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Ro/ie Book 

^//Ieri)ifn ul . Sterne J^iorar^ 
^niiiersity of c/l\ahama in Jjirminpam 

Digitized by the Internet Archive 

in 2010 with funding from 

Lyrasis IVIembers and Sloan Foundation 









ED^i^lgQ^. YOUMANS, 


"the class-book op chbmistbt," "chemical atlas" and "chabt," 
"alcohol and thh oonsto^ij^oh <oer*aSS.1f 

D. APPLETON" & CO., 346 & 848 BROADWAY. 



Entered according to Act of Congress, in the year 1857, by 


In the Clerk's Office of the District Court of the United States for the 

Southern District of New York. 

An edition of the present loorJc has been issKecl, 
arranged with Questions for the use of Academies, /Semi- 
naries, and Schools. 






I. Sources and Distribution of Terrestrial Heat, .... 17 
II. Inflttencb of Heat upon the Living World, . . . . 19 

III. Measurement of Heat — The Thermometer, 23 

IV. Radiation and its Effects, ... - 27 

V. Conduction of Heat, and its Effects, 34 

VI. Heat conveyed bx moving Matter, 36 

VII. Various properties and effects of Heat, 37 

VIII. Physiological effects of Heat, 48 

IX. Artificial Heat — Properties of Fuel, 49 

X. Air-currents — Action and management of Chimneys, . . . 55 

XI. Apparatus of Warming, 60 

1. Open fireplaces, 62 

2. Stoves 67 

3. Hot-air arrangements, 70 


I. Nature of Light — Law of its Diffusion, 76 

II. Reflection of Light, 79 

III. Transmission and Refraction of Light, 82 

IV. Theory of Light — Wave movements in Nature, .... 84 
V. Composition and mutual relation of Colors, 88 

VI, Practical suggestions in combining Colors, . . . . 102 



VII. Peoduction of Artificial Light. 

1. The Chemistry of Illumination, 105 

2. Illumination by means of Solids, 103 

3. Illumination by means of Liquids, 112 

4. Illumination by means of Gases, 119 

5. Measurement of Light, 124 

VIII. Structure and Optical powers of the Eye, 126 

IX. Optical defects of Vision — Spectacles, 131 

X. Injurious action of Artificial Light, 137 

XI. Management of Artificial Light, 146 


I. Properties and composition of the Atmosphere, .... 150 
II. Effects of the constituents of Air. 

1. Nitrogen, . , . 154 

2. Oxygen, 154 

S. Moisture, 157 

4. Carbonic acid, IGl 

5. Ozone and electricity, . . " 164 

III. Condition of Air provided by Nature, 165 

IV. Sources of impure Air in Dwellings, 168 

V. Morbid and fatal effects of impure Air, 174 

VI. Rate of contamination within doors, 181 

VII. Air in Motion — Currents — Draughts, 185 

VIII. ARRi\jfGEMENTS for Ventilation, . 192 


I. Source of Aliments — Order of the subject, 205 

II. General properties of Alimentary Substances. 

1. Principles containing no Nitrogen. 

A Water, ... 207 

B The Starches, 213 

C The Sugars, 216 

D The Gums, 223 

E The Oils, . 223 

F The Vegetable Acids, 225 

2. Principles containing Nitrogen. 

A Vegetable and Animal Albumen, 227 

B Vegetable and Animal Casein, 223 

C Vegetable and Animal Fibrin, 228 

D Gelatin, 280 


8. Compound Aliments— Vegetable Foods. 

A The Grains, 231 

B Leguminous Seeds, 241 

C Fruits, 243 

D Leaves, Leafstalks, etc., 244 

E Roots, Tubers, Bulbs and Shoots, 245 

4. Compound Aliments — Animal Foods. 

A Constituents of Meat, 248 

. 250 


. 259 

. 267 

. 274 

. 281 

, 287 


. 293 


. 800 


. 306 

. 311 

. 818 

. 330 

. 344 

. 353 

B Production and composition of Milk, 
IIL CuLiNAET Changes of Alimentary Substances. 

1. Combining the elements of Bread, 

2. Bread raised by Fermentation, 
8. Properties and action of Yeast, . . ...,, 

4. Raising Bread without Fermentation, 

5. Alterations produced in baking Bread, 

6. Iniiuence of foreign substances upon Bread, 

7. Vegetable Foods changed by boiling,. 

8. How cooking changes Meat, 

9. Preparation and properties of Butter, 
10. Preparation and properties of Cheese, . 

rV. Common Bevehages. 

1. Properties and preparation of Tea, . 

2. Properties and preparation of Coffee, 

3. Cocoa and Chocolate, 

V. Peeseevation of Alimentaet Substances. 

1. Causes of their Changeableness, 

2. Preservation by exclusion of Air, 

3. Preservation at Low Temperatures, 

4. Preservation by Drying, .... 

5. Preservation by Antiseptics 

6. Preservation of Milk, Butter, and Cheese, 
VI. Materials of Culinaett and Table Utensils, . 

VII. Physiological effects of Food. 

1. Basis of the demand for Aliment, 

2. Digestion— Changes of food in the Mouth, . 

3. Digestion— Changes of food in the Stomach, 

4. Digestion— Changes of food in the Intestines, 

5. Final destination of Foods, .... 

6. Production of Bodily Warmth, 

Production of Bodily Strength, 360 



8. Mind, Body, and Aliment, 364 

9. Influence of Special Substances. 

A Saline Matters, 869 

B Liquid Aliments, 874 

C Solid Aliments 383 

10. Nutritive value of Foods, 892 

^ 11. The Vegetarian Question, 402 

12. Considerations of Diet, 408 


I. Principal Cleansing Agents, 422 

II. Cleansing of Textile Aeticles, 428 

III. Cleansing of the Peeson, 431 

IV. Cleansing of the Air, 436 

V. Poisons, 441 


INDEX, 445 


A DESiEE to prepare a better statement than has hitherto 
been offered, of the bearings of science upon the economy of 
the household, has led to the following work. The purpose 
has been, to condense within the limits of a convenient manual 
the largest possible amount of interesting and valuable scien- 
tific information of those agents, materials, and operations in 
which we have a concern, chiefly as dwellers in houses. 

The subjects are treated somewhat in an elementary way, 
but with constant reference to their domestic and practical 
relations. Principles are universal; their applications are 
special and peculiar. There are general laws of light, heat, 
and air, but they may be studied in various connections. 
There are many things about them which a person, as a resi- 
dent of a house, cares little to know ; while there are others 
in which he has a profound interest. To consider these, we 
assume to be the province of household science. The question' 
of moisture in the air, for example, is one of universal scien- 
tific interest to meteorologists ; but it has also a special and 
vital import for the occupants of stove and furnace heated 
rooms. Different colors, when brought together, alter and 
modify each other according to a simple and beautiful law ; 
and the Painter, the Decorator, and the Dyer, have each a 
technical interest in the principle ; but hardly more than the 
Lady at her toilette or engaged in furnishing her house. The 
Agriculturist is interested in the composition of food, as a 
•producer ; the Householder equally, as a consumer. The 


Doctor must know the constituents of air and its action upon 
the living system for professional purposes, and he studies 
these matters as parts of his medical education ; but for the 
same reasons of life and death, the inhabitants of houses are 
concerned to understand the same things. 

These examples illustrate the leading conception of the 
present work. Its preparation has been attended with grave 
difficulties. Of course, a volume of this compass can present 
only a compend of the subjects it considers. Heat, light, air, 
and aliment are topics of large extent, wide and complex in 
their principles, which are of boundless apph cation. We do 
not profess to have treated them with any completeness, 
but only to have brought distinctly forward those aspects 
which have been formerly too much neglected. In deciding 
what to state, and what to omit, we have been guided by two 
rules ; Jirst^ to present such facts and principles as have the 
directest bearing upon household phenomena ; and, second, to 
bring into prominence many important things not found in 
common books nor included in the ordinary range of school 
study. As elementary principles may be found fully treated 
elsewhere, we have been brief in their statement, thus gaining 
opportunity for important hints and views not generally acces- 
sible. Our chemistries are deficient in information of the 
composition and properties of food, while the physiological 
class-books are equally meagre in statements of its effects ; 
we have accordingly dwelt upon these points with something 
of the fulness which their importance demands. So with 
heat, hght, and air. It is hoped that the following pages will 
vindicate the fidelity with which we have labored to enrich the 
volume with new and valuable facts and suggestions, not pro- 
curable in our family manuals or school class-books. Many 
of the subjects presented have recently undergone searching 
investigation. They are rapidly progressive ; facts are multi- 
plying, and views widening. We have spared no pains to 
give the latest and most authentic results. Although the vol- 
ume is to a great extent self-explanatory, and adajited for 
family and general reading, yet in the proper order of school 


Study it will find its most appropriate place after a course of 
elementary lessons in cliemistry and physiology. 

We have striven to present the subject in such a manner 
as to make reading and study both agreeable and instructive. 
Technical terms constitute a formidable obstacle, on the part 
of many, to the perusal of scientific books. This is a very 
serious difficulty, and requires to be managed as best we can. 
In works designed for general use they should be avoided as 
far as possible, and yet it is out of the question to think of 
escaping them entirely. If we would enjoy the thoughts of 
science we require to learn at least a portion of the language in 
which alone these thoughts are conveyed. The new objects 
and relations must be named, or they cannot be described and 
considered. We have studiously avoided obstructing the 
course of the common reader with many technical words, yet 
there are some which it was impossible to omit. The terms 
carbon, oxygen, hydrogen, nitrogen, carbonic acid, and some 
others, though hardly yet famiUarized ui popular speech, must 
soon become so. They are the names of substances of univer- 
sal interest and importance ; the chief elements of air, water, 
food, and organized bodies by which Providence carries on 
the mighty scheme of terrestrial activity and life. They are 
the keys to a new department of intellectual riches — the latest 
revelation of time respecting the conditions of human exist- 
ence. The time has come when all who aspire to a character 
for real intelligence, must know something of the objects 
which these terms represent. 

As respects the body of its facts and principles, any work 
of this kind must necessarily be of the natm-e of a compilation. 
We make no claim to discovery. The materials of the volume 
— ^the result of laborious and life-long investigations of many 
men — have been gathered from numberless sources, — from 
standard books upon the various topics, scientific magazines, 
original memoirs, personal correspondence, observation, house- 
hold experience and laboratory examinations. Constant refer- 
ence is made to authorities followed, and the language of 
others employed whenever it appeared to convey the most 


suitable statement. Exemption from errors can hardly be 
expected m a work of this kind — errors of oversight and 
errors of judgment. Besides, many of its questions are in an 
unsettled state and involve conflicting views. Yet the utmost 
care has been taken to make an accurate and reUable presenta- 
tion of the subjects considered. 

The Author desires to acknowledge his indebtedness to 
his sister, Eliza A. Youmaks, for constant and invalua- 
ble aid in the preparation of the work, not only in various 
experimental operations incident to its progress, but also in 
several parts of its hterary execution. To his friend Mr. 
Richard H. Manning, who, though engaged in absorbing 
mercantile pursuits, has yet found time for thought in the di- 
rection of science and its appHcations, his thanks are due for 
valuable suggestions and important manuscript corrections. 

If the work shall serve, in however small a degree, to ex- 
cite thought, to give additional interest to household phe- 
nomena, and awaken a stronger desire for domestic improve- 
ment, the labor of its preparation will not have been performed 
in vain. 

New Yoek, Augiist, 1857. 


When a work is presented, claiming place in a systematic course of 
Bcliool study, two questions at once arise in the mind of the discrimi- 
nating educator : Jirst^ what is the nature, rank, and value of the 
knowledge it imparts? and, second, what wiU be its general mfluence 
upon the mind of the student ? In this twofold connexion there are 
some thoughts to which we solicit the reader's earnest and considerate 

The present volume has been prepared under a conviction that the 
knowledge it communicates is first in the order of importance among 
things to be considered by rational and civilized people. "Every 
man's proper mansion-house and home," says Sir Henet "Wotton", 
" is the theatre of his hospitality, the seat of self-fruition, the com- 
fortablest part of his own life, the noblest of his son's inheritance, a 
kind of private princedom ; nay, to the possessors thereof an epitome 
of the whole worid." Nothing needs to be added in eulogy of the 
household home, the place of life's purest pleasures and sweetest ex- 
periences, the perpetual rallying point of its hopes and joys. What- 
ever can render it more pleasant or attractive, or invest it with a new 
interest, or in any way improve or ennoble it, is at once commended 
to our sympathy and regard. To consider all the agencies which in- 
fluence the course and character of household life, is far from the ob- 
ject of the present work. Our concern is chiefly with its more mate- 
rial circumstances and conditions. That we should understand some- 
thing of the wonderful physical agencies which have control of our 
earthly being, and which are so incessantly illustrated in the dwelling, 
and be at least partially acquainted with those fixed natural ordi- 
nances upon which our daUy welfare, comfort, health, and even life, 
immediately depend, must certainly be acknowledged by all. One of 
the most startling facts of man's history is, that placed in a world of 
immutable order, and endowed with such exalted gifts of understand- 


ing and reason, he should yet have contrived to maintain so dense and 
perfect an ignorance of himself and the familiar objects by which he 
is surromided. That exact knowledge of the ways of nature which puts 
her powers at human command, and hears the daily fruit of substan- 
tial improvement and universal beneficence, would seem to be the last 
and noblest achievement of mind; a fruition of long intellectual 
growth, the highest form in the latest time, after the prehminary and 
preparatory experience of ages. In its earlier strivings we observe 
the mind of man intently occupied with itself, and regarding material 
nature with unutterable disdain. It wandered aimless and dissatisfied 
in the misty regions of speculation. Its first great conquest was in 
the reahn of abstraction, farthest removed from the vxdgarities of 
mere matter — the discovery of mathematical principles. The earhest 
application of thought to physical subjects was away in the distant 
spheres, where imagination had revelled wildest from immemorial time, 
to the luminous points and mysterious movements of the heavens, 
which, according to Plato, were most admirably fitted .to illustrate 
geometry. The skies were mapped and charted long before the earth. 
OoPEENicTJS struck out the grand law of celestial circulation before 
Haevet discovered that of the blood. The genius of Newton flashed 
an immortal light upon the mechanism of the universe, many years 
before Etjmfoed began his humbler domestic investigations. Centuries 
have passed since the establishment of universal gravitation, while 
there are men now living who may recollect the most gigantic stride 
of modem science, the discovery of oxygen gas by Peiestly, and the 
earliest analysis of the air we breathe. Chemistry, which is the name 
given to the first serious grapphng of human intelligence with all 
forms of common matter, belongs chiefly to our own century. This, 
too, has been progressive, and in its course has conformed to the gen- 
eral law we are indicating. Its earliest investigations were directed 
to inert mineral substances, stones and rocks ; while the formal and 
systematic elucidation of those conditions and phases of matter in 
which we have the deepest interest — vegetable and animal compounds 
and processes, agricultm*al, physiological, and dietetical chemistry — ^is 
eminently an affair of our own day. Thus, the spirit of inquiry, at 
first recoiling from matter, and circling wide through metapliysical 
vacuities, gradually closed with the physical world, and now finds its 
last and highest inquest into tlie material conditions of man's daily 
life. The course of knowledge has been expansive, as weU as pro- 
gressive ; from narrow views to universal principles ; from empty 
speculations to world-wide utilities ; from the pleasure of a few to 

rNTKODucnoN. xm 

the advantage of the many ; from utter ignorance and contempt of 
nature, to the revelation of all-embracing laws, and a beautiful and 
harmonious order in the commonest objects and operations of daily- 
experience. To the truth of this general statement, the existence of 
the present book may be taken as a strong attestation. The mass of 
its facts and principles are the result of recent investigation. A 
hundred years ago such a work would have been, in all its essential 
features, a blank impossibility; indeed, it had lacked its richest mate 
rials if prepared for the last generation. 

These facts should not be without their influence upon the schemt 
of popular education. It is its first duty to communicate that infor- 
mation which can be reduced to daily practice, and yield the largest 
measure of positive good. If recent inquiry has opened new treasures 
of available truth, it is bound to take charge of them for the general 
benefit. It must report the advance of knowledge, and keep pace 
with the progress of the human mind, or it is false to its trust. The 
subjects of study should be so modified and extended as to afibrd the 
largest advantage, intellectual and practical, of the labors of the great 
expounders of nature, — especially in those departments where knowl- 
edge can be made most useful and improving. A rational and com- 
prehensive plan of education for all classes, which shall be based upon 
man's iutrinsio and essential wants, and promptly avail itself of every 
new view and discovery in science, to enlighten him in his daily rela- 
tions and duties, is the urgent demand of the time. Nor can it be 
always evaded. We are not to trundle round for ever in the old ruts of 
thought, clinging with blind fatuity to crude schemes of instruction, 
which belong, where they originated, with the bygone ages. He who 
has surrendered his life to the inanities of an extinct and exploded 
mythology, but who remains a stranger to God's administration of 
the living universe ; who can skilfully rattle the skeletons of dead lan- 
guages, but to whom the page of nature is as a sealed book, and her 
voices as an unknown tongue, is not always to be plumed with the 
supereminent designation of ' educated.' 

There are many things, unquestionably, which it would be most 
desirable to study : but opportunity is brief, and capacity limited ; 
and the acquisition of one thing involves the exclusion of another. We 
cannot learn every thing. The question of the relative rank of vari- 
ous kinds of knowledge — what shall be held of primary importance 
and what subordinate, is urgent and serious. As hfe and health are 
the first of all blessings, to maintain them is the first of all duties, 
and to understand their conditions the first of mental requirements. 


Shall the thousand matters of mere distant and curious concernment 
be suffered to hold precedence of the solemn verities of being which 
are woven into the contexture of familiar life ? The physical agents 
■which perpetually surround, and act upon, and within us, heat, light, 
air, and aliment, are hable to perversion through ignorance, so as to 
produce suffering, disease, and death; or they are capable through 
knowledge of promoting health, strength, and enjoyment. What 
higher warrant can be asked that their laws and effects shall become 
subjects of general and earnest study. It may seem strange that in 
regard to the vital interests of life and health, man should be left 
without the natural guidance of instinct, and be driven to the necessity 
of reflection and study ; that he for whom the earth seems made 
should be apparently less cared for in these respects than the inferior 
animals. Nevertheless, such is the divine ordination. Neither our 
senses, instincts, nor uninstructed faculties are sufficient guides to good, 
or guards from evil, in even the ordinary conditions of the civilized 
state. Things which most deeply affect our welfare, the senses fail to 
appreciate. They can neither discern the properties nor the presence 
of the most deadly agents. The breathing medium may be laden with 
noxious gases to the peril of life, and the senses fail to detect the dan- 
ger. Hunger and thirst impel us instinctively to eat and di'ink, but 
they fail to inform us of the nutritive value of alimentary substances 
or their dietetical fitness to our varying requirements. Tor aU those 
things which are independent of man's will. Providence has taken 
abundant care to provide ; while in the domain of voluntary action, 
blind instinct is replaced by rational forecast. Whatever may have 
been those original conditions of bare animal existence which some 
yet sigh for, as the ' true state of nature,' we are far removed from 
them now. They have been successively disturbed as, generation 
after generation, intelligent ingenuity has been exercised to gain con- 
trol of natural forces for the securing of comforts and luxuries, and 
to liberate man from the privations and drudgeries of the uncivilized 
condition. But unmingled good seems not permitted ; the benefits are 
alloyed with evU. Thus, the introduction of the stove, while afford- 
ing the advantage of economy and convenience in the management 
of fire, was a step backward in the matter of ventilation. Gas- 
lighting was a great advance on the methods of artificial illumination, 
but there came with it augmented contamination of the breathing 
medium and new dangers to the eyes. Against these and similai* in- 
cidental mischiefs — ' residues of evil ' that accumulate against the pre- 
dominating good, there is no other protection than intellect, instructed 


in the material conditions wMcli influence our health and life. For 
these, and kiudred considerations of practical moment to all who oc- 
cupy dwellings and assume civilized relations, we urge the study 
of TiomeTiold science as an essential part of general education. 

