Elements of Agricultural Chemistry Thomas Anderson 1988 downloads.pdf

The Project Gutenberg eBook of Elements of Agricultural
Chemistry
This eBook is for the use of anyone anywhere in the United States and most
other parts of the world at no cost and with almost no restrictions
whatsoever. You may copy it, give it away or re-use it under the terms of
the Project Gutenberg License included with this eBook or online at
www.gutenberg.org. If you are not located in the United States, you will
have to check the laws of the country where you are located before using
this eBook.

Title: Elements of Agricultural Chemistry

Author: Thomas Anderson

Release date: March 28, 2008 [eBook #24931]

Language: English

Other information and formats: www.gutenberg.org/ebooks/24931

Credits: Produced by Steven Giacomelli, Jeannie Howse, Josephine
Paolucci and the Online Distributed Proofreading Team at
http://www.pgdp.net. (This file was produced from images
produced by Core Historical Literature in Agriculture
(CHLA), Cornell University).

*** START OF THE PROJECT GUTENBERG EBOOK ELEMENTS OF
AGRICULTURAL CHEMISTRY ***

ELEMENTS
OF

AGRICULTURAL CHEMISTRY
BY

THOMAS ANDERSON, M.D.
F.R.S.E., F.C.S.

PROFESSOR OF CHEMISTRY IN THE UNIVERSITY OF GLASGOW,
AND CHEMIST TO THE HIGHLAND AND AGRICULTURAL
SOCIETY OF SCOTLAND.

EDINBURGH:

ADAM AND CHARLES BLACK.

1860.
ERRATUM.
Page 190, line 11, for "gallon" read "ton."
PRINTED BY R. AND R. CLARK, EDINBURGH.

Transcriber's note: Many of the tables needed to be split to
fit space constraints.

PREFACE.
The object of the present work is to offer to the farmer a concise outline of
the general principles of Agricultural Chemistry. It has no pretensions to be
considered a complete treatise on the subject. On the contrary, its aim is
strictly elementary, and with this view I have endeavoured, as far as
possible, to avoid unnecessary technicalities so as to make it intelligible to
those who are unacquainted with the details of chemical science, although I
have not hesitated to discuss such points as appeared essential to the proper
understanding of any particular subject.
The rapid progress of agricultural chemistry, and the numerous researches
prosecuted under the auspices of agricultural societies and private
experimenters in this and other countries, render it by no means an easy
task to make a proper selection from the mass of facts which is being daily
accumulated. In doing this, however, I have been guided by a pretty
intimate knowledge of the wants of the farmer, which has induced me to
enlarge on those departments of the subject which bear more immediately
on the every-day practice of agriculture; and for this reason the composition
and properties of soils, the nature of manures, and the principles by which
their application ought to be governed, have been somewhat minutely
treated.
In all cases numerical details have been given as fully as is consistent with
the limits of the work; and it may be right to state that a considerable
number of the analyses contained in it have been made in my own
laboratory, and that even when I have preferred to quote the results of other
chemists, they have not unfrequently been confirmed by my own
experiments.
University of Glasgow,
1st November 1860.

CONTENTS.
Page

Introduction 1

CHAPTER I.

The Organic Constituents of Plants.

Carbon ... Carbonic Acid ... Hydrogen ... Nitrogen ... Nitric Acid ...
Ammonia ... Oxygen ... Sources whence obtained ... The Atmosphere ... The
Soil ... Source of the Inorganic Constituents of Plants ... Manner in which
the Constituents of Plants are absorbed 8

CHAPTER II.

The Proximate Constituents of Plants.

The Saccharine and Amylaceous Constituents ... Cellulose ... Incrusting
Matter ... Starch ... Lichen Starch ... Inuline ... Gum ... Dextrine ... Sugar ...
Mucilage ... Pectine and Pectic Acid ... Oily or Fatty Matters ... Margaric,
Stearic, and Oleic Acids ... Wax ... Nitrogenous or Albuminous Constituents
of Plants and Animals ... Albumen ... Fibrine ... Casein ... Diastase 40

CHAPTER III.

The Changes which take place in the Food of Plants during their
Growth.

Changes occurring during Germination ... Changes during the After-Growth

of the Plant ... Decomposition of Carbonic Acid ... Decomposition of Water
... Decomposition of Ammonia ... Decomposition of Nitric Acid 54

CHAPTER IV.

The Inorganic Constituents of Plants.

The Amount of Inorganic Matters in Different Plants ... The Relative
Proportions of Ash in the Different Parts of Plants ... Influence of the Nature
of the Soil on the Proportion of Mineral Matters in the Plant ... The
Composition of the Ashes of Plants ... Classification of Different Plants 63

CHAPTER V.

The Soil—Its Chemical and Physical Characters.

The Origin of Soils ... Composition of Crystalline and Sedimentary Rocks
... their Disintegration ... Chemical Composition of the Soil ... Fertile and
Barren Soils ... Mechanical Texture of Soils ... Absorbent Action of Soils ...
their Physical Characters ... Relation to Heat and Moisture ... The Subsoil ...
Classification of Soils 83

CHAPTER VI.

The Improvement of the Soil by Mechanical Processes.

Draining ... Its Advantageous Effects ... Subsoil and Deep Ploughing ...
Improving the Soil by Paring and Burning ... Warping ... Mixing of Soils ...
Chalking 137

CHAPTER VII.

The General Principles of Manuring.

Fundamental Principles upon which Manures are applied ... Special and
General Manures ... Importance of this distinction ... Views regarding the
Theory of Manures ... Remarks on Special Manures ... Action of Manures
on the Chemical and Physical Properties of a Soil ... Remarks on the
Application of Manures152

CHAPTER VIII.

The Composition and Properties of Farm-yard and Liquid Manures.

Farm-yard Manure ... Urine ... Composition of ... Dung ... Composition of
... Farm-yard Manure ... Composition of ... Management of Dung-Heaps ...
Box-feeding ... Fermentation and application of Manure ... Liquid Manure
... Composition and application of ... Sewage Manure ... Its composition and
application 166

CHAPTER IX.

The Composition and Properties of Vegetable Manures.

Rape-Dust, Mustard, Cotton and Castor Cake ... Composition of various
Oil-Cakes ... Malt-Dust, Bran, Chaff, etc. ... Straw and Saw-dust ...
Manuring with Fresh Vegetable Matter ... Green Manuring ... Sea-Weed ...
Composition of various Sea-Weeds ... Leaves ... Peat 195

CHAPTER X.

The Composition and Properties of Animal Manures.

Guano, different varieties of ... Average composition of ... Division into
Ammoniacal and Phosphatic ... Characters of ... Adulteration of ...
Application of ... Pigeons' Dung ... Urate and Sulphated Urine ... Night-Soil
and Poudrette ... Hair, Skin, Horn, Wool, etc. ... Blood ... Fish ... "Fish-

Guano"—Bones 204

CHAPTER XI.

The Composition and Properties of Mineral Manures.

Mineral Manures ... Sulphate and Muriate of Ammonia ... Sulphomuriate of
Ammonia ... Ammoniacal Liquor ... Nitrates of Potash and Soda ... Muriate
and Sulphate of Potash ... Chloride of Sodium, or Common Salt ...
Carbonates of Potash and Soda ... Silicates of Potash and Soda ... Sulphate
of Magnesia ... Phosphate of Lime ... Bone-ash ... Coprolites ... Apatite ...
Sombrero Guano ... Superphosphates and Dissolved Bones ... Biphosphate
of Lime or Soluble Phosphates ... Phospho-Peruvian Guano ... Lime ...
Chalk ... Marl ... Application and Action of Lime on Soils ... Sulphate of
Lime or Gypsum 226

CHAPTER XII.

The Valuation of Manures.

The Principle on which Manures are valued ... Its application to different
simple and complex Manures ... Method of Calculation ... General Remarks
255

CHAPTER XIII.

The Rotation of Crops.

Its necessity explained ... Quantity of Mineral Matters in the produce of an
Acre of Different Crops ... The Theory of Rotation266

CHAPTER XIV.

The Feeding of Farm Stock.

The Principles of Feeding ... The Composition of different Animals in
different stages of Fattening ... The Composition of the Food of Animals ...
Milk ... The Principal Varieties of Cattle Food ... General Observations on
Feeding 276

AGRICULTURAL CHEMISTRY.

INTRODUCTION.
That the phenomena of vegetation are dependent on certain chemical
changes occurring in the plant, by which the various elements of its food
are elaborated and converted into vegetable matter, was very early
recognised by chemists; and long before the correct principles of that
science were established, Van Helmont maintained that plants derived their
nourishment from water, while Sir Kenelm Digby, Hook, Bradley, and
others, attributed an equally exclusive influence to air, and enlarged on the
practical importance of the conclusions to be deduced from their views.
These opinions, which were little better than hypotheses, and founded on
very imperfect chemical data, are mentioned by Jethro Tull, the father of
modern agriculture, only to deny their accuracy; and he contended that the
plants absorb and digest the finer particles of the earth, and attributed the
success of the particular system of husbandry he advocated to the
comminution of the soil, by which a larger number of its particles are
rendered sufficiently small to permit their ready absorption by the roots.
Popular opinion at that time was in favour of the mechanical rather than the
chemical explanation of agricultural facts, and Tull's work had the effect of
confirming this opinion, and turning attention away from the application of
chemistry to agriculture. Indeed, no good results could have followed its
study at that time, for chemistry, especially in those departments bearing
more immediately on agriculture, was much too imperfect, and it was only
towards the close of the last century, when Lavoisier established its true
principles, that it became possible to pursue it with any prospect of success.
Very soon after Lavoisier's system was made known, Lord Dundonald
published his "Treatise on the Intimate Connexion between Chemistry and
Agriculture," in which the important bearings of the recent chemical
discoveries on the practice of agriculture were brought prominently under
the notice of the farmer, and almost at the same time De Saussure
commenced those remarkable researches, which extended over a long series
of years, and laid the foundation of almost all our accurate knowledge of
the chemistry of vegetation. Saussure traced with singular care and
accuracy the whole phenomena of the life of plants, and indicated the mode

in which the facts he established might be taken advantage of in improving
the cultivation of the soil. But neither his researches, nor Lord Dundonald's
more direct appeal to the farmer, excited the attention they deserved, or
produced any immediate effect on the progress of agriculture. It was not till
the year 1812 that the interest of practical men was fairly awakened by a
course of lectures given by Sir Humphrey Davy, at the instance of Sir John
Sinclair, who was at that time president of the Board of Agriculture. In these
lectures, written with all the clearness and precision which characterised
their author's style, the results of De Saussure's experiments were for the
first time presented to the farmer in a form in which they could be easily
understood by him, the conclusions to which they led were distinctly
indicated, and a number of useful practical suggestions made, many of
which have been adopted into every-day practice, and become so
thoroughly incorporated with it, that their scientific origin has been
altogether forgotten. A lively interest was excited by the publication of
Davy's work, but it soon died out, and the subject lay in almost complete
abeyance for a considerable number of years. Nor could any other result be
well expected, for at that time agriculture was not ripe for chemistry, nor
chemistry ripe for agriculture. The necessities of a rapidly increasing
population had not yet begun to compel the farmer to use every means
adapted to increase the amount of production to its utmost limit; and though
the fundamental principles of chemistry had been established, its details,
especially in that department which treats of the constituents of plants and
animals, were very imperfectly known. It is not surprising, therefore, that
matters should have remained almost unchanged for the comparatively long
period of nearly thirty years. Indeed, with the exception of the investigation
of soils by Schübler, and some other inquiries of minor importance, and
which, in this country at least, excited no attention on the part of the
agriculturist, nothing was done until the year 1840, when Liebig published
his treatise on Chemistry, in its application to Agriculture and Physiology.
Saussure's researches formed the main groundwork of Liebig's treatise, as
they had before done for Davy's; but the progress of science had supplied
many new facts which confirmed the opinions of the older chemists in most
respects, and enabled Liebig to generalise with greater confidence, and
illustrate more fully the principles upon which chemistry ought to be
applied to agriculture. Few works have ever produced a more profound

impression. Written in a clear and forcible style, dealing with scientific
truths in a bold and original manner, and producing a strong impression, as
well by its earnestness as by the importance of its conclusions, it was
received by the agricultural public with the full conviction that the
application of its principles was to be immediately followed by the
production of immensely increased crops, and by a rapid advance in every
branch of practical agriculture. The disappointment of these extravagant
expectations, which chemists themselves foresaw, and for which they vainly
attempted to prepare the agriculturist, was followed by an equally rapid
reaction; and those who had embraced Liebig's views, and lauded them as
the commencement of a new era, but who had absurdly expected an
instantaneous effect, changed their opinion, and contemned, as strongly as
they had before supported, the application of chemistry to agriculture.
That this effect should have been produced is not unnatural; for practical
men, having at that time little or no knowledge of chemistry, were
necessarily unable to estimate its true position in relation to agriculture, and
forgetting that this department of science was still in its early youth, and
burthened with all the faults and errors of youth, they treated it as if it were
already perfect in all its parts. Neither could they distinguish between the
fully demonstrated scientific truths, and the uncertain, though probable
conclusions deduced from them; and when the latter, as occasionally
happened, proved to be at variance with practice, it is not surprising: that
this should have produced a feeling of distrust on the part of persons
incapable, from an imperfect, and still oftener from no knowledge of
science, of drawing the line of demarcation, which Liebig frequently
omitted to do, between the positive fact and the hypothetical inference,
which, however probable, is, after all, merely a suggestion requiring to be
substantiated by experiment. This omission, which the scientific reader can
supply for himself, becomes a source of serious misapprehension in a work
addressed to persons unacquainted with science, who adopt indiscriminately
both the facts and the hypotheses of the author. And this is no doubt the
cause of the vary different estimation in which the work of the Giessen
Professor was held by scientific and practical men.
Liebig's treatise was followed, in the year 1844, by the publication of
Boussingault's Economic Rurale, a work winch excited at the time infinitely
less interest than Liebig's, although it is really quite as important a

contribution to scientific agriculture. It is distinguished by entering more
fully into the special details of the application of chemistry to agriculture,
and contains the results of the author's numerous searches both in the
laboratory and the field. Boussingault possesses the qualification, at present
somewhat rare, of combining a thorough knowledge of practical agriculture
with extended scientific attainments; and his investigations, which have
been made with direct reference to practice, and their results tested in the
field, are the largest and most valuable contribution to the exact data of
scientific agriculture which has yet been made public.
The year 1844 was also distinguished by the foundation of the Agricultural
Chemistry Association of Scotland, an event of no small importance in the
history of scientific agriculture. That association was instituted through the
exertions of a small number of practical farmers, for the purpose of
pursuing investigations in agricultural chemistry, and affording to its
members assistance in all matters connected with the cultivation of the soil,
and has formed the model of similar establishments in London, Dublin, and
Belfast, as well as in Germany; and it is peculiarly creditable to the
intelligence and energy of the practical farmers of Scotland, that with them
commenced a movement, which has already found imitators in so many
quarters, and conferred such great benefits on agriculture. Within the last
ten or twelve years, and mainly owing to the establishment of agricultural
laboratories, great progress has been made in accumulating facts on which
to found an accurate knowledge of the principles of agricultural chemistry,
and the number of chemists who have devoted themselves to this subject
has considerably increased, though still greatly less than its exigencies
require.
Notwithstanding all that has recently been done, it must not be forgotten
that we have scarcely advanced beyond the threshold, and that it is only by
numerous and frequently repeated experiments that it is possible to arrive at
satisfactory results. Agricultural inquiries are liable to peculiar fallacies due
to the perturbing influence of climate, season, and many other causes, the
individual effects of which can only be eliminated with difficulty, and much
error has been introduced, by hastily generalising from single experiments,
in place of awaiting the results of repeated trials. Hence it is that the
progress of scientific agriculture must necessarily be slow and gradual, and
is not likely to be marked by any great or startling discoveries. Now that the

relations of science to practice are better understood, the extravagant
expectations at one time entertained have been abandoned, and, as a
necessary consequence, the interest in agricultural chemistry has again
increased, and the conviction daily gains ground that no one who wishes to
farm with success, can afford to be without some knowledge of the
scientific principles of his art.

CHAPTER I.
THE ORGANIC CONSTITUENTS OF PLANTS.

When the water naturally existing in plants is expelled by exposure to the
air or a gentle heat, the residual dry matter is found to be composed of a
considerable number of different substances, which have been divided into
two great classes, called the organic and the inorganic, or mineral
constituents of plants. The former are readily combustible, and on the
application of heat, catch fire, and are entirely consumed, leaving the
inorganic matters in the form of a white residuum or ash. All plants contain
both classes of substances; and though their relative proportions vary within
very wide limits, the former always greatly exceed the latter, which in many
cases form only a very minute proportion of the whole weight of the plant.
Owing to the great preponderance of the organic or combustible matters, it
was at one time believed that the inorganic substances formed no part of the
true structure of plants, and consisted only of a small portion of the mineral
matters of the soil, which had been absorbed along with their organic food;
but this opinion, which probably was never universally entertained, is now
entirely abandoned, and it is no longer doubted that both classes of
substances are equally essential to their existence.
Although they form so large a proportion of the plant, its organic
constituents are composed of no more than four elements, viz.:—
Carbon.
Hydrogen.
Nitrogen.
Oxygen.
The inorganic constituents are much more numerous, not less than thirteen
substances, which appear to be essential, having been observed. These are
—
Potash.
Soda.

Lime.
Magnesia.
Peroxide of Iron.
Silicic Acid.
Phosphoric Acid.
Sulphuric Acid.
Chlorine.
And more rarely
Manganese.
Iodine.
Bromine.
Fluorine.
Several other substances, among which may be mentioned alumina and
copper, have also been enumerated; but there is every reason to believe that
they are not essential, and the cases in which they have been found are quite
exceptional.
It is to be especially noticed that none of these substances occur in plants in
the free or uncombined state, but always in the form of compounds of
greater or less complexity, and extremely varied both in their properties and
composition.
It would be out of place, in a work like the present, to enter into complete
details of the properties of the elements of which plants are composed,
which belongs strictly to pure chemistry, but it is necessary to premise a
few observations regarding the organic elements, and their more important
compounds.
Carbon.—When a piece of wood is heated in a close vessel, it is charred,
and converted into charcoal. This charcoal is the most familiar form of
carbon, but it is not absolutely pure, as it necessarily contains the ash of the
wood from which it was made. In its purest form it occurs in the diamond,
which is believed to be produced by the decomposition of vegetable
matters, and it is there crystallized and remarkably transparent; but when
produced by artificial processes, carbon is always black, more or less
porous, and soils the fingers. It is insoluble in water, burns readily, and is

converted into carbonic acid. Carbon is the largest constituent of plants, and
forms, in round numbers, about 50 per cent of their weight when dry.
Carbonic Acid.—This, the most important compound of carbon and
oxygen, is best obtained by pouring a strong acid upon chalk or limestone,
when it escapes with effervescence. It is a colourless gas, extinguishing
flame, incapable of supporting respiration, much heavier than atmospheric
air, and slightly soluble in water, which takes up its own volume of the gas.
It is produced abundantly when vegetable matters are burnt, as also during
respiration, fermentation, and many other processes. It is likewise formed
daring the decay of animal and vegetable matters, and is consequently
evolved from dung and compost heaps.
Hydrogen occurs in nature only in combination. Its principal compound is
water, from which it is separated by the simultaneous action of an acid, such
as sulphuric acid and a metal, in the form of a transparent gas, lighter than
any other substance. It is very combustible, burns with a pale blue flame,
and is converted into water. It is found in all plants, although in
comparatively small quantity, for, when dry, they rarely contain more than
four or five per cent. Its most important compound is water, of which it
forms one-ninth, the other eight-ninths consisting of oxygen.
Nitrogen exists abundantly in the atmosphere, of which it forms nearly four-
fifths, or, more exactly, 79 per cent. It is there mixed, but not combined with
oxygen; and when the latter gas is removed, by introducing into a bottle of
air some substance for which the former has an affinity, the nitrogen is left
in a state of purity. It is a transparent gas, which is incombustible and
extinguishes flame. It is a singularly inert substance, and is incapable of
directly entering into union with any other element except oxygen, and with
that it combines with the greatest difficulty, and only by the action of the
electric spark—a peculiarity which has very important bearings on many
points we shall afterwards have to discuss. Nitrogen is found in plants to the
extent of from 1 to 4 per cent.
Nitric Acid.—This, the most important compound of nitrogen and oxygen,
can be produced by sending a current of electric sparks through a mixture of
its constituents, but in this way it can be obtained only in extremely small
quantity. It is much more abundantly produced when organic matters are

decomposed with free access of air, in which case the greater proportion of
their nitrogen combines with the atmospheric oxygen. This process, which
is known by the name of nitrification, is greatly promoted by the presence
of lime or some other substance, with which the nitric acid may combine in
proportion as it is formed. It takes place, to a great extent, in the soil in
India and other hot climates; and our chief supplies of saltpetre, or nitrate of
potash, are derived from the soil in these countries, where it has been
formed in this manner. The same change occurs, though to a much smaller
extent, in the soil in temperate climates.
Ammonia is a compound of nitrogen and hydrogen, but it cannot be formed
by the direct union of these gases. It is a product of the decomposition of
organic substances containing nitrogen, and is produced when they are
distilled at a high temperature, or allowed to putrefy out of contact of the
air. In its pure state it is a transparent and colourless gas, having a peculiar
pungent smell, and highly soluble in water. It is an alkali resembling potash
and soda, and, like these substances, unites with the acids and forms salts,
of which the sulphate and muriate are the most familiar. In these salts it is
fixed, and does not escape from them unless they be mixed with lime, or
some other substance possessing a more powerful affinity for the acid with
which it is united.
Oxygen is one of the most widely distributed of all the elements, and, owing
to its powerful affinities, is the most important agent in almost all natural
changes. It is found in the air, of which it forms 21 per cent, and in
combination with hydrogen, and almost all the other chemical elements. In
the pure state it possesses very remarkable properties. All substances burn
in it with greater brilliancy than they do in atmospheric air, and its affinity
for most of the elements is extremely powerful. When diluted with nitrogen,
it supports the respiration of animals; but in the pure state it proves fatal
after the lapse of an hour or two. It is found in plants, in quantities varying
from 30 to 36 per cent.
It is worthy of observation, that of the four organic elements, carbon only is
fixed, and the other three are gases; and likewise, when any two of them
unite, their compound is either a gaseous or a volatile substance. The
charring of organic substances, which is one of their most characteristic
properties, and constantly made use of by chemists as a distinctive reaction,

is due to this peculiarity; for when they are heated, a simpler arrangement
of their particles takes place, the hydrogen, nitrogen, and oxygen unite
among themselves, and carry off a small quantity of carbon, while the
remainder is left behind in the form of charcoal, and is only consumed
when access of the external air is permitted.
Now, in order that a plant may grow, its four organic constituents must be
absorbed by it, and that this absorption may take place, it is essential that
they be presented to it in suitable forms. A seed may be planted in pure
carbon, and supplied with unlimited quantities of hydrogen, nitrogen,
oxygen, and inorganic substances, and it will not germinate; and a plant,
when placed in similar circumstances, shows no disposition to increase, but
rapidly languishes and dies. The obvious inference from these facts is, that
these substances cannot be absorbed when in the elementary state, but that
it is only after they have entered into certain forms of combination that they
acquire the property of being readily taken up, and assimilated by the
organs of the plant.
It was at one time believed that many different compounds of these
elements might be absorbed and elaborated, but later and more accurate
experiments have reduced the number to four—namely, carbonic acid,
water, ammonia, and nitric acid. The first supplies carbon, the second
hydrogen, the two last nitrogen, while all of them, with the exception of
ammonia, may supply the plant with oxygen as well as with that element of
which it is the particular source.
There are only two sources from which these substances can be obtained by
the plant, viz. the atmosphere and the soil, and it is necessary that we should
here consider the mode in which they may be obtained from each.
The Atmosphere as a source of the Organic Constituents of Plants.—
Atmospheric air consists of a mixture of nitrogen and oxygen gases, watery
vapour, carbonic acid, ammonia, and nitric acid. The two first are the largest
constituents, and the others, though equally essential, are present in small,
and some of them in extremely minute quantity. When deprived of moisture
and its minor constituents, 100 volumes of air are found to contain 21 of
oxygen and 79 of nitrogen. Although these gases are not chemically
combined in the air, but only mechanically mixed, their proportion is

exceedingly uniform, for analyses completely corresponding with these
numbers have been made by Humboldt, Gay-Lussac, and Dumas at Paris,
by Saussure at Geneva, and by Lewy at Copenhagen; and similar results
have also been obtained from air collected by Gay-Lussac during his ascent
in a balloon at the height of 21,430 feet, and by Humboldt on the mountain
of Antisano in South America at a height of 16,640 feet. In short, under all
circumstances, and in all places, the relation subsisting between the oxygen
and nitrogen is constant; and though, no doubt, many local circumstances
exist which may tend to modify their proportions, these are so slow and
partial in their operations, and so counterbalanced by others acting in an
opposite direction, as to retain a uniform proportion between the main
constituents of the atmosphere, and to prevent the undue accumulation of
one or other of them at any one point.
No such uniformity exists in the proportion of the minor constituents. The
variation in the quantity of watery vapour is a familiar fact, the difference
between a dry and moist atmosphere being known to the most careless
observer, and the proportions of the other constituents are also liable to
considerable variations.
Carbonic Acid.—The proportion of carbonic acid in the air has been
investigated by Saussure. From his experiments, made at the village of
Chambeisy, near Geneva, it appears that the quantity is not constant, but
varies from 3·15 to 5·75 volumes in 10,000; the mean being 4·15. These
variations are dependent on different circumstances. It was found that the
carbonic acid was always more abundant during the night than during the
day—the mean quantity in the former case being 4·32, in the latter 3·38.
The largest quantity found during the night was 5·74, during the day 5·4.
Heavy and continued rain diminishes the quantity of carbonic acid, by
dissolving and carrying it down into the soil. Saussure found that in the
month of July 1827, during the time when nine millimetres of rain fell, the
average quantity of carbonic acid amounted to 5·18 volumes in 10,000;
while in September 1829, when 254 millimetres fell, it was only 3·57. A
moist state of the soil, which is favourable to the absorption of carbonic
acid, also diminishes the quantity contained in the air, while, on the other
hand, continued frosts, by retaining the atmosphere and soil in a dry state,
have an opposite effect. High winds increase the carbonic acid to a small
extent. It was also found to be greater over the cultivated lands than over

the lake of Geneva; at the tops of mountains than at the level of the sea; in
towns than in the country. The differences observed in all these cases,
though small, are quite distinct, and have been confirmed by subsequent
experimenters.
Ammonia.—The presence of ammonia in the atmosphere appears to have
been first observed by Saussure, who found that when the sulphate of
alumina is exposed to the air, it is gradually converted into the double
sulphate of alumina and ammonia. Liebig more recently showed that
ammonia can always be detected in rain and snow water, and it could not be
doubted that it had been absorbed from the atmosphere. Experiments have
since been made by different observers with the view of determining the
quantity of atmospheric ammonia, and their results are contained in the
subjoined table, which gives the quantity found in a million parts of air.

Kemp 3·6800
{12 feet above the surface 3·5000
Pierre
{25 feet do. do. 0·5000
Graeger 0·3230
{By day 0·0980
Fresenius
{By night 0·1690
{ {Maximum 0·0317
{ In Paris {Minimum 0·0177
{ {Mean 0·0237
Ville
{ {Maximum 0·0276
{ Environs {Minimum 0·0165
{ of Paris {Mean 0·0210

Of these results, the earlier ones of Kemp, Pierre, and Graeger are
undoubtedly erroneous, as they were made without those precautions which
subsequent experience has shown to be necessary. Even those of the other
observers must be taken as giving only a very general idea of the quantity
of ammonia in the air, for a proportion so minute as one fifty-millionth
cannot be accurately determined even by the most delicate experiments. For
this reason, more recent experimenters have endeavoured to arrive at
conclusions bearing more immediately upon agricultural questions, by
determining the quantity of ammonia brought down by the rain. The first

observations on this subject were made by Barral in 1851, and they have
been repeated during the years 1855 and 1856 by Mr. Way. In 1853,
Boussingault also made numerous experiments on the quantity of ammonia
in the rain falling at different places, as well as in dew and the moisture of
fogs. He found in the imperial gallon—

Grs.
Rain { Paris 0·2100
{ Liebfrauenberg 0·0350
Dew, Liebfrauenberg { Maximum 0·4340
{ Minimum 0·0714
{ Liebfrauenberg 0·1790
Fog { Paris 9·6000

It thus appears that in Paris the quantity of ammonia in rain-water is just six
times as great as it is in the country, a result, no doubt, due to the ammonia
evolved during the combustion of fuel, and to animal exhalations, and to the
same cause, the large quantity contained in the moisture of fogs in Paris
may also be attributed. Barral and Way have made determinations of the
quantity of ammonia carried down by the rain in each month of the year, the
former using for this purpose the water collected in the rain-gauges of the
Paris Observatory, and representing, therefore, a town atmosphere; the
latter, that from a large rain-gauge at Rothamsted, at a distance from any
town. According to Barral the ammonia annually deposited on an acre of
land amounts to 12·28 lbs., a quantity considerably exceeding that obtained
by Way, whose experiments being made at a distance from towns, must be
considered as representing more accurately the normal condition of the air.
His results for the years 1855 and 1856 are given below, along with the
quantities of nitric acid found at the same time.
Nitric Acid.—The presence of nitric acid in the air appears to have been
first observed by Priestley at the end of the last century, but Liebig, in 1825,
showed that it was always to be found after thunder-storms, although he
failed to detect it at other times. In 1851 Barral proved that it is invariably
present in rain-water, and stated the quantity annually carried down to an
acre of land at no less than 41·29 lbs. But at the time his experiments were
made, the methods of determining very minute quantities of nitric acid were

exceedingly defective, and Way, by the adoption of an improved process,
has shown that the quantity is very much smaller than Barral supposed, and
really falls short of three pounds. His results for ammonia, as well as nitric
acid, are given in the subjoined table.

Nitric Acid in Ammonia in Total Nitrogen in
Grains. Grains. Grains.
1855. 1856. 1855. 1856. 1855. 1856.
January 230 1564 1244 5,005 1084 4,526
February 944 544 2337 4,175 2169 3,579
March 1102 866 4513 2,108 3995 1,945
April 325 1063 1141 8,614 1024 7,369
May 1840 3024 4206 18,313 3939 15,863
June 3303 2046 5574 4,870 5447 4,540
July 2680 1191 9620 2,869 8615 2,670
August 3577 2125 4769 4,214 4870 4,021
September 732 1756 3313 5,972 2917 5,373
October 4480 2075 7592 3,921 7414 3,767
November 1007 1371 3021 2,591 2749 2,489
December 664 2035 2438 4,070 2180 3,352
Total in pounds for
2·98 ·280 7·11 9·53 6·63 8·31
the whole year

No attempts have been made to determine the proportion of nitric acid in
air, but its quantity is undoubtedly excessively minute, and materially
smaller than that of ammonia. At least this conclusion seems to be a fair
inference from Way's researches, as well as the recent experiments of
Boussingault on the proportion of nitric acid contained in rain, dew, and
fog, made in a manner exactly similar to those on the ammonia, already
quoted. According to his experiments an imperial gallon contains—

Grs.
Rain. {Paris 0·0708
{Liebfrauenberg 0·0140
Dew. {Maximum 0·0785
{Minimum 0·0030

Fog. {Paris 0·7092
{Liebfrauenberg 0·0718

Although it thus appears that Barral's results have been only partially
confirmed, enough has been ascertained to show that the quantity of
ammonia and nitric acid in the air is sufficient to produce a material
influence in the growth of plants. The large amount of these substances
contained in the dew is also particularly worthy of notice, and may serve to
some extent to explain its remarkably invigorating effect on vegetation.
Carburetted Hydrogen.—Gay-Lussac, Humboldt, and Boussingault have
shown, that when the whole of the moisture and carbonic acid have been
removed from the air, it still contains a small quantity of carbon and
hydrogen; and Saussure has rendered it probable that they exist in a state of
combination as carburetted hydrogen gas. No definite proof of this position
has, however, as yet been adduced, and the function of the compound is
entirely unknown. It is possible that the presence of carbon and hydrogen
may be due to a small quantity of organic matter; but, whatever be its
source, its amount is certainly extremely small.
Sulphuretted Hydrogen and Phosphuretted Hydrogen.—The proportion of
these substances is almost infinitesimal; but they are pretty general
constituents of the atmosphere, and are apparently derived from the
decomposition of animal and vegetable matters.
The preceding statements lead to the important conclusion, that the
atmosphere is capable of affording an abundant supply of all the organic
elements of plants, because it not only contains nitrogen and oxygen in the
free state, but also in those forms of combination in which they are most
readily absorbed, as well as a large quantity of carbonic acid, from which
their carbon may be derived. At first sight it may indeed appear that the
quantity of the latter compound, and still more that of ammonia, is so
trifling as to be of little practical importance. But a very simple calculation
serves to show that, though relatively small, they are absolutely large, for
the carbonic acid contained in the whole atmosphere amounts in round
numbers to
2,400,000,000,000 tons,

and the ammonia, assuming it not to exceed one part in fifty millions, must
weigh
74,000,000 tons,
quantities amply sufficient to afford an abundant supply of these elements
to the whole vegetation of our globe.
The Soil as a Source of the Organic Constituents of Plants.—When a
portion of soil is subjected to heat, it is found that it, like the plant, consists
of a combustible and an incombustible part; but while in the plant the
incombustible part or ash is small, and the combustible large, these
proportions are reversed in the soil, which consists chiefly of inorganic or
mineral matters, mixed with a quantity of combustible or organic
substances, rarely exceeding 8 or 10 per cent, and often falling considerably
short of this quantity.
The organic matter exists in the form of a substance called humus, which
must be considered here as a source of the organic constituents of plants,
independently of the general composition of the soil, which will be
afterwards discussed.
The term humus is generic, and applied by chemists to a rather numerous
group of substances, very closely allied in their properties, several of which
are generally present in all fertile soils. They have been submitted to
examination by various chemists, but by none more accurately than by
Mulder and Herman, to whom, indeed, we owe almost all the precise
information we possess on the subject. The organic matters of the soil may
be divided into three great classes; the first containing those substances
which are soluble in water; the second, those extracted by means of caustic
potash; and the third, those insoluble in all menstrua. When a soil is boiled
with a solution of caustic potash, a deep brown fluid is obtained, from
which acids precipitate a dark brown flocculent substance, consisting of a
mixture of at least three different acids, to which the names of humic,
ulmic, and geic acids have been applied. The fluid from which they have
been precipitated contains two substances, crenic and apocrenic acids, while
the soil still retains what has been called insoluble humus.

The acids above named do not differ greatly in chemical characters, but
they have been subdivided into the humic, geic, and crenic groups, which
present some differences in properties and composition. They are
compounds of carbon, hydrogen, and oxygen, and are characterised by so
powerful an affinity for ammonia that they are with difficulty obtained free
from that substance, and generally exist in the soil in combination with it.
They are all products of the decomposition of vegetable matters in the soil,
and are formed during their decay by a succession of changes, which may
be easily traced by observing the course of events when a piece of wood or
any other vegetable substance is exposed for a length of time to air and
moisture. It is then found gradually to disintegrate with the evolution of
carbonic acid, acquiring first a brown and finally a black colour. At one
particular stage of the process it is converted into one or other of two
substances, called humin and ulmin, both insoluble in alkalies, and
apparently identical with the insoluble humus of the soil; but when the
decomposition is more advanced the products become soluble in alkalies,
and then contain humic, ulmic, and geic acids, and finally, by a still further
progress, crenic and apocrenic acids are formed as the result of an oxidation
occurring at certain periods of the decay.
The roots and other vegetable debris remaining in the soil undergo a similar
series of changes, and form the humus, which is found only in the surface
soil, that is to say, in the portion which is now or has at some previous
period been occupied by plants, and the quantity of humus contained in any
soil is mainly dependent on the activity of vegetation on it. Numerous
analyses of humus compounds extracted from the soil have been made, and
have served to establish a number of minor differences in the composition
even of those to which the same name has been applied, due manifestly to
the fact that their production is the result of a gradual decomposition, which
renders it impossible to extract from the soil one pure substance, but only a
variable mixture of several, so similar to one another in properties, that their
separation is very difficult, if not impossible. For this reason great
discrepancies exist in the statements made regarding them by different
observers, but this is a matter of comparatively small importance, as their
exact composition has no very direct bearing on agricultural questions, and
it will suffice to give the names and chemical formulæ of those which have
been analysed and described,—

Ulmic acid from long Frisian turf C40 H18 O16
Humic acid from hard turf C40 H15 O15
Humic acid from arable soil C40 H16 O16
Humic acid from a pasture field C40 H14 O14
Geic acid C40 H15 O17
Apocrenic acid C48 H12 O24
Crenic acid C24 H12 O16

It is only necessary to observe further, that these formulæ indicate a close
connection with woody fibre, and the continuous diminution of the
hydrogen and increase of oxygen shows that they must have been produced
by a gradually advancing decay.
The earlier chemists and vegetable physiologists attributed to the humus of
the soil a much more important function than it is now believed to possess.
It was formerly considered to be the exclusive, or at least the chief source of
the organic constituents of plants, and by absorption through the roots to
yield to them the greater part of their nutriment. But though this view has
still some supporters, among whom Mulder is the most distinguished, it is
now generally admitted that humus is not a direct source of the organic
constituents of plants, and is not absorbed as such by their roots, although it
is so indirectly, in as far as the decomposition which it is constantly
undergoing in the soil yields carbonic acid, which can be absorbed. The
older opinion is refuted by many well-ascertained facts. As regards the
exclusive origin of the carbon of plants from humus, it is easy to see that
this at least cannot be true, for humus, as already stated, is itself derived
solely from the decomposition of vegetable and animal matters; and if the
plants on the earth's surface were to be supported by it alone, the whole of
their substance would have to return to the soil in the same form, in order to
supply the generation which succeeds them. But this is very far from being
the case, for the respiration of animals, the combustion of fuel, and many
other processes, are annually converting a large quantity of these matters
into carbonic acid; and if there were no other source of carbon but the
humus of the soil, the amount of vegetable life would gradually diminish,
and at length become entirely extinct. Schleiden, who has discussed this

subject very fully, has made an approximative calculation of the total
quantity of humus on the earth's surface, and of the carbon annually
converted into carbonic acid by the respiration of man and animals, the
combustion of wood for fuel, and other minor processes; and he draws the
conclusion that, if there were no other source of carbon except humus, the
quantity of that substance existing in the soil would only support vegetation
for a period of sixty years.
The particular phenomena of vegetation also afford abundant evidence that
humus cannot be the only source of carbon. Thus Boussingault has shown
that on the average of years, the crops cultivated on an acre of land remove
from it about one ton more organic matter than they receive in the manure
applied to them, although there is no corresponding diminution in the
quantity of humus contained in the soil. An instance which leads still more
unequivocally to the same conclusion is given by Humboldt. He states that
an acre of land, planted with bananas, yields annually about 152,000
pounds weight of fruit, containing about 32,000 pounds, or almost exactly
14 tons of carbon; and as this production goes on during a period of twenty
years, there must be withdrawn in that time no less than 280 tons of carbon.
But the soil on an acre of land weighs, in round numbers, 1000 tons, and
supposing it to contain 4 per cent of humus, the total weight of carbon in it
would amount to little more than 20 tons.
It is obvious from these and many other analogous facts that humus cannot
be the only or even a considerable source of the carbon of plants, although
it is still contended by some chemists that it may be absorbed to a small
extent. But even this is at variance with many well-known facts. For if
humus were absorbed, it might be expected that vegetation would be most
luxuriant on soils containing abundance of that substance, especially if it
existed in a soluble and readily absorbable form; but so far from this being
the case, nothing is more certain than that peat, in which these conditions
are fulfilled, is positively injurious to most plants. On the other hand, our
daily experience affords innumerable examples of plants growing
luxuriantly in soils and places where no humus exists. The sands of the sea-
shore, and the most barren rocks, have their vegetation, and the red-hot
ashes which are thrown out by active volcanoes are no sooner cool than a
crop of plants springs up on them.

The conclusions to be drawn from these considerations have been further
confirmed by the direct experiments of different observers. Boussingault
sowed peas, weighing 15·60 grains, in a soil composed of a mixture of sand
and clay, which had been heated red-hot, and consequently contained no
humus, and after 99 days' growth, during which they had been watered with
distilled water, he found the crop to weigh 68·72 grains, so that there had
been a fourfold increase. Similar experiments have been made by Prince
Salm Horstmar, on oats and rape sown in a soil deprived of organic matter
by ignition, in which they grew readily, and arrived at complete maturity.
One oat straw attained a height of three feet, and bore 78 grains; another
bore 47; and a third 28—in all 153. These when dried at 212° weighed
46·302 grains, and the straw 45·6 grains. The most satisfactory
experiments, however, are those of Weigman and Polstorf, these observers
having found that it was possible to obtain a two-hundred-fold produce of
barley in an entirely artificial soil, provided care was taken to give it the
physical characters of a fertile soil. They prepared a mixture of six parts of
sand, two of chalk, one of white bole, and one of wood charcoal; to which
was added a small quantity of felspar, previously fused with marble and
some soluble salts, so as to imitate as closely as possible the inorganic parts
of a soil, and in it they planted twelve barley pickles. The plants grew
luxuriantly, reaching a height of three feet, and each bearing nine ears,
containing 22 pickles. The grain of the twelve plants weighed 2040 grains.
These experiments show that plants can grow and produce seed when the
most scrupulous care is taken to deprive them of every trace of humus. But
Saussure has gone further, and shown that even when present, humus is not
absorbed. He allowed plants of the common bean and the Polygonum
Persicaria to grow in solutions of humate of potash, and found a very
trifling diminution in the quantity of humic acid present; but the value of his
experiments is invalidated by his having omitted to ascertain whether the
diminution of humic acid which he observed was really due to absorption
by the plant. This omission has been supplied by Weigman and Polstorf.
They grew plants of mint (Mentha undulata) and of Polygonum Persicaria
in solutions of humate of potash, and placed beside the glass containing the
plant, another perfectly similar, and containing only the solution of humate
of potash. The solution, which contained in every 100 grains, 0·148 grains
of solid matter, consisting of humate of potash, etc. was found to become

gradually paler, and at the end of a month, during which time the plants had
increased by 6-1/2 inches, the quantity of solid matter in 100 grains had
diminished to 0·132. But the solution contained in the other glass, and in
which no plant had grown, had diminished to 0·136, so that the absorption
could not have amounted to more than 0·004 grains for every 100 grains of
solution employed. This quantity is so small as to be within the limits of
error of experiment, and we are consequently entitled to draw the
conclusion that humus, even under the most favourable circumstances, is
not absorbed by plants.
But though not directly capable of affording nutriment to plants, it must not,
on that account, be supposed that humus is altogether devoid of importance,
for it is constantly undergoing decomposition in the soil, and thus becomes
a source of carbonic acid which can be absorbed, and, as we shall
afterwards more particularly see, it exercises very important functions in
bringing the other constituents of the soil into readily available forms of
combination.
It has been already observed that carbon, hydrogen, nitrogen, and oxygen,
cannot be absorbed by plants when uncombined, but only in the forms of
water, carbonic acid, ammonia, and nitric acid. It is scarcely necessary to
detail the grounds on which this conclusion has been arrived at in regard to
carbon and hydrogen, for practically it is of little importance whether they
can be absorbed or not, as the former is rarely, the latter never, found
uncombined in nature. Neither can there be any doubt that water and
carbonic acid are the only substances from which these elements can be
obtained. Every-day experience convinces us that water is essential to
vegetation; and Saussure, and other observers, have shown that plants will
not grow if they are deprived of carbonic acid, and that they actually absorb
that substance abundantly from the atmosphere. The evidence for the non-
absorption of oxygen lies chiefly in the fact that plants obtain, in the form
of water and carbonic acid, a larger quantity of that element than they
require, and in place of absorbing, are constantly exhaling it. The form in
which nitrogen may be absorbed has given rise to much difference of
opinion. In the year 1779, Priestley commenced the examination of this
subject, and drew from his experiments the conclusion, that plants absorb
the nitrogen of the air. Saussure shortly afterwards examined the same
subject, and having found, that when grown in a confined space of air, and

watered with pure water, the nitrogen of the plants underwent no increase,
he inferred that they derived their entire supplies of that element from
ammonia, or the soluble nitrogenous constituents of the soil or manure.
Boussingault has since re-examined this question, and by a most elaborate
series of experiments, in which the utmost care was taken to avoid every
source of fallacy, he was led to the conclusion, that when haricots, oats,
lupins, and cresses were grown in calcined pumice-stone, mixed with the
ash of plants, and supplied with air deprived of ammonia and nitric acid,
their nitrogen underwent no increase. It has been objected to these
experiments, that the plants being confined in a limited bulk of air, were
placed in an unnatural condition, and Ville has recently repeated them with
a current of air passing through the apparatus, and found a slight increase in
the nitrogen, due, as he thinks, to direct absorption. It is much more
probable, however, that it depends on small quantities of ammonia or nitric
acid which had not been completely removed from the air by the means
employed for that purpose, for nothing is more difficult than the complete
abstraction of these substances, and as the gain of nitrogen was only 0·8
grains, while 60,000 gallons of air, and 13 of water, were employed in the
experiment, which lasted for a considerable time, it is reasonable to suppose
that a sufficient quantity may have remained to produce this trifling
increase.
While these experiments show that plants maintain only a languid existence
when grown in air deprived of ammonia and nitric acid, and hence, that the
direct absorption of nitrogen, if it occur at all, must do so to a very small
extent, the addition of a very minute quantity of the former substance
immediately produces an active vegetation and rapid increase in size of the
plants. Among the most striking proofs of this are the experiments of Wolff,
made by growing barley and vetches in a soil calcined so as to destroy
organic matters, and then mixed with small quantities of different
compounds of ammonia. He found that when the produce from the calcined
soil was represented by 100, that from the different ammoniacal salts was—

Barley. Vetches.
Muriate of Ammonia 257·2 176·4
Carbonate of Ammonia 123·6 173·8
Sulphate of Ammonia 203·6 125·2

These experiments not only prove that ammonia can be absorbed, but they
also indirectly confirm the statement already made, that humus is not
necessary; for in some instances the produce was higher than that obtained
from the uncalcined soil with the same manures, although it contained four
per cent of humus.
On such experiments Liebig rests his opinion that ammonia is the exclusive
source of the nitrogen of plants, and although he has recently admitted that
it may be replaced by nitric acid, it is obvious that he considers this a rare
and exceptional occurrence. The evidence, however, for the absorption of
nitric acid appears to rest on as good grounds as that of ammonia, for
experience has shown that nitrate of soda acts powerfully as a manure, and
its effect must be due to the nitric acid, and not to the soda, for the other
compounds of that alkali have no such effect. Wolff has illustrated this point
by a series of experiments on the sunflower, of which we shall quote one.
He took two seeds of that plant, and sowed them on the 10th May, in a soil
composed of calcined sand, mixed with a small quantity of the ash of
plants, and added at intervals during the progress of the experiment, a
quantity of nitrate of potash, amounting in all to 17·13 grains. The plants
were watered with distilled water, containing carbonic acid in solution, and
the pot in which they grew was protected from rain and dew by a glass
cover. On the 19th August one of the plants had attained a height of above
28 inches, and had nine fine leaves and a flower-bud; the other was about
20 inches high, and had ten leaves. On the 22d August, one of the plants
having been accidentally injured, the experiment was terminated. The
plants, which contained 103·16 grains of dry matter, were then carefully
analysed, and the quantity of nitrogen contained in the soil after the
experiment and in the seed was determined.

