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Title: Hygiene: a manual of personal and public health (New Edition)

Author: Sir Arthur Newsholme

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Language: English

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Obvious typographical errors have been silently corrected. Variations in hyphenation
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HYGIENE:
A MANUAL

OF

Personal and Public Health

BY
ARTHUR NEWSHOLME, M.D., F.R.C.P., Lond.,
UNIVERSITY SCHOLAR IN MEDICINE; DIPLOMATE IN PUBLIC HEALTH, UNIV. LOND.; MEDICAL
OFFICER OF HEALTH OF BRIGHTON; MEMBER OF THE COUNCIL AND EXAMINER TO THE
SANITARY INSTITUTE; EXAMINER IN STATE MEDICINE TO THE UNIVERSITY OF
LONDON; LATE EXAMINER IN PREVENTIVE MEDICINE TO THE UNIVERSITY OF
OXFORD, AND PRESIDENT OF THE INCORPORATED SOCIETY OF MEDICAL
OFFICERS OF HEALTH.

NEW EDITION, 1902. ILLUSTRATED.

LONDON:
Geo. Gill & Sons, Ld., Minerva House, Warwick Lane.

PREFACE.
The writing of a preface is perhaps superfluous for a book which has had
a large and steady sale for nearly twenty years, and which has evidently met
with the approval of a large constituency. A few words of introduction
appear, however, desirable in view of the facts that the present edition has
been almost entirely re-written; that a large amount of new matter has been
introduced; and that, so far as is known, the comments on each subject
represent the most recent and authoritative knowledge upon it.
An attempt has been made to meet the requirements of medical students,
as well as of science students and general readers, for whom former editions
were chiefly intended. A large class of medical students and practitioners do
not require the detailed statement of the subject contained in the larger text-
books. For them, and, it is hoped, also for a large number of candidates for
diplomas in public health and in sanitary science, the present edition will
prove to be useful. At the same time, the subject has been treated as non-
technically as is consistent with accuracy, in order to retain its suitability for
non-medical readers. A large number of new illustrations have been
introduced.
The new chapters dealing with Dietetics, Trade Nuisances,
Meteorological Observations, Tuberculosis, Disinfection, and Vital
Statistics will, it is believed, enhance the value of the book.
Attention is also drawn to the solutions of mathematical problems in the
different branches of hygiene, of which a table of contents is given on page
viii.
In its new form, it is hoped that this work will be found to have retained
its value as a plain and straightforward account of its subject for the general
public and for science students; and to have become a practical guide to
sanitary inspectors and to medical students, whether preparing for a
diploma in public health, or studying hygiene as an important branch of
medicine. The use of smaller type for specially technical matter of less
general interest will facilitate discriminative reading.

ARTHUR NEWSHOLME.
Brighton,
February 28th, 1902.

TABLE OF CONTENTS.
Chapter. PAGE
I. —Introductory 1
II. —Food 4
III. —The Varieties of Food 9
IV. —Diseases due to Food 23
V. —Diet 29
VI. —The Preparation and Preservation of Food 38
VII. —Condiments and Beverages 45
VIII. —Fermented Drinks 55
IX. —Water 65
X. —The Storage and Delivery of Water 74
XI. —Impurities of Water 78
XII. —Origin and Effects of the Impurities of Water 89
XIII. —The Purification of Water 94
XIV. —Composition and Properties of Air 100
XV. —Suspended Impurities of Air 105
XVI. —Gaseous and Other Impurities of Air 111
XVII. —Trade Nuisances 120
XVIII. —The Examination of Air 125
XIX. —The Purification of Air 129
XX. —General Principles of Ventilation 132
XXI. —Problems as to Ventilation 137
XXII. —Methods of Ventilation 146
XXIII. —Ventilation by the Introduction of Warmed Air 155
XXIV. —The Warming of Houses 158
XXV. —House Drainage 165
XXVI. —Cesspools and Main Sewers 183
XXVII. —Problems as to Flow in Sewers 187
XXVIII. —The Disposal of Sewage 190
XXIX. —Conservancy Methods 194
XXX. —Position of the House 201
XXXI. —The Materials used in the Construction of a House 205
XXXII. —Construction of the House 209
XXXIII. —The Soil 219
XXXIV. —Climate and Weather 227
XXXV. —Meteorological Observations 237
XXXVI. —Personal Hygiene 245
XXXVII. —Personal Hygiene—Exercise 249
XXXVIII. —Personal Hygiene—Rest and Sleep 257

XXXIX. —Personal Hygiene—Cleanliness 260
XL. —Clothing 265
XLI. —Parasites 273
XLII. —The Rôle of Insects in Spreading Disease 281
XLIII. —Infective Diseases 284
XLIV. —Acute Infective Diseases 291
XLV. —Tuberculosis 309
XLVI. —Notification and Isolation 317
XLVII. —Disinfection 324
XLVIII. —Vital Statistics 335

SPECIAL TABLE OF CONTENTS FOR ARITHMETICAL PROBLEMS
IN HYGIENE.
PAGE
Problems in Milk Analysis 12
Problems in Dietetics 35
Problems in Water Analysis 86
Problems in Air Analysis 126
Problems as to Ventilation 137
Problems as to Flow in Sewers 187
Problems in Meteorology 242
Problems as to Work 254
Problems in Vital Statistics 336

HYGIENE.

CHAPTER I.
INTRODUCTORY.
In classical mythology, Æsculapius was worshipped as the god of
Medicine, while his daughter Hygeia had homage done to her as the sweet
and smiling goddess of Health. The temples of these two deities were
always placed in close contiguity; and statues representing Hygeia were
often placed in the temple of Æsculapius. In these statues she is represented
as a beautiful maid, holding in her hand a bowl, from which a serpent is
drinking—the serpent typifying the art of medicine, then merely an art, now
establishing its right more and more to the dignity of a science.
That considerable attention was paid in very early times to matters
relating to health, is also shewn by the elaborate directions contained in the
Mosaic law as to extreme care in the choice of wholesome foods and
drinks, in isolation of the sick, and attention to personal and public
cleanliness. It is not surprising, therefore, to find that the Jews, throughout
the whole of their history, have apparently enjoyed a high standard of
health.
In this country great ignorance of the laws of Health has prior to the last
fifty years prevailed, and consequently preventible diseases have been
rampant, and have claimed innumerable victims. Each century has been
marked by great epidemics, which have swept through the country,
scattering disease and death in their course. In the fourteenth century, for
instance, there was the Black Death, a disease so fatal that it left scarcely
one-fourth part of the people alive; while Europe altogether is supposed to
have lost about 40 millions of its inhabitants, and China alone 13 millions.
A century and a half later came the Sweating Sickness (though there were a
score of minor epidemics in between). This was carried by Henry the
Seventh’s army throughout the country, and so great was the mortality, that
“if half the population in any town escaped, it was thought great favour.”
Considerable light is thrown on the rapid spread of this disease after its
importation, when we remember that there were no means of ventilation in
the houses; that the floors were covered with rushes which were constantly

put on fresh without removing the old, thus concealing a mass of filth and
exhaling a noisome vapour; while clothing was immoderately warm and
seldom changed; baths were very seldom indulged in, and soap hardly used.
In the sixteenth and seventeenth centuries there were five or six
epidemics of The Plague, and it was only eradicated from London, when all
the houses from Temple Bar to the Tower were burned down in the Great
Fire of September 2nd, 1666, which destroyed the insanitary and
necessitated the building of new and larger houses.
Scurvy, jail-fever, and small-pox, are other diseases which were formerly
frightfully prevalent. Jail-fever, the same disease as the modern typhus-
fever, has now become practically extinct in its former habitat, owing
largely to the noble work of John Howard, “whose life was finally brought
to an end by the fever, against the ravages of which his life had been
expended.” This disease was fostered by overcrowding, ill-ventilation, and
filth.
Scurvy formerly produced a very great mortality, especially among sea-
faring men. In Admiral Anson’s fleet in 1742, out of 961 men, 626 died in
nine months, or nearly two out of every three, and this was no solitary case.
Captain Cook, on the other hand, conducted an expedition round the world,
consisting of 118 men; and although absent over three years, only lost one
life. He was practically the first to demonstrate the potency of fresh
vegetables in preventing scurvy.
The striking facts respecting small-pox will be found on page 293. The
general death-rate has also greatly declined. Thus while the annual death-
rate in London 200 years ago was 80 per 1,000, it only averaged 18.8 in the
four years 1896-99; and the death-rate of England and Wales has declined
from 22.4 in 1841-50 to 18.7 per 1,000 in 1891-95 and 17.6 in 1896-99.
That much still remains to be done is evident on every hand. There is
little doubt that the general death-rate might be reduced to 15 per 1,000 per
annum, instead of the present 18, were the laws of health applied in every
household and community. It has been estimated that on the average at least
20 cases of sickness occur for every death; therefore nearly half of the
population is ill at least once a year. A simple calculation will show how
much loss the community annually suffers from this vast mass of

preventible sickness. It amounts to many millions of pounds, leaving out of
the reckoning the suffering and distress which are always associated with
sickness. For details relating to special diseases, see page 297.
In the prevention of this mass of sickness, the knowledge of its causation
is half the battle; when once a disease is traced to its source, as a rule, the
agency which produces it can be avoided.
The reason why even more progress has not been made in the prevention
of disease is not far to seek. In order to prevent a disease it is necessary to
remove its causes. The causes of disease can only be ascertained by a
careful investigation of its phenomena; and it is only within the last century
that these have been studied to any large extent scientifically. Such
knowledge of morbid processes not only results in improved measures of
treatment, but in more rational and complete measures of prevention. Thus,
not only is the number of diseases which are curable becoming gradually
augmented, but the number preventible is even more rapidly on the
increase.
Inasmuch as the preservation of health involves the prevention of disease,
Hygiene, the science of health, is sometimes called Preventive Medicine.
The subject of Hygiene naturally divides itself into two parts, the health
of the individual, and that of the community, or Personal and Public
Health.
The former treats of the influence of habits, cleanliness, exercise,
clothing, and food on health; while the latter is concerned with the interests
of the community at large, as affected by a pure supply of air and water, the
removal of all excreta, the condition of the soil, and with the administrative
measures required to secure the removal of evil conditions. It is obvious,
however, that these two divisions are not mutually exclusive. What is
important to the health of the community, is equally so to each individual
member of it. The purity of air and water, for instance, is of immense
importance both personally and collectively.
It will be convenient to study first the three main factors in relation to
health—food, water, and air—subsequently considering other matters of
importance to health (see pages 4-157).

CHAPTER II.
FOOD.
Physiological Considerations.—All substances are foods which, after
undergoing preparatory changes in the digestive organs (rendering them
capable of absorption into the circulation), serve to renew the organs of the
body, and maintain their functions. Foods have been classified as tissue
producers or energy producers, the first class renewing the composition of
the organs of the body, and the second class supplying the combustible
material, the oxidation (or more correctly the metabolism) of which is the
source of the energy manifested in the body. The two main manifestations
of energy in the body are heat and mechanical motion, which are to a large
extent interchangeable.
All foods come under one of these heads; they are either tissue or energy
producers. They may be both, and in many cases are so. Thus, all
nitrogenous foods (as meat, legumens, etc.) not only help to form the
nitrogenous tissues of the body, but their largest share becomes split up into
fats and urea, and so forms a source of heat to the body. Similarly fats may
possibly, after assimilation, enter into the composition of the various tissues
containing fat (of which the brain is the most important), though they
usually supply an immediate source of heat. Proteid foods are, however, the
tissue producers par excellence, other foods serving as the immediate
sources of energy when metabolised in the body.
Certain foods do not directly serve either as tissue or energy producers,
but are useful in aiding the assimilation of food. Such are the various
condiments which may be classed as adjuncts to food. Salt is so necessary
to the assimilation of food and to the composition of the various tissues,
that it may be ranked as an important food. Water, again, though already
oxidised, and so not an immediate source of energy, is absolutely necessary
to the assimilation of food, to the interchange between the various tissues
and the blood, and to the elimination of effete products.

Classification of Foods.—Inasmuch as milk supplies all the food
necessary for health and growth during the first year of life, it may
reasonably be expected to afford some guidance as to the necessary
constituents of a diet for the adult; although the conditions of life being
altered in the latter, we can hardly expect the same proportions of the
different materials to hold good. In the infant rapid growth and building up
of new tissues and organs are going on, involving the necessity for a larger
proportional amount of nitrogenous food than in the adult.
The following is the average composition of 100 parts of
HUMAN MILK. COW’S MILK.
Casein 2.4 4.0
Albumin .6 .9
Fat 2.9 3.5
Sugar 5.9 4.0
Salts .16 .7
───── ─────
Total Solids 11.96 13.1
Water 88.04 86.9

It is evident from this analysis of milk that our food must contain (at
least) representatives of all the above divisions. We have, therefore:—

1. Nitrogenous Foods.
2. Hydrocarbons or Fats.
3. Carbohydrates or Amyloids.
4. Salts.
5. Water.

Condiments and stimulants (tea, coffee, alcohol) are not foods in the
strict sense of the word, and will be discussed in a later chapter.
Nitrogenous Foods include albumin, casein, gluten, legumen, fibrin, and
gelatin. They all agree in consisting of a complex molecule containing
many atoms of carbon, hydrogen, oxygen, and nitrogen, with the addition of
smaller quantities of sulphur, and in some cases phosphorus. The
nitrogenous substances used as food may be divided into two groups, (a)
those containing gelatin, and (b) numerous bodies which receive the
common name of proteids or albuminoids.

The percentage composition of gelatin is:—
CARBON. HYDROGEN. NITROGEN. OXYGEN.
50.0 6.6 18.3 25.1

The percentage composition of all proteids lies within the following
limits:—
CARBON. HYDROGEN. NITROGEN. OXYGEN. SULPHUR.
52.7 to 6.9 to 15.4 to 20.9 to 0.8 to
54.5 7.3 16.5 23.5 1.6

Proteids also contain a small amount of phosphorus, chiefly as phosphate
of lime, but also in minute quantity in their essential structure. Various
proteids are used in food, e.g. serum-albumin in the blood and tissues of
animals; egg-albumin in the white of eggs; myosin in flesh; casein in milk;
legumin, or plant-casein, in the seeds of leguminous plants; gluten in wheat-
flour, etc.
Proteid foods are pre-eminently important, as they construct and keep in
repair the tissues of the body. They are not used solely for this purpose. A
large share of the energy of the body is derived from the metabolism of
proteids. The amount required for these purposes will be discussed on page
32. Meanwhile, it may be said that it is not found to be compatible with
efficient health simply to supply an amount of proteid food which will
suffice to replace the wear and tear of the tissues, leaving fats and
carbohydrates to supply the energy of the body. Deficiency of proteid food
always leads to ill-health; and it would appear that in all cases proteid food
determines, to a large extent, the metabolism of non-nitrogenous food, and
so is favourable to all vital action. The action of nitrogenous food in thus
increasing metabolism may make it, when in relative excess, a tissue waster.
Banting’s cure for corpulence is founded on this principle, lean meat alone
being taken, all starchy and saccharine foods being carefully avoided.
By metabolism is meant the changes undergone by food before it reaches
the state in which it is finally eliminated from the body. It is commonly
spoken of as oxidation, but this word less exactly represents the facts. The
complexity of the changes undergone by food in the body may be better
appreciated by a glance at the following schematic statement, which only
gives an approximation to the truth:-

HYPOTHETICAL TYPICAL FAT GRAPE-
STARCH.
ALBUMINOID. (STEARIN). SUGAR.
C₇₂H₁₁₂N₁₈SO₂₂. C₃H₅(C₁₈H₃₅O₂)₃. x(C₆H₁₀O₅). (C₆H₁₂O₆).
─────────────────────┬────────────────────
Various intermediate products, which are finally broken down
into and eliminated as
┌──────────┬────────────┐
Urea, CH₄N₂O. Carbonic acid, CO₂. Water, H₂O.>

Hydrocarbons, or fats, consist of three elements, carbon, hydrogen, and
oxygen, the amount of oxygen present not being sufficient to oxidise
completely either the hydrogen or the carbon. Thus the molecule of stearin,
which may be taken as a typical fat, has the formula C₃H₅ (C18H35O₂)₈.

In respect to their comparatively unoxidised condition fats compare
favourably with starch and sugar, C₆H10O₅ and C₆H12O₆ respectively. It is
evident that in starch the H10O₅ = 5H₂O, and that in sugar H12O₆ = 6H₂O,
so that in both cases only carbon remains uncombined with oxygen. Dried
fats produce by their oxidation 2¼ times as much heat as a corresponding
amount of sugar or starch; but the relative advantage of fat is not quite so
great as would appear from this comparison, inasmuch as metabolism
within the body is not identical with oxidation.
The fat obtained from food is not simply deposited in the body as such, to
form a store of combustible matter, and to fill up the interstices between the
different tissues. If this were so, the kind of fat deposited would vary with
the food, which is not the case. The fat of the body is probably not formed
directly from fatty food, but as the result of the metabolism of nitrogenous
foods when this metabolism is incomplete. In the formation of milk this can
be distinctly proved: the fat cells are formed from the protoplasm of the
cells of the mammary gland.
Possibly carbohydrate food may be a source of fat, as well as nitrogenous
and fatty food. This appears to be the case in the Strasburg goose, which is
kept penned up in a warm room, and fed entirely on barley-meal, in order to
produce an enormous fatty liver for the delicacy termed pâté de foie gras.
But it may be that the large accumulation of fat in the liver is due to the
warmth and inaction of the goose diminishing metabolism, and producing a
fatty degeneration of the nitrogenous material of the liver.

Fats and carbohydrates, unlike proteids, do not excite metabolism in the
system, and so, if in excess of the requirements of the system, can be stored
up with comparative ease. Quiet and warmth, diminishing metabolism,
conduce to the accumulation of fat in animals being fed for the market; and
the same applies to human beings.
Carbohydrates or amyloids include the various starchy and saccharine
foods. They are inferior to fats in nutritive power, but, being very digestible,
are in much greater favour. In the process of digestion, starch is converted
into grape sugar, and starch and sugar are practically equal in nutritive
power.
Even when carbohydrates are entirely absent from the food, they may be
produced in the organism by the breaking up of nitrogenous matter. This
certainly happens in diabetes, in which the nitrogenous food rapidly
becomes converted into sugar and urea.
The deprivation of carbohydrate food is much better borne than that of
fats, because in the latter the hydrogen is not completely oxidized, and
because fats aid the assimilation of other food.
Salts, and especially common salt (chloride of sodium), are essential to
health. An average adult human body contains about seven pounds of
mineral matter, of which about five-sixths is in the bones. On analysis the
whole body yields about five per cent. of ash.
Chloride of sodium is necessary for the production of the acid
(hydrochloric) of gastric juice, and of the salts of bile; half the weight of the
ash of blood consists of it. An adult requires 150 to 200 grains of salt per
day; a large part of this is taken in meat, bread, etc.; and but little need be
taken as a condiment. Potassium salts form an important part of milk,
muscle juice, and the blood corpuscles. They are obtained from bread and
fresh vegetables and fruits. It has been maintained that deficiency of
potassium salts causes scurvy (see page 28); but this is now discredited, and
probably potash is chiefly useful because of the vegetable acids with which
it is associated in fruits and vegetables, which when oxidised, help to
maintain the alkalinity of the blood, e.g., tartrates, citrates, and malates,
which become carbonates in the circulation. Calcium phosphate (bone
earth) is essential for the growth of bones, and is very important for the

young. The best source for it is milk. There is more lime in a pint of milk
than in a pint of lime water. Next to milk, come eggs, and then cereals,
especially rice as a source of calcium. Lime salts and phosphates as drugs
do not benefit like the same substances taken in natural food, and rickets is
not curable by taking such drugs.
Oxide of iron is always present in the ash of blood and muscles, and in
smaller quantities in milk. Fish and veal are usually deficient in it, while
beef and yolk of egg are foods richest in iron. The amount of iron required
in food is minute, and it is amply supplied by ordinary diet.
Phosphorus is an essential building material for the body. It is contained
in foods chiefly in organic combination. The foods richest in it are yolk of
egg, sweetbread (thymus), fish-roe, calves’ brains, and the germ of wheat.
Milk and cheese are very rich in phosphates.
Water forms an important article of diet. This is evident from the fact
that 80 per cent. of the blood consists of it, and 75 per cent. of the solid
tissues; and from the fact that the daily loss of water from the system
averages 50 ounces (2½ pints) by the kidneys, and about 40 ounces by the
skin and lungs. Water is not simply received into the system as a liquid. It
forms a large proportion of the solid food taken. Thus, 87 per cent. of milk,
78 per cent. of fish, 72 per cent. of lean meat, 38 per cent. of bread, 13 per
cent. of peas, and 92 per cent. of cabbage, consist of water.
Solid food is dissolved in the alimentary canal by the watery secretions
derived from the blood. Water swallowed as food, begins to pass on into the
intestine at once. The statement that free consumption of water at meals
delays digestion by diluting the gastric juice is therefore not well grounded.
In the blood, water serves to carry nutrient materials to all the tissues; and,
at the same time being circulated all over the system, equalises the
temperature, favours chemical changes, and washes all the tissues. By water
again, the effete matters which have been separated by the kidneys are
washed out of its tubes.
The Oxygen of the air, in a broad sense, forms one of the foods of the
system. This will be considered later.

Besides the above classification, foods have also been classified as
follows:—
1. Inorganic food—Oxygen, salts.
Nitrogenous.
Animal
Non-nitrogenous.
2. Organic foods
Nitrogenous.
Vegetable
Non-nitrogenous.
Or, as—
Nitrogenous.
Animal
Non-nitrogenous.
1. Solid foods
Nitrogenous.
Vegetable
Non-nitrogenous.
Water.
Milk and its products.
2. Liquid foods
Tea and similar beverages.
Alcoholic beverages.
3. Gaseous foods—Air.

CHAPTER III.
THE VARIETIES OF FOOD.
Nitrogenous Animal Foods.—These are divided into two groups, the one
containing gelatin, and the other all the proteid or albuminoid substances,
which are taken in the flesh of various animals, and in milk and eggs.
Gelatin is obtainable from bones, and from connective tissue wherever
found. Being easily digested, and absorbed, it has been very popular as an
invalid’s food; but the fact that animals cannot sustain life on it without the
addition of proteids proves that its value is limited. It is incapable of
building tissues, but is a valuable proteid-saver, being able to save from
metabolism half its weight of proteid, or twice as much as is spared by an
equal weight of carbohydrate. Its utility in this direction is, however,
limited, because of the dilute form in which it is taken in ordinary foods. It
is useful for invalids, partly because it forms a bulk, and prevents the evil
tendency to give their food in too concentrated a form; partly because it
forms a source of easily metabolised material, and so prevents tissue-waste;
and partly because it commonly contains phosphate of lime, derived from
the bones forming the source of gelatin.
Gelatin as prepared for the table contains a considerable proportion of
water; as little as one per cent. of gelatin in water will cause it to gelatinise
on cooling. Isinglass obtained from the floating bladder of the sturgeon is
an example of the purest kind of gelatin; glue is an inferior sort, made from
bones, etc.
Gelatin is only a cheap food when obtained, for instance, from bones
which cannot otherwise be utilised. When made from veal it is costly out of
proportion to its dietetic value.
The Flesh of various animals is one of the main sources of our
nitrogenous and fatty food. Meats may be divided into two kinds, viz., red
meat and white meat. These gradually merge into one another. As common

examples of red meats, we have beef, mutton, pork, game, wild fowl, and
salmon.
The common fowl and turkey, most fishes, rabbits, crustaceans, and
molluscs, are examples of white meat. As a rule white meats are more
digestible than red, having more delicate fibres, and containing a smaller
proportion of nitrogenous matter.
Flesh consists almost entirely of muscular tissue, of which there are two
kinds, striped and unstriped.
The striped is the variety most commonly used as food. Unstriped muscle
has a softer texture, but is not so easily masticated as striped, and for this
reason may be indigestible. Tripe is composed of the unstriped muscle and
connective tissue of the stomach of the cow, and if well cooked forms a
cheap and easily digested dish.
The influence of feeding on the quality of the meat is great. In ill-fed or
old animals, connective tissue is more abundant, and the meat is tougher.
Well-fed and fattened meat contains for equal weights much more nutritious
matter than non-fattened meat, the fat which is deposited in the muscle
replacing water and not proteid. Hence the gain in nutritive value is an
absolute one, and is not attained at the expense of the proteid part of the
meat. Young animals, again, contain more water and fat and a larger
proportion of connective tissue than the full-grown, and are consequently
not so nourishing.
Meat ought to be eaten either before the onset of rigor mortis, or near its
end, before putrefaction has commenced. During rigor mortis it is denser,
tougher, and more difficult to digest than after it.
The proportion of fat in meat varies greatly in different individuals of the
same species, in different animals, and in different parts of the same animal.
According to Dr. Ed. Smith, the proportion of fat in fat oxen is ⅓, in fat
sheep ½, in calves ⅙, lambs ⅓, and fat pigs ½.
Good meat, whether beef or mutton, ought to have a marbled appearance,
a medium colour, neither pale pink nor deep purple; its texture should be
firm, and not leave the impress of the finger; its odour slight and pleasant,

the juice reddish and acid, the bundles of fibres not coarse, and free from
foreign particles imbedded in them; and lastly, it should not be taken from
an animal killed near the time of parturition, nor in consequence of any
accident or disease.
Beef is, as a rule, more lean than mutton or pork; it has a closer texture,
and more nutritive material in a given bulk. It is also fullest of the red-blood
juices, and possesses a richer flavour than the two others.
Liebig’s beef extract contains little if any albumin or gelatin. It is a useful
stimulant to the gastric secretion, as in soups at the beginning of a meal, but
is not a food. Its chief constituents are the various extractives of meat, the
most important of which are inosinic acid, kreatin (C₄H₉N₃O₂,H₂O), and
inosite, or muscle sugar (C₆H12O₆, 2H₂O). Even in substances like Bovril,
containing powdered meat fibre mixed with Liebig’s extract, the amount of
nutritive material is very small. The white of one egg contains as much
nutritive matter as three teaspoonsful of bovril. None of these substances
can be trusted like eggs or milk to keep a patient alive for several weeks.
Mutton is regarded as being more suitable for people of sedentary
occupation than beef. Lamb is more watery than mutton, and less
nutritious.
Veal, as ordinarily prepared in this country, is difficult of digestion; its
shreddy, juiceless fibres eluding the teeth, and consequently not undergoing
proper mastication.
Pork is not so digestible as beef or mutton, partly because of the large
proportion of fat, and partly because its fibres are hard and difficult to
masticate. Its digestibility varies greatly with its age, breeding, and
proportion of fat.
The Flesh of Birds contains very little fat, and that found separate from
the meat is rarely nice. Most birds are edible, but fish-eating birds are apt to
be nasty. As a rule, the flavour of the male bird is richer than that of the
female. The chief virtues in poultry are their tenderness, and the large
proportion of phosphates they contain. They are deficient in fat and in iron.
To compensate for the former, one commonly takes with them melted butter
and fat bacon or pork sausages; to compensate for the latter, the addition of

Liebig’s extract to the gravy is useful. Young, and consequently tender,
birds are known by their large feet and leg-joints. When a bird appears at
table with violet-tinged thighs and a thin neck, if possible avoid being
helped to the leg. Wild fowls are harder and less digestible than tame. In
ducks and geese fat is more abundant, and of a stronger flavour; they are,
consequently, not so digestible as fowls.
Fish forms an important article of diet. It is easily cooked, and usually
very digestible; it possesses a larger bulk in proportion to its nutritive
quality, and hence is very valuable for those who habitually take an excess
of meat food, which is commonly the case with those leading sedentary
lives, and in declining years. There appears to be no foundation for the
statement that fish is rich in phosphorus, and is thus a good brain food.
Generally, white-fleshed fish is more digestible than red-fleshed (such as
salmon), the latter usually containing more fat than the former. When the fat
is distributed throughout the flesh, as in the salmon, fish is more satisfying
than when it is mainly stored up in the liver, as in the cod-fish. According to
Payen, the percentage proportion of fat in soles is only 0.248, in whiting
0.383, conger eel 5.021, mackerel 5.758, eels 23.861. The addition of some
fatty food, as melted butter, is very advisable to such meats as poultry,
rabbits, soles, whiting, plaice, haddock, cod, turbot, and other fishes;
whereas sprats, eels,. herrings, pilchards, salmon, etc., are more or less rich
in fat.
A Hen’s Egg usually weighs a little under two ounces. It consists of 74
per cent. of water and 26 per cent. of solid matter. The white of the egg is
chiefly albumin, the yolk consists of a very digestible oil, rich in
phosphorus and iron, each particle of the oil being enveloped in a form of
albumin called vitellin. The salts are chiefly contained in the shell. There is
no sugar in the egg, the necessity for such oxidisable material for the chick
being obviated by the heat produced by incubation. Eggs, when kept for
some time, lose weight, owing to evaporation through the porous shell;
similarly, air entering from without sets up decomposition. In a solution of
brine containing an ounce of common salt to half a pint of water, fresh eggs
sink, stale ones float; rotten eggs may even float in fresh water. Eggs may
be preserved by keeping them in brine, or, better still in lime water, or by
smearing them over with lard or butter, as soon as possible after they are
laid.

Cow’s Milk has a specific gravity of 1028-34, and on allowing it to stand
in a long narrow vessel ought to form ten or twelve per cent. of its volume
of cream. The percentage composition of human and cow’s milk has been
given on page 5. The legal minimum standard for dairy milk, which is
presumably derived from a number of cows, is now 3 per cent. of fat, and
8.5 per cent. of “solids not fat.” This standard is unfortunately very low, and
allows a considerable margin of adulteration, which cannot be prevented by
legal means. Thus ordinary milk derived from a herd of cows would
probably contain 4.5 per cent. of fat; and it is, therefore, practicable to mix
pure new milk with a large proportion of separated milk, and yet keep
within the legal standard. This is largely done in towns, and infants suffer
much from the deficiency of cream in their sole food (see page 28). The
lactometer determines the specific gravity, which should be taken at a
temperature of 60° F. In skimmed or separated milk it will be over 1034;
watering on the contrary lowers the specific gravity. If the milk has been
both watered and skimmed the specific gravity will give an uncertain
indication. Measurement of the cream in a tall narrow glass will enable one
to detect the second possible source of fallacy; but the composition of milk
can only be certainly determined by analysis. This is done (a) by
evaporating a weighed amount of milk to dryness and then re-weighing. (b)
From a separate amount of dried milk the fat is extracted by ether, the ether
then evaporated, the remaining fat weighed, and its percentage calculated.
The weight of fat deducted from the total solids i.e. (b) from (a), gives the
“solids not fat.” The following example will make the method then
followed clear. The sample gives 7.9 per cent. of “solids not fat.” Genuine
milk contains at least 8.5 per cent. of “solids not fat.”
Then the sample contains—
100 × 7.9 ∕ 8.5 = 92.9 per cent. of genuine milk,
i.e. 7.1 per cent. of water has been added to it.

Half a pint of milk supplies as much nitrogenous nutriment as two good-
sized eggs, and as three and a half ounces of beef. Milk may be deteriorated
(1) by skimming or “separating” by machinery, or (2) by the addition of
water—the first diminishing the proportion of fats, and the second the total
amount of solids.

Skim Milk still contains nearly 1 per cent. of fat, but Separated Milk, in
which the cream has been removed by centrifugal apparatus, contains less
than 1 ∕ 8 per cent.

Skim or separated milk forms a cheap source of nitrogenous food; but
when it is sold mixed with new or alone as new milk, the public is
defrauded, and infants fed on it are robbed of the fat which is so essential
for their growth.
Condensed Milk is milk deprived of a large part of its water. It
represents three times its volume of fresh milk. There are in the market (a)
unsweetened and condensed whole milk, (b) sweetened and condensed
whole milk, and (c) sweetened and condensed skim or separated milk.
Unfortunately the latter is most largely sold because cheapest; and infants
are thus often robbed of fat, a most important element in their food. Always
examine the label of each tin carefully, to ascertain whether the milk has
been deprived of its cream. The law requires that this fact should be stated
on the label. Tins which have bulged should be rejected. Condensed milk is
more easily digested by infants than new cow’s milk, but it lacks the anti-
scorbutic properties of new milk (see page 28). Even the condensed whole
milk if diluted beyond 1 part of milk to 3 of water is deficient in fat.
Sweetened condensed milk has one-third its weight of extraneous sugar
added to it, and on this account it tends in children to produce fatness, and a
distaste for simple food; in children fed on it alone ossification (formation
of bone) is retarded, and resistance to illness is diminished. The only
dietetic advantages it possesses over fresh cow’s milk are its freedom from
possible disease germs and easier digestibility.
The digestion of milk is preceded by its clotting in the stomach. The
same thing happens when junket is formed by the addition of rennet to
milk. This is a different process from the curdling of milk, which occurs
when milk turns sour. The latter is caused by the splitting up of milk sugar
and the formation of lactic acid by certain micro-organisms in the milk.
When milk is heated, a skin is formed, consisting of coagulated albumin, in
which is also a little casein, fat, and salts of lime. Boiled milk becomes
sterilized. Cow’s milk should always be boiled, unless it is quite certain that
the cows from which it is derived are perfectly healthy, and that the milk
has not been exposed to infection before reaching the house. The

disadvantages of boiling which are outweighed by its advantages, are that
the taste of the milk is altered, some nutritive matter is lost by the formation
of the “skin,” and the casein is not quite so easily digested. Pasteurization
of milk, i.e. keeping it at a temperature of 70° C. (158° F.) for 20 to 30
minutes has been proposed as an alternative to boiling. This appears to
destroy the bacilli causing tuberculosis (see page 312). The typhoid bacilli
are killed at 60° C. in five minutes when suspended in emulsion.
Pasteurization is not, however, so certainly efficacious for other disease-
germs as is boiling, and is not so easily carried out in domestic life as
boiling. By boiling milk in a double saucepan, i.e. in a water-bath, very
little change occurs in the taste of the milk, especially if it be cooled rapidly
and strained.
Cheese is prepared by coagulating milk by “rennet,” the mucous
membrane of the fourth stomach of the calf, salted and dried before using.
By this means the casein is precipitated, carrying down with it the cream,
and a large proportion of the salts of milk. The whey, containing the sugar,
soluble albumin, and remaining salts, is separated by straining, while the
mixed curd and fat are pressed in moulds. Cheese thus consists of casein,
fat in varying proportions, water and salts, especially phosphate of lime. It
is coloured with annatto, a vegetable colouring matter. When new, cheese is
tough; when old, its oils tend to become rancid; the best age is from nine to
twenty months. It is probable that cheese in small amount helps the
digestion of other foods, though it is itself a highly concentrated and
comparatively indigestible food. When toasted it is proverbially
indigestible.
There are many different kinds of cheese. The following classification
gives the more important varieties:—
(1) Cream cheese is the new curd only slightly pressed, and is more digestible than ordinary
cheese.
(2) Next to these are cheeses made with whole milk rich in cream, such as Stilton, Gorgonzola,
Cheshire, and Cheddar.
(3) Cheeses made of poor or partially skimmed milk, such as Shropshire, Single Gloucester, and
Gruyère.
(4) Cheeses made of skimmed milk, such as Suffolk, Parmesan, and Dutch.

American cheeses may belong to any of these classes; they are generally
pure, but occasionally are made from separated milk, margarine being
added to take the place of cream. The sale of such cheeses, except under the
name of “margarine cheese,” is now illegal.
Non-Nitrogenous Animal Foods.—These are all fats, and the most
important are the various meat fats and butter. They possess a higher food
value than carbohydrates in the proportion of 2¼; to 1. The composition of
the various fats differs somewhat; they usually contain varying proportions
of olein, palmitin, and stearin, which are compounds of glycerine with the
radicle of a fatty acid (stearin = C₃H₅ (C18H35O₂)₃). Thus mutton suet
consists of stearin, olein, and palmitin, with a preponderance of stearin.
Beef suet contains less stearin and more olein than mutton suet. The more
olein a fat contains the less solid it is. Olive oil is composed almost entirely
of olein. Palmitin, which melts sooner than stearin, is the chief solid
constituent of butter, while olein is its chief liquid constituent. Butter is
specially distinguished by containing 7 to 8 per cent. of “volatile fatty
acids,” such as butyric, caproic, etc., combined with glycerine. The
presence and amount of these compounds is an important test for the
freedom of butter from adulterating fats.
Cod-liver oil is next to butter the most digestible animal fat known. The
best cod-liver oil is frozen at a low temperature, by which means the stearin
is frozen out, and nearly pure olein is left. Traces of iodine have been found
in it, and more commonly a small amount of bile, which probably increases
its digestibility.
The temperature at which a fat becomes hard is a fair guide to its
digestibility. Thus we know that beef, and still more, mutton fat, would
become solid, under conditions in which bacon dripping is still soft. Where
digestion is weak, there may be an instinctive loathing of fat meat; for such
persons, especially for children, some other fat should always be
substituted. Thus the addition of butter to the potatoes makes up the
deficiency.
Butter forms 3½ to 4½ per cent. of cow’s milk. It is separated from milk
by churning, the oil particles being deprived by this means of their
albuminous coats. The more completely the butter-milk is separated the

longer the butter keeps. It can be kept longer if salt is added, or in hot
weather by keeping it under frequently-changed water. Rancidity indicates
the decomposition of traces of the fat of butter into its fatty acid and
glycerine.
Cream contains about 30 per cent. of butter fat, Cheshire cheese 25 per
cent., and skim milk cheese 7 per cent.
Butter milk differs from skim milk in the presence of lactic acid. It is
more digestible than skim milk, the casein being in a more flocculent
condition.
The odour and flavour of butter are not due to olein and palmitin, the two
chief constituents, but to a smaller quantity of butyrin, caproin, and caprylin
fats of a much lower series. Ordinary butter contains a considerable
proportion of water, and the presence of about 8 per cent. renders it more
palatable; if it is over 15 per cent., the butter is considered adulterated. An
excessive amount of salt is sometimes present. The most frequent
adulteration is the substitution of foreign fats for butter fat, e.g. lard, palm
oil, rape seed oil, or cocoa-nut oil. Margarine is most frequently used for
this purpose.
Margarine is prepared from beef-fat by melting, the stearin becoming
solid again at a temperature at which olein and margarine still remain
liquid. It forms a wholesome and cheap food, being nearly as digestible as
butter, for which more expensive food it is often fraudulently sold. When
mixed with a small proportion of butter its recognition by smell, etc., is
almost impossible, but on careful chemical analysis, it is found to have a
higher melting point and a lower specific gravity than butter, and a much
smaller percentage of soluble fatty acids than the latter. Thus:—
MELTING SPECIFIC SAPONIFICATION AND FORMATION
POINT. GRAVITY. OF INSOLUBLE FATTY ACID.
Butter 32° C. .913 88 per cent. insoluble fatty acid
1
Margarine 35° C. .904-.907 952 per cent. insoluble fatty acid

Cereal Foods.—Gluten is peculiar to plants, and is chiefly found in
plants belonging to the great family of grasses. Gluten is to bread what
casein is to milk, and myosin to flesh. If one takes a piece of dough made
from wheat flour, and holds it under a stream of water from the tap, a large

part of it is washed away, while a sticky adherent mass is left behind. This
is gluten, and it is its tenacity which enables bread to be made. If the fluid
with which the dough was washed is collected, it will be found to contain a
large quantity of starch, a small amount of sugar, of albumin, and certain
salts. All cereals possess these constituents in various proportions, as may
be seen from the following table:—
CARBO- MINERAL
WATER. PROTEID. FAT. CELLULOSE.
HYDRATES. MATTER.
Wheatmeal 12.1 12.9 1.9 70.3 1.6 1.2
Fine wheat flour 13.0 9.5 0.8 75.3 0.7 0.7
Oatmeal 7.2 14.2 7.3 65.9 3.5 1.9
Barley meal 11.9 10.0 2.2 71.5 1.8 2.6
Maize meal 11.4 8.5 4.6 72.8 1.4 1.3
Rice (husk
12.0 7.2 2.0 76.8 1.0 1.0
removed)

The proteid varies in character in the different cereals; wheat flour has
the largest proportion of gluten (8 to 12 per cent.) and therefore makes the
best bread.
Good wheat flour ought to be white, not gritty or lumpy, not acid or
musty, forming a coherent stringy dough. Examined microscopically, it
should show the absence of any fungi, or acarus farinæ, or of foreign
starches, such as barley, maize, rice, potato, known by the different shape of
their starch granules. (See Fig. 1.) Alum has been occasionally added to
flour, to enable the baker to make a white and porous bread from damaged
wheat flour. It can be detected as follows:—Pour over the freshly cut
surface of a slice of bread some freshly prepared decoction of logwood
chips, and then a solution of carbonate of ammonia. If alum is present, the
bread turns a marked blue to violet colour; but if the bread is pure, it is only
stained pink.
The wheat grain may be used as food in its entirety. Thus boiled in milk,
after having been soaked in water, it forms the chief constituent of
frumenty. Usually it is converted into flour by grinding or milling. A grain
of wheat consists of three parts, an outer envelope, the bran, consisting
chiefly of indigestible cellulose, and composing 13½ per cent. of the grain;
the kernel, or endosperm, which makes up 85 per cent. of the grain; and the
germ, forming 1½ per cent. of the grain. In the old method of stone

grinding, the bran was removed, and the germ left along with the
endosperm. In the elaborate processes of modern roller milling, the bran is
removed as in the old grinding, because it cannot without the greatest
difficulty be reduced to powder; and the germ is also removed, because the
oil abundantly present in it is apt to become rancid and spoil the flour, and
because the soluble proteids in it are apt to change some of the flour into
dextrin and sugar, which become brown in baking and spoil the appearance
of the bread. The germ is easily removed, because its toughness causes it to
be flattened out in the milling, while the endosperm becomes powdery. The
central part of the endosperm is the source of ‘patents.’ It is very rich in
starch and is used for making fancy breads and pastry. The outer part of the
endosperm is ‘households.’ ‘Households flour’ is subdivided into (a) second
patents, or ‘whites’; (b) first households; (c) second households or
‘seconds.’ ‘Seconds’ is richest in gluten, ‘whites’ in starch. Ordinary bread
is normally derived from a blend of these three. Some ‘strong’ wheats, e.g.
Australian, yield a ‘patents’ which is rich in gluten, and such flour is used
for making Vienna bread. ‘Strong’ wheats take up most water in baking, and
so yield most loaves per sack. ‘Seconds’ flour yields a bread which is richer
in proteid than most other kinds; but the dark colour of the loaf makes it
unpopular. Various schemes have been devised to utilise the germ and the
bran, which are ordinarily discarded. In the preparation of Hovis flour the
separated germ is partially cooked by superheated steam. This kills the
ferment contained in the soluble proteids, and thus prevents it from
changing starch into maltose and dextrin. The action thus prevented is
represented by the following formula:—
STARCH. MALTOSE. DEXTRIN.

10 C12H20O10 + 6 H₂0 = 6 C12H22O11 + 4 C12H20O10.

The germ thus treated is ground to a fine meal, of which one part to three
of ordinary flour, forms Hovis flour. Other ‘germ breads’ are also in the
market. In the making of Frame food the bran is boiled with water under
high pressure. The watery extract, containing the mineral and part of the
nitrogenous constituents of the bran, is evaporated to dryness, and forms the
basis of various preparations. It is doubtful if this food possesses any great
value.

Brown bread is a somewhat vague expression, meaning either an
admixture of bran or of germ or of both with flour, or bread made from
whole wheat flour. In each of these cases the loaf would be brown. The bran
is rich in fat as well as in phosphates. It acts as a mechanical irritant, ill
borne by delicate stomachs, but very useful where a tendency to
constipation exists. The excess of nitrogenous matter in brown bread and its
richness in fat, do not prove its greater nutritiveness, as it is present in a
condition in which only a portion is absorbable from the alimentary canal
into the circulation.
The harder wheats, such as Sicilian wheat, contain a larger percentage of
gluten; and from them macaroni and vermicelli are obtained, which are
nearly pure gluten. They are very nutritious and useful foods. Semolina is
prepared from wheat, the millstones being left sufficiently apart to leave the
product in a granular condition. In malted breads, a syrupy infusion of
malted barley (malt extract) is added to the flour. Malt extract contains in
addition to malt sugar (maltose) and dextrins, a ferment (diastase) which,
like the saliva, is able to convert starch into the soluble substances, maltose
and dextrin (see formulæ above). The action of this ferment is stopped by
the temperature of baking. Hence even when the malt extract is allowed a
considerable time for its operation on the dough, only about 10 per cent. of
the starch in the loaf becomes soluble, as compared with 4 per cent. in an
ordinary loaf.
Oatmeal, obtained from the common oat, contains very little gluten, and
so cannot be made into vesiculated bread. It contains a large proportion of
other nitrogenous material and of fat. As porridge and oatmeal cake it forms
a very nutritious diet. The husk ought to be carefully removed from the
meal intended for human food, as, although very nitrogenous, it acts as a
mechanical irritant. Groats consists of oats from which the husk has been
entirely removed. The substitution of rolling for grinding in preparing oats
for food and the application of heat during the rolling process, have made
oatmeal more digestible, as in Quaker, Provost, and Waverley oats.
Barley contains very little gluten; on this account, like oatmeal, it does
not admit of being made easily into bread.

Malt is barley which has been made to germinate by heat and moisture
and then dried, “diastase” being formed in the process. Extract of malt,
containing diastase in an active condition, is useful in cases of impaired
digestion and deficient assimilation of food.
Rye is rarely used in this country for making bread. In Germany it is
known as “black bread,” but its colour and acid taste make it disagreeable,
and it is laxative in its action.
Maize, or Indian Corn, is deficient in gluten, and so not suitable for
making vesiculated bread. Like oatmeal, it is made into cakes, called in
America “Johnny cake.” It contains much fatty matter, and is largely used
for fattening poultry and other animals. Oswego flour and corn flour are
maize flour deprived by a weak solution of soda, of its proteids and fat;
hominy contains all its constituents. Maize is a cheap and nutritious food.
When wheat flour is dear, it is occasionally adulterated with maize. The
adulteration can be detected by the forms of the starch granules, examined
under a low power of the microscope.
Rice contains less proteids and fat than any other cereal. Its chief value
as a food depends on the large amount of starch it contains (table, page 16).
Leguminous Foods.—The chief seeds belonging to this group are peas,
beans, and lentils. They contain a smaller proportion of starch, and a larger
proportion of nitrogenous materials than cereals. Thus while flour contains
9.5 and bread 8 per cent. of proteid, lean meat 15.18 per cent., and cheese
about 30 per cent., peas and beans contain 21 to 26 per cent. (green peas
only 4 per cent., dried peas 21 per cent.) of proteid. The nitrogenous
material exists chiefly as legumin, which has been called vegetable casein.
Although leguminous seeds contain more nutritive material in a given
weight than cereals, dietetically they are inferior, owing to the fact that they
are less digestible, often causing flatulence and other dyspeptic symptoms.
Cereals, again, are more palatable than leguminous seeds, and are more
prolific, and consequently cheaper. In the absence of animal food, legumens
form a useful substitute. They are advantageously diluted with oily
substances, or with rice. The farm-labourer’s dish of broad beans and fat
bacon is founded on strict physiological principles. A mixture of lentil and
barley flour is sold under the name of Revalenta Arabica. Lentil flour costs

2½d., Revalenta 3s. 6d. per lb. Green peas, French beans, and scarlet
runners are much more easily digested than are dried peas or beans. Lentils
contain the largest proportion of proteid of any of the pulses. They also
contain very little sulphur, and so do not give rise to the same liberation of
sulphuretted hydrogen in the intestine, as other pulses. The ash of the
Egyptian lentil is particularly rich in iron.
Amylaceous Foods. Amylaceous or starchy substances are contained in
many of the preceding foods; but some other foods consist almost entirely
of starch. The chief of these are sago, tapioca, and arrowroot.
Sago is obtained from the pith of the stems of various species of palm; a
single tree may yield several hundred pounds. Alone it is easy of digestion.
Boiled with milk it forms a light, nutritious, and non-irritating food.
Fictitious sagos are frequently sold, made from potato starch.
Tapioca and Cassava are derived from the tubers of more than one
species of the poisonous family, Euphorbiaceæ. The juices are removed,
and the prussic acid removed by heat. Tapioca only differs from cassava in
being a purer form of starch; the latter is more nutritious, and among the
Indians takes the place of bread.
Arrowroot is obtained from the tubers of Maranta Arundinacea.
Tous-les-mois is a form of starch obtained from the tubers of a West
Indian plant, the Canna edulis.

Fig. 1.—Different Forms of Starch Granules.
Potato. Wheat. Rice.
Oats. Barley. Pea.