It deserves to be better understood, that the highest value of science 
is derived from its power of advancing the public good. It is more 
and more to be consecrated to human improvement, as a sublime re- 
generative agency. Workiog jointly and harmoniously with the great 
moral forces of Christian Civilization, we believe it is destined to effect 
extensive social ameliorations. That it is not yet fully accepted in this 
relation is hardly surprising. The work of presenting scientific truth 
in those forms which may best engage the popular mind, is not to be 
fairly expected of those who give their lives to its original development. 
There is a deep satisfaction, an intrinsic compensating interest to the 
discoverer in the naked quest of truth, which is largely independent of 
any utility that may flow from the inquiry. In the exalted conscious- 
ness of achievement, the man of science finds an intellectual remunera- 
tion, so royal and satisfying that other considerations have compara- 
tively little weight. Hence the indifference, to a great degree inevi- 
table, with which original explorers contemplate the reduction of sci- 
entific principles to practical use. Moreover, this utter carelessness of 
results, where the mind is not biased, nor the vision blurred by ulterior 
considerations, is far the most favorable for successful investigation. 
Conscious that the effects of his labors are finally and always beneficial 
in society, the enthusiast of research may be excused his indifference 
to their immediate reception and uses. But the formal denial that the 
allegiance of mind is supremely due to the good of society is quite 
another affair. The sentiment too widely entertained in learned and edu- 
cational circles, that knowledge is to be firstly and chiefly prized for its 
own sake, and the mental gratification it produces, we cannot accept. 
The view seems narrow and illiberal, and is not inspired of human sym- 
pathy. It took origin in times when the improvement of man's con- 
dition, his general education and elevation, were not dreamed of. It 
came from the ancient philosophy, which was not a dispensation of pop- 
ular beneficence, an all-diffusive, ennobling agency in society, but con- 
fessed its highest aim to be a personal advantage, shut up in the indi- 
vidual soul. It was not radiant and outflowing like the sun, but drew 
all things inward, engulfing them in a malstrom of selfishness. 

The baneful ethics of this philosophy have given place to the higher 
and more generous inculcations of Christianity, which lays upon hu- 
man nature its broad and eternal requirement, ' to do good.' From 


this authoritative moral demand science cannot be exempted. The 
power it confers is to be held and used as power is exercised by God 
himself, for pm*poses of universal blessing. 

We place a high estimate upon the advantages which society may 
reap from a better acquaintance with material phenomena, for life is a 
stern realm of cause and effect, fact and law. To the poetic day-dreamer 
it may be an affair of sentiment, an ' illusion,' or a ' vapor,' but to 
the mass of mankind, life is a solid,- unmistakable reality, that will not 
dissolve into mist and cannot be conjured out of its qualities. As such, 
we would deal with it in education, giving prominence to those forms 
of knowledge which will work the largest practical alleviations and 
most substantial improvement throughout the community. But it is 
wisely designed that those studies which may become in the highest 
degree useful are also first in intellectual interest. It is a grievous mis- 
take to suppose that the study of natural science martyrizes the more 
ethereal faculties of the soul, and dooms the rest to painful toil among 
th.e naked sterilities of commonplace existence. So far from being un- 
friendly to the imagination, as is sometimes intimated, science is its 
noblest precursor and ally. Can that be unfavorable to this faculty, 
which infinitely multij^lies its materials, and boundlessly amplifies its 
scope ? Can that be restrictive of mental sweep, which unlocks the 
mysteries of the universe and pioneers its way far into the councils of 
Omniscience ? Who was it that lifted the veil, and disclosed a new 
world of exquisite order and beauty in all the commonest and vulgar- 
est forms of matter, below the former reach of eye or thought ? Who 
was it that dissipated the fabulous 'firmament,' which primeval igno- 
rance had mounted over its central and stationary earth ; set the world 
in motion, and unfolded a plan of the heavens, so appalling in ampli- 
tude that imagination itself falters in the survey ? Who was it that 
first read the handwriting of God upon the rocks, revealing tlie history of 
our planet and its inhabitants through durations of which the mind had 
never before even presumed to dream ? In thus unsealing the mysteries 
of being — in turning the commonest spot into a museum of wonders — 
who can doubt that science has opened a new and splendid career for 
the play of the diviner faculties ; and that its pursuit aftbrds the most 
exhilarating, as well as the healthiest and purest of intellectual enjoy- 
ments ? Kor should we forget its elevating tendencies ; for in con- 
templating the varied scheme of being around, its beauties, harmonies, 
adaptations, and purposes of profoundest wisdom, the thoughts ascend 
in unspeakable admiration to the infinite Source of truth and light. 
We should educate and elevate our nature by these studies, storing our 

rNTEODucnoN. xvn 

minds with the richest materials of thought, enlarging our capacities 
of henign exertion, and rising to a more intimate conmaunion with the 
spirit of the Great Maker of all. 

But heyond these considerations, physical science has another claim 
upon the Instructor, in the kind and extent of the mental discipline it 
affords. The study of mathematics has a conceded value in this rela- 
tion, being eminently favorable to precision and persistence of the 
mental operations — ^to steadfast concentration of thought upon ab- 
stract and difficult subjects. But we hope not to incur the charge of 
educational heresy,by expressing the opinion, that its training is some- 
what defective — ^is neither sufficiently comprehensive, nor altogether 
of the right kind. Its influence is limited to certain faculties only, and 
the method to which it accustoms the mind is too little available in 
grappling with the practical problems of life. The starting-point of 
the mathematician is certain universal truths of consciousness, intui- 
tive axioms — assumed without proof, because they are self-evident, and 
therefore incapable of proof. From these, by various operations and 
chains of reasoning, he proceeds to work out special applications. His 
direction is from generals to particulars — it is inferential — deductive. 
But when we come to deal with the phenomena of the external 
world, and the actualities of daily experience, this plan fails, and we 
are driven to the very reverse method. In the phenomenal world we 
are without the eternal principles, settled and assumed at the outset ; 
these become themselves the objects of investigation ; they have to be 
established, and we must begin with particulars, special inquiries, 
experimental investigations, the observation of facts, and from these 
we cautiously proceed to general truths — to universal principles. 
The process is an ascent from particulars — generalization — indiic- 
tion. That the whole is greater than a part, or that two parallel lines 
vdll never intersect each other, are irresistible intuitions, taken for 
granted at once by all minds. But that matter attracts matter with 
a force proportional to the square of its distance ; or that chemical 
combination takes place in definite unalterable proportions, are truths 
of induction — general laws, only arrived at after long and laborious in- 
vestigation of particular facts. These are essentially opposite methods 
of proceeding in different departments of inquiry, each correct in its 
own sphere, but false out of it. The human mind started with the 
mathematical method, and the greatest obstruction to the progress of 
physical science for many centuries arose from the attempt to apply 
it to outward phenomena ; that is, to assume certain principles as true 
of the external world, and to reason from them down to the facts ; in- 


stead of beginning with the facts, and carefully evolving the general 
laws. The splendid achievements of modern science are the fruit of 
the inductive method. This should be largely joined with the mathe- 
matical to secure a full and harmonious mental discipline. It edu- 
cates the attention by establishing habits of accurate observation, 
strengthens the judgment, teaches the supremacy of facts, cultivates 
order in their classification, and develops the reason through the es- 
tablishment of general principles. It is claimed, as an advantage of 
mathematics, that it deals with certainties, and, raising the mind above 
the confusions and insecurities of imperfect knowledge, habituates it 
to the demand of absolute truth. That benefits may arise from this 
exalted state of intellectual requirement, we are far from doubting, 
and are conscious of the danger of resting satisfied with any thing 
short of perfect certitude, where that 'can be attained. But here 
again there is possibility of error. Mathematical standards and pro- 
cesses are totally inapplicable in the thousand-fold contingencies of 
common experience ; and the mind which is deeply imbued with its 
spirit, is little attracted to those depai'tments of thought, where, after 
the utmost labor, there still remain doubt, dimness, uncertainty and 
entanglement. And yet, such is precisely the practical field in which 
our minds must daily work. The mental discipline we need, there- 
fore, is not merely a narrow deductive training of the faculties of cal- 
culation, with their inflexible demand for exactitudes ; but such a sys- 
tematic and symmetric exercise of its several powers as shall render 
it pliant and adaptive, and train it in that class of intellectual opera- 
tions which shaU best prepare it for varied and serviceable intellec- 
tual duty in the practical afiairs of life. 

There is still another thought in this connection which it is im- 
portant should be expressed. It has been too much the pohcy of the 
past so to train the mind as to enslave, rather than to arouse it. Edu- 
cation, from the earliest time, has been imder the patronage of civU 
and ecclesiastical despotisms, whose necessary policy has been tlie re- 
pression of free thouglit. The state of mind for ever insisted on has 
been that of submissive acceptance of authority. Instead of laying 
open tlie limitations, uncertainties, and conflicts of knowledge, which 
arise from its progressive nature, the spirit of the general teaching 
has been that all tilings are settled, and that wisdom has reached its 
last fulfilment. Instead of encouraging bold inquiry, and inciting to 
noble conquest, the efltect lias rather been to reduce the student to a 
mere tame, unquestioning recipient of established formulas and 
time-honored dogmas. It is obvious on all sides that this state 


of things has been deeply disturbed. The introduction of Ee- 
publicanism, with political freedom of speech and action; the 
advent of Protestantism, with religious liberty of thought; and 
the splendid march of science, which has enlarged the circle 
of knowledge, multiplied the elements of power, and scattered social 
and industrial revolution, right and left, for the last hundred years — 
these new dispensations have invaded the old repose, and fired the 
minds of multitudes with a new consciousness of power. Yet we 
cannot forget that our education still retains much of its ancient 
spirit, is yet largely scholastic and arbitrarily authoritative. "We 
believe that this evil may be, to a considerable degree, corrected 
by a frank admission of the incompleteness of much of our knowl- 
edge; by showing that it ia necessarily imperfect, and that the 
only just and honest course often involves reservation of opinion 
and suspension of judgment. This may be consonant neither with 
the teacher's pride nor the pupil's ambition, nevertheless it is 
imperatively demanded. "We need to acquire more humility of 
mind and a sincerer reverence for truth ; to understand that much 
which passes for knowledge is unsettled, and that we should be 
constant learners through life. The active influences of society, 
as well as the school-room, teach far other lessons. "We are com- 
mitted in early childhood to blind partisanships, — political and 
religious, — and drive on through life in the unquestioning and unscru- 
pulous advocacy of doctrines which are quite as likely to be false as 
true, and are perhaps utterly incapable of honest definitive adjustment. 
Science inculcates a different spirit, which is most forcibly illustrated 
in those branches where absolute certainty of conclusion is diflacult of 
attainment. Mr. Paget has urged the salutary influence of the study 
of physiology in this relation. He says, " It is a great hindrance to the 
progress of truth, that some men will hold with equal tenacity things 
that are, and things that are not, proved ; and even things that, from 
their very nature, do not admit of proof. They seem to think (and 
ordinary education might be pleaded as justifying the thought) that a 
plain ' yes ' or ' no ' can be answered to every question that can be 
plainly asked ; and that every thing thus answered is to be maintained 
as a point of conscience. I need not adduce instances of this error, 
while its mischiefs are manifested every where in the wrongs done by 
premature and tenacious judgments. I am aware that these are faults 
of the temper, not less than of the judgment ; but we know how much 
the temper is influenced by the character of our studies ; and I think 
if any one were to be free from this over-zeal of opinion, it should be 


one who is early instructed in an uncertain science such as physiology." 
In the present work, the chief statements comprised under heat, light, 
and air, may be regarded as settled with a high degree of certainty, 
while much of the matter relating to food and its effects is less clearly 
determined ; — its truth is only approximative, and we have stated it, 
as such, without hesitation. While the reader is informed, he is at 
the same time apprised of the incompleteness of his knowledge. 

An important result of the more earnest and general pursuit of 
science, by the young, vsdU be, to find out and develop a larger number 
of minds having natural aptitudes for research and investigation. As 
there are born poets, and born musicians, so also there are born in- 
ventors and experimenters ; minds originally fitted to combine and 
mould the plastic materials of nature into numberless forms of useful- 
ness and value. It is a vulgar error that the work of discovery and 
improvement is already mainly accomplished. The thoughtful well 
understand that man has hardly yet entered upon that magnificent 
career of conquest, in the peaceful domain of nature, to which he is 
destined, and which will be hastened by nothing so much as a more 
general kindling of the minds of the young with enthusiasm for science. 
The harvest awaits the reapers — how strange that man should have 
neglected it so long. Fuel, air, water, and the metals, as we see them 
acting together, now, in the living, laboring steam-engine, have been 
waiting from the foundation of the world for a chance to relieve man 
of the worst drudgeries of toil. Long and fruitlessly did the sunbeam 
court the opportunity of leaving upon the earth permanent impressions 
of the things he revealed ; while the lightning, though seemingly a 
lawless and rollicking spirit of the skies, was yet impatient to be 
pressed into the quiet and useful service of man. Can there be a 
doubt that other powers and forces, equally potent and marvellous, 
await the discipline of human genius ? Not in vain was man called 
upon, at the very morning of creation, to ' subdue the earth.' Already 
has he justified the bestowmeut of the viceroyal honor : who shall 
speak of the possibilities that are waiting for him in the future ! 





1. Ifatare of our Knowledge conceming Heat. — When we place the 
hand upon a stove with a fire in it, a feeling of warmth is experienced, 
while if it he made to touch ice, there is a sensation of cold. The im- 
pressions are supposed to he caused in hoth cases by the same force or 
agent ; in the first instance, the impulse passing from the heated iron to 
the hand ; in the second, from the hand to the ice. "What the nature 
or essence of this thing is, which produces such different feelings by 
moving in opposite directions, and which makes the difference be- 
tween summer and winter, nobody has yet discovered. It is named 
heat. Some have conjectured it to be a kind of material fluid, exceed- 
ingly subtle and ethereal, having no weight, existing diffused through- 
out all things, and capable of combining with every known species of 
matter ; and this supposed fluid has received the name of caloric. 
Others thiok heat is not a material tlung, but merely motion : either 
waves, or undulations produced in a universal ether, or a very rapid 
vibration, or trembliag of the particles of common matter, which is in 
some way contagious, and passes from object to object. Of the essen- 
tial nature of heat we xmderstand nothing, and are acquainted only 
with its effects: — our information is limited to its behavior. It resides 
in matter, moves through it, and is capable of variously changing its 
conditions. It is an agent producing the most wonderful results every 
where ai'ound and even within us ; — a force of such tremendous energy, 
such far-reaching, all-pervading influence, — that we may almost venture 
to say it has been appointed to take control of the material universe ; 


wMle in the plan of the Creator, it is so disciplined to the eternal re- 
straints of law, as to become the gentle minister of xmiversal benefi- 

2. To what Extent the Earth Is wanned by the Sunt Heat comes 
from the sun to the earth in streams or rays associated with light. It 
has been ascertained by carefol measurement, that the quantity of 
solar heat which falls upon a square foot of the earth's surface in a 
year would be sufficient to melt 5400 lbs. weight of ice ; and as a 
cubic foot of ice weighs 54 lbs,, the heat thus annually received would 
melt a column of it 100 feet high, or a shell of ice enveloping our 
globe 100 feet thick. As the sun turns aroimd once in 25 days, thus 
constantly exposing different parts, we conclude that equal quantities 
of heat are thrown from all portions of his surface, and are thus ena- 
bled to calculate the total amount of heat which he imparts annually. 
K there were a sphere of ice 100 feet in thickness completely sur- 
rounding the sun, at the same distance from him as the earth's orbit, 
his heat would be sufficient to melt it in the course of a year. This 
quantity of heat would melt a shell of ice enveloping tJie sun's surface 
38.6 feet thick in a minute, or 10.5 miles in thickness in a year. We 
are, therefore, warmed" by heat-rays shot through a hundred million 
miles of space, from a vast self-revolving grate having fifteen hundred 
thousand miles of fire-surface heated seven times hotter than our 
fiercest blast furnaces. 

8. We get Heat also from the Stars. — Although the sun is the most 
obvious and conspicuous source of heat for the earth it is by no means 
its sole source. Of the enormous quantity of heat that streams away 
in all directions from his surface, the earth receives but a small frac- 
tion. But it is neither lost nor wasted ; he not only warms the earth, 
but assists to warm the universe. Our globe catches a trifling portion 
of his rays ; but the rest fly onward to distant regions, where all are 
finally intercepted by the wandering host of orbs with which the 
heavens are filled. And what the sun does, all the other stars and 
planets are also doing. A mighty system of exchanges (32)* is estab- 
lished among the bodies of space, by which each radiates heat to all 
the rest, and receives it in turn from all the rest, according to the 
measure of its endowments. The whole stellar universe thus contrib- 
utes to our warmth. It is a startling fact, that if the earth were de- 
pendent alone upon the sun for heat, it would not get enough to make 
the existence of animal and vegetable life possible upon its surface. 

* These numbers refer to paragraphs. 


It results from the researchieg of Poutllet, that the starry spaces fur- 
nish heat enough in the course of a year to melt a crust of ice upon 
the earth 85 feet thick, almost as much as is supplied by the sun. 
This may appear strange, when we consider how immeasurably small 
must be the amount of heat received from any one of these distant 
bodies. But the surprise vanishes, when we remember that the whole 
firmament of heaven is so thickly sown with stars, that in some places 
thousands are crowded together within a space no greater than that 
occupied by the full moon. (Dr. Laedistee.) 

4. Heat unequally Distributed upoa the Earth. — The quantity of heat 
which the earth receives from the sun is very unequal at different 
times and places. The earth turns around every day ; it is globular 
in form, and is constantly changing the position of its surface in rela- 
tion to the sun, as it travels about him in its annual circuit. The con- 
sequence is, that we receive more heat during the day than at night ; 
more at the equator than toward the poles ; more in summer than in win- 
ter. "We are all aware that the temperature may fall from blood heat 
at mid-day, to the point of frost or freezing at night ; and while at the 
equator they have a temperature averaging, the year round, 81-5 
degrees, at Few York (less than 3,000 miles north), the average annual 
heat falls to 60 degrees ; and at Labrador (less than a thousand miles 
farther north), the average temperature of the year sinks below freez- 
ing. Nor do places at the same distance from the equator receive 
equal amounts of solar heat. A great number of circumstances 
connected with the surface of the earth, disturb its regular and uniform 
distribution. Dublia for example, though between eight and nine 
hundred miles farther from the equator than New York, has as high 
a yearly temperature. Some places also experience greater contrasts 
than others between the different seasons: thus while New York 
has the summer of Rome, it has also the winter of Copenhagen. 