Grains.
Nitrogenin the dry plants 1·737 }
" remaining in the soil 0·697 } 2·434
" in the nitrate of potash 2·370 }
" in the seeds 0·029 } 2·399
———
Difference 0·035

Hence, the nitrogen contained in the plants must, in this instance, have been
obtained entirely from the nitrate of potash, for the quantity contained in it
and in the seeds is exactly equal to that in the plants and the soil, the
difference of 0·03 grains being so small that it may be safely attributed to
the errors inseparable from such experiments. For the sake of comparison,
an exactly similar experiment was made on two seeds grown without nitrate
of potash, and in this instance, after an equally long period of growth, the
largest plant had only attained a height of 7·5 inches, and had three small
pale and imperfectly developed leaves. They contained only 0·033 grains of
nitrogen, while the seeds contained 0·032—indicating that, under these
circumstances, there was no increase in the quantity of that element.
But, independently of these experimental results, it may be inferred from
general considerations, that nitric acid must be one of the sources from
which plants derive their nitrogen. It has been already stated, that the humus
contained in the soil consists of the remains of decayed plants, and there is
every reason to suppose that the primeval soil contained no organic matters,
and that the first generation of plants must have derived the whole of their
nitrogen from, the atmosphere. If, therefore, it be assumed that ammonia is
the only source of the nitrogen of plants, it would follow, that as that
substance cannot be produced by the direct union of its elements, the
quantity of ammonia in the air could only remain undiminished in the event
of the whole of the nitrogen of decaying plants returning into that form. But
this is certainly not the case, for every time a vegetable substance is burned,
part of its nitrogen is liberated in the free state, and in certain conditions of
putrefaction, nitric acid is produced. Now, if ammonia be the only form in
which nitrogen is absorbed, there must be a gradual diminution of the
quantity contained in the air; and further, there must either be some
continuous source of supply by which its quantity is maintained, or there
must be some other substance capable of affording nitrogen in a form fitted
for the maintenance of plant life. As regards the first alternative, it must be
stated that we know of no source other than the decomposition of plants
from which ammonia can be derived, and we are therefore compelled to
adopt the second alternative, and to admit that there must be some other
source of nitrogen, and it cannot be doubted, from what has been already
stated, that it is from nitric acid only that it can be obtained.

It must be admitted, then, that carbonic acid, ammonia, nitric acid, and
water, are the great organic foods of plants. But while they have afforded to
them an inexhaustible supply of the last, the quantity of the other three
available for food are limited, and insufficient to sustain their life for a
prolonged period. It has been shown by Chevandrier, that an acre of land
under beech wood accumulates annually about 1650 lb. of carbon. Now, the
column of air resting upon an acre of land contains only about 15,500 lb. of
carbon, and the soil may be estimated to contain 1 per cent., or 22,400 lb.
per acre, and the whole of this carbon would therefore be removed, both
from the air and the soil, in the course of little more than 23 years. But it is
a familiar fact, that plants continue to grow with undiminished luxuriance
year after year in the same soil, and they do so because neither their carbon
nor their nitrogen are permanently absorbed; they are there only for a
period, and when the plant has finished its functions, and dies, they sooner
or later return into their original state. Either the plant decays, in which case
its carbon and nitrogen pass more or less rapidly into their original state, or
it becomes the food of animals, and by the processes of respiration and
secretion, the same change is indirectly effected. In this way a sort of
balance is sustained; the carbon, which at one moment is absorbed by the
plant, passes in the next into the tissues of the animal, only to be again
expired in that state in which it is fitted to commence again its round of
changes.
But while there is thus a continuous circulation of these constituents
through both plants and animals, there are various changes which tend to
liberate in the free state a certain quantity both of the carbon and nitrogen of
plants, and these being thus removed from the sphere of organic life, there
would be a gradual diminution in the amount of vegetation at the earth's
surface, unless this loss were counterbalanced by some corresponding
source of gain. In regard to carbonic acid the most important source is
volcanic action, but the loss of nitrogen, which is far more important and
considerable, is restored by the direct combination of its elements. The
formation of nitric acid during thunder storms has been long familiar; but it
would appear from the recent experiments of Clöez, which, should they be
confirmed by farther enquiry, will be of much importance, that this
compound is also produced without electrical action when air is passed over
certain porous substances, saturated with alkaline and earthy compounds.

Fragments of calcined brick and pumice stone were saturated with solution
of carbonate of potash, with carbonates of lime and magnesia and other
mixtures, and a current of air freed from nitric acid and ammonia passed
over them for a long period, at the end of which notable quantities of nitric
acid were detected.
Source of the Inorganic Constituents of Plants.—The inorganic constituents
of plants being all fixed substances, it is sufficiently obvious that they can
only be obtained from the soil, which, as we shall afterwards see, contains
all of them in greater or less abundance, and has always been admitted to be
the only substance capable of supplying them. The older chemists and
physiologists, however, attributed no importance to these substances, and
from the small quantities in which they are found in plants, imagined that
they were there merely accidental impurities absorbed from the soil along
with the humus, which was at that time considered to be their organic food.
This opinion, sufficiently disproved by the constant occurrence of the same
substances in nearly the same proportions, in the ash of each individual
plant, has been further refuted by the experiments of Prince Salm Horstmar,
who has established their importance to vegetation, by experiments upon
oats grown on artificial soils, in each of which one inorganic constituent
was omitted. He found that, without silica, the grain vegetated, but
remained small, pale in colour, and so weak as to be incapable of supporting
itself; without lime, it died when it had produced its second leaf; without
potash and soda, it grew only to the height of three inches; without
magnesia, it was weak and incapable of supporting itself; without
phosphoric acid, weak but upright; and without sulphuric acid, though
normal in form, the plant was feeble, and produced no fruit.
Manner in which the Constituents of Plants are absorbed.—Having treated
of the sources of the elements of plants, it is necessary to direct attention to
the mode in which they enter their system.
Water.—The absorption of water by plants takes place in great abundance,
and is connected with many of the most important phenomena of
vegetation. It is principally absorbed by the roots, and passes into the
tissues of the plant, where a part of it is decomposed, and goes to the
formation of certain of its organic compounds; while by far the larger
quantity, in place of remaining in it, is again exhaled by the leaves. The

extent to which this takes place is very large. Hales found that a sunflower
exhaled in twelve hours about 1 lb. 5 oz. of water, but this quantity was
liable to considerable variation, being greater in dry, and less in wet
weather, and much diminished during the night. Saussure made similar
experiments, and observed that the quantity of water exhaled by a
sunflower amounted to about 220 lb. in four months. The exhalation of
plants has recently been examined with great accuracy by Lawes. His
experiments were made by planting single plants of wheat, barley, beans,
peas, and clover, in large glass jars capable of holding about 42 lb. of soil,
and covered with glass plates, furnished with a hole in the centre for the
passage of the stem of the plant. Water was supplied to the soil at certain
intervals, and the jars were carefully weighed. The result of the
experiments, continued during a period of 172 days, is given in the
following table, which shows the total quantity of water exhaled in grains:
—

Wheat 113,527
Barley 120,025
Beans 112,231
Peas 109,082
Clover, cut 28th June 55,093

It further appears, that the exhalation is not uniform, but increases during
the active growth of the plant, and diminishes again when that period is
passed. These variations are shown by the subjoined tables, of which the
first gives the total exhalation, and the second the average daily loss of
water during certain periods.

Table I.—Showing the Number of Grains of Water given off by the
Plants during stated divisional Periods of their Growth.

Description 31 27
9 Days. 27 Days. 34 Days. 30 Days. 14 Days.
of Plant. Days. Days.
From From From From From From From
Mar. 19 Mar. 28 Apr. 28 May 25 June 28 July 28 Aug. 11

to Mar. to Apr. to May to June to July to Aug. to Sept.
28. 28. 25. 28. 28. 11. 7.
Wheat 129 1268 4,385 40,030 46,060 15,420 6235
Barley 129 1867 12,029 37,480 45,060 17,046 6414
Beans 88 1854 4,846 30,110 58,950 12,626 3657
Pease 101 1332 2,873 36,715 62,780 5,281 ...
Clover 400 1645 2,948 50,100 ... ... ...

Table II.—Showing the average daily Loss of Water (in Grains) by the
Plants, within several stated divisional Periods of their Growth.

31 27 27
9 Days. 34 Days. 30 Days. 14 Days.
Days. Days. Days.
Description From From From From From From From
of Plant. Mar. 19 Mar. 28 Apr. 28 May 25 June 28 July 28 Aug. 11
to Mar. to Apr. to May to June to July to Aug. to Sept.
28. 28. 25. 28. 28. 11. 7.
Wheat 14·3 40·9 162·4 1177·4 1535·3 1101·4 230·9
Barley 14·3 60·2 445·5 1102·3 1502·0 1217·6 237·5
Beans 9·7 59·8 179·5 885·6 1965·0 901·8 135·4
Peas 11·2 42·9 106·4 1079·8 2092·7 377·2 ...
Clover 44·4 53·0 109·2 1473·5 ... ... ...

Similar experiments were made with the same plants in soils to which
certain manures had been added, and with results generally similar.
Calculating from these experiments, we are led to the apparently anomalous
conclusion that the quantity of water exhaled by the plants growing on an
acre of land greatly exceeds the annual fall of rain; although it is obvious
that of all the rain which falls, only a small proportion can be absorbed by
the plants growing on the soil, for a large quantity is carried off by the
rivers, and never reaches their roots. It has been calculated, for instance,
that the Thames carries off in this way at least one-third of the annual rain
that falls in the district watered by it, and the Rhine nearly four-fifths. Of
course this large exhalation must depend on the repeated absorption of the
same quantity of water, which, after being exhaled, is again deposited on

the soil in the form of dew, and passes repeatedly through the plant. This
constant percolation of water is of immense importance to the plant, as it
forms the channel through which some of its other constituents are carried
to it.
Carbonic Acid.—While the larger part of the water which a plant requires is
absorbed by its roots, the reverse is the case with carbonic acid. A certain
proportion no doubt is carried up through the roots by the water, which
always contains a quantity of that gas in solution, but by far the larger
proportion is directly absorbed from the air by the leaves. A simple
experiment of Boussingault's illustrates this absorption very strikingly. He
took a large glass globe having three apertures, through one of which he
introduced the branch of a vine, with twenty leaves on it. With one of the
side apertures a tube was connected, by means of which the air could be
drawn slowly through the globe, and into an apparatus in which its carbonic
acid was accurately determined. He found, in this way, that while the air
which entered the globe contained 0·0004 of carbonic acid, that which
escaped contained only 0·0001, so that three-fourths of the carbonic acid
had been absorbed.
Ammonia and Nitric Acid.—Little is known regarding the mode in which
these substances enter the plant. It is usually supposed that they are entirely
absorbed by the roots, and no doubt the greater proportion is taken up in
this way, but it is very probable that they may also be absorbed by the
leaves, at least the addition of ammonia to the air in which plants are
grown, materially accelerates vegetation. It is probable, however, that the
rain carries down the ammonia to the roots, and there is no doubt that that
derived from the decomposition of the nitrogenous matters in the soil is so
absorbed.
Inorganic Constituents.—The inorganic constituents of course are entirely
absorbed by the roots; and it is as a solvent for them that the large quantity
of water continually passing through the plants is so important. They exist
in the soil in particular states of combination, in which they are scarcely
soluble in water. But their solubility is increased by the presence of
carbonic acid contained in the water, and which causes it to dissolve, to
some extent, substances otherwise insoluble. It is in this way that lime,
which occurs in the soil principally as the insoluble carbonate, is dissolved

and absorbed. And phosphate of lime is also taken up by water containing
carbonic acid, or even common salt in solution. The amount of solubility
produced by these substances is extremely small; but it is sufficient for the
purpose of supplying to the plant as much of its mineral constituents as are
required, for the quantity of water which, as we have already seen, passes
through a plant is very large when compared with the amount of inorganic
matters absorbed. It has been shown by Lawes and Gilbert, that about 2000
grains of water pass through a plant for every grain of mineral matter fixed
in it, so that there is no difficulty in understanding how the absorption takes
place.
It is worthy of notice, however, that the absorption of the elements of plants
takes place even though they may not be in solution in the soil, the roots
apparently possessing the power of directly acting on and dissolving
insoluble matters; but a distinction must be drawn between this and the
view entertained by Jethro Tull, who supposed that they might be absorbed
in the solid state, provided they were reduced to a state of sufficient
comminution. It is now no longer doubted that, whatever action the roots
may exert, the constituents of the plant must be in solution before they can
pass into it—experiment having distinctly shown that the spongioles or
apertures through which this absorption takes place are too minute to admit
even the smallest solid particle.

CHAPTER II.
THE PROXIMATE CONSTITUENTS OF PLANTS.

The substances absorbed by the plant, which are of simple composition, and
contain only two elements, are elaborated within it, and converted into the
many complicated compounds of which its mass is composed. Some of
these, as, for example, the colouring matters of madder and indigo, the
narcotic principle of the poppy, &c., are confined to a single species, or
small group of plants, while others are found in all plants, and form the
main bulk of their tissues. The latter are the only substances which claim
notice in a treatise like the present. They have been divided into three great
classes, of widely different properties, composition, and functions.
1st. The Saccharine and Amylaceous Constituents.—These substances are
compounds of carbon, hydrogen, and oxygen, and all possess a certain
degree of similarity in composition, the quantities of hydrogen and oxygen
they contain being always in the proportion required to form water, so that
they may be considered as compounds of carbon and water; not that it can
be asserted that they actually do contain water, as such, for of that there is
no evidence, but only that its elements are present in the proportion to form
it.
Cellulose.—This substance forms the fundamental part of all plants. It is the
principal constituent of woody fibre, and is found in a state of purity in the
fibre of cotton and flax, and in the pith of plants; but in wood it is generally
contaminated with another substance, which has received the name
incrusting matter, because it is deposited in and around the cells of which
the plant is in part composed. Cellulose is insoluble in all menstrua, but,
when boiled for a long time with sulphuric acid, is converted into a
substance called dextrine. Cellulose consists of—

From pith of Elder-tree. Spongioles of roots.
Carbon 43·37 43·00
Hydrogen 6·04 6·18

Oxygen 50·59 50·82
——— ———
100·00 100·00

It is represented chemically by the formula, C24H21O21, which shows it to
be a compound of 24 atoms of carbon with 21 of hydrogen and 21 of
oxygen.
Incrusting matter.—Large quantities of this substance enter into the
composition of all plants. Of its chemical nature little is known, as it cannot
be obtained separate from cellulose, but it is analogous to that substance in
its composition, and probably contains hydrogen and oxygen in the
proportion to form water.
Starch.—Starch is one of the most abundant constituents of plants, and is
found in most seeds, as those of the cereals and the leguminous plants; in
the tubers of the potatoe, the bulbs of tulips, &c. &c. It is obtained by
placing a quantity of wheat flour in a bag, and kneading it under a gentle
stream of water. When the water is allowed to stand, it deposits the starch as
a fine white powder, which, when examined by the microscope, is found to
be composed of minute grains, formed of concentric layers deposited on
one another. These grains vary considerably in size and structure in
different plants; but in the same plant they are generally so much alike as to
admit of their recognition by a practised observer. They were formerly
believed to be composed of an external coating of a substance insoluble in
water, and containing in their interior a soluble kernel; but this opinion has
been refuted, and distinct evidence been brought to show that the exterior
and interior of the globules are identical in chemical properties. Starch is
insoluble in cold water, but by boiling, it dissolves, forming a thick paste.
By long continued boiling with water containing a small quantity of acid, it
is completely dissolved and converted into dextrine, and eventually into
sugar. The same change is produced by the action of fermenting substances,
such as the extract of malt; when heated in the dry state to a temperature of
about 390 Fahr., it becomes soluble in cold water. It is distinguished by
giving a brilliant blue compound with iodine. Starch contains—

Carbon 44·47
Hydrogen 6·28

Oxygen 49·25
———
100·00

and its composition is represented by the formula C12H10O10, so that it
differs but little from cellulose in composition, although its chemical
functions in the plant are extremely different. It is connected with some of
the most important changes which occur in the growing plants, and by a
series of remarkable transformations is converted into sugar and other
important compounds.
Lichen Starch is found in most species of lichens, and is distinguished from
common starch by producing a green colour with iodine. Its composition is
the same as that of ordinary starch.
Inuline.—The species of starch to which this name is given is characterised
by its dissolving in boiling water, and giving a white pulverulent deposit in
cooling. It is found in the tuber of the dahlia, in the dandelion, and some
other plants. Its composition is identical with that of cellulose, and its
formula is C24H21O21.

Gum is excreted from various plants as a thick fluid, which dries up into
transparent masses. Its composition is identical with that of starch. It
dissolves readily in cold water, and is converted into sugar by long
continued boiling with acids. Its properties are best marked in gum arabic,
which is obtained from various species of acacia; that from other plants
differs to some extent, although its chemical composition is the same.
Dextrine.—When starch is exposed to a heat of about 400°, or when treated
with sulphuric acid, or with a substance extracted from malt called diastase,
it is converted into dextrine. It may also be obtained from cellulose by a
similar treatment. The dextrine so obtained has the same composition as the
starch from which it is produced, but its properties more nearly resemble
those of gum. It plays a very important part in the process of germination,
and may be converted into sugar on the one hand, and apparently also into
starch on the other.

Sugar.—Under this name are included four or five distinct substances, of
which the most important are, cane sugar, grape sugar, and the
uncrystallisable sugar found in many plants.
Cane Sugar.—This variety of sugar, as its name implies, is found most
abundantly in the sugar cane, but it occurs also in the maple, beet-root, and
various species of palms, from all of which it is extracted on the large scale.
It is extremely soluble in water, and can be obtained in large transparent
prismatic crystals, as in common sugar-candy. It swells up, and is converted
into a brown substance called caramel, when heated, and by contact with
fermenting substances, yields alcohol and carbonic acid. It contains—

Carbon 42·22
Hydrogen 6·60
Oxygen 51·18
———
100·00

and its chemical formula is C12H11O11.

Grape Sugar is met with in the grape, and most other fruits, as well as in
honey. It is produced artificially when starch is boiled for a long time with
sulphuric acid, or treated with a large quantity of diastase. It is less soluble
in water than cane sugar, and crystallises in small round grains. Its
composition, when dried at 284°, is—

Carbon 40·00
Hydrogen 6·66
Oxygen 53·34
———
100·00

and its formula is C12H12O12; but when crystallised it contains two
equivalents of water, and is then represented by the formula C12H12O12 +
2H2O.

The uncrystallisable sugar of plants is closely allied to grape sugar, and, so
far as at present known, has the same composition, although, from the
difficulty of obtaining it quite free from crystallised sugar, this is still
uncertain.
Mucilage is the name applied to the substance existing in linseed, and in
many other seeds, and which communicates to them the property of
swelling up and becoming gelatinous when treated with water. It is found in
a state of considerable purity in gum tragacanth and some other gums. Its
composition is not known with absolute certainty, but it is either
C24H19O19, or C12H10O10; and in the latter case it must be identical with
starch and gum.
It will be observed that all the substances belonging to this class are very
closely related in chemical composition, some of them, as starch and gum,
though easily distinguished by their properties, being identical in
constitution, while others only differ in the quantity of water, or of its
elements which they contain. In fact, they may all be considered as
compounds of carbon and water, and their relations are, perhaps, more
distinctly seen when their formulæ are written so as to show this, as is done
in the following table, in the second column of which those containing
twelve equivalents of carbon are doubled, so as to make them comparable
with cellulose:—

Water.
Grape sugar, C12H12O12 C24H24O24 C24 + 24
Cane sugar, C12H11O11 C24H22O22 C24 + 22
Cellulose, C24H21O21 C24H21O21 C24 + 21
Inuline, C24H21O21 C24H21O21 C24 + 21
Starch, C12H10O10 C24H20O20 C24 + 20
Dextrine, C12H10O10 C24H20O20 C24 + 20
Gum, C12H10O10 C24H20O20 C24 + 20
Mucilage, C12H10O10 C24H20O20 C24 + 20

The relation between these substances being so close, it is not difficult to
understand how one may be converted into another by the addition or

subtraction of water. Thus, cellulose has only to absorb an equivalent of
water to become grape sugar, or to lose an equivalent in order to be
converted into starch, and we shall afterwards see that such changes do
actually occur in the plant during the process of germination.
Pectine and Pectic Acid.—These substances are met with in many fruits and
roots, as, for instance, in the apple, the carrot, and the turnip. They differ
from the starch group in containing more oxygen than is required to form
water along with their hydrogen; but their exact composition is still
uncertain, and they undergo numerous changes during the ripening of the
fruit.
2d. Oily or Fatty Matters.—The oily constituents of plants form a rather
extensive group of substances all closely allied, but distinguished by minor
differences in properties and constitution. Some of them are very widely
distributed throughout the vegetable kingdom, but others are almost
peculiar to individual plants. They are all compounds of carbon, hydrogen,
and oxygen, and are at once distinguished from the preceding class, by
containing much less oxygen than is required to form water with their
hydrogen. The principal constituents of the fatty matters and oils of plants
are three substances, called stearine, margarine, and oleine, the two former
solids, the latter a fluid; and they rarely, if ever, occur alone, but are mixed
together in variable proportions, and the fluidity of the oils is due
principally to the quantity of the last which they contain. If olive oil be
exposed to cold, it is seen to become partially solid; and if it be then
pressed, a fluid flows out, and a crystalline substance remains; the former is
oleine, though not absolutely pure, and the latter margarine. The perfect
separation of these substances involves a variety of troublesome chemical
processes; and when it has been effected, it is found that each of them is a
compound of a peculiar acid, with another substance having a sweet taste,
and which has received the name of glycerine, or the sweet principle of oil.
Glycerine, as it exists in the fats, appears to be a compound of C3H2O, and
its properties are the same from whatever source it is obtained. The acids
separated from it are known by the names of margaric, stearic, and oleic
acids.
Margaric Acid is best obtained pure by boiling olive oil with an alkali until
it is saponified, and decomposing the soap with an acid, expressing the

margaric acid, which separates, and crystallising it from alcohol. It is a
white crystalline fusible solid, insoluble in water, but soluble in alcohol and
in solutions of the alkalies. Its composition is—

Carbon 75·56
Hydrogen 12·59
Oxygen 11·85
———
100·00

and its formula C34H34O4.

Stearic Acid.—Although this acid exists in many plants, it is most
conveniently extracted from lard. It is a crystalline solid less fusible than
margaric acid, but closely resembling it in its other properties. Its formula is
C36H36O4.

Oleic Acid.—Under this name two different substances appear to be
included. It has been applied generally to the fluid acids of all oils, while it
would appear that the drying and non-drying oils actually contain
substances of different composition. The acid extracted from olive oil
appears to have the formula C36H34O4, while that from linseed oil is
C46H38O6, but this is still doubtful.

Other fatty acids have been detected in palm oil, cocoa-nut oil, &c. &c.,
which so closely resemble margaric and stearic acids as to be easily
confounded with them. Though presenting many points of interest, it is
unnecessary to describe them in detail here.
Wax is a substance closely allied to the oils. It consists of two substances,
cerine and myricine, which are separated from one another by boiling
alcohol, in which the former is more soluble. They are extremely complex
in composition, the former consisting principally of an acid similar to the
fatty acids, called cerotic acid, and containing C54H54O4. The latter has the
formula C92H92O4. The wax found in the leaves of the lilac and other plants
appears to consist of myricine, while that extracted from the sugar-cane is
said to be different, and to have the formula C48H50O2. It is probable that

other plants contain different sorts of wax, but their investigation is still so
incomplete, that nothing definite can be said regarding them. Wax and fats
appear to be produced in the plant from starch and sugar; at least it is
unquestionable that the bee is capable of producing the former from sugar,
and we shall afterwards see that a similar change is most probably produced
in the plant. The fatty matters contained in animals are identical with those
of plants.
3d. Nitrogenous or Albuminous Constituents of Plants and Animals.—The
nitrogenous constituents of plants and animals are so closely allied, both in
properties and composition, that they may be most advantageously
considered together.
Albumen.—Vegetable albumen is found dissolved in the juices of most
plants, and is abundant in that of the potato, the turnip, and wheat. In these
juices it exists in a soluble state, but when its solution is heated to about
150°, it coagulates into a flocky insoluble substance. It is also thrown down
by acids and alcohol. Coagulated albumen is soluble in alkalies and in nitric
acid. Animal albumen exists in the white of eggs, the serum of blood, and
the juice of flesh; and from all these sources is scarcely distinguishable in
its properties from vegetable albumen.
It is a substance of very complicated composition, and chemists are not
agreed as to the formula by which its constitution is to be expressed, a
difficulty which occurs also with most of the other nitrogenous compounds.
The results of the analyses of albumen from different sources are however
quite identical, as may be seen from those subjoined—

From Wheat. From Potatoes. From Blood. From White of Egg.
Carbon 53·7 53·1 53·4 53·0
Hydrogen 7·1 7·2 7·0 7·1
Nitrogen 15·6 ... 15·5 15·6
Oxygen } { ... 22·1 22·9
Sulphur }23·6{ 0·97 1·6 1·1
Phosphorus } { ... 0·4 0·3
—— —— ——
100·0 100·0 100·0

Closely allied to vegetable albumen is the substance known by the name of
glutin, which is obtained by boiling the gluten of wheat with alcohol. It
appears to be a sort of coagulated albumen, with which its composition
completely agrees.
Vegetable Fibrine.—If a quantity of wheat flour be tied up in a piece of
cloth, and kneaded for some time under water, the starch it contains is
gradually washed out, and there remains a quantity of a glutinous substance
called gluten. When this is boiled with alcohol, the glutin above referred to
is extracted, and vegetable fibrine is left. It dissolves in dilute potash, and
on the addition of acetic acid is deposited in a pure state. Treated with
hydrochloric acid, diluted with ten times its weight of water, it swells up
into a jelly-like mass. When boiled or preserved for a long time under
water, it cannot be distinguished from coagulated albumen.
Animal Fibrine exists in the blood and the muscles, and agrees in all its
characters and composition with vegetable fibrine, as is shown by the
subjoined analyses—

Wheat Flour. Blood. Flesh.
Carbon 53·1 52·5 53·3
Hydrogen 7·0 6·9 7·1
Nitrogen 15·6 15·5 15·3
Oxygen 23·2 24·0 23·1
Sulphur 1·1 1·1 1·2
—— —— ——
100·0 100·0 100·0

Caseine.—Vegetable caseine exists abundantly in most plants, especially in
the seeds, and remains in the juice after albumen has been precipitated by
heat, from which it may be separated in flocks by the addition of an acid. It
has been obtained for chemical examination, principally from peas and
beans, and from the almond and oats. When prepared from the pea it has
been called legumine, from almonds emulsine, and from oats avenine; but
they are all three identical in their properties, although formerly believed to
be different, and distinguished by these names. Vegetable caseine is best
obtained by treating peas or beans with hot water, and straining the fluid.

On standing, the starch held in suspension is deposited, and the caseine is
retained in solution in the alkaline fluid; by the addition of an acid it is
precipitated as a thick curd. Caseine is insoluble in water, but dissolves
readily in alkalies; its solution is not coagulated by heat, but, on
evaporation, becomes covered with a thin pellicle, which is renewed as
often as it is removed.
Animal Caseine is the principal constituent of milk, and is obtained by the
cautious addition of an acid to skimmed milk, by which it is precipitated as
a thick white curd. It is also obtained by the use of rennet, and the process
of curding milk is simply the coagulation of its caseine. It is soluble in
alkalies, and precipitated from its solution by acids, and in all other respects
agrees with vegetable caseine.
The composition of animal caseine has been well ascertained, but
considerable doubt still exists as to that of vegetable caseine, owing to the
difficulty of obtaining it absolutely pure. The analyses of different chemists
give rather discordant results, but we have given those which appear most
trustworthy—

From Peas.
Carbon 50·6 50·7
Hydrogen 6·8 6·6
Nitrogen 16·5 15·8
Oxygen 25·6 23·8
Sulphur 0·5 0·8
Phosphorus ... 2·3
—— ——
100·0 100·0

Other results differ considerably from these, and some observers have even
obtained as much as eighteen per cent of nitrogen and fifty-three of carbon.
The composition of animal caseine differs from this principally in the
amount of carbon. Its composition is—

Carbon 53·6
Hydrogen 7·1

Nitrogen 15·8
Oxygen 22·5
Sulphur 1·0
——
100·0

The most cursory examination of these analytical numbers is sufficient to
show that a very close relation subsists between the different substances just
described. Indeed, with the exception of vegetable caseine, they may be
said all to present the same composition; and, as already mentioned, there
are analyses of it which would class it completely with the others. While,
however, the quantities of carbon, hydrogen, nitrogen, and oxygen are the
same, differences exist in the sulphur and phosphorus they contain, and
which, though very small in quantity, are indubitably essential to them.
Much importance has been attributed to these constituents by various
chemists, and especially by Mulder, who has endeavoured to make out that
all the albuminous substances are compounds of a substance to which he
has given the name of proteine, with different quantities of sulphur and
phosphorus. The composition of proteine, according to his newest
experiments, is—

Carbon 54·0
Hydrogen 7·1
Nitrogen 16·0
Oxygen 21·4
Sulphur 1·5
——
100·0

and is exactly the same from whatever albuminous compound it is obtained.
Although the importance of proteine is probably not so great as Mulder
supposed, it affords an important illustration of the close similarity of the
different substances from which it is obtained, the more especially as there
is every reason to believe that the different albuminous compounds are
capable of changing into one another, just as starch and sugar are mutually
convertible; and the possibility of this change throws much light on many
of the phenomena of nutrition in plants and animals. Indeed, it would seem

probable that these compounds are formed from their elements by plants
only, and are merely assimilated by animals to produce the nitrogenous
constituents they contain.
Diastase is the name applied to a substance existing in malt, and obtained
by macerating that substance with cold water, and adding a quantity of
alcohol to the fluid, when the diastase is immediately precipitated in white
flocks. It is produced during the malting process, and is not found in the
unmalted barley. Its chemical composition is unknown, but it is
nitrogenous, and is believed to be produced by the decomposition of gluten.
If a very small quantity of diastase be mixed with starch suspended in hot
water, the starch is found gradually to dissolve, and to pass first into the
state of dextrine, then into that of sugar. The change thus effected takes
place also in a precisely similar manner in the plant, diastase being
produced during the process of germination of all seeds and tubers, for the
purpose of effecting this change, and to fulfil other functions less
understood, but no doubt equally important. Diastase is found in the seeds
only during the period when the starch they contain is passing into sugar; as
soon as that change has taken place, its function is ended, and it disappears.

CHAPTER III.
THE CHANGES WHICH TAKE PLACE IN THE FOOD OF
PLANTS DURING THEIR GROWTH.

The simple compounds which the plant absorbs from the atmosphere and
soil are elaborated within its system, and converted into the various
complex substances of which its tissues are composed, by a series of
changes, the details of which are still in some respects imperfectly known,
although their general nature is sufficiently well understood. They may be
best rendered intelligible by reference, in the first instance, to the changes
occurring during germination, when the young plant is nourished by a
supply of food stored up in the seed, in sufficient quantity to maintain its
existence until the organs by which it is afterwards to draw its nutriment
from the air and soil are sufficiently developed to serve that purpose.
Changes occurring during Germination.—When a seed is placed in the soil
under favourable circumstances, it becomes the seat of an important and
remarkable series of chemical changes, which result in the production of the
young plant. Experiment and observation have shown that heat, moisture,
and air, are necessary to the production of these changes, and though
probably not absolutely essential, the absence of light is favourable in the
early stages. The temperature required for germination varies greatly in
different seeds, some germinating readily at a few degrees above the
freezing point, and others requiring a tolerably high temperature. The
rapidity with which it takes place appears to increase with the temperature;
but this is true only within very narrow limits, for beyond a certain point
heat is injurious, and when it exceeds 120° or 130° Fahrenheit, entirely
prevents the process. The presence of oxygen is also essential, for it has
been shown that if seeds are placed in a soil exposed to an atmosphere
deprived of that element, or if they be buried so deep that the air does not
reach them, they may lie without change for an unlimited period; but so
soon as they are exposed to the air, germination immediately commences.
Illustrations of this fact are frequently observed where earth from a

considerable depth has been thrown up to the surface, when it often
becomes covered with plants not usually seen in the neighbourhood, which
have sprung from buried seeds. When all the necessary conditions for
germination are fulfilled, the seed absorbs moisture, swells up, and sends
out a shoot which rises to the surface, and a radicle which descends—the
one destined to develop the leaves, the other the roots, by which the plant is
afterwards to derive its nutriment from the air and the soil. But until these
organs are properly developed, the plant is dependent on the matters
contained in the seed itself. These substances are mostly insoluble, but are
brought into solution by the atmospheric oxygen acting upon the gluten,
and converting it into a soluble substance called diastase, which in its turn
reacts upon the starch, converting it first into dextrine, and then into
cellulose, and the latter is finally deposited in the form of organised cells,
and produces the first little shoot of the plant. At the first moment of
germination, the oxygen absorbed appears simply to oxidize the
constituents of the seed, but this condition exists only for a very limited
period, and is soon followed by the evolution of carbonic acid, water being
at the same time formed from the organic constituents of the seed, which
gradually diminishes in weight. The amount of this diminution is different
with different plants, but always considerable. Boussingault found that the
loss of dry substance in the pea amounted in 26 days to 52 per cent, and in
wheat to 57 per cent in 51 days. Against this, of course, is to be put the
weight of the young plant produced; but this is never sufficient to
counterbalance the diminished weight of the seed, for Saussure found that a
horse bean and the plant produced from it weighed, after 16 days, less by 29
per cent than the seed before germination. The same phenomenon is
observed in the process of malting, which is in fact the artificial
germination of barley, the malt produced always weighing considerably less
than the grain from which it was obtained. It was believed by Saussure, and
the older investigators, that the carbonic acid evolved was entirely produced
from starch and sugar; and as these substances may be viewed as
compounds of carbon and water, the change was very simply explained by
supposing that the carbon was oxidised and converted into carbonic acid
and its water eliminated. But this hypothesis is incapable of explaining all
the phenomena observed; for woody fibre, which is one of the chief
constituents of the young plant, contains more carbon than the starch and
sugar from which it must have been produced, and we are, therefore, forced

to admit that the action must be more complicated. There is every reason to
believe that the nitrogenous constituents of the seed are most abundantly
oxidized, for they are remarkably prone to change; but the action of the air
is not confined to them, and it appears most probable that all the substances
take part in the decomposition, and the process of germination may, in some
respects, be compared to decay or putrefaction, which, like it, is attended by
the absorption of oxygen and evolution of carbonic acid; but while in the
latter case the residual substances remain in a useless state, in the former
they at once become part of a new organism.
Changes occurring during the After-growth of the Plant.—When the plant
has developed its roots and leaves, and exhausted the store of materials laid
up for it in the seed, it begins to derive its subsistence from the surrounding
air, and to absorb carbonic acid, water, ammonia, and nitric acid, and to
decompose and convert them into the different constituents of its tissues.
These changes take place slowly at first, and more rapidly as the organs
fitted for the elaboration of its food are developed. The roots and the leaves
are equally active in performing this duty, the former absorbing the mineral
matters along with the carbonic acid, ammonia, nitric acid, and moisture in
the soil, or the manure added to it; the latter gathering the gaseous
substances existing in the air. Each of these undergoes a series of changes
claiming our consideration.
Decomposition of Carbonic Acid.—Carbonic acid, which appears to be
absorbed with equal readiness by the roots, leaves, and stems, undergoes
immediate decomposition, its carbon being retained, and its oxygen, in
whole or in part, evolved into the air. This decomposition occurs only under
the action of the sun's rays, and has been found to be proportionate to the
amount of light to which the plant is exposed. It takes place only in the
green parts of plants, for though the roots absorb carbonic acid, they cannot
decompose it, or evolve oxygen; and the coloured parts, the flowers, fruits,
etc., have an entirely opposite effect, absorbing oxygen and giving off
carbonic acid. The absorption of carbonic acid and escape of oxygen has
been proved by numerous direct experiments by Saussure and others, in
which both atmospheric air and artificial mixtures containing an increased
quantity of carbonic acid have been employed. Saussure allowed seven
plants of periwinkle (Vinca minor) to vegetate in an atmosphere containing
7·5 per cent of carbonic acid for six days, during each of which the

apparatus was exposed for six hours to the sun's rays. The air was analysed
both before and after the experiment, and the results obtained were—

Volume of the air. Nitrogen.Oxygen. Carbonic Acid.
Before the experiment, 5746 4199 1116 431
After " 5746 4338 1408 0
—— —— —— ——
Difference, 0 +139 +292 -431

In this experiment the whole of the carbonic acid, amounting to 431
volumes, was absorbed, but only 292 volumes of oxygen were given off.
Had the carbonic acid been entirely decomposed, and all its oxygen
eliminated, its volume would have been equal to that of the acid, or 431, so
that in this instance 139 volumes of the oxygen of the carbonic acid have
been retained to form part of the tissues of the plant. On the other hand, the
nitrogen is found to be increased after the experiment. It might be supposed
that the nitrogen evolved had been derived from the decomposition of the
nitrogenous constituents of the plant, but this cannot be the true
explanation, because in this particular case it greatly exceeded the whole
nitrogen contained in the plants experimented on. Its source is not well
understood, but Boussingault supposes it to have existed in the interstices of
the plant, and to have escaped during the course of the experiment.
Saussure found that the oak, the horse-chesnut, and other plants, absorb
oxygen and give off carbonic acid in less volumes than the oxygen, while
the house-leek and the cactus absorb oxygen without evolving carbonic
acid. The absorption and decomposition of carbonic acid takes place only
during the day, and matters are entirely reversed during the night, when
oxygen is absorbed and carbonic acid eliminated from all parts of the
plants.
Although the action occurring during the night is the reverse of that which
takes place during the day, it is in no degree to be attributed to a re-
oxidation of the carbon which had been deposited in the tissues of the plant.
It appears, on the contrary, to be a purely mechanical, and not a chemical
process. During the night the sap continues to circulate through the vessels
of the plant, and moisture, carrying with it carbonic acid in solution, is
absorbed by the roots; but when it reaches the leaves, where the sun's light

would have caused its decomposition during the day, it is again exhaled
unchanged. The oxygen absorbed during the night must, however, take part
in some chemical processes, for if it were merely mechanical, the
absorption would not be confined to that gas alone, but would be
participated in by the other constituents of the air. Moreover, the amount of
absorption varies greatly in different plants—being scarcely appreciable in
some, and very abundant in others. Plants containing volatile oils, which are
readily converted into resins by the action of oxygen, or those containing
tannin or other readily oxidizable substances, take up the largest quantity.
This is remarkably illustrated by an experiment in which the leaves of the
Agave americana, after twenty-four hours' exposure in the dark, were found
to have absorbed only 0·3 of their volume of oxygen, while those of the fir,
in which volatile oil is abundant, had taken up twice, and those of the oak,
containing tannin, eighteen times as much oxygen.
In the flowers, both by day and night, there is a constant absorption of
oxygen, and evolution of carbonic acid. In fact, an active oxidation is going
on, attended by the evolution of heat, which, in the Arum maculatum and
some other plants, is so great as to raise the temperature of the flower 10° or
12° above that of the surrounding air.
Decomposition of Water in the Plant.—In addition to the function which
water performs in the plant, as the solvent of the different substances which
form its nutriment, and hence as the medium through which they pass into
its organs, it serves also as a direct food, undergoing decomposition, and
yielding hydrogen to the organic substances. Its constituents, along with
those of the carbonic acid absorbed, undergo a variety of transformations,
and form the principal part of the non-nitrogenous constituents. It has been
already observed that starch, sugar, and the other allied substances, may be
considered as compounds of carbon with water; and they might be supposed
to owe their origin to the carbonic acid losing the whole of its oxygen, and
direct combination then ensuing between the residual carbon and a certain
proportion of water; but this would imply that the latter substance
undergoes no decomposition, and though undoubtedly the simplest view of
the case, it is by no means the most probable. It is much more likely that the
carbonic acid is only partially decomposed, half its oxygen being separated,
and replaced by hydrogen, produced by the decomposition of a certain
quantity of water into its elements. Thus, for instance, sugar may be

produced from twelve equivalents of carbonic acid and twelve equivalents
of water, twenty-four equivalents of oxygen being eliminated, as thus
represented:

12equivalents of carbonic acid, C12O12O12
12 " water, H12O12
1 " sugar, and 24 of ox. C12H12O12 + O24

It must not be supposed that we are in a condition to assert that sugar is really
produced in the manner here shown, the illustration being given merely for the
purpose of pointing out how it may be supposed to occur, and on a similar
principle it is possible to explain the formation of most other vegetable
compounds; and this subject has been very fully discussed by the late Dr.
Gregory, in his "Handbook of Organic Chemistry." That water must be
decomposed, is evident from the fact, established by analysis, that the hydrogen
of the plant generally exceeds the quantity required to form water with its
oxygen, so that this excess at least must be produced by the decomposition of
water. The hydrogen of the volatile oils, many of which contain no oxygen, and
that of the fats, which contain only a small quantity, must manifestly be
obtained in a similar manner.
Decomposition of Ammonia.—The nitrogenous or albuminous compounds of
vegetables must necessarily obtain their nitrogen from the decomposition either
of ammonia or nitric acid, experiment having distinctly shown that they are
incapable of absorbing it in the free state from the atmosphere. It has been
clearly ascertained that the albuminous substances do not contain ammonia, and
it is hence apparent that a complete decomposition of that substance must take
place in the plant. No doubt carbonic acid and water take part with it in these
changes, which must be of a very complex character, and in the present state of
our knowledge it seems hopeless to attempt any explanation of them.
Decomposition of Nitric Acid.—Chemists are not entirely at one as to whether
nitric acid is directly absorbed by the plant, or is first converted into ammonia.
But there are certain facts connected with the chemistry of the soil, to be
afterwards referred to, which seem to us to leave no doubt that it may be
directly absorbed; and in that case it must be decomposed, its oxygen being
eliminated, and the nitrogen taking part with carbon and hydrogen in the
formation of the organic compounds. It must be clearly understood that while
such changes as those described manifestly must take place, the explanations of
them which have been attempted by various chemists are not to be accepted as
determinately established facts; they are at present no more than hypothetical
views which have been expressed chiefly with the intention of presenting some
definite idea to the mind, and are unsupported by absolute proof; they are only

inferences drawn from the general bearings of known facts, and not facts
themselves. Although, therefore, they are to be received with caution, they have
advantages in so far as they present the matter to us in a somewhat more
tangible form than the vague general statements which are all that could
otherwise be made.

CHAPTER IV.
THE INORGANIC CONSTITUENTS OF PLANTS.