The detection of the varieties of starch is usually possible owing to their
fairly characteristic appearance under the microscope. Fig. 1 shows the
most important starches. It must be noted that in oats, maize, and rice the
contour is completely marked by facets or surfaces, while there are less
complete markings in tapioca and sago. In wheat, rye, pea, bean, barley,
potato, and arrowroot the contour is even, though there are minor
differences of size and shape.
Other Vegetable Foods.—Green Vegetables contain comparatively
little nutriment, but form valuable additions to other foods. Cellulose, which
forms their main constituent, although indigestible, forms a bulk in the
alimentary canal, which is necessary to ensure peristalsis. Concentrated
nourishment can only be digested in limited quantity, and is very apt to
produce digestive disorder. Cabbage contains 92 per cent. of water, and 2½
per cent. nitrogenous matter. Carrots contain 6 per cent. and turnips 2 per
cent. of nitrogenous matter; parsnips are intermediate between these. Green

vegetables possess valuable anti-scorbutic properties. They may be made an
important vehicle for giving fatty food, by adding butter, etc.
Rhubarb and sorrel contain oxalates and tartrates of potash and lime, to
which they owe their tartness. Spinach is cooling and laxative, like rhubarb,
but not tart. Sea-kale, artichoke, and asparagus are all wholesome
vegetables. Asparagus is somewhat diuretic, and gives a peculiar,
disagreeable odour to the urine. Salads, such as mustard and cress, water-
cress, endive, and the garden lettuce are very useful as anti-scorbutics.
Some of them possess a peculiar pungency due to a volatile oil analogous to
that contained in horse-radish.
The Potato contains 26 solid parts in 100, of which nearly 20 are starch
and 2½ nitrogenous matter. It forms one of our best-appreciated vegetable
foods, and as it possesses valuable anti-scorbutic properties, its universal
use is, perhaps, the chief cause of the present rarity of scurvy. Alone, it
possesses too small a proportion of nitrogenous material to support life, but
the addition of butter milk makes up this deficiency; and these two together
form a sufficient diet to maintain life and health for a long time.
The Onion, Garlic, Leek, and Shalot, all members of the lily family, are
chiefly used as condiments. They contain an acid volatile oil, which gives
them a peculiar odour and flavour. By long boiling, this is dissipated (as in
the case of the Spanish onion), and the onion is then fairly digestible, as
well as nutritious.
Celery possesses a more delicate flavour and odour than the preceding,
but even the most tender celery is digested with difficulty; less so, when
boiled or stewed, or a constituent of soups.
Only four Fungi are, with us, commonly regarded as safe—mushrooms,
champignons, morels, and truffles; but there are many others which are
equally edible. The food value of fungi has been exaggerated. They are
difficult of digestion and contain little nutritive material. Poisonous fungi
usually have an astringent styptic taste and a disagreeable pungent odour. In
any doubtful case it is better to abstain.
Oily Seeds contain a considerable amount of fixed oil which renders
them unfit for persons of weak digestion. The almond, walnut, hazel-nut,

and cocoa-nut are common examples. The sweet almond, when eaten
unbleached, occasionally produces nettlerash, and its solid texture and large
proportion of fixed oils render it difficult of digestion. The chestnut
contains less oil, but a large amount of carbohydrate. It is extensively used
as a food in Italy and some other countries. In the uncooked condition it is
very difficult of digestion.
Fruits are chiefly used as adjuncts to other foods; but the vegetable salts
and the cellulose and sugar which they contain, make them very valuable.
Cucurbitaceous fruits are used as vegetables rather than as fruits.
Vegetable marrow is wholesome and agreeable, but not very nutritive.
Cucumber is most digestible when rapidly grown and freshly gathered.
Stone-fruits or drupes, such as the peach, nectarine, plum, cherry, are
rather luxuries than foods, like many other fruits. Before ripening they are
unfit for food; when ripening is complete, the acids and astringent matter
largely disappear. The date contains chiefly sugar, and forms an important
food in the East.
Pomaceous Fruits, as the apple, pear, and quince, are more digestible
when cooked; and, speaking generally, all fruit not perfectly ripe should be
cooked before eating. The presence of vegetable acids in fruit soon converts
the sucrose of cane sugar into dextrose, a less sweet variety of sugar. It is
therefore more economical to sweeten after than before cooking.
The chief Berries are the grape, currant, gooseberry, cranberry, and
elderberry. The grape is the most important, and 1,500 varieties of it have
been described. Its juice contains a large amount of grape sugar (dextrose),
and small quantities of glutinous material, bitartrate of potash, tartrate of
lime, malic acid, etc.
Besides the above fruits, we have strawberries, mulberries, figs,
plantains, melons, etc., which are all refreshing and anti-scorbutic. The
orange family furnishes us with the orange, lemon, citron, lime, shaddock,
and pomelo, of which the orange is by far the most important, and possesses
most valuable refreshing qualities.
Sugar exists in two chief forms, viz. sucroses and glucoses. Sucroses,
known chemically as disaccharids (Sucrose = C12H22O11; compare starch =

C12H20O10) are exemplified in cane, beet, maple, malt (maltose), and milk
sugar (lactose). Cane sugar has been gradually displaced by beet sugar. The
two are chemically identical, and equally nutritious. Maltose is given in
malt extract as a food, and because of the digestive action of the ferment
also contained in the extract on starchy food. Thus:—
STARCH. MALTOSE.
C12H20O10 + H2O = C12H22O11.

Lactose is comparatively free from sweetness, and is hardly capable of
being fermented by yeasts.
Of Glucoses the best example is dextrose = C6H12O6, H2O, which can be
seen crystallised in dried raisins; it only possesses one-third the sweetening
power of sucrose. Starchy food becomes changed into glucose by the action
of saliva and pancreatic juice in the alimentary canal. Grapes, cherries,
gooseberries, figs, and honey contain lævulose in addition to glucose
(glucose = C6H12O6, H2O, lævulose = C6H12O6). Lævulose resembles
dextrose except in being uncrystalline, and in its effect on polarised light.
Many ripe fruits, such as pineapples, strawberries, peaches, citrons, contain
sucrose and lævulose, the latter being not quite so sweet as sucrose.
In the alimentary canal sucroses are inverted into dextrose and lævulose.
Thus natural foods containing these sugars are more readily assimilated
than those containing sucrose.
The sweetening power of the varieties of sugar depends on their degree
of solubility in water. Sucrose is soluble in one-third of its weight of cold,
and in rather more of hot water. Dextrose is soluble in its own weight of
water; lævulose is more soluble, and therefore sweeter than dextrose.
Lactose requires five to six parts of cold and two of hot water, and is
therefore not so sweet as the other varieties.

CHAPTER IV.
DISEASES DUE TO FOOD.
Diseases may arise from the noxious character or from deficiency or
excess of some particular food, or of the food as a whole.
Diseases from Unwholesome Food.—I. The Meat of Diseased Animals.
(1) The flesh of animals which have not been slaughtered should be
prohibited from sale, whether death has resulted from accident or disease.
The meat from diseased animals is also generally dangerous, sometimes
owing to the drugs with which the animals have been dosed before death,
e.g. tartar emetic, or opium.
(2) Meat may be unwholesome from the presence of parasites. Of these
the most common is—
(a) The cysticercus cellulosæ, which is the undeveloped embryo of the
tape-worm; that from the pig becomes the tænia mediocanellata. The
cysticercus of the pig is the most common; it forms a cyst about the size of
a hemp-seed, commonest on the under surface of the tongue. In hams oval
holes are found or opaque white specks, which are the remains of the cysts
converted into calcareous matter. When meat containing the cysticercus
alive (as in under-cooked or raw meat) is swallowed, it develops into the
tape-worm, which consists of a number of flat segments, each capable of
producing numerous ova of new cysticerci, with a minute head at the
narrow end surrounded by hooklets. A temperature of 174° F. kills the
cysticercus. Another kind of tape-worm common on the continent, called
bothriocephalus latus, is derived from the cysticercus of fish.
(b) The trichina spiralis is not a solid worm like the tænia, but possesses
an intestine. In pork it forms a minute white speck, just visible to the naked
eye, which forms a nest, and in this one or two coiled up worms can be seen
by a magnifying glass in active movement. They are effectually killed by
the temperature of boiling water; but no form of drying, salting, or even
smoking at a low temperature is sufficient for this purpose. Boiling or

roasting does not suffice to destroy
all the trichinæ unless the joint is
completely cooked in its interior.
When trichinous pork is swallowed,
the eggs develop in the alimentary
canal in about a week into complete
worms, and in three or four days
more each female produces over a
hundred young ones. These burrow
into every part of the body, Fig. 2.
Cysticercus (“Measles”) in Pork.
producing great irritation and (Natural Size.)
inflammation. In one case after
death upwards of 50,000 worms were estimated to exist in a square inch of
muscle. Most of the cases of trichinosis have occurred in Germany, from
eating imperfectly cooked sausages. The pig becomes trichinous by eating
offal, and man is infected by eating pork. This disease is rare in England.
(3) Tuberculous Meat, from animals
suffering from tuberculosis, has been
found to cause tuberculosis in small
animals experimentally fed on it. Koch
has recently thrown doubt on the
communicability of bovine tuberculosis to
man; but this point must be regarded as Fig. 3.
still unsettled (see page 312). Sheep are Trichinæ Capsulated in Flesh.
Magnified.
rarely affected by it, but it is very
common in cattle, especially in cows, and
it is a serious economical question whether the meat of all such animals
should be condemned. The ideal would be to condemn all such animals, as
tuberculosis is an infective disease, and the bacillus which causes it (as well
as the toxic products of its activity) may be present in meat which shows no
actual signs of disease, except in the lungs or other internal organs. In
practice, however, the rules laid down by the Royal Commission on
Tuberculosis, in 1898, should be followed for the present. These state that:
—
“The entire carcase and all the organs may be seized (a) when there is miliary tuberculosis of both
lungs, (b) when tuberculous lesions are present on the pleura and peritoneum, or (c) in the muscular
system, or in the lymphatic glands embedded in or between the muscles, or (d) when tuberculous

lesions exist in any part of an emaciated carcase. The carcase, if otherwise healthy, shall not be
condemned, but every part of it containing tuberculous lesions shall be seized (a) when the lesions
are confined to the lungs and the thoracic lymphatic glands, (b) when the lesions are confined to the
liver, (c) or to the pharyngeal lymphatic glands, or (d) to any combination of the foregoing, but are
collectively small in extent.” They also add that any degree of tuberculosis in the pig should secure
the condemnation of the entire carcase, owing to the greater tendency to generalisation of
tuberculosis in this animal; and that in foreign meat, seizure should ensue in every case where the
pleura has been “stripped.” (See also page 312.)

(4) Other Infective diseases besides tuberculosis may render meat
wholly or partially unfit for food. Of these pleuro-pneumonia may not
require condemnation of the entire carcase; but in the following this course
should be adopted, cattle-plague, pig typhoid (pneumo-enteritis), anthrax,
and quarter ill, as well as in sheep-pox. In puerperal fever, actinomycosis,
and sheep-rot (liver flukes) each case must be decided on its merits.
II.—Decomposed Meat.—Putrid meat has often produced diarrhœa and
other severe symptoms. Putrid sausages are especially dangerous, and
incipient putridity seems to be more dangerous than advanced.
Tinned Meats occasionally produce severe illness, which has been in
several cases fatal. It is important to secure a good brand, and to eat the
meat as early as possible after the tin is opened. Tins in which any bulging
is present, showing the presence of putrefactive gases, must be rejected; and
still more tins which have been pricked and resoldered in a second place.
All tinned meats and fruits are stated by Hehner to contain compounds of
tin in solution. These do not seem to be perceptibly injurious, unlike lead
salts, which are now rarely found.
The general subject of Meat Poisoning has had much light thrown on it
during the last few years. Brieger, about 1886, showed that during the
cultivation of bacteria, alkaloidal bodies known as ptomaines and
leucomaines, were formed, which were virulently poisonous. It was
commonly supposed that the poisoning occasionally produced by eating
meat pies, sausages, hams, brawn, and similar food, was due to these
ptomaines. It is now known, however, that there are far more important
toxines than the alkaloidal, which result from bacterial life in meat, etc. (see
page 286). These are more closely related to substances of an albuminous or
proteid nature than the ptomaines. These toxines may be fatal when as small
a dose as a fraction of a milligramme (mgm. = about 1 ∕ 64 grain) is given

subcutaneously. The evidence now shows that neither ptomaines nor other
toxines (albumoses) or any other bacterial products besides these, cause the
outbreaks of acute poisoning occasionally traced to food, but that these are
due to bacteria. There is, in other words, actual infection, as well as
poisoning. The microbe chiefly found as the cause of these outbreaks is the
Bacillus enteritidis of Gaertner, and some allied microbes. In an outbreak at
Oldham, 160 pies made on a Thursday, from the veal of a calf killed on the
preceding Tuesday, were baked in several batches, and of the persons eating
these pies fifty-four became ill. That the contamination was not introduced
after cooking was shown by the fact that several persons were made ill who
ate pies still warm from baking. The facts indicated that one batch was
imperfectly cooked, the time allowed being only twenty minutes, as
compared with fifty minutes allowed in corresponding cooking in domestic
life. Experimentally it has been found that an exposure for one minute to
70° C. kills the Bacillus enteritidis of Gaertner. That this bacillus was the
cause of the outbreak was subsequently shown by the fact that the serum of
blood taken from some of the patients showed characteristic clumping with
a pure culture of this bacillus, just as happens with the blood of a patient
suffering from enteric fever when a cultivation of the microbe of this fever
is mixed with it (see page 301). In this outbreak the symptoms were usually
diarrhœa, vomiting, intense thirst, desquamation of the skin, and a slow
convalescence, lasting from three to six weeks. (See page 26 for poisoning
by Bacillus enteritidis sporogenes.)
III.—Meat injuries from the food eaten before killing.—Pheasants fed
on laurel, hares on rhododendron chrysanthemum, and other animals fed on
the lotus, wild cucumber, and wild melon of Australia, have caused
dangerous symptoms.
IV.—Fish, especially some kinds, occasionally produce nettlerash and
other disorders, especially in warm weather. Leprosy has been ascribed to
the eating of decomposing fish, but it occurs in countries where a fish diet is
impossible.
Shell-fish and crustaceans (as lobster, crab) are very prone to produce
evil results. Shell-fish (mollusca), such as mussels, cockles, and oysters, are
dangerous foods. They are generally grown in estuaries, to which the
sewage of towns has access; and not infrequently cases of enteric (typhoid)

fever, as well as more acute attacks of diarrhœa and vomiting, have been
traced to them. Mussels and cockles are seldom sufficiently cooked to
render them safe; and oysters are eaten raw. They should never be eaten,
unless from personal direct knowledge it is certain that they have been
derived from an estuary in which there was no possibility of contamination
by sewage.
V.—Milk has been a common carrier of disease. Cows eating the rhus
toxicodendron get the “trembles,” and their milk produces serious gastric
irritation in young children. The milk of goats fed on wild herbs or
spurgeworts has produced severe disorders.
The milk of animals suffering from foot-and-mouth disease, although
frequently drunk with impunity, occasionally produces inflammation of the
mouth (aphthous ulceration). The milk derived from cows fed on grass from
sewage farms is, per se, as wholesome as any other, and its butter has no
more tendency to become putrid than that derived from any other source.
The great dangers in respect to milk are of its becoming mixed with
contaminated water; or of its absorbing foul odours. The absorptive power
of milk for any vapour in its neighbourhood, is shewn by exposing it in an
atmosphere containing a trace of carbolic acid vapour: the milk speedily
tastes of the acid.
Milk also tends to undergo rapid fermentative changes, especially in
warm weather, or when tainted by traces of putrefying animal matter.
Diarrhœa in children is frequently due to such a condition, or to the rapid
decomposition of milk in an imperfectly cleaned bottle. Milk should always
be boiled in warm weather; and it should never be stored in ill-ventilated
larders, or where there is a possibility of the access of drain effluvia; nor
ought it to be kept in lead or zinc vessels.
Epidemic diarrhœa has been ascribed by Klein to a microbe called the Bacillus enteritidis
sporogenes. This is not killed by heating the liquid containing it to 80°C. for twelve to fifteen
minutes, as is the typhoid bacillus and other non-spore-forming bacilli. In an outbreak of diarrhœa
among the patients in St. Bartholomew’s Hospital, London, there was strong evidence that this
microbe taken in rice pudding had caused the mischief. Eighty-four patients and two nurses were
attacked, and the patients who had eaten rice pudding were almost exclusively attacked. A portion of
this pudding after being kept twenty-four hours was found sour and acid. The Bac. enteritidis sporog.
was found in it. Furthermore it was shewn that the temperature at which the rice puddings were

cooked never exceeded 98°C., whereas the spores of this microbe withstand 100°F. a considerable
time.

Very many epidemics of enteric fever and scarlet fever, and a smaller
number of epidemics of diphtheria have been traced to contaminated milk.
Usually in enteric fever the contamination of the milk was traced to the use
of water “for washing the milk-cans,” derived from specifically polluted
sources, and doubtless the water was the real source of the disease. In most
of the milk outbreaks of scarlet fever, either there was scarlet fever in the
dairy, or persons employed in the dairy were in attendance on patients
suffering from the disease; but in an outbreak connected with a supply of
milk from Hendon, it was suspected that a certain eruptive disease of the
udders of the cow might have been the cause of scarlet fever in man,
without infection from a previous case of the disease. This point is still sub
judice.
Tubercular disease of the intestines and mesenteric glands may be
produced by taking milk derived from tuberculous cows. This was proved
in the case of calves (page 311), and there are strong reasons for thinking
that the same is true for infants, though doubt has been thrown by Koch on
the communicability of bovine tuberculosis to the human being. The only
safe plan is to sterilise the milk (page 13).
VII.—Vegetable Food (especially greens) is indigestible if stale, and all
mouldy vegetables are dangerous. Over-ripe and rotten fruit is liable to
produce diarrhœa; but the diarrhœa prevalent in summer is due much less to
this than to other decomposing foods, particularly milk.
Poisonous symptoms have been produced by the admixture of darnel
(lolium temulentum) with flour.
The eating of damaged maize in Italy is the cause of an endemic skin
disease, called pellagra, which commonly proves fatal.
Ergotism is due to the growth on cereals (and most commonly on the rye)
of a poisonous fungus, the claviceps purpurea, which produces a deep
purple deposit on the grain. If bread made from such flour is eaten for
prolonged periods, severe symptoms result; in some cases, a dry rotting of
the limbs. There have been several epidemics on the continent, due chiefly
to eating bad rye bread.

Starvation Diseases.—Simple Starvation causes death in a period
varying with the previous state of nutrition. Usually death occurs when the
body has lost two-fifths of its weight, whether this be after days, months, or
years (Chossat). A supply of water prolongs the duration of life, to as much
as three times what it would otherwise be. Good nourishment doubles the
power of resisting disease; while deficient food prepares the way for many
diseases. A large share of the decline in the English death-rate during the
last forty years is due to free trade, and the great cheapening of wholesome
food which has resulted from it.
An ill-balanced is more frequent than a deficient diet. Deficiency of fat is
more serious than deficiency of carbohydrates, and deficiency of proteid is
most serious.
Scurvy is caused by the absence of fresh vegetables. The use of the
potato and the orange, as well as of lime juice (the juice of citrus limetta),
has led to its extinction among adults in this country. In former times, it
caused more deaths among seamen than all other causes put together,
including the accidents of war. In infants fed upon tinned foods, whether
condensed milk or patent foods, a form of scurvy still occurs. Infants fed on
new-milk never suffer in this way. If, therefore, it is necessary to feed an
infant on condensed milk for many consecutive months, potato gruel or raw
meat juice or fresh milk must occasionally be given.
Rickets is chiefly due to improper feeding in childhood. The substitution
of artificial foods (most of them containing starch) for the natural milk is its
chief cause. The lower incisor teeth of an infant appear between the sixth
and seventh months. Starchy food given before this age is undigested. Such
food likewise leads to less fat and proteid being given, which are essential
for growth. Deficiency of lime salts in the food does not cause it, and giving
them in food or medicine will not cure it. Enrichment of the diet by cream
or failing this by cod liver oil is the best means of preventing and curing it.
Abundant fresh air and warm clothing are also necessary.
Relapsing fever generally follows epidemics of typhus fever, and is
greatly favoured by starvation. Ophthalmia has been chiefly prevalent in
charity schools in which the children are underfed, though its essential
cause is contagion.

Diseases Connected with Over-Feeding.—A fire may go out for want
of fuel, or from becoming choked with ashes; and it is the latter state of
things which occurs in Gout and allied diseases. Weakness is commonly
complained of, but this is due to excess of food embarrassing vital action;
and abstinence and exercise are required to restore the balance. Excess of
nitrogenous food—especially if combined with the use of sweet, or strong,
or very acid wines, and beer—is particularly prone to produce gout. In these
cases, animal food should only be taken once a day, and vegetable food
should be allowed to preponderate.
Obesity is favoured by excess of starchy food and sugar, and by copious
drinking of water or other beverages. The plan of curing obesity by
restricting oneself almost entirely to meat food is only advisable, however,
under certain conditions. Gall-stones are favoured by rich foods and excess
of sugar; also by alcoholic indulgence. Dyspepsia is commonly due to
loading the stomach at too frequent intervals; but on the other hand, it not
infrequently leads to the taking of insufficient food, because of the
discomfort produced. The result of this is that a chronic starvation results,
with impaired vital powers. Dyspeptic patients should abstain from pastry
and from tea and coffee, except in small quantities. Alcohol in any form, as
a rule, does harm. Not uncommonly mastication is imperfectly performed,
and a good dentist may cure the indigestion which has resisted all other
treatment.

CHAPTER V.
DIET.
The importance of a duly proportioned and sufficient dietary is shown by
its great influence on health and constitution. An ill-proportioned or
deficient diet is certain to lead to failure of health. The anatomy of an
animal may be modified in the course of generations by altered diet, as well
as its character; thus, the alimentary canal of the cat has increased in length
to adapt it to its omnivorous habits. In the case of the bee we have a still
more remarkable instance. If by any accident the queen bee dies, or is lost,
the working bees (which are sexually undeveloped) select two or three
eggs, which they hatch in large cells, and then feed the maggot on a
stimulating jelly, different from that supplied to the other maggots, thus
producing a queen bee.
The food of mankind varies naturally with—
I.—Climate. A cold climate leads to increased metabolism, and
consequently a large amount of fatty matter can be eaten without producing
nausea. Witness the difference between a Laplander’s and a Hindoo’s diet.
The season of the year has likewise some influence. Vital processes are
more active in spring than autumn, and more food is consequently required
in the former season.
II.—Occupation. Although muscular exercise is not associated with an
immediate increase of elimination of urea, yet as a matter of experience
more nitrogenous food is required and can be metabolised by hard workers
than by idlers. The trappers on the North American prairies can live for
weeks together on meat alone, accompanied by copious draughts of tea.
They are constantly in the open air, undergoing fatiguing exercises, in a dry
and rare atmosphere. For brain workers no special food is required. Foods
containing phosphorus have no special value, so far as is known, for mental
work. Such work, however, is apt to affect digestion; consequently the

digestibility of food is more important for those engaged in sedentary
occupations than its chemical composition.
III.—Sex. As a rule, women require about one-tenth less food than men,
but probably this rule hardly holds good in the case of women engaged in
laborious work.
IV.—Age. Infants require only milk, and the less they have of any other
food before a year old the better. Atwater has calculated that——
A child under 2 requires 3 ∕ 10 the food of a man doing moderate work.
A child of 3 to 5 requires 4 ∕ 10 the food of a man doing moderate work.
A child of 6 to 9 requires 5 ∕ 10 the food of a man doing moderate work.
A child of 10 to 13 requires 6 ∕ 10 the food of a man doing moderate work.
A girl of 14 to 16 requires 7 ∕ 10 the food of a man doing moderate work.
A boy of 14 to 16 requires 8 ∕ 10 the food of a man doing moderate work.

Vital processes are more active in early life, and food is required not only
to carry on the functions of the body, but also to furnish the materials for
growth. Hence, while the proportion of proteids to carbohydrates and fats
should be—
As 1:5.3 in adults, it should be about as 1:4.3 in children.
After the age of thirty-five or forty, the tendency is to take too much
food. All the tissues of the body are established, and excess of food
(especially nitrogenous food) is liable to produce tissue degeneration by
loading the system with partially metabolised matter, and may lead to gouty
diseases. It is much safer to take what may be regarded as too little than too
much food after this period.
Times for Eating.—The best arrangement seems to be to have three
meals, each fairly nutritious, and containing all the constituents required.
The Romans only had two meals daily, prandium and cœna. This is
common among the French at present, but it tends to overloading the
digestive organs at these meals.
An ordinary full meal has usually passed from the stomach in four hours.
Fresh food ought never to be introduced before this period; it is advisable to

allow an interval of five hours between meals for the healthy, so as to give
time for the digestive organs to rest, and for the absorption of food. The
practice of taking tea with the chief meal, or a “meat tea,” is bad. Tea is
better taken an hour or two after food.
Regularity in the time of taking meals is important, as the digestive
organs acquire habits like other parts of the body. Work ought not, if
possible, to be resumed immediately after meals, nor active exercise of any
kind. These tend to abstract blood from the digestive organs, and so
diminish the efficiency of digestion.
Vegetable and Animal Foods.—The fact that the food we require can be
obtained from the vegetable world has led to the proposition that vegetable
food should be taken alone. It is urged in favour of this plan, that a large
amount of suffering to animals would be prevented. Also that animal food is
not so economical as vegetable, land being more economically employed in
producing corn than in feeding cattle. Thirdly, there is the indubitable fact
that health can be maintained for prolonged periods on vegetable food
(including nuts, cereals, fruits, etc.)
On the other hand, the chief objections to a purely vegetable diet are that
the undigested refuse is greater than with an equal quantity of animal food;
that a longer time and more exertion than for animal foods are required in
digesting the most nutritious vegetable foods, such as legumens, while other
vegetable foods do not contain a sufficient proportion of nitrogenous
material. Also, if one lived entirely on vegetable food, a greater bulk would
be required, and owing to the fact that such food is less easily absorbed,
satisfaction to the appetite would not so soon be produced. Animal food has
a great advantage as regards convenience. Man is not an eating machine; he
requires food which is easily converted into the body substance, and this is
supplied by the flesh of animals, milk and eggs, with a due proportion of
non-nitrogenous food; sheep and oxen work up indigestible vegetable
materials into easily assimilable mutton and beef. The greater convenience
of animal food as a supply of proteid is shown by the following examples of
foods after the removal of water:—
100 parts of rice contain 7 parts of proteid.
„ wheat „ 16 ”
„ pea flour „ 27 ”

„ dried lean beef „ 89 ”

On the other hand, vegetable foods are a cheaper source, not only of
carbohydrates and fats, but also of proteids as well. Thus the approximate
cost of—
1 lb. of proteid in beef is 2s. 8d.
„ „ milk is 2s. 2d.
„ „ bread is 1s. 6d.
„ „ oatmeal is 7½d.
„ „ peas is 7d.

Under the ordinary conditions of town life, there is considerable danger
of indulging in an excess of nitrogenous food, and vegetarians may
therefore do good by showing that meat is not absolutely necessary, and can
often with advantage be largely replaced by vegetable food.
If we include milk, cheese, and eggs in the vegetarian diet, the objections
to it partially disappear; and it would be well if it were much more widely
known, especially among the poor, that on these, together with vegetables,
health can be maintained with the addition of little or no meat.
The Determination of Diet.—The first principle in making a dietary is
that it must be mixed, containing all the necessary constituents, proteids,
hydrocarbons, carbohydrates, water, and salts. No one of these alone will
support life for any considerable period. Carbohydrates (sugar and starch)
can be most easily dispensed with; fats, on the other hand, are essential for
the maintenance of health.
The next point is to ascertain the proportion in which these different
foods are required. Salts are commonly taken with other foods, common
salt being the only one taken alone. The amount required is given on p. 7.
The amount of water required varies with the season of the year, the amount
of exercise and perspiration, and other factors. As a rule, not more than two
pints of water are required per day, and still less if fruit is freely taken. We
may therefore confine our attention to the carbonaceous and nitrogenous
foods, and try to ascertain the amount of each of these required. Every diet
must be subjected to the following tests, to fully ascertain its value:—

1. The Chemical Test.—The metabolism undergone by food in the body
being essentially a process of oxidation (though partially modified and
incomplete), the amount of heat yielded on complete combustion of a food
may be taken as a measure of its value as a source of energy, of which heat
and work are convertible forms. The standard of heat production is the
calorie, the amount of heat required to raise the temperature of one gramme
of water 1° C. This is the small calorie. The kilo-calorie (called the Calorie)
is the amount of heat required to raise 1 kilo (1 litre) of water 1° C., or 1 lb.
of water 4° F. In calculations on this basis, allowance must be made for
foods which are incompletely oxidised in the body. Rubner has shown that
the heat value of 1 gramme (=15½ grains) of each of the chief food stuffs is
as follows:—
Proteid 4.1 Calories.
Carbohydrates 4.1 „
Fat 9.3 „

The method of applying this standard to a food is as follows: the
percentage of proteid or carbohydrate given in the following table is
multiplied by 4.1, and the percentage of fat by 9.3:—
IN 100 PARTS.
ALBUMINATES CARBO-
WATER. FATS. SALTS.
OR PROTEIDS. HYDRATES.
Uncooked meat with little fat 74.4 20.5 3.5 — 1.6
Cooked meat—without loss 54 27.6 15.45 — 2.95
Salt beef 49.1 29.6 0.2 — 21.0
White fish 78.0 18.1 2.9 — 1.0
Bread, white wheaten 40. 8. 1.5 49.2 1.3
Wheat flour 15. 11. 2. 70.3 1.7
Rice 10 5 .8 83.2 0.5
Oatmeal 15 12.6 5.6 63.0 3.
Peas (dry) 15 22 2. 53. 2.4
Potatoes 74 1.5 .1 23.4 1.
Butter 8 2. 88 — variable
Eggs (including shell, for which deduct
73.5 13.5 11.6 — 1
10 per cent.
Cheese 36.8 33.5 24.3 — 5.4
Milk 87.0 4. 3.5 4.8 .7

Thus for bread—

Proteid 8 × 4.1 = 32.8
Fat 1.5 × 9.3 = 13.95
Carbohydrate 49.2 × 4.1 = 201.72
———
Total Caloric value of 100 grammes of bread = 248.47

The total fuel value in Calories of one pound of certain typical foods is
given by Hutchison as follows:—Butter 3,577, peas 1,473, cheese 1,303,
bread 1,128, eggs 739, beef 623, potatoes 369, milk 322, fish (cod) 315,
apples 238.
2. The Physiological Test.—Not only is a proper proportion of proteid,
fat, and carbohydrates required, but these must be capable of digestion and
absorption and of oxidation in the body. Cheese is a highly concentrated
food, but its value is less than its percentage composition would indicate,
because of the difficulty of digesting considerable quantities of it. Green
vegetables consist largely of cellulose, which is only imperfectly capable of
absorption into the blood, although it can experimentally be oxidised by
combustion. The proportion between absorbed food and food rejected in the
fæces can be ascertained by analysis. Many experiments made on these
lines show that on a purely animal diet (meat, eggs, milk) but little nitrogen
is lost, while with vegetable foods (carrots, potatoes, peas, etc.) the waste of
nitrogen is considerable. Fats are very completely absorbed from the
alimentary canal. The amount remaining unabsorbed is greatest with mutton
fat (10 per cent.), least with butter (2½ per cent.). Experimentally it has
been found that an amount up to 150 grammes (about 5½ oz.) of fat can be
absorbed without appreciable loss. Carbohydrates are very completely
absorbed, even starchy foods rarely escaping digestion. Completeness of
absorption from the alimentary canal is not desirable for all foods; a certain
amount of unabsorbed residue is required to stimulate peristalsis. With a
purely vegetable diet this amount is excessive, and there is physiological
waste of effort.
3. In practical dietetics the Economic test is important. Carbohydrate is
by far the cheapest food, and generally vegetable are cheaper than animal
foods. Thus a shilling’s-worth of bread yields 10,764 Calories, while the
same sum spent on milk would only yield 1 ∕ 3, and on beef 1 ∕ 10 this number
of heat units. Similarly a shilling’s-worth of peas contains 572 grammes of
proteid, about double as much as the same money’s-worth of cheese; while

to obtain the same amount of proteid from eggs would cost more than eight,
and from beef more than five times as much as from peas (Hutchison). The
market price of foods is no certain indication of their nutritive value. Thus
haddock will supply as much nutriment as sole at a fourth of the cost; Dutch
as much nutriment as Stilton cheese at less than half the cost. Similarly the
most economical fats are margarine and dripping.
4. An Examination of Actual Dietaries under various conditions has
strikingly confirmed the results obtained by other methods. It has been
found that (a) the potential energy required by a healthy man weighing 11
stones, and doing a moderate amount of muscular work is 3,000 to 3,500
Calories (=310 grains); and that (b) about 20 grammes of nitrogen and 320
grammes (=4,960 grains) of carbon are excreted by such a man. (c)
Expressing the 3,000 Calories required in terms of grammes of food, it is
found that 125 grammes of proteid, 500 of carbohydrate and 50 of fat are
necessary. These facts are expressed in the following table (Hutchison):—
STANDARD AMOUNT
OF SAME AMOUNT OF FOOD
FOOD IN TERMS OF YIELDING
FOOD
ENERGY IN
CONSTITUENTS
Calories.
REQUIRED
CARBON. NITROGEN.
(IN GRAMMES).
Proteid 125 62 20 512·5
Fat 500 200 ─── 2050·
Carbohydrate 50 38 ─── 465·
675 300 20 3027·5

Three of the best known standard dietaries give the amounts in grammes
of each food constituent as follows:
PLAYFAIR. MOLESCHOTT. ATWATER. AVERAGE.
Proteid 119 130 125 125
Fat 51 40 125 72
Carbohydrate 531 550 450 510
Calories 3140 3160 3520 3273

Expressing the same facts in English ounces instead of grammes, 42 ∕ 5 oz.
of proteid, 2½ oz. of fat, and 18 oz. of carbohydrate, would represent the
ounces of each constituent required according to
(1) (2)

AVERAGE OF ABOVE
HUTCHISON.
THREE DIETARIES.
Proteid 4∕ 4∕
25 25
Fat 21∕2 1∕
45
Carbohydrate 18 17 ∕ 35
Ounces of dry food 24 ∕ 23 ∕
910 45

The chief point of divergence in the above standard dietaries is in the
relative proportion of carbohydrate and fat. Probably the correct proportion
between these is as 1 to 10; but it will vary according to climate and other
circumstances. Detailed examination of a large number of dietaries shows
that the amount of daily proteid should be about 125 grammes, or 4⅖ozs.
This is contained in 20 eggs, or in 18 oz. i.e. about 4½ ordinary platesful of
cooked meat.
It must be noted that the 23-24 oz. of food given above as the standard
daily amount represents dry food. This represents 40 oz. or nearly 3 lbs. of
ordinary food.
The following example by Waller, gives a rather liberal standard English
diet, for a man doing a moderate amount of muscular work.
CARBON. NITROGEN.
Foundation: 1 lb. bread 117 5.5
½ lb. meat 34 7.5
¼ lb. meat 84 —
Accessories: 1 lb. potatoes 45 1.3
½ pint milk 20 1.7
¼ lb. eggs 15 2.0
⅛ lb. cheese 20 3.0
—- ——
Total 335 21 grammes.

This divided up into meals works out roughly as follows (Hutchison):—

Two slices of thick bread and butter.
Breakfast
Two eggs.

One plateful of potato soup.
A large helping of meat with some fat.
Dinner
Four moderate sized potatoes.
One slice of thick bread and butter.
Tea A glass of milk and two slices of thick bread and butter.
Supper Two slices of thick bread and butter and 2 oz. of cheese.

From the preceding data, practical problems as to dietaries are easily
solved. Thus if it be required to find
how much oatmeal, milk, and butter would be required to give a sufficient quantity of albuminoids,
fats, and carbohydrates to an adult male,
the calculation may be based on the figures in the table on p. 32, or the
following figures may, for the sake of convenient calculation, be taken as
representing the percentage amount of each of these chief food principles
contained in the foods named:—
ALBUMINOIDS. FATS. CARBOHYDRATES.
Oatmeal 12 6 60
Milk 4 3 5
Butter 2 88 —

Let
o = number of ounces of oatmeal required.
m = number of ounces of milk required.
b = number of ounces of butter required.
Then
(12o + 4m + 2b ∕ 100 = 4.5 ozs. of albuminoid
(6o + 3m + 88b)/100 = 3 ozs. of fat
(60o + 5m)/100 = 14.25 ozs. of carbohydrate,

according to Moleschott’s diet.
When these equations are worked out by substitution and transference—

o = 19.2 ounces.
m = 55.4 ounces.
b = 0.24 ounces.

Similarly if it is required to find how much meat, bread, and butter of the following percentage
composition will be required to give a man a sufficient amount of albuminoids, fats, and
carbohydrates.

ALBUMINOIDS. FATS. CARBOHYDRATES.
Meat 25 15 0
Bread 8 1.5 50
Butter 2 88 0

Let
m = number of ounces of meat required.
b = number of ounces of bread required.
B = number of ounces of butter required.
Then
(12m + 8b + 2B)/100 = 4.5 ozs. of albuminoid
(15m + 1.5b + 88B)100 = 3 ozs. of fat
50b ∕ 100 = 14.25 ozs. of carbohydrates

When these equations are worked out—

m = 6.28 ounces.
b = 28.5 ounces.
B = 1.15 ounces.

Relation of Food to Mechanical Work.—In the body the movements of
every part are constant sources of heat. It is evident therefore that the
potential energy of food can be expressed by (a) the amount of heat
obtained by its complete combustion, or (b) by the amount of work capable
of being obtained from it. Joule discovered by exact experiment that the
mechanical power obtainable from a given amount of fuel is directly
proportional to the amount of fuel used, being in fact due to the oxidation of
this fuel, the heat produced being transformed into mechanical power. The
heat unit or calorie has been already given (p. 32). The gram-metre is the
work unit. The heat unit corresponds to 425.5 units of work. Thus the same
energy required to heat one gramme of water 1° C. will raise a weight of
425.5 grammes to the height of 1 metre. Conversely a weight of 425
grammes if allowed to fall from a height of 1 metre, will by its concussion
produce heat sufficing to raise the temperature of 1 gramme of water 1° C.
In England the amount of work done is commonly expressed as foot tons,
i.e. tons lifted one foot; while in France it is similarly expressed as
kilogrammetres. Gramme-metres can be converted into foot-pounds by
multiplying them by .007233, and kilogrammetres into foot-tons by
dividing by 311.
Frankland estimated that—
1 oz. dry albumin yields 174 foot-tons of potential energy.
1 oz. fat „ 378 „ „
1 oz. starch „ 135 „ „
1 oz. cane sugar „ 129 „ „
1 oz. glucose or lactose „ 122 „ „

In practical dietetics digestibility of food as well as chemical composition
is an important factor. Furthermore metabolism in the body is not in every
instance so complete as oxidation outside it. Hence estimates of potential
energy can only be regarded as theoretically correct. Examination questions
like the following are occasionally asked:—
A man does work equal to 176.8 foot-tons in a day. Supposing that he eats only bread, how much
will he require to give the amount of energy required, if bread contains 8 per cent. proteid, 1.5 per
cent. fat, and 49.2 per cent. carbohydrate?
On the above basis, from 100 ounces of bread the amount of potential energy obtainable is:—

8 × 174 = 1,392 foot-tons
1.5 × 378 = 567 „
49.2 × 135 = 6,642 „
———
Total energy = 8,601 „ obtained from 100 ozs. bread.

Let b = number of ounces of bread required to develop 176.8 foot-tons of energy.
Then 8,601: 100:: 176.8: b.
Therefore b = 2.05 ounces.

CHAPTER VI.
THE PREPARATION AND PRESERVATION OF
FOOD.
Objects of Cooking.—Food may be taken in its crude condition, as
directly derived from the animal or vegetable world, or after it has
undergone a preparatory process of cooking. Man is the only animal who
cooks his food. Many foods, in the uncooked condition are almost entirely
incapable of digestion by him—such as the proteid and farinaceous
materials contained in the seeds of cereal and leguminous plants. But
cooking, as a preparatory help to the digestion of food, is not equally
required by all foods. Thus, fruit is commonly taken uncooked, and does
not undergo any important alteration on cooking. Salads are taken
uncooked, but not for their nutritive properties so much as for a relish to
other foods, and for their quasi-medicinal properties. Milk, again, may be
taken cooked or uncooked. The oyster is the only animal which is eaten
habitually, and by preference, in the uncooked condition; and there is a
physiological reason for this universal custom. The large fawn-coloured
liver, which constitutes the delicacy of the oyster, is little else than
glycogen, associated with its appropriate ferment diastase, so that the oyster
is almost self-digestive. When cooked, the ferment is destroyed, and
digestion of the oyster becomes more difficult.
Cooking is intended—1. To make the food softer, and in part to
mechanically disintegrate it, thus rendering it more easily masticated and
digested. In fact, cooking, in the best sense, is an artificial help to digestion;
and digestion may well be said to commence in the kitchen.
2. To produce certain chemical changes. Thus, starch is partially
converted into dextrine; gelatin is formed from connective tissue, etc.
3. To destroy any noxious parasites present in the food, or obviate any ill
effects from putrefactive changes. Diseased meat chiefly produces bad
effects when imperfectly cooked.

4. To make the food more pleasant to the eye and agreeable to the palate.
The improved savour in cooked meat, for instance, has a very appetising
effect, and consequently makes digestion easier.
The Cooking of Flesh.—1. Roasting is, perhaps, the most perfect way of
cooking meat. It exalts its flavour more than any other method. In roasting,
place the meat at first sufficiently near a brisk fire, so that the albumin on its
surface may be readily coagulated, and the juices retained in the interior of
the joint. After about fifteen minutes, the joint ought to be removed
somewhat further from the fire, and allowed to cook slowly. Frequent
basting is desirable to obtain a good result. Brown meats, such as beef,
mutton, and goose, require a quarter of an hour per pound weight; veal and
pork require about ten minutes additional, to ensure the absence of redness.
White-fleshed birds require a somewhat shorter time. The time required in
roasting will be a little more if the joint is large, or the fire not very clear. To
ascertain if the meat is sufficiently cooked, press the fleshy part; if it
remains depressed, it is done; if not done, it retains its elasticity. At the first
incision, gravy should flow out of a reddish colour.
The changes undergone during roasting are, that the connective tissues
uniting the muscular fibres is converted by the gradual heat into gelatin,
which is soluble and easily digested; the muscular fibres, consequently,
become more separable, and the myosin of which they consist is rendered
more digestible. The fat is partly melted out of its fat cells, and partly
combines with the alkali from the blood-serum. Empyreumatic oils (i.e. fat
partially burnt), developed by charring of the surface of the joint, are
carried off when it is roasted in front of the fire; and so, to a large extent, is
acrolein. Acrolein (C₃H₄O) is always produced by the destructive
distillation of neutral fats containing glycerine, and is the cause of the
intolerably pungent odour accompanying the process. Osmazome, a
peculiar extractive matter, on which the flavour and odour of meat depend,
is developed better by roasting than by any other method of cooking.
It is useful to remember, in buying beef or mutton, that 20 per cent. must
be allowed for bone and 20 to 30 per cent. for the loss during cooking.
The following figures are by Johnston:
IN ROASTING. IN BAKING. IN BOILING.

4 lb. of mutton lose in weight 1 lb. 6 oz. 1 lb. 4 oz. 14 oz.
„ beef „ 1 lb. 5 oz. 1 lb. 3 oz. 1 lb.

Thus roasting is the least economical method of cooking. The chief loss,
however, is of water; the dripping and gravy are recoverable.
2. Baking of meat in a closed oven does not produce so agreeable a result
as roasting in front of an open fire. The oven ought always to be very hot
before the meat is put in, in order to rapidly coagulate its surface. Baked
meat may have an unpleasant flavour, owing to its saturation with
empyreumatic oils, which escape in open roasting. The unpleasant flavour
can be prevented by covering the meat with a layer of some non-conducting
material, as a pie-dish or a crust, no empyreuma being then formed. Baked
white of egg, as in the dish of fried ham and eggs, is one of the most
indigestible forms of albumin obtainable.
3. Boiling of meat requires the same time as roasting. If the flavour and
juices are to be retained, the joint ought first to be plunged into soft boiling
water, and then, after three minutes, allowed to stand aside in water at 170°
Fahr. The preliminary boiling forms a coating of coagulated albumin over
the joint. Where there is no thermometer to guide the cooking—after the
preliminary boiling for three to five minutes, add three pints of cold water
to each gallon of boiling water, and retain at the same temperature for the
rest of the process, i.e., at about 170° Fahr. If the meat is boiled in an inner
vessel surrounded by water (water-bath), the temperature of the inner vessel
does not rise above 160°-170° F. Ordinary “simmering” means that the
meat is kept all the time at a temperature of 212° F. and is thus spoilt. The
boiling of an egg is an example of the same point. If an egg is kept in water
at a temperature of 170° F. for 10 to 15 minutes, its contents form a tender
jelly, while an egg kept in water at 212° F. for the same length of time is
hard and tough. An egg is more digestible when cooked in water at 170° F.
for 10 minutes than when boiled in water for 2½ minutes.
The use of soft water for cooking purposes is always advisable; otherwise
a longer period must be allowed. A preliminary boiling for a few minutes
renders hard water softer, and the addition of a little carbonate of soda has a
like effect.

When meat is inserted in water at a temperature below its boiling point,
the juices are gradually extracted, while the meat is left a mass of
indigestible fibres. A good soup is produced, but the meat is almost
valueless. In order that the soups and broths may be nutritious, the less heat
is employed in their preparation the better. If a soup is strained to make it
clear, much of the most valuable part is removed.
Stewing is a process intermediate between boiling and baking. It
possesses the great advantage over dry baking that no empyreumatic gases
are produced, and there is no charring. The temperature of the stew-pan
ought never to be above 180° Fahr.; at this heat the roughest and coarsest
kinds of meat are made tender. The only objection to stewing is that the
meat becomes saturated with fat and gravy, and is too rich for weak
stomachs. It is advisable to stew lean meats only.
Hashing is a process of stewing applied to meat which has been
previously cooked. The consequence of this double cooking, is that the
meat becomes tough and leathery. A modified hash in which the meat is
simply well warmed throughout is preferable.
Frying, unless carefully done, renders meat difficult of digestion, each
fibre becoming coated with fat. The art is to “fry lightly,” that is, to burn
quickly and evenly, so that no charring is produced. Two methods of frying
are described. In the first, the substance to be fried, as an omelette or
pancake, is placed with a little fat or oil in a frying-pan. This is really a
modified process of roasting, the fat merely serving to prevent the object
from adhering to the shallow pan. In the second, the substance to be fried is
immersed in fat; for this purpose a frying kettle is required. Olive oil or
good cotton seed oil is best for use in the frying-kettle. Lard is a bad
material for frying; both it and butter are apt to burn unless heated slowly.
Dripping is a good substance for frying. The fat used must be heated to
from 350° to 390° F., and then the substance to be fried, e.g. a sole, plunged
into it and left for two or three minutes. In this process the substance of the
sole is really being steamed by the steam generated in the substance of the
sole.
6. Broiling and Grilling are really processes of roasting applied to small
portions of meat. In grilling, it is important that the gridiron should be hot

before putting anything on it. An external coagulation of albumin is
produced, as in good roasting and boiling.
The Cooking of Mixed Dishes.—A few instances may be given of
common errors in preparing compound dishes. An egg in a custard, or just
coagulated in a poached egg, is a light and easily-digested food; baked half
an hour in a pudding, it is much less digestible; fried with ham, it is almost
as indigestible as leather. Spices, if mixed with a dish before it is boiled,
lose nearly all their flavouring power, while they remain irritating. They
ought to be added near the end of the cooking process. A soup containing
vegetables, as well as meat juices, should be prepared in two parts. The
vegetables require prolonged boiling; gravy is spoilt by this. Similarly, the
jam in a tartlet, if inserted before baking, loses its proper fruity flavour; and
oysters baked in a beef-steak pie are indigestible.
The Cooking of Vegetable Foods.—Bread is either vesiculated or
unvesiculated; the latter being what is called unleavened bread. Vesiculation
of bread has usually been produced by fermentation of some of the sugar of
the flour. The starch first becomes sugar (dextrose) and then the growth of
the yeast plant in the dough splits this up into alcohol and carbonic acid gas.
The carbonic acid percolates the substance of the dough, rendering it
porous. When it has “risen” sufficiently, the dough is placed in the oven.
The heat of the latter kills the yeast plant, thus preventing any further
fermentation, but at the same time expands the carbonic acid gas in the
bread, rendering the latter still more porous, and drives off in a gaseous
condition the greater part of the alcohol produced by the previous
fermentation.
It is objected to this plan of making bread, that a little of the sugar is
wasted in producing alcohol and carbonic acid. To remedy this, another
plan is sometimes adopted, as first proposed by Dr. Dauglish. In it the
dough is charged with carbonic acid dissolved in water under considerable
pressure. The gas escapes in the substance of the dough, and on baking
expands as in the ordinary method of making bread. Bread made in this
manner, is called “aerated bread.” Nevill’s bread has a solution of carbonate
of ammonia incorporated in the dough, which is dissipated by heat, thus
causing vesiculation of the bread.

On the continent, a mixture of hydrochloric acid and carbonate of soda is
commonly used, carbonic acid and common salt being formed in the dough.
Thus NaHCO₃ + HCl = NaCl + H₂O + CO₂. The hydrochloric acid
employed should be perfectly pure and free from arsenic. Baking powders
are also largely used for making cakes. “Self-raising” flour is flour with
which baking-powder has already been mixed. Most baking-powders
consist of a mixture of carbonate of soda and tartaric acid or bitartrate of
potash, diluted with starch. When wetted, carbonic acid gas is evolved. A
few contain alum, which is now an illegal material for this purpose.
Ten pounds of flour ought to make thirteen to fourteen of bread. The use
of stale bread is much more economical than of newly-made bread; besides
this, it is more digestible. Newly-made bread is more palatable than stale,
but it is more cohesive, and does not crumble into separate particles like
stale bread. The consequence is, that it is less digestible, being less easily
penetrated by the saliva and other digestive juices. The effect of toasting is
to render bread more friable, and consequently more digestible. It ought,
however, to be thin and eaten soon after it is made; when thick and kept too
long, it becomes tough and leathery.
Pastry is less easily digested than ordinary bread. The lard or dripping
added renders it more flaky and less easily pulverised; and, in addition, the
fat coats over the starch cells; and thus the action of the digestive juices on
the pastry is impeded.
Potatoes ought to be boiled in their jackets, or steamed, to avoid loss of
nitrogenous material and salts. Moist heat causes the starch granules to
swell, and ultimately softens and bursts the cellulose envelopes in which
these are contained. Dry heat, as when potatoes are baked, converts starch
into a soluble form, and ultimately into dextrine (= C₆H10O₅), an
intermediate stage towards the formation of dextrose (i.e. glucose =
C₆H12O₆).

Peas and Beans ought to be boiled slowly and for a long time to render
them more digestible. If old, they ought to be soaked in cold water for
twenty-four hours, then crushed, and stewed. Hard water must be avoided
in the cooking of peas and beans as well as of other vegetables, as the lime-
salts form insoluble compounds with legumin.

