, is diluted with water and one cubic centimeter of a
citrate solution of sodium chlorid added, cooled, filled to the mark, filtered, and fifty
cubic centimeters taken for the determination of the phosphoric acid, according to
the citrate method and the same quantity for the determination of the ammonia by
distillation.

THE CITRATE METHOD.

63. General Principles.—It has been seen that in the molybdic method there is
introduced a process at considerable cost, both of reagents and time, having for its
object the separation of the phosphoric acid from all the other acids and bases which
may have been present in the original sample. The phosphorus is thus obtained in
composition with molybdenum and ammonium in a form easily soluble in ammonia,
from which it can be accurately separated by means of a soluble salt of magnesia.
The citrate method has for its object the suppression of this intermediate step and
the determination of the phosphoric acid by direct precipitation in presence of iron,
lime, and alumina. The principle on which it is based rests on the well-known power
of an alkaline ammonium citrate to hold in solution the salts of iron, alumina, and
lime, while at the same time it permits of the separation of phosphoric acid, as
ammonium magnesium phosphate. In no case can the citrate method be regarded as

an exact analytical process, but large experience has shown that the errors of the
method are compensatory and that it affords a good and ready method for fertilizer
control.
When phosphoric acid solutions which contain no iron, lime, alumina, or
manganese, are precipitated in presence of ammonium citrate the results obtained
vary markedly with the quantity of magnesia mixture employed. Grupe and
Tollens[48] were the first to point out that a portion of the phosphoric acid might
remain in solution, but that the precipitate might contain a sufficient excess of
magnesia to compensate for the loss. It has been further shown by Glaser[49] that a
portion of the phosphoric acid may be lost by volatilization in the citrate method.
When the ignition is carried on in a crucible where the cover is coated with magnesia
to intercept the volatilized acid, a considerable quantity of it can be recovered by the
molybdic method.
Where too little magnesia mixture is employed, therefore, two sources of loss are
to be guarded against; viz., a part of the phosphoric acid may remain in solution and
another part be volatilized on ignition. The explanation of the volatilization is as
follows: In the presence of ammonium citrate, magnesium chlorid may be partly
converted into magnesium citrate and ammonium chlorid. There may be a time,
therefore, in the precipitation with not too great excess of magnesia mixture, when
proportionally there is little magnesium chlorid and much ammonium chlorid
present. The formation of a salt represented by the formula Mg(NH₄)₄(PO₄)₂ may
take place which, upon ignition, breaks up into Mg(PO₃)₂ and finally passes into
Mg₂P₂O₇ with loss of P₂O₅. This theoretical condition has but little weight, however,
practically in the analysis of fertilizers, since in these cases a large quantity of lime is
always present. But even in these cases traces of volatile P₂O₅ may be discovered.
Wells[50] has shown that the citrate method gives good results in certain
conditions but that this accuracy is reached by a fortunate compensation of errors.
The ammonium magnesium salt does not precipitate all the phosphoric acid in this
process, but contains enough impurities to make up for this loss.
Johnson[51] in conjunction with Osborne has shown that the results by the citrate
method practiced in accordance with the details laid down by Vögel, are too low, but
that this difficulty could be overcome by using more and stronger magnesia mixture
and a larger quantity of strong ammonia solution. The citrate method was found to
give unsatisfactory results when iron and alumina were present in any considerable
quantity. In the examination of the final ignited precipitate, which should be pure
magnesium pyrophosphate, it was found to consist of only 94.98 to 97.83 per cent of
that salt. The chief impurity found was calcium oxid, the percentage of which varied
from 2.05 to 3.95 in six cases. There was also a considerable percentage of loss due,
probably, to magnesia and pyrophosphoric acid.

The presence of large quantities of iron and alumina also impairs the accuracy of
the molybdate method when the precipitation of the yellow salt takes place at too
high a temperature. When the temperature of precipitation in the method is above
50° the results are likely to be too high while a great excess of nitric acid in the
reagent may produce a contrary effect. In the latter case the filtrate from the yellow
salt should be mixed with additional quantities of molybdate solution until no further
precipitate takes place.
Many methods of conducting the citrate method have been proposed but the best
of them are based on the one elaborated at the experiment station of Halle by
Bühring, and which will be given in the next paragraph, followed by some other
methods in use in other localities.
64. Method of the Halle Agricultural Experiment Station.[52]—The citrate
method, as described by Morgen, is the one employed.[53] The principle depends
upon the direct precipitation of the phosphoric acid by magnesia mixture. By the
addition of a solution of ammonium-citrate the precipitation of lime, iron, alumina,
and other bases, is prevented. The precipitate of ammonium magnesium phosphate is
converted by ignition into magnesium pyrophosphate and weighed as such. By the
use of this method a part of the phosphoric acid sometimes escapes precipitation and
a portion of the other bases is sometimes thrown down with the precipitate.
Experience has shown that by adhering to certain precautions the weight of
impurities in the precipitate may be made to correspond exactly to the weight of the
phosphoric acid which escapes precipitation.

Figure. 3.
Shaking Apparatus for Superphosphates.

(1) Soluble Acid.—The soluble phosphates are first brought into solution in such a
way that one liter of water contains the soluble phosphoric acid from twenty grams of
the substance. Twenty grams are rubbed in a porcelain mortar with water and through
a wide-necked funnel washed into a bottle-shaped flask in which a little water has
been previously placed. The flasks employed are made of thick glass in order to
withstand shaking. After the substance is washed, the flasks are filled to the mark and
closed with rubber stoppers. They are then placed upon a shaking rack as indicated in
Fig. 3, which is also furnished with an apparatus for separating the fine meal from
basic slag.
On a table, as shown in the figure, is fastened a movable horizontal board by
means of hinges. At the left hand of this movable board is placed an open wooden box
in which is a perforated shelf for the purpose of holding the flasks, so as to prevent
their striking together during the shaking.
For the best results the substance to be examined should be placed in the flask in a
dry state and then 800 cubic centimeters of water added and shaken by means of the
machine indicated for half an hour. Afterwards the flasks are filled up to the mark,
well shaken, and filtered through double folded filters into ordinary flasks of about
400 cubic centimeters capacity. Before any of the filtrate is collected, the first that
runs through should be well shaken in the receiving flasks and rejected. Fifty cubic
centimeters of the filtrate thus collected, corresponding to one gram of the substance,
should be used for the determination.

(2) Total Acid.—For total phosphoric acid, including the insoluble portions, the
material is treated as follows: Five grams of the substance are placed in a 500 cubic
centimeter flask with twenty cubic centimeters of nitric acid of 1.42 specific gravity,
and fifty cubic centimeters of pure concentrated sulfuric acid, and boiled briskly for
half an hour. With substances which contain much organic material, a little paraffin is
added to avoid frothing. Such substances also require a larger quantity of nitric acid
than that above specified. The flasks are allowed to cool, water added, again allowed
to cool, and filled up to the mark at 17°.5. If hydrochloric instead of sulfuric acid be
used in making the above solution, when the citrate method is employed, the results
are always too high because the precipitate contains lime and alumina in such
quantities as to render any compensation for them inaccurate. In addition to this the
sulfuric has this great advantage over the hydrochloric acid; viz., in not separating
silicic acid, inasmuch as the silicic acid is insoluble in boiling sulfuric acid.
(3) Citrate-Soluble Acid.—Two grams of the sample are digested with 100 cubic
centimeters of citrate solution, 1.09 specific gravity, for half an hour at 50° in a
beaker. Afterwards the soluble matter is separated by filtration with the aid of a filter-
pump and the residue washed with a solution of one part water and one part citrate
solution until all the dissolved phosphoric acid is removed from the filter. Generally
three or four washings are sufficient. The residue on the filter is dried, ignited, and
dissolved in a mixture of two cubic centimeters of nitric and twenty cubic centimeters
of sulfuric acid, the solution made up to a volume of 200 cubic centimeters, filtered,
and 100 cubic centimeters of the filtrate taken for the determination. The acid in the
filtrate is nearly neutralized and fifty cubic centimeters of citrate solution are added,
and afterwards twenty-five cubic centimeters of magnesia mixture and twenty cubic
centimeters of twenty-four per cent ammonia. After standing for forty-eight hours, the
precipitate is separated by filtration, ignited, and weighed in the usual way. The
difference between the total phosphoric acid and that in the insoluble residue, after
treatment with ammonium citrate, as above, gives the quantity of phosphoric acid
soluble in the citrate solution. The difference between the total citrate-soluble and the
water-soluble gives the quantity of the reverted phosphoric acid.
The ammonium citrate solution used for the digestion is made as follows: Two
hundred and fifty grams of crystallized citric acid are dissolved in half a liter of hot
water, diluted with 550 cubic centimeters of water, 276 cubic centimeters of twenty-
four per cent ammonia added, and finally, exactly neutralized by adding, little by
little, fifty per cent citric acid solution.
The Halle methods of separating the water and citrate-soluble acids appear to be
less complete and reliable than those in use by the Official Agricultural Chemists of
this country. The precipitation of basic phosphates, when large quantities of water are
used at once in separating soluble acid, must tend to diminish the quantity obtained,
while the lack of care in assuring the neutrality of the citrate solution might lead to
varying results.

(4) Double Superphosphates.—In the case of double superphosphates, which
sometimes contain large quantities of pyrophosphate, the solution is made in the usual
way so that in 100 cubic centimeters there will be contained two grams of the
substance. Usually ten grains are taken and the volume made up to half a liter.
Twenty-five cubic centimeters of the filtrate are diluted with seventy-five cubic
centimeters of water and the pyro converted to orthophosphoric acid by heating with
ten cubic centimeters of strong nitric acid on a sand-bath. The heating should be
continued until the volume be reduced to twenty-five cubic centimeters. The strongly
acid liquid is made alkaline with ammonia, and afterwards slightly acid with nitric,
and the rest of the process is carried on in the usual way.
(5) Phosphoric Acid in the Residue of Superphosphate Manufacture.—In the
mixture of superphosphates and gypsum, the residue of the manufacture of double
superphosphates, the phosphoric acid is estimated in the following manner: Five
grams of the substance are placed in a dish, rubbed up with absolute alcohol, and
washed into a 250 cubic centimeter flask. The flask is filled with absolute alcohol to
the mark, closed with a stopper, and with frequent shaking, allowed to stand for two
hours; it is thereupon filtered as quickly as possible; fifty cubic centimeters of the
filtrate corresponding to one gram of the substance, are taken for the estimation. This
fifty cubic centimeters is evaporated on a sand-bath to a sirupy consistence, diluted
with water, and treated, as in the case of the soluble phosphates above mentioned. In
all cases as described above, after the solutions are obtained they are treated with the
ammonium citrate solution and the phosphoric acid estimated as in the first instance
given.
(6) Solutions Employed.—
(a) The citrate solution is made as follows: 1,500 grams of
citric acid are dissolved in water, treated with five liters of
twenty-four per cent ammonia, and made up to fifteen liters.
(b) The magnesia mixture is made as follows: 500 grams of
magnesium chlorid, 1,050 grams of ammonium chlorid, three
and five-tenths liters of twenty-four per cent ammonia, and six
and five-tenths liters of distilled water are used.
In the case of the superphosphates fifty cubic centimeters of the citrate solution
are employed and with the basic slags 100 cubic centimeters; and in both cases
twenty-five cubic centimeters of the magnesia mixture.
(7) Details of the Manipulation.—On the addition of the citrate solution there
should be no permanent troubling of the liquid but there should be a total clearing up
thereof. In order to facilitate this, after the addition of the citrate solution, the flasks
should be gently shaken in order to distribute the solution throughout the mass.
Solutions from bone-black superphosphates show sometimes, after the addition of the

citrate solution, a more or less strong opalescence, but this opalescence does not
influence the results. Should it happen that with superphosphates which are made
from raw material containing large excesses of iron or clay, fifty cubic centimeters of
the citrate solution are not sufficient to prevent the other bases from being
precipitated, an additional quantity up to twenty-five cubic centimeters may be added.
The addition of the magnesia mixture must follow as quickly as possible after the
addition of the citrate solution to avoid a separation of crystalline calcium phosphate.
On the addition of the citrate solution there is always a rise in temperature. Inasmuch
as the precipitation of the phosphoric acid with magnesia must take place in the cold,
the liquid must be cooled after the addition of the citrate,[54] and the cooling should
take place as quickly as possible.
The above method was adopted by the chemical section of the International
Agricultural Congress held at Vienna, September, 1890.[55]

Figure. 4.
Shaking Machine for Ammonium Magnesium Phosphate.

In order to hasten the precipitation of the ammonium magnesium phosphate and
to prevent the fixation of the precipitate on the walls of the erlenmeyer, the flask
should be shaken for half an hour. For this purpose the flasks should be closed with
smooth well-fitting rubber stoppers and placed in a shaking machine. The shaking
machine of the form given in Fig. 4, recommended by the Halle station, is very
conveniently used for this purpose.
On a vertical axis are carried two stages for holding the flasks. The flasks are
prevented from striking each other by means of the partitions shown. The apparatus is
conveniently driven by a small water-motor, as indicated, which imparts to the stages
a partial back and forth revolution.

After shaking for half an hour, any precipitate adhering to the rubber stoppers is
carefully washed off with ammonia water into the flask. The filtration can be made
immediately after the shaking or after two or three days; the results are the same.

Figure. 5.
Rössler Ignition Furnace.

The filtration of the ammonium magnesium phosphate is made through perforated
crucibles. The asbestos felt is prepared in the following way: The coarse fibers of
asbestos are chopped up with a sharp knife on a glass plate and boiled for two hours
with strong hydrochloric acid; afterwards, by repeated washing with distilled water
they are freed from acid and the too fine particles of asbestos which would tend to
make the filter too impervious. After the last wash-water is poured off, the asbestos is
suspended in water and used for making the felt on the filter. The preparation of the
crucible and the filtration under pressure are accomplished in the usual way.
The ignition of the precipitate is accomplished in a Rössler ignition oven, Fig. 5.
When the muffle of the furnace shows a white heat or a white-red heat it is at the
proper temperature for the estimation. At higher temperatures, the asbestos felt is
easily injured. Generally, an ignition of five minutes is sufficient, but with double
superphosphates, ten minutes are required.
65. The Swedish Citrate Method.[56]—This method of determining phosphoric
acid is founded on the fact that phosphoric acid in the presence of calcium salts,
without it being necessary, previously, to convert it into phosphomolybdate, is

precipitated directly by magnesia mixture from a solution, to which ammonium
citrate has been added, provided first, that the solution contain a sufficient quantity of
sulfuric acid, and second, that only as much citrate be added as is required to keep the
calcium salts in alkaline solution.[57]
Reagents. (1) Citric Acid Solution.—Prepared by dissolving 500 grams of citric
acid in water, and completing to a volume of one liter.
(2) Ten Per Cent Ammonia of 0.959 specific gravity.
(3) Magnesia Mixture, of the usual composition.
The various processes are conducted as follows:
(a) Water-Soluble Phosphoric Acid.—Add twenty cubic centimeters of citric acid
solution to fifty cubic centimeters of the water-soluble solution obtained according to
the Swedish molybdenum method, and then add thirty-three cubic centimeters of
ammonia. When the mixture has cooled, add slowly twenty-five cubic centimeters of
the magnesia mixture, and then forty-two cubic centimeters of the ammonia. Keep the
solution stirred by means of a closely clipped feather which is pressed tightly against
the sides of the beaker; by this process the phosphate is precipitated after half an hour
in pure condition and completely, without, in the least, sticking to the wall of the
beaker; filter, wash, and ignite, as usually directed.
(b) Insoluble Phosphoric Add.—Moisten, in a porcelain dish, ten grams of the
powdered sample with water; add fifty cubic centimeters of concentrated sulfuric
acid, and heat for fifteen minutes so high that fumes of sulfuric acid will escape.
When the mass has cooled, wash it into a half liter graduated flask, fill to the mark,
and shake well. After filtration, the clear filtrate may, after some time, turn turbid by
separation of calcium sulfate, but as the ammonium citrate, which is afterwards
added, again brings the precipitate into solution, it is of no importance. Take fifty
cubic centimeters of the solution, corresponding to one gram of the powdered sample,
add twenty cubic centimeters of the citric acid solution, neutralize the mixture
approximately, but not exactly, by ammonia; after cooling, add twenty-five cubic
centimeters of magnesia mixture; stir the fluid by means of a feather, as described
above, till no more precipitate is formed, and finally add thirty-three cubic
centimeters of ammonia while stirring for a couple of minutes more; after half an
hour the precipitate may be separated by filtration, washed, and ignited, as usually
directed.
The above process is essentially the one used with basic slags. When much
organic matter is present, by continuing the heating with sulfuric acid for some time,
it may be destroyed.
66. Methods Adopted by the Brussels Congress, 1894.—The report of the
committee on methods of analysis of phosphoric acid requires the molybdate method

to be used in all cases where the quantity to be determined is very small. In other
cases the citrate method may be employed.[58]
(1) Soluble Phosphoric Acid.—The soluble phosphoric acid is determined by the
method adopted at Brussels in the following manner: Five grams of the sample are
rubbed to a powder in a mortar, and then from fifty to sixty cubic centimeters of water
added. After allowing to settle for a few minutes the liquid portion is decanted upon a
filter. This operation is repeated three or four times. Finally the solid portions are
washed upon the filter, and the washing with water is continued until the filtrate
amounts to about three-quarters of a liter. A few drops of hydrochloric acid are added
until the filtrate is perfectly clear, and the volume is then made up to one liter. Fifty
cubic centimeters of the solution are then treated with thirty cubic centimeters of
ammonium citrate solution and one-third as much ammonia. Afterwards thirty cubic
centimeters of magnesia mixture are added, drop by drop, with constant stirring.
For superphosphates containing more than eighteen per cent of phosphoric acid
only one gram is taken, for ordinary superphosphates two grams, and for compound
fertilizers four grams. The sample is first treated as above for soluble acid until the
filtrate amounts to 200 cubic centimeters, then clarified with a drop of nitric acid, and
made up to a quarter of a liter.
(2) Reverted Phosphoric Acid.—The filter containing the residue is then
introduced into a quarter liter flask and treated with 100 cubic centimeters of
Petermann’s alkaline ammonium citrate solution, vigorously shaken, and left at room
temperature for fifteen hours. It is then digested for an hour at 40° and filtered. Fifty
cubic centimeters of the filtrate are placed in a flask and, with constant shaking,
thirty-five cubic centimeters of magnesia mixture added. The aqueous solution is
treated in the same way. The precipitate is collected, ignited and weighed, and
multiplied by 0.64 for phosphoric acid. The total acid is determined in the usual way.
67. Dutch Method for Citrate-Soluble Phosphoric Acid.[59]—The reagents
necessary are:
(1) Citrate solution, prepared according to Petermann. Dissolve 165 grams of
citric acid in 700 cubic centimeters of water, mix with 250 cubic centimeters of
ammonia of 0.92 specific gravity, and, after cooling, bring to the volume of one liter.
(2) Magnesia mixture prepared according to Petermann. Dissolve 400 grams of
crystallized magnesium chlorid, 800 grams of ammonium chlorid, and 1,600 cubic
centimeters of ammonia of 0.96 specific gravity in water, and dilute to five liters.
The quantity to be taken for the analysis is five grams where the fertilizer contains
less than six per cent of phosphoric acid (mixed fertilizers); two grams where it
contains more than six and less than fifteen per cent (common superphosphates); and
one gram where it contains more than fifteen per cent (double superphosphates).
Place the weighed substance in a mortar and cover with 100 cubic centimeters of

citrate solution. Gently rub up, wash into a half liter flask, and heat in a water-bath for
an hour to a temperature between 35° and 38°. Allow to cool, fill up to 500 cubic
centimeters, and filter through a dry double filter. If it is not clear at the first filtration,
pour through the filter again, repeating this till clearness is attained. Measure 100
cubic centimeters and add seventy-five cubic centimeters of magnesia mixture,
allowing the latter to flow into the former very slowly, and constantly stirring during
the influx. Allow to stand fifteen hours, filter, wash with ammonia of 0.96 specific
gravity, dry, ignite, and weigh.
The per cent of phosphoric acid, except where otherwise indicated, is always to be
given as per cent of anhydrous acid (P₂O₅).
68. Comparative Accuracy of the Citrate and Molybdate Methods.—The
general use of the citrate method of determining phosphoric acid by the German
chemists has led Johnson[60] to review some trials of that method in the Yale
laboratory made as early as 1880. These determinations have lately been repeated in
comparison with the ordinary molybdate methods with the result that in sixty-seven
determinations on bone-dust, superphosphate, cotton-hull ashes, cottonseed-meal,
tankage, bone-char, phosphatic guano, and phosphate rock, only three citrate results
differed from those obtained by the molybdate method by more than three-tenths of
one per cent. The greatest discrepancy between the two methods was 0.41 per cent,
and the average difference was 0.09 per cent.
The citrate method was found to give poor results when iron and alumina were
present in considerable quantity. Ignited precipitates by the citrate method were found
to contain as high as four per cent of lime, and iron and alumina in small quantities
when these bodies were abundant in the original substance.
In the molybdate method the rapid precipitation from solutions at 65° was found
to give unsatisfactory results and it was found necessary to conduct the process at
temperatures between 40° and 50°. With a relative excess of nitric or a relative
deficiency of molybdic acid some phosphoric acid may easily escape precipitation.
The chief objection to precipitating at 65° is found in the fact that in presence of
considerable iron and alumina some of these bodies may be found in the yellow
precipitate, whence they pass to the final ammonium magnesium phosphate.
The citrate method, therefore, only gives safe results by compensating errors
which in every class of phosphates must be empirically determined.
The molybdate method gives results too high when iron and alumina are present
in considerable quantity and the yellow precipitate is obtained at temperatures above
50°. On the other hand, if there, be a great relative excess of nitric acid the results
may be too low unless the filtrates from the yellow precipitate be mixed with
additional molybdic solution and digested until no further precipitate is formed.

Comparative determinations made, by both methods, by the Association of
German Experiment Stations have led to the conclusion that both give practically the
same results when each one is conducted with the proper precautions peculiar to it.[61]
In the latter part of 1892, at the general meeting of the Association, it was declared
that the citrate method, after having been subjected to repeated tests, was found to be
satisfactory, changing the composition of the solution so that it might have 1,100
instead of 1,000 grams of citric acid and four liters of twenty-four per cent ammonia
to each ten liters. The data afforded by the citrate method, when applied to an
artificial mixture of known composition, were more satisfactory than those obtained
by the molybdic process.
In this laboratory the citrate method has been found to give nearly agreeing results
with the old process. It is much shorter and less expensive; and is recommended most
favorably for practical use, suggesting, however, that with every new kind of
phosphate or phosphatic fertilizer varying notably in composition from the standard,
the work should be checked at first by comparison with the molybdenum method.

BASIC PHOSPHATIC SLAGS.

69. History and Manufacture.—The basic process for the manufacture of
Bessemer steel is known in Europe as the Thomas or Thomas and Gilchrist process,
and the slags rich in phosphate, one of the waste products of the process, are known
by the same name. In this country all the phosphatic slags which have been made in
the manufacture of steel have been obtained working under the patents of Reese, and,
when prepared for the market, are known as odorless phosphate. The only place
where these slags have been made in this country is Pottstown, Pennsylvania. In
Europe they are extensively manufactured, in England, France, and Germany, and
their use for agricultural purposes has increased until it is quite equal to that of
superphosphates.
The quantity of basic slag manufactured in Germany in 1893 was 750,000 tons; in
England 160,000; in France 115,000, making the total production of central Europe
about 1,000,000, a quantity sufficient to fertilize nearly 5,000,000 acres.
70. Process of Manufacture.—The principle of the process depends upon the
arrangement of the furnaces, by means of which the phosphoric acid in the pig iron is
caused to combine with the lime which is used as a flux in the converters. A general
outline of the process is as follows:
The pigs, which contain from two to four per cent of phosphorus, are melted and
introduced into a Bessemer converter lined with dolomite powder cemented with
coal-tar, into which has previously been placed a certain quantity of freshly-burned
lime. For an average content of three per cent of phosphorus in the pig iron, from
fifteen to twenty pounds of lime are used for each 100 pounds of pig iron. As soon as

the melted pig iron has been introduced into the converter, the air-blast is started, the
converter placed in an upright position, and the purification of the mass begins. The
manganese in the iron is converted into oxid, the silicon into silica, the carbon into
carbon dioxid and oxid, and the phosphorus into phosphoric acid.
By reason of the oxidation processes, the whole mass suffers a rise of temperature
amounting in all to about 700° above the temperature of the melted iron. At this
temperature the lime which has been added, melts, and, in this melted state, combines
with the phosphoric acid, and the liquid mass floats upon the top of the metallic
portion, which has, by this process, been converted into steel.
As soon as the process, which occupies only about fifteen minutes, is completed,
the fused slag is poured off into molds, allowed to cool, broken up, and ground to a
fine powder. For each five tons of steel which are made in this way, about one ton of
basic slag is produced.
In another process, in order to make a slag richer in phosphoric acid, a lime is
employed which contains a considerable percentage of phosphate. Although the slag
thus produced is richer in phosphoric acid, it is doubtful whether it is any more
available for plant growth than that made in the usual way with lime free from
phosphoric acid. In other words, when a basic slag is made with a lime free from
phosphoric acid, nearly the whole of the phosphoric acid is combined as tetrabasic
calcium phosphate. On the other hand, when the lime employed contains some of the
ordinary mineral phosphate the basic slag produced becomes a mixture of this mineral
phosphate with the tetracalcium salt. The mineral phosphate is probably not rendered
any more available than it was before.
It is easily seen from the above outline of the process of manufacture, that basic
slags can have a very widely divergent composition. When made from pig iron poor
in phosphorus, the slag will have a large excess of uncombined lime and consequently
the content of phosphoric acid will be low. When made from pigs rich in phosphorus
there may be a comparative deficiency of lime, and in this case the content of
phosphoric acid would be unusually high.
It is found also that the content of iron in the slag varies widely. In general, the
greater the content of iron the harder the slag and the more difficult to grind. If the pig
iron contain sulfur, as is often the case, this sulfur is found also in the slag in
combination with the lime, either as a sulfid or sulfate.
No certain formula can therefore be assigned to basic slags and the availability of
each one must be judged by its chemical composition.
71. Composition of Basic Slag.—The slags produced by the method above
outlined may be amorphous or crystalline. When large masses are slowly cooled the
interior often discloses a crystalline composition. In some samples analyzed in this

laboratory the crystals were found to be of two forms; viz., acicular and tabular.[62]
They had the following composition:

Calculated Per Cents as
CaO. Fe₂O₃. Al₂O₃. MgO. V₂O₂ . P₂O₅. SiO₂.
Acicular crystals 42.69 20.98 3.71 0.49 0.18 27.06 4.96
Tabular crystals 53.61 9.64 0.91 0.08 —— 33.92 1.75

These data show that the two sets of crystals belong to two distinct mineral forms.
The presence of vanadium in one of the samples is worthy of remark, and leads to the
suggestion that in the slags made of phosphoriferous pigs may be found any of the
rare metals which may exist in the ores from which the pigs were made. The
amorphous portions may have a widely varying composition and consequent content
of phosphoric acid. In all good slags, however, whether in crystalline form or as
amorphous powder, the lime and phosphoric acid will be found combined as
tetracalcium phosphate (Ca₄P₂O₉).
72. Molecular Structure of Tetracalcium Phosphate.—Several theories have
been advanced in respect of the atomic arrangement of the elements contained in a
molecule of tetracalcium phosphate. It must be confessed that so little is known
concerning the reactions of this body as to make theories of its constitution largely
visionary. But the existence in definite crystalline form of this salt shows that it is not
merely an intimate mechanical mixture, but a true molecular form. As a type of the
supposed arrangement of its particles the graphic formula proposed by Kormann may
be consulted; viz.,

The crystals of this salt, as may be seen by inspection of the analytical data,
contain other bodies than calcium, oxygen, and phosphorus. It would be of interest to
push the investigation of their constitution further and see if crystals of pure
tetracalcium phosphate could be obtained, and under what conditions they would be

contaminated by other metallic oxids. Usually, by the color of the crystals, it will be
easy to determine something of the nature, if not the extent of the contamination.
73. Solubility of Phosphatic Slags.—The high agricultural value of basic slags
led to an early study of their solubility in ammonium citrate, citric acid, and other
organic solutions. Even finely ground mineral phosphates and bones are soluble to
some extent in ammonium citrate, as was pointed out as long ago as 1882.[63] The
most common solvents used for basic slags are ammonium citrate and citric acid. The
ammonium citrate should be the same as that used for the determination of reverted
phosphoric acid and the citric acid solution commonly used contains five grams in a
hundred cubic centimeters. The slags of different origin and even of different age vary
greatly in respect of the quantity of soluble matter they contain. It is believed,
however, that a very fair idea of the agricultural value of a slag may be obtained by
determining its degree of solubility in one of the menstrua named.
74. Separation by Sifting.—The relative availability of a slag, as in the case of a
mineral phosphate, is determined by the percentage of fine material it contains. Sieves
of varying apertures are used to determine this percentage. A one-half millimeter or a
one-quarter millimeter circular aperture is best, and the percentage of the total
material passing through is determined. A method used in Germany consists in sifting
the slag in a sieve twenty centimeters in diameter the meshes of which are from 0.14
to 0.17 millimeter square and which measure diagonally from 0.22 to 0.24 millimeter.
75. Solution of Phosphatic Slags.—Sulfuric acid has been found to be an
excellent solvent for basic slags preparatory to the determination of phosphoric acid.
There is, however, no unanimity of opinion concerning the best method or means of
solution. Aqua regia and nitric acid are objected to because they may convert any
phosphorus in combination with the iron into phosphoric acid and thus increase the
quantity present.[64] But iron phosphid is seldom or ever found in slags and therefore
this objection is not always tenable. Sulfuric acid has also been deemed objectionable
because the gypsum separated is likely to carry with it some of the other substances to
be determined.
Hydrochloric acid is also excluded by some from the list of solvents because it
dissolves so many of the foreign elements in the slag and thus tends to complicate the
subsequent determination, especially of magnesia. Further than this a hydrochloric
acid solution is not suited to the use of the citrate method now so commonly
employed. When hydrochloric acid is used, moreover, the dissolved silica must be
removed and thus the time required for making a phosphoric acid determination is
much increased.
If the sample be sufficiently fine the occlusion of undissolved phosphate particles
by the gypsum formed when sulfuric acid is used is not to be feared and the
disturbance of volume by the gypsum is pretty nearly constant and can be allowed for.

When five grams of slag are used the mean volume of gypsum in the solution is about
two cubic centimeters.
76. Estimation of Total Acid.—In the determination of total phosphoric acid in a
slag, twenty-five cubic centimeters of the strongest sulfuric acid are placed in an
erlenmeyer having a wide neck, and with careful shaking five grams of the fine slag
meal gradually added. The flask is heated over a naked flame until solution is
complete. When the mass is cold it is washed into a quarter liter flask; again allowed
to cool, filled with water to the mark, and two cubic centimeters of water
corresponding to the volume of gypsum undissolved, are added, well mixed, and
filtered. In fifty cubic centimeters of the filtrate the phosphoric acid is determined by
either the molybdic or citrate methods already described.
77. Alternate Method.—The following method may also be used: Ten grams of
the substance are heated with fifty cubic centimeters of concentrated sulfuric acid
until white vapors have been evolved for some time. The operation lasts for about
fifteen minutes and can be carried on in a half liter flask or in a porcelain dish.
Without regarding the undissolved material the volume of the liquid is now made up
to half a liter and filtered. The filtered liquid becomes turbid after some time through
the separation of calcium sulfate, but this turbidity should not be regarded. To fifty
cubic centimeters of the solution, corresponding to one gram of substance, twenty
cubic centimeters of citric acid solution (500 grams citric acid to the liter) are added,
and it is afterwards nearly neutralized by the addition of ten per cent ammonia and the
liquid, which is warmed by this operation, cooled. There are now added twenty-five
cubic centimeters of the ordinary magnesium chlorid mixture and the solution stirred
until turbidity is produced, one-third of its volume of ten per cent ammonia added,
and again stirred for about a minute.
Instead of the addition of the citric acid and ammonia the ammonium citrate
prepared as follows, may be added: 1,500 grams of citric acid are dissolved with
water, made up to three liters and five liters of twenty-four per cent ammonia and
seven liters of water added. The rest of the operation is carried on in the usual manner.
78. Halle Method for Basic Slag.—The total phosphoric acid is estimated at the
Halle Station by the following process:[65]
Ten grams of the substance are moistened in a porcelain dish with a few drops of
water and about five cubic centimeters of a one to one solution of sulfuric acid added,
and after the mass has hardened, which takes place very soon, fifty cubic centimeters
of concentrated sulfuric acid are added and stirred with a glass rod until it is evenly
distributed throughout the whole mass. In stirring this mixture the greatest care must
be taken, otherwise the substance would remain attached to the sides of the dish,
which during later heating would cause loss through spurting. The complete solution
now takes place after a few hours’ heating on a sand-bath. During the cooling the
jelly-like mass must be stirred with a glass rod, and after it is cool, by means of a

washing-bottle, gently along the sides of the dish, water is added, and when the
mixture becomes hot it is again cooled and washed into a half liter flask, which is
made up to the mark at a temperature of 17°.5 and filtered. When the acid filtrate
stands for some time there is often a separation of gypsum which, however, does not
in any way influence the subsequent analysis, which is made in the usual manner.
Fifty cubic centimeters of the filtrate, representing one gram of the original
substance, are placed in an erlenmeyer. In the case of double superphosphates which
often contain large quantities of pyrophosphates, twenty-five cubic centimeters of the
filtrate just obtained, equivalent to five grams of the substance, are diluted with
seventy-five cubic centimeters of water, ten cubic centimeters of nitric acid of 1.42
specific gravity added, and heated on a sand-bath to convert the pyro into
orthophosphates. The heating should be continued until the liquid is reduced to its
original volume of twenty-five cubic centimeters. The strongly acid liquid is saturated
with ammonia and with the addition of a drop of rosolic acid as an indicator, again
acidified with nitric acid, and treated as with superphosphates.
79. Dutch Method for Basic Slag.—Heat ten grams of the sample with fifty
cubic centimeters of sulfuric acid (1.84 specific gravity) till white vapors are evolved,
shaking or stirring constantly. After cooling make the fluid up to 500 cubic
centimeters with water, taking no account of the undissolved substance. Filter, and to
fifty cubic centimeters of the filtrate add 100 cubic centimeters of the ammoniacal
citrate solution, and after cooling, twenty-five cubic centimeters of magnesia mixture.
Stir or shake for a sufficient time. After the lapse of two hours the precipitate is to be
separated by filtration and treated in the usual manner.
80. Estimation of Citrate-Soluble Phosphoric Acid in Basic Slag.—Experience
has shown that the manurial value of basic slags does not depend alone on their
content of phosphoric acid. Slags may contain tri- as well as tetracalcium phosphate,
and even this latter salt may exist in states of differing availability. In determining the
availability of basic slag for manurial purposes its solubility in ammonium citrate is
considered the best standard. But this solubility will evidently be influenced by the
basicity of the sample, or in other words, by the quantity of lime present. A slag rich
in calcium oxid would deport itself differently with a given ammonium citrate
solution from one in which the lime had been chiefly converted into carbonate. If
possible, therefore, all samples should be reduced to the same state of basicity before
the action of any given solvent is determined.
Wagner proposes to neutralize the basicity of a slag in the following manner:[66]
Five grams of the slag are placed in a half liter flask which is then filled up to the
mark with a one per cent solution of citric acid and shaken for half an hour. After
filtering, fifty cubic centimeters are titrated with a standard soda solution using
phenolphthalein as indicator. This gives the quantity of citric acid necessary to
neutralize the slag. To a second portion of five grams of the sample in a half liter flask

are added 200 cubic centimeters of water and enough five per cent citric acid solution
to neutralize the lime and then 200 cubic centimeters of acid ammonium citrate made
as indicated below. After filling to the mark with water it is shaken for half an hour
and filtered. To fifty cubic centimeters of the filtrate are added 100 cubic centimeters
of molybdic solution and heated to 80°. After cooling, the precipitate is filtered and
the phosphoric acid estimated in the usual way.
The acid ammonium citrate solution used is made as follows: Dissolve 160 grams
of citric acid with enough ammonia to represent about twenty-eight grams of nitrogen
and make up with water to one liter. The exact method is given in 82.
The molybdic solution is made by dissolving 125 grams of molybdic acid in a
slight excess of two and a half per cent of ammonia, adding 400 grams of ammonium
nitrate, diluting to one liter and pouring the solution into one liter of nitric acid having
a specific gravity of 1.19. After allowing to stand at room temperature for one day the
mixture is filtered and is then ready for use.
81. Wagner’s Shaking Apparatus.—The latest directions given by Wagner for
determining the phosphoric acid in slags and raw phosphates soluble in citrate
solutions, are the following:[67] Five grams of the material as it is sent into commerce
without grinding or sifting, are placed in a half liter flask and covered with nearly a
quarter liter of water, and then 200 cubic centimeters of citrate solution added,
prepared as described below. The flask is filled to the mark with water. The flasks,
which are of the shape shown in the figure, are closed with rubber stoppers, and
without delay placed for half an hour in a rotating apparatus, (Fig. 6) which is turned
on its axis from thirty to forty times a minute. If a shaking apparatus be used instead
of the one mentioned, 200 cubic centimeters of the citrate solution should be placed in
a half liter flask, filled to the mark with water, and the contents poured into a liter
flask containing the phosphate. This flask should be placed in a nearly horizontal
position in the apparatus and the agitation be continued for half an hour. On removal
from the apparatus the mixture is filtered and fifty cubic centimeters thereof treated
with double the quantity of molybdic solution at 80° and the precipitate separated
after cooling. The precipitate is carefully washed with one per cent nitric acid
mixture, after which the filter is broken and the precipitate washed into a beaker with
two per cent ammonia and the filter washed therewith until about 100 cubic
centimeters have been used. If the solution is turbid from the presence of silicic acid it
should be precipitated a second time by addition of molybdic solution until the acid
reaction is restored. The ammoniacal solution of the yellow precipitate is treated, drop
by drop, with constant stirring, with fifteen cubic centimeters of magnesia mixture,
and set aside for two hours. The precipitate is collected, washed, ignited, and weighed
in the usual manner. The direct precipitation of the phosphoric acid by the magnesia
solution in presence of citrate is not advisable because of the almost general presence
of silicic acid which would cause the results to be too high.

Figure. 6.
Wagner’s Digestion Apparatus for Slags.

The chief objection to this method of Wagner lies in the failure to control the
temperature at which the digestion with citrate solution is made. Huston has shown,
as will be described further on, that the temperature exercises a great influence in
digestion with citrate. Since the laboratory temperature, especially in this country,
may vary between 10° and 35°, it is evident that on the same sample the Wagner
method would give very discordant results at different seasons of the year.
82. Solutions Employed in the Wagner Method.—1. Ammonium Citrate.—In
one liter there should be exactly 150 grams of citric acid and 27.93 grams of
ammonia, equivalent to twenty-three grams of nitrogen. The following example
illustrates the preparation of ten liters of the solution: In two liters of water and three
and a half liters of eight per cent ammonia, 1,500 grams of citric acid are dissolved
and the cooled solution made up exactly to eight liters. Dilute twenty-five cubic
centimeters of this solution to 250 cubic centimeters and treat twenty-five cubic
centimeters of this with three grams of calcined magnesia and distill into forty cubic
centimeters of half normal sulfuric acid. Suppose the ammonia nitrogen found
correspond to twenty cubic centimeters of fourth normal soda-lye. Then in the eight
liters are contained

(20.0 × 0.0035 × 8000)
————————— = 224 grams
2.5

of ammonia nitrogen. Then in order to secure in the ten liters the proper quantity of
ammonia there must be added two liters of water containing 230 - 224 = six grams of
nitrogen or seven and three-tenths grams ammonia; viz., ninety-four cubic centimeters
of 0.967 specific gravity.
2. Molybdate Solution.—Dissolve 125 grams of molybdic acid in dilute two and
five-tenths per cent ammonia, avoiding a large excess of the solvent. Add 400 grams
of ammonium nitrate, dilute with water to one liter and pour the solution into one liter
of nitric acid of 1.19 specific gravity. Allow the preparation to stand for twenty-four
hours at 35° and filter.
3. Magnesia Mixture.—Dissolve 110 grams of pure crystallized magnesium
chlorid and 140 grams of ammonium chlorid in 700 cubic centimeters of eight per
cent ammonia and 130 cubic centimeters of water. Allow to stand several days and
filter.
83. Estimation of Lime.—When the lime is to be determined in basic slags some
difficulty may be experienced by reason of danger of contamination of the oxalate
precipitate with iron and especially manganese, which is often present in slags.
Holleman[68] proposes to estimate the lime in basic slag by a modification of the
methods of Classen and Jones. The manipulation is as follows: Fifty cubic
centimeters of the solution of slag, equivalent to one gram of substance, are
evaporated to a small volume, twenty cubic centimeters of neutral ammonium oxalate
solution (one to three) added to the residue and heated on a water-bath with frequent
stirring, until the precipitate is pure white and free from lumps. The time required is
usually about ten minutes. The precipitate is collected on a filter and washed with hot
water until the filtrate contains no oxalic acid. The precipitated calcium oxalate must
be snow-white. The filter is broken and the calcium oxalate washed through, first with
water and finally with warm, dilute hydrochloric acid (one to one). The calcium
oxalate is dissolved by adding fifteen cubic centimeters of concentrated hydrochloric
acid, the solution evaporated to a volume of about twenty-five cubic centimeters and
ten cubic centimeters of dilute sulfuric acid (one to five), and 150 cubic centimeters
of ninety-six per cent alcohol added. After standing three hours or more the
precipitate is separated by filtration and washed with ninety-six per cent alcohol until
the washings show no acid reaction with methyl orange. The calcium sulfate
precipitated is dried to constant weight. This method gives a pure precipitate of
calcium sulfate, containing only traces of manganese.