When treating of the general constituents of plants, it has been already stated
that the older chemists and vegetable physiologists, misled by the small
quantity of ash found in them, entertained the opinion that mineral matters were
purely fortuitous components of vegetables, and were present merely because
they had been dissolved and absorbed along with the humus, which was then
supposed to enter the roots in solution, and to form the chief food of the plant.
This supposition, which could only be sustained at a time when analysis was
imperfect, has been long since disproved and abandoned, and it has been
distinctly shown by repeated experiment that not only are these inorganic
substances necessary to the plant, but that every one of them, however small its
quantity, must be present if it is to grow luxuriantly and arrive at a healthy
maturity. The experiments of Prince Salm Horstmar, before alluded to, have
established beyond a doubt, that while a seed may germinate, and even grow, to
a certain extent, in absence of one or more of the constituents of its ash, it
remains sickly and stunted, and is incapable of producing either flower or seed.
Of late years the analysis of the ash of different plants has formed the subject of
a large number of laborious investigations, by which our knowledge of this
subject has been greatly extended. From these it appears that the quantity of ash
contained in each plant or part of a plant is tolerably uniform, differing only
within comparatively narrow limits, and that there is a special proportion
belonging to each individual organ of the plant. This fact may be best rendered
obvious by the subjoined table, showing the quantity of ash contained in a
hundred parts of the different substances dried at 212°. Most of these numbers
are the mean of several experiments:—
Table showing the quantity of inorganic matters in 100 parts of different plants
dried at 212°.

SEEDS.
Wheat 1·97
Barley 2·48
Oats (with husk) 3·80

Oats (without husk) 2·06
Rye 2·00
Millet 3·60
Rice 0·37
Maize 1·20
Peas 2·88
Beans 3·22
Kidney Beans 4·09
Lentils 2·51
Tares 2·60
Buckwheat 2·13
Linseed 4·40
Hemp seed 5·60
Rape seed 4·35
Indian Rape-seed[A] 4·06
Sunflower 3·26
Cotton seed 5·93
Guinea Corn 1·99
Gold of Pleasure 4·10
White Mustard 4·15
Black Mustard 4·31
Poppy 6·56
Niger seed (Guizotia oleifera) 7·00
Earth nut 3·88
Sweet Almond 4·90
Horse-chesnut 2·81
Grape 2·76
Clover 6·19
Turnip 3·98
Carrot 10·03
Sainfoin 5·27
Italian Ryegrass 6·91
Mangold-Wurzel 6·58
STRAWS AND STEMS.
Wheat 4·54
Barley 4·99

Oat 7·24
Winter Rye 5·15
Summer Rye 5·78
Millet 8·32
Maize 3·60
Pea 4·81
Bean 6·59
Tares 6·00
Lentil 5·38
Buckwheat 4·50
Hops 4·42
Flax straw 4·25
Hemp 4·14
Gold of Pleasure 6·05
Rape 4·41
Potato 14·90
Jerusalem Artichoke 4·40
ENTIRE PLANT.
Potato 17·70
Spurry 10·06
Red Clover 8·79
White Clover 8·72
Yellow Clover 8·56
Crimson Clover (T. incarnatum) 10·81
Cow Grass (T. medium) 11·31
Sainfoin 6·51
Ryegrass 6·42
Meadow Foxtail (Alopecurus pratensis) 7·81
Sweet-scented Vernal Grass (Anthoxanthum odoratum) 6·32
Downy Oat Grass (Avena pubescens) 5·22
Bromus erectus 5·21
Bromus mollis 5·82
Cynosurus cristatus 6·38
Dactylis glomeratus 5·31
Festuca duriuscula 5·42
Holcus lanatus 6·37

Hordeum pratense 5·67
Lolium perenne 7·54
Poa annua 2·83
Poa pratensis 5·94
Poa trivialis 8·33
Phleum pratense 5·29
Plantago lanceolata 8·68
Poterium Sanguisorba 7·97
Yarrow 13·45
Rape Kale 8·00
Cow Cabbage 10·00
Asparagus 6·40
Parsley 1·10
Furze 3·11
Chamomile (Anthemis arvensis) 9·66
Wild Chamomile (Matricaria Chamomilla) 9·10
Corn Cockle (Agrostemma Githago) 13·20
Corn Blue Bottle (Centaurea Cyanus) 7·32
Foxglove 10·89
Hemlock (Conium maculatum) 12·80
Sweet Rush (Acorus Calamus) 6·90
Common Reed (Arundo Phragmites) 1·44
Celandine (Chelidonium majus) 6·85
Equisetum fluviatile 23·60
Equisetum hyemale 11·80
" arvense 13·80
" linosum 15·50
Fucus nodosus 19·03
Fucus vesiculosus 27·63
Laminaria digitata 39·68
LEAVES.
Turnip 9·37
Beet 20·30
Kohl-rabi 18·54
Carrot 10·95
Jerusalem Artichoke 28·30

Hemp 22·00
Hop 17·25
Tobacco 22·62
Spinach 19·76
Chicory 15·67
Poplar 23·00
Red Beech 6·00
White Beech 10·51
Oak 9·80
Elm 16·33
Horse-chesnut 9·08
Maple 28·05
Ash 14·76
Fir 2·31
Acacia 18·20
Olive 6·45
Orange 13·73
Potato 15·10
Tussac Grass 7·15
ROOTS AND TUBERS.
Potato 4·16
Jerusalem Artichoke 5·38
Turnip 13·64
Beet 8·27
Kohl-rabi 6·08
Rutabaga 7·34
Carrot 5·80
Belgian White Carrot 6·22
Mangold-Wurzel 8·78
Parsnip 5·52
Radish 7·35
Chicory 5·21
Madder 8·33
WOODS.
Beech 0·38
Apple 1·29

Cherry 0·28
Birch 1·00
Oak 2·50
Walnut 1·57
Lime 5·00
Horse-chesnut 1·05
Olive 0·58
Mahogany 0·81
Vine 2·57
Larch 0·32
Fir 0·14
Scotch Fir 0·17
Filbert 0·50
Chesnut 3·50
Poplar 0·80
Hazel 0·50
Orange 2·74
Vine 2·57
BARKS.
Beech 6·62
Cherry 10·37
Fir 1·79
Oak 6·00
Horse-chesnut 7·85
Filbert 6·20
Cork 1·12
FRUITS.
Plum 0·40
Cherry 0·43
Strawberry 0·41
Pear 0·41
Apple 0·27
Chesnut 0·99
Cucumber 0·63
Vegetable Marrow 5·10

On examining this table it may be observed that, notwithstanding the very great
variety in the proportion of ash in different plants, some general relations may
be traced. A certain similarity may be observed between those belonging to the
same natural family, the seeds of all the cereal grains, for instance, containing in
round numbers two per cent of inorganic matters. Leguminous seeds (peas and
beans) contain about three per cent, while in rape-seed, linseed, and the other
oily seeds, it reaches four per cent. In the stems and straws less uniformity
exists, but with the exception of a few extreme cases, the quantity of ash in
general approaches pretty closely to five per cent. Still more diversified results
are obtained from the entire plants; but this diversity is probably much more
apparent than real, and must be, in part at least, dependent on the proportion
existing between the stem and leaves, for the leaves are peculiarly rich in ash,
and a leafy plant must necessarily yield a higher total percentage of ash,
although, if stems and leaves were separately examined, they might not show so
conspicuous a difference.
The leaves surpass all other parts of plants, in the proportion of inorganic
constituents they contain, the table showing that in some instances, as in the
maple and Jerusalem artichoke, they exceed one-fourth of the whole weight of
the dry matter. In other leaves, and more especially in those of the coniferæ, the
proportion is much smaller. Taking the average of all the analyses hitherto
made, it appears that leaves contain about thirteen per cent of ash, but the
variations on either side are so large that little value is to be attached to it except
as an indication of the general abundance of mineral matters.
In roots and tubers the variations are less, and all, except the potato and the
turnip, contain about seven per cent of ash.
The smallest proportion of mineral matter is found in wood. In one case only
does the proportion reach five per cent, while the average scarcely exceeds one,
and in the fir the quantity amounts to no more than one six-hundredth of the dry
matter. In the bark the quantity is much larger, and may be stated at seven per
cent.
The general proportion of ash found in different parts of plants is given in round
numbers in the subjoined table:—

Wood 1
Seeds 3
Stems and straws 5

Roots and tubers 7
Bark 7
Leaves 13

The differences in the quantity of ash contained in different parts of plants are
obviously intended to serve a useful purpose, and it is interesting to observe that
the wood which is destined to remain for a long period, sometimes for several
centuries, a part of the plant, contains the smallest proportion, and it is not
improbable that what it does contain is really due, not to the actual woody
matter itself, but to the sap which permeates its vessels. By this arrangement but
a small proportion of these important mineral matters, which the soil supplies in
very limited quantity, is locked up within the plant, and those which are
absorbed, after circulating through it, and fulfilling their allotted functions, are
accumulated in the leaves, and annually returned to the soil.
The different proportions of mineral matters contained in the individual organs
of plants is most strikingly illustrated when parallel experiments are made on
the same species; but the number of instances in which a sufficiently extensive
series of analyses has been made to show this, is comparatively limited, and is
confined to the oat, the orange-tree, and the horse chesnut—each of which has
formed the subject of a very elaborate investigation. The following table gives
the results obtained on the oat:—

Hopetoun Black Sandy
Hopetoun Oats, Potato Oats,
Oats, Oats, Oats, Mean.
Northumberland. Northumberland.
Fifeshire. Edinburgh. Fifeshire.
Grain 2·14 1·81 2·22 2·11 1·76 2·00
Husk 6·47 6·03 6·99 8·24 6·03 6·75
Chaff 16·53 17·23 15·59 19·19 18·97 16·06
Leaves 8·44 7·19 14·59 10·29 15·92 10·88
Upper
part of 4·95 5·44 9·22 8·25 11·0 7·77
straw
Middle
part of 6·11 5·23 7·41 6·53 9·01 6·66
straw
Lower
part of 5·33 5·18 9·76 7·11 7·30 6·93
straw

The specimens of oats on which these analyses were made were from different
districts of country, grown on soils of different quality, and were, further, of
different varieties; and yet they show, on the whole, a remarkable similarity in
the proportion of ash in each part, and indicate that there is a normal quantity
belonging to it. Such a series of analyses also affords the most convincing proof
that the inorganic matters cannot be fortuitous, and merely absorbed from the
soil along with their organic food, as the old chemists supposed, because, in that
case, they ought to be uniformly distributed throughout the entire plant, and not
accumulated in particular proportions in each individual organ.
Not only does the proportion of ash vary in the different parts of a plant, but
even in the same part it is greatly influenced by its period of growth. The laws
which regulate these variations are very imperfectly known, but in general it is
observed that during the period of active growth the quantity of ash is largest.
Thus, it has been found that in early spring the wood of the young shoots of the
horse-chesnut contains 9·9 per cent of ash. In autumn this has diminished to
3·4, and the last year's twigs contain only 1·1 per cent, while in the old wood
the quantity does not exceed 0·5. Saussure has also observed that the quantity
of ash diminishes in certain plants when the seed has ripened. Thus, he found
that the percentages of ash, before flowering, and after seeding, were as
follows:—

Before flowering. With ripe seed.
Sunflower 14·7 9·3
Wheat 7·9 3·3
Maize 12·2 4·6

On the other hand, the quantity of ash in the leaves of trees increases
considerably in autumn, as shown by this table:—

Per-centage of ash in
May. September.
Oak leaves 5·3 5·5
Poplar 6·6 9·3
Hazel 6·1 7·0
Horse-chesnut 7·2 8·6

In general, the proportion of ash appears to increase as the plant reaches
maturity, and this is particularly seen in the oat, of which very complete

analyses have been made at different periods of its growth:—

Proportion of Ash in different parts of the Oat at different periods of its
growth.

Date. Stalks. Leaves. Chaff. Grain with husk.
2d July 7·83 11·35 ... 4·91
9th July 7·80 12·20 ... 4·36
16th July 7·94 12·61 6·00 3·38
23d July 7·99 16·45 9·11 3·62
30th July 7·45 16·44 12·28 4·22
5th August 7·63 16·05 13·75 4·31
13th August 6·62 20·47 18·68 4·07
20th August 6·66 21·14 21·07 3·64
27th August 7·71 22·13 22·46 3·51
3d September 8·35 20·90 27·47 3·65

The increase is here principally confined to the leaves and chaff, while the
stalks, which owe their strength to a considerable extent to the inorganic matters
they contain, are equally supplied at all periods of their growth. In the grain
only is there a diminution, but this is apparent and not real, and is due to the fact
that the determination of the quantity of ash, as made on the grain with its husk,
and the former, which contains only a small quantity of mineral matters,
increases much more rapidly in weight than the latter, when it approaches the
period of ripening, and it is accordingly during the last three weeks of its
growth that this diminution becomes apparent.
The nature of the soil has also a very important influence on the proportion of
mineral matters, and of this an interesting illustration is given in the following
table, which shows the quantities found in the grain and straw of the same
variety of the pea grown on fourteen different soils:—

Seed. Straw.
1 2·30
2 3·25 3·43

3 4·27 3·62
4 3·40 3·39
5 2·99 3·90
6 3·19 6·80
7 2·53 3·90
8 2·27 6·59
9 2·69 3·49
10 1·61 3·91
11 3·11 5·28
12 3·34 7·57
13 2·78 3·76
14 3·01 3·38

Although those differences are very large, especially in the straw, and must be
attributed to the soil, it has hitherto been found impossible to ascertain the
nature of the relation subsisting between it and the crops it yields; indeed, it
must obviously be dependent on very complicated questions, which cannot at
present be solved, for it may be observed that the increase in the grain does not
occur simultaneously with that in the straw, and in several cases a large
proportion of ash in the former is associated with an unusually small amount in
the latter. A priori, it might be expected that those soils which are especially
rich in the more important constituents of the ash should yield a produce
containing more than the average quantity, but this is very far from being an
invariable occurrence, and not unfrequently the very reverse is the case. In
some instances the variations may be traced to the soil, as in the following
analyses of the fruit of the horse-chesnut, grown on an ordinary forest soil, and
on a rich soil, produced by the disintegration of porphyritic rock, in which the
latter yields a much larger quantity of ash:—

Kernel of seed. Green husk.Brown husk.
Forest soil 2·26 4·53 1·70
Porphyry soil 3·36 7·29 2·20

In the majority of instances we fail to establish any connection between the
nature of the soil and the plants it yields, chiefly because we are still very
deficient in analyses of those grown on uncultivated soils; and on cultivated
land it is impossible to draw conclusions, because the nature of the manure
exerts an influence quite as great, if not greater, than that of the soil itself.

The relative proportion in which the different mineral matters enter into the
composition of the ash varies within very wide limits, as will be apparent from
the following table, containing a selection of the best analyses of our common
cultivated and a few uncultivated plants.

Table of the Composition of the Ash of different Plants in 100 Parts.

Note.—Alumina and oxide of manganese occur so rarely, that separate columns
have not been introduced for them, but their quantity is stated in notes at the
end of the table.

Chloride of Chloride of
Potash. Soda. Lime. Magnesia.
Potassium. Sodium.
Wheat, grain 30·02 3·82 ... ... 1·15 13·39
straw 17·98 2·47 ... ... 7·42 1·94
chaff 9·14 1·79 ... ... 1·88 1·27
Barley, grain 21·14 ... 5·65 1·01 1·65 7·26
straw 11·22 ... ... 2·14 5·79 2·70
Oats, grain[B] 20·63 ... 1·03 ... 10·28 7·82
straw 19·46 1·93 2·71 4·27 7·01 3·79
chaff[C] 6·33 3·93 ... 0·24 1·95 0·38
Rye, grain 33·83 0·39 ... ... 2·61 12·81
straw 17·20 ... 0·30 0·60 9·10 2·40
Maize, grain 28·37 1·74 ... trace 0·57 13·60
stalks and leaves 35·26 ... ... 2·29 10·53 5·52
Rice, grain 20·21 2·49 ... ... 7·18 4·26
Buckwheat, straw 31·71 ... 7·42 4·55 15·71 1·66
Peas (gray), seed 41·70 ... 3·82 1·24 4·78 5·78
straw 21·30 4·22 ... ... 37·17 7·17
Beans (common
field),
grain 51·72 0·54 ... ... 5·20 6·90
straw 32·85 2·77 ... 11·54 19·85 2·53
Tare, straw 32·82 ... 3·27 4·03 20·78 5·31
straw 31·72 ... 7·41 4·55 15·71 1·66
Flax, seed 34·17 1·69 ... 0·36 8·40 13·11
straw 21·53 3·68 ... 9·21 21·20 4·20

Rape, seed[D] 16·33 0·34 ... 0·96 8·30 8·80
straw[E] 16·63 10·57 ... 2·53 21·51 2·92
Spurry 26·12 1·14 ... 8·90 14·46 8·88
Chicory root 34·64 ... 8·92 2·98 ... ...
Red clover 25·60 ... 9·08 6·02 21·57 8·47
Cow grass,
22·78 ... 12·39 1·86 24·42 8·86
Trifolium medium
Yellow clover 27·48 ... 11·72 8·16 17·26 8·39
Alsike clover 29·72 ... 6·29 1·05 26·83 4·01
Lucerne 27·56 ... 11·64 1·91 20·60 5·22
Anthoxanthum
32·03 ... 7·03 4·90 9·21 2·53
odoratum
Alopecurus
37·03 ... 9·50 ... 3·90 1·28
pratensis
Avena pubescens 31·21 ... 4·05 5·66 4·72 3·17
Bromus erectus 20·33 ... 10·63 1·38 10·38 4·99
Bromus mollis 30·09 0·33 ... 3·11 6·64 2·60
Cynosurus cristatus 24·99 ... 11·60 ... 10·16 2·43
Dactylis glomerata 29·52 ... 17·86 3·09 5·82 2·22
Festuca duriuscula 31·84 ... 8·17 0·62 10·31 2·83
Holcus lanatus 34·83 ... 3·91 6·66 8·31 3·41
Lolium perenne 24·67 ... 13·80 7·25 9·64 2·85
Annual ryegrass 28·99 0·87 ... 5·11 6·82 2·59
Poa annua 41·86 ... 0·47 3·35 11·69 2·44
Poa pratensis 31·17 ... 11·25 1·31 5·63 2·71
Poa trivialis 29·40 ... 6·90 ... 8·80 3·22
Phleum pratense 31·09 ... 0·70 3·24 14·94 5·30
Plantago lanceolata 33·26 ... 4·53 8·80 19·01 3·51
Poterium
30·26 ... 3·27 1·35 24·82 4·21
Sanguisorba
Achillea Millefolia 30·37 ... 20·49 3·63 13·40 3·01
Potato, tuber 43·18 0·09 ... 7·92 1·80 3·17
stem 39·53 3·95 ... 20·43 14·85 4·10
leaves 17·27 ... 4·95 11·37 27·69 7·78
Jerusalem
55·89 ... 4·88 ... 3·34 1·30
Artichoke

stem 38·40 0·69 ... 4·68 20·31 1·91
leaves 6·81 3·72 ... 1·82 40·15 1·95
Turnip, seed 21·91 1·23 ... ... 17·40 8·74
bulb 23·70 14·75 ... 7·05 11·82 3·28
leaves 11·56 12·43 ... 12·41 28·49 2·62
Mangold Wurzel,
21·68 3·13 ... 49·51 1·90 1·79
root
leaves 8·34 12·21 ... 37·66 8·72 9·84
Carrot, root 42·73 12·11 ... ... 5·64 2·29
leaves 17·10 4·85 ... 3·62 24·05 0·89
Kohl-rabi, bulb 36·27 2·84 ... 11·90 10·20 2·36
leaves 9·31 ... 5·99 6·66 30·31 3·62
Cow cabbage, head 40·86 2·43 ... ... 15·01 2·39
stalk 40·93 4·05 ... 2·08 10·61 3·85
Poppy seed 9·10 ... 7·15 1·94 35·36 9·49
leaves 36·37 ... 2·50 2·51 30·24 6·47
Mustard seed
25·78 0·33 ... ... 19·10 5·90
(white)
Radish root 21·16 ... 1·29 7·07 8·78 3·53
Tobacco leaves 36·37 ... 2·50 2·51 30·24 6·47
Fucus nodosus[F] 20·03 4·58 ... 24·33 9·60 6·65
Fucus
20·75 6·09 ... 24·81 8·92 5·83
vesiculosus[G]
Laminaria
12·16 ... 2·30 19·34 4·62 10·94
digitata[H]

Oxide of Phosphoric Sulphuric Carbonic
Silica.
Iron. Acid. Acid. Acid.
Wheat, grain 0·91 46·79 ... ... 3·89
straw 0·45 2·75 3·09 ... 63·89
chaff 0·37 4·31 ... ... 81·22
Barley, grain 2·13 28·53 1·91 ... 30·68
straw 1·36 7·20 1·09 ... 68·50

Oats, grain 3·85 50·44 ... ... 4·40
straw 1·49 5·07 3·35 1·36 49·56
chaff 1·58 1·04 9·61 ... 72·85
Rye, grain 1·04 39·92 0·17 ... 9·22
straw 1·40 3·80 0·80 ... 64·50
Maize, grain 0·47 53·69 ... ... 1·55
stalks and leaves 2·28 8·09 5·16 2·87 27·98
Rice, grain 2·12 62·23 ... ... 1·37
Buckwheat, straw ... 10·34 4·67 20·37 3·57
Peas (gray), seed 0·18 36·50 4·47 0·82 0·68
straw 1·07 4·65 8·68 12·48 3·23
Beans (common
field),
grain ... 28·72 3·05 3·42 0·42
straw 0·61 0·49 1·40 25·32 2·61
Tare, straw 0·65 10·59 2·52 18·73 1·28
straw ... 10·34 4·67 20·37 3·57
Flax, seed 0·50 38·54 1·56 0·22 1·45
straw 5·58 7·53 3·39 15·75 7·92
Rape, seed 1·79 31·90 5·38 5·44 19·98
straw 1·30 4·68 3·90 23·04 11·80
Spurry ... 10·20 1·79 27·38 1·14
Chicory root ... ... ... ... ...
Red clover 1·26 4·09 2·96 18·05 1·95
Cow grass, Trifolium
1·09 4·94 2·66 20·16 1·12
medium
Yellow clover 1·40 ... 4·82 4·31 1·76
Alsike clover 0·71 5·64 3·25 20·74 1·73
Lucerne 2·23 6·47 4·80 15·94 2·63
Anthoxanthum
1·18 10·09 3·39 1·26 28·35
odoratum
Alopecurus pratensis 0·47 6·25 2·16 0·65 38·75
Avena pubescens 0·72 10·82 3·37 ... 36·28
Bromus erectus 0·26 7·53 5·46 0·55 38·48
Bromus mollis 0·28 9·62 4·91 9·07 33·34
Cynosurus cristatus 0·18 7·24 3·20 ... 40·11

Dactylis glomerata 0·59 8·60 3·52 2·09 26·65
Festuca duriuscula 0·78 12·07 3·45 1·38 28·53
Holcus lanatus 0·31 8·02 4·41 1·82 28·31
Lolium perenne 0·21 8·73 5·20 0·49 27·13
Annual ryegrass 0·28 10·07 3·45 ... 41·79
Poa annua 1·57 9·11 10·18 3·29 16·03
Poa pratensis 0·28 10·02 4·26 0·40 32·93
Poa trivialis 0·29 9·13 4·47 0·29 37·50
Phleum pratense 0·27 11·29 4·86 4·02 31·09
Plantago lanceolata 0·90 7·08 6·11 14·40 2·37
Poterium Sanguisorba 0·86 7·81 4·84 21·72 0·83
Achillea Millefolia 0·21 7·13 2·44 9·36 9·92
Potato, tuber 0·44 8·61 15·24 18·29 1·94
stem 1·34 6·68 6·56 ... 2·56
leaves 4·50 13·60 6·37 ... 6·47
Jerusalem Artichoke 0·45 16·99 3·77 11·80 1·52
stem 0·88 2·97 3·23 25·40 1·51
leaves 1·14 6·61 2·21 24·31 17·25
Turnip, seed 1·95 40·17 7·10 0·82 0·67
bulb 0·47 9·31 16·13 10·74 2·69
leaves 3·02 4·85 10·36 6·18 8·04
Mangold Wurzel, root 0·52 1·65 3·14 15·23 1·40
leaves 1·46 5·89 6·54 6·92 2·35
Carrot, root 0·51 12·31 4·26 18·00 1·11
leaves 3·43 6·21 5·08 23·15 11·61
Kohl-rabi, bulb 0·38 13·45 11·43 10·24 0·83
leaves 5·50 9·43 10·63 8·97 9·57
Cow cabbage, head 0·77 12·53 7·27 16·68 1·66
stalk 0·41 19·57 11·11 6·33 1·04
Poppy seed 0·41 31·38 1·92 ... 3·24
leaves 2·14 3·28 5·09 ... 11·40
Mustard seed (white) 0·39 44·97 2·19 ... 1·31
Radish root 1·19 41·09 7·71 ... 8·17
Tobacco leaves 2·18 3·24 5·09 ... 11·40
Fucus nodosus 0·26 1·71 21·97 6·39 0·38
Fucus vesiculosus 0·35 2·14 28·01 2·20 0·67

Laminaria digitata 0·45 1·75 7·26 15·23 1·20

A simple inspection of this table leads to various interesting conclusions. It is
particularly to be observed that some of the constituents of the ash are not
invariably present, and two at least—namely, alumina and manganese—are
found so rarely as to justify the inference that they are not indispensable. Of the
other substances, iodine is restricted exclusively to sea-plants, but to them it
appears to be essential. Oxide of iron, which occurs only in small quantities, has
sometimes been considered fortuitous, but it is almost invariably present, and
the experiments of Prince Salm Horstmar leave no doubt that it is essential to
the plant. Its function is unknown, but it is an important constituent of the blood
of herbivorous animals, and may be present in the plant, less for its own benefit
than for that of the animal of which it is destined to become the food.
Soda appears to be a comparatively unimportant constituent of the ash, of which
it generally forms but a small proportion, although the instances of its entire
absence are rare. In the cruciferous plants (turnip, rape, etc.) it is found
abundantly, and to them it appears indispensable, but in most other plants it
admits of replacement by potash. It seems probable that where the soil is rich in
the latter substance, plants will select that alkali in preference to soda; but as
they must have a certain quantity of alkali, the latter may supply the place of the
former where it is deficient. Cultivation, probably by enriching the soil in that
element, increases the proportion of potash found in the ash of plants, as is
remarkably seen in the asparagus, which gave the following quantities of
alkalies and chlorine:—

Wild. Cultivated.
Potash 18·8 50·5
Soda 16·2 trace.
Chlorine 16·5 8·3

The soda having almost entirely disappeared in the cultivated plant, while a
corresponding increase had taken place in the quantity of potash.
Potash is one of the most important elements of the ash of all plants, rarely
forming less than 20, and sometimes more than 50 per cent of its weight. The
latter proportion occurs chiefly in the roots and tubers, but it is also abundant in
all seeds and in the grasses. The straw, and particularly the chaff of the cereals,
and the leaves of most plants, contain it in smaller quantity, although exceptions
to this are not unfrequent, one of the most curious being the case of poppy-seed,

which contains only about 12 per cent, while the leaves yield upwards of 37 per
cent.
The proportion of lime varies within very wide limits, being sometimes as low
as 1, and in other plants reaching 40 per cent of their ash. The former proportion
occurs in the grains of the cerealia, and the latter in the leaves of some plants,
and more especially in the Jerusalem artichoke. The turnip and some of the
leguminous plants also contain it abundantly.
Magnesia is generally found in small quantity. It is largest in the grains,
amounting in them to about 12 or 13 per cent of the ash, but in other plants it
varies from 2 to 4 per cent. Although small in quantity, it is an important
substance, and apparently cannot be dispensed with; at least there is no instance
known of its entire absence.
Chlorine is by no means an invariable constituent of the ash, although it is
generally present, and sometimes in considerable quantity. It is most abundant
when the proportion of soda is large, and exists in the ash principally in
combination with that base as common salt. The relation between these two
elements may be traced more or less distinctly throughout the whole table of
analyses, and conspicuously in that of mangold-wurzel, where the common salt
amounts to almost exactly one-half of the whole mineral matter. The analyses of
the cultivated and uncultivated asparagus also show that a diminution in the
soda is accompanied by a reduction in the proportion of chlorine.
Sulphuric Acid is an essential constituent of the ash. But it is to be observed that
it is in some instances entirely, and in all partially, a product of the combustion
to which the plant has been submitted in order to obtain the ash. It is partly
derived from the sulphur contained in the albuminous compounds, which is
oxidised and converted into sulphuric acid during the process of burning the
organic matter, and remains in the ash. The quantity of sulphuric acid found in
the ash is, however, no criterion of that existing in the plant, for a considerable
quantity of it escapes during burning. The extent to which this occurs in
particular instances is well illustrated by reference to the case of white mustard,
which yields an ash containing only 2·19 of sulphuric acid, equivalent to 0·9 of
sulphur; and if calculated on the seed itself, this will amount to no more than
0·039 per cent, while experiments made in another manner prove it to contain
about thirty times as much, or more than 1 per cent. For the purpose of
determining the total quantity of sulphur which the plants contain in their
natural state, it is necessary to oxidise them by means of nitric acid; and from

such experiments the following table, showing the total amount of sulphur
contained in 100 parts of different plants, dried at 212°, has been constructed:—

Poa palustris 0·165
Lolium perenne 0·310
Italian Ryegrass 0·329
Trifolium pratense 0·107
repens 0·099
Lucerne 0·336
Vetch 0·178
Potato tuber 0·082
tops 0·206
Carrot, root 0·092
tops 0·745
Mangold-Wurzel, root 0·058
tops 0·502
Swede, root 0·435
tops 0·458
Rape 0·448
Drumhead Cabbage 0·431
Wheat, grain 0·068
straw 0·245
Barley, grain, 0·053
straw 0·191
Oats, grain 0·103
straw 0·289
Rye, grain 0·051
Beans 0·056
Peas 0·127
Lentils 0·110
Hops 1·063
Gold of Pleasure 0·253
Black Mustard 1·170
White Mustard 1·050

Phosphoric acid, which may be looked upon as the most important mineral
constituent of plants, is found to be present in very variable proportions. The

straws, stems, and leaves contain it in comparatively small quantity, but in the
seeds of all plants it is very abundant. In these of the cereals it constitutes nearly
half of their whole mineral components, and it rarely falls below 30 per cent.
Carbonic acid occurs in very variable quantities in the ash. It is of
comparatively little importance in itself, and is really produced by the oxidation
of part of the carbonaceous matters of the plant; but it has a special interest, in
so far as it shows that part of the bases contained in the plant must in its natural
state have been in union with organic acids, or combined in some way with the
organic constituents of the plant.
Silica is an invariable constituent of the ash, but in most plants occurs but in
small quantity. The cereals and grasses form an exception to this rule, for in
them it is an abundant and important element. It is not, however, uniformly
distributed through them, but is accumulated to a large extent in the stem, to the
strength and rigidity of which it greatly contributes. The hard shining layer
which coats the exterior of straw, and which is still more remarkably seen on
the surface of the bamboo, consists chiefly of silica; and in the latter plant this
element is sometimes so largely accumulated, that concretions resembling opal,
and composed entirely of it, are found loose within its joints. The necessity for
a large supply of silica in the stems of other plants does not exist, and in them it
rarely exceeds 5 or 6 per cent, but in some leaves it is more abundant.
A knowledge of the composition of the ash of plants is of considerable
importance in a practical point of view, and enables us in many instances to
explain why some plants will not grow upon particular soils on which others
flourish. Thus, for instance, a plant which contains a large quantity of lime,
such as the bean or turnip, will not grow in a soil in which that element is
deficient, although wheat or barley, which require but little lime, may yield
excellent crops. Again, if the soil be deficient in phosphoric acid, those plants
only will grow luxuriantly which require but a small quantity of that element,
and hence it follows that on such a soil plants cultivated for the sake of their
stems, roots, or leaves, in which the quantity of phosphoric acid is small, may
yield a good return; while others, cultivated for the sake of their seed, in which
the great proportion of that constituent of the ash is accumulated, may yield a
very small crop. It is obvious also that even where a soil contains a proper
quantity of all its ingredients, the repeated cultivation of a plant which removes
a large quantity of any individual element, may, in the course of time, so far
reduce the amount of that substance as to render the soil incapable of any longer
producing that plant, although, if it be replaced by another which requires but

little of the element thus removed, it may again produce an abundant crop. On
this principle also, attempts have been made to explain the rotation of crops,
which has been supposed to depend on the cultivation in successive years of
plants which abstract from the soil preponderating quantities of different
mineral matters. But though this has unquestionably a certain influence, we
shall afterwards see reason to doubt whether it affords a sufficient explanation
of all the observed phenomena.
It may be observed, on examining the table of the percentage and position of the
ash, that some plants are especially rich in alkalies, while in others lime or silica
preponderate, and it would therefore be the object of the farmer to employ, in
succession, crops containing these elements in different proportions. In carrying
out this view, attempts have been made to classify different plants under the
heads of silica plants, lime plants, and potash plants; and the following table,
extracted from Liebig's Agricultural Chemistry, in which the constituents of the
ash are grouped under the three heads of salts of potash and soda, lime and
magnesia, and silica, gives such a classification as far as it is at present
possible:—

Salts of Potash Salts of Lime and
Silica.
and Soda. Magnesia.
Oat straw with
34·00 4·00 62·00
seeds
Wheat straw 22·50 7·20 61·50
Silica
Barley straw with
Plants. 19·00 25·70 55·30
seeds
Rye straw 18·65 16·52 63·89
Good hay 6·00 34·00 60·00
Tobacco 24·34 67·44 8·30
Lime Pea straw 27·82 63·74 7·81
Plants Potato plant 4·20 59·40 36·40
Meadow Clover 39·20 56·00 4·90
Maize straw 72·45 6·50 18·00
Turnips 81·60 18·40 —
Potash Beet root 88·00 12·00 —
Plants. Potatoes 85·81 14·19 —
Jerusalem
84·30 15·70 —
Artichoke

The special application of these facts must be reserved till we come to treat of
the rotation of crops.
It is manifest that, as the crops removed from the soil all contain a greater or
less amount of inorganic matters, they must be continually undergoing
diminution, and at length be completely exhausted unless their quantity is
maintained from some external source. In many cases the supply of these
substances is so large that ages may elapse before this becomes apparent, but
where the quantity is small, a system of reckless cropping may reduce a soil to a
state of absolute sterility. A remarkable illustration of this fact is found in the
virgin soils of America, from which the early settlers reaped almost unheard-of
crops, but, by injudicious cultivation, they were soon exhausted and abandoned,
new tracts being brought in and cultivated only to be in their turn abandoned.
The knowledge of the composition of the ash of plants assists us in ascertaining
how this exhaustion may be avoided, and indicates the mode in which such
soils may be preserved in a fertile state.

FOOTNOTES:
[A] Apparently a species of Sinapis.
[B] Oxide of Manganese, 0·42.
[C] Oxide of Manganese, 0·92.
[D] Alumina, 1·02.
[E] Alumina, 0·63.
[F] Iodide of Potassium, 0·44; Sulphuret of Sodium, 3·66.
[G] Iodide of Potassium, 0·23.
[H] Iodide of Potassium, 1·68.

CHAPTER V.
THE SOIL—ITS CHEMICAL AND PHYSICAL CHARACTERS.

No department of agricultural chemistry is surrounded with greater difficulties
and uncertainties than that relating to the properties of the soil. When chemistry
began to be applied to agriculture, it was not unnaturally supposed that the
examination of the soil would enable us to ascertain with certainty the mode in
which it might be most advantageously improved and cultivated, and when, as
occasionally happened, analysis revealed the absence of one or more of the
essential constituents of the plant in a barren soil, it indicated at once the cause
and the cure of the defect. But the expectations naturally formed from the facts
then observed have been as yet very partially fulfilled; for, as our knowledge
has advanced, it has become apparent that it is only in rare instances that it is
possible satisfactorily to connect together the composition and the properties of
a soil, and with each advancement in the accuracy and minuteness of our
analysis the difficulties have been rather increased than diminished. Although it
is occasionally possible to predicate from its composition that a particular soil
will be incapable of supporting vegetation, it not unfrequently happens that a
fruitful and a barren soil are so similar that it is impossible to distinguish them
from one another, and cases even occur in which the barren appears superior to
the fertile soil. The cause of this apparently anomalous phenomenon lies in the
fact that analysis, however minute, is unable to disclose all the conditions of
fertility, and that it must be supplemented by an examination of its physical and
other chemical properties, which are not indicated by ordinary experiments. Of
late years very considerable progress has been made in the investigation of the
properties of the soil, and many facts of great importance have been discovered,
but we are still unable to assert that all the conditions of fertility are yet known,
and the practical application of those recently discovered is still very
imperfectly understood.
It must not be supposed that a careful analysis of a soil is without value, for
very important practical deductions may often be drawn from it, and when this
is not practicable it is not unfrequently due to its being imperfect or incomplete,
for it is so complex that the cases in which all the necessary details have been
eliminated are even now by no means numerous. In fact, the want of a large

number of thorough analyses of soils of different kinds is a matter of some
difficulty, and so soon as a satisfactory mode of investigation can be determined
upon, a full examination of this subject would be of much importance.
Origin of Soils.—The constituents of the soil, like those of the plant, may be
divided into the great classes of organic and inorganic. The origin of the former
has been already discussed: they are derived from the decay of plants which
have already grown upon the soil, and which, in various stages of
decomposition, form the numerous class of substances grouped together under
the name of humus. The organic substances may therefore be considered as in a
manner secondary constituents of the soil, which have been accumulated in it as
the consequence of the growth and decay of successive generations of plants,
while the primeval soil consisted of inorganic substances only.
The inorganic constituents of the soil are obtained as the result of a succession
of chemical changes going on in the rocks which protrude through the surface
of the earth. We have only to examine one of these rocks to observe that it is
constantly undergoing a series of important changes. Under the influence of air
and moisture, aided by the powerful agency of frost, it is seen to become soft,
and gradually to disintegrate, until it is finally converted into an uniform
powder, in which the structure of the original rock is with difficulty, if at all
distinguishable. The rapidity with which these changes take place is very
variable; in the harder rocks, such as granite and mica slate it is so slow as to be
scarcely perceptible, while in others, such as the shales of the coal formation, a
very few years' exposure is sufficient for the purpose. These actions, operating
through a long series of years, are the source of the inorganic constituents of all
soils.
Geology points to a period at which the earth's surface must have been
altogether devoid of soil, and have consisted entirely of hard crystalline rocks,
such as granite and trap, by the disintegration of which, slowly proceeding from
the creation down to the present time, all the soils which now cover the surface
have been formed. But they have been produced by a succession of very
complicated processes; for these disintegrated rocks being washed away in the
form of fine mud, or at least of minute particles, and being deposited at the
bottom of the primeval seas, have there hardened into what are called
sedimentary rocks, which being raised above the surface by volcanic action or
other great geological forces, have been again disintegrated to yield different
soils. Thus, then, all soils are directly or indirectly derived from the crystalline
rocks, those overlying them being formed immediately by their decomposition,

while those found above the sedimentary rocks may be traced back through
them to the crystalline rocks from which they were originally formed.
Such being the case, the composition of different soils must manifestly depend
on that of the crystalline rocks from which they have been derived. Their
number is by no means large, and they all consist of mixtures in variable
proportions of quartz, felspar, mica, hornblende, augite, and zeolites. With the
exception of quartz and augite, these names are, however, representatives of
different classes of minerals. There are, for instance, several different minerals
commonly classified under the name of felspar, which have been distinguished
by mineralogists by the names of orthoclase, albite, oligoclase, and labradorite;
and there are at least two sorts of mica, two of hornblende, and many varieties
of zeolites.
Quartz consists of pure silica, and when in large masses is one of the most
indestructible rocks. It occurs, however, intermixed with other minerals in small
crystals, or irregular fragments, and forms the entire mass of pure sand.
The four kinds of felspar which have been already named are compounds of
silica with alumina, and another base which is either potash, soda, or lime.
Their composition is as follows, two examples of each being given—

Orthoclase. Albite. Oligoclase. Labradorite.
Silica 65·72 65·00 67·99 68·23 62·70 63·51 54·66 54·67
Alumina 18·57 18·64 19·61 18·30 23·80 23·09 27·87 27·89
Peroxide of iron traces 0·83 0·70 1·01 0·62 — — 0·31
Oxide of manganese traces 0·13 — — — — — —
Lime 0·34 1·23 0·66 1·26 4·60 2·44 12·01 10·60
Magnesia 0·10 1·03 — 0·51 0·02 0·77 — 0·18
Potash 14·02 9·12 — 2·53 1·05 2·19 — 0·49
Soda 1·25 3·49 11·12 7·99 8·00 9·37 5·46 5·05
100·00 99·47 100·08 99·83 100·79 101·37 100·00 99·19

It is obvious that soils produced by the disintegration of these minerals must
differ materially in quality. Those yielded by orthoclase must generally abound
in potash, while albite and labradorite, containing little or none of that element,
must produce soils in which it is deficient. The quality of the soil they yield is
not however entirely dependent on the nature of the particular felspar which
yields it, but is also intimately connected with the extent to which the
decomposition has advanced. It is observed that different felspars undergo

decomposition with different degrees of rapidity but after a certain time they all
begin to lose their peculiar lustre, acquire a dull and earthy appearance, and at
length fall into a more or less white and soft powder. During this change water
is absorbed, and, by the decomposing action of the air, the alkaline silicate is
gradually rendered soluble, and at length entirely washed away, leaving a
substance which, when mixed with water, becomes plastic, and has all the
characters of common clay. The nature of this change will be best seen by the
following analysis of the clay produced during this composition, which is
employed in the manufacture of porcelain under the name of kaolin, or china
clay—

Silica 46·80
Alumina 36·83
Peroxide of iron 3·11
Carbonate of lime 0·55
Potash 0·27
Water 12·44
——
100·00

In this instance the decomposition of the felspar had reached its limit, a mere
trace of potash being left, but if taken at different stages of the process, variable
proportions of that alkali are met with. This decomposition of felspar is the
source of the great deposits of clay which are so abundantly distributed over the
globe, and it takes place with nearly equal rapidity with potash and soda felspar.
It is rarely complete, and the soils produced from it frequently contain a
considerable proportion of the undecomposed mineral, which continues for a
long period to yield a supply of alkalies to the plants which grow on them.
Mica is a very widely distributed mineral, and two varieties of it are
distinguished by mineralogists, one of which is characterised by the large
quantity of magnesia it contains. Different specimens are found to vary very
greatly in composition, but the following analyses may represent their most
usual composition:

Mica.
Potash. Magnesia.
Silica 46·36 42·65
Alumina 36·80 12·96

Peroxide of iron 4·53 —
Protoxide of iron — 7·11
Oxide of manganese 0·02 1·06
Magnesia — 25·75
Potash 9·22 6·03
Hydrofluoric acid 0·70 0·62
Water 1·84 3·17
—— ——
99·47 99·35

Mica undergoes decomposition with extreme slowness, as is at once illustrated
by the fact that its shining scales may frequently be met with entirely
unchanged in the soil. Its persistence is dependent on the small quantity of
alkaline constituents which it contains; and for this reason it is observed that the
magnesian micas undergo decomposition less rapidly than those containing the
larger quantity of potash. Eventually, however, both varieties become converted
into clay, their magnesia and potash passing gradually into soluble forms.
Hornblende and augite are two widely distributed minerals, which are so similar
in composition and properties that they may be considered together. Of the
former two varieties, basaltic and common have been distinguished, and their
composition is given below:—

Hornblende.
Common. Basaltic. Augite.
Silica 41·50 42·24 50·12
Alumina 15·75 13·92 4·20
Protoxide of iron 7·75 14·59 11·60
Oxide of manganese 0·25 0.33 —
Lime 14·09 12·24 20·55
Magnesia 19·40 13·74 13·70
Water 0·50 — —
—— —— ——
99·24 97·05 99·67

In these minerals alkalies are entirely absent, and their decomposition is due to
the presence of protoxide of iron, which readily absorbs oxygen from the air,
when the magnesia is separated and a ferruginous clay left.