5. It Controls the Distribution of Vegetable Life. — ^It is this variable 
quantity of heat received at different places and seasons, which deter- 
miues the distribution of life upon the globe. Certain tribes of plants, 
for example, flourish in the hot regions of the tropics, and cannot live 
with a diminished^intensity of heat. Accordingly, as we pass to the 
cooler latitudes, they disappear, and new varieties adapted to the new 
conditions take their place. As we pass into stiU colder regions, these 
again give way to others of a hardier nature, or which are capable of 


living where there is less heat. As we proceed from the hot equator 
to the frozen poles, or as we pass upward from the warm valley to the 
snowy summit of a lofty mountain, we cross successive belts of varying 
vegetation, which are, as it were, definitely marked off by the different 
quantities of heat which they receive. " In the tropics wo see the 
palms, which give so striking a characteristic to the forests, the broad- 
leaved bananas, and the great climbing plants, which throw them- 
selves from stem to stem, like the rigging of a ship. Next follows a 
zone described as that of evergreen woods, in which the orange and 
the citron come to perfection. Beyond this, another of deciduous 
trees — the oak, the chestnut, and the fruit trees with which, in this 
climate, we are so well acquainted ; and here the great climbers of 
the tropics are replaced by the hop and the ivy. Still further advanc- 
ing, we pass through a belt of conifers — ^firs, larches, pines, and other 
needle-leaved trees — and these, leading through a range of birches, 
which become more and more stunted, introduce us to a region of 
mosses and saxifrages, but which at length has neither tree nor, shrub; 
and finally, as the perpetual polar ices are reached, the red snow algae 
is the last trace of vegetable organization." 

6. Heat Regulates the Distribution of Animals. — It is the same also 
with animal life. Difterent animated races are adapted to different 
degrees of temperature, and belong within certain heat-limits, just like 
plants. In going from the equator to the poles, different classes of 
animals appear and fade away, as the temperature progressively de- 
clines. Some are adapted to the alternations of winter and summer 
by changes of their clothing ; and others, as birds, are pursued from 
region to region by the advancing temperatures. Animals whose con- 
stitutions are conformed to one condition of heat, if transported to 
another, suffer and perish: while the lion is confined to his torrid 
desert of sand, the polar bear is imprisoned in the frigid desert of ice ; 
and, in both cases, the sunbeam is the chain by which they are bound. 

7. Heat Influences Man's Physical DeTelopmcnt. — Nor does man fur- 
nish an exception to these controlling effects of temperature. The 
striking peculiarities of physical appearance and endowment, exhibited 
by different tribes and communities of men, is well known ; and it has 
long been understood that much of these differences is due to the all- 
powerful influence of heat. " The intense cold, dwarfs and deforms the 
inhabitant of the polar regions. Stunted, squat, large-headed, fish- 
featured, short-limbed and stiff-jointed, he resembles in many points 
the wolves and bears in whoso skins he wraps himself. As he ap- 
proaches the sunny south, his stature expands, his limbs acquire shape 


and proportion, and his features are ameliorated. In the genial region, 
he is heheld with that perfect conformation, that freedom of action 
and intellectual expression, ia which grace and beauty consist." 

8. Extremes of Dress in Diflfereut Localities. — The remarkable contrasts 
of temperature which different races experience, is well illustrated by 
their circumstances of dress. "While in the West Indian Islands a 
single fold of cotton is often found to be an incumbrance, the Green- 
lander wraps himself in layer after layer of wooUens and furs, fox-skins, 
sheep-skms, wolf-skins, and bear-sMns, untU we might suppose him 
well guarded against the cold ; yet with a temperature often a hundred 
degrees below the freezing-point, he cannot always protect himself 
against frozen extremities. Dr. Kane observes, " rightly clad, he is a 
lump of deformity waddling over the ice: unpicturesque, uncouth, 
-and seemingly helpless. It is only when you meet him covered with 
frost, his face peering from an icy halo, his beard glued with frozen 
respiration, that you look with inteUigent appreciation on his many- 
coated panoply against king Death." 

9. Temperatnre and Character. — The effect of cold is to benumb the 
body and blunt the sensibihty ; whUe warmth opens the avenues of 
sensation, and increases the susceptibility to external impressions. 
Thus, the intensity with which the outward world acts upon the inward 
through the sensory channels, is regulated by temperature. In cold 
countries the passions are torpid and sluggish, and man is plodding, 
austere, stolid, and unfeeling. "With the barrenness of the earth, there 
is sterUity of thought, poverty of invention, and coldness of fancy. 
On the other hand, the inhabitants of torrid regions possess feverish 
sensibilities. They are indolent and effeminate, yet capable of furious 
action ; capricious in taste, often ingenious in device ; they are extrav- 
agant and wild in imagination, delighting in the gorgeous, the daz- 
zUng, and the marvellous. In the medium heat of temperate climates, 
these marked excesses of character disappear; there is moderation 
without stupidity, and active enterprise without fierce impetuosity. 
Society has more freedom and justice, and the individual more con- 
stancy and principle : with loftiness of thought, there is also chastening 
of the imagination. By comparing the effects of climate in the tor- 
rid, temperate, and frigid zone, we observe the determining influence 
of external conditions, not only upon the physical nature of man, but 
over the mind itself. " We may appeal to individual experience for 
the enervating effects of hot climates, or to the common understanding 
of men as to the great control which atmospheric changes exercise, 
not only over the intellectual powers, "but even on our bodily well- 


being. It is within a narrow range of climate that great men have 
been bom. In the earth's sonthern hemisphere, as yet, not one has 
appeared ; and ia the northern, they come only \ri.thin certain paral- 
lels of latitude. I am not speaMng of that class of men, who in all 
ages and ia every conntry, have risen to an ephemeral elevation, and 
have sunk agam into their native insignificance so soon as the causes 
which have forced them from obscnrity cease, but of that other class 
of whom God makes bnt one In a century, and gives hiTn a power of 
enchantment over his fellows, so that by a word, or even by a look, 
he can electrifv, and gnide, and govern mankind." — (Dr. Deapee.) 

10. Inflaeaee of the Supply of Fuel. — The abundance or scarcity of the 
snpply of fael, as it controls the amonnt of artificial heat, exerts a power- 
fol influence upon the condition of the people in various ways ; indeed, 
it may involve the health and personal comfort of whole nations, to 
snch an extent, as even to contribute to the formation of national char- 
acter. Where fuel is scarce, houses are small, and their occupants 
crowded together ; the external air is as much as possible excluded ; 
the body becomes dwarfed ; and the intellect duU. The diminutive 
Laplander spends his long and dreary winter in a hut heated by a 
smoky lamp of putrid oil ; an arrangement which afflicts the whole 
nation with blear eyes. Scarcity of fuel has not been without its 
effect in forming the manners of the polished Parisians, by transfer- 
ring to the theatre and the cafe those attractions, which, in countries 
where fuel is common and cheap, belong essentially to the domestic 

11. Temperature and Language. — AEBrmsroT suggested not only that 
heat and air fashion both body and mind, but that they also have a 
great effect in forming language. He thought the serrated, close 
way of speaking among the northern nations, was owing to their 
reluctance to open their mouths wide in cold air, which made their 
speech abound in consonants. From a contrary cause, the inhabitants 
of warm climates formed a softer language, and one abounding in 
vowels. The Greeks, inhaling air of a happy medium, were celebrated 
for speaking with the wide-open mouth and a sweet-toned, sonorous 

12. Man may Make his own Climate. — So controlling is this agent, 
and yet man comes into the world defenceless from its invasions; 
provided with no natural means of protection from its disturbing and 
destructive influence. But in the exercise of that intelligence which 
gives him command over nature, he has studied the laws, properties, 
and effects of, and the methods by which it may be produced 


and regulated. He has devised the means of creating an artificial and 
portable climate, and thus of releasing himself, in a great measure, 
from the vicissitudes of temperature. We are to regard the production 
and control of artificial climate, as an art involving the development 
and expansion of mind and body, the preservation of health and the 
prolongation of life. Such has been the thought expended upon this 
subject, and so important the results to the well-being of man, that we 
may almost venture to measure the civilization of a people, by the per- 
fection of its plans and contrivances for the management of heat. 


13. Heat tends to Equal Siffasion. — "We have said that heat is a force, 
or energy, existing everywhere throughout nature. Every kind of 
matter which we know contaios heat, but all objects do not contain 
equal quantities of it. If left to foUow its own law, heat would dis- 
tribute itself through all the matter around, untU each body received 
a certain share ; and it would then be in a condition of general rest, or 
equal balance, (equilibrium.) It is to this state that heat constantly 
tends. If a very hot body of any kind is brought into a room, we all 
know it will at once begin to lose its heat, and that the temperature 
continues to descend until it is the same as the surrounding air, walls, 
and forniture. 

14. How do we get acquainted with Heat?— But before heat can 
tend to equilibrium, it must first be thrown out of this state. There 
are forces which tend to disturb the equal lalance of heat, causing it 
to leave some bodies, and accumulate in others in unusual or excessive 
quantities. It is the passing of heat from body to body, from place to 
place, — ^robbiug one substance of it and storing it up in another ; in 
short, its motimi, and the effects it produces, which enable ns to 
become acquainted with it. How, then, may we know when one. sub- 
stance has been deprived of heat and another has received it ? or how 
can we ascertain the quantity of it which a body possesses? 

15. Heat aeemnnlating in Bodies, cnlai^es them.— -It is an effect of 
heat, that when it enters into bodies it makes them larger ; it increases 
their bulk, or expands them, so that they occupy more space than they 
did before, A measure that will hold exactly a gallon in winter, will 
be expanded by the heat of summer so as to hold more than a gallon. 
The heat of summer lengthens the foot-rule and yard-stick. A pen- 
dulum is longer in summer than in winter, and therefore swings or 
vibrates slower, which causes the clock to lose time. Twenty-three 


pints of water, taken at the freezing point, wonld expand into twenty- 
fonr by being heated to boiUng. The difference in the heat of the 
seasons affects sensibly the bulk of liquors. In the height of summer, 
Fig. 1. spirits will measure five per cent, more than in the 

depth of winter. (Geaham.) "When 180 degrees of 
"* ' heat are added to iron, 1000 cubic inches become 

1045 ; 1000 cubic inches of air become 1365. Some 
substances, however, in solidifying expand. This is 
the case with water, which attains its greatest 
density, or shrinks into its smallest space, at the 
temperature of 38"8°, as seen in fig. 1. Prom this 
point, either upward or downward, it enlarges ; and 
greatest at freezing, or 32°, the expansion amounts to about 
ensi y. j^^^ ^^ .^^^ bulk, Ico therefore floats upon the surface 
of water. The wisdom of this exception is seen, 
when we reflect, that if it sank as fast as it is formed, 
whole bodies of water would be changed to solid ice. 

16. Relation betweeu Heat and Expansion. — In the same manner, all 
the objects about us are changed in their dimensions as heat enters or 
leaves them. Different substances expand differently by the same 
quantities of heat ; but when a certain measured amount is added to, or 
taken from the same kind of substance, it always swells or shrinks to 
exactly the same extent. The variation of size produced in solid sub- 
stances, such as wood, stone, or iron, is very small ; we should not be 
aware of it without careful measurement. The same proportion of 
heat causes liquids, such as water, alcohol, and mercury, to vary in 
bulk more than solids ; while heat added to gases, or airs, produces a 
much greater expansion than it does in liquids. Although heat thus 
causes bodies to occupy more space and become larger, yet it does not 
make them heavier. The same substance weighs exactly the same, no 
matter how cold or how hot it is ; hence heat is called imponderable. 

17. Principle and Constrnction of the Thermometer. — ^If, then, when 
a substance receives a certain quantity of heat, it undergoes a certain 
amount of enlargement, we can use that enlargement as a measure of 
the heat ; and this is what is done by the thermometer or heat-meas- 
urer. A common thermometer is a small glass tube, with a firfo 
aperture or hole through it, like that in a pipe stem, and a hollow 
bulb on one end of it fig. 2. This bulb and part of the tube is fiUed 
with the liquid metal mercury. By suitable means, the air is removed 
from the empty part of the tube, and its open end sealed up. The 
bulb is then dipped into water containing ico, and a mark is made 









upon the tube at the top of the mercurial column. This point of 
melting ice is the same as that at which water freezes, and is hence 
called the freezing point. The tube is then Fia. 2. 

removed, and dipped into boding water. 
The heat passes from the water, through 
the glass, into the mercury, which rapidly 
expands and rises through the narrow 
bore. It passes up a considerable distance, 
and then stops ; that amount of heat will 
expand it no more. The height of the 
mercury is again marked upon the tube, 
and this is called the ioiling point of water. 
The distance upon the tube between these 
two points is then marked off into 180 
spaces, which are called degrees, and 
marked (°). Now, it is clear that the 
amount of heat which runs the mercury 
up tlirough these 180 spaces is precisely 
the same quantity that changed the water 
from the freezing to the boding point ; so 
that we may say that the water in this 
case received 180 degrees of heat. If we 
mis a pound of water at the bodiug point with another pound at the 
freezing point, the result wiU be a medium ; and if the thermometer 
is plunged into it, the mercury wiU stand at the ninetieth space — that 
is, it contatas 90 degrees of heat according to this scale of meas- 
urement. And so, by dipping the thermometer into any vessel of 
water, we ascertain how much heat it contains. 

18. How Tbermometers are Graduated or Marked.— But this is not 
the way that the scale of the common thermometer is actually marked. 
Its inventor, Faheenheit, instead of beginning to count his degree3 
upward from the freezing point, thought it would be better to begin 
,to count from a point of the extremest cold. Accordingly, he mixed 
salt and snow (55) together, and putting his thermometer in it, the 
mercury feU quite a distance lower than the freezing point of water. 
This he supposed to be the greatest cold it is possible to get, though 
an intensity of cold has since been obtained 150° lower. Marking 
off this new distance through which the mercury had fallen, in the 
same way as above, he got 32 additional spaces or degrees. Calling 
this point of least heat or greatest cold he could get, nought or zero, 
he counted up to the fi-eezing point of water, which was 32°, and 




adding tWs to the 180 above, he got 213 as the boiling point of water. 
This is the way we find the common thermometer scale marked (Fig. 
2) upon brass plates, to which the glass tube is attached. The centi- 
grade thermometer calls the point of melting ice zero^ and marks the 
space up to boiling water into 100 degrees. In Eeaumur's thermometer, 
the same space is divided into 80 degrees. Degrees below zero are 
marked with the minus sign, thus — . It deserves to be remarked, 
that the glass tube expands by heat as well as the mercury, but by no 
means to so great a degree. And besides, there being a considerable 
quantity of mercury in the bulb, it requires but a very small expansion 
of it to push the quicksilver up the narrow tube, through a perceptible 

19. Exactly what the Thermometer indicates. — The word thermometer 
is derived from thermo, heat, and metron, measure, and it therefore 
signifies heat-measurer. But what does it measure ? That which is 
measured we usually name quantity. But we must not suppose that 
the thermometer indicates quantities of heat in any absolute sense. 
For example, if we dip a giU of water from a spring in one vessel, 
and a gallon in another vessel, a thermometer will indicate exactly 
the same degree of heat in one as in the other ; but we cannot thence 
infer that the absolute quantity of heat is as great in the gUl of water 
as in the gallon. The thermometer shows us simply the degree of in- 
tensity of the heat in its mercury ; and as this constantly tends to the 
same point as that of surrounding bodies, we take its degree to be 
their degree. If the thermometer suspended in a room stands at 70°, 
we say the room is at 70°, because heat tends to equalization. 
If by opening windows or doors the thermometer falls to 60°, we say 
the room has lost 10° of heat, — speaking of it as a measured quantity. 
The instrument indicates variable degrees of intensity, which are con- 
verted into expressions of quantity. We shall shortly see that there 
are certain conditions of heat which the thermometer totally fails to 

20. Importance of the Domestic use of the Thermometer. — As the ques- 
tion of temperature is one of daily and hourly interest, not only of 
the utmost importance in conducting numerous household operations, 
but of the highest moment in relation to the maintenance of health, 
it will at once be seen that a thermometer is indispensable. Every 
family should have one, and accustom themselves to rely upon it as a 
practical guide in relation to heat, and not to depend upon feeling or 
guessing. Thermometers costing from fifty cents to a dollar and a half, 
will answer all ordinary purposes. They are so mounted that the scale 


and tube may be drawn out of the frame, so that the bulb can be im- 
mersed in a liquid, if required. They must be gradually warmed before 
dipping in hot liquids to prevent fracture of the glass, and of course 
need to be handled with much care. Their scales extend no higher 
than the boiling point of water. There is usually some departure from 
the accurate standard in the indications of the cheaper class of instru- 
ments. Mr. Tagliabtje, a prominent maker of this city, states that these 
variations rarely exceed from 1 to 2 degrees. 

21. Interesting Facts of Temperature. — "We group together a few 
points of temperature of familiar interest.* 

Best temperature for a room 65°-68° 

Lowest temperature of human body (in Asiatic cliolera) 67° 

Mean temperature at the equator 81° 

Heat of the blood 98° 

Beefs tallow melts 100° 

Mutton tallow melts 106° 

Highest temperature of human body (in tetanus or lockjaw) .... 110° 

Stearine melts 111° 

Spermaceti melts 112° 

Temperature of hot bath 110°-180° 

Phosphorus inflames, Friction matches ignite 120° 

Tea and coffee usually drank , . ISO'-liO' 

Butter melts 130°-140° 

Coagulation of albumen , 145° 

Scalding heat . . , • , . . 150° 

Wax melts 155° 

Milk boils • . . . . 199° 

Sulphur melts 226° 

Cane sugar melts 320° 

Baking temperature of the oven 320°^00° 

Sulphur ignites 560° 

Heat of the common flre 1000° 


22. Heat passing through Bodies.— Heat in motion around us is coil-^- 
stantly passing through some substance, or from one material body to 
another. But all substances do not behave alike toward it. They do 
not aU receive, retain, or part with it in the same way. Through cer- 
tain bodies it passes rapidly in straight lines, like rays of light, and is 
then termed radiant heat, and this kind of heat-motion is called radi- 
ation, and the substances which allow it to pass through them are said 
to trammit it. We receive radiant heat from the sun and from arti- 
ficial fires ; and the air is one of those substances which permit it to 
pass through. 

* For a further list of temperatures, see Appendix A. 



23. Decrease in the Force of Heat-rays. — When heat radiates from 
any source, as the sun, a stove, an open fire, or flame, it passes from 
each point in all directions Fig. 3 ; it spreads out or diverges as it 

Fig. 3. 



Kadiation of heat. 