Green vegetables require thorough and prolonged cooking. This renders
their tissues softer and more easily attacked in digestion. The members of
the cabbage tribe and carrots can hardly be boiled too long. Soft water
ought always to be used; this is one reason why steaming is preferable.
Before boiling, all vegetables should be well washed in cold water. A little
vinegar will remove any insects present.
Cooking Apparatus.—The apparatus required in cooking may be divided
into kitchen utensils and cooking ranges.
To ensure good cooking, perfect cleanliness of all apparatus is
indispensable. The use of the frying-pan, gridiron, spit, and oven has been
sufficiently indicated under the description of the different methods of
cooking. The form of stove to be used for cooking meat is gradually being
settled against the old open stove. Although this secures a somewhat more
savoury joint than when meat is baked, it is extravagant in working. The
closed kitchener in which coal is employed is less economical than a gas
stove at the present price of gas, if the latter is carefully used.
Various appliances for economising fuel have been devised, and at the
same time of allowing of the prolonged action of a moderate degree of heat.
These are usually constructed on the principle of an ordinary bath,
consisting of a double pan, with a layer of water between the two
compartments. Warren’s cooking-pot belongs to this type. The Aladdin oven
consists of an iron box with an opening above to let off superfluous steam.
This box is surrounded by another composed of non-conducting material,
while a lamp below furnishes the heat. Dr. Atkinson has calculated that in
an ordinary oven 2 lbs. of fuel must be expended for every pound of food
cooked, while in his Aladdin oven 2½ lbs. of fuel will cook 60 lbs. of food.
Time is an important element in cooking. Food is most thoroughly cooked
and most digestible when subjected to a temperature below that of boiling
water for a prolonged period.
The Preservation of Food.—All organic foods tend rapidly to decompose
and putrefy. Putrefaction only occurs when a warm and moist substance is
exposed to the air. The problem of preserving any food, therefore, may be
solved (1) by keeping it at a very low temperature, (2) by desiccating it, or
(3) by boiling or steaming it so as to destroy any microbes in the food

which would otherwise start putrefaction, and then fastening it in an air-
tight case.
Milk is commonly preserved as condensed milk, and in this condition is
very valuable. A pure condensed milk is now supplied, prepared without the
addition of sugar or any antiseptic, but in which, as in other condensed
milks, all disease-producing or decomposition-producing microbes have
been destroyed during the process of concentration. Milk may also be
desiccated; in this condition it is difficult of digestion.
In addition to the household methods of preserving fruits, large quantities
of fruits—both moist and dry—are now imported, protected by syrup or
sugar, in sealed canisters; and they retain the original flavour almost
unchanged.
The preservation of meat is effected by—
1. Drying.—This must be done rapidly. It is a process which is best
applicable to fish, but has been applied also to beef. Dried Hamburg beef is
used for making sausages. Pemmican, largely used by Arctic voyagers,
consists of a mixture of meat and fat, dried and powdered along with some
spices; it is generally eaten with some kind of meal.
2. Cold.—Frozen meat now forms a very large part of the food of the
English people. If the meat has been frozen before rigor mortis (rigidity
after death) has commenced, it keeps well; if frozen later, it rapidly
decomposes after being thawed. Freezing arrests putrefaction and tends to
conceal its odour. Hence the bad condition of frozen fish may not be
detected until it is cooked. In cooking frozen meat, time should be allowed
for thawing to occur, before the meat is placed in the oven. Much of the ill-
founded prejudice against frozen meat arises from inattention to this point.
Frozen meat is equal in nutritive value to and does not lose more in cooking
than fresh meat.
3. Salting may be done with brine or saltpetre (nitrate of potassium); the
latter does not decolourize the meat like the former. Salted meats have lost
much of their nutritive material, in the form of albumin and salts, and the
remaining meat is harder and more difficult of digestion than fresh meat.

4. Immersion in antiseptic liquids or gases, as sulphite of soda, is
objectionable, on account of the addition of extraneous, and not altogether
innocuous, salts. Boric acid powder is largely used for sprinkling on meat,
particularly rabbits, etc., and for preserving hams and other meats. Its use is
to be deprecated. All such meats should be thoroughly washed with water,
before being cooked.
Solutions of boric acid and borax are frequently added to milk. Their use
is objectionable (a) because they tend to conceal incipient decomposition,
but do not prevent its possible evil effects, and (b) because they enable the
farmer to palm off dirty milk on the public. Were the addition of
preservatives to milk forbidden, the farmer could perfectly well keep his
milk sweet until it reached the town-consumer by adopting strict measures
of cleanliness, and by cooling his milk before it leaves the farm. At the least
it should be made obligatory on the milk retailer to declare the presence of
preservatives in milk sold by him.
The presence of borax or boric acid can be detected by evaporating the milk to dryness,
incinerating and then moistening the ash with a drop of strong sulphuric acid. If a little alcohol be
now added, on applying a light, a green flame indicates boric acid. Milk or cream containing boric
acid turns blue litmus paper red.

Formalin is also sometimes used as a preservative for milk in very weak
solution.
Its presence can be determined by diluting the milk with water in a test-tube, and running strong
sulphuric acid down the side of the tube, taking care to prevent mixing. At the junction of the acid
and diluted milk a violet ring is seen if formalin is present.

Salicylic acid was formerly used as a milk preservative, but is now
seldom used except in beers. All these preservatives are objectionable in
milk, although their injurious action may be difficult to prove.
5. Coating with fat or gelatine has only succeeded in conjunction with
the exclusion of air. This process is especially applicable to fishes, as tinned
sardines. In a modified form, it is useful in coating potted meats, etc.
6. Heating and Air-tight Cases.—Tinned meats prepared according to
this method are imported in large quantities. In the process of preparation,
the cases are packed with meat and filled up with gravy, and then closed
with a cover which is hermetically sealed, except at one point. The case is

then heated to 250° Fahr., in order to drive out all air, and destroy any
putrefactive germs present. The open point is sealed while the gravy is still
boiling, thus making the case completely air-tight. Albumin is coagulated at
about 170° Fahr.; the higher temperature, which it is found necessary to
employ, overcooks the meat and renders it less digestible (see also p. 40).

CHAPTER VII.
CONDIMENTS AND BEVERAGES.
Condiments, etc.—The name condiment is used in various senses by
different writers. In its strictest sense it is a substance containing a volatile
oil or ether, which may be taken with salt, and the object of which is to
excite the senses of taste and smell, and consequently produce an appetising
effect. This definition excludes spices, substances allied to condiments, but
usually taken with sugar, as cinnamon, ginger, etc.; also flavouring agents,
such as vanilla; and acids, such as vinegar and lemon-juice. If we use the
word in its widest sense, to include these various groups of substances, we
find that all condiments are taken with the object of improving the taste or
flavour of food, or of assisting its digestion; but that they are not foods in
the sense of supplying any elements towards building up the body or
maintaining its heat. The only partial exception is lemon-juice, the salts of
which have a quasi-medicinal use.
Taste is usually a compound sensation, the organs of which are the nerves
of taste and smell. True taste is confined to the appreciation of sensations of
bitter and sweet; but the flavour of meats is nearly entirely appreciated by
the sense of smell. This is shown by the fact that meats appear tasteless and
insipid, during “a cold in the head.” In the appreciation of acid, astringent,
and fiery substances, the sense of touch is also employed. The excitement of
these different nerves results in a stimulus which is carried up to the central
nervous system, and causes by reflex action an increased flow of the
digestive juices. Hot substances, like cayenne and ginger, also cause an
increased flow of gastric juice, by directly congesting the mucous
membrane. This action is not so desirable as that through the influence of
the nervous system. All natural foods are sapid and possessed of flavour,
and thus stimulate secretion; but any local irritating effect ought to be
avoided.
1. Condiments proper comprise chiefly mustard, pepper, cayenne, garlic,
onion, capers, mint, sage, morels, mushrooms, truffles. The last three on the
list are also foods, but are more commonly used as condiments.

All these act as stimulants to the digestive organs, and in small quantities
aid digestion. The active principle of mustard and horse-radish is
sulphocyanide of allyl. Horse-radish is not so wholesome as mustard, the
scraped root being apt to adhere to the stomach like the skins of grapes, and
produce indigestion. Pepper contains an acrid resin, a volatile oil, and an
alkaloidal substance, called piperine. Cayenne contains an analogous
substance, called capsicin. Cayenne, unless in extreme moderation, is
harmful, as its small particles adhere to the mucous membrane of the
stomach, and may set up considerable irritation.
2. Spices are those condiments which contain an aromatic oil, and which
harmonize with sugar. They are, as a rule, less irritating to the stomach than
those of the pepper group. Cinnamon, cloves, camphor, ginger, and curry
powder are the chief of these. Curry powder really belongs to both the first
and second divisions. When genuine, it is said to contain turmeric,
cardamoms, ginger, allspice, cloves, black pepper, coriander, cayenne, and a
few other substances.
3. Flavouring agents, such as vanilla, lemon peel, and fruit essences, are
used to give a pleasant flavour to various dishes.
4. Acidulous substances are taken chiefly because of their sharp and
agreeable taste. Vinegar is the chief acid employed. It is produced by the
action of a fungus (Mycoderma aceti) on alcoholic liquids, as wine, or beer,
C₂H₅OH (alcohol) becoming C₂H₄O₂ (acetic acid). It is also produced by
the destructive distillation of wood. In small quantities it does not stop
digestion, but, by exciting the nerves of taste, may be of actual service. It
helps to soften the vegetable fibres in a salad; and is also useful for the
same purpose with hard meats, as lobster, etc. In large quantities it
diminishes the power to assimilate food.
Good vinegar ought not to contain less than 3 per cent. of acetic acid; and sulphuric acid beyond 1
in 1000 in vinegar is to be regarded as an adulteration. A specific gravity below 1015 indicates the
addition of water.

Citric acid and lemon-juice are useful for their refreshing properties, and
the latter also because of its alkaline salts.
Oils, such as olive oil, have been sometimes classed under condiments,
but as they have great nutritive properties, this is hardly accurate. For the

same reason, salt is not classed under this head.

BEVERAGES.

Water is the universal beverage, and for healthy persons is preferable to
any other. All other beverages necessarily contain it as their basis.
It will be convenient to consider first aërated and other natural waters;
then tea, coffee, and cocoa; and finally, alcohol.
1. Aerated Waters contain carbonic acid (carbon dioxide) in solution,
which gives to them their characteristic sharp taste and sparkling character.
Thus distilled water charged with gas is sold as Salutaris or Puralis water.
Soda water contains three to five grains, and medicinal soda water fifteen
grains of bicarbonate of soda to the bottle. Potash water contains fifteen
grains of bicarbonate of potash to the pint, in each case carbonic acid being
dissolved under pressure. In lemonade, ginger-beer, etc., the basis is
sweetened water, rendered tart by the addition of an acid, and finally
charged with carbonic acid. Lemonade frequently contains acetic or
phosphoric acid instead of citric or tartaric, and ginger-beer the same
constituents with some added tincture of ginger. Home-made lemonade
prepared from fresh lemons is a much more wholesome drink. Ginger-beer
(stone ginger) is produced by the fermentative action of yeast on a solution
containing sugar, bruised ginger, tartaric acid, and oil of lemon. It usually
contains at least two per cent. of alcohol.
Natural Mineral Waters usually contain common salt (chloride of
sodium) and alkaline salts of soda or lime, and are impregnated with
carbonic acid gas. Apollinaris, Rosbach, and Johannis possess these
characteristics. The carbonic acid in natural waters is partially combined,
and is given off more gradually than that in artificial mineral waters.
In all the preceding waters there is considerable carbonic acid. This acts
as a sedative to the mucous membrane of the stomach, and is useful in
indigestion. An aërated water added to milk renders it more digestible by
diluting it, and by preventing the formation in the stomach of a heavy clot
of casein. In the making of artificial aërated waters, it is essential that the
water employed should be pure, that the acid used in generating the

carbonic acid should be free from arsenic or other impurities, and that the
water should not be allowed to come into contact with lead at any stage, as
in pewter fittings. One per cent. of proof spirit is allowed in temperance
beverages by the Excise.

TEA.

Tea is the leaf of an evergreen shrub, the Camellia thea, which is
cultivated in China, Japan, British India, Ceylon, Java, and other countries.
The tea leaves, as seen in this country, uncurl in hot water. They are
lanceolated, with a serrated edge, and the veins do not extend to the edge of
each leaf. By these characteristics they may be distinguished from foreign
leaves, e.g., the sloe and willow used as adulterants (Fig. 4). The use of old
and exhausted leaves can be detected by a determination of the percentage
of soluble matter dissolved by boiling water from a given weight of tea.
This on evaporation to dryness should be 28 to 30 per cent. of the total
weight of the original tea. The presence of clay, iron dust or other forms of
dust is detected by igniting a given amount of tea and determining the
amount of ash. This should be only about six per cent.
In black tea, the leaves are dried in the sun, rolled and allowed to become
soft and to ferment. During this process, some of the tannin appears to be
converted into less soluble forms. The leaves are afterwards sun-dried, and
these “fired” in a furnace. Green tea leaves are dried in the fresh condition
over wood fires. Indian teas have more “body” and astringency than China
teas. The smallest and topmost leaves of the tea plant give the finest sort of
tea (Orange Pekoe); next to this comes Pekoe; the next largest leaves
producing Souchong; after these Congou; while the coarser leaves nearer
the base used to yield Bohea, which is now seldom seen.
Tea consists of three important constituents—volatile oil, theine or
caffeine, and tannin—and soluble and insoluble extractive matters.
The amount of caffeine varies from 2 to 4 per cent.
„ „ „ tannin „ „ 10 to 12 „ „
„ „ „ volatile oil is about ½ „ „

(1) Volatile Oil gives the aroma and flavour to each particular tea. It is
this which causes the headache, trembling, wakefulness, and restlessness,

occasionally produced by tea, especially by green tea.

Leaves of
(A) Elder. (B) Tea. (C) Tea. (D) Sloe. (E) Elder.
Fig. 4.

(2) Theine or caffeine, is an alkaloidal crystalline principle. Its
composition is represented by the formula C₈H10N₄O₂, H₂O. Ceylon tea,
broken leaf contains 4·03 per cent., Assam (Indian) tea, broken leaf 4·02
per cent., while Chinese teas contain from 2·89 (Moyune Gunpowder) to
3·74 (Moning, black leaf) per cent. of caffeine (Allen).
Theine is the most important constituent of tea and coffee. It is a
stimulant, but unlike alcohol, acts even more upon the central nervous
system than upon the heart. It removes the sense of fatigue, and may,
especially if taken in excessive doses, produce sleeplessness. Its stimulant
action on the heart is followed by increased flow of urine, and it thus helps
in the removal of waste products from the system. The effect on the tissue-
changes of the body is somewhat doubtful. It has been stated to arrest or
diminish the waste, i.e., the metabolism, constantly going on in the system,

and so diminish the amount of food required to repair this waste. This is
highly improbable; we cannot conceive the likelihood of the development
of energy without a corresponding expenditure of material, and that is what
would be the case if theine increased the activity of various organs while
retarding their waste. The experiments of Conty and Guimarès on the action
of coffee show that this (and tea has the same essential constituent) does not
diminish tissue waste. It does not prolong life in starvation, though it may
lessen the feeling of hunger. Hence tea and coffee, which owe their value
mainly to the caffeine or theine contained in them, are in no sense foods.
(3) The amount of Tannin varies from 12·31 in Ceylon tea (broken leaf,
Pekoe) to 11·76 in Moning, black leaf, and 9·9 per cent. in Natal Pekoe
Souchong (Allen). The difference in tannin between Chinese and Indian
teas is not therefore so great as is usually supposed. Tannin is a powerful
astringent, and possesses a bitter styptic taste, and a constipating effect on
the bowels. Its amount is increased by long “brewing,” as is shown by the
following results (Hale White):—
Three Minutes’ Fifteen Minutes’
Infusion. Infusion.
Finest Assam 11·30 per cent. 17·73 per cent.
Finest China 7·77 per cent. 7·97 per cent.
Common Congou 9·37 per cent. 11·15per cent.

The Mode of Preparation of Tea is important. It is clear that the
percentage of tannin to weight of leaf used in making the infusion increases
with the protraction of the infusion. On the other hand caffeine is so soluble
that it is nearly completely dissolved as soon as infusion has begun.
Dittmann found that five minutes infusion of Indian tea extracted 3·63 and
ten minutes infusion 3·73 per cent. of caffeine. The Chinese put the tea
leaves in a cup, and having poured boiling water on them, drink the
resulting infusion after a very short time, without adding anything. The
Russians drink the infusion with a squeeze of lemon, and with or without
sugar. We add cream or milk and generally sugar, and so render it more
nutritious, though the delicate flavour is veiled. The Chinese plan of
infusion for a short time is the best, as it ensures the extraction of the
aromatic and stimulant principles of the tea with only a proportion of the
tannin.

In making tea it is important to use a tea-pot which is quite dry, in order
to avoid mustiness; to pour a small quantity of boiling water into the tea-pot
and then out again, so that the infusion may be made at the temperature of
boiling water; and to use water which has only freshly come to the boil, and
so has not been rendered flat, and not to infuse longer than five minutes.
For persons of weak digestion, the best kind of tea is that obtained by
pouring boiling water on the leaves, and then immediately pouring the
resulting infusion into another hot tea-pot. In all cases where tea has to be
kept a considerable time, it should be poured into a second tea-pot, the
leaves being left behind.
Indigestion is not an uncommon consequence of tea-drinking; caused by
the excess of tannin in the tea, by the other constituents of the tea, or more
commonly by the practice of drinking tea in small sips, with bread and
butter. The tea infusion usurps the place of the saliva, the secretion of saliva
remaining partially in abeyance. The presence of tannin in tea renders it an
undesirable part of a substantial meal. Tannin coagulates albumin, and
retards its solution by the digestive juices. Hence “high teas” and “tea-
dinners,” unless the tea is very weak, are objectionable. The practice of
drinking tea with every meal is inexcusable.
For quenching thirst during active exercise, and rendering possible
prolonged exertions, tea is unsurpassed.

COFFEE.

Coffee is the seed of the berry of the Caffea Arabica. Each berry contains
two seeds, or beans as they are sometimes incorrectly called. The coffee is
prepared by roasting the seeds until they assume a reddish-brown colour, in
which process they lose 15 per cent. in weight and gain 30 per cent. in bulk.
During the process of roasting, a volatile oil having a powerful aromatic
smell is developed. This is not produced in such large quantities from fresh
seeds; the best time for roasting varying, however, for different varieties of
coffee.
The amount of Volatile Oil in coffee is much less than in tea. As it is
elicited during the process of roasting, this should be done with nicety and
care. It is effected in an iron cylinder made to revolve over a fire. After the

roasting, the sooner the seeds are ground the better the coffee. When it
cannot be immediately used, it should be kept in closed canisters, and not in
paper or open jars.
In addition to the volatile oil, which is contained in roasted coffee in the
proportion of about 1 part in 50,000, coffee contains caffeine, of which
there is ¾ to 1 per cent., and an astringent acid, called caffeo-tannic or
caffeic acid, which differs from ordinary tannin in that it does not blacken a
solution of an iron salt.
The chief adulteration of coffee is Chicory, which is thought by some to
improve the coffee. It is generally harmless, though in some people it
produces heartburn and diarrhœa. Chicory is prepared from the root of the
wild endive. It contains a volatile oil and a bitter principle, but no caffeine.
It is, therefore, of no utility as a stimulant. Its presence can be detected by
shaking a little of the suspected coffee on to the surface of the water in a
wine-glassful of cold water. Coffee swims on the surface, and gives little or
no colouration to the water; while chicory sinks, and gives a deep red tint.
The aqueous extract of pure coffee (extracted by boiling water) is, when
evaporated, 25 to 30 per cent. of the weight of the original decoction of
coffee; while that of chicory is 65 to 70 per cent.; and on this basis, as well
as on the fact that a filtered decoction of 10 grammes of coffee in 100 c.c.
of distilled water, cooled to 60° F. has a specific gravity of 1009, while that
of a similar solution of chicory would be 1021, the proportion of chicory in
a mixture of coffee and chicory can be calculated. The microscopical
appearances of the two powders differ, coffee showing hexagonal cells and
no laticiferous vessels, unlike chicory. There is no law against selling mixed
coffee and chicory, if the fact that it is a mixture is stated; and the
proportion of the two unfortunately is not required to be stated. As a pound
of coffee costs five times as much as a pound of chicory, it is obviously to
the purchaser’s advantage to make his own mixture in the proportions
desired.
The Preparation of Coffee ought to be effected as in the case of tea—by
making an infusion and not a decoction, i.e. by pouring boiling water on the
coffee and allowing it to stand, but not continuing the boiling. Continuance
of boiling dissipates the delicate aroma.

Inasmuch as coffee contains a much smaller percentage of theine than
tea, more of the former must be used to obtain a beverage equally
refreshing with tea. Two ounces to a pint of boiling water are required. The
infusion thus made should be mixed with an equal part of boiled milk. The
coffee ought, if possible, to be freshly roasted.
The colour of coffee is no guide to its strength. Many of the black
coffees, especially “French coffee,” owe their colour to the caramel (burnt
sugar) contained in the chicory mixed with them.
Coffee has similar properties to tea, with some minor differences. (1)
Like tea, it is restorative and sustaining in its action, but seems to act more
quickly than tea. (2) Unlike tea, it does not tend to produce perspiration, but
rather a dry hot skin. (3) With some it is decidedly laxative; while tea,
especially if badly made, has an opposite effect; but this is not always true.
(4) It seems to have a greater power of antagonising the effects of alcohol
than tea; and is a valuable antidote, after the action of an emetic, in
poisoning by opium or arsenic or alcohol.
As a rule, coffee is not so prone to disorder the digestion as tea, but this is
not universally true, and in some persons it always produces “biliousness.”
When taken in excess, it produces—besides indigestion—palpitation,
restlessness, irritability, sleeplessness, and a condition of general nervous
prostration; in fact, similar symptoms to those produced by a prolonged
over-indulgence in tea.
While the consumption of tea is rapidly on the increase, that of coffee is
steadily diminishing. This is partly owing to the greater expense of coffee—
a larger quantity being required to form a good beverage; and partly to the
greater difficulty in preparing good coffee.

COCOA.

Cocoa, or more properly cacao, is obtained from the seeds of the
Theobroma Cacao—a native of the West Indies, Mexico, and the central
parts of America. Its name Theobroma was given it by Linnæus, and means
the “food of gods.” The fruit is a large leathery capsule, having nearly the
form of a cucumber. It contains from 25 to 30 seeds, each about the size of

an almond. Before using, these are roasted like coffee berries, and a
peculiar aroma is developed in this process as in the case of coffee. The
beans or seeds are then manufactured into three different products. (1) They
are simply deprived of their husks and broken to pieces; this forms Cocoa-
Nibs. (2) They are ground, husk and all, between hot rollers into a paste,
and mixed with starch and sugar; this forms Cocoa. (3) They are shelled
and then ground into a paste, as in making cocoa; sugar and some
seasoning, usually vanilla, being subsequently thoroughly mixed; this paste
is Chocolate.
The purest form is the cocoa-nibs. When these are boiled in water, a
brownish decoction is formed, with the fat as a scum at the top; this may be
removed, and the decoction flavoured with milk and sugar. In this form,
cocoa can be taken by invalids with weak digestion, who would be
nauseated by the fat of ordinary cocoa or chocolate.
The best cocoa is prepared as above; but the lowest quality contains the
husks of the beans, with hardly any of the beans in it; a somewhat better,
though still inferior sort, is made from the smaller fragments of the nibs,
and a good deal of husk. In some cases the cacao butter is removed during
the process of preparation, and starch or sugar substituted. This form is less
likely to disagree with dyspeptics than whole cocoa.
The action of the Volatile Oil (not the cacao-butter) developed during
roasting, is probably similar to that of tea and coffee, though it is less in
amount. The bitterness is greater than that of coffee, but the astringency
less than in either tea or coffee.
The Concrete Oil, or fat of cocoa, forms about half its weight. It is
white, and not apt to turn rancid, and possesses an agreeable flavour. Cocoa
also contains a certain amount of starch and cellulose.
Theobromine is a white crystalline alkaloid, the exact analogue of
caffeine. The latter, in fact, is methyl-theobromine—that is, theobromine
plus the theoretical group CH₂. Theobromine possesses similar properties to
caffeine. It amounts to 1.5 to 2 per cent. of the whole bean. The ordinary
preparations of cocoa differ considerably in composition as may be seen
from the following table of per centage composition (Ewell). In each

instance other nitrogenous and non-nitrogenous constituents go to make up
the total 100:
FAT. FIBRE. CANE-SUGAR. ASH. ADDED STARCH.
Fry’s Cocoa Extract 30·9 3·9 — 4·2 None.
Schweitzer’s Cocoatina 31·1 3·7 — 6·3 Do.
Rowntree’s Cocoa Extract 27·6 4·4 — 8·5 Do.
Van Houten’s Cocoa 29·8 4·4 — 8·6 Do.
Epps’s Prepared Cocoa 25·9 1·5 26 3·1 Much arrowroot.

Some of the preparations of cocoa (e.g. Van Houten’s) have added to
them alkaline salts to increase their solubility. Cocoa is not such a valuable
food as might appear from the large amount of fat in it, because only
moderate quantities of this can be taken without deranging digestion. In Vi-
Cocoa a certain amount of kola is added, which contains a considerable
proportion of caffeine. The addition of such a drug to a beverage is
distinctly to be deprecated.
Minor Stimulants.—Beverages containing theine, or some analogous
principle, appear to be employed in most countries. In moderate doses, they
may assist the assimilation of other foods, but their main influence is on the
nervous system. Theine-containing substances may be described as both
sedative and exciting. They are sedative, in that they allay nervous
irritability, and tend to “take the edge off” the disturbance caused by
outward circumstances; and they are exciting, inasmuch as they are known
to form an admirable antidote to the stupefying effects of opium or alcohol.
The wakefulness from tea is an instance of the same thing, while the
allaying of sensations of cold and hunger by a cup of tea is an instance of
the sedative effect.
In Brazil, Guarana (from Paullinia sorbilis) is used as a drink; it contains theine, the quantity of
which is twice as much as in good black tea, and five times as much as in coffee. Like green tea, a
cup of guarana infusion is sometimes extremely valuable in nervous headaches.
In Peru, the natives use the leaves of the Coca plant (Erythroxylon coca), which must be carefully
distinguished from cocoa. It is chewed somewhat in the same way as the betel-nut. It contains two
alkaloids—cocaine and hygrine, as well as tannin. In its stimulant action it resembles tea and coffee.
The active principle of this plant, Cocaine, is a valuable local anæsthetic. Internally it has been taken
as a stimulant and restorative. Various wines containing Coca, with vaunted restorative powers, are
advertised. They are mischievous when taken frequently. Nature’s remedy for fatigue, whether
mental or body, is rest and recreation. Stimulants of this class, even though they enable work to be
continued for awhile, eventually increase the exhaustion for which they are taken.

The Kola-nut is used in some parts of Western Africa as a stimulant. It is about the size of a
pigeon’s egg, and has a bitter taste. The natives of Guinea generally take a piece of the seeds before
each meal, and sometimes nibble it throughout the day.
Kava is prepared from the root of a kind of pepper. The natives of the Fiji islands commonly
indulge in it. Its effects resemble those of coffee. In large doses, it destroys the power of walking, and
may possibly produce impairment of vision.
The leaves of the Ilex Paraguayense, Ilex Gongorrha, and Ilex Theezans are made into the
beverage commonly known as Paraguay tea or maté.
The leaves of the Hydrangea Thunbergii are made into a beverage, which is designated in Japan
“the tea of heaven.”
Among certain nations of Asia, the Betel-nut (from a palm called Areca Catechu) is chewed, after
mixing small fragments with pepper and quicklime, and rolling in a palm leaf. The saliva is tinged
blood-red, and a narcotic effect is said to be produced.
The dried flowering tops of the Indian Hemp (Cannabis Indica) are smoked by the Malays and
others, or made into a beverage, called haschisch, which produces a kind of intoxication, in which
murder has often been committed (hence, assassins equals haschascheens).
The Kamtschatkans drink an infusion made from a fungus, known as the Fly Agaric (Amanita
Muscaria), thus producing an intoxication similar to that from haschisch.
Opium in small doses is a stimulant, in large doses narcotic. The crude drug is sometimes taken,
and less frequently the active principle, Morphia. It is frequently smoked, as well as taken internally.
It is to be feared that secret opium taking is considerably increasing. The taking of morphia,
especially hypodermically, is too common. Generally it has been first prescribed for neuralgia or
some other complaint causing acute pain; and the patient, having experienced relief by its means, is
tempted to revert to the practice apart from medical advice. Such a line of action is most pernicious.
Eventually both the physical and the moral nature of the victim are shattered by it; and to break off
this insidious habit, when once thoroughly established, is most difficult.
Tobacco may be conveniently mentioned here, though its usual effects are certainly not stimulant.
It is smoked, chewed, or taken as snuff; when indulged in to excess it produces serious depression of
the heart’s action, with frequent intermittence. In moderate doses it is sedative as well as slightly
laxative. Prolonged indulgence in tobacco has produced many cases of incomplete blindness
(tobacco amblyopia), in some cases it comes on with much smaller doses, and in all cases is only
curable by ceasing to smoke. There is no sufficient ground for the statement that cigarette smoking is
more injurious than smoking tobacco in a pipe or cigar, unless in the former case the smoke is
inhaled into the lungs. The practice of smoking is injurious to growing boys, and should be strictly
forbidden.
Other Drugs are now not infrequently taken, apart from medical advice. Of these the most
commonly used are Antipyrin and Phenacetin, for headaches. Their use is injurious, and should not
be entertained as a frequent practice. Sleeplessness frequently leads to the practice of taking chloral
or sulphonal, or occasionally the inhalation of chloroform to induce sleep. (See also page 259).
Remedies to induce sleep should never be taken except under immediate medical advice. They are
only justifiable in extreme conditions, and if frequently taken tend to aggravate the conditions for
which they are given.

CHAPTER VIII.
FERMENTED DRINKS.
Properties of Alcohol.—When a saccharine solution is subjected to the
influence of warmth and moisture, and exposed to the air, it rapidly
undergoes a process of fermentation. The most favourable temperature is
about 70° Fahr. The ferment or agent exciting the change in the sugar is
derived from the atmosphere; it is a minute fungus (torula cerevisiæ), the
spores of which are constantly floating in the air. When once fermentation
has started, exposure in the air is no longer necessary; the process continues
in closed vessels. The essential change occurring in the vinous fermentation
is that grape sugar (C₆H12O₆,H₂O) becomes split up into alcohol (C₂H₅OH)
and carbonic acid (CO₂). Thus—

C₂H₆O
Two of alcohol
C₂H₆O
C₆C₆H₁₂O₆ =
CO₂
Two of carbonic acid.
CO₂

There are other fermentations allied to the vinous. Thus the Acetous
fermentation results in the conversion of alcohol into vinegar, as in the
souring of beer or wine. The Lactic fermentation leads to the conversion of
milk-sugar into lactic acid, with consequent souring of the milk.
Alcohol, or more correctly ethylic alcohol, is a colourless liquid, having
a pleasant vinous odour, and evaporating rapidly on exposure to air. It burns
with a bluish sootless flame, and is a capital solvent for resins and other
substances.
Rectified spirit is absolute alcohol mixed with 16 per cent. of water.
Proof-spirit is a mixture of 42·7 per cent. by volume of absolute alcohol,
and 57·3 per cent. of water. Thus the ratio of alcohol to proof-spirit being as
1: 1·76, the amount of alcohol in any liquid being given, the amount of

proof-spirit can readily be calculated. The fermented drinks containing
alcohol may be classed as (1) malt liquors, (2) wines, and (3) distilled
spirits. The relative properties of these will be considered afterwards; in the
next two sections will be considered the effects of diluted alcohol in
whatever form it is taken.
Effects of Moderate Doses of Alcohol on the System.—In studying the
physiological effects of alcohol, one has to guard against the fallacy that
these are the same, only differing in degree, whatever the dose may be. The
effects of large doses of alcohol are almost exactly the reverse of those
produced by small doses. It will be necessary to define, therefore, what we
mean by a moderate dose. By a moderate dose, we understand the amount
of alcohol which can be taken without any alcohol being eliminated in the
urine. Dr. Anstie found that 1½ ounces, that is three tablespoonsful, of
absolute alcohol, taken in twenty-four hours, caused its appearance in the
urine; and Dr. Parkes and Count Wollowicz obtained almost precisely the
same result. Anything below some quantity between 1 and 1½ fluid ounces
per day can be disposed of in the system, and is probably oxidised like
ordinary foods.
The amount of alcohol, in the form of alcoholic beverages, corresponding
to this maximum dose of absolute alcohol is approximately as follows:—
One imperial pint (20 fluid ounces) of bottled beer (5 per cent. of alcohol).
of claret, hock, and
One tumblerful (10 fluid ounces) (10 „ ).
and other weaker wines
of port, sherry, and
2½ glasses (5 fluid ounces) (20 „ ).
other strong wines
One glass (2 fluid ounces) of brandy or whiskey (50 „ ).

It will be understood, therefore, that in describing the effects of a
moderate amount of alcohol on the system, an amount below 1½ ounces of
absolute alcohol per day is meant, freely diluted, and taken as a rule with
meals.
1. Effect on the Stomach.—In very small quantities, alcohol seems to
stimulate digestion in the same way as mustard. But like all other artificial
helps to digestion, it is best avoided in the healthy condition.

2. The Effect on the Liver is similar to that on the stomach—a
temporary redness and congestion being produced; this effect soon
disappearing if the dose is small and well diluted. But in all cases where
there is a tendency to biliousness, even small doses of alcohol are injurious.
3. The Effect on the Heart and Blood-Vessels is first to increase the
force of the heart’s action and the rapidity of the pulse. The stimulation of
the heart is rapidly followed by a universal dilatation of the small arteries of
the body, which diminishes the blood-pressure. Parkes and Wollowicz
found that the daily administration of from 1 to 7½ ounces of rectified spirit
raised the pulse rate by ten beats per minute, as compared with other
periods; and that this effect was followed by a period of depression in
which the beat was both slower and feebler than usual.
4. The Effect on the Nervous System varies. In persons unaccustomed
to its effects, even small doses dull the power of thought and the rapidity of
perception, owing to the paralyzing effect which it exerts on nerve cells. In
most cases, however, it at first produces increased rapidity of thought and
excites the imagination, though even here it makes it more difficult to keep
to one train of thought. This is clearly owing to the more rapid circulation
of blood through the brain. Dr. E. Smith’s experiments show that it
diminishes the acuteness of the senses. Its influence even in dietetic doses,
on the capacity for mental work, is slightly to diminish it.
5. The Effect on the Muscular System is never beneficial. Even when
only small quantities are taken, the power of controlling delicate
movements is slightly diminished. For persons engaged in laborious
occupations, a small quantity does not produce much apparent effect, but
where the quantity exceeds two fluid ounces per day the capacity for strong
and sustained muscular work is manifestly lessened (Parkes). This effect is
probably due partly to the dulling of the nervous system, rendering the
muscles less amenable to the will, and partly to the over-excitation of the
heart causing palpitation and breathlessness.
6. The Effect on Metabolism is to diminish it, thus favouring the deposit
of fat in the tissues. It acts as a poison to the protoplasm of the cells of the
body, diminishing their power to break down the floating nutriment,
especially fat and carbohydrate.

The Effect on the Temperature is to lower it; but unless the dose is
excessive, this effect is hardly appreciable. The resistance to excessive cold
is diminished by even moderate doses of alcohol, still more by large doses.
In the Arctic regions, this has been abundantly proved. This effect is
produced, notwithstanding the fact that alcohol becomes oxidised in the
system. The dilatation of the surface blood vessels leads to a greater loss of
heat than that produced by the oxidation of the alcohol.
Effects of Immoderate Doses of Alcohol on the System.—Bearing in
mind the definition given of a moderate dose, one is bound to admit that a
large number of individuals exceed this amount daily, apparently without
any very serious results. The system becomes habituated to large doses, and
if the occupation is a laborious one, they may in part be oxidised in the
system. Such, however, are exceptional cases. In the majority of cases evil
results are by no means confined to those who indulge in very large
quantities of alcohol at varying intervals. In fact these very often escape
comparatively free, while others who never take a quantity sufficient to
incapacitate them for their work, are sowing the seeds of chronic and oft
incurable disease. The labourer who has a drinking bout at intervals is
thoroughly nauseated; and the condition of liver and stomach induced,
enforces abstinence on him for a time sufficient to bring his organs back to
a normal condition; while the city merchant who indulges more moderately,
but whose organs are almost continuously impregnated with alcohol,
becomes gouty and prematurely old.
The Stomach may become acutely inflamed, when a large dose of
alcohol is taken. The chronic irritation of alcohol, especially when taken
apart from meals, causes atrophy of the walls of the stomach, and a change
analogous to that in the liver.
The Liver, when alcohol is daily taken immoderately, becomes seriously
diseased. In some cases it becomes large and fatty; in others the chronic
irritation excites an overgrowth of fibrous tissue between the lobules of the
liver, which, gradually shrinking, squeezes the liver cells and causes them
to atrophy, at the same time obstructing the small branches of the portal
vein in the substance of the liver. The consequence of this obstruction to the
flow of blood through the liver is that all the organs from which the portal

vein brings blood become overloaded with blood, and vomiting of blood
and dropsy of the abdomen occur at a later period.
The Lungs are irritated to a less extent by alcohol in large doses. The
tendency to chronic bronchitis is increased, followed by emphysema, and
sometimes an overgrowth of fibrous tissue (cirrhosis) like that in the liver
occurs.
The Heart and Blood-vessels tend to become diseased, owing largely to
the gouty condition of system developed.
The powers of Metabolism are diminished. Corpulence is, consequently,
a common result of alcoholism. There may also be fatty deposit in the
internal organs, such as the heart. This must not, however, be confounded
with a much more serious condition, fatty degeneration of the heart, in
which the substance of the muscular fibres becomes partially converted into
fat, and which also is sometimes due to alcoholism.
The Nervous System is more prone to suffer in chronic alcoholism than
any other part of the body, except perhaps the liver. The first effect of a
large dose of alcohol is to stimulate the nervous system, as already
described. This is followed by a dulling of the nervous faculties, which
comes on rapidly in proportion to the amount taken. The phenomena of
intoxication are unhappily too familiar to require description, mental
incoherence and muscular incoordination (lack of control over the muscles)
being the most prominent features.
When the dose of alcohol is still larger, a condition of profound
unconsciousness is produced (coma), which may be difficult to distinguish
from other forms of unconsciousness.
Delirium Tremens is another nervous condition, which may rarely
follow a single debauch, but much more commonly affects the chronic
toper. In some cases the immediate exciting cause is a mental shock, or lack
of food, or a surgical injury. Alcoholic subjects suffering from any acute
disease are liable to this form of delirium, and their chance of recovery is
greatly diminished.
Insanity of a more prolonged character than that characterising delirium
tremens is an occasional result of alcoholism.

Besides the nervous diseases already named, a chronic thickening of the
membranes covering the brain and spinal cord, gradually progressing and
finally fatal, is often the consequence of prolonged alcoholic indulgence.
Various Degenerative Diseases are produced by alcohol. It has been
well called by Dickinson the very “genius of degeneration.” Such
degenerations are by no means confined to the intemperate; they are seen in
those who are of what would usually be considered moderate habits. The
stomach, liver, lungs, and probably the kidneys, are the main organs to
suffer in this way. It is probable that the effect on the kidneys only occurs
when a gouty condition is developed. In all these cases there is an
overgrowth of fibrous tissue, with atrophy of the proper gland structures.
Gout is the common nemesis of those indulging in alcoholic beverages,
more especially wine and beer, due to the excessive formation or retention
of urate of soda in the body. This produces inflammation of the joints, and
other evils—among them the gouty kidney, named above, which is always
ultimately fatal. Rigid arteries are likewise commonly due to alcoholism
and gout. If one of these bursts in the brain, apoplexy results.
Longevity is diminished by immoderate indulgence in alcohol. The
statistics of Temperance Insurance Societies, show much better results
among teetotalers than among moderate drinkers. It is only fair to add that
although the latter are supposed to consist of moderate drinkers—and
particular enquiries are always made on this point before insurance—it is
probable that a large proportion of them exceed 1½ ounces of alcohol per
day. Making due allowance for this fact, the statistics show a great
superiority in the expectation of life of teetotalers.
Factors Modifying the Effects of Alcohol.—1. Age and Sex.—Until
adult life is reached, total abstinence from alcohol should be enforced. The
delicate nervous system of children is easily disturbed by it, and it appears
in some measure to retard growth. Another argument against giving alcohol
before adult age is reached, is still more important. It is at this period of life
that habits are chiefly formed, and a craving for alcohol may be insidiously
produced, destined to have most baneful results.
Old people, if ordered spirits for medical reasons, should drink them well
diluted.

Women are much more easily affected by alcohol than men, and if they
acquire the habit of excess, the hope of reformation is even less than with
men.
2. Exercise has a most important influence in modifying the effects of
alcohol. Those of sedentary occupations and living in towns, cannot oxidise
as much as those engaged in active out-door work, and are consequently
much more prone to suffer. A game-keeper in the Scotch Highlands may
possibly live to a good old age, notwithstanding the fact that he consumes
an amount of whiskey that would have sent a sedentary man to his grave in
the course of a few years.
3. The Condition of the Stomach has also great influence. When the
stomach is empty, alcohol produces at once a powerful reflex stimulation of
the heart, and becomes quickly absorbed into the circulation. Thus
intoxication may be produced by a quantity that would have had little effect
if taken with a meal.
4. The State of Concentration or Dilution modifies greatly the action of
alcohol, the local action on the stomach and the reflex stimulation being
much greater than when it is concentrated, and injurious effects being much
more likely to occur.
5. Cold and Heat modify the action of alcohol. A smaller quantity of hot
spirits and water will intoxicate than of cold; the heat stimulating the heart,
and so making the absorption of the alcohol more rapid. A glass of hot
spirits and water will often cause sleep, by drawing the blood towards the
abdominal organs. The fact that persons, who have been drinking spirits in a
warm room, on going out into the cold air become suddenly intoxicated,
seems opposed to what has been already said. But probably this is due to
the cold causing contraction of the arteries of the skin, and so driving more
of the blood loaded with alcohol to the internal organs and the brain
(Brunton).
6. Mental Occupation has some influence in modifying the effects of
alcohol. Topers have found that if they try to converse during their debauch
—the conversation implying increased functional activity of the brain, and
therefore a freer circulation of blood in it—intoxication occurs much more
readily, than when the mind is not active.

7. Disease modifies greatly the effects of alcohol. In some diseases, as in
inflammation of the lungs and in fevers, it can be given in large quantities
without producing intoxication; and in these conditions it lowers the
temperature. In other diseases, especially gout and kidney disease, its use is
nearly always followed by bad results.
The Advisability of Alcohol as an Article of Diet in Health.—In
dealing with this difficult point, two sets of facts require consideration,
those obtained as the result of Physiological observations (see page 56),
and those which are the result of Experience. There can be no doubt that
the former are much more reliable than the latter. Experience is very prone
to give fallacious results, especially when questions of appetite are
concerned. In making a trial of abstinence, the mistake has been commonly
made of only prolonging the investigation for a few weeks, and then
comparing results. Such a method is, however, very unfair, and is certain to
lead to an unreliable conclusion.
The records of experience under certain conditions have, however, been
so extensive, as to lead to trustworthy results. It has been abundantly proved
that prolonged muscular work is best undergone during total abstinence
from alcohol; and that the extremes of heat and cold and the exposure and
exertions of marching armies, are best borne under similar conditions.
The artificial character of town life is commonly adduced as an argument
for the moderate use of alcohol. In the case of healthy workers, this does
not hold good; many of our hardest workers and thinkers take no alcohol.
The universality of the habit of taking stimulants is a curious argument
on the same side, though if the habit be bad, this can be no more reason for
continuing it than can the prevalence of vice be an excuse for indulgence in
it.
The two chief physiological points bearing on the advisability of alcohol
as a part of one’s daily diet are—its food properties, and its effect on the
appetite and digestion.
It has been already stated that a quantity of alcohol under 1 or 1½ ounces
may become oxidised in the system, and may thus form a source of heat.
But in all probability, although it may be regarded as a food, it is a most

inconvenient one, inasmuch as it diminishes the oxidation of other foods. It
has been aptly compared in this respect to sulphur, which is an oxidisable
material, but which, when it is burnt in a chimney, in which the soot is on
fire, will put an end to the combustion of the latter. Its value as a food,
under normal conditions, is practically nil.
Its Effect on the Digestive Organs is three-fold. (a) The contact of
alcohol with the mucous membrane of the mouth and stomach, acts as a
reflex nervous stimulus, which in moderation excites an increased flow of
gastric juice. (b) It also increases the activity of the movements of the
stomach. In cases of weak digestion, therefore, small doses of alcohol may,
at times, be useful. (c) The effect of alcohol on the food taken varies with
its degree of dilution. Concentrated alcohol coagulates albumin, and so
stops digestion; largely diluted alcohol has no such effect.
The late Dr. Parkes, the greatest authority on the dietetic use of alcohol,
has summarised the argument as to the dietetic use of alcohol as follows:—
“But what, now, should be the conclusion as to the use of alcohol in
health after growth is completed? Admitting the impossibility of proving a
small quantity to be hurtful, and at the same time acknowledging the
dangers of excess, there arises an argument which seems to me somewhat in
favour of total abstinence. No man can say when he has passed the
boundary which divides safety from harm; he may call himself temperate,
and yet may be daily taking a little more than his system can bear, and be
gradually causing some tissue to undergo slow degeneration. He may be
safe, but he may be on the verge of danger.
“This uncertainty, coupled with the difficulty at present of saying what
dietetic advantage is gained by using alcohol, seems to me rather to turn the
scale in favour of total abstinence instead of moderate drinking. But if any
one honestly tries, and finds he is better in health for a little alcohol, let him
take it, but he should keep within the boundary line, viz., that 1½ ounces of
pure or absolute alcohol in twenty-four hours form the limit of moderation.
I do not then think he can do himself any harm.”
The Varieties of Fermented Drinks.—The three chief kinds of
alcoholic beverages are malt liquors, wines, and ardent spirits. In addition,
we may mention cider and perry, which are the fermented juices of apples

and pears respectively; and koumiss, which the Tartars prepare by
fermenting mare’s milk, though it may also be made from the milk of other
animals.
All Beers, Ales, and Porters are prepared from malt, which is the
germinating grain of barley. The fermentation of the sugar in the barley
produces alcohol, the amount of which varies in different cases. In Pilsener
beer it is 3½ per cent. of absolute alcohol; in stout and porter 5 to 6 per
cent. The hop which is added to the fermenting barley, gives to beer its
characteristic bitterness.
London Porter is coloured with black or roasted malt; stout is only a
stronger form of porter. Bottled ales are generally stronger than those on
draught, and being slightly effervescent, may agree better.
The effect of alcohol in beer is modified by the hops, which help in
producing drowsiness. Beer has a marked tendency to produce obesity,
more so than any other alcoholic beverage. Its influence in the production
of gout is also very great.
Substitutes for Malt have been largely used. Thus by the action of
sulphuric acid on starch, an artificial form of sugar is produced, which is
largely used in place of malt for making beer. Many recent cases of
poisoning by arsenic have been traced to the use of impure sulphuric acid in
manufacturing this form of sugar.
The detection of arsenic in organic liquids requires great care, as so many compounds of arsenic
are volatile, especially in the presence of chlorides, as in beer. To detect arsenic in beer a pint of the
beer is evaporated to dryness, and treated with 20 c.c. of strong sulphuric acid, heated, and 20 c.c. of
strong nitric acid added drop by drop. Violent action occurs: if possible 20 c.c. more of nitric acid are
worked in. Transfer the liquid to a small flask, and expel the nitric acid by boiling. By this means all
chlorine is expelled, the arsenic is oxidised and the organic matter destroyed. SH₂ gas is now passed
into the acid liquid for some hours, the precipitated sulphur and any sulphide filtered off and
extracted with ammonia, which dissolves any sulphide of arsenic. The liquid so obtained is subjected
to Marsh’s test. (See page 216.)

In the making of beer from malt, the first stage is to malt the barley, i.e.
leave it spread on floors for ten days after soaking. This allows germination
to take place, in which process the insoluble starch is converted into starch,
dextrine, maltose and glucose. After the dried malt has been screened to
break off the sproutings, the brewer places it in the mash-tub, with water, at
a temperature of 160° F. This completes the transformation of the starch

into glucose. The wort is now boiled to stop the process, and the albumin
from the grain is thus coagulated. Hops are added at this stage. The boiled
liquid is passed into shallow vessels and cooled. The proper temperature for
“top” yeast is 60° F., for “bottom,” or Bavarian yeast, a much lower
temperature is desirable. When the desired temperature is reached, the
liquid is run into the fermenting tun along with yeast. The varieties of beer
are due in part to the degree of completeness of fermentation of sugar
allowed. If too complete, the beer does not keep well.
Wines are produced by the fermentation of the juice of the grape. The
wine produced may be bottled before or after fermentation is complete; in
the former case, an effervescing wine is produced, such as the sparkling
wines of the Rhine and the Moselle, or champagne. When the sugar is
nearly all fermented a dry wine is obtained, of which Bordeaux and
Burgundy, Hock and Moselle, are examples.
The difference in colour between red and white wines is produced by
allowing the juice in the former to ferment in contact with the skins, from
which the colouring matter is extracted by the alcohol. Both red and white
wines may be obtained from either red or white grapes. From the skins also
are extracted a salt of iron, and a peculiar form of tannin. Tartaric and acetic
acids, and tartrate of potass, are present in varying quantities in wines; in
old wines the tartrate separates as bitartrate of potass, forming with tannin
and colouring matter the “crust” of port and other wines. The “bouquet” of
wines is due chiefly to certain volatile bodies, such as pelargonic ether. The
proportion of alcohol in wines varies from 6 to 14 per cent. As fermentation
is stopped by the presence of 14 per cent. of alcohol, any larger amount of
alcohol than this must have been added to the wine.
Wine, like beer, has a strong tendency to produce gout, especially the
sweet and strong wines. It has not, however, the same tendency to induce
obesity.
Spirits differ from the two last groups, to begin with, in the amount of
alcohol they contain. Thus, English beers contain from 3 to 6 per cent.,
German beers from 2 to 5 per cent., wines from 8 to 20, and all kinds of
spirits from 37 to 58 per cent. of alcohol. They differ in the absence of the
bitter principle of beer and much of the salts and sugar and ether of wines.