The minerals just referred to, constitute the great bulk of the mountain masses,
but they are associated with many others which take part in the formation of the
soil. Of these the most important are the zeolites which do not occur in large
masses but are disseminated through the other rocks in small quantity. They
form a large class of minerals of which Thomsonite and natrolite may be
selected as examples—

Thomsonite.Natrolite.
Silica 38·73 48·68
Alumina 30·84 26·36
Lime 13·43 —
Potash 0·54 0·23
Soda 3·85 16·00
Water 13·09 9·55
—— ——
100·48 100·83

They are chiefly characterized by containing their silica in a soluble state, and
hence may yield that substance to the plants in a condition particularly
favourable for absorption.
It is obvious from what has been stated that all these minerals are capable, by
their decomposition, of yielding soft porous masses having the physical
properties of soils, but most of them would be devoid of many essential
ingredients, while not one of them would yield either phosphoric acid, sulphuric
acid, or chlorine. It has, however, been recently ascertained that certain of these
minerals, or at least the rocks formed from them, contain minute, but distinctly
appreciable traces of phosphoric acid, although in too small quantity to be
detected by ordinary analysis; and small quantities of chlorine and sulphuric
acid may also in most instances be found.
Still it will be observed that most of these minerals would yield a soil
containing only two or three of those substances, which, as we have already
learned, are essential to the plant. Thus, potash felspar, while it would give
abundance of potash, would be but an inefficient source of lime and magnesia;
and labradorite, which contains abundance of lime, is altogether deficient in
magnesia and potash.
Nature has, however, provided against this difficulty, for she has so arranged it
that these minerals rarely occur alone, the rocks which form our great mountain

masses being composed of intimate mixtures of two or more of them, and that
in such a manner that the deficiencies of the one compensate those of the other.
We shall shortly mention the composition of these rocks.
Granite is a mixture of quartz, felspar, and mica in variable proportions, and the
quality of the soil it yields depends on whether the variety of felspar present be
orthoclase or albite. When the former is the constituent, granite yields soils of
tolerable fertility, provided their climatic conditions be favourable; but it
frequently occurs in high and exposed situations which are unfavourable to the
growth of plants. Gneiss is a similar mixture, but characterised by the
predominance of mica, and by its banded structure. Owing to the small quantity
of felspar which it contains, and the abundance of the difficulty decomposable
mica, the soils formed by its disintegration are generally inferior. Mica slate is
also a mixture of quartz, felspar, and mica, but consisting almost entirely of the
latter ingredient, and consequently presenting an extreme infertility. The
position of the granite, gneiss, and mica slate soils in this country is such that
very few of them are of much value; but in warm climates they not unfrequently
produce abundant crops of grain. Syenite is a rock similar in composition to
granite, but having the mica replaced by hornblende, which by its
decomposition yields supplies of lime and magnesia more readily than they can
be obtained from the less easily disintegrated mica. For this reason soils
produced from the syenitic rocks are frequently possessed of considerable
fertility.
The series of rocks of which greenstone and trap are types, and which are very
widely distributed, differ greatly in composition from those already mentioned.
They are divisible into two great classes, which have received the names of
diorite and dolerite, the former a mixture of albite and hornblende, the latter of
augite and labradorite, sometimes with considerable quantities of a sort of
oligoclase containing both soda and lime, and of different kinds of zeolitic
minerals. Generally speaking, the soils produced from diorite are superior to
those from dolerite. The albite which the former contains undergoes a rapid
decomposition, and yields abundance of soda along with some potash, which is
seldom altogether wanting, while the hornblende supplies both lime and
magnesia. Dolerite, when composed entirely of augite and labradorite, produces
rather inferior soils; but when it contains oligoclase and zeolites, and comes
under the head of basalt, its disintegration is the source of soils remarkable for
their fertility; for these latter substances undergoing rapid decomposition
furnish the plants with abundant supplies of alkalies and lime, while the more
slowly decomposing hornblende affords the necessary quantity of magnesia. In

addition to these, the basaltic rocks are found to contain appreciable quantities
of phosphoric acid, so that they are in a condition to yield to the plant almost all
its necessary constituents.
The different rocks now mentioned, with a few others of less general
distribution, constitute the whole of our great mountain masses; and while their
general composition is such as has been stated, they frequently contain
disseminated through them quantities of other minerals which, though in trifling
quantity, nevertheless add their quota of valuable constituents to the soils.
Moreover, the exact composition of the minerals of which the great masses of
rocks are composed is liable to some variety. Those which we have taken as
illustrations have been selected as typical of the minerals; but it is not
uncommon to find albite containing 2 or 3 per cent of potash, labradorite with a
considerable proportion of soda, and zeolitic minerals containing several per
cent of potash, the presence of which must of course considerably modify the
properties of the soils produced from them. They are also greatly affected by the
mechanical influences to which the rocks are exposed; and being situated for
the most part in elevated positions, they are no sooner disintegrated than they
are washed down by the rains. A granite, for instance, as the result of
disintegration, has its felspar reduced to an impalpable powder, while its quartz
and mica remain, the former entirely, the latter in great part, in the crystalline
grains which existed originally in the granite. If such a disintegrated granite
remains on the spot, it is easy to see what its composition must be; but if
exposed to the action of running water, by which it is washed away from its
original site, a process of separation takes place, the heavy grains of quartz are
first deposited, then the lighter mica, and lastly the felspar. Thus there may be
produced from the same granite, soils of very different nature and composition,
from a pure and barren sand to a rich clay formed entirely of felspathic debris.
The sedimentary or stratified rocks are formed of particles carried down by
water and deposited at the bottom of the primeval seas from which they have
been upheaved in the course of geological changes. The process of their
formation may be watched at the present day at the mouths of all great rivers,
where a delta composed of the suspended matters carried down by the waters is
slowly formed. The nature of these rocks must therefore depend entirely on that
of the country through which the river flows. If its course runs through a
country in which lime is abundant, calcareous rocks will be deposited, and if it
passes through districts of different geological characters the deposit must
necessarily consist of a mixture of the disintegrated particles of the different
rocks the river has encountered. For this reason it is impossible to enter upon a

detailed account of their composition. It is to be observed, however, that the
particles of which they are composed, though originally derived from the
crystalline rocks, have generally undergone a complex series of changes,
geology teaching that, after deposition, they may in their turn undergo
disintegration and be carried away by water, to be again deposited. Their
composition must therefore vary not merely according to the nature of the rock
from which they have been formed, but also according to the extent to which
the decomposition has gone, and the successive changes to which they have
been exposed. They may be reduced to the three great classes of clays,
including the different kinds of clay slates, shales, etc., sandstone and
limestone. It must be added also, that many of them contain carbonaceous
matters produced by the decomposition of early races of plants and animals, and
that mixtures of two or more of the different classes are frequent.
The purest clays are produced by the decomposition of felspar, but almost all
the crystalline rocks may produce them by the removal of their alkalies, iron,
lime, etc. Where circumstances have been favourable, the whole of these
substances are removed, and the clay which remains consists almost entirely of
silica and alumina, and yields a soil which is almost barren, not merely on
account of the deficiency of many of the necessary elements of plants, but
because it is so stiff and impenetrable that the roots find their way into it with
difficulty. It rarely happens, however, that decomposition has advanced so far as
to remove the whole of the alkalies, which is exemplified by the following
analyses of the fire clay of the coal formation, and of transition clay slate:—

Transition Clay Slate. Fire Clay.
Silica 60·03 54·77
Alumina 14·91 28·61
Peroxide of iron 8·94 4·92
Lime 2·08 0·58
Magnesia 4·22 1·14
Potash 3·87 1·00
Soda — 0·24
Carbonic acid { 5·67 8·24
Water {
—— ——
99·72 99·50

The sandstones are derived from the siliceous particles of granite and other
rocks, and consist in many cases of nearly pure silica, in which case their
disintegration produces a barren sand, but they more frequently contain an
admixture of clay and micaceous scales, which sometimes form a by no means
inconsiderable portion of them. Such sandstones yield soils of better quality, but
they are always light and poor. Where they occur interstratified with clays, still
better soils are produced, the mutual admixture of the disintegrated rocks
affording a substance of intermediate properties, in which the heaviness of the
clay is tempered by the lightness of the sandstone.
Limestone is one of the most widely distributed of the stratified rocks, and in
different localities occurs of very different composition. Limestones are divided
into two classes, common and magnesian; the former a nearly pure carbonate of
lime, the latter a mixture of that substance with carbonate of magnesia. But
while these are the principal constituents, it is not uncommon to find small
quantities of phosphate and sulphate of lime, which, however trifling their
proportions, are not unimportant in an agricultural point of view. The following
analyses will serve to illustrate the general composition of these two sorts of
limestone as they occur in the early geological formations:—

Common. Magnesian.
Mid-Lothian. Sutherland. Sutherland. Dumfries.
Silica 2·00 7·42 6·00 2·31
Peroxide of iron and alumina 0·45 0·76 1·57 2·00
Carbonate of lime 93·61 84·11 50·21 58·81
Carbonate of magnesia 1·62 7·45 41·22 36·41
Phosphate of lime 0·56 ... ... ...
Sulphate of lime 0·92 ... ... 0·10
Organic matter 0·20 ... ... ...
Water 0·50 ... 0·69 ...
—— —— —— ——
99·86 99·74 99·69 99·63

These limestones are hard and possess to a greater or less extent a crystalline
texture. They are replaced in later geological periods by others which are much
softer, and often purer, of which the oolitic limestones, so called from their
resemblance to the roe of a fish, and chalk are the most important. Other
limestones are also known which contain an admixture of clay. The soils
produced by the disintegration of limestone and chalk are generally light and

porous, but when mixed with clay, possess a very high degree of fertility, and
this is particularly the case with chalk, which yields some of the most valuable
of all soils. But it is true only of the common limestones, for experience has
shown that those which contain magnesia in large quantity are often prejudicial
to vegetation, and sometimes yield barren or inferior soils.
Such are the general characters of the three great classes of stratified rocks; any
attempt to particularise the numerous varieties of each would lead us far beyond
the limits of the present work. It is necessary, however, to remark, that in many
instances one variety passes into the other, or, more correctly speaking,
sedimentary rocks occur, which are mixtures of two or more of the three great
classes. In fact, the name given to each really expresses only the preponderating
ingredient, and many sandstones contain much clay, shales and clay slates
abound in lime, and limestones in sand or clay, so that it may sometimes be a
matter of some difficulty to decide to which class they belong. Such mixtures
usually produce better soils than either of their constituents separately, and
accordingly, in those geological formations in which they occur, the soils are
generally of excellent quality. The same effect is produced where numerous thin
beds of members of the different classes are interstratified, the disintegrated
portions being gradually intermixed, and valuable soils formed.
The fertility of the soils formed from the stratified rocks is also increased by the
presence of organic remains which afford a supply of phosphoric acid, and
which are sometimes so abundant as to form a by no means unimportant part of
their mass. They do not occur in the oldest sedimentary rocks, but as we ascend
to the more recent geological epochs, they increase in abundance, until, in the
greensands and other recent formations, whole beds of coprolites and other
organic remains are met with. Great differences are observed in the quality of
the soils yielded by different rocks. In general, those formed by the
disintegration of clay slates are cold, heavy, and very difficult and expensive to
work; those of sandstone light and poor, and of limestone often poor and thin.
These statements must, however, be considered as very general; for individual
cases occur in which some of these substances may produce good soils,
remarkable exceptions being offered by the lower chalk and some of the shales
of the coal formation. Little is at present known regarding the peculiar nature of
many of these rocks, or their composition; and the cause of the differences in
the fertility of the soil produced from them is a subject worthy of minute
investigation.

Chemical Composition of the Soil.—Reference has been already made to the
division of the constituents of the soil into the two great classes of organic and
inorganic. And when treating of the sources of the organic constituents of
plants, we entered with some degree of minuteness into the composition and
relations of the different members of the former class, and expressed the
opinion that they did not admit of being directly absorbed by the plant. But
though the parts then stated lead to the inference that, as a direct source of these
substances, humus is unimportant, it has other functions to perform which
render it an essential constituent of all fertile soils. These functions are
dependent partly on the power which it has of absorbing and entering into
chemical composition with ammonia, and with certain of the soluble inorganic
substances, and partly on the effect which the carbonic acid produced by its
decomposition exerts on the mineral matters of the soil. In the former way, its
effects are strikingly seen in the manner in which ammonia is absorbed by peat;
for it suffices merely to pour upon some dried peat a small quantity of a dilute
solution of ammonia to find its smell immediately disappear. This peculiar
absorptive power extends also to the fixed alkalies, potash and soda, as well as
to lime and magnesia, and has an important effect in preventing these
substances being washed out of the soil—a property which, as we shall
afterwards see, is possessed also by the clay contained in greater or less
quantity in most soils. On the other hand, the air and moisture which penetrate
the soil cause its decomposition, and the carbonic acid so produced attacks the
undecomposed minerals existing in it, and liberate the valuable substances they
contain.
In considering the composition of a soil, it is important to bear in mind that it is
a substance of great complexity, not merely because it contains a large number
of chemical elements, but also because it is made up of a mixture of several
minerals in a more or less decomposed state. The most cursory examination
shows that it almost invariably contains sand and scales of mica, and other
substances can often be detected in it. Now it has been already observed that the
minerals of which soils are composed, differ to a remarkable extent in the
facility with which they undergo decomposition, and the bearing of this fact on
its fertility is a matter of the highest importance, for it has been found that the
mere presence of an abundant supply of all the essential constituents of plants is
not always sufficient to constitute a fertile soil. Two soils, for instance, may be
found on analysis to have exactly the same composition, although in practice
one proves barren and the other fertile. The cause of this difference lies in the
particular state of combination in which the elements are contained in them, and

unless this be such that the plant is capable of absorbing them, it is immaterial
in what quantity they are present, for they are thus locked up from use, and
condemn the soil to hopeless infertility.
It is admitted that unless the substances be present in a state in which they can
be dissolved, the plant is incapable of absorbing them; but it is a matter of doubt
whether it is necessary that they be actually dissolved in the water which
permeates the soil, or whether the plant is capable of exercising a directly
solvent action. The latter view is the most probable, but at the same time it
cannot be doubted, that if they are presented to the plant in solution, they will
be absorbed in that state in preference to any other. Hence it has been
considered important in the analysis of a soil, not to rest content with the
determination of the quantity of each element it contains, but to obtain some
indication of the state of combination in which it exists, so as to have some idea
of the ease or difficulty with which they may be absorbed. For this purpose it is
necessary to determine, 1st, The substances soluble in water; 2d, Those
insoluble in water, but soluble in acids; 3d, Those insoluble both in water and
acids; and if to these the organic constituents be added, there are four separate
heads under which the components of a soil ought to be classified. This
classification is accordingly adopted in the most careful and minute analyses;
but the difficulty and labour attending them has hitherto precluded the
possibility of making them except in a few instances; and, generally speaking,
chemists have been contented with treating the soil with an acid, and
determining in the solution all that is dissolved. Such analyses are often useful
for practical purposes, as for example, when they show the absence of lime, or
any other individual substance, by the addition of which we may rectify the
deficiency of the soil; but they are of comparatively little scientific value, and
throw but little light on the true constitution of the soil, and the sources of its
fertility. Nor is it likely that much satisfactory information will be obtained until
the number of minute analyses is so far extended as to establish the fundamental
principles on which the various properties of the soil depends.
The separation of the constituents of a soil into the four great groups already
mentioned, is effected in the following manner:—A given quantity of the soil is
boiled with three or four successive quantities of water, which dissolves out all
the soluble matters. These generally amount to about one-half per cent of the
whole soil, and consist of nearly equal proportions of organic and inorganic
substances. In very light and sandy soils, it occasionally happens that not more
than one or two-tenths per cent dissolve in water, and in peaty soils, on the

other hand, the proportion is sometimes considerably increased, principally
owing to the abundance of soluble organic matters.
When the residue of this operation is treated with dilute hydrochloric acid, the
matters soluble in acids are obtained in the fluid. The proportion of these
substances is liable to very great variations, and in some soils of excellent
quality, and well adapted to the growth of wheat, it does not exceed 3 per cent;
while in calcareous soils, such as those of the chalk formation, it may reach as
much as 50 or 60 per cent. In general, however, it amounts to about 10 per cent.
The organic constituents are also very variable in amount; ordinary soils of
good quality containing from 2 to 10 per cent, while in peat soils they not
unfrequently reach 30 or even 50 per cent. But these cannot be considered
fertile soils. The insoluble constituents are likewise subject to great variations,
but, in the ordinary clay and sandy soils of this country, they generally form
from 70 to 85 per cent of the whole.
The distribution of the constituents under these different heads will be best
illustrated by a few analyses of soils of good quality, and for this purpose we
shall select two, noted for the excellent crops of wheat they produce, and for
their general fertility. The analyses were made from the upper 10 inches, and a
quantity of the 10 inches immediately subjacent was analysed as subsoil. The
first is the ordinary wheat soil of the county of Mid-Lothian, the other the
alluvial soil of the Carse of Gowrie in Perthshire, so celebrated for the
abundance and luxuriance of the crops it produces.

Mid-Lothian. Perthshire.
Soil. Subsoil. Soil. Subsoil.
SUBSTANCES SOLUBLE IN WATER.
Silica 0·0149 0·0104 0·0072 0·0461
Lime 0·0300 0·0072 0·0184 0·0306
Magnesia 0·0097 0·0016 0·0040 0·0034
Chlor. of magnesium — — — 0·0033
Potash 0·0034 0·0037 — —
Soda 0·0065 0·0049 — —
Chloride of potassium — — 0·0088 0·0080
Chloride of sodium — — 0·0110 0·0166
Sulphuric acid 0·0193 0·0124 0·0089 0·0239
Chlorine trace trace — —
Organic matters 0·1481 0·2228 0·0608 0·1342
0·2319 0·2630 0·1191 0·2661
SOLUBLE IN ACIDS.
Silica 0·1490 0·0680 0·0482 0·1697
Peroxide of iron 5·1730 3·4820 4·8700 4·6633
Alumina 2·1540 1·8130 2·6900 3·9070
Lime 0·4470 0·3810 0·3616 0·5050
Magnesia 0·4120 0·2850 0·3960 0·9420
Potash 0·0650 0·1650 0·3445 0·1670
Soda 0·0050 0·0560 0·1242 0·1920
Sulphuric acid 0·0250 0·0850 0·0911 0·0160
Phosphoric acid 0·4300 0·1970 0·2400 0·2680
Carbonic acid — — 0·0500 —
8·8600 6·5320 9·2156 10·8300
INSOLUBLE IN ACIDS.
Silica 71·3890 82·5090 63·1400 61·4200
Alumina 4·7810 3·5120 11·3500 10·3400
Peroxide of iron trace trace — 1·5670
Lime 0·7520 0·5500 0·4500 0·7400
Magnesia 0·6610 0·5500 0·6200 0·4450
Potash 0·2860 — 2·4500 2·0030

Soda 0·4220 — 1·3100 0·8440
78·2910 87·1210 79·3200 77·3590
ORGANIC MATTERS.
Insoluble organic matter 8·8777 4·2370 7·7400 6·2910
Humine 0·8850 0·3450 0·0700 0·0840
Humic acid 0·1340 0·0310 0·6800 0·3600
Apocrenic acid 0·1533 — — 0·0929
Water 2·6840 1·7670 2·7000 4·5750
12·7340 6·3800 11·1900 11·4020
Sum of all the
100·1169 100·2960 99·8447 99·8571
constituents
AMOUNT OF CARBON, HYDROGEN, NITROGEN, AND OXYGEN
CONTAINED IN 100 PARTS OF EACH SOIL.
Carbon 4·510 1·3060 2·55 2·03
Hydrogen 0·550 0·3324 0·71 0·53
Nitrogen 0·220 0·0973 0·21 0·17
Oxygen 4·918 3·1001 5·08 4·09
10·198 4·8358 8·55 6·82

In examining these analyses, it is particularly worthy of notice that by far
the larger proportion of the substances soluble in water consists of organic
matter, lime, and sulphuric acid, the two last being in combination as
sulphate of lime, while some of those substances which are usually
considered to be the most important mineral constituents of plants are
present in very small quantity—potash, for instance, forming not more than
1-25,000th of the whole soil, and phosphoric acid being entirely absent. On
the other hand, this portion contains the whole of the chlorine which exists
in the soil, and this might be anticipated from the ready solubility in water
of the compounds of that substance.
The portion soluble in acids consists of alumina and oxide of iron, both of
which are comparatively unimportant to the plant, but very important, as we
shall afterwards see, in relation to the physical properties of the soil. The
remainder of the substances soluble in acids, amounting to from 1 and 2 per
cent, is composed of some of the most essential constituents of plants.
Lime, magnesia, potash, and soda, appear again in larger quantity than in

the soluble part, and along with them we have the phosphoric acid to the
amount of from 0·2 to 0·4 per cent of the whole soil, and sulphuric acid in
much smaller quantity.
The insoluble matters differ remarkably in the two soils, that from the Carse
of Gowrie being characterised by a large quantity of potash and soda,
indicating an important difference in the materials from which they have
been formed. In the Perthshire soil it is obvious that the felspathic element
has been abundant, and that its decomposition has been arrested at a time,
when it still contained a large quantity of alkalies. And this difference is of
great practical importance, because those soils, which contain a large
quantity of potash in their insoluble portion, have within them a source of
permanent fertility, the alkali being gradually liberated by the
decomposition which is constantly in progress, owing to the air and
moisture permeating the soil. As regards the special distribution of the
inorganic matters, it is to be observed that some of them occur in each of
the three heads under which they are arranged, while others are confined to
one or two. Silica and the alkalies occur generally, though not invariably, in
all three. Chlorine is met with only in the part soluble in water, phosphoric
acid only in that soluble in acids, while sulphuric acid occurs in both the
last-named divisions.
The greater part of the organic matters are insoluble both in water and acids.
At least it is generally believed that any portion dissolved by strong acids,
in the course of analysis, has been entirely decomposed, and is in a
completely different state from that in which it existed actually in the soil.
As an example of a calcareous soil, forming a striking contrast to those
given above, we select one from the island of Antigua, from which very
large crops of sugar-cane are obtained. The soil is of great depth, and
analyses of the subsoil at the depth of 18 inches and 5 feet are given. These
last analyses are not so minute as that of the soil itself, the soluble matters
not having been separately determined, but included in that soluble in acids.

Surface Soil. 18 inches deep. 5 feet deep.
SOLUBLE IN WATER.
Lime 0·07 ... ...
Magnesia trace ... ...

Potash 0·06 ... ...
Soda 0·04 ... ...
Chlorine 0·05 ... ...
Organic matter 0·15 ... ...
——
0·37
SOLUBLE IN ACIDS.
Silica 0·74 ... ...
Peroxide of iron 2·22 1·67 1·87
Protoxide of iron 0·77 9·05 3·10
Alumina 1·90 2·52 4·21
Lime 10·43 3·04 25·75
Magnesia 0·20 0·54 0·51
Potash 0·03 0·29 0·28
Soda 0·02 0·11 0·16
Sulphuric acid trace 0·02 0·13
Phosphoric acid 0·14 trace 0·04
Carbonic acid 7·38 0·82 20·23
—— —— ——
23·83 18·06 56·28
INSOLUBLE IN ACIDS.
Silica 41·44 51·24 27·67
Protoxide of iron 3·24 0·26 1·40
Alumina 9·00 1·50 1·00
Lime 0·08 0·88 trace
Magnesia 0·80 0·54 trace
Potash ... 0·74 ...
Soda ... 0·25 ...
—— —— ——
54·56 55·41 30·07
ORGANIC MATTERS.
Humine 1·58 }

Humic acid 1·15 } 12·05 7·49
Insoluble organic matters 7·66 }
Water 11·13 14·69 6·06
—— —— ——
21·52 26·74 13·55
Sum of all the constituents 100·28 100·21 99·90

In this soil there is a general resemblance in the composition of the portion
soluble in water to those of the wheat soils. But the part soluble in acids is
distinguished by the great abundance of carbonate of lime.
The subsoil contains also a large quantity of protoxide of iron, a substance
frequently found in subsoils containing much organic matter, and to which
the air has imperfect access. Under these circumstances peroxide of iron is
reduced to protoxide; and when present abundantly in the soil in that form,
iron has been found to exercise a very injurious influence on vegetation;
and it has frequently happened that when subsoils containing it have been
brought up to the surface, they have in the first instance caused a manifest
deterioration of the soil, although after some time, when it had become
peroxidised by the action of the air, it ceased to be injurious.
The soil of Holland, from the neighbourhood of the Zuider Zee, which is an
alluvial deposit from the waters of the Rhine, and produces large crops,
gave the results which follow—

15 inches 30 inches
Surface.
deep. deep.
Insoluble silica 57·646 51·706 55·372
Soluble silica 2·340 2·496 2·286
Alumina 1·830 2·900 2·888
Peroxide of iron 9·039 10·305 11·864
Protoxide of iron 0·350 0·563 0·200
Oxide of manganese 0·288 0·354 0·284
Lime 4·092 5·096 2·480
Magnesia 0·130 0·140 0·128
Potash 1·026 1·430 1·521

Soda 1·972 2·069 1·937
Ammonia 0·060 0·078 0·075
Phosphoric acid 0·466 0·324 0·478
Sulphuric acid 0·896 1·104 0·576
Carbonic acid 6·085 6·940 4·775
Chlorine 1·240 1·302 1·418
Humic acid 2·798 3·991 3·428
Crenic acid 0·771 0·731 0·037
Apocrenic acid 0·107 0·160 0·152
Other organic matters and Combined
8·324 7·700 9·348
water
Loss 0·540 0·611 0·753
——— ——— ———
100·000 100·000 100·000

It is unnecessary to multiply analyses of fertile soils, those now given being
sufficient to show their general composition. They are all characterised by
the presence, in considerable quantity, of all the essential constituents of
plants, in a state in which they may be readily absorbed. The absence of one
or more of these substances immediately diminishes or altogether destroys
the fertility of the soil; and the extent to which this occurs is illustrated by
the following analysis of a soil from Pumpherston, Mid-Lothian, forming a
small patch in the lower part of a field, and on which nothing would grow.
Being naturally wet, it had been drained and sowed with oats, which died
out about six weeks after sowing, and left a bare soil on which weeds did
not show the slightest disposition to grow.

SOLUBLE IN ACIDS.

Soluble silica 0·173
Peroxide of iron 6·775
Alumina 1·150
Oxide of manganese trace
Carbonate of lime 0·856
Magnesia 0·099

Potash 0·132
Soda 0·123
Phosphoric acid trace
Chlorine trace
—— 9·308
Silica 73·096
Peroxide of iron 1·371
Alumina 4·263
Lime 0·858
Magnesia 0·520
—— 80·108
Organic matter 8·012
Water 2·391
—— 10·403
———
99·819

In this instance the barrenness of the soil is distinctly traceable to the
deficiency of phosphoric acid, sulphuric acid, and chlorine. There is also a
remarkably large quantity of oxide of iron, which, when acted on by the
humic acid, is well known to be highly prejudicial to vegetation, and that
this took place was shown by the fact that the drains, a couple of months
after being laid, were almost stopped up by humate of iron. Still more
striking are the following analyses:—

Moorland soil near
Sandy soil near Soil from near
Aurich, East
Wettingen. Muhlhausen.
Friesland.
Silica and sand 70·576 96·000 77·490
Alumina 1·050 0·500 9·490
Oxide of iron 0·252 2·000 5·800
Oxide of
{ trace 0·105
manganese } trace
Lime } { 0·001 0·866
Magnesia 0·012 trace 0·728

Potash }
trace
Soda }
Phosphoric
trace 0·003
acid }
Sulphuric acid
trace
}
Carbonic acid ... ... 0·200
Chlorine trace trace trace
Humic acid 11·910 0·200 0·732
Insoluble
16·200 1·299 0·200
humus
Water ... ... 4·096
100·000 100·000 100·000

The results contained in these analyses are peculiarly remarkable, for they
indicate the almost total absence of all those substances which the plant
requires. They must, however, be considered as in a great measure
exceptional cases, as it is but rarely that so large a number of constituents is
absent, and it is much more frequent to find the deficiency restricted to one
or two substances. They are illustrations of barrenness dependent on
different circumstances. The first shows the unimportance of the organic
matters of the soil, which are here unusually abundant, without in any way
counteracting the infertility dependent on the absence of the other
constituents. The second is that of a nearly pure sand; and the third, though
it contains a greater number of the essential ingredients of the ash, is still
rendered unfruitful by the deficiency of alkalies, sulphuric acid, and
chlorine.
An examination of the foregoing analyses indicates pretty clearly some of
the conditions of fertility of the soil, which must obviously contain all the
constituents of the plants destined to grow upon it. But it by no means
exhausts the subject, for numerous instances are known of soils containing
all the essential elements of plants in abundance, but on which they
nevertheless refuse to grow. In these instances the defect is due either to the
presence of some substance injurious to the plant, or to the state of
combination of those it requires being such as to prevent their absorption.
Reference has been already made to the bad effects of protoxide of iron, and

it would appear that organic matter is sometimes injurious. Even water, by
excluding air, and so preventing those decompositions which play so
important a part in liberating the essential elements from their more
permanent compounds, although it cannot render a soil absolutely barren,
not unfrequently materially diminishes its fertility.
The state of combination of the soil constituents unquestionably exercise a
most important influence on its fertility. That this must be the case is an
inference which may be easily drawn from the statements already made
regarding the different minerals from which it is directly or indirectly
produced. If, for instance, a soil consist to a large extent of mica, it would
be found on analysis to contain abundance of potash and some other
matters, and yet our knowledge of the difficulty with which that mineral is
decomposed, would enable us to pronounce unfavourably of the soil; and
practical experience here fully confirms the scientific inference.
The forms of combination most favourable to fertility is a subject on which
our information is at present comparatively limited. It was at one time
believed that solubility in water was an indispensable requisite, but recent
investigations appear to lead to a directly contrary conclusion. The analyses
of soils already given, show that the part directly soluble in water embraces
only a certain number of the constituents of the plant, and of those
dissolved the quantity is very small. This becomes still more apparent if we
estimate from the analyses the actual quantities of those substances
contained in an acre of soil. It is generally assumed that the soil on an
imperial acre of land 10 inches deep weighs in round numbers about 1000
tons; and calculating from this, we find that the quantity of potash soluble
in water in the Mid-Lothian wheat soil, amounts to no more than 70 lb. per
acre. But a crop of hay carries off from the soil about 38 lb. of potash, and
one of turnips, including tops, not less than 200 lb., so that if only the
matters soluble in water could be taken up by the plant, such soils could not
possess the amount of fertility which they are actually found to have.
It is to be remembered, also, that in these analyses the experiment is made
under the most favourable circumstances for ascertaining the whole
quantity of matters which are capable of dissolving in water; that practically
dissolved is very different. The recent analysis by Krocker and Way of the
drainage water of soils afford a means of estimating this. Way found in one

gallon of the drainage water from seven different fields, collected in the end
of December—

1 2 3 4 5 6 7
Potash, trace trace 0·02 0·05 trace 0·22 trace
Soda, 1·00 2·17 2·26 0·87 1·42 1·40 3·20
Lime, 4·85 7·19 6·05 2·26 2·52 5·82 13·00
Magnesia, 0·68 2·32 2·48 0·41 0·21 0·93 2·50
Iron and Alumina, 0·40 0·05 0·10 none 1·30 0·35 0·50
Silica, 0·95 0·45 0·55 1·20 1·80 0·65 0·85
Chlorine, 0·70 1·10 1·27 0·81 1·26 1·21 2·62
Sulphuric acid, 1·65 5·15 4·40 1·71 1·29 3·12 9·51
Phosphoric acid, trace 0·12 trace trace 0·08 0·06 0·12
Ammonia, 0·018 0·018 0·018 0·012 0·018 0·006 0·018
Nitric acid, 7·17 14·74 12·72 1·95 3·45 8·05 11·45
Organic matter, 7·00 7·40 12·50 5·60 5·70 5·80 7·40

Some of the soils from which these waters were obtained had been manured
with unusually large quantities of nitrogenous matters, which accounts for
the large amount of nitric acid, as well as the lime which that acid has
extracted. Dr. Krocker's analyses were made on soils less highly manured,
and the water was collected in summer.

IN 10,000 PARTS.
1 2 3 4 5 6
Organic matter 0·25 0·24 0·16 0.06 0·63 0·56
Carbonate of lime 0·84 0·84 1·27 0·79 0·71 0·84
Sulphate of lime 2·08 2·10 1·14 0·17 0·77 0·72
Nitrate of lime 0·02 0·02 0·01 0·02 0·02 0·02
Carbonate of magnesia 0·70 0·69 0·47 0·27 0·27 0·16
Carbonate of iron 0·04 0·04 0·04 0·02 0·02 0·01
Potash 0·02 0·02 0·02 0·02 0·04 0·06
Soda 0·11 0·15 0·13 0·10 0·05 0·04
Chloride of sodium 0·08 0·08 0·07 0·03 0·01 0·01
Silica 0·07 0·07 0.06 0·05 0·06 0·05

In order to obtain from these experiments an estimate of the quantity of the
substances actually dissolved, we shall select the results obtained by Way.
The average rainfall in Kent, where the waters he examined were obtained,
is 25 inches. Now, it appears that about two-fifths of all the rain which falls
escapes through the drains, and the rest is got rid of by evaporation. An inch
of rain falling on an imperial acre weighs rather more than a hundred tons;
hence, in the course of a year, there must pass off by the drains about 1000
tons of drainage water, carrying with it, out of the reach of the plants, such
substances as it has dissolved, and 1500 tons must remain to give to the
plant all that it holds in solution. These 1500 tons of water must, if they
have the same composition as that which escapes, contain only two and a
half pounds of potash, and less than a pound of ammonia. It may be alleged
that the water which remains, lying longer in contact with the soil, may
contain a larger quantity of matters in solution; but even admitting this to be
the case, it cannot for a moment be supposed that they can ever amount to
more than a very small fraction of what is required for a single crop. It may
therefore be stated with certainty that solubility in water is not essential to
the absorption of substances by the plant, which must possess the power of
itself directly attacking, acting chemically on, and dissolving them. The
mode in which it does this is entirely unknown, but it in all probability
depends on very feeble chemical actions, and hence the importance of
having the soil constituents, not in solution, but in such a state that they
may be readily made soluble by the plants. Many of the minerals from
which fertile soils are formed are probably not attackable by plants when in
their natural condition, and even after disintegration the quantity of the
essential elements of their food, which are present in an easily assimilable
state, is at no one time very large. But this is of comparatively little
importance, for the soil is not an inert unchangeable substance; it is the
theatre of an important series of chemical changes effected by the action of
air and moisture, and producing a continued liberation of its constituents.
This decomposition is effected partly by the carbonic acid of the
atmosphere, but to a much larger extent by its oxygen acting upon the
organic matters of the soil, and causing a constant though slow evolution of
that acid, which in its turn attacks the mineral matters. Boussingault and
Levy have illustrated the extent of this action by examining the composition
of the air contained in the pores of different soils, and have obtained the
following results:—

No. of cubic 100 VOLUMES OF AIR
inches of air in CONTAIN
Nature of Soil. Crop.
34 cubic inches Carbonic
Oxygen. Nitrogen.
of soil acid.
Light sandy
soil, newly ... 8·0 2·17 ... ...
manured
Do.
manured 8 ... ... 1·54 18·80 79·66
days before
Do. long Yellow
7·9 0·93 19·50 79·57
after manuring turnip
Very sandy Vineyard 9·6 1·06 19·72 79·22
Sandy, with
Forest 4·0 0·87 19·61 79·52
many stones
Loamy ... 2·4 0·46 ... ...
Sandy, subsoil
... 3·0 0·24 ... ...
of the last
Sandy soil,
long after Trefoil 7·6 0·74 19·02 80·24
manuring
Do.
Recently ... ... 0·85 19·41 79·74
manured
Do.
manured 8 ... ... 1·54 18·80 79·66
days before
Jerusalem
Heavy clay 7·0 0·66 19·99 79·35
artichoke
Fertile soil
Meadow 5·5 1·79 19·41 78·80
(moist)

From these analyses it appears that the air contained in the pores of the soil
is much richer in carbonic acid than the atmosphere, the poorest soil
containing about 25 times, and a recently manured soil 250 times as much.
This carbonic acid, which is obviously produced by the decomposition of

the vegetable matters and manure, acting partly as gas and partly dissolved
in the soil water, exerts a solvent action on its constituents. And, though a
very feeble acid, its continuous action produces in the course of time a large
effect; while, during the interval, the constituents of the soil are safely
stored up, and liberated only as the plant requires them, by which bountiful
provision of nature they are exposed to fewer risks of loss than if they had
been all along in a state in which they could be absorbed. Carbonic acid not
only assists in effecting the decomposition of the minerals of the soil, but its
aqueous solution acts as a solvent of many substances, which are quite
insoluble in pure water. It is in this way that much of the lime contained in
natural waters is held in solution, and it has been ascertained that magnesia,
iron, and even phosphate of lime, may also be dissolved by it. It is probable
that when these substances are dissolved, the plants will take them from
solution in place of themselves attacking the insoluble matters; but of the
extent to which this may occur nothing is yet known—the action of solvents
on the soil being a subject which is as yet scarcely examined.
Carbonic acid is, however, a most important agent in producing the
chemical changes in the soil, and the particular value of humus lies in its
affording a supply of that substance exactly when it is wanted; but the
carbonic acid of the atmosphere also takes part in these changes, although
with different degrees of rapidity according to the character of the soil,
acting rapidly in light, and slowly in stiff, clay soils. The solvent action of
the carbonic acid is, no doubt, principally exerted on the substances soluble
in acids, but not entirely, for it is known that the insoluble part is gradually
being disintegrated and made soluble; and hence it is that the composition
of that part of the soil which resists the action of acids, and which at first
sight might appear of no moment, is really important. It is obvious that this
circumstance must at once confer on the soil of the Carse of Gowrie a great
superiority over those of Mid-Lothian and most other districts; for it
contains in its insoluble part a quantity of alkalies which must necessarily
form a source of continued fertility. Accordingly, experience has all along
shown the great superiority of that soil, and of alluvial soils generally,
which are all more or less similar to it. The facility with which these matters
are attackable by carbonic acid is also an important element of the fertility
of a soil, and it is to the existence of compounds which are readily
decomposed by it that we attribute the high fertility of the trap soils.

By a further examination of the analyses of fertile soils, it is at once
apparent that the most essential constituents of plants are by no means very
abundant in them. In fact, phosphoric and sulphuric acids, lime, magnesia,
and the alkalies, which in most instances make up nine-tenths of the ash of
plants, form but a small portion of even the most fertile soils; while silica,
which, except in the grasses, occurs in small quantity, oxide of iron which is
a limited, and alumina a rare, constituent of the ash, constitute by far their
larger part. Thus the total amount of potash, soda, lime, magnesia,
phosphoric and sulphuric acids and chlorine, contained in the Mid-Lothian
wheat soil amounts only to 3·5888 per cent, and in the Perthshire to 6·4385,
the entire remainder being substances which enter into the plant for the
most part in much smaller quantity. And, as these small quantities of the
more important substances are capable of supplying the wants of the plant,
it must be obvious that a very small fraction of the silica, oxide of iron, and
alumina, which the soils contain, would afford to it the whole quantity of
these substances it requires, and that the remainder must have some other
functions to perform.
The soil must be considered not merely as the source of the inorganic food
of plants, for it has to act also as a support for them while growing, and to
retain a sufficient quantity of moisture to support their life; and unless it
possess the properties which fit it for this purpose, it may contain all the
elements of the food of plants, and yet be nearly or altogether barren.
The adaptation of the soil to this function is dependent to a great extent on
its mechanical texture, and on this considerable light is frequently thrown
by a kind of mechanical analysis.
If a soil be shaken up with water and allowed to stand for a few minutes, it
rapidly deposits a quantity of grains which are at once recognised as
common sand; and if the water be then poured off into another vessel and
allowed to stand for a longer time, a fine soft powder, having the properties
and composition of common clay, is deposited, while the clear fluid retains
the soluble matters. By a more careful treatment it is possible to distinguish
and separate humus, and in soils lying on chalk or limestone, calcareous
matter or carbonate of lime.

In this way the components can be classified into four groups, a mixture of
two or more of which in variable proportions is found in all soils.
The relative proportions in which these substances exist in soils are, as we
shall afterwards see, the foundation of their classification into the light,
heavy, calcareous, and other sub-divisions. But they are also intimately
connected with certain chemical and mechanical peculiarities which have
an important bearing on its fertility. It is a familiar fact, that particular soils
are specially adapted to the growth of certain crops; and we talk of a wheat
or a turnip soil as readily distinguishable. It is to be observed, however, that
in many such instances the mere analysis may show no difference, or, at
least, none sufficient to account for the peculiarity. A remarkable illustration
is offered by the following analyses of two soils, on one of which red clover
grows luxuriantly, while on the other it invariably fails.

Clover fails. Clover succeeds.
Insoluble silicates 83·90 81·34
Soluble silica 0·08 0·02
Peroxide of iron 4·45 6·68
Alumina 2·40 3·00
Lime 1·23 1·33
Magnesia 0·45 0·25
Potash 0·20 0·22
Soda 0·07 0·09
Sulphuric acid 0·05 0·08
Phosphoric acid 0·38 0·07
Carbonic acid 0·09 0·34
Chlorine trace trace
Humic acid 0·42 0·43
Humine ... 0·10
Insoluble organic matters 3·70 3·61
Water 2·54 2·52
—— ——
99·96 100·08
Nitrogen 0·15 1·15

In this instance such difference as exists is rather in favour of the soil on
which clover fails, but it is exceedingly trifling; and it is necessary to seek
an explanation in the special properties of its mechanical constituents.
These properties are partly mechanical and partly chemical, and in both
ways exercise an important influence on the fertility of the soil.
Sand and clay, the most important of the mechanical constituents, confer on
the soil diametrically opposite properties; the former, when present in large
quantity, producing what are designated as light, the latter stiff or heavy
soils. The hard indestructible siliceous grains, of which sand is composed,
form a soil of an open texture, through which water readily permeates;
while clay, from its fine state of division, and peculiar adhesiveness or
plasticity, gives it a close-textured and retentive character, and their proper
intermixture produces a light fertile loam, each tempering the peculiar
properties of the other. Indeed, their mixture is manifestly essential, for
sand alone contains little or none of the essential ingredients of plants; and
if present in large quantity, the openness of the soil is excessive, water
flows through it with rapidity, manures are rapidly wasted, and on the
accession of drought, the plants growing upon it soon languish and die.
Clay, on the other hand, is by itself equally objectionable; the closeness of
its texture prevents the spreading of the roots of plants, and the access of
carbonic acid, which, as we have already seen, is so important an agent in
the changes occurring in the soil. In fact, a pure clay, that is to say, a clay
unmixed with sand, even though it may contain all the essential constituents
of the plant, is for this reason unfertile. Practically, of course, these extreme
cases rarely occur; the heaviest clay soils being mixtures of true clay with
sand, and the most sandy containing their proportion of clay; but frequently
the preponderance of the one over the other is so great, as to produce soils
greatly inferior to those in which the mixture is more uniform.
It is easy to understand how the proportions in which sand and clay are
mixed must affect the suitability of soils to particular crops, and that an
open soil must be favourable to the turnip, and a heavy clay, owing to the
resistance it offers to the expansion of the bulbs, unfavourable. But these
substances also exercise an important chemical action on the soluble
constituents of the food of plants, combining with them, and converting
them into an insoluble, or nearly insoluble state, so as to prevent their being

washed away by the rain or other water which percolates through the soil. It
has long been known to chemists that clay has a tendency to absorb a small
proportion of ammonia, and even when brought up from a great depth
frequently contains that substance. It is to Mr. Thompson of Moat Hall,
however, that we owe the important observation, that arable soils rapidly
remove ammonia from solution, and Way, who pursued this investigation,
showed that not only ammonia, but potash, and several of the other
important elements of the food of plants, are thus absorbed. The removal of
these substances from solution is easily illustrated by a simple experiment.
It suffices to take a tall cylindrical vessel open at both ends, and filled with
the soil to be operated upon, which is retained by a piece of rag tied over its
lower end. A quantity of a dilute solution of ammonia being then poured
upon the surface of the soil, and allowed to percolate, the first quantity
which flows away is found to have entirely lost its peculiar smell and taste;
and in a similar manner the removal of potash may be illustrated. This
action is by no means confined to those substances when in the free state,
but is equally marked when they are combined with acids in the form of
salts, and in the latter case the absorption is attended with a true chemical
decomposition, the base only being retained, and the acid escaping most
commonly in combination with lime. Thus, if sulphate of ammonia be
employed, the water which flows from the soil contains sulphate of lime,
and if muriate of ammonia be used, it is muriate of lime which escapes.
This absorbent action is most remarkably manifested in the case of
ammonia and potash, but it takes place also with magnesia and soda. With
the latter, however, it is incomplete, only a half or a fourth of the soda being
removed from solution, the difference depending to some extent on the acid
with which it is in combination. The extent to which absorption takes place
varies also with the nature of the soil, and the state of combination of the
substance used. Exact experiments have hitherto been chiefly confined to
ammonia, potash, and lime in the free state, and as bicarbonate; and the
following table gives the results obtained by Way, with solutions containing
about 1 per cent of these substances in solution:—

Loamy soil, Red soil, Subsoil clay,
Pure clay.
Dorsetshire. Berkshire. Somersetshire.
Ammonia, caustic 0·3438 0·1570 ... ...

" from muriate 0·3478 0·1966 0.2847 0·0818
Potash, caustic ... ... 1·050 2·087
" from nitrate ... ... 0·4980 ...
Lime, caustic ... ... 1·468 ...
" from bicarbonate ... ... 0·731 ...