Fig. 4 

passes away so as to hecome weaker and much 
less intense. It decreases in power at a regular 
numerical rate, as seen in Fig. 4. It is commonly 
said that the intensity of radiant heat decreases 
inversely as the square of the distance ; that is, 
if in standing before the fire at a distance of two 
feet from it, we receive a certain amount of 
heat, and then we step hack to twice that dis- 
tance, we shall receive but one fourth the quan- 
tity ; at thrice the distance, but one ninth ; and 
at four times the distance, but one sixteenth the 
quantity, as is shown in Fig. 4. But this state- 
ment is only true when we consider the heat as passing from a single 
point. When it flows from an infinite number of adjacent points, — that 

is, a surface, which is the way 
it is practically emitted, it does 
not decrease at so rapid a rate. 
24. Different kinds of Heat.— 
We all know that some substan- 
ces will let light pass through 
them, and others will stop it. 
It is just so with heat : but the 
same substances which transmit 
light, do not always transmit 
heat. Air allows both to pass 

Showin;; the rate at which radiant heat is without obstruction ; but water, 
diffused and weakened. ^^.^^^ ^^ ^^.^^^^ ^^^^^^ ^^^ ^^^_ 

sage of light, has very little power to transmit heat. Eays of light, 
passing through water, are strakied of nearly all their heat. But 
there seems to be a difference in the source and nature of the heat 
itself, as to its power of getting through various bodies. Glass allows 
solar heat to go through it, but not artificial heat. A pane of glass 
held between the sun and one's face will not protect it from the 
heat ; but it may be used as a fire-screen. If we place a plate of 
glass and of rock-salt before a hot stove, the dark heat -will pass 
freely through the salt, but not through the glass. The glass is, 
therefore, opaque to heat (if we may borrow the language of light), 
while salt is tramparent to it, and is hence called the glms of heat. 


Meloni has shown that if the quantity of dark, radiant heat transmit- 
ted through air, be expressed by 100, the quantity transmitted through 
an equal thickness of a plate of rock-salt will be 92 ; flint glass, 67 ; 
crown glass, 49 ; alum, 12 ; water, 11. 

25. Heat which does not go throngh is Absorhed. — ^When a substance 
does not permit all the rays of heat which strike upon it, to pass 
through, those which are detained, or lodged within it, are said to be 
absorhed by it. Thus, fine window-glass transmits only 49 heat rays in 
a hundred, the remaining 51 being absor'bed by it. Now it is clear, 
that if all the heat pass through a substance, none can accumulate in 
it to warm or heat it. It is the heat detained or lodged in a body that 
warms it. The heating power is proportional to absorption. The 
atmosphere lets the sun's heat all pass — does not absorb it ; it is there- 
fore not warmed by it. 

26. Conditioas of Radiation. — The power of a body to emit or radiate 
heat, depends first, upon the quantity which it contains. Other things 
being the same, the higher its temperature compared with the sur- 
rounding medium, the more rapidly will it throw off its heat. As it 
cools, the radiation becomes slower and slower. But aU subtances at 
the same temperature, do not throw out their heat alike. The condi- 
tion of surfaces exerts a powerful control over radiation. Eough, 
uneven surfaces radiate freely, while smooth, polished surfaces offer a 
barrier to heat, which greatly hinders its escape. Metals, as their sur- 
faces are capable of the highest polish, are the worst radiators. Ac- 
cording to Meloni, smfaces smoked or covered with lampblack, radi- 
ate most heat. If the power of radiation of such a surface be repre- 
sented by 100, that of glass wiU be 90 (it is therefore an excellent 
radiator), polished cast-iron, 25 ; polished wrought iron, 23 ; polished 
tin, 14 ; brass, 7 ; silver, 3. By tarnishing, or rusting metallic surfaces, 
their radiating power is increased. Leslie has shown that, compared 
with a smoke-blacked surface, as 100, clean bright lead is 19, whUe if 
tarnished, it is 45. If the actual radiating surface is metallic, it matters 
little what substance is under it. Glass covered with gold-leaf, is re- 
duced in its radiating power to the condition of a polished metal. K the 
bright, planished, metallic sm'face is in any way dulled or roughened, 
as by scratching or rusting, its power of throwing off heat is greatly 
increased. Indeed, if the polished surface is only covered, the same 
effect is produced. Etjmfoed took two similar brass cylinders, cov- 
ered one Avith a tight investment of linen, and left the other naked ; 
he then fiUed each with hot water, and found that the same amount of 



heat which was thrown off by the covered cylinder in 36^ minutes, 
required 55 minutes to radiate from the naked cylinder. 

27. How Polishing affects Surfaces. — Dr. Laednee says "the diminu- 
tion of radiating power, -vyhich ordinarily accompanies increased polish 
of surface, is not a consequence of the polish in itself, hut of the in- 
creased density of the outer surface^ produced by the act of polishing; 
and the effect of roughening is to he ascribed to the removal of the 
outer and denser coating." 

28. Best Mode of Confining and Retaining Heat. — ^These principles show 
us how best to enclose and retain heat when we wish to prevent waste 
from radiation. Glass, porcelain, and stone ware surfaces, radiate 
freely : vessels of these materials are not the best to preserve foods 
and fluids hot at table. They should either be of polished metal, or 
have bright metallic covers, which will confine the heat. Bright tea- 
urns and coffee-pots are best to retain their contents hot ; and a tea- 
kettle keeps hot water much more effectually if clean and bright, than 
if covered with soot, though it is much harder to boil. Pipes intended 
to convey heat should be bright and smooth, while those designed to 
radiate or expend it, should be rough. For the same reason, polished 
stoves and stove-pipes are less useful in warming rooms than those 
with rougher surfaces. 

29. Color of Surfaces does not influence Radiation. — It is very generally 
supposed that the color of a substance influences the escape of heat 
from it. But the experiments of Dr. Bache have shown that this is 
a popular fallacy. He has proved that color exerts no control on the 
radiation of non-luminous heat, or such as is unaccompanied with light. 
A body will emit heat from a white or black surface with equal 

30. Heat thrown off from Bodies. — Eadiant heat striking upon bodies, 
if it is not permitted to pass instantly through them in straight lines, 
is either absorbed or reflected. If reflected, it is instantaneously thrown 
back from the surface of the body, and therefore does not enter to 
warm it. If absorbed, it is gradually taken into the substance, and 
raises its temperature. A bright metallic surface wiU reflect the heat 
rays and itself remain quite cold. As heat cannot get out through a 
bright surface, so it cannot get in through it. AU the heat that is 
thrown upon such a body, is either reflected or absorbed ; that which is 
not disposed of one way goes the other. If half of it is absorbed, the 
other half will be reflected. Glass absorbs 90 per cent, and reflects 10, 
while polished silver reflects 97 per cent, and absorbs but 3. A good 
absorbing surface is a bad reflecting surface, and a good reflector is a 


bad absorber. So a good radiating surface absorbs -well and reflects 
badly, wbile a bad radiating sni-face absorbs badly but reflects well. 
The density, or polish of a surface controls the admission as -well as 
the escape of radiant heat. Two kinds of heat may thus pass in straight 
lines from a body — radiant heat and reflected heat. The former comes 
from within, and therefore cools it ; the latter strikes against it, and 
rebounds without either warming or cooling it. 

31. Color of Snrfaee inflaenees the admission of Heati — We have seen 
(29) that color has no influence over radiating surfaces ; but the power 
which bodies possess of alsorhing heat, depends very much upon color. 
Feanklik spread differently colored pieces of cloth upon snow in the 
sunshine. That of the black color sunk farthest below the surface ; 
which showed that it melted the most snow, and consequently received 
most heat. The blue piece sunk to a less depth, the brown stiU less, 
and the white hardly at aU, which showed that it absorbed least heat. 
Hence, by scattering soot over snow, its melting may be hastened : it 
wiU absorb more of the solar heat. A dark-colored soil warms easier 
in spring, is earlier, and has a higher temperature during summer, than 
one in other respects similar but of a lighter color. Darkening a soil 
in color, therefore, is equivalent to removing it farther south. Grapes, 
and other fruits, placed against a dark wall, wiU mature or ripen 
earlier than if against light-colored walls, because, for the same reason, 
they are warmer. So, also, in the matter of clothing, white throws 
off the solar heat, while black absorbs it. 

32. Exchanges of Heat— it escapes from aO Snhstances. — It has been 
stated that, down to 200° below the freezing point of water, substances 
contain heat and may part with it : and as we know of no means by 
-which heat can be absolutely enclosed or confined within bodies, all 
are regarded as not only possessing the power of radiation, but as actu- 
ally exercising it. Eays of heat pass away in every direction, from all 
points of the surfaces of all bodies. "When several objects of various 
temperatures, some cold and some hot, are placed near each other, 
their temperatures gradually approach the same degree, and after a 
time they will be found to have reached it. Now all these bodies are 
supposed to be constantly radiating heat to each other, and hence con- 
stantly exchanging it. If we place a cannon-ball at a temperature of 
1000° or a red heat, beside another at 100°, it will part with its heat 
rapidly to the latter, as illustrated by the radiant lines in Fig. 5. But 
the ball at 100° also radiates its heat, although more slowly, and thus 
returns a portion to the hotter ball ; so that there is an exchange estab- 
lished. But if a baU of ice at 82° be placed beside the cannon-baU at 


100°, the same thing takes place, only in a less iatense degree; and if 
Fig. 5. an ice-ball from the 

Arctic region at 100" 
below the freezing 
point, were placed be- 
side another at 32°, ex- 
actly the same thing 
would occur. Thns all 
bodies are constantly 

Exchanges of heat ; it radiates from hodies at all temper- interchanging heat and 

tending to equahzation. 

S3. Starlight Jfiglits colder than cloudy Ones. — The various objects 
upon the earth's surface, are not only continually radiating their heat 
to each other, but also upward through the au* into space. If there 
be clouds above, they throw it back again to the earth's surface ; but 
if the sky is cloudless, the heat streams away into space, and there is 
none returned. At night, therefore, when there is no heat coming 
down from the sun, and no clouds to prevent its escape from the earth, 
the temperature of the earth's surface and the objects thereon, falls. 
Those which radiate best, cool fastest, and siuk to the lowest tempera- 
ture. Clear, starlight nights are thus colder than cloudy nights ; and 
although more pleasant and inviting for evening walks, require that 
more clothing should be worn. 

34. How Dew is Prodnced. — The cause of dew was not imderstood 
untU lately. Many were persuaded that it came out of the earth; 
while others thought it fell as a fine rain from the elevated regions of 
the atmosphere. The alchemists regarded it as an esudation from the 
stars. They believed dew-water contained celestial principles, and 
tried to obtain gold from it. The problem was solved about forty 
years ago, by Dr. Wells, who first considered it in connection with 
the radiation of heat. The air contains moisture in the state of invis- 
ible vapor ; if its temperature be high, it will hold more moisture, if 
low,less (286). When, therefore, the air is sufliciently cooled, its moisture 
is condensed, and appears as drops of water. These are often seen in 
summer days upon the outside of the pitcher of cold water ; improp 
erly called the sweating of the pitcher. The moisture that is seen 
trickling down the window-pane in winter, is condensed from the 
vapor of the air in the room, by the outward escape of heat from the 
glass, and the consequent cooling of the air in contact with it inside. 
When, therefore, by nightly radiation, any objects upon the earth's 
surface have become so cold as to cool the aii' in contact with them, 


sufficiently to condense its moisture, dew is formed, and the degree of 
temperature at which this effect takes place, is known as the dew-point. 
85. Conditions of the Deposit of Dew. — Every calm and clear night 
the surface of the ground cools by radiation from lO'^ to 20°. But 
this surface is composed of various objects, which radiate unequally. 
Some part with their heat so rapidly as to cool the air down to the 
point of condensation, and dew is deposited upon them. Others ra- 
diate so slowly that their temperatures do not sink to the dew point, 
and no dew is formed upon them. Good radiators become covered 
with dew, while bad radiators remain dry. Grass, for example, is an 
excellent radiator, and it receives dew copiously, while under the same 
circumstances, stones, being bad radiators, are not moistened. Dew 
is deposited from a stratum of air only a few inches thick, which is 
condensed by contact with the cold body. If, however, that stratum 
of air is moved away before it gets sufficiently cooled, no 'dew will be 
formed. Hence, when the air is in motion, as on windy nights, there 
is no dew. Fall of temperature always precedes the formation of dew, 
and the greater the fall, the heavier the dews ; the quantity of moist- 
ure in the atmosphere, m both cases being the same. Farmers very 
well know that nights with heavy dews are very cold ; but the cold 
is the cause^ not the effect^ of the dew. The moister the air is, with 
the same descent of temperature, the more dew falls. Thus, arid 
deserts are dewless, notwithstanding the intense nightly radiation. 

36. Exchanges of Heat may prevent Dewt — ^We have noticed Peevost's 
theory of the exchanges of heat, by which, all bodies are assumed to 
radiate heat to each other constantly (32). This explains why little 
or no dew is found under trees. "While the grass radiates upward, the 
foliage radiates downward, and thus checks cooling. For this reason, 
no dew is precipitated on cloudy nights. As objects radiate upward, 
the clouds radiate back again, and prevent the falling of the tempera- 
ture. More dew falls upon the summits of mountains, where objects 
are most open to the sky, than in valleys, where the angle of radiation 
or access to the open heavens is much less. Objects protected in an_, 
way from exposure to the sky, are, to that extent, guarded from dew. 

37. Frost Caused in the same way as Dew. — As a certain amount of 
cooling, deposits moisture from the air, more still, freezes it ; and 
hence, frost or frozen dew. This extreme cooling is often hurtful to 
vegetation, and during the serene nights of spring, tender plants are 
often killed, as is frequently the case with immature fruits aud grain 
of autumn. Here, again, all circumstances which oppose radiation, 
prevent the cooling. "Vegetables, sheltered by trees, suffer less than 


those not so protected. A thin covering of cloth or straw, preserves 
plants, as may also fires that fill the air with smoke. 


38. Heat creeps slowly tlirongh some Bodies. — If we place one end of 
a bar of metal in a fire, that end becomes hotter than the other parts 
of the bar. But this effect is only temporary ; the heat will gradually 
;)ass through it, being communicated from particle to particle, until 

Fig. 6. the other extremity becomes 

heated. This is easily shown 
by taking several marbles, and 
sticking them to an iron or 
copper wire with wax Tig. 
6. If now heat is applied 
to one end of the wire, it 

The balls drop successively as the heat moves in, i i ,-, 

along the rod. gradually travels along, the 

wax is melted, and the marbles drop off successively. The heat in 
this case is conducted by the metal. 

39. Different Substances conduct at different Rates. — Heat diffuses in 
this manner, at very unequal speed through different substances. If 
we hold one end of a nail in a candle flame, it soon gets so hot as to 
burn the fingers ; while we can fuse the end of a glass rod in a lamp, 
although holding it within an inch of the melting extremity. Iron 
thus conducts heat much better than glass. Those substances through 
which heat is diffused most rapidly, are called good conductors, while 
those through which it passes slowly, are iad conductors. In general, 
the denser a body is, — that is, the closer are its particles, — the better 
does it conduct heat ; while the more porous, soft, loose and spongy 
it is, the lower is its conducting power. The metals, therefore, are the 
best conductors, while bodies of a fibrous nature, such as hair, wool, 
feathers, and down, are the worst conductors of heat. 

40. Enmford's Scale of Conductors. — Rumfoed arranged bodies in 
the following order, their conducting power progressively diminishing 
as the list proceeds. Gold, silver, copper, iron, zinc, tin, lead, glass, 
marble, porcelain, clay, woods, fat or oil, snow, air, silk, wood-ashes, 
charcoal, lint, cotton, lampblack, wool, raw silk, fur. 

41. Conducting Power of Building materials. — Bad conductors, — non- 
conductors, as they are called, — afford the best barriers to heat, and 
they are employed when it is desired to confine it. In winter, nature 
protects the earth and crops from excessive cold, by a layer of non- 


conducting snow. The birds, she prc)tects by feathery and downy plu- 
mage ; quadrupeds, by hair, wool, fur ; — and even the trees, by porous, 
non-conducting ^bark. In the management of heat, man finds the 
variation in the conducting powers of bodies, of the highest import- 
ance. In building houses, the worst conductors are the best materials 
for the walls. WhUe they promote warmth in winter, by retaining 
the heat generated by fires within, they are favorable to coolness in 
suromer, by excluding the external heat. HuTCHrisrsoN examined 
some building materials, and ascertained their conducting powers 
to be as follows, omitting fractions. (Slate being taken as 100.) 
Marble 75 to 58, fire brick 62, stock brick 60, oak wood 34, 
lath and plaster 25, plaster of Paris 20, plaster and sand 18. The 
hard woods conduct better than soft, and green woods better than 
dry. Dry straw, leaves, &c., are good non-conductors, and are used 
to cover tender plants in winter, but if wetted, they convey heat 
much better. 

42. Non-condaeting properties of Air. — Air is one of the most perfect 
non-conductors; Etjmfoed thinks it is the best of all. The conduct- 
ing power of air, however, is greatly increased by moisture. If we 
represent the power of common dry air to conduct heat, by 80, its 
power, when loaded with moisture, rises to 230, — it is nearly trebled. 
For this reason, damp air feels colder to the body — ^it conducts away its 
heat faster. Those substances which enclose and contain air, as pow- 
dered charcoal, tan-bark, sawdust, chafi', &e., are good non-conductors 
of heat. Sawdust is an excellent bar to heat ; it should not be too 
much pressed together, as then, the particles, being in too close con- 
tact, conduct better : — nor too loose, as the air circulates through it, 
and thus conveys the heat. A layer of air between double windows, 
checks the escape of heat, but we do not, in such a case, avail our- 
selves of its perfect non-conducting power, otherwise we might use 
it to enclose ice-houses, &c. It is easily set in motion (97), and thus 
becomes a ready transporter of heat. Loose, porous bodies are filled 
with it, and they act as non-conductors by preventing its motion, 

43. Non-conducting Properties of Clotliing. — Winter apparel is made 
of non-conducting woollen fabrics, which prevent the escape of heat 
from the body. Cotton carries ofi" the heat faster than wool ; and 
linen still faster than cotton. Linen is pleasantest in summer to re- 
lieve the body of heat, but it cannot defend the system like flannel 
against the sudden changes of temperature in an inconstant climate. 
In local inflammation of the body, linen is the best for dressings and 
applications, as it is a better conductor, and therefore cooler than cot- 


ton.* The tigh, non-conducting power of the -woollens, is shown 
hy the common practice of preserving ice in hot weather, by simply 
wrapping it in flannel. 

44. Oar Sensations of Heat depend upon Conduction. — The sense of 
touch is an unreliable guide to the degree of heat, because substances 
are so diverse in conducting power. The badly conducting carpet 
feels warmer to the naked feet than the better conducting oilcloth, 
because the latter will carry away the heat faster from the skin, al- 
though both are at exactly the same temperature. This influence of 
conduction over sensation, as also the remarkable difference of con- 
ducting power among solids, liquids, and gases, may be shown in a 
forcible manner. If the hand be placed upon metal at 120° it will be 
burned, owing to the rapidity with which the heat enters the flesh. 
"Water will not scald, provided the hand be kept in it without motion, 
till it reaches the temperature of 150° ; while the contact of dir at 
250° or 300° may be endured. Sir Joseph Banks went into a room, 
heated to 260°, and remained there a considerable time without incon- 
venience. The particles of air are so far asunder, that the heat crosses 
their inter-spaces with difficulty ; and as but few of them can come 
in contact with the body at once, the amount of heat that they can 
impart is comparatively small. 