84. Estimation of Caustic Lime.—The lime mechanically present in basic slags
is likely to be found as oxid or hydroxid, especially when the sample is of recent
manufacture. In the form of oxid the lime may be determined by solution in sugar. In
this process one gram of the fine slag meal is shaken for some time with a solution of
sugar, as suggested by Stone and Scheuch.[69] The dissolved lime is separated as
oxalate by treatment of the solution with the ammonium salt. The calcium oxalate
may be determined by ignition in the usual way or volumetrically by solution in
sulfuric acid and titration of the free oxalic acid with potassium permanganate
solutions. The standard solution of permanganate should be of such a strength as to
have one cubic centimeter equivalent to about 0.01 gram of iron. The iron value of the
permanganate used multiplied by 0.5 will give the quantity of calcium oxid found.
85. Detection of Adulteration of Phosphatic Slags.—The high agricultural value
of phosphatic slags has led to their adulteration and even to the substitution of other
bodies. Several patents have also been granted for the manufacture of artificial slags
of a value said to be an approximation to that of the by-products of the basic pig iron
process.
(1) Method of Blum.—One of the earliest methods of examining basic slag for
adulterations is the method of Blum.[70] This method rests upon the principle of the
determination of the carbon dioxid in the sample. The basic phosphatic slag is
supposed to contain no carbon dioxid. This is true only in case it is freshly prepared.
The tetrabasic phosphate, after being kept for some time, gradually absorbs carbon
dioxid from the air. As high as nineteen per cent of carbon dioxid have been found in
slags which have been kept for a long while. When the slag has absorbed so much of
carbon dioxid and water from the air as to be no longer profitable for market, it can be
restored to its original condition by ignition.
(2) Method of Richter-Forster.—One of the common adulterants of tetrabasic
phosphate is aluminum phosphate. The method of detecting this when mixed with the
slag is described by Richter-Forster.[71] The method depends on the fact that soda-lye
dissolves the aluminum phosphate, although it does not dissolve any calcium
phosphoric acid from the slag. Two grams of the sample to be tested are treated with
ten cubic centimeters of soda-lye of from 7° to 8° C. in a small vessel with frequent
shaking for a few hours at room temperature. After filtration the filtrate is made acid
with hydrochloric and afterwards slightly alkaline with ammonia. With pure basic
slag there is a small trace of precipitate produced, but this is due to a little silica
which can be dissolved in a slight excess of acetic acid. If, however, the basic slag
contain aluminum phosphate, a dense jelly-like precipitate of aluminum phosphate is
produced.
(3) Method of Jensch.—Edmund Jensch[72] determines the tetrabasic phosphate in
slags by solution in organic acids, and prefers citric acid for this purpose. This method

was also recommended by Blum[73].
It is well known that the tetrabasic phosphate in slags is completely soluble in
citric acid while the tribasic phosphate is only slightly, if at all, attacked. The neutral
ammonium salts of organic acids do not at first attack the tribasic phosphate at all,
and they do not completely dissolve the tetrabasic phosphate. The solution used by
Jensch is made as follows: Fifty grams of crystallized citric acid are dissolved in one
liter of water. A weaker acid dissolves the tetrabasic phosphate too slowly and a
stronger one attacks the tribasic phosphate present.
Schucht recommends the following method of procedure:[74] One gram of the
slag, finely ground, is treated in a beaker glass with about 150 cubic centimeters of
Jensen’s citric acid solution and warmed for twelve hours in an air-bath at from 50° to
70° with frequent shaking. Afterwards it is diluted with 100 cubic centimeters of
water, boiled for one minute and filtered. The filter is washed thoroughly with hot
water and the phosphoric acid is estimated in the filtrate in the usual way. With
artificial mixtures of basic slags and other phosphates the quantity of basic slag can
be determined by the above method.
(4) Method of Wrampelmeyer.—According to Wrampelmeyer the most convenient
method for discovering the adulteration of basic slag is the use of the microscope.[75]
All finely ground natural phosphates are light colored and with a strong magnification
appear as rounded masses. In basic slags the particles are mostly black but there are
often found red-colored fragments having sharp angles which refract their light in a
peculiar way so that, with a very little experience, they can be recognized as being
distinctive marks of pure basic slag.
In artificial mixtures of these two phosphates, which we have made in our
laboratory, we have been able to detect with certainty as little as one per cent of added
mineral phosphate.
One form of adulterating natural mineral phosphates has been mixing them with
finely pulverized charcoal or soot to give them the black appearance characteristic of
the basic slags. This form of adulteration is at once disclosed by simple ignition or by
microscopic examination.
(5) Loss on Ignition.—If all doubts cannot be removed by the use of the
microscope, the loss on ignition should be estimated. Natural phosphates all give a
high loss on ignition, ranging from eight to twenty-four per cent, while a basic slag
gives only a very slight loss on ignition, especially when fresh. A basic slag which has
stood for a long while and absorbed carbon dioxid and moisture, may give a loss on
ignition approximating, in a maximum case, the minimum loss on ignition from a
natural phosphate.

In experiments made in this laboratory in testing for loss on ignition, we have
uniformly found that natural mineral phosphates will lose from nearly one to two and
one-half times as much on ignition as a basic slag which has been kept for two years.
A basic slag in the laboratory more than two years old gave, as loss on ignition, 4.12
per cent. Several samples of finely ground Florida phosphates gave the following
percentages of loss on ignition, as compared with a sample of slag.
Odorless phosphate 4.12.
Florida phosphates 8.06, 6.90, 9.58, 6.40, 10.38, and 10.67 respectively.
There are some mineral phosphates, however, which are ignited before being sent
to the market. We have one such sample in our laboratory from Florida which gave,
on ignition, a loss of only one and four-tenths per cent. In this case it is seen that the
application of the process of ignition would not discriminate between a basic slag and
a mineral phosphate.
It may often be of interest to know what part of the loss, on ignition, is due to
water in form of moisture. In such cases the sample should first be dried to constant
weight in a steam-bath and then ignited. In the following data are found the results
obtained here with samples treated as above indicated and also ignited directly.
Number one is a basic slag two years old and the others Florida phosphates.
Heated to 100° C. then ignited. Ignited directly.
Loss at Loss on Total Loss on
100° C. ignition. loss. ignition.
No. 1 (Slag) 2.57 1.77 4.34 4.12
No. 2 (Rock) 2.61 5.19 7.80 8.06
No. 3 “ 1.09 5.77 6.86 6.90
No. 4 “ 0.42 9.20 9.62 9.58
No. 5 “ 1.81 4.83 6.64 6.40
No. 6 “ 4.36 6.52 10.88 10.83
No. 7 “ 3.31 7.01 10.32 10.67

(6) Presence of Sulfids.—Another point noticed in this laboratory is that the basic
slags uniformly contain sulfids which are decomposed upon the addition of an acid
with an evolution of hydrogen sulfid.
(7) Presence of Fluorin.—In applying the test for fluorin, it has been uniformly
found here that the mineral phosphates respond to the fluorin test while the basic
slags, on the contrary, respond to the hydrogen sulfid test. This test, however, was
applied only to the few samples we have had and may not be a uniform property.

The absence of fluorin might not prove the absence of adulteration, but its
presence would, I believe, certainly prove the fact of the adulteration in that particular
sample.
The fluorin test is applied by Böttcher in the following manner:[76] From ten to
fifteen grams of the slag are placed in a beaker ten centimeters high and from five to
six centimeters in diameter, with fifteen cubic centimeters of concentrated sulfuric
acid, stirred with a glass rod, and covered with a watch-glass on the under side of
which a drop of water hangs. If there be formed upon the drop of water a white murky
rim, it is proof that a mineral phosphate containing fluorin has been added. After from
five to ten minutes you can notice on the clean watch-glass the etching produced by
the hydrofluoric acid. According to Böttcher an adulteration of ten per cent of raw
phosphate in slag can be detected by this method.
(8) Solubility in Water.—Solubility in water is also a good indication, natural
phosphates being totally insoluble in water, while a considerable quantity of the basic
slag will be dissolved in water on account of the calcium oxid or hydroxid which it
contains. If the loss on ignition is low, and the volume-weight and water-solubility
high, the analyst may be certain that the sample is a pure slag.
In comparative tests made in our laboratory with a sample of basic slag and seven
samples of Florida phosphate, the percentages of material dissolved by water and by a
five per cent solution of citric acid were found to be as follows:
Sol. in
five per cent
Water-soluble. citric acid.
Per cent. Per cent.

Odorless phosphate 0.97 16.10
Florida phosphate 0.01 4.15
“ “ 0.09 4.66
“ “ 0.02 3.43
“ “ 0.08 3.61
“ “ 0.02 3.79
“ “ 0.05 4.46
“ “ 0.02 4.24

From the above data it is seen that the solvent action of water especially would be
of value inasmuch as it dissolves only a mere trace of the mineral phosphates,
approximating one per cent of the amount dissolved from basic slag. In the case of the
citric acid it is found that the amount of materials soluble in this solvent for basic slag

is fully four times as great as for the mineral phosphates. Both of these processes,
therefore, have considerable value for discriminating between the pure and
adulterated article of basic slag.
(9) Specific Gravity.—The estimation of the volume specific gravity is also a good
indication for judging of the purity of the slag. This is best done by weighing directly
a given volume. Basic slag will have a volume-weight of about one and nine-tenths,
while natural phosphates will have about one and six-tenths.
(10) Conclusions.—From the above résumé of the standard methods which are in
use for determining the adulteration of basic slag, it is seen that there are many cases
in which grave doubt might exist even after the careful application of all the methods
mentioned. If we had only to consider the adulteration of basic slag with certain of the
mineral phosphates, that is, tricalcium phosphate, the problem would be an easy one,
but when we add to this the fact that iron and aluminum phosphates are employed in
the adulteration, and that artificial slags may be so used, the question becomes more
involved.
In doubtful cases one after another of the methods should be applied until there is
no doubt whatever of the judgment which should be rendered.

VOLUMETRIC DETERMINATION
OF PHOSPHORIC ACID.

86. Classification of Methods.—The time required for a gravimetric
determination of phosphoric acid has led analysts to try the speedier if less accurate
processes, depending on the use of volumetric methods. The chief difficulty with
these methods has been in securing some sharp method of distinguishing the end
reaction. In most cases it has been found necessary to remove a portion of the titrated
solution and prepare it for final testing by subsidence or filtration. As is well known,
this method of determining the end reaction is less accurate and more time-consuming
than those processes depending on a change of color in the whole mass. All the
volumetric processes now in general use may be divided into two classes; viz., (1) the
direct precipitation of phosphoric acid and the determination of the end reaction by
any appropriate means, and (2) the previous separation of the phosphoric acid, usually
by means of a citro-magnesium or molybdenum mixture, and in the latter case the
subsequent titration of the yellow ammonium phosphomolybdate either directly or
after reduction to a lower form of oxidation. In respect of extent of application by far
the most important volumetric method is the one depending on titration by a uranium
salt after previous separation by ammoniacal magnesium citrate. A promising method
after previous separation by molybdenum is the one proposed by Pemberton, but it
has not yet come into general use. For small quantities of phosphoric acid or of
phosphorus, such as are found in steels and irons, the method of Emmerton, either as

originally proposed or as modified by Dudley and Noyes, is in frequent use. Where
volumetric methods are applied to products separated by molybdic solution, the
essential feature of the analytical work is to secure a yellow precipitate of constant
composition. If this could be uniformly done such methods would rival the
gravimetric processes in accuracy. Hence it is highly important in these methods that
the yellow precipitate should be secured as far as possible, under constant conditions
of strength of solution, duration of time, and manner of precipitation. In these cases,
and in such only, can the quicker volumetric methods be depended on for accurate
results.
The direct volumetric precipitation of the phosphoric acid by a uranium salt or
otherwise is practiced only when the acid is combined with the alkalies and when iron
and alumina are absent and only small quantities of lime present. This method has
therefore but little practical value for agricultural purposes. In all volumetric analyses
the accuracy of the burettes, pipettes, and other graduated vessels should be proved by
careful calibration. Many of the disagreements in laboratories where the analytical
work is conducted equally well can be due to no other cause than the inaccuracy of
the graduated vessels which are found in commerce. Burettes should not only be
calibrated for the whole volume but for at least every five cubic centimeters of the
graduation.

URANIUM METHOD AS PRACTICED
BY THE FRENCH CHEMISTS.

87. The Uranium Method.—Since the phosphoric acid of practical use for
agricultural purposes is nearly always combined with lime, alumina, and iron, its
volumetric estimation by means of a standard solution of a uranium salt is to be
preceded by a preliminary separation by means of an ammoniacal magnesium citrate
solution. The principle of the method was almost simultaneously published by Sutton,
[77]
Neubauer,[78] and Pincus.[79] The phosphoric acid may also be separated by means
of molybdic solution or by tin or bismuth.[80] In practice, however, it has been found
that when the uranium method is to be used the magnesium citrate separation is the
most convenient. Since this is the method practiced almost universally in France, the
method there used will be given in detail. It is based essentially on the process
described by Joulie.[81]
88. Preparation of Sample.—(1) Incineration.—Since the organic matters
present in a phosphatic fertilizer often interfere with the employment of uranium as a
reagent, it is necessary to incinerate the sample taken for analysis.[82]
(2) Solution of the Material.—All phosphates, with the exception of certain
aluminum phosphates, amblygonite for example, are easily dissolved in nitric and
hydrochloric acids more or less dilute, especially on ebullition. The best solvent,

however, for calcium phosphates for the uranium method is incontestably
hydrochloric acid which also very easily dissolves the iron and aluminum phosphates,
which are often found present with calcium phosphates.
(3) Nitric Acid.—In many laboratories nitric acid is preferred in order to avoid, in
part, the solution of ferric oxid which interferes with the determination of phosphoric
acid in certain processes. Since it does not act in this way for the citro-magnesium
uranium method, it is preferable to employ hydrochloric acid, especially because it
dissolves the iron completely and permits thus the operator to judge of the success of
the solvent action by the completely white color of the residue.
(4) Pyritic Phosphates.—Certain phosphates contain pyrites which hydrochloric
acid does not dissolve, and there is left consequently, a residue more or less colored.
In this case it is necessary to add some nitric acid and to prolong the boiling until the
pyrite has disappeared, since it might retain a small quantity of phosphoric acid in the
state of iron phosphate.
(5) Sulfuric Acid.—Some chemists decompose the phosphates by means of dilute
sulfuric acid. This method, which is certainly able to give good results for certain
products and for certain processes, presents numerous inconveniences which tend to
render its use objectionable for volumetric purposes. The calcium sulfate which is
formed, requires prolonged washings which lead to chances of fatal error.
If an aluminum phosphate be under examination, containing only very little or no
lime, sulfuric acid is to be preferred to hydrochloric and nitric acids, since it attacks
amblygonite, which, as has been before stated, resists the action of the other two
acids. But these are cases which are met with very rarely, and which can always be
treated by the general method by previously fusing the material with a mixture of
sodium and potassium carbonate.
In the great majority of cases the decomposition by hydrochloric acid is very
easily accomplished by simply boiling in a glass vessel, and without effecting the
separation of the silica. This operation is only necessary after the substance has been
fused with alkaline carbonates, or, in case of substances which contain decomposable
silicates giving gelatinous silica with hydrochloric acid.
There are two methods [see (6) and (7)] of securing a solution of the sample taken
which varies from one to five, and even ten grams, according to the apparent
homogeneity of the material to be analyzed.
(6) Solution by Filtration and Washing.—The ordinary method can be employed
consisting in decomposing the substance by an acid, filtering, and washing the residue
upon the filter, and combining all the wash-waters to make a determinate volume.
Afterwards an aliquot fraction of the whole is taken for the precipitation. This method
is long, and presents some chances of error, when the insoluble residue is voluminous

and contains silica which obstructs the pores of the paper and renders the filtration
difficult.
(7) Volumetric Solution.—It is advisable to substitute volumetric solution for
solution by filtration and washing, which is accomplished by decomposing the
substances in a graduated flask, the volume being afterwards made up to the mark
with distilled water after cooling. The solution is then filtered without washing, and
by means of a pipette an aliquot part of the original volume is taken for precipitation.
Thus all retardations in the process are avoided, and likewise the chances of error
from washing on the filter. It is true that this method may lead to a certain error due to
the volume of the insoluble matter which is left undecomposed, but since this
insoluble matter is usually small in quantity, and since it is always possible to
diminish the error therefrom by increasing the volume of the solution, this cause of
error is much less to be feared than those due to the difficulties which may occur in
the other method. Let us suppose, in order to illustrate the above, that we are dealing
with a phosphate containing fifty per cent of insoluble sand which may be considered
as an extreme limit. In working on four grams of the material in a flask of 100 cubic
centimeters capacity, there will be an insoluble residue of two grams occupying a
volume of about one cubic centimeter, the density of the sand being generally nearly
two. The one hundred cubic centimeter flask will then contain only ninety-nine cubic
centimeters of the real solution, and the error at the most would be 0.01. This error
could be reduced to one-half by dissolving only two grams of the material in place of
four, or by making the volume up to 200 instead of 100 cubic centimeters.
In general it may be said that the errors which do not exceed 0.01 of the total
matter under treatment, are negligible for all industrial products. The method of
volumetric solution does not present any further inconvenience. It deserves to be and
has been generally adopted by reason of its rapidity in all the laboratories where many
analyses are to be made. In the volumetric method great care should be taken not to
make up to the volume until after the cooling to room temperature, which may be
speedily secured by immersing the flask in cold water. Care should also be exercised
in taking the sample for analysis by means of the pipette immediately after filtration,
and filtration should take place as soon as the volume is made up to the standard. By
operating in this way the possible variations from changes of volume due to changes
of temperature are avoided.
(8) Examination for Arsenic Acid.—When the sample examined contains pyrites,
arsenic is often present. When the decomposition has been effected by means of nitric
acid, arsenic acid may be produced. This deports itself in all circumstances like
phosphoric acid, and if it is present in the matter under examination it will be found
united with the phosphoric acid and determined therewith afterwards. It is easy to
avoid this cause of error by passing first a current of sulfurous acid through the
solution, carrying it to the boiling-point in order to drive out the excess of sulfurous

acid, and afterwards precipitating the arsenic by a current of hydrogen sulfid. After
filtration, the rest of the operation can be carried on as already described.
89. Precipitation of the Phosphate by Magnesium Citrate.—By means of an
accurate pipette a quantity of the solution representing from 0.125 to 0.250 gram or
more is taken, according to the presumed richness of the product to be examined. In
order that the following operations may go on well, it is necessary that the quantity of
phosphoric acid contained in the sample should be about fifty milligrams. The sample
being measured is run into a beaker, and there are added, first, ten cubic centimeters
of magnesium citrate solution, and second, a large excess of ammonia. If the quantity
of the magnesium citrate solution be sufficient, the mixture should at first remain
perfectly limpid and only become turbid at the end of some moments and especially
after the mixture is stirred.
If there should be an immediate turbidity produced it is proof that the quantity of
magnesium citrate solution employed has been insufficient, and it is necessary to
begin again by doubling its amount. Good results cannot be obtained by adding a
second portion of the magnesium citrate solution to the original, since the iron and
aluminum phosphates which are once formed are redissolved with difficulty. Many
chemists at the present time abstain from using the magnesium citrate solution and
replace it by a solution of citric acid and one of magnesium sulfate, which they pour
successively into the sample under examination. This is a cause of grave errors which
it is necessary to point out. Joulie has indeed recognized the fact that the precipitation
of the phosphoric acid is not completed in presence of ammonium citrate except it is
employed in conjunction with a sufficient excess of magnesia. But the foreign matters
which accompany the phosphoric acid require different quantities of ammonium
citrate in order to keep them in solution, and it is important to increase the magnesium
solution at the time of increasing the citric acid in order to maintain them always in
the same proportion. This is easily accomplished by measuring the two solutions, but
it is much more easily done by uniting them and adding them together.
90. The Magnesium Citrate Solution.—The formula originally proposed by
Joulie, and modified by Millot, and adopted by the French Association of Chemists, is
as follows: Citric acid, 400 grams; pure magnesium carbonate, forty grams; caustic
magnesia, twenty grams; distilled water, half a liter. After solution, add enough of
ammonia to render strongly alkaline, requiring about 600 cubic centimeters. Make the
volume up with distilled water to one and a half liters. If the solution be turbid, it is
proof that the magnesia or the carbonate employed contains some phosphoric acid
which is to be separated by filtration, and the solution can then be preserved
indefinitely.
91. Time of Subsidence.—When the phosphoric acid is precipitated by the
mixture above mentioned, it is necessary to allow it to subside for a certain time
under a bell jar in order to avoid the evaporation of the ammonia. In order to give

plenty of time for this subsidence, it is well to make the precipitations in the afternoon
and the filtrations the following morning. There are thus secured twelve to fifteen
hours of repose, which is time amply sufficient for all cases.
92. Filtration and Washing.—Filtration is performed easily and rapidly upon a
small filter without folds placed in a funnel with a long stem of about two millimeters
internal diameter. Placed in a series of six or eight, they allow the filtration to take
place in regular order without loss of time, the first filter being always empty by the
time the last one is filled. The supernatant liquid from the precipitate should first be
decanted on the filter, avoiding the throwing of the filtrate on the filter which would
greatly retard the process, especially if it should contain a little silica, as often
happens.
When the clear liquid is thus decanted as completely as possible, the rest of the
precipitate is treated with water to which one-tenth of its volume of ammonia has
been added, and the washing is continued by decantation as at first, and afterwards by
washing upon the filter until the filtered solution gives no precipitate with sodium
phosphate. Four washings are generally sufficient to attain this result.
If the operations which precede have been well-conducted, the total phosphoric
acid contained in the material under examination is found upon the filter-paper,
except the small portion which remains adhering to the beaker in which the
precipitation has been made. The determination of the phosphoric acid comprises the
following operations: First, solution of the ammonium magnesium phosphate and
second, titration by means of a standard solution of uranium.
93. Solution of the Ammonium Magnesium Phosphate.—The phosphate which
has been collected upon the filter is dissolved by a ten per cent solution of pure nitric
acid. This solution is caused to pass into the beaker in which the precipitation was
made in order to dissolve the particles of phosphate which remain adherent to its
sides; and this solution is then thrown upon the filter. The filtrate is then received in a
flask of about 150 cubic centimeters capacity, marked at seventy-five cubic
centimeters. After two or three washings with the acidulated water, the filter itself is
detached from the funnel and introduced into the vessel which contains the solution.
The whole of the filtrate being collected in the flask it is saturated by one-tenth
ammoniacal water until a slight turbidity is produced. One or two drops of dilute
nitric acid are now added until the liquor becomes limpid, and the flask is placed
upon a sand-bath in order to carry the liquid to the boiling-point. After ebullition there
are added five cubic centimeters of acid sodium acetate in order to cause the free
nitric acid to disappear and immediately the titration, by means of a standard solution
of uranium, is undertaken.
94. Acid Sodium Acetate.—The acid sodium acetate is prepared as follows:
Crystallized sodium acetate, 100 grams; glacial acetic acid, fifty cubic centimeters;

distilled water, enough to make one liter.
95. Standard Solution of Uranium.—A solution of uranium is to be prepared as
follows: Pure uranium nitrate, forty grams; distilled water, about 800 cubic
centimeters. Dissolve the uranium nitrate in the distilled water and add a few drops of
ammonia until a slight turbidity is produced, and then a sufficient amount of acetic
acid to cause this turbidity to disappear. The volume is then completed to one liter
with distilled water.
The uranium nitrate often contains some uranium phosphate and some ferric
nitrate. It is important that it be freed from these foreign substances. This is secured
by dissolving it in distilled water and precipitating it by sodium carbonate, which
redissolves the uranium oxid and precipitates the iron phosphate and oxid.
The filtered liquor is saturated with nitric acid, and the uranium oxid
reprecipitated by ammonia. It is then washed with distilled water by decantation and
redissolved in nitric acid, as exactly as possible, evaporated, and crystallized.
The crystals are taken up with ether, which often leaves still a little insoluble
matter. The solution is filtered, and the ether evaporated. The salt which remains is
perfectly pure. It frequently happens when the uranium nitrate has not been properly
purified that the solution prepared as has been indicated above, deposits a light
precipitate of phosphate which alters its strength and affords a cause of error. Only
those solutions should be employed which have been prepared some days in advance,
and which have remained perfectly limpid.
The solution of uranium thus obtained contains uranium nitrate, a little
ammonium nitrate, a very small quantity of uranium acetate, some ammonium
acetate, and a little free acetic acid. Its sensibility is the more pronounced as the
acetates present in it are less in quantity. It is important, therefore, never to prepare
the solution with uranium acetate.
96. Typical Solution of Phosphoric Acid.—In order to titrate a solution of
uranium, it is necessary to have a standard solution of phosphoric acid; that is to say,
a solution containing a precise and known quantity of that acid in a given volume.
This solution is prepared by means of acid ammonium phosphate, a salt which is
easily obtained pure and dry. Sometimes as it may contain a small quantity of neutral
phosphate which modifies the relative proportions of phosphoric acid and ammonia,
and it is indispensable to have its strength verified. The titer of the typical solution
should be such that it requires for the precipitation of the phosphoric acid which it
contains, a volume of the solution of uranium almost exactly equal to its own, in order
that the expansions or contractions which the two liquors undergo, by reason of
changes in the temperature of the laboratory, should be without influence upon the
results.

The solution of uranium prepared as has been indicated above, precipitates almost
exactly five milligrams of phosphoric acid per cubic centimeter; the typical solution
of phosphoric acid is prepared with eight and one-tenth grams of acid ammonium
phosphate pure and dry, which is dissolved in a sufficient quantity of distilled water to
make one liter.
The acid ammonium phosphate containing 61.74 per cent of anhydrous
phosphoric acid, the quantity above gives exactly five grams of that acid in a liter, or
five milligrams in a cubic centimeter.
97. Verification of the Strength of the Standard Solution of Phosphoric Acid.
—The strength of the standard solution of phosphoric acid is verified by evaporating
a known volume, fifty cubic centimeters for example, with a solution of ferric
hydroxid containing a known quantity of ferric oxid. The mass having been
evaporated to dryness, and ignited in a platinum crucible, gives an increase in the
weight of the iron oxid exactly equal to the amount of anhydrous phosphoric acid
contained therein, both the nitric acid and ammonia being driven off by the heat.
To prepare the solution of ferric hydroxid, dissolve twenty grams of iron filings in
hydrochloric acid. The solution is filtered to separate the carbon, and it is converted
into ferric nitrate by nitric acid, and the solution diluted with distilled water, and the
ferric oxid precipitated by a slight excess of ammonia. The precipitate, washed by
decantation with distilled water until the wash-water no longer gives a precipitate
with silver nitrate, is redissolved in nitric acid, and the solution is concentrated or
diluted, as the case may be, to bring the volume to one liter.
In order to determine the quantity of ferric oxid which it contains, fifty cubic
centimeters are evaporated to dryness, ignited, and weighed.
A second operation like the above is carried on by adding fifty cubic centimeters
of the standard solution of phosphoric acid, and the strength of the solution thus
obtained is marked upon the flask.
If the operation have been properly carried on, three or four duplicates will give
exactly the same figures. If there are sensible differences, the whole operation should
be done over from the first.
98. Titration of the Solution of Uranium.—In a 150 cubic centimeter flask
marked at seventy-five cubic centimeters, are poured ten cubic centimeters of the
standard solution of phosphoric acid measured with an exact pipette; five cubic
centimeters of the acid sodium acetate are added, and distilled water enough to make
about thirty cubic centimeters, and the whole carried to the boiling-point. The titration
is then carried on by allowing the solution of uranium to fall into the flask from a
graduated burette, thoroughly shaking after each addition of the uranium, and trying a
drop of the liquor with an equal quantity of a ten per cent solution of potassium
ferrocyanid upon a greased white plate. Since the quantity of the uranium solution

present will be very nearly ten cubic centimeters at first, nine cubic centimeters can
be run in without testing. Afterwards, the operation is continued by adding two or
three drops at a time until the test upon the white plate with the potassium ferrocyanid
shows the end of the reaction. When there is observed in the final test a slight change
of tint, the flask is filled up to the mark with boiling distilled water and the process
tried anew. If in the first part of the operation the point of saturation have not been
passed, it is still usually necessary to add a drop or two of the uranium solution in
order to produce the characteristic reddish coloration, and this increase is rendered
necessary by the increase in the volume of the liquid. Proceeding in this manner two
or three times allows the attainment of extreme precision, inasmuch as the analyst
knows just when to look for the point of saturation.
Correction.—The result of the preceding operation is not absolutely exact. It is
evident indeed that in addition to the quantity of uranium necessary for the exact
precipitation of the phosphoric acid, it has been necessary to add an excess sufficient
to produce the reaction upon the potassium ferrocyanid.
This excess is rendered constant by the precaution of operating always upon the
same volume; namely, seventy-five cubic centimeters. It can be determined then once
for all by making a blank determination under the same conditions but without using
the phosphoric acid.
The result of this determination is that it renders possible the correction which it is
necessary to make by subtracting the quantity used in the blank titration from the
preceding result in order to obtain the exact strength of the uranium solution.
The operation is carried on as follows: In a flat-bottomed flask of about 150 cubic
centimeters capacity and marked at seventy-five cubic centimeters, by means of a
pipette, are placed five cubic centimeters of the solution of sodium acetate; some hot
distilled water is added until the flask is filled to the mark, and it is then placed upon a
sand-bath and heated to the boiling-point. It is taken from the fire, the volume made
up to seventy-five cubic centimeters with a little hot distilled water, and one or two
drops of the solution of uranium are allowed to flow into the flask from a graduated
burette previously filled exactly to zero. After each drop of the solution of uranium
the flask is shaken and the liquid tried upon a drop of potassium ferrocyanid, as has
been previously indicated. For a skilled eye, four to six drops are generally necessary
to obtain the characteristic coloration; that is from two-tenths to three-tenths of a
cubic centimeter. Beginners often use from five-tenths to six-tenths, and sometimes
even more.
The sole important point is to arrest the operation as soon as the reddish tint is
surely seen, for afterwards the intensity of the coloration does not increase
proportionally to the quantity of liquor employed.

It is well to note that at the end of some time the coloration becomes more intense
than at the moment when the solutions are mixed, so that care must be taken not to
pass the saturation-point. This slowness of the reaction is the more marked as there is
more sodium or ammonium acetate in the standard solutions. This is the reason that it
is important to introduce always the same quantity; namely, five cubic centimeters.
This is also the reason why the uranium acetate should not be employed in preparing
the standard solution of uranium which ought to contain the least possible amount of
acetate in order that the necessary quantity which is carried into each test should be as
small as possible and remain without appreciable influence. If it were otherwise, the
sensibility of the reaction would be diminished in proportion as a larger quantity of
uranium solution was employed, giving rise to errors which would be as much more
important as the quantities of phosphoric acid to be determined were greater. The
correction for the uranium solution having been determined it is written upon the
label of the bottle containing it.
Causes of Errors.—In the work which has just been described, some causes of
error may occur to which the attention of analysts should be called.
The first is the error which may arise from the consumption of the small quantity
of uranium phosphate which is taken with a stirring rod when the liquid is tested with
potassium ferrocyanid. It is very easy to be assured that the end of the reaction has
really been reached. For this purpose it is only necessary to note the quantity of the
solution already employed and to add to it afterwards four drops; shake, and make a
new test with a drop of the potassium ferrocyanid placed near the spot which the last
one occupied. If a decidedly reddish tint does not appear at the moment of removing
the glass rod, it is to be concluded that the first appearance was an illusion, and the
addition of uranium is to be continued. If, on the contrary, the coloration appear of a
decided tint, the preceding number may be taken for exact. It is then always beneficial
to close the titration by this test of four supplementary drops which will exaggerate
the coloration and confirm the figure found.
The second cause of error, and one moreover which is the most frequently met
with, consists in passing the end of the reaction by adding the uranium too rapidly. In
place of giving then a coloration scarcely perceptible, the test with the drop of
potassium ferrocyanid gives a very marked coloration. In this case the analysis can
still be saved. For this purpose the analyst has, at his disposal, a tenth normal solution
prepared with 100 cubic centimeters of the standard solution of phosphoric acid
diluted to one liter with distilled water. Ten cubic centimeters of this tenth normal
solution are added, and the titration continued. At the end, the amount of additional
phosphoric acid used is subtracted from the total.
A third cause of error is found in the foam which is often found in the liquid, due
to the shaking. This foam may retain a portion of the last drops of the solution of
uranium which fall upon its surface and prevent its mixture with the rest of the liquid.

If the glass stirring rod in being removed from the vessel pass through this froth
charged with uranium, the characteristic coloration is obtained before real saturation
is reached. Consequently it is necessary to avoid, as much as possible, the formation
of the foam, and especially to take care never to take the drop for test after agitation
except in the middle of the liquid where the foam does not exist.
Suppose the titration has been made upon ten cubic centimeters of the normal
solution of phosphoric acid in the conditions which we have just indicated, and the
figure for the uranium obtained is 10.2 cubic centimeters; if now the correction,
which may be supposed to amount to two-tenths cubic centimeter, be subtracted there
will remain ten cubic centimeters of the uranium solution which would have
precipitated exactly fifty milligrams of phosphoric acid.
The quantity of phosphoric acid which precipitates one cubic centimeter of the
solution will be consequently expressed by the proportion ⁵⁰/₁₀ = five milligrams,
which is exactly the strength required. In the example which has just been given, the
inscription upon the flask holding the standard solution would be as follows: Solution
of uranium, one cubic centimeter equals five milligrams of phosphorus pentoxid;
correction, two-tenths cubic centimeter.
99. Titration of the Sample.—The strength of the solution of uranium having
been exactly determined, by means of this solution the strength of the sample in
which the phosphoric acid has been previously prepared as ammonium magnesium
phosphate is ascertained. In this case the quantity of phosphoric acid being unknown,
it is necessary to proceed slowly and to duplicate the tests in order not to pass beyond
the point of saturation. From this there necessarily results a certain error in
consequence of the removal of quite a number of drops of the solution of the sample
before the saturation is complete. It is therefore necessary to make a second
determination in which there is at once added almost the quantity of the solution of
uranium determined by the first analysis. Afterwards the analysis is finished by
additions of very small quantities of uranium until saturation is reached. Suppose, for
instance, that the sample was that of a mineral phosphate, five grams of which were
dissolved in 100 cubic centimeters, and of which ten cubic centimeters of the solution
prepared as above required 15.3 cubic centimeters of the standard solution of
uranium. We then would have the following data:
Mineral phosphate, five grams of the material dissolved in
twenty cubic centimeters of hydrochloric acid.
Water, sufficient quantity to make 100 cubic centimeters.
Quantity taken, ten cubic centimeters = 0.50 gram of the
sample taken.
Solution of uranium required 15.3 cubic centimeters.
Correction 0.2 “ “

Actual quantity of uranium solution 15.1 “ “
Strength of the solution of uranium, one cubic centimeter =
fivemilligrams P₂O₅.
Then P₂O₅ in 0.50 gram of the material = 5 × 15.1 = 75.50
milligrams.
75.5 x 100
Then the per cent of P₂O₅ = = 15.10.
50
The sample under examination ought always to be prepared in duplicate, either by
making a single precipitation and re-solution of the ammonium magnesium phosphate
which is made up to a certain volume and an aliquot portion of which is taken for the
analysis, or by making two precipitations under the conditions previously described.
When the content of phosphoric acid in the material under examination is very nearly
known, the double operation may be avoided, especially if it be required to have rapid
and only approximate analyses, such as those which are made for general control and
for the conduct of manufacturing operations. But when analyses are to be used to
serve as the basis of a law or for the control of a market, they should always be made
in duplicate, and the results ought not to be accepted when the numbers obtained are
widely different, since the agreement of the two numbers will show that the work has
been well executed.
This method of analysis, much longer to describe than to execute, gives results
perfectly exact and always concordant when it is well carried out, provided that the
standard solutions, upon which it rests for its accuracy, are correctly prepared and
frequently verified in the manner indicated.
The strength of the solution of uranium ought to be verified every three or four
days. The strength of the standard solution of phosphoric acid should be verified each
time that the temperature of the laboratory undergoes any important change. A
solution prepared, for example, in winter when the temperature of the laboratory is
from 15° to 18° would no longer be exact in summer when the temperature reaches
28° or 30°.
100. Condition of Phosphoric Acid in Superphosphates.—Superphosphates are
the products of the decomposition of phosphates by sulfuric or hydrochloric acid.
They contain phosphoric acid combined with water, with lime, with magnesia, and
with iron and alumina in various proportions.
These combinations may be classed in three categories: First, those compounds
soluble in water; second, those insoluble in water, but very soluble in ammoniacal
salts of the organic acids such as the citrate and oxalate; and third, phosphates not
soluble in any of the above-named reagents.

In the products soluble in water are met free phosphoric acid, monocalcium
phosphate, acid magnesium phosphate, and the iron and aluminum phosphates
dissolved in the excess of phosphoric acid. In the products insoluble in water but
soluble in the ammonium citrate are found bicalcium phosphate and iron and
aluminum phosphates, which together constitute the phosphates called reverted.
These compounds reduced to a very fine state of division in the process of
manufacture are considered to contain phosphoric acid of the same economic value.
101. Determination of the Total Phosphoric Acid in Superphosphates and
Fertilizers.—The process is carried on exactly as for an ordinary phosphate, and with
all the care indicated in connection with the sampling, the incineration, the solution
by means of hydrochloric acid, and the separation of the phosphoric acid in the state
of ammonium magnesium phosphate, and finally in the titration by uranium.
102. Determination of Soluble and Reverted Phosphoric Acid.—To make this
determination a method unique and applicable to all cases consists in extracting, at
first, the soluble constituents in distilled water, and following this operation by
digestion in the ammonium citrate. The products soluble in water can be determined
either separately or at the same time as the products soluble in the ammonium citrate
according to the taste of the people interested, without its being necessary to modify
very greatly the method of operation.
The determination of the soluble phosphoric acid comprises first, the solution of
the soluble constituents in distilled water; second, the solution of the reverted
phosphates in ammonium citrate; third, the precipitation of the phosphoric acid
dissolved in the two preceding operations, and its determination.
103. Preparation of the Sample for Analysis.—The sample sent to the chemical
expert is prepared as has been indicated; that is to say, it is poured on a sieve of which
the meshes have a diameter of one millimeter, and sifted upon a sheet of white paper.
The parts which do not pass the sieve are broken up either by the hand or in a mortar
and added, through the sieve, to the first portions. The product is well mixed and, in
this state, the mass presents all the homogeneity desirable for analysis.
Some fertilizers are received in a pasty state which does not permit of their being
sifted. It is necessary in such a case to mix them with their own weight either of
precipitated calcium sulfate dried at 160° or with fine sand washed with hydrochloric
acid and dried, which divides the particles perfectly and permits of their being passed
through the meshes of the sieve.
104. Extraction of the Products Soluble in Distilled Water.—The substance
having been prepared as has just been indicated, one and a half grams are placed in a
glass mortar. Twenty cubic centimeters of distilled water are added, and the substance
gently suspended therein. After standing for one minute, the supernatant part is
decanted into a small funnel provided with a filter-paper and placed in a flask marked

at 150 cubic centimeters. This operation is repeated five times and is terminated by an
intimate breaking up of the matter with distilled water. When the volume of 100 cubic
centimeters of the filtrate has been obtained, the residue in the mortar is placed on the
filter, and the washing is continued until the total volume reaches 150 cubic
centimeters. The filtrate is shaken in order to render the liquor homogeneous, and is
transferred to a precipitating glass of about 300 cubic centimeters capacity.
105. Solution of the Reverted Phosphates by Ammonium Citrate.—The filter
from the above process is detached from the funnel and is introduced into a flask
marked at 150 cubic centimeters together with sixty cubic centimeters of alkaline
ammonium citrate prepared in the following manner:

Pure citric acid, 400 grams.
Ammonia of 22°, 500 cubic centimeters.

The ammonia is poured upon the citric acid in the form of crystals in a large dish.
The mass becomes heated, and the solution takes place rapidly. When it is complete
and the solution is cold it is poured into a flask of one liter capacity, and the flask is
filled up to the mark with strong ammonia. It is preserved for use in a well-stoppered
bottle. The solution must be strongly alkaline.
The flask in which the filter-paper is introduced, together with the ammonium
citrate, is stoppered and shaken violently in order to disintegrate the filter-paper and
put the reverted phosphates in suspension. There are added then about sixty cubic
centimeters of distilled water, and the flask is shaken and left for twelve hours at least,
or at most for twenty-four hours. The volume is made up to 150 cubic centimeters
with distilled water, and, after mixture, the solution is filtered.
There are thus obtained two solutions which can be precipitated together or
separately according to circumstances. The most usual process is to combine the two
equal volumes of twenty-five, fifty, or one hundred cubic centimeters, representing
one-quarter, one-half, or one gram of the material according to its presumed richness,
in a precipitating flask to which are added from ten to twenty cubic centimeters of the
solution of magnesia made up as follows:
Magnesium carbonate, 50 grams.
Ammonium chlorid, 100 “
Water, 500 cubic centimeters.
Hydrochloric acid, 120 “ “
After complete solution of the solid matters in the above, add 100 cubic
centimeters of ammonia of 22° strength, and distilled water enough to make one liter.
The solutions are thoroughly mixed in a precipitating glass, an excess of ammonia
added, and allowed to stand for twelve hours under a bell jar. The phosphoric acid

contained in the liquor is separated as ammonium magnesium phosphate. It is
collected upon a small filter, washed with a little ammoniacal water, redissolved, and
titrated with the uranium solution in the manner already indicated.
Example: The following is an example of this kind of a
determination:
(1) One and one-half grams of the superphosphate and
distilled water enough to make 150 cubic centimeters.
(2) Filter-paper with reverted phosphates, sixty cubic
centimeters of ammonium citrate, and a sufficient quantity of
distilled water to make 150 cubic centimeters.
Aqueous solution (1) 25 cc
= 0.25 grams of the sample.
Citrate solution (2) 25 cc
Add magnesium solution twenty cubic centimeters and
ammonia in excess, and allow from twelve to twenty-four hours
of digestion, then filter and wash, dissolve and titrate.
Required of solution of uranium 8.55 cubic centimeters (1
cubic centimeter = 5 milligrams P₂O₅).
Correction 0.20.
Remainder 8.35 × 0.005 = 0.04175 gram P₂O₅ for 0.25 gram
of the sample. Then 0.04175 ÷ 0.25 = 16.7 per cent.
From the above data there would be 16.7 per cent of
phosphoric acid soluble in water and in ammonium citrate.
If it be desirable to have separately the phosphoric acid soluble in water, a
separate precipitation is made of the aqueous solution alone by means of the
magnesium citrate solution. The precipitate washed with ammoniacal water is
redissolved and titrated in the manner indicated.
In subtracting from the figures obtained with the two solutions together the
number obtained for the phosphoric acid soluble in water, the number representing the
phosphoric acid soluble in ammonium citrate alone, is obtained.
It is to be noted that the determinations with uranium require always two
successive titrations. It would therefore be an advantage in all operations to
precipitate a weight of ammonium magnesium phosphate sufficient for allowing this
precipitate to be dissolved and made up to 100 cubic centimeters on which amount it
would be possible to execute two, three, or four determinations, and thus to obtain a
figure absolutely incontestable.

106. Conclusions.—It has been seen from the above data that the French chemists
have worked out the uranium volumetric method with great patience and attention to
detail. Where many determinations are to be made it is undoubtedly possible for an
analyst to reach a high degree of accuracy as well as to attain a desirable rapidity, by
using this method. For a few determinations, however, the labor of preparing and
setting the standard solutions required would be far greater than the actual
determinations either by the molybdate or citrate gravimetric methods. For control
work in factories and for routine work connected with fertilizer inspection, the
method has sufficient merit to justify a comparison with the processes already in use
by the official chemists of this country.
The use of an alkaline ammoniacal citrate solution, however, for the determination
of reverted acid renders any comparison of the French method with our own
impossible. On the other hand the French method for water-soluble acid is based on
the same principle as our own; viz., washing at first with successive small portions of
water, and thus avoiding the decomposition of the soluble phosphates, which is, likely
to occur when too great a volume of water is added at once.
In the matter of the temperature and time as affecting the solubility of reverted
acid, the French method is also distinctly inferior to our own. The digestion is allowed
to continue from twelve to twenty-four hours, at the pleasure of the analyst, and
meanwhile it is subjected to room temperature. It is not difficult to see that this
treatment in the same sample would easily yield disagreeing results between twelve
hours at a winter temperature and twenty-four hours at summer heat.

THE DETERMINATION OF PHOSPHORIC ACID
BY TITRATION OF THE YELLOW PRECIPITATE.

107. Pemberton’s Volumetric Method.—In order to shorten the work of
determining the phosphoric acid, numerous attempts have been made to execute the
final determination directly on the yellow precipitate obtained by treating a solution
of a phosphate with ammonium molybdate in nitric acid. The composition of this
precipitate appears to be somewhat variable, and this fact has cast doubt on the
methods of determination based on its weight. Its most probable composition is
expressed by the following formula, (NH₄)₃PO₄(MoO₃)₁₂. For convenience in writing
reactions this formula should usually be doubled. Pemberton has described a
volumetric determination of phosphoric acid in the yellow precipitate which has the
merit of being rapid.[83]
In this laboratory the method has not given very satisfactory results when
compared with the molybdate gravimetric process. It has however attracted so much
attention from analysts as to merit description, and the details of the process are
therefore given.