From these numbers it appears that very great differences exist in the
absorbent power of different soils, the first of those experimented on being
capable of taking more than twice as much ammonia as the second, and
nearly four times as much as the subsoil clay. It appears also, as far as
absorption goes, to be immaterial whether the ammonia is free or combined.
But it is different with potash, which is absorbed from the nitrate to the
extent of about O·6 per cent, and from a caustic solution of potash to double
that amount.
The circumstances under which absorption takes place modify, in a manner
which cannot well be explained, the amount absorbed by the same soil. It is
found generally to be most complete with very dilute solutions, and if a soil
be agitated with a quantity of ammonia larger than it can take up, it will
absorb only a certain amount of that substance, but by a further increase of
the amount of ammonia a still larger quantity will be absorbed.
It is important to observe that when a salt is used, the base only is absorbed,
and the acid escapes in combination with lime; even nitric acid,
notwithstanding its importance as a food of plants, being in this
predicament. From this it may be gathered that lime is not readily absorbed
from solutions of its salts; indeed, it would appear that the only salt of that
substance liable to absorption is the bicarbonate, from which it is taken to
the extent of 1·4 per cent by the soil. The absorption of lime from this salt,
and that of phosphoric acid, which takes place to a considerable extent,
probably occurs, however, quite independently of the clay present in the
soil, and is occasioned by its lime, which forms an insoluble compound
with phosphoric acid, and by removing half the carbonic acid of the
bicarbonate of lime converts it also into an insoluble state.
In addition to these mineral substances, organic matters are also removed
from solution. This is conspicuously seen in the case of putrid urine, which
not only loses its ammonia, but also its smell and colour, when allowed to

percolate through soil; and an equally marked result was obtained with flax
water, from which the organic matter was entirely abstracted.
The cause of this absorptive power is still very imperfectly known. Mr. Way
having observed that sand has no such property, while clay, even when
obtained from a considerable depth, always possesses it, supposed that the
absorption was entirely due to that substance. A difficulty, however,
presents itself in explaining how it should happen that while a pure clay
absorbs only 0·2847 of ammonia, a loamy soil, of which one-half probably
is sand, should absorb a larger quantity. The inference is, that the effect
cannot be due to the clay as a whole, and Mr. Way has sought to explain it
by supposing that there exist in the soil particular double silicates of
alumina and lime. He has shown that felspar and the other minerals from
which the soil is produced have no absorbent power, but that artificial
compounds can be formed which act upon solutions of ammonia and potash
in a manner very similar to the soil; but there is not the slightest evidence
that these compounds exist in the soil, and in the year 1853[I] I pointed out
the probability that clay is not the only agent at work, but that the organic
matters take part in the process. So powerful indeed is the affinity of these
substances for ammonia, that chemists are at one as to the difficulty of
obtaining humic and other similar acids pure, owing to the obstinacy with
which they retain it; and there cannot be a doubt that in many soils these
substances are in this point of view of much importance. This is particularly
the case in peat soils, which, though naturally barren, may be made to
produce good crops by the application of sand or gravel; and as neither of
these can cause any absorption of the valuable matters, we must attribute
this effect to the organic matter. Referring to an earlier series of experiments
made in 1850, I showed that, if a quantity of dry peat be taken and ammonia
poured on it, its smell disappears; and this may be continued until upwards
of 1·5 per cent of dry ammonia has been absorbed, and this quantity is
retained by the peat.
In this case pure ammonia was used, but Way's experiments having shown
that this alkali is not absorbed from its salts by organic matters, I expressed
the opinion that humate of lime (which certainly exists in most soils) ought
on chemical grounds to decompose the salts of ammonia and cause the
retention of their base. The recent researches of Brustlein have shown that
lime does cause the organic matters to absorb ammonia from its salts. He

confirms the fact that pure ammonia is absorbed by peat, and shows that
decayed wood has the same effect, although both are without action on
solutions of its salts. A stiff clay, on the other hand, containing organic
matters and much carbonate of lime, readily absorbed ammonia, both when
pure and combined; but after extracting the lime by means of a dilute acid,
it lost the power of taking it from its salts, although it retained the free
alkali as completely as before. On the addition of a small quantity of lime, it
again acquired the power of withdrawing ammonia from its compounds.
These experiments may be explained, either on the supposition of the
presence of humate of lime, or by supposing that the carbonate of lime first
decomposed the salts of ammonia, and that the liberated alkali combined
with the organic matter. It must be admitted, however, that it is very
doubtful whether the ammonia and other substances are fixed in the soil by
a true chemical combination. They are certainly retained by a very feeble
attraction, for it appears from Brustlein's experiments that ammonia may be,
to a considerable extent, removed by washing with abundance of water, and
that if the soil which has absorbed ammonia be allowed to become dry in
the air, it loses half its ammonia, and after four times moistening and
drying, three-fourths have disappeared. These facts are certainly not
incompatible with the presence of a true chemical compound, for the
humate of ammonia is not absolutely insoluble, and many cases occur of
actions taking place in the presence of water, which are entirely reversed
when that fluid is removed; and it is quite possible that when humate of
ammonia is dried in contact with carbonate of lime, it may be decomposed,
and carbonate of ammonia escape. There are other circumstances, however,
which render it, on the whole, most probable that the combination is not
wholly chemical, but rather of a physical character, among which may be
more especially mentioned the fact, that the quantity of the substances
retained by the soil is dependent on the degree of dilution of the fluid from
which they are taken; and that the quantity absorbed never exceeds a very
small fraction of the weight of the soil.
The practical inferences to be drawn from these facts regarding the value of
soils are of the highest importance. It is obvious that two soils having
exactly the same chemical composition may differ widely in absorptive
power, and that which possesses it most largely must have the highest
agricultural value. The examination of different soils, in this point of view,

is a subject of much importance, and deserves the best attention of both
farmers and chemists, although little has as yet been done in regard to it,
and the results which have been obtained are not of a very satisfactory
character. Liebig states, that in his experiments, all the arable soils
examined possessed the same absorptive power, whether they contained a
large or a small proportion of lime or alumina. It can scarcely be expected,
however, that this should be true in all cases, and there are many facts
which seem to indicate that differences must exist. It is well known that
there are some soils in which the manure is very rapidly exhausted, and it is
more than probable that this effect is due to deficient absorptive power,
which leaves the soluble matters at the mercy of the weather, and liable at
any moment to be washed out by a heavy fall of rain.
The more strictly mechanical properties of the soil, such as its relations to
heat and moisture, are not less important than its chemical composition. It is
known that soils differ so greatly in these respects as sometimes materially
to affect their productive capacity. Thus, for instance, two soils may be
identical in composition, but one may be highly hygrometric, that is, may
absorb moisture readily from the air, while the other may be very deficient
in that property. Under ordinary circumstances no difference will be
apparent in their produce, but in a dry season the crop upon the former may
be in a flourishing condition, while that on the latter is languishing and
enfeebled, merely from its inability to absorb from the air, and supply to the
plant the quantity of water required for its growth. In the same way, a soil
which absorbs much heat from the sun's rays surpasses another which has
not that property; and though in many cases this effect is comparatively
unimportant, in others it may make the difference between successful and
unsuccessful cultivation in soils which lie in an unfavourable climate or
exposure.
The investigation of the physical characters of soils has attracted little
attention, and we owe all our present knowledge of the subject to a very
elaborate series of researches on this subject, published by Schübler, nearly
thirty years ago. He determined 1st, The specific gravity of the soils; 2d,
The quantity of water which they are capable of imbibing; 3d, The rapidity
with which they give off by evaporation the water they have imbibed; that
is, their tendency to become dry; 4th, The extent to which they shrink in
drying; 5th, Their hygrometric power; 6th, The extent to which they are

heated by the sun's rays; 7th, The rapidity with which a heated soil cools
down, which indicates its power of retaining heat; 8th, Their tenacity, or the
resistance they offer to the passage of agricultural implements; 9th, Their
power of absorbing oxygen from the air. Each of these experiments was
performed on several different soils, and on their mechanical constituents.
Schübler's experiments are undoubtedly important, and though the methods
employed are some of them not altogether beyond cavil, they have
apparently been performed with great care. It is nevertheless desirable that
they should be repeated, for such facts ought not to rest on the authority of
one experimenter, however skilful and conscientious, nor on a single series
of soils, which may not give a fair representation of their general physical
properties. In fact, Schübler appears to imagine that having once
determined the extent to which the sand, clay, and other mechanical
constituents of the soil possess these properties, we are in a condition to
predicate the effect of their mixture in variable proportions, although this is
by no means probable.
In examining these properties, Schübler selected for experiment, pure
siliceous sand, calcareous sand (carbonate of lime in coarse grains), finely
powdered carbonate of lime, pure clay, humus, and powdered gypsum. He
used also a heavy clay consisting of 11 per cent of sand and 89 of pure clay,
a somewhat stiff clay containing 24 per cent of sand and 76 of clay, a light
clay with 40 per cent of sand and 60 of pure clay, a garden soil consisting of
52·4 per cent of clay, 36·5 of siliceous sand, 1·8 of calcareous sand, 2 per
cent of finely divided carbonate of lime, and 7·2 of humus, and two arable
soils, one from Hoffwyl, and one from a valley in the Jura, the former a
somewhat stiff, the latter a light soil.

Water Of 100 parts of Diminution in
Specific absorbed by water absorbed bulk during drying
gravity. 100 parts per there evaporate in of 100 parts moist
cent. four hours at 66° soil.
Siliceous
2·753 25 88·4 0·0
sand
Calcareous
2·822 29 75·9 0·0
sand
Light clay 2·701 40 52·0 6·0

Stiff clay 2·652 50 45·7 8·9
Heavy clay 2·603 61 34·9 11·4
Pure clay 2·591 70 31·3 18·3
Carbonate
2·468 85 28·0 5·0
of lime
Humus 1·225 190 20·5 20·0
Gypsum 2·358 27 71·7 0·0
Garden soil 2·332 96 24·5 14·9
Soil from
2·401 52 32·0 12·0
Hoffwyl
Soil from
2·526 47 40·1 9·5
Jura

Power of
Quantity of hygrometric water absorbed by
retaining heat.
77·165 grains of the soil spread on a
Calcareous sand,
surface of 141·48 square inches.
100.
12 hours. 24 hours. 48 hours. 72 hours.
Siliceous
0 0 0 0 95·6
sand
Calcareous
0·154 0·231 0·231 0·231 100·0
sand
Light clay 1·617 2·002 2·156 2·156 76·9
Stiff clay 1·925 2·310 2·618 2·695 71·1
Heavy clay 2·310 2·772 3·080 3·157 68·4
Pure clay 2·849 3·234 3·696 3·773 66·7
Carbonate
2·002 2·387 2·695 2·695 61·8
of lime
Humus 6·160 7·469 8·470 9·240 49·0
Gypsum 0·077 0·077 0·077 0·077 73·2
Garden soil 2·695 3·465 3·850 4·004 64·8
Soil from
1·232 1·771 1·771 1·771 70·1
Hoffwyl

Soil from
1·078 1·463 1·540 1·540 74·3
Jura

Quantity of oxygen absorbed by 77·165
Tenacity of the
grains f the moist soil in 30 days, from 15
soils. Pure clay,
cubic inches of atmospheric air. Expressed in
100.
cubic inches.
Siliceous
0 0·24
sand
Calcareous
0 0·84
sand
Light clay 57·3 1·39
Stiff clay 68·8 1·65
Heavy clay 83·3 2·04
Pure clay 100·0 2·29
Carbonate of
5·0 1·62
lime
Humus 8·7 3·04
Gypsum 7·3 0·40
Garden soil 7·6 2·60
Soil from
33·0 2·43
Hoffwyl
Soil from
22·0 2·25
Jura

The experiments detailed in the preceding table speak in a great measure for
themselves, and scarcely require detailed comment. It may be remarked,
however, that the columns illustrating the relations of the soil to water are
probably more important than the others. The superiority of a retentive over
an open soil is sufficiently familiar in practice, and though this is no doubt
partly due to the former absorbing and retaining more completely the
ammonia and other valuable constituents of the manures applied to it, it is
also dependent to an equal if not greater extent upon the power it possesses

of retaining moisture. A reference to the table makes it apparent that this
power is presented under three different heads, which are certainly related
to one another, but are not identical. In the second column of the table is
given the quantity of water absorbed by the soil, determined by placing a
given weight of the perfectly dry soil in a funnel, the neck of which is
partially stopped with a small piece of sponge or wool, pouring water upon
it, and weighing it after the water has ceased to drop from it. This may be
considered as representing the quantity of water retained by these different
soils when thoroughly saturated by long continued rains. The column
immediately succeeding gives the quantity of that water which escapes by
evaporation from the same soil after exposure for four hours to dry air at the
temperature of 66°. The fifth, sixth, seventh, and eighth columns indicate
the quantity of moisture absorbed, when the soil, previously artificially
dried, is exposed to moist air for different periods. These characters are
dependent principally, though not entirely, on the porosity of the soil. The
last may also be in some measure due to the presence of particular salts,
such as common salt, which has a great affinity for moisture, but is chiefly
occasioned by their peculiar structure. It is to be remarked that clay and
humus are two of the most highly hygrometric substances known, and it is
peculiarly interesting to observe, that by a beneficent provision of nature,
they also form a principal part of all fertile soils. The quantity of water
imbibed by the soil is important to its fertility, in so far as it prevents it
becoming rapidly dry after having been moistened by the rains. It is
valuable also in another point of view, because if the soil be incapable of
absorbing much water, it becomes saturated by a moderate fall of rain, and
when a larger quantity falls, the excess of necessity percolates through the
soil, and carries off with it a certain quantity of the soluble salts. Important
as this property is, however, it must not be possessed in too high a degree,
but must permit the evaporation of the water retained with a certain degree
of rapidity. Soils which do not admit of this taking place are the cause of
much inconvenience and injury in practice. By becoming thoroughly
saturated with moisture during winter, they remain for a long time in a wet
and unworkable condition, in consequence of which they cannot be
prepared and sown until late in the season, and though chemically
unexceptionable, they are always disadvantageous, and in some seasons
greatly disappoint the hopes of the farmer.

The extent to which the imbibition and evaporation of water takes place is
very variable, but they are obviously related to one another, the soils which
absorb it least abundantly parting with it again with the greatest, facility; for
it appears that siliceous sand absorbs only one-fourth of its weight of water,
and again gives off in the course of four hours four-fifths of that it had
taken up, while humus, which imbibes nearly twice its weight, retains nine-
tenths of that quantity after four hours' exposure. Long-continued and slow
evaporation of the water absorbed by a soil is injurious in another way, for
it makes the soil "cold"—a term of practical origin, but which very
correctly expresses the peculiarity in question. It is due to the fact, that
when water evaporates it absorbs a very large quantity of heat, which
prevents the soil acquiring a sufficiently high temperature from the sun's
rays. The soils which have absorbed a large quantity of moisture shrink
more or less in the process of drying, and form cracks, which often break
the delicate fibres of the roots of the plants, and cause considerable injury:
the extent of this shrinking is given in the fourth column.
The relation of the soils to heat divides itself into two considerations: the
amount of heat absorbed by the soil, and the degree in which it is retained.
Of these the latter only is illustrated in the table. The former is dependent
on so many special considerations, that the results cannot be tabulated in a
satisfactory manner. It is independent of the chemical nature of the soil, but
varies to a great extent according to its colour, the angle of incidence of the
sun's rays, and its state of moisture. It is, however, an important character,
and has been found by Girardin to exercise a considerable influence on the
rapidity with which the crop ripens. He found in a particular year that, on
the 25th of August, 26 varieties of potatoes were ripe on a very dark-
coloured sandy vegetable mould, 20 on an ordinary sandy soil, 19 on a
loamy soil, and only 16 on a nearly white calcareous soil.
The tenacity of the soil is very variable, and indicates the great differences
in the amount of power which must be expended in working them.
According to Schübler, a soil whose tenacity does not exceed 10, is easily
tilled, but when it reaches 40 it becomes very difficult and heavy to work.
On examining the table it becomes manifest, that as far as its mechanical
properties are concerned, humus is a substance of the very highest
importance, for it confers on the soil, in a high degree, the power of

absorbing and retaining water, diminishes its tenacity and permits its being
more easily worked, adds to its hygrometric power and property of
absorbing oxygen from the air, and finally, from its dark colour, causes the
more rapid absorption of heat from the sun's rays. It will be thus
understood, that though it does not directly supply food to the plant, it
ministers indirectly in a most important manner to its well-being, and that to
so great an extent that it must be considered an indispensable constituent of
a fertile soil. But it is important to observe that it must not be present in too
large a quantity, for an excess does away with all the good effects of a
smaller supply, and produces soils notorious for their infertility.
Such are the important physical properties of the soil, and it is greatly to be
desired that they should be more extensively examined. The great labour
which this involves has, however, hitherto prevented its being done, and
will, in all probability, render it impossible except in a limited number of
cases. Some of these characters are, however, of minor importance, and for
ordinary purposes it might be sufficient to determine the specific gravity of
the soil in the dry and moist state, the power of imbibing and retaining
water, its hygrometric power, its tenacity, and its colour. With these data we
should be in a condition to draw probable conclusions regarding the others;
for the higher the specific gravity in the dry state, the greater is the power of
the soil to retain heat, and the darker its colour the more readily does it
absorb it. The greater its tenacity the more difficult is it to work, and the
greater difficulty will the roots of the young plant find in pushing their way
through it. The greater the power of imbibing water, the more it shrinks in
drying; and the more slowly the water evaporates, the colder is the soil
produced. The hygrometric power is so important a character that Davy and
other chemists have even believed it possible to make it the measure of the
fertility of a soil; but though this may be true within certain limits, it must
not be too broadly assumed, the results of recent experiments by no means
confirming the opinion in its integrity, but indicating only some relation
between the two.
The Subsoil.—The term soil is strictly confined to that portion of the
surface turned over by the plough working at ordinary depth; which, as a
general rule, may be taken at 10 inches. The portion immediately subjacent
is called the subsoil, and it has considerable agricultural importance, and
requires a short notice. In many instances, soil and subsoil are separated by

a purely imaginary line, and no striking difference can be observed either in
their chemical or physical characters. In such cases it has been the practice
with some persons not to limit the term soil to the upper portion, but to
apply it to the whole depth, however great it may be, which agrees in
characters with the upper part, and only to call that subsoil which
manifestly differs from it. This principle is perhaps theoretically the more
correct, but great practical advantages are derived from limiting the name of
soil to the depth actually worked in common agricultural operations. The
subsoil is always analogous in its general characters to a soil, but it may be
either identical with that which overlies it or not. Of the former, striking
illustrations are seen in the wheat subsoils, the analyses of which have been
already given. In the latter case great differences may exist, and a heavy
clay is often found lying on an open and porous sand, or on peat, and vice
versa. Even where the characters of the subsoil appear the same as those of
the soil, appreciable chemical differences are generally observed, especially
in the quantity of organic matter, which is increased in the soil by the decay
of plants growing upon it and by the manure added. In general, then, all that
we have said regarding the characters of soils both chemically and
physically, will apply to the subsoils, except that, owing to the difficulty
with which the air reaches the latter, some minor peculiarities are observed.
The most important is the effect of the decay of vegetable matter, without
access of air, which is attended by the reduction of the peroxide of iron to
the state of protoxide, and not unfrequently by the production of sulphuret
of iron, compounds which are extremely prejudicial to vegetation, and
occasionally give rise to some difficulties when the subsoil is brought to the
surface, as we shall afterwards have to notice.
The physical characters of the subsoil are often of much importance to the
soil itself. As, for instance, where a light soil lies on a clay subsoil, in which
case its value is much higher than if it reposed on an open or sandy subsoil.
And in many similar modes an important influence is exerted; but these
belong more strictly to the practical department of agriculture, and need not
be mentioned here.
Classification of Soils.—Numerous attempts have been made to form a
classification of soils according to their characters and value, but they have
not hitherto proved very successful; and the result of more recent chemical
investigations has not been such as to encourage a farther attempt. We have

not at present data sufficient for the purpose, nor, if we had, would it be
possible to arrange any soil in its class except after an elaborate chemical
examination. The only classification at present possible must be founded on
the general physical characters of the soil; and the ordinary mode followed
in practice of dividing them into clays, loams, etc. etc., which we need not
here particularize, fulfils all that can be done until we have more minute
information regarding a large number of soils. Those of our readers who
desire more full information on this point are referred to the works of Thaer,
Schübler, and others, where the subject is minutely discussed.

FOOTNOTES:
[I] Transactions of the Highland and Agricultural Society, vol. vi., p. 317.

CHAPTER VI.
THE IMPROVEMENT OF THE SOIL BY MECHANICAL
PROCESSES.

Comparatively few uncultivated soils possess the physical properties or
chemical composition required for the production of the most abundant
crops. Either one or more of the substances essential to the growth of plants
are absent, or, if present, they are deficient in quantity, or exist in some state
in which they cannot be absorbed. Such defects, whether mechanical or
chemical, admit of diminution, or even entire removal, by certain methods
of treatment, the adaptation of which to particular cases is necessarily one
of the most important branches of agricultural practice, as the elucidation of
their mode of action is of its theory. The observations already made with
regard to the characters of fertile soils must have prepared the reader for the
statement that these defects may be removed, either by mechanical or
chemical processes. The former method of improvement may at first sight
appear to fall more strictly under the head of practical agriculture, of which
the mechanical treatment of the soil forms so important a part, and that their
improvement by chemical means should form the sole subject of our
consideration in a treatise on agricultural chemistry. But the line of
demarcation between the mechanical and the chemical, which seems so
marked, disappears on more minute observation, and we find that the
mechanical methods of improvement are frequently dependent on chemical
principles; and those which, at first sight, appear to be entirely chemical, are
also in reality partly mechanical. It will be necessary for us, therefore, to
consider shortly the mechanical methods of improving the soil.
Draining.—By far the most important method of mechanically improving
the soil is by draining—a practice the beneficial action of which is
dependent on a great variety of circumstances. It is unnecessary to insist on
the advantage derived from the rapid removal of moisture, which enables
the soil to be worked at times when this used to be almost impossible, and
other direct practical benefits. Of its more strictly chemical effects, the most

important is probably that which it produces on the temperature of the soil.
It has been already remarked that the germination of a seed is dependent on
the soil in which it is sown acquiring a certain temperature, and the rapidity
of the after-growth of the plant is, in part at least, dependent on the same
circumstance. The necessary temperature is speedily attained by the heating
action of the sun's rays, when the soil is dry; but when it is wet, the heat is
expended in evaporating the moisture with which it is saturated; and it is
only after this has been effected that it acquires a sufficiently high
temperature to produce the rapid growth of the seeds committed to it.
The extent to which this effect occurs may be best illustrated by reference
to some experiments made by Schübler, in which he determined the
temperature attained by different soils, in the wet and dry state, when
exposed to the sun's rays, from 11 till 3 o'clock, in the latter part of August,
when the temperature in the shade varied from 73° to 77°.

Description of Soil. Wet. Degs.Dry. Degs.
Siliceous sand 99·1 112·6
Calcareous sand 99·3 112·1
Sandy clay 98·2 111·4
Loamy clay 99·1 112·1
Stiff clay 99·3 112·3
Fine bluish-grey clay 99·5 113·0
Garden mould 99·5 113·5
Arable soil 97·7 111·7
Slaty marl 101·8 115·3

In a soil which is naturally dry or has been drained, the superfluous
moisture escapes by the drains, and only that comparatively small quantity
which is retained by capillary attraction is evaporated, and hence the soil is
more frequently and for a longer period in a condition to take advantage of
the heating effect of the sun's rays, and in this way the period of
germination, and, by consequence also, that of ripening is advanced. The
extent of this influence is necessarily variable, but it is generally
considerable, and in some districts of Scotland the extensive introduction of
draining has made the harvest, on the average of years, from ten to fourteen
days earlier than it was before. It is unnecessary to insist on the importance

of such a change, which in upland districts may make cultivation successful
when it was previously almost impossible. The removal of moisture by
drainage affects the physical characters of the soil in another manner; it
makes it lighter, more friable, and more easily worked; and this change is
occasioned by the downward flow of the water carrying with it to the lower
part of the soil the finer argillaceous particles, leaving the coarser and sandy
matters above, and in this way a marked improvement is produced on heavy
and retentive clays. The access of air to the soil is also greatly promoted by
draining. In wet soils the pores are filled with water, and hence the air,
which is so important an agent in their amelioration, is excluded; but so
soon as this is removed, the air is enabled to reach and act upon the organic
matters and other decomposable constituents present. In this way also
provision is made for the frequent change of the air which permeates the
soil; for every shower that falls expels from it a quantity of that which it
contains, and as the moisture flows off by the drains, a new supply enters to
take its place, and thus the important changes which the atmospheric
oxygen produces on the soil are promoted in a high degree. The air which
thus enters acts on the organic matters of the soil, producing carbonic acid,
which we have already seen is so intimately connected with many of its
chemical changes. In its absence the organic matters undergo different
decompositions, and pass into states in which they are slowly acted on, and
are incapable of supplying a sufficient quantity of carbonic acid to the soil;
and they thus exercise an action on the peroxide of iron, contained in all
soils, reduce it to the state of protoxide, or, with the simultaneous reduction
of the sulphuric acid, they produce sulphuret of iron, forms of combination
which are well known to be most injurious to vegetation.
The removal of water from the lower part of the soil, and the admission of
air, which is the consequence of draining, submits that part of it to the same
changes which take place in its upper portion, and has the effect of
practically deepening the soil to the extent to which it is thus laid dry. The
roots of the plants growing on the soil, which stop as soon as they reach the
moist part, now descend to a lower level, and derive from that part of it
supplies of nourishment formerly unavailable. The deepening of the soil has
further the effect of making the plants which grow upon it less liable to be
burned up in seasons of drought, a somewhat unexpected result of making a
soil drier, but which manifestly depends on its permitting the roots to

penetrate to a greater depth, and so to get beyond the surface portion, which
is rapidly dried up, and to which they were formerly confined.
It may be added also that the abundant escape of water from the drains acts
chemically by removing any noxious matters the soil may contain, and by
diminishing the amount of soluble saline matters, which sometimes produce
injurious effects. It thus prevents the saline incrustation frequently seen in
dry seasons on soils which are naturally wet, and which is produced by the
water rising to the surface by capillary attraction, and, as it evaporates,
depositing the soluble substances it contained, as a hard crust which
prevents the access of air to the interior of the soil.
It is thus obvious that the drainage of the soil modifies its properties both
mechanically and chemically. It exerts also various other actions in
particular cases which we cannot here stop to particularize. It ameliorates
the climate of districts in which it is extensively carried out, and even
affects the health of the population in a favourable manner. The sum of its
effects must necessarily differ greatly in different soils, and in different
districts; but a competent authority[J] has estimated, that, on the average,
land which has been drained produces a quarter more grain per acre than
that which is undrained. But this by no means exhausts the benefits derived
from it, draining being merely the precursor of further improvement. It is
only after it has been carried out that the farmer derives the full benefit of
the manures which he applies. He gains also by the increased facility of
working the soil, and by the rapidity with which it dries after continued
rain, thus enabling him to proceed at their proper season with agricultural
operations, which would otherwise have to be postponed for a considerable
time.
It would be out of place to enlarge here upon the mode in which draining
ought to be carried out; it may be remarked, however, that much
inconvenience and loss has occasionally been produced by too close
adherence to particular systems. No rules can be laid down as to the depth
or distance between the drains which can be universally applicable, but the
intelligent drainer will seek to modify his practice according to the
circumstances of the case. As a general rule, the drains ought to be as deep
as possible, but in numerous instances it may be more advantageous to
curtail their depth and increase their number. If, for instance, a thick

impervious pan resting on a clay were found at the depth of three feet below
the surface, it would serve no good purpose to make the drains deeper; but
if the pan were thin, and the subjacent layer readily permeable by water, it
might be advantageous to go down to the depth of four feet, trusting to the
possible action of the air which would thus be admitted, gradually to
disintegrate the pan, and increase the depth of soil above it. It is a common
opinion that if we reach, at a moderate depth, a tenacious and little
permeable clay, no advantage is obtained by sinking the drains into it; but
this is an opinion which should be adopted with caution, both because no
clay is absolutely impermeable, even the most tenacious permitting to a
certain extent the passage of water, and because the clay may have been
brought down by water from the upper part of the soil, and may have
stopped there merely for want of some deeper escape for the water, and
which drains at a lower level might supply. In some cases it may even be
advisable to vary the depth of the drains in different parts of the same field,
and the judicious drainer may sometimes save a considerable sum by a
careful observation of the peculiarities of the different parts of the ground to
be drained.
Subsoil and Deep Ploughing.—It frequently happens, when a soil is
drained, that the subsoil is so stiff as to permit the passage of water
imperfectly, and to prevent the tender roots of the plant from penetrating it,
and reaching the new supplies of nourishment which are laid open to them.
In such cases the benefits of subsoil ploughing and deep ploughing are
conspicuous. The mode of action of these two methods of treatment is
similar but not identical. The subsoil plough merely stirs and opens the
subsoil, and permits the more ready passage of water and the access of air
and of the roots of plants—the former to effect the necessary
decompositions, the latter to avail themselves of the valuable matters set
free. But deep ploughing produces more extensive changes; it raises new
soil to the surface, mixes it with the original soil, and thus not only brings
up fresh supplies of valuable matters to it, but frequently changes its
chemical and mechanical characters, rendering a heavy soil lighter by the
admixture of a light subsoil, and vice versa. Both are operations which are
useless unless they are combined with draining, for it must manifestly serve
no good purpose to attempt to open up a soil unless the water which lies in
it be previously removed. In fact, subsoiling is useless unless the subsoil

has been made thoroughly dry; and it has been found by experience that no
good effects are obtained if it be attempted immediately after draining, but
that a sufficient time must elapse, in order to permit the escape of the
accumulated moisture, which often takes place very slowly. Without this
precaution, the subsoil, after being opened by the plough, soon sinks
together, and the good effects anticipated are not realized. The necessity for
allowing some time to elapse between draining and further operations is
still more apparent in deep ploughing, when the soil is actually brought to
the surface. In that case it requires to be left for a longer period after
draining, in order that the air may produce the necessary changes on the
subsoil; for if it be brought up after having been for a long time saturated
with moisture, and containing its iron as protoxide, and the organic matter
in a state in which it is not readily acted upon by the air, the immediate
effect of the operation is frequently injurious in place of being
advantageous. One of the best methods of treating a soil in this way is to
make the operation a gradual one, and by deepening an inch or two every
year gradually to mix the soil and subsoil; as in this way from a small
quantity being brought up at a time no injurious effects are produced. Deep
ploughing may be said to act in two ways, firstly, by again bringing to the
surface the manures which have a tendency to sink to the lower part of the
soil, and, secondly, by bringing up a soil which has not been exhausted by
previous cropping—in fact a virgin soil.
The success which attends the operation of subsoiling or deep ploughing
must manifestly be greatly dependent on the character of the subsoil, and
good effects can only be obtained when its chemical composition is such as
to supply in increased quantity the essential constituents of the plant; and it
is no doubt owing to this that the opinions entertained by practical men,
each of whom speaks from the results of his own experience, are so varied.
The effects produced by deep ploughing on the estates of the Marquis of
Tweeddale, are familiarly known to most Scottish agriculturists, and they
are at once explained by the analyses of the soil and subsoil here given,
which show that the latter, though poor in some important constituents,
contains more than twice as much potash as the soil.

Soil. Subsoil.
Insoluble silicates 87·623 82·72

Soluble silica 0·393 0·12
Alumina and peroxide of iron 4·129 8·60
Lime 0·341 0·18
Magnesia 0·290 0·24
Sulphuric acid 0·027 0·03
Phosphoric acid 0·240 trace
Potash 0·052 0·12
Soda 0·050 0·04
Water 1·956 3·26
Organic matter 5·220 4·02
——— ——
100·321 99·33

In addition to the difference in the amount of potash, something is probably
due to the large proportion of alumina and oxide of iron in the subsoil,
which for this reason must be more tenacious than the soil itself, which
appears to be rather light. In other instances, the use of the subsoil plough
has occasioned much disappointment, and has led to its being decried by
many practical men; but of late years its use having become better
understood, its merits are more generally admitted. We believe, that in all
cases in which the soil is deep, more or less marked good effects must be
produced by its use, but of course there must be cases in which, from the
defective composition of the subsoil or other causes, it must fail. It may
sometimes be possible a priori to detect these cases, but in a large majority
of them our knowledge is still too limited to admit of satisfactory
conclusions being arrived at.
Improving the Soil by Paring and Burning.—It has long been familiarly
known, that a decided improvement has been produced on some soils by
burning. Its advantages have chiefly been observed on two sorts, heavy
clays and peat soils, on both of which it has been practised to a great extent.
The action of heat on the heavy clays appears to be of a twofold character,
depending partly on the change effected in its physical properties, and
partly on a chemical decomposition produced by the heat. The operation of
burning is effected by mixing the clay with brushwood and vegetable
refuse, and allowing it to smoulder in small heaps for some time. It is a
process of some nicety, and its success is greatly dependent on the care

which has been taken to keep the temperature as low as possible during the
whole course of the burning.
Experience has shown that burning is by no means equally advantageous to
all clays, but is most beneficial on those containing a considerable quantity
of calcareous matter, and of silicates of potash. In such clays heat operates
by causing the lime to decompose the alkaline silicates, and liberate a
quantity of the potash which was previously in an unavailable state. Its
effect may be best illustrated by the following analyses by Dr. Voelcker of a
soil, and the red ash produced in burning it.

Soil. Red Ash.
Water 0·93 1·18
Organic matter 10·67 3·32
Oxides of iron and alumina 13·40 18·42
Carbonate of lime 23·90 8·83
Sulphate of lime trace 1·15
Carbonate of magnesia 1·10 "
Magnesia " 1·76
Phosphoric acid trace 0·71
Potash 0·38 1·08
Soda 0·13 "
Chloride of sodium " 1·03
Insoluble matter, chiefly clay 49·66 62·52
—— ——
100·17 100·00

In this instance the quantity of burned soil amounted to about fifteen tons
per acre, and it is obvious that the quantity of potash which had been
liberated from the insoluble clay and the phosphoric acid are equal to that
contained in a considerable manuring. In order to obtain these results, it is
necessary, as has been already observed, to keep the temperature as low as
possible during the process of burning, direct experiment having shown that
when this precaution is not observed another change occurs, whereby the
potash, which at low temperatures becomes soluble, passes again into an
insoluble state. A part of the beneficial effect is no doubt also due to the

change produced in the physical characters of the clay by burning, which
makes it lighter and more friable, and by mixture with the unburnt clay
ameliorates the whole. This improvement in the physical characters of the
clay also requires that it shall be burnt with as low a heat as possible; for if
it rises too high, the clay coheres into hard masses which cannot again be
reduced to powder, and the success of the operation of burning may always
be judged of by the readiness with which it falls into a uniform friable
powder.
The improvement of peat by burning has been practised to some extent in
Scotland, though less frequently of late years than formerly; but it is still the
principal method of reclaiming peat soils in many countries, and
particularly in Finland, where large breadths of land have been brought into
profitable cultivation by means of it. The modus operandi of burning peat is
very simple; it acts by diminishing the superabundant quantity of humus or
other organic matters, which, in the previous section we have seen to be so
injurious to the fertility of the soil. It may act also in the same way as it
does on clay, by making part of the inorganic constituents more really
soluble, although it is not probable that its effect in this way can be very
marked. Its chief action is certainly by destroying the organic matters, and
by thus improving the physical character of the peat, and causing it to
absorb and retain a smaller quantity of water than it naturally does. For this
reason it is that it proves successful only on thin peat bogs, for if they be
deep, the inorganic matters soon sink into the lower part, and the surface
relapses into its old state of infertility. It is probably for this reason that the
practice has been so much abandoned in Scotland, more especially as other
and more economical modes of treating peat soils have come into use.
Warping.—This name has been given to a method of improving soils by
causing the water of rivers to deposit the mud it carries in suspension upon
them, and which has been largely practised in the low lying lands of
Lincoln and Yorkshire, where it was introduced about a century ago. It is
most beneficial on sandy or peaty soil, and by its means large tracts of
worthless land have been brought under profitable cultivation. It requires
that the land to be so treated shall be under the level of the river at full tide,
and it is managed by providing a sluice through which the river water is
allowed to flood the land at high tide, and again to escape at ebb, leaving a
layer of mud generally about a tenth of an inch in thickness, which it

brought along with it. By the repetition of this process, a layer of several
feet in thickness, of an excellent soil, is accumulated on the surface.
Herapath, who has carefully examined this subject chemically, has shown
that in one experiment where the water used contained 233 grains of mud
per gallon, 210 were deposited during the warping. The following analyses
will show the general nature of the matters deposited, and the change which
they produce on the soil:—No. 1 is the mud from the Humber in its natural
state, No. 2 a specimen of warp of average quality artificially dried, No. 3 a
sandy soil before warping, and No. 4, the same fifteen years after having
received a coating of 11 inches of mud.

1 2 3 4
Water 47·49 ... 1·06 2·00
Organic matter 5·94 6·93 2·20 7·61
Chloride of Calcium ... ... } ... ...
Magnesium } ... 0·10 } ... ...
Sodium } 1·66 } 0·94 } 0·14 0·16
Potassium } } }
Sulphate of Soda } ... 0·31 } ... ...
Magnesia } ... 1·18 } ... ...
Lime trace 1·10 trace trace
Carbonate of Magnesia 2·60 0·31 trace 0·29
Lime 3·59 8·18 trace 0·46
Potash and Soda 0·18 0·47 trace 0·17
Magnesia 1·69 2·60 trace 0·26
Lime 0·39 0·68 trace 0·14
Peroxide of Iron } 6·63 5·05 0·08 1·17
Alumina } 8·18 0·39 0·41
Phosphate of Iron 0·58 1·04 trace 0·28
Silica ... 9·05 0·14 2·77
Sand and Stones 29·15 55·87 95·91 84·97
———————————— ————
100·00 100·00 100·00 100·00

It is easy to understand the importance of the effects produced by adding to
any soil large quantities of a mud containing upwards of one per cent of

phosphate of iron; and in point of fact, Herapath has calculated that in one
particular instance the quantity of phosphoric acid brought by warping upon
an acre of land, exceeded seven tons per acre. As, moreover, the matters are
all in a high state of division, they must exist in a condition peculiarly
favourable to the plant. The overflow of the Nile is only an instance of
warping on the large scale, with this difference, that it is repeated once only
in every year, whereas, in this country, the operation is repeated at every
tide until a deposit sometimes of several feet in thickness is obtained, after
which it is stopped, and the soil brought under ordinary cultivation.
An operation which is, in some respects, the converse of warping, has been
carried out on Blair-Drummond Moss, where the peat has been dislodged
and carried off by the action of water, leaving the subjacent soil in a state
fitted for cropping. Of course both this and warping are restricted to special
localities, but they are most important means of ameliorating the soil when
circumstances admit of their being carried out.
Mixing of Soils.—When soils possess conspicuous defects in their physical,
and even in their chemical properties, great advantages may, in some
instances, be derived from their proper admixture. A light sandy soil, for
instance, is greatly improved by the addition of clay, and vice versa; so that,
when two soils of opposite properties occur near to one another, both may
be improved by mixture. It has been applied to the improvement of heavy
clay soil and of peat, the former being mixed with sand or marl so as to
diminish its tenacity; the latter with clay or gravel to add to its inorganic
matters, and in both instances it has proved successful.
The process of chalking, which has been carried out on a large scale in
some parts of England, and which consists in bringing up the chalk from
pits, penetrating through the overlying tenacious clay, and mixing it with
the soil, operates, to some extent, in a similar manner, though no doubt the
lime also exercises a strictly chemical action. It is probable that the mixing
of soils might be advantageously extended, and it merits more minute study
than it has yet obtained. Its use is obviously limited by the expense,
because, of course, where good effects are to be obtained, it is necessary to
remove large quantities of soil, in some instances as much as 50 or 100 tons
per acre, but the expense might be much diminished if it were carried out
methodically, and on a considerable scale. The admixture of highly fertile

soils with others of inferior quality is also worthy of attention; indeed, it is
understood that this has been done, to some extent, with the rich trap soils
of some parts of Scotland, but the extent of the benefit derived from it has
not been made public.

FOOTNOTES:
[J] Mr. Dudgeon, Spylaw. Transactions of the Highland Society, vol. cxxix., p.
505.

CHAPTER VII.
THE GENERAL PRINCIPLES OF MANURING.

In their natural condition all soils not absolutely barren are capable of
supporting a certain amount of vegetation, and they continue to do so for an
unlimited period, because the whole of the substances extracted from them
are again restored, either directly by the decay of the plants, or indirectly by
the droppings of the wild animals which have browzed upon them. Under
these circumstances, a soil yields what may be called its normal produce,
which varies within comparatively narrow limits, according to the nature of
the season, temperature, and other climatic conditions. But the case is
completely altered if the crop, in place of being allowed to decay on the
soil, is removed from it, for, though the air will continue to afford an
undiminished supply of those elements of the food of plants which may be
derived from it, the fixed substances, which can only be obtained from the
soil, decrease in quantity, and are at length entirely exhausted. In this way a
gradual diminution of the fertility of the soil takes place, until, after the
lapse of a period, longer or shorter, according to its natural resources, it will
become entirely incapable of maintaining a crop, and fall into absolute
infertility unless the substances removed from it are restored from some
other source in the form of manure. When this is done, the fertility of the
soil may not only be sustained but greatly increased, and, in point of fact,
all cultivated soils, by the use of manure, are made to yield a much larger
crop than they can do in their natural condition.
The fundamental principle upon which a manure is employed is that of
adding to the soil an abundant supply of the elements removed from it by
plants in the condition best fitted for absorption by their roots; but looked at
in its broadest point of view, it acts not merely in this way, but also by
promoting the decomposition of the already partially disintegrated rocks of
which the soil is composed, setting free those substances it already contains,
and facilitating their absorption by the plants.

In considering the practical applications of the broad general principle just
stated, it might be assumed that a manure ought invariably to contain all the
elements of plants in the quantities in which they are removed by the crops,
and that when this has been accurately ascertained by analysis, it would
only be necessary to use the various substances in the proportions thus
indicated. But this, though a very important, and no doubt in many cases
essential condition, is by no means the only matter which requires to be
taken into consideration in the economical application of manures. And this
becomes sufficiently obvious when the circumstances attending the
exhaustion of the soil are minutely examined. When a soil is cropped during
a succession of years with the same plant, and at length becomes incapable
of longer maintaining it, the exhaustion is rarely, if ever, due to the
simultaneous consumption of all its different constituents, but generally
depends upon that of one individual substance, which, from its having
originally existed in the soil in comparatively small quantity, is removed in
a shorter time than the others. To restore the fertility of a soil in this
condition, it is by no means necessary to supply all the different substances
required by the plant, for it will suffice to add that which has been entirely
removed. On the other hand, if an ordinary soil be supplied with a manure
containing a very small quantity of one of the elements of plant food, along
with abundance of all the others, the amount of increase which it yields
must obviously be measured, not by those which are abundant, but by that
which is deficient; for the crop which grows luxuriantly so long as it obtains
a supply of all its constituents, is arrested as effectually by the want of one
as of all, as has been proved by the experiments of Prince Salm Horstmar
and others, referred to in a previous chapter; and hence, in order to obtain a
good crop, it would be necessary to use the manure in such abundance as to
supply a sufficiency of the deficient element for that purpose. If this course
were persevered in for a succession of years, the other substances which
would have been used in much more than the quantity required by the
crops, must either have been entirely lost or have accumulated in the soil. In
the latter case it is sufficiently obvious that the soil must have been
gradually acquiring an amount of resources which must remain dormant
until the system of manuring is changed. To render them available, it is only
necessary to add to it a quantity of the particular substance in which the
manure hitherto employed has been deficient, so as to restore the lost
balance, and enable the plant to make use of those which have been stored

up within it. The substance so used is called a special manure; that
containing all the constituents of the crop is a general manure.
The distinction of these two classes of manures is very important in a
practical point of view, because a special manure is not by itself capable of
maintaining the life of plants, but is only a means of bringing into use the
natural and acquired resources of the soil. In place of preventing or
retarding its exhaustion, it rather accelerates it by causing the increased
crops to consume more abundantly, and within a shorter period of time,
those substances which it contains. On the other hand, a general manure
prevents or diminishes the consumption of the elements of plant-food
contained in the soil, and if added in sufficient abundance, may cause them
to accumulate in it, and even enable an almost absolutely barren soil to
yield a tolerable crop. General manures must therefore always be the most
important and essential, and no others would be used if it were possible to
obtain them of a composition exactly suited to the requirements of the crop
to be raised. Practically, however, this condition cannot be fulfilled, because
all the substances available for the purpose, and particularly farm-yard
manure, are refuse matters, the exact composition of which is not under our
control, and they do not necessarily contain their constituents either in the
most suitable proportions, or the most available forms, and consequently
when they are used during a succession of years, certain of their
constituents may accumulate in the soil, and it is under such circumstances
that special manures are both necessary and advantageous.
Several different substances, but more especially farm-yard manure, fulfil
in a very remarkable manner the conditions of a general manure, and supply
abundantly, not merely the mineral, but also the carbonaceous and
nitrogenous matters necessary for building up the organic part of the plant;
and hence its use is governed by principles of comparative simplicity, and
really resolves itself into determining the best mode of managing it so as
effectually to preserve its useful constituents, and, at the same time, to bring
them into those forms of combination in which they are most available to
the plant. But the employment of a special manure opens up nice questions
as to the relative importance of the different elements of plants which have
given rise to much controversy and difference of opinion.