They are all prepared by the distillation of some previously fermented
liquor. Brandy ought to be made by the distillation of wine; and then
contains, besides alcohol and water, small quantities of acetic, œnanthic,
butylic, and valerianic ethers. But much of the brandy sold is simply made
from potato spirit, by the addition of acetic ether, burnt sugar, etc. The
starch of potatoes is converted into dextrin and dextrose by dilute acids, and
then fermentation allowed. By the use of patent stills, all bye-products can
be separated, a fairly pure alcohol known as silent spirit being produced.
This is largely employed in manufacturing spirits and in fortifying wines.
Whiskey is prepared from malted barley, or from a mixture of grains, to
which a sufficiency of malt to convert their starch into sugar has been
added. In grain whiskey the distillation is effected by steam in a patent
(Coffey’s) still, which separates most of the bye-products (fusel oil, etc.)
from the spirit. In malt whiskey, distilled in the old-fashioned pot-still, these
bye-products are not separated.
The improvement of whiskey effected by keeping is not due (Bell) to the
diminution of fusel oil. Such a diminution does not occur. The percentage of
alcohol diminishes by keeping, 6 to 8 per cent. proof spirit being lost by
five years’ storage in wood. “Fusel oil” is a mixture of alcohols of higher
boiling point than ethylic alcohol (amylic, propylic, etc.). Even in a bad
whiskey not more than 1 ∕ 10 per cent. of fusel oil is present (about one grain
in a glassful). Experimentally no marked effects have been produced by
fusel oil, when it is less than 1 per cent. Possibly the presence of furfurol, of
which there is a trace in malt whiskey, which disappears on keeping, may
partially explain the disagreeable flavour of new whiskey. But it is fairly
clear that those who argue that it is bad whiskey and not good whiskey
which does harm are speaking without knowledge. It is not the quality but
the quantity of whiskey which is responsible for so much moral and
physical evil.
Gin and Hollands are obtained from barley, and flavoured with juniper
berries and other materials. The oil of juniper stimulates the urinary
excretion.
Rum is obtained by the distillation of molasses, and is usually kept for a
long time in oak barrels. It is said thus to acquire more astringent matters

than other spirits contain.
The legal limits of dilution of whiskey, brandy and rum is down to 25
degrees under proof, and of gin down to 35 degrees under proof. (For
definition of proof spirit, see page 55). The amount of alcohol in an
alcoholic liquor is determined by distillation of 100 c.c., making up the
distillate to 100 c.c. by the addition of distilled water, and then taking the
specific gravity of a portion of this liquid by the aid of the specific gravity
bottle. The percentage of alcohol corresponding to a given specific gravity
is given in tables prepared for this purpose.
Prolonged indulgence in spirits produces the various organic diseases
already described, and unless well diluted they are more harmful than beers
or wines. They differ from wines and beers in not tending to produce gout,
and from beer in not leading to obesity.

CHAPTER IX.
WATER.
Uses of Water.—Water is a prime necessity of life. In its absence life can
only exist in lowly organised beings, and in them only in a dormant state.
From a hygienic point of view, the uses of water are four-fold:—(1) It is an
essential part of our food, not only serving to build up the tissues of the
body, but also preserving the fluidity of the blood and aiding excretion of
effete matters. (2) It is necessary for personal cleanliness, of which the
importance can scarcely be exaggerated. (3) In the household it is essential
for cooking, as well as for washing the house, the linen, and various
utensils. (4) By the community at large it is required for water-closets and
sewers, for public baths, for cleansing the streets, and for horses and other
domestic animals, as well as in many manufacturing processes. It is obvious
that the water to be used for domestic and general purposes, need not be so
pure as that for drinking purposes. Hence, a double supply was proposed for
London in 1878, by the Metropolitan Board of Works—a less pure river
supply for general purposes, and a deep chalk-well supply for drinking
purposes. The scheme, however, rightly fell through, because of the
expense of a double source of supply, and the danger that the impure water
would, through carelessness or ignorance, be often used for drinking
purposes, when it happened to be nearest at hand.
Quantity of Water Required.—The quantity of water required for all
purposes has been variously stated by different authorities. The quantity
required for drinking purposes is found to bear a relation to the weight of
the individual, being nearly half an ounce for every pound weight, or 1½
gills for every stone weight. Thus, a man weighing 150 lbs. would require
3¾ pints. Of this water, about one-third is taken in the food; the remainder,
averaging 2½ pints, being required as drink. If we add the water required
for other purposes, according to De Chaumont, 1 gallon is required for
drinking and cooking, 2 gallons (not including a bath) for personal
cleanliness, 3 gallons for a share of utensil and house washing, 3 gallons for
clothes washing; and if a general bath be taken, 3 gallons more; making a

total of about 12 gallons, to which 5 gallons must be added if there is a
water closet.
In hot summer weather the consumption is about 20 per cent. above the
average of the year; and frost often increases the amount 30—40 per cent.
above the average, owing to the bursting of pipes, or the loss from taps
foolishly left open to prevent bursting.
Water companies usually reckon 30-60 gallons for each individual, to
allow for the water required for scavenging and manufactories and for
waste. In large houses and hotels where baths are freely used, often as much
as 70 gallons per head is used, and in hospitals the amount averages from
60 to 90 gallons per head. The following is Parkes’ estimate of the daily
allowance for all purposes:—
GALLONS PER HEAD
OF POPULATION.
Domestic supply 12
General baths 4
Water-closets 6
Unavoidable waste 3
—
Total house supply 25
Municipal purposes 5
Trade purposes 5
—
Total 35

It has been proposed to put a water-meter to each house, so that the rate
may be in proportion to the amount of water used. The plan is objectionable
for two reasons: 1st—Because it tends to restrict the necessary use of water
for purposes of cleanliness. A scant supply of water is always followed by
uncleanliness of house and person, with its consequent diseases; at the same
time closets may be imperfectly flushed, and may become choked. 2nd—
Because of the primary expense of the meter, and of its maintenance.
Sources of Water Supply.—All our drinking water is obtained in the first
instance, by a natural process of distillation on a large scale. The sun is
constantly causing evaporation from sea and land. The vapour produced,
being condensed by a lower temperature, returns to the earth as snow, dew

or rain. All these natural products have been at times utilised as sources of
drinking water.
1. Dew has on rare occasions been utilised at sea by hanging out fleeces
of wool at night and wringing them out in the morning. A much better plan
is—
2. The Distillation of Sea-water. This can easily be managed now that
steam power is so largely used. It has even been employed on land, when it
was necessary temporarily to continue the use of water derived from an
impure source. The first part distilled should always be rejected, as it is
always impure. Distilled water is “flat” in taste, owing to its containing no
dissolved gases. It can be aërated by letting it drop a considerable distance
from one cask into another, through small openings in the upper one, and by
filtration through charcoal. Non-aërated water is not easily absorbed into
the circulation, and occasionally causes illness.
3. The utility of Melted Snow and Ice is obviously very limited.
Moreover, its use is not free from danger if the ice is derived from
contaminated water. Outbreaks of enteric fever have been traced in the
United States to the taking of ice obtained from impure water.
4. Rain-water is a much more important source of water supply, and
after passing through the soil it constitutes the chief part of the water we
drink. The term, however, is properly restricted to the water collected
immediately after its descent from roofs, etc. Its purity depends on three
conditions—the character of the air it passes through, the cleanliness of and
absence of lead from the channels through which it runs, and the condition
of the water-butts in which it is stored. Rain-water is soft; in fact, too soft to
be pleasant to the palate. In passing through the air, it carries with it a
certain proportion of its constituents; in towns especially ammonia, soot,
etc.; near the sea, it generally contains some salt; and being soft and having
dissolved oxygen from the air, it dissolves an appreciable amount of lead
from roofs or gutters.
The Rivers Pollution Commissioners found that out of eight samples of
stored rain-water only one was fit to drink. They came to the conclusion
that rain-water, collected from the roofs of houses and stored in
underground tanks, is “often polluted to a dangerous extent by

excrementitious matters, and is rarely of sufficiently good quality to be used
for domestic purposes with safety.” Also, that in Great Britain, and more
particularly in England, we shall “look in vain to the atmosphere for a
supply of water pure enough for dietetic purposes.”
The use of rain-water for drinking purposes is only justified in isolated
country houses where no better source is available; and under these
circumstances the greatest care should be taken to prevent contamination
with lead or organic impurities.
The amount of water falling on any impervious material obtainable from
rain can easily be estimated, if the amount of rainfall and the area of the
receiving surface are known. The average annual rainfall in this country is
33 inches (see page 236).
We may assume the amount practically available to be 20 inches per annum, and the area of the
receiving surface 500 square feet. Multiply the area by 144, to bring it into square inches, and this by
the rainfall, and the product gives the number of cubic inches of rain which fall on the receiving area
in a year. One cubic foot, or 1,728 cubic inches, of water being equivalent to 6·23 gallons, the
number of gallons of water can be easily calculated. To calculate the receiving surface of the roof of a
house, do not take into account the slope of the roof, but merely ascertain the area of the flat space
actually covered by the roof. This may be done roughly by calculating the area of all the rooms on
the ground floor, and allowing an additional amount for the space occupied by the walls. It has been
estimated that, even if a rain-water supply for towns were desirable, the amount collected from the
roofs of houses would scarcely average two gallons per person daily—assuming the average rainfall
to be 20 inches, and that there was a roof area of 60 square feet for each individual.

The amount practically available from rain falling on different soils
varies with their porosity and slope. Thus, according to Professor Rankine,
the proportion of the total rainfall available is as follows:—

Nearly the whole on steep surfaces of granite, gneiss, and slate;
From three to four-fifths on moorland hilly pastures;
From two-fifths to half on flat cultivated country; and
None on chalk.

By available rainfall is meant the amount remaining after allowing for
percolation, etc., which can be stored in reservoirs.
5. Upland Surface Water is the water collected in hilly districts, as on
moorlands, at the head of a river. By its utilisation for drinking purposes,
the sources of water for the river are interfered with, and any water

company or local authority using such a source is, therefore, required to run
into the stream a quantity of water equal to a third of the available rainfall.
The limited and regular supply thus furnished to the stream is found to be
advantageous for industrial purposes as its flow is equalised, and the
violence of floods mitigated.
In the utilization of upland surface water the water from the surrounding
hills is collected at the bottom of a valley, in an artificial, strongly-
constructed lake; or in a natural lake, as in Loch Katrine (from which
Glasgow is now supplied).
Upland surface water is nearly always soft. Its use is much more
economical than that of hard water. It may be brownish, from the presence
of peat, but this is not objectionable, so far as health is concerned. Its
occasionally solvent action on lead is a more serious objection. The
population of many parts of Yorkshire and Lancashire have suffered
severely from chronic lead poisoning, due to the action of certain upland
surface water on lead service pipes. Only the waters giving an acid reaction
possess this plumbo-solvent power. (See also page 82.)
6. Springs supply water which, originally derived from rain-water, has
percolated through the soil until it reaches some impervious stratum, and
has then run along this, until it arrives at the point at which the impervious
stratum reaches the surface of the soil. A spring is thus the outcrop of the
underground water. Springs are divided into (1) land springs, and (2) main
springs. The former flow from beds of drift or gravel lying on an
impervious stratum. They are very subject to seasonal variation, and may
dry up in certain years; while main springs occurring in chalk, greensand, or
other regular geological formation, constantly supply a certain amount of
water. Springs often occur in connection with “faults” in geological strata,
and then may appear on table-lands and high elevations, unlike springs
caused by alternation of strata in valleys of denudation. The two kinds of
springs are shewn in Fig. 5 and 6.
In the land spring water crops out at the point where the porous stratum
ceases. Deep springs may crop out in the same way as land springs, except
that they appear at the bottom of deeper strata. Or they may be formed by
faults. Both these are shown in water having percolated through the chalk

beneath the superficial clay, is stopped at the “fault” by the lack of
continuity of the chalk stratum, and is consequently confined under
pressure. It therefore makes its way to the surface, forming a spring. In its
passage underground, water (owing partly to the carbonic acid it has
obtained from the air and soil), is able to dissolve small quantities of chalk,
sulphate of lime and of magnesium, and traces of oxide of iron, aluminium
oxide, and silica. Spring-water possesses an equable temperature, generally
about 50° Fahr., while impounded or river water is always warm in summer
and cold in winter. Spring water is well-aerated, while river water, and still
more rain-water, are flat.

Fig. 5.—Land Spring.

Fig. 6.
Main Springs formed in Valley of Denudation and by a Fault.

7. Wells may form the best or worst sources of water-supply according to
their depth and the means of protection against contamination. There are
two kinds—Surface wells and deep wells.
Surface Wells do not usually descend further than 15 or 20 feet, and
have no impervious stratum between the source of water and the surface of
the well. They catch the subsoil or underground-water, which percolates

into them from the surrounding soil, and the character of the water they
receive will therefore vary with the nature of their surroundings. If there is a
cesspool near, this may simply drain into the well. All the soakage from a
considerable distance may find its way into the well. In villages and isolated
places the water of surface wells is commonly contaminated. One hole may
be dug in the garden for a well, and another for a cesspool, while there is
possibly a farmyard near at hand—the soakage from the cesspool and
farmyard soaking into the well. Danger may also arise from more distant
contamination. The ground water which is tapped by the well is an
underground stream flowing towards the nearest brook. Heavy rains
swelling the ground water may wash impurities from cesspools, leaky
drains, etc., at a considerable distance, and carry these into wells lying
between these sources of pollution and the brook into the bed of which the
underground water ultimately discharges. The danger of contamination of
the water in the well by the contents of the cesspool is much greater in the
relative position shown in A than in the position shown at B, Fig. 7. After
heavy rain, when the underground water is swollen, the danger of
contamination is still further increased. The model bye-laws of the Local
Government Board state that a cesspool must be at least 40 feet distant from
any well, spring, or stream. Probably this is insufficient for safety;
cesspools ought to be entirely forbidden. If necessary to retain a surface
well, it should be protected nearly to the bottom with brick, lined with an
impervious layer of cement so as to prevent water from entering the well
except near its bottom. In modern wells iron cylinders are employed to line
the upper part of the well; and large glazed earthenware pipes arranged
vertically and with water-tight joints are sometimes used for the same
purpose.

Fig. 7.
Showing Varying Danger of Contamination of a Shallow Well, according to Level of
Underground Water and Relative Position of Cesspool and Well (after Galton).

Deep Wells are made by digging a surface well, as above, except that the
ground water is prevented from entering the well by means of impervious
steining; and then boring from the bottom down through the subjacent
impervious stratum until a water-bearing stratum is reached. The difference
between a surface well and a deep well is shown in Fig. 8 by A and B.
Where the water in this stratum is retained under pressure, deep wells are
known as Artesian Wells. Such Artesian wells have been sunk in London.
Rain, falling on the chalk hills which lie to the south and north of London,
percolates through the chalk downwards, and then laterally, until it lies in
the concave London basin. Here the clay stratum above it prevents its
escape upwards; and being confined under considerable pressure, it rises to
the surface, or into a well in the superficial gravel, when the clay is tapped.
In Fig. 8, B is an Artesian well if the pressure is such as to make the water
rise through the London clay, when this is cut through and the underlying
chalk is reached. C is a well in the chalk, which does not pass through an
impervious stratum, and therefore comes within the above definition of a
surface well; but as regards depth required to be dug before water is reached
it is more like a deep well.

Fig. 8.
Showing Difference between Deep and Superficial Well. A.—Surface Well in Gravel.
B.—Deep Well, going through Gravel and Clay to Chalk. C.—Well in Chalk
District.

Among the deepest Artesian wells are Grenelle (1,800 feet), and
Kissingen (1,878 feet.) The sinking of a deep well and severe pumping of
its water may exhaust all the neighbouring wells for two or three miles.
There is also danger of contamination from neighbouring cesspools when
the upper part of the deep well is not properly constructed. The area
exhausted by a deep well undergoing pumping is represented by an inverted
cone, having a very wide base, and with a convex inner surface pointing
towards the well.
For country places deep-well water is much preferable to water from
streams, as streams are very liable to be contaminated by the sewage of
houses higher up in their course, or even by that of houses close by. A good
well should be at least thirty feet deep—preferably fifty feet and should
always be lined with impervious material, except near its bottom. The
absolutely water-tight and impervious condition as well as the distance of
all drains or cesspools in the vicinity should be ascertained before deciding
whether the drinking water from a given well is above suspicion. The
direction of flow of the underground water should also be determined. This
may be done by measuring the level of all the wells in the neighbourhood.
Possible sources of pollution at points from which ground water is flowing
towards the well are much more dangerous than those nearer than the well
to the river towards which the underground water is flowing (see Fig. 7).
Steam pumping greatly increases the area from which contamination may
be derived.
An excellent plan to obtain water for villages, in a gravelly soil, is to sink
a Norton’s Abyssinian tube well for fifty or sixty feet.

In towns it is preferable to trust to the public water supplied, rather than
to any private well; and in villages, a general supply from a pure source
should also be provided.
The water is obtained from a well by a pump or a draw-well. The former
is a safer as well as a less laborious plan. The pump should be fixed some
distance from the well, and the aperture through which the pump pipe
passes should be rendered water tight. Lead pipes should be avoided, as
well water not infrequently has plumbo-solvent properties.
8. Rivers and running streams originate in upland surface water or
springs, and their water should be of the same quality as these.
Unfortunately, they acquire a large amount of impurities in their course.
Towns commonly pour their more or less clarified sewage into them; and
the discharge of crude sewage from hamlets and single houses on the banks
is still far from uncommon. With the more rigid enforcement of the Rivers
Pollution Acts, this pollution of rivers will become less frequent; but river
water previously contaminated by even small amounts of sewage cannot be
regarded as an ideal source of water-supply.
If no contamination be present in the water of a river, it forms a good
source of water-supply; being running water, it is always fairly well aërated,
and is not usually so hard as spring-water.
Even if sewage has entered a river, it is asserted that it becomes a safe
source of water-supply, after passage through filter beds, the sewage having
been got rid of in four ways.
1st.—By subsidence, the organic matter settling to the bottom.
2nd.—By the influence of water-plants, which assimilate ammonia,
nitrates, etc., and give out nascent oxygen.
3rd.—Oxidation. Doubtless a large amount of the nitrogenous matter
does become oxidised in its course down a river, and in this condition is
harmless. The river Seine becomes greatly polluted as it passes through
Paris, but so far as chemical analysis can determine its condition, it is purer
30 miles below the city than it was before it received the sewage of the city.

4th.—It is highly probable that the germs (or micro-organisms) of enteric
fever and other diseases known to be propagated by polluted water, are
practically or wholly destroyed in the struggle for existence with the natural
micro-organisms of river-water. When to this is added the fact that river-
water supplied to large communities is carefully filtered through sand, after
having been stored in reservoirs, in which the chief impurities have time to
settle, it is not surprising that the experience of those communities like
London, which are supplied with river-water, usually shows no evidence of
evil ascribable to drinking this water. For over 30 years the inhabitants of
London have been drinking filtered water from the river Lea and from the
Thames above Teddington, and this gigantic experiment on a population
which has increased from 2½ to 5 millions has not been accompanied by
any conclusive evidence of evil effect.
In regard to the comparative merits of the various waters described, it
will be useful to give here the classification made by the Rivers Pollution
Commissioners in their sixth report:—

1. Spring Water
Very palatable.
Wholesome 2. Deep-well Water
3. Upland Surface Water
Moderately palatable.
4. Stored Rain Water
Suspicious
5. Surface Water from
Cultivated Land
6. River Water to which Palatable.
Dangerous Sewage gains access
7. Shallow-well Water

Passage through certain geological strata has a great influence in
rendering water palatable, colourless, and wholesome by percolation.
The following strata are said by the Commissioners to be the most
efficient:—(1) Chalk, (2) oolite, (3) greensand, (4) Hastings sand, (5) new
red and conglomerate sandstone. Fissures or cracks in these strata may
cause the water to pass through them unpurified by filtration.

CHAPTER X.
THE STORAGE AND DELIVERY OF WATER.
The methods of storing and delivering water will vary with its source. In
rural districts, deep wells and springs are the best sources of supply; but in
large towns they are found to be insufficient for the wants of a rapidly-
increasing population; and they can only be multiplied in a given district
within certain limits, as every well drains a large surrounding area. The
supply from surface wells in gravel or sand beds or in chalk districts is
liable to fail in seasons of drought; but deep wells in oolite or chalk
formations, and in the new red sandstone, generally yield a constant and
abundant supply.
When the water is supplied from upland surfaces, springs, or small
streams, a collecting reservoir is required. This is generally a natural
valley below the level of the source of supply, but of sufficient elevation
above the place supplied to allow the water to be distributed by gravity,
without any pumping apparatus. The reservoir should be large enough to
hold five or six months’ supply, and its embankment should be perfectly
water-tight, and of great strength.
When water is collected from upland surfaces, it is important to know the
amount of rainfall to be reckoned on. If we know the area of the surface
which drains towards the reservoir, and the average rainfall, the total
rainfall is easily calculated. This will, however, differ greatly from the
available rainfall, owing to the losses from penetration into the ground,
evaporation, and other causes. The amount lost will vary, according to the
season, from one-half to seven-eighths of the total rainfall; and according to
the soil (page 68). The proportion of percolation in the chief water-bearing
strata surrounding London varies from 48 to 60 per cent. (Prestwich). It is
less when the ground is steep and the rainfall rapid, and usually less in
winter than in summer.
Water collected near its actual place of fall, and from uncultivated
districts, is always purer than that collected further from its source, and

from cultivated land.
From the collecting or impounding reservoir, water is carried by the
aqueduct or conduit either directly into the service-pipes, or when the
pressure is too great, into a second service-reservoir, resembling the
impounding reservoir in general structure, and capable of holding a few
days’ supply.
This must be high ground, above the level of the highest houses to which
water has to be supplied, as water cannot rise above its own level. When
this cannot be arranged, the water is pumped into tanks at a higher level,
and distributed from them.
The greatest hourly demand for water being double the average hourly
demand, the water-mains supplying a town must have double the
discharging power that would be required, supposing the demand was
uniform. The first requisite of a supply of water is that it should be
abundant, and sufficient in amount for any extra strain on its capacities.
Water ought to be laid on to every house, and to at least two floors of the
house. Anything preventing free access to water, militates against
cleanliness.
Cast-iron is the most serviceable material used in the construction of the
main water-pipes; it is coated with pitch, or Dr. Angus Smith’s varnish, or
with magnetic oxide of iron (Barff). The service-pipes to each house are
generally made of lead, and the ease with which this material can be bent
and curved, and carried to the different floors of a house, makes its use very
convenient. Lead pipes, furthermore, can be easily obliterated in case of
bursting, and so any waste of water and flooding of the house minimised.
Some kinds of water, unfortunately, act on and dissolve lead; this is
especially true of soft waters and those containing organic matter. Shallow
wells, being very liable to organic pollution, ought never to have the
supply-pipe of their pumps made of lead. With hard waters, lead pipes may
generally be used safely. When the quality of the water renders lead pipes
objectionable, the use of iron, tin, zinc, tinned copper, earthenware, gutta-
percha, and other materials, has been suggested. Of these, cast and wrought-
iron pipes are the most serviceable, or pipes composed of an inner lining of
block-tin and an outer of lead, a layer of asbestos intervening to prevent

galvanic action between the metals. According to Rawlinson, “supply-pipes
of wrought-iron are cheaper, stronger, and more easily fitted than service-
pipes of lead;” but it is urged against them by Perry, that with soft water
they become choked by rust in a few years. If galvanized they are more
durable. Cast-iron pipes are rusted less easily than wrought-iron.
When the water-supply is from a river, filtering beds are needed, in
addition to the parts of a water-service hitherto described. Moreover, since
the river is usually at a low level, the water, after passing through the
filtering beds, requires to be pumped into raised tanks, from which it is
delivered.
In laying down water-pipes, in the streets and to houses, it is very
important to make the distance between them and all drains and gas-pipes
as great as possible. Suction of gases or liquids may occur into leaky pipes,
even though these contain water, and still more when they are empty; and
disease has occasionally been traced to this source. Thus if sewers and
water-mains are laid in the same trench, foul matters which have escaped
into the soil from the former may be sucked into the latter. This may happen
if the water-mains are leaky, even when they are running full. Experiments
have shewn that the flow of water causes a partial vacuum and insuction at
the defective points. During intermissions of supply when the mains are
partially or entirely empty, the danger of leakage into them is still greater.
Coal-gas has been similarly sucked into water-mains.
The pipes bringing the water to a house may be kept constantly filled
with water, or only for a limited time once or twice a day. The intermittent
system of supply necessitates the provision of cisterns or water-tanks, in
which water can be stored in the intervals of flow of water. With a sufficient
and properly-distributed public supply of water, no cistern ought to be
required.
Cisterns.—Cisterns for the supply of potable water may be made of iron,
slate, stone, glass, glazed earthenware, or brick lined with Portland cement.
Other materials have been used, as timber, lead, and zinc. Timber is
inadvisable, as it easily rots; lead is very objectionable, owing to the
possible solvent action of the water on it. Zinc or galvanized iron cisterns
are also acted on by soft water; but they may be used with most waters.

Galvanized iron is iron coated with a thin layer of zinc. Iron cisterns soon
rust; but this may be prevented by giving them a coating of boiled linseed
oil before they leave the foundry. Stone cisterns are too heavy for use,
except in basements. Slate cisterns are good, but are apt to leak; the points
of leakage have occasionally been stopped with red lead, which is attacked
by the water, and thus lead poisoning results. If the slate is set in good
cement (not mortar, as this makes the water hard), it is a good material for a
cistern.
Every cistern should have a well-fitting lid, always kept closed, to avoid
the entrance of dust of various kinds, or even dead cats, birds, etc. Noxious
gases may be absorbed by the stagnant water.
The cistern should be easy of access. If it is indoors, the cistern room
should be well ventilated; and in any case the cistern should be periodically
visited and cleaned out. When the cistern is full, a ball-tap prevents any
further flow of water; and if this does not act properly, an overflow pipe
carries off the excess of water.
Cisterns badly arranged or neglected have been in the past a common
source of disease. (1) The overflow pipe should not pass into any part of the
water-closet apparatus or the soil-pipe, or into the supply pipe to the water-
closet.
Where the overflow-pipe discharges into the soil-pipe or closet pan, foul
gases or even solid particles may find their way into the cistern.
(2) No water-closet ought to be supplied from the same cistern as
supplies drinking water, as the pipe leading down to the closet may when
the cistern is accidentally empty carry noxious effluvia into the cistern. A
separate flushing cistern capable of discharging two to three gallons of
water should be provided for each closet.
With a constant supply of water, cisterns are only required for water-
closets and for hot-water apparatus (see pages 168 and 164).
Constant and Intermittent Services.—With an intermittent service of
water, during the intervals of supply, water is only obtainable from cisterns,
water-butts, etc. The objections against this system are that—(1) The
cisterns required are expensive, and liable to get out of order and become

foul. (2) Their overflow pipes may improperly communicate with the soil
pipe or with some other part of the drainage, instead of opening into the
external air. (3) Putrid gases, from neighbouring ventilating-pipes or other
parts of the drainage system, are liable to be absorbed by the stagnant water
in the cistern. (4) The chief objection to an intermittent supply is that,
during the intervals in which the water-mains are empty, foul air and liquids
from the contiguous soil and drains are liable to be sucked through
imperfect joints into the pipes. (5) In case of fire, the supply of water in the
system is insufficient. In certain towns rates of insurance against fire have
been reduced on replacing an intermittent by a constant service of water.
On the other hand it is urged that more expensive fittings are required for
a constant service; and that, when taps are left open or pipes burst, the
waste of water is much greater than with a cistern supply. The balance is
decidedly in favour of a constant supply without storage cisterns. Where
storage cisterns are in use, the taps for drinking-water should be connected
with the “rising-main,” before it supplies the cistern.
The Advantages of the Constant Service may be thus summarised:—
(1) Owing to the absence of cisterns, the risks connected with stagnant
water, and with improper arrangement of overflow pipes, are obviated.
(2) The risk of suction into supply mains of external contaminations is
reduced to a minimum, since the pipes are never empty.
(3) The pipes are less liable to rust. Air in the presence of a little
moisture, causes rapid corrosion.
(4) There is an abundant supply of water in case of fire.
Of course, when there is a temporary stoppage of supply, as for repairs,
some of the dangers incurred by an intermittent supply will arise.

CHAPTER XI.
IMPURITIES OF WATER.
Properties of Water.—When pure, water is colourless, or bluish when
seen in large quantity. It should be quite inodorous. If, after keeping it for
some time in a perfectly clean vessel, or if on heating it a smell is
developed, the water is bad. Its taste should be pleasant and sparkling from
the atmospheric gases dissolved in it. Bitterness generally indicates the
presence of sulphate of magnesium (Epsom salts). Saltness is always a
suspicious property, except in water obtained in the neighbourhood of salt
mines or brine springs, or near the sea. It should be soft to the touch, and
should dissolve soap easily. It should be bright and clear, and contain no
suspended matters. Clear water is not necessarily pure, but turbid water is
always to be rejected; the only exception being the brownish-tinged water
from moors, which is not hurtful. In all other cases, printed matter should
be legible through at least 18 inches of water in a clear glass cylinder.
Thoroughly dissolved organic matter is less dangerous than suspended; the
turbidity of water is therefore of great importance. But water may be bright
and sparkling and apparently perfectly clear, and yet highly dangerous. The
most important of the physical properties of water in regard to health are the
absence of smell and turbidity, and these can be ascertained by even the
most inexperienced. The chemical tests for the more important impurities
are given (pages 85 to 87).
The impurities of water may be classed under four heads—gaseous,
mineral, vegetable, and animal.
The gases ordinarily present in water cannot properly be regarded as
impurities, inasmuch as they are always present, and greatly increase its
palatableness. The dissolved nitrogen and oxygen bear to each other the
proportion 1·42 to 1; where sewage contamination occurs, the oxygen will
be diminished or disappear, owing to oxidation of the organic matter.
The amount of carbonic acid gas in water varies greatly. It may be
considerable in chalk waters, and in contaminated well-water.

Mineral Impurities.—Mineral impurities are dissolved by water in its
course through the soil, and so will vary with the character of the latter. 1.
The water obtained from granitic formations contains very little mineral
matter, often not more than two to six grains per gallon. Clay slate water is
also generally very pure, as is the water from hard trap rocks. 2. The water
from millstone grit and hard oolite is very pure, often containing only four
to eight grains per gallon, chiefly calcium and magnesium sulphate and
carbonate. 3. Soft sand-rock waters usually contain thirty to eighty grains
per gallon of sodium salts, with a little lime and magnesia. 4. Loose sand
and gravel waters vary greatly. They may be almost free from mineral
matter, or the solids may be more than seventy grains per gallon, including
much organic matter. 5. Waters from the lias clays vary somewhat, but
commonly contain a large quantity of calcium and magnesium sulphates. 6.
Chalk waters generally contain from seven to twenty grains of calcium
carbonate, with smaller quantities of other salts. 7. Limestone and
magnesian limestone waters differ from the last, in containing more
calcium sulphate and less calcium carbonate, as well as much magnesium
sulphate and carbonate in the dolomite districts. 8. Selenitic waters contain
calcium sulphate in considerable quantities. 9. Clay waters usually possess
the characters of water from surface wells, and are objectionable. 10.
Alluvial waters generally contain a large amount of various salts, including
the various calcium, magnesium, and sodium salts. 11. Artesian well water
varies greatly in composition. It may contain a large amount of sodium and
potassium salts, or a small quantity of iron, or calcium salts.
The commonest and most important mineral constituent of water is
calcium carbonate, next to this calcium sulphate. These two salts are the
chief causes of hardness of water. For practical purposes as regards use in
domestic matters and in manufactures, the most important classification of
waters is into hard and soft. The degree of hardness varies within wide
limits—from rain-water, which has no hardness at all, to the water from
new red sandstone rocks which sometimes possesses a hardness of 90
degrees; or wells in the gravel, in which it may be as much as 152 degrees.
The following classification of waters, according to the degree of
hardness, beginning with the least hard and gradually increasing in
hardness, is from the sixth report of the Rivers Pollution Commissioners:—

1. Rain-water. 2. Upland surface. 3. Surface from cultivated land. 4. River.
5. Spring. 6. Deep-well. 7. Shallow-well water.
Calcium carbonate is the most common cause of hardness, and the
hardness produced by it is remediable by boiling or chemical means.
Calcium carbonate (chalk) is rendered soluble in water, by the carbonic acid
contained in the latter, a double bicarbonate being thus formed. The air
contained in the interstices of the soil through which water passes, often
contains 250 times as much carbonic acid as ordinary air. The water, in
percolating through the soil, dissolves this carbonic acid, and thus is able to
take up a considerable amount of chalk.
The amount of hardness in any given water is expressed in degrees, one
degree being equivalent to a grain of calcium carbonate in a gallon of water.
Clarke’s soap test is employed to detect the amount of hardness. It consists
of a solution of soap of a known strength. Soft water will form a lather at
once with this; hard water will only form a lather after all the calcium salt is
neutralised. The amount of Clarke’s solution required before a lather is
produced, will give an estimate of the amount of hardness.
To Determine the Total Hardness take 70 c.c. of the water and place in a stoppered bottle. From
a burette run in a sufficient quantity of the standard soap solution (of which 1 c.c. equals 1° of
hardness), to produce a lather on shaking the water, which remains unbroken after standing five
minutes. Thus, if 7·5 c.c. of the soap solution were required, the hardness is 6°·5, as 1 c.c. of the
solution is required to produce a lather in soft water. The 6°·5 means 6·5 milligrammes of calcium
carbonate in 70 c.c. or 6·5 grains in a gallon of the water.
To Determine the Permanent Hardness boil 70 c.c. of the water in a flask for half-an-hour;
allow the precipitated carbonates of calcium and magnesium to settle. Some of the latter will be re-
dissolved. Carefully decant, and make up the liquid to the original 70 c.c. with distilled water. Filter
through fine filter paper and estimate hardness as above.

The amount of soap wasted in consequence of the hardness of water is
very great. Thus, in the case of water of one degree of hardness, as every
gallon contains one grain of chalk, 7,000 gallons would contain 7,000
grains—that is, a pound. But every grain of chalk wastes 8 or 9 grains of
soap; therefore, a pound of chalk, contained in 7,000 gallons, would waste
about 8½ pounds of soap. But nearly all waters are harder than this, and
they not uncommonly possess a hardness of 20° or more. If the hardness be
20°, the waste would be 170 pounds of soap. This quantity would be easily
used annually in a family of seven or eight persons, if we include the

washing of clothes. The amount of money thus wasted can be easily
estimated.
Not only does soft water require less soap, but it is much more suitable
for making tea and soup, and for boiling meat and vegetables—both time
and fuel being saved. The reason why better tea is made when a little
carbonate of soda is added to the water is that the chalk is by this means
precipitated.
Carbonate of calcium is precipitated from water by boiling it; carbonic
acid being driven off, the neutral salt falls to the bottom of the vessel. This
is the origin of the “fur” inside kettles, which lessens their conductivity to
heat, and renders necessary a greater consumption of fuel.
The chalk may also be removed by adding to the water, while still in the
reservoir, some milk of lime—that is, quicklime made into a milky solution
with water. This is done on a large scale at various waterworks. The
reaction may be expressed thus:—
Calcium bicarbonate + calcium oxide = calcium carbonate + calcium
carbonate.
The calcium carbonate, as it is precipitated, carries down with it organic
and other matters, thus clearing and purifying the water.
The hardness due to calcium sulphate is not removable by boiling. It is,
therefore, called permanent hardness, to distinguish it from the temporary
hardness of chalk waters, which is removable by boiling. It may, however,
be partially removed by the addition of washing soda to the water, as well
as the nitrate and chloride of calcium which are also present. The
magnesium salts are not removable by boiling or soda. This is shown by the
fact that the “fur” inside kettles does not usually contain magnesium salts.
The amount of hardness varies greatly in different waters. In the deep
wells in magnesium limestone, it varies from 14°-57°; in the deep wells
from chalk beds, it varies from 13° to 27° and may be higher. In the water
from Bala Lake, Wales, the temporary hardness is 0°·1, the permanent
hardness 0°·3; in the Loch Katrine water there is no temporary hardness,
0°·9 permanent hardness; in the water from the new red sandstone
(Nottingham), the temporary hardness is 9°·6, permanent 10°·2; in a chalk

spring at Ryde, temporary hardness 16°·7, permanent 3°·9 (Wanklyn). The
total hardness in the metropolitan water supplies from the rivers Thames
and Lea, varies from 13°·2 (Southwark Company) to 14°·6 (New River
Company); in the Kent Deep Wells 20°·1; in deep wells from the chalk at
Brighton it varies from 12° to 13°. In all these, the hardness is chiefly
temporary.
The amount of permanent hardness is always great in water from clays,
as the London, Oxford, Kimmeridge, and Lower Lias clays; or in places
where there are large deposits of calcium sulphate, as at Montmartre, near
Paris (hence the name Plaster of Paris, given to desiccated calcium
sulphate). Water from fissures in the clay often contains, also, a large
amount of organic matter.
Chlorides are always present in small quantities in water. As a rule the
presence of more than 1 grain per gallon, i.e. ·7 parts per 100,000 of water,
indicates contamination with some animal refuse, unless the water is
derived from new red sandstone, or brine springs, or from the
neighbourhood of the sea. This rule does not, however, hold universally
good. The absence or the presence of only a minute quantity of chlorides
indicates the probable absence of animal contamination; but in exceptional
cases waters of the highest organic purity may contain more chlorides than
the same bulk of sewage.
To determine the amount of Chlorine take 70 c.c. of the water, add a few drops of solution of
potassium monochromate (KCrO₄). From a burette run in gradually a standard solution of silver
nitrate (of such a strength that 1 c.c. of the solution is equivalent to 1 milligramme of chlorine). The
silver solution forms milky chloride of silver (AgCl) by combination with the chlorine of the
chlorides in the water. When all the chlorine is thus combined, the next drop of the silver solution
forms a deep red tint with the chromate. The number of c.c.’s of the silver solution required to
produce this effect, equals the number of milligrammes of chlorine in 70 c.c. of water, or the number
of grains of chlorine in a gallon of water. To convert this into parts per 100,000, divide by 7 and
multiply by 10.
To express the amount of chlorine in terms of common salt (NaCl), multiply the parts per 100,000
of chlorine by 1·65.

Nitrates in any water are suspicious; but their import varies with the
circumstances under which they occur. A minute quantity of ammonium
nitrate is present in nearly all waters; and the water of deep wells, especially
of wells in the chalk, which, as a rule is perfectly free from sewage, may be
highly charged with nitrates. Nitrates, when derived from sewage, represent

a completely oxidised condition of its nitrogenous matter. Crude sewage
generally contains no nitrates. Nitrites as a rule indicate more recent
contamination, and therefore greater danger than nitrates. The presence of
more than a trace of phosphates is a strong indication of contamination with
sewage matter.
To determine the amount of Nitrites and Nitrates the best known methods are by the indigo, the
phenol-sulphuric, the aluminium, or the zinc-copper couple tests. For nitrites the metaphenylene-
diamine test is employed (page 85). The following qualitative tests will suffice for elementary work.
Nitrates. An equal amount of a solution of brucine is added to the suspected water in a test-tube,
then a little pure sulphuric acid is poured down the side of the tube. A pink zone is produced if
nitrates are present in considerable amount.
Nitrites. A few drops of each of diluted sulphuric acid and of metaphenylene-diamine solution
give a red colour with water after standing for a few minutes, if nitrites are present.

Lead is an occasional contamination of slightly acid waters. The purest
and most oxygenated waters act most readily on lead; as also those
containing organic matter, nitrates or nitrites. Waters containing chlorides
also act on lead, the chloride of lead being sufficiently soluble to produce
poisonous symptoms. Upland surface waters derived from moorlands in
certain districts, e.g. around Sheffield, have been found to be capable of
dissolving considerable lead from lead service-pipes. The water taken first
from the tap in the early morning is the most heavily charged with lead.
Such waters are very soft; but other moorland soft waters do not dissolve
lead. It is the water having a slightly acid reaction which possesses this
property. The source of this acid, whether sulphuric acid from the products
of combustion in a neighbouring town, or an organic acid, is uncertain. The
plumbo-solvent action of such water is greatest in autumn, when the
amount of acid is at its maximum. The property of dissolving lead is
removed by passing the water on a large scale over filters of sand, spongy
iron, chalk, or limestone. The addition of a small quantity of carbonate of
soda has the same effect. In such districts the use of tin-lined iron pipes for
domestic services has been recommended, but these are liable to fracture
when bent. Pipes consisting of an outer case of lead and an inner pipe of tin
with a layers of asbestos between have also been placed on the market. (See
also page 68.)
Hard waters have the least action on lead; a coating of insoluble
carbonate of lead being formed on the interior of the pipe, which prevents

any further action. Thus the use of lead pipes for water containing
carbonates or sulphate, or calcium phosphate, is comparatively safe. Hard
water containing carbonic acid gas under pressure will dissolve a small
amount of carbonate of lead; this explains the cases of lead poisoning from
soda water which was formerly supplied in syphon bottles with lead tubes.
Lead is dissolved much more easily by water if other metals are in
contact with it, as iron, zinc, or tin, galvanic action being thus set up. Zinc
pipes containing some lead are very dangerous, especially with the distilled
water used on board ships.
To determine the presence of lead in water, place a given quantity, say 100 c.c. in a white dish,
and stir with a rod dipped in a solution of ammonium sulphide; if the water becomes coloured, this is
generally due to the presence of iron or lead. If the colour remains after adding a drop or two of
hydrochloric acid, lead is present.

To determine the amount of lead, a standard solution of lead acetate containing 1 ∕ 10
milligrammes of lead in 1 c.c., is made by dissolving ·183 gramme of crystallised lead acetate in a
litre of distilled water. Place 100 c.c. of the water to be examined in a Nessler glass, acidify by a few
drops of acetic acid; now add ½ c.c. of a saturated solution of ammonium sulphide. A brownish-black
discoloration is produced if lead is present. To a second Nessler glass, containing 100 c.c. of distilled
water, the same amounts of acetic acid and ammonium sulphide are added, and then a sufficient
quantity of the standard lead solution is added, until the tints of the contents of the two Nessler
glasses are identical. The amount of the standard solution added being known, we know the amount
of lead in 100 c.c., and the amount per litre (1,000 c.c.) will be tenfold. Thus if 2 c.c. of the solution
were required for matching colours, there were ·2 parts of lead per 100,000 of water, or ·14 grains
per gallon.

Traces of Iron are sometimes present in water, giving it an astringent
taste. Such water is apt to turn brown; and tea made from it is very dark.
Organic Impurities.—Organic impurities may be either vegetable or
animal, the latter being by far the most dangerous. The water from
moorlands is often brown, but this is not noxious. Growing plants, again,
may be beneficial to water, by absorbing dissolved organic matter, and
aiding its oxidation. Decaying vegetable matter is objectionable in water,
and may set up diarrhœa.
The most important organic impurity of water has an animal origin—
from sewage; the liquid or solid excreta (i.e. the urine or fæces) gaining
accidental access to the water. Besides sewage, the eggs of various
intestinal worms have been swallowed with water; and in a few cases, even
leeches. But whatever the source of the organic matter contained in water, it

contains nitrogen as an essential constituent; and tends under the influence
of warmth, and therefore especially in summer, to undergo putrefactive
changes, owing to the action of bacteria. These split up the more complex
molecules of organic matter into simpler matter; ammoniacal compounds
and salts, of which the most important are nitrites and nitrates, being final
products of their activity. The detection of nitrates, and still more of nitrites,
is important, as they may indicate the occurrence of previous sewage
contamination. These products are quite harmless in water, except as an
indication that the water has been polluted, and that possibly a certain
proportion of the nitrogenous matter in the form of the complex organic
matter forming the germs of such diseases as enteric fever, may still be
present. Organic matter may be suspended or dissolved, the former being
most dangerous to health. The germs or microbes causing disease consist of
suspended, i.e. particulate matter. The amount of organic matter is
determined by the amount of free ammonia and albuminoid ammonia which
are present (Wanklyn’s process), by Frankland’s combustion process, or by
Forschammer’s oxygen process; all of which give indications, rather than
an exact estimate of its amount.

METHODS OF WATER ANALYSIS.
The following scheme of qualitative examination may be followed, when an immediate opinion
is required as to a water. It can only be trusted when the examination shows pollution. The following
results will be obtained, for instance, when a minute quantity of urine is added to a gallon of water.
(1) The water has a faint odour.
(2) Its colour is greenish yellow in bulk.
(3) On adding a few drops of Nessler’s solution, a deep yellow colour appears.
(4) A few drops of an acid solution of permanganate of potassium become yellow when added to it.
(5) Acidify some of the water in a test-tube with nitric acid, then add silver nitrate solution. Distinct
cloudiness is produced, much greater than with pure tap water.
(6) Addition of hydrochloric acid and barium chloride solution shows a much greater quantity of
sulphates than the same quantity of tap water.
(7) A quantity of the water evaporated in a porcelain dish over a Bunsen’s flame gives a white
residue, which speedily turns brown, with a urinous odour.
(8) Ignite the ash and add some nitric acid to oxidise it more completely. Then dissolve in distilled
water, and add acid molybdate solution. A yellow colour, followed by a precipitate, indicates high
phosphates and sewage pollution.

The Complete Systematic Examination is (a) physical, (b) bacteriological, and (c) chemical. Of
the physical tests, colour, which should never be yellow or brown except for peaty water, is
important. Taste is a somewhat uncertain guide, but any badly-tasting water should be rejected. The
odour on heating to 80° F. in a closed flask may indicate pollution. The degree of hardness can be
roughly tested by rubbing between the hands. The absence of turbidity is most important, as
suspended impurities are more dangerous than all others. Printed matter should be legible through a
column of 18 inches of water.
Microscopally the suspended matter in water which has been allowed to settle should be
examined. Particles of vegetable matter, e.g. fibres of cotton, linen, cells of potato, or spiral cells of
cabbage, are important as indicating domestic impurities. Bits of wool, hair, wings and legs of insects
and epithelium may be discovered. The presence of algæ, diatoms and desmids, or of water-fleas,
cannot be held to indicate pollution, as these are found in all running streams and in many wells. The
eggs and embryos of worms are much more serious.
Bacteria are almost invariably present in water. The majority of these micro-organisms are
harmless. But as they may number among them the germs producing diseases like enteric fever and
cholera, the estimation of their number and particularly of any deviation from the number usually
present in a given water, and if possible the detection of special disease-producing bacteria, are very
important. This method has been made more practicable since Koch’s method of “plate cultivation”
of bacteria was discovered. A small quantity of the water to be examined (kept surrounded by ice
until this test is applied, to prevent multiplication of bacteria in the bottle), is mixed with sterilised
gelatine which has been melted over a water bath. Then the mixture is spread in a thin layer on a
glass plate and allowed to solidify, having been covered to prevent atmospheric germs from settling
on the gelatine. The bacteria in the water thus become fixed, each growing and forming “colonies”
dotted over the plate. These colonies can be recognised by their size and appearance, and by sub-
culturing according to recognised methods. The number of such colonies, and the number of bacteria,
from which, presumably, such colonies sprang in 1 c.c. of filtered Thames water is usually much
below 100; in the water before filtration many thousands are present. It has been suggested that no
water should be regarded as wholesome which contains more than 100 bacteria in each c.c.
This standard is, however, obviously arbitrary. Chalk water ought to have a smaller number than
this; river waters may have more, and yet be wholesome. Everything depends on the character of the
bacteria found. The detection of the Bacillus coli communis, which is present in sewage, and
normally in the human intestine, is very suggestive of contamination by sewage. The bacteriological
method of examination of water is still in its infancy.

CHEMICAL ANALYSIS.
(1) The total solids are ascertained by evaporating a given quantity of the water to dryness, and
weighing.
(2) Determination of Chlorine (see page 81).
(3) Determination of Hardness (see page 80).
(4) The Determination of Nitrites is based on the reddish-brown colouration produced when an
acid solution of metaphenylene diamine is brought into contact with a weak solution of nitrous acid.
100 c.c. of the water under examination are placed in a clean glass cylinder. Add 1 c.c. of H₂SO₄
solution (1 in 3), then 2 c.c. of metaphenylene diamine solution (5 grains in 1 litre of water with a
little H₂SO₄ added). Stir well with a glass rod. If a colouration is produced at once, a smaller quantity

of water must be taken, and made up to 100 c.c. with pure distilled water. The quantity of nitrous acid
present is measured by introducing different fractions of a c.c. of the standard sodium nitrate
solution3 into similar glass cylinders. Each is then made up to 100 c.c. with distilled water, and the
metaphenylene diamine solution and acid added as before. The colour develops slowly; time must,
therefore, be allowed in matching.
(5) The Determination of Nitrates can be conveniently made by the following method. When
phenyl-hydrogen sulphate solution is poured upon a nitrate, and sulphuric acid is formed, picric acid
is formed:—
(C₆H₅)HSO₄ + 3 HNO₃ = C₆H₂(NO₂)₃OH + H₂SO₄ + 2 H₂O.
The addition of free ammonia in excess forms yellow ammonium picrate, the intensity of the
colour of which is an index of the picrate, and of the nitrate from which it was produced. (a)
Evaporate 25 c.c. of the water under examination, and (b) 5 c.c. of standard KNO₃ solution
(containing 1 part N in 100,000) to dryness in two porcelain dishes over the water bath. Add 1 c.c. of
phenyl-sulphate solution to each of these as soon as cool, stir well with a glass rod, then add 1 c.c.
distilled water to each dish and 3 drops of strong H₂SO₄. Next add 25 c.c. of water to each dish, and
after heating for five minutes over the water bath, add solution of ammonia to each dish in excess. A
yellow colour is produced in proportion to the amount of nitrate present. Transfer the liquids to glass
cylinders, and dilute each to 100 c.c. Take 50 c.c. of the solution showing the least colour, and dilute
the other with distilled water, until it has the same tint.
Supposing the 100 c.c. of the sample required to be diluted to 150 c.c.—

Then the amount of N will be 150 ∕ 100 × 5 ∕ 25 = ·3 parts per 100,000.