108. The Process.—One gram of phosphate rock, or from two to three grams of
phosphatic fertilizer, are dissolved in nitric acid, and, without evaporation, diluted to
250 cubic centimeters. Without filtering, twenty-five cubic centimeters are placed in a
four-ounce beaker and ammonia added until a slight precipitate begins to form. Five
cubic centimeters of nitric acid of one and four-tenths specific gravity are then added,
and afterwards ten cubic centimeters of saturated solution of ammonium nitrate and
enough water to make the volume about sixty-five cubic centimeters. The contents of
the beaker are boiled, and while still hot, five cubic centimeters of the aqueous
solution of ammonium molybdate added. Additional quantities of the molybdate are
added, if necessary, until the whole of the phosphorus pentoxid is thrown-out.
After allowing to settle for a moment the contents of the beaker are poured upon a
filter seven centimeters in diameter. The precipitate is thoroughly washed with water,
both by decantation and on the filter. The filter with its precipitate is transferred to a
beaker and titrated with standard alkali, in the presence of phenolphthalein. Each
cubic centimeter of alkali employed should correspond to one milligram of
phosphorus pentoxid, (P₂O₅).
The reagents employed have the composition indicated below:
Ammonium Molybdate.—Ninety grams of the crystals of ammonium molybdate
are placed in a large beaker and dissolved in a little less than one liter of water. The
beaker is allowed to stand over night and the clear liquor decanted. Any undissolved
acid is brought into solution in a little ammonia water and added to the clear liquor. If
a trace of phosphoric acid be present a little magnesium sulfate is added and enough
ammonia to produce a slight alkaline reaction. The volume of the solution is then
made up to one liter. Each cubic centimeter of this solution is capable of precipitating
three milligrams of phosphorus pentoxid.
Standard Potassium Hydroxid.—This solution is made of such strength that one
cubic centimeter is equivalent to one milligram of phosphorus pentoxid. Treated with
acid of normal strength, 100 cubic centimeters are required to neutralize 32.37 cubic
centimeters thereof.
Standard Acid.—This should have the same strength, volume for volume, as the
standard alkali solution. It is made by diluting 323.7 cubic centimeters of normal acid
to one liter.
Indicator.—The indicator to be used is an alcoholic solution of phenolphthalein,
one gram in 100 cubic centimeters of sixty per cent alcohol, and half a cubic
centimeter of this should be used for each titration.
Thomson has shown[84] that of the three hydrogen atoms in phosphoric acid two
must be saturated with alkali before the reaction with phenolphthalein is neutral.
Therefore, when the yellow precipitate is broken up by an alkali, according to the
reaction to follow, only four of the six molecules of ammonium are required to form a

neutral ammonium phosphate as determined by the indicator employed. The
remaining two molecules of ammonium unite with the molybdenum forming also a
salt neutral to the indicator.
Phenolphthalein is preferred because, as has been shown by Long, its results are
reliable in the presence of ammonium salts unless they be present in large quantity,
and if the solution be cold and the indicator be used in sufficient quantity.[85] To
prepare the indicator for this work, one gram of phenolphthalein is dissolved in 100
cubic centimeters of sixty percent alcohol. At least one-half of a cubic centimeter of
the solution is used for each titration.
The advantages claimed for the method are its speed and accuracy. Much time is
saved by avoiding the necessity for the removal of the silica by evaporation. The
results of analyses with and without the removal of the silica are practically identical.
When the silica is not removed it is noticed that the filtrate from the yellow
precipitate has a yellow tint.
The reaction is represented by the following formula:
(NH₄)₆(PO₄)₂(MoO₃)₂₄ + 46KOH = (NH₄)₄(HPO₄)₂ + (NH₄)₂MoO₄
+ 23K₂MoO₄ + 22H₂O.
From this reaction it is seen that the total available acidity of one molecule of the
yellow precipitate titrated against phenolphthalein is equivalent to twenty-three
molecules of potassium hydroxid.
Calculation of Results.—The standard alkali is of such strength that one cubic
centimeter is equal to one per cent of phosphoric acid when one gram of material is
employed and one-tenth of it taken for each determination. In a given case one gram
of a sample was taken and one-tenth of the solution used. Fifty cubic centimeters of
alkali were added to the yellow precipitate. It required thirty-two cubic centimeters of
standard alkali to neutralize the excess.
The alkali consumed by the yellow precipitate was 50 - 32 = 18. The sample
therefore contained eighteen per cent of phosphoric acid.
Comparison with Official Method.—A comparison of the Pemberton volumetric
with the official method of the Association of Agricultural Chemists has been made
by Day and Bryant.[86] The comparisons were made on samples containing from 1.45
to 37.28 per cent of phosphoric acid and resulted as follows:
Per cent Per cent
Substance. P₂O₅, P₂O₅,
Official. Pemberton.
No. 1. Florida rock 1.45 1.32

Per cent Per cent
Substance. P₂O₅, P₂O₅,
Official. Pemberton.
“ 2. “ “ 4.40 4.53
“ 3. Sodium phosphate 19.78 19.99
“ 4. “ “ 19.72 19.73
“ 5. Florida rock 37.28 37.22

This near agreement shows the reliability of the method. The comparison of the
Pemberton volumetric method with the official gravimetric method was investigated
by the reporter of the Association of Official Agricultural Chemists in 1894.[87] The
individual variations were found to be greater than in the regular method but the
average results were nearly identical therewith. The method works far better with
small percentages of phosphoric acid than with large. Where the average of the results
by the official methods gave 12.25 per cent, the volumetric process gave 11.90 per
cent, whereas in the determination of a smaller percentage the results were 2.72 and
2.73 per cent, respectively. Kilgore proposes a variation of the method which differs
from the original in two principal points.[88] First the temperature of precipitation in
the Pemberton process is 100°; but in the modified form from 55° to 60°. At the
higher temperature there is danger of depositing molybdic acid.
The second difference is in the composition of the molybdate solution employed.
The official molybdate solution contains about sixty grams of molybdenum trioxid in
a liter while the Pemberton solution contains sixty-six grams. There is therefore not
much difference in strength. The absence of nitric acid, however, from the Pemberton
solution favors the deposition of the molybdic acid when heat is applied. Kilgore,
therefore, conducts the analysis as follows: The solution of the sample is made
according to the official nitric and hydrochloric acid method for total phosphoric acid.
For the determination, twenty or forty cubic centimeters are taken, corresponding to
two-tenths or four-tenths gram of the sample. Ammonia is added until a slight
precipitate is produced and the volume is then made up, with water, to seventy-five
cubic centimeters. Add some ammonium nitrate solution, from ten to fifteen cubic
centimeters, but this addition is not necessary unless much of the nitric acid has been
driven off during solution. Heat in water-bath to 60° and precipitate with some freshly
filtered official molybdate solution. Allow to stand for five minutes, filter as quickly
as possible, wash four times by decantation using from fifty to seventy-five cubic
centimeters of water each time, and then wash on a filter until all acid is removed.
The solution and titration of the yellow precipitate are accomplished as in the
Pemberton method. The agreement of the results obtained by this modified method
was much closer with the official gravimetric method than those obtained by the
Pemberton process.

109. Estimation of Phosphoric Acid as a Lead Compound.—In the volumetric
lead method, as described by Wavelet, the phosphoric acid is precipitated by the
magnesium citrate solution as in the uranium method of Joulie, as practiced by the
French chemists, and the washing of the precipitate and its solution in nitric acid are
also conducted as in that method.[89] After solution in nitric acid ammonia is added to
neutrality and the solution is then made acid with acetic. The phosphoric acid is
precipitated in the acid solution by a standard solution of lead nitrate, the precipitate
having the formula P₂O₅3PbO.
The end reaction is determined by placing a drop of the titrated mixture on a white
greased dish in contact with a drop of a five per cent solution of potassium iodid.
When all the phosphoric acid is precipitated the least excess of the lead salt is
revealed by the characteristic yellow precipitate of lead iodid.
The author of the process claims that the lead phosphate is insoluble in the excess
of acetic acid and that the phosphate itself does not give any yellow coloration with
potassium iodid. The process is quite as exact as the uranium method and the end
reaction is far sharper and the standard reagents are easily made and preserved.[90]
The method described merits, at least, a comparative trial with the uranium process,
but cannot be recommended as exact until further approved by experience.
The reagents employed have the following composition:
(1) Disodium phosphate solution containing 10.085 grams per liter
(2) Sodium acetate “ “ 50.000 “ “ “
(3) Lead nitrate “ “ 40.000 “ “ “
(4) Potassium iodid “ “ 50.000 “ “ “
The titrations should be conducted in the cold.

110. Water-Soluble Phosphoric Acid.—Glaser has modified the volumetric
method of Kalmann and Meissels for the volumetric estimation of water-soluble
phosphoric acid so as to avoid the double titration required by the original method.[91]
If methyl orange be used as an indicator in the original method, the determination
does not at once lead to the tricalcium salt, but the liquid still contains, after
neutralization, some monocalcium phosphate, which is determined by a further
titration with phenolphthalein. In the modified method the total phosphoric acid is
estimated in one operation as a tricalcium salt. This is secured, by adding, at the
proper time, an excess of calcium chlorid. Two grams of the superphosphate are
shaken with water several times, and, after settling, filtered, and the insoluble residue
finally washed on the filter until the total volume of the filtrate is a quarter of a liter.
Of this, fifty cubic centimeters are taken and titrated with tenth normal soda-lye, with
addition of two drops of methyl orange, until the acid reaction has entirely
disappeared. There is then added some neutral calcium chlorid solution in excess. If
iron and alumina be present, a precipitate is produced of which no account need be

made. The acid reaction is thus restored. Five drops of the phenolphthalein solution
are added and the titration continued until the alkaline reaction is noted throughout
the whole mass. Each cubic centimeter of the soda-lye corresponds, in the first
titration, to 7.1, and in the second to 3.55 milligrams of phosphoric acid.
111. Estimation of Phosphoric Acid in the Presence of a Large Excess of Iron.
—The method given below, due to Emmerton, depends upon the precipitation of a
phosphomolybdate, of constant composition, in the presence of a large excess of iron,
as in the analysis of iron and steel and iron ores.[92] The molybdenum trioxid obtained
is reduced by zinc to Mo₁₂O₁₉. The action of permanganate on this compound is
shown in the following equation:
5Mo₁₂O₁₉ + 17(K₂OMn₂O₇) = 60MoO₃ + 17K₂O + 34MnO.
Seventeen molecules of permanganate are equal to sixty molecules of
molybdenum trioxid. The iron or steel is dissolved in nitric acid, evaporated to
dryness, heated, and redissolved in hydrochloric acid, then treated again with nitric
acid and evaporated until a clear and concentrated solution is obtained free from
hydrochloric acid.
The solution obtained is diluted to forty cubic centimeters with water and washed
into a 400 cubic centimeter flask, making the total volume about seventy-five cubic
centimeters. Add strong ammonia, shaking after each addition, until the mass sets to a
thick jelly from the ferric hydroxid. Add a few more cubic centimeters of ammonia
and shake thoroughly, being sure the ammonia is present in excess. Add next nitric
acid gradually, with shaking, until the precipitate has all dissolved; add enough more
nitric acid to make the solution a clear amber color. The volume should now be about
250 cubic centimeters. Bring the solution to 85° and add, at once, forty cubic
centimeters of molybdate solution of the following strength: Dissolve 100 grams of
molybdic acid in 300 cubic centimeters of strong ammonia and 100 cubic centimeters
of water, and pour the solution into 1,250 cubic centimeters of nitric acid (1.20); close
the flask with a rubber stopper, wrap it in a thick cloth, and shake violently for five
minutes. Collect the precipitate on a filter, using pump, and wash with dilute nitric
acid (1 HNO₃ : 50 H₂O). If a thin film of the precipitate should adhere to the flask it
can be removed by the ammonia in the next operation. Wash the molybdate
precipitate into a 500 cubic centimeter flask with dilute ammonia (1 H₃N : 4 H₂O),
using about thirty cubic centimeters. Add hot dilute sulfuric acid (1 H₂SO₄ : 4 H₂O)
and cover the flask with a small funnel. Add ten grams of granulated zinc and heat
until rapid action begins, and then heat gently for five minutes. The reduction is then
complete. During the reduction the colors, pink, plum, pale green, and dark green, are
seen in the molybdate solution, the latter color marking the end of the reaction.
To remove the zinc, pour through a large folded filter, wash with cold water, and
fill up the filter once with cold water. But little oxidation takes place in this way. A

port-wine color is seen on the filter, but this does not indicate a sufficient oxidation to
make an error.
In titrating, the wine color becomes fainter and finally the solution is perfectly
colorless and shows a single drop in excess of the permanganate. The permanganate
solution, for convenience, is made so that one cubic centimeter is equal to 0.0001
gram of phosphorus. With iron its value is one cubic centimeter equals 0.006141 gram
of iron; and one cubic centimeter equals 0.005574 gram of molybdenum trioxid.
112. Variation of Dudley and Noyes.—The method of Emmerton to determine
small quantities of phosphoric acid, or of phosphorus in presence of a large excess of
iron, has been modified by Dudley and Pease,[93] and by Noyes and Royse.[94] As
modified, the method is not intended for fertilizer analysis, but the principle on which
it rests may some time, with proper modifications, find application in fertilizer work.
The reduction is accomplished in a Jones’ tube,[95] much simplified, so as to render it
suitable for common use. The molybdic acid is reduced to a form, or series of forms,
corresponding to molybdenum sesquioxid, as in the Emmerton method, and
subsequently as in that method, titrated by a set solution of potassium permanganate.
The iron or steel filings, containing phosphorus, are brought into solution by
means of nitric acid. For this purpose two grams of them are placed in a half liter
flask together with fifty cubic centimeters of nitric acid of 1.18 specific gravity. The
mixture is boiled for one minute, and ten cubic centimeters of permanganate solution
of one and a quarter per cent added. Boil again until the pink color disappears.
Ferrous sulfate solution is next to be carefully added, shaking meanwhile, until the
solution clears. Cool to 50° and add eight cubic centimeters of ammonia of 0.90
specific gravity, stopper the flask, and shake until any precipitate which may form is
redissolved. Cool or warm, as the case may be, until the solution is as many degrees
above or below 60° as the molybdic solution is above or below 27°. Add sixty cubic
centimeters of molybdic solution, stopper, and shake on a machine or by hand for five
minutes. After remaining at rest for five minutes pour into a nine centimeter filter of
fine texture and wash with the acid ammonium sulfate solution in quantities of from
five to ten cubic centimeters each time. The filtrate and washings must be perfectly
bright. Continue the washings until the filtrate gives no color with hydrogen sulfid.
Dissolve the yellow precipitate with twelve cubic centimeters of 0.96 ammonia
diluted with an equal volume of water, and wash the filter with 100 cubic centimeters
of water. Finally add to the filtrate and wash-water eighty cubic centimeters of water
and ten of strong sulfuric acid. Pass the mixture through the Jones’ reducing tube and
follow it with 200 cubic centimeters of water, taking care that no air enter the tube
during the operations. The solution collected in the flask should be at once titrated
with potassium permanganate.

Solutions used: (1) Nitric acid.—One part of nitric acid of 1.42 specific gravity
and two parts of water by volume. The specific gravity of the mixture is about 1.18.
(2) Permanganate solution for oxidizing.—Dissolve 12.5 grams of potassium
permanganate in one liter of water.
(3) Ferrous sulfate.—Fresh crystals not effervesced and free from phosphorus.
(4) Ammonia.—The strong ammonia used should have a specific gravity of about
0.90 and the dilute of 0.96 at 15.5°.
(5) Molybdic Solution.—Dissolve 100 grams of molybdic anhydrid in 400 cubic
centimeters of ammonia of 0.96 specific gravity and pour the solution slowly, with
constant stirring, into one liter of nitric acid of about 1.20 specific gravity. Heat the
mixture to 45° and add one cubic centimeter of a ten per cent solution of sodium
phosphate, stir vigorously, and allow to stand in a warm place for eighteen hours.
Filter before using.
(6) Add Ammonium Sulfate.—To half a liter of water add 27.5 cubic centimeters
of 0.96 ammonia and twenty-four cubic centimeters of strong sulfuric acid, and make
the volume one liter with water.
(7) Potassium Permanganate for Titration.—Dissolve four grams of potassium
permanganate in two liters of water, heat nearly to boiling for an hour, allow to stand
for eighteen hours, and filter on asbestos felt. The solution must not come in contact
with rubber or other organic matter. The solution may be standardized with
thoroughly air-dried ammonium oxalate in solution with a little dilute sulfuric acid
and with ammonium ferrous sulfate partly crystallized in small crystals from a
slightly acid solution. The crystals should be well washed and quickly air-dried in a
thin layer. The factors 1/1 1/4 2/2 and 1/7 should be used respectively to calculate the
iron equivalent. The phosphorus equivalent is obtained by multiplying the iron
equivalent by 31 ÷ (36 × 56) = 0.01538.
Reduction Apparatus.—The reduction of the molybdic acid to molybdenum
trioxid is accomplished in a tube first proposed by Jones. The apparatus is shown in
Figure 7. A piece of moderately heavy glass tubing thirty-five centimeters long with
an internal diameter of two centimeters is drawn out at the lower end so as to pass
into the stopper of a flask. A circular piece of perforated platinum or porcelain rests
on the constricted portion of the tube and this is covered with an asbestos felt. The
tube is then nearly filled with powdered zinc which is washed, before using, with
dilute sulfuric acid (1 : 20). A, B, C represent different methods of filtering the
molybdic solution. In A a platinum cone is placed in the constricted portion of the
tube and the asbestos felt placed thereon and the tube then filled with the granulated
zinc. In B there is first inserted a perforated disk then some very fine sand and this is
covered with another disk. In C there is a perforated disk which is covered with
asbestos felt. The filtering arrangement should be such as to prevent any zinc particles

from reaching the flask and yet permitting the filtration to go on
without much difficulty. A blank determination is first made by adding
to 180 cubic centimeters of water, twelve of 0.96 ammonia and ten of
strong sulfuric acid. This is poured through the reducing tube and
followed with 200 cubic centimeters of water taking care that no air
enter the apparatus. Hydrogen peroxid is formed if air enter. Even after
standing for a few moments the tube should be washed with dilute
sulfuric acid before again using it. The filtrate should be titrated with
the permanganate solution and the amount required deducted from the
following amounts obtained with the molybdic salt.
Calculations.—The calculations of the amount of phosphorus in a
given sample of iron or steel are made according to the following data:
In a given case let it be supposed that the permanganate solution is set
with a solution of piano wire and it is found that one cubic centimeter
of permanganate liquor is equal to 0.003466 gram of metallic iron. It is
Figure. 7. found that 90.76 parts of molybdic acid will produce the same effect
on permanganate as 100 parts of iron. Hence one cubic centimeter of
Jones’ permanganate solution is equivalent to 0.003466 × 0.9076 = 0.003145
Reduction gram of molybdic acid. In the yellow precipitate formed, in the
Tube. conditions named for the analysis it is found that the phosphorus is one
and nine-tenths per cent of the molybdic acid present. Therefore one
cubic centimeter of permanganate liquor is equal to 0.003145 × 0.019
= 0.0000597 gram of phosphorus. If then, for example, in a sample of iron or steel
eight and six-tenths cubic centimeters of permanganate solution, after correction, be
found necessary to oxidize the molybdic solution after passing through the Jones’
reducing tube, the amount of phosphorus found is 0.0000597 × 8.6 = 0.051 per cent.
113. The Silver Method.—The separation of the phosphoric acid by silver
according to the method of Perrot has been investigated by Spencer, who found the
process unreliable.[96] By a modification of the process, however, Spencer obtained
fairly satisfactory results. The principle of this method depends on the separation of
the phosphoric acid by silver carbonate and the subsequent titration thereof with
standard uranium solution after the removal of the excess of silver. The operation is
conducted as follows: The fertilizer is first ignited until all organic matter and residual
carbon are destroyed. Solution is then accomplished by means of nitric acid and the
volume completed to a definite quantity. An aliquot part is taken, after filtration,
varying with the supposed strength of the solution so as to contain about 100
milligrams of phosphorus pentoxid. In the slightly nitric acid solution add freshly
prepared silver carbonate in excess, that is, sufficient to saturate any free acid present
and also to combine with all the phosphoric acid. Wash thoroughly with hot water and
then dissolve the mixed phosphate and silver carbonate in nitric acid and remove the
silver from the solution with sodium chlorid. The phosphoric acid is determined in the

filtrate by means of a standard solution of uranium nitrate in the manner already
described. Spencer found that the separation of the phosphoric acid by the silver
method was more exact than by the Joulie magnesium citrate process. With practice
on the part of the analyst in determining the end reaction the process is both rapid and
accurate. The method is also inexpensive, as both the silver and uranium are easily
recovered from the waste.
114. Volumetric Silver Method.—Holleman has proposed a modification of the
silver method for the volumetric determination of phosphoric acid, which is
conducted in the following manner:[97]
In a flask of 200 cubic centimeters capacity, are placed fifty cubic centimeters of
the liquid to be analyzed, which should not contain more than two-tenths gram of
phosphoric acid. The solution is treated with ten cubic centimeters of a normal
solution of sodium acetate and afterwards with a slight excess of decinormal silver
solution, four and five-tenths cubic centimeters for each 0.01 gram of phosphoric
acid. The solution is then neutralized with tenth normal sodium hydroxid, the amount
required having been previously determined by titrating ten cubic centimeters of the
liquid to be analyzed, using phenolphthalein as an indicator. Five times the quantity
required for the neutralization of the ten cubic centimeters is added, less one-half
cubic centimeter. By this treatment the phosphoric acid in the presence of sodium
acetate is completely precipitated as silver phosphate. The excess of silver is
determined by diluting the mixture to 200 cubic centimeters, filtering, and titrating
100 cubic centimeters of the filtrate with ammonium thiocyanate. The presence of
sulfuric and nitric acids does not interfere with the reaction, but of course
hydrochloric acid must be absent. Alkalies and alkaline earth metals may be present,
but not the heavy metals.
When iron and aluminum are present 100 cubic centimeters of the solution are
precipitated with thirty cubic centimeters of normal sodium acetate, the phosphoric
acid is determined in fifty cubic centimeters of the filtrate, and the precipitate of iron
and aluminum phosphates is ignited and weighed, and its weight multiplied by 2.225
is added to the phosphoric anhydrid found volumetrically. If ammonia be present it
must be removed by boiling, as otherwise it affects the titration with phenolphthalein.
For agricultural purposes this method can have but little value inasmuch as the
phosphates to be examined almost always have a certain proportion of iron and
aluminum. Inasmuch as the amount of these bases has to be determined
gravimetrically, there would be no gain in time and no simplification of the processes
by the use of the volumetric method as proposed.

TECHNICAL DETERMINATION
OF PHOSPHORIC ACID.

115. Desirability Of Methods.—In the preceding paragraphs, has been given a
statement of the principal methods now in use by chemists and others connected with
fertilizer control for the scientific and agronomic determinations of phosphoric acid,
and its agricultural value.
A résumé of the important methods, in a form suited to use in a factory for
preparing phosphatic fertilizers for the market, seems desirable. In these factories the
chemists have been accustomed to use their own, or private methods, and there has
not been a general disposition among them to publish their methods and experience
for the common benefit. For factory processes, a method should be not only
reasonably accurate, but also simple and rapid. It is evident, therefore, that the general
principles already indicated must underlie any method which would prove useful to
factory work. Albert has made a résumé of such methods applicable for factory
control, and these are given here for convenience, although they are, in many
respects, but condensed statements of methods already described.[98]
116. Reagents.—Molybdate Solution.—One hundred and ten grams of pure
molybdic acid are dissolved in ammonia of nine-tenths specific gravity and diluted
with water to one liter. The solution is poured into one liter of nitric acid, of one and
two-tenths specific gravity, and, after standing a few days, filtered.
Concentrated Ammonium Nitrate Solution.—Seven hundred and fifty grams of
pure ammonium nitrate are dissolved in water and made up to one liter.
Magnesia Mixture.—Fifty-five grams of magnesium chlorid; seventy grams of
ammonium chlorid; 130 cubic centimeters of ammonia of nine-tenths specific gravity
are dissolved and diluted with water to one liter.
Two and One-Half Per Cent Ammonia.—One hundred cubic centimeters of
ammonia of nine-tenths specific gravity are diluted with water to one liter.
Joulie’s Citrate Solution.—Four hundred grams of citric acid are dissolved in
ammonia of nine-tenths specific gravity and diluted to one liter with ammonia of the
same strength.
Wagner’s Citrate Solution.—One hundred and fifty grams of citric acid are
exactly neutralized with ammonia, then ten grams of citric acid added and diluted to
one liter with water.
Sodium Acetate Solution.—One hundred grams of sodium acetate, crystallized,
are dissolved in water, treated with 100 cubic centimeters of acetic acid, and diluted
to one liter with water.
Calcium Phosphate Solution.—About ten grams of dry, pure tribasic calcium
phosphate are dissolved in nitric acid and diluted with water to one liter. In this
solution the phosphoric acid is determined gravimetrically by the molybdate or citrate
method, and the value of the solution marked on the flask containing it.

Titrated Uranium Solution.—Two hundred and fifty grams of uranium nitrate are
dissolved in water, twenty-five grams of sodium acetate added, and the whole diluted
to seven liters. One cubic centimeter of this solution corresponds to about 0.005 gram
of phosphorus pentoxid. In order to determine its exact value proceed as follows:
Twenty-five cubic centimeters of the calcium phosphate solution which, for example,
has been found to contain 0.10317 gram of phosphorus pentoxid, are neutralized in a
porcelain dish with ammonia, acidified with acetic, treated with ten cubic centimeters
of sodium acetate solution, and warmed. Through a burette as much uranium solution
is allowed to flow as is necessary to show in a drop of the solution taken out of the
dish, when treated with a drop of pure potassium ferrocyanid, a slight brown color. In
order to be certain, this operation is repeated two or three times with new quantities of
twenty-five cubic centimeters of calcium phosphate solution. Example:

Twenty-five cubic centimeters of the calcium phosphate solution
containing 0.10317 gram of phosphorus pentoxid, gave as a mean of three
determinations 23.2 cubic centimeters of the uranium solution necessary to
produce the brown color with potassium ferrocyanid. Consequently
0.10317 ÷ 23.2 = 0.00445 gram of phosphorus pentoxid equivalent to one
cubic centimeter of uranium solution. If, for instance, a quantity of
fertilizer weighing exactly five grams, require ten cubic centimeters of the
uranium solution for the complete precipitation of its phosphoric acid, then
the quantity of phosphoric acid contained in the fertilizer would be
equivalent to 10 × 0.0045, equivalent to 0.0445 gram of phosphorus
pentoxid. The fertilizer, therefore, contains eight and nine-tenths per cent
of phosphorus pentoxid.
Conduct of the Molybdenum Method.—This method rests upon the precipitation of the
phosphorus pentoxid by a solution of ammonium molybdate in nitric acid, solution of the
precipitate in ammonia, and subsequent precipitation with magnesia.
Manipulation.—Twenty-five or fifty cubic centimeters of a solution of the phosphate which
has been made up to a standard volume and containing about one-tenth gram of phosphorus
pentoxid, are placed in a beaker together with 100 cubic centimeters of the molybdate solution and
treated with as much ammonium nitrate solution as will be sufficient to give the liquid a content of
fifteen per cent of ammonium nitrate. The contents of the beaker are well mixed and warmed for
about twenty minutes at from 60° to 80°. After cooling, they are filtered and the precipitate washed
on the filter with cold water until a drop of the filtrate saturated with ammonia does not become
opaque on treatment with ammonium oxalate. The filtrate is then washed from the filter with two
and one-half per cent ammonia solution and precipitated slowly and with constant stirring by the
magnesia mixture. After standing for two hours the ammonium magnesium phosphate is separated
by filtration, washed with two and one-half per cent ammonia until the filtrate contains no more
chlorin, and ignited.
Conduct of the Citrate Method.—The principle of this method depends upon the fact that when
a sufficient quantity of ammonium citrate is added to phosphate solutions, iron, alumina, and lime
are retained in solution when, on the addition of the magnesia mixture in the presence of free
ammonia, the phosphoric acid is completely precipitated as ammonium magnesium phosphate.
Manipulation.—From ten to fifty cubic centimeters of the solution of the phosphate to be
determined are treated with fifteen cubic centimeters of the Joulie citrate solution avoiding
warming. A few pieces of filter-paper, the ash content of which is known, are thrown in and, with
stirring, fifteen cubic centimeters of magnesia mixture slowly added and if necessary also some
free ammonia. By the small pieces of filter-paper the collection of the precipitate against the sides
of the vessel and on the stirring rod is prevented and in this way the production of the precipitate
hastened. After standing from one-half an hour to two hours the mixture is filtered, ignited, and
weighed. If it be preferred to estimate the phosphoric acid by titration, the precipitate is dissolved
in a little nitric acid, made slightly alkaline with ammonia, and then acid with acetic and then
afterwards titrated with the standard uranium solution.
Conduct of the Uranium Method.—The principle upon which this method rests depends upon
the fact that uranium nitrate or acetate precipitates uranium phosphate from solutions containing
phosphoric acid and which contain no other free acid except acetic. In the presence of ammonium
salts the precipitate is uranium ammonium phosphate having the formula PO₄NH₄UrO₂. The

smallest excess of soluble uranium salt is at once detected by the ordinary treatment with
potassium ferrocyanid.
Manipulation.—In all cases the solution is first made slightly alkaline with ammonia and then
acid by a few drops of acetic, so that no free mineral acid may be present.
(1) With liquids free from iron:
If, on the addition of ammonium or sodium acetate, no turbidity be produced, the liquid is free
from iron and alumina. In this case from ten to fifty cubic centimeters of the solution containing
about one-tenth gram of phosphorus pentoxid are treated with ten cubic centimeters of sodium
acetate, and afterwards with a quantity of uranium solution corresponding, as nearly as possible, to
its supposed content of phosphorus pentoxid, and heated to boiling. From the heated liquid by
means of a glass rod, one or two drops are taken and placed upon a porcelain plate and one drop of
a freshly prepared solution of potassium ferrocyanid allowed to flow on it. If no brown color be
seen at the point of contact of the two drops, additional quantities of the uranium solution are
added and, after boiling, again tested with potassium ferrocyanid until a brown color is distinctly
visible. The quantity of the uranium solution thus having been determined, duplicate analyses can
be made and the whole quantity of the uranium solution added at once with the exception of the
last drops, which are added as before.
(2) Solutions containing iron and alumina.
The solution is treated with the ammonium citrate solution of Joulie, the magnesia mixture
added slowly, and the precipitate collected on a filter and washed with two and one-half per cent
ammonia. The precipitate is then dissolved in nitric acid, made alkaline with ammonia, and then
acid with acetic. This solution is then treated with ten cubic centimeters of sodium acetate and
titrated with uranium, as described in (1). As an alternative method, 200 cubic centimeters of the
superphosphate solution may be treated with fifty cubic centimeters of sodium acetate, allowed to
stand for some time, and filtered through a filter of known ash content. In fifty cubic centimeters
of the filtrate, which correspond to forty cubic centimeters of the original solution, phosphoric acid
may be determined as described above. The precipitate, consisting of iron and aluminum
phosphates, is washed three times on the filter with boiling water, dried, and ignited in a platinum
dish. The weight of ignited precipitate, diminished by the weight of the ash contained in the filter
and divided by two, gives the quantity of phosphorus pentoxid which it is necessary to add to that
obtained by titration.
117. Determination of the Phosphoric Acid in all Phosphates and Basic Slags.—
(1) Total phosphoric Acid:
Five grams of the fine phosphate meal, or slag meal, are moistened in a flask of 500 cubic
centimeters content with some water and boiled on a sand-bath with forty cubic centimeters of
hydrochloric acid of from 16° to 20° Beaumé. The boiling is continued until only a few cubic
centimeters of a thick jelly of silicic acid remain. After cooling, some water is added and the
phosphate shaken until the thick lumps of silica are finely divided. The flask is then filled to 500
cubic centimeters and its contents filtered. Fifty cubic centimeters of the filtrate are treated with
fifteen cubic centimeters of the Joulie solution and treated in the manner described with magnesia
mixture, precipitated, ignited, and weighed. The precipitate can also be dissolved and treated with
uranium solution as described.
The method used by Oliveri may also be employed and it is carried out as indicated in the
following description:[99]

A weighed quantity of the slag is reduced to a fine powder. To five grams of the sample is
added three times its weight of potassium chlorate and the whole is intimately mixed. The mixture
is then placed in a porcelain dish and hydrochloric acid is added, little by little, until the potash salt
is completely decomposed. It is evaporated until the mass is dry. The material is then treated with
fuming nitric acid, and the determination of the phosphorus is made by the ordinary gravimetric
method.
By carrying on the operation as described above, a reduction of phosphoric acid is avoided,
and the presence of an abundant quantity of potash prevents the formation of basic iron phosphate
which is insoluble in nitric acid.
(2) Citrate-Soluble Phosphoric Acid.—One gram of the basic slag or phosphate is placed in a
100 cubic centimeter flask and covered with Wagner’s acid citrate solution making the total
volume up to 100 cubic centimeters. With frequent shaking the flask is kept at 40° for an hour, or it
may be allowed to stand for twelve hours at room temperature with frequent shaking. In fifty cubic
centimeters of the filtrate from this flask the phosphoric acid is determined by the magnesia
mixture as described. Since, in the present case, the precipitate of ammonium magnesium
phosphate contains some silicic acid it cannot be directly ignited but must be treated in the
following manner: The precipitate and the filter are thrown into a porcelain dish, the filter-paper
torn up into shreds with a glass rod, the precipitate dissolved in nitric acid, neutralized with
ammonia, acidified with acetic, and treated with uranium solution. The phosphoric acid may also
be estimated by the gravimetric method by dissolving the precipitate again in hydrochloric or nitric
acid, evaporating to dryness, and drying for one hour at from 110° to 120°, dissolving again in
hydrochloric acid, filtering, and washing the precipitate well. The filtrate, which is now free from
silica, can be treated with Joulie’s solution, precipitated with magnesia mixture, the precipitate
washed, ignited, and weighed as described. The molybdenum method is preferred in the estimation
of citrate-soluble phosphoric acid, especially in slags. For this purpose fifty cubic centimeters of
the filtrate from the solution of one gram of slag in 100 cubic centimeters of Wagner’s citrate
liquid are treated with 100 cubic centimeters of molybdenum solution and thirty cubic centimeters
of ammonium nitrate solution, warmed for twenty minutes at 80°, filtered after cooling, and the
yellow precipitate washed with cold water. The water will gradually dissolve all the silicic acid
from the yellow precipitate and carry it into the filtrate. The yellow precipitate is then dissolved in
two and one-half per cent liquid ammonia and precipitated with magnesia mixture and the
precipitate washed, ignited, and weighed in the way described.
118. Determination of Phosphoric Acid in Superphosphates.—(1) Citrate-Soluble
Phosphoric Acid.—Five grams of the superphosphate are rubbed with 100 cubic centimeters of
Wagner’s acid citrate solution in a mortar and washed into a flask of 500 cubic centimeters content
and diluted to 500 cubic centimeters with water. With frequent shaking the flask is allowed to
stand for twelve hours, after which its contents are filtered. Fifty cubic centimeters of the filtrate
are treated with ten cubic centimeters of the Joulie solution and fifteen cubic centimeters of the
magnesia mixture and, if necessary, made distinctly alkaline with ammonia, vigorously stirred,
and, after two hours, filtered. The precipitate is washed, ignited, and weighed as described, or
titrated, after solution in nitric acid and the addition of sodium acetate, with uranium solution.
Example:
The weighed precipitate has 0.1272 gram Mg₂P₂O₇ then the phosphate
contains 12.72 × 2 × 0.64 = 16.28 per cent of citrate-soluble P₂O₅.
(2) Water-Soluble Phosphoric Acid.—Twenty grams of superphosphate are rubbed in a mortar
and washed into a flask of one liter content and made up to the mark with water. After two hours’

digestion with frequent shaking, the contents of the flask are filtered through a folded filter.
Twenty-five cubic centimeters of the filtrate equivalent to five-tenths gram of the substance are
precipitated with magnesia mixture, the precipitate filtered, washed, ignited, and weighed, or the
moist filtrate may be dissolved upon the filter with a little nitric acid, treated with sodium acetate,
and titrated, as described, with uranium solution.
Example: 14.5 cubic centimeters of the uranium solution are required for
the precipitate from twenty-five cubic centimeters of the original solution
= 0.5 gram superphosphate; it contains then 14.5 × 0.00445 = 0.0645 gram
P₂O₅. Consequently the superphosphate contains 12.90 per cent of water-
soluble P₂O₅.
Total Phosphoric Add.—Twenty grams of the superphosphate are boiled with fifty cubic
centimeters of hydrochloric acid of from 16° to 18° Beaumé for about ten minutes and, after
cooling, made up to one liter with water and filtered. Twenty-five cubic centimeters of the filtrate
are treated with ten cubic centimeters of Joulie’s citrate solution, a few pieces of filter-paper
thrown in, fifteen cubic centimeters of magnesia mixture added, and the whole thoroughly stirred.
After standing two hours the contents of the flask are filtered and the precipitate is washed with
dilute ammonia and the filter and the precipitate are placed in a platinum crucible. The crucible is
heated slowly until the moisture is driven off and the filter burned. Then the temperature is
gradually raised to a white heat. The residue is cooled and weighed. Example:
The precipitate weighs, after the subtraction of the filter ash, 0.1390 gram;
then the superphosphate contains 13.90 × 2 × 0.64 = 17.79 per cent
phosphoric acid.

MISCELLANEOUS NOTES ON PHOSPHATES
AND PHOSPHATIC FERTILIZERS.