45. It is carried by Particles in Motion. — The freedom with which the 
particles of liquids and gases move among each other, is another source 
of the motion of heat. Water conducts heat but very imperfectly. 
If a glass tube filled with water, be inclined over a lamp, so that the 

^10- '''■ flame is applied at the upper end Fig. 7, the 

water will boil at the top of the column, but 
below the point where the flame is applied, 
the temperature of the water will be but lit- 
tle elevated in a long time. The conduction 
of heat is not influenced by the position of the 
body along which it passes. It moves through 
a conductor as swiftly downward as upward, 
or horizontally. Had the heat, in this case, 

The water doea not conduct ■^. iii , ni 

the heat downwards. been conducted^ it would have travelieQ as 
readily down the water column as upward. Yet all understand that 

* Linen is also best for dressing local inflammations, because its fibres are round and 
smooth, and therefore, less irritating. The fibres of cotton are flat and angular, and of 
woollen, rough and jagged, and consequently, uufit for this purposo (795). 



a large amount of water may be heated by a small fire, if the beat 
be applied at the bottom. The cause of this is, that the lower layer 
of water in the vessel, being warmed, expands, becomes lighter, and 
for the same reason that a cork would rise, ascends through the mass 
of liquid above. Its place is taken by the colder liquid, which in 
turn warms, expands and ascends ; and thus currents are formed, by 
which the heat is conveyed upward, and diffused through the mass. 
This mode of heat movement is hence called convection of heat. 

46. How the Water-currents may be shown. — The circulation thus pro- 
duced by ascending and descending currents, may be beautifully seen 
by nearly filling a pretty large glass fiask with water, and dropping 
into it a few small pieces of soHd litmus {a cheap^ Hue coloring sub- 
stance), which sink through the liquid. On applying heat to the bot- 
tom of the vessel by a small lamp, a central current of water, made 
visible by the blue tint it has acquired from the litmus, is seen rising 
to the surface of the liquid, when it bends ^ „ 

over m every direction like the branches of 
the palm tree, and forms a number of descending 
currents, which travel downward near the 
sides of the vessel Fig. 8. Two causes 
operate here to distribute the heat. The 
warm liquid constantly conveys it away, and 
at the same time, the colder particles are con- 
tinually brought back to the source of heat, 
at the bottom. Exactly the same thing takes 
place when ak is heated ; it expands, becomes 
lighter, rises in currents, and carries with it 
the heat. "We shall refer to this principle 
again, when speaking of the contrivances for __, 

warming rooms. Currents produced in water 

' by boiling. 

47. Heat added to SoUds, liquefies them.— Not only is the size of 
bodies influenced by heat, but also their state, ovform. A§ heat enters 
a solid body, its particles are forced asunder, until at length they lose 
their cohesive hold of each other, and faU down into the liquid state. 
The particles have become loosened and detached, and glide freely 
among each other in all directions. Carbon and pure alumina are 
the only substances that have not been Uquefied by any amount of 
heat yet applied. Some solids, at a given point of temperature, enter 


suddenly into the liquid state, and others pass gradually through an 
intermediate stage of pastiness or softening. 

48. Melting Points. — That degree of temperature which is required 
to melt a substance, is called its melting or fusing point. The com- 
mon temperature of the air is sufficient to melt some substances. 
From this point all along up to the highest heat, at which carbon re- 
fuses to liquefy, various substances melt at diiferent temperatures, 
showing that each requires its particular dose of heat to throw it into 
the liquid state. Thus, mercury is a liquid at common temperatures, 
and is the only metal that exhibits this peculiarity. Phosphorus melts 
at 108°, wax 142°, sulphm- 226°, sugar cane 320°, tin 442°, lead 612'', 
zinc 773°, silver 1873°, gold 2016°, iron 2800°, Liquidity seems thus 
to be produced by the combination of solids with heat. Take the 
heat from a liquid and it sohdifies. Take away the heat from water 
until it falls to 32°, and it becomes solid water, or ice. If kept per- 
fectly stiU, it may be lowered below 32° before the atoms lock to- 
gether into the crystalline or congealed state ; but if the water is 
jarred or agitated, crystalline ice results at that temperature. Heat 
taken from mercury until it falls to 39° below zero, causes it to harden 
into a solid, ringing rnQisil— freezes it. - 180° of heat taken from alco- 
hol, do not freeze, but make it thick and oily. As heat combined 
with solids produces liquids, so heat combined with liquids produces 
vapors or gases. Heat added to ice generates water — added to Avater 
generates steam. The heat which converts solids into liquids, is called 
caloric of fluidity, and as gases are known as elastic fluids, the heat 
which changes liquids to gases is called calorie of elasticity. 

49. What is meant by Specific Heat. — If we take equal weights of 
different substances, and expose them to the same sources of heat, 
they do not aU receive it with equal readiness ; in the same length 
of time some will be much more warmed than others. If a lamp 
flame of a given size wUl raise the temperature of a pound of spirits 
of turpentine 50° in ten minutes, it wUl take two flames of the same 
size to raise a pound of water through the same temperature in the 
same time, or it will take the same flame twenty minutes, or twice as 
long. It is clear that the water in this case, in being raised through 
the same temperature, has received twice as much heat as the spirits 
of turpentine. If a flame of a certain size wUl heat a pound of mercury 
through a certain number of degrees in a certain time, it wUl take 30 
flames of the same heating power, to raise a pound of water through 
the same range of temperature in the same period ; to raise it through 
the same number of degrees, therefore, water requires thirty times 


the heat that mercury does. This would seem to show that different 
bodies have different capabilities of holding or containing heat, or, as 
it is usually said, they have different capacities for heat : and, as each 
substance seems to take a peculiar or particular quantity for itself, 
that quantity is said to be its ' specific ' heat. The specific heat of 
water is greater than that of any other substance. In ascending from 
a given lower to a higher point, it takes into itself or swallows up 
more heat than any other body ; and in cooling down through that 
temperature, as it contains more to impart, so it gives out more heat 
than any other body. If the specific heat of water is represented by 
1000, that of an equal weight of charcoal is 241, sulphur 203, glass 
198, iron 113.79, zinc 95.55, copper 95.15, mercury 33.32. 

50. Why Water was made to hold a large amount of Heat. — ^When we 
consider the extent to which water is distributed upon the earth, we 
see the wisdom of the arrangement by which it is made to hold a 
large amount of heat, and the necessity that it should slowly receive, 
and tardUy surrender what it possesses. Suppose that the water of 
oceans, lakes, rivers, and that large proportion of it contained in our 
own bodies, responded to changes of temperature, lost and acquired 
its heat as promptly as mercury : the thermal variations would be 
inconceivably more rapid than now, the slightest changes of weather 
would send their fatal undulations through aU living systems, and the 
inconstant seas would freeze and thaw with the greatest facility. But 
now the large amount of heat accumulated in bodies of water during 
summer is given out at a slow and measured rate, the climate is 
moderated, and the transitions from heat to cold are gradual and 

51. Why Water is so cooling when drank. — It is because water is 
capable of receiving so much heat, that it is better adapted than any 
other substance to quench thirst. A small quantity of it will go 
much further in absorbing the feverish heat of the mouth, and throat, 
than an equal amount of any other liquid. When swallowed and 
taken into the stomach, or when poured over the inflamed skin, it is 
the most grateful and cooling of all substances. For the same reason, 
a bottle of hot water will keep the feet warm much longer than a hot 
stone or block. 

52. Concealed or latent Heat. — All changes in the densities of bodies 
by which their particles are forced into closer union, or to greater 
distances apart, are invariably accompanied by changes of heat.. 
Caloric is supposed to be contained in bodies, something as water is 
held in a sponge — ^lodged in its cavities or pores. If a wet sponge is 


compressed, water is squeezed out ; but, when it expands again, it 
will again imbibe tbe liquid. In like manner material substances, 
when condensed into less space, give out heat, and, when dilated, 
they take it in or absorb it. If a piece of cold iron is smartly ham- 
mered upon an anvil, its particles are forced closer together, and its 
heat is driven out of its concealment, the iron becomes hot. By 
suddenly condensing the air as in the instrument called the fire-syringe, 
Pj^ g , in which a close fitting piston is driven down a tube (Fig. 
r- — -1 9), the condensed air gives out so much heat as to set fire 
to tinder. Now, before condensing the iron, or the air, in 
these cases, they appeared cold, the thermometer de- 
tected in them no heat; yet they contained heat, and 
condensation brought it out. As we cannot find it by 
n] the ordinary test, we infer that it was concealed or latent 
in the iron and air. Heat is capable, therefore, of be- 
coming lost or hidden in bodies, and then of again 
re-appearing under proper circumstances. "We call this 
latent heat, because we must call it something, and the 
term is convenient ; but we are probably very far from a 




Air condenser. . -, ,. i- j.t_ ^ j. • j.i 

true explanation oi the tacts m the case. 

53. now much Concealed Heat Water holds. — Whenever a solid ia 
changed to a liquid, a certain amount of heat disappears — goes into 
the latent state. If we take a lump of ice at zero, fix a thermometer 
in it, and expose it to a source of heat, the mercury in the thermo- 
meter will be seen to gradually rise up to 32 degrees. It then becomes 
stationary, although the application of heat is continued. But another 
change now sets in — the ice begins to melt. While this continues, 
the thermometer does not rise, and the water at the end of the melting 
is at exactly the same temperature that the ice was at its commence- 
ment. As soon, however, as the ice is all melted, the mercury begins 
again to ascend, and the water becomes warm. Now, all the heat 
which entered the ice to liquefy it while the mercury was standing 
still, went into retirement in the water which was produced — became 
latent. It is very easy to find out how much heat becomes thus 
hidden when ice changes to water. If we take an ounce of ice at 
32°, and an ounce of water at 174°, and add them together, the ice 
will melt and we shall have two ounces of water at 32°. The ounce 
of hot water, therefore, parted with 142° of its heat, which has disap- 
peared in melting the ice. 142° is thus the latent heat of fusion of 
ice, which is hidden in the resulting water. The quantity of latent 
heat absorbed by difierent solids in entering upon the liquid condition 


is variable, but a certain amount disappears in all cases. Thus, if a 
mass of lead be heated to 594°, it will then become stationary, although 
the addition of heat is continued ; but the moment the temperature 
ceases to rise, it will begin to fuse, and the temperature will continue 
steadily at 594° until the last particle of lead has been melted, when 
it will again begin to rise. Those who have attempted to procure hot 
water from snow for culinary purposes, know by the delay of the 
result the great loss of heat which is involved. The heat necessary 
simply to melt 100 pounds of ice, without raising its temperature a 
single degree, would be sufficient to raise more than 80 pounds of ice- 
cold water up to boiling. 

54. Beneficial Effects of this Law. — This law of the latent heat of 
liquidity, operates admirably to preserve the /orms of material objects 
against the effects of fluctuating temperatures. The stability of bodies 
is too important a circumstance, and their liquefaction too consider- 
able an event, to be made dependent upon transient causes. If, when 
ice is at 32°, the addition of one degree of heat would raise it to 33°, 
and thus throw it into the liquid form, all the accumulated snows of 
winter might be turned almost in an hour into floods of water, by 
which whole countries would be inundated. But so large a quantity 
of heat is required to produce this change, that time must become an 
element of the process ; the snows are melted gradually in spring, and 
all evil consequences prevented. 

55. Principle of Artificial Freezing,— A solid may be changed to a 
liquid without the direct addition of heat. Attraction or affinity may 
produce the change. Yet the same amount of heat is required to go 
into the latent state. Salts have a strong attraction for water. If we 
put some common salt or saltpetre into water at the common temper- 
ature, it will become colder. The salt in dissolving, that is, in assum- 
ing the liquid state, must have heat ; it therefore takes it from the 
surrounding water, which, of course, becomes colder. A mixture of 
five parts sal-ammoniac and five of saltpetre, finely powdered, and put 
in nineteen parts of water, will smk its temperature from 50° to 10° ; 
that is, 40 degrees. When snow is mixed with a third of its weight of 
salt, it is quickly melted. The powerful attraction of the salt forces 
the snow into a liquid state ; but it cannot take on this state without 
robbing surrounding bodies of the heat necessary to its fluidity. Ices 
for the table are made in summer by mixing together pounded ice and 
salt, and immersing the cream or other liquid to be frozen (contamed 
in a thin metaUic vessel,) into the cold brine, produced by the melting 
of the ice and salt. A convenient method of freezing a little water 


without the use of ice, is to drench powdered sulphate of soda (glauher's 
salt) with mnriatic acid. The salt dissolves to a greater extent in this 
acid than in water, and the temperature may sink from 50° to zero. 
The vessel in which the mixture is made, becomes covered with frost ; 
and water in a tube, immersed in it, becomes speedily frozen. 

56. Freezing liberates Heat. — If the change of a sohd to a liquid ab- 
sorbs heat, the change of that liquid back again to the solid state, must 
liberate it. If the liquefying process swallows up heat, the solidifying 
process must produce the contrary effect — set it free again. As the 
thawing of snow and ice in spring, is delayed by the large amount of 
heat that must be stored away in the forming water, so the freezing 
processes of autumn are delayed, and the warm season prolonged, by 
the large quantities of heat that escape into the air by the changing of 
water to ice. The same principle is made available to prevent the 
freezing of vegetables, fruits, &c., in cellars during intense cold weather. 
Pails or tubs of water are introduced, which, in freezing, give out 
sufficient heat to raise the temperature of the room several degrees. 
Freezing is thus made a means of warming. 

57. Evaporation of Water. — "Water, at the surface, is constantly 
changing into invisible vapor, and rising into the air, which is called 
evaporation. It goes on at all temperatures, no matter how cold the 
water is : indeed, evaporation constantly takes place from the surface 
of ice and snow. The ice upon the window often passes off as vapor, 
without taking on the intennediate form of water. Still, the rate of 
evaporation increases as the temperature rises, so that it proceeds 
faster from the surface of waters in temperate, than in higher latitudes ; 
and more rapidly still at the equator. Evaporation into the air pro- 
ceeds more rapidly when the weather is dry, and is checked when it 
is damp. It is also hastened by a current. "Water will evaporate 
much quicker when the wind blows, than when the atmosphere is 
still, because, as fast as the air becomes loaded with moisture, it is re- 
moved and drier air takes its place. Extent of surface also facilitates 
evaporation. The same quantity of water will disappear much quicker 
in shallow pans, than in deep vessels. 

58. What occurs in Boiling. — "When water is gradually heated in a 
vessel, minute bubbles may be seen slowly to rise through it. These 
consist of air, which is diffused through all natural waters, to the ex- 
tent of about four per cent., and which is partially expelled by heating. 
As the temperature increases, larger bubbles are formed at the bottom 
of the vessel, which rise a little way, and are then crushed in and dis- 
appear. These bubbles consist of vaporized water, or steam, which la 



formed in the hottest part of tlie vessel ; but as they rise through the 
colder water above, are cooled and condensed. The simmering or singing 
sound of vessels upon the fire just before boiling, is supposed to be caused 
by vibratory movements produced in the liquid by the formation and 
collapse of these vapor bubbles. As the heating continues, these steam 
globules rise higher and higher, until they reach the surface and escape 
into the air. This causes that agitation of the liquid which is called 
boding or ebullition. 

59. laflnence of the vessel in Boiling. — Different liquids boil at differ- 
ent temperatures : but the boiling point of each liquid varies with 
circumstances. The nature of the vessel has something to do with it, 
which depends upon its attraction for the water. To glass, and pol- 
ished metallic surfaces, it adheres with greater force than to vessels of 
rough surfaces. Before the water can be changed to vapor in boiling, 
this adhesion must first be overcome. Water upon the surface of oil, 
boils two degrees below water in a glass vessel, in consequence of the 
oU having no attraction for the water. 

60. Measoring the Pressure of the Air.— Air has weight like visible 
ponderable matter, and presses down upon the surface of water the 
same as upon the ground. The pressure of the air is measured by a 
J)arometer^ which is simply a glass tube about Fig. lo. 

a yard long, closed at one end, filled with 
mercury, and then inverted with its open 
end in a vessel of mercury, as shown in 
Fig. 10. The liquid metal in the tube, is thus 
balanced against the air outside, and falls to 
a point upon the scale, which exactly indi- 
cates the pressure of the air. A column of 
atmosphere from the ground to its upper 
limit, is about as heavy as a column of mer- 
cury 30 inches high. "We represent in the 
figure, but a single column of air pressing 
down upon the mercury; but we must re- 
member that its surface is completely cov- 
ered by such columns of air. Of course, the 
empty space or vacuum in the upper part of the tube permits the mer- 
cury to rise and fall without disturbance. From various causes the 
weight of the atmosphere varies ; when it is heavier, it presses harder 
upon the mercury, and drives it up ; when it is lighter, the mercury 
falls. The ordinary fluctuations of atmospheric pressure, cause the 
mercury to play along a scale of some two inches. As there is only a 

place of no 
pressure. «.. 

Barometer tube. 


certain quantity of air to press down upon the earth, in going up a 
mountain we leave much of it below us : of course, what remains 
above, is lighter, and presses with less weight. Hence, in ascending 
a mountain, the mercury in the barometer sinks in proportion as we 
rise higher. 

61. Influence of Air-pressnTe upon Boiling. — It is reported by travel- 
lers that, upon high mountains, meat cannot be cooked by the common 
method of boUing. The reason is, that the boiling water is not hot 
enough ; and the reason of that is that the pressure of the air being 
partially taken off, the water finds less resistance to rising into vapor, 
and a lower degree of heat produces the effect. The boiling point 
thus fluctuates with the barometric column : the natural variations of 
atmospheric pressure, at the same level, make a difference of 4| de- 
grees in the boUing point of water. 

62. Employment of the Principle in Refining Sugar.— It is often useful 
to boil off liquids at low temperatures. In order to change coarse, 
brown sugar into refined, white sugar, it has to be dissolved and 
purified. It is then reproduced by evaporating away the water. But 
the heat of the common boding point is too great. So the refiner 
pumps out the air from above the boiling pans, by means of a steam- 
engine. The pressure is taken off, and the water boUs away at a low 
temperature, leaving the sugar crystals perfect. 

63. Elevation of the Boiling Point. — If the weight of air pressing 
upon a liquid affects its boiling point, for the same reason the weight 
of the liquid itself, must affect it. When salts are dissolved in water, 
they render it heavier, and its boiling point is always raised. Some 
salts, however, raise it more than others. Water saturated with com- 
mon salt (100 water to 30 salt), boils at 224° ; saturated with nitrate 
of potash ( 100 water to 74 salt), it boils at 238° ; with chloride of 
calcium, at 264°. Ether boils at 96° {blood heat); alcohol, at 174°; 
turpentine, at 316°; mercury, at 662°. The viscidity of a liquid, or 
the glutinous coherence of its particles is opposed to its free ebullition, 

64. Spheroidal state of Water. — Water in contact with highly heated 
metallic surfaces does not boil or vaporize. All may have noticed it 
dancing or darting about in globules upon a hot stove. The reason 
offered why a globule does not evaporate from a red-hot surface is, 
that a stratum of steam is formed under it, which props it up, so that 
it is not really in contact with the iron ; and steam being a noncon- 
ductor, cuts off also the heat. Water enters upon the spheroidal state 
between 288° and 340° of the hot surface : but when the temper- 
ature falls, the steam no longer sustains the drop ; it is brought into 



contact with the iron, and is at once exploded into vapor. This prin- 
ciple is made available in the laundry in judging of the degree of heat. 
The temperature of the smoothing-iron is determined by its effects 
upon a drop of saliva let fall upon it. If the drop adheres, wets the 
iron, and is rapidly vaporized, the temperature is considered low; 
but if it run along the surface of the metal, it is regarded as suf- 
ficiently hot. 