If the two solutions (a) and (b) when diluted have the same tint, then the

Amount of N in the sample = 5 ∕ 25 = ·2 parts per 100,000.

(6) Determination of Organic Matter. Frankland’s combustion process involves the use of
delicate and costly apparatus, and is seldom employed. In this process the organic carbon is evolved
as carbonic acid, and the nitrogen as such.
Wanklyn’s ammonia process is based on the reduction of organic matter to ammonia. Part of this
ammonia, free or saline ammonia, is simply combined with carbonic, nitric, or other acids, or is
easily derived from the urea of urine, CH₄N₂O + 2H₂O = 2(NH₄)₂CO₃. Another part is only set free
when the water is boiled with a strongly alkaline solution of permanganate of potassium. This is
called the albuminoid ammonia.
In carrying out this method, a retort is taken, and after having been washed out, first with a little
sulphuric acid, and then with some of the water to be analysed, 500 c.c. of the latter is put in, and the
retort is connected with a condenser, and distillation begun; 50 c.c. of the distilled water is collected
in a cylindrical glass tube called a Nessler glass. To this 1½ c.c. of Nessler’s reagent (mercuric iodide
dissolved in a solution of potassic iodide and made alkaline by potass) are added. A rich brown
colour is produced, if any ammonia is present in the distillate. The amount of ammonia in the
distillate is determined by exactly imitating its colour by adding a known quantity of a standard
solution of ammonium-chloride to 50 c.c. of ammonia-free distilled water, and then Nesslerising as
before. Each c.c. of the dilute standard ammonium chloride solution is equivalent to ·00001 gramme
of ammonia (NH₃).

If the first 50 c.c. of water distilled over gives only a slight colouration with the Nessler solution,
no more water needs to be distilled over for free ammonia. If more is present, two more 50 c.c.’s
must be distilled over, and the amounts of the standard solution required for imitating the test in each
Nesslerised 50 c.c. added together. Thus, if 2 c.c. were needed. This
= ·00002 grm. NH₃, which is contained in 500 c.c. of the water
= ·00002 × 200 = ·004 parts saline NH₃ in 100,000 of water.
The free ammonia having been distilled over, 50 c.c. of an alkaline permanganate solution
(containing 8 grammes KMnO₄ and 200 grammes of NaOH in 1100 c.c. of distilled water, boiled
until the bulk is reduced to 1,000 c.c.) is poured into the retort, and distillation is begun again. Three
successive 50 c.c.’s of water are collected, and then the distillation stopped. Each of these is
Nesslerised, and the tint imitated as before with standard ammonia solution. The three amounts of
ammonia thus found to be present are added together; and when multiplied by 200, we obtain the
amount of albuminoid ammonia in 100,000 parts of water. This test is universally employed by water
analysts along with the next test.
The amount of Oxygen Absorbed from permanganate of potassium is regarded as an approximate
test of the amount of organic matter in water. Qualitatively this forms a favourite method of testing
the purity of water. Two glass cylinders are taken, one filled with distilled water, one with the water
to be tested. To each is added a given small amount of an acid solution of permanganate of
potassium. The distilled water to which permanganate has been added will retain its pink colour;
while, if the water being tested is very impure, it will speedily become decolourised. The rapidity and
degree of decolourisation are a rough test of the amount of impurity. A rapid decolourisation proves
the presence of organic matter having an animal origin, or of sulphuretted hydrogen, iron, or nitrites.
Sulphuretted hydrogen is rarely present, and can be easily recognised by its smell; iron or nitrites are
readily distinguished by their appropriate tests. In the absence of these, the rapid discolouration is an
indication of animal contamination.
To Determine the Amount of Oxygen Absorbed, two glass-stoppered bottles, each holding about
350 c.c. are required. Into one, 250 c.c. distilled water, and into the other the same amount of the
water under examination are placed. To each are then added 10 c.c. of standard permanganate of
potassium solution4 and 10 c.c. of a standard pure 25 per cent sulphuric acid solution. The two
bottles, after being shaken, are placed in a water-bath at 27°C for four hours. At the end of this time
add a few drops of potassium iodide solution to each bottle. The pink is now replaced by a yellow
colour.5 A standard thiosulphate solution (Na₂S₂O₃, 5H₂O)6 is placed in a burette. From this the
thiosulphate solution is run into the control bottle until the yellow colour almost disappears. Now a
few drops of starch solution are added, and a blue colour is produced. The thiosulphate is then added
cautiously until all the blue colour disappears. The amount of thiosulphate necessary for this is read
off on the burette. The same process is repeated with the bottle containing the sample of water. The
starch acts as an indicator. The amount of iodine liberated is an index of the amount of permanganate
in the water, which has not been used up by its impurities. The amount of iodine liberated is
measured by the amount of thiosulphate required to decolourise the solution. Thus—
2 Na₂S₂O₃ + I₂ = 2 NaI + Na₂S₄O₆.
Suppose that 20 c.c. of thiosulphate solution were required to decolourise the iodine liberated in
250 c.c. of a sample of water, while the distilled water required 25 c.c. Then 25 c.c. thiosulphate
represents 10 c.c. of the permanganate solution = ·001 grains of available oxygen.
25-20 = 5

As 25 c.c. = ·001 grm. O, 5 c.c. = 5 ∕ 25 of ·001 = ·0002 grm.

This is the amount of O absorbed by 250 c.c. of the sample.
Therefore the amount of O absorbed by 100,000 c.c. of the sample. = ·08 grm.
It is usual to make a similar determination of the amount of oxygen absorbed in fifteen minutes.
The Interpretation of Results of analysis is more difficult than the analysis. A single analysis may
be misleading, unless the source of the water is known. Constancy in composition or analysis is
almost as important a criterion of purity as the actual character of the constituents. A knowledge of
the source is essential in interpreting results of analysis, as the chemical composition of water varies
with its source. The following rules are only approximately correct, and are subject to the above
general considerations. The total dissolved solids in river-water are usually 10 to 30 parts in 100,000.
Shallow well-water may contain from 30 to 200 parts or even more, and deep well-water from 20 to
70 parts.
Saline Ammonia in water is commonly of animal origin, ammonia (NH₃) being one of the first
products of decomposition of nitrogenous animal refuse. Upland surface water usually contains about
·002 parts per 100,000, but it may reach ·008 or more if the land over which the water passes has
been manured. Shallow well-water may be free from ammonia, or this may be very excessive in
amount. Deep well-water may contain no ammonia or any amount up to ·1 per 100,000. Its presence
is suspicious if the albuminoid ammonia is above a trace, or if the oxygen absorbed is appreciable in
amount. Generally water is suspicious if saline ammonia is up to ·01 per 100,000. Albuminoid
Ammonia indicates the amount of organic nitrogenous matter present in the water. It should not
exceed ·005 parts per 100,000, while at the same time the saline ammonia should not usually exceed
·01 per 100,000. For Oxygen consumed the following table of the weight of oxygen required for
100,000 parts of water is given by Clowes and Coleman:—

UPLAND SURFACE WATER FROM
WATER. OTHER SOURCES.
Water of
Not exceeding ·1 Not exceeding ·05
Great purity
Medium purity From ·1 to ·3 From ·05 to ·15
Doubtful purity From ·3 to ·4 From ·15 to ·20
Impure Exceeding ·4 Exceeding ·20

The presence of more than 1 and still more so of 2 grains of Chlorine per 100,000 of water is most
suspicious, except in saline districts. Nitrites if present in an appreciable quantity indicate
comparatively recent contamination by sewage. In deep well-water they may be produced by
deoxidation of nitrates. Nitrates in upland surface waters should not be equivalent to more than ·03
of N. per 100,000; in shallow well-waters the amount varies greatly; in deep well-waters it may be
excessive. As a rule it ought not to be equivalent to more than 5 parts of N. per 100,000 of water; but
the significance of nitrates depends greatly on the source of the water and on the amount of the other
constituents present.
Chemical analysis alone cannot ascertain the safety of a given drinking water. A minute amount of
impurity inappreciable to analysis may be competent to produce disease; while another water may be
drunk with impunity, which contains considerable organic matter. Chemical analysis “can tell us of
impurity and hazard, but not of purity or safety” (Buchanan). An accurate opinion as to the character
of a drinking water can only be expressed when one knows the amount of each chief constituent (as

above), and whether these amounts deviate from the same water at other times or from other waters
in the vicinity.

CHAPTER XII.
ORIGIN AND EFFECTS OF THE IMPURITIES
OF WATER.
Origin of Impurities of Water.—Parkes classifies impurities of water
as:
1. Those Received at the Source.—The character of water varies with
the geological structures through which it has passed; with its origin from
the subsoil or cultivated land, or deep wells, or graveyards, or near the sea,
etc. It is a mistaken policy to commence with an impure water and proceed
to purify it; though communities supplied from rivers may be compelled to
submit to this. They must then insist on the most stringent measures of
purification (see p. 96). Inorganic impurities are of much smaller
consequence as regards health than organic; hence the great advantage of
deep well-water over river water. It has been suggested, however, that when
deep well-water becomes polluted, it is more dangerous than equally
polluted river-water, because in the latter the normal bacteria of water are
more abundant, and possibly interfere with the continued life in water of
disease-producing bacteria. This statement is unproved; and if correct, is
rather an indication for further precautions being taken to prevent access of
pollution to deep wells, than in favour of the continued use of river-water.
2. Impurities of Transit from Source to Reservoir, acquired during the
flow in rivers, canals, or other conduits. These impurities have been broadly
divided by the Rivers Pollution Commissioners into “sewage” and
“manufacturing;” the former including the solid and liquid excreta, the
house and waste water, etc.; the latter including the refuse from
manufacturing processes, as from dye and bleaching works, tanneries, etc.
3. Impurities of Storage, whether in wells, reservoirs, or cisterns.
Organic impurities are commonly received at this stage. A well, for
instance, drains the soil around it in the shape of an inverted cone, with a
very broad base, unless the entrance of water from its sides is prevented.

4. Impurities of Distribution. Lead, and occasionally other metals, are
dissolved by certain waters. If the pipes are left empty, as with an
intermittent supply, sewage may be drawn into them; in a few cases coal-
gas has found its way into the water pipes (page 76).
Effects of Impure Water.—1. Effects of Mineral Impurities.
Suspended Mineral matters in unfiltered water occasionally produce
diarrhœa. The hill diarrhœa of some parts of India has been traced to water
containing fine mica particles in suspension.
Hard water is said by some to be hurtful, but the salts causing hardness
are probably innocuous when not amounting to more than 12 or 16 grains
per gallon. Persons in the habit of drinking hard water find soft water
unpalatable. Hard water has been thought to favour gout and calculus
(stone), but this is not so. The salts producing permanent hardness are said
to be injurious, producing indigestion, but this is doubtful in the amounts
ordinarily drunk.
Goitre, a swelling of the thyroid gland in the neck, is often associated
with the use of drinking water from magnesian limestone formations; but
that any kind of excessively hard water causes goitre is very doubtful.
Lead dissolved in water may produce serious and lasting ailments, and
they are often present for a long time before their cause is detected. The
amount of lead capable of producing poisonous symptoms has been as little
as 1 ∕ 100 grain per gallon of water (Dr. Angus Smith). According to De
Chaumont, 1 ∕ 10 grain per gallon, that is 1 part in 700,000 is usually
required to produce such symptoms. In the well-known case of the
poisoning of Louis Phillippe’s family at Claremount, there was 7 ∕ 10 grain of
lead in a gallon of water; and this affected 34 per cent. of those who drank
it. The symptoms produced by lead poisoning are those of indigestion,
accompanied by colic; a blue line at the junction of the gums with the teeth;
“wrist drop,” a paralysis of the muscles of the forearm, or some other
paralysis; and if the poisoning is continued, attacks of gout, followed by its
usual consequences, chronic kidney disease. The latter affections chiefly
occur when the poisoning is continued for a long time, as in the case of
painters or type-setters: poisoning from water is generally discovered before
any other than dyspeptic symptoms and colic are produced.

The presence of traces of iron in water may give it a slightly astringent
taste; and such water is liable to cause headache and constipation.
2. Effects of Vegetable Impurities.—Living plants are unobjectionable,
but decomposing vegetable matter may produce diarrhœa and other severe
symptoms.
3. Effects of Animal Impurities.—Animal impurities of water are by far
the most important from a sanitary point of view. They are most commonly
derived from leaky drains or cesspools, or from surface accumulations of
filth. The quality of the contamination is more important than its quantity;
and this will explain why water containing a large amount of sewage may
be drunk for a prolonged period with impunity, while at another time the
least trace, if it contain the active germs of disease, will lead to serious
mischief.
Suspended animal impurities are much more dangerous than those
completely dissolved. Hence the examination of the colour and turbidity of
drinking water is very important. Fæcal contamination is by far the most
dangerous of all, and chiefly so when it is derived from a patient suffering
from some communicable disease, like enteric fever or cholera.
Certain Parasites occasionally are swallowed with water in the form of
embryo or egg. The liver fluke, round worm, and less frequently other kinds
of entozoa have been introduced in this way. The occasional swallowing of
small leeches has occasionally given rise to hæmorrhage.
Diarrhœa may be caused by animal contamination of water. It most
often occurs in summer, when all the circumstances are favourable to active
fermentative changes. The summer diarrhœa of infants is caused by similar
changes in milk or other foods. The presence of fœtid gases in water may
lead to diarrhœa. This may occur when the overflow pipe of a cistern opens
into the soil pipe or into the trap of the W.C.
Dysentery, like cholera and enteric fever, may be propagated by water
contaminated with the stools of a patient suffering from the same disease.
Malaria or Ague has been stated to be caused by the water of malarious
marshes. The evidence on this point requires revision, in view of the part

which the mosquito is now known to play in the propagation of this disease
(pages 282 and 307).
Enteric (otherwise called Typhoid) fever is most often due to the
drinking of water contaminated with sewage.
The balance of evidence is in favour of the view that in order to produce
enteric fever water must be contaminated with the stools or urine of a
patient who has suffered from this disease. Numerous instances are on
record in which villages, the inhabitants of which drink sewage-
contaminated water, have remained free from enteric fever, until a patient
suffering from it has come to the village, when the spread by water has been
very rapid. Occasionally no known contamination from a case of enteric
fever has preceded the outbreak of this disease which has been caused by
sewage-contaminated water. It must be remembered on this point that the
urine of an enteric fever patient may occasionally contain large numbers of
the bacillus causing this disease for several months after the patient is well
(page 301).
The contamination of water with sewage may occur in various ways. In
country places surface wells and small streams commonly supply the
drinking water, and these are frequently contaminated. The illustration (Fig.
9) shows the percolation of excretory matters from an out-door closet
through the porous gravel, into a neighbouring well; the result being an
epidemic of enteric fever among those who drank the water of the well.
Alterations in the level of the subsoil water are sometimes followed by an
outbreak of enteric fever (p. 70). A sudden fall of rain occurs, and the
excess of water in the soil absorbs the soakings from country privies or
cesspools, and carries them into the nearest well. The percolation of tainted
water through a considerable tract of land, possibly along fissures, is
sometimes insufficient to purify it, as proved by a remarkable epidemic in
the small village of Lausen, in Switzerland.
In other cases sewage gains access into leaky water-pipes. Formerly
contamination was occasionally due to improper connection between the
overflow pipe of the cistern and the soil-pipe, or to the water-closet being
flushed by a pipe directly connected with a water-main (as in the Caius

College outbreak at Cambridge), or connected with the drinking-water
cistern (page 76).
Milk may, by the admixture of water, become contaminated with enteric
matter, and produce widespread epidemics. Where the water is very impure,
the small amount used in washing cans may suffice to cause infection.
Cholera was first proved by Dr. Snow, in 1849, to be due to the specific
contagium of cholera gaining an entrance into drinking water. This
contagium is derived as in enteric fever from the intestinal evacuations, the
urine, and the vomit of patients suffering from the same disease.

Fig. 9.

The close connection of the spread of cholera with an impure water
supply has been repeatedly shown in this country. The cholera epidemic of
1854 was very severe in the southern districts of London. At that period
these districts were supplied with water by the Southwark and Vauxhall
Company, deriving its water from the Thames at Battersea, and by the
Lambeth Company, having its intake at Thames Ditton, where the water
was purer. The two companies were acting in rivalry, so that in many streets
their mains ran side by side; and houses in the same street similar in all
other respects, received a different water supply. An investigation of the
distribution of cholera in these districts gave the following results:—

CHOLERA CHOLERA DEATHS
POPULATION
DEATHS IN PER 10,000
IN 1851.
14 WEEKS. OF POPULATION.
Houses supplied by Southwark Co. 266,516 4,093 153
Houses supplied by Lambeth Co. 173,748 461 26

The facts, when examined in detail, brought out still more strikingly the
exemption of the houses supplied by the Lambeth Company; the infection
picking out in a given street the houses supplied by the Southwark
Company. The great epidemic of cholera at Hamburg in 1892 proves the
same point. Hamburg, Wandsbeck and Altona are three towns adjoining
each other, and really forming one large community; but while Hamburg
suffered terribly, the two other towns had no cases of cholera, except the
few that were brought into them. In all respects except water-supply the
conditions were alike; but Wandsbeck obtained filtered water from a lake,
Altona obtained filtered water from the Elbe below the town, while
Hamburg was supplied, previous to the epidemic, by unfiltered water from
the Elbe just above the town.
Diphtheria and scarlet fever have never been traced to polluted water.
Effects of an Insufficient Supply of Water.—The influence on personal
health is most baneful. Water is used sparingly for purposes of cleanliness,
with the necessary results that cutaneous diseases become more common,
and the whole body suffers; the linen is imperfectly and infrequently
washed; the house becomes dirty; drains are imperfectly flushed; the streets
are not cleaned; and the whole atmosphere becomes loaded with impurities.
According to Parkes, it is probable that the almost complete disappearance
of typhus fever from civilized and cleanly nations, is not merely owing to
better ventilation, but also to more frequent and thorough washing of
clothes.
Insufficient cleansing of the surfaces of streets and of sewers, owing to a
deficient supply of water, has a very important influence on the spread of
enteric fever and epidemic diarrhœa. A heavy fall of rain often causes a
rapid diminution in the prevalence of the latter disease.

CHAPTER XIII.
THE PURIFICATION OF WATER.
When a public water-supply is provided, it may reasonably be expected
to be furnished pure and fit for use; but this, occasionally is not so. The
reports, for instance, of the condition of the London Water Supply,
occasionally show that it is turbid and contains a slight excess of organic
matter. This is especially the case when, after heavy rainfall, storm-water is
brought into the reservoirs, and owing to deficient storage, sufficient time is
not allowed for deposit. Rain-water always and other waters frequently
require to be purified before use.
Methods of Purification.—The only certain way of obtaining pure water
is by Distillation; but this plan is scarcely applicable to water on a large
scale. Furthermore distilled water is not so palatable as ordinary water. The
distillation of water is more especially required on board ship, during long
voyages. It should be followed by the use of some measure to secure
efficient aeration.
2. Boiling water serves to remove the temporary hardness, and the chalk
carries down with it a large proportion of any organic matter that may be
present. Boiling deprives the water of its dissolved gases, and renders it flat;
it is desirable, therefore, to aerate it by filtration or from a gazogene after
boiling. All the microbes which are known to produce disease are destroyed
by efficient boiling. Certain putrefactive microbes are more persistent of
life, owing to the fact that they form spores, which are not killed at the
temperature of boiling water. Tyndall showed that by boiling the liquid
containing these spore-forming microbes on three successive days, thus
giving time for the spores to develop into less resistant microbes, they could
be effectually destroyed. Boiled water will not cause enteric fever or
cholera, the two chief water-borne diseases.
3. The exposure of water in divided currents to the air by passing it
through a sieve has been proposed as a means of purifying water, but it is
inefficient when trusted to alone. Plants in reservoirs help to absorb organic

matter; and fish, by destroying small crustaceans, have been found useful.
Hard waters do not bear exposure to light, as a thick green growth of chara
occurs, which may block pipes, and give a bitter taste to the water.
4. The Addition of Chemical Substances.—(1) Clarke’s process
consists in adding milk of lime, i.e. an emulsion of quicklime with water, to
the water in the reservoir on a large scale. By this means calcium carbonate
is precipitated, but no effect is produced on calcium and magnesium
sulphates and chlorides. The hardness of the Thames water can thus be
reduced from 16° to 3° or 4° (Clarke’s scale). The calcium carbonate carries
down with it suspended and possibly dissolved organic matter. In the
Porter-Clarke process lime-water, i.e. milk of lime diluted, and the excess
of lime separated by settlement or filtration, is mixed with the water to be
purified, the water being freed from the precipitated calcium carbonate
either by subsidence or by being forced through a filter of stretched canvas.
(2) Carbonate of Soda added to boiling water throws down calcium
carbonate, and possibly lead if present. Much less is required when added to
boiling than to cold water. Maignen’s process consists in adding anti-
calcaire powder, containing chiefly carbonate of soda, lime, and alum.
(3) Aluminous salts are very effectual in removing suspended organic
matter, if the water contains calcium carbonate. On the addition of alum,
calcium sulphate and aluminium hydrate are formed, both of which fall to
the bottom, carrying with them other impurities. The amount of alum
required is about 6 grains per gallon of water. If the water is not hard, a
little calcium chloride and carbonate of soda should be put in before the
alum is added, in order that a precipitable substance may be formed.
(4) Potassium permanganate readily removes the offensive smell of
stagnant water, but it gives a yellow tint to the water. The addition of a little
alum will help to carry down the decomposed permanganate.
(5) Perchloride of Iron, in the proportion of 2½ grains to a gallon of
water, has been found to completely purify water from finely suspended
organic matters and clay.
(6) More recently, other substances, such as iodine and hyposulphite of
soda, have been recommended. These are supposed to act by sterilizing the

water, and iodine in suitable quantities undoubtedly effects this.
Chemical processes for the purification of water, with the exception of
the softening process, are not to be recommended for general use. Efficient
filtration, or boiling, is safer than chemical treatment; and it would only be
justifiable to trust to the latter, when, as in a military campaign, an attempt
at purification was necessary, and no means were available for filtering or
boiling water.
7. Filtration.—The object of filtration is to remove the impurities of
water. The most dangerous impurities are suspended in it, especially the
microbes causing infectious diseases. Hence the most perfect filter is the
one which most completely prevents the passage through it of microbes. If
the water supply is pure, domestic filtration is not only useless, but likely to
do more harm than good. This is true for such upland surface waters as
those supplied to Liverpool, Glasgow, and Manchester; for such deep well-
water supplies as those of Brighton (deep chalk), of Nottingham (new red
sandstone), and others, when pumped from wells remote from inhabited
houses. For upland surface waters known to attack lead pipes, filtration
through charcoal or spongy iron may be advisable; for river water, filtration
through a germ-proof filter is best.
Filtration on a large scale is generally carried on as follows:—A
preliminary step consists in collecting the water into settling reservoirs,
wherein the more bulky substances subside. The water is then filtered
through beds of gravel and sand, containing perforated tubular drains
below, into which the filtered water flows. The drains are covered by a bed
of gravel about 3 feet deep, over which is spread a layer of sand about 1½
to 2 feet deep. Sharp angular particles of sand are the best; and the gravel
should gradually increase in its coarseness as it descends.
The effect of this filtration is chiefly mechanical; it separates any
suspended matter, whether organic or inorganic. A certain amount of
biological action possibly also takes place. Piefke found that a perfectly
cleaned and sterilised filter when first used, increases the microbes in water,
instead of decreasing them. Gradually a gelatinous layer of slimy matter is
formed on the top of the sand; the water now filters through much more
slowly, but it gradually becomes freer from microbes, these being

intercepted by the slimy layer. It is important that this layer should not be
disturbed by too rapid or forced filtration, and that when the surface layer
requires to be removed, because the filter has become impervious, time
should be allowed for another thin film to form before the filtered water is
again utilised. Koch concluded that the rapidity of filtration should never be
allowed to exceed 100 millimetres (about 4 inches) per hour; and that the
number of microbes per c.c. in the filtered water should never exceed 100.
Some oxidation of organic matter, as well as detention of microbes, may
take place during the filtration of water, nitrates being formed by the vital
activity of certain “nitrifying” microbes in the filter. (On nitrification, see
pages 195 and 274.) P. Frankland’s observations show that the number of
microbes in Thames water is reduced by filtration through sand and gravel
beds, as practised by the London Water Companies, so that only 3·4 per
cent. of those originally present remained. He also concludes that the
majority of the microbes present in filtered water are derived from post-
filtration sources. Thus the number is greater in tap-water than in water
derived from near the reservoirs.
Other materials besides sand have been used for filtration on a large
scale, but none with proved success.
Domestic Filtration ought, as already explained, not to be needed, but
circumstances often arise in which the public supply is open to suspicion,
and a second domestic line of defence against infection through the water
supply is desirable. When this is so, the form of filter which will best
protect the household is one attached to the house-tap, so that all drinking-
water is perforce filtered. When filtering involves the transfer of water from
the tap to the interior of the filter, opportunity is left for carelessness or
forgetfulness. The one essential point of a domestic filter is that it will
prevent the passage through it of microbes. Every filter must be tested from
this standpoint.
On this point the experiments of Woodhead and Cartwright Wood are
conclusive. They first of all experimented on various filters with fine
artificial ultramarine containing particles 16 µ to 0·6 µ or even less in
diameter in suspension; and milk containing granules and globules of fat
0·5 µ to 30 µ or more in diameter, freely diluted with water.

TIME IN MINUTES PRESENCE OR
PRESENCE OR
REQUIRED FOR ABSENCE OF
ABSENCE OF MILK
FILTRATION OF 1 ULTRAMARINE IN
IN FILTRATE
PINT OF WATER. FILTRATE.
Silicated carbon filter 68 ++ +++
Carbon filter 18 + +++
Maignen’s Filtre Rapide 4 0 ++
Spongy iron filter 14 0 +++
Pasteur-Chamberland filter 420 0 0
Berkefeld filter 140 0 0

The number + indicates the relative amount of the experimental
substances that made their way through the filtering medium.
Experiments were then made with the actual microbes of certain
infectious diseases, and it was found that certain filters allow these to pass.
Thus a silicated carbon filter allowed 1,000 out of 15,000 typhoid bacilli
suspended in water to pass through its substance; a manganous carbon filter
allowed 600 to 800 out of 10,000 cholera vibrios to pass through;
Maignen’s filter on the second day of experiment allowed 150 out of 5,000
cholera vibrios to pass through; Lipscombe’s charcoal filter experimentally
only reduced typhoid bacilli from 20,000 to 5,000; the magnetic carbide
filter only reduced them from 20,000 to 10,000; the spongy iron filter from
20,000 to 3,000; while, on the contrary, the Pasteur-Chamberland and the
Berkefeld filter completely stopped all microbes and produced a sterile
water. (As to these two, see page 98.)
Of the materials enumerated animal charcoal was formerly regarded as
an excellent filtering medium. It is capable of oxidising organic matter
dissolved in water, but so far from sterilizing water, it favours the growth of
microbes in it. Water filtered through charcoal, after the first few days of
use of the charcoal, deteriorates, as the charcoal yields up impurities to it.
Manganous Carbon consists of animal charcoal and black oxide of
manganese mixed with oil, and heated strongly together out of contact with
the air. The oxidising power of the carbon is said to be thus greatly
increased. It shares the objections to carbon.
Silicated Carbon consists of 75 per cent. of charcoal and 22 per cent. of
silica, with a little oxide of iron and alumina. It is not an efficient filtering
medium.

Spongy iron is prepared by the reduction of hæmatite ore with fusion, so
that the iron is obtained in a porous and finely-divided condition. The
Rivers Pollution Commissioners found spongy iron to be “a very active
agent, not only in removing organic matter from water, but also in
materially reducing its hardness, and otherwise altering its character.” It is a
powerful oxidising agent, some of the water being decomposed, and
hydrogen set free, and the oxygen acting upon any organic matter present. It
also removes lead from water. As already seen, it does not, however, fulfil
the primary object of water, by depriving it of any microbes contained in it.
Magnetic carbide of iron is obtained by heating hæmatite ore with
sawdust. Its action is similar to that of spongy iron.
The Pasteur-Chamberland filter consists of a cylinder of unglazed fine
porcelain made from a well-baked Kaolin of a certain degree of porosity
and hardness. (Fig. 10.)
The water passes through the porcelain from without inwards, and with
the pressure of 1½ to 2½ atmospheres which is usually present in the pipes
of a water-service, passes through at the rate of about three quarts per hour.
The filter can easily be cleaned by brushing it in a stream of hot water, or by
subjecting to the heat of a Bunsen burner. The filtration is entirely
mechanical, the filtered water being quite freed of microbes. No chemical
action takes place.
The Berkefeld filter is cylindrical like the Pasteur-Chamberland filter,
and is used in the same way. It is made of infusorial earth, which is soft and
friable and liable to break. The cylinder becomes gradually worn thin by
cleaning, and it then ceases to filter efficiently. Its sole advantage over the
Pasteur-Chamberland filter is the more rapid rate of filtration; and against
this is to be set the greater liability to fracture and the lack of continuance of
efficient filtration. Woodhead and Wood in the report already quoted, state:
“The Berkefeld filter appears to have the largest pores among the efficient
filters, as is evidenced by the fact that the water organisms were not
apparently weakened, that more species of organisms appeared in its
filtrate, and that lowering the temperature to 11° C. did not prevent their
appearance. The Pasteur-Chamberland filter, on the other hand, at 11° C.
was able to give an apparently sterile filtrate for a prolonged period.” More

recent experiments have shewn that
pathogenic (disease-producing) microbes
contained in water after awhile grow through
the substance of a Berkefeld filter, and that
this does not happen with a Pasteur-
Chamberland filter. The latter is therefore
preferable.
In determining the number of bougies
required for any filter to secure a given
amount of pure water, it is necessary to
calculate on the basis of the output after
several weeks’ use, not on the original
output. If this is done, pure water will be
secured without disappointment as to the
amount supplied.

Fig. 10.
Pasteur-Chamberland Filter.
A.—Outlet of filtered water. B.—
Pasteur tube. C.—Metal tube
containing unfiltered water. D.
—Unfiltered water delivered
through tap.

CHAPTER XIV.
COMPOSITION AND PROPERTIES OF AIR.
An abundant supply of fresh air is necessary at all times. And yet its
importance is commonly ignored in practical life. Strenuous efforts are
made to ensure a supply of food, and water is commonly filtered or
otherwise purified before drinking; but many are content to live in an
impure atmosphere, which hardly suffices for the preservation of life, and
certainly not of health. Deprivation of food, or even of water, only kills
after several days or weeks; deprivation of air kills in a few minutes. Only
about three pints of water are required daily, while at least 1,500 gallons of
air are necessary every day for carrying on the vital functions.
Composition of Air.—The air constitutes a gaseous ocean in which we
live, as fishes live in water. In virtue of its weight, it exerts a pressure of
about 15 lbs. on every square inch. This pressure is usually measured by the
barometer, and is equivalent on an average to that of a column of 30 inches
of quicksilver. (See page 331).
Chemically, air consists of a mixture of various gases and vapours. These
are chiefly Oxygen and Nitrogen; but in addition, there are minute
quantities of carbonic acid, argon, hydrogen, water vapour, ammonia,
ozone, and suspended matters.
The oxygen and nitrogen exist, in the proportion by volume of 20·9 of
oxygen to 79·1 of nitrogen, or of 23·16 grains of oxygen to 76·84 of
nitrogen, by weight.
These two gases do not exist in chemical combination, but mechanically
mixed. This is proved by the fact, that they do not exist in air in the
proportion of their combining weights, or any multiple of these; that the
proportion varies slightly at different parts; and that the air which is
dissolved in water does not contain the nitrogen and oxygen in the
proportion 4 to 1 (as in the atmosphere), but in the proportion 1·87 to 1.
This means that oxygen, being more soluble in water than nitrogen, has

dissolved in a larger proportion; as it certainly would not have done, had the
oxygen and nitrogen been chemically combined. The oxygen dissolved in
water supplies fishes with the necessary oxygen for their respiratory
processes. Similarly the oxygen in the atmosphere is its most essential
constituent, being required in all processes of oxidation (i.e., combustion),
whether in living organisms or in the inanimate world. Nitrogen serves as a
diluting agent. It is incapable of supporting life alone; and many of the fatal
accidents which have occurred through men descending deep wells without
first testing, by means of a lit candle held well below them, the quality of
the air near the bottom, have been due to an accumulation of nitrogen in the
well.
Ozone is a condensed form of oxygen, which is present in minute
quantities in pure air, and especially during a thunder-storm or after a fall of
snow, and in the air near the sea. In it three volumes of oxygen are
condensed so as to occupy two volumes. In this condensed condition it has
powerful chemical affinities; often oxidising substances which oxygen
cannot attack. It is generally absent from the close air of towns and
dwelling houses, having been used up to oxidise the organic matter present
in these places. Air without it is said to be “devitalised”; and ozone has been
described as the scavenger of the air.
Ozone can be produced by hanging a piece of moist phosphorus in a
room; and it is stated by Dr. Daubeny, that part of the oxygen given out by
plants, especially by scented flowering plants, is in the condition of ozone.
A small quantity is produced when an electrical machine is worked; its
presence is evidenced by a peculiar smell (the name ozone is derived from
the Greek word for smell).
Test of Ozone in Air.—Traces of ozone in air are detected by exposing strips of blotting paper
moistened with a mixture of a solution of potassic iodide and starch. If ozone is present, the paper
assumes a blue tint, due to the liberation of iodine, and its combination with the starch. Other acid
gases may, however, produce the same effect. A second test should, therefore, be tried. Soak red
litmus paper with a very dilute solution of potassic iodide, and expose as before. Potassic oxide is
produced if ozone is present, and this turns the litmus blue.

Aqueous Vapour is always present in air, though the amount varies
greatly. It is invisible in the ordinary condition, but by condensation
becomes cloud or fog, rain, snow, or hail. The quantity of moisture present
varies with the temperature of the air; the higher the temperature, the more

water can be vaporised, without the point of saturation being reached. An
increase of 27° Fahr. doubles the capacity of air for moisture. The amount
of moisture that would saturate air at 50° Fahr. only gives 71 per cent. of the
saturation amount at 60° Fahr. The amount of moisture is estimated by the
hygrometer (page 240).

Air saturated with moisture at 32° Fahr., holds vapour equal to 1 ∕ 160 of
its weight; at 59° it holds 1 ∕ 80, at 86° 1 ∕ 40, at 113° 1 ∕ 20, and at 140° 1 ∕ 10.

Ammonia in normal air does not exceed one part in a million of air; but
it is always present—either as free ammonia or as sulphate, chloride,
carbonate, or sulphide of ammonia. From this source, plants derive some of
the nitrogen they require as food; some also from the free nitrogen, which is
fixed by certain microbes, growing in the nodules connected with the roots
of peas, lentils, and other plants (page 274).
Traces of nitrous and nitric acid are also present in the air, produced by
the direct combination of nitrogen and oxygen occurring as the result of the
electric spark during lightning.
Carbonic Acid or carbon dioxide is always present in air, in the
proportion of 3·36 to 4 parts in 10,000; but in impure air may be present in
much larger amount. It is a heavy gas, incapable of supporting combustion,
and therefore of supporting animal life. Being a heavy gas, it tends to
accumulate where it is produced, as about lime-kilns by the heating of
chalk. Thus CaCO₃ (chalk) (heated) = CaO (lime) + CO₂ (carbonic acid).
Tramps have occasionally died of carbonic acid poisoning through sleeping
near lime-kilns.
It is produced by the oxidation of carbonaceous matters, hence in all
ordinary combustion, in many cases of putrefaction and fermentation, and
in the respiratory processes of all animals.
Plants diminish the amount of carbonic acid in the atmosphere. Two
processes occur in most plants: a process of respiration, as in animals; and a
process of assimilation, by which the leaves and all other green parts of a
plant under the influence of sunlight decompose the carbonic acid of the
atmosphere, fixing its carbon and liberating its oxygen. Plants such as
fungi, which are destitute of green colouring matter, cannot decompose

carbonic acid; nor can any plants during the night. During the day green
plants are air purifiers; during the night all plants vitiate the air to a slight
extent.
The Air in Relation to Respiration.—The oxygen of air is absolutely
essential for the continuance of life. In every organised animal, lungs or
analogous organs are provided, in order to supply the necessary oxygen to
the system, and to remove the impure air from it.
The act of breathing occurs in man about seventeen times per minute.
While the inspired air is in contact with the interior of the lungs, it
undergoes important alterations. It comes into contact with the five or six
millions air-vesicles which form the minute dilated terminations of the
windpipe, and have an aggregate area of ten to twenty square feet. Each of
the air-vesicles has extremely thin walls; and outside these delicate walls lie
capillary blood-vessels, full of impure blood. An active interchange now
occurs between the air and the gases dissolved in the blood. Oxygen passes
through the intervening membrane into the blood, while carbonic acid and
other impurities of the blood pass into the air-vesicle. The consequence of
this is that the impure dark-coloured blood becomes bright scarlet and pure.
This purification is not confined to any one portion of the blood; for the
heart contracting 60 or 70 times per minute, pours successive portions of
blood into the capillaries surrounding the air-vesicles; while at the same
time, pure air is brought into the air-vesicles seventeen times per minute,
and so the interchange is constantly kept up.
In view of the incessant character of respiration and circulation, it is clear
that all the blood will be purified if the external air is pure; and that if there
is any detrimental matter in the air, it probably will come into contact with
the blood in the lungs.
The amount of air taken in with each inspiration is about thirty cubic
inches. This is called the tidal air, as it is constantly ebbing and flowing
from and to the lungs. By means of a very forced inspiration, about 100
cubic inches of additional air can be inspired; and similarly after an
ordinary inspiration, one can expire forcibly an additional 100 cubic inches,
though there will still be left in the lungs another 100 cubic inches of air.
Thus:—

Tidal air 30 cub. in.
Complemental air 100 „
Supplemental air 100 „
Residual air 100 „
——
Total capacity of lungs 330 „

Corresponding to the respiratory changes in the lungs, there are changes
in the tissues throughout the body. The pure and oxygenated blood leaving
the lungs, is carried to all parts of the system. Oxidation and allied
processes are actively carried on, the result of which is the formation of
urea, carbonic acid, and smaller quantities of other effete matters. These are
then carried by the blood to the excretory organs, urea being chiefly
eliminated by the kidneys, and carbonic acid by the lungs.
Examination of Expired Air shows that—1. It is heated; in its passage
through the nose and deeper respiratory passages it has acquired a
temperature approaching that of the blood.
2. Its moisture is increased. By the skin and lungs from 25 to 40 ounces
of water pass off in the twenty-four hours; the relative amount varies
somewhat.
3. It contains 4 to 5 per cent. less oxygen, and 4 per cent. more carbonic
acid than inspired air. The carbonic acid, instead of being 4 parts in 10,000
of air, becomes over 400 in 10,000, while the oxygen is diminished in a
somewhat larger proportion. Thus:—
CARBONIC
OXYGEN. NITROGEN.
ACID.
Inspired air contains 20·81 79·15 ·04
Expired air contains 16·033 79·557 4·38

The amount of carbonic acid expired varies under different
circumstances. It is increased by active work, by an increase of food, by a
diminution of the external temperature; it is greater when the surrounding
air is pure, and when it is moist; and it varies with the season, being greatest
in spring, and least in autumn.
Children require more oxygen, and expire more carbonic acid than
adults, weight for weight. A child six or seven years old requires nearly as

much oxygen as one twice that age. Boys usually require more air than
girls, as they are more active and exhale a larger amount of carbonic acid
and other impurities.
The average amount of carbonic acid eliminated by a healthy adult is at
least 0·6 cubic foot per hour, or 14·4 cubic feet per day. This reckoned as
carbon is equivalent to 160 grains per hour, or half a pound of carbon in the
twenty-four hours. Liebig gives the amount of carbonic acid expired as 0·79
cubic foot per hour, or 19 cubic feet per day.
4. It contains organic impurities. These are chiefly gaseous, solid
particles only being expired during coughing, or possibly during
conversation. The danger from the “breath” of patients in infectious
diseases is really associated rather with the dried discharges on
handkerchiefs, etc., than from the “breath” itself; unless droplets of saliva
discharged during speaking, or mucus during coughing, are directly inhaled.

CHAPTER XV.
SUSPENDED IMPURITIES OF AIR.
Pure air being essential to life and health, it is important to ascertain the
character and origin of the impurities of air. Innumerable substance—in the
condition of gases, vapours, or solid particles—constantly pass into it, and
deteriorate its quality. To counteract this, certain purifying agencies are at
work, the mechanism of which will be considered hereafter.
Impurities are much commoner and more abundant in the air of enclosed
spaces than in the external air, as the natural processes of purification
cannot be brought to bear so efficiently in the former case. In sick rooms,
hospitals, etc., impurities arise, which are not present where only healthy
people are collected. The most important impurities are derived from the
respiration of animals, and the combustion of gases, candles, or lamps in
rooms, from sewage emanations, from various occupations, and the air of
marshes, mines, church-yards, etc. These may be classed under two heads—
solid and gaseous; the solid being simply suspended in the air in a finely
divided condition, or floated about in a coarser condition by currents of air.
They are revealed in an atmosphere in which one did not previously suspect
their existence, by the passage of a beam of sunlight. Light itself is
invisible, but its course is rendered visible by the particles from which its
rays are reflected. Tyndall demonstrated the presence of minute particulate
matter in the air of all ordinary situations, and showed that a large
proportion of this matter consists of germs (microbes). In his experiments
with vapours in closed tubes, floating matter was always revealed by a
concentrated beam of light, even though the air entering the tube had been
first drawn through sulphuric acid and through a strong solution of caustic
potash. If this air was then passed through a red-hot platinum tube and
across folds of red-hot platinum gauze, it became optically empty; the
floating matter had been burnt, and disappeared. It was therefore organic. In
subsequent experiments, he took organic solutions, as of meat, turnip, and
the like, and rendered them sterile by repeated boiling. They remained
sterile when kept in air-tight vessels or in vessels covered with a thick layer

of cotton-wool, which would efficiently filter any entering air; but when
exposed to the air, they invariably became turbid, owing to an enormous
multiplication of germs. Clearly, therefore, air contains organic, matter, and
much of this organic matter consists of living germs. Most of these germs
are comparatively harmless under ordinary conditions. They are, however,
the causes of fermentation, putrefaction, and all the processes of
decomposition which occur in organic substances. The importance of the
exclusion of the dust of air has received an important application in Lister’s
antiseptic and in the aseptic system of treatment of wounds. Formerly
accidents and operations were frequently fatal; now vast numbers of lives
are saved by improved surgical methods. The original antiseptic method
acted on the supposition that some germicidal application to the wounds
was necessary; now it is realized that if, during the operation, germs are not
allowed to remain in the wound, all that is afterwards necessary to insure
rapid recovery is that they shall be prevented from entering the wound from
the external air during its process of recovery. By the adoption of such
means, large wounds can be made to heal, without the formation of a drop
of “pus” or “matter.” (See also page 110.)
Suspended Matters are mineral or organic, the two being commonly
associated together. The mineral matters consist largely of fine particles of
common salt, silica, clay, iron rust, dried mud, chalk, coal, soot, and similar
substances. Not uncommonly the mineral particles are coated by, or mixed
with, organic matter, the comparative lightness of the organic matter
enabling the mineral matter to float about more easily. The objection to dust
is thus intensified, for not only is it irritating to the respiratory passages and
generally disagreeable, but it carries with it putrescent and possibly
morbific particles. The prevention of infectious diseases resolves itself
largely into means for preventing the inhalation of dust.
Organic Suspended Matters in the open air are, most commonly,
minute fragments of wood and straw, dried horse litter, fragments of insects,
the spores and pollen of plants, and microscopic plants and animals. In
addition, there is the putrescent organic matter resulting from respiration
and other organic functions.
Indoors, the air commonly contains, in addition, fragments of cotton,
linen, silk, or other fibres, fragments of vegetables, starch cells, soot,

charred wood, splinters from floors, etc.
In Sick Rooms, products of the morbid conditions may be evolved; thus,
pus-cells, particles from the expectoration, blood cells, fat particles,
epithelium, or the special germs or microbes to which infectious diseases
are due. These are disturbed by the movements of persons, causing the dust
to rise; and thus the infection of consumption, and of the acute infectious
diseases, is frequently spread.
Flies and other winged insects are important auxiliaries in the diffusion
of disease-carrying particles. Receiving some morbid secretions on their
limbs, or other parts of their bodies, they have occasionally been the means
of spreading erysipelas in hospitals, and glanders in veterinary stables. The
specific contagia of cholera, enteric fever, and summer diarrhœa are
occasionally conveyed to food by flies which have previously alighted on
latrines or privies or other places where the stools of such patients have
been deposited (page 281). The excreta of flies, which are not uncommonly
deposited on food, or on articles of furniture, have occasionally being found
to contain the minute ova of intestinal worms.
Effects of Suspended Matters.—The inhalation of dust is followed by
deleterious effects. We may divide the solid substances inhaled as dust into
three kinds:—dead substances, living substances, and the contagia
(microbes or germs) of various diseases.
1. Dead Substances inhaled for a prolonged period in various
occupations are a common cause of premature death. The potter draws into
his lungs a fine silicious dust, which irritates his lungs, and finally produces
a fatal disease, known as potter’s asthma.
Mill-stone Cutters and Stone Masons inhale the fine particles of stone
given off from the material which is being chiselled. These produce serious
disease of the lungs.
Pearl Cutters inhale fine particles of pearl-dust, and as they generally
work in close rooms, and the dust is light and tasteless, serious disease of
the lungs results.
Sand-paper Makers inhale minute portions of glass and sand; and
needle and knife grinders are exposed to similar dangers, and at one time

the mortality among them was frightful. It has greatly diminished since the
introduction of wet grinding, the use of steam fans, and wearing of
respirators.
Hemp and Flax Dressers inhale a dust which is peculiarly irritating.
Workers in rags and in wool suffer in like manner from dust. The dust
from fleeces of wool, and especially from the alpaca fleece, has produced in
many cases (in the neighbourhood of Bradford and elsewhere) an acute
disease (anthrax) proving fatal in a few days. The spores of this disease are
very persistent of life (page 274), and remain active for mischief for months
after the death of the animal which had suffered from it. The fleece can be
disinfected by steam; and the use of fans for diverting the dust created
during “sorting” minimises the danger from it.
The miller commonly suffers from a form of asthma, not so severe as
potter’s asthma, as the particles in this case are not equally irritating. The
hairdresser is liable to inhale the short fragments of hair cut by the
scissors, and the mortality of this class of workers is high. Miners in coal
have a surprisingly low mortality, when accidents are excluded from the
calculation; except in South Wales, where it is slightly higher than for all
males in the same district. Coal dust is relatively free from sharp angles,
and is therefore not so irritating to the lungs as metallic dust. Consumption
is relatively rare among miners.
The Fur-dyer is very prone to suffer from the dust of the dyed furs, great
irritation and disease resulting in many cases.
Artificial Flower-makers, and those engaged in colouring arsenical
wall-papers, suffer from the inhalation of arsenical vapours, as well as from
the irritating effects of its absorption by the skin. These are now seldom
seen, owing to the almost complete abandonment of the use of arsenic for
wall-pigments.
Cigar-makers are liable to have their lungs irritated by inhalation of the
dust of the tobacco-leaf; and may suffer from tobacco-poisoning.
Workers in Lead are very liable to be poisoned by the metal, e.g., house
painters, potters engaged in the glazing process, in which the ware is dipped
into a solution containing lead, manufacturers of white lead, and others. The

lead is partly absorbed by the skin; in some cases it is inhaled as dust; and
more often it is swallowed, when the workman eats his meals with
unwashed hands. Of the symptoms “painter’s colic” and “drop-wrist” are
the two most important, though, in some cases, lead shews its effects more
insidiously, leading to gout and chronic renal disease. It is now compulsory
on employers to provide in the workshop, complete washing arrangements
for the use of workers in lead. Every doctor called to attend a case of lead or
phosphorus or arsenic poisoning or anthrax, which has been acquired in an
industrial occupation, must notify the same to H.M. Inspector of Factories.
This implies inspection of the factory or workshop and the subsequent
adoption of further measures of precaution.
Brass-founders occasionally inhale the fumes of oxide of zinc; and
diarrhœa, cramp, waterbrash, and other troubles are the result. Those
engaged in the manufacture of bichromate of potass, are liable to partial
destruction of the mucous membrane of the nose, and to irritation of the
skin, with the formation, in some cases, of small ulcers.
Workers with Phosphorus, as those engaged in the making of
phosphorus matches, not uncommonly suffer from a gradual necrosis
(death) of the jaw-bone. Those having carious teeth are especially attacked
by this disease, which is due to the fumes of oxide of phosphorus, attacking
the jaw. Improved ventilation of workshops, careful attention to the teeth,
and other measures, have greatly diminished this disease; and it has
disappeared where safety matches made from red non-volatile phosphorus,
have replaced matches made from the yellow variety.
Chimney Sweeps occasionally suffer from irritative skin diseases, as
well as bronchitis. In some cases the chronic irritation of the soot has
produced cancer of the skin.
The effect of dust on workers can be seen in the mortality returns: Among men aged 25 to 65 years
in 1881-90, the comparative mortality figure in England and Wales was as follows, all males
throughout the country being taken as a standard and given as 1,000:—

Comparative Mortality Figures.
All males 1000
OCCUPATIONS WITH NO DUST. DUSTY OCCUPATIONS.
Clergyman 533 Coal miner (Derby and Notts.) 727
Gardener 553 Carpenter 783

Farmer 563 Bricklayer, mason 1,001
Teacher 604 Coal miner (Lanc.) 1,069
Tool and scissors maker 1,412
Potter 1,706
File-maker 1,810

Remedial Measures.—Means have been taken to diminish the
prevalence of the above dust diseases, in several cases with remarkable
success. In the case of steel-grinding, for instance, the mortality is greatest
with dry grinding, and least with wet grinding. Wet processes have been
applied to others of the industries named, with a like success. Where the
dust cannot be avoided, the use of steam or electric fans, to deflect the dust
away from the workman, has been found successful; and in many cases,
free ventilation of the workshops has greatly diminished the mortality.
Where none of the above measures suffice, the use of respirators ought to
be insisted on. Breathing through the nostrils ought to be carefully
maintained, as thus the dust is to a large extent stopped before reaching the
lungs.
The dangers of lead poisoning may be avoided by absolute cleanliness,
the hands being always washed before taking meals, and the nail-brush used
to secure complete cleanliness beneath the nails.
2. Living Substances.—The pollen of plants in some persons produces a
distressing form of disease, called hay-asthma, which is apt to recur each
year, and is sometimes only curable by living in a town or removing to the
sea-coast. The amount of pollen floating about in the atmosphere is
considerable; 95 per cent. of it is grass-pollen, and this form and the pollen
from pine-trees appear to be the most powerful in inducing hay-asthma.
According to some authorities, hay-asthma is rather due to the minute
particles constituting the scent of various flowers, than to the pollen; but
that is probably not the usual mode of origin of the disease, though it may
be in some cases. In some cases, true asthma results from smelling
particular plants. Here as in the case of hay-asthma a peculiar idiosyncrasy
is involved, only a very small proportion of those exposed to the minute
particles suffering from asthma.
The spores of many fungi and of other living organisms are constantly
being floated about in the air, until they find a suitable resting place, when

they settle and proceed to grow and multiply. The souring of milk, the
fermentation of a saccharine solution, the moulding of bread, the presence
of mildew, the blighting of corn, and numerous other phenomena are due to
the growth of organisms carried by the atmosphere from one part to another.
3. The Contagia (microbes or germs) of the acute infectious diseases are
minute living organisms, known as bacteria. Hence these diseases may be
carried about by currents of air, some much more easily than others. Some
of the contagia have a persistent vitality. Thus the contagia of scarlet fever,
diphtheria, or small-pox may infect a room for months, causing the disease
in question, when infected articles in the room are disturbed. The contagia
of typhus fever and of measles, on the other hand, are short-lived, and do
not usually resist free ventilation and exposure to sunlight.
Besides the contagia of the acute fevers, septic organisms may be carried
by the atmosphere. Formerly, blood-poisoning from operation and other
wounds was common; but Lister, by insisting on absolute cleanliness of
wounds, and only allowing air to have access to the wound which had been
filtered through layers of gauze and deprived of its septic germs, has
secured that wounds can now be kept perfectly “sweet,” the suppuration in
them reduced to a minimum, and the danger of blood-poisoning almost
annihilated (page 106). It had often been noticed that recovery from even
very severe injuries was common, if only the skin remained unbroken;
while the same injuries, with the addition of a rupture of the skin, and
consequent access of air, were rapidly fatal. But to Lister is due the great
honour of proving that it was not the air which produced the mischief, but
the germs it contained, and that filtered air might be admitted with
impunity.
Erysipelas and hospital gangrene have occasionally been carried about in
hospital wards by dirty sponges and dressings; and if the ventilation is not
perfect, particles of epithelium and pus from diseased persons may be
carried to other patients at a distance. Some forms of purulent disease of the
eyes are transferable from patient to patient, and in children some forms of
eczema are also contagious.