119. Time Required for Precipitation of Phosphoric Acid.—The length of time required for
the complete precipitation of the phosphoric acid by molybdate mixture is perhaps much less than
generally supposed. At 65° the precipitation, as shown by de Roode, is complete in five minutes.
[100]
In a given case the weight of pyrophosphate obtained after five minutes was 0.0676 gram, and
exactly the same weight was found after twenty-four hours. In view of these facts analysts would
often be able to save time by omitting the delay usually demanded by the setting aside of the
yellow precipitate for a few hours in order to secure a complete separation of the phosphoric acid.
In the method of the official chemists it is directed that the digestion at 65° be continued for one
hour, and this time may possibly be shortened with advantage. In all cases, however, where there is
any doubt in regard to the complete separation, some of the molybdate solution should be added to
the filtrate and, with renewed digestion, it should be noted whether any additional precipitate be
formed.
120. Examination of the Pyrophosphate.—In fertilizer control it is not usually thought
necessary to examine the magnesium pyrophosphate for impurities. Among those most likely to be
found is silica. It is proper, in all cases where accuracy is required, to dissolve the precipitate in
nitric acid, boil for some time to convert the pyro- into orthophosphate, and reprecipitate with
molybdate and magnesia mixture. This treatment will separate the silica which remains practically
insoluble after the first ignition. It has been observed by some analysts that the results obtained by
the official method are a trifle too high and also that on re-solution the second precipitate of

pyrophosphate weighs less than the first.[101] The difference in most cases is very little but it may
become a quantity of considerable magnitude in samples where soluble silica is found in notable
quantities. The danger of contamination with iron, alumina, and arsenic has already been
mentioned but it is not of sufficient importance to warrant further attention.
121. Iodin in Phosphates.—The presence of iodin has been detected in many natural
phosphates and is of interest in the discussion of the problem of their origin.[102] A qualitative test
for the detection of iodin may be applied in the following manner: Some finely ground phosphate
is mixed with strong sulfuric acid and the gases arising from the reaction are aspired into some
carbon disulfid or chloroform. The violet coloration arising indicates the presence of iodin. The
gases carrying the iodin may also be brought into contact with starch-paste producing the well-
known blue color.
The quantity of iodin present in a phosphate is rarely more than one or two-tenths of one per
cent. It can be determined as a silver salt, in the absence of chlorin or by any of the standard
methods found in works on qualitative analysis.
Iodin is quite a constant constituent of Florida phosphates.
For a quantitative determination, the sample is treated with an excess of strong sulfuric acid in
a closed flask and during the decomposition a stream of air is aspired through the flask and caused
to bubble through absorption bulbs containing sodium hydroxid in solution.
The temperature of the decomposition may be raised to about 200°. After the solution of the
sample the sodium iodid formed is oxidized by heating with potassium permanganate, acidulated
and mixed with a solution of potassium iodid to hold the free iodin in solution. The free iodin is
determined in the usual way by titration with standard sodium thiosulfate solution. The reactions
preparatory to the titration are represented by the following formulas:
2KI + H₂SO₄ = K₂SO₄ + 2HI.
2HI + H₂SO₄ = 2H₂O + SO₂ + 2I.
6I + 6NaOH = NaIO₃ + 5NaI + 3H₂O.
NaI + 2KMnO₄ + H₂O = NaIO₃ + 2KOH + 2MnO₂.
HIO₃ + 5HI = 6I + 3H₂O.
The titration is represented by the following reaction:
2Na₂S₂O₂ + 2I = 2NaI + 2NaI + Na₂S₄O₄.
The decinormal solution of sodium thiosulfate may be used. Grind the crystals of the salt to a
fine powder, dry between blotting papers, and use 24.8 grams of the dried salt per liter. The
quantity of iodin found in phosphates is so minute that it is hardly worth while to make a
quantitative determination of it.
122. Occurrence of Chromium in Phosphates.—In some phosphates a small quantity of
chromium has been found. In a sample of phosphate from the Island of Los Roques in the
Caribbean Sea, Gilbert found three-fourths per cent of chromium oxid (Cr₂O₃). The phosphates
containing chromium have a greenish color and are characterized by great insolubility in solutions
containing organic acids. The chromium is to be determined by the usual methods described in
mineral analysis.
123. Estimation of Vanadium.—In the complete analysis of basic slags it becomes necessary
to determine the presence of vanadium and its quantity. The method used in this laboratory for the

purpose is the volumetric process of Lindemann.[103] It is conducted as follows: Dissolve four
grams of the finely powdered slag in sixty cubic centimeters of dilute sulfuric acid (1 : 4), boil for
a few minutes, cool, make the volume up to 100 cubic centimeters, filter, and take an aliquot part
for the determination. Add decinormal potassium permanganate solution in slight excess to secure
the oxidation of the vanadium to vanadium pentoxid. Add, drop by drop, a weak solution of
ferrous sulfate until the pink color just disappears. Prepare a ferrous sulfate solution by dissolving
2.183 grams of piano wire in sulfuric acid and making the volume to one liter. Titrate the vanadic
mixture with this solution until a drop of the clear liquor removed and brought in contact with
potassium ferricyanid shows a distinctive blue-green color.
One cubic centimeter of the ferrous sulfate solution is equivalent to 0.002 gram of vanadium,
0.002888 gram of vanadium dioxid, and 0.003648 gram of vanadium pentoxid. The ferrous sulfate
solution may also be made and standardized by any of the approved methods in common use.
The method described by Blair, designed especially for the estimation of vanadium in iron and
steel, is conducted in the following manner:[104] Five grams of the drillings are dissolved in fifty
cubic centimeters of nitric acid of 1.24 specific gravity. The solution is evaporated to dryness in a
porcelain dish and heated thereafter until the nitrates are nearly decomposed. After cooling, the
dried mass is transferred to a mortar and finely ground with thirty grams of dry sodium carbonate
and three grams of sodium nitrate. The finely ground materials are placed in a platinum dish and
fused for an hour at a high temperature. Spread the fused mass over the sides of the dish while
cooling, and afterwards dissolve in hot water, filter, and wash until the volume is a little over half a
liter. Add nitric acid to decompose carbonates, but not completely, and boil to get rid of carbon
dioxid, being careful to keep the mass always slightly alkaline. Add nitric acid, drop by drop, until
slightly in excess, and then sodium carbonate to marked alkalinity, boil, and filter. Add a slight
excess of nitric acid to the filtrate, and the development of a yellow color will indicate the
presence of vanadic acid. Add to the solution a small quantity of mercurous nitrate and then an
excess of mercuric oxid, suspended in water to render the solution neutral and insure the complete
precipitation of mercurous vanadate. The mercurous salt also precipitates phosphoric, chromic,
tungstic, and molybdic acids which may be present. Boil, filter, and wash the precipitate with hot
water, dry, and ignite. Fuse the residue with sodium carbonate and a little nitrate. Dissolve the
fused mass, after cooling, in a little water and filter. Add to the filtrate, ammonium chlorid in
excess, from three to five grams for each 100 cubic centimeters of the solution, and allow to stand,
with occasional stirring, for some time. Ammonium vanadate, insoluble in a saturated solution of
ammonium chlorid, separates as a white powder. It is necessary to keep the solution alkaline, and a
drop of ammonia should be added from time to time for this purpose. The appearance of a
yellowish tint at any time indicates that the solution has become acid, and this acidity must be
corrected, or else the results will be too low. Separate the ammonium vanadate by filtration; wash
first with a saturated solution of ammonium chlorid containing a little free ammonia, and then with
alcohol. Dry, ignite, and moisten with a few drops of nitric acid; again ignite to obtain the
compound as vanadium pentoxid. This compound contains 56.22 per cent of vanadium. The
method of Rosenheim and Holversheet may also be used.[105] It is based on the preliminary
precipitation of the vanadic acid as a barium or lead salt. The substance supposed to contain
vanadium is first brought into solution in such a manner as to secure it as vanadic acid, which is
then precipitated with barium chlorid or lead acetate. The precipitate is boiled with hydrochloric
acid and potassium bromid, and the liberated bromin determined by the quantity of iodin set free
from potassium iodid. In the absence of bodies, such as molybdic acid, which are reduced by
sulfurous acid or hydrogen sulfid, the vanadic acid may also be determined by reducing it with one
of these reagents and, after removing the excess by boiling, titrating the vanadium tetroxid with

potassium permanganate. When vanadic and phosphoric acids occur together the former may be
first reduced to tetroxid with sulfurous acid, and after expelling excess of this reagent, the
phosphoric acid may be separated with molybdate solution and removed by filtration. When the
amount of vanadic acid is large the phosphoric acid should be separated rapidly at 55°-60°, using a
considerable excess of the molybdate; or the vanadic acid may first be determined in the solution
volumetrically by the bromin process above described, and afterwards the phosphoric acid
obtained by evaporating to dryness with a little sulfuric acid, taking the residue up with water,
reducing the vanadic with sulfurous acid and precipitating the phosphoric acid with molybdate
solution as described above.
124. Fluorin in Bones.—Fluorin is not only a constituent of mineral phosphates but also of
bones. According to the researches of Carnot there is often as much as one-half per cent of calcium
fluorid in bones and teeth.[106] Gabriel has suggested a means of determining a minimum limit of
fluorin in bones and teeth by the development of etchings in comparison with known quantities of
pure calcium fluorid. The minimum quantity of calcium fluorid necessary to produce a distinct
etching, in known conditions, having been determined, the test is applied to known weights of
ignited bone or teeth. He concludes from his results, that the ash of bones and teeth often contains
less than one-tenth per cent of fluorin. Since, however, there is a loss of fluorin from calcium
fluorid, on ignition, the whole of the fluorin may not have been available in the tests described.
125. Note on the Separation of Iron and Aluminum Phosphates from the Calcium
Compound.—There are many points of difference noted in the descriptions given by authors of
the deportment of the iron, and aluminum phosphates in presence of a large excess of the calcium
salt. Especially is this true of the statements made by Hess and Glaser[107] in paragraphs 34 and 35.
The subject is of such importance, from an analytical point of view, as to merit a careful study.
In this laboratory a thorough investigation of the mutual deportment of these three phosphates
has been made by Brown with the following results:[108] When a mixture containing a known
weight of the salts was treated exactly as Hess directs, in no case was there a complete separation
of the iron aluminum phosphate from the calcium salt. In order to discover the cause of the failure,
pure solutions of calcium and iron aluminum phosphates were treated under identical conditions
by the necessary reagents. Fifty cubic centimeters of a solution of calcium phosphate, containing
about one gram of the salt, were treated with 100 cubic centimeters of water and fifty cubic
centimeters of the commercial ammonium acetate containing 150 grams of the salt in a liter. An
immediate precipitate was produced at ordinary temperature, and on heating to 60° it became
abundant. The addition of ammonium chlorid, phosphate, and nitrate in successive portions, does
not prevent the precipitation. Making the solution more dilute lessens the difficulty when twenty
cubic centimeters of a ten per cent solution of ammonium phosphate are first added, followed by
the usual quantity of ammonium acetate; a clear crystalline precipitate is sometimes observed.
Experience also shows that the trouble is not due to an excess of the ammonium acetate.
In treating a solution of iron aluminum phosphate, in similar circumstances, with the
ammonium acetate, it is found that a complete precipitation takes place.
Since diluting the solution of the calcium salt diminishes its tendency to form a precipitate
with the ammonium acetate the true method of separation seems to lie in that direction. The
calcium salt is held completely in solution when the separation is made in the following way.
The solution containing the mixed phosphates is diluted so as to contain not more than one
gram thereof in half a liter. To this is added one drop of dimethylanilin orange, and afterwards
ammonium hydroxid, until a very slight precipitate is formed. The mixture is heated to 70° and

from twenty to twenty-five cubic centimeters of a twenty-five per cent solution of acid ammonium
acetate are added, enough to change the rose color of the indicator to orange. The iron aluminum
phosphate is separated by filtration and washed with a hot five per cent solution of ammonium
nitrate.
The washed precipitate shows no impurity due to calcium, as proved by dissolving it,
reprecipitating and filtering, adding ammonium hydroxid to the filtrate, and heating for a long
time. Sometimes a slight troubling of the clear liquid may be observed which may be due to a
slight solubility of the iron aluminum phosphate in washing, an accident that may occur if the
temperature be allowed to fall below 70°, but no weighable amount of material is obtained. If due
to calcium phosphate, a greater dilution in the first precipitation will remove even this mere trace
of that salt. In the above conditions the contamination of the iron aluminum precipitate with
calcium phosphate may be entirely avoided. We had also undertaken here the problem of
separating the phosphoric acid by the citrate method, followed by a destruction of the citric acid in
the filtrate by combustion with sulfuric acid according to the kjeldahl process, and final separation
of the iron and alumina in the residues when our attention was called to substantially the same
process as described by Jean.[109] The method merits a further critical examination.
126. Phosphoric Acid Soluble in Ammonium Citrate.—There is no other point connected
with the determination of phosphoric acid which has excited so much discussion and about which
there is such difference of opinion as the solubility of phosphates in ammonium citrate. It was
clearly established by Huston, in 1882, that the ammonium citrate, as used in fertilizer analysis,
would attack normal tricalcium phosphate as it exists in bones.[110]
In a raw bone, finely ground, containing 20.28 per cent of phosphoric acid, the following
quantities were found to be soluble in a neutral ammonium citrate solution of 1.09 specific gravity.
Time of digestion, thirty minutes.
Temperature 30° 40° 50° 60°
Per cent P₂O₅ dissolved 2.76 4.01 3.39 5.88

From this it appears that the quantity of acid dissolved increases with the temperature of
digestion with the exception of the number obtained at 50°. When the time of digestion was
increased there was also found a progressive increase in the amount of acid passing into solution.
At 40° for forty-five minutes the per cent dissolved was 4.97, and at 40° for one hour it was 5.92.
These early determinations had the effect of calling attention to the thoroughly empirical process
which was in use, in many modified forms, by agricultural chemists, the world over for
determining so-called reverted phosphoric acid in fertilizers. Since the publication of the paper
above named many investigations have been undertaken by Huston and others relating to this
matter.[111] The general results of these studies, tabulated by Huston, are given below.[112]

Influence of the Time of Digestion.

(A) = Temperature, degrees C.
(B) = Citrate-soluble phosphoric acid.
(C) = Total phosphoric acid.

Time of (B) (C)
Material. Authority. (A)
digestion. Per cent. Per cent.
65 ½ hour 10.60 19.75
Bone meal, F. B. Dancy,
65 1 “ 11.28 19.75
65 ½ “ 6.62 21.68
Orchilla guano, F. B. Dancy,
65 1 “ 6.85
65 ½ “ 4.64 31.27
Navassa rock, F. B. Dancy
65 1 “ 4.81 31.27
Navassa 65 ½ “ 9.00 11.47
F. B. Dancy,
superphos., 65 1 “ 9.21 11.47
40 ½ “ 4.01 20.28
Bone meal, H. A. Huston,
40 1 “ 5.92 20.28
Bone meal, H. A. Huston and 65 ½ “ 6.17 23.58
raw, W. J. Jones, Jr., 65 1 “ 6.49 23.58
65 2 hours 8.22 23.58
65 5 “ 9.31 23.58
Steamed bone, H. A. Huston and 65 ½ hour 10.59 27.67
W. J. Jones, Jr., 65 1 “ 12.21
65 2 hours 14.61
65 5 “ 17.94
65 10 “ 19.73
Florida H. A. Huston and 65 ½ hour 0.56 19.75
soft rock, W. J. Jones, Jr., 65 2 hours 1.69
65 5 “ 1.47
Precipitated H. A. Huston and 65 ¼ hour 26.72 33.34
calcium W. J. Jones, Jr., 65 ½ “ 27.26
phosphate from 65 1 “ 27.28
glue works 65 2 hours 27.29
Pamunky H. A. Huston and 65 ½ hour 4.43 13.84
[113] W. J. Jones, Jr.,
phosphate, 65 1 “ 8.28
65 2 hours 10.34
65 5 “ 11.80
65 10 “ 12.58
Calcined H. A. Huston and 65 ½ hour 21.24 45.15
Redonda, W. J. Jones, Jr., 1 “ 31.70
2 hours 36.92
5 “ 41.00
10 “ 42.70

Time of (B) (C)
Material. Authority. (A)
digestion. Per cent. Per cent.
South H. A. Huston and 65 ½ hour 2.82 25.51
Carolina W. J. Jones, Jr., 1 “ 3.13
rock, 2 hours 3.57
5 “ 3.88

Influence of Temperature.

(A) = Temperature, degrees C.
(B) = Citrate-soluble phosphoric acid.
(C) = Total phosphoric acid.

Time of (B) (C)
Material. Authority. (A)
digestion. Per cent. Per cent.
Apatite ½ hour 40 0.30
T. S. Gladding[114]
Canadian, ½ “ 65 0.56
½ “ 40 4.63
Orchilla guano, T. S. Gladding,
½ “ 65 4.81
South Carolina ½ “ 40 1.09
T. S. Gladding,
river rock, ½ “ 65 1.35
½ “ 40 2.73
Navassa rock, T. S. Gladding,
½ “ 65 2.53
Grand ½ “ 40 1.16
T. S. Gladding,
Connetable, ½ “ 65 1.96
S. W. Johnson and ½ “ 40 1.70 36.68
Redonda,
E. H. Farrington, ½ “ 65 1.85
South Carolina S. W. Johnson and ½ “ 40 1.32 25.48
rock, E. H. Farrington, ½ “ 65 1.65
S. W. Johnson and ½ “ 40 4.92 21.05
Orchilla guano,
E. H. Farrington, ½ “ 65 5.85
S. W. Johnson and ½ “ 40 4.10 29.90
Navassa rock,
E. H. Farrington, ½ “ 65 4.22
S. W. Johnson and ½ “ 40 11.95 16.50
Acid Navassa,
E. H. Farrington, ½ “ 65 13.53
Fine-ground S. W. Johnson and ½ “ 40 9.40 23.50
bone, E. H. Farrington, ½ “ 65 12.90
South Carolina C. V. Sheppard, Jr. ½ “ 40 1.72 24.50
land rock, also H. C. White, ½ “ 65 2.11
C. V. Sheppard, Jr. ½ “ 40 6.48 15.85
Orchilla guano,
also H. C. White, ½ “ 65 6.75

Time of (B) (C)
Material. Authority. (A)
digestion. Per cent. Per cent.
Calcined C. V. Sheppard, Jr. ½ “ 40 5.70 44.85
Redonda, also H. C. White, ½ “ 65 10.20
C. V. Sheppard, Jr. ½ “ 40 4.49 43.79
Raw Redonda,
also H. C. White, ½ “ 65 7.92
Acid phosphate, C. V. Sheppard, Jr. ½ “ 40 3.55 18.25
S. C. 10.35 per cent also H. C. White, ½ “ 65 4.05
water-soluble,
Acid Navassa, C. V. Sheppard, Jr. ½ “ 40 10.85 16.20
2.85 per cent also H. C. White, ½ “ 65 11.00
water-soluble,
Bone, H. A. Huston, ½ “ 30 2.76 20.28
½ “ 40 4.01
½ “ 50 3.39
½ “ 60 5.88
Acid phosphate, Sheppard and ½ “ 40 3.46 15.95
11.41 per cent Robertson, ½ “ 60 3.82
water-soluble,
Calcined H. A. Huston, ½ “ 40 2.18 45.46
Redonda, ½ “ 50 5.52
½ “ 65 21.24
½ “ 75 32.90
½ “ 85 39.52
Calcined H. A. Huston and 5 hours 40 26.78 42.90
Redonda, W. J. Jones, Jr., 5 “ 65 38.19
5 “ 85 41.57
Pamunky H. A. Huston and 5 “ 40 3.10 13.84
phosphate, W. J. Jones, Jr., 5 “ 65 11.80
5 “ 85 12.82
Raw bone, H. A. Huston and 2 “ 40 5.96 23.58
W. J. Jones, Jr., 2 “ 65 8.22
2 “ 85 8.71
Steamed bone, H. A. Huston and 5 “ 40 16.02 27.67
W. J. Jones, Jr., 5 “ 65 20.22
5 “ 85 20.66
Precipitated H. A. Huston and 2 “ 40 24.14 33.34
calcium phosphate W. J. Jones, Jr., 2 “ 65 23.45
from glue works, 2 “ 85 22.46

Time of (B) (C)
Material. Authority. (A)
digestion. Per cent. Per cent.
Florida H. A. Huston and 2 “ 40 0.00 19.75
soft rock, W. J. Jones, Jr., 2 “ 65 1.69
2 “ 85 1.99

Influence of Quantity of Material Used.

(A) = Temperature, degrees C.
(B) = Quantity of material used.
(C) = Citrate-soluble phosphoric acid.
(D) = Total phosphoric acid.

(B) (C) (D)
Material. Authority. Time (A)
Grams. Per cent. Per cent.
⅔ hour 40 2.0 9.94 21.68
Orchilla guano, F. B. Dancy, ⅔ “ 40 1.0 12.14
⅔ “ 40 0.5 13.51
½ “ 65 2.0 6.62
½ “ 65 1.0 9.33
Redonda, S. W. Johnson and ½ “ 40 2.0 1.70 36.68
E. H. Farrington, ½ “ 40 0.4 3.46
½ “ 65 2.0 1.85
½ “ 65 0.4 5.26
South Carolina S. W. Johnson and ½ “ 40 2.0 1.32 25.48
rock, E. H. Farrington, ½ “ 40 0.4 1.33
½ “ 65 2.0 1.65
½ “ 65 0.4 3.36
½ “ 65 2.0 5.87
Orchilla guano, T. S. Gladding,
½ “ 65 0.4 13.05
Calcined H. A. Huston, ½ “ 65 0.5 16.80 45.46
Redonda, ½ “ 65 1.0 18.26
½ “ 65 2.0 21.24
½ “ 65 3.0 23.22
½ “ 65 5.0 24.66
½ “ 65 10.0 28.64
Calcined H. A. Huston, 5 “ 65 0.5 41.77 45.46
Redonda, 5 “ 65 2.0 41.53
5 “ 65 8.0 39.86

(B) (C) (D)
Material. Authority. Time (A)
Grams. Per cent. Per cent.
Pamunky H. A. Huston and 5 “ 65 0.5 11.81 13.84
phosphate, W. J. Jones, Jr., 5 “ 65 2.0 11.80
5 “ 65 4.0 11.44
Raw bone, H. A. Huston and 2 “ 65 0.5 16.49 23.58
W. J. Jones, Jr., 2 “ 65 2.0 8.22
2 “ 65 4.0 7.22
Steamed bone, H. A. Huston and 5 “ 65 0.5 26.40 27.67
W. J. Jones, Jr., 5 “ 65 2.0 17.94
5 “ 65 4.0 12.12
Precipitated H. A. Huston and 2 “ 65 0.5 33.34 33.34
calcium phosphate W. J. Jones, Jr., 2 “ 65 2.0 27.29
from glue works, 2 “ 65 4.0 19.49
Florida H. A. Huston and 2 “ 65 0.5 5.50 19.75
soft rock, W. J. Jones, Jr., 2 “ 65 2.0 1.69
2 “ 65 4.0 1.27

Influence of Acidity and Alkalinity.

(A) = Temperature, degrees C.
(B) = 100 cc neutral citrate + citric acid.
(C) = 100 cc neutral citrate + ammonia equivalent to citric acid.
(D) = Per cent of phosphoric acid dissolved.
(E) = Per cent total phosphoric acid.

Material. Authority. Time (A) (B) (C) (D) (E)

Navassa rock, T. S. Gladding[115] ½ hour 65 0.00 0.00 2.53
½ “ 65 0.733 gm 4.87
½ “ 65 0.733 gm 1.22
South Carolina T. S. Gladding ½ “ 65 0.00 0.00 1.35
rock, ½ “ 65 0.733 “ 2.89
½ “ 65 0.733 “ 1.06
Grand T. S. Gladding, ½ “ 65 0.00 0.00 1.97
connetable, ½ “ 65 0.733 “ 1.12
½ “ 65 0.733 “ 11.44
Dissolved H. B. McDonnell, ½ “ 65 0.00 0.00 2.49 11.51
bone-black and ½ “ 65 0.01 “ 2.42
cottonseed-meal, ½ “ 65 0.01 “ 2.37

Material. Authority. Time (A) (B) (C) (D) (E)
Ground bone, H. B. McDonnell, ½ “ 65 0.00 0.00 8.66 26.62
½ “ 65 0.01 “ 9.18
½ “ 65 0.01 “ 8.00
Calcined H. B. McDonnell, ½ “ 65 0.00 0.00 30.61 45.11
Redonda, ½ “ 65 0.01 “ 29.42
½ “ 65 0.01 “ 32.47
Dissolved H. A. Huston, ½ “ 65 0.00 0.00 2.24 11.32
bone-black and ½ “ 65 1.00 “ 2.24
cottonseed-meal, ½ “ 65 1.00 “ 2.21
Ground bone, H. A. Huston and ½ “ 65 0.00 0.00 8.78 26.35
W. J. Jones, Jr., ½ “ 65 1.00 “ 13.48
½ “ 65 1.00 “ 5.35
Calcined H. A. Huston and ½ “ 65 0.00 0.00 25.54 45.15
Redonda, W. J. Jones, Jr., ½ “ 65 1.00 “ 18.84
½ “ 65 1.00 “ 35.20
South Carolina H. A. Huston and ½ “ 65 0.00 0.00 1.81 27.67
rock, W. J. Jones, Jr., ½ “ 65 1.00 “ 4.59
½ “ 65 1.00 “ 0.74
Basic slag, H. A. Huston and ½ “ 65 0.00 0.00 6.98 19.42
W. J. Jones, Jr., ½ “ 65 1.0 “ 10.12
½ “ 65 1.0 “ 5.49
Pamunky H. A. Huston and 5 h’rs 65 0.00 0.00 11.80 13.84
phosphate, W. J. Jones, Jr., 5 “ 65 1.0 “ 11.79
5 “ 65 1.0 “ 12.28
Raw bone, H. A. Huston and 2 “ 65 0.00 0.00 8.22 23.58
W. J. Jones, Jr., 2 “ 65 1.0 “ 11.20
2 “ 65 1.0 “ 4.02
Steamed bone, H. A. Huston and 5 “ 65 0.00 0.00 17.94 27.67
W. J. Jones, Jr., 5 “ 65 1.0 “ 22.55
5 “ 65 1.0 “ 9.64
Precipitated H. A. Huston and 2 “ 65 0.00 0.00 24.20 33.34
calcium phosphate,W. J. Jones, Jr., 2 “ 65 1.0 “ 30.70
from glue works, 2 “ 65 1.0 “ 20.67
Florida soft H. A. Huston and 2 “ 65 0.00 0.00 1.69 19.75
rock, W. J. Jones, Jr., 2 “ 65 1.0 “ 3.37
2 “ 65 1.0 “ 0.72
Calcined H. A. Huston and 5 “ 65 0.00 0.00 40.64 44.30
Redonda, W. J. Jones, Jr., 5 “ 65 1.0 “ 40.05
5 “ 65 1.0 “ 41.01

In the above tabulations no mention is made of the work of Fresenius, Neubauer, and Luck, on
whose researches the citrate method is based, but an examination of their original paper shows that
the temperature conditions are not carefully enough controlled to justify us in tabulating their
results.[116] An attempt has been made to include in the above tables, work made under well-
defined conditions, which will illustrate the various points under consideration. While each
authority of value upon the subject is represented, no attempt has been made to include all the
work done by any of them. One element that seems to have been generally overlooked in
discussing the problem is that nearly all results have been obtained from one-half hour’s treatment
of the material. This means simply the study of an incomplete reaction, and one which is
interrupted while the solution is very rapidly going on. This, of course, is only clearly brought out
by a comparison of long-time and short-time work in the various tables. In the opinion of Huston
very much more work will have to be done before it can be assumed that we have any very clear
knowledge of this subject, and very likely the final result will be that all kinds of goods cannot be
examined by the same method. The fact that half a gram of dicalcium phosphate is instantly
soluble in 100 cubic centimeters of citrate solution, at ordinary temperatures, while an equal
amount of iron and aluminum phosphate is acted upon very slowly at ordinary temperatures will
probably have to be taken into consideration, as well as the fact that dicalcium phosphate is less
soluble in hot solutions of ammonium citrate than it is in cold solutions, while the reverse is true of
the precipitated iron and aluminum phosphate.
At present, the only conclusion that can be safely drawn from the work, is that it would be
unsafe to make any generalization upon the subject until more facts are at hand, except that the
present methods are unscientific and, unsatisfactory. As the work progresses, new features present
themselves, and in such a way as to show that they must be given careful consideration before
drawing any final conclusions in the matter.
127. Arbitrary Determination of Reverted Phosphoric Acid.—The so-called reverted
phosphoric acid, that is, the acid insoluble in water and soluble in a solution of ammonium citrate,
is the most difficult constituent of commercial fertilizers from the point of view of the scientific
analyst. A review of all the standard methods which have been given in the preceding pages for its
determination must convince every careful observer that, as a rule, each process is based on
arbitrary standards, and can give only concordant results when carried out under strictly unvarying
conditions. For this reason there can be no just comparison between the results obtained by
different methods, which vary from each other only in slight particulars. When, on the other hand,
the processes are radically different, the deviations in data become more pronounced.
In such a condition of affairs the analyst is left to choose between methods. He must be guided
in his choice not only by what seems to be the most scientific and accurate process, but also, to a
certain extent, by the general practice of his professional brethren. For this country, therefore, it is
strongly urged that the methods adopted by the Association of Official Agricultural Chemists, be
followed in every detail.
By the phrase “reverted phosphoric acid,” was originally meant an acid once soluble in water,
as CaH₄(PO₄)₂, and afterwards changed to a form insoluble in water, but soluble in ammonium
citrate as Ca₂H₂(PO₄)₂. But in practice this has never been the true signification of the term. In the
manufacture of acid and superphosphates there is formed, more or less of the dicalcium phosphate,
either directly or after a time, and this salt which, in no sense can be called reverted, is entirely
soluble in ammonium citrate. The iron and aluminum phosphates are also, to a certain degree,
soluble in the same reagent. When an acid phosphate, containing various forms of calcium
phosphate, is applied to a soil containing iron and alumina, the soluble parts of the compound tend

to become fixed by union with those bases, or by precipitation as Ca₂H₂(PO₄)₂. But it is not alone
reverted phosphate formed in this way, which the analyst is called on to determine in a fertilizer,
although he may have occasion to treat it in soil analysis.
The expression “reverted phosphoric acid,” therefore, in practice not only includes a dicalcium
phosphate, which once may have been the monocalcium salt, but also all of that salt originally
existing in the superphosphate, and formed directly during its manufacture, as well as any iron and
aluminum phosphates present which are soluble in ammonium citrate. The expression “citrate-
soluble” is, therefore, to be preferred to “reverted” phosphoric acid.
In the reversion of the phosphoric acid in superphosphates the iron plays a far more important
role than the aluminum sulfate. It was formerly supposed that the reversion took place as indicated
in the following formula: 2CaH₄(PO₄)₂ + Fe₂O₃ = 2(CaHPO₄, FePO₄) + 3H₂O, while Wagner
affirms that the reverted acid compounds consist of varying quantities of ferric oxid, aluminum
oxid, phosphorus pentoxid, and calcium oxid, in various states of combination.[117] The more
probable reaction is the following: 3CaH₄(PO₄)₂ + Fe₂(SO₄)₃ + 4H₂O = 2(FePO₄, 2H₃PO₄, 2H₂O)
+ 3CaSO₄. This reaction can be demonstrated by adding to a superphosphate solution one of a
ferric salt. In addition to free phosphoric acid, iron phosphate is separated, which gradually passes
into an insoluble form by the abstraction of water due to the crystallization of the gypsum. The
alumina present in a superphosphate seems to have no direct influence on the process of reversion.
Its phosphate salt is not acted on by the acid calcium phosphate. Even when a superphosphate
solution is treated with alum no precipitation is produced, except on warming, and this disappears
when the mass is again cold.
It is therefore not necessary in the process of manufacture to separate the alumina by digestion
with a hot soda-lye before treating the mass with sulfuric acid.
In order to avoid the reversion of the phosphoric acid several plans have been proposed. One of
the best is to use a little excess of sulfuric acid in the manufacture. This tends to hold the
phosphoric acid in soluble form but is objectionable on account of drying, handling, and shipping
the fertilizer. During the digestion, moreover, it is important that the temperature does not rise
above 120°. Another method consists in adding to the dissolved rock a quantity of common salt
chemically equivalent to its iron content. Ammonium sulfate also helps to hold the phosphoric acid
water-soluble.
128. Influence of Movement.—The influence of time and temperature of digestion, and of
variations in the composition of the ammonium citrate on the quantity of phosphoric acid
dissolved by that reagent has been pointed out. Of great importance also in the process is the
character of the movement to which the materials are subjected during the digestion. For this
reason various mechanical devices have been constructed to secure uniformity of solution.
Inasmuch as the temperature factor must also be faithfully observed, the best of these devices are
so arranged as to admit of a uniform motion within a bath of water kept at the desired temperature
which, by the Association method, is 65°.

Figure. 8.
Huston’s Digesting Apparatus.

129. Digestion Apparatus for Reverted Phosphates.—The digestion apparatus used by
Huston consists of two wheels twenty-five centimeters in diameter, mounted on the same axis,
having a clear space of four and one-half centimeters between them.[118] In the periphery of each
wheel are cut twelve notches, which are to receive the posts bearing the rings through which the
necks of the flasks pass. The posts are held in place by nuts which are screwed down on the faces
of the wheel. Should it become necessary to take the apparatus apart, it is only necessary to loosen
the nuts and the set screw holding one wheel to the shaft and all the parts can at once be removed.
The posts extend ten centimeters beyond the face of the wheels, and the rings are four centimeters
in internal diameter. Perforated plates, bearing a cross-bar, and held in place by strong spiral
springs attached to the plate and the base of the posts, serve to hold the flasks in place. Each plate
has a number stenciled through it for convenience in identifying the flasks when it is time to
remove them. Attached to the outside of each post, close to the outer end, is a heavy wire which
passes entirely around the apparatus, serving to keep the plates in place after they are removed
from the flasks.
The apparatus is mounted on a substantial framework, thirty-six centimeters high and thirty
centimeters wide at the base. The space in which the wheel revolves is fourteen centimeters wide.
The base bars connecting the two sides are extended seven centimeters beyond one side, and serve
for the attachment of lateral bracing. At the top of the framework, at one side, is attached a heavy
bar forty-five centimeters long, which serves to carry the cog gearing which transmits the power.
The upright shaft carries a cone pulley to provide for varying the speed. The usual speed is two
revolutions a minute for the wheel carrying the flasks. The entire apparatus is made of brass. The
details of construction are shown in Fig. 8. Round-bottomed flasks are used, and rubber stoppers
are held in place by tying or by a special clamp shown at the lower right-hand of the figure.

When high temperatures are used, the plates and flasks are handled by the hooks shown at the
left and right-hand upper corners of the figure.
When any other than room temperature is desired, the whole apparatus is immersed in water
contained in the large galvanized tank forming the back-ground of the figures. The tank is seventy-
five centimeters long, seventy-five centimeters high, and thirty centimeters wide. At one end, near
the top, is an extension to provide space for heating the fluid in the flasks before introducing the
solid in such cases as may be desired.
The apparatus is held in place by angle irons soldered to the bottom of the tank and a brace
resting against the upright bar bearing the gear-wheels.
The water in the tank is heated by injecting steam, or by burners under the tank. As the tank
holds about 300 pounds of water the work is not subject to sudden changes of temperature, and
little trouble has been experienced in raising and maintaining the temperature of the water,
especially when steam is used.
An electric motor, or a small water-motor with only a very moderate head of water, will furnish
ample power.
130. Comparison of Results.—The following data show the results obtained by the digester
as compared with those furnished by the official method, temperature and time of digestion being
the same in each instance.

Ammonium Citrate Solution on Phosphates.
Removed
Total by official Removed
Substance. Time of phos. acid. method. by digester.
treatment. Per cent. Per cent. Per cent.
½ hour 27.67 10.59 14.52
1 “ 12.21 14.82
2 hours 14.61 17.56
Steamed bone, 3½ “ 16.48 18.53
5 “ 17.94 20.22
7½ “ 18.99 20.25
10 “ 19.73 21.18
½ hour 13.86 4.43 4.11
1 “ 8.28 6.82
2 hours 10.34 9.76
Marl, 3½ “ 11.00 11.31
5 “ 11.80 11.83
8 “ 12.51 12.64
10 “ 12.58 13.00
Acidulated bone, ½ hour 19.38 12.09 12.28
1 “ 12.47 12.40
2 hours 12.20 12.43

Removed
Total by official Removed
Substance. Time of phos. acid. method. by digester.
treatment. Per cent. Per cent. Per cent.
3½ “ 12.40 12.24
5 “ 12.43 12.26
Bone, ½ hour 21.40 6.97 8.48
Ammoniated dissolved bone, ½ “ 18.22 9.28 10.63
Cottonseed-meal and
castor pomace, ½ “ 2.52 0.23 0.25
Phospho bone, ¼ “ 16.55 7.06 7.21
In comparing duplicates, the results from the use of the digester are found to be subject to less
variation than those from the usual method.
131. Huston’s Mechanical Stirrer.—The stirring apparatus shown in Fig. 9 differs from those
which have heretofore come into use, in requiring but a single belt to drive all the stirring rods, and
in having all the parts protected from the laboratory fumes.[119] The details of the belt system are
shown in the small diagram in the lower central part of the figure. The apparatus is mounted on a
substantial wooden box, 200 centimeters long, thirty centimeters high, and eighteen centimeters
wide. The driving pulleys, ten centimeters in diameter, are enclosed in the upper part of the case.
The shafts on which these pulleys are mounted extend through the bottom of the enclosing box and
carry a wooden disk, eleven centimeters in diameter, to prevent particles of foreign matter from
falling into the beakers. The shafts extend two centimeters below these disks, and to the end of the
shafts the bent stirring rods are attached by rubber tubing.
The board forming the support of the driving pulleys is extended two centimeters in front of
the apparatus, and in this extension twelve notches are cut, in which are held the corks carrying the
tubes which contain the solution to be used in precipitating the material in the beakers.

Figure. 9.
Huston’s Mechanical Stirrer.

The ends of these tubes are drawn out to a fine point so as to deliver the liquid at the rate of
about one drop per second.
The front of the apparatus is hinged and permits the whole to be closed when not in use, or
during the precipitation.

The apparatus has proven extremely satisfactory in the precipitation of ammonium magnesium
phosphate. The precipitate is very crystalline, and where the stirring is continued for some
minutes, after the magnesia solution has all been added, no amorphous precipitate is observed on
longer standing.
132. The Citrate Method Applied to Samples with Small Content of Phosphoric Acid.—It
is well established that the citrate method does not give satisfactory results when applied to
samples containing small percentages of phosphoric acid, especially when these are of an organic
nature, as for instance, cottonseed cake-meal. In this laboratory attempts have been made to
remedy this defect in the process so as to render the use of the method possible even in such cases.
[120]
Satisfactory results have been obtained by adding to the solution of the cake-meal a definite
volume of a phosphate solution of known strength. Solutions of ordinary mineral phosphates are
preferred for this purpose. The following example will show the application of the modified
method:
In a sample of cake-meal, (cottonseed cake and castor pomace) the content of phosphoric acid
obtained by the molybdate method, was 2.52 per cent.
Determined directly by the citrate method, the following data were obtained:
Allowing to stand thirty hours after adding magnesia mixture, 1.08 and 1.53 per cent in
duplicates.
Allowing to stand seventy-two hours after adding magnesia mixture, 2.17 and 2.30 per cent in
duplicates.
In each case fifty cubic centimeters of the solution were taken, representing half a gram of the
sample.
In another series of determinations twenty-five cubic centimeters of the sample were mixed
with an equal volume of a mineral phosphate solution, the value of which had been previously
determined by both the molybdic and citrate methods. The fifty cubic centimeters thus obtained
represented a quarter of a gram each of the cake-meal and mineral phosphates. The filtration
followed eighteen hours after adding the magnesia mixture. The following data show the results of
the determinations:
Per cent P₂O₅ Per cent P₂O₅ Per cent P₂O₅ Per cent P₂O₅
mineral in organic found in in organic
phosphate. sample. mixture × 2. sample.
1 15.37 2.52 17.90 2.53
2 29.16 2.52 31.68 2.52
3 31.37 2.52 33.83 2.45
4 31.58 2.52 34.20 2.62
Mean content of P₂O₅ in organic sample 2.53
It is thus demonstrated that the citrate method can be applied with safety even to the
determination of the phosphoric acid in organic compounds where the quantity present is less than
three per cent. It is further shown that solutions of mineral phosphates varying in content of
phosphoric acid from fifteen to thirty-two per cent may be safely used for increasing the content of
that acid to the proper degree for complete precipitation. In cases where organic matters are
present they should be destroyed by moist combustion with sulfuric acid as in the determination of
nitrogen to be described in the next part.

133. Direct Precipitation of the Citrate-Soluble Phosphoric Acid.—The direct
determination of citrate-soluble phosphoric acid by effecting the precipitation by means of
magnesia mixture in the solution obtained from the ammonium citrate digestion, has been
practiced for many years by numbers of European chemists, and the process has even obtained a
place in the official methods of some European countries. Various objections have been urged,
however, against the general employment of this method in fertilizer analysis on account of the
inaccuracies in the results obtained in certain cases, and it has, therefore, been used to but a very
limited extent in this country. Since it is impracticable to effect the precipitation with ammonium
molybdate in the presence of citric acid the previous elimination or destruction of this substance
has been recognized as essential to the execution of a process involving the separation of the
phosphoric acid as phosphomolybdate.
It is evident from the data cited in the preceding paragraph, that great accuracy may be secured
in this process by adding a sufficient quantity of a solution of a mineral phosphate and proceeding
by the citrate method.
Ross has also proposed to estimate the acid soluble in ammonium citrate directly by first
destroying the organic matter by moist combustion with sulfuric acid.[121] He recommends the
following process:
After completion of the thirty minutes’ digestion of the sample with citrate solution, twenty-
five cubic centimeters are filtered at once into a dry vessel. If the liquid be filtered directly into a
dry burette, twenty-five cubic centimeters can be readily transferred to another vessel without
dilution. After cooling, run twenty-five cubic centimeters of the solution into a digestion flask of
250-300 cubic centimeters capacity, add about fifteen cubic centimeters of concentrated sulfuric
acid and place the flask on a piece of wire gauze over a moderately brisk flame; in about eight
minutes the contents of the flask commence to darken and foaming begins, but this will occasion
no trouble, if an extremely high, or a very low flame be avoided. In about twelve minutes the
foaming ceases and the liquid in the flask appears quite black; about one grain of mercuric oxid is
now added and the digestion is continued over a brisk flame. The operation can be completed in
less than half an hour with ease, and in many cases, twenty-five minutes. After cooling, the
contents of the flask are washed into a beaker, ammonia is added in slight excess, the solution is
acidified with nitric, and after the addition of fifteen grams of ammonium nitrate, the process is
conducted as usual.
In case as large an aliquot as fifty cubic centimeters of the original filtrate be used, ten cubic
centimeters of sulfuric acid are added, and the digestion is conducted in a flask of 300-500 cubic
centimeters capacity; after the liquid has blackened and foaming has progressed to a considerable
extent, the flask is removed from the flame, fifteen cubic centimeters more of sulfuric acid are
added, and the flask and contents are heated at a moderate temperature for two or three minutes;
the mercuric oxid is then added and the operation completed as before described.
Following are some of the advantages offered by the method described:
(1) It dispenses with the necessity of the execution of the frequently tedious operation of
bringing upon the filter and washing the residue from the ammonium citrate digestion, while the
ignition of this residue together with the subsequent digestion with acid and filtration are also
avoided.
(2) It affords a means for the direct estimation of that form of phosphoric acid which, together
with the water-soluble, constitutes the available phosphoric acid, thus enabling the latter to be
determined by making only two estimations.

(3) In connection with the advantages above mentioned it permits of a considerable saving of
time, as well as of labor required in manipulation.
In addition to the tests with mercuric oxid, both potassium nitrate and potassium sulfate were
used in the digestion to facilitate oxidation. With the former, several additions of the salt were
necessary to secure a satisfactory digestion, and even then the time required was longer than with
the mercury or mercuric oxid digestion. With potassium sulfate, the excessive foaming which took
place interfered greatly with the execution of the digestion process.
134. Availability of Phosphatic Fertilizers.—There is perhaps no one question more
frequently put to analysts by practical farmers than the one relating to the availability of fertilizing
materials. The object of the manufacturer should be to secure each of the valuable ingredients of
his goods in the most useful form. The ideal form in which phosphoric acid should come to the soil
is one soluble in water. Even in localities where heavy rains may abound, there is not much danger
of loss of soluble acid by percolation. As has before been indicated, the soluble acid tends to
become fixed in all normal soils, and to remain in a state accessible to the rootlets of plants, and
yet free from danger of leaching. For this reason, by most agronomists, the water-soluble acid is
not regarded as more available than that portion insoluble in water, yet soluble in ammonium
citrate.
In many of the States the statutes, or custom, prescribe that only the water and citrate-soluble
acid shall be reckoned as available, the insoluble residue being allowed no place in the estimates of
value. In many instances such a custom may lead to considerable error, as in the case of finely
ground bones and some forms of soft and easily decomposable tricalcium phosphates. There are
also, on the markets, phosphates composed largely of iron and aluminum salts, and these appear to
have an available value often in excess of the quantities thereof soluble in ammonium citrate.
As a rule the apatites, when reduced to a fine powder and applied to the soil, are the least
available of the natural phosphates. Next in order come the land rock and pebble phosphates
which, in most soils, have only a limited availability. The soft fine-ground phosphates, especially
in soils rich in humus, have an agricultural value, almost, if not quite equal to a similar amount of
acid in the acid phosphates. Fine-ground bones also tend to give up their phosphoric acid with a
considerable degree of readiness in most soils. Natural iron and aluminum phosphates, have also,
as a rule, a high degree of availability. In each case the analyst must consider all the factors of the
case before rendering a decision. Not only the relative solubility of the different components of the
offered fertilizer in different menstrua must be taken into consideration, but also the character of
the soil to which it is to be applied, the time of application, and the crop to be grown. By a diligent
study of these conditions the analyst may, in the end, reach an accurate judgment of the merits of
the sample.
135. Direct Weighing of the Molybdenum Precipitate.—It has already been stated that many
attempts have, been made to determine the phosphoric acid by direct weighing as well as by
titration, as in the Pemberton method. The point of prime importance in such a direct
determination is to secure an ammonium phosphomolybdate mixture of constant composition.
Unless this can be done no direct method, either volumetric or gravimetric, can give reliable
results. Hanamann[122] proposes to secure this constant composition by varying somewhat the
composition of the molybdate mixture and precipitating the phosphoric acid under definite
conditions. The molybdate solution employed is prepared as follows:
Molybdic acid 100 grams.
Ten per cent ammonia 1.0 liter.

Nitric acid (1.246 sp. gr.) 1.5 liters.

The precipitation of the phosphoric acid is conducted in the cold with constant stirring. It is
complete in half an hour. The ammonium phosphomolybdate is washed with a solution of
ammonium nitrate and then with dilute nitric acid, dried, and ignited at less than a red heat. It
should then have a bluish-black color throughout. Such a body contains 4.018 per cent of
phosphoric anhydrid.
Twenty-five cubic centimeters of a sodium phosphate solution containing fifty milligrams of
phosphoric acid, treated as above, gave a bluish-black precipitate weighing 1.249 grams, which,
multiplied by 0.041018, equaled 50.018 milligrams of phosphorus pentoxid. The method should be
tried on phosphates of various kinds and contents of phosphorus pentoxid before a definite
judgment of its merits is formed.

CHEMISTRY OF THE MANUFACTURE
OF SUPERPHOSPHATES.