In treating of the food of plants, it has been already observed that the fixed
or mineral constituents which are contained in their ash, are necessarily
derived exclusively from the soil, but that the carbon, hydrogen, nitrogen,
and oxygen, of which their organic part is composed, may be obtained
either from that source or from the air. The important distinction which thus
exists between these two classes of substances, has given rise to two
different views regarding the theory of manures. Basing his views on the
presence of the organic elements in the air, Liebig has maintained that it is
unnecessary to supply them in the manure, while others, among whom
Messrs. Lawes and Gilbert have taken a prominent position, hold that, as a
rule, fertile soils, cultivated in the ordinary manner, contain a sufficient
supply of mineral matters for the production of the largest possible crops,
but that the quantity of ammonia and nitric acid which the plants are
capable of extracting from the air is insufficient, and must be supplemented
by manures containing them. A large number of experiments have been
made in support of these views, but the inferences which can be drawn from
them are not absolutely conclusive on either side, and it is necessary to
consider the matter in a general point of view.
Setting out from the proposition already so frequently referred to, that the
plant cannot grow unless it receives a supply of all its elements, it must be
obvious that if, to a soil containing a sufficiency of mineral matters to raise
a given number of crops, a supply of ammonia be added, its total productive
capacity cannot be thus increased; and though it may yield larger crops than
it would have done without that substance, this can only be accomplished
by a proportionate diminution of their number. In either case, the same
quantity of vegetable matter will be produced, but the time within which it
is obtained will be regulated by the supply of ammonia. That substance
differs in no respect from any other element of plant-food, and used in this
way is to all intents and purposes a special manure, and acts merely by
bringing into play those substances which the soil already contains. Its
effect may not be apparent until after the lapse of a very long period of
time, but it ultimately leads to the exhaustion of the soil. If, on the other
hand, a soil be continuously cropped until it ceases to yield any produce, it
is manifest that the exhaustion must in this instance be entirely due to the
removal of its available mineral nutriment, because the superincumbent air
constantly changed by the winds must continue to afford the same

unvarying supply of the organic elements, and the power of supporting
vegetation would be restored to it, by adding the necessary inorganic
matters. Hence when a soil, which in its natural condition is capable of
yielding a certain amount of vegetable matter, is rendered barren by the
removal of the crop, it may be laid down as an incontrovertible position,
that its infertility is due to the loss of mineral matters, and that it may be
restored to its pristine condition by the use of them, and of them only.
But the case is materially altered when we come to consider the course of
events in a cultivated soil. The object of agriculture is to cause the soil, by
appropriate treatment, to yield much more than its normal produce, and the
question is, how this can be best and most economically effected in
practice. According to Liebig, it is attained by adding to the soil a liberal
supply of those mineral substances required by the plant, and that it is
unnecessary to use any of the organic elements, because they are supplied
by the air in sufficient quantity to meet the requirements of the most
abundant crops. Other chemists and vegetable physiologists again hold that
though a certain increase may be obtained in this way, a point is soon
reached beyond which mineral matters will not cause the plant to absorb
more ammonia from the air, although a further increase may be obtained by
the addition of nitrogen in that or some other available form.
It is admitted on both sides, that all the elements of plant food are equally
essential, and the controversy really lies in determining what practically
limits the crop producible on any soil. The point at issue may be put in a
clear point of view by considering the course of events on a soil altogether
devoid of the elements of plants. If a small quantity of mineral matters be
added to such a soil, it immediately becomes capable of supporting a certain
amount of vegetation, deriving from the air the organic elements necessary
for this purpose, and with every increase of the former, the air will be laid
under a larger contribution of the latter, to support the increased growth,
and this must proceed until the limit of supply from the atmosphere is
reached. At this point a further supply of mineral matters alone must
obviously be incapable of again increasing the crop, and it would thus be
absolutely necessary to conjoin them with a proportionate quantity of
organic substances. Liebig maintains that this limit is never attained in
practice, but that the air affords ammonia and the other organic elements in
excess of the requirements of the largest crop, while mineral matters are

generally though not invariably present in the soil in insufficient quantity.
Messrs. Lawes and Gilbert, on the other hand, believe that the soil generally
contains an excess of mineral matters, and that a manure which is to bring
out their full effect must contain ammonia, or some other nitrogenous
substance fitted to supplement the deficient supply afforded by the
atmosphere. In short, the question at issue is, whether there is or is not a
sufficiency of atmospheric food to meet the demands of the largest crop
which can practically be produced.
An absolutely conclusive reply to this question is by no means easy. The
experiments by which it is to be resolved are complicated by the fact, that
all soils capable of supporting anything like a crop, contain not only the
mineral, but the organic elements of its food in large and generally in
greatly superabundant quantity, and it is impossible satisfactorily to
ascertain how much is derived from this source, and how much from the
atmosphere. There are in fact no experiments in which the effects of a
purely mineral soil have been ascertained. The important and carefully
performed researches of Messrs. Lawes and Gilbert were made upon a soil
which had been long under cultivation, and contained decaying vegetable
matters in sufficient abundance to supply nitrogen to many successive
crops, and it would be most unreasonable to assert that the produce they did
obtain by means of mineral manures, drew the whole of its nitrogen from
the air. On the contrary, it may be fairly assumed that the soil did yield a
certain quantity of its nitrogenous compounds, but to what extent this
occurs, it is impossible to determine. This difficulty is encountered more or
less in all the other experiments, and precludes absolute conclusions. The
same fallacy also besets the arguments of Liebig when he holds that the
crop, increased by means of mineral manures alone, must derive the whole
of the additional quantity of nitrogen which it contains from the air, as
appears to be tacitly assumed throughout the whole discussion. So far from
this being the case, it is just as likely that the mineral matters should cause
the plants to take it from the soil, if it is there, as from the atmosphere.
Taking a general view of the whole question, it is evident that a certain
amount of vegetation may always be produced by means of mineral
manures, and the quantity obtained is generally much beyond the normal
produce of the soil. But it is still open to doubt whether the largest possible
crop can be thus obtained, although the balance of evidence is against it,

and in favour of the addition of ammonia, and other nitrogenous and
organic substances, to the soil. In actual practice manures containing
nitrogen are more important, and more extensively applied than any others,
and the quantity of that element thus used is very much larger than is
generally supposed. Twenty tons of farm-yard manure, a quantity
commonly applied, and often exceeded on well cultivated land, contain a
sufficiency of organic matters to yield about 2-1/2 cwt. of nitrogen. A
complete rotation, according to the six-course shift, contains almost exactly
the same quantity of nitrogen, when we assume average crops throughout
the whole, and it is thus made up.[K]

Lbs. of Nitrogen.
1. Turnips (13-1/2 tons) 60
2. { Wheat (28 bushels at 60 lbs.) 29
{ Straw 16
3. Hay (2-1/2 tons) 56
4. { Oats (34 bushels at 40 lbs.) 27
{ Straw 14
5. Potatoes (3 tons) 27
6. Wheat and straw as before 45
——
Total 274

The supply is therefore quite sufficient for the requirements of the crop; and
when it is borne in mind that a considerable quantity of ammonia and nitric
acid is annually carried down by the rain, and that during a long rotation
other substances are very generally used in addition to farm-yard manure, it
is obvious that the crop need not depend to any extent upon what it derives
from the air. What is true of the nitrogenous matters applies with still
greater force to the mineral constituents of the manure. Twenty tons of
farm-yard manure contain 32 cwt. of mineral matters, while the average
crops of a six course-shift contain only 1088 lbs., or less than one-third of
this quantity. It is obvious, therefore, that in well manured land there must
be a gradual increase of all the constituents of plants, but that of the mineral
matters is relatively much greater than that of the nitrogenous. If therefore
from any cause the crop produced on a soil to which farm-yard manure had
been applied were greatly to exceed the average, the amount of produce, so
far as the soil is concerned, would be limited not by deficiency of mineral,
but of nitrogenous food. Hence also when farm-yard manure is liberally
applied, there is a gradual accumulation of valuable matters, and a
progressive improvement of the productive capacity of the soil.
It is far otherwise, however, if a special manure is employed, because in
that case the crop is thrown upon the resources of the soil itself for all its
constituents except those contained in the substance employed, and by
persisting in its exclusive use exhaustion is the inevitable result. It would be
wrong, however, to infer from this, that special manures are to be avoided.

On the contrary, great benefits are derived from their judicious
employment, and the circumstances under which they are admissible may
be readily gathered from what has already been said. They are agents which
bring into useful activity the dormant resources of the soil, they restore the
proper balance between its different constituents, and supply the excessive
demand of some particular elements. Thus, for instance, in a soil containing
an abundant supply of mineral matters, a salt of ammonia or nitric acid
increases the crop, by promoting the absorption of the substances already
present. So likewise a soil on which young cattle and milch cows have been
long pastured has its fertility restored by phosphate of lime, because that
substance is removed in the bones and milk in relatively much larger
proportion than any others.
The choice of a special manure is necessarily dependent on a great variety
of circumstances, and is governed partly by the nature of the soil, and partly
by that of the crop. It is obvious that cases may occur in which any
individual element of the plant may be deficient, and ought to be supplied,
but experience has shown that, as a rule, nitrogen and phosphoric acid are
the substances which it is most necessary to furnish in this way, and which
in all but exceptional cases produce a marked effect on the crop. The other
substances, such as potash, soda, magnesia, etc., occasionally act
beneficially, but the results obtained from them are very uncertain, and
frequently entirely negative.
It has been commonly asserted that phosphates are specially adapted to root
crops, and ammonia or nitrates to the cereals, and this statement is so far
true, that the former are used with advantage on the turnip, while the latter
act with great benefit on grain crops and more especially on oats and barley.
The effect of the latter, however, is more or less apparent in all crops and on
all soils, because it promotes the assimilation of the mineral matters already
present. But its peculiar importance lies in the power which it has of
promoting the rapid development of the young plant, causing it to send its
roots out into the soil, and to spread its leaves into the air, thus enabling it to
take from those two sources, abundance of the useful substances existing in
them. But it ought to be distinctly understood, that the statement that
particular manures are specially suited to particular crops must be assumed
with some reservation, because everything depends upon the nature of the
food contained in the soil. It is well known that there are many soils in

which ammonia acts more favourably on the turnip than phosphates, and
vice versa, and the difference is often due to the previous treatment. In
many cases in which ammonia when first used proved most beneficial, it
now begins to lose its effect, and the reason no doubt is, that by its means
the phosphates existing in these soils have been reduced in amount, while
the ammonia has accumulated, so that a change in the system of manuring
becomes necessary. A general manure may be used year after year in a
perfectly routine manner, but where a special manure is employed, the
importance of watching its effects, and altering it as circumstances indicate,
cannot be over-estimated. The length of time during which special manures
have been extensively used has not been sufficient to bring this prominently
before the agriculturist, but its importance must sooner or later force itself
upon him, and he will then see the necessity for studying the succession of
manures as well as that of crops.
Hitherto we have considered a manure merely as a source from which
plants derive their food, but it exercises a scarcely less important action on
the chemical and physical properties of the soil. Farm-yard manure, which,
as we shall afterwards see, contains a large amount of decomposing
vegetable and animal matters, yields a supply of carbonic acid, which
operates on the mineral constituents, promotes their further disintegration,
and thus liberates their useful elements. It affects also their physical
properties, for it diminishes the tenacity of heavy clays; each straw as it
decomposes forming a channel through which the roots of plants, air, and
moisture can penetrate more readily than through the stiff clay itself. On the
other hand, it diminishes the porosity of light sandy soils, causes them to
retain moisture, and generally makes their texture more suitable to the plant.
Special manures probably act to some extent chemically on the soil, but the
nature of the changes they produce is as yet imperfectly understood.
Superphosphates which are highly acid in all probability act powerfully on
the mineral substances, and common salt, which, though of little importance
to the plant, occasionally produces very striking effects, appears to exercise
some decomposing action on the soil. It is difficult, however, to trace the
mode in which they operate on a substance of such complexity as the soil.
Lime, as we shall afterwards see, acts by promoting the decomposition of
the vegetable matters on the soil, and possibly some other substances may
have a similar effect.

In the application of manures to the soil there are several circumstances
which must be taken into consideration. It is generally stated that they ought
to be distributed as uniformly as possible, but this is not always necessary
nor even advisable, and certainly is not acted on in practice. Much must
depend upon the nature both of crop and soil. When the former throws out
long and widely penetrating roots, the more uniformly the manure is
distributed the better; but if the rootlets are short, it is clearly more
advisable that it should be deposited at no great distance from the seed.
Practically this is observed in the case of the potato and turnip, which are
short rooted, and where the manure is generally deposited close to the seed.
But this course is never adopted with the long rooted cereals, the manure
being usually applied to the previous crop, so that the repeated ploughings
to which the soil is subjected in the interval may distribute what remains as
widely and uniformly as possible. In soils which are either excessively
tenacious or light, the accumulation of the manure close to the plants has
also the effect of producing an artificial soil in their immediate
neighbourhood, containing abundance of plant-food, and having physical
properties better fitted for the support of the plant. On the other hand, when
a special manure is used alone, and with the view of promoting the
assimilation of substances already existing in the soil, the more uniform its
distribution the better, because it is essential that the roots which penetrate
through it should find at every point they reach not only the original soil
constituents, but also the substances used to supplement their deficiencies.

FOOTNOTES:
[K] The quantities here taken are the averages deduced from the agricultural
statistics taken in Scotland some years since, with the exception of hay and
straw, which are not included in them. I have therefore assumed a reasonable
quantity in these cases.

CHAPTER VIII.
THE COMPOSITION AND PROPERTIES OF FARM-YARD
AND LIQUID MANURES.

In the preceding chapter, a general manure has been defined as one
containing all the constituents of the crop to which it is to be applied, in a
state fitted for assimilation. This condition is fulfilled only by substances
derived from the vegetable and animal kingdoms, and most effectually by a
mixture of both. On this account, and also because its properties are such as
enable it to act powerfully on the soil, farm-yard manure must always be of
the highest importance. It is, in fact, the typical manure, and in proportion
as other substances approach it in properties and composition, is their value
for general purposes on the farm.
Farm-yard manure is a mixture of the dung and urine of domestic animals,
with the straw used as litter; and its value and composition must necessarily
depend upon that of these substances, as well as on the proportion in which
they are mixed. The dung of animals consists of that part of their food
which passes through the intestinal canal without undergoing assimilation;
the urine containing the portion which has been assimilated and is again
excreted, in consequence of the changes which are proceeding in the tissues
of the animal. Their composition is naturally very different, and must be
separately considered.
Urine.—Urine consists of a variety of earthy and alkaline salts, and of
certain organic substances, generally rich in nitrogen, dissolved in a large
quantity of water. That of the different domestic animals has been
frequently examined, but the analyses of Fromberg give the most complete
view of their manurial value:—

Horse. Swine. Ox. Goat. Sheep.
Extractive matter soluble in
2·132 0·142 2·248 0·100 0·340
water

Extractive matter soluble in
2·550 0·387 1·421 0·454 3·330
spirit
Salts soluble in water 2·340 0·909 2·442 0·850 1·957
Salts insoluble in water 1·880 0·088 0·155 0·080 0·052
Urea 1·244 0·273 1·976 0·378 1·262
Hippuric acid 1·260 ... 0·550 0·125 ...
Mucus 0·005 0·005 0·007 0·006 0·025
Water 88·589 98·196 91·201 98·007 92·897
——— ——— ——— ——————
100·000 100·000 100·000 100·000 99·863

Composition of the Ash of these Urines.

Horse. Swine. Ox. Goat. Sheep.
Carbonate of lime 12·50 ... 1·07 trace 0·82
Carbonate of magnesia 9·46 ... 6·93 7·3 0·46
Carbonate of potash 46·09 12·10 77·28 trace ...
Carbonate of soda 10·33 ... ... 53·0 42·25
Sulphate of potash ... ... 13·30 ... 2·98
Sulphate of soda 13·04 7·00 ... 25·0 7·72
Phosphate of soda ... 19·00 ... ... ...
Phosphate of lime }
Phosphate of magnesia } ... 8·80 ... ... 0·70
Chloride of sodium 6·94 53·10 0·30 14·7 32·01
Chloride of potassium ... trace ... ... 12·00
Silica 0·55 ... 0·35 ... 1·06
Oxide of iron and loss 1·09 ... 0·77 ... ...
———————————————
100·00 100·00 100·00 100·00 100·00

Human urine has been accurately examined by Berzelius, although his
estimate of the proportion of urea is generally admitted to be above the
average. His analysis gives the following numbers:—

Dry
Natural.
Residue.
Urea 3·010 44·70
Lactic acid, lactate of ammonia, and extractive
1·714 25·58
matter
Uric acid 0·100 1·49
Mucus 0·032 0·48
Sulphate of potash 0·371 5·54
Sulphate of soda 0·316 4·72
Phosphate of soda 0·294 4·39
Biphosphate of ammonia 0·165 2·46
Chloride of sodium 0·445 6·64
Muriate of ammonia 0·150 2·46
Phosphates of magnesia and lime 0·100 1·49
Silica 0·003 0·05
Water 93·300
——— ———
100·000 100·00

Among the special organic constituents of the urine are three substances,
urea, uric acid, and hippuric acid, which are of much importance in a
manurial point of view. The first of these is found in considerable quantity
in the urine of all animals, but is especially abundant in the carnivora. Uric
acid is found only in these animals, and is the most remarkable constituent
of the excrement of birds, serpents, and many of the lower animals.
Hippuric acid is most abundant in the herbivora. These substances are all
highly nitrogenous. They contain—

Urea. Uric Acid. Hippuric Acid.
Carbon 20·00 36·0 60·7
Hydrogen 6·60 2·4 5·0
Nitrogen 46·70 33·4 8·0
Oxygen 26·70 28·2 26·3
——— —— ——
100·00 100·0 100·0

They are extremely prone to change, and in presence of animal matters
readily ferment, and are converted into salts of ammonia. Thus human
urine, which, at the time of emission is free from smell of ammonia, and has
a slightly acid reaction, becomes highly ammoniacal if it be kept for a few
days. This is due to the conversion of urea into carbonate of ammonia; and
the same change takes place, though more slowly, with uric and hippuric
acids.
It is obvious, from the foregoing analyses, that great differences must exist
in the manurial value of the urine of different animals. Not only do they
vary greatly in the proportion of solid matters which they contain, but also
in the kind and quantity of their nitrogenous constituents. They differ also
in regard to their saline ingredients; and while salts of potash and soda form
the principal part of the ash of the urine of the ox, sheep, goat, and horse,
and phosphoric acid and phosphates are entirely absent, that of the pig
contains a considerable quantity of the latter substances, and in this respect
more nearly resembles the urine of man. Human urine is also much richer in
urea and nitrogenous constituents generally, and has a higher value than any
of the others.
It is especially worthy of notice that the urine of the purely herbivorous
animals (with the exception of the sheep, which contains a small quantity),
are devoid of phosphates and urea; and consequently, when employed
alone, they are not general manures—a matter of some importance in
relation to the subject of liquid manuring, which will be afterwards
discussed.
Dung.—The solid excrement of animals is equally variable in composition.
That of the domestic animals which had the ordinary winter food was found
to have the following composition:—

Horse. Cow. Sheep. Swine.
Per-centage of water in the fresh excrement 77·25 82·45 56·47 77·13
Ash in the dry excrement 13·36 15·23 13·49 37·17

100 parts of ash contained—

Horse. Cow.Sheep. Swine.

Silica 62·40 62·54 50·11 13·19
Potash 11·30 2·91 8·32 3·60
Soda 1·98 0·98 3·28 3·44
Chloride of sodium 0·03 0·23 0·14 0·89
Phosphate of iron 2·73 8·93 3·98 10·55
Lime 4·63 5·71 18·15 2·63
Magnesia 3·84 11·47 5·45 2·24
Phosphoric Acid 8·93 4·75 7·52 0·41
Sulphuric acid 1·83 1·77 2·69 0·90
Carbonic acid ... trace trace 0·60
Oxide of manganese 2·13 ... ... ...
Sand ... ... ... 61·37
—— —— —— ——
99·80 99·29 99·64 99·82

Human fæces contain about 75 per cent of water; and their dry residue was
found by Way to have the following composition:—

Organic matter 88·52
Insoluble siliceous matters 1·48
Oxide of iron 0·54
Lime 1·72
Magnesia 1·55
Phosphoric acid 4·27
Sulphuric acid 0·24
Potash 1·19
Soda 0·31
Chloride of sodium 0·18
———
100·00

In a sample analyzed by myself there were found—

Organic matter 86·75
Phosphates 8·19

Alkaline salts, containing 1·18 of phosphoric acid 2·53
Insoluble matters 2·53
———
100·00
Nitrogen 4·59
Equal to ammonia 5·57

It is to be observed that the urine and dung of animals differ conspicuously
in the composition of their ash, the former being characterized by the
abundance of alkaline salts, while the latter contains these substances in
small proportion, but is rich in earthy matters, and especially in phosphoric
acid. Salts of potash, for example, form nine-tenths of the inorganic part of
the urine of the ox, while less than three per cent of that alkali is found in its
dung. Phosphoric acid, on the other hand, is not met with in the urine, but
forms about ten per cent of the dung. Silica is the most abundant constituent
of the dung, but a large proportion of that found on analysis has been
swallowed in the shape of grains of sand and particles of soil mechanically
mixed with the food, although part is also derived from the straw and
grains, which contain that substance in great abundance. The difference in
the quantity of nitrogen they contain is also very marked, and is distinctly
shown by the following analyses by Boussingault, which give the quantity
of carbon, hydrogen, nitrogen, oxygen, and ash in the dung and urine of the
horse and the cow in their natural state, and after drying at 212°.

HORSE. COW.
Natural. Dry. Natural. Dry.
Urine. Dung. Urine. Dung. Urine. Dung. Urine. Dung.
Carbon 4·46 9·56 36·0 38·7 3·18 4·02 27·2 42·8
Hydrogen 0·47 1·26 3·8 5·1 0·30 0·49 2·6 5·2
Nitrogen 1·55 0·54 12·5 2·2 0·44 0·22 3·8 2·3
Oxygen 1·40 9·31 11·3 37·7 3·09 3·54 26·4 37·7
Ash 4·51 4·02 36·4 16·3 4·68 1·13 40·0 12·0
Water 87·61 75·31 0·0 0·0 88·31 90·60 0·0 0·0
100·00 100·00 100·0 100·0 100·00 100·00 100·0 100·0

Hence, weight for weight, the urine of the horse, in its natural state,
contains three times as much nitrogen as its dung; that of the cow twice as
much; and the difference, especially in the horse, is still more conspicuous
when they are dry.
It is obvious that the quality of farm-yard manure must depend—1. On the
kind of animal from which it is produced; 2. On the quantity of straw which
has been used as litter; 3. On the nature of the food with which the animals
have been supplied; 4. On the extent to which its valuable constituents have
been rendered available by the treatment to which it has been subjected; and
5. On the care which has been taken to prevent the escape of the urine, or of
the ammonia produced by its decomposition.
The composition of farm-yard manure has engaged the attention of several
chemists; but there are still many points on which our information regarding
it is less complete than might be desired. Its investigation is surrounded
with peculiar difficulties, not merely on account of its complexity, but
because its properties render it exceedingly difficult to obtain a sample
which fairly represents its average composition. In the case of long dung,
these difficulties are so great that it is scarcely possible to overcome them;
and hence, discrepancies are occasionally to be met with in the analyses of
the most careful experimenters. The most minute and careful analyses yet
made are those of Voelcker, who has compared the composition of fresh and
rotten dung, and studied the changes which the former undergoes when
preserved in different ways. He employed in his experiments both fresh and
rotten dung, and subjected them to different methods of treatment. His
analyses are given in the accompanying table, in which column 1 gives the
composition of fresh long dung, composed of cow and pig dung. 2. Is dung
of the same kind, after having lain in a heap against a wall, but otherwise
unprotected from the weather for three months and eleven days in winter,
during which time little rain fell. 3. The same manure, kept for the same
time under a shed. 4. Well rotten dung, which had been kept in the manure
heap upwards of six months. 5. The same, after having lain against a wall
for two months and nine days longer.

1 2 3
Water 66·17 69·86 67·32
Soluble organic matters 2·48 3·86 2·63

Soluble inorganic matters·
Silica 0·237 0·279 0·239
Phosphate of lime 0·299 0·300 0·331
Lime 0·066 0·048 0·056
Magnesia 0·011 0·019 0·004
Potash 0·573 1·096 0·676
Soda 0·051 0·187 0·192
Chloride of sodium 0·030 0·106 0·058
Sulphuric acid 0·055 0·160 0·119
Carbonic acid and loss 0·218 0·775 0·445
—— 1·54 ... 2·97 —— 2·12
Insoluble organic matters 25·76 18·44 20·46
Insoluble inorganic matters—
Soluble silica 0·967 0·712 1·893
Insoluble silica 0·561 0·857 1·075
Oxide of iron, alumina, and phosphates 0·596 0·810 1·135

4 5
Water 75·42 73·90
Soluble organic matters 3·71 2·70
Soluble inorganic matters
Silica 0·254 0·147
Phosphate of lime 0·382 0·129
Lime 0·117 0·018
Magnesia 0·047 0·018
Potash 0·446 0·960
Soda 0·023 0·082
Chloride of sodium 0·037 0·052
Sulphuric acid 0·058 0·072
Carbonic acid and loss 0·106 0·584
—— 1·47 —— 2·06
Insoluble organic matters 12·82 14·39

Insoluble inorganic matters—
Soluble silica 1·424 1·10
Insoluble silica 1·010 1·54
Oxide of iron, alumina, and phosphates 0·947 0·37

1 2 3
Containing phosphoric acid (0·178) (0·177) (0·298)
Equal to bone earth (0·386) (0·277) (0·646)
Lime 1·120 1·291 1·868
Magnesia 0·143 1·029 0·078
Potash 0·099 0·127 0·208
Soda 0·019 0·046 0·038
Sulphuric acid 0·061 0·099 0·098
Carbonic acid and loss 0·484 0·929 1·077
—— 4·05 —— 4·90 —— 7·47
—— —— ———
100·00 100·00 100·00
Containing nitrogen 0·149 0·270 0·170
Equal to ammonia 0·181 0·320 0·206
Containing nitrogen 0·494 0·470 0·580
Equal to ammonia 0·599 0·570 0·700
Total nitrogen 0·643 0·740 0·750
Equal to ammonia 0·780 0·890 0·906

4 5
Containing phosphoric acid (0·274) (0·06)
Equal to bone earth (0·573) (0·10)
Lime 1·667 2·25
Magnesia 0·091 0·02
Potash 0·045 0·12
Soda 0·038 0·01
Sulphuric acid 0·063 0·10

Carbonic acid and loss 1·295 1·44
—— 6·58 —— 6·95
—— ———
100·00 100·00
Containing nitrogen 0·297 0·149
Equal to ammonia 0·360 0·180
Containing nitrogen 0·309 0·613
Equal to ammonia 0·375 0·744
Total nitrogen 0·606 0·762
Equal to ammonia 0·735 0·924

On examining and comparing these analyses, it appears that the differences
are by no means great, although, on the whole, they tend to show that,
weight for weight, well-rotten dung is superior to fresh, provided it has
been properly treated. Not only is the quantity of valuable matters existing
in the soluble state materially increased, whereby the dung is enabled to act
with greater rapidity, but, owing to evaporation and the escape of carbonic
acid, produced by the decomposition of the organic substances, the
proportion of those constituents which are most important to the plant is
increased. This is particularly to be noticed, in regard to the nitrogen, which
has distinctly increased in all cases in which the dung has been kept for
some time; and the practical importance of this observation is very great,
because it has been commonly supposed that, during the process of
fermentation, ammonia is liable to escape into the air. It would appear,
however, that there is but little risk of loss in this way, so long as the dung-
heap is left undisturbed; and it is only when it is turned that any appreciable
quantity of ammonia volatilizes. It is different, however, with the action of
rain, which soon removes, by solution, a considerable quantity of the
nitrogen contained in farm-yard manure; and the deterioration must
necessarily be most conspicuous in rotten dung, which sometimes contains
nearly half of its nitrogen in a soluble condition. The effect produced in this
way is conspicuously seen, by the results of weighings and analyses of
small experimental dung-heaps, made by Dr. Voelcker at different periods.
The subjoined table shows the composition of the heap, lying against a
wall, and exposed to the weather at different periods:—

When Put up.
Nov 3d April 30th Aug 23d Nov 15th
1854. 1855. 1855. 1855.
Weight of manure in
2838 2026 1994 1974
lbs.
Water 1877·9 1336·1 1505·3 1466·5
Dry Matter 960·1 689·9 488·7 507·5
Consisting of—
Soluble organic
70·38 86·51 58·83 54·04
matter
" mineral matter 43·71 57·88 39·16 36·89
Insoluble organic
731·07 389·74 243·22 214·92
matter
" mineral matter 114·94 155·77 147·49 201·07
Total nitrogen 18·23 18·14 13·14 13·03
Equal to ammonia 22·14 22·02 15·96 15·75

In this case, during the winter six months, which were very dry, the manure
lost 541·8 lbs. of water and 270·2 lbs. of dry matter, but the nitrogen
remained completely unchanged. But during the succeeding semi-annual
period, when rain fell abundantly, the quantity of nitrogen is diminished by
nearly a third, while the water has increased, and the loss of dry matter by
fermentation, notwithstanding the high temperature of the summer months,
was only 182·4 lbs. The soluble mineral matters also, which increased
during the first period, are again reduced during the second, until they also
fall to about two-thirds of their maximum quantity. That this effect is to be
attributed to the solvent action of rain is sufficiently obvious, from a
comparison of the results afforded by the other heaps, which had been kept
under cover during the same period, as shown below.

When Put up.
Nov 3d April 30th Aug 23d Nov 15th
1854. 1855. 1855. 1855.
Weight of manure in
3258 1613 1297 1235
lbs.
Water 2156·0 917·6 563·2 514·5

Dry Matter 1102·0 695·4 733·8 720·5
Consisting of—
Soluble organic
80·77 74·68 53·56 66·28
matter
" mineral matter 50·14 54·51 39·55 54·68
Insoluble organic
839·17 410·24 337·32 341·97
matter
" mineral matter 131·92 155·97 303·37 257·57
Total nitrogen 20·93 19·26 16·54 1·79
Equal to ammonia 25·40 23·33 20·08 2·81

The loss of nitrogen is here comparatively trifling, and during the whole
year, but little exceeds two pounds, of which the greater part escapes during
the first six months, and the soluble inorganic matters are almost
unchanged. The total weight of the manure, however, undergoes a very
great reduction, due chiefly to evaporation of water, but in part also to the
loss of organic matters evolved in the form of carbonic acid during
fermentation.
When the manure is spread out, as it is usually found under cattle in open
yards, the deterioration is very great, a quantity thus treated having lost, in
the course of a year, nearly two-thirds of its nitrogen, and four-fifths of its
soluble inorganic matters.
The general conclusion deducible from these analyses is that, provided it be
carefully prepared, farm-yard manure does not differ very largely in value,
although the balance is in favour of the well-rotten dung. This result is in
accordance with that obtained by other experimenters, who have generally
found from 0·5 to 0·6 per cent of nitrogen, and 1 or 2 per cent of
phosphates. But when carelessly managed, it may fall greatly short of this
standard, as is particularly seen in a sample examined by Cameron, which
had been so effectually washed out by the rain, as to retain only 0·15 per
cent of ammonia. These cases, however, are exceptional, and well made and
well preserved farm-yard manure will generally be found to differ
comparatively little in value; and when bought at the ordinary price, the
purchaser, as we shall afterwards more particularly see, is pretty sure to get
full value for his money, and the specialities of its management are of

comparatively little moment to him. But the case is very different when the
person who uses the manure has also to manufacture it. The experiments
already quoted have shown that, though the manure made in the ordinary
manner may, weight for weight, be as valuable as at first, the loss during the
period of its preservation is usually very large, and it becomes extremely
important to determine the mode in which it may be reduced to the
minimum.
In the production of farm-yard manure of the highest quality, the object to
be held in view is to retain, as effectually as possible, all the valuable
constituents of the dung and urine. But in considering the question here, it
will be sufficient to refer exclusively to its nitrogen, both because it is the
most important, and also because the circumstances which favour its
preservation are most advantageous to the other constituents. In the
management of the dung-heap, there are three things to be kept in view:—
First, To obtain a manure containing the largest possible amount of
nitrogen; secondly, To convert that nitrogen more or less completely into
ammonia; and thirdly, To retain it effectually.
As far as the first of these points is concerned, it must be obvious that much
will depend on the nature and quantity of the food with which the animals
yielding the dung are supplied, and the period of the fattening process at
which it is collected. When lean beasts are put up to feed, they at first
exhaust the food much more completely than they do when they are nearly
fattened, and the manure produced is very inferior at first, and goes on
gradually improving in quality as the animal becomes fat.
When the food is rich in nitrogenous compounds, the value of the manure is
considerably increased. It has been ascertained, for instance, that when oil-
cake has been used, not less than seven-eighths of the valuable matters
contained in it reappear in the excrements; and as that substance is highly
nitrogenous, the dung ought, weight for weight, to contain a larger amount
of that element. That it actually does so, I satisfied myself by experiments,
made some years since, when the dung and urine of animals fed on turnips,
with and without oil-cake, were examined; but unfortunately, no
determination of the total quantity of the excretions could be made, so that
it was impossible to estimate the increased value. It has been commonly
supposed that when cattle are fed with oil-cake, the increased value of the

manure is equal to from one-half to two-thirds the price of the oil-cake; but
this is a rather exaggerated estimate as regards linseed-cake, although it
falls short of the truth in the case of rape, as we shall afterwards more
particularly see.
Although it may be possible, in this way, to increase the quantity of
nitrogen as a manure, there is a limit to its accumulation, due to the fact,
that it is contained most abundantly in the urine, which can only be retained
by the use of a sufficient supply of litter. Where that is deficient, the dung-
heap becomes too moist, and the fluid and most valuable part drains off,
either to be lost, or to be collected in the liquid manure-tank. In the well
managed manure-heap, the quantity of litter should be sufficient to retain
the greater part of the liquid manure, and to admit of only a small quantity
draining from it, which should be pumped up at intervals, so as to keep the
whole in a proper state of moisture. Attention to this point is of great
moment, and materially affects the fermentation. When it is too moist or too
dry, that process is equally checked; in the former case by the exclusion of
air, which is essential to it; and in the latter, by the want of water, without
which the air cannot act. The exact mode in which the manure is to be
managed must greatly depend on whether the supply of litter is large or
small. In the latter case the urine escapes, and is collected in the liquid
manure-tank, and must be used by irrigation, and in some cases this mode
of application has advantages, but in general, it is preferable to avoid it, and
have recourse to substances which increase the bulk of the heap sufficiently
to make it retain the whole of the liquid. For this purpose, clay, or still
better, the vegetable refuse of the farm, such as weeds, ditch cleanings,
leaves, and, in short, any porous matters, may be used. But by far the best
substance, when it can be obtained, is dry peat, which not only absorbs the
fluid, but fixes the ammonia, by converting it more or less completely into
humate. Reference has been already made to the absorbent power of peat in
the section on soils, but it may be mentioned here that accurate experiment
has shown that a good peat will absorb about 2 per cent[L] of ammonia, and
when dry will still retain from 1 to 1·5 per cent, or nearly twice as much as
would be yielded by the whole nitrogen of an equal weight of farm-yard
manure. Peat charcoal has been recommended for the same purpose, but
careful experiment has shown that it does not absorb ammonia, although it
removes putrid odour; and though it may be usefully employed when it is

wished to deodorize the manure heap, it must not be trusted to for fixing the
ammonia.
Much stress has frequently been laid on the advantage to be derived from
the use of substances capable of combining chemically with the ammonia
produced during the fermentation of dung and gypsum, sulphate of iron,
chloride of manganese, sulphate of magnesia, and sulphuric acid, have been
proposed for this purpose, and have been used occasionally, though not
extensively. They all answer the purpose of fixing the ammonia, that is, of
preventing its escaping into the air; but the risk of loss in this way appears
to have been much exaggerated, for a delicate test-paper, held over a
manure-heap, is not affected; and during fermentation, humic acid is
produced in such abundance, as to combine with the greater part of the
ammonia. The real source of deterioration is the escape of the soluble
matters in the drainings from the manure-heap, which is not prevented by
any of these substances; and where no means are taken to preserve or retain
this portion, the loss is extremely large, and amounts, under ordinary
circumstances, to from a third to a half of the whole value of the manure.
Manure, therefore, cannot be exposed to the weather without losing a
proportion of its valuable matters, depending upon the quantity of rain
which falls upon it. Hence it is obvious that great advantage must be
derived, especially in rainy districts, from covered manure-pits. This plan
has been introduced on some farms with good effect; but the expense and
doubts as to the benefits derived from it, have hitherto prevented the
practice becoming general. The principal difficulty experienced in the use
of the covered dung-pit is, that, where the litter is abundant, the urine does
not supply a sufficiency of moisture to promote the active fermentation of
the dung, and it becomes necessary to pump water over it at intervals; but
when this is properly done, the quality of the manure is excellent, and its
valuable matters are most thoroughly economized.
Although covered dung-pits have been but little used, their benefits have
been indirectly obtained by the method of box-feeding, one of the great
advantages of which is held to be the production of a manure of superior
quality to that obtained in the old way. In box-feeding none of the dung or
urine is removed from under the animals, but is trampled down by their
feet, and new quantities of litter being constantly added, the whole is
consolidated into a compact mass, by which the urine is entirely retained.

Whatever objection may be taken to this system, so far as the health of the
animals is concerned, there is no doubt as to the complete economy of the
manure, provided the quantity of litter used be sufficient to retain the whole
of the liquid. But its advantage is entirely dependent on the possibility of
fulfilling this condition.
Whether box manure is really superior to that which can be prepared by the
ordinary method is very questionable, but it undoubtedly surpasses a large
proportion of that actually produced. It is more than probable, however, that
the careful management of the manure-heap would yield an equally good
product. It is manifest that the same number of cattle, fed in the same way,
on the same food, and supplied with the same quantity of litter, must always
excrete the same quantities of valuable matters; and the only question to be
solved is, whether they are more effectually preserved in the one way than
the other? It will be readily seen that this cannot be done by analysis alone,
but that it is necessary to conjoin with it a determination of the total weight
of manure produced; for though, weight for weight, box manure may be
better than ordinary farm-yard manure, the total quantity obtained by the
latter method, from a given number of cattle, may be so much greater, that
the deficiency in quality may be compensated for. At the present time our
knowledge is too limited to admit of a definite opinion on this subject, but it
is highly deserving of the combined investigation of the farmer and the
chemist.
Supposing the conditions which produce the manure containing the largest
quantity of nitrogen to have been fulfilled, we have now to consider those
which affect its evolution in the form of ammonia. This change is effected
by fermentation. When a quantity of manure is left to itself it becomes hot,
and gradually diminishes in bulk, and if it be turned over after some time,
the smell of ammonia may be more or less distinctly observed. This
ammonia is produced, in the first instance, from the urine, the nitrogenous
constituents of which are rapidly decomposed, and the fermentation thus set
up in the mass of manure extends first to the solid dung, and then to the
straw of the litter, and gradually proceeds until a large quantity of ammonia
is produced.
When fresh manure is deposited in the soil, the same changes occur, but
they then proceed more slowly, and experience has shown that a much

smaller effect is produced on the crop to which it has been applied than
when it has been well fermented in the heap. This effect is consistent with
theory, which would further indicate that well-fermented dung must be
especially advantageous when applied to quick-growing crops, and less
necessary to those which come slowly to maturity. As a rule, well fermented
manure is to be preferred, provided it has been well managed and carefully
prepared; but when this has not been done, and the manure has been
exposed to the weather, or made in open courts or hammels, the economic
advantages are all on the side of the fresh dung. It may be questioned also
whether, now that there are so many other available sources of ammonia, it
may not in many instances be advantageous to use the dung fresh,
conjoined with a sufficient quantity of some salt of ammonia, or other
substance fitted to supply the quantity of that element necessary for the
requirements of the crop.
After the farm-yard manure has been prepared at the homestead, it is often
necessary to cart it out to the field some time before it is to be applied, and
it is a question of some importance to determine how it may be best
preserved there. The general practice is to store it in heaps in the corners of
the fields, but some difference of opinion exists as to whether it should be
lightly thrown up so as to leave it in a porous state, and so promote its
further fermentation, or whether it should be consolidated as much as
possible by driving the carts on to the top of the heap during its
construction. Considering the risks to which the manure is exposed on the
field, the latter plan would appear to be the best. It is advisable also to
interstratify the dung with dry soil, so as to absorb any liquid which may
tend to escape from it, and it should also be covered with a well-beaten
layer of earth, in order to exclude the rain. Although these precautions must
not be omitted if the manure is to be stored in heaps, it will probably be
often found quite as advantageous to spread it at once, and leave it lying on
the surface until it is convenient to plough it. The loss of ammonia by
volatilization will, under such circumstances, especially in the cold season
of the year, be very trifling, and the rain which falls will only serve to
incorporate the soluble matters with the soil, where they will be retained by
its absorptive power.
In the actual application of the manure to the crop, several points require
consideration. It is especially important to determine whether it ought to be

uniformly distributed through the soil, or be kept near the roots of the
plants. Both systems have their advocates, and each has advantages in
particular cases. The choice between the two must greatly depend upon the
nature of the crop and the soil. When the former is of a kind which spreads
its roots wide and deep through the soil, the more uniformly the manure can
be distributed the better; but when it is used with plants whose roots do not
travel far, it is more advantageous to accumulate it near the seeds. Obvious
advantages also attend this practice in soils which are either too heavy or
too light. When, for example, it is necessary to cultivate turnips in a heavy
clay, the manure put into the drills produces a kind of artificial soil in the
neighbourhood of the plants, in which the bulbs expand more readily than
in the clay itself. On the other hand, when a large quantity of dung, in a
state of active fermentation, comes into immediate contact with the roots,
its effect is not unfrequently injurious. These and many other points, which
will readily suggest themselves to any one who studies the composition and
properties of farm-yard manure, belong more strictly to the subject of
practical agriculture, and need not be enlarged on here.
In the present state of agriculture, a proper estimate of the money value of
farm-yard manure is of much importance in an economic point of view, and
many matters connected with the profitable management of a farm must
hinge upon it. If an estimate be made upon the principle which will be
explained when we come to treat of artificial manures, it appears that fresh
farm-yard manure of good quality is worth from 12s. to 15s. per ton, and
well-rotted dung rather more. It is questionable, however, whether the
system of valuation which is accurate in the case of a guano or other rapidly
acting substance, is applicable to farm-yard manure, the effects of which
extend over some years. A deduction must be made for the years during
which the manure remains unproductive, and also for the additional expense
incurred in carting and distributing a substance so much more bulky than
the so-called portable manures, and it would not be safe to estimate its
value at more than 7s. or 8s. per ton.
Liquid Manure.—This term is applied to the urine of the animals fed on the
farm, and to the drainings from the manure-heap, which, in place of being
returned to it, are allowed to flow away, and collected in tanks, from which
they are distributed by a watering-cart, or according to the method recently
introduced in Ayrshire, and since adopted in other places, by pipes laid

under-ground in the fields, and through which the manure is either pumped
by steam-power, or, where the necessary inclination can be obtained, is
distributed by gravitation. That liquid manure must necessarily be valuable,
is an inference which maybe at once drawn from the analyses of the urine
of different animals already given, and of which it chiefly consists. In
addition to the urine, however, it contains also the soluble organic and
mineral matters of the dung, as well as a quantity of solid matters in
suspension, among which phosphates are found, and thus it possesses a
supply of an element which would be almost entirely deficient if it were
composed of urine alone. In the following analyses by Professor Johnston,
No. 1 is the drainings of the manure-heap when exposed to rain; and No. 2
the same, when moistened with cows' urine pumped over it, the results
being expressed in grains per gallon:—

No. 1. No. 2.
Ammonia 9·6 21·5
Organic matter 200·8 77·6
Ash 268·8 518·4
—— ——
Total solids in a gallon 479·2 617·5

The ash contained—

Alkaline salts 207·8 420·4
Phosphates 25·1 44·5
Carbonate of lime 18·2 31·1
Carbonate of magnesia, and loss 4·3 3·4
Silica and alumina 13·4 19·0
—— ——
268·8 518·4

More elaborate analyses of the same fluid have since been made by Dr.
Voelcker, with the subjoined results per gallon:—

1. 2. 3.
Organic matters and ammoniacal salts 263·80 250·63 70·121
Silica 2·49 9·98 1·154

Oxide of iron 0·70 0·68 ...
Lime 5·34 25·18 13·011
Magnesia 2·96 15·33 1·660
Potash 103·23 112·26 13·411
Chloride of potassium 72·00 77·38 7·712
Chloride of sodium 17·18 46·03 17·258
Phosphoric acid 2·70 9·51 2·304
Sulphuric acid 22·31 37·60 3·408
Carbonic acid, and loss 33·90 27·95 14·025
—————— ———
Total solids 526·61 612·53 144·064
Ammonia 114·16 22·31 26·647

The differences are here very remarkable, especially in the quantity of
ammonia, which is exceedingly large in the first sample. All of them are
particularly rich in potash, and contain but a small proportion of phosphoric
acid. The general inference to be deduced from them is, that liquid manure
is a most important source of the alkalis and ammonia, and must be
peculiarly valuable on soils in which these substances are deficient.
The system of liquid manuring, originally introduced by Mr. Kennedy of
Myremill, Ayrshire, and which has since been adopted in some other places,
differs from liquid manuring in its strict sense, for not only are the drainings
of the manure-heap employed, but the whole solid excrements are mixed
with water in a tank, and rape-dust and other substances occasionally added,
and distributed through the pipes.
It has been abandoned on Mr. Kennedy's farm, but is in use at Tiptree Hall,
and on the farm of Mr. Ralston, Lagg, where the fluid is distributed by
gravitation.
The arrangements employed by Mr. Mechi are identical with those formerly
in use at Myremill. The greater part of the stock is kept on boards, and the
liquid and solid excrements are collected together in the tank, and largely
diluted before distribution. The liquid from the tanks has been recently
examined by Dr. Voelcker, who found it to contain per gallon—

Organic matter and ammoniacal salts 53·03
Soluble silica 6·47
Insoluble siliceous matter (clay) 15·17
Oxide of iron and alumina 2·36
Lime 6·60
Magnesia 1·73
——
Potash 0·35
Chloride of potassium 1·95
Chloride of sodium 4·81
Phosphoric acid 3·72
Sulphuric acid 1·94
Carbonic acid, and loss 0·47
——
Total solids 96·60
Ammonia 8·10

The quantity of this liquid distributed per acre is about 50,000 gallons, at a
cost of 2d. per gallon. As this quantity contains about 39 lbs. of ammonia, it
must be nearly equivalent to 2 cwt. of Peruvian guano, which costs, with
the expense of spreading, from 28s. to 30s. per acre, while the cost of
distributing the liquid exceeds £1: 17s. per acre. On the other hand, the
rapidity with which liquid manure produces its effect must be taken into
account. It is on this that its chief value depends, and especially when
applied to grass land in early spring, it produces an abundant crop just when
turnips and other winter food are exhausted. Mr. Telfer, Cunning Park, who
has used this system for a good many years, has come to the conclusion that
it is only in this way that it can be made profitable; and though pipes are
laid all over his farm, he has latterly restricted the use of the liquid manure
entirely to Italian ryegrass. Its effect on the cereals is much less marked,
and it can scarcely be considered as capable of advantageous application to
the general operations of the farm. Neither can liquid manure be applied to
all soils. It fails entirely on heavy clays, but is peculiarly adapted to light
sandy soils; and even barren sand may by its repeated application, be made
to yield luxuriant crops. It is not likely that the system of liquid manuring
will extend, except in localities where it is possible to distribute it by

gravitation; and even then, it will probably be found most economical to
restrict its use to one portion of the farm; and for that purpose, the poorest
and most sandy soil ought to be selected.
Sewage Manure.—The use of the sewage of towns as a manure is closely
connected with that of the liquid manure produced on the farm. Its
application must take place in a similar manner, and be governed by the
same principles. Although numerous attempts have been made to convert it
into a solid form, or to precipitate its valuable matter, none of them have
succeeded; nor can it be expected that any plan can be devised for the
purpose, because the most important manurial constituents are chiefly
soluble, and cannot be converted into an insoluble state, or precipitated
from their solution. In its liquid form, however, sewage manure has been
employed with the best possible effect in the cultivation of meadows. The
most important instance of its application is in the neighbourhood of
Edinburgh, where 325 acres receive the sewage of nearly half the town, and
have been converted from barren sand into land which yields from £20 to
£30 per acre. The contents of the sewer, taken just before it flows into the
first irrigated meadow, near Lochend, were found to contain per gallon—

Soluble organic matter 21·90
Insoluble organic matter 21·70
Peroxide of iron and alumina 2·01
Lime 10·50
Magnesia 2·00
Sulphuric acid 6·09
Phosphoric acid 6·14
——
Chlorine 12·20
Potash 2·89
Soda 13·27
Silica 6·50
———
105·20
Ammonia 14·90

It is interesting to notice that this sewage is superior in every respect to the
liquid manure used at Tiptree Hall; and the good effects obtained from its
application, in the large quantities in which it is used in the Craigentinny
meadows, may be well imagined. It operates, not merely by the substances
which it holds in solution, but also by depositing a large quantity of matters
carried along in suspension, and is in reality warping with a substance
greatly superior to river-mud. A deposit collected in a tank, where the
sewage passes through a farm, is used as a manure, and contains—

Peroxide of iron and alumina 4·45
Lime 1·74
Magnesia 0·39
Potash 0·10
Soda 0·06
Phosphoric acid 1·08
Sulphuric acid 0·16
Organic matter 17·95
Sand 20·51
Water 53·56
———
100·00
Ammonia 0·93

And even, though containing more than half its weight of water and 20 per
cent of sand, this substance has considerable value as a manure.
The growing evils of the existing system of sewage, and the enormous
waste of a manurial matter, which the experience of the Craigentinny
meadows has shewn to be productive of the most important effects, has
recently directed much attention to the conversion of the contents of our
sewers into a useful manure. Numerous plans for its precipitation and
conversion into a solid manure have been proposed, but most of these have
shewn an entire ignorance of the fundamental principles of chemistry, and
the best only succeed in precipitating a very small proportion of its valuable
matters, and leave almost the whole of the ammonia, as well as the greater
part of the fixed alkalies, in solution. Nor is it to be expected that any
process will be discovered by which these substances can be precipitated,

because solubility is the special characteristic of their compounds, and no
means is known by which it is possible to convert them into an insoluble
form. If sewage is to be used at all, there seems little doubt that it must be
by applying it entire, and in the liquid state. But here again, the expense of
conveying it on to the land becomes an obstacle which it must frequently be
impossible to overcome. When it can be conveyed by gravitation, as is the
case in the neighbourhood of Edinburgh, it may undoubtedly be used with
the utmost advantage, and with the very best economic results. But when it
requires to be carried to a great distance through pipes, and raised to a high
level by pumping, all these advantages disappear. If the cost of application
amounts to 2d. a gallon, as in Mr. Mechi's case, or even to half that sum, it
may be fairly concluded that it cannot be used with any great prospect of
large economic results, and that, unless under very exceptional cases, it
must be unprofitable.
The chances of success must also greatly depend upon the kind of soil on
which it is used. Experience has shewn that its effects are most beneficial
on light and deep sandy soils, but that on heavy retentive clays it is without
effect, or even absolutely injurious. In clay soils it is important to use every
means of getting rid of moisture, and any plan which adds 200 or 300 tons
of water to them, only aggravates their natural defects to an extent which
more than counterbalances the benefits derived from the manurial matter it
contains. Whatever the ultimate result of the use of town sewage in the
liquid form may be, it is unlikely that it will be employed in general
agricultural practice. It is more probable that it will be found necessary to
set apart a certain breadth of land to be treated by it exclusively. Many plans
have been proposed for conveying it through considerable districts, and
selling to the surrounding farmers the quantities which they require, but
wherever large sewage-works are established, it will be impossible to
depend on a precarious demand, and the promoters of such schemes will be
compelled, as part of their speculation, to supply not only the manure, but
the land on which it is to be used. Indeed, the difficulties attending the
whole question are so formidable, that even those who are most anxious to
see a stop put to the waste of manurial matter must admit that the prospect
of a successful economic result is not encouraging. Nor is it likely that
anything will be done until the whole system of managing town refuse is
changed, and in place of deluging it with water, some plan can be contrived

which, while fulfilling sanatory requirements, shall preserve it in a
concentrated form, or convert it into a dry and inodorous substance.