CHAPTER XVI.
GASEOUS AND OTHER IMPURITIES OF AIR.
Gaseous impurities of the air are very commonly associated with
suspended matters, and it is often difficult to separate the effects of the two.
Different gases are also often associated, and so produce modified
results. It will be convenient to consider, first of all, certain well-marked
gaseous impurities, and then others in which there is a mixture of several
gases, or of these with suspended solid particles.
Under the first head the most important impurity is—
(1) Carbonic Acid.—This is reckoned an impurity if amounting to more
than 5 parts in 10,000 of air. Owing to the large amount produced in the
respiration of animals, in the combustion of fires, gas, lamps, etc., and in
other natural processes, it would be much greater in populous parts, were it
not for the rapid diffusion occurring in the air, and the purifying action of
plants. The following analyses (Angus Smith) illustrate the facts that in
towns the amount rises, and is greatest in the most populous parts, while
during fogs it is greatly increased.
VOLUMES OF
CARBONIC ACID IN
10,000 VOLUMES OF AIR.
On the mountains and moors of Scotland—mean of 57 analyses 3·36
In the streets of Glasgow—mean of 42 analyses 5·02
London, N., N.E., and N.W. postal districts—mean of 30 analyses 4·384
London, E. and E.C.—mean of 12 analyses 4·745
Manchester streets, ordinary weather 4·03
During fogs in Manchester 6·79

The effects of carbonic acid gas alone must be carefully distinguished
from those of the same gas plus the organic impurities from respiration,
with which it is commonly associated. Dr. Angus Smith found that air
containing 3 per cent. of carbonic acid produced difficulty of breathing, but
he was able to breathe comfortably an atmosphere containing 0·2 per cent.

carbonic acid. Other observers have found they could breathe without
discomfort air containing 1 per cent. carbonic acid. When the carbonic acid
is derived from respiration, headache and giddiness are produced in many
persons when the carbonic acid amounts to 0·15 per cent. A fatal result has
occasionally occurred from the inhalation of the carbonic acid at the bottom
of brewing vats, or about lime-kilns. The gaseous impurity at the bottom of
wells is more commonly nitrogen than carbonic acid (page 102).
The presence of an excess of carbonic acid diminishes the elimination of
carbonic acid from the lungs, nutrition and muscular energy being
consequently impaired. This is seen in workshops where the air is confined
and gaslight is commonly employed; though the air here also contains
carbonic oxide, sulphurous acid, and organic impurities, and these probably
have a large share in producing the evil results.
(2) Carbonic Oxide in the proportion of more than 1 per cent. is rapidly
fatal, and has poisoned when under ½ per cent. Poisoning by its means
occurs where charcoal stoves are used, and especially when the charcoal is
burnt in rooms with no chimney flue. This is an occasional mode of suicide
on the continent. Carbonic oxide is a much more deadly poison than the
dioxide (carbonic acid); it forms a stable compound with the hæmoglobin of
the red blood-corpuscles, displacing oxygen from them, and is got rid of
with great difficulty. Lace-frame makers place a coke stove under their
work, and thus inhale the invisible gas. Headache, giddiness, irregular
action of the heart, and depression of the general health result. Carbonic
oxide is the most poisonous constituent of coal-gas, and is present in much
larger quantity in carburetted water-gas with which coal-gas is now
commonly mixed, than in pure coal-gas (page 115).
(3) The inhalation of Sulphuretted Hydrogen produces headache,
nausea, and diarrhœa; but in manufactures involving the inhalation of a
small proportion of this gas the symptoms are much slighter.
(4) Sulphurous Acid is always present in small quantities in the air of
towns, derived from the combustion of coal and coal-gas. Straw-bleachers
and the bleachers in cotton and worsted manufactories, often suffer from
severe cough and bronchitis due to inhaling its irritating vapours.

(5) Carbon Disulphide when vaporised and inhaled produces headache,
general muscular pains, and nervous depression. It is used in the
manufacture of waterproof coats, toy balloons, etc.
(6) Ammonia produces irritation of the eyes and bronchial irritation.
Hat-makers commonly suffer from its effects, being generally pale and
feeble. It is difficult to say how much is due to the ammonia, and how much
to the high temperature at which they work.
(7) Acid Fumes are very irritating to the lungs, and in the case of alkali
manufactures, they destroy all vegetation for considerable distances.
Hydrochloric acid produces great irritation, and chlorine even more so. The
fur-dyer is not only subject to the dangers of dust, but also of the fumes of
nitric acid, used to remove fat and give certain shades of colour to the fur.
(8) Other Vapours evolved in various processes produce special
symptoms. House-painters suffer from the inhalation of turpentine vapour,
headache and loss of appetite commonly resulting. The symptoms from the
commonly coexistent lead-poisoning are distinct. Brush-makers have a
persistent cough, due to the inhalation of resinous fumes, evolved in making
brushes.
Workers in paraffin are liable to an irritative disease of the hair-follicles
of the body, followed by the formation of scars, almost like small-pox
marks.
Workers in quicksilver, as those engaged in making mirrors or
thermometers, are prone to suffer from mercurial poisoning. The gums
become spongy, and there is profuse salivation, also generally alimentary
disturbance; and in some cases nervous affections, resulting in persistent
muscular tremblings, etc.
Under the second head—cases of inhalation of mixed gaseous and
particulate contamination—we must consider
(1) The Effects of Air Rendered Impure by Respiration.—It has been
already stated that an amount of carbonic acid which could easily be borne
alone, is intolerable when other products of respiration are mixed with it.
These are chiefly organic gases and solids, which (unless removed quickly)
render the atmosphere close and “stuffy”—an effect which is readily

perceptible by the sense of smell of those entering an occupied room
immediately from the outer air. When such a room is inhabited for a few
hours, headache, langour, drowsiness, and yawning (which is really a cry
for purer air) result. The soporific effects so commonly produced in
churches, etc., are commonly due to the vitiated atmosphere, rather than as
is supposed to the soothing effects of the sermon.
When the exposure to foul air is more chronic, and occurs day after day,
there results a general lowering of strength and vigour—both bodily and
mental—even where no actual disease is set up. Oxidation processes are
retarded; the consequence is an anæmic sallow complexion, which
compares badly with the ruddy complexion of those spending a great part of
the day out of doors.
The prolonged breathing of air, foul from the products of respiration, is
perhaps more common in workshops and schools than in private houses; but
in both, a faint smell is commonly perceptible on entering from the open air,
indicating imperfect ventilation and accumulation of organic putrescible
matter. The preceding remarks are left as in the last edition. It must be
noted, however, that recent research attaches more importance to the
particulate matter (dust) in the atmosphere than to the amount of gaseous
impurity, though the latter remains a convenient index of impurity.
Experiments made by Drs. Haldane and L. Smith on themselves negative
the older conclusion that a special organic poison exists in expired air. They
were able without any appreciable effect on themselves to breathe air which
was vitiated to such an extent as to completely prevent a match from
burning; and they conclude that excess of carbonic acid and deficiency of
oxygen are the sole cause of danger from breathing air highly vitiated by
respiration. This conclusion may be accepted under the conditions of these
experiments. Under ordinary conditions, however, the evil effects produced
by breathing the air of crowded rooms, are due not only to the excess of
carbonic acid and deficiency of oxygen, but also to the dust which is
usually associated with them. This dust, which may be derived from
handkerchiefs of patients suffering from influenza, consumption, sore
throat, &c., or from other sources, is apt to be inhaled by the persons
occupying such rooms.

The tendency to catarrhs is greatly increased by living in a vitiated
atmosphere. In the causation of “colds” two elements are concerned, the
infective agent, and the condition of the patients. “Colds” are caused
primarily by infection from previous patients. The nasal discharge of a
“cold in the head” contains the contagium. This is dried on handkerchiefs,
and is subsequently scattered as dust, and thus conveyed to others.
Ordinarily there is considerable resisting power against such catarrhs.
When, however, the general vitality or the local vitality of the mucous
membrane of the nose, throat, and lungs is impaired by the breathing of
impure air or by sitting in wet clothes after exposure to wet and cold, a
catarrh is produced.
The close connection of phthisis (consumption) with overcrowding and
the breathing of a vitiated atmosphere will be discussed hereafter (page
313). The polluted air acts in producing consumption by depressing vital
functions, and diminishing the powers of resistance against the actual
contagium of the disease, which is inhaled as dust, produced by the drying
of the expectoration of consumptive patients.
The germs of infectious diseases are propagated very rapidly in an
impure atmosphere; and typhus fever occurs almost solely in conditions of
overcrowding.
In the cattle-plague of 1866, it was found that nearly all the cows died
when crowded together in unventilated sheds, while only a third died when
there was free ventilation.
The effects of air containing the products of respiration in a concentrated
condition, and of a deficient supply of air, have been shown only too well in
the oft-quoted case of the Black Hole of Calcutta. In this case, 146 persons
were confined in a space eighteen feet every way, with two small windows
on one side. Next morning 123 were found dead, and the remaining 23 were
very ill.
In the experience of this country, the highest death-rates are in the most
densely populated districts. The death-rate from phthisis, childbirth, and
typhus fever for instance, is far higher in cities than in country-places. The
fact may be explained in various ways. Density of population commonly
implies insufficient or unwholesome food, unhealthy work, and poverty; but

especially impurity of the air, uncleanliness, and imperfect removal of
excreta. Of these factors, the vitiated air is probably the most powerful for
evil. Children suffer more than adults from close aggregation of population,
largely owing to the greater ease with which infectious diseases spread in
towns.
(2) Coal-gas is obtained by the destructive distillation of coal, free from
access of air. The average composition of London coal-gas is hydrogen 50
to 53, saturated hydrocarbons 33 to 66, unsaturated hydrocarbons 3·5 to
3·6, carbonic oxide 5·7 to 7·1, carbonic acid 0 to 0·6, nitrogen 2·5 to 4·1,
and oxygen 0·2 to 0·3 per cent. Of these the illuminants are olefiant gas
(C₂H₄) and the higher hydrocarbons. Sulphuretted hydrogen and other
sulphur compounds are present in small quantities, averaging 12 grains of
sulphur per 100 cubic feet of London gas.
The inhalation of coal-gas, even in small quantities, is liable to produce
headache, and may lead to chronic poisoning if allowed to continue. Where
the escape of gas is more extensive, as when a tap is left turned on
accidentally during the night, two dangers may arise. If a light is struck in
the room an explosion occurs; or persons may be poisoned in their sleep by
inhalation of the gas. The most poisonous gas in coal-gas is the carbonic
oxide. The chief product of the combustion of coal-gas is carbonic acid.
Some sulphurous acid is also produced, which is irritating to breathe, and
injurious to bookbindings, picture-frames, etc. If the flame is imperfect, as
when the pressure of gas is too great, some carbonic oxide may also escape.
In recent years Carburetted water-gas has been largely mixed with
coal-gas in certain districts. This is made by passing steam over heated
coke. Thus
C + H₂O = CO + H₂
(coke) (steam) (carbonic oxide) (hydrogen)

The product is water-gas which burns with a non-luminous flame and has
no smell. For illuminating purposes it is enriched with vaporised paraffin
oil, which gives it a high illuminating power, and a smell rather like that of
coal-gas. In some towns as much as 60 per cent. of this carburetted water-
gas is mixed with 40 per cent. of coal-gas. Now as the former contains
about 30 per cent. of carbonic oxide, and the latter only 7 per cent., a

mixture of equal parts of the two gases would contain 18·5 per cent. of
carbonic oxide, and would therefore be much more dangerous than coal-
gas. This has been found to be so in actual experience of escapes of gas.
In speaking of these products of different illuminants, it is necessary to
adopt a standard of light. In this country the standard has hitherto been a
light known as “one-candle power” which is given by a sperm candle
burning 120 grains per hour, or in V. Harcourt’s standard flame by a mixture
of air and pentane (C₅H12). A good fish-tail or bat’s wing burner for coal-
gas gives an illuminating power equal to 16 candles, and burns from 4 to 5
cubic feet of gas per hour. Most flat flame burners known as 4 or 5, and
supposed to burn that number of cubic feet of gas per hour, really consume
nearly double this amount of gas. In the following table the amount of
various products produced and of vitiation of air caused by various forms of
illuminants is compared, when an illumination equal to 16 candles is
produced in each instance:—
AMOUNT OF
VITIATION
PRODUCED STATED
CARBONIC
AMOUNT MOISTURE OXYGEN IN TERMS OF THE
ACID
BURNT. PRODUCED. REMOVED. NUMBER OF
PRODUCED.
ADULTS WHO
WOULD CAUSE AN
EQUAL VITIATION.
Sperm candles 1740 grains 6·6 c.ft. 6·6 c.ft. 9·6 c.ft. 11
Paraffin oil 992 „ 4·5 „ 3·5 „ 6·2 „ 7
Coal gas
burned in
4·8 c.ft. 2·5 „ 6·4 „ 5·8 „ 4
Argand
burner
Flat-flame
5·5 „ 3·5 „ 7·4 „ 6·5 „ 6
burner

Thus as an adult expires 0·6 cubic feet of carbonic acid per hour, it
follows that the amount of carbonic acid produced in one hour by the
various illuminants named in the above table, burning so as to give a light
equal to 16 standard candles, varies from 4 to 11 times the amount produced
by the adult. Candle and oils possess the advantage over coal-gas that no
sulphurous acid is produced in combustion. If the pressure in the mains is
excessive, some gas may escape through the burner unburnt or carbonic
oxide may escape.

In England the flashing-point of mineral oils has been fixed at 73° Fahr.
The material of which the reservoirs of lamps are composed should not be
glass or other breakable material, and the wick should be contained in a
small wick chamber extending nearly to the bottom of the reservoir. Only a
tight fitting wick must be used.
The best illuminant for domestic purposes is incandescent electricity, in
which no products of combustion are formed, and only a comparative small
amount of heat is produced. Electrical illumination possesses the further
advantages that there is no blackening of ceilings and no damaging of other
decorations as in illumination by gas.
(3) Air Rendered Impure by Exhalations from the Sick. In addition to
the ordinary impurities of occupied rooms, special impurities are produced,
varying with the character of the disease. They may include infectious
particles from the sick. In wards for consumptives and for diphtheria, dust
in the room has been found to contain the special microbes of these
diseases. Making beds, sweeping floors, &c. may help to scatter infectious
dust; hence the importance of adopting means of cleansing which will not
scatter dust, and of keeping sick-rooms spotlessly clean. In many diseases
e.g. consumption, a patient may re-infect himself with such infectious dust,
and thus diminish his own chance of recovery (see page 311). Hospital
wards can scarcely be too freely ventilated; but even more important than
ventilation is the strictest cleanliness in every minute detail.
(4) The Air of Sewers, Cesspools, etc., may contain the products of
decomposition of sewage, such as volatile fœtid organic matter, carbo-
ammoniacal substances, sulphuretted hydrogen, carbonic acid, etc. The
amount of these various products varies greatly under different
circumstances, such as dilution of the sewage, ventilation of sewers,
temperature, etc. The effluvia from cesspools are usually more concentrated
than those from sewers. It appears fairly certain that the emanations from
sewers or drains may give rise to diarrhœa and gastric disturbances, and to
certain forms of sore throat, which favour the production of diphtheria. On
the other hand, there is much evidence showing that the danger from sewer-
emanations has been exaggerated. Carnelley and Haldane found that the air
of the sewers of the Houses of Parliament and of certain sewers of Dundee
was not very impure, containing a smaller number of bacteria than external

air. There is reason to believe that the emanations from well-ventilated
sewers, possessing a good gradient, so that the contents of the sewers are
hurried away to the outfall, are free from danger. The chief source of
possible danger would be the escape of the bacteria of such diseases as
enteric fever or diphtheria, which had been discharged into the sewer from
patients suffering from these diseases. But, in the absence of splashing,
these bacteria could not escape from a liquid medium. Their escape could
only occur when the sewer became dry, and the dust was carried up by rapid
currents of air, a very improbable occurrence in sewers. Hence in the
majority of instances sewer emanations must be freed from the accusation
of producing infectious diseases. Sewer-men usually enjoy good health, and
there is no excess of infectious diseases among them.
The emanations from obstructed drains or sewers may cause serious
mischief, similarly to that occasionally produced by the emanations from
cesspools. Under such conditions, sulphuretted hydrogen, carburetted
hydrogen, and other gases are evolved, and fatal asphyxia has been caused
by these. In other instances acute sewer-gas poisoning, without pneumonia,
has followed.
The exhalations from cesspools or privies while cleaning them out, may
produce severe disorders, which are sometimes fatal. When a drain is newly
opened or sewer gas gets into a house, a less marked form of poisoning
sometimes occurs, chiefly characterised by languor, headache, vomiting,
and diarrhœa. In some cases there may be febrile attacks lasting a few days.
Children are especially sensitive to such conditions and quickly fall into ill
health.
The direct origin of acute infectious diseases from the effluvia from
drains or cesspools has occasionally occurred. Leaky and choked drains
under a house are especially dangerous. The subsoil becomes contaminated
more and more as time goes on; foul gases are aspirated into the house,
owing to its interior being warmer than the subsoil; and finally infectious
matter may find its way into the house, or carried by insects or vermin,
through cracks in the earth.
Diphtheria has been ascribed to emanations from drains and sewers.
There is reason to believe that a non-specific form of sore throat may

originate in this way; but diphtheria is generally, if not always, spread by
personal infection. Diarrhœa has been occasionally ascribed to sewer-
emanations. It chiefly occurs in hot weather, and is usually associated with
a foul condition of the surface soil, and speedily ceases after this has been
scoured by copious rain.
Enteric or typhoid fever, has been frequently ascribed to drain and sewer
effluvia. It was formerly thought that putrefactive changes alone, under
certain conditions of temperature, etc., would produce it, and Dr.
Murchison, one of the greatest authorities on the subject, who adopted this
view, proposed for enteric fever the name “pythogenic fever” (i.e. filth-
produced). Isolated cases of enteric fever, occurring where there is no
system of drainage, support the same view, as does also the fact that, with
the adoption of drainage, the enteric mortality has steadily diminished. On
the other hand, numerous cases can be quoted to show that emanations from
excreta have been breathed, and sewage-contaminated water drunk, for
years, without the production of a single case of enteric fever—until a case
is accidentally imported. The weight of evidence is clearly on the side of the
view that only emanations from the liquid or solid dejecta of previous
enteric patients will produce enteric fever, and that it is the solid particles of
the urine or fæces, either inhaled as dust or carried on to food by flies, &c.,
or mixed with food by contaminated water, &c., which cause infection.
Furthermore, modern investigation shows that infection by dust is the
exception in England; and that the enteric infection is usually swallowed
and not inhaled, being taken in infected water or milk or other food.
(5) Effluvia from Decomposing Organic Matter.—(a) The air of
marshes contains an excess of carbonic acid, marsh gas, etc., in addition to
other organic matters. Malarial diseases are commonly ascribed to the
inhalation of the marsh effluvia under certain conditions, though the recent
proof of the part played by the mosquito in spreading malaria, puts the
inhalation of such effluvia in the background as cause of this disease (page
307). Some forms of diarrhœa and dysentery have been ascribed, with a less
degree of probability, to the same cause. In this case, as in that of
emanations from other organic sources, the impurities received by the air
are both gaseous and particulate.

(b) The Air of Graveyards contains an excess of carbonic acid. The
older intramural graveyards appear to have been a cause of illness; but
modern graveyards, kept under good regulations have never been shown to
cause illness.
(c) The Effluvia from Decomposing Carcases, especially of horses on
the battle-field, have led to outbreaks of diarrhœa and dysentery among the
soldiers.
(d) The Effluvia from Manure and Similar Manufactories do not
seem to injure the workmen as a rule, but attacks of diarrhœa have been
produced in the neighbourhood when the wind has wafted the effluvia
towards any particular part. Sore throat, and occasionally diphtheria, have
been ascribed to the inhalation of London manure taken into Essex.
(6) The Effluvia from Certain Manufacturing Processes seem to be
rather nuisances than actually productive of ill health. The vapours given
off by tallow-making and bone-burning processes are most disagreeable,
but there is little or no positive evidence of their direct insalubrity.
The air of brickfields and cement works is peculiarly disagreeable.
The Degree of Moisture and the Temperature of air are of great
importance in relation to health. Air which is unduly moist or dry, hot or
cold, may be injurious apart from any foreign matters it contains.
The relative amount of moisture is of greater importance than its actual
amount. An atmosphere which contains aqueous vapour up to the point of
saturation is very oppressive; the normal evaporation of insensible
perspiration (and with it of the organic impurities removed from the skin) is
interfered with; and consequently the “oppressiveness of the day” is
complained of.
An unduly hot air is generally productive of pallor and ill health, though
it is difficult to know how much to ascribe to the high temperature, and how
much to the commonly coexistent vitiated atmosphere. The temperature of
living-rooms ought not to be over 60° to 65° Fahr., and of bedrooms not
over 60° Fahr.

The devitalising influence of extreme cold is well known. Its effects are
more particularly seen in young children and the very old, who require to be
carefully tended during severe and long-continued cold weather. Dry, cold
weather, with the temperature near the freezing point of water, and a cutting
east wind prevailing, is not uncommonly described as “bracing.” This is so
far from being the case, that it requires all the vital powers of the strong and
healthy to resist its depressing influence, and the feeble of both extremes of
age succumb.

CHAPTER XVII.
TRADE NUISANCES.
Many occupations are the source of considerable danger to the workers
engaged in them. They are chiefly injurious by the inhalation into the lungs
of some foreign agent, which produces serious local inconveniences and
irritation, and may be also absorbed into the circulation and produce more
remote effects.
The injurious agents may be classified under four heads:—
(1) Insoluble particles or dust.
(2) Soluble or partially soluble substances.
(3) Injurious gases or vapours.
(4) Effluvia from offensive trades.
It is evident that, as regards the effluvia named under (4), they might
generally be included under the three previous heads, though it is
convenient for our present purpose to keep them separate.
The occupations in which dust and soluble substances are productive of
injurious effect have already been described, pages 107 to 109.
Injurious gases and vapours have received consideration on pages 111
and 112. The special offensive trades still require attention.
Offensive Trades.—The legal enactments relating to offensive trades are
contained in sect. 112 of the Public Health Act, 1875, which states, any
person who, after the passing of this Act, establishes within the district of an
urban sanitary authority, without their consent in writing, any offensive
trade, that is to say, the trade of—

Blood boiler, or
Bone boiler, or

Fellmonger, or
Soap boiler, or
Tallow melter, or
Tripe boiler, or
any other noxious or offensive trade, business, or manufacture,

shall be liable to a penalty not exceeding fifty pounds in respect of the
establishment thereof, and a penalty not exceeding forty shillings for every
day on which the offence is continued.
These provisions can only be enforced in rural districts with the sanction
of the Local Government Board.
The “other noxious or offensive trades,” in order to be brought within the
operation of the section, must be analogous to those which are specially
enumerated.
The most exhaustive and authoritative report on this subject is by the late
Dr. Ballard, whose report is largely quoted in the following remarks.
We may consider (1) the extent to which the public is inconvenienced by
various effluvium nuisances. The majority of the nuisances arise from trade
processes in which animal matters are chiefly used. Among the most
disgusting are the effluvia from gut-scraping, and the preparation of sausage
skins and catgut, the preparation of artificial manures from “skutch” (the
refuse matter of the manufacture of glue), the manufacture of some kinds of
artificial manures, and the melting of some kinds of fat. Manufacturing
businesses dealing with vegetable substances are often offensive, but rarely
give out disgusting effluvia. The most offensive vegetable effluvia are
probably those thrown off during the heating of vegetable oils, as in the
boiling of linseed oil, the manufacture of palmitic acid from cotton oil or
palm oil, the manufacture of some kinds of varnish, the drying of fabrics
coated with such varnishes, and the burning of painted articles, such as
disused meat-tins.
Occasionally offensive effluvia arise in connection with industries in
which neither vegetable nor animal matters are used; as in the manufacture
of sulphate or chloride of ammonia, and some other processes in which
sulphuretted hydrogen is copiously evolved; and in the making of gas and

the distillation of tar. The fumes from the manufacture of alkali and
bleaching powder are acid and irritating, and produce very injurious effects
on vegetation in the neighbourhood.
The distances to which nuisances extend vary greatly according to
circumstances—as, for instance, the elevation at which the effluvia are
discharged into the air. Discharge from a high chimney may relieve the
immediate vicinity of the works at the partial expense of those living at a
greater distance. With a damp and comparatively stagnant atmosphere,
effluvia have a much greater tendency to cling about a neighbourhood.
(2) The industrial processes in which offensive effluvia are produced are
classified by Dr. Ballard as follows:—
1. The keeping of animals.
2. The slaughtering of animals.
3. Other branches of industry in which animal matters or substances of animal origin are chiefly
dealt with.
4. Branches of industry in which vegetable matters are chiefly dealt with.
5. Branches of industry in which mineral matters are chiefly dealt with.
6. Branches of industry in which matters of mixed origin (animal, vegetable, and mineral) are dealt
with.

(3) It is important to inquire to what extent offensive trade effluvia are
injurious to the public health. It is impossible to bring statistics to bear on
the inquiry, as other influences, apart from occupation, can scarcely be
eliminated. The term “injurious to health” is capable of a double
interpretation. It might mean either serious damage to health, or the mere
production of bodily discomfort or other functional disturbance by the
offensive effluvia, leading by its continuance to an appreciable impairment
of vigour, though not to any actual disease.
In the latter sense offensive effluvia have a deleterious effect on health.
Such symptoms as loss of appetite, nausea, headache, occasionally
diarrhœa, and general malaise are produced by effluvia of various kinds, but
agreeing in being all offensive. “A condition of dis-ease or mal-aise is
produced.”

There is little difficulty in proving bad effects on the workmen, though
the invariable defence of manufacturers is an appeal to the condition of
health of their workmen. The workmen only remain such so long as they are
healthy, and as they become disabled they necessarily cease to rank among
workmen. The decomposition of putrefying organic matters is
unquestionably dangerous. The general doctrine of sanitation that filth is
one of the chief factors in producing disease is certainly applicable to trade
effluvia as well as to general sanitation. It has been alleged on behalf of
such effluvia as chlorine sulphurous acid and tar vapours that they are
useful disinfectants; but modern research has shown that disinfectants, in
order to be of practical use, must be in such a concentrated condition that
the air containing them is irrespirable. Probably such septic diseases as
erysipelas are favoured by organic trade effluvia.
(4) The means available to prevent or minimise the nuisances arising
from trade effluvia vary with the character of the processes. The general
principles on which treatment must be founded depend, as Dr. Ballard
points out, on a recognition of the following kinds of effluvia:—
Effluvia dependent—
1. On the accumulation of filth on or about business premises, or on its removal in an offensive
condition.
2. On a generally filthy condition of the interior of buildings and premises and utensils generally.
3. On an improper mode of disposal of offensive refuse, liquid or otherwise.
4. On insufficient or careless arrangements in reception of offensive materials of the trade, or in
removal of offensive products.
5. On an improper mode of storing offensive materials or products.
6. On the escape of offensive gases or vapours given off during some part of the trade processes.

It is evident that under the first two headings the proper remedy is
cleanliness. Filth should be removed in impervious covered vessels, at
regular intervals. Structural arrangements should be made, which will
facilitate cleansing operations. Solid refuse should, as far as possible, be
separated from liquid refuse, as thus putrefaction is retarded.
Under the last head important remedies are applicable. In many cases a
careful selection of the materials of manufacture will form an effective

remedy. Thus much of the nuisance connected with soap or candle works
arises from the putrid condition of the fat collected from butchers and
marine store dealers, and might be obviated by more regular and more
frequent collection of the materials of manufacture. The offensive vapours
arising during processes of manufacture may be intercepted before reaching
the external air, and so treated that they lose their obnoxious character.
Various methods of interception are adopted, according to the processes
involved. Occasionally it is necessary to have the air of the entire workshop
drawn by means of artificial ventilation in a special direction; usually the
interception of air from special chambers suffices. When thus collected, the
offensive air may be dealt with by (1) passing it through water or some
other liquid capable of absorbing the offensive materials; or (2) passing it
through some powder with which it has chemical affinity; or (3) if its
offensive materials are capable of condensation by cold, passing them
through an appropriate condensing apparatus; or (4) if the evolved matters
are organic in nature, conducting them through a fire. (5) Occasionally it is
sufficient to discharge the offensive gases into the air from a high chimney;
and this always produces a mitigation of nuisance, as compared with
discharge at a low level.
It is usually found that the adoption of one or other of these methods is
directly or indirectly profitable to the offender.
Nuisances from the Keeping of Animals.—The 47th section of the
Public Heath Act prohibits the keeping of pigs in towns so as to be a
nuisance, and, as a general rule, it is possible to obtain a magistrate’s order,
entirely prohibiting the keeping of pigs in towns. The excreta of the pig
have a very offensive and penetrating odour, and however carefully kept,
pigs in towns form an intolerable nuisance.
Not only is there nuisance from the accumulation of manure and dirtiness
of the piggeries, but also from the storage and subsequent preparation of
food. The boiling of hog-wash is often an even greater nuisance than the
filth of the styes.
Cow-keeping and horse-keeping in towns are still allowed and, as
compared with pig-keeping, form a small nuisance. Mews, if kept clean and
well drained, need not be offensive, though it is objectionable for persons to

sleep over stables. The removal of manure also constitutes a difficulty. The
manure should not be allowed to accumulate in deep wet pits, but in an iron
cage-work over a cement paving at or above the ground-level, thus allowing
free drainage, and keeping the manure dry, and reducing ammoniacal
decomposition to a minimum.
Cowsheds are generally very badly ventilated, as the cowkeeper finds
that more milk is produced by the cows when the temperature of the shed is
maintained at 65° or higher; and he does not see the necessity for providing
artificial means of warmth. The grains which are used so largely for food
are stored in a wet condition, and speedily give rise to nuisance. Cowsheds
and stables should be well paved and well drained. At least 800 cubic feet
should be allowed for each cow in the shed.
Cowsheds are regulated under the Dairies’, Cowsheds’, and Milkshops’
Order of the Local Government Board. This order provides for and insists
on the registration of cowkeepers, dairymen, and purveyors of milk, by the
local authority. It also provides that no cowshed or dairy shall be occupied
as such, unless provision is made to the satisfaction of the local authority,
for the lighting and ventilation, including air-space, and the cleansing,
drainage, and water-supply of the same; and for the protection of the milk
against infection or contamination. With the view of preventing
contamination of milk, no person suffering from an infectious disorder, or
having recently been in contact with a person so suffering, is allowed to
milk cows or take any part in any stage of the business of a milk-seller. The
milk of a cow suffering from cattle plague, pleuro-pneumonia, or foot and
mouth disease must not be mixed with other milk, must not be sold or used
for human food, nor for food for swine or other animals, unless it has been
boiled. By the order of 1899 this regulation is made to extend to tubercular
disease of the udder.
Slaughtering of Animals.—Nuisance may arise in slaughter-houses from
various causes:—(1) the uncleanly way in which animals are kept in the
pound or lair before being killed; (2) the insanitary condition, bad paving,
lack of lime-whiting of walls, etc., of the slaughter-house; (3) the
accumulation of hides, blood, fat, offal, dung, or garbage on the premises;
(4) the uncleanly condition of the blood-pits, or the receptacles for garbage;

(5) the flowing of blood or offal into the drains and thence into the public
sewer.
Private slaughter-houses ought to be abolished, and all animals intended
for human food slaughtered in public abattoirs under efficient supervision.
When a large number of private slaughter-houses exist in different parts of a
large town, it is impossible for the sanitary officials to properly supervise
the slaughtering, or to ensure that diseased meat shall not enter the market.
The inspector may only have the opportunity of examining the flesh, the
internal organs which more particularly show the presence of a diseased
condition having been concealed. Such concealment and the consequent
foisting of diseased meat upon the public, can only be efficiently prevented
by forbidding the slaughtering of any animal intended for food in a private
slaughter-house.
Most local authorities have bye-laws regulating the slaughtering of
animals. These provide for a cleanly condition of the lairs, and prevent
keeping the animals longer in the lairs than is necessary for the purpose of
preparation for slaughtering. They also insist on the provision of proper
covered receptacles of iron or other non-absorbent material for the
reception of garbage, and similar receptacles for blood; for cleansing of the
floor, etc. after slaughtering; for lime-whiting of the walls four times a year;
and for other matters of detail.
For knackers’ yards similar regulations are applicable. The flesh should
not be kept until it becomes putrid before being boiled, and the boiling of
the flesh and fat should be so arranged as to avoid the escape of offensive
vapours into the external air.
In smoking bacon, the singeing has formed a serious nuisance. Fish-
frying in small shops is often a most troublesome nuisance. A hopper over
the pan in which the frying is conducted has not been always successful in
carrying the fumes up the chimney. The frying should preferably be done in
a closed outhouse, close to a chimney with a good up-draught.
The fellmonger prepares skins for the leather-dresser, the chief operations
being taking off the wool, liming the skins, etc. The skins deprived of wool
are called “pelts.” The pelts are thrown into a pit containing milk of lime,
and thence sent direct to the leather-dresser. Nuisance may arise from (1)

the odour of the raw skins; (2) the ammoniacal odour from the lime-painted
skins hanging in the yard; (3) the emptying and cleansing of the “poke” or
tank in which the hides are washed; (4) the foul condition of the waste lime
taken from the exhausted lime pits; (5) the odour from the dirty unpaved
yards.
The leather-dresser only deals with “pelts,” derived from sheep-skins;
the tanner with bullocks’-hides. The skins brought from the fellmonger to
the leather-dresser are first deprived of lime, and then soaked in a solution
of dog’s dung, called “pure,” until they become soft. In winter this “pure”
solution is warmed for use. The odour is very abominable, both from the
“pure” tub, and from the discharge of the exhausted “pure” liquid into the
drain.
At each stage of tanning nuisance may arise unless great precautions are
taken, as when the hides are soaked in lime and water, when the hair is
being removed, when the loose inner skin of the hide is being removed, and
especially when the hides are soaked in pits containing pigeons’ or other
dung. Nuisance may arise again during the passage of offensive hides
through the street. Cleanliness is the great rule. If every process is carried
on with due precaution, including frequent washing out of receptacles and
the free use of disinfectants, little complaint need arise.
The manufacturers of glue and size boil out the gelatine from bits of
hides and “fleshings” from leather dressers and tanners, from damaged
“pelts,” ox or calves’ feet, horns, and other similar substances. The raw
material is apt to be offensive in collection or while accumulating on the
premises. The process of boiling causes offence by the effluvia from the
steam. The residue remaining after the process is known as “scutch,” and
this, unless frequently removed, is a most serious source of nuisance.
Prussiate of Potass is manufactured by heating carbonate of potass with
refuse animal matters. In order to avoid nuisance the pot in which the
boiling is done should have a pipe to conduct away the steam, first running
horizontally and then vertically down to the back part of the fire.
Fat-melting and Dip-candle-making, as usually carried on, give rise to
nuisance. The fat which is melted down usually comes from butchers and
marine-store dealers in a rancid or even putrid condition, and it may be

stored on the premises for some time before it is boiled. The vapours from
the melting-vat are very offensive. They should be carried by means of a
pipe down until they discharge just under the boiler-fire. The residue from
the fat-melting process (known as “greaves”) requires frequent removal to
avoid nuisance.
Bone-boiling, in order to extract the fat and gelatine, is most offensive,
and most difficult to deal with. After boiling, the bones are apt to give off
offensive smells. The vapours from the closed boiler should be condensed
as far as possible in a worm condenser, and the remainder passed through a
furnace fire.
In the manufacture of artificial manures nuisance is apt to arise (1) from
the reception and accumulation of the raw materials, as putrid fish, putrid
blood, scutch (the residue from the manufacture of glue), recently boiled
bones, etc.; (2) from the preparation of the raw material for use. Thus the
drying of condemned fish or meat on open kilns is very offensive; similarly
the drying of sewage sludge. (3) From the process of mixing the materials
of manufacture, irritant and offensive vapours being evolved, as for instance
in the manufacture of manure by crushing bones, and converting into super-
phosphate by the addition of sulphuric acid. (4) From the removal of the
manure from the hot den, after it has been dried. When sulphuric acid is
mixed with coprolites or other mineral phosphates, most irritant and
offensive vapours are produced, which may be perceived in some cases at
the distance of a mile.
Blood-boiling is now almost obsolete, having been replaced by albumen-
making and clot-drying. Nuisance may arise from the blood collected from
slaughter-houses being in a putrid state; and from the effluvia evolved
during the drying process.
Gutscraping, gut-spinning, and the preparation of sausage-skins are very
closely akin. In gut-scraping the putrid intestines are deprived of their
interior soft parts by scraping with pieces of wood, and are then, after being
cleansed, ready for sausage-skins. In gut-spinning the prepared gut is
twisted into a cord. The small intestines of hogs and sheep are used for this
purpose. The stench from these establishments is indescribably horrible.
Extreme cleanliness is desirable. Immersion of the guts in common salt is

useful; so also the use of impervious vessels, early removal of all refuse
material, etc.
Brick and ballast burning are a frequent source of complaint in the
neighbourhood of towns. Brick burning is conducted either in kilns or
clamps. When bricks are burnt in closed kilns comparatively little nuisance
arises; but when they are burnt in open clamps the effluvia are very
irritating, partly owing to the fact that very commonly house refuse,
containing vegetable and animal matters, is burnt with the bricks. Clamp
burning should be absolutely prohibited in the neighbourhood of large
towns.
In Ballast burning stiff clay is converted by the agency of heat into a
brick-like material, which is of use in road-making. The clay is usually
burnt in heaps, mixed with ashes and breeze from dust-bins. The process is
offensive unless carried on with precautions similar to those for brick-
burning.

CHAPTER XVIII.
THE EXAMINATION OF AIR.
There are various methods of ascertaining the quality of the air in
enclosed spaces, of which not the least useful is the information furnished
by the sense of smell, on entering a room from the external air. Besides the
evidence given by the senses, chemical and microscopical examination of
the air gives important information, while the thermometer and hydrometer
ascertain the temperature and degree of moisture.
Examination by the Senses.—The dull grey haze hanging over a town,
when it is viewed from a distance, indicates comparative impurity of its
atmosphere, and the presence of a considerable amount of suspended
matter, including smoke.
The smell of a stagnant atmosphere is a good preliminary guide to its
condition. The fact that a room has been occupied for some time without
efficient ventilation can be at once detected on entering a room from the
external air. The sense of smell is extremely delicate; it has been estimated
that the 3 ∕ 100,000,000 part of a grain of musk can be apprehended by it. But
nothing is so soon dulled as the sense of smell. An atmosphere which did
not appear to be unpleasant while remaining in a room, is intolerable when
one returns to it after a few minutes in the open air. It is important not to
confound the “closeness” perceived by the sense of smell, with the
oppression due to the high temperature of a room. The two are easily
distinguished (unless the two co-exist) by a reference to the thermometer,
which ought always to be placed in rooms inhabited during the evening.
The remedy for a close room is to allow free entry of fresh air, and not
allow the fire to go down, as is so commonly done, under the impression
that the closeness is due to heat.
De Chaumont has made many experiments, shewing how accurate is the
information given by an acute sense of smell. Carbonic acid is destitute of
odour, but as its amount is usually proportionate to that of the organic
matter producing closeness, it may be taken as an index of the amount of

impurity present in living rooms. De Chaumont found that the limit of smell
is reached when carbonic acid amounts to 6 parts in 10,000 of air, or half as
much again as in the external air. In the following extracts from his
experiments, there was a close accordance between the evidence of his
sense of smell and the amount of carbonic acid:—
At 14·80 per 10,000 Extremely close and unpleasant.
„ 10·90 „ Extremely close.
„ 9·62 „ Very close.
„ 9·21 „ Close.
„ 8·43 „ Not very foul.
„ 8·04 „ Close.
„ 6·58 „ Not very close.
„ 5·68 „ Not close.

He also found that humidity of the air had marked influence in rendering
the smell of organic matter perceptible, even more than a rise of
temperature. The sense of smell is doubtless aided in detecting impurities in
the air, by the besoin de respirer, a feeling of oppression caused by the
deficiency of interchange between the blood and air. The state of cleanliness
of the room as well as of the persons in it influences smell; hence there may
not be in particular instances exact correspondence between excess of
carbonic acid and of organic matter.
Chemical Examination.—The estimation of nitrogen and oxygen in air
is usually unnecessary, as these vary but little. The oxygen is, however,
reduced in frequently re-breathed air. The ill effects of an often-breathed
atmosphere are due not only to deficiency of oxygen, but also to the
addition of carbonic acid and organic matters, rendering difficult the
interchange between oxygen and the blood.
The Estimation of Carbonic Acid is of great importance, as under
ordinary circumstances, its amount is a fairly exact indication of the amount
of contamination in the air.
Pettenkofer’s Method.—A carefully dried glass vessel containing a gallon of water is filled with
the air to be examined, by emptying the water in the room, the air of which is to be examined. Fifty
cubic centimetres of clear freshly prepared baryta water are then added, and the stopper of the bottle
then replaced. It is then well shaken, and afterwards allowed to stand for an hour. The carbonic acid
combines with part of the baryta to form barium carbonate; and the baryta water remaining is
consequently diminished in alkalinity. Given the alkalinity of the baryta water before and after the

experiment, and the difference will give the amount of baryta which has combined with carbonic
acid.
The alkalinity of the baryta is estimated by a standard solution of oxalic acid, of such a strength
that 1 c.c. is the equivalent of 0·5 c.c. of CO₂. The indicator used in making this test is
phenolphthalein, which colours baryta water red, but its colour disappears when neutralization is
reached.
The following example is taken from “Pakes’ Laboratory Text Book of Hygiene,” p. 292:—
The jar is found to contain 3,950 c.c.
As 50 c.c. baryta water were run into the jar, the air experimented on = 3,950-50 = 3,900 c.c.
On titrating 25 c.c. of the original baryta water, 22·50 c.c. standard acid solution were required to
neutralise it.
The baryta water in the jar required 19·35 c.c.
22·50-19·35 = 3·15 c.c. = difference of acid used.
But 1 c.c. acid = 0·5 c.c. CO₂ at 0° C. and 760 mm. of mercury.
Therefore CO₂ taken up by 25 c.c. of baryta = 3·15∕ 2 = 1·575 c.c.
As 50 c.c. were used the CO₂ absorbed by the baryta = 3·15 c.c. This was present in 3,900 c.c. of
air. Therefore the CO₂ = 0·80 per cent.
Correction may be required for variations from the normal pressure of 760 mm. and normal
temperature of 0° C., in accordance with ordinary rules.
In Lunge and Zeckendorf’s Method, the air to be examined is pumped through a glass bottle in
which is 10 c.c. of a N ∕ 500 solution of Na₂CO₃ containing phenolphthalein as an indicator. The air is
pumped by a hand pump through this solution until the phenolphthalein is decolourized. The number
of times the ball of the pump has been squeezed indicates the amount of CO₂ present in accordance
with a table prepared from separate experiments by Pettenkofer’s method.
Dr. Angus Smith’s plan for the estimation of carbonic acid in air is similar in principle to the last
calculations. It is based on the fact that the amount of carbonic acid in a given volume of air will not
render turbid a given amount of lime water, unless the carbonic acid is in excess.
Table.—To be used when the point of observation is “No precipitate.” Half an
ounce of lime water containing ·0195 gramme lime.
Air at 0° C. and 760 M. M. Barometric pressure.

CARBONIC ACID VOLUME OF AIR IN SIZE OF BOTTLE IN SIZE OF BOTTLE IN
IN THE AIR PER CUBIC CUBIC OUNCES
CENT. CENTIMETRES CENTIMETRES AVOIRDUPOIS.
·03 571 584 20·63
·04 428 443 15·60
·05 342 356 12·58
·06 285 299 10·57
·07 245 259 9·13
·08 214 228 8·05

·09 190 204 7·21
·10 171 185 6·54
·11 156 170 6·00
·12 153 157 5·53
·13 132 146 5·15
·14 123 137 4·82
·15 114 128 4·53
·20 86 100 3·52
·25 69 83 2·92
·30 57 71 2·51
The foregoing table shows how to apply this method. The first and second columns state the ratio
of carbonic acid in a quantity of air which will give no turbidity or precipitate in half an ounce of
lime water; the third column gives the corresponding size of the bottle in cubic centimetres; and the
fourth column gives the same in ounces. Thus different sized bottles, each containing half an ounce
of lime water, will indicate with a fair degree of accuracy the ratio of carbonic acid in the air
containing them, by giving no precipitate when the bottle is well shaken. For instance, if a pint bottle
is used and there is no precipitate with half an ounce of lime water, it indicates that the ratio of
carbonic acid does not amount to ·03 per cent.; if an eight-ounce bottle be used, and there is no
precipitate, it indicates that the ratio does not amount to ·08 per cent., and so on. The air of a room
ought never to contain more than six parts of carbonic acid in 10,000 of air, or ·06 per cent., i.e. a
10½ ounce bottle full of the air shaken up with half an ounce of clear lime water ought to give no
precipitate.
Dr. Haldane has recently described (Journal of Hygiene, No. 1, 1901) a method of estimating
CO2, which, although it appears complicated, is really both simple and convenient. For particulars,
see the above Journal.
The Estimation of Organic Impurities may be accomplished approximately by drawing a
definite amount of air by means of an aspirator, through a dilute solution of permanganate of
potassium of known strength. The result is stated by giving the number of cubic feet of air required to
decolourise .001 gramme of the permanganate in solution. Sulphuretted hydrogen, sulphurous acid,
and other substances in air likewise decolourise the permanganate; these ought to be separately tested
for, and allowance made.
The Estimation of Ammonia, whether free or derived from albuminoid impurities, is a matter
requiring very delicate processes. It is accomplished in the same way as the estimation of ammonia in
water, the air being drawn through perfectly pure distilled water, and then the analysis proceeded
with as a water analysis. The mere presence of free ammonia may be determined by exposing to the
air strips of filtering paper dipped in Nessler’s solution, which become brown if there is any
ammonia in the air.