136. Reactions with Phosphates.—In this country the expressions “acid” and “super”
phosphates are used interchangeably. A more correct use of the terms would designate by “acid”
the phosphate formed directly from tricalcium phosphate by the action of sulfuric acid, while by
“super” would be indicated a similar product formed by the action of free phosphoric acid on the
same materials. In Germany the latter compound is called double phosphate.
The reaction which takes place in the first instance is represented by the following formula:
3Ca₃(PO₄)₂ + 6H₂SO₄ + 12H₂O = 4H₃PO₄ + Ca₃(PO₄)₂ + 6(CaSO₄·2H₂O);
and 4H₃PO₄ + Ca₃(PO₄)₂ + 3H₂O = 3[CaH₄(PO₄)₂·H₂O].
A simpler form of the reaction is expressed as follows:
Ca₃(PO₄)₂ + 2H₂SO₄ + 5H₂O = CaH₄(PO₄)₂·H₂O + 2[CaSO₄·2H₂O].
If 310 parts, by weight, of fine-ground tricalcium phosphate be mixed with 196 parts of
sulfuric acid and ninety parts of water, and the resulting jelly be quickly diluted with a large
quantity of water, and filtered, there will be found in the filtrate about three-quarters of the total
phosphoric as free acid. If, however, the jelly, at first, formed as above, be left to become dry and
hard, the filtrate, when the mass is beaten up with water and filtered, will contain monocalcium
phosphate, CaH₄(PO₄)₂.
If the quantity of sulfuric acid used be not sufficient for complete decomposition, the dicalcium
salt is formed directly according to the following reaction:
Ca₃(PO₄)₂ + H₂SO₄ + 6H₂O = Ca₂H₂(PO₄)₂·4H₂O + CaSO₄·2H₂O.
This arises, doubtless, by the formation, at first, of the regular monocalcium salt and the further
reaction of this with the tricalcium compound, as follows:
CaH₄(PO₄)₂ + H₂O + Ca₃(PO₄)₂ + 7H₂O = 2[Ca₂H₂(PO₄)₂·4H₂O].
This reaction represents, theoretically, the so-called reversion of the phosphoric acid. When
there is an excess of sulfuric acid there is a complete decomposition of the calcium salts with the

production of free phosphoric acid and gypsum. The reaction is represented by the following
formula:
Ca₃(PO₄)₂ + 3H₂SO₄ + 6H₂O = 2H₃PO₄ + 3[CaSO₄·2H₂O].
The crystallized gypsum absorbs the six molecules of water in its molecular structure.
137. Reactions with Fluorids.—Since calcium fluorid is present in nearly all mineral
phosphates, the reactions of this compound must be taken into consideration in a chemical study of
the manufacture of acid phosphates. When treated with sulfuric acid the first reaction which takes
place consists in the formation of hydrofluoric acid: CaF₂ + H₂SO₄ = 2HF + CaSO₄. Since,
however, there is generally some silica in reach of the nascent acid, all, or a portion of it, combines
at once with this silica, forming silicon tetrafluorid: 4HF + SiO₂ = 2H₂O + SiF₄. This compound,
however, is decomposed at once in the presence of water, forming hydrofluosilicic acid: 3SiF₄ +
2H₂O = SiO₂ + 2H₂SiF₆. The presence of calcium fluorid in natural phosphates is extremely
objectionable from a technical point of view, both on account of the increased consumption of oil
of vitriol which it causes, but also by reason of the injurious nature of gaseous fluorin compounds
produced. Each 100 pounds of calcium fluorid entails the consumption of 125.6 pounds of sulfuric
acid.
138. Reaction with Carbonates.—Most mineral phosphates contain calcium carbonate in
varying quantities. This compound is decomposed on treatment with sulfuric acid according to the
reaction: CaCO₃ + H₂SO₄ = CaSO₄ + H₂O + CO₂. When present in moderate amounts, calcium
carbonate is not an objectionable impurity in natural phosphates intended for acid phosphate
manufacture. The reaction with sulfuric acid which takes place produces a proper rise in
temperature throughout the mass, while the escaping carbon dioxid permeates and lightens the
whole mass, assisting thus in completing the chemical reaction by leaving the residual mass
porous, and capable of being easily dried and pulverized. Where large quantities of carbonate in
proportion to the phosphate are present the sulfuric acid used should be dilute enough to furnish
the necessary water of crystallization to the gypsum formed. For each 100 parts, by weight, of
calcium carbonate, eighty parts of sulfuric anhydrid are necessary, or 125 parts of acid of 1.710
specific gravity = 60° Beaumé.
In some guanos a part of the calcium is found as pyrophosphate, and this is acted upon by the
sulfuric acid in the following way: Ca₂P₂O₇ + H₂SO₄ = CaH₂P₂O₇ + CaSO₄.
139. Solution of the Iron and Alumina Compounds.—Iron may occur in natural phosphates
in many forms. It probably is most frequently met with as ferric or ferrous phosphate, seldom as
ferric oxid, and often as pyrite, FeS₂. The iron also may sometimes exist as a silicate. The alumina
is found chiefly in combination with phosphoric acid, and as silicate.
Where a little less sulfuric acid is employed, as is generally the case, than is necessary for
complete solution, the iron phosphate is attacked as represented below:
3FePO₄ + 3H₂SO₄ = FePO₄·2H₂PO₄ + Fe₂(SO₄)₃.
When an excess of sulfuric acid is employed, the formula is reduced to the simple one:
2FePO₄ + 3H₂SO₄ = 2H₃PO₄ + Fe₂(SO₄)₃.
A part of the iron sulfate formed reacts with the acid calcium phosphate present to produce a
permanent jelly-like compound, difficult to dry and handle. As much as two per cent of iron
phosphate, however, may be present without serious interference with the commercial handling of

the product. By using more sulfuric acid as much as four or five per cent of the iron phosphate can
be held in solution. Larger quantities are very troublesome from a commercial point of view. The
reaction of the ferric sulfate with monocalcium phosphate, is as follows:
3CaH(PO₄)₂ + Fe₂(SO₄)₃ + 4H₂O = 2(FePO₄·2H₃PO₄·2H₂O) + 3CaSO₄.
Pyrite and the silicates containing iron are not attacked by sulfuric acid, and these compounds
are therefore left, in the final product, in a harmless state. If the pyritic iron is to be brought into
solution aqua regia should be employed.
With sufficient acid the aluminum phosphate is decomposed with the formation of aluminum
sulfate and free phosphoric acid:
AlPO₄ + 3H₂SO₄ = Al₂(SO₄)₃ + 2H₃PO₄.
140. Reaction with Magnesium Compounds.—The mineral phosphates, as a rule, contain
but little magnesia. When present it is probably as an acid salt, MgHPO₄. Its decomposition takes
place in slight deficiency or excess of sulfuric acid respectively as follows:
2MgHP₄ + H₂SO₄ + 2H₂O = [MgH₄(PO₄)₂·2H₂O] + MgSO₄
and MgHPO₄ + H₂SO₄ = H₃PO₄ + MgSO₄.
The magnesia, when in the form of oxid, is capable of producing a reversion of the
monocalcium phosphate, as is shown below:
CaH₄(PO₄)₂ + MgO = CaMgH₂(PO₄)₂ + H₂O.
One part by weight of magnesia can render three and one-half parts of soluble monocalcium
phosphate insoluble.
141. Determination of Quantity of Sulfuric Acid Necessary for Solution of a Mineral
Phosphate.—The theoretical quantity of sulfuric acid required for the proper treatment of any
phosphate may be calculated from its chemical analysis and by the formulas and reactions already
given. For the experimental determination the method of Rümpler may be followed.[123]
Twenty grams of the fine phosphate are placed in a liter flask with a greater quantity of
accurately measured sulfuric acid than is necessary for complete solution. The acid should have a
specific gravity of 1.455 or 45° B. The mixture is allowed to stand for two hours at 50°. It is then
cooled, the flask filled with water to the mark, well shaken, and the contents filtered. Fifty cubic
centimeters of the filtrate are treated with tenth normal soda-lye until basic phosphate begins to
separate. The excess of acid used is then calculated. Example: Twenty grams of phosphate
containing 28.3 per cent of phosphoric acid, 10.0 per cent of calcium carbonate, 5.5 per cent of
calcium fluorid, and 2.4 per cent of calcium chlorid were treated as above with sixteen cubic
centimeters of sulfuric acid containing 10.24 grams of sulfur trioxid. In titrating fifty cubic
centimeters of the filtrate obtained as described above, 10.4 cubic centimeters of tenth normal
soda-lye were used, equivalent to 0.0416 gram of sulfur trioxid. Then 10.24 × 50 ÷ 1000 = 0.5120
= total sulfur trioxid in fifty cubic centimeters of the filtrate, and 0.5120 - 0.0416 = 0.4704 gram,
the amount of sulfur trioxid consumed in the decomposition.
Therefore the sulfur trioxid required for decomposition is 47.04 per cent of the weight of the
phosphate employed. One hundred parts of the phosphate would therefore require 47.04 parts of
sulfur trioxid = to 73.6 parts of sulfuric acid of 1.710 specific gravity or 92.1 parts of 1.530
specific gravity.

A more convenient method than the one mentioned above consists in treating a small quantity
of the phosphate, from one-half to one kilogram, in the laboratory, or fifty kilograms in a lead box,
just as would be practiced on a large scale. A few tests with these small quantities, followed by
drying and grinding will reveal to the skilled operator the approximate quantity and strength of
sulfuric acid to be used in each case. The quantities of sulfuric acid as determined by calculation
from analyses and by actual laboratory tests agree fairly well in most instances. There is, however,
sometimes a marked disagreement. The general rule of practice is to use always an amount of
sulfuric acid sufficient to produce and maintain water-soluble phosphoric acid in the fertilizer, but
the sulfuric acid must not be used in such quantity as to interfere with the subsequent drying,
grinding, and marketing of the acid phosphate.
For convenience the following table may be used for calculating the quantity of oil of vitriol
needed for each unit of weight of material noted:

One Part by Weight of Each Substance Below Requires:
Sulfuric Acid by Same Unit of Weight.
At 48° B. At 50° B. At 52° B. At 54° B. At 55° B.
Tricalcium phosphate 1.590 1.517 1.446 1.382 1.352
Iron phosphate 1.630 1.558 1.485 1.420 1.390
Aluminum phosphate 2.025 1.930 1.839 1.756 1.721
Calcium carbonate 1.640 1.565 1.495 1.428 1.411
Calcium fluorid 2.006 2.010 1.916 1.830 1.794
Magnesium carbonate 1.940 1.860 1.775 1.690 1.660

Example.—Suppose for example a phosphate of the following
composition is to be treated with sulfuric acid; viz.,[124]
Moisture and organic 4.00 per cent.
Calcium phosphate 55.00 “
Calcium carbonate 3.00 “
Iron and aluminum phosphate
nearly all alumina 6.50 “
Magnesium carbonate 0.75 “
Calcium fluorid 2.25 “
Insoluble 28.00 “
Using sulfuric acid of 50° B., the following quantities will be required
for each 100 kilograms.
Kilos of acid
required.
Calcium phosphate, fifty-five kilos 83.44
“ carbonate three and a half kilos 5.48
“ fluorid, two and a quarter “ 4.52
Aluminum and iron phosphate, six and a half kilos 12.55
Magnesium carbonate, three-quarters of a kilo 1.40
Total 107.39

142. Phosphoric Acid Superphosphates.—If a mineral phosphate be decomposed by free
phosphoric in place of sulfuric acid the resulting compound will contain about three times as much
available phosphoric acid as is found in the ordinary acid phosphate. The reaction takes place
according to the following formulas:
(1) Ca₃(PO₄)₂ + 4H₃PO₄ + 3H₂O = 3[CAH₄(PO₄)₂·H₂O].
(2) Ca₃(PO₄)₃ + 2H₃PO₄ + 12H₂O = 3[Ca₂H₂(PO₄)₂·4H₂O].
In each case the water in the final product is probably united as crystal water with the calcium
salts produced. The monocalcium salt formed in the first reaction is soluble in water and the
dicalcium salt in the second reaction in ammonium citrate. Where fertilizers are to be transported
to great distances there is a considerable saving of freight by the use of such a high-grade
phosphate, which may, at times, contain over forty per cent of available acid. The phosphoric acid
used is made directly from the mineral phosphate by treating it with an excess of sulfuric acid.

AUTHORITIES CITED IN
PART FIRST.

[1] Day, Mineral Resources of the United States 193, pp. 703, et seq.
[2] Massachusetts Agricultural Experiment Station, Bulletin 51, March, 1894.
[3] Brown, Manual of Assaying, p. 24.
[4] Bulletin de l’Association des Chimistes de Sucrèrie, No. 2, pp. 7, et seq.
[5] Proceedings of the Twelfth and Thirteenth Meetings of the Society for the Promotion of Agricultural
Science, p. 140.
[6] Chemical Division, U. S. Department of Agriculture, Bulletin 43, p. 341.
[7] Rapport adressé par le Comité des Stations agronomiques au sujet des Methodes à suivre dans
l’Analyse des Matières fertilisantes.
[8] Die Landwirtschaftlichen Versuchs-Stationen, Band 38, S. 303.
[9] Vid. op. cit. 6, p. 341.
[10] Zeitschrift für analytische Chemie, 1890, S. 390.
[11] Vid. op. cit. 6, p. 342.
[12] Chemisches Centralblatt, Band 2, S. 813.
[13] Transactions of the American Institute of Mining Engineers, Vol. 21, p. 165.
[14] Phosphates of America, p. 144.
[15] Vid. op. et loc. cit. 13.
[16] U. S. Geological Survey, Bulletin No. 47.
[17] Vid. op. et loc. cit. 14.
[18] Vid. op. et loc. cit. 13.
[19] Vid. op. cit. 14, p. 147.
[20] Transactions of the American Institute of Mining Engineers, Vol. 21, p. 168.
[21] Phosphates of America, p. 153.
[22] Die Landwirtschaftlichen Versuchs-Stationen, Band 34, S. 379.
[23] Zeitschrift für analytische Chemie, 1892, S. 383.
[24] Zeitschrift für angewandte Chemie, 1894, Ss. 679 und 701.
[25] Vid. op. cit. supra, 1889, p. 636.
[26] Vid. op. cit. 24, 1891, p. 3.

[27] Rapports presentèes au Congrès International de Chimie Appliqué, Bruxelles, Août, 1894, p. 26.
[28] Vid. op. et loc. cit. 20.
[29] Le Stazioni Sperimentali Agrarie Italiane, Vol. 23, p. 31.
[30] Crookes’ Select Methods, p. 538.
[31] Journal of Analytical and Applied Chemistry, Vol. 5, p. 671. For additional authorities on these
methods consult Meyer and Wohlrab, Zeitschrift für angewandte Chemie, 1891, Ss. 170 und 243. Gruber,
Zeitschrift für analytische Chemie, Band 30, S. 206. Shephard, Chemical News, May 29, 1891, p. 251.
Vögel, Zeitschrift für angewandte Chemie, 1891, Band 12, S. 357.
[32] Journal of the American Chemical Society, April, 1895.
[33] Vid. op. cit. 21, p. 150.
[34] Transactions of the American Institute of Mining Engineers, Vol. 21, p. 170.
[35] Vid. op. cit. supra, p. 173.
[36] Comptes rendus, Tome 54, p. 468.
[37] Crookes’ Select Methods, p. 500.
[38] For details of method see Fresenius quantitative Analysis.
[39] U. S. Department of Agriculture, Chemical Division, Bulletin 43, p. 341.
[40] Letter to B. W. Kilgore, Reporter for Phosphoric Acid to the Association of Official Agricultural
Chemists.
[41] Die Landwirtschaftlichen Versuchs-Stationen, Band 38, S. 304.
[42] Communicated by Dr. Solberg.
[43] From the Official Swedish Methods; translated for the author by F. W. Woll.
[44] Methoden van Onderzock aan de Rijkslandbouw-proefstations, 1893, p. 4.
[45] Zeitschrift für analytische Chemie, 1893, S. 64.
[46] Journal of the American Chemical Society, Vol. 16.
[47] Zeitschrift für angewandte Chemie, 1894, S. 678.
[48] Journal für Landwirtschaft, Band 30, S. 23.
[49] Vid. op. cit. 47, p. 544.
[50] Vid. op. cit. 46, Vol. 16, p. 462.
[51] Vid. op. et loc. cit. supra.
[52] Die Agricultur-Chemische Versuchs-Station, Halle a/S., Ss. 56, et seq.
[53] Chemische Industrie, 1890.
[54] Vid. op. et loc. cit. 52.
[55] Chemiker Zeitung, 1890, No. 75, S. 1246.
[56] Vid. op. cit. 43.
[57] Glaser, Zeitschrift für analytische Chemie, 24, 178 (1885). Laubheimer, Ibid, 25, 416 (1886).
Müller, Tagebl. d. Naturforscher-Vers. zu Wiesbaden, 1886, 365. Vögel, Chemiker Zeitung, 1888, 85.
Stutzer, Ibid, 492. Seifert, Ibid, 1390. v. Reis, Zeitschrift für angewandte Chemie, 1888, 354. Loges,
Reportorium für analytische Chemie, 7, 85 (1887). Kassuer, Zeitschrift für Nahrungsmitteluntersuchung
und Hygiene, 2, 22 (1888). C. Müller, Die Landwirtschaftlichen Versuchs-Stationen, 35, 438 (1888).
[58] L’Engrais, Tome 9, p. 928.
[59] Vid. op. et loc. cit. 44.
[60] Journal of the American Chemical Society, Vol. 16, p. 462.
[61] Die Landwirtschaftlichen Versuchs-Stationen, Band 41, S. 329.
[62] Journal of Analytical and Applied Chemistry, Vol. 5, p. 685.
[63] Vid. op. cit. supra, Vol. 3, p. 413.
[64] Zeitschrift für angewandte Chemie, 1886, S. 354.
[65] Vid. op. cit. 52, p. 61.
[66] Vid. op. cit. 55, Vol. 18, p. 1153.

[67] Chemiker Zeitung, 1894, No. 88, p. 1934.
[68] Op. cit. supra, 1892, p. 1471.
[69] Vid. op. cit. 60, p. 721.
[70] Zeitschrift für analytische Chemie, Band 29, S. 408.
[71] Mitteilungen der deutschen Landwirtschafts Gesellschaft, 1890-’91, No. 11, S. 131.
[72] Zeitschrift für angewandte Chemie, 1888, S. 299.
[73] Vid. op. cit. 70, p. 409.
[74] Vid. op. cit. 72, 1890, p. 595.
[75] Vid. op. cit. 61, Tome 43, p. 183.
[76] Chemiker Zeitung, Band 18, S. 565.
[77] Chemical News, Vol. 1, p. 97.
[78] Archive für Wissenschaftliche Heilkunde, Band 4, S. 228.
[79] Journal für praktische Chemie, Band 70, S. 104.
[80] Sutton’s Volumetric Analysis, p. 237.
[81] Bulletin de la Société des Agriculteurs de France, 1876, p. 53.
[82] Manual Agenda des Fabricants de Sucre, 1889, p. 307.
[83] Journal of the American Chemical Society, Vol. 15, p. 382, and Vol. 16, p. 278.
[84] Chemical News, Vol. 47, p. 127.
[85] American Chemical Journal, Vol. 11, p. 84.
[86] Vid. op. cit. 83, Vol. 16, p. 282.
[87] Bulletin 43, Chemical Division, U. S. Department of Agriculture, p. 88.
[88] Vid. op. cit. supra, p. 91.
[89] Repertoire de Pharmacie, 1893, p. 153.
[90] Revue de Chimie Analytique Appliqué, 1893, p. 113.
[91] Chemiker Zeitung, 1894, S. 1533.
[92] Blair, Analysis of Iron and Steel, p. 95.
[93] Journal of Analytical and Applied Chemistry, Vol. 7, p. 108.
[94] Journal of the American Chemical Society, Vol. 17, p. 129.
[95] Vid. op. cit. 92, p. 99.
[96] Eighth Annual Report of Purdue University, p. 238.
[97] Receuil des Travaux Chimiques, Tome 12, pp. 1, et seq. Journal of the Chemical Society
(Abstracts), Vol. 64, p. 496.
[98] Zeitschrift für angewandte Chemie, 1891, Ss. 279, et seq.
[99] Le Stazioni Sperimentali Agrarie Italiane, February, 1891.
[100] Journal of the American Chemical Society, Vol. 17, p. 43.
[101] Vid. op. et loc. cit. supra.
[102] L’Engrais, Tome 10, p. 65.
[103] Journal of Analytical and Applied Chemistry, Vol. 5, p. 694. Zeitschrift für analytische Chemie,
Band 18, S. 99.
[104] Vid. op. cit. 92, p. 103.
[105] Journal of the Chemical Society (Abstracts), Vol. 58, p. 1343.
[106] Comptes rendus, Tome 114, p. 1189.
[107] Vid. op. cit. 24 and 25.
[108] Report communicated to author by W. G. Brown.
[109] Chemisches Centralblatt, 1895, p. 562.
[110] Wiley, Report on Fertilizers to Indiana State Board of Agriculture, 1882.

[111] Proceedings of the Association of Official Agricultural Chemists, Atlanta, 1884, p. 19. Report of
Indiana State Board of Agriculture, 1882, p. 230, and Proceedings of the Association of Official
Agricultural Chemists, Atlanta, 1884, p. 30. Huston and Jones. (These gentlemen are now investigating
all materials used as sources of phosphoric acid in fertilizers; their results here quoted are from
unpublished work, and include but a small part of the work so far done.) American Chemical Journal,
March, 1884, p. 1. Proceedings of the Association of Official Agricultural Chemists, Atlanta, 1884, p. 23.
Ibid, p. 28. Ibid, p. 38. Ibid, p. 45. U. S. Department of Agriculture, Chemical Division, Bulletin No. 7, p.
18. Ibid, Bulletin No. 28, p. 171. Ibid, Bulletin No. 31, p. 100. Ibid, Bulletin No. 31, p. 99.
[112] Manuscript communication to author.
[113] Pamunky phosphate is the so-called “olive earth” found along the Pamunky river, in Virginia. It is
almost all precipitated iron and aluminum phosphates, and the product is peculiar in that the iron is
almost all in the ferrous condition.
[114] In the work of T. S. Gladding only fifty cubic centimeters of citrate were used.
[115] In the work of T. S. Gladding only fifty cubic centimeters of citrate were used.
[116] Zeitschrift für analytische Chemie, Band 10, S. 133.
[117] Lehrbuch der Düngerfabrication.
[118] Bulletin 54, Purdue Agricultural Experiment Station, p. 4.
[119] Vid. op. cit. supra, p. 7.
[120] Runyan and Wiley; Paper presented to Washington Section of the American Chemical Society,
April 11, 1895.
[121] Bulletin 38, Chemical Division, U. S. Department of Agriculture, p. 16.
[122] Chemiker Zeitung, 1895, S. 553.
[123] Die Käuflichen Dungermittel Stoffe, dritte Auflage, 1889.
[124] Wyatt, Phosphates of America, p. 128.

PART SECOND.
NITROGEN IN FERTILIZERS.

143. Kinds of Nitrogen in Fertilizers.—Nitrogen is the most costly of the
essential plant foods. It has been shown in the first volume, paragraph 23, that the
popular notion regarding the relatively great abundance of nitrogen is erroneous. It
forms only 0.02 per cent of the matter forming and pertaining to the earth’s crust. The
great mass of nitrogen forming the bulk of the atmosphere is inert and useless in
respect of its adaptation to plant food. It is not until it becomes oxidized by
combustion, electrical discharges, or the action of certain microorganisms that it
assumes an agricultural value.
Having already, in the first volume, described the relation of nitrogen to the soil it
remains the sole province of the present part to study it as aggregated in a form suited
to plant fertilization. In this function nitrogen may claim the attention of the analyst in
the following forms:
1. In organic combination in animal or vegetable substances, forming a large class
of bodies, of which protein may be taken as the type. Dried blood or cottonseed-meal
illustrates this form of combination.
2. In the form of ammonia or combinations thereof, especially as ammonium
sulfate, or as amid nitrogen.
3. In a more highly oxidized form as nitrous or nitric acid usually united with a base
of which Chile saltpeter may be taken as a type.
The analyst has often to deal with single forms of nitrogenous compounds, but in
many instances may also find all the typical forms in a single sample. Among the
possible cases which may arise the following are types:
a. The sample under examination may contain nitrogen in all three forms
mentioned above.
b. There may be present nitrogen in the organic form mixed with nitric nitrogen.
c. Ammoniacal nitrogen may replace the nitric in the above combination.
d. The sample may contain no organic but only nitric and ammoniacal nitrogen.
e. Only nitric or ammoniacal nitrogen may be present.
144. Determination of the State of Combination.—Some of the sample is mixed
with a little powdered soda-lime. If ammoniacal nitrogen be present free ammonia is
evolved even in the cold and may be detected either by its odor or by testing the
escaping gas with litmus or turmeric paper. A glass rod moistened with strong

hydrochloric acid will produce white fumes of ammonium chlorid when brought near
the escaping ammonia.
If the sample contain any notable amount of nitric acid it will be revealed by
treating an aqueous solution of it with a crystal of ferrous sulfate and strong sulfuric
acid. The iron salt should be placed in a test-tube with a few drops of the solution of the
fertilizer and the sulfuric acid poured down the sides of the tube in such a way as not to
mix with the other liquids. The tube must be kept cold. A dark brown ring will mark the
disk of separation between the sulfuric acid and the aqueous solution in case nitric acid
be present. If water produce a solution of the sample too highly colored to be used as
above, alcohol of eighty per cent strength may be substituted. The coloration produced
in this case is of a rose or purple tint.
Nitric nitrogen may also be detected by means of brucin. If a few drops of an
aqueous solution of brucin be mixed with the same quantity of an aqueous extract of
the sample under examination and strong sulfuric acid be added, as described above,
there will be developed at the disk of contact between the acid and the mixed solutions
a persistent rose tint varying to yellow.
To detect the presence of organic albuminoid nitrogen the residue insoluble in
water, when heated with soda-lime, will give rise to ammonia which may be detected
as described above.
145. Microscopic Examination.—If the chemical test reveal the presence of
organic nitrogen the next point to be determined is the nature of the substance
containing it. Often this is revealed by simple inspection, as in the case of cottonseed-
meal. Frequently, however, especially in cases of fine-ground mixed goods, the
microscope must be employed to determine the character of the organic matter. It is
important to know whether hair, horn, hoof, and other less valuable forms of
nitrogenous compounds have been substituted for dried blood, tankage, and more
valuable forms. In most cases the qualitative chemical, and microscopic examination
will be sufficient. There may be cases, however, where the analyst will be under the
necessity of using other means of identification suggested by his skill and experience or
the circumstances connected with any particular instance. In such cases the general
appearance, odor, and consistence of the sample may afford valuable indications which
will aid in discovering the origin of the nitrogenous materials.

SOURCES OF NITROGENOUS FERTILIZERS.

146. Seeds and Seed Residues.—The proteid matters in seeds and seed residues,
after the extraction of the oil, are highly prized as sources of nitrogenous fertilizers
either for direct application or for mixing. Typical of this class of substances is
cottonseed-meal, the residue left after the extraction of the oil which is accomplished at
the present time mostly by hydraulic pressure. The residual cakes contain still some oil

but nearly half their weight consists of nitrogenous compounds. The following table
gives the composition of a sample of cottonseed-meal:
Ash 7.60 per cent.
Fiber 4.90 “
Oil 10.01 “
Protein 51.12 “
Digestible carbohydrates, etc. 26.37 “
While the above shows the composition of a single sample of the meal it should be
remembered that there may be wide variations from this standard due either to natural
composition or to different degrees of the extraction of the oil.
The composition of the ash is given below:
Phosphoric acid, P₂O₅ 31.01 per cent.
Potash, K₂O 35.50 “
Soda, Na₂O 0.57 “
Lime, CaO 5.68 “
Magnesia, MgO 15.19 “
Sulfuric acid, SO₃ 3.90 “
Insoluble, 0.69 “
Carbon dioxid and undetermined, 7.46 “
The cakes left after the expression of the oil from flaxseed and other oily seeds are
also very rich in nitrogenous matters; but these residues are chiefly used for cattle-
feeding and only the undigested portions of them pass into the manure. Cottonseed
cake-meal is not so well suited for cattle-feeding as the others mentioned, because of
the cholin and betaïn which it contains; often in sufficient quantities to render its use
dangerous to young animals. The danger in feeding increases as the total quantity of the
two bases and also as the relative quantity of cholin to betaïn, the former base being
more poisonous than the latter. In a sample of the mixed bases prepared in this
laboratory from cottonseed cake-meal the cholin amounted to 17.5 and the betaïn to
82.5 per cent of the whole.[125]
The nitrogen contained in these bases is also included in the total nitrogen found in
the meal. The actual proteid value of the numbers obtained for nitrogen is therefore less
than that obtained for the whole of the nitrogen by the quantity present as nitrogenous
bases.
In the United States cottonseed cake-meal is used in large quantities as a direct
fertilizer but not so extensively for mixing as some of the other sources of nitrogen. Its
delicate yellow color serves to distinguish it at once from the other bodies used for
similar purposes. No special mention need be made of other oil-cake residues. They are
quite similar in their composition and uses, and manner of treatment and analysis to the
cottonseed product.

147. Fish Scrap.—Certain species of fish, such as the menhaden, are valued more
highly for their oil and refuse than for food purposes. But even where fish in large
quantities are prepared for human food, there is a considerable quantity of waste matter
which is valuable for fertilizing purposes. The residue of fish from which the fat and oil
have been extracted, is dried and ground for fertilizing uses. The fish scrap thus
obtained is used extensively, especially on the Atlantic border of the United States, for
furnishing the nitrogenous ingredient in mixed fertilizers, and also for direct
application to the fields. In fish flesh deprived of oil and water, the content of
phosphoric acid is about two and one-half per cent, while the proteid matter may
amount to three-quarters of the whole.[126]
The use of fish for fertilizing purposes is not new. As early as 1621 the settlers at
Plymouth were taught to fertilize their maize fields by Squanto, an Indian. According to
Goode, the value of nitrogen derived from the menhaden alone was two million dollars
in 1875.[127] In 1878 it is estimated that 200,000 tons of these fish were captured
between Cape Henry and the Bay of Fundy. The use of fish scrap for nitrogenous
fertilizing has, since then, become an established industry, and the analyst may well
examine his samples for this source of nitrogen when they are manufactured at points
on the Atlantic coast, in proximity to great fishing centers.
148. Dried Blood and Tankage.—The blood and débris from abattoirs afford
abundant sources of nitrogen in a form easily oxidized by the microorganisms of the
soil. Blood is prepared for use by simple drying and grinding. The intestines, scraps,
and fragments of flesh resulting from trimming and cutting, are placed in tanks and
steamed under pressure to remove the fat. The residue is dried and ground, forming the
tankage of commerce. Dried blood is richer in proteid matter than any other substance
in common use for fertilizing purposes. When in a perfectly dry state, it may contain as
much as fourteen per cent of nitrogen, equivalent to nearly eighty-eight per cent of
proteid or albuminoid matter. Tankage is less rich in nitrogen than dried blood, but still
contains enough to make it a highly desirable constituent of manures. Naturally, it
would vary more in its nitrogen content than dried blood.
149. Horn, Hoof, and Hair.—These bodies, although quite rich in nitrogen, are not
well suited to fertilizing purposes on account of the extreme slowness of their
decomposition. Their presence, therefore, should be regarded in the nature of a fraud,
because by the usual methods of analysis they show a high percentage of nitrogen, and
therefore acquire a fictitious value. The relative value of the nitrogen in these bodies as
compared with the more desirable forms, is given in paragraph 5.
150. Ammoniacal Nitrogen.—In ammonia compounds, nitrogen is used chiefly for
fertilizing purposes as sulfate. The ideal nitrogenous fertilizer would be a combination
of the ammoniacal and nitric nitrogen found in ammonium nitrate. The high cost of this
substance excludes its use except for experimental purposes.

151. Nitrogen in Guanos.—The nitrogen in guanos may be found partly as
organic, partly as ammoniacal, and partly as nitric nitrogen. The high manurial value of
guanos and bat deposits in caves, is due not only to their phosphoric acid, but also to
the fact that part of the nitrogen is immediately available, while a part becomes
assimilable by nitrification during the growing season. The content of nitrogen in
guanos is extremely variable, and depends largely on the climatic conditions to which
the deposit has been subjected. The state in which it exists is also a variable one, but
with a constant tendency to assume finally the nitric condition.
The well-known habits of birds in congregating in rookeries during the nights, and
at certain seasons of the year, tend to bring into a common receptacle the nitrogenous
matters which they have gathered and which are deposited in their excrement and in the
decay of their bodies. The feathers of birds are particularly rich in nitrogen, and the
nitrogenous content of the flesh of fowls is also high. The decay therefore, of remains
of birds, especially if it take place largely excluded from the leaching of water, tends to
accumulate vast deposits of nitrogenous matter. If the conditions in such deposits be
favorable to the processes of nitrification, the whole of the nitrogen, or at least the
larger part of it, which has been collected in this débris, becomes finally converted into
nitric acid, and is found combined with appropriate bases as deposits of nitrates. The
nitrates of the guano deposits, and of the deposits in caves, arise in this way. If these
deposits be subject to moderate leaching, the nitrate may become infiltered into the
surrounding soil, making it very rich in this form of nitrogen. The beds and
surrounding soils of caves are often found highly impregnated with nitrates.
While for our purpose, deposits of nitrates only are to be considered which are of
sufficient value to bear transportation, yet much interest attaches to the formation of
nitrates in the soil even when they are not of commercial importance.
In many soils of tropical regions not subject to heavy rainfalls, the accumulation of
these nitrates is very great. Müntz and Marcano[128] have investigated many of these
soils, to which attention was called first by Humboldt and Boussingault. They state that
these soils are incomparably more rich in nitrates than the most fertile soils of Europe.
The samples which they examined were collected from different parts of Venezuela and
from the valleys of the Orinoco, as well as on the shore of the Sea of Antilles. The
nitrated soils are very abundant in this region of South America, where they cover large
surfaces. Their composition is variable, but in all of them calcium carbonate and
phosphate are met with, and organic nitrogenous material. The nitric acid is found
always combined with lime. In some of the soils as high as thirty per cent of calcium
nitrate have been found. Nitrification of organic material takes place very rapidly the
year round in this tropical region. These nitrated soils are everywhere abundant around
caves, as described by Humboldt, which serve as the refuge of birds and bats. The
nitrogenous matters, which come from the decay of the remains of these animals, form
true deposits of guano, which are gradually spread around, and which, in contact with

the limestone and with access of air, suffer complete nitrification with the fixation of
the nitric acid by the lime.
Large quantities of this guano are also due to the débris of insects, fragments of
elytra, scales of the wings of butterflies, etc., which are brought together in those places
by the millions of cubic meters. The nitrification, which takes place in these deposits,
has been found to extend its products to a distance of several kilometers through the
soil. In some places the quantity of calcium nitrate is so great in the soils that they are
converted into a plastic paste by this deliquescent salt.
152. Nitric Nitrogen.—In its purer forms, and suited to manurial purposes, nitric
acid exists in combination with sodium as a compound commonly known as Chile
saltpeter.
The existence of these nitrate deposits has long been known.[129] The old Indian
laws originally prohibited the collection of the salt, but nevertheless it was secretly
collected and sold. Up to the year 1821, soda saltpeter was not known in Europe except
as a laboratory product. About this time the naturalist, Mariano de Rivero, found on the
Pacific coast, in the Province of Tarapacà, immense new deposits of the salt. Later the
salt was found in equal abundance in the Territory of Antofagasta, and further to the
south in the desert of Atacama, which forms the Department of Taltal.
At the present time the collection and export of saltpeter from Chile is a business of
great importance. The largest export which has ever taken place in one year was in
1890, when the amount exported was 927,290,430 kilograms; of this quantity
642,506,985 kilograms were sent to England and 86,124,870 kilograms to the United
States. Since that time the imports of this salt into the United States have largely
increased.
According to Pissis[130] these deposits are of very ancient origin. This geologist is
of the opinion that the nitrate deposits are the result of the decomposition of feldspathic
rocks, the bases thus produced gradually becoming united with the nitric acid provided
from the air.
According to the theory of Nöllner[131] the deposits are of more modern origin, and
due to the decomposition of marine vegetation. Continuous solution of soils beneath
the sea gives rise to the formation of great lakes of saturated water, in which occurs the
development of much marine vegetation. On the evaporation of this water, due to
geologic isolation, the decomposition of nitrogenous organic matter causes generation
of nitric acid, which, coming in contact with the calcareous rocks, attacks them,
forming calcium nitrate, which, in presence of sodium sulfate, gives rise to a double
decomposition into sodium nitrate and calcium sulfate.
The fact that iodin is found in greater or less quantity in Chile saltpeter is one of the
chief supports of this hypothesis of marine origin, inasmuch as iodin is always found in
sea plants, and not in terrestrial plants. Further than this, it must be taken into

consideration that these deposits of sodium nitrate contain neither shells nor fossils, nor
do they contain any calcium phosphate. The theory, therefore, that they are due to
animal origin is scarcely tenable.
Lately extensive nitrate deposits have been discovered in the U. S. of Columbia.
[132]
These deposits have been found extending over thirty square miles and vary in
thickness from one to ten feet. The visible supply is estimated at 7,372,800,000 tons,
containing from 1.0 to 13.5 percent of nitrate. The deposits consist of a mixture of
sodium nitrate, sodium chlorid, calcium sulfate, aluminum sulfate, and insoluble silica.
It is thought that the amount of these deposits will almost equal those in Chile and
Peru.

METHODS OF ANALYSIS.

153. Classification of Methods.—In general there are three direct methods of
determining the nitrogen content of fertilizers. First the nitrogen may be secured in a
gaseous form and the volume thereof, under standard conditions, measured and the
weight of nitrogen computed. This process is commonly known as the absolute
method. Practically it has passed out of use in fertilizer work, or is practiced only as a
check against new and untried methods, or on certain nitrogenous compounds which do
not readily yield all their nitrogen by the other methods. The process, first perfected by
Dumas, who has also given it his name, consists in the combustion of the nitrogenous
body in an environment of copper oxid by which the nitrogen, by reason of its
inertness, is left in a gaseous state after the oxidation of the other constituents; viz.,
carbon and hydrogen, originally present.
In the second class of methods the nitrogen is converted into ammonia which is
absorbed by an excess of standard acid, the residue of which is determined by
subsequent titration with a standard alkali. There are two distinct processes belonging
to this class, in one of which ammonia is directly produced by dry combustion of an
organic nitrogenous compound with an alkali, and in the other ammonium sulfate is
produced by moist combustion with sulfuric acid, and the salt thus formed is
subsequently distilled with an alkali, and the free ammonia thus formed estimated as
above described. Nitric nitrogen may also be reduced to ammonia by nascent hydrogen
either in an acid or alkaline solution as described in volume first.
In the third class of determinations is included the estimation of nitric nitrogen by
colorimetric methods as described in the first volume. These processes have little
practical value in connection with the analyses of commercial fertilizers, but find their
chief use in the detection and estimation of extremely minute quantities of nitrites and
nitrates. In the following paragraphs will be given the standard methods for the
determination of nitrogen in practical work with fertilizing materials and fertilizers.
154. Official Methods.—The methods adopted by the Association of Official
Agricultural Chemists have been developed by more than ten years of co-operative

work on the part of the leading agricultural chemists of the United States. These
methods should be strictly followed in all essential points by all analysts in cases where
comparison with other data are concerned. Future experience will doubtless improve
the processes both in respect of accuracy and simplicity, but it must be granted that, as
at present practiced, they give essentially accurate results.
155. Volumetric Estimation by Combustion with Copper Oxid.—This classical
method of analysis is based on the supposition that by the combustion of a substance
containing nitrogen in copper oxid and conducting the products of the oxidation over
red-hot copper oxid and metallic copper, all of the nitrogen present in whatever form
will be obtained in a free state and can subsequently be measured as a gas. The air
originally present in all parts of the apparatus must first be removed either by a
mercury pump or by carbon dioxid or by both together, the residual carbon dioxid
being absorbed by a solution of caustic alkali. Great delicacy of manipulation is
necessary to secure a perfect vacuum and as a rule a small quantity of gas may be
measured other than nitrogen so that the results of the analyses are often a trifle too
high. The presence of another element associated with nitrogen, or the possible
allotropic existence of that element, may also prove to be a disturbing factor in this
long-practiced analytical process. For instance, if nitrogen be contaminated with
another element, e. g., argon, of a greater density the commonly accepted weight of a
liter of nitrogen is too great and tables of calculation based on that weight would give
results too high.
First will be given the official method for this process, followed by a few simple
variations thereof, as practiced in this laboratory.
156. The Official Volumetric Method.—This process may be used for nitrogen in
any form of combination.[133]
The apparatus and reagents needed are as follows:
Combustion tube of best hard Bohemian glass, about sixty-six centimeters long and
12.7 millimeters internal diameter.
Azotometer of at least 100 cubic centimeters capacity, accurately calibrated.
Sprengel mercury air-pump.
Small paper scoop, easily made from stiff writing paper.
Coarse cupric oxid.—To be ignited and cooled before using.
Fine cupric oxid.—Prepared by pounding ordinary cupric oxid in a mortar.
Metallic copper.—Granulated copper, or fine copper gauze, reduced and cooled in a
current of hydrogen.
Sodium bicarbonate.—Free from organic matter.

Caustic potash solution.—Make a supersaturated solution of caustic potash in hot
water. When absorption of carbon dioxid, during the combustion, ceases to be prompt,
the solution must be discarded.
Filling the tube.—Of ordinary commercial fertilizers take from one to two grams
for analysis. In the case of highly nitrogenized substances the amount to be taken must
be regulated by the amount of nitrogen estimated to be present. Fill the tube as follows:
(1) About five centimeters of coarse cupric oxid: (2) Place on the small paper scoop
enough of the fine cupric oxid to fill, after having been mixed with the substance to be
analyzed, about ten centimeters of the tube; pour on this the substance, rinsing the
watch-glass with a little of the fine oxid, and mix thoroughly with a spatula; pour into
the tube, rinsing the scoop with a little fine oxid: (3) About thirty centimeters of coarse
cupric oxid: (4) About seven centimeters of metallic copper: (5) About six centimeters
of coarse cupric oxid (anterior layer): (6) A small plug of asbestos: (7) From eight-
tenths to one gram of sodium bicarbonate: (8) A large, loose plug of asbestos; place the
tube in the furnace, leaving about two and five-tenths centimeters of it projecting;
connect with the pump by a rubber stopper smeared with glycerol, taking care to make
the connection perfectly tight.
Operation.—Exhaust the air from the tube by means of the pump. When a vacuum
has been obtained allow the flow of mercury to continue; light the gas under that part
of the tube containing the metallic copper, the anterior layer of cupric oxid (see (5)
above), and the sodium bicarbonate. As soon as the vacuum is destroyed and the
apparatus filled with carbon dioxid, shut off the flow of mercury and at once introduce
the delivery-tube of the pump into the receiving arm of the azotometer just below the
surface of the mercury seal, so that the escaping bubbles will pass into the air and not
into the tube, thus avoiding the useless saturation of the caustic potash solution.
Set the pump in motion and when the flow of carbon dioxid has very nearly or
completely ceased, pass the delivery-tube down into the receiving arm, so that the
bubbles will escape into the azotometer. Light the gas under the thirty centimeter layer
of oxid, heat gently for a few moments to drive out any moisture that may be present,
and bring to a red heat. Heat gradually the mixture of substance and oxid, lighting one
jet at a time. Avoid a too rapid evolution of bubbles, which should be allowed to escape
at the rate of about one per second or a little faster.
When the jets under the mixture have all been turned on, light the gas under the
layer of oxid at the end of the tube. When the evolution of gas has ceased, turn out all
the lights except those under the metallic copper and anterior layer of oxid, and allow
to cool for a few moments. Exhaust with the pump and remove the azotometer before
the flow of mercury is stopped. Break the connection of the tube with the pump, stop
the flow of mercury, and extinguish the lights. Allow the azotometer to stand for at
least an hour, or cool with a stream of water until a permanent volume and temperature
have been reached.