FOOTNOTES:
[L] Report on the economic uses of peat. Highland Society's Transactions, N.S.,
vol. iv. p. 549.

CHAPTER IX.
COMPOSITION AND PROPERTIES OF VEGETABLE
MANURES.

Many vegetable substances have been employed as manures, either alone or
as auxiliaries to farm-yard manure. Like that substance, they are general
manures, and contain all the constituents of ordinary crops; but, owing to
the absence of animal matter, they in general undergo decomposition and
fermentation much more slowly, although some of them contain a so largely
preponderating proportion of nitrogen, that they may in some respects be
compared to the strictly nitrogenous manures.
Rape-dust, Mustard, Cotton and Castor Cake.—Rape-dust has long been
employed as a manure, and the success which has attended its use has led to
the introduction of the refuse cake from some other oil seeds, such as those
of mustard and castor-oil, which cannot be employed for feeding. Like the
seeds of all plants, these substances are rich in nitrogen, and their ash,
containing of course all the constituents of the plant, supplies the necessary
inorganic elements. The following are analyses of these substances, which,
in addition to the amount of nitrogen and phosphates, shew also that of
water and oil, to which reference will be made in a future chapter, in
relation to the feeding value of some of them. The detailed composition of
their ash may be judged of from that of the seeds from which they are
made, and which have been given under that head.

Rape- Poppy- Cotton-seed Castor-
Cake. Cake. Cake. Cake.
Water 10·68 11·63 11·19 12·31
Oil 11·10 5·95 9·08 24·32
Albuminious compounds 29·53 31·16 25·16 21·91
Ash 7·79 12·98 5·64 6·08
Other constituents 40·90 38·18 48·93 35·38
100·00 100·00 100·00 100·00

Nitrogen 4·38 4·94 3·95 3·20
Silica 1·18 3·36 1·32 1·96
Phosphates 3·87 69·3 2·19 2·81
Phosphoric acid in
0·39 3·27 0·15 0·64
combination with alkalies

A general similarity may be observed in the composition of all these
substances; they are rich in nitrogen, and contain as much of that element as
is found in six or seven times their weight of farm-yard manure, and a
somewhat similar proportion exists in the amount of phosphates, and
probably of their other constituents. They have all been employed with
success, but the most accurate observations have been made with rape-dust,
which has been longer and more extensively used than any of the others. It
has been employed alone for turnips, or mixed with farm-yard manure, and
also as a top-dressing to cereals. But the most marked advantage is derived
from it when applied in the latter way on land which has been much
exhausted, and its effects are then very striking. An adequate supply of
moisture is essential to the production of its full effects, and hence it often
proves a failure in very dry seasons, and on dry soils. It must not be applied
in too great abundance, experience having shewn that after a certain point
has been reached, an increase in the quantity produces no benefit, and even
sometimes positively diminishes the crop. The other substances of the same
class, in all probability, act in the same way, but as their introduction is
recent, and their use limited, less is known regarding their effects.
Malt-Dust, Bran, Chaff, etc.—The value of these substances as manures is
chiefly dependent on the nitrogen they contain, though to some extent also
on their inorganic constituents. Malt-dust contains about 4·5 per cent, and
bran 3·2 per cent of nitrogen. But they are little used as manures, as they
can generally be more advantageously employed for feeding. The value of
chaff more nearly resembles that of straw.
Straw is occasionally employed as a manure, and sometimes even as a top-
dressing for grass land. It is generally admitted, however, that its
application in the dry state, and especially as a top-dressing, is a practice
not to be recommended, as it decomposes too slowly in the soil; and it is
always desirable to ferment it in the manure heap, so as to facilitate the
production of ammonia from its nitrogen. Still circumstances may occur in

which it becomes necessary to employ it in the dry state, and it will
generally prove most valuable on heavy soils, which it serves to keep open,
and so promotes the access of air, and enables it to act on the soil. On light
sandy soils it generally proves less advantageous, as its tendency of course
is to increase the openness of the soil, and render it less able to retain the
essential constituents of the plant.
The quantity of nitrogen in straw does not exceed 0·2 per cent, and its value
is mainly due to its inorganic constituents and to its mechanical effect on
the soil.
Saw-dust has little value as a manure, as it undergoes decomposition with
extreme slowness. It is a good mechanical addition to heavy soils, and
diminishes their tenacity; and though its manurial effects are small, it
sooner or later undergoes decomposition, and yields what valuable matters
it contains. The saw-dust of hard wood is to be preferred, both because it
contains more valuable matters than that of soft wood, and because the
absence of resinous matters permits its more rapid decomposition. It is a
useful absorbent of liquid manure, and may be advantageously added to the
dung-heap for that purpose.
Manuring with Fresh Vegetable Matter—Green Manuring.—The term
green manuring is applied to the system of sowing some rapidly growing
plant, and ploughing it in when it has attained a certain size, and the success
attending it, especially on soils poor in organic matters, is very marked. It is
obvious that this mode of manuring can add nothing to the mineral matters
contained in the soil, and its utility must therefore be due to the plant
gathering organic matters from the air, which, by their decomposition, yield
nitrogen and carbonic acid—the former to be directly made use of by
subsequent crops, the latter, in all probability, acting also on the soil, and
setting free its useful constituents. Hence those plants which obtain the
largest quantity of their organic elements from the air ought to be most
advantageous for green manuring. The plants used for this purpose act also
as a means of bringing up from the lower parts of the soil the valuable
matters which exist in it out of reach of ordinary crops, and mixing them
again with the surface part. Many of the plants found most useful for green
manuring send down their roots to a considerable depth; and when they are
ploughed in, all the substances which they have brought up are of course

deposited in the upper few inches of the soil. Vegetable matter when
ploughed in in the fresh state, also decomposes rapidly, and is therefore able
immediately to improve the subsequent crop; and as this decomposition
takes place in the soil without the loss of ammonia and other valuable
matters, which is liable to occur to a greater or less extent when they are
fermented on the dung-heap, it will be obvious that in no other mode can
equally good results be obtained by its use.
Many plants have been employed as green manure, and different opinions
have been expressed as to their relative values. In the selection of any one
for the purpose, that should of course be taken which grows most rapidly,
and produces within a given time the largest quantity of valuable matters,
but no general rule can be given for the selection, as the plant which fulfils
those conditions best will differ in different soils and climates. The plants
most commonly employed in this country are spurry, white mustard, and
turnips. Rye, clover, buckwheat, white lupins, rape, borage, and some
others, have been largely employed abroad. Some of these are obviously
unfitted for the climate of the British Islands; and the others, although they
have been tried occasionally, do not appear to have been very extensively
employed. The turnip is sown broadcast at the end of harvest, and ploughed
in after two months. White mustard and spurry are employed in the same
way as a preparation for winter wheat, and with the best results. The latter is
sometimes sown as a spring crop in March, ploughed in in May, and
another crop sown which is ploughed in in June, and immediately followed
by a third. The effect of this treatment is such that the worst sands may be
made to bear a remunerative crop of rye.
It is not easy to estimate the addition made by green manuring to the
valuable matters contained in the soil, but it is probably far from
inconsiderable. A crop of turnips, cultivated on the ordinary agricultural
system, after two months' growth, weighs between five and seven tons per
acre, and contains nitrogen equivalent to about 48 lbs. of ammonia, and half
a ton of organic matters; but nothing is known as to the quantity produced
when it is sown broadcast, and is not thinned, although it must materially
exceed this. Neither is it possible to determine the relative proportions
derived from the soil and the air, although it is, in all probability, dependent
on the resources of the soil itself,—plants grown on a rich soil obtaining
their chief supplies from it, while, on poorer soils, a larger proportion is

drawn from the atmosphere. Hence light and sandy soils are most benefited
by green manuring, partly on this account, and partly also, no doubt,
because the valuable inorganic matters, which are so liable to be washed out
of these soils, are accumulated by the plants and retained in them in a state
in which they are readily available for the subsequent crop.
Sea-Weed.—Sea-weeds have been employed from time immemorial as a
manure on the coasts of Scotland and England, in quantities varying from
10 to 20 tons per acre. Their action is necessarily similar to that of green
manure ploughed in, as they contain all the ordinary constituents of land
plants.
The subjoined analyses of three of the most abundant species will
sufficiently indicate their general composition.

Laminaria Digitata.
Mixed
Weeds
Stem and
state in
Fucus Fucus Collected Frond
which
nodosus. vesiculosus. in Autumn. collected in
they
Spring.
actually
are used.
Water 74·31 70·57 88·69 77·31 80·44
Albuminous
1·76 2·01 0·93 3·32 2·85
compounds
Fibre, etc. 19·04 22·05 4·92 10·39 6·40
Ash 4·89 5·37 5·46 8·98 10·31
100·00 100·00 100·00 100·00 100·00
Nitrogen 0·28 0·32 0·15 0·53 0·45
The ash
consisted of
Stem.
Frond.
Peroxide of
0·25 0·35 0·20 0·50 0·45 2·35
iron
Lime 9·60 8·92 7·21 7·29 4·62 18·15

Magnesia 6·65 5·83 2·73 5·91 10·94 6·48
Potash 20·03 20·75 5·55 11·91 12·16 12·77
Chloride of 58·42
... ... 25·83 9·10
potassium 26·59
Iodide of
0·44 0·23 1·51 2·09 1·22 1·68
potassium
Soda 4·58 6·09 ... ... ... ...
Sulphuret of
3·66 ... ... ... ... ...
sodium[M]
Chloride of 15·29
24·33 24·81 19·34 22·08
sodium 30·77
Phosphoric
1·71 2·14 2·42 2·66 1·75 4·59
acid
Sulphuric acid 21·97 28·01 2·23 8·80 7·26 6·22
Carbonic acid 6·39 2·20 4·11 2·49 15·23 13·58
Silicic acid 0·38 0·67 0·33 0·99 1·20 3·00
———
—— ——— ——— ———
———
100·00
100·00 100·00 100·00 100·00
100·00

The first four analyses give the composition of the weeds after they have
been separated from all foreign substances; the last, that of the mixture
taken from the heap just as it is used in Orkney; and its value is then
enhanced by small shells and marine animals adhering to the plants, which
increase the amount of phosphoric acid and nitrogen.
The ease with which all sea-weeds pass into a state of putrefaction, adapts
them in a peculiar manner to the manurial requirements of a cold and damp
climate. The rapidity of their decomposition is such, that when spread on
the land they are seen to soften and disappear in a short time. They form
therefore a rapid manure, and their effects are said to be confined to the
crop to which they are applied; but this is probably due to the fact, that they
are chiefly used in inferior sandy soils, in which any manure is rapidly
exhausted. In good soils there is no reason why their effect should not be as
lasting as that of farm-yard manure, which, in many particulars, they

considerably resemble. The method of applying sea-weeds most generally
in use, is to spread them on the soil, and plough them in after putrefaction
has commenced, and it is on the whole the most advantageous. But they are
sometimes composted with lime and earth, or mixed with farm-yard
manure, and occasionally, also, they are used as a top-dressing to grass
land.
On some parts of the western coast of Scotland and in the Hebrides, sea-
weed is the chief manure. It gives excellent crops of potatoes, but they are
said to be of inferior quality, unless marl or shell-sand is employed at the
same time.
Leaves may be used as a manure, simply by ploughing them in, by
composting them with lime, or by adding them to the manure heap.
Peat.—As a source of organic matter, peat may be used with advantage,
especially on soils in which it is naturally deficient. Dry peat of good
quality contains about one per cent of nitrogen, and a quantity of ash
varying from five to twenty per cent. These substances, however, become
available very slowly, owing to the tardy decay of peat in its natural state;
and in order to make it useful, it is necessary to compost it with lime, or to
mix it with farm-yard manure, or some readily putrescible substance, so that
its decomposition may be accelerated. It may be most advantageously used
as an absorbent of liquid manure, and on this account, forms a useful
addition to the manure heap.
The observations which have been made regarding the use of these
substances, lead directly to the inference that all vegetable matters possess a
certain manurial value, and that they ought to be carefully collected and
preserved. In fact, the careful farmer adds everything of the sort to his
manure heap, where, by undergoing fermentation along with the manure,
their nitrogen becomes immediately available to the plant; while the seeds
of weeds are destroyed during the fermentation, and the risk of the land
being rendered dirty by their springing up when the manure comes to be
used is prevented.

FOOTNOTES:

[M] The presence of sulphuret of sodium in this case is due to the difficulty of
completely burning the ash. It exists in the plant as sulphate of soda.

CHAPTER X.
COMPOSITION AND PROPERTIES OF ANIMAL
MANURES.

Manures of animal origin are generally characterized by the large quantity
of nitrogen they contain, which causes them to undergo decomposition with
great rapidity, and to yield the greater part of their valuable matters to the
crop to which they are applied.
Guano.—By far the most important animal manure is guano, which is
composed of the solid excrements of carnivorous birds in a more or less
completely decomposed state, and is accumulated in immense quantities on
the coasts of South America and other tropical countries. It has been used as
a manure in Peru from time immemorial, but the accounts given by the
older travellers of its marvellous effects were considered to be fabulous,
until Humboldt, from personal observation, confirmed their statements. It
was first imported into this country in 1840, in which year a few barrels of
it were brought home; and from that time its importation rapidly increased.
Soon after large deposits of it were found in Ichaboe; and it has since been
brought from many other localities. The quantity of guanos of all kinds
imported into this country and retained for home consumption now exceeds
240,000 tons a year.
The value of guano differs greatly according to the extent to which its
decomposition has gone, and this is chiefly dependent on the climate of the
locality from which it is obtained. When deposited in the rainless districts
of Peru it still retains some of the uric acid and the greater part of the
ammonia naturally existing in it, and the quantity which has escaped by
decomposition is unimportant. But that obtained from other districts has
suffered a more or less complete decomposition according to the humidity
of the climate, which reduces the quantity of organic matters and ammonia,
until, in some varieties, they are so small as to be of little importance. The
following are minute analyses of three specimens of Peruvian guano,

shewing all the different constituents it contains, and the amount of
difference which may exist:—

I. II. III.
Urate of ammonia 10·70 9·0 3·24
Oxalate of ammonia 12·38 10·6 13·35
Oxalate of lime 5·44 7·0 16·36
Phosphate of ammonia 19·25 6·0 6·45
Phosphate of magnesia and ammonia ... 2·6 4·20
Sulphate of potash 4·50 5·5 4·23
Sulphate of soda 1·95 3·8 1·12
Sulphate of ammonia 3·36 ... ...
Muriate of ammonia 4·81 4·2 6·50
Phosphate of soda ... ... 5·29
Chloride of sodium ... ... 0·10
Phosphate of lime 15·56 14·3 9·94
Carbonate of lime 1·80 ... ...
Sand and alumina 1·59 4·7 5·80
Water 9·14 }
} 32·3 23·42
Undetermined humus-like organic matters 10·00 }
——— —————
100·48 100·0 100·00

These analyses illustrate two points—first, that in some samples the
decomposition has advanced to a greater extent than in others; for we
observe that the quantity of uric acid, or rather of urate of ammonia, is
greatly less in the last analysis than in the other two, and much smaller than
in the fresh dung, which contains from 50 to 70 per cent of uric acid; and
secondly, that guano is rich in all the constituents of the plant, but especially
in ammonia, the best form in which nitrogen can be supplied, in uric acid
which by decomposition yields ammonia, and in phosphoric acid. But such
analyses are too elaborate for ordinary purposes, and much less convenient
for comparison and for estimating the value of the guano than the shorter
analysis commonly in use, which gives the water, the loss by ignition (that
is, the sum of the organic matters and ammoniacal salts), the phosphates,

the alkaline salts, and the quantity of phosphoric acid contained in them,
and existing there in a state similar to that in which it is found in the soluble
phosphates of a superphosphate. In addition to these, the quantities of sand
and other less valuable ingredients are also stated.
In the subjoined tables the composition of a great variety of different kinds
of guano is given. Most of these are averages deduced from a considerable
number of analyses of good samples. Those of some kinds of guano, such
as Peruvian, which present a considerable amount of uniformity, afford a
sufficiently accurate idea of the general composition of the variety, but in
other cases they are of less value, because the imports of different seasons,
and even of different cargoes, differ so greatly in composition that no
proper average can be made. Several of these varieties are already
exhausted, the importation of others has ceased, and new varieties are
constantly being introduced.

Table showing the Average Composition of different varieties of Guano.

Angamos. Peruvian. ICHABOE. Bolivian or Upper Peruvian.
Old. New. Old. Government. Inferior
Water 12·36 13·73 24·21 18·89 12·55 16·44 14·15
Organic
matter and
59·92 53·16 39·30 32·49 35·89 12·28 26·14
ammoniacal
salts
Phosphates 17·01 23·48 30·00 19·63 27·63 56·09 23·13
Sulphate of
... ... ... ... ... ... 9·65
lime
Carbonate
... ... ... ... ... ... 12·87
of lime
Alkaline
7·20 7·97 4·19 8·82 15·29 11·33 5·97
salts
Sand 3·51 1·66 2·30 6·72 8·64 2·81 8·09
100·00 100·00 100·00 100·00 100·00 100·00 100·00
Ammonia 21·10 17·00 8·50 10·42 8·99 2·57 3·26

Phosphoric
acid in
1·20 2·50 ... ... ... 3·11 ...
alkaline
salts

Pacquico Latham
Saldanha. Australian. Kooriamooria.
Island. Bay.
Water 8·38 24·96 21·03 13·20 8·91
Organic matter
and ammoniacal 23·10 10·96 14·93 13·77 7·72
salts
Phosphates 32·36 54·47 56·40 44·47 44·15
Sulphate of lime 2·92 2·82 ... 4·55 3·19
Carbonate of lime ... 2·20 ... 8·82 3·37
Alkaline salts 25·43 4·06 6·10 7·34 11·23
Sand 7·81 0·51 1·54 7·85 21·43
100·00 100·00 100·00 100·00 100·00
Ammonia 6·58 1·26 1·62 1·01 0·42
Phosphoric acid
3·50 ... ... ... ...
in alkaline salts

Patagonian. Chilian. Mexican.
Water 20·61 14·89 18·80
Organic matter and ammoniacal salts 19·72 16·81 12·88
Phosphates 30·66 36·90 18·38
Sulphate of lime 1·30 ... 27·79
Carbonate of lime 3·06 10·28 ...
Alkaline salts 7·01 6·84 16·95
Sand 17·04 14·26 5·20
100·00 100·00 100·00

Ammonia 2·69 1·42 0·42
Phosphoric acid in alkaline salts 3·00 ... ...

Table shewing the Composition of some of the less common varieties of
Guano.

Note.—The numbers in this Table are mostly derived only from a single
analysis and have no value as determining the average composition of these
Guanos, but they serve to give a general idea of their value.

Sea Bear Holme's Ascension Possession
Indian.
Bay. Bird Island. Island. Island.
Water 30·82 23·62 25·00 15·97 10·92
Organic matter and
31·78 60·05 32·10 23·15 15·42
ammoniacal salts
Phosphates 24·33 7·18 27·36 32·54 46·41
Sulphate of lime 3·84 ... ... ... 7·46
Carbonate of lime 0·58 2·79 ... ... ...
Alkaline salts 7·38 5·58 8·82 15·92 6·15
Sand 1·27 0·78 6·72 12·42 13·64
100·00 100·00 100·00 100·00 100·00
Ammonia 10·45 10·27 7·75 6·06 1·34
Phosphoric acid in
... ... ... 1·82 ...
alkaline salts

Algoa New Bird's Leone
Bay. Island. Island. Island.
Water 30·55 28·78 16·52 23·65
Organic matter and
6·85 13·78 14·84 4·27
ammoniacal salts
Phosphates 21·24 22·46 25·21 13·58
Sulphate of lime 36·42 ... 40·47 29·95

Carbonate of lime ... 13·78 ... ...
Alkaline salts 3·32 12·62 1·16 5·40
Sand 1·62 11·58 1·80 23·15
100·00 100·00 100·00 100·00
Ammonia 0·54 0·84 1·26 0·67
Phosphoric acid in alkaline
... ... ... ...
salts

On examining the tables given above, it is obvious that guanos may be
divided into two classes, the one characterized by the abundance of
ammonia, the other by that of phosphates; and which, for convenience sake,
may be called ammoniacal and phosphatic guanos. Peruvian and Angamos
are characteristic of the former, and Saldanha Bay and Bolivian of the latter
class. The value of these two classes of guano differs materially, and they
are also applicable under different circumstances, but to these points
reference will afterwards be made.
Very special precautions are necessary on the part of the farmer in order to
insure his obtaining a guano which is not adulterated, and of good quality if
genuine. In the case of Peruvian guano, which is tolerably uniform in its
qualities, it is possible to form some opinion by careful examination, and
the following points ought to be attended to:
1st, The guano should be light coloured. If it is dark, the chances are that it
has been damaged by water.
2d, It should be dry, and when a handful is well squeezed together it should
cohere very slightly.
3d, It should not have too powerful an ammoniacal odour.
4th, It should contain lumps, which, when broken, appear of a paler colour
than the powdery part of the sample.
5th, When rubbed between the fingers it should not be gritty.
6th, A bushel of the guano should not weigh more than from 56 to 60 lbs.
These characters must not, however, be too implicitly relied on, for they are
all imitated with wonderful ingenuity by the skilful adulterator, and they are

applicable only to Peruvian guano; the others being so variable that no
general rules can be given for determining whether they are genuine.
Neither are they so precise as to enable us to give any opinion regarding the
relative values of several samples where all are genuine. The only way in
which adulteration can with certainty be detected, and the value of different
guanos be determined, is by analysis, and the importance of this can easily
be illustrated.
In the table above, the average composition of the different guanos is given;
but in order to shew how much individual cargos may differ from the mean,
we give here analyses of samples of the highest and lowest quality of the
genuine guanos of most importance:

Angamos. Peruvian. Bolivian.
Highest. Lowest. Highest. Lowest. Highest. Lowest.
Water 12·60 7·09 10·37 21·49 11·53 16·20
Organic matter and
65·62 50·83 55·73 46·26 11·17 12·86
ammoniacal salts
Phosphates 10·83 8·70 25·20 18·93 62·99 52·95
Alkaline salts 7·50 16·30 7·50 10·64 9·93 13·83
Sand 3·45 17·08 1·20 2·68 4·38 4·16
100·00 100·00 100·00 100·00 100·00 100·00
Ammonia 25·33 17·15 18·95 14·65 1·89 2·23

The differences are here exceedingly large; and when the values of the two
Peruvian guanos are calculated according to the method to be afterwards
described, it appears that the highest exceeds the lowest in value by nearly
£3 per ton. Of course, this is an extreme case, but it is no uncommon
occurrence to find a difference of £1 or even £2 per ton between the values
of cargos of Peruvian guano, which are sold at the same price.
The adulteration of guano is carried on to a very large extent; and though
perhaps not quite so extensively now as it was some years since, it is only
kept in check by the utmost vigilance on the part of the purchaser. The chief
adulterations are a sort of yellow loam very similar in appearance to guano,
sand, gypsum, common salt, and occasionally also ground coprolites and
inferior guano. These substances are rarely used singly, but are commonly
mixed in such proportions as most closely to imitate the colour and general
appearance of the genuine article. The extent to which the adulteration is
carried may be judged of from the following analyses taken at random from
those of a large number of guanos, all of which were sold as first-class
Peruvian.

Water 12·85 15·19 12·06 27·86 6·32
Organic matter and ammoniacal salts 26·84 44·31 34·14 30·41 27·42
Phosphates 15·54 20·95 22·08 22·17 33·61
Sulphate of lime ... ... 11·08 ... 22·11
Alkaline salts 6·07 9·40 12·81 7·92 22·50
Sand 38·70 10·15 7·83 1·64 10·15

100·00 100·00 100·00 100·00 100·00
Ammonia 9·34 13·90 9·77 8·64 9·76

In all those cases a very large depreciation in the value has taken place, and
several of them are worth considerably less than half the price of the
genuine guano, while they are generally offered for sale at about £1 under
the usual price. The adulteration is chiefly practised in London, and cases
occasionally occur which can be traced to Liverpool and other places; but it
always takes place in the large towns, because it is only there that facilities
exist for obtaining the necessary materials and carrying it out without
exciting suspicion. The sophisticated article then passes into the hands of
the small country dealers, to whom it is sold with the assurance that it is
genuine, and analysis quite unnecessary. In other instances, adulterated and
inferior guanos are sold by the analysis of a genuine sample, and sometimes
an analysis is made to do duty for many successive cargos of a guano
which, though all obtained from one deposit, may differ excessively in
composition. In order to insure obtaining a genuine guano, it is above all
things important to deal only with a person of established character, who
will generally, for his own sake, satisfy himself that the article he vends is
genuine and of good quality; and it is always important that the buyer
should examine the analysis, and in all cases where there is the slightest
doubt, should ascertain that the bulk sent corresponds with it. In the case of
a Peruvian guano, a complete analysis is not necessary for this purpose; but
an experienced chemist, by the application of a few tests, can readily
ascertain whether the sample is genuine. Where the difference in value
between different samples is required, a complete analysis is necessary, and
this is indispensable in the case of the inferior guanos. Many of these are
obtained from deposits of limited extent, and in loading it considerable
quantities of the subjacent soil are taken up, so that very great differences
may exist even in different parts of the same cargo. Nor must it be forgotten
that, except in the case of Peruvian, the name is no guarantee for the quality
of the guano, even if genuine. Peruvian guano is all obtained from the same
deposits, those of the Chincha Islands, but the guanos which are brought
into the market under the name of Patagonian, Chilian, etc., are obtained
from a great variety of deposits scattered along the coasts of these countries,
sometimes at a distance of several hundred miles from each other, and
which have been accumulated under totally different circumstances. In

illustration of this, it is only necessary to refer to the subjoined analysis of
samples, all of which I believe to be genuine as imported, and which were
sold under the name of Upper Peruvian Guano.

I. II. III.
Water 7·80 6·65 8·85
Organic matter and ammoniacal salts 10·85 19·16 10·20
Phosphates 67·00 20·41 17·10
Carbonate of lime ... 21·15 ...
Alkaline salts 11·10 5·31 61·30
Sand 3·25 27·32 2·55
—————————
100·00 100·00 100·00
Ammonia 2·29 5·73 1·48
Phosphoric acid in the alkaline salts 2·24 ... 1·70
Equal to phosphate of lime 4·89 ... 3·70

With the exception of Peruvian, the supply of good guanos of uniform
composition is by no means large, and phosphatic guanos of good quality
are now especially rare. The Saldanha Bay, and other similar deposits, have
been exhausted, and few guanos of equally good quality have been lately
discovered. There is no doubt, however, that such guanos are very useful,
and if obtained in large quantity, and of uniform composition, would be
used to a much larger extent than they at present are.
The value and use of guano are now so well understood, that it is scarcely
necessary to enlarge on the mode of its application. Peruvian guano owes its
chief value to its ammonia and phosphates, but it also contains potash, soda,
and all the other constituents of plants in small quantity, although in a
readily available condition, as is seen in the detailed analysis given in page
205.
In other guanos which have undergone more complete decomposition, and
from which the soluble matters have been more or less completely
exhausted by rain, the alkaline salts, or at least the potash they originally
contained, have almost entirely disappeared. Hence an important difference
between Peruvian guano and most other varieties. The former can be used

as a complete substitute for farm-yard manure, and excellent crops of
turnips and potatoes can be raised by means of it alone, and at a less cost
than with ordinary dung. But though this may be done, and in many cases is
attended with great economic advantages, it is a practice that cannot be
recommended for general use, because the quantity of valuable matters
contained in the usual application of guano is much smaller than in farm-
yard manure, and the probability is that it would not, if used alone during a
succession of years, be sufficient to maintain the soil permanently in a high
state of fertility. Five cwt. of Peruvian guano, which is a liberal application
per acre, contains about 95 lbs. of ammonia, and 130 of phosphates, while
20 tons of good farm-yard manure contain 312 of ammonia, and about the
same quantity of phosphates, and when the other constituents, such as
potash and soda, are compared with those in guano, the difference is still
more striking. On the other hand, guano is a rapidly acting manure; its
constituents are in a condition in which they are more immediately
accessible by the plant, and its immediate effect is far more marked, as it is
chiefly expended on the crop to which it is applied. It has indeed been
alleged that it produces no effects on the subsequent crops, but this opinion
can scarcely be considered as well founded. In no case does the crop raised
by means of it contain the whole of the ammonia or phosphates present in
the manure, and the unappropriated quantity, though it may, and probably
does, escape from the lighter soils, must be retained and preserved for the
use of subsequent crops by heavy and retentive clay soils. The general
inference is, that though guano may at an emergency be used as an entire
substitute for farm-yard manure, the practice is one to be generally avoided.
When, however, as occasionally happens after a long continued use of farm-
yard manure, organic matters have accumulated in the soil, and passed into
an inert condition, then Peruvian guano may be used alone with very great
advantage. In all cases the rapidity of the action of guano makes it an
important auxiliary of farm-yard manure, and it is in this way that it may be
most advantageously employed. Experience has shewn that one-half the
farm-yard manure may be replaced by guano with the production of a larger
crop than by the former alone in its full quantity. The proportion of guano
usually employed is from three to five cwt., and it is alleged that a much
larger quantity produces prejudicial effects on the subsequent crops,
although it is not very easy to see on what this depends.

The variety of guano to be selected must depend to a great extent on the use
to which it is to be put. Peruvian guano is most advantageously applied as a
top-dressing to young corn and particularly to oats. For the turnip, the
ammoniacal guanos were formerly preferred, and on strong soils, under
good cultivation, their effects are excellent, but on light soils they are less
applicable, their soluble salts being more rapidly washed out, and their
effects lost, and in these cases they are surpassed by the phosphatic guanos.
No definite rules can be given for determining the soils on which these
different varieties are most applicable, but each individual must determine
by experiment that which best suits his own farm; and the inquiry is of
much importance to him, as, of course, if the phosphatic guanos will answer
as well as the ammoniacal, there is a large saving in the cost of the manure.
A very excellent practice is to employ a mixture of equal parts of the two
sorts of guano.
Pigeons' Dung.—The dung of all birds, which more or less closely
resembles guano, may be employed with much advantage as a manure, but
that of the pigeon and the common fowl are the only ones which can be got
in quantity. Pigeons' dung, according to Boussingault, contains 8·3 per cent
of nitrogen, equivalent to 10·0 of ammonia. Its value, therefore, will be
more than half that of guano, but it varies greatly, and a sample imported
from Egypt into this country, and analysed by Professor Johnston, contained
only 5·4 per cent of ammonia. Hens' dung has not been accurately analysed,
but its value must be about the same as pigeons'.
Urate and Sulphated Urine.—We have already discussed the urine of
animals, in reference to farm-yard manure. But human urine, the
composition of which was then stated, is of much higher value than that of
the lower animals, and many attempts have been made to preserve and
convert it into a dry manure. Urate is prepared by adding gypsum to urine,
and collecting and drying the precipitate produced. It contains a
considerable quantity of the phosphoric acid of the urine, but very little of
its ammonia; and as the principal value of urine depends on the latter, it is
necessarily a very inefficient method of turning it to account. A better
method has been proposed by Dr. Stenhouse, who adds lime-water to the
urine, and collects the precipitate, which, when dried in the air, contains
1·91 per cent of nitrogen, and about 41 per cent of phosphates. This method

is subject to the same objection as that by which urate is made, namely, that
the greater part of the ammonia is not precipitated. This might probably be
got over to some extent by the addition of sulphate of magnesia, or, still
better, of chloride of magnesium, which would throw down the phosphate
of magnesia and ammonia. By much the best mode of employing urine is in
the form of sulphated urine, which is made by adding to it a sufficient
quantity of sulphuric acid to neutralize its ammonia, and evaporating to
dryness. In this form all the valuable constituents are retained, and excellent
results are obtained from it. Its effects, though mainly attributable to its
ammonia, are also in part dependent on the phosphates and alkaline salts
which it contains; and it is therefore capable of supplying to the plant a
larger number of its constituents than the animal matters already mentioned.
Night-Soil and Poudrette.—The value of night-soil, which is well known,
depends partly on the urine, and partly on the fæces of which it is formed.
Its disagreeable odour has prevented its general use, and various methods
have been contrived both for deodorising and converting it into a solid and
portable form. The same difficulties which beset the conversion of urine
into the solid form occur here, and in most of the methods employed the
loss of ammonia is great. It is sometimes mixed with lime or gypsum, and
dried with heat, and sometimes with animal charcoal or peat charcoal. The
manufacture of a manure from night-soil, called "poudrette," has long been
practised in the neighbourhood of Paris and other continental towns. The
process employed at Montfauçon and at Bondy is very simple. The contents
of the cesspools are conveyed to the work in large barrels, which are then
emptied into tanks capable of containing the accumulation of several
months. When filled they are allowed to stand for some time, during which
the smell diminishes and the contents become nearly dry. The residue is
then dug out and mixed with ashes, dry loam, charcoal powder, peat, peat-
charcoal, saw-dust, and other matters, so as to deodorize it, and render it
sufficiently dry for transport. Its general composition may be judged of
from the subjoined analyses of samples from different places:—

Montfauçon. Bondy. Dresden. American.
Water 28·00 13·60 19·50 39·97
Organic matters 29·00 24·10 20·80 20·57
Phosphates 7·65 4·96 5·40 1·88

Carbonates of lime and Magnesia,
7·35 14·14 11·30 7·63
alkaline salts, etc.
Sand 28·00 43·20 43·00 29·95
—————— ——— ———
100·00 100·00 100·00 100·00
Ammonia 1·54 1·98 2·60 1·23

These analyses shew sufficiently the extent to which the animal matters
have been mixed with valueless driers, the second and third samples
containing considerably more than half their weight of worthless matters.
Hair, Skin, and Horn.—The refuse of manufactories in which these
substances are employed, are frequently used as manures. They are highly
nitrogenous substances, and owe their entire value to the nitrogen they
contain, their inorganic constituents being in too small quantity to be of any
importance, wool and hair having only 2 per cent, and horn 0·7 per cent of
ash. In the pure and dry state, and after subtraction of the ash, their
composition is,—

Skin. Human hair. Wool. Horn.
Carbon 50·99 50·65 50·65 51·99
Hydrogen 7·07 6·36 7·03 6·72
Nitrogen 18·72 17·14 17·71 17·28
Oxygen 23·22 20·85 } 24·61 24·01
Sulphur ... 5·00}
——— —————————
100·00 100·00 100·00 100·00

It rarely if ever happens, however, that the refuse offered for sale as a
manure is pure. It always contains water, sand, and other foreign matters.
Woollen rags are mixed with cotton which has no manurial value, and the
skin refuse from tan-works contains much lime. Due allowance must
therefore be made for such impurities which are sometimes present in very
large quantity.
Refuse horse hair generally contains 11 or 12 per cent of nitrogen. Woollen
rags of good quality contain 12·7 per cent of nitrogen; woollen cuttings

about 14; and what is called shoddy only 5·5 per cent. Horn shavings are
extremely variable in their amount of nitrogen; when pure, they sometimes
contain as much as 12·5 per cent, but a great deal of the horn shavings from
comb manufactories, etc., contain much sand and bone dust, by which their
percentage of nitrogen is greatly diminished, and it sometimes does not
exceed 5 or 6 per cent.
All these substances are highly valuable as manures, but it must be borne in
mind that they undergo decomposition very slowly in the soil, and hence
are chiefly applicable to slow growing crops, and to those which require a
strong soil. Woollen rags have been largely employed as a manure for hops,
and are believed to surpass every other substance for that crop. As a manure
applicable to the ordinary purposes of the farm they have scarcely met with
that attention which they deserve, probably because their first action is slow
and the farmer is more accustomed to look to immediate than to future
results; but they possess the important qualification of adding permanently
to the fertility of the soil.
Blood is a most valuable manure, but it is not much employed in this
country, at least in the neighbourhood of large towns, as there is a demand
for it for other purposes, and it can rarely be obtained by the farmer in large
quantity, and at a sufficiently low price. In its natural state it contains about
3 per cent of nitrogen, and after being dried up, the residue contains about
15 per cent. It is best used in the form of a compost with peat or mould, and
this forms an excellent manure for turnips, and is also advantageously
applied as a top-dressing to wheat.
Flesh.—The flesh of all animals is useful as a manure, and is especially
distinguished by the rapidity with which it undergoes decomposition, and
yields up its valuable matters to the plant. It is rarely employed in its natural
state, but horse flesh was at one time converted into a dry and portable
manure, although, I understand, this manufacture is not now prosecuted.
The dead animal after being skinned is cut up and boiled in large cauldrons
until the flesh is separated from the bones. The latter are removed, and the
flesh dried upon a flat stove. The flesh as sold has the following
composition:—

Water 12·17

Organic matter 78·44
Phosphate of lime, etc. 3·82
Alkaline salts 3·64
Sand 1·93
———
100·00
Nitrogen 9·22
Ammonia to which the nitrogen is equivalent 11·20

The dried flesh and small bones of cattle, from the great slaughtering
establishments of South America, was at one time imported into this
country under the name of flesh manure. Its composition was—

Water 9·05
Fat 11·13
Animal matter 39·52
Phosphate of lime 28·74
Carbonate of lime 3·81
Alkaline salts 0·57
Sand 7·18
———
100·00
Nitrogen 5·56
Ammonia to which the nitrogen is equivalent 6·67

But owing to the large proportion of phosphates contained in it, it may be
most fairly compared with bones. It is not now imported, the results
obtained from its use being said not to have proved satisfactory, although
this statement appears very paradoxical.
Fish have been employed in considerable quantity as a manure. That most
extensively employed in this country is the sprat, which is occasionally
caught in enormous quantities on the Norfolk coast, and used as an
application for turnips. They are sold at 8d. per bushel, and their
composition is—

Water 64·6
Organic matter 33·3
Ash 2·1
——
100·0
Nitrogen 1·90
Phosphoric acid 0·91

The refuse of herring and other fish-curing establishments, whales' blubber,
and similar fish refuse, are all useful as manure, and are employed
whenever they can be obtained. They are not usually employed alone, but
are more advantageously made into composts with their own weight of soil,
and allowed to ferment thoroughly before being applied.
Many attempts have been made to convert the offal of the great fish-curing
establishments, and the inedible fish, of which large quantities are often
caught, into a dry manure, which has received the name of "fish guano."
The processes employed have consisted in boiling with sulphuric acid and
other agents, and then evaporating, or sometimes by simply drying up the
refuse by steam heat. A manure made in this way proved to have the
following composition:—

Water 8·00
Fatty matters 7·20
Nitrogeneous organic matters 71·46
Phosphate of lime 8·70
Alkaline salts 3·80
Sand 0·84
———
100·00
Nitrogen 11·25
Equal to ammonia 13·68
Phosphoric acid in the alkaline salts, equal to 1·41 phosphate of
0·65
lime

The expense of manufacturing manures of this description has hitherto
acted as a barrier to their introduction. In this country several manufactories
have been established, but either owing to this cause, or to the difficulty of
obtaining sufficiently large and uniform supplies of the raw material, some
of them have not proved successful, but a manufactory is now in operation
in Norway, which exports the manure to Germany. It is probable that most
of the processes used in this country failed because they were too costly,
and it is much to be desired that the subject should be actively taken up. It is
said that the refuse from the Newfoundland fisheries is capable of yielding
about 10,000 tons of fish guano annually; and the quantity obtainable on
our own coasts is also very considerable.
Bones.—Bones have been used as a manure for a long period, but they first
attracted the particular attention of agriculturists from the remarkable
effects produced by their application on the exhausted pasture lands of
Cheshire. During the present century they came into general use on arable
land, and especially as a manure for turnips; and they are now imported in
large quantities from the continent of Europe. The bones used in agriculture
are chiefly those of cattle, but sheep and horse bones are also employed.
They do not differ much in quality when genuine. The subjoined analysis is
that of a good sample.