65. But little Heat reqnircd to maintaia Boiling. — If a liquid be con- 
fined in a sufficiently strong vessel, so that its vapor cannot escape, it 
may be heated to any desired point of temperature ; though at high 
heats, vapors acquire such an expansive and explosive energy as to 
burst vessels of the greatest strength. But if the liquid be exposed to 
the air, it is impossible to raise its temperature above its natural boil- 
ing point. All the heat that is added after boiling commences, is car- 
ried away by the vapor. The rapidity with which water is raised to 
the boiling point, depends upon the amount of heat which is made to 
enter it. But when this point is reached, a comparatively small quan- 
tity of heat will maintain it there just as well as more. Water boiling 
violently, is not a particle hotter than that which boils moderately. 
When water is brought to the boiling point, the fire may he at once 
reduced. Attention to this fact would save fuel in many culinary 

66. DouMe Vessels to Regulate Heat. — If we have a substance which, 
placed directly over the fire, would receive an indefinite quantity of 
heat, but which we desire to raise only to a Fio. ll. 
certain temperature, we place it in a vessel 
surrounded by another vessel ; the outer one 
being filled with a liquid which boils at the 
desired temperature. Heokee's farina ket- 
tle. Fig. 11, is a culinary contrivance of 
this kind. The outer vessel is fiUed with 
water, while the inner one contains the 
material to be cooked, which, of course, can- 
not be heated higher than the boiling point, 
and is therefore protected from burning. By 
using any of the salt solutions mentioned 
(63), higher heats may be communicated to 
the internal vessel, 

67. Why Paddings, Pies, &c., cool slowly. — 
We have seen that water is a bad conductor of heat ; that is, heat does 
not readily pass across its intervening spaces, from particle to particle, 

Section of a culinary batli : 
opening to introduce water. 


and so become diffused through it. We do not, therefore, heat it by 
conduction, but by currents produced within it (46), which distribute 
and commingle the heat throughout its mass. It cools in the same 
way. As the particles at the surface or sides lose their heajt, they fall 
to the bottom, and others succeed them. If the particles of water 
could remain stationary, it would be slow and difficult to heat, and 
equally slow to cool. For this reason soups, puddings, pies, &c., which 
contain large amounts of hot water, so enclosed and detained in their 
places that they are not free to circulate, and therefore, are not in a 
condition to lose their heat, keep hot longer, and cool slower than 
equal bulks of simple fluids. 

68. Concealed Heat of Vapor. — As the liquid state is the result of 
heat combined with solids, the vaporous state is the further result 
of heat combined with liquids. Enormous amounts of heat are 
necessary to convert liquids into vapor, but the vapors are no hotter, 
according to the thermometer, than the liquids were ; they are, there- 
fore, reservoirs of insensible heat. All the heat which is necessary to 
boil off a liquid, becomes latent in its vapor. The heat that thus 
enters the boiling liquid without raising its temperature, must go 
somewhere. It is not sensible in the vapor which ascends from its 
surface, for that is no hotter than the liquid from which it came. It 
is contained in the vapor, for it may aU be again recovered from it. 
The quantity of heat which becomes latent in the process of evapora- 
tion, is very large. "With the same intensity of heat it takes 5^ times 
as long to evaporate a ponnd of water, as it does to raise it from 
freezing to boiling ; it therefore receives 5^ times as much heat. If, 
therefore, 180° were required to bod the pound of water, 1000° are 
required to change it into a pound of vapor ; but, as the pound of 
vapor is no hotter than the pound of Avater, 1000° of heat must of 
course be concealed in it. The latent heat of steam is then 1000° ; 
when condensed, it surrenders that 1000° of heat. The condensation 
of a pound of steam wiU raise 5|- pounds of water from the freezing 
to the boiling point. This fact makes steam a valuable agent for 
transporting heat, as is done by means of steam pipes for warming 
buildings (129). Wherever condensed, it liberates large quantities of 

69. Cooling effect of Evaporation. — Evaporation is therefore a cooling 
process — it buries or temporarily destroys active heat. For this reason 
damp soils, although in all other respects like diy ones, are colder. 
Evaporation dissipates the heat which falls upon them. The heat 
poured down from the sun in torrid regions would be intolerable. 


were it not for the cooling effect of rapid evaporation. Apartments 
are cooled in hot countries by evaporation, which proceeds from wet 
curtains. The skin of the body contains millions of little microscopic 
pores, through which water {perspiration) is constantly pouring out 
to the surface. As it then evaporates into the air and absorbs 
heat, it becomes a powerful cooling agency and regulator of bodUy 
temperature ; while the vapor, which escapes from the breath, exerts 
a cooling effect within the body. It is very interesting to observe 
how the great capacity of liquid water for heat, makes it so gratefully 
cooling as it enters the body ; and how its stUl greater capacity for 
heat, when passing from the liquid state to the condition of vapor, 
enables it so constantly to bear away from us the germs of fever as it 
escapes from the system, in the form of insensible perspiration or 
vapor. The cooling effect of fanning the face, is partly due to the 
more rapid removal of the vapor of perspiration from the skin, and 
partly to the conduction of heat by the particles of moving air. 
Breezes cool us in the same way. Wet floors become a source of cold, 
in rooms, through vaporization. The pernicious effect of wearing wet 
clothing is caused by the rapid evaporation which proceeds from it, 
thus robbing the body of large quantities of heat. "When a person is 
obliged to remain in wet clothing, evaporation may be stopped by 
putting on an outer garment, which cuts off the external air. 

70. Season of " Mowing Hot and blowing Cold." — It was stated that 
when air or gases are condensed, heat is set free ; on the contrary, 
when they are expanded, their capacity for latent heat is increased, 
it is absorbed, and cold is produced. This is a main cause of the 
danger when streams of air reach us through cracks and apertures, 
although a part of the mischief is caused by conduction. This peril 
is expressed in the old distich — 

"If cold air reach you through a hole, 
Go make your will and mind your soul." 

Air, spouting in upon us in this manner, not only cools by conduction 
and evaporation, but, having been condensed in its passage through 
the chink, it expands again, and thus absorbs heat. This is also 
familiarly illustrated by the process of cooling and warming by the 
breath. If we wish to cool any thing by breathing on it, the air is 
compressed by forcing it out through a narrow aperture between the 
lips ; as it then rarefies, it takes heat from any thing upon Avhich it 
strikes. , If we desire to warm any thing with the brecth, as cold 
hands, for example, we open the mouth and impel upon it the warm 
air from the lungs without disturbance from compression. 



71. Local inflaence of Heat upon the Body. — It has been noticed that 
the general effect of heat upon bodies is to expand them (15). It acts 
in this way upon the living system, just as upon all other objects. The 
pleasant sensation of warmth is occasioned by an expansion of the 
vessels of the skin, and the liquids which they contain ; these are ren- 
dered less viscid and thick by heat, and made to flow more readily, 
which produces an agreeable feeling. If the application of heat to a 
part be continued, the surface becomes red. The diameters of the 
minute capillary blood-vessels are so expanded, that the red blood-disks 
are enabled to enter tubes which would not previously admit them. 
The temperature rises, and there is a slight sweUing or increase of the 
volume of the part, owing partially to the dilatation of the solids and 
liquids, but chiefly to the presence of an increased quantity of blood. 
The living tissues at the same time become more relaxed, soft and 
flexible, and allow rapid perspiration. More heat still produces greater 
expansion. There is a sense of pain, the organic structure is decom- 
posed, the liquids begin rapidly to dissipate in vapor, and the surface 
becomes inflamed, blistered, and burned. 

72. General influence of Heat upon the System. — The body is subject 
to the action of two kinds of stimulants. Vital stimulants are those 
external conditions, such as air, water, food and warmth, which are 
necessary to the maintenance of life. Medicinal or alterative stimulants 
are those agents or forces which produce temporary excitement within 
the system, but ultimately depress and exhaust it. Now, in the pro- 
portion that is necessary simply to maintain the system at its natural 
temperature, heat is a healthful, vital stimulant; but beyond this it 
becomes a disturbing, exhaustive, health-impairing agent. The first 
effect in undue quantity is excitation ; the secondary effect, exhaustion. 
In the first instance, sensibility is agreeably promoted, voluntary 
muscular movement assisted, and the mind's action somewhat exalted ; 
but to these effects succeed languor, relaxation, listlessness, indispo- 
sition to physical and mental labor, and tendency to sleep. The body 
possesses a powerful means of self-defence against excessive heat, in 
tlie cooling influence of surface evaporation (69), but this power of the 
system cannot be taxed with impunity. The rush of the circulation 
to the surface, and the increased transpiration and secretion of the 
skin, are accompanied by a necessary diminution in the activity of 
some of the internal organs. As the exhalation from the skin rises, 
the secretion of the kidneys and mucous membranes faUs. The pre- 


vailing maladies of hot climates may be referred to, in illustration of 
the effect of continued heat on the body. Fevers, diarrhoea, dysen- 
tery, cholera, and liver diseases, may be regarded as the special mala- 
dies of the burning, equatorial regions. — (Pereika.) 

73. Consequences of snddea Cliangest — But the worst effect of exces- 
sive heat, is not always the immediate stimulation, and consequent ex- 
haustion which it iaduces ; it is the sudden exposure to various de- 
grees of cold which often follows, when the system is iu a relaxed and 
depressed condition, that accomplishes the most serious mischief, lay- 
ing the traiQ for so many cases of afflicting disease, and premature 
death. The effect of passing from an over-heated apartment out into 
a freezing air bath, is suddenly to check the cutaneous circulation, and 
drive the blood inward upon the vital organs, thus often engendering 
fatal internal disease. It is thought that a temperature from 60° to 
65° is, perhaps, the safest medium at which an apartment should be 
kept, so that the individual may not suffer from transition to external 
cold. If this temperature seem uncomfortably low, it is better to in- 
crease the apparel than to run up the heat, and risk the consequences 
of subsequent exposure. 


74. Artificial heat may be produced in various ways, but the comr 
mon method is by combustion^ which is a chemical operation carried 
on in the air. All the heat which we generate for household purpo^ 
ees, is caused by the chemical action of air upon fuel. But what part 
of the air takes effect ? The main bulk of the air is composed of 
two elementary gases, oxygen and nitrogen. In every five gallons of 
air, there are 4 of nitrogen and 1 of oxygen, mixed and diffused 
through each other (281). Nitrogen, when separated, proves to have 
no active qualities ; it cannot carry on combustion, — ^it puts out fire. 
Oxygen, orr the contrary, when separated, proves to be endowed with 
wonderful chemical energy. A fire kindled in it, burns with unnatu- 
ral violence ; its chemical powers constitute the active force of tho 
air. The nitrogen dilutes and weakens it, thus restraining its ac- 

75. Composition of Fuel,— Office of Carbon. — The fuel upon which 
oxygen of the air takes effect in the burning process, consists of vari- 
ous kinds of wood and coal. These are chiefly composed of three ele^ 
ments — oxygen, hydrogen, and carbon, in various proportions. The 
oxygen they contain, contributes nothing to their value as fuel; tha^ 



depends upon the other elements : hence, the more oxygen, the less 
there can be of these other substances, and, of course, the poorer the 
fuel. Carbon exists largely in all woods and coals. Oxygen and hy- 
drogen, when in their free state, — ^that is, uncombined, are always 
gases ; they never appear as liquids or solids, and no one has yet been 
able to force them into these states. Carbon, on the other hand, is 
an unyielding solid. No chemist has ever yet been able to prepare 
either liquid carbon or gaseous carbon. At the intensest white heat, 
where nearly every other substance melts, or dissipates into vapor, 
carbon remains fixed. It is the solidifying element of fuel, and it is 
this property which makes our fires stationary. 

76. Hydrogen, and its OfiSce in Fuel. — Hydrogen gas, the other ele- 
ment of fuel, when set free is the lightest substance known, being 14 
times lighter than air. It is of so light and volatile a nature, that it 
will combine with solid carbon, and even iron, and carry them up with 
it into the gaseous state. "When cembined with fuel, it is condensed 
down iuto a solid state, but in the act of burning, it is released, and 
escapes into the gaseous form. It therefore hums in motion, and it 
is this which produces Jiame. In all ordinary combustion, the flame 
is caused by the burning hydrogen, and the larger the quantity of this 
substance in fuel, the greater the flame it wiU yield when burnt. 

Y7. Why it is necessary to kindle a Fire. — Now, for these two sub- 
stances, oxygen has powerful attractions, and combines with them, 
producing combustion and heat. Yet atmospheric oxygen is every 
where in contact with all kinds of fuel without setting them on fire. 
"Why is this ? Because the natural attractions of these substances are 
so graduated, that they do not come into active play at low tempera- 
tures. If carbon combined with oxygen at common temperatures, 
with the same readiness and force that phosphorus does, wood and 
coal would be ignited like a match, at the slightest friction, and com- 
bustive processes would be ungovernable. But as man, all over the 
world, civilized and savage, is designed to develope and manage fire 
through the agency of these substances, their energies have been 
wisely restrained within the limits of universal safety. This makes it 
necessary to resort to some means, as friction or percussion, to gener- 
ate heat necessary to start conibustion, or kindle the fire. 

78. Prodncts of Comlinstion. — "When the combustive process has 
commenced, two things take place ; the fuel disappears, and the air is 
changed. The substance of fuel is not destroyed, it only changes its 
shape, takes on the invisible form, and mounts into the air. Oxygen 
combines with carbon, both elements disappear, and a new product 


results — carbonic acid gas (293). As carbonic acid is thns given off 
every where by combustion, it is a constant and universal constituent 
of the atmospliere. It forms 1— 2000th of the air^ and would increase 
in quantity, but it is ,. .nstantly withdrawn by plants. "When pure, it 
extinguishes fire, and when mingled with the air it rapidly diminishes 
its power of sustaining combustion. "When oxygen combines with the 
hydrogen of fuel, it produces vapor of water, which rises with the 
carbonic acid and disperses through the air. 

79. Fuel is cbanged before it is burned. — In burning, oxygen does not 
combine directly with hydrogen and carbon, changing them at once 
to water and carbonic acid. The heat of combustion first decomposes 
the fuel and re- combines its atoms, forming various compounds 
under different circumstances, and it is with these that oxygen 
unites. They consist mainly of hydrogen and carbon, and are 
more abundant as the proportion of hydrogen in the fuel increases. 
It is rare that these products, thus distilled out of fuel in the burning 
process, are completely consumed by oxygen; a portion of them 
escapes, constituting smoke. 

80. Heating powers of Hydrogen and Carbon. — The proportion of 
carbon in fuel is always very much greater than that of hydrogen, but 
the amount of heat which they give out is not in proportion to their 
relative weights, A given weight of hydrogen, when burned, will 
produce three times as much heat as the same weight of carbon. A 
pound of charcoal, which is nearly pure carbon, in burning, produced 
sufficient heat to change 75 pounds of water from freezing to boiling ; 
while a pound of hydrogen yielded heat enough in burning, to change 
236.4 pounds through the same number of degrees. The heat is in 
proportion to the oxygen consumed ; the pound of hydrogen united 
with 8 pounds of oxygen ; while a pound of carbon took but 2| pounds 
of it. The heating power of fuel thus depends upon chemical com- 
position, but it is also influenced by other circumstances. 

81. How Moisture affects the Value of Wood. — ^When wood is newly 
cut, it contains a large quantity of water (sap), varying in different 
varieties, from 20 to 50 per cent. Trees contain more water in those 
seasons when the flow of sap is active, than when growth is suspend- 
ed ; and soft woods contain more than hard. Exposed to air a year, 
wood becomes air dried^ and parts with about half its water ; 15 per 
cent, more may be expelled by artificial heat ; but before it loses the 
last of its moisture, it begins to decompose, or char. The presence of 
water in wood diminishes its value as fuel in two ways ; it hinders 
and delays the combustive process, and wastes heat by evaporation. 



Suppose that 100 pounds of wood contain 30 of water, they have 
then but 70 of true combustive material. When burned, 1 pound 
of the wood will be expended in raising the temperature of the water 
to the boiling point, and 6 more in converting it into vapor ; making 
a loss of 7 pounds of real wood, or J^ of the combustive force. Be- 
sides this dead loss of 10 per cent, of fuel, the water present is an an- 
noyance by hindering free and rapid combustion. 

82, Heating Value of different kinds of Wood. — ^Equal weights of differ- 
ent varieties of wood in similar conditions, produce equal quantities 
of heat ; but it will not do to purchase wood by weight, on account 
of the varying quantity of its moisture. It is sold by measure; but 
equal measures or bulks of wood do not yield equal amounts of heat. 
According to the careful experiments of Mr. Maeous Bttll, the rela- 
tive heating values of equal bulks {cords) of several American woods, 
are expressed as follows ; — shell-bark hickory being taken as 100. 

Shell-bark Hickory 
Pignut Hickory 
White Oak 
White Ash 
Scrub Oak 
Witch Hazel 
Apple tree . 
Bed Oak 
White Beech 
Black Walnut 
Black Birch 


Yellow Oak . 

. . 60 

Hard Maple 

. 60 

White Elm 

. . 53 

Eed Cedar 


Wild Cherry 

. 55 

Yellow Pine 


Soft Maple . 

. 54 

Chestnut . 


Yellow Poplar 

. . 52 

Butternut . 

. . 51 

White Birch 

. . 48 

White Pine 


83. Soft and Hard Woods. — Some woods are softer and lighter than 
others, the harder and heavier having their fibres more densely packed 
together. But the same species of wood may vary in density, accord- 
ing to the conditions of its growth. Those woods which grow in for- 
ests, or in rich, wet grounds, are less consolidated than such as stand 
exposed in the open fields, or grow slowly upon dry, barren soils. 

84. Wliy Soft and Hard Woods burn differently. — There are two stages 
in the burning of wood : in the first, heat comes chiefly from flame ; 
in the second, from red-hot coals. Soft woods are much more active 
in the first stage than hard ; and hard woods more active in the 
second stage than soft. The soft woods burn with a voluminous 
flame, and leave but little coal ; while the hard woods pi-oduce less 
flame, and yield a larger mass of coal. The cause of this is partly, 
that the soft woods, being loose and spongy, admit the air more freely, 
but it is chiefly owing to differences in chemical composition. Pure 


woody fibre, or lignin, from all kinds of wood, has exactly the same 
composition ; a compound atom of it containing 12 atoms of carbon, 
10 of hydrogen, and 10 of oxygen — or there is just enough oxygen in 
it to combine with all its hydrogen and change it to water in burning. 
But in ordinary wood, the fibre is impure ; that is, associated with 
other substances which practically alter its composition. The hard 
woods are nearest in composition, to pure lignin, but the softer woods 
contain an excess of hydrogen. For this reason, they burn with more 
vehemence at first ; more carbon is taken up by the hydrogen, in pro- 
ducing flame and smoke, and the residue of coal is diminished. The 
common opinion, that soft wood yields less heat than hard (equal 
weights) is an error ; it burns quicker, but it gives out an intenser heat 
in less time, and is consequently better adapted to those uses where a 
rapid and concentrated heating effect is required. 