Adjust accurately the level of the potash solution in the bulb to that in the
azotometer; note the volume of gas, temperature, and height of barometer; make
calculation as usual, or read results from tables.
156. Note on Official Volumetric Method.—The determination of nitrogen in its
gaseous state by combustion with copper oxid, has practically gone out of use as an
analytical method. The official chemists rarely use it even for control work on samples
sent out for comparative analysis. The method recommended differs considerably from
the process of Jenkins and Johnson, on which it is based. The only source of oxygen in
the official method is in the copper oxid. Hence it is necessary that the oxid in
immediate contact with the organic matter be in a sufficiently fine state of subdivision,
and that the substance itself be very finely powdered and intimately mixed with the
oxidizing material. Failure to attend to these precautions will be followed by an
incomplete combustion and a consequent deficit in the volume of nitrogen obtained.
The copper oxid before using is ignited, and is best filled into the tube while still
warm by means of a long pointed metal scoop, or other convenient method. The copper
spiral, after use, is reduced at a red heat in a current of hydrogen, and may thus be used
many times.
157. The Pump.—Any form of mercury pump which will secure a complete
vacuum may be used. A most excellent one can be arranged in any laboratory at a very
small expense. The pump used in this laboratory for many years answers every
purpose, and costs practically nothing, being made out of old material not very valuable
for other use.
The construction of the pump and its use in connection with the combustion tube
will be clearly understood from the following description:
A glass bulb I is attached, by means of a heavy rubber tube carrying a screw clamp,
to the glass tube A, having heavy walls and a small internal diameter, and being one
meter or more in length. The tube A is continued in the form of a U, the two arms being
joined by very heavy rubber tubing securely wired. The ends of the glass tubes in the
rubber should be bent so that they come near together and form the bend of the U, the
rubber simply holding them in place. This is better then to have the tube continuous,
avoiding danger of breaking. A tee tube, T, made of the same kind of glass as A, is
connected by one arm, a, with the manometer B, by a heavy rubber union well wired.
The union is made perfectly air-tight by the tube filled with mercury held by a rubber
stopper. The middle arm of the tee, a′, is expanded into a bulb, E, branching into two
arms, one of which is connected with A and the other with the delivery-tube F, by the
mercury-rubber unions, MM′, just described. The interior of the bulb E should be of
such a shape as to allow each drop of mercury to fall at once into F without
accumulating in large quantity and being discharged in mass. The third arm of the tee
a″ is bent upwards at the end and passes into a mercury sealing tube, D, where it is
connected by means of a rubber tube with the delivery-tube from the furnace. The flow

of the mercury is regulated by the clamp C, and care
should be taken that the supply does not get so low in
I as to permit air bubbles to enter A. The manometer
B dips into the tube of mercury H. A pump thus
constructed is simple, flexible, and perfectly tight.
The only part which needs to be specially made is the
tee and the one in use here was blown in our own
laboratory. The bent end of the delivery-tube F may
also be united to the main tube by a rubber joint thus
aiding in inserting it into the V-shaped nozzle of the
azotometer.
The azotometer used is the one devised by Schiff
and modified by Johnson and Jenkins.[134]
We prefer to get the V nozzles separately and join
them to any good burette by a rubber tube. The water-
jacket is not necessary, but the apparatus can be left
exposed until it reaches room temperature.
Any form of mercury pump capable of securing a
Figure. 10. vacuum may be used, but the one just described is
commended by simplicity, economy, effectiveness,
Mercury Pump and and long use.
Azotometer.
158. The Pump and Combustion Furnace.—
The pump and combustion furnace, as used in the
laboratory, are shown in Fig. 10. The pump is
constructed as just described, and rests in a wooden tray which catches and holds any
mercury which may be spilled. The furnace is placed under a hood which carries off the
products of the burning lamps and the hot air. A well-ventilated hood is an important
accessory to this process, especially when it is carried on in summer. A small mercury
pneumatic trough catches the overflow from the pump and also serves to immerse the
end of the delivery-tube during the exhaustion of the combustion tube.
The other details of the arrangement and connections have been sufficiently shown
in the previous paragraph.
159. Volumetric Method in this Laboratory.—It has been found convenient here
to vary slightly the method of the official chemists in the following respects: The tube
used for the combustion is made of hard refractory glass, which will keep its shape at a
high red heat. It is drawn out and sealed at one end after being well cleaned and dried.
It should be about eighty centimeters in length and from twelve to fourteen millimeters
in internal diameter. The relative lengths of the spaces occupied by the several contents
of the tube are approximately as follows: Sodium bicarbonate, two; asbestos, three;
coarse copper oxid, eight; fine copper oxid, containing sample, sixteen; coarse copper

oxid, twenty-five; spiral copper gauze, ten to fifteen; copper oxid, eight; and asbestos
plug, five centimeters, respectively.
The copper oxid should be heated for a considerable time to redness in a muffle
with free access of air before using and the copper gauze be reduced to pure metallic
copper in a current of hydrogen at a low red heat. The anterior layer of copper oxid
serves to oxidize any hydrogen that may have been occluded by the copper. When a
sample is burned containing all or a considerable part of the nitrogen as nitrates, the
longer piece of copper gauze is used.
160. The Combustion.—The tube having been charged and connected with the
pump it is first freed from air by running the pump until the mercury no longer rises in
the manometer. The end of the tube containing the sodium bicarbonate is then gently
heated so that the evolution of carbon dioxid will be at such a rate as to slowly depress
the mercury in the manometer, but never fast enough to exceed the capacity of the
pump to remove it. The lamp is extinguished under the sodium carbonate and the
carbon dioxid completely removed by means of the pump. The delivery-tube is then
connected with the azotometer, and the combustion tube carefully heated from the front
end backwards, the copper gauze and coarse copper oxid being raised to a red heat
before the part containing the sample is reached. When the nitrogen begins to come off,
its flow should be so regulated by means of the lamps under the tube, as to be regular
and not too rapid. From half an hour to an hour should be employed in completing the
combustion. Since most samples of fertilizer contain organic matter, the nitrogen will
be mixed with aqueous vapor and carbon dioxid. The former is condensed before
reaching the azotometer, and the latter is absorbed by the potassium hydroxid. When
the sample is wholly of a mineral nature it should be mixed with some pure sugar,
about half a gram, before being placed in the tube. When bubbles of gas no longer
come over, the heat should be carried back until there is a gradual evolution of carbon
dioxid under the conditions above noted. Finally the gas is turned off and the pump
kept in operation until the manometer again shows a perfect vacuum when the
operation may be considered finished. In the manipulation our chief variation from the
official method consists in connecting the combustion apparatus with the measuring
tube before the heat is applied to the front end of the combustion tube. Any particles of
the sample which may have stuck to the sides of the tube on filling will thus be subject
to combustion and the gases produced measured. Where it is certain that no such
adhesion has taken place it is somewhat safer on account of the possible presence of
occluded gases to heat the front end of the tube before connecting the combustion
apparatus with the azotometer.
161. Method of Johnson and Jenkins.—In the method of Johnson and Jenkins the
principal variation from the process described consists in introducing into the
combustion tube a source of oxygen whereby any difficultly combustible carbon may
be easily oxidized and all the nitrogen be more certainly set free.[135] The potassium
chlorate used for this purpose is placed in the posterior part of the tube, which is bent at

slight angle to receive it. The sodium bicarbonate is placed in the anterior end of the
tube. The combustion goes on as already described, and at its close the potassium
chlorate is heated to evolve the oxygen. The free oxygen is absorbed by the reduced
copper oxid, or consumed by the unburned carbon. Any excess of oxygen is recognized
at once by its action on the copper spiral. As soon as this shows signs of oxidation the
evolution of the gas is stopped. Care must be taken not to allow the oxygen to come off
so rapidly as to escape entire absorption by the contents of the combustion tube. In
such a case the nitrogen in the measuring tube would be contaminated.
It is rarely necessary in fertilizer analysis to have need of more oxygen than is
contained in the copper oxid powder in contact with the sample during the progress of
combustion.
162. Calculation of Results.—The nitrogen originally present in a definite weight
of any substance having been obtained in a gaseous form its volume is read directly in
the burette in which it is collected. This instrument may be of many forms but the
essential feature of its construction is that it should be accurately calibrated; and the
divisions so graduated as to permit of the reading of the volume accurately to a tenth of
a cubic centimeter. For this purpose it is best that the internal diameter of the measuring
tube be rather small so that at least each ten cubic centimeters occupies a space ten
centimeters long. The volume occupied by any gas varies directly with the temperature
and inversely with the pressure to which it is subjected. The quantity of aqueous vapor
which a moist gas may contain is also a factor to be considered. Inasmuch as the
nitrogen in the above process of analysis is collected over a strong solution of
potassium hydroxid capable of practically keeping the gas in a dry state the tension of
the aqueous vapor may be neglected.
163. Reading the Barometer.—Nearly all the barometers in use in this country
have the scale divided in inches and the thermometers thereunto attached are graduated
in Fahrenheit degrees. This is especially true of the barometers of the Weather Bureau
which are the most reliable and most easy of access to analysts. It is not necessary to
correct the reading of the barometer for altitude, but it is important to take account of
the temperature at the time of observation. There is not space here to give minute
directions for using a barometer. Such directions have been prepared by the Weather
Bureau and those desiring it can get copies of the circular.[136]
The temperature of a barometer affects its accuracy in two ways. First the metal
scale expands and contracts with changing temperatures: Second, the mercury expands
and contracts also at a much greater rate than the scale. If a barometer tube hold thirty
cubic inches of mercury the contents will be one ounce lighter at 80° F. than at 32° F.
The true pressure of the air is therefore not shown by the observed height of the
mercurial column unless the temperature of the scale and of the mercurial column be
considered.

Tables of correction for temperature are computed by simple formulas based on the
known coefficients of expansion of mercury and brass. For barometers with brass
scales the following formula is used for making the correction:
t - 28.63
C = -h .
1.113t + 10978
In this formula t = temperature in degrees Fahrenheit and h = observed reading of
the barometer in inches.
Example:—Temperature observed 72°.5
Barometer reading observed, 29.415 inches,
from which C = 0.1165, and this number, according to the
conditions of the formula, is to be subtracted from the observed
reading. The true reading in the case given is, therefore,
29.298 inches or 744.2 millimeters.
The observed reading 747.1 “
And the correction 2.9 “
Unless extremely accurate work be required the correction for temperature is of
very little importance in nitrogen determinations in fertilizers. Each instrument sent out
by the Weather Bureau is accompanied by a special card of corrections therefor, but
these are of small importance in fertilizer work. In order then to get the correct weight
of the gas from its volume the reading of the thermometer and barometer at the time of
measurement must be carefully noted. However, after the end of the combustion, the
azotometer should be carried into another room which has not been affected by the
combustion and allowed to stand until it has reached the room temperature.
Every true gas changes its volume under varying temperatures at the same rate and
this rate is the coefficient of gaseous expansion. For one degree of temperature it
amounts to 0.003665 of its volume. Representing the coefficient of expansion by K the
volume of the gas as read by V, the volume desired at any temperature by V′, the
temperature at which the volume is read by t and the desired temperature by t′, the
change in volume may be calculated by the following formula:
V′ = V[1 + K(t′ - t)].
Example.—Let the volume of nitrogen obtained by combustion be thirty-five cubic
centimeters, and the temperature of observation 22°. What would be the volume of the
gas at 0°?
Making the proper substitutions in the formula the equation is reduced to the form
below:
V′ = 35[1 + 0.003665(0°-22°)]
or V′ = 35(1 - 0.08063) = 32.18.

Thirty-five cubic centimeters of nitrogen therefore measured at 22° become 32.18
cubic centimeters when measured at 0°.
When gases are to be converted into weight after having been determined by
volume, their volume at 0° must first be determined; but this volume must also be
calculated to some definite barometric pressure. By common consent this pressure has
been taken as that exerted by a column of mercury 760 millimeters in height. Since the
volume of a gas is inversely proportional to the pressure to which it is subjected, the
calculation is made according to that simple formula. Let the reading of the barometer,
at the time of taking the volume of gas, be H, and any other pressure desired H′. Then
we have the general formula:
HV
V : V′ = H′ : H; and V′ = .
H′
Example: Let the corrected reading of the barometer at the
time of noting the volume of the gas be 740 millimeters, and the
volume of the gas reduced to 0° be 32.18 cubic centimeters. What
will this volume be at a pressure of 760 millimeters?
Substituting the proper values in the formula, we have:
(32.18 × 740)
V′ = = 31.33
760
Therefore, a volume of nitrogen which occupies a space of thirty-five cubic
centimeters at a temperature of 22°, and at a barometric pressure of 740 millimeters,
becomes 31.33 cubic centimeters at a temperature of 0° and a pressure of 760
millimeters.
One liter of nitrogen at 0° and 760 millimeters pressure weighs 1.25456 grams; and
one cubic centimeter therefore 0.00125456 gram. To find the weight of gas obtained in
the above supposed analysis, it will only be necessary to multiply this number by the
volume of nitrogen expressed in cubic centimeters under the standard conditions; viz.,
0.0125456 × 31.33 = 0.039305 gram. If the sample taken for analysis weighed half a
gram, the percentage of nitrogen found would be 7.85.
164. Tension of the Aqueous Vapor.—It has been shown by experience that when
a gas is collected over a potash solution containing fifty per cent of potassium
hydroxid, the tension of the aqueous vapor is so far diminished as to be of no
perceptible influence on the final result. To correct the volume of a gas, therefore, so
collected for this tension, would involve an unnecessary calculation for practical
purposes. If a gas thus collected should be transferred to a burette over mercury, on
which some water floats, then the correction should be made.
At 0° the tension of aqueous vapor will support a column of mercury 4.525
millimeters high, and at 40° one of 54.969 millimeters.

The following table gives the tension of aqueous vapors in millimeters of a
mercurial column for each degree of temperature from zero to forty.
Tension of Tension of
Temperature. vapor in Temperature. vapor in
millimeters. millimeters.
0° 4.525 21° 18.505
1° 4.867 22° 19.675
2° 5.231 23° 20.909
3° 5.619 24° 22.211
4° 6.032 25° 23.582
5° 6.471 26° 25.026
6° 6.939 27° 26.547
7° 7.436 28° 28.148
8° 7.964 29° 29.832
9° 8.525 30° 31.602
10° 9.126 31° 33.464
11° 9.751 32° 35.419
12° 10.421 33° 37.473
13° 11.130 34° 39.630
14° 11.882 35° 41.893
15° 12.677 36° 44.268
16° 13.519 37° 46.758
17° 14.409 38° 49.368
18° 15.351 39° 52.103
19° 16.345 40° 54.969
20° 17.396
When a gas is in contact with water the aqueous vapor is diffused throughout the
mass, and the pressure to which the mixture is subjected, is partly neutralized by the
tension of the water vapor. The real pressure to which the gas, whose volume is to be
determined is subjected, is therefore diminished by that tension. If for instance a gas in
contact with water show a volume of thirty-five cubic centimeters at 22° and 740
millimeters barometric pressure its volume is really greater than if it were perfectly dry.
How much greater can be determined by inspecting the table, for at 22° the tension of
water vapor is 19.675 millimeters of mercury. The real pressure to which the volume of
gas is subjected is therefore 740 - 19.675 = 720.325 millimeters.
If, therefore, in the example given, the nitrogen were in contact with water, the
calculation would proceed as follows:

32.18 × 720.325
V′ = = 30.5
760
and 30.5 × 1.25456 = 38.26.
Hence, 38.26 milligrams of nitrogen correspond to 7.65 per cent, when half a gram
of substance is taken for the combustion.
165. Aqueous Tension in Solutions of Potassium Hydroxid.—Even in strong
solutions of potassium hydroxid the tension of aqueous vapor is not destroyed, but is
reduced to a minimum, which is negligible in the calculation of the percentage by
weight of the nitrogen in a sample of fertilizer. When dilute solutions of a caustic alkali
are used however, the neglect of the tension of the aqueous vapor may cause an error of
some magnitude. In such cases the strength of the solution should be known and
correction made according to the following table:[137]
Millimeters tension of aqueous vapor for KOH solutions of
9.09 16.66 23.08 28.57 32.89
Temperature.
per cent. per cent. per cent. per cent. per cent.
10°.00 8.62 8.01 7.31 6.50 5.62
11°.00 9.21 8.56 7.82 6.95 6.01
12°.10 9.90 9.21 8.41 7.47 6.46
13°.00 10.50 9.77 8.92 7.93 6.86
13°.95 11.17 10.39 9.49 8.44 7.30
15°.15 12.06 11.22 10.25 9.11 7.86
16°.00 12.74 11.85 10.82 9.62 8.33
17°.00 13.57 12.63 11.54 10.26 8.88
18°.00 14.46 13.45 12.29 10.93 9.47
19°.00 15.39 14.33 13.09 11.65 10.09
20°.00 16.38 15.25 13.93 12.40 10.75
21°.00 17.42 16.22 14.82 13.20 11.44
21°.82 18.32 17.06 15.59 13.88 12.04
23°.00 19.68 18.32 16.75 14.92 12.94
24°.00 20.92 19.47 17.80 15.86 13.76
25°.00 22.19 20.67 18.91 16.85 14.62
26°.00 23.55 21.94 20.07 17.89 15.53
26°.98 24.95 23.25 21.27 18.96 16.46
27°.93 26.38 24.59 22.51 20.07 17.45
29°.00 28.08 26.18 23.96 21.38 18.59
30°.00 29.76 27.74 25.40 22.67 19.72

Millimeters tension of aqueous vapor for KOH solutions of
9.09 16.66 23.08 28.57 32.89
Temperature.
per cent. per cent. per cent. per cent. per cent.
31°.00 31.51 29.38 26.91 24.03 20.91
32°.13 33.61 31.34 28.72 25.65 22.34
33°.00 35.30 32.93 30.18 26.97 23.50
34°.00 37.34 34.84 31.94 28.56 24.89

166. Use of Volumetric Method.—For practical purposes it may be said that the
volumetric determination of nitrogen in fertilizer analysis has gone entirely out of use.
For control and comparison it is still occasionally practiced but it has had to give way
to the more speedy and fully as accurate processes of moist combustion with sulfuric
acid which have come into general use in the last decade. The student and analyst
however should not fail to master its details and become skilled in its use. There are
certain nitrogenous substances such as the alkaloids which are quite refractory when
subjected to moist combustion. While such bodies may not occur in fertilizers it is well
to have at hand a means of accurately determining their nitrogen content.
167. Tables for Calculating Results.—Where many analyses are to be made by
the copper oxid process it has proved convenient to shorten the work of calculating
analyses by taking the data given in computation tables.[138] Before using these tables it
must be known whether they are calculated on the supposition that the gas is measured
in a moist state, partly moist, or wholly dry. Where the nitrogen is collected over water
a table must be used in which allowance has been made for the tension of aqueous
vapor. In case a saturated solution of a caustic alkali be used in the azotometer it is
customary to take no account of the tension and the table employed must be
constructed on this supposition. In point of fact even in the strongest alkali solution
there is a certain amount of tension but this is so slight as only to affect the results in
the second place of percentage decimals. Since, as a rule, only a few analyses are made
by this method it will be found safer to use a caustic alkali solution of given strength
and to calculate the results from the tables of aqueous tensions given above.
168. The Soda-Lime Process.—This process originally perfected by Varrentrap
and Will, and improved by Peligot, was used almost exclusively by analysts until
within the last decade for the determination of nitrogen not existing in the nitric form.
It is based on the principle that when nitrogen exists as a salt of ammonia, or as an
amid, or as proteid matter, it is converted into gaseous ammonia by combustion with an
alkali. This ammonia can be carried into a set solution of acid by a stream of gas free of
ammonia and the excess of acid remaining after the combustion is complete can be
determined by titration against a standard alkali solution. The results under proper
conditions are accurate even when a small quantity of nitric nitrogen is present. When,
however, there is any considerable quantity of this compound in the sample the method

becomes inapplicable by reason of non-reduction of some of the nitrogen oxids
produced by the combustion.
In bodies very rich in nitrogen such as urea all the nitrogen is not transformed
directly into ammonia at the commencement of the combustion. A portion of it may
unite with a part of the carbon to form cyanogen, which may unite with the soda to
form sodium cyanid. With an excess of alkali, however, and prolonged combustion this
product will be finally decomposed and all the nitrogen be secured as ammonia.
The nascent hydrogen which unites with the nascent nitrogen during the
combustion is also derived from the organic matter which always contains enough
carbon to decompose the water formed in order to be oxidized to carbon dioxid. While
at first, therefore, during combustion, the hydrogen may unite with the oxygen, it
becomes again free by the oxidation of the carbon and in this condition unites with the
nascent nitrogen to form ammonia. In addition to carbon dioxid, ammonia, and free
hydrogen there may also be found among the products of combustion marsh and
olefiant gases and other hydrocarbon compounds which dilute, to a greater or less
extent, the ammonia formed and help to carry it out of the combustion tube and into the
standard acid.
169. The Official Method.—Reagents and Apparatus.—(1) Standard solutions and
indicator the same as for the kjeldahl method:
(2) Dry granulated soda-lime, fine enough to pass a 2.5 millimeter sieve:
(3) Soda-lime, fine enough to pass a 1.25 millimeter sieve.[139]
Soda-lime may be easily and cheaply prepared by slaking two and one-half parts of
quicklime with a strong solution of one part of commercial caustic soda, care being
taken that there is enough water in the solution to slake the lime. The mixture is then
dried and heated in an iron pot to incipient fusion, and, when cold, ground and sifted as
above.
Instead of soda-lime Johnson’s mixture of sodium and calcium carbonate, or slaked
lime may be used. Slaked lime may be granulated by mixing it with a little water to
form a thick mass, which is dried in the water-oven until hard and brittle. It is then
ground and sifted as above. Slaked lime is much easier to work with than soda-lime,
and gives excellent results, though it is probable that more of it should be used in
proportion to the substance to be analyzed than is the case with soda-lime.
(4) Asbestos, which has been ignited and kept in a glass-stoppered bottle.
(5) Combustion tubes about forty centimeters long and twelve millimeters internal
diameter, drawn out to a closed point at one end.
(6) Large-bulbed U tubes with glass stop-cock, or Will’s tubes with four bulbs.
Manipulation.—The substance to be analyzed should be powdered finely enough to
pass through a sieve of one millimeter mesh; from seven-tenths to one and four-tenths

grams, according to the amount of nitrogen present, are taken for the determination.
Into the closed end of the combustion tube, put a small loose plug of asbestos, and
upon it about four centimeters of fine soda-lime. In a porcelain dish or mortar, mix the
substance to be analyzed, thoroughly but quickly, with enough fine soda-lime to fill
about sixteen centimeters of the tube, or about forty times as much soda-lime as
substance, and put the mixture into the combustion tube as quickly as possible by
means of a wide-necked funnel, rinsing out the dish and funnel with a little more fine
soda-lime, which is to be put in on top of the mixture. Fill the rest of the tube to within
about five centimeters of the end with granulated soda-lime, making it as compact as
possible by tapping the tube gently while held in a nearly upright position during the
filling. The layer of granulated soda-lime should not be less than twelve centimeters
long. Lastly, put in a plug of asbestos about two centimeters long, pressed rather
tightly, and wipe out the end of the tube to free it from adhering soda-lime.
Connect the tube by means of a well-fitting rubber stopper or cork with the U tube
or Will’s bulbs, containing ten cubic centimeters of standard acid, and adjust it in the
combustion furnace so that the end of the tube projects about four centimeters from the
furnace, supporting the U tube or Will’s bulb suitably. Heat the portion of the tube
containing the granulated soda-lime to a moderate redness, and when this is attained
extend the heat gradually through the portion containing the substance, so as to keep up
a moderate and regular flow of gases through the bulbs, maintaining the heat of the first
part until the whole tube is heated uniformly to the same degree. Continue the
combustion until gases have ceased bubbling through the acid in the bulbs, and the
mixture of substance and soda-lime has become white, or nearly so, which shows that
the combustion is finished. The process should occupy about three-quarters of an hour,
or not more than one hour. Remove the heat, and when the tube has cooled below
redness break off the closed tip and aspirate air slowly through the apparatus for two or
three minutes to bring all the ammonia into the acid. Disconnect the tube, wash the acid
into a beaker or flask, and titrate with the standard alkali.
During the combustion the end of the tube projecting from the furnace must be kept
heated sufficiently to prevent the condensation of moisture, yet not enough to char the
stopper. The heat may be regulated by a shield of tin slipped over the projecting end of
the combustion tube.
It is found very advantageous to attach a bunsen valve to the exit tube, allowing the
evolved gases to pass out freely, but preventing a violent sucking back in case of a
sudden condensation of steam in the bulbs.
170. The Official French Method.—The French chemists prefer to drive out the
traces of ammonia remaining in the combustion tube by means of the gases arising
from the decomposition of oxalic acid.[140] The operation is conducted by mixing about
one gram of oxalic acid with enough of dry granular soda-lime to form a layer of four
centimeters in length at the bottom of the tube. The rest of the tube is then charged
substantially as directed above. At the end of the combustion the oxalic acid is

decomposed by heat furnishing sufficient hydrogen to remove from the tube all traces
of ammonia which it may contain. The French chemists employ, for titration, either
normal acids and alkalies or some decimal thereof or else an acid of such strength as to
have each cubic centimeter thereof correspond to ten milligrams of nitrogen, thus
making the computation of results exceedingly simple. Such an acid is secured when
one liter thereof contains thirty-five grams of pure monohydric sulfuric acid or forty-
five grams of pure crystallized oxalic acid. The corresponding alkaline reagent should
contain, in each liter, forty grams of pure potassium hydroxid.
171. The Hydrogen Method.—Thibault and Wagner recommend that the
combustion with soda-lime be conducted in an atmosphere of hydrogen,[141] and Loges
replaces this by common illuminating gas freed from ammonia by conducting it
through a tube filled with glass balls moistened with dilute sulfuric acid.[142]
In these cases the combustion tube is left open at both ends and the materials under
the tube confined to the proper position by asbestos plugs. The gases used act in a
merely mechanical manner and their use affords so few advantages over the method of
aspirating air at the end of the combustion as to render it unadvisable.
172. Coloration of the Product.—It often happens, especially in the combustion
of animal products, such as tankage and fish scrap, that the acid securing the ammonia
is deeply colored by the condensation of some of the other products of combustion.
This coloration interferes in a very serious way with the delicacy of the indicator used
to determine the end of the reaction. In this case the liquid may be mixed with an alkali
and distilled and the ammonia secured in a fresh portion of the standard acid as in the
moist combustion process to be hereafter described.
173. General Considerations.—(1) Preparation of Sample.—In the soda-lime
method it is of great importance that the organic substances be in a fine state of
subdivision so as to admit of intimate mixture with the alkali. In cases where fragments
of hoof, horn, hair, or similar substances are to be prepared for combustion it is
advisable to first decompose them by heating with a small quantity of sulfuric acid. The
excess of acid may be neutralized with marble dust and the resulting mixture dried,
rubbed to a fine powder, and mixed with the soda-lime in the usual way. Care must be
taken not to lose any of the ammonia from the sulfate which may be formed in mixing
with the soda-lime in filling the tube.
(2) Purity of Soda-Lime.—The soda-lime employed must be entirely free of
nitrogenous compounds and some blank combustions should be made in proof of its
purity.
(3) Temperature.—The temperature of the combustion should not be allowed to
exceed low redness. At very high temperatures there would be danger of decomposing
the ammonia.

(4) Aspiration of Air.—Before aspiring a current of air through the tube to remove
the last traces of ammonia the gas should be put out under the furnace and the tube be
allowed to cool below redness to avoid any danger of acting on the nitrogen in the air.
174. The Ruffle Soda-Lime Method.—Many attempts have been made to adapt
the soda-lime method to the determination of nitric nitrogen. Of these the process
devised by Ruffle is the only one which has proved successful.[143] The method is
founded on the action of sulfurous vapors on the nitrogen oxids produced during the
combustion whereby sulfuric acid is formed and the nascent nitrogen is joined with
hydrogen to form ammonia. By this process all the nitrogen contained in the sample,
even if in the nitric form, is finally obtained as ammonia. In the original method the
reagents employed were a mixture of sodium thiosulfate and soda-lime and a mixture
of charcoal, sulfur, and granulated soda-lime. Subsequently the official chemists
substituted sugar for the charcoal.[144] The method was used for a long time by the
official chemists and came into general favor until displaced by the simpler and
cheaper processes of the moist combustion method adapted to nitric nitrogen. As finally
modified and used by the official chemists the process was conducted as described
below.
175. The Official Ruffle Method.—[145]Reagents.—(1) Standard solutions and
indicator the same as for the kjeldahl method.
(2) A mixture of equal parts by weight of fine-slaked lime and finely powdered
sodium thiosulfate dried at 100°:
(3) A mixture of equal parts of weight of finely powdered granulated sugar and
flowers of sulfur:
(4) Granulated soda-lime, as described under the soda-lime method:
(5) Combustion tubes of hard Bohemian glass seventy centimeters long and one
and three-tenths centimeters in diameter:
(6) Bulbed U tubes or Will’s bulbs, as described under the soda-lime method:
Manipulation.—(a) Clean the U tube and introduce ten cubic centimeters of
standard acid.
(b) Fit the cork and glass connecting tube. Fill the tube as follows: (1) A loosely
fitting plug of asbestos, previously ignited, and then two and five-tenths to three and
five-tenths centimeters of the thiosulfate mixture: (2) The weighed portion of the
substance to be analyzed is intimately mixed with from five to ten grams of the sugar
and sulfur mixture: (3) Pour on a piece of glazed paper or in a porcelain mortar a
sufficient quantity of thiosulfate mixture to fill about twenty-five centimeters of the
tube; then add the substance to be analyzed, as previously prepared, mix carefully, and
pour into the tube; shake down the contents of the tube; rinse off the paper or mortar
with a small quantity of the thiosulfate mixture and pour into the tube; then fill up with

soda-lime to within five centimeters of the end of the tube: (4) Place another plug of
ignited asbestos at the end of the tube and close with a cork: (5) Hold the tube in a
horizontal position and tap on the table until there is a gas-channel along the top of the
tube: (6) Make connection with the U tube containing the acid; aspirate and see that the
apparatus is tight.
The Combustion.—Place the prepared combustion tube in the furnace, letting the
open end project a little, so as not to burn the cork. Commence by heating the soda-
lime portion until it is brought to a full red heat. Then turn on slowly jet after jet toward
the outer end of the tube, so that the bubbles come off two or three a second. When the
whole tube is red hot and the evolution of the gas has ceased and the liquid in the U
tube begins to recede toward the furnace, attach the aspirator to the other limb of the U
tube, break off the end of the tube, and draw a current of air through for a few minutes.
Detach the U tube and wash the contents into a beaker or porcelain dish; add a few
drops of the cochineal solution, and titrate.
176. Observations.—In our experience we have found it much more satisfactory to
adhere to the earlier directions for preparing the mixture of thiosulfate and alkali. We
much prefer to make the mixture with soda-lime and without the previous drying of the
sodium salt. Ruffle himself says that the sodium thiosulfate should be dry but not
deprived of its water of crystallization.[146] The best method to dry the crystal powder
without depriving it of its crystal water is to press it between blotting papers. The
official method also contains a typographical error in prescribing that the combustion
tube should have a length of thirty centimeters where evidently thirty inches were
meant. Ruffle’s original tube was twenty-two inches in length.
As is seen from the above description the method is essentially a reduction process
by the action of a powerful deoxidizer in the presence of an alkali. The crystals of the
thiosulfate salt cannot be brought into direct contact with a pure alkali, like soda or
potash, without forming at once a wet mass which would tend to cake and obstruct the
tube. The soda-lime is therefore a mechanical device to prevent this fusion. Where
many analyses are to be made an iron tube, for economical reasons, may be substituted
for the glass; but the glass tube permits a more intelligent observation of the progress of
the analysis.
Since charcoal has very high absorbent powers it will be found always to contain a
little nitrogen which may be in a form to generate ammonia during the combustion. The
charcoal used should therefore be previously boiled with caustic soda or potash
solution, dried, powdered, and preserved in well-stoppered bottles. Although pure sugar
is practically free of nitrogen, even when it is used, it is advisable to occasionally make
a blank determination and thus ascertain the correction to be made for possible
contamination.
177. Boyer’s Modification of Ruffle’s Method.—The principle of the method
rests on the observation that if nitrates be heated in a combustion tube with calcium

oxalate and soda-lime, not more than two-thirds of the total nitrogen appear as
ammonia; but if a certain proportion of sulfur be added the whole of the nitrogen is
recovered.[23] The process may be divided into two reactions; viz.:
(1) Action of the calcium oxalate upon the sodium nitrate in presence of soda-lime:
(2) The action of sulfurous acid and of calcium oxalate upon the sodium nitrate in
presence of soda-lime.
The analysis is conducted as follows: Dry and pulverize one-half gram of nitrate
(Na or K) and mix it intimately with fifty grams of the reducing compound containing
approximately ten per cent sulfur, 22.5 per cent neutral calcium oxalate, and 67.5 per
cent soda-lime. The combustion tube is charged as follows:
Length of tube fifty-five centimeters:
Diameter of tube seventeen millimeters:
Add first two grams pulverized calcium oxalate:
Add next ten grams pulverized soda-lime:
“ “ ten grams of the reducing compound:
“ “ the nitrate incorporated with fifty grams of the reducing mixture:
Add next ten grams of the reducing mixture:
“ “ ten grams pulverized soda-lime:
The tube is then lightly closed with an asbestos plug.
The tube is heated gradually from the front backwards, the calcium oxalate
furnishing finally the gas necessary to drive out the last traces of ammonia. The process
is equally applicable to the determination of nitrogen in all its forms or to mixtures
thereof.
The method has also been applied to the mixture of ammoniacal and organic
nitrogen and to the mixture of ammoniacal, nitric, and organic nitrogen, the
combustions having been made both in an iron and a glass tube. The amounts of
material to be used vary from one-half gram to a gram, according to its richness in
nitrogen.
The combustion should be terminated in forty minutes.
When a combustion is terminated, the acid containing the ammonia is placed in a
beaker and boiled for two or three minutes to drive off the sulfurous and carbonic
acids. The titration is then conducted in the usual manner.
The combustion can be carried on just as well in an iron tube as in a glass one. The
reagents employed, especially soda-lime, being hygroscopic, a little water is
disengaged in heating, which is condensed at the cold extremity of the tube, and which
may absorb a little ammonia, unless special precautions are taken to have the materials
dry.

THE MOIST COMBUSTION PROCESS.

178. Historical.—As long ago as 1868 Wanklyn proposed to conduct the
combustion of organic bodies in a wet way, using potassium permanganate as the
oxidizing body.[147] About ten years after this he attempted to extend the method so as
to estimate the quantity of proteid matter in a sample by treatment with an alkaline
solution in presence of the permanganate salt. One gram of the finely pulverized
sample was treated in a liter flask with one-tenth normal potash lye. After digestion for
some time, from ten to twenty cubic centimeters were taken for the determination.
According to the supposition of Wanklyn, pure albuminoid matters thus treated yielded
one-tenth of their weight of ammonia, or about fifty per cent of the total nitrogen
appeared as ammonia. The ammonia content of the sample was determined by the
colorimetric process devised by Nessler. It is needless to add that the process of
Wanklyn proved to be of no practical use whatever, acting differently on different
albuminoid matters, and even on the same substance. No other attempt was made to
perfect the moist combustion process until Kjeldahl[148] introduced the sulfuric acid
method in 1883. The simplicity, economy, and adaptability of this method have brought
it into general use. At first the process was only applied to organic nitrogenous
compounds in the absence of nitrates, but especially by the modifications proposed by
Asboth, Jodlbaur, and Scovell, it has been made applicable to all cases, with the
possible exception of a few alkaloidal and allied bodies. The moist combustion process
for determining nitrogen is now generally employed by chemists in all countries, not
only for fertilizer control, but also for general work.
179. The Method of Kjeldahl.—The process originally proposed by Kjeldahl is
applicable only to nitrogenous bodies free of nitric nitrogen. The principle of the
process is based on the action of concentrated sulfuric acid at the boiling-point in
decomposing nitrogenous compounds without producing volatile combinations and the
subsequent completion of the oxidation by means of potassium permanganate. The
original process has been modified by many analysts but the basic principle of it has
remained unchanged. It will therefore prove useful here to describe the process as
originally given.[149]
The weighed substance is placed in a small flask. With solid bodies this is a very
simple operation, but with liquids more difficult. Liquids which are not decomposed,
on heating, should be evaporated in a thin glass dish which can be ground up and
placed in the digestion flask with the desiccated sample. The strongest sulfuric acid is
added in sufficient quantity to secure complete decomposition, not less than ten cubic
centimeters in any case. The acid must be free of ammonia and be kept in such a way
as not to absorb ammonia from the atmosphere of the laboratory. To guard against
danger of error from such an impurity frequent control determinations should be made.
In control experiments one or two grams of pure sugar should be used as the organic
matter. If the acid employed contain traces of ammonia the necessary corrections

should be made in each analysis. The flask having been charged is placed on a wire
gauze over a small flame. The organic matter becomes black and tar-like and soon there
is a rapid decomposition attended with the evolution of gaseous products among which
sulfur dioxid is found. To avoid danger from spurting, the digestion flask should be
placed in an oblique position. The flask should have, at least, a capacity of 100 cubic
centimeters and a long neck and be made of a kind of glass capable of withstanding the
action of the boiling acid. Particles of the carbonized organic matter left on the sides of
the flask by the foaming of the mass at first are gradually dissolved by the vapors of the
boiling acid as the digestion proceeds. The action of the sulfuric acid is not entirely
finished when gases cease to be given off but the digestion should be continued until
the liquid in the flask is clear and colorless or nearly so. Usually about two hours are
required to secure this result. When aided by the means mentioned below the time of
digestion can be very materially shortened. By adding some fuming sulfuric acid, or
glacial phosphoric acid, the dilution caused by the formation of water in the
combustion of the organic matter, can be avoided. For albuminoid bodies it is hardly
necessary to continue the combustion until all carbonaceous matter is destroyed. The
full complement of ammonia is usually obtained after an hour’s combustion even if the
liquid be still black or brown, but with other nitrogenous bodies the case is different so
that upon the whole it is safest to secure complete decoloration.
The temperature must be maintained at the boiling-point of the acid or near thereto
since at a lower temperature, for instance from 100° to 150°, the formation of ammonia
is incomplete. Since all organic substances of whatever kind are dissolved by the
boiling acid the previous pulverization of the material need be carried only far enough
to secure a fair sample. Many substances give up practically all their nitrogen as
ammonium sulfate when heated with sulfuric acid as, for instance, urea, asparagin, and
the glutens. In most of the other organic bodies fully ninety per cent of the nitrogen are
likewise secured as the ammonium salt. In the aromatic compounds, or even in the
form of amid in anilin salts, the nitrogen is more resistant to the action of sulfuric acid.
In the alkaloids where the nitrogen is probably a real component of the benzol skeleton
the formation of ammonia is very incomplete. But even in the cases where the
conversion of the nitrogen into ammonia is practically perfect it is advisable to finish
the process by completing the oxidation with potassium permanganate. The
permanganate should be used in a dry powdered form and added little by little to the
hot contents of the digestion flask, the latter being held in an upright position and
removed meanwhile from the lamp. When carefully performed there is no danger of
loss of ammonia although the oxidation is, at times, so vigorous as to be attended with
evolution of light. The permanganate must always be added in excess and until a
permanent green color is produced. The flask is then gently heated for from five to ten
minutes over a small flame, but this is not important. The heating must not be too
strong or else a strong evolution of oxygen will take place with a consequent reduction
of the manganese compound. When this happens the liquid again becomes clear and
there is a loss of ammonia.

After cooling, the contents of the flask are diluted with water, the green color
giving place to a brown with a rise of temperature. After cooling a second time the
whole is brought into a distillation flask of about three-quarters of a liter capacity and
attached to a condenser which ends in a vessel containing titrated sulfuric acid. About
forty cubic centimeters of sodium hydroxid solution of one and three-tenths specific
gravity are added and the stopper at once inserted to prevent any loss of ammonia. To
prevent bumping during the distillation some zinc dust is added securing an evolution
of hydrogen during the progress of the distillation. In this case the bumping is
prevented until near the end of the operation when it begins anew, probably by reason
of the separation of solid sodium sulfate. After the end of the distillation, the excess of
acid remaining in the receiver is determined by a set alkali solution and thus the
quantity of ammonia obtained easily calculated. Kjeldahl, however, preferred to titrate
the solution after adding potassium iodate and iodid, a mixture which in the presence of
a strong acid sets free a quantity of iodin equivalent to the free acid present. The iodin
thus set free is titrated by a set solution of sodium thiosulfate using starch as an
indicator. The merits of this method are sharpness of the end reaction and the
possibility of using only a small quantity of the nitrogenous body for the combustion.
The sulfuric acid used in the receiver is made of the same strength as the thiosulfate
solution; viz., about one-twentieth normal. Thirty cubic centimeters of this were found
to be the proper amount for use with substances taken in such quantities as to produce
ammonia enough to neutralize about half of it. The titration is carried on as follows: A
few crystals of potassium iodid are dissolved in the acid mixture obtained after the
distillation is completed, then a few drops of the starch-paste and finally a few drops of
a four per cent solution of potassium iodate. The iodin set free is then oxidized by the
addition of the one-twentieth normal sodium thiosulfate solution until the blue color
disappears.
Example: Sulfuric acid used, 30 cc.
Equivalent to sodium thiosulfate, 30 cc.
Blank combustion required, 29.8 cc. thiosulfate solution.
Combustion of 0.645 gram of barley required, 14.5 cc. “ “
Thiosulfate corresponding to barley, 15.3 cc.
In the computation it is more simple to multiply the corresponding number of cubic
centimeters of thiosulfate by seven, half the atomic weight of nitrogen, and divide the
product by the weight of the substance taken, which will give the per cent of nitrogen
therein.
15.3 × 7
Then × 100 = 1.66 = per cent of nitrogen in sample taken.
0.645
A more detailed description of the method of making the titration follows: After the
distillation is finished the condensing-tube is rinsed with a little water, after which the
sulfuric acid unneutralized in the receiver is determined. It is advisable first to test the

reaction of the distillate with litmus paper before going any further; for if at any time
all the acid should be found neutralized it will be necessary to add a sufficient quantity
of one-twentieth normal sulfuric acid before adding the potassium iodid, etc., otherwise
the determination will be irreparably lost. Add to the contents of the flask ten cubic
centimeters of the potassium iodid and two cubic centimeters of the potassium iodate
solutions, described further on, and the sodium thiosulfate is then run in from a burette
till the fluid, which is constantly kept agitated by shaking the flask, shows only a bare
trace of yellow coloration from the iodin still present. Starch solution is then added,
and the blue color obtained is at once removed by additional thiosulfate solution. When
some experience has been gained, the eye is able to discern, with great certainty, even
the slight coloration caused by only a small trace of free iodin.
In regard to the sensitiveness of the end reaction and the accuracy of the result, this
method of titration leaves nothing to be wished for. The strength of the thiosulfate
solution is determined in exactly the same manner, and with starch as an indicator. For
this purpose, measure ten cubic centimeters of one-twentieth normal sulfuric acid into
an erlenmeyer, add 120 cubic centimeters of ammonia-free water, ten cubic centimeters
of potassium iodid solution, and two cubic centimeters of iodate solution; add
thiosulfate solution till the fluid shows only the above-mentioned light yellow tint, then
add starch, and finally thiosulfate. In this way the strength of the thiosulfate is
ascertained, which of course must be occasionally re-determined, under exactly the
same conditions as with the nitrogen determinations themselves, and every possible
error is thereby excluded. That the solution once decolorized within a short time again
assumes a deep blue color, is a matter of no concern, inasmuch as both solutions are
added in such a manner that the end reaction lies exactly at the point when the starch
iodid reaction distinctly disappears.
180. Theory of the Reactions.—As has been seen above the final product of
heating a nitrogenous organic compound with sulfuric acid and an oxidizing body is
ammonium sulfate. The various steps by which this is obtained have been traced by
Dafert:[150]
(1) The sulfuric acid abstracts from the organic matter the elements of water:
(2) The sulfur dioxid produced by the action of the residual carbon on sulfuric acid
exercises a reducing effect on the nitrogenous bodies present:
(3) From the nitrogenous bodies produced by the above reduction ammonia is
formed by the action of an oxidizing body:
(4) The ammonia formed is at once fixed by the acid as ammonium sulfate.
According to the theory of Asboth the hydrogen which is formed during the action of
sulfuric acid on organic matter, when in a nascent state, also aids greatly in the
production of ammonia. This idea is based on the fact that with those bodies which
afford a deficit of hydrogen the formation of ammonia is imperfect.[151]

181. Preparation of Reagents.—(1) Pure Sulfuric Acid.—As is well known the so-
called pure sulfuric acid in the market usually contains ammonia, a fact which
compelled Kjeldahl to determine the quantity of nitrogen in the acid in every instance,
and to make correction for the same in the analysis. An acid absolutely free from this
impurity may, however, easily be prepared by the distillation of the commercial article
in a small glass retort holding easily about 400 cubic centimeters. To conduct this
operation without danger it is only necessary to arrange the apparatus so that the heavy
fluid is heated to boiling, not from the bottom of the retort, but from its sides, and that
the upper portion of the body and neck is kept sufficiently warm so that the sulfuric
acid fumes are not allowed to condense and flow back into the retort. Both these ends
are attained simply by surrounding the retort with a piece of sheet iron, cylinder-shaped
beneath, and with an oval upper part, having an opening of about one centimeter in
diameter for the neck of the retort. To conduct the distillation a burner is used with an
arrangement for spreading the flame. To avoid with certainty all bumping of the
sulfuric acid and the resulting danger therefrom, the lamp is so arranged that only the
products of combustion go up between the retort and its iron hood, without allowing
the flame itself to come into contact with the glass vessel. The retort should be filled
about half full, or with 200 cubic centimeters of acid. By this device, without any
danger whatever, about one liter of sulfuric acid may be distilled in a day. The retort
will stand numerous distillations. Once begun, the distillation takes care of itself; it is
necessary to discontinue it when only the bottom of the retort is covered with sulfuric
acid, and to fill fresh acid through a funnel when the retort has cooled off. The first
twenty cubic centimeters of the distillate going over are collected by themselves and
rejected. What comes over later is, as shown by experience, absolutely ammonia-free,
and can be used without any correction, for the nitrogen determinations according to
Kjeldahl. The acid is kept in a stoppered bottle in a place not reached by ammonia
fumes. The ten cubic centimeter pipette used for measuring the quantity of sulfuric acid
required for each determination, is fastened in the perforated rubber stopper with which
the bottle is kept closed, and is itself closed above by a small rubber tube with a plug of
glass wool in it.
(2) Potassium Permanganate.—Crystals of this salt are crushed (not pulverized)
with a pestle into small pieces of about one-half millimeter size, which are kept in a
long glass tube of about ten millimeters diameter, closed with a stopper.
(3) Ammonia-free Water.—Common distilled water cannot be used in the
determination of nitrogen according to Kjeldahl, since it contains ammonia. It may be
obtained free from the same by redistillation in a large glass retort with the addition of
a few drops of sulfuric acid. All vessels used in the determination are rinsed out
beforehand with this water.
(4) Ammonia-free Soda-lye is most conveniently prepared by adding 270 grams of
common sodium hydroxid in sticks, little by little, to one liter of distilled water which
is kept continually boiling, by means of a small flame, in a good-sized silver dish. The

dish is kept covered with a glass plate. Care has to be exercised not to add the alkali too
rapidly, nor in too large quantities at a time for in this case the fluid will boil too
violently at every addition of the alkali. After the operation is finished the lye is at once
siphoned into a glass flask, and when cold, is poured into a glass-stoppered bottle.
(5) One-twentieth Normal Sulfuric Acid is prepared from sulfuric acid and water
both absolutely ammonia-free, and is kept in a place where no fumes of ammonia can
reach it, in a well-stoppered glass bottle, the stopper being smeared with vaseline.
(6) Sodium Thiosulfate Solution.—This should be of the same strength as the one-
twentieth normal sulfuric acid. It is prepared by dissolving the salt in ammonia-free
water, and is compared with the acid, to which has been added potassium iodid and
iodate, using starch as an indicator, in the manner described above. The solution is kept
in a well-stoppered bottle, in the dark. When the salt and water used are perfectly pure,
it will keep unchanged for a long time.
(7) Potassium Iodid.—Dissolve five grams of chemically pure potassium iodid in
ammonia-free water and make the volume 100 cubic centimeters. Ten cubic
centimeters of this solution are used for each determination; keep the solution in the
dark and in a well-stoppered bottle.
(8) Potassium Iodate.—Dissolve four grams of chemically pure potassium iodate in
ammonia-free water and make the volume 100 cubic centimeters. Use two cubic
centimeters of this solution for each determination.
(9) Starch Solution.—Digest pure starch for about a week with dilute hydrochloric
acid, wash perfectly free from chlorin by decantation, and finally dry it between filter-
paper. The starch is then dissolved in water with the aid of heat. Such a solution will
keep for an indefinite time, if it be saturated with common salt. Ten grams of this starch
are dissolved in 1,000 cubic centimeters of ammonia-free water; use one or two cubic
centimeters for each determination.
182. Kjeldahl Method as Practiced by the Holland Royal Experiment Station.
—Necessary Reagents: 1. Phosphosulfuric acid, made by mixing a liter of sulfuric acid
of specific gravity 1.84 with 200 grams of phosphoric anhydrid:
2. Alkaline sodium sulfid solution, made by dissolving 500 grams of sodium
hydroxid and six grams of sodium sulfid or eight and one-half grams of potassium
sulfid, in a liter of water:
3. Mercury:
4. Paraffin in small pieces:
5. Dilute sulfuric acid and dilute potash solution, both of known strength:
6. Pieces of previously ignited pumice stone or of granulated zinc:
7. Neutral solution of rosolic acid or litmus.