Microscopical Examination is required for the detection of suspended
matters. These are the most potent for harm, containing sometimes the
germs of infectious diseases. The suspended matters scattered throughout
the air may be collected by Pouchet’s aeroscope. This consists of a small
funnel drawn out to a fine point, under which a slip of glass is placed
moistened with glycerine. Both funnel and glass are enclosed in an air-tight

chamber, connected by tubing with an aspirator, by means of which when
water is allowed to escape from it, air is drawn through the funnel and its
particles impinging on the glycerine are there arrested. Glycerine may be
objectionable from the foreign particles previously contained in it. Various
other plans have been devised, one of which is to draw the air through a
small quantity of pure distilled water and then examine a drop of it. By
microscopic examination large particles can be detected. For the detection
of bacteria and their spores more delicate methods are required.
The Bacteriological Examination of air is usually conducted as follows.
Air is drawn through a wide glass tube (Hesse’s tube), which has been
previously sterilised, and on the inner side of which liquid gelatine has been
allowed to solidify. The air as it passes over the gelatine deposits any germs
present in it. The entrance of any further germs is prevented by closing the
tube, and it is then left to stand for two or three days. Moulds and colonies
of bacteria will develop in the gelatine, and these can be counted and
differentiated by their appearance and by further tests. In closed rooms the
number of microbes (i.e., bacteria and moulds) ought not to be more than
20 per litre of air in excess of those in the outside air; and the ratio of
bacteria to moulds ought not to exceed 30 to 1.
Examination of Temperature and Moisture.—The temperature should
be observed at the point most remote from an open fire-place, and
compared with the external temperature. For methods of estimating
moisture, see page 240.
It may be useful to recapitulate at this point the desiderata in an inhabited
room. The temperature should be 60-62° Fahr., the amount of carbonic acid
should not exceed ·06 per cent. and the humidity should range between 73
and 75 per cent. of the amount required to produce saturation. The dry bulb
thermometer should read 63-65° Fahr., the wet bulb 58°-61° Fahr., and the
difference between the two should not be less than 4° or more than 8°.

CHAPTER XIX.
THE PURIFICATION OF AIR.
In addition to the artificial measures which will be discussed in the next
chapter, various natural agencies are constantly at work for the removal of
the impurities discussed in preceding chapters. Of these, the most important
are the action of plants, the fall of rain, natural methods of ventilation, and
certain natural constituents of the atmosphere.
1. Plants, by virtue of the chlorophyll contained in their green parts,
absorb carbonic acid from the atmosphere, liberating oxygen in an active
condition. In addition, ammonia and nitrous and nitric acids are dissolved
from the air by rain-water, and assimilated by plants. During the night
plants only give off carbonic acid.
2. The Fall of Rain clears the atmosphere of any solid particles
contained in it, the impurities being transferred to rain-water which
generally contains an appreciable amount of ammonia as well as other
impurities. Rain not only washes and purifies the air, but by washing the
ground, diminishes dust, and prevents its escape into the air. It is the great
natural scavenger.
3. Ventilation—that is, the interchange of pure and impure air, is
constantly being effected. Before entering on the details of ventilation, we
must consider the physical causes at work which tend to purify the air, apart
from all artificial contrivances. These are three in number—namely,
diffusion, winds, and differences of temperature of masses of air.
(1) Diffusion causes the rapid mixture of gases placed together. Every
gas diffuses at a certain rate—namely, inversely as the square root of its
density. In any room which is not air-tight, diffusion is constantly occurring,
air passing in and out at every possible point. Through chinks and openings
in the carpentry-work of a room, the air diffuses rapidly. Bricks and stone
commonly allow air to pass through them; diffusion occurs to a slight extent
even if the wall is plastered, but very little through paper. Diffusion alone is

quite insufficient to purify a room under ordinary circumstances; and solid
particles including the organic matter evolved from the skin and lungs, not
being gaseous, are unaffected by it. To remove these, the room must be
periodically flushed with air, and washing of all dirty surfaces must be
carried out.
Diffusion sometimes produces evil results, when the sanitary
arrangements of a house are bad. If there is a leakage of sewage under the
kitchen floor, the foul gases from it diffuse upwards; occasionally foul air
diffuses from the dust-bin through the wall into the rooms of a house. These
results are helped by the fact that the internal temperature of a house is
commonly higher than the external.
(2) Differences of Temperature cause active movements of air. In fact
winds are caused by movements between large masses of air of unequal
temperature and consequently of unequal density. Light gases ascend, as
familiarly illustrated by the smell of dinner perceived in bedrooms, or the
smell of a cigar lit in the hall perceived in the attic. In rooms differences of
temperature of the air are caused by the heat of fire, gas, and our own
bodies. Currents of air result; the warmer and lighter air ascends up the
chimney or towards the ceiling, while colder and denser air rushes in under
the door or through the floor, etc. The lighter gases carry with them solid
particles in suspension and thus tend to remove the most important
impurities. Assuming that the external air is colder, if admitted into the
lower part of a room, it produces a draught; if admitted at the top of a room,
being heavier, it falls by its own weight on the heads of those in the room.
The problem of ventilation is to secure a sufficient interchange of air
without the production of perceptible currents.
Movements of air are constantly occurring, so long as the temperature of
the air is subject to changes. This cause alone will suffice to ventilate all
rooms in which the air is hotter than the external air. It may thus happen
that a room with windows and doors closed in winter, may possess purer air
than the same room in summer with these thrown widely open. The value of
diffusion of air through the walls, and the influence of temperature on this
diffusion are well illustrated by some experiments of Pettenkofer.
When the difference between the outside and inside temperatures was 34° Fahr. (66° inside and
32° outside), and the doors and windows were shut, an ordinary room in his house, of the capacity of

2,650 cubic feet, which was built of brick, and furnished with a German stove instead of an open fire-
place, had its entire atmosphere changed once in an hour. With the same difference of temperature,
but with the addition of a good fire in the stove, the change of air rose to 3,320 cubic feet per hour.
On lessening the difference between the external and internal temperature to 7° Fahr. (64° and 71°),
the change of air was reduced to only 780 cubic feet per hour. In these experiments, all crevices and
openings in doors and windows were pasted up.

It is instructive to note the greater amount of ventilation effected through
the walls, etc., than by the draught of the stove.
The amount of ventilation through walls varies with the material of
which they are built. Mortar is exceedingly porous when dry; sandstones
and bricks are easily permeated by both water and air. Limestone is almost
impervious to air, but requires much mortar in building, which effects a
partial compensation (see page 206).
The rise of temperature caused by the bodily heat and by the combustion
of illuminating agents, is well shown by some figures of Dr. Angus Smith.
He found that the rise of temperature of 170 cubic feet of air in one hour,
produced by the bodily heat of one man was 5°·6 Fahr.; by the combustion
of a candle 3°·8 Fahr. Thus, in a room 8 feet high, 4 feet broad, and 6 feet
long, a man burning a candle would in an hour raise the temperature from
60° to 70° Fahr. This rise in temperature would not only cause currents of
hot air towards the upper part of the room, but would probably make the
room uncomfortable, and so lead to the opening of a door, etc.
(3) Winds are of great value in flushing rooms with fresh air. They ought
to be utilised as often as possible, by throwing windows widely open;
without, however, taking the place of constant ventilation in the intervals.
They are especially valuable in getting rid of organic matters which are
unaffected by diffusion.
The wind will pass through wood, and even brick and stone walls. When
it is allowed to pass directly through a room, as from window to door, it
produces a more powerful effect than can be produced in any other way.
The average rate of movement of winds in this country is 10 feet per
second, or about 7 miles an hour. If the surface which a man exposes to this
average wind = 6’ × 1½’ = 9 square feet, then 90 cubic feet of air flows over
him in one second, and 324,000 in an hour. If 3,000 cubic feet were the
allowance for each person indoors—a much greater allowance than is

usually given—he only receives 1 ∕ 108 of the air with which he is supplied in
the open.
Winds act as a ventilating agent in two ways—directly by perflation,
driving impure air before them, or freely mixing with it; and indirectly by
aspiration, drawing the impure air along with them. In the last case, the
wind causes a partial vacuum on each side of its path, towards which all the
air in its vicinity flows. Thus, the wind blowing over the top of a chimney
causes a current at right angles to itself up the chimney. In a spray-
producing apparatus we have a familiar instance of the same principle, the
current of air or steam along the horizontal tube causing the fluid to rise in
the vertical tube till it is scattered in spray. In Sylvester’s plan of
ventilation, both these forces are used (see page 150).
4. Certain Constituents of the Atmosphere have an important purifying
effect. Of these oxygen is by far the most important. By its means organic
impurities become oxidised, and thus rendered harmless. It is probable that
much of this oxidation is effected by means of ozone—a peculiarly active
and concentrated form of oxygen. A large part of this ozone is probably
produced during thunderstorms and similar electrical disturbances of the
atmosphere. The ammonia and organic impurities in air become changed
into nitrites and nitrates—chiefly of ammonium—and being washed down
by rain, form an important part of the food of plants.
5. For Chemical Measures of purification of the atmosphere see page
324.

CHAPTER XX.
GENERAL PRINCIPLES OF VENTILATION.
The Amount of Air required.—Ventilation is chiefly concerned with the
removal of the products of respiration, just as sewage is chiefly concerned
with the removal of the solid and liquid excreta.
In a less degree it is required for removing the impurities produced by the
burning of gas, candles, and lamps. The main problem, however, is the
removal of the respiratory products.
The amount of carbonic acid in air is usually fairly proportional to that of
the other respiratory products. It may therefore be taken as a measure of the
impurity of the air. There are, however, certain fallacies in this test. In soda
water manufactory, for instance, there would be a comparatively harmless
excess of carbonic acid. In dirty rooms, and in hospitals and other
institutions where rooms are not vacated for a considerable period, the
amount of organic matter present is often in excess of what would have
been anticipated, judging by an estimation of the carbonic acid. This is
strikingly shown by some valuable researches at Dundee, which are
summarised in the following table. If we take the average amount (in excess
of outside air) of carbonic acid, organic matter, and micro-organisms
respectively in houses of four or more rooms as unity, then in one or two-
roomed houses or tenements we have as follows:—
HOUSES OF FOUR
TWO-ROOMED ONE-ROOMED
ROOMS AND
HOUSES. HOUSES.
UPWARDS.
Carbonic acid 1 1·5 2·0
Organic matter 1 1·6 4·4
Micro-
1 5·1 6·7
organisms

It is evident that in these cases the carbonic acid did not increase in the
same proportion as the organic matter and micro-organisms, and that it
alone does not form a sufficient test of the impurity of any given
atmosphere. The amount of carbonic acid, however, is a valuable and

convenient test of the condition of the air of a room, and the problems of
ventilation, of which examples are given on page 137, are based on its
amount.
The Standard of purity is somewhat difficult to fix. The external air
ought only to contain 4 parts of carbonic acid to 10,000 parts; but it is
almost impossible to maintain this degree of purity in inhabited rooms. The
experiments made by Drs. Parkes and De Chaumont showed that when the
carbonic acid is ·06 per cent., or in the proportion of 6 parts in 10,000 of air,
the air begins to be perceptibly stuffy (page 125); this may therefore be
taken as the limit of impurity. Pettenkofer has adopted the limit of ·07 per
cent.7
The problem then is to discover the amount of pure external air
(containing ·04 per cent. of carbonic acid) that will be required to pass
hourly through a room, for every person in that room, in order to keep the
carbonic acid at the ratio of ·06 per cent.
This may be ascertained by actual observation of the air of rooms in
which a given number of persons are placed; or by calculations from
physiological data.
As the result of numerous experiments on the atmosphere of prisons,
barracks, etc., where the amount of fresh air supplied per hour is exactly
known, it is found that in order to keep the carbonic acid at ·06 per cent.,
3,000 cubic feet of pure air are required per head per hour; 2,000 cubic feet
keep the carbonic acid at ·07 per cent.; 1,500 cubic feet at ·08 per cent.; and
1,200 cubic feet at ·09 per cent.
For the removal of the products of combustion of gas, an additional
supply of air is required, for the amount of which, see page 116.
Where a number of sick persons are collected, as in hospitals and
workhouses, a much freer supply of air is required. Much depends,
however, on the cleanliness of the wards, and on whether the ventilation is
constant in character. In St. Thomas’s Hospital, the space allotted to each
ordinary patient is 1,800 cubic feet, and to each patient in the fever wards
2,500 cubic feet. Thus, by changing the air of the wards twice in the hour,

an abundant supply of fresh air is ensured. The mortality after operations,
and in all fevers, is much diminished by a free supply of air.
Soldiers are allowed 600 cubic feet of space per head in their sleeping
rooms, which involves a change of the air five times per hour, in order that
the carbonic acid may be maintained at ·06 per cent. The limit of
overcrowding for lodging-houses is usually fixed at 300 to 500 cubic feet,
but this is too little.
The amount of pure air required in order to keep the carbonic acid in a
room at ·06 per cent., may also be ascertained from physiological data.

An average adult expires 3 ∕ 5 (·6) cubic foot of carbonic acid per hour.
Now as the carbonic acid in air to be breathed must not contain more than
two parts in 10,000 (·02 per cent.) in excess of what is present in external
air (·04 per cent.), it follows that if x = the amount of fresh air required by
an adult per hour in order to keep the carbonic acid in the room down to .06
per cent., then:—
·02 : ·6 :: 100 : x.
x = 3,000 cubic feet.
Relation of Air Required to Cubic Space of Room.—If we accept
3,000 cubic feet of air as the amount required per head per hour, this may
clearly be furnished by having a large room with comparatively little
circulation of air, or by having a small room with frequent interchanges.
Thus, supposing the cubic space allowed to each individual is 1,000 cubic
feet—that is, 10 feet in every direction—the atmosphere will require
changing three times per hour.
Now, it is found that when a current of air, at the temperature of 55°-60°
Fahr., is moving at the rate of less than one mile per hour, it is not
perceptible—that is, produces no draught. The rate of a breeze, which is just
perceptible, is 18 inches per second, or one mile per hour. As draughts are
objectionable, ventilation, in the best sense of the word, means the
supplying of abundant fresh air at a rate of less than one mile per hour, or
warmed air at a higher rate. Air moving at the rate of 2½ miles per hour, or
3½ feet per second, is perceived as a slight draught by all, at the average
temperature of our climate (about 50° Fahr.)

Where natural ventilation is employed, the difficulties of thoroughly
ventilating a small space, without draught, are very great.
A change of air three or four times in an hour is all that can be borne
under ordinary conditions in this country, and this necessitates a supply of
1,000 or 750 cubic feet of space respectively for each individual. And a
change of this frequency is commonly not effected; the ventilating
apparatus may fail temporarily, or may be wilfully stopped up, or there may
be no means of ventilation; it is essential therefore to have as large a cubic
space as possible. A large cubic space, does not obviate the necessity for
efficient circulation of air. It is, however, advantageous, not only on account
of the initial longer time before the air reaches the limit of impurity, but also
because there are less draughts, and there is a larger wall surface and larger
windows for unperceived ventilation.
Common Errors as to Ventilation.—(1) In relation to the cubic space of
a room, it is most important to note that a lofty ceiling does not compensate
for deficiencies in floor-space. One hears, “lofty” and “airy” rooms spoken
of as though the two terms were necessarily synonymous. This is by no
means the case. The impurities produced by respiration tend to accumulate
about the persons who have evolved them, although it is true that in rooms
heated by gaslight, a large amount of hot and impure air collects near the
ceiling. The necessity of an abundant floor-space is shown by the fact that a
space enclosed by four high walls and without a roof, will, if crowded,
speedily become offensive. Twelve feet is quite high enough for large
rooms in schools, hospital wards, etc., and nine feet suffices for the rooms
of a private dwelling-house. There is no objection to a greater height, if it is
remembered that in reckoning the practical cubic dimensions of a room, the
height should only be reckoned as twelve feet. Supposing 500 cubic feet is
the amount allowed per individual, then the floor-space should be forty-two
square feet, which would be furnished by a room about 8½ feet long and 5½
feet wide. In barracks, soldiers are allowed fifty square feet of floor-space.
In school-rooms the Education Code requires that at least ten square feet of
floor-space, and at least 120 cubic feet shall be allowed for each child in
average attendance.
(2) It is commonly supposed that a large room compensates for a
deficient circulation of air. The cubic space of a room is really of less

importance than the capacity for frequent interchanges of air. Even the
largest enclosed space can only supply air for a limited period, after which
the same amount of fresh air must be supplied, whether the space be small
or large. Thus, supposing that as large a space as 10,000 cubic feet per head
were allowed, the limit of purity would in the absence of ventilation be
reached in three hours, and after that time an hourly supply of 3,000 cubic
feet of air would be just as necessary as if the space were only 200 cubic
feet.
(3) It must not be overlooked that the furniture in a room must be
deducted from the breathing space, as the amount of air is diminished by
the space occupied by the furniture. About 10 cubic feet ought to be
allowed for each bed, and 3 to 5 cubic feet for each individual in a room;
projecting surfaces must be allowed for by subtraction, and recesses by
addition. The deductions to be made for furniture are not of any great
consequence, if there is a free interchange of air; as the cubic space is of
less importance than free ventilation.
General Rules respecting Ventilation.—The two great objects in
ventilating being to remove all impurities from the air, and to avoid
draughts, it is important that—
1. The entering air should be, if possible, of a temperature of 55° to 60°
Fahr. Whenever the temperature of a room differs from the external
temperature by 10° Fahr., a draught is certain to ensue. It is impossible at all
times to ensure the incoming air being of the temperature of 60°, without
some artificial means of warming it. In this country it is seldom necessary
to cool the incoming air, but this may be managed in artificial systems of
ventilation by passing the incoming air over ice, or by using compressed air
which becomes cooled on expansion, or by passing the incoming air
through subterranean tunnels.
2. The entering air should be pure. When a room is hotter than the
passages and kitchens, air from the latter, whatever may be its character, is
drawn into the room. Similarly the ground-air under the kitchen-floor or the
air from ash-pits may be drawn into the house, when no other means of
ventilation are provided; and this is often followed by evil results.

3. No draught or current should be perceptible from the incoming air,
except when it is wished to flush the room with air, by opening the
windows wide. It is a common complaint that a room is draughty, and, to
remedy this, keyholes are stopped up, and mats are placed at the bottom of
the door, etc. The draught can often be remedied by increasing the size and
number of the openings through which air is admitted, so that the current of
air is not concentrated and rapid. When this does not remedy it, the
incoming air should be warmed. A feeling of draught is very often due to
the radiation to and from a window, and disappears when a curtain or screen
is placed between the radiating surface and the occupant of the room.
4. The entry of air should be constant, not intermittent. The occasional
opening of a window or door will not compensate for the lack of a constant
interchange of air, although it forms a very valuable adjunct, especially in
the removal of organic particles which do not follow the law of diffusion.
5. An exit should be provided for impure air, as well as an entrance for
pure air. The chimney furnishes this in most living-rooms, and diminishes
the necessity for other means of exit.
If the openings in a room for entrance and exit are properly regulated, a
rate of 5 feet per second (about 3½ miles per hour) will provide sufficient
air without any unpleasant draught in a room. For instance, if the opening
measure 1 square foot, then a rate of 5 feet per second will give five cubic
feet of air per second, that is, 18,000 cubic feet per hour. But as only 3,000
cubic feet are required, it follows that an opening one-sixth this size, i.e. 24
square inches, is sufficient for each individual. Reckoning the same amount
for means of exit, 48 square inches is the size of the ventilating orifices
required by each individual.
6. A number of small divided openings are not collectively equal in
ventilating power to one large one having the same area. Thus, when a
ventilating orifice is divided into four parts, which have the same collective
area as the original orifice, it is found that only half as much air passes
through these as through the original orifice. In order to obtain as much air,
therefore, each opening must be equal in size to half the original opening.
This is in accordance with the rule that the friction for air passing through

openings is inversely to the diameter of these openings, i.e. inversely to the
square-root of the area of the openings.
7. The most important requirements of perfect ventilation may be
recapitulated as follows:—
1st. The maximum impurity of air vitiated by respiration should not
exceed 6 parts carbonic acid per 10,000 volumes.
2nd. To ensure the maintenance of this standard, 3,000 cubic feet of pure
air must be supplied per head per hour.
3rd. In order to supply this amount of pure air, with ordinary means of
ventilation, 1,000 cubic feet at least must be allowed per head in buildings
always occupied.

CHAPTER XXI.
PROBLEMS AS TO VENTILATION.
The following formula enables many problems relating to ventilation to
be solved. Let p = the amount of poison (carbonic acid) in every cubic foot
of fresh air, viz. ·0004 cubic foot. Let A = the number of cubic feet of fresh
air delivered or available, P = the amount of carbonic acid exhaled, and x =
the amount of carbonic acid per cubic foot in the room at the end of a given
time. Then—
x = p + P ∕ A, whence A = P ∕ (x - p).
If the carbonic acid in the air of a room is ·75 per 1,000 volumes (that in the outer air being ·4 per
1,000 volumes), and there are five persons in the room, how much air is entering the room per hour?

Here x = ·00075.
p = ·0004.
P = ·6 (i.e. number of cubic feet of carbonic acid expired by each person per
hour).
Now x = p + P ∕ A.
·00075 = ·0004 + ·6 ∕ A.

Therefore A = about 1,700.
Thus 1,700 cubic feet are required for each individual to keep the air within the given limit, and
five times this amount will be required for five persons = 8,500 cubic feet.
A room has been occupied for one hour, at the end of which the total carbonic acid present was
found to be 1·1 per 1,000 parts. The carbonic acid in the open air amounting to ·0004 per cubic foot,
find the quantity of air supplied per hour.

Here x = ·0011.
p = ·0004 and P = ·6.
Hence ·0011 = ·0004 + ·6 ∕ A.
Therefore A = 857 cubic feet.

If six persons are in a room containing 3,000 cubic feet, and there is a supply of 2,000 cubic feet of
air per head per hour; how much carbonic acid is there in the air of the room at the end of 4 hours?

Here p = ·0004.
P = ·6 × 6 × 4 = 14·4.
A = 2,000 × 6 × 4 + 3,000 = 51,000.
x = ·004 + 14·4 ∕ 51,000 = ·000682 = 6·82 parts CO₂ in 10,000 of air.

The air of a room occupied by 6 persons and containing 5,000 cubic feet of space, yields 7·5 parts
of CO₂ per 10,000 parts of air. How much air is being supplied per hour?
A = P ∕ (x - p) = ·6 x 6/(·00075 - ·0004) = 10,280 cubic feet.
In the same room what would be the condition of the air at the end of 4 hours?
x = ·0001 + ·6 × 6 × 4/(10280 × 4 + 5,000)
= ·0004 + 14·4 ∕ 46,120 = ·000712 = 7·12 of CO₂ in 10,000 of air.
Given two sleeping rooms, Y 10 ft. by 15 ft. and 10 ft. high, Z 15 ft. by 20 ft. and 12 ft. high, with
three adults in each; how much fresh air would you supply in each? What would be the condition of
the air of each of the rooms after, ¼;, ½, 1, and 2 hours respectively?
Amount of fresh air to be supplied in Y—
A = P ∕ (x - p) = ·6 × 3/(·0005 - ·0004) = 9,000 cubic feet per hour.
Condition of air in Y after ¼ hour—
Here p = ·0004.
P = ·6 × 3 ∕ 4= ·45.
A = 9,000 ∕ 4 + 1,500 = 3,750.
x = ·0004 + ·45 ∕ 3,750 = ·00052.
At the end of 2 hours—
x = ·0004 + 3·6∕(18,000 + 1,500) = ·000584.
And similarly for Z.
Suppose two rooms, one 10 feet cube, the other 50 feet by 20 feet and 15 feet high, have
continuously admitted into each of them a volume of fresh air containing ·04 parts carbonic acid per
100 parts, amounting to 2,000 cubic feet per hour, so as to replace to that extent the air of the room;
suppose also that an average adult be placed in each room: show by detailed calculation what would
be the condition of impurity of air in each room, as measured by carbonic acid, at the end of 4 hours
and 12 hours respectively.
In the case of the first room—

P = ·6 × 4 = 2·4.
A = 2,000 × 4 + 1,000 = 9,000.
p = ·0004.
x = ·0004 + 2·4 ∕ 9,000 = ·000667.

The amount of impurity at the end of 12 hours, and in the second room may be similarly
ascertained.

Ventilation in relation to Temperature.—The temperature of a given
atmosphere is a most important factor in determining the ease with which it
is replenished from the external air. Speaking generally, the greater the
difference between the temperature of two masses of air the more rapidly an
interchange occurs.

Air has weight. A column of it one inch square and extending to the
uppermost limit of the atmosphere weighs about 14·6 lbs., and exerts this
pressure on all substances at the surface of the earth. This pressure is
exerted uniformly in all directions; but for this fact our chests would be
crushed in by the external pressure on them, which amounts to over four
tons. If the atmospheric pressure is diminished at any point, it is evident that
the surrounding air will tend to press in this direction. Now, when air is
heated it expands, and consequently the heavier fresh air flows in from all
sides and pushes the lighter air upwards.
The expansion of air for every increase of 1° Cent. is ·003665 (1 ∕ 273), for every increase of 1°
Fahr. is ·00203 (1 ∕ 492). Thus if the air in a room is 20° F. warmer than that outside, it will be
expanded to 1 ∕ 25 additional bulk.

Thus if M = volume of a given air at 32°, with the barometer at 30 inches, and
M1 = volume at temperature t° above 32°, while a = co-efficient of expansion for each degree of
elevation of temperature, then the dilatation effected by heat will be expressed by the formula—
M1 = M (1 + at).

When the temperature is decreasing
M1 = M (1-at).

If the air in a chimney flue is cooler than the air of the room with which it communicates, it will
flow down into the room. It is the object of an economical fire-place to cause the chimney to act as
an outlet for the products of combustion and for the impurities of the air of the room with the
smallest possible waste of heat. Short of producing a down draught of cold air and smoke, the smaller
the difference between the temperature of the air of a room and of the air escaping near the top of the
chimney, the greater the economy of fuel.
The movement of air in flues and other outlets is governed by general laws, like those governing
the general movements of fluids, but allowances require to be made for friction in the channels of
entrance and outlet.
The theoretical velocity, when friction is not taken into account, may be calculated by a formula
based on what is known as the law of Montgolfier, or the law of spouting fluids. According to this
law, fluids pass through an opening in a partition with the same velocity as a body would attain in
falling through a height equal to the difference in depth of the fluid on the two sides of the partition,
i.e. to the difference of pressure on the two sides. Thus, if AB equals the height of a column of air at,
say, 50° F., and AC is the height of the same quantity of air heated to 60°, then the velocity with
which the warmer air ascends will be that which a body would acquire in falling from C to B.
Now the velocity in feet per second of falling bodies is about eight times the square root of the
height from which they have fallen; and the formula for determining this is—
v = c √(2gh) = 8·2c √h.

g = 32·17 feet per second;
h = distance fallen through by the body;
c = a constant determined by experiment, and expressing the proportion
of the actual to the theoretical velocity.

Adapting this formula to the special circumstances under which Montgolfier’s formula
holds, we find that the force which drives the warm air up the flue is the force of gravity, i.e.
of the excess of the weight of a column of cold air over the weight of a column of warm air
of exactly the same size (represented by BC in the preceding diagram). The difference of the
two weights or pressures is found by multiplying the distance from the point of escape of
heated air out of the room (fire-place or elsewhere) to the point of escape into the outer air
(top of chimney or other point of exit), by the difference in temperature inside and outside,
and again multiplying this product by 1 ∕ 492 for degrees of Fahrenheit temperature, or
1∕
273 for degrees Centigrade.
Thus omitting c for the present, we have—

v = √(2gh(t - t1)/492) = 8·2√(h(t - t1)/492)
Where t = temperature in the chimney,
t1 = temperature of the external air, and
h = height of chimney.
Example.—The chief means of ventilating a given room is by its open fire-place. The temperature
in the chimney is 100° F., that of the external air 40°, and the height of the chimney 50 feet; what is
the velocity with which air is leaving the room?

v = 8·2 √((100 - 40) × 50 ∕ 492)
= 20.
This gives the theoretical velocity, but the real velocity will differ from the theoretical by an
amount varying from 20 to 50 per cent.
It will be evident, from what has been said, that the movements of the air in a confined space are
dependent upon (1) the difference between the internal and external temperatures; (2) the area and
friction at the apertures through which air enters and leaves the room; and (3) the height of the
column of ascending warm air. The higher the chimney (assuming it to contain warm air), the greater
the draught and the more efficient the ventilation of the room communicating with it. Hence
ventilation is more difficult in upper rooms of large houses and in single-storeyed houses than in the
lower storeys of large houses.
Allowance for Friction.—Practically the friction varies greatly according to the size, form, and
material of outlet for air. A rough or sooty or angular chimney greatly impedes the outgoing current
of air.
It is usual to reduce the theoretical velocity by 20 to 50 per cent. Apart from the friction which is
governed by roughness and length of channels, that due to bends in the channel may be calculated by
the formula 1/(1-sin2 θ), θ being the angle at any bend in this channel.
(It may be convenient to note that—

sin2 90° = 1,
sin2 60° = ¾
sin2 45° = ½,
sin2 30° = ¼.)

Thus every right angle in a bent shaft reduces the velocity in it by one-half.
The loss by friction in two similar tubes of equal sectional area varies (1) directly with the square
of the velocity of the air currents; and (2) directly with the length of the outlet channel. In two similar
tubes of unequal size the loss by friction is (3) inversely as the diameter of the cross-section in each.
When two tubes are of different shapes, the loss by friction is inversely as the square roots of the
sectional areas.
Owing to the variable value of the co-efficient of friction (called c in the first formula given), it is
usually preferable to measure the actual rate of progress of air through a given flue by means of an
anemometer (wind measure). Then the velocity of the current of air and the area of the cross section
of the flue being given, the volume of air discharged in a given time is represented by the product of
these two and the time which has elapsed.
Thus, q = a × v.
Where q = quantity of air discharged in a given time, a = area of cross section of flue, v = velocity
of current.
By means of this formula, the area of chimney required to discharge a given volume of air at a
given average velocity can be ascertained. Thus—
a = q ∕ v.
The application of the preceding principles and formulæ will be rendered clearer by the following
examples.
How much inlet and outlet area per head will be required to give 10 persons in a room of 5,000
cubic feet capacity, 2,000 cubic feet of air per head per hour, supposing that the outside temperature
is 40°, while the internal temperature is 60°, and the height of the heated column of air 20 feet?
First ascertain the velocity of entrance and exit of air.

v = 8·2√(h(t - t1)/492)
= 8·2√(20(60 - 40)/492) = 8·2 × ·902.
= 7·3964 = velocity in feet per second.
If we allow one-fourth for friction, then there remains a velocity of 5·5473 feet per second.
5·5473 feet per second = 19700·8 feet per hour.

Now, a = q ∕ v

= 2,000 ∕ 19700·8 = ·1015 square feet.

= 14·6 square inches.

Thus the size of the outlet required per head is 14·6 square inches. The size of the room and the
number occupying it do not enter into the question, except for a short time at the beginning. (See
page 135.)
The amount of inlet required will also be 14·6 square inches per head. Theoretically it ought to be
slightly less than that required for outlet, as the outgoing air is more expanded than that entering the
room; but practically no allowance need be made for this fact.
The total amount of inlet and outlet required per head = 29·2 square inches.
If the mean temperature of a room is 61°, the external temperature 45°, while the heated column of
air is 50 feet, and the required delivery of air 2,000 cubic feet per hour, find the size of inlet and
outlet.

v = 8·2√(h(t - t1) ∕ 492)
= 8·2√(50(61 - 45) ∕ 492)
= 10·55 feet per second.
= 37,980 feet per hour.
If we make no allowance for friction, then
a=q ∕ v
= 2,000 ∕ 37,980 square feet.
= 2,000 × 144 ∕ 37,980 = 7·58 square inches.
This gives the required size of outlet. The size of inlet and outlet together = 15·16 square inches.
If 3,000 cubic feet of air are supplied in one hour through an aperture of 12 square inches to a
room containing 1,000 cubic feet of space, at what rate does the air enter the room?

12 square inches = 1 ∕ 12 square foot.
a=q ∕ v
1 ∕ = 3,000 ∕ v
12
Therefore
v = 36,000 feet per hour.
= 10 feet per second.
If a room is supplied with 3,000 cubic feet of air per hour, through a single opening, what must be
its area, if the rate of movement of the air is 5 feet per second?
5 feet per second = 18,000 feet per hour.
a = 3000 ∕ 18000 = 1 ∕ 6 square foot.
= 24 square inches.
As already stated, the difficulties connected with the estimation of amount of friction greatly
detract from the practical value of the formulæ just given. Even the results given by anemometers are
not always trustworthy, but by comparing the results given by them with those obtained by the use of
Montgolfier’s formula an approximation to the truth can be obtained.
The ordinary anemometer consists of four tiny vanes fixed to a spindle, so that revolutions are
caused by the current of air the velocity of which is to be measured. The revolutions are counted by a
mechanical arrangement. The value of the revolutions of the vanes has to be first determined by
direct experiment; a known bulk of air being forced through a channel of known size at a uniform

rate, and the instrument graduated accordingly. In Fletcher’s anemometer a modification of the
manometer or pressure-gauge has been used for the same purpose.
Inlets and Outlets.—Having given the average velocity of the wind, the size of a room, and the
number of persons occupying it, the size of inlet opening required can easily be calculated.
Find the size of inlet for air in a room occupied by one person, the air moving at the average
velocity of 5 feet per second, assuming that 3,000 cubic feet of air are to be supplied per hour.
Let x = size of inlet.
Then x × 60 × 60 × 5 = 3,000.
Therefore x = 3000 ∕ 18000 = 1 ∕ 6 square foot.
= 24 square inches.
Given that the air moves at a velocity of 10 feet per second, and that the area of the inlet aperture
into a room is 12 square inches, find how much air enters the room in an hour.
Let y = amount of air.
Then 10 × 60 × 60 × 12 ∕ 144 = y.
Therefore y = 3,000 cubic feet of air.
Calculations as to supply of air in a room founded on the average velocity of air-currents are,
however, much less trustworthy than when the velocity is determined, as previously explained, by
means of Montgolfier’s formula, or, better still, by an anemometer.
The Commissioners on Improving the Sanitary Condition of Barracks and Hospitals, in their report
(1861) recommended for inlets, one square inch for every 60 cubic feet in the contents of the room;
or one square inch for every 120 cubic feet in the contents, if warm air is admitted round the fire-
grate. For outlet shafts on lower floors, one square inch to every 60 cubic feet, slightly increasing for
the higher storeys.

Amount of Air-space required.—We may take 3,000 cubic feet of air as
the average amount of air required hourly by each individual, and inasmuch
as the air of a room cannot be changed oftener than three times an hour
without producing an unpleasant draught, it follows that at least 1,000 cubic
feet of space must be allowed per person.
This may be compared with the amount actually supplied under various circumstances.

In the British Army for each soldier—
In permanent barracks 600 cubic ft.
In wooden huts 400 „
In hospital wards at home 1,200 „
In hospital wards in the tropics 1,500 „
In general hospitals 1,000-1,500 „
In fever hospitals 2,000-3,000 „
In workhouse hospitals 850-1,200 „
In common lodging houses 300 or 350 „
Do., if occupied night and day 350 or 400 „

In workhouses 300 „
In schools—
London School Board requires per scholar 130 „
English Educational Code per scholar (minimum), in old schools 80 „
Do., in new schools 120 „

Floor-space has an important bearing on ventilation. In calculating the available cubic space of a
room, the height over 12 feet should be disregarded. Thus, if 500 cubic feet is allowed for each
individual, the floor-space should be 42 square feet. In barracks, soldiers are allowed 50 square feet
of floor-space.
In the Government regulations for workhouses it is stated that there must not be more than two
rows of beds, and that the height of rooms above 12 feet must not be reckoned. This gives a
minimum floor-space of 25 square feet per occupant, or with dormitories 17 feet wide, a bed-space of
about 3 feet.
In hospitals, the question of floor-space is extremely important, as it regulates the distance between
the sick inmates and the convenience of nursing. Assuming each bed to be 3 feet wide and 6½ feet
long, the distance between any two beds should be at least 5 feet. This makes the wall-space for each
bed 8 feet long, and allows from 80 to 96 square feet of floor-space per bed. At St. Thomas’s
Hospital, London, the floor-space is 112 square feet, and in fever hospitals it is from 150 to 300
square feet per bed. In regard to the ventilation of hospitals, it has been well said that nothing less
than too much is enough.
Means of ascertaining Cubic Space.—Circumference of a circle = Diameter (D) × 3.1416.

Area of circle = D2 × .7854.
Area of square = square of one of its sides.
Area of rectangle = product of two adjacent sides.
Area of triangle = base × ½ height, or height × ½ base.
Area of ellipse = product of the two diameters × ·7854.
Circumference of ellipse = half the sum of the two diameters × 3·1416.
Area of any polygon found by dividing into triangles, and taking the sum of their areas.
Cubic capacity of a cube found by multiplying the three dimensions together.
Cubic capacity of a cylinder = area of base × height.
Cubic capacity of a cone or pyramid = area of base × 1 ∕ 3 height.
Cubic capacity of a dome = area of base (circle) x 2 ∕ 3 height.
Cubic capacity of a sphere = D3 x ·5236.
Area of segment of a circle found by adding to ⅔ of product of chord and height, the cube of
the height divided by twice the chord.

(Ch x H x ⅔) + H3 ∕ (2 Ch)
Give the dimensions of a circular ward for 12 patients, each to have 1,750 cubic feet of available
air-space.
Capacity of ward = 1,750 X 12 = 21,000 cubic feet.
If we allow 120 square feet floor-space for each patient, then the total floor-space will be 1,440
square feet. Consequently the height of the ward = 21000 ∕ 1440 = 14·75 feet.

Area of circle = D2 x ·7854.
1,440 ∕ ·7854 = D2.
Therefore D = 43·2 feet.
Circumference of circle = D x 3·1416.
= 43·2 x 3·1416.
= 135·7 feet.

The dimensions of the circular ward required are therefore a height of 14·75 feet, diameter of 43·2
feet, and circumference of 135·7 feet.
Find the cubic capacity of a circular hospital ward 28 feet in diameter, 10 feet high, and with a
dome-shaped roof 5 feet high.

Area of floor-space = D2 x ·7854.
= 614·8 square feet.
Cubic capacity of the cylinder below the dome is 614·8 x 10 = 6,148 cubic feet.
Cubic capacity of dome = 614·8 x ⅔ x 5 = 2049·3 cubic feet.
Total cubic capacity of the ward = 8197·3 cubic feet.

In practical measurements of rooms, deductions must be made from the cubic space for the
furniture contained in it and for its inmates. About 10 cubic feet ought to be allowed for each bed and
bedding, and 2½ to 4 cubic feet for each individual. Projecting surfaces must be allowed for by
subtraction, and recesses by addition.
A circular ward with a diameter of 36 feet has a dome-shaped roof, the height of whose centre is
18 feet. The height to the dome is 12 feet. Find the floor-space and total cubic contents. How many
patients ought the ward to accommodate?

Area of floor-space = (36)2 x ·7854.
= 1017·8784 square feet.
Cubic capacity of cylinder below dome = 1017·87 x 12 = 12214·5 cubic feet.
Cubic capacity of dome = 1017·87 x ⅔ x 6 = 4071·48 cubic feet.
Total cubic capacity of the ward = 16285·98 cubic feet.

Assuming that 1,500 cubic feet are required for each patient, then the ward is large enough for 10
patients. It is well to test this conclusion by calculating whether sufficient floor-space has been
allowed for each patient. The floor-space has been found to be about 1,018 square feet, which would
give 100 feet for each of 10 patients and more than the minimum standard previously stated.
What number of people should be allowed to sleep in a dormitory 40 feet long, of which the
accompanying sketch is a section?
The cubic capacity of the quadrilateral space below the roof = 16 x 9 x 40 = 5,760 cubic feet.
Area of floor = area of base of roof = 40 x 10 = 640 square feet.

Cubic capacity of roof = 640 x ⅓(13 - 9).
= 853·3 cubic feet.
Total cubic capacity of dormitory = 6613·3 cubic feet.

If we take the low standard of common lodging houses
and allow 350 cubic feet of space for each inmate, then
18 persons may be allowed to sleep in the dormitory.
How much space would a man occupy supposing him
to weigh 175 lbs.? How much is usually allowed for a
man with his clothes, bed and bedding?
The space occupied by a man is stated by Parkes to be
from 2½ to 4 cubic feet (say 3 for the average). He gives
the following rule: The weight of a man in stones divided
by 4 gives the cubic feet he occupies. Thus, a man
weighing 175 lbs. would occupy 3⅛ cubic feet of space.
About 10 additional cubic feet must be allowed for
clothing, bedding, and bed for each person.
What size of inlet and outlet aperture should be allowed per head? How large should each
individual inlet be made? If an inlet aperture 100 square inches in area is divided into four, with
apertures of 25 square inches each, what is the loss by friction?
A size of 24 square inches per head for inlet and the same for outlet meets common conditions.
It is desirable to make each individual inlet not larger than 48 to 60 square inches in area, i.e. large
enough for two or three men; and each outlet not larger than one square foot, or enough for six men
(Parkes). This ensures more uniform diffusion of the air throughout a room. On the other hand, the
loss by friction is greatly increased by having a number of small openings instead of one large
opening. This loss is inversely to the square roots of the respective areas. Thus the square root of 100
is 10; the sum of the square roots of the four apertures of 25 square inches each is 20. The loss by
friction is double in the second case what it was in the undivided opening. It is evident, therefore, that
in order to get as much air through the four openings as through the original large opening, each must
be equal in size to half the original opening.
Why is ventilation more difficult in upper rooms of large houses and in single-storied houses than
in the lower storeys of large houses?
Cold external air being heavier than the internal warm air presses downwards to the lowest point,
and pushes up the warmer air. If there were a vacuum in the room, air would rush into it with a
velocity which, as seen before, is represented by the formula—
v = √(gs).
Where g = 32, s = height of column of air, which we may take as roughly 5 miles.
From this formula we obtain v = 1,306 feet per second.
It is evident that in such a case the velocity of entry of air into a vacuum on the ground floor would
be greater than into a vacuum on any of the higher storeys, owing to the greater velocity acquired
through the increased action of gravity.
And the same increased facility of entry of air into lower rooms must hold good under ordinary
circumstances, inasmuch as by Montgolfier’s formula (which is founded on the fundamental formula
v = √2(gs))

v = √2(gh(t-t1) ∕ 492)

h = distance between top of chimney and floor of room in question, and thus the velocity with
which air enters is governed by the difference between the internal and external temperature, and the
height from which the cold air descends in order to take the place of the air which has escaped.

CHAPTER XXII.
METHODS OF VENTILATION.
In most houses no special means of ventilation are provided, windows,
doors and fire-places being trusted for ensuring a sufficient supply of fresh
air. These do not suffice in well-built houses, unless the inhabitants train
themselves into enduring the currents of air necessarily associated with
open windows and doors. They are, however, aided in the majority of
houses by the porosity of walls, by currents of air through crevices of
wood-work, and so on. It is desirable that adequate special provision for
ventilation should be made for every house when it is built, and that as
much care and forethought should be exercised in this respect as in the
laying on of a water-supply or sanitary appliances connected with drainage.
Whatever the system of ventilation adopted, it is wise to flush rooms
frequently with fresh air. This is best effected by throwing the windows
wide open whenever a room is left unoccupied. In this way a much more
thorough and complete purification is effected than by any other means.
This is especially important in the case of bedrooms, in which organic
impurities are most prone to accumulate.
Not only should rooms be ventilated, but likewise the furniture they
contain. This again is most important for bedrooms. Beds should not be
“made” till sometime after using; and in the interval, should be freely
exposed to the air. The same applies to night apparel.
It is well to allow rooms to lie fallow at intervals. Organic matter
accumulates about a room, and devitalises any air which enters. If the room
is vacated, and flushed with air for a continuous period, it becomes sweeter
and purer. The importance of this is now well recognised in the case of
hospital wards. Such temporary disuse of rooms must not, however, be
regarded as sufficient without thorough cleansing of every surface in them,
in order effectively to remove all organic and other dust.

An Inlet and Outlet for air should both be provided. According to some
an inlet only is required, while others would only provide an outlet; but a
perfect system of ventilation requires both. As heated air expands, the
outlets should theoretically be larger than the inlets; but as the average
difference of temperature is only 10°-15° Fahr., the expansion is only slight,
and may be practically neglected.
The necessity for both inlets and outlets may be illustrated by a single
apparatus like that shown in Fig. 11. A taper is burning at the bottom of the
jar, in the stopper of which two tubes, A and B, are placed. So long as both
tubes are kept open the candle will keep alight, but if A be blocked, the
candle goes out.
Inlets should bring air from a pure source,
and should be arranged at intervals in large
rooms. Externally, inlets should be protected
from the wind; and the shorter the inlet tubes
the better, as thus a current is ensured, and
they can be easily cleaned. The position of
inlets should not be too near the outlets,
otherwise the fresh air may escape
immediately. The best position for inlets is at
the floor, but this necessitates warming the
entering air, as otherwise it would be
intolerable, except in summer time. If the air
cannot be warmed, it should he admitted
about seven feet above the floor, and directed
upwards. For size of inlets, see page 142.
Fig. 11.
Outlets, under ordinary circumstances, are Illustrating Necessity of Inlet and
best placed near the ceiling. They should be Outlet.
enclosed as far as possible within walls, so as
to prevent the outgoing air being cooled; and should have smooth walls,
reducing friction to a minimum. Where artificial warmth increases the
temperature of the air, the discharge of outlets is much more certain and
constant. The chimney with an open fire forms one of the best outlets. Gas,
again, may be made to heat an outlet tube, which carries off the products of
combustion.

Two forms of ventilation are usually described—natural and artificial.
The former term is used to describe any plan not requiring heating
apparatus or the motive power of steam, or gas, or electricity, while the
latter implies the use of some such motive power or source of heat.
Obviously, however, there is no sharp line of demarcation between the two.
A lighted fire is strictly an artificial plan of ventilation, but inasmuch as no
apparatus intended for ventilating purposes is required, it is hardly a means
of artificial ventilation.
Natural Ventilation.—The most important means of natural ventilation
are the window and the chimney; but openings in outer walls and over the
door may form valuable adjuncts.
The Window is perhaps the most important agent in purifying a room—
both the light and air it admits being essential for health. The window is
invaluable (1) for flushing the room with fresh air at intervals. Where
possible, opposite windows should be opened, or window and door. Cross-
ventilation by opposite windows open at the top forms one of the best
means of natural ventilation, in large rooms, such as school-rooms. This
can, as a rule, be borne without discomfort, while the room is occupied,
unless the wind is very high.
(2) The Upper Segment of a window may be made to work inwards on a
hinge, and turned so that the current of air may be upwards. Where this plan
is adopted, triangular pieces of glass should be placed at the two sides to
prevent cold air from falling directly down at the sides of the opening.
(3) A Block of Wood, two or three inches wide, may be inserted at the
bottom of the window sash at A (Fig. 12), and then the window pulled
down on this. The consequence is that air is admitted between the two
sashes at B, its current being necessarily directed upwards (Fig. 12). This
plan answers admirably in admitting pure air; but it possesses a
disadvantage common to all the plans in which external air much colder
than the internal is admitted into a room. The current of cold air passes
upwards for some distance, but may then fall down on the heads of those
occupying the room.
(4) The top sash of the window may be opened, and some zinc gauze
fastened across the open part. This is practically the same as the last

arrangement, except that the air is admitted through
the apertures of the zinc, and the amount admitted is
greatly diminished (page 136).
(5) In Louvre Ventilators, a number of parallel
pieces of glass, each directed upwards, are substituted
for a pane of glass. They may be fixed or made
movable, as in Moore’s ventilator. The incoming
current of air may be similarly directed upwards, in an
open window, by arranging Venetian blinds with the
laths inclined upwards.
Fig. 12.
Window Ventilation. (6) In windows that will not open, Cooper’s
Ventilators are often used. Each of these consists of a
circular disc of glass, having five oval apertures in it, which works on a
pivot through its centre, close in front of one of the panes of a window,
which has five similar holes pierced in it. Consequently, when the disc is
turned, so that its holes are opposite those of the window, fresh air is
admitted. The amount thus admitted is necessarily small.
The Chimney forms the best means of escape of foul air. No room ought
to be built without a fire-place, which should never subsequently be
boarded up. In bedrooms the chimney forms a most important means of
ventilation. If there is no fire, the chimney occasionally furnishes an
undesirable source of air; but as a rule the current is upwards, owing to the
aspirating action of winds at the top of the chimney. The downfall of air
from a chimney chiefly occurs when there is an insufficient inlet for pure
air. This is the explanation of smoky chimneys in nine cases out of ten;
then the cure is easy by laying on a pipe from the outside of the house to the
hearth. When the smoky chimney is due to the contiguity of higher
buildings, the chimney must be raised, or a cowl placed over it.
(1) The action of the chimney in carrying impure air away from the room
may be considerably increased by narrowing the two ends, so as to
produce a more rapid current at the entrance and exit of air.
(2) The heat of the chimney may be utilised by having a separate
smaller flue alongside it, with openings from the rooms on each floor. The
air in this being heated aspirates the air from each room in succession.

Openings may be made into the chimney-flue at a higher point than the
fire-place. These are very valuable for carrying off the heated and impure
air resulting from the combustion of gas, as well as for carrying off the
respiratory products, which, in their warmed condition, tend to rise towards
the ceiling.
(3) Dr. Neil Arnott first devised a valve for this purpose. An opening
being made through the upper part of the wall into the chimney, an iron box
was inserted, in which was placed a light metal valve capable of swinging
towards the chimney flue, but not towards the room. The objections to this
apparatus are that it is apt to make irregular clicking noises, and to admit
blacks from the chimney when out of order.
(3) In Boyle’s Valve these objections are partially obviated. It consists of
an iron frame, across which lie iron rods; and from these are suspended thin
talc plates, only capable of moving in the direction of the chimney (Fig.
13). Even this apparatus is rather noisy when there is a strong wind.
Neither of these plans answers so
well as a second flue alongside the
chimney flue, communicating with
each room near its ceiling; but the
latter can only be arranged for when
the house is built, while the valves
may be inserted at any time. View from room. View from chimney.
Fig. 13.
Boyle’s Mica Flap Ventilator.
The Ceiling may be utilised for
removing foul air; and thus serve to
diminish the draught which is often produced by the currents of air towards
the chimney, when this forms the only means of outlet.
In large rooms (1) a sunlight gas-burner forms an important means of
ventilation. It causes a strong up-current from every part of the room. If
there is a fire in the room, the burner is apt to become an inlet for air, or the
chimney to smoke, according to the relative strength of the two currents.
(2) Benham’s and other forms of Ventilating Gas Burners serve the
same purpose. In each of them the products of combustion are conveyed by
special ducts above the ceiling to the outer air.