Water 6·20
Organic matter 39·13
Phosphate of lime 48·95
Lime 2·57
Magnesia 0·30
Sulphuric acid 2·55
Silica 0·30
———
100·00
Ammonia which the organic matter is capable of yielding 4·80

In general, bones may be said to contain about half their weight of
phosphate of lime, and 10 or 12 per cent of water. But, in addition to their
natural state, they are met with in other forms in commerce, in which their
organic matter has been extracted either by boiling or burning. The latter is

especially common in the form of the spent animal charcoal of the sugar
refiners, which usually contains from 70 to 80 per cent of phosphate of
lime, but when deprived of their organic matter, they may be more correctly
considered under the head of mineral manures.
From the analysis given above, it is obvious that the manurial value of
bones is dependent partly on their phosphates and partly on the ammonia
they yield. It has been common to attribute their entire effects to the former,
but this is manifestly erroneous; and although there are no doubt cases in
which the former act most powerfully, the benefit derived from the
ammonia yielded by the organic matter is unequivocal. When the
phosphates only are of use, burnt bones or the spent animal charcoal of the
sugar refiners are to be preferred.
At their first introduction, bones were applied in large fragments, and in
quantities of from 20 to 30 cwt., or even more, per acre, but as their use
became more general they were gradually employed in smaller pieces, until
at last they were reduced to dust, and it was found that, in a fine state of
division, a few hundredweights produced as great an effect as the larger
quantity of the unground bones. Even the most complete grinding which
can be attained, however, leaves the bones in a much less minute state of
division than guano, and they necessarily act more slowly than it does, the
more especially as they contain no ready-formed ammonia. They may be
still further reduced by fermentation, which acts by decomposing the
organic matter, and causing the production of ammonia; but not as is
frequently, though erroneously supposed, by converting the phosphates into
a soluble condition, for this does not occur to any extent, and their more
rapid action is solely due to the partial decomposition of the organic matter,
by which it is brought into a condition capable of undergoing a more rapid
change in the soil. The rapidity of action of bones is still more promoted by
solution in sulphuric acid, by which they are converted into the form of
dissolved bones or superphosphate. At the present moment, however, very
little of the superphosphates sold in the market are made exclusively from
bones in their natural state, by far the larger portion being manufactured
from mineral phosphates, or from bones after destruction of their organic
matter, sometimes with the addition of small quantities of unburnt bones,
but more frequently of sulphate of ammonia, to yield the requisite quantity

of ammonia. These substances may therefore be best considered under the
head of mineral manures.

CHAPTER XI.
COMPOSITION AND PROPERTIES OF MINERAL
MANURES.

Mineral manure is a term which is now used with great laxity. In its strict
sense, it means manures which contain only, and owe their exclusive value
to the presence of, those substances which go to make up the inorganic part
or ash of plants. It has, however, been usually taken to include all saline
matters, and especially the compounds of ammonia and nitric acid, which
are indebted for their manurial effects to the nitrogen they contain; and thus
is so far incorrect. It would, however, be manifestly impossible to arrange
these compounds with any degree of accuracy among either animal or
vegetable manures, and hence the necessity of including them amongst
those which are strictly mineral. The most important practical distinction
between them and the substances discussed in the two preceding chapters
is, that the latter generally contain the whole or the greater part of the
constituents of plants. Even bones yield a certain quantity of alkalies,
magnesia, sulphuric acid, and chlorine, and may in some sense be
considered as a general manure. But those to which the term mineral
manure is applied for the most part contain only one or two of the essential
elements of plants, and hence cannot be applied as substitutes for the
substances already discussed, although they are frequently most important
additions to them.
Sulphate and Muriate of Ammonia.—These and other salts of ammonia
have been tried experimentally as manures, and it has been ascertained that
they may all be used with equal success; but as the sulphate is by much
cheaper, it is that which probably will always be employed to the exclusion
of every other. It contains, when pure, 25·7 per cent ammonia.
It is now manufactured of excellent quality for agricultural use, and when
good, contains from 95 to 97 per cent of actual sulphate, the remainder
consisting chiefly of moisture and a small quantity of fixed residue; but
specimens are occasionally met with containing as much as 10 per cent of

impurities, which, as its price is high, makes a material difference in its
value. Inferior descriptions are also occasionally sold, among which is a
variety distinguished by containing a large quantity of water and fixed salts,
although it appears to the eye a good article. Its composition is—

I. II.
Water 9·05 5·77
Sulphate of ammonia 79·63 85·21
Fixed salts 11·17 9·02
——————
100·00 100·00
Ammonia 20·55 21·94

An article called sulphomuriate of ammonia is also sold for agricultural use.
It is obtained as a refuse product in the manufacture of magnesia, and is a
mixture of sulphate and muriate of ammonia, with various alkaline salts. It
differs somewhat in quality, and is sold by analysis at a price dependent on
the ammonia it contains.

I. II.
Water 14·49 25·39
Sulphate of ammonia 62·55 47·79
Muriate of ammonia 15·3 ...
Sulphate of soda ... 9·12
Sulphate of magnesia ... 18·38
Chloride of potassium 4·75 2·94
Chloride of sodium 17·35 0·35
——————
100·00 100·00
Ammonia 16·50 11·28

The quality of sulphate of ammonia may generally be judged of from its dry
and uniformly crystalline appearance, and it may be tested by heating a
small quantity on a shovel over a clear fire, when it ought to volatilize
completely, or leave only a trifling residue. Some care, however, is
necessary in applying this test, as in the hands of inexperienced persons it is

sometimes fallacious. The salts of ammonia may be applied in the same
way as guano; but they are most advantageously employed as a top-
dressing, and principally to grass lands. In this way very remarkable effects
are produced, and within a week after the application, the difference
between the dressed and undressed portions of a field is already
conspicuous. Experience has shewn that success is best insured when the
salt is applied during or immediately before rain, so that it may be at once
incorporated with the soil; as when used in dry weather little or no benefit is
derived from it. It seems also to exert a peculiarly beneficial effect upon
clover; and hence it ought to be employed only on clover-hay, as where
ryegrass or other grasses form the whole of the crop we have better
manures.
Ammoniacal Liquor of the Gas-Works, and of the Animal Charcoal
Manufacturers.—Both of these are excellent forms in which to apply
ammonia, when they can be obtained. The ammoniacal liquor of the gas-
works is very variable in quality, but contains generally from 4 to 8 ounces
of dry ammonia per gallon, which corresponds in round numbers to from 1
to 2 lb. of sulphate of ammonia. It is best applied with the watering-cart, but
must be diluted before use with three or four times its bulk of water, as if
concentrated it burns up the grass, and it is also advisable to use it during
wet weather. The ammoniacal liquor of the ivory-black works contains
about 12 per cent of ammonia, or about four or five times as much as gas
liquor. It has been used in some parts of England, made into a compost, and
applied to the turnip and other crops, and, it is said, with good effect. Bone
oil, which distils over along with it, has also been used in the form of a
compost; it contains a large quantity of ammonia and of nitrogen in other
forms of combination; the total quantity of nitrogen it contains being 9·04
per cent, which is equivalent to 10·98 of ammonia. Only part of this
nitrogen is actually in the state of ammonia; and some circumstances
connected with the chemical relations of the other nitrogenous compounds
in this substance render it probable that they may pass very slowly into
ammonia, and may therefore be of inferior value; but the substance
deserves a trial, as it is very cheap. It must be carefully composted with
peat, and turned over several times before being used.
Nitrates of Potash and Soda.—Nitrate of potash has long been used as a
manure, but its high price has prevented its general application, and its

place has now been almost entirely taken by nitrate of soda, which is much
cheaper and contains weight for weight a larger quantity of nitrogen. Both
these salts are employed as sources of nitrogen; but nitrate of potash owes
also a certain proportion of its value to the potash it contains. Nitrate of
soda, on the other hand, must be considered to owe its entire value to its
nitric acid, as soda is of little value to the plant; and, moreover, can be
obtained in common salt at a price so low, as to make it a matter of no
moment in the valuation of the nitrate. In its ordinary state, as imported
from Peru, nitrate of soda contains from 5 to 10 per cent of impurities, and
it bears a price proportionate to the quantity of the pure salt present in it.
When of good quality it contains about 15 per cent of nitrogen, equivalent
to 18 of ammonia, and is, therefore, richer in that constituent of plants than
Peruvian guano. It is essentially a rapidly acting manure, and produces a
marked effect within a very few days after its application; but owing to the
fact that nitric acid cannot be absorbed and retained by the soil in the same
manner as ammonia, it is liable to be lost unless it can be at once
assimilated by the plant. For this reason it acts best when applied in small
quantity as a top-dressing to grass-land, and to young corn. A large
application has no advantages, and there can be no doubt that the best effect
would be produced by several very small quantities, applied at intervals. In
one experiment, Mr. Pusey found 42 lb. per acre to increase the produce of
barley by 7 bushels, and very favourable results have been obtained by
other experimenters. The beneficial effects of nitrate of soda appear to be
almost entirely confined to the grasses and cereals. At least experience here
has shewn that it produces little or no effect on clover; and one farmer has
stated, that having recently adopted the practice of sowing clover with a
very small proportion of ryegrass only, he has been led to abandon the use
of nitrate of soda, which he formerly employed abundantly, when ryegrass
formed a principal part of his crop. The action of nitrate of soda is very
remarkable, not only in this respect, but also because a given quantity of
nitrogen in it appears to produce a greater effect than the same quantity in
sulphate of ammonia or guano. At the same time this statement must be
taken as very general, definite experiments being still too few to admit of its
being stated as an absolute fact. The probability is, that the same quantity of
nitrogen, in the form either of ammonia or nitrate of soda, will produce the
same effect, although the conditions necessary for its successful action may
not be the same with the two manures. It is alleged that nitrate of soda is

advantageously conjoined with common salt, which is said to check its
tendency to make the grain crops run to straw, and to prevent their lodging,
as they are apt to do, when it is employed alone. But considerable
difference of opinion exists in this point, many farmers believing that salt
produces no effect. When employed for hay, especially when mixed with
clover, it is advisable to use it along with an equal quantity of sulphate of
ammonia, which gives a better result than either separately.
Salts of Potash and Soda.—The substances just mentioned must be
considered to owe their chief manurial value to nitric acid; but other salts
have been used as manures in which the effect is undoubtedly due to the
alkalies themselves. With the exception of common salt, most of the
alkaline salts have only been used to a limited extent; and it is remarkable
that, so far as our present experience goes, there is no class of substances
from which more uncertain results are obtained.
Muriate and Sulphate of Potash have both been used, and the former has in
some cases, and in particular seasons, produced a very remarkable effect in
the potato; but in other instances it has proved quite useless. The cause of
this difference has not been ascertained. Sulphate of soda has also been
used to some extent, but apparently without much benefit; and there is no
reason to expect that it should act better than common salt, which can be
obtained at a much lower price.
Chloride of Sodium, or Common Salt, has at different times been employed
as a manure, but its effects are so variable and uncertain, that its use, in
place of increasing, has of late years rather diminished, it having frequently
been found that on soils in all respects similar, or even on the same soil, in
different years, it sometimes proves advantageous, at others positively
injurious. Its use as an addition to nitrate of soda has been already alluded
to, and it is said that it produces the same effect when mixed with guano
and salts of ammonia. The accuracy of this statement is doubted by many
persons, and the explanation which has been given of the cause of its action
is more than dubious. It is supposed to enable the plant to absorb more
silica from the soil; but this is a speculative explanation of its action, and
has not been supported by definite experiment. Although little effect has
been observed from salt, it deserves a more accurate investigation, as not

withstanding the extent to which it has been employed, we are singularly
deficient in definite experiments with it.
Carbonates of Potash and Soda have only been tried experimentally, and
that to a small extent, nor is it likely that they will ever come into use,
owing to their high price. The remarks we have made in the section on the
ashes of plants regarding the subordinate value of soda, will enable the
reader to see that greater effects are to be anticipated from the former than
from the latter of these salts. They may, however, exert a chemical action on
the soil, altogether independent of their absorption by the plant, but its
nature and amount are still to determine.
Silicates of Potash and Soda have been employed with the view of
supplying silica to the plant, but the results have been far from satisfactory.
This may perhaps have been due to the doubtful nature of the commercial
article, but now that silicate of soda can be obtained of good quality, it is
desirable that the experiments should be repeated. It is said to have
produced good effects on the potato.
Sulphate of Magnesia can be obtained at a low cost, and has been used as a
manure in some instances with very marked success. It has been chiefly
applied as a top-dressing to clover hay, but it seems probable that it might
prove a useful application to the cereals, the ash of which is peculiarly rich
in magnesia.
Many other saline substances have been tried as manures; but in most
instances on too limited a scale to permit any definite conclusions as to their
value. The experiments have also been too frequently performed without
the precautions necessary to exclude fallacy, so that the results already
arrived at must not be accepted as established facts, but rather as indications
of the direction in which further investigation would be valuable. There is
little doubt that many of these substances might be usefully employed, if the
conditions necessary for their successful application were eliminated; and
no subject is at present more deserving of elucidation by careful and well-
devised field experiments.
Phosphate of Lime.—The use of bones in their natural state as a manure has
been already adverted to, and it was stated, that though their value
depended mainly on the phosphates, the animal matters and other

substances contained in them were not without effect. The action of
phosphates is greatly promoted by solution in sulphuric acid, and the
application of the acid has brought into use many varieties of phosphates of
purely mineral origin, or which have been deprived of their organic matters
by artificial processes. Of these, the spent animal charcoal of the sugar-
refiners, usually containing about 70 per cent of phosphates, and South
American bone ash, are the most important. The latter is now imported in
very large quantity, and has the composition shewn in the following
analyses:—

I. II. III.
Water 6·10 6·28 3·03
Charcoal 5·05 2·19 2·02
Phosphates 79·20 71·10 88·55
Carbonate of lime 4·05 3·55 5·60
Alkaline salts 0·15 traces ...
Sand 5·45 16·90 0·80
—————————
100·00 100·00 100·00

Bone ash has hitherto been almost entirely consumed as a raw material for
the manufacture of superphosphates; but as it is sold at from £4: 10s. to £5:
10s. per ton when containing 70 per cent of phosphates, it is, in reality, a
very cheap source of these substances, and merits the attention of the farmer
as an application in its ordinary state.
Of strictly mineral phosphates, a considerable variety is now in use, but
they are employed exclusively in the manufacture of superphosphates, as in
their natural state they are so hard and insoluble, that the plant is incapable
of availing itself of them.
Coprolites.—This name was originally applied by Dr. Buckland to
substances found in many geological strata, and which he believed to be the
dung of fossil animals. It has since been given to phosphatic concretions
found chiefly in the greensand in Suffolk and Cambridgeshire, which are
certainly not the same as those described by Dr. Buckland, but consist of
fragments of bones, ammonites, and other fossils. Coprolites are now

collected in very large quantities, and about 43,000 tons are annually
employed. They are extremely hard, and require powerful machinery to
reduce them to powder, and hence their price is considerable, being about
£2: 10s. per ton. Their composition varies somewhat according to the care
taken in selecting them, and the locality from which they have been
obtained. A general idea of their composition may be derived from the
subjoined analyses:—

Water 1·95 1·90
Organic matter 2·59 6·85
Phosphate of lime 55·21} 61·15
Phosphate of iron 3·84}
Carbonate of lime 26·70 16·20
Sulphate of lime 1·97 "
Alkaline salts 1·85 3·21
Sand 5·89 11·65
——————
100·00 100·00

Within the last two or three years, coprolites have been found in great
abundance in France, but they are of inferior quality, and rarely contain
more than 40 per cent of phosphates.
Apatite, or mineral phosphate of lime, is found in large deposits in different
places. It is particularly abundant in Spain, and occurs also in America and
Norway. From the latter country it has been imported to some extent; and
during the last year considerable quantities have been brought from Spain,
and the importations will undoubtedly increase very largely as the means of
transport improve in that country. Spanish apatite contains—

Water 0·80
Phosphate of lime 93·30
Carbonate of lime 0·50
Chlorine, etc. traces
Sand 4·70
———

99·30

Several other varieties of mineral phosphates have been imported under the
name of guano. The most important is Sombrero Island guano, which is
found on a small island in the Gulf of Mexico, where it occurs in a layer
said to be forty feet thick. It contains—

Water 8·96
Phosphate of lime 37·71
Phosphates of alumina and iron 44·21
Phosphate of magnesia 4·20
Sulphate of lime 0·86
Carbonate of lime 3·36
Sand 0·70
———
100·00

A somewhat similar substance, but in hard crusts, has been imported, under
the names of Maracaybo guano, Pyroguanite, etc., which contains—

Water 1·03
Organic matter 6·78
Phosphates 75·69
Alkaline salts 4·91
Sand 11·64
———
100·00
Phosphoric acid in the alkaline salts = 1·68 phosphate of lime 0·78

These substances are all excellent sources of phosphates, but they are so
hard that the plants cannot extract phosphoric acid from them, and they are
only useful when made soluble by chemical processes.
Superphosphate; Dissolved Bones.—These names were at first applied to
bones which had been treated with sulphuric acid; but superphosphates are
now rarely made from bones alone, but bone ash and some of the mineral
phosphates just described are employed, either along with them, or very

frequently alone. The manufacture of superphosphates depends on the
existence of two different compounds of phosphoric acid and lime, one of
which contains three times as much lime as the other. That which contains
the larger quantity of lime is found in the bones and all other natural
phosphates, and is quite insoluble in water; but when two-thirds of its lime
are removed, it is converted into the other compound, which is exceedingly
soluble. This change is effected by the use of sulphuric acid, which
combines with two-thirds of the lime of the ordinary insoluble phosphate of
lime, and converts it into the biphosphate of lime, which is soluble. When,
therefore, we add to 100 lbs. of common phosphate of lime the necessary
quantity of sulphuric acid, it yields 64 lbs. of biphosphate, containing the
whole of the phosphoric acid, which is the valuable constituent, the
diminution in weight being due to the removal of the valueless lime. Hence
it follows, also, that as the lime so removed is converted into sulphate, there
must, for every 100 lbs. of phosphate of lime converted into biphosphate, be
produced 87 lbs. of dry sulphate of lime, or 110 of the ordinary sulphate
called gypsum. This is the minimum quantity which can be present, but in
actual practice it is liable to be greatly exceeded, more especially where
coprolites are used, owing to the large amount of carbonate of lime they
contain, which is also converted into sulphate by the action of the acid, so
that it is far from uncommon to find the gypsum twice as great as it would
be if materials free from carbonates could be obtained. By employing a
sufficiency of sulphuric acid, the whole quantity of phosphoric acid in the
bones may be thus brought into a soluble state, but in actual practice it is
found preferable to leave part of it in the insoluble condition; as where it is
entirely soluble, its effect is too great during the early part of the season,
and deficient at its end. In order to dissolve bones, bone ash, or mineral
phosphates, they are mixed with from a third to half their weight of
sulphuric acid, of specific gravity 1·70 or 140° Twaddell. When mineral
phosphates, and particularly coprolites, are used, the quantity of sulphuric
acid must be increased so as to compensate for the loss of that which is
consumed in decomposing the carbonate of lime they contain. When
operating on the small scale, the materials are put into a vessel of wood,
stone, or lead (iron is to be avoided, as it is rapidly corroded by the acid),
and mixed with from a sixth to a fourth of their weight of water, which may
with advantage be used hot. The sulphuric acid is then added, and mixed as
uniformly as possible with the bones. Considerable effervescence takes

place, and the mass becomes extremely hot. At the end of two or three days
it is turned over with the spade, and after standing for some days longer,
generally becomes pretty dry. Should it still be too moist to be sown, it must
be again turned over, and mixed with some dry substance to absorb the
moisture. For this purpose everything containing lime or its carbonate must
be carefully avoided, as they bring back the phosphates into the insoluble
state, and undo what the sulphuric acid has done. Peat, saw-dust, sand,
decaying leaves, or similar substances, will answer the purpose, and they
should all be made thoroughly dry before being used. An excellent plan is
to sift the bones before dissolving, to apply the acid to the coarser part, and
afterwards to mix in the fine dust which has passed through the sieve, to dry
up the mass; or a small quantity of bone ash, of good quality, or Peruvian
guano, may be used. On the large scale, mechanical arrangements are
employed for mixing the materials, so as to economise labour, and mineral
phosphates, such as apatite, can then be used with advantage. In such cases,
blood, sulphate of ammonia, soot, and other refuse matters, are occasionally
used to supply the requisite quantity of nitrogenous substances, but large
quantities are also made from bone ash, etc., without these additions.
The composition of superphosphates must necessarily vary to a great extent,
and depends not only on the materials, but on the proportion of acid used
for solution. The following analysis illustrates the composition of good
samples made from different substances—

Bones alone. Bone-Ash.
Water, 7·74 ... 7·79 5·33 ... 10·40
Organic matters and ammoniacal salts, 17·83 ... 21·69 6·94 ... 4·92
Biphosphate of lime 13·18 ... 9·87 21·35 ... 23·09
Equivalent to soluble phosphates, (20·57)...(15·39) (33·33)...(36·02)
Insoluble phosphates 10·31 ... 21·17 5·92 ... 6·08
Sulphate of lime, 46·00 ... 35·30 56·16 ... 47·78
Alkaline salts, 1·46 ... 0·94 trace.
Sand, 3·48 ... 3·00 4·23 ... 4·30
100·00 ...100·00 100·00 ...100·00
Ammonia, 2·11 ... 3·01 0·23 ... 0·31

Chiefly Mixtures containing Salts of
Coprolites. Ammonia, etc.
Water, 5·90 ... 10·17 7·07 ... 15·82
Organic matters and
5·10 ... 4·13 9·87 ... 13·96
ammoniacal salts,
Biphosphate of lime 12·24 ... 13·75 17·63 ... 12·67
Equivalent to soluble (19·10)...
(27·50)...(19·77)
phosphates, (21·43)
Insoluble phosphates 16·90 ... 0·17 12·60 ... 8·40
Sulphate of lime, 52·39 ... 62·62 49·77 ... 45·14
Alkaline salts, 2·47 ... 0·96 0·06 ... 1·07
Sand, 6·00 ... 8·20 3·00 ... 2·94
100·00
100·00 ...100·00
...100·00
Ammonia, 0·11 ... 0·57 1·28 ... 1·55

Superphosphates made from bones alone are generally distinguished by a
large quantity of ammonia, and a rather low per centage of biphosphate of
lime. This is owing to the difficulty experienced in making the acid react in
a satisfactory manner on bones, the phosphates being protected from its
action by the large quantity of animal matter which, when moistened, swells
up, fills the pores, and prevents the ready access of the acid to the interior of
the fragments. Superphosphates from bone-ash, on the other hand, contain a
mere trifle of ammonia, and when well made a very large quantity of
biphosphate of lime. Their quality differs very greatly, and depends, of
course, on that of the bone-ash employed, which can rarely be obtained of
quality sufficient to yield more than 30 or 35 per cent of soluble phosphates.
Coprolites are seldom used alone for the manufacture of superphosphates,
but are generally mixed with bone-ash and bone dust. Mixtures containing
salts of ammonia, flesh, blood, etc., are also largely manufactured, and
some are now produced containing as much as four or five per cent of
ammonia, and the consumption of such articles is largely increasing.

The analyses above given are all those of good superphosphates, in which
abundance of acid has been used so as to convert a large proportion of
insoluble into soluble phosphates; but there are many samples of very
inferior quality to be met with in the market, in which the proportion of acid
has been reduced, and the quantity of phosphates made soluble is
consequently much lower than it ought to be. The following analyses
illustrate the composition of such manures, which are all very inferior and
generally worth much less than the price asked for them.

Water 21·60 5·37 7·19
Organic matter and ammoniacal salts, 11·62 13·91 8·80
Biphosphate of lime 2·98 2·02 6·42
Equivalent to soluble phosphates (4·65) (3·15) (10·02)
Insoluble phosphates 25·70 15·80 14·03
Sulphate of lime 23·66 47·52 51·93
Alkaline salts 10·70 3·73 3·43
Sand 3·80 11·65 8·20
—————— ———
100·00 100·00 100·00
Ammonia, 1·32 0·59 0·33

The deliberate adulteration of superphosphate, that is, the addition to it of
sand or similar worthless materials, I believe to be but little practised. The
most common fraud consists in selling as pure dissolved bones, articles
made in part, and sometimes almost entirely, from coprolites. Occasionally
refuse matters are used, but less with the intention of actually diminishing
the value of the manure as for the purpose of acting as driers. It is said that
sulphate of lime is sometimes employed for this purpose, but this is rarely
done, because that substance is always a necessary constituent of
superphosphate in very large quantities; and as farmers look upon it with
great suspicion, all the efforts of the manufacturers are directed towards
reducing its quantity as much as possible. It is very commonly supposed by
farmers that the sulphate of lime found in so large quantity in all
superphosphates, and often amounting to as much as fifty per cent, has been
added to the materials in the process of manufacture, but this is a mistake; it
is a necessary and inevitable product of the chemical action by which the

phosphates are rendered soluble, although its quantity depends on the
materials from which the manure is made. When pure bones are used its
quantity is small, and it does not greatly exceed twice that of the
biphosphate of lime; but in a manure made from coprolites, or other
substances containing a large proportion of carbonate of lime, which must
in the process of manufacture be converted into sulphate, it may be four or
five times as much.
Although there is no manure which varies more in quality, or requires
greater vigilance on the part of the purchaser, in order to obtain a good
article, there is no doubt that superphosphates, owing to the process of
manufacture being better understood, and to increased competition, have
considerably improved in quality. Six or eight years since a manure
containing thirty per cent of phosphates, of which twelve or fifteen had
been converted into biphosphate, was considered a fair sample, but now the
proportion rendered soluble is greatly increased; and where bone ash alone
is employed, as much as thirty and even forty per cent of soluble
phosphates is occasionally found. This, of course, is an exceptional case,
and great attention and care in the selection of materials are necessary to
obtain so large a proportion. The analyses already given will shew the
farmer what he has to expect in good superphosphates, but it is very
necessary that he should take care to obtain from the manufacturer a
manure equal to the guarantee; and he ought to bear in mind that, owing to
the difficulty of getting materials of constant composition, variations often
take place to a considerable extent in manures which are supposed to be
made in exactly the same manner.
Phospho-Peruvian Guano.—Under this name a kind of superphosphate,
which is understood to be made by dissolving a native "rock guano," has
recently attracted considerable attention, and is used to a large extent. Its
composition is—

Water 9·54
Organic matter 21·38
Biphosphate of lime, equivalent to 25·22 soluble phosphates 16·81
Insoluble phosphates 10·88
Sulphate of lime 37·21

Alkaline salts, containing 1·32 of phosphoric acid, and equivalent
2·22
to 2·86 soluble phosphates
Sand 1·81
———
100·00
Ammonia, 3·50

It is chiefly distinguished by the large proportion of valuable ingredients it
contains, and the care taken to secure uniformity of composition.
A variety of substances are sold under the name of nitrophosphate, potato
manure, cereal manure, etc. etc., which are all superphosphates, differing
only in the proportion of their ingredients, and in the addition of small
quantities of alkaline salts, sulphate of magnesia, and other substances, but
they present little difference from ordinary superphosphates in their effects.
The use of superphosphate has greatly extended of late years, and its
consumption has increased in a greatly more rapid ratio than that of guano
or any other manure. Ten or twelve years since it was comparatively little
known, but it has now come to be used in many cases in which Peruvian
guano was formerly employed. It produces a better effect than that manure
on light soils, although in general a mixture of the two answers better than
either separately. When Peruvian guano is to be applied along with it, the
farmer will naturally select a superphosphate made from bone ash, and
containing the largest obtainable quantity of soluble phosphates; but when it
is to be used alone, it is advisable to take one made from bones, or at all
events one containing a considerable quantity of nitrogenous matter or
ammonia. The kind to be selected must, however, be greatly dependent on
the particular soil, and the situation in which it is to be used.
Lime.—Lime is by far the most important of the mineral manures, and an
almost indispensable agent of agricultural improvement. It has been used as
chalk, marl, shell and coral sand, ground limestone, and as quick and slaked
lime, and its action varies according as it is applied in any of its natural
forms, or after being burnt. In all of its native forms the lime is combined
with carbonic acid in the proportion of fifty-six parts of lime to forty-four of
carbonic acid, and the carbonate is generally mixed with variable quantities

of earthy ingredients, which in some instances are important additions to it,
and affect its utility as a manure.
Chalk is a very pure form of carbonate of lime, and where it abounds has
been largely employed as an application on the soil. It is dug out of pits and
exposed to the action of the winter's frost, by which it is thoroughly
disintegrated, and in spring it is applied in quantities, which, in many
instances, are only limited by the question of cost.
Marl is a name given to a mixture of finely-divided carbonate of lime, with
variable proportions of clay and siliceous matters, which is found at the
bottom of valleys and in hollow places in beds often of considerable extent
and thickness, where it is deposited from the waters of lakes holding lime in
solution, fed by streams passing over limestone, or rocks rich in lime. The
composition of marls differs greatly in different districts, and they have
been divided into true marls, and clay marls, according as the carbonate of
lime or clay is the preponderating ingredient. The following table illustrates
the composition of different varieties:—

Barbadoes. Luneburg. Ayrshire. Wesermarsh.
Carbonate of lime 93·2 85·4 8·4 8·2
Carbonate of magnesia ... 1·3 ... 3·0
Sulphate of lime ... 0·1 ... 0·5
Phosphate of lime 0·1 2·3 ... 1·2
Alumina and oxide of iron 1·6 4·6 2·2 7·2
Alkaline salts ... 0·1 ... 1·0
Silica and clay 4·6 5·6 84·9 78·9
Organic matter 0·5 0·6 2·8 ...
Water ... ... 1·4 ...
100·00 100·00 99·7 100·00

The true marls, that is those in which carbonate of lime abounds, are greatly
preferable to clay marls, the latter, indeed, operate chiefly mechanically, by
altering the texture of the soil—the lime they contain being frequently too
small to exercise much appreciable effect.
Shell and coral sands consist chiefly of fragments of shells and coral
disintegrated by the action of the waves, and mixed with more or less

siliceous sand, and containing small quantities of phosphate of lime. They
occur to a considerable extent both on our own coasts and those of France,
and have been used with good effect on some descriptions of soil.
The general composition of limestones has been already adverted to, when
treating of the origin of soils, and a distinction drawn between the common
limestones and dolomite or magnesium limestone. Few limestones can be
considered as even approaching to purity, and they almost all contain a
small quantity of carbonate of magnesia as well as earthy matters, and
occasionally a little phosphate of lime. In good specimens the quantities of
these substances are generally small, and they usually contain about half
their weight of lime. When limestone is burnt in the kiln, the change which
ensues consists in the expulsion of the carbonic acid, and the consequent
conversion of the lime into the uncombined or quick state. If water be
thrown upon it when in this condition, it becomes hot, swells up, and falls
to a fine soft powder, and has then entered into combination with water. If it
be exposed to the air, the same action takes place, although, of course, more
slowly; and if it be left for a sufficient time, it at length absorbs carbonic
acid, and reverts to its original form of carbonate of lime, although now in a
state of very fine division.
While lime may be applied in the state of carbonate, either as chalk, marl,
or pounded limestone, and with a certain amount of advantage, much
greater effects are obtained from the use of lime itself in the quick or slaked
state. These advantages are dependent partly on the mechanical effect of the
burning and slaking, which enable us to reduce the lime to a much more
minute state of division, and consequently to incorporate it more uniformly
and thoroughly with the soil, and partly on the more powerful chemical
action which it exists when in the quick or caustic state. Other minor
advantages are also secured, such as the production of a certain quantity of
sulphate of lime, produced by the oxidation of the sulphur of the coal used
in burning, etc., which, though comparatively trifling, may, under particular
circumstances and in some soils, be of considerable importance.
The action of lime is of a complicated character. Where the soil is deficient
in lime, it must necessarily act by supplying that substance to the plants
growing in it. But this is manifestly a very subordinate part of its action,—
1st, Because no soil exists which does not contain lime in sufficient

quantity to supply that element to the plants. 2d, Because its effects are not
restricted to those soils in which it exists naturally in small quantity; and,
3d, Because it is found that a small application, such as would suffice for
the wants of the crops, is not sufficient to produce its best effects.
It is a familiar fact that the quantity of lime applied to the soil for
agricultural purposes is very large, as much as ten, and even twenty tons per
acre having been used, while the smallest application is exceedingly large
when compared with the mere requirements of the crops. Of late years the
very large applications once in use have become less common, as it has
been found preferable to employ smaller doses more frequently repeated.
The quantity used depends, however, to a great extent, on the nature and
condition of the soil, heavy clays, especially if undrained, and soils of a
peaty nature, requiring a large application; while on well drained and light
soils a smaller quantity suffices. Thin soils also require only a small
application. The geological origin of the soil is also not without its
influence, and its beneficial effect is peculiarly seen on granite, porphyry,
and gneiss soils, both because these are naturally deficient in lime, and
because the decompositions by which their valuable constituents are
liberated take place with extreme slowness.
The greater part of the action of lime is unquestionably dependent on its
exerting a chemical decomposition on the soil; and it acts equally on both
the great divisions of its constituents, the inorganic and the organic. On the
former, it operates by decomposing the silicates, which form the main part
of the soil, and the alkalies they contain being thus set free, a larger supply
becomes available to the plant. On the organic constituents its effects are
principally expended in promoting the decomposition which converts their
nitrogen into ammonia; and thus a supply of food, which might remain for a
long period locked up, is set free in a state in which the plant can at once
absorb it. But these chemical decompositions are attended by a
corresponding change in the mechanical characters of the soil. Heavy clays
are observed to become lighter and more open in their texture; and those
which are too rich in organic matter have it rapidly reduced in quantity, and
the excessive lightness which it occasions diminished.
The effects of an application of lime are not generally observed
immediately, but become apparent in the course of one or two years, when

it has had time to exert its chemical influence on the soil; but from that time
its effects are seen gradually to diminish and finally to cease entirely. The
period within which this occurs necessarily varies with the amount of the
application and the nature of the soil, but it may be said generally that lime
will last from ten to fifteen years. The cessation of its effects is due to
several circumstances, partly of course to the absorption of lime by the
plants, partly to its being washed out of the soil by the rains, and partly to
its tendency to sink to a lower level, a tendency which most practical men
have had opportunities of observing. In the latter case, deep-ploughing
often produces a marked effect, and sometimes makes it possible to
postpone for a year or two the reapplication of lime. All these circumstances
have their influence in bringing its action to an end, but the most important
is, that after a time it has exhausted its decomposing effect on the soil,
having destroyed all the organic matter, or liberated all the insoluble
mineral substances which the quantity added is competent to do, and so the
soil passes back to its old state. It does even more, for unless active
measures are taken to sustain it by other means, it is found that the fertility
of the soil is apt to become less than it was before the use of lime. And that
it should be so is manifest, if we consider that the lime added has liberated a
quantity of inorganic matter, which, in the natural state of the soil, would
have become slowly available to the plant, and that it must have acted
chiefly in those very portions which, from having already undergone a
partial decomposition, were ready to pass into a state fitted for absorption,
and thus as it were must have anticipated the supplies of future years. This
effect has been frequently observed by farmers, and is indeed so common,
that it has passed into a proverbial saying, that "lime enriches the fathers
and impoverishes the sons." But this is true only when the soil is stinted of
other manures, for when it is well manured the exhausting effect of lime is
not observed; and it must be laid down as a practical rule, that its use
necessitates a liberal treatment of the soil in all other respects. But when
lime has been once employed it becomes almost necessary to resort to it
again; and generally so soon as its effects are exhausted a new quantity is
applied, not so large as that which is used when the soil is first limed, but
still considerable. When this is done very frequently, however, bad effects
ensue; the soil gets into a particular state, in which it is so open that the
grain crops become uncertain, and such land is said, in practical language,
to be overlimed. The explanation of this state of matters commonly

assumed by those unacquainted with chemistry is, that the land has become
too full of lime; but a moment's consideration of the very small fraction of
the soil which even the largest application of lime forms, will serve to shew
that this cannot be the cause. Ten tons of lime per acre amounts to only one
per cent of the soil, and as a considerable part of the lime is carried off by
drainage in the course of years, it is obvious that even very large and
frequently repeated doses are not likely to produce any great accumulation
of that substance. In point of fact, analyses of overlimed soils have proved
that the lime does not exceed the ordinary quantity found in fertile land. The
explanation of the phenomenon is probably to be found in the rapid
decomposition of organic matter by the lime, and its escape as carbonic
acid, by which the soil is left in that curious porous condition so well
known in practice. The cure for overliming is found to be the employment
of such means as consolidate the soil, such as eating off with sheep, rolling,
or laying down to permanent pasture.
The immediate effect of lime on the vegetation of the land to which it is
applied is very striking. It immediately destroys all sorts of moss, makes a
tender herbage spring up, and eradicates a number of weeds. It improves the
quantity and quality of most crops, and causes them to arrive more rapidly
at maturity. The extent to which it produces these effects is dependent on
the form in which it is applied. When the lime is used hot, that is,
immediately after it has been slaked, they are produced most rapidly and
effectually; but if it has been so long exposed to the air as to absorb much of
the carbonic acid it lost in burning, and has got into what is commonly
called the mild state, it operates more slowly; and when it is applied as
chalk, marl, or pounded limestone, its action is still more tardy. Various
circumstances, which must depend upon very different considerations, must
necessarily influence the farmer in the selection of one or other of these
different forms of lime; but on the whole, it will be found that the greatest
advantages are on the side of the well-burned and freshly slaked lime. The
consideration of all the minutiæ to be attended to, however, would carry us
far beyond the limits of this work, and trench to some extent on the subject
of practical agriculture.
Various kinds of refuse matters containing lime have been used in
agriculture, but they are generally inferior to good lime, and not generally
more economical. The most important of these is gas lime, or lime which

has been used for purifying coal gas. In going through this process it
absorbs carbonic acid from the gas, and consequently passes back, more or
less, completely into the form of carbonate of lime. But it also takes up
sulphur, which remains in it in the form of sulphuret of calcium. It is well
known that all sulphurets are prejudicial to vegetable life, and hence, when
fresh gas lime is used, its effects are often injurious rather than beneficial.
But if it be exposed for some time to the air, oxygen is absorbed, the
sulphur is converted into sulphuric acid, gypsum is produced to the extent
of some per cent, and the lime then becomes innocuous. When composted
with dry soil, the admission of air into the interior of the lime is facilitated,
and this change takes place with greater rapidity. The waste lime from
bleach-works, tanneries, and other manufactories, is occasionally used by
farmers; but unless obtained at a nominal price, it cannot compete with
good quick lime, owing to the large amount of water it contains, and the
consequent increase in the cost of carriage.
Sulphate of Lime or Gypsum.—Gypsum has been extensively used as a
manure, and is found to exert a very remarkable influence upon clover, and
leguminous crops generally. It is employed in quantities varying from two
cwt. per acre up to a very large quantity, and almost invariably with good
results, in some instances even with the production of double crops. Much
speculation has taken place as to the cause of this action which is so
specific in its character, and from Sir Humphrey Davy down to the present
time, many chemists and agriculturists have considered the matter. Sir
Humphrey Davy attributed its action to its supplying sulphur to those plants
which, according to him, contain an unusually large quantity of that
element. That opinion has been since entertained by others, but it can
scarcely be considered as well founded, for the more accurate experiments
recently made do not point to any conspicuous differences between the
quantities of sulphur contained in these and other plants. It is, moreover, to
gypsum alone that these effects are due, and if it were merely as a source of
sulphur that it was employed, there are other salts which could be equally,
perhaps more advantageously, used; such, for instance, as sulphate of soda.
Others have attributed its action to its power of fixing ammonia, but this
explanation is certainly untenable, for the soil itself possesses this property
very powerfully, and it is inconceivable that the addition of a few hundred
weights of gypsum should have any effect in promoting this action. The

experiments which have been made with gypsum leave no doubt as to its
effect, more especially on leguminous plants, but they do not afford an
explanation of its mode of action, for which further inquiries, directed
especially to that object, are required.
The application of gypsum to the soil appears to have diminished of late
years, and this is probably due to the large consumption of superphosphates,
and other manufactured manures, which contain it in abundance. In an
ordinary application of these substances, there are contained from one to
two hundredweight of gypsum; and it is not likely that when they have been
extensively used, much benefit will be derived from a further application of
it by itself.

CHAPTER XII.
THE VALUATION OF MANURES.

The determination of the value of a manure is in many respects a
commercial rather than a chemical question, but as it must be founded on
the analysis, and presents some peculiarities dependent on the complicated
nature of the substances to be valued, it has fallen to some extent into the
hands of the chemist. The principle on which the value of any commercial
sample is estimated is very simple. It is only necessary to know the price of
the pure article, and that of the particular sample to be valued is obtained by
making a deduction from this price proportionate to the per centage of
impurities shewn by the analysis. Thus, for example, if pure sulphate of
ammonia sells at £16 per ton, a sample containing 10 per cent of impurities
ought to be purchased for £14: 8s., and so on for any other quantity. This
system which answers perfectly with sulphate of ammonia, nitrate of soda,
or any other substance whose value depends on one individual element, is
inapplicable in the case of complex manures, such as guano and the like, in
which several factors combine to make up the value. In such cases, manures
of very different composition may have the same value, the deficiency in
one particular element being counterbalanced by the excess of another.
Hence it becomes necessary to obtain an estimate of the value of each
factor, from which that not only of one particular substance, but of every
possible mixture may be determined.
When we come to inquire minutely into this question, it appears that the
commercial value of any substance is not estimated solely by considerations
of composition, but is dependent to a great extent on questions of demand
and supply, and applicability to particular purposes. Thus coprolites
containing from 55 to 60 per cent of phosphates sell at about £2: 12s. per
ton, while bone-ash containing the same quantity of that ingredient brings
about twice as much; in other words, phosphates are nearly twice as
valuable in bone-ash as in coprolites, and as a phosphatic guano their price
is generally still higher; and the reason for this is obvious, in bones and
guano the phosphates are in a high state of division, in which they are easily

attacked and disintegrated by the carbonic acid of the soil, and rendered
available to plants; while in coprolites they are in a hard and compact form,
and are of little use unless they have previously undergone an expensive
preparation. In the same way, if the market price of different kinds of guano
be inquired into, very great differences are found to exist in the rate at
which phosphates are sold, and this is attributable in part to the fact that the
price at which any article is charged commercially, is such as to cover the
prime cost, expense of freight, and other charges, and to leave a profit to the
importer; and partly, also, no doubt, to the carelessness with which manures
are often purchased, and to the want of careful field experiments in which
the effects produced by them are properly compared. It will be readily
understood that the state of division of any substance, the readiness with
which its constituents can be rendered available to the plants, care of
application, and many other circumstances must influence its price; but
making due allowance for these, differences are met with which appear to
some extent to be merely the result of caprice. It is easy to understand why
bone-ash should sell at double the price of coprolites, but no good reason
can be shewn why the phosphates in one kind of guano should be sold at a
much higher price than another, and the difference would probably
disappear if greater attention were paid to the results of field experiments.
However great and inexplicable these differences may be, it is not the
business of the valuator of a manure to discuss them. On the contrary, he is
bound to accept them as the basis of his calculation, and to endeavour to
deduce from them a proper system of estimation for each substance. Strictly
speaking, each individual manure ought to be valued according to a plan
special to itself, and deduced from its own standard market price; but it is
obvious that this would lead to innumerable complications and defeat its
own ends, and hence an attempt has been made to contrive a general system
suited to all manures, and which, though not absolutely correct, is a
sufficient approximation for all practical purposes, and a tolerably accurate
guide to the determination of their relative values.
The constituents of a manure which are of actual value are ammonia,
insoluble phosphates, biphosphate of lime (soluble phosphates), sulphate of
lime, nitric acid (as nitrate of soda), potash, soda, and organic matter. These
substances differ greatly in value. Ammonia and phosphates, soluble and
insoluble, are costly; and by far the larger part of the value of all guanos,

and the common manufactured manures, depends on them. Nitric acid and
potash are also very valuable substances, but as they are rarely found in
manufactured manures, and never in sufficient quantity to exert any
material influence in their price, it is not usual to take them into
consideration except in particular cases. The alkali which commonly exists
in artificial manures is soda, and when alkaline salts appear in any analysis,
they must be assumed to consist almost entirely of that substance generally
in the form of common salt, and be valued accordingly. Sulphate of lime
and organic matter though abundant constituents of most manures, add but
little to their value, and it is a moot point whether they ought to be taken
into consideration, although most persons allow a small value for them.
Carbonate of lime, sand, or siliceous matter, and water, of course, are
altogether worthless.
In order to obtain the value of a manure containing several of these
substances, it is necessary to ascertain the average commercial price of each
individually. This is easily done when they are met with in commerce
separately, or at least mixed only with worthless substances, but some of
them are only found in complex mixtures, and in these cases it is necessary
to arrive at a result by an indirect process, according to methods which will
be immediately explained. The question to be solved is the price actually
paid for a ton of each substance in a pure state, and we shall proceed to
consider them in succession.
Insoluble Phosphates.—These are purchased alone, chiefly in the form of
coprolites and bone-ash, or the spent animal charcoal of the sugar refiners.
Ground coprolites, containing about 58 per cent of phosphates, sell at £2:
12s. per ton, which is at the rate of £4: 8s. for pure phosphates. Bone-ash
varies considerably in price, but of late samples containing 70 per cent of
phosphates have sold as low as £4: 10s. per ton, and consequently pure
phosphates in this form are worth £6: 8s. per ton. Although these are the
only forms in which phosphates are purchased alone, it is possible to
determine the price at which they are sold in bones and phosphatic guanos,
by first deducting the value of the ammonia they contain, and assuming the
remainder to represent the price paid for the phosphates. In this way we find
the following values for insoluble phosphates:—

In Coprolites £4 10 0