Apparatus: The apparatus necessary consists of oxidation flasks of about 200 cubic
centimeters capacity and distillation flasks of about 500 cubic centimeters capacity,
both of bohemian glass. Copper may be used for the distillation flasks.[152]
The Process: A gram of the sample to be analyzed is placed in an oxidation flask
together with twenty cubic centimeters of phosphosulfuric acid and a drop of mercury,
about 600 milligrams, and heated till the fluid becomes colorless. After cooling, dilute
and wash the contents of the flask into a distillation flask. The resulting volume should
be about 300 cubic centimeters. Add 100 cubic centimeters of the alkaline sodium
sulfid solution and some pieces of ignited pumice stone or granulated zinc. Distill the
ammonia, receiving the distillate in a flask containing a known volume of the standard
sulfuric acid. Titrate with tenth-normal potash, using litmus or rosolic acid as indicator.
183. The Kjeldahl Method as Practiced at the Halle Station.—The method at
present in vogue in the German stations of conducting the moist combustion process is
well illustrated by the method of procedure followed at Halle.[29] From seven-tenths to
one and five-tenths grams of the sample are taken for analysis according to its richness
in nitrogen. Because of the fact that so small a quantity of the sample is taken it is of
the highest importance that it be perfectly homogeneous throughout its entire mass.
Otherwise, grave errors may arise. From the sample, as sent to the laboratory, the
analyst should take a subsample and this should be rubbed to a fine powder and the part
used for analysis carefully taken therefrom. If the sample be moist it may be rubbed up
with an equal weight of gypsum, in which case a double quantity is taken for the
determination. Substances like bone-meal, which do not keep well mixed, especially
when occasionally shaken, should be intimately mixed before each weighing. The
sample taken for analysis is placed in a glass flask of about 150 cubic centimeters
capacity. The flasks should be made of a special glass to withstand the tension of the
combustion. Those made by Kavalier at Sazava, in Bohemia, have proved to be the
most lasting. A globule of mercury weighing a little less than one gram is placed in the
flask and also twenty cubic centimeters of pure sulfuric acid of 1.845 specific gravity.
The mercury is conveniently measured by an apparatus suggested by Wrampelmayer. It
consists of an iron tube holding mercury, and is conveniently filled, from time to time,
from a supply vessel placed in a higher position and joined by means of a heavy glass
tube and rubber tube connections. The lower end of the iron tube is provided with a
movable iron stopper having a pocket just large enough to hold a globule of mercury,
weighing a little less than a gram. On turning the stopper the pocket is brought opposite
a discharge orifice and the measured globule of mercury is discharged. With substances
which tend to produce a strong foaming a little paraffin is used. The flasks after they
are charged are placed on circular digesting ovens under a hood as shown in figure 11.

Figure. 11.
Moist Combustion Apparatus of the
Halle Agricultural Laboratory.

At first the tripodal support of the flasks is so turned as to bring them between the
lamps and in this way a too rapid reaction is at first avoided. After half an hour the
tripods are so turned as to bring each flask directly over the lamp, the flame of which is
allowed to impinge directly against the glass. The flame is so regulated that after the
evolution of the sulfur dioxid has nearly ceased the contents of the flask are brought
into gentle ebullition. The boiling is continued until the contents of the flask are
colorless, usually about two hours. As a rule such substances as cottonseed-meal and
dried blood will take a longer time for complete combustion than other fertilizing
materials. During the combustion the flasks are closed with an oblong loose-fitting
unground glass stopper. When the oxidation is finished the contents of the flasks are
allowed to cool, the stoppers are removed, and enough water is added to fill the flasks
about three-quarters full. The flasks are gently shaken, and the possibility of breaking,
from the heat developed, must not be overlooked. To avoid confusion the flasks are all
numbered before beginning the work, and the numbers noted by the analyst in
connection with the samples. The contents of each one are next poured into the
distillation flask and the digestion vessels are washed with 100 cubic centimeters of
water in three portions, and the wash-water added to the liquid. Sometimes in washing
out the digestion flask yellow basic mercury compounds separate on its walls, but this
does not, in any way, influence the accuracy of the results. The distillation flasks
should have about 600 cubic centimeters capacity. To avoid the transfer the digestion
may take place in the distillation flask in which case the latter must be made of special
glass as indicated.

To the liquid thus transferred are added seventy-five cubic centimeters of soda-lye
containing one and one-half times as much potassium sulfid as is necessary to combine
with the mercuric sulfate present. The lye is of such a strength that sixty cubic
centimeters are sufficient to neutralize the acid present. It has a specific gravity of
1.375 and contains thirty-three grams of potassium sulfid in a liter.
In order to avoid the bumping which may take place during the distillation, some
granulated zinc should be added.
The distillation flask is closed with a rubber stopper carrying a bulb-tube which
ends above in a glass tube about three-quarters of a meter long, bent at an acute angle,
and passing obliquely downward on a convenient support. This tube is connected by a
rubber, with the end tube bent nearly at a right angle and dipping into the standardized
acid in the erlenmeyer receiver. The general arrangement of the distilling apparatus is
shown in figure 12. Since the contents of the vessel are warmed by mixing with the
soda-lye, the flame can be turned on at full head at once at the commencement of the
operation. In about a quarter of an hour the liquid in the receiver will be at the boiling-
point, and the boiling should be continued for five minutes more, making twenty
minutes in all for the completion of the distillation. By this boiling the contents of the
receiver are not charged with carbon dioxid, as might happen if a condenser were used.
The receiver contains twenty cubic centimeters of a standardized sulfuric acid solution
and about fifty cubic centimeters of water.

Figure. 12.
Distillation Apparatus of
Halle Agricultural Laboratory.

The acid used should contain 38.1 grams of sulfuric acid of 1.845 specific gravity
in a liter; and it should be set by titration with chemically pure sodium carbonate. For

this purpose seven-tenths gram of sodium carbonate is heated in a platinum crucible for
two hours over a small flame, weighed, and placed in an erlenmeyer together with
twenty cubic centimeters of the sulfuric acid, care being taken to avoid loss from the
vigorous evolution of carbon dioxid. After boiling for ten minutes all the carbon dioxid
is removed from solution. After cooling, the excess of acid is determined by titration
with a standardized barium hydroxid solution, using rosolic acid as indicator.
The solution of barium hydroxid is made as follows: Digest, with warm water, 260
grams of caustic baryta, Ba(OH)₂, until it is nearly all dissolved, filter, and make up to
a volume of ten liters and keep in a flask free of carbon dioxid. A solution of barium
hydroxid is to be preferred to the corresponding sodium compound for titration. If
traces of carbonate be formed in the two liquids, the sodium salt will remain in solution
while the barium compound will settle at the bottom of the flask.
The Indicator.—The indicator used to determine the end of the reaction is made by
dissolving one gram of rosolic acid in fifty cubic centimeters of alcohol. From one to
two drops are enough for each titration. The color reaction is less definite as the
quantity of ammonia in the liquid increases. When the titration solutions have been
prepared as above described it is found to require about ninety of the barium hydroxid
to neutralize twenty cubic centimeters of the sulfuric acid.
By direct titration with sodium carbonate it is ascertained how many grams of
nitrogen the twenty cubic centimeters of sulfuric acid represent.
Example.—Suppose the weight of the dried sodium carbonate
prepared as above directed is 0.6989 gram.
½Na₂CO₃, ½N₂
Then 0.6989 : 53 =x : 14
Whence x = 0.184615 gram of nitrogen.
Suppose further that twenty cubic centimeters of sulfuric acid
solution require ninety-four cubic centimeters of barium hydroxid
for complete saturation and after treatment with the above amount
of sodium carbonate, ten and a half cubic centimeters of the
barium solution to neutralize the remaining acid.
Then 94 - 10.5 = 83.5
And 0.184615: 83.5 = x: 94.
Whence x = 0.207830 gram of nitrogen corresponding to
twenty cubic centimeters of the sulfuric acid used.
Then 0.20783 ÷ 94 = 0.002211 gram of nitrogen
corresponding to one cubic centimeter of the barium hydroxid
solution.

If then in the analysis of a fertilizer it is found that 60.5 cubic
centimeters are required to neutralize the excess of sulfuric acid
after distillation the percentage of nitrogen in the sample is found
as follows:
60.5 × 0.002211 = 0.13377.
0.20783 - 0.13377 = 0.07406.
0.07406 × 100 = 7.406 = per cent nitrogen in sample when one
gram is taken for the combustion.
184. The Official Kjeldahl Method. Not Applicable in the Presence of Nitrates.
[153]
—Reagents.—(1) Acids.—(a) Standard hydrochloric acid the absolute strength of
which has been determined by precipitating with silver nitrate, and weighing the silver
chlorid as follows:
To any convenient quantity of the acid to be standardized, add solution of silver
nitrate in slight excess, and two cubic centimeters of pure nitric acid, of specific gravity
1.2. Heat to boiling-point, and keep at this temperature for some minutes without
allowing violent ebullition, constantly stirring until the precipitate assumes the granular
form. Allow to cool somewhat, and then pass the fluid through the asbestos. Wash the
precipitate by decantation, with 200 cubic centimeters of very hot water, to which have
been added eight cubic centimeters of nitric acid and two cubic centimeters of dilute
solution of silver nitrate containing one gram of the salt in 100 cubic centimeters of
water. The washing by decantation is performed by adding the hot mixture in small
quantities at a time, and beating up the precipitate well with a thin glass rod after each
addition. The pump is kept in action all the time, but to keep out dust during the
washing the cover is only removed from the crucible when the fluid is to be added.
Put the vessels containing the precipitate aside, return the washings once through
the asbestos so as to obtain them quite clear, remove them from the receiver, and set
aside to recover the excess of silver. Rinse the receiver and complete the washing of the
precipitate with about 200 cubic centimeters of cold water. Half of this is used to wash
by decantation and the remainder to transfer the precipitate to the crucible with the aid
of a trimmed feather. Finish washing in the crucible, the lumps of silver chlorid being
broken down with a glass rod. Remove the second filtrate from the receiver and pass
about twenty cubic centimeters of ninety-eight per cent alcohol through the precipitate.
Dry at from 140° to 150°. Exposure for half an hour is found more than sufficient, at
this temperature, to dry the precipitate thoroughly.
(b) Standard sulfuric acid, the absolute strength of which has been determined by
precipitation with barium chlorid and weighing the resulting barium sulfate:
For ordinary work half normal acid is recommended, i. e., containing 18.2285
grams of hydrochloric or 24.5185 grams sulfuric acid to the liter; for work in

determining very small amounts of nitrogen, one-tenth normal acid is recommended. In
titrating mineral acids against ammonia solutions, use cochineal as indicator.
(c) Sulfuric acid, specific gravity 1.84, free of nitrates and also of ammonium
sulfate, which is sometimes added in the process of manufacture to destroy nitrogen
oxids:
(2) Standard alkali, the strength of which, relative to the acid, has been accurately
determined. One-tenth normal ammonia solution, i. e., containing 1.7051 grams of
ammonia to the liter, is recommended for accurate work:
(3) Metallic mercury or mercuric oxid, prepared in the wet way: That prepared from
mercuric nitrate can not be safely used.
(4) Potassium permanganate finely pulverized:
(5) Granulated zinc, pumice stone, or one-half gram of zinc dust is to be added to
the contents of the flasks in distillation, when found necessary, in order to prevent
bumping:
(6) Potassium sulfid.—A solution of forty grams of commercial potassium sulfid in
one liter of water:
(7) Soda.—A saturated solution of sodium hydroxid free of nitrates:
(8) Indicator.—Solution of cochineal prepared as follows: Tincture of cochineal is
prepared by digesting for a day or two, at ordinary temperatures, and frequently
agitating, three grams of pulverized cochineal in a mixture of fifty cubic centimeters of
strong alcohol with 200 cubic centimeters of distilled water. The solution is decanted or
filtered through Swedish paper.
Apparatus.—(1) Kjeldahl digestion flasks of hard, moderately thick, well-annealed
glass: These flasks are about twenty-two centimeters long, with a round, pear-shaped
bottom, having a maximum diameter of six centimeters and tapering out gradually in a
long neck, which is two centimeters in diameter at the narrowest part, and flared a little
at the edge. The total capacity is from 225 to 250 cubic centimeters.
(2) Distillation flasks of ordinary shape, of 550 cubic centimeters capacity, or
preferably flasks of well-annealed glass, of the same capacity, of pear-shaped bottom,
for both digestion and distillation, fitted with a rubber stopper and a bulb-tube above to
prevent the possibility of sodium hydroxid being carried over mechanically during
distillation: The bulbs are about three centimeters in diameter, the tubes being of the
same diameter as the condenser and cut off obliquely at the lower end. This is adjusted
to the tube of the condenser by a rubber tube.
Manipulation.—(1) The Digestion.—From seven-tenths to three and five-tenths
grams of the substance to be analyzed, according to its proportion of nitrogen, are
brought into a digestion flask with approximately seven-tenths gram of mercuric oxid
or its equivalent in metallic mercury and twenty cubic centimeters of sulfuric acid. The

flask is placed in an inclined position, and heated below the boiling-point of the acid
for from five to fifteen minutes or until frothing has ceased. If the mixture froth badly,
a small piece of paraffin may be added to prevent it. The heat is then raised until the
acid boils briskly. No further attention is required until the contents of the flask have
become a clear liquid, which is colorless or at least has only a very pale straw color.
The flask is then removed from the frame, held upright, and while still hot, potassium
permanganate is dropped in carefully and in small quantities at a time until, after
shaking, the liquid remains of a green or purple color.
(2) The distillation.—After cooling, the contents of the flask are transferred to the
distilling flask with about 200 cubic centimeters of water, a few pieces of granulated
zinc, pumice stone, or one-half gram of zinc dust when found necessary to keep the
contents of the flask from bumping, and twenty-five cubic centimeters of potassium
sulfid solution are added, shaking the flask to mix its contents. Next add fifty cubic
centimeters of the soda solution, or sufficient to make the reaction strongly alkaline,
pouring it down the sides of the flask so that it does not mix at once with the acid
solution. Connect the flask with the condenser, mix the contents by shaking, and distil
until all ammonia has passed over into the standard acid. The first 150 cubic
centimeters of the distillate will generally contain all the ammonia. This operation
usually requires from forty minutes to one hour and a half. The distillate is then titrated
with standard alkali.
The use of mercuric oxid in this operation greatly shortens the time necessary for
digestion, which is rarely over an hour and a half in case of substances most difficult to
oxidize, and is more commonly less than an hour. In most cases the use of potassium
permanganate is quite unnecessary, but it is believed that in exceptional cases it is
required for complete oxidation, and in view of the uncertainty it is always used. The
potassium sulfid removes all the mercury from the solution, and so prevents the
formation of mercurammonium compounds which are not completely decomposed by
soda solution. The addition of zinc gives rise to an evolution of hydrogen and prevents
violent bumping. Previous to use, the reagents should be tested by a blank experiment
with sugar, which will partially reduce any nitrates that are present, which might
otherwise escape notice.

Figure. 13.
Distilling Apparatus.

185. The Distillation Apparatus in Use in the Laboratory of the Department of
Agriculture.—In this laboratory the distilling apparatus is arranged as shown in Figure
13. The flasks are the same as are used in the digestion. They are connected to the
block tin condensers by the bulb and rubber tubes, shown hanging on the projecting
ends of the block tin condensers on the right and left of the figure. The condensers are
contained in a trough through which cold water flows during the distillation. The bulb
above the flask carries an emergent tube which extends to near the center of the bulb
and is bent laterally to avoid any danger of carrying over any alkali that may be
projected into the bulb during boiling. The boiling is continued usually for nearly an
hour or until bumping begins. The table on which the apparatus is placed is so arranged
as to permit of easy access on all sides. The standard acid is held in erlenmeyers placed
on wooden blocks so that the end of the condenser which is a drawn-out glass tube,
dips beneath the surface of the acid.
186. Patrick’s Distilling Flask.—To avoid the expense and annoyance attending
the breaking of the distilling flasks Patrick has proposed to make them of copper.[154]
The size, about half a liter, made for the evolution of oxygen for experimental
purposes, may be used. A little excess of potassium sulfid is used to make up for any of
it which might be consumed by the copper. About twenty-five cubic centimeters of this
solution are recommended. No zinc or pumice stone is required to prevent bumping

and the distillation may be finished within thirty minutes, thus securing a saving of
time. There will doubtless be a slight corrosion of the flasks by the sulfid employed but
where the gunning oxidation process is practiced this danger would be avoided.
187. Modifications of the Kjeldahl Process.—It would be impracticable here to
give even a summary of the many unimportant changes which the moist combustion
process has undergone since the first papers of its author were published. These
changes may be divided into three classes; viz., 1. Those changes which refer solely to
the quantities of substance taken for analysis, to the composition of the acid mixture, to
the duration of the digestion, to the form and size of the flasks, both for digestion and
distillation, and to the manner of distillation and of titration. For references to the
papers on these subjects the reader may consult the periodic journals.[155] The most
important of these minor changes are the following: Instead of the titration by means of
separated iodin most chemists have had recourse to the simpler method of direct
titration of the excess of acid by a set solution of an alkali. Barium, sodium, and
potassium hydroxids are the alkaline solutions most employed. This process permits of
a larger quantity of the sample being taken for combustion and of the use of a larger
quantity of acid in the receiver. It also implies the use of a larger digestion flask. In fact
it is now quite common to make the digestion in a special glass flask large enough to be
used also for the distillation. This saves one transfer of the material with the possible
danger of loss attending it.
In the distillation it is a common practice, especially in Germany, to do away with
the condensing worm and to carry a long glass tube from the distilling flask directly
into the acid on the receiver. The only inconvenience in this method is the heating of
the contents of the receiving flask, but this is attended with no danger of loss of
ammonia and the distillate, on account of the high temperature it acquires, is left free of
carbon dioxid. Many of these minor changes have tended to simplify the process, but
without affecting the principle of the method in the least.
2. In the second place a class of changes may be mentioned in which there is a
marked difference in the method of effecting the oxidation secured by the introduction
of a substance, usually a metal, during the digestion for the purpose of accelerating the
oxidation. In the original process the only aid to oxidation was applied at the end of the
digestion in the use of potassium permanganate. In the modifications now under
consideration a metallic oxid or metal is applied at the beginning of the digestion.
Copper and mercury are the metals usually employed. A separate paragraph will be
given to the description of this modification known as the process of Wilfarth.
3. The third class of changes is even more radical in its nature, having for its object
the adaptation of the moist combustion method to oxidized or mineral nitrogen. The
chief feature of this class of changes consists in the introduction of a substance rich in
hydrocarbons, and capable of easily forming nitro compounds, for the purpose of
holding the oxids of nitrogen which are formed during the combustion and helping
finally to reduce them to the form of ammonia. The chief varieties of this class of

changes were proposed by Asboth, Jodlbaur, and Scovell, and will be fully set forth in
separate paragraphs.
188. Method of Wilfarth.—The basis of this modification as already noted rests on
the fact that certain metallic oxids have the power of carrying oxygen, and thus
assisting in a katalytic way in the combustion of organic matter.[156] The copper and
mercury oxids are best adapted for this purpose and experience has shown that
mercuric oxid, or even metallic mercury gives the best results. The manipulation is
carried out as follows: From one to three grams of the sample, according to its richness
in nitrogen, are heated with a mixture of twenty cubic centimeters of acid containing
two-fifths fuming and three-fifths ordinary sulfuric acid. To this is added about seven-
tenths gram of mercuric oxid prepared in the wet way from a mercury salt free of
nitrogen. The combustion takes place in the usual kjeldahl flask. If the boiling be
continued until the liquid is entirely colorless, final oxidation with potassium
permanganate is unnecessary. To save time the combustion may be stopped when a
light amber color is reached, and then the oxidation finished with permanganate.
Before distilling, a sufficient quantity of potassium sulfid is added to precipitate all the
mercury as sulfid and thus prevent the formation of mercurammonium compounds
which would produce a deficit of ammonia. A convenient strength of the sulfid solution
is obtained by dissolving forty grams of potassium sulfid in one liter of water. Bumping
at the end of the distillation is not usual, especially if potash-lye be used, but should it
occur it may be stopped by the addition of zinc dust.
Only when a large excess of potassium sulfid is used is there an evolution of
hydrogen sulfid, the presence of which, however, does not influence the accuracy of the
results.
The presence of mercuric sulfid in the solution tends to prevent bumping during the
distillation, but it is advisable, nevertheless, to use a little zinc dust. Other minor
modifications consist of forming the acid mixture with equal volumes of concentrated
and fuming sulfuric acid containing in one liter 100 grams of phosphoric acid anhydrid,
[157]
and using metallic mercury instead of mercuric oxid; or a mixture of half a gram
of copper sulfate and one gram of metallic mercury,[158] or half a gram of copper oxid
and a few drops of platinic chlorid solution containing 0.04 gram of platinum in a cubic
centimeter.[159]
189. Modification of Asboth.—In order to adapt the moist combustion process to
nitric nitrogen Asboth proposed the use of benzoic acid.[160] For half a gram of
saltpeter 1.75 grams of benzoic acid should be used. At the end of the combustion the
residual benzoic acid is oxidized by means of potassium permanganate with a
subsequent reheating. If the nitrogen be present as an oxid or as cyanid, one gram of
sugar is added. The metallic element added is half a gram of copper oxid. Asboth also
recommends that the soda-lye used in the distillation be mixed with sodium potassium
tartrate for the purpose of holding the copper and manganese oxids in solution and thus

preventing bumping. The alkaline liquor contains in one liter 350 grams of the double
tartrate and 300 grams of sodium hydroxid.
The principle on which the use of benzoic acid rests is found in the fact that it
easily yields nitro-compounds and thus prevents the loss of the nitrogen oxids, these
readily combining with the benzoic acid. The nitro-compounds can be subsequently
converted into ammonia by treatment with potassium permanganate.
The pyridin and chinolin groups of bodies do not yield all their nitrogen as
ammonia by the above treatment.
The conclusions drawn by Asboth from the analytical data obtained were:
(1) Sugar should be used in the ordinary kjeldahl process in those cases where the
nitrogen in the organic substance is present as oxids or as cyanogen.
(2) In the case of nitrates good results may be secured with benzoic acid but
permanganate must be added at the end.
(3) The kjeldahl-wilfarth process can be applied with substances difficultly
decomposed, e. g., alkaloidal bodies.
190. Variation of Jodlbaur.—The benzoic acid method, although a step forward, is
not entirely satisfactory in the treatment of nitrates by moist combustion. Jodlbaur has
proposed to substitute for the benzoic, phenolsulfuric acid.[161]
From two to five-tenths gram of a nitrate are treated with twenty cubic centimeters
of concentrated sulfuric and two and a half of phenolsulfuric acid, together with three
grams of zinc dust and five drops of a solution of platinic chlorid of the strength
mentioned above. The phenolsulfuric acid is prepared by dissolving fifty grams of
phenol in 100 cubic centimeters of strong sulfuric acid. The combustion is continued
until the solution is colorless, which may take as much as five hours. If phosphoric acid
anhydrid be used as recommended above, the time of the combustion may be
diminished by one-half, but in such a case the glass of the combustion flask is strongly
attacked and is quite likely to break.
With substances very rich in nitrates it is advisable to rub them first with dry
gypsum.
The theory of the process rests on the fact that by a careful admixture of a
nitrogenous substance diluted with land plaster, with phenolsulfuric acid, it is possible
to change the nitric acid into nitro-phenol, and by the reducing action of zinc dust to
change the nitro-product formed into amido-phenol. This afterwards is transformed into
ammonium sulfate by heating with sulfuric acid, by which process, at the same time, all
other nitrogenous compounds present in the substance, as with Kjeldahl’s method,
likewise form ammonium sulfate, only with the difference that addition of mercury is
here absolutely necessary for the complete transformation of the slowly decomposed
amido-phenol which again brings about the necessity of decomposing the nitrogenous

mercury compounds formed in the solution by potassium sulfid, which is added after or
with the soda-lye.
191. The Dutch Jodlbaur Method.—The Royal Experiment Station of Holland
directs that the jodlbaur process be carried out as indicated below.[162]
The reagents necessary are:
1. Phenolsulfuric acid, prepared by dissolving 100 grams of pure crystallized
phenol in pure sulfuric acid (1.84) and making up the solution to a liter with the same
sulfuric acid:
2. Zinc, carefully washed and thoroughly dried:
3. Sodium hydroxid solution, the same as is used in the kjeldahl method:
4. Potassium sulfid solution, made by dissolving 355 grams of potassium sulfid
(K₂S), or sodium sulfid solution, made by dissolving 250 grams of sodium sulfid
(Na₂S) in a liter of water.
As apparatus, are necessary oxidation flasks holding about 200 cubic centimeters,
and distillation flasks holding about 750 cubic centimeters, both of bohemian glass.
Manipulation.—Weigh one gram of substance, moisten it with water, dry, and
introduce into an oxidation flask. Cover with fifteen cubic centimeters of
phenolsulfuric acid and, after cooling, thoroughly mix by gently shaking. After five
minutes add from two to three grams of zinc in small proportions, keeping the flask
cool, then twenty cubic centimeters of sulfuric acid, and finally two drops of mercury.
Boil the mixture till the fluid is colorless. Cool and dilute. Wash into a distillation flask
and add an excess of sodium hydroxid solution and twenty-five cubic centimeters of
the sodium (or potassium) sulfid solution. Distil and titrate as in the kjeldahl method.
192. The Halle-Jodlbaur Method.—At the Halle station it is the uniform practice
to mix the nitrate with gypsum before the combustion.[163] In the case of Chile
phosphates ten grams are rubbed with an equal amount of gypsum, and two grams of
the mixture, equal to one gram of the nitrate, taken for the determination. In the case of
saltpeter mixtures which contain over eight per cent of nitrogen, one gram of the
mixture with gypsum is taken, of guanos one and a half grams, and of lower forms of
nitrates or mixtures thereof, from three to five grams.
The sample, as prepared above, is treated with thirty cubic centimeters of a mixture
of phenolsulfuric acid and phosphoric acid anhydrid. The mixture is prepared by
dissolving sixty-six grams of phenol and 250 grams of phosphoric anhydrid in strong
sulfuric acid, and, after cooling, mixing the two solutions and making the volume up to
1,650 cubic centimeters with pure sulfuric acid. The mixture contains, in thirty cubic
centimeters, one and two-tenths grams of phenol and four grams of phosphoric
anhydrid. In the use of phenolsulfuric acid the the presence of phosphoric anhydrid is

indispensable in keeping the sulfuric acid water-free and in absorbing the water
produced by the combustion.
The phenolsulfuric acid used contains only enough phenol to reduce half a gram of
saltpeter.
The sample and acid mixture having been put in the combustion flask the latter is
shaken, at intervals, for an hour, and the contents cooled.
The conversion of the nitrates into nitro-phenol compounds is finished in this time,
and the next step consists in reducing these bodies to the amido-phenol group. This is
accomplished in the cold by nascent hydrogen produced by the addition of zinc dust to
the mixture. From one to three grams of the dust are to be used in proportion to the
quantity of nitrates originally present.
The flask should be placed in a cooling mixture and the zinc dust added in small
portions to prevent a too violent evolution of hydrogen. After the reduction is ended the
flask is allowed to stand for two hours, after which the combustion, distillation, and
titration are accomplished in the usual way. On cooling, after the end of the
combustion, the contents of the flask become solid. They may be brought again into
liquid state by shaking and gentle warming.
193. The Official Kjeldahl Method for Nitric Nitrogen.—As has already been
stated, the presence of certain organic compounds, rich in hydrocarbons, permits the
reduction of nitric nitrogen to ammonia by combustion with sulfuric acid. Benzol,
phenol, and salicylic acid have all been used for this purpose. The official chemists
have adopted for their method the salicylic acid process first proposed by Scovell.[164]
Besides the reagents and apparatus given under the Kjeldahl method there will be
needed:
(1) Zinc dust: This should be an impalpable powder; granulated zinc or zinc filings
will not answer.
(2) Sodium thiosulfate:
(3) Commercial salicylic acid:
It is found most convenient to prepare a solution of 33.3 grams of salicylic acid in
one liter of the strongest sulfuric acid, and keep it for use rather than to mix it for each
combustion. We prefer the thiosulfate process first mentioned below. In the zinc dust
method there has been noticed a tendency for the distillation flask to break just at the
end of the process.
The Manipulation.—Place from seven-tenths to three and five-tenths grams of the
substance to be analyzed in a kjeldahl digesting flask, add sixty cubic centimeters of
sulfuric acid containing one gram of salicylic acid, and shake until thoroughly mixed,
then add five grams of crystallized sodium thiosulfate; or add to the substance thirty
cubic centimeters of sulfuric acid containing two grams of salicylic acid, then add

gradually two grams of zinc dust, shaking the contents of the flask at the same time.
Finally place the flask on the stand for holding the digestion flasks, where it is heated
over a low flame until all danger from frothing has passed. The heat is then raised until
the acid boils briskly and the boiling continued until white fumes no longer pour out of
the flask. This requires about five or ten minutes. Add now approximately seven-tenths
gram of mercuric oxid or its equivalent in metallic mercury, and continue the boiling
until the liquid in the flask is colorless or nearly so. In case the contents of the flask are
likely to become solid before this point is reached add ten cubic centimeters more of
sulfuric acid. Complete the oxidation with a little potassium permanganate in the usual
way, and proceed with the distillation as described in the kjeldahl method. The reagents
should be tested by blank experiments.
194. The Gunning Moist Combustion Process.—The modification proposed by
Gunning was based upon the observation that in the ordinary kjeldahl process the
excess of sulfur trioxid in the beginning of the operation soon escapes or unites with
water in a form not easily decomposed.[165] During the progress of the combustion the
acid diminishes in strength until it is below the concentration represented by the
formula H₂SO₄, and in this diluted condition the oxidation takes place more slowly.
Gunning proposes to avoid this difficulty by mixing potassium sulfate with the sulfuric
acid. This salt forms with the sulfuric acid, acid salts which, by heating, lose water
easier than acid and as is well known, they not only act as decomposing and oxidizing
media as well as sulfuric acid, but even in a higher degree, resembling the action of
sulfuric acid at high temperatures and under pressure.
By heating this mixture of sulfuric acid and potassium sulfate with organic matters
in an open vessel, not only the water originally present, but that which is formed during
the oxidation is driven off without loss of acid. For this reason instead of the oxidizing
mixture becoming weaker, the acid becomes stronger, the boiling-point rises and this,
combined with the fluidity of the mass favors the decomposition and oxidation of the
organic matter in a constantly increasing ratio.
The original mixture used by Gunning had the following composition; viz., one part
of potassium sulfate and two parts of strong sulfuric acid. The substances are united by
heat and, on cooling, are in a semi-solid state, melting, however, easily on the
application of heat and assuming a condition to be easily poured from vessel to vessel.
The quantity of the sample taken should vary in proportion to its nitrogenous content
from half a gram to a gram. The combustion takes place in flasks entirely similar to
those used in the ordinary kjeldahl process. In the case of liquids, they should be
previously evaporated to dryness before the addition of the oxidizing mixture. At the
beginning of the combustion there is a violent foaming attended with evolution of some
acid and much water, and afterwards of stronger acid. This loss of acid should not be
allowed to go far enough to produce too great concentration of the material in the flask.
One of the best ways to avoid it is to place a funnel in the flask covered with a watch-
glass which will permit of the condensation and return of the escaping acid. As soon as

the foaming ceases, the flame should be so regulated as to permit of the volatilized acid
being condensed upon the sides of the flask. In the end a colorless mass is obtained in
which no metallic oxids are present, and this mass can at once be diluted with water,
treated with alkali, and distilled. According to the nature of the substance from half an
hour to an hour and a half are required for the complete combustion.
Modifications of the Gunning Method.—As in the case of the kjeldahl method,
numerous minor modifications of the gunning method have been made, the most
important of which relate to its application to substances containing nitrates. In general
the same processes are employed in this case as with the kjeldahl method. One of the
best modifications consists in the use of the mixture of salicylic and sulfuric acids
followed by the addition of sodium thiosulfate or of potassium sulfate or sulfid. These
modifications will be given in detail under the official methods.
195. Reactions of the Gunning Process.—The various reactions which take place
during the combustion according to the gunning method have been tabulated by Van
Slyke.[166]
The first reaction to take place is the union of sulfuric acid and potassium sulfate to
form potassium acid sulfate in accordance with the following equation:
(1) K₂SO₄ + H₂SO₄ = 2KHSO₄.
When heated, the potassium acid sulfate decomposes, forming potassium disulfate and
water, thus:
(2) 2KHSO₄ = K₂S₂O₇ + H₂O.
The potassium disulfate at a higher temperature decomposes, forming normal
potassium sulfate and sulfur trioxid, thus:
(3) K₂S₂O₇ = K₂SO₄ + SO₃.
At a sufficiently high temperature the two preceding reactions may take place in one,
thus:
2KHSO₄ = K₂SO₄ + H₂O + SO₃.
At the temperature at which these reactions take place, the water that is set free
does not recombine with the sulfur trioxid nor with the sulfuric acid that is present in
excess, but is expelled from the mixture; hence the mixture becomes more concentrated
during the digestion. The sulfur trioxid set free acts upon the organic matter in the
powerful manner peculiar to it, and the potassium sulfate formed in the last reaction
above unites with another molecule of sulfuric acid, and the same round of reactions is
repeated continuously so long as there is an excess of free sulfuric acid present in the
mixture. As the liquid becomes more concentrated with the continuation of the
digestion, the boiling-point increases so that the effect is the same as heating under

pressure. The danger of too great concentration and risk of consequent loss of nitrogen
is avoided by using increased proportions of sulfuric acid.
As compared with the kjeldahl the gunning method presents the following
advantages:
(1) The gunning method requires fewer reagents. As no form of mercury is used no
potassium sulfid is needed, and there is no risk of loss from the presence of
mercurammonium compounds.
(2) The solution to which caustic soda is added is clear, so that in neutralizing, it is
an easy matter to avoid great excess of alkali, and so, in most cases, to avoid foaming
and bumping in distillation.
(3) In the blank determinations less nitrogen is found in the reagents used in the
gunning method. In only one case was more nitrogen reported in a blank by this
method; in all the others the amount averaged considerably less.
196. The Official Gunning Method.—In a digestion flask holding from 250 to
500 cubic centimeters place from seven-tenths to two and eight-tenths grams of the
substance to be analyzed, according to its proportion of nitrogen. Then add ten grams
of powdered potassium sulfate and from fifteen to twenty-five cubic centimeters
(ordinarily about twenty cubic centimeters) of concentrated sulfuric acid. Conduct the
digestion as in the kjeldahl process, starting with a temperature below boiling-point and
increasing the heat gradually until frothing ceases. Digest until colorless or nearly so.
Do not add either potassium permanganate or potassium sulfid. Dilute, neutralize, and
distil as in the kjeldahl method. In neutralizing, it is convenient to add a few drops of
phenolphthalein indicator, by which one can tell when the acid is completely
neutralized, remembering that the pink color, which indicates an alkaline reaction, is
destroyed by a considerable excess of strong fixed alkali. The distillation and titration
are conducted as in the kjeldahl method. In distilling, the use of zinc or of any
substance to prevent bumping or foaming is generally unnecessary, if too great an
excess of fixed alkali be avoided. The amount of sulfuric acid recommended by
Gunning is two grams for each gram of potassium sulfate; but Voorhees has found that
this mixture is so viscous as to cause troublesome foaming frequently, and after cooling
it cakes in a hard mass, which may be difficult to redissolve.[167] To avoid foaming and
caking, he has found it an effective means to increase the amount of sulfuric acid used,
taking instead of two grams to one of potassium sulfate three or four grams of acid to
one of potassium sulfate. It is, therefore, suggested in carrying out the work, to use
from five to twenty-five cubic centimeters (ordinarily about twenty cubic centimeters)
of sulfuric acid for ten grams of potassium sulfate. In case the potassium sulfate is not
free from nitrogen compounds, one or two recrystallizations will make it pure.
197. Gunning Method Adapted to Nitrates.—The essential features of this
modification are due to Winton and Voorhees.[168] The modifications of the kjeldahl
method, for similar purposes, furnished the material details for the gunning modified

process. Winton reports good results from digesting for two hours, from half a gram to
a gram of the sample with thirty cubic centimeters of sulfuric containing two grams of
salicylic acid, in a flask of half a liter capacity. Two grams of zinc dust are then slowly
added, with constant shaking, and the flask heated, at first gently, until, after a few
minutes boiling, dense fumes are no longer emitted. Three grams of potassium sulfate
are next added and the boiling continued until the solution is colorless, or if iron be
present, until a light straw color is produced. On cooling, when the mixture begins to
solidify, water is added with caution, and afterwards sodium hydroxid, and the
ammonia is obtained by distillation.
In the process, as conducted by Voorhees, about one gram of the sample is digested
with ten grams of potassium sulfate and thirty cubic centimeters of sulfuric containing
one gram of salicylic acid, and three grains of zinc sulfid. The heat is kept down until
frothing ceases, and then the mass kept in gentle ebullition until clear. The distillation
is accomplished with the usual precautions. The voorhees process is superior to that
recommended by Winton in adding the potassium sulfate at the beginning of the
combustion.
198. Official Gunning Method Modified to Include the Nitrogen of Nitrates.—
In a digestion flask holding from 250 to 500 cubic centimeters, place from seven-tenths
to three and five-tenths grams of the substance to be analyzed, according to the amount
of nitrogen present. Add from thirty to thirty-five cubic centimeters of salicylic acid
mixture, namely, thirty cubic centimeters of sulfuric to one gram of salicylic acid,
shake until thoroughly mixed, and allow to stand from five to ten minutes, with
frequent shaking; then add five grams of sodium thiosulfate and ten grams of potassium
sulfate. Heat very gently until frothing ceases, then strongly until nearly colorless.
Dilute, neutralize, and distil the same as in the gunning method.

DETERMINATION OF NITROGEN IN
DEFINITE FORMS OF COMBINATION.