85. Cbarcoal as Fnel. — Charcoal is the part that remains, when wood 
has been slowly burned in pits or close vessels, with but a limited sup- 
ply of air, so that all its volatile or gaseous elements are expelled. 
Wood yields from 15 to 25 per cent, of its weight of charcoal ; the 
more the process is hastened, the less the product. "When newly made, 
charcoal burns without flame, but it soon absorbs a considerable por- 
tion of moisture from the air, which it condenses within its pores. 
When this is burned, a portion of the water is decomposed, hydi-ogeu 
is set free, and there is produced a small amount of flame. Being very 
light and porous, and its vacancies being filled with condensed oxygen, 
(811) it ignites readily, and consumes rapidly. "Wood charcoal produces 
a larger amount of heat than equal weights of any other fuel. 

86. Mineral Coal as Fuel — Anthracite. — The pit coal which is dug from 
beds in the earth, is a kind of mineral charcoal. It gives evidence of 
having been derived from an ancient vegetation, which was by some 
unknown means buried in the earth, and there slowly charred. Indeed, 
the properties of the different varieties of coal, depend upon the degree 
to which this charring operation has been carried. In anthracite, 
which is the densest and stoniest of all, it has reached its last stage ; 
the volatile substances are nearly all expelled, so that nothing remains 
but pure carbon with a trace of sulphur, and the incombustible ash. 
From its great density, when we attempt to kindle it, instead of 
promptly taking fire, the heat is rapidly conducted away, so that the 
whole mass has to be raised together to the point of ignition. "When 
once tlioroughly fired, this coal burns with an intense heat for a long 
time, though less freely in a grate than in a stove. It is diflicult in the 
grate to keep the whole mass of coal in a state of vivid redness, as the 


air conveys away so much heat from the surface of the fire as to cool 
it doAvn below the poiat of combustion (114). Anthracite burns without 
flame, smoke, or soot, although with sulphurous vapors, which, when 
the draught is imperfect, or when burned in a stove, are liable to 
accumulate in the room, to the serious detriment of its inmates. The 
anthracite fire is objected to by many as causing headache, and other 
bad symptoms. Aside from its sulphurous emanations, the extreme in- 
tensity of its heat, undoubtedly, has a share in producing these effects. 
8V. Combustion of Bituminous Coal. — "When the great natural process 
of underground charring is less advanced, the coals are Mtuminous ; 
that is, they contain bitumen or pitch, a substance rich in hydrogen. 
These ignite readily, and burn with much flame and smoke. Those 
which contain the largest proportion of pitchy material, are known as 
' fat' bituminous coal, and in burning, they soften or melt down into a 
cake, {caking coal) and stop the draught of air. Those with less hy- 
drogenous matter, are termed ' dry,' or ' semi-bituminous ' coal ; 
they burn freely without cementing or caking. Bituminous coals fur- 
nish illuminating gas by distillation in ii'on retorts ; a process of char- 
ring with entire exclusion of air. The residue left after charring bitu- 
minous coal, is called coke ; it is procured of the gas manufacturers 
and used as fuel, burning quietly like anthracite, though, owing to 
its sponginess, it is more easily kindled and yields less heat. Good 
bituminous coal burns freely and pleasantly in an open fire, with an 
agreeable, white flame, producing carbonic acid in large quantity, a 
smaU proportion of svilphurous vapor, and the common carbonaceous 
constituents of smoke (103). Its heat is mucli less violent than that 
of anthracite. 

88. Lignite or Brovrn Coal is that variety which seems to have been 
least charred, and still retains the woody structure ; its combustive 
value is low. 

89. Heating Effects of the different Fuels. — The heating value of these 
fuels, when burned under the same circumstances, have been deter- 
mined as follows : One pound of wood charcoal wiE raise from the 
freezing to the boiling point, 73 pounds of water. One pound of min- 
eral coal wiU heat 60 pounds of water through the same number of 
degrees ; and one pound of dry wood, 35 pounds of water in the same 
way. These are the highest results obtained by careful experiments. 
In practice, we do not get so great a heating effect ; and besides, the 
circumstances under whicli the fuel is burned, whether it be in a stove 
or fire-j^lace, makes considerable ditFerence in the result. 

90. Amount of Air required to consume Fuel. — As the weight of air 


necessary to bum fuel is vastly greater than the fuel itself, and as air 
is exceedingly light, it wiU be seen that immense bulks of it are con- 
sumed in combustion. It requires 11.46 pounds of air to burn one 
pound of charcoal; and as one pound of air occupies nearly 13 cubic 
feet of space, the pound of charcoal will require about 150 cubic feet 
of air. One pound of mineral coal is burned by 9.26 pounds of air, or 
120 cubic feet ; and one pound of dry wood consumes 5.96 pounds, or 
75 cubic feet of air. These are the smallest possible amounts that can 
be made to effect the combustion; as fuel is usually burned, much 
more is consumed. 

91. Too much Air binders Comlmstion. — Yet if the object is simply to 
produce heat^ the contrivances we employ should be adapted to admit 
the least possible quantity of air beyond what actively carries forward 
the combustion. Excess of air becomes detrimental to the burning pro- 
cess, by conveying away heat which it does not generate, cooling the 
fuel, and checking the rate of combustion. Indeed, so much air may 
be projected upon a fire, as to cool it down below the burning point, 
and thus put it out as effectually as water (114). 


92. Cause of the CMnmey Draught. — The candle flame tends upward; 
its hot gases and the surrounding heated air rising in a vertical stream, 
which illustrates the universal tendency of warmed air. No matter 
how it is heated, it expands, because rarer and lighter, and is pressed 
upward by that which surrounds it. Not that heated air has any 
mysterious tendency to ascend, but there being less of it in the same 
space, the earth does not attract it downward with the same force that 
it does the denser and colder surrounding air. As the atmospheric 
particles move among each other with the most perfect freedom, the 
colder and heavier air takes the lower position, to which gravitation 
entitles it, and thus drives the warmer air upward. This upward 
tendency of rarified gases is the force made use of to supply our fires 
with the large amount of air which they demand. The fire is kindled 
at the bottom of a tube of iron or brick- work, called &Jlue or cMmney. 
The atmospheric column within it is heated and rarified, and the outer 
air drives in to displace it. This, in its turn, is also heated and ascends ; 
a continuous current is established, and a stream of fresh air secured 
to maintain the combustion. The chimney also serves to remove from 
the apartment the noisome and poisonous products of combustion. 

93. Conditions of the Force of Draught.— The force of the chimney 


draught depends upon the velocity of the rising curientj and that again 
upon the diiference of weight between the column of air in the chim- 
ney, and one of equal size outside of it. Three circumstances influ- 
ence the force of draught : the temperature, length, and size of the air 
column within the chimney. The hotter it is, the higher it is, and the 
larger it is, within certain limits, the greater will be its ascensional 
force. All high chimney stacks, with large channels, containing 
highly rarified air, produce roaring draughts ; wliile if they be short 
and narrow, and their temperature low, the draught is proportionally 
enfeebled. Friction against the sides of \he chimney, especially if it 
be small, operates powerfully to retard the draught. If the chimney 
be contracted at the bottom, the velocity of the entering air will be 
increased. If it be narrowed at top, the smoke and hot air wiU be 
discharged above with more force, and hence be less likely to be 
driven down by slight changes in the direction of the wind ; yet con- 
tractions in the diameter of the chimney at any point, diminish the 
total amount of air passing through. In practice, chimney-draughts 
are influenced by several other circumstances, and are frequently so 
interrupted, that they refuse to carry off the products of combustion, 
and are then said to smoJce. Yet these general statements require 
qualification. A chimney may be so high that the loss of heat through 
its walls shall cool the current down to a point of equilibrium with, 
the outer air ; the draught of a high chimney shafl has been greatly 
augmented by enclosing it in an outer case to prevent radiation. Nor 
is the current of air that passes through a chimney, strictly in propor- 
tion to the degree of its heat. The draught, at first, increases very 
rapidly with the temperature, but gradually diminishing, it becomes 
constant between 480° and 570°, beyond which it diminishes, and at 
1800° it is less than at 212°. The reason of this is found in the 
great expansion of air at a high temperature, by which its volume is 
so much increased, that, although the velocity may be Very great, the 
quantity, when reduced to the temperature of the atmosphere, is less 
than at a lower temperature. — Wtmait. 

94. Winds eansc Chimneys to Smoke. — A high building, or a tree 
standing close to a chimney aud overtopping it, often disturbs its 
draught. The wind passing over these objects, tails down like water 
over a dam, and stops the ascending current so that smoke is forced 
back into the room ; or the wind mny strike against the higher object, 
and, rebounding, form eddies, and thus beat down the smoke. "When 
chimneys are not thus commanded by eminences in the vicinity, gusts 
of air may still interfere with their draught. To prevent this, they 



are often mounted with turncaps, cowls, or ejectors (354) -wliicli are 
so constructed that the eflFect of the passing wind is to draw off 
the air from the chimney, forming a partial vacuum into which the 
gases and smoke rush from below, and so establish an upward current. 

95. New and Damp ChinmeySi — "When chimneys are new, the brick 
and mortar being damp, are good conductors of heat, and take it 
rapidly from the rising current of warm air. This condenses it, 
obstructs its ascent, and if the fire below be very hot, the chimney 
smokes. As it becomes dry, however, and is gradually covered with 
non-conducting soot, this source of difficulty is removed. 

96. Cold Exposures — Descending Draughts. — Chimneys in the north 
end of a house, exposed to cold winds, often draw much less perfectly 
than those on other sides, or in the stiU more favorable warm interior 
of a building. The air in a chimney in the north or shaded side of a 
house is liable to cool in summer, so as to have a downward, draught 
when not used. If the temperature of the chimney be nearly the 
same as that of the outer air during the day, the external cooling at 
night may also create a descending current. When, therefore, the 
smoke from the neighboring chimneys passes over tlie tops of those 
that are drawing downwards, it is sucked in with the current and 
fills the room below. 

97. Currents connteracting each other. — We have seen that it is 
only when the atmosphere is of a perfectly uniform temperature that 
it is perfectly still ; the slightest inequality in its Fig. 13. 
degree of heat, throws it promptly into movement. 
We are apt to forget the exceeding dehcacy with 
which the different portions of air are balanced 
against each other. This may be easily shown. 
If two tubes of unequal height be united by a third 
(Fig 13), the candle in the longer tube wiU. over- 
come that in the shorter, and create a downward 
current in the latter; or if two tubes of equal 
length, xmited by a third, as in Fig. 14, have a 
candle in each, one is soon overcome by the other ; 
and this may happen, even when an opening is made in the third 
tube, admitting a limited supply of air. It is sometimes attempted to 
make a current proceeding from a fire, traverse two flues, which join 
again before discharging their smoke into the air. But this is 
difficult, if not impossible ; for though currents may be commenced in 
both routes, one quickly neutralizes the other, and but a single flue 
's used. 



Fig. 14. 

98. One Chimney OTerpowering another. — Wlien 

there are two fire-places in a room, or in rooms 
communicating by open doors, a fire in the one 
may burn very well by itself; but, if we attempt to 
light fires in both, the rooms are filled with smoke. 
The stronger burning fire draws upon the shaft of 
the weaker for a supply of air, and of course brings 
the smoke down with it. This difiiculty may be 
remedied by opening a door or window, so as to 
supply both fires with the necessary air. The same 
efiect may take place, even though the two rooms 
be separated by a partition, when they communi- 
cate atmospherically by the joints and doors. Some- 
times, where the windows are tight, a strong kitchen fire may over- 
power all the other chimneys in the house and cause them to smoke. 

99. Upper and lower Flues — A current entering a chimney through 
a flue horizontally^ may interrupt its draught ; in all cases of flues 
entering chimneys, they should be so arranged that the smoke may 
assume an upward direction corresponding to the course of the main 
current. There is great danger of smoke when the flue of an upper 
room is turned into the chimney of a lower room. If a fire is kindled 
in an upper room when there is none below, the cold air in the main 
shaft rises, and, mixing with the warm air, dilutes it, and thus checks 
or obstructs the ascent j while if the lower fire only be kindled, the 
cold air from the upper flue will rush into the shaft, and cooling it 
down at that point, may cause the smoke to descend into both rooms. 
The remedy is, either to keep a fire in both fire-places or to close one 
with a fireboard. 

100. Admission of too much Air. — Too large openings in fire-places 
often occasion smoke by admitting so much air from the room as to 
cool the upward current, and thus impair its ascensional force. If 
the fire-place be too high or capacious, or its throat too large, the air 
is drawn from a large space, or it may pass round behind the fire by 
way of the jambs on both sides ; the current is thus impeded, and 
the flame, which should be drawn backward, rises directly against the 
mantel-bar and escapes into the room. The fire-place should be so 
constructed as to compel all the air which enters it, to pass through 
or close to the fire. 

101. Admission of too little Air. — It is well known that a smoky 
chimney is often relieved by opening a window or outer door ; where 
this is the case, the difficulty is a deficiency of air to supply the 



Fig. 15. 

draught. "Want of a copious and regular supply of air is by far the 
most common cause of smoky chimneys. However well constructed 
and arranged may be the flues and fire-places, if they are not supplied 
with a proper amount of air they will inevitably smoke. Of course 
if the room be nearly air-tight, there is no air to supply a current, and 
there will be no current, for as much air as escapes through the 
chimney must be constantly furnished from some other source. In 
such a case, the smoke not being carried off will diffuse through the 
room. There may even be a double current in the 
chimney, one upwards from the fire and another from 
the top downwards, as shown in Fig. 15 ; these two 
currents meeting just above the fire, part of the smoke 
is driven into the room. To ascertain the quantity 
needed to be brought in under these circumstances, 
Dr. Feanklin's plan was to set the door open until 
the fire burned properly, then gradually close it nntil 
again smoke began to appear. He then opened it a 
little wider, until the necessary supply was admitted. 
Suppose now the opening to be half an inch wide, and 
the door 8 feet high, the air-way wUl be 48 square 
inches, equal to an orifice 6 inches by 8. The intro- 
duction of this air is to be in some way effected, the 
question being where the opentug shall be made. It 
has been proposed to cut a crevice in the upper part 
of the window-frame ; and, to prevent the cold air 
from falling down in a cataract upon the heads of the . 'Double current 

1 • 1 in • , 1 1111 . •. ^i* cbimney caus- 

mmates, a thin shell is to be placed below it, sloping ing smoke, 
upwards, which would direct the air toward the ceiling. The modes 
of introducing air will be noticed in another place (351). 

102. Draughts througli a Boom. — Currents of air through a room, 
as from door to door, or window to window, when open, may coun- 
teract the chimney draught ; or a door in the same side of the room 
with the chimney may, when suddenly opened or shut, whisk a cur- 
rent across the fire-place, to be followed by a puff of smoke into the 

103. Visible Elements of Smoke. — Smoke consists of all the dust and 
visible particles of the fuel which escape unbnrnt, and which are so 
minute as to be carried upward by ascending currents of air. It is 
chiefly unconsumed carbon in a state of impalpable fineness, which is 
deposited as soot along the fiue, or, swept upward by the air current, 
is carried to a greater or lesser height, and finally falls again to the 


earth. Thus all that is visible of smoke is really heavier than air, 
which may be shown by placing a lighted candle in the receiver of an 
air-pump. By then exhausting the air, the flame is extinguished ; 
and the stream of smoke that continues to pour from the wick, falls 
Fig. 16. °^ *^® pump-plate, as is seen in Fig. 16, because there 
is no air to support it. Often, in days when the wea- 
ther is said to be ' close' we notice that the smoke 
floats away from the chimney-top and falls instead of 
rising ; so that the air, even within the zone of breath- 
ing, becomes charged with the sooty particles. The 
atmosphere is so rare and light that it cannot sustain 
the heavy smoke. The common impression that the 
air on these occasions is heavy^ which prevents smoke 
from rising, is quite erroneous. The visibility of smoke is not entirely 
due to sooty exhalations. Watery vapor is a large product of com- 
bustion, and, when the air is warm and dry, it remains dissolved and 
invisible ; but, when it is cold or saturated with moisture, it will 
absorb no more, and that which rises from the chimney appears as a 
vapor-cloud, and thus adds greatly to the apparent bulk of the smoke. 

104. Other constitnents of Smoke. — Smoke contains many sub- 
stances beside the carbonaceous dust, which vary with the conditions 
of combustion and the kind of fuel used. Coal smoke is alkaline from 
the presence in it of ammoniacal compounds, while wood-smoke is 
acidulous fi'om the ligneous acids it contains. The smarting sensation 
produced by wood-smoke in the eyes, is due to the highly irritating 
and poisonous vapor of creosote formed in the burning process. 


105. The various devices for warming are to be considered in a 
twofold relation, as generating heat and affecting the breathing quali- 
ties of the air. These topics are often treated together ; but, as we 
desire to present the subject of air and breathing with the utmost 
distinctness, a separate part wiU be assigned to it, and the heating 
contrivances will then be reconsidered in respect of then* atmospheric 

106. How Booms lose Heat, — Apartments lose their heat at a rate 
proportional to the excess of their temperature above the external 
air ; the higher the heat, the more rapidly it passes away. Large 
quantities of heat escape through the thin glass windows. The win- 
dow panes both radiate the heat outward, and it is conducted away 


by tlie external air. Glass is a bad conductor of beat, yet the plates 
used are so tbin as to oppose but a very sligbt barrier to its escape ; 
on tbe other hand, it is an excellent absorber and radiator, — so that, 
in fact, it permits tbe escape of heat almost as readily as plates of iron 
of equal thickness. Tbe loss of heat in winter, by single windows, is 
enormous. Three-fourths or 75 per cent, of the heat which escapes 
through tbe glass, would be saved by double windows, whether of 
two sashes or of double panes only half an inch apart in the same 
sash. Heat is also lost by leakage of warm rarefied air through 
crevices and imperfect joinings of windows and doors, while cold air 
rushes in to supply its place. Heat also escapes through walls, floors, 
and cedings, at a rate proportioned to the conducting power of the 
substances of which they are composed. Another source of loss is 
from ventilation where that is attended to, whether it be by the chim- 
ney, or through apparatus made on purpose, and it may be estimated 
as about 4 cubic feet of air per minute for each person. This is the 
lowest estimate ; authorities differ upon the point, the ablest putting 
it much higher (325). The loss from this source is proportional to 
tbe scale adopted. Much heat, besides, is conveyed away by tbe cur- 
rents necessary to maintain combustion. To renew the heat thus 
rapidly lost in these various ways, different arrangements have been 
resorted to, which wdl now be noticed. 