(3) McKinnell’s Ventilator is useful in single-storied buildings, like
certain barracks. It consists of two tubes encircling one another, the inner
forming an outlet tube, because the casing of the outer tube maintains the
temperature of the air in it. It is made higher than the outer tube, and is
protected by a hood. The outer tube forms the inlet for fresh air. The
entering air is thrown up towards the ceiling and then to the walls by a
flange placed at the bottom of the inner tube. The air after traversing the
room, and becoming heated, passes upwards to the inner tube. When doors
and windows are open, both tubes become outlets; if there is a fire in the
room, they may both become inlets; but this may be prevented by closing
the outlet tube.
(4) Various other means have been
devised for carrying foul air from the
ceiling through channels between the
ceiling and the floor of the room above.
All share the disadvantage that the
channels become dirty and are difficult or
impossible of access for cleaning.
(5) Various cowls connected by metal
tubes with the ceilings of rooms have
been placed on roofs, and their aspirating
effect used in ventilating these rooms.
When a room is furnished with a chimney
such cowls are most undesirable. In large
rooms without a fire-place they are
helpful, but much more confidence can be
placed in cross-ventilation by hinged
Fig. 14.
McKinnell’s Roof Ventilator.
windows. It is doubtful if any of the
advertised fixed cowls produce materially
greater aspiration of air from rooms than a
simple open tube of the same size. It is desirable that the tube should be
protected at its upper end against the entry of rain, and that a grating should
be provided to prevent birds building their nests in the tube.
In the preceding plans of ventilation, the ceiling serves almost entirely as
an outlet for impure air. In the following plan, it is used as an inlet for pure

air.
(6) In Sylvester’s Method of Ventilation, the perflating force of the
wind is employed to produce an abundant entry of fresh air. A cowl is
placed, always turning towards the wind; the air received is conducted to
the basement, where it is warmed by a stove or hot-water pipes, and then
passed through tubes into the upper rooms. From these it is carried by tubes
above the roof, these tubes being covered with cowls turning from the wind,
so that in this way the aspirating power of the wind is likewise used.
Ships are often ventilated in a somewhat similar manner. The tube to
which a windward cowl is attached above, ought to be bent at right angles,
so as to lessen the velocity of the entering air. By covering other air-shafts
with movable cowls, turning from the wind, the aspirating action of the
wind is brought into action to aid the escape of foul air.
The Walls of a room, unless covered with an impervious material, are
constantly traversed by gentle currents of air, which play an important part
in the ventilation of rooms. Special apertures may be made to furnish a freer
supply, and these may be in various forms.
(1) A Simple Grating, may be inserted; but this is apt to become blocked
with dirt, and does not allow a large amount of air to enter. Louvred
openings in the walls are objectionable, except for very large rooms.
(2) Sheringham’s Valve is the most convenient means of ventilating
through the wall. An opening in the external wall is made by a ventilating
brick or grating; into the wall is fixed an iron box, which has in front of it
an iron valve hinged along its lower edge, so that it can open towards the
room. On the sides of the valve cheeks are attached, which fit into the box
when the valve is shut. A heavy piece of iron pressing against the valve
from within the box, tends to keep it constantly open. By means of a string
and pulley, the valve can be opened or closed at will, or fixed in any
intermediate position.
In a very large room, it is better to have several medium-sized valves,
than a few larger ones, the air being thus more completely diffused. If there
are two valves, they should not be opposite one another, as the air may then
simply pass from one to the other, without becoming diffused through the

room. If there is only one valve, it may
occasionally serve as an outlet when the
wind is to leeward. By means of this form
of valve, the air is projected upwards in a
diverging current towards the ceiling. The
valve should be placed above the level of
Fig 15.
one’s head, but not too near the ceiling; as Sheringham’s Ventilator
in the latter case, the current of air is
driven hard against the ceiling, and falls
thence with considerable force towards the floor. A combination of
Sheringham’s inlet and Boyle’s mica outlet into the chimney at the opposite
side of the room ensures efficient ventilation in a dining-room. Better than
the outlet into the chimney is an opening into a special flue alongside the
chimney-flue, if this be available.
(4) Ellison’s Inlet consists of a brick pierced with conical holes, the apex
of the cone being towards the external air. By this means any great draught
is avoided, and the air is distributed over a considerable area. In order that
this may prove an efficient means of ventilation, a considerable number of
bricks are required.
The Floor of a room is always the source of considerable currents of air,
even when well carpeted. Air mounts up through the crevices of the wood-
work, being aspirated into the room when its temperature is higher than that
of the rooms below. In the case of rooms on the ground floor, air is often
drawn from the subjacent soil, or through dust-bins, etc.
Theoretically, in all measures of ventilation, the floor would be the best
point for the entry of cold air. This, however, is intolerable when the
incoming air is cold, and the floor must therefore be abandoned as a means
of ventilation, apart from heating apparatus.
The floor may be used as a means of entry of fresh air in a modified
manner, by directing the air entering at the floor-level for some distance up
a tube at the side of the wall. This apparatus is known as Tobin’s tube. It
consists of a rectangular or cylindrical tube from 4 to 6 feet high, which
communicates at the lowest point with the external air by means of a
perforated brick or grating. The air enters the room in an upward direction,

and is consequently sent towards the ceiling, where it becomes mixed with
warmer air, before diffusing itself throughout the room. But when the
incoming air is very cold, it may fall more rapidly, causing cold draughts on
the heads of those in the room.
As the air enters directly from outside the house, it often carries with it
particles of dirt, soot, etc. This may be remedied by placing a pan
containing a shallow layer of water at the lowest part of the tube, or by
placing cotton wool at the point of entry of the tube into the room. The tray
of water soon dries up and is rarely replaced, while the cotton wool
diminishes the amount of entering air. It is very useful however in cold
weather, or when fogs occur. A gauze funnel is sometimes inserted in the
tube, or a sheet of gauze arranged diagonally across the tube from its
highest to its lowest point. The gauze does not keep out minuter particles of
dust, and requires occasional cleaning. All Tobin’s tubes, like other
ventilating openings, should be made to open, so that their interior can be
frequently cleaned.
Summary as to Domestic Ventilation.—Open windows, doors, and fire-
places may be in most instances trusted. If gas is used as an illuminant, they
should be combined with special arrangements for carrying off the products
of combustion from the room. For delicate people, and especially in small
rooms, outlet ventilation into the chimney breast combined with a
Sheringham’s valve on the opposite wall is desirable.
Artificial Ventilation.—Artificial ventilation may include two important
and very different measures. In one of them currents of air and an exchange
of pure for impure air are effected by means of various forms of heating
apparatus. In the other mechanical measures are used for the same purpose,
—the air being either driven out of the room or drawn out of it. In this
chapter we shall consider only the mechanical means of artificial
ventilation. There are two kinds, the first being known as ventilation by
aspiration, or the vacuum system; and the second as ventilation by
propulsion, or the plenum system.
In Ventilation by Aspiration the foul air is drawn out of the room by
machinery, its place being supplied by fresh air, which may be warmed

before entry or not. This plan and the next have been employed chiefly in
connection with large buildings, such as hospitals, etc., and in mines.
The extraction of foul air may be effected by—(1) a steam-jet, which is
allowed to pass into a chimney, and sets in motion a body of air more than
200 times its own bulk. Tubes from each room of the building are
connected with this chimney, and the strong upward current extracts the air
from them. This plan is useful in factories, where there is a superfluous
supply of steam.
(2) A fan or screw may also be used. The vanes of the fan, when set in
motion by electrical or some other motive power, produce a powerful
current of air, which can be regulated according to requirements. As in the
last plan, the aspirating influence of the fan may be exerted over a system of
rooms, by means of connecting tubes.
In Ventilation by Propulsion a fan is used as in the last plan, the air
being propelled along conduits leading from it into the room to be
ventilated. The size of the conduits being known, the amount of air to be
discharged can be regulated by timing the rapidity of the revolutions of the
fan.
This plan is suitable for crowded places, where a large amount of air is
required in a short time. It is excellent for large schools, churches, and
theatres. Its superiority for large elementary schools has been proved at
Dundee by the experiments of Drs. Carnelley, Haldane, and Anderson, the
results of which are summarised in the following table:—
CUBIC FT. CARBONIC MICRO-ORGANISMS
NO. OF NO. OF ALLOWED ACID IN PER LITRE
SCHOOLS. ROOMS. PER 10,000 OF
PERSON. AIR. BACTERIA. MOULDS.
Mechanical
ventilation by 6 32 160 12·3 17·5 1·0
warmed air
Natural
ventilation 17 43 176 16·3 96·5 1·1
andhot pipes
Natural
ventilation 33 84 145 19·2 153·2 4·8
and open fires

The air to be admitted may be warmed by passing it over hot-water or
steam-pipes. In large establishments, as in hospitals, theatres, etc., it has
been arranged so that the incoming air is passed through a screen of coarse
cloth, which is kept wet by water trickling down each cord. The air is thus
kept moist and freed from dust.
The great advantage of the plan of propulsion, is its certainty. By it the
temperature, moisture, and freedom from suspended matters of the
incoming air can be exactly regulated and controlled. Its chief
disadvantages are that (1) it is somewhat costly, and (2) the apparatus
requires skilled supervision. On the other hand it maintains the air in
crowded rooms in a condition which cannot be secured by any other
method. When combined, as is done in the Houses of Parliament, with the
use of a flue for the extraction of foul air, this plan answers admirably.
The Relative Value of Artificial and Natural Ventilation scarcely
needs to be discussed. They are both valuable, but under different
circumstances. In dwelling-rooms natural ventilation by doors, windows
and chimney usually suffices, especially if the products of combustion of
gas are removed through a special flue. Natural ventilation is always
occurring, and only needs a little aid in domestic life. For large rooms
occupied by many persons artificial ventilation is necessary to maintain
pure air.
Whatever method of ventilation is adopted, the atmosphere will remain to
some extent polluted, if the room and its occupants are dirty. In certain
experiments made by Carnelley in schools, it was found that dirty children
increased the number of micro-organisms per litre of air more rapidly than
dirty rooms. Thus:—
DEGREE OF CLEANLINESS OF CLEAN. MEDIUM. DIRTY.
Children 63 99 159
Rooms 85 94 139

Number of micro-organisms per litre of air.
Hence cleanliness of rooms and of their occupants is quite as important
as a good system of ventilation.

CHAPTER XXIII.
VENTILATION BY THE INTRODUCTION OF
WARMED AIR.
Ventilation by the Burning of Coal. In winter and at any time of the
year when the out-door temperature is below 50° Fahr., the warming and
ventilation of a room are necessarily combined. If air is admitted unwarmed
it will produce draughts, unless directed upwards by Tobin’s tubes or
otherwise. In dwelling-rooms such contrivances may suffice; but in any
larger building, in order to ensure sufficient ventilation, it is necessary to
warm the incoming air.
The Open Fire-place forms the most common means of ventilation by
heat (see also page 159). The ascent of warm air up the chimney, causes
cold air to rush along the floor to the fire-place from all parts of the room,
especially the door. Part of the air thus approaching the fire is carried up the
chimney with the smoke, while the remainder, after having been warmed,
flows upwards towards the ceiling near the chimney-breast. It passes along
the ceiling, and cooling in its progress towards the opposite wall, descends,
and is again drawn towards the fire-place. Thus there is a continuous
circulation of the air in a room.
In the experiments of the Barrack Commissioners (1861), it was found
that the amount of air passing up the chimney while a fire was lit, ranged
from 5,300 to 16,000 cubic feet per hour, the mean of 25 experiments being
9,904 cubic feet. We may conclude, then, that with an ordinary grate, a
chimney provides outlet for impure air sufficient for four or five persons. Its
lack of economy as a heat-producer will be considered later. Its efficiency
as a ventilator within the above limits is evident.
When a fire is burning in the grate, all other openings in the room, except
openings into the chimney, serve as inlets. If the room is insufficiently
supplied with openings, a double current may be established in the chimney,
with the result that occasional down-puffs of smoke occur.

As a rule the chimney serves only as an outlet for impure air. It may by
appropriate means be made to serve as an inlet for pure and warmed air, the
heat which would otherwise escape up the chimney being utilised for this
purpose. Galton’s stove is one of the best for this purpose. At the back of
this stove is an air-chamber, communicating with the external air, and in
which the fresh air is heated before it enters the room. On the back of the
stove broad iron flanges are cast, in order to present as large a heating
surface as possible. They project backwards into the air chamber; and their
heating surface is aided by the iron smoke-flue, which passes through the
air-chamber. The warmed fresh air enters the room by a louvred opening
above the mantel-piece, or by an opening in each side of the chimney
breast. By this stove one-third of the total heat of the fire is utilised, as
against one-eighth in an ordinary fire-place.

Fig. 16.
Vertical Section through Two Rooms, showing—A. Currents of cold air with an
ordinary fire; B. Direction of currents of warmed fresh air with a Galton’s
Ventilating Stove.

Shorland’s Manchester and other stoves are constructed on the same
principle as Galton’s.
The Ventilation of Mines is effected by lighting a fire at the bottom of a shaft. The air for the
combustion comes down another shaft (the intake shaft), or down another half of the same shaft
separated by a partition. The consequence is that constant up and down currents of air are produced.
The air from the intake shaft is made to traverse the galleries of the mines, its course being directed
by partitions, before it is allowed to reach the fire and s be carried up out of the mine.

In addition to, or instead of, an ordinary coal-fire, the power for
extracting impure air may be obtained from Hot Water or Steam Pipes.
There are various plans founded on this principle.

When hot-water pipes are used for baths, etc., they may also be utilised
for ventilation, in two ways:—1st. The hot-water pipe may be made to coil
round the tube by which fresh air is admitted into a room, thus warming the
air as it enters. 2nd. The hot-water pipe in its course upwards may be
enclosed in a shaft, which opens into the external air above. The air in this
shaft being heated, the impure air may be collected and removed from the
different rooms by tubes connected with it. Thus, a hot-water apparatus,
when well arranged and complete, may furnish pure warm air, and carry
away impure air. The ventilation by this plan is found in practice to be
somewhat irregular.
The plan proposed by Drs. Drysdale and Hayward of Liverpool is similar in principle:—Fresh air
is warmed by a coil of hot-water pipes in the basement, and is admitted into the staircase and
landings, when it is supplied to the different rooms by openings provided with valves. From the
rooms, special outlets converge to a foul-air chamber under the roof. This is connected with a shaft
leading from the kitchen-fire, the latter, therefore, acting as an extraction furnace.

Lighted Gas may be employed to produce a current for ventilating
purposes, as well as fire or hot-water.
Sunlight and Benham’s Ventilating Gas-burners, have already been
mentioned in this connection (page 149). They are extremely valuable
means of ventilation, producing powerful currents of air from all quarters of
the room unless they are specially enclosed.
In theatres and similar buildings the Chandeliers may be made to extract
vitiated air. Where a number of chandeliers exist, they may be connected by
tubes with a main shaft, and all made to contribute to the same object.
According to the experiments of General Morin, the discharge of 1,000
cubic feet of air is produced by the combustion of one cubic foot of gas.
Various forms of gas-stoves are now sold, which act as ventilators as well
as sources of heat. Among these is George’s Calorigen Stove (Fig. 17). It
can be obtained in various forms suitable for burning coal-gas, or coal, or
oil. Within its outer case is contained a special iron tube, which
communicates at its lower end with the outer air, and opens at its upper end
into the room. The heat generated in the stove warms the air in the spiral
tube, which accordingly ascends into the room. The ascent of warm air
causes a draught from below, and the consequence is, that so long as the
combustion is going on, a current of warm air continues to ascend into the

room. The products of combustion are carried out of the room by the pipe
F. This stove is free from most of the objections appertaining to gas-stoves;
it can be fixed into an ordinary fire-place, and made to keep the temperature
of a room uniform.

Fig 17.
George’s Calorigen Stove.

A—The interior of the room.
B—Exterior of building.
C—Wall.
D—The Calorigen.
E—A cylinder.
FF—Pipes communicating with stove and cylinder to supply air for
combustion, and to carry off the products of combustion.
G—Pipe for passage of fresh cold air to Calorigen. Can be carried above the
floor between the joists, as may be more convenient.
H—Outlet for air into the apartment after being made warm.

Bond’s Euthermic Stove is similarly constructed to the above, but is
open below so that the air needed for the gas combustion is drawn from the
interior of the room, and the continuous change of air is thus favoured.
Objections to Ventilation by Heating Apparatus.—When warmed air
is admitted into a room, it is very apt to be dry and irritating. This can be
usually avoided by having water standing in the room, so as to allow
evaporation. A more difficult problem is to ensure the complete absence of
all products of combustion, particularly of the products of incomplete
combustion.

CHAPTER XXIV.
THE WARMING OF HOUSES.
Physiological and Physical Considerations.—The warmth of our
bodies is naturally kept up by the oxidation changes constantly going on in
the system. In Chapter XL., p. 265, are discussed the modes in which heat is
lost by the system, and the influence of clothing in controlling the amount
of this loss. Artificial warming of houses has a similar action to clothing. It
diminishes the demand on the system, and so economises the amount of
food required.
The degree to which this diminution of loss of heat by clothing and
artificial warming of houses may be carried varies with circumstances.
There can be no doubt that if food be abundant, exposure to external cold, if
not too extreme, is on the whole beneficial, for vigorous people. But for old
people and young children, means of artificial warmth require to be more
carefully provided. Severe cold is for them often the harbinger of death.
The Degree of Temperature at which living-rooms should be kept will
vary with circumstances.
For healthy adults, any temperature between 50° and 60° Fahr., will be
moderately comfortable; for delicate children and old people it may be 65°
with advantage.
For sick rooms and hospitals the temperature of 60° is usually adopted,
but this is by no means always necessary. A temperature of the room as low
as 50°, except for such diseases as whooping cough and bronchitis, suffices
if the patient is well covered with warm personal and bed coverings.
Convalescents from any acute illness bear low temperatures badly.
The Different Kinds of Heat.—Heat may be communicated by
radiation, conduction, and convection. By radiation of heat is meant the
process by which heat passes from a fire or other source of heat, through a
vacuum, dry air or any other medium, without heating any of the media

through which it passes, but only the bodies against which it finally
impinges. The solid bodies (including ourselves) which are warmed by
radiant heat, by a process of conduction then warm the surrounding air. This
method is the nearest imitation of the natural warmth of the sun.
Conduction of Heat is the passage of heat from one particle to another,
whether it be of a gas or solid. It is an extremely slow process when air is
concerned, and may be practically ignored.
Convection of Heat is the process by which a gas or liquid actually
carries the heat in itself from one part to another. The heated particles are
relatively lighter, and ascend to the higher parts of a room, while colder and
heavier particles descend, and are subjected to the same process. Heat can
be carried by convection only by gases and liquids. It is quite possible,
therefore, for a person to be cold in a room filled with warm air, if the walls,
etc., are cold; and on the other hand, to feel comparatively warm in a room
filled with cold air, if more heat is radiated from an open fire-place or the
warm walls to his body than he radiates to his surroundings. The feeling of
“draught” when sitting near a wall is sometimes caused by radiation of heat
from the body to the colder wall. The ideal arrangement, were it practicable,
would be to have cool air to breathe, but to be surrounded by warm walls,
floors, and furniture. A room warmed by an open fire is more comfortable
than a room warmed by hot air from a furnace, assuming the temperature of
the air is the same in both instances, because the walls of the room are
several degrees lower in temperature in the latter than in the former. For
warming walls as well as the air high pressure steam pipes are more
efficient than hot-water pipes. The great advantages of radiant heat are that
—(1) it heats the body without appreciably heating the air; while at the
same time (2) there is no possibility of impure gases being added to the air.
It has, however, considerable disadvantages. (1) It is costly, though its
expense may be greatly diminished by a well-constructed fire-place. (2) It
only acts on bodies near it to any useful extent. Its effect lessens as the
square of the distance; thus, its warming effect at five feet distance, is
twenty-five times less than at a distance of one foot. It is evident, therefore,
that for long rooms, and for large assembly-rooms, a single source of
radiant heat is quite inadequate. The immense loss of heat in our ordinary
fire-places is slowly leading to their modification; and although it is

probable that radiant heat will always be the favourite source of warmth in
dwelling-houses, it will be used for larger buildings chiefly as an adjunct to
convection of heat.
The different sources of heat are employed, either singly or combined, in
the following methods of warming our dwellings and other buildings:—

1. Warming by the open grate.
2. Warming by closed stoves.
3. Warming by hot-water pipes.
4. Warming by steam in pipes.
5. Warming by hot air.
6. Warming by electricity.

Warming by the open Grate.—In the open fire-place radiation is the
source of heat chiefly employed.
The position of the fire-place is important. It should not be on the
external wall of the house, as thus a large proportion of heat is lost; but
should be placed where the heat from the flue may be utilised in keeping up
the temperature of the house.
The construction of a fire-place is commonly faulty in several respects.
(1) The fire-place may be too far included in the wall, so that the heat at
once passes up the chimney. (2) It may be composed chiefly of iron, which
rapidly conducts away the heat, and does not furnish a surface for radiation.
(3) The bars and bottom of the grate may be so arranged, that coal and
cinders fall out in an incompletely burnt condition.
It has been estimated that with an ordinary fire-place, seven-eighths of
the possible heat is lost, one-half being carried up the chimney with the
smoke, one-quarter carried off in the ascending current of warm air, and
one-eighth of the combustible matter remaining unconsumed, forming the
solid matter of the smoke.
The defects which have been indicated may be remedied by bringing the
fire-place rather further out into the room; by substituting fire-brick for iron
behind and at the sides of the fire, and by having a layer of fire-brick at the

bottom of the grate, or the grate lowered, so that as in Teale’s stove, it lies
on a bed of fire-brick at or below the floor level.
The shape of the grate is important. The width of the back of the grate
should be about one-third that of the front, the sides sloping out towards the
front of the recess. The depth of the grate from before backwards should be
equal to the width of the back. The sides and back of the fire-place must be
made of fire-brick, thus ensuring the heat being retained in the grate. And
finally, the chimney throat must be contracted so as to ensure more
complete combustion. The chief objections to an open fire-place are (1)
the great waste of fuel involved, even after the improvements indicated
have been carried out. (2) The unequal heating at different distances from
the fire. (3) The smoke and dust always produced to some extent, from
accidental smoking of the fire, or from the escape of ashes. (4) The trouble
involved in frequently replenishing the fire. (5) The cold draughts produced
by the currents of air towards the chimney. These travel chiefly along the
floor, when, as is commonly the case, the space between the bottom of the
door and the floor forms the chief place for the entry of fresh air.
Many patents have been brought out for the introduction of the fuel at
the lowest part of the fire. The uppermost part of the fuel being first burnt,
and the remainder attacked from above, the smoke is consumed in passing
through the red part of the fire. Thus a comparatively smokeless fire is
produced, and the amount of heat evolved is greatly increased. So far none
of these have been altogether satisfactory. The production of a
comparatively smokeless fire is a great boon. Smoke means so much
unburnt fuel, and not only so but the sooty particles float about in the
atmosphere, rendering it impure, and changing comparatively harmless
mists into town fogs, which are loaded with soot and the products of
combustion, and do incalculable mischief to health and property. The
prevention of this smoke nuisance demands more consideration than it has
yet received. The Public Health Acts constitute the emission of black smoke
from the chimneys of manufacturing premises a nuisance; and
manufacturers can if they use proper boilers, especially those in which
mechanical stokers are employed, almost completely obviate this nuisance.
The great principle is to prevent the escape of smoke before it is completely
burnt. This may be accomplished by careful stoking, by keeping the unburnt
coal at the front of the fire, and by ridges exposing the smoke to red-hot

fire-clay before it escapes. In domestic fires, gas is gradually replacing coal
for cooking, with a corresponding reduction of the smoke-nuisance.
The Utilization of the Heat Produced in the fire-place to warm the air
on its way into the room, as in Galton’s and other similar stoves has been
already described (page 156).
A larger amount of heat can be obtained out of a given quantity of fuel by
cutting off some of the cold air, which rushes through the fire, and carries
the half-burnt gases and much of the heat up the chimney. This is effected
by having a solid fire-brick bottom to the grate, or by closing up the front of
the open chamber under the grate, by means of a close-fitting shield or door.
These “Economisers,” as Mr. Teale calls them, appear to answer better than
solid fire-brick bottoms, as they do not prevent the ashes falling under the
grate.
The Fuel burnt in an open fire-place may be either coal or coal-gas.
Occasionally coke is also employed. Coke and coal-gas have the advantage
over coal, that (1) no smoke is produced. Coal-gas presents the additional
advantages, that (2) it can be turned on at any moment, without having to
go through a tedious process of lighting the fire; and that (3) the amount of
heat can be exactly graduated by regulating the supply of gas. A gas fire is
however, as a rule, more expensive than a coal fire.
Open Gas-stoves are made in various forms. In the common one, small
jets of gas are lit under the grate, which is filled with pieces of asbestos.
These become red hot, and radiant heat is emitted. To obtain the greatest
value from the heat generated by the combustion of gas, a stove should be
chosen in which the heat generated is brought into contact with a large
surface of the grate before the products of combustion are allowed to escape
to the flue.
Gas stoves which are advertised as not needing a flue, should be avoided.
A large amount of carbonic acid is discharged by them into the room, and
the sulphurous acid also produced by the combustion of gas is not
completely absorbed in the water of condensation which collects in a tray
under such stoves.

Closed Stoves form the most economical and efficient warmers for
rooms of moderate size, and coal, coke, coal-gas or paraffin may be burnt in
them.
The advantages rightly claimed for coal stoves of this type are that (1)
the amount of fuel consumed is small; (2) by adjusting the damper,
combustion may be rendered as slow as desired, so that but little heat is lost
by the flue or chimney; and (3) heat radiates from all parts of the stove into
the room, and not simply from a small area of fire-front.
The chief objections to closed stoves are, that (1) they dry the air
excessively, rendering it somewhat unpleasant. (2) They produce a peculiar
close smell, apparently caused by the charring of minute particles of organic
matter in the air, coming in contact with the stove. If the air of the room is
not heated above 75° Fahr., no smell is produced, and the relative humidity
is not lessened to any appreciable extent (Parkes). But when the heat
produced by the stove is excessive, these results do follow. The
unpleasantness may be modified though not entirely removed, by placing
shallow pans of water near the stove.
(3) Portions of the products of combustion may pass through cracks or
fissures in the stove, or even through the joints of the stove. Independently
of such accidental cracks, cast-iron stoves, when red hot, appear to allow
gases to pass through them with comparative ease. Thus carbonic oxide and
other gases may find their way into the room, and it is probable that this
rather than the dryness of the air, is the cause of the unpleasant symptoms
sometimes complained of in rooms where closed stoves are in use. This
escape of carbonic oxide does not occur with earthenware stoves properly
encased with fire-clay.
Many modifications of the older closed stoves are now in common use.
In the stove shown in Fig. 18, excessive heating of the air is prevented by
the presence of two air chambers, only the outer one, which brings external
air to be warmed, having its air emptied into the room.
Warming by open grates or closed stoves is specially applicable to the
rooms of private houses; warming by hot air or steam, or hot water, is
chiefly used for large buildings. It is quite possible that these methods will
be applied at some future time on a large scale to the warming of private

houses. In some large towns of the
United States this has been already
done, blocks of a hundred or more
houses being warmed from the
same centre, by the same system.
But apart from such a central
system, hot air and hot water lend
themselves to the heating of houses
on what may be called the Whole
House System (page 156). We have
mentioned in the last chapter some
methods of doing this, and shall
now describe others.
Fig. 18. Hot-water Pipes are probably
Slow Combustion Stove. the best means of carrying heat to
various parts of a large house, and
hot water is more thoroughly under control and less dangerous than either
hot air or steam. There are two systems of heating by hot water.
In the first, which we may call the low pressure system, there is a boiler
from which water circulates through pipes to every part of the building, and
as it cools down returns again to the boiler. At the highest points of the
pipes, outlets are provided for air. In this system the water is not heated
above 200° Fahr., and there is consequently no great pressure on the pipes.
In the high pressure system (Perkin’s patent), the pipes have an internal
diameter of about ½ an inch, and have thick walls made of two pieces of
welded iron. There is no boiler, but one portion of the tube passes through
the fire and the water is heated to 300-350° Fahr., thus subjecting the pipes
to great pressure. In dwelling-houses with the low pressure system, for
every 1,000 cubic feet of space to be warmed to 50°, 12 feet of 4-inch pipe
should be given; with Perkin’s pipes, probably about two-thirds of this will
suffice.
Steam Distributed by Pipes may be employed instead of hot water. This
method has been used in factories in which there is a surplus supply of
steam.

Warming by Hot Air is only applicable on a large scale, and should only
be used in association with a system of ventilation by propulsion (page
153), in which the temperature, humidity, and freedom from dust of the
entering air are carefully regulated.
Warming by Electricity both for cooking food and for warming rooms
has a large future, but in most districts the supply of electricity is not
hitherto sufficiently cheap to be used for these purposes. By its means the
atmosphere will be prevented from becoming impure, labour will be
reduced, and life rendered more pleasant.
Hot Water Supplies.—Nearly every modern house is supplied with a
bathroom, and this may be supplied with hot water either from a geyser or
from the kitchen boiler. In a geyser the water is made to flow over a large
heating surface furnished by burning coal-gas, and with the best varieties a
bath of 98° F. can be supplied in from five to ten minutes. As the bathroom
is usually small and unprovided with an open fire-place, persons have
occasionally been suffocated by remaining in such a room while the gas
continues burning. This is due to the production and in-breathing of
carbonic oxide. No geyser ought to be allowed to be used which is
unprovided with a flue passing into the chimney flue or in its absence
through an external wall of the house. Short of fatal poisoning, violent
headaches often occur when a warm bath obtained by means of a geyser is
taken, unless such a flue is provided. In Ewart’s lightning geyser, additional
protection is furnished by the fact that a dual valve is so arranged, that
immediately the water is turned off or the supply fails from any cause, the
supply of gas is also cut off.
Hot water supplies from kitchen boilers, unless carefully arranged, may
be responsible for serious explosions during severe frosts.
Four plans are in common use. (1) The worm-boiler system. This system is unsafe unless the
supply of water to the boiler is attended to; and as the hot water supply to the kitchen is drawn from
the boiler itself and not from the worm, the hot water supply for the rest of the house may be
deficient. Usually the small feed cistern for the boiler in this system is too near the boiler to freeze.
(2) The cylinder system is very effective. In this system a metallic cylinder, capable of
withstanding a pressure of 20 lbs. to the square inch, is placed in the kitchen or bathroom between the
cold and hot supplies, its contained water being heated by circulation from the boiler, hot water
ascending and cold descending. On the top floor of a house is a cistern from which cold water is
supplied. Both the supply pipe and escape pipe for hot water may become frozen during frost. Then
the supply of water is stopped, and the boiler and reservoir may boil dry. This would not occur

without some indication in unusually vigorous boiling.
Boilers sometimes explode, and cylinders sometimes
explode. This can be effectually prevented by (3) A
Double-cylinder apparatus one within another. In this
the water in the outer cylinder supplied from the main
cistern can only be heated to 212° F., and the water in the
boiler and inner cylinder supplied from a lower feed
cistern can only be heated to 214° F., on account of the
small head of water. Two escape pipes give free
communication with the atmosphere. (4) In the tank
system, which being cheap, is usually adopted in poor
houses, the tank is placed high up in the system. The hot
water branch pipes are usually taken from the flow-pipe
between the boiler and tank. Hence when the supply
fails, as during frost, the tank is drained empty, the
circulation of water ceases, and the system is changed
from a circulation system to a high-pressure one.
Safety valves cannot always be relied on to prevent
explosions. If they lead to the lighting of fires in frosty
weather, when pipes are frozen, they may cause
explosions. Explosions from frost only occur when both
pipes are blocked. Incrustation of the boiler and pipes
increases the danger of explosions; hence the necessity
for their periodical cleaning.

CHAPTER XXV.
HOUSE DRAINAGE.
The Removal of Impurities.—In order that health may be maintained in
any inhabited house, it is essential that the impurities produced by animal
life should be removed. These impurities may be divided into two classes—
the first including the gaseous and volatile products evolved from the lungs
and skin; and the second, the liquid excretion from the kidneys, and the
solid from the bowels. The former are got rid of by efficient ventilation and
by cleanliness; the latter, ought to be as quickly removed, but require more
elaborate arrangements to ensure this.
The average daily amount of solid excreta is about 4 ounces, and of
fluid excreta about 50 ounces for each adult male. Taking all ages and both
sexes into consideration, the amount per head is about 2¾ ounces of fæces
and 32 ounces of urine. When dried, the daily fæces amount to 1·04 oz., the
daily urine to 1·74 oz., so that the manurial value as well as the possible
polluting power of urine is much greater than that of the fæces.
After a variable interval urine and fæces begin to decompose, ammonia
and fœtid gases being disengaged in large quantities. Urea the chief
constituent of urine is decomposed into carbonic acid and carbonate of
ammonia. Thus
CH₄N₂O + 2H₂O = (NH₄)₂CO₃
In addition to the excreta, house-slops have to be got rid of, and “dust.”
House-slops vary greatly in quantity, but probably amount to as much as
sixteen gallons per head daily. They consist chiefly of the water used in
cooking and washing and for baths. It would be a mistake to suppose that
only urine and fæces need careful disposal. There are masses of decaying
epithelium from lavatories and baths, organic matters from soiled apparel,
and various organic matters from culinary operations, all of which may
cause serious nuisance unless promptly disposed of.

The Dust consists chiefly of the ashes from fires; but the dust-bin also
forms a favourite refuge for kitchen refuse, composed of various animal and
vegetable matters, as well as for broken pots and tins. It is dealt with apart
from the house-slops and excreta, except in certain dry methods of disposal
of sewage.
Two chief plans of getting rid of the sewage have been proposed, though
there are many varieties of these. They are—

1. The Water Method, and
2. The Dry Methods.

For towns the water carriage of sewage is indispensable, and in this
chapter we shall confine ourselves to the part of this system which relates to
the Drainage of the House.
The chief sanitary appliances of a house, which empty their contents into
the drain and thence into the street sewer, are—(1) Rain-water Pipes; (2)
Bath-room and Sink-pipes; (3) Water-closets; (4) Soil-pipes; and (5) The
House Drain. We will consider these in detail.
Rain-water Pipes collect the water from the roof by means of gutters,
and carry it down to the house drain, except in the few cases in which the
rain-water is collected for use. The rain-water or stack pipe was formerly
joined directly at its base with the underground drain. This was evidently
bad, because the upper end of the pipe was frequently near windows, and
foul gases from the drain might be conducted by it into the house. It is
equally objectionable to connect the rain-water pipe with the soil pipe and
for the same reasons as above.
The general rule with regard to all pipes carrying away water from the
house, with the sole exception of the soil-pipe, is that they must be
disconnected from the underground drain and discharge into the open air
over a gulley-trap. This rule applies to

rain-water pipes, and to
waste pipes from baths,
lavatories,
sinks.

It does not apply to the soil-pipes leading from

water-closets and
slop-sinks,

Overflow or waste-pipes from cisterns for drinking water or from cisterns
for flushing w.c.’s or to safe trays under the seat of water-closets should all
be made to discharge into the open air, where the leakage can at once be
discovered.
The form of gully-trap to be used at the junction with the drain is
described on page 167.
Other Waste-pipes as from bath, lavatories, and sinks, must be similarly
disconnected from the drain, and made to discharge over gully-traps. When
the pipe leading from the bath, lavatory basin, or sink, is long, it is apt to
become foul from the accumulation on its inner surface of slimy matter,
consisting of soap, dirt, and other offensive matter. For this reason it is wise
to have a syphon bend in the waste-pipe near its junction with the sink or
basin. Such a trap is shown in Fig. 19.
The syphon bend alone in the waste-pipe without disconnection from the
drain at its lower end would not suffice to ensure complete absence of
nuisance, especially for sinks and lavatories which may be disused for a
considerable period. Under these circumstances the water in the syphon trap
may become evaporated, and then foul drain gases be wafted into the house.
Furthermore, even if the water in the syphon trap remained, foul gases may
be absorbed from the drain and given out at the end nearest the house (a,
Fig 19). Hence it is always best to disconnect all waste-pipes from the
drain, except the soil-pipe which cannot be treated in this way. The waste-
pipe from the upstairs lavatory or bath may be made to discharge over a
hopper-head and thence into the rain-water pipe, which is disconnected
below from the drain. This plan should only be adopted when the hopper-
head is not close to a bedroom window.
Under the bath is usually placed a leaden tray, called a safe, to catch any
accidental spillings of water. The overflow pipe from this safe should
discharge direct into the open air. Formerly much evil was caused by
allowing waste-pipes from baths, sinks, and lavatory-pipes, or overflow

pipes from drinking-water cisterns or from
the bath-safe, to be connected directly either
with the trap of the w.c., or with the soil-pipe
beyond it.

Fig. 19.
Syphon Trap under Sink, with
Screw-opening for Cleansing.

Fig. 20.

A Stoneware Gully-trap. B Section of the same, showing a Water-
seal 3 inches in Depth.

Sinks are not uncommonly the source of offensive smells, when made of
wood or stone. A hard glazed sink should be provided; as this is non-porous
and can be kept clean. The sink should be placed against an external wall,
so that the waste pipe can be carried through the wall to a gully-trap outside
the house. Formerly the sink-pipe was joined below directly into the drain,
the only obstacle to the entry of sewer or drain gases into the kitchen being
a bell-trap at the sink. This is quite insufficient for the purpose. The waste-
pipe from the sink should have a syphon trap under it, with an inspection
opening at its lowest point (Fig. 19), and should discharge in the open air
over a gully-trap (Fig. 20), as in the case of rain-water and bath-waste
pipes. It is usually stated that the waste-pipes from sinks, etc., should
discharge at least 18 inches distant from the grating of the gully. This is too

far, because some of the foul water may become dried up in the channel,
and its solid particles be blown about. They may be allowed to discharge
directly over the grating of the gully (Fig. 20) or even into the side of the
gully below the grating, but above and on the house side of the water-seal
shown at B. Fig. 20.
The gully-trap is connected with the socket of the first drain-pipe, and the
junction is made water-tight by means of a cement joint. On this account,
and because it gives a better water-seal than the bell-trap or D trap, the
gully-trap should be always used. The best form of gully-trap, the P trap, is
shown in Fig. 20 B. This is better than the S trap (Fig 19), which involves a
bend in the drain at its junction with the trap.
Water-closets require to be skilfully constructed and well-situated, if
they are not to become a serious nuisance. In building a house, the position
of the closet should be carefully considered. In all cases it should be in an
out-standing part of the house, against an external wall, and separated from
other parts of the house by a passage, preferably a passage which is cross-
ventilated. Instead of this, one commonly finds it in any convenient recess,
abutting on a bedroom, or where it cannot be properly ventilated. Usually
the closet is placed at the back of the house; and as the main-sewer is
generally situated in the front street, it follows that the drain must in terrace
houses pass under the house. Hence the importance of having it completely
water-tight. Water-closets in bathrooms are very inadvisable.
The ventilation of the closet should be good—if possible, by two
opposite windows; and where practicable a cross-ventilated lobby should
intervene between the closet and the rest of the house. This is now always
provided in hospitals.
The water-supply to the closet should be abundant. Every flush of water
should be sufficient to carry the contents of the basin through the soil-pipe
and the drain into the sewer. The quantity allowed by the Water Companies
in London is two gallons, which is barely sufficient for this purpose, unless
the form of closet pan is good, and the down-pipe to it of sufficient
diameter. Each closet should have a separate cistern, the best being the so-
called “water-waste preventer,” by means of which a certain quantity of
water, and no more, can be discharged each time the handle is pulled. One

of the best of these is shown in Fig 21. When the handle of this is pulled,
the whole of the water in the cistern is syphoned out by the syphon and
carried down to the water-closet, whether the handle be held down or not.
The amount of fall from the cistern to the closet should not be less than
four feet, and the pipe should be free from bends in order to ensure a
thorough scouring of the trap and soil-pipe; and the flushing-pipe should
have an internal diameter of not less than 1½ inches. It is commonly
supposed that a small flow of water, trickling continuously down a closet,
tends to keep it clean, and prevent smells; but the water thus used is simply
wasted. Others fasten up the handle of valve-closets so as to allow a large
flow of water. This does not answer the desired end, and renders the
offending person liable to a penalty for wasting water.
Many different forms of water-closet are in use. In all of them the main
requisites are that there should be (1) a good flush of water, (2) a rapid
removal of the excreta, and (3) no possibility of reflux of gases. The chief
varieties of closets are the pan, valve, wash-out, and wash-down closets.

Fig. 21.
Syphon Flushing Cistern.

In Fig. 21 a portion of the bell of the syphon is shown cut out, so as to
display the movable plug at the bottom of the cistern. An objectionable
feature in most cisterns is their noisiness in use. In the above cistern, the

pipe admitting water is carried down to within an inch of the bottom of the
cistern, thus ensuring noiseless entry of water.]
Pan-closets (sometimes called double-pan closets) are essentially bad,
though largely employed in the past. The construction is shown in Fig 22.
Below the conical basin there is a metal pan capable of holding a certain
amount of water, the lower end of the basin dipping into this water. By
means of a pull-up apparatus the contents of the pan can be tilted into a
second larger pan or container, and the bottom of the container is connected
by means of a short pipe with a leaden [bowl-shaped symbol] shaped trap,
from the side of which the soil-pipe passes out to be carried down to the
drain. The arrangement insures the production of nuisance. The container
and [bowl-shaped symbol] trap always arrest a certain amount of foul
matter; and each time the handle of the closet is pulled up a puff of foul air
comes into the operator’s face. Occasionally the [bowl-shaped symbol trap
becomes corroded by the filth it contains, and foul gases from the drain
escape into the house.
Valve Closets differ from the last in
having no container, but only a small box
containing a movable water-tight valve,
exactly fitting the lower edge of the basin
(Fig. 23). They are much superior to the pan-
closet, but require an overflow pipe in order
to avoid accidental flooding of the closet.
The overflow pipe should be made with a
syphon bend in it, and the flushing of the
closet should be so arranged that each time it
is performed water enters the overflow pipe.
Fig. 22. (See Fig. 23.) The trap below the valve
Insanitary Pan Closet, showing D
Trap below. should be in the form of a syphon (see under
traps, page 179), as this is not easily fouled.
It is preferably made of lead, securely jointed
to the soil-pipe and to the valve box of the closet. A lead tray or “safe” is
required on the floor beneath a valve closet, in view of accidental spillings
or overflow; and this should be provided with an overflow pipe discharging
into the open air.

Valveless or Hopper Closets, of
which the Wash-out, Wash-down and
Syphonic Closets, are the chief forms,
present certain advantages over the
valve closet. There is less apparatus to
get out of order and no metal to become
foul. They do not require an overflow
pipe, as water can escape freely through
the trap of the closet. Valveless closets
need not be encased by wood-work,
thus ensuring freedom from spillings of
foul water, and they are more easily
used than valve closets for the Fig. 23.
discharge of bedroom slops, thus A—Pan. B—Overflow pipe with
obviating the necessity for a special syphon trap. C—Valve shut. C1—
Valve open. D—Valve box. E—
housemaid’s sink. Valveless or hopper Floorline. F—Water-seal of trap.
closets are cheaper and simpler in use
than valve closets, and when in use are
equally sanitary. If a house is left empty for a considerable time, the water
in the trap may, however, become evaporated, an event much less likely to
occur with a valve-closet. The latter are furthermore less noisy when
flushed. With a valve to hold up the water in the pan, as in the valve-closet,
a much larger quantity of water can be retained than with a hopper closet.
Hence the importance of the latter having such a shape as shall prevent
fouling of the basin by fæces.
One of the older hopper closets was the long hopper shewn in Fig. 25. In
this form the pan is conical in shape, its sides necessarily becoming fouled
by its use, and the spiral flush, the point of entry of which is shewn in the
figure is quite insufficient for cleansing the pan.
Of Short hoppers the best has a nearly vertical back as shewn in Fig. 24,
a rim-flush, by means of which at least two gallons of water are discharged
with the fæces, and the pan is thoroughly cleansed.
The wash-out closet is shewn in Fig. 26. In it a certain amount of water
is kept in the upper part of the pan by a ridge over which the fæces have to
be driven before entering the trap. The force of the flush is thus broken. In

this closet a large area is liable to be
fouled, and it is now almost entirely
disused.

Fig. 24.
Rim Flushing Wash-down Basin.

Fig. 25.
Short Hopper Closet. Long Hopper Closet with Spiral Flush.

Syphonic water-closets are wash-down closets, in which the flushing out
is aided by syphonic action. They need to be fitted with a flushing cistern,
giving an after-flush as well as a flush; otherwise the basin is left untrapped.
One of the most elaborate closets of this type is Jennings’ Closet of the
Century. Fig. 27 shows that the flushing cistern has two connections with
the closet, one in the usual manner with the flushing rim of the pan, the

other connected to the long arm of the syphon (A Fig. 27). B is a puff pipe
allowing the escape of air from this syphon when started. Thus while one
part of the flush scours the basin, the other expels the air from A through the
puff-pipe B, fills both arms of the syphon with water, and thus starts the
syphonic action by which all the contents of the basin are sucked out of it.
In this form of w.c., syphonage is intended to be produced, and the after-
flush prevents the w.c. from being left untrapped.
Syphonic water-closets appear to me to be
unnecessarily elaborate and complicated, and the only
advantage over the wash-down closet is the deeper
layer of water in the basin. With a well-shaped wash-
down closet this is of little importance.

Fig. 26.
Wash-out Closet.

Fig. 27.
Syphonic Closet.

In other forms of wash-down w.c., unsyphoning may also occur, for
instance, by pouring the contents of a slop-pail into the pan. This is
particularly apt to occur, when two or three water-closets are on different
floors of a house, one over another. This unsyphoning is prevented in the
case of the highest w.c. by the soil-pipe ventilator, but not always for the
lower w.c.’s. For these it may be necessary to carry a pipe from the highest
point of the trap of the closet, where it joins the soil-pipe, through the wall
into the external air. Such a pipe is called an anti-syphonage pipe (Fig. 28).
It effectually prevents the water being sucked out of the trap of a lower w.c.
when the w.c. on a higher floor is being flushed.

A Fig. 28. B
A—Elevation. B—Section through wall of house, showing connection of w.c.’s on
three floors, with soil-pipe and anti-syphonage pipe. b—Junction of closet trap with

soil-pipe, a being a P and b an S trap. c—Junction of soil-pipe with earthenware
drain. d—Anti-syphonage pipe, seen best in elevation A. e—Soil-pipe. f—Anti-
syphonage pipe. g—Underground drain. h—Soil-pipe ventilator. i—Cage-work
protecting top of h. j—Point at which anti-syphonage pipe is connected with soil-
pipe ventilator, above the highest w.c.

In the forms of w.c. already described, clean water is used for flushing,
and we have seen that two gallons, the quantity usually allowed, does not
suffice for this purpose, unless the closet pan is of the best possible shape,
and the service pipe sufficiently wide to project the water by means of a
rim-flush forcibly over the pan and into and beyond its trap. Other forms of
w.c. have been employed of which the most important are slop-water
closets, and trough-closets.
In Slop-Water Closets the waste water from sinks and baths is utilised
for flushing, and thus a saving of water is effected. This form of closet is
used considerably in manufacturing districts, and is less liable to freeze than
an ordinary w.c. The sink discharges on to a gully in the usual manner, but
the outlet of this gully is connected with a tilting vessel or tipper, holding
3½ gallons in Duckett’s closet, which is the best known of this type. The
tipper is balanced on brass bearings, and tips over when full, discharging its
contents into the closet trap, which is thus flushed. The slop-closet is a great
improvement on the privy-middens or pail-closets, which in some towns it
has superseded, but is not so cleanly as an ordinary w.c.
Trough Closets are also known as “latrines.” The best type consists of a
glazed earthenware trough under a series of w.c. seats. The trough is
slightly inclined towards the outlet, at which is a weir, beyond which is a
trap. An automatic flushing tank connected with the upper end of the trough
and five to six feet above it, discharges water at intervals and drives the
fæcal matter over the weir and through the trap. This form of closet is only
suitable for factories. It is to be deprecated for schools, and even for
factories, unless there are exceptional reasons for its continuance, as fæcal
matter possibly of an infectious character may be retained a considerable
time in the trough.
The domestic Slop Closet or “housemaid’s sink” must not be confused
with slop-water closets mentioned above. The slop-closet or sink is used for
emptying the contents of bedroom pails. These being necessarily foul and
liable to early putrefaction must be treated exactly like other sewage

matters. An ordinary pedestal w.c. with a lift-up seat answers excellently as
a slop-closet; but in large houses and public establishments a separate slop-
sink is desirable with a larger surface than most water-closets. The slop-
closet must be connected with the soil-pipe, just in the same way as a w.c.

Fig. 29—Section through a House from Front to Back shewing Drainage
Arrangements.
A.—Sewer; B.—Intercepting trap; C.—Cleaning eye for pipes between chamber
and sewer; D.—Inspection chamber; E.—Inlet ventilator; F.—Gully-trap for
forecourt; G.—Air-bricks for ventilation under floors; H.—Damp-proof course8; I.
—Concrete 6” thick over site of house; J.—Drain, fall 1 in 24, imbedded in concrete;
K.—Soil-pipe carried up full size above eaves; L.—Upstairs w.c.; M.—Gully-trap
receiving water from N scullery-sink, O bath and P rain-water stack-pipe; S.—
Ventilating pipe at upper end of drain; T.—Pipes leading to same.

The soil pipe is the vertical pipe carrying the contents of the water-
closets in the drain. It must be distinguished from the drain, which is
chiefly, if not entirely, underground. The exact position of the soil-pipe and
its relation to the drain can be seen in Fig. 28 and 29, which should be
carefully studied. The soil-pipe should be made of drawn lead without