199. Introductory Considerations.—In the foregoing pages has been given a
summary of the methods most in vogue for the estimation of nitrogen in fertilizers and
fertilizing materials. There are many cases in which the analyst may have to deal with a
definite chemical compound, and where a modified or shorter method may be used.
There are other cases in which the nitrogen may be present in two or three definite
forms, as in artificially mixed fertilizers, and where it is desirable to show the
proportions in which the various forms are present. For these reasons it is necessary to
be able to use methods by which the percentage of nitrogen in its various forms may be
relatively as well as absolutely determined. Such a case would be presented for
instance, in that of a fertilizer containing dried blood, sodium nitrate, and ammonium
sulfate. It is evident here that the total nitrogen could be determined by the volumetric
method by combustion with copper oxid, or by the moist combustion process adapted

to nitric nitrogen, but the method of determining the percentage of each constituent has
not yet been described.
We have to deal here with a case entirely similar to that of phosphoric acid in a
superphosphate. There is no doubt whatever of the uneven assimilability of the
different forms of nitrogen. A nitrate, for instance, is already in condition for
assimilation by plants. An ammoniacal salt is only partly changed to a state suited to
plant nutrition while organic nitrogen is forced to undergo a complete transformation
before it becomes available to supply the needs of the growing plant. It is important,
therefore, equally to the analyst, the merchant, and the agronomist, to know definitely
the forms of combination in which the nitrogen exists and the relative proportion of the
different combinations.
200. Nitrogen as Ammonia.—The most frequent form in which nitrogen as
ammonia is used for fertilizing is as sulfate. The method of determination to be
described is, however, equally applicable to all ammonia salts. When no other form of
nitrogenous compound is present the ammonia can be easily and directly determined by
distillation with soda- or potash-lye, as described in the final part of the moist
combustion process.
To one gram of the ammonia salt add from 200 to 300 cubic centimeters of water
and thirty grams of the soda-lye used in the moist combustion process; distil, collect the
ammonia, and titrate the excess of sulfuric acid exactly as there described.
Fresenius recommends that the ammonia expelled by distillation be taken up by
one-fifth normal sulfuric acid, the excess of which is titrated with one-fifth normal
soda, using phenolphthalein as an indicator. If the distillate, on examination, be found
to contain thiocyanate, soda-lye cannot be used for the expulsion of ammonia, but, in
its place, caustic magnesia is applied.
In all cases where organic matter containing nitrogen is present, caustic magnesia
must be substituted for the soda solution. The magnesia must be added in sufficient
excess and the distillation continued a little longer than is necessary when soda-lye is
used. Otherwise the details of the operation are the same.
In a mixed fertilizer containing organic nitrogen and ammonia salts, the total
nitrogen can be determined by the moist combustion process, and the ammoniacal
nitrogen by distillation with magnesia. The difference between the two results will give
the nitrogen due to the organic matter.
To avoid any danger whatever of decomposing organic nitrogenous compounds, the
ammonia may be determined in the cold by treatment with soda-lye, under a bell-jar
containing some set sulfuric acid. The operation must be allowed to continue for many
days. Even at the end of a long time it will be found that some ammonia is still
escaping. It may therefore be finally inferred that all the nitrogen as ammonia is not
obtained by this process, or that even magnesia may gradually convert other

nitrogenous compounds into ammonia. In this connection the methods of determining
ammonia in soils 406, 407, and 408 of volume one may be consulted.
201. Method of Boussingault.—The official French method is essentially the
original method of Boussingault with slight modifications. It is conducted as follows:
[169]
In case the sample is ammonium sulfate about half a gram is placed in a flask of
half a liter capacity, together with 300 cubic centimeters of distilled water and two
grams of caustic magnesia. The flask is connected with a condenser of glass or metal
which ends in a tube drawn out to a point and dipping beneath the set acid in the
receiver in the usual way. The acid is colored with litmus or lacmoid tincture. The
distillation is continued until about 100 cubic centimeters have gone over. The receiver
is then removed with the usual precautions and the residual acid titrated. Suppose
twenty cubic centimeters of normal acid have been employed and twelve and a half
cubic centimeters of normal alkali be necessary to neutralize the excess of the acid.
Then the nitrogen is found by the following equations: 20.0 - 12.5 = 7.5 and 7.5 ×
0.014 = 0.105 gram = weight of nitrogen found. Then 0.105 × 100 ÷ 5 = 21.00 = per
cent of nitrogen found.
The distilling apparatus of Aubin is preferred by the French chemists, an apparatus
so arranged with a reflux partial condenser, that nearly all the aqueous vapor is returned
in a condensed state to the flask while the ammonia, on account of its great volatility, is
carried over into the receiver. To avoid the regurgitation which might be caused by the
concentrated ammonia gas coming in contact with the acid the separable part of the
condensing tube is expanded into a bulb large enough to hold all the acid which lies
above its mouth. By the means of this apparatus the ammonia is all collected in the
standard acid without greatly increasing its volume and the titration is thus rendered
sharper. The employment of caustic magnesia has the advantage of not decomposing
any organic matters or cyanids that may be present.
If the sample under examination hold part of its ammonia as ammonium
magnesium phosphate it will be necessary first to treat it with sulfuric acid in order to
set the ammonia free and then to use enough of the magnesium oxid to neutralize the
excess of the sulfuric acid and still supply the two grams necessary for the distillation.
When the sample contains a considerable quantity of organic matter it sometimes tends
to become frothy towards the end of the distillation. This trouble can be avoided by
introducing into the flask one or two grams of paraffin.
Where carbon dioxid is given off during the distillation the contents of the receiver
must be boiled before titration, or else lacmoid must be used as an indicator instead of
litmus.
202. Determination of Thiocyanates in Ammoniacal Fertilizers.—The extended
use of ammonium sulfate as a fertilizer renders it important to determine the actual
constituents which may be present in samples of this material. The following bodies
have been found in commercial ammonium sulfates: Sulfuric acid, chlorin, ammonia,

thiocyanic acid, potash, soda, lime and iron oxid. These are found in the soluble
portions. In the insoluble portions have been found silica, sulfuric acid, lime, magnesia
and iron oxid. A sample of commercial ammonium sulfate analyzed by Jumeau
contained the following substances:[170]
Per cent.
Moisture 10.5109
Ammonium sulfate 67.8453
Ammonium thiocyanate 9.3935
Sodium sulfate 9.2429
Potassium sulfate 0.9774
Calcium sulfate 0.6800
Iron thiocyanate 0.5000
Magnesium chlorid traces
Silica 0.0830
Undetermined 0.7670
The determination of the thiocyanic acid in the thiocyanate is generally made by the
oxidation of the sulfur to sulfuric acid and its subsequent weighing in the form of
barium sulfate. Jumeau has modified the method by determining the amount of the
thiocyanate by means of a titrated liquid. The method is practiced as follows:
A solution of ammonium thiocyanate is prepared, containing eight grams of this salt
per liter, and its exact content of thiocyanate is rigorously determined by titration with
silver nitrate or by the weight of the barium sulfate produced after the oxidation of the
sulfur. Ten cubic centimeters of the titrated liquor are taken and diluted with water to
about 100 cubic centimeters and ten cubic centimeters of pure sulfuric acid added.
Afterward, drop by drop, a solution of potassium permanganate is added, containing
about ten grams of that salt per liter. The permanganate is instantly decolorized. There
is an evolution of hydrocyanic acid as the thiocyanate passes to the state of sulfuric
acid. A single drop in excess gives to the mixture the well-known rose coloration of the
permanganate solution which persists for several hours. The number of cubic
centimeters necessary to produce the persistent rose tint is noted and the same
operation is carried on with from one-half to one gram of the unknown product which
is to be assayed. A simple proportion indicates the content of the thiocyanate in the
unknown body. The process is of great exactitude and permits the rapid determination
of thiocyanic acid in the presence of chlorids, cyanids, etc., which remain without
action upon the permanganate. In case chlorids and cyanids are absent the thiocyanate
can be determined directly by silver nitrate either by weighing the precipitate or by the
process of Volhardt based upon the precipitation of the silver by thiocyanate in the
presence of a ferric salt. The end of the reaction is indicated by the red coloration
which the liquid shows when the thiocyanate is in excess.
203. Separation of Albuminoid from Amid and Other Forms of Nitrogen in
Organic Fertilizers.—It may be of interest to the dealer, farmer, and analyst, to

discriminate between the albuminoid and other nitrogen in fertilizers, such as oil-cakes.
The final value of the nitrogen for plant nourishment is not greatly different, but the
immediate availability for nitrification is a matter of some importance. The most
convenient process in such a case is the copper hydroxid separation process as
improved by Stutzer.[171] The process is conveniently carried out in accordance with
the method prescribed by the official chemists.[172]
Total Crude Protein.—Determine nitrogen as directed for nitrogen in fertilizers and
multiply the result by 6.25 for the crude protein.
Determination of Albuminoid Nitrogen.—To from seven-tenths to eight-tenths gram
of the substance in a beaker add 100 cubic centimeters of water, heat to boiling, or in
the case of substances rich in starch, heat on the water-bath ten minutes, and add a
quantity of cupric hydroxid mixture containing from one-half to six-tenths gram of the
hydroxid; stir thoroughly, filter when cold, wash with cold water, and put the filter and
its contents into the concentrated sulfuric acid for the determination of nitrogen. The
filter-papers used must be practically free of nitrogen. Add sufficient potassium sulfid
solution to completely precipitate all copper and mercury, and proceed as in the moist
combustion process for nitrogen. If the substance examined consist of seed of any kind,
or residues of seeds, such as oil-cake or anything else rich in alkaline phosphates, add a
few cubic centimeters of a concentrated solution of alum just before adding the cupric
hydroxid, and mix well by stirring. This serves to decompose the alkaline phosphates.
If this be not done cupric phosphate and free alkali may be formed, and the protein-
copper may be partially dissolved in the alkaline liquid.
Cupric Hydroxid.—Prepare the cupric hydroxid as follows: Dissolve 100 grams of
pure cupric sulfate in five liters of water, and add twenty-five cubic centimeters of
glycerol; add a dilute solution of sodium hydroxid until the liquid is alkaline; filter, rub
the precipitate up with water containing five cubic centimeters of glycerol per liter, and
then wash by decantation or filtration until the washings are no longer alkaline. Rub the
precipitate up again in a mortar with water containing ten per cent of glycerol, thus
preparing a uniform gelatinous mass that can be measured out with a pipette.
Determine the quantity of cupric hydroxid per cubic centimeter of this mixture.
Amid Nitrogen.—The albuminoid nitrogen determined as above subtracted from the
total, gives that part of the organic nitrogen existing in the sample as amids and in other
allied forms.
204. Separation of Nitric and Ammoniacal from Organic Nitrogen.—The
nitrogen being present in three forms, viz., organic, ammoniacal, and nitric, the
separation of the latter two may be accomplished by the following procedure:[173] One
gram of the fertilizer is exhausted on a small filter with a two per cent solution of
tannin, using from thirty to forty cubic centimeters in small portions. This is sufficient
to dissolve all the nitrates and the greater portion of the ammoniacal salts, while the
tannin renders insoluble all the organic nitrogenous compounds. The filter and its

contents are treated for nitrogen by the kjeldahl process. When the distillation and
titration are completed the solution obtained by the aqueous tannin is added to the
distilling flask and the operation continued. This represents the ammoniacal nitrogen.
The nitric acid is estimated by the ferrous iron or other appropriate method in
another portion of the substance.
This method can be used even when the fertilizer contains ammonium magnesium
phosphate. In this case digest one gram for fifteen hours in dilute soda-lye solution,
which easily dissolves the ammonium magnesium phosphate. Filter and wash the
insoluble part with the tannin solution. The residue is treated as above. The filtered
solution distilled with soda-lye furnishes the ammonia. The nitrates are estimated by
one of the methods above mentioned.
205. Nitric Nitrogen.—The methods of estimating nitric nitrogen, both when
present in weighable quantities and as mere traces have been sufficiently described in
the first volume. For convenience, however, the standard methods of procedure will be
given here. The moist combustion methods adapted to nitrates and the volumetric
copper oxid process have already been described. Of the reduction methods the process
of Ulsch is one of the easiest of application and also reliable. As practiced by the
official chemists the manipulation is conducted as described in the first volume, page
539.
206. Ulsch Method, Applicable to Mixed Fertilizers.—The method of Ulsch
which is found to give good results with pure nitrates or with nitrates in the absence of
other forms of nitrogen may also be adapted to mixed fertilizers containing nitrogen in
more than one form. Street has developed such a method and shown, by analytical data,
that it is applicable in a great number of cases.[174] The process is based on the
substitution of magnesia for soda in the distillation and is carried on as follows:
Place one gram of the sample in a half liter flat-bottomed flask. Add about thirty
cubic centimeters of water, one gram of reduced iron, and ten cubic centimeters of
sulfuric acid diluted with an equal volume of water, shake well, and allow to stand for a
short time. This will remove the danger of an explosion caused by the otherwise violent
action which takes place. Close the neck of the flask with a rubber stopper through
which passes a glass dropping-bulb filled with water. The flask having been stoppered,
place it on a slab to which a moderate heat is applied. Allow the solution to come
slowly to a boil and then boil for five minutes and cool. Add about 100 cubic
centimeters of water, a little paraffin, and about five grams of magnesium oxid. Boil for
forty minutes, after which time all the ammonia will be distilled, and collect the
ammonia in set acid.
The magnesia causes a slight frothing, which can easily be controlled by adding a
little paraffin and by bringing to a boil very gradually. Fully forty minutes are
necessary to distil all the ammonia. Tests were made after thirty minutes boiling and

traces of ammonia were still found; after forty minutes these traces entirely
disappeared.
The method is a quick one. One man can easily do six determinations at a time, and
these six determinations can be made in but a little over an hour. Magnesia gives results
closely agreeing with theory and causes a very slight frothing, which can be easily
controlled. One gram of reduced iron is sufficient in all ordinary complete fertilizers.
Magnesia is preferred to caustic soda in the distillation because it produces less
frothing and by reason of the danger of some of the soda-lye being carried over
mechanically and thus tending to produce an error of a plus nature. In the use of
magnesia, assurance must be had that it is strongly in excess. Being less active in its
effects a longer time for the distillation must be taken than when soda-lye is used. The
modified ulsch method just described is recommended provisionally and with the
expectation that each analyst will ascertain its true merits before allowing it to displace
longer approved processes.
207. Method of Schlösing-Wagner.—The Schlösing-Wagner method for
estimating nitrogen in the nitrates of fertilizers is carried out at the Halle Experiment
Station as follows:[175]
A flask, figure 14, of about 250 cubic centimeters capacity, is provided with a
rubber stopper with two holes. Through one of them is passed the stem of a funnel
carrying a glass stop-cock. The other carries a delivery-tube leading to the receiving
vessel. The end of the delivery tube is bent so as to pass easily under the mouth of the
measuring burette and is covered with a piece of rubber tubing.
Fifty cubic centimeters of saturated ferrous chlorid solution and the same quantity
of ten per cent hydrochloric acid are placed in the flask. The ferrous chlorid solution is
obtained by dissolving nails or other small pieces of iron in hot hydrochloric acid and it
is kept in glass stoppered flasks, of about fifty cubic centimeters capacity, entirely
filled. The content of one flask is enough for about twelve determinations and by using
the whole content of a flask as soon as possible after opening, any danger of oxidation
which would take place in a large flask frequently opened is avoided.

Figure. 14.
Schlösing-Wagner Apparatus.

The contents of the flask are boiled until all the air is driven off. The
delivery-tube is then placed under the measuring-tube, which is filled with
forty per cent potash-lye. The measuring-tube is previously almost filled
with potash-lye and then a few drops of water added and the tube covered
with a piece of filter-paper. By a careful and quick inversion the measuring-
tube can be brought into the vessel receiving it without any danger of air
entering. The boiling is continued for some time and when no more air
escapes, the end of the delivery-tube is brought into another freshly filled
measuring-tube and the estimation is commenced.
Ten cubic centimeters of a normal saltpeter solution, containing two and
a half grams of pure sodium nitrate in 100 cubic centimeters are placed in
the funnel and, with continued boiling, allowed to pass, drop by drop, into
the flask. When almost all has run out the funnel is washed three times with
ten cubic centimeters of ten per cent hydrochloric acid and this is allowed to
pass, drop by drop, into the flask. When no more nitric oxid is evolved the
measuring-tube is transferred to a large jar filled with distilled water.

The solution of the substance to be examined should be taken in such
quantity as will give about the same quantity of gas as is furnished by the
ten cubic centimeters test nitrate solution before described; viz., about
seventy cubic centimeters. Eight or ten determinations can be made, one
following the other, and at the end another determination with normal
sodium nitrate solution should be made as a check. At the end of the
operation all of the measuring-tubes are in the large jar filled with distilled
water. The temperature of the surrounding water will soon be imparted to
the contents of each tube and the volume of nitric oxid is read by bringing
the level within and without the measuring-tube to the same point. The
percentages are calculated for the given temperature and barometer pressure
in the usual way; or to avoid computation the volume can be compared
directly with the volume furnished by a normal nitrate solution, which is a
much simpler method.
208. Schmitt’s Modified Method.—The method is a modification of
that already described by the author in which a mixture of powdered zinc
and iron is used as a reducing agent.[176] The process is carried out as
follows: Ten grams of the nitrate are dissolved and the volume made up to
half a liter. Ten cubic centimeters of glacial acetic acid and ten grams of the
fine metallic powder, iron and zinc, are placed in a flask of a capacity of
about three-quarters of a liter and twenty-five cubic centimeters of the
solution of the nitrate added. The flask is covered during the reduction to
prevent loss by spraying, and after the solution is complete, which is the
case in about ten minutes, the contents of the flask are diluted with from
200 to 300 cubic centimeters of water, thirty cubic centimeters of caustic
soda of 1.25 specific gravity added, and the whole distilled as in the
kjeldahl process. It must be noted that it is essential that the iron be finely
divided; it is mixed with the powdered zinc in equal parts. The total
nitrogen can be determined in guanos and nitrate mixtures by the following
simple alteration in procedure: One gram of the substance is dissolved in
water, five cubic centimeters of glacial acetic acid, and from two to three
grams of the mixed metallic powder added, and the whole gently heated for
ten or fifteen minutes. After the contents of the flask have cooled, twenty-
five cubic centimeters of sulfuric acid are cautiously added in small
portions, undue frothing being restrained by the addition of a fragment of
paraffin wax. The acetic acid is then driven off by heating, and the
remaining contents of the flask boiled until the organic matter is completely

decomposed, as in the kjeldahl process. About two hours boiling is
required. Neutralization and distillation are then practiced as in the ordinary
manner. The method is also applicable to the determination of nitrates in
drinking water, provided nitrites and ammonia be absent.
209. Krüger’s Method for Nitric Acid.—About three-tenths gram of
the substance dissolved in water is mixed with twenty cubic centimeters of
a hydrochloric acid solution of stannous chlorid holding 150 grams of tin
per liter.[177] One and a half grams of spongy tin prepared by the action of
zinc on stannous chlorid are added. The flask containing the mixture is
heated until the tin is dissolved, by which time the nitric acid is completely
reduced. The subsequent distillation and titration are accomplished as usual.
In the case of nitro and nitroso compounds, after the solution of the tin,
twenty cubic centimeters of sulfuric acid are added and heated until sulfuric
vapors escape. After cooling, the amido substances formed are oxidized by
potassium bichromate before the distillation takes place.
Krüger also estimates the nitrogen in benzol, pyridin, and chinolin
derivatives by dissolving them in sulfuric acid, using from two-tenths to
eight-tenths of a gram of the alkaloidal bodies and, after cooling the
solution, oxidizing by adding finely powdered potassium bichromate.[178]
About half a gram more of the potassium bichromate should be used than is
necessary for the oxidation of the substances in solution. The entire
oxidation does not consume more than from fifteen to thirty minutes.

SODIUM NITRATE.

210. Functions of Sodium Nitrate.—Practically the only form of
oxidized nitrogen which is of importance from an agronomic point of view
is sodium nitrate, often known in commerce by the name Chile saltpeter.
Applied to a growing crop it at once becomes dissolved at the first rainfall
or by the natural moisture of the soil. It carries thus to the rootlets of plants
a supply of nitrogen in the most highly available state. There is perhaps no
other kind of plant food which is offered to the living vegetable in a more
completely predigested state, and none to which a quicker response will be
given. By reason of its high availability, however, it must be used with care.
A too free use of such a stimulating food may have, in the end, an injurious
effect upon the crop, and is quite certain to lead to the waste of a

considerable portion of expensive material. For this reason sodium nitrate
should be applied with extreme care, in small quantities at a time and only
when it is needed by the growing crop. It would be useless, for instance, to
apply this fertilizer in the autumn with the expectation of its benefitting the
crop to a maximum degree the following spring. Again, if the application of
this salt should be made just previous to a heavy rain almost or quite the
whole of it would be removed beyond the reach of the absorbing organs of
the plant.
When once the nitric acid has been absorbed by the living rootlet it is
held with great tenacity. Living plants macerated in water give up only a
trace of nitric acid, but if they be previously killed with chloroform the
nitric acid they contain is easily leached out.
The molecule of sodium nitrate is decomposed in the process of the
absorption of the nitric acid. The acid enters the plant organism and the
soda is excreted and left to combine with the soil acids. The nascent soda
may thus play a role of some importance in decomposing particles of
minerals containing potash or phosphoric acid. It is probable that the
decomposition of the sodium nitrate takes place in the cells of the absorbing
plant organs for it is difficult to understand how it could be accomplished
externally. While the soda therefore is of no importance as a direct plant
food it can hardly be dismissed as of no value whatever in the process of
fertilization. Many of the salts of soda as, for instance, common salt, are
quite hygroscopic and serve to attract moisture from the air and thus
become carriers of water between the plant and the air in seasons of
drought; and sodium nitrate itself is so hygroscopic as not to be suited to the
manufacture of gunpowder.
To recapitulate: The chief functions of sodium nitrate are to give to the
plant a supply of oxidized nitrogen ready for absorption into its tissues and
incidentally to aid, by the residual soda, in the decomposition of silt
particles containing potash or phosphoric acid and in supplying to the soil
salts of a more or less deliquescent nature.
211. Commercial Forms of Chile Saltpeter.—The Chile saltpeter of
commerce may reach the farmer or analyst in the lumpy state in which it is
shipped or as finely ground and ready for application to the fields. Unless
the farmer is provided with means for grinding, the latter condition is much

to be preferred. It permits of a more even distribution of the salt and thus
encourages economy in its use. For the chemist also it is advantageous to
have the finely ground material, which condition permits more easily a
perfect sampling, a process which, with the unground salt, is attended with
no little difficulty.
212. Percentage of Nitrogen in Chile Saltpeter.—Chemically pure
sodium nitrate contains 16.49 per cent of nitrogen. The salt of commerce is
never pure. It contains moisture, potash, magnesia, lime, sulfur, chlorin,
iodin, silica and insoluble materials, and traces of other bodies. The value of
the salt depends, therefore, not only on the market value of nitrogen at the
time of sale, but also on its content of nitrogen. The nitrate of commerce
varies greatly in its nitrogen content and is sold on a guaranty of its purity.
The best grades range in nitrogen from fifteen to sixteen per cent. The
content of nitrogen has long been estimated in the trade by determining the
other constituents and counting the rest as nitrogen. This practice arose in
former times when no convenient method was at hand for determining nitric
nitrogen. The process is tiresome and unreliable because all errors of every
kind are accumulated in the nitrogen content, but inasmuch as the method is
still required by many merchants, the analyst should be acquainted with it,
and it is therefore given further along. The usual methods for determining
nitric nitrogen may be applied in all cases where samples of sodium nitrate
are under examination, but some special processes are added for
convenience.
213. Adulteration of Chile Saltpeter.—The analyst is the only
protector of the farmer in guarding against the practice of adulteration of
sodium nitrate aside from the honesty of the dealer. Even the honest dealer
is compelled to protect himself against fraud, and therefore, the world over,
commerce in this fertilizer is now conducted solely on the analyst’s
certificate. Happily, therefore, adulteration is almost unknown because it is
certain to be detected. Formerly, the saltpeter was adulterated with common
salt, or low grade salts from the potash mines; but it is an extremely rare
thing now to find any impurities in the salts other than those naturally
present.
In every case the analyst may grow suspicious when he finds the
content of nitrogen in a sample to fall below thirteen per cent. It must not be
forgotten, however, that some potassium nitrate may be present in the

sample, and since that salt contains only 13.87 per cent of nitrogen its
presence would tend to lower the value of the fertilizer; but although the
potash itself is a fertilizer of value it is not worth more than one-third as
much as nitrogen. In all cases of suspected adulteration, it is advisable to
make a complete analysis. The results of this work will, as a rule, lead the
analyst to a correct judgment.

Figure. 15.
Halle Nitric Acid Apparatus.

214. The Halle Zinc-Iron Method.—For determining the nitrogen in
Chile saltpeter the reduction method is conducted at the Halle Station as
follows:[179] Ten grams of the nitrate are dissolved in one liter and fifty
cubic centimeters of the solution corresponding to half a gram of the
sample, taken for each determination. The apparatus employed is shown in
Fig. 15. A mixture of five grams of zinc dust and an equal weight of iron
filings is employed as the source of hydrogen. The reduction takes place in
an alkaline medium secured by adding to the other materials mentioned,
eighty cubic centimeters of soda-lye of 1.30 specific gravity. The respective
quantities of iron and zinc may be measured instead of weighed, as exact

proportions are not required. After the addition of all the materials the flask
is allowed to stand for an hour at room temperature. The distillation is then
commenced and continued until at least 100 cubic centimeters of distillate
have been collected. The receiving flasks are ordinary erlenmeyers, each of
which contains twenty cubic centimeters of set sulfuric acid, as in the usual
kjeldahl process. The flasks are sealed with a few drops of water by the
device shown in the figure. After the end of the operation the water in each
one is washed back into its proper flask with freshly boiled water. During
the vigorous evolution of hydrogen, at the beginning of the operation, some
kind of a safety arrangement is necessary to prevent the particles of soda-
lye being carried over by the bubbles of that gas. The siphon bulb shown in
the figure is found effective for this purpose. In this operation better results
are obtained by condensing the escaping steam, and for this reason the
block tin tubes are conducted through a tank supplied with a current of cold
water. The ends of the tubes should not dip below the surface of the liquid
in the receivers. When the condensed liquid collects in considerable
quantities in the safety tube the lamp should be extinguished under the
flask, which permits the return of the liquid to the flask by means of the
siphon. This should be done two or three times during the progress of the
distillation to prevent a too high concentration of the soda-lye, thus
endangering the flask. The excess of the acid in the receiver is determined
by titration, as in the regular kjeldahl method. Blank determinations should
be made, from time to time, and corrections made in harmony therewith.
215. Method of the French Sugar Chemists.—The nitrogen in Chile
saltpeter is estimated by the French chemists according to the method of
Schlösing, described in the first volume, page 500. In order to avoid the
trouble of calculating the results from the volume of nitric oxid obtained, a
determination is first made with a pure salt, sodium or potassium nitrate.
The volume of gas obtained is read directly without correction and taken for
direct comparison. The comparison is made as follows:
The solutions of the pure salts and of the sample to be analyzed are
made of such a strength as to contain sixty-six grams of sodium nitrate, or
eighty grams of potassium nitrate, in a liter. Five cubic centimeters of such
a solution will yield a little less than 100 cubic centimeters of nitric oxid
under usual conditions. Let the volume of gas obtained with the pure salt be

v; and that with the sample be v′. The calculation is then made from the
equation:
v′ x
=
v 100

Example: Let ninety-five cubic centimeters be the
volume of gas from five cubic centimeters of the pure salt
(sodium nitrate), and 91.5 cubic centimeters be the
volume of gas from five cubic centimeters of the sample;
then
91.5 x
= , whence x = 96.31.
95 100
Hence the sample analyzed contains 96.31 per cent of
sodium nitrate. Since the pure sodium nitrate contains
16.47 per cent of nitrogen the sample under examination
would contain
16.47 × 96.31
= 15.86 per cent.
100

It is evident that this comparative method is quite easy of application
when the sample under examination has no other nitrate in it except that
combined with the one base.
216. Volumetric Method of Gantter.—The process proposed by
Gantter for determining the nitrogen, volumetrically, in Chile saltpeter and
other nitrates is based on the following principles:[180]
(1) If a nitrate be heated in contact with sulfuric and phosphorous acids,
nitrous acid will be formed.
(2) If nitrous acid be boiled with ammonium chlorid, nitrogen will be
quantitatively evolved from both compounds. These processes are
illustrated by the following formulas:
(a) N₂O₅ + P₂O₃ = N₂O₃ + P₂O₅.
(b) N₂O₃ + 2NH₄Cl = 2N₂ + 3H₂O + 2HCl.

Figure. 16.
Gantter’s Nitrogen Apparatus.

It is seen from the above that the nitrate will give, by this treatment,
double the volume of nitrogen which it contains. In practice, the two
reactions may be secured in one operation by warming the nitrate solution
slowly with sulfuric and phosphorous acids and ammonium chlorid. The
nitric acid, as it becomes free, gives a part of its oxygen to the phosphorous
compound, and the nitrous acid, in a nascent state, is at once reduced by the
ammonium chlorid. There are two sources of error which must be guarded
against in the work; a portion of the nitrogen may escape reduction to the
elementary state, or some of the nitrate may fail to be decomposed. These
errors are easily avoided if the reaction be begun slowly, so that the
evolution of gas may be gradual. The temperatures at first should, therefore,
be kept as low as possible. The development of red fumes, showing the
presence of undecomposed nitrogen oxids, shows that the results will be too
low. It is necessary, also, to provide for the absorption of the hydrochloric
acid which is formed. The reaction is very conveniently conducted in the
apparatus shown in Fig. 16. The decomposition takes place in the flask A

and the mixed gases pass into the absorption bulb C. The delivery-tube is
very much expanded, as shown in the figure, so that no soda-lye can enter A
during the cooling of the flask. The absorption bulb is connected with A and
B by the tubes a and b as shown. The tube d connects the apparatus with the
gasvolumeter.[181] The bulb B serves as a pipette for the introduction of the
decomposing acid. The operation is conducted as follows: Three cubic
centimeters of the nitrate solution, containing no more than 300 milligrams
of substance, are placed in the flask A with half a gram each of crystallized
ammonium chlorid and phosphorous acid. In the bulb B are placed seven
cubic centimeters of sulfuric acid to which has been added one-third its
volume of water. Two cubic centimeters of acid are allowed to flow from B
into A. The apparatus is brought to a constant temperature by being
immersed in a large cylinder, E, containing water at a temperature which
can easily be controlled. When this constant temperature has been reached
the apparatus is taken from the cooling cylinder which contains also a
smaller cylinder, D, nearly filled with water and connected through f′ with
the measuring apparatus M. The barometer-tube F is half filled with colored
water so that the pressure may be equalized before and after the operation.
The flask A is warmed very gently at first, and the nitrogen evolved is
conducted into D driving an equivalent volume of water into M. The
evolution of the gas must be carefully controlled and the heat at once
removed if it become too rapid. The appearance of a red color shows the
evolution of oxids of nitrogen rendering the analysis inexact. When the
evolution of nitrogen has nearly ceased the lamp is removed and some more
sulfuric acid allowed to flow into A from B, after which A is again heated,
this time to the boiling-point. All vapors of hydrochloric acid produced are
absorbed by the soda-lye in C. The boiling is continued a few minutes, but
not long enough to darken the liquid in A. After replacing the apparatus in
the cylinder E and bringing both temperature and pressure to the same point
as before the beginning of the operation, the volume of nitrogen evolved is
determined by measuring the water in M.
The apparatus is first set by using pure potassium or sodium nitrate.
Since the temperature and pressure do not vary much within an hour or two
the volume of water obtained with a sample of white saltpeter can be
compared directly with that given off by the same weight of a pure
potassium or sodium nitrate without correction.

Example.—Two hundred and fifty milligrams of potassium nitrate,
containing 34.625 milligrams of nitrogen, displaced in a given case sixty
cubic centimeters of water; therefore one cubic centimeter of water equals
0.578 milligram of nitrogen. If 289 instead of 250 milligrams be taken then
the number of cubic centimeters of water displaced divided by five will
give the per cent of nitrogen.
217. Method of Difference.—In the analysis of Chile saltpeter by the
direct method a variation of 0.25 per cent in the content of nitrogen is
allowed from the dealers’ guaranty. This would allow a total variation in the
content of sodium nitrate of 1.52 per cent. Dealers and shippers have
always been accustomed to estimate the quantity of sodium nitrate in a
sample by difference; i. e., by estimating the constituents not sodium nitrate
and subtracting the sum of the results from 100. Chile saltpeter usually
contains sodium nitrate, water, insoluble ferruginous matters, sodium
chlorid, sodium sulfate, magnesium chlorid, sodium iodate, calcium sulfate
and sometimes small quantities of potassium nitrate.
When the total sodium nitrate is to be estimated by difference the
following procedure, arranged by Crispo,[182] may be followed:
Water.—Dry ten grams of the finely powdered sample to constant
weight at 150°-160°.
Chlorin.—The residue, after drying, is dissolved and the volume made
up to one-fourth liter with water and the chlorin determined in one-fifth
thereof and calculated as sodium chlorid.
Insoluble.—Twenty grams are treated with water until all soluble matter
has disappeared, filtered on a tared gooch, and the filtrate dried to constant
weight.
Sulfuric Acid.—The sulfuric acid is precipitated by barium chlorid in
the slightly acid filtrate from the insoluble matter. The acidity is produced
by a few drops of nitric acid. The rest of the process is conducted in the
usual way.
Magnesia.—This is precipitated by ammonium sodium phosphate,
filtered, ignited, and weighed as pyrophosphate. The magnesium is then
calculated as chlorid. Magnesia is rarely found in excess of one-fourth per
cent. When this amount is not exceeded the estimation of it may be

neglected without any great error. As has already been said the chlorin is all
calculated as sodium chlorid. If a part of it be combined with one-fourth per
cent of magnesia it would represent 0.59 per cent of magnesium chlorid
instead of 0.73 per cent sodium chlorid. In omitting the estimation of the
magnesia therefore the importer is only damaged to the extent of 0.14 per
cent of sodium nitrate.
Sodium Iodate.—This body, present only in small quantities, may also
be neglected. In case the content of this body should reach one-fourth per
cent the estimation of chlorin by titration using potassium chromate as
indicator is impracticable. Such an instance, however, is rarely known.
Approximate Results.—When the determinations outlined above have
been carefully made it is claimed that the result obtained by subtraction
from 100 will not vary more than from two-tenths to three-tenths per cent
from the true content of sodium nitrate. The method, however, cannot be
considered strictly scientific and is much more tedious and chronophagous
than the direct determination. In the direct determination, however, the
analyst must assure himself that potassium is present in only appreciable
quantities otherwise the per cent of sodium nitrate will be too low.
The presence of potassium nitrate is a detriment in this respect only;
viz., that it contains a less percentage of nitrogen than the corresponding
sodium salt. As a fertilizer, the value of Chile saltpeter may be increased by
its content of potassium.
218. The Application of Chile Saltpeter to the Soil.—The analyst is
often asked to determine the desirability of the use of sodium nitrate as a
fertilizer and the methods and times of applying it. These are questions
which are scarcely germane to the purpose of this work but which,
nevertheless, for the sake of convenience may be briefly discussed. In the
first place it may be said that the data of a chance chemical analysis will not
afford a sufficiently broad basis for an answer. A given soil may be very
rich in nitrogen as revealed by chemical analysis, and yet poor in an
available supply. This is frequently the case with vegetable soils,
containing, as they do, large quantities of nitrogen but holding it in
practically an inert state. I have found such soils very rich in nitrogen, yet
almost entirely devoid of nitrifying organisms. It is necessary therefore in
reaching a judgment on this subject from analytical data to consider the

different states in which the nitrogen may exist in a soil and above all the
nitrifying power of the soil if the nitrogen be chiefly present in an organic
state. Culture solutions should therefore be seeded with samples of the soil
under examination and the beginning and rapidity of the nitrification
carefully noted. In conjunction with this the nitrogen present in the soil in a
nitric or ammoniacal form should be accurately determined. These
determinations should be made according to the directions given in the first
volume, pp. 448-548.
For the determination of nitrifying power we prefer the following
method:
219. Taking Samples of Soil in Sterilized Tubes.—Brass tubes are
prepared twenty centimeters in length and one and a half in diameter. One
end is ground to a beveled edge and compressed in a mold so as to make the
cutting edge slightly smaller in diameter than the internal diameter of the
tube. It is then ground or filed until smooth and sharp. The blunt end of the
tube is stoppered loosely with cotton and it is then sterilized by heating for
an hour to 150°. Rubber caps are provided and each one has placed at the
bottom a rubber ball to prevent the rubber from being cut by the edges of
the brass tube. The caps should be of two distinct colors. Half of the rubber
caps are sterilized by being boiled for an hour in water for three successive
days. The caps cannot be heated to 150° dry heat with safety. On removing
the brass tube from the sterilizing oven as soon as it is cool enough to
handle, a sterilized rubber cap is slipped over its cutting end. An
unsterilized cap is then slipped over the other end containing the cotton
plug. Inasmuch as the cotton plug is never removed it is not necessary to
sterilize the cap covering it. Large numbers of the tubes can thus be
prepared for use and they can be safely transmitted to a distance by express
or mail. For convenience, each tube is encased in a small cloth bag, which
is tied with a cord carrying a tag on which the necessary data can be
recorded at the time of taking the sample.
The tubes and their rubber caps thus carefully sterilized should not be
removed from their cloth envelopes until the moment of taking each
sample. After the sample has been taken and the cap replaced on the tube
the latter should be immediately enclosed in the cloth sack and labeled with
one of the tags therewith enclosed. The sample should be taken in two kinds
of soil, in one instance in a cultivated soil, which is most characteristic of

the locality, and in the second place a virgin soil of the same type. The
virgin soil may be either soil which has been covered with grass or in forest.
The spots at which the samples are to be taken having been previously
selected, the tags for each tube should be prepared beforehand so as to
avoid delay at the time of sampling. A pit with straight walls should be dug,
the sides of which are at least two feet wide and even three feet would be
better. The pit should be about forty-two inches deep. One of the sides
having been made perfectly smooth and without allowing the loose
fragments from the top to fall down and adhere to the walls below, the spots
at which the samples are to be taken should be marked with a tape line at
the following points; viz., three, fifteen, twenty-seven, and thirty-nine
inches, respectively, below the surface. Beginning at the bottom point,
carefully scrape off the surface of the wall over an area slightly larger than
that of the end of the sample tube by means of a spatula, which, just
previous to use, has been held for a moment or two in the flame of an
alcohol or other convenient lamp. The sample tube having been removed
from its sack, it will be noted that the end covered with black rubber is the
one which is to be held in the hand, and this black rubber cap should be first
removed being careful not to extract the plug of sterilized cotton which
closes the end of the tube. Holding the tube firmly by the end, the fingers
extending only about two inches from the end, remove the light-colored cap
and push the tube with a turning motion into the side of the pit at the point
where the surface has been removed with the sterilized spatula. When this is
properly done the tube will be filled with a cylinder of soil equal to the
length of the part of the tube penetrating the wall of the pit. The tube is then
withdrawn, the light rubber cap first replaced, and then the black one. The
light rubber cap should be held in the hand during the process in such a way
that no dust or particles of soil are permitted to contaminate its inner walls.
For this purpose the open end of the cap should be held downward. For the
same reason after the removal of the light rubber cap the brass tube should
be carefully preserved from dust or fragments, the open end, that is the
cutting end, being held downward until ready for use. After one tube has
been filled, capped, replaced in the sack and labeled, the spatula should be
again sterilized and samples taken in regular order until the top one is
finished.
220. Directions for Taking Bulk Samples.—From the sides of the pit
described above, bulk samples should be taken as follows:

By means of a spade the soil should be removed from the four sides to
the depth of six or nine inches or until the change of color between the soil
and subsoil is noted; in all enough to make about 150 pounds of the air-
dried soil. In the same way take a sample of the subsoil to the depth of nine
additional inches. Remove all stones, large pebbles, sticks, roots, etc., and
spread the samples in a sheltered place where they can be air-dried as
rapidly as possible. The bulk samples should be taken both from the
cultivated and virgin soils. In selecting the cultivated soil, preference should
be given to those soils which have not been fertilized within a few years. If
recent fertilization have been practiced the character and amount of it
should be noted.
221. The Nitrifiable Solution.—The solution to test the nitrifying
power of the samples collected as above described is conveniently made as
follows:

Potassium phosphate, one gram per liter.
Magnesium sulfate, half a gram per liter.
Calcium chlorid, a trace.
Ammonium sulfate, 200 milligrams of nitrogen per liter.
Calcium carbonate, in excess.

One liter of the above solution is enough for ten samples, each of 100
cubic centimeters. This quantity is placed in an erlenmeyer, which is
stoppered with cotton and sterilized by being kept at 100° for an hour on
three successive days. The erlenmeyer should be sterilized beforehand by
heating for an hour at 150°. The freshly precipitated and washed calcium
carbonate should be sterilized separately and added to each erlenmeyer at
the time of seeding. Enough should always be used to be in excess of the
nitrous and nitric acids found. The seeding is accomplished by filling a
sterilized spoon which holds approximately half a gram of the soil, from the
contents of one of the brass tubes, lifting the plug in the erlenmeyer and
transferring quickly to the flask. This should be done in a perfectly still
room, preferably as high above the ground as possible and in a place free
from dust and under cover. The cotton plug being replaced the erlenmeyer
is shaken until the sample of soil added is thoroughly disintegrated and
intimately mixed with its contents. With care and experience the seeding is
easily accomplished without danger of accidental contamination.

At the end of each period of five days the beginning and progress of
nitrification should be determined by some of the methods described in
volume first. Either the ammonia can be determined by nesslerizing or the
nitrous and nitric acids estimated. For nitrous acid we prefer the method
described in volume first, paragraph 504, and for nitric the one in same
volume paragraphs 497 and 498.
By supplementing the analysis of a soil by the above described
experiments in nitrification the analyst will be able to judge with sufficient
accuracy of its needs for nitric nitrogen.
222. Quantity of Chile Saltpeter to be Applied.—The quantities of
Chile saltpeter which should be applied per acre vary with so many
conditions as to make any definite statement impossible. On account of the
great solubility of this salt no more should be used than is necessary for the
nutrition of the crop. For each 100 pounds used, from fourteen to fifteen
pounds of nitrogen will be added to the soil. Field crops, as a rule, will
require less of the salt than garden crops. There is an economic limit to the
application which should not be passed. As a rule 250 pounds per acre will
prove to be a maximum dressing. The character of the crop must also be
considered. Different amounts are required for sugar beets, tobacco, wheat,
and other standard crops. It is rarely the case that a crop demands a dressing
of Chile saltpeter alone. It will give the best effects, as a rule, when applied
with phosphoric acid or potash. But this is a branch of the subject which
cannot be entered into at greater length in this manual. The reader is
referred to Stutzer’s work on Chile saltpeter for further information.[183]
223. Consumption of Chile Saltpeter.—The entire consumption of
sodium nitrate for manurial purposes in the whole world for 1894 was
992,150 metric tons, valued at $41,000,000. For the several countries using
it the consumption was distributed as follows:
Germany 397,200 tons.
France 187,100 “
England 117,000 “
Belgium 123,000 “
United States 100,000 “
Holland 56,700 “
Italy and Spain 5,200 “

Other countries 5,950 “
Total 992,150 “
The above figures represent the actual commerce of each country in
Chile saltpeter, and may not give the exact consumption.[184] For instance,
Germany exports sodium nitrate to Russia and Austria, but it imports this
salt from Holland and Belgium. Belgium imports from France, but its
exportation is greater than its importations from that country, so that its
actual consumption on the farm probably falls considerably below that
given on the table. Holland also exports larger quantities than are imported
from neighboring states. The exports from England are inconsiderable
compared with the quantities received, amounting only to about 5,000 tons
a year, while the exportations from France reach nearly 10,000 tons.
Sodium nitrate has a moderate value at the factories where it is prepared
for shipment in Chile. Its chief value at the ports where it is delivered for
consumption comes from freights and profits of the syndicate. The
factories, where it is prepared for the market, are at or near the deposits, and
the freights thence to the sea coast are very high. The rail roads which have
been constructed to the high plateaux which contain the deposits, have been
built at a very great cost, and the freights charged are correspondingly high.
There is also a tax of $1.20 levied on each ton exported. Deducting all costs
of transportation and export duties the actual value of sodium nitrate at the
factory, ready for shipment, is about sixteen dollars in gold a ton.

AUTHORITIES CITED IN
PART SECOND.

[125] American Chemical Journal, Vol. 13, No. 7.
[126] Atwater: Report of the U. S. Commissioner of Fish and Fisheries, 1888,
pp. 679-868.
[127] American Naturalist, Vol. 14, p. 473.
[128] Wiley: Retiring Address as President of American Chemical Society,
Baltimore Meeting, Dec. 1893, Journal of the American Chemical Society, Vol.
16, pp. 17-20.
[129] Vid. op. et. loc. cit. supra.
[130] Vid. op. et. loc. cit. 4.
[131] Vid. op. et. loc. cit. 4.