107. Onr Bodies help to Warm the Rooms. — In estimating the sources 
of heat in apartments, we must not overlook that generated in our 
own systems. Tbe beat lost by the body in radiation, is gained to the 
apartment ; in the case of an individual, the amount is small ; but 
where numbers are collected, tbe effect is considerable. In experi- 
ments made upon this point, by enclosing different individuals succes- 
sively in a box lined with non-conducting cotton, open above and be- 
low, and suspended in the air, it was found first, that there is a current 
ascending from the person on all sides ; and second, that the air was 
found, on an average, 4° higher above the bead than below the feet. 
In a dense crowd, air admitted slowly through the floor at 60°, rises 
to 70° or 80° before reaching the head. The temperature of a lecture 
room 9 feet high, and 34 by 23 square, occupied by 67 persons, and 
the outer air at 32°, rose by the escape of bodily heat during the lea 
ture, twelve degrees. 

108. Ancient Method of Warming. — The chimney is a modern device, 
coming into use only 500 or 600 years ago, with the mariner's compass, 
the printing press, mineral coal, and that array of capital inventions 
and discoveries which appeared with tbe daybreak of the new civili- 


zation that succeeded the dark ages. Previously to that time, houses 
were heated as Iceland huts are now, — by an open fire in the middle 
of the apartment, the smoke escaping by the door, or passing out 
through apertures in the roof, made for this purpose. The Greeks and 
Romans had advanced no further than this in the domestic manage- 
ment of heat. They kept fires in open pans called hraziers. Those 
of the Romans were elegant bronze tripods, supported by carved im- 
ages with a round dish above for the fire. A small vase below con- 
tained perfumes, odorous gums, and aromatic spices, which were used 
to mask the disagreeable odor of the combustive products. The por- 
tion of the walls most exposed were painted black, to prevent the 
visible effects of smoke ; and the rooms occupied in winter had plain 
cornices and no carved work or mouldings, so that the soj>t might be 
easily cleared away. 


109. Structure and Improvements. — With the chimney came the 
fire-place, which is an opening on one side of its base. At first it was 
an immense recess with square side- walls (jambs) and large enough to 
contain several persons, who were provided with seats inside the 
jambs. These fire-places were enormously wasteful of fuel, and Avero 
in other respects very imperfect. They have been gradually improved 
in various ways. By reducing their dimensions and greatly contract- 
ing the throat, the force of draught is increased and the liability to 
smoke diminished. By lowering the mantle or breast, the flow of 
large masses of air which entered the chimney without taking part in 
the combustion, was stopped ; while, by bringing the back of the fire- 
place forward, the fire was advanced to a more favorable position for 
heating the room. Rays of heat, like those of light, when they strike 
on an object, are reflected at the same angle as that at which they 
faU, — that is, the " angle of incidence is equal to the angle of reflec- 
tion." Now, when the jambs were placed at right angles with the 
back, that is, facing each other, they threw their heat by reflection 
(and when hot by radiation) backward and forward to each other 
across the fire. By arranging the jambs at an angle, they disperse 
the heat through the room. Cottnt RujUfoed states that the proper 
angle for the positions of jambs is 135 degrees with the back of the 

110. How the open Fire-place warms the Eoom. — The heat of com- 
bustion from the open fire is entirely radiant — thrown off directly 
from the burning fuel, or reflected from the sides and back of the fire- 



place. It strikes upon tlie walls, ceiling, floor, and furniture of the 
room ; a portion of it is reflected in various directions, and the rest is 
absorbed. The objects which receive it are wanned, and gradually 
impart their heat to the air in contact with them ; — gentle currents 
are thus produced, which help to equalize the temperature of the 
room. Those portions of the air which are in contact with the fire, 
become heated by conduction, but they immediately rise into the 
chimney, and are, therefore, of no use in heating the room. As a fire- 
place is situated at the side of the apartment, and as radiant heat 
passing from its source decreases rapidly in intensity (23), it is 
obvious that the room will be very unequally heated. Near the fire 
it wUl be hot, whUe the remote places will be in the opposite condi- 
tion. There is a semicircular line around the fire-place, in which 
persons must sit to be comfortable, within which .ine they are too 
hot, and beyond which they are too cold. Of course, in this method of 
warming, the body receives the excess of heat only upon one side at once. 

111. Tlie open Fire not Economical. ^Fuel gives out its heat in 

two ways, by radiation and by immediate contact. Peolet has shown, 
by ingenious experiments, that the radiated heat from wood was i ; 
from charcoal and hard coal about J, of the whole amoimt produced. 
As a general result, those combustibles which burnt with the least 
flame yielded the most radiant heat. As the radiant heat is thus the 
smaller quantity, the arrangements in which it alone 
is employed are by no means economical ; yet the open 
fire-place heats entirely by radiation, and is therefore 
the most wasteful of all the arrangements for heating. 
It is said that in the earlier fire-places 7-8ths, and 
KuMFOED says 15-1 6ths of aU the heat generated^ 
ascended the chimney and was lost. It is probable 
that in the best constructed fire-place, from 1-2 to 
3-4ths of all the heat is thus wasted. The fire-place 
is greatly improved in economy and heating eflBciency 
by so constructing it that it may supply a current of 
heated air to the room. This is done in numerous 
ways, as by setting up a soap-stone fire-place within \A} 
the ordinary one, and leaving a vacant space between ^ 
them, into wbich cold air is admitted from without, 
which is then thrown into the room through an open- 
ing or register above. This is an excellent plan ; it is 
executed with various modifications, but, if well done, out warmed by the 
it answers admirably. Even a flue made of some thin ^''^-P^ace. 

Fia. 17 


material, and contained in the chimney, the lower extremity com- 
municating with the external air, and the upper with the room 
(Fig. 17), answers a most useful purpose. Heat is saved; abundance 
of air is furnished to the room without unpleasant draughts, while a 
common cause of smoke is avoided (101). 

112. Franklin Stovct — Dr. Feanklin contrived a heating apparatus 
of cast iron, which he called the Pennsylvania fire-place^ but which 
is generally known as the FranTcUn stove. It otfers one of the best 
methods of managing an open fire. It is set up within the room, and 
the hot air and smoke from the fuel, instead of escaping from the iire 
directly up the chimney, is made to traverse a narrow ani circuitous 
smoke flue, which gives out its heat like a stove-pipe ; at the same 
time air is introduced from out of doors through air-passages which 
surround and intersect the smoke-flue, and, after being warmed, it is 
discharged into the room by means of proper openings. This appa- 
ratus warms, not only by radiation from the burning fuel like the 
common fire-place, but also by radiation from the hot iron ; besides, 
the air of the room is heated by contact with the metallic plates, and 
there is still another source of warmth in the hot air brought in from 

113. Coal Gratesi — As coal contains more combustible matter in 
the same space than wood, and produces a more intense heat, a much 
smaller fire-place answers for it. A very narrow throat in the chim- 
ney is Buflicient to carry off the smoke. The coal-grate is a more 
economical contrivance for warming than the larger wood fire-place, 
chiefly because it lessens the current of air which enters the flue. In 
the wood fire-place a copious stream of warm air passes up the chim- 
ney, which takes no part in combustion, but carries off with it much 
heat, the place of the escaping warm air being supplied by cold air 
from without. The coal-grate is closed, like the fire-place, on three 
sides, the front consisting of metallic bars or grates, which, while they 
confine the coal, suffer the heat to radiate between them into the 
room. The sides and back of the grate should be formed of fire-brick, 
soap-stone, or some slowly-conducting substance, and not of iron, 
which conducts away the heat so fast as to deaden the combustion — 
for a fire may be effectually extinguished by contact of a good con- 
ducting solid body. For this reason, as Eumfoed first pointed out, 
there should be as little metal about a grate as possible, the bars 
being made as slender and as wide apart as practicable, so as to inter- 
cept the fewest radiations from the burning surface. 

114. Conditions of Comtustion in the Grate. — The form of the grate 


should be such as to expose the largest surface of incandescent coal to 
the apartment. If it has a circular front, there will be not only more 
surface, but the heat may then be radiated in all directions ; yet, if too 
great a surface is exposed to air, in extreme cold weather it carries 
off the heat faster than combustion renews it ; and the coal, if it be 
anthracite, grows black upon the exposed side and burns feebly. The 
art of burning fuel to the best advantage in open grates, is to main- 
tain the whole mass in a state of bright incandescence, by preventing 
all unnecessary obstruction of heat, either by contact of surrounding 
metal, or currents of cold air flowing over the fire. It is very difficult, 
however, to expose a large fire-surface to the atmosphere, and at the 
same time properly regulate the quantity of air admitted. It is pos- 
sible for fuel to smoulder away and entirely disappear with the pro- 
duction of very little sensible heat. To be burned with economy, 
therefore, it must be burned rapidly under the most favorable condi- 
tions of vivid combustion. The heat absorbed by the fuel, the sur- 
rounding solids, or the rising vapor, is of course not available, but 
only the excess which is emitted into the room. To cause this lively 
and perfect combustion, aU the air which comes in contact with the 
fuel must be decomposed and part with the whole of its oxygen. 
Every particle of air passing up through the fire, which does not help 
the combustion, hinders it, first by carrying off a portion of the heat, 
and second by cooling the ignited surface so that it attracts the oxygen 
with less vehemence, and thus causes the fire to languish. The air 
should also be pure, that is, as little as possible mingled with tho 
gaseous products of combustion. Air entering below a fire, rapidly 
loses its oxygen and becomes contaminated with carbonic acid ; both 
changes unfitting it for carrying on the process actively in the upper 
regions of the fire. If, therefore, the mass of burning material is too 
deep, the upper portions burn feebly and at least advantage ; yet if 
the pieces of coal be large, scarcely any depth of fuel wUl be sufficient 
to intercept and decompose the cold air which rises through the wide 
spaces. If the coal be not large, perhaps a depth of four or five 
inches wUl be found most economical. 

115. Different kinds of Grate— The modifications and variations of 
the fire-place and coal-grate are innumerable : and the multiplied de- 
vices which are continually pressed upon public attention, are, many 
of them, but reproductions of old plans. The use of a simple iron plate 
for a fire-back, has been employed to warm an adjoining room situated 
behind the fire-place. For the same purpose grates have been hung 
upon pivots, so as to revolve, and thus warm two rooms, as library 


and bedroom alternately. In Golson's stove-grate, the fire is contained 
in an urn or vase-sliaped grating, and is surrounded by a circular re- 
flector whicb throws the rays, both of heat and light, into the room in 
parallel lines. Ooal-grates are also constructed on the principle of the 
double fire-place, by which warmed air is introduced into the room from 
without. Dr. Feanexin devised an ingenious grate called the cirailar 
fire-cage. It was so hung as to allow it to revolve. The coal was 
ignited, as usual, at the bottom, and when the combustion was well 
advanced, the cage was turned over so as to bring the fire at the top 
By this means, the fresh coals at the bottom were gradually ignited, 
and their smoJce having to pass through the fire above them, was en- 
tirely consumed. 

116. Arnott's new Grate. — Dr. Aenott has recently constructed a 
new grate, in which the same benefit — the consumption of smoke, is 
secured. The bottom of the grate is a movable piston, which may be 
made to fall a considerable distance below the lower grate bar. A 
large charge of coals is then introduced, which rests upon the piston 
and fills the grate. They are lighted at the top, so that the heat passes 
downward and consumes the smoke as it is formed below. As the 
coals waste away at the top, the piston may be raised by the poker 
used as a bar, and thus fresh coal is supplied to the fire from ieneath. 
"When the first charge is consumed and the piston is raised to the bot- 
tom of the grate, a broad, flat shovel is pushed in upon the piston 
which supports the burning coals, and afibrds a temporary support for 
the fire. The piston is then let down to the bottom of the box, and a 
new charge of coal shot in. This arrangement is valuable for abating 
the smoke nuisance where bituminous coal is burned. Much inge- 
nuity has been spent upon contrivances to burn or consume smoke. 
The thing however is impracticable. "When smoke is once produced 
by fire, we can no more advantageously convert it to heating purposes 
than we can the smoke of a badly burning candle to the purposes of 
lighting. When smoke escapes from the ill-adjusted flame of a lamp, 
we notice that the flame itself is duU and murky, with diminished light ; 
but if it burn without smoke, the flame is white and clear. But we 
do not say in this case, the lamp turitis its smoTce^ but that it hums 
without smoTce. The aim should be, so to conduct the first combustion 
that smoke shall be prevented. 

117. Grates should not be set too low. — As the open fire warms by 
radiation, it should be so placed as to favor this mode of diffusing heat. 
The tendency of currents of heated an* to rise, secures suflBciently the 
warmth of the upper portion of the room, so that the main object of 



Fio. 18. 

the grate should be to heat the floor. If the fire is situated very low, 
the radiation will be considerable upon the hearth, while but few heat- 
rays will strike further back upon the floor. They will pass nearly 
parallel along the carpet or floor, just as the solar rays, at sunrise, 
dart along the surface of the earth. If, however, the fire be raised, 
its downward radiations strike upon the floor and carpet at some dis- 
tance back, with sufficient force to warm them, just as the sun's rays 
are more powerful when he shines from a considerable distance above 
the horizon. If a in (fig. 18), represent a radiating point or fire in a 
room, and & c the floor, it will be seen 
that no heat-rays fall upon it ; while 
if the floor be at d e, it will receive 
rays from the fire. " In such arrange- 
ment it is seen by where the ray-lines 
intersect this floor, that much of the 
heat of the fire must spread over it, 
and chiefly between the middle of the 
room and the grate, where the feet of «| 
the persons forming the fireside cir- 
cle are placed. Striking proof of the ^^ 
facts here set forth, is obtained by 

laying thermometers on the floors of rooms with low fires, and with 
similar rooms with fires as usual of old, at a height of about 15 or 16 
inches above the hearths. The temperature in the upper parts of all 
these being the same, the carpets in the rooms with low fires are colder 
by several degrees than in the others." 

2.— STOVES. 

118. How Rooms are warmed by Stoves. — The stove is an enclosure, 
with us, commonly of iron, so tightly constructed as to admit through 
an aperture or damper, only sufficient air to maintain the combustion 
of the fuel, which may be either wood or coal. The heat generated 
within is communicated, first to the metal, and then by that to the 
apartment. It is usually situated quite within the room, the products 
of burning being conveyed away by a fine or pipe. The stove imparts 
its heat by radiation in all directions ; it also heats the air in contact 
with it, which immediately rises to the upper part of the room, that 
which is cooler taking its place in the same manner as heat is dis- 
tributed through water in boiling (46). 

119. Briek, Earthenware, and Porcelain Stoves.— Stoves made of these 

68 APPAEATXrS OF ■wakmhstg. 

materials are most common in Germany and Kussia. They are gen- 
erally made to project into the room from one side, like a chest of 
drawers or a sideboard ; the door for the fire being sometimes in an 
adjoining apartment. These stoves heat more slowly, and conse- 
quently give out their warmth for a longer time than those made of 
iron, which are subject to rapid variations of temperature. 

120. Self-regnlating Stoves. — These are stoves to which are appended 
contrivances for regulating the draught. The principle employed is 
the expansion of bodies by heat, and their contraction by cold. A 
bar of brass or copper is so attached to the stove, that when the heat 
within increases, it lengthens ; it then moves a lever and closes the 
aperture which admits the draught. This checks the fire, and causes 
the bar slowly to cool ; it now contracts, and again opens the aper- 
ture of draught. Dr. Aenott produced the same result by means of 
a column of air contained within a tube acting upon mercury which 
moved a valve, and thus controlled the air-aperture. As the addition 
and subtraction of heat cause gases to change their bulk m ore readily 
than solids, a well constructed regulator of this kind woUd be more 
sensitive and prompt in action than one of metal. 

121. Air-tight Stoves. — The so called air-tight stoves are very 
common. They are designed to admit the air in small and regulated 
quantities, so as to produce a slow and protracted combustion. This 
mode of generating heat is less economical than is generally supposed. 
To become most perfectly available, heat must be set free at certain 
rates of speed. The compounds formed by combustion at a low tem- 
perature, generate much less heat than those which result from quick 
burning. Indeed, in the low, smothered combustion, the fuel under- 
goes a kind of dry distillation^ producing carburetted hydrogen gases 
which escape into the chimney as unburnt volatile fuel, and are of 
course lost. These gases are inflammable, and when mixed with air, 
often cause explosions in air-tight stoves. Dr. TJee found that 
while 3i pounds of coke evaporated 4^ pounds of water, from a cop- 
per pan, when burned in a single hour^ yet that when the same 
amount was burned in twelve hours, but httle over half that quantity 
of water was evaporated. As has been previously stated, to evolve 
the largest amount of heat from fuel it must bo burned rapidly, and 
with a supply of air sufficient to oarry the oxidation at once to its 
highest point, by the production of carbonic acid and water. Where 
the fuel is quickly and completely burned, and the hot, escaping gases 
are made to traverse a sufficient length of pipe to have parted with 
nearly all their heat before entering the chimney, there remains noth- 


ing to be desired on the score of economy. It is evident that all the 
heat has been retained in the room, and in this case the stove becomes 
the most efficient heating apparatus. 

122. EflTect of Elbows ia Stovepipes. — The heating action of the sheet- 
iron flue or stovepipe, is derived from the hot current of air within it. 
In proportion therefore as it contributes to the warmth of the room, 
this current of escaping air is cooled. That this cooling of air within 
the pipe takes place rapidly, may be shown by the difference of tem- 
perature at its connection with the stove, and where it enters the 
chimney. The cooling takes place of course from without inwards ; 
the outer stratum of the hot air current which is in contact with the 
pipe cools faster than the interior portion, so that the centre of the 
current is the hottest. Now it is well known that the effect of elbow- 
joints in a pipe, is to make the same length of it much more efficacious 
in warming a room, than it would be if straight. The cause of this is, 
that the heated air, in making abrupt turns, strikes against the sides 
with sufficient force to break up and invert its previous arrangement, 
and so mingle it, that the hotter air from the interior of the current 
is brought more into contact with the sides of the pipe, and more heat 
is thus imparted. It also checks the rapidity of the current. As radi- 
ation proceeds much slower at low temperatures than at liigh ones, 
the pipe, as it recedes from the stove, becomes rapidly less and less 
useful as a means of diffusing heat into the apartment ; it gives out 
less heat, in proportion to what it contains^ than the hotter parts of the 
pipe. There will, therefore, be little gained by greatly lengthening it. 

123. Best qnalities of a Stove. — The desirable points to be secured in 
the construction and management of stoves, are, Jirst^ ready contriv- 
ances for regulating the draught; second^ accurate fitting in the joinings, 
doors, dampers, and valves, to prevent the leakage of foul gases into 
the room ; third, enclosure of the fire-space, with slow conductors, as 
fire-brick or stone ; fourth, a high temperature, attained by the rapid 
and perfect combustion of the fuel ; and fifth, to bring all the heated 
products of the combustion in contact with the largest possible alsorl)- 
ing and radiating metallic surface, so that the iron in contact with 
the air may not be overheated, but give out its warmth at a low 
temperature. Large stoves, moderately heated, are therefore most 
desirable. The cooler the surface of the stove, or the nearer it is in 
temperature to the air of the room, the more agreeable and salubrious 
will be its influence. This desirable result is to be obtained only by 
exposing the greatest quantity of heating surface to the least quantity 
of fuel — a condition almost reversed in onr modern stoves. 




124. Hot-air Furnaces. — Heating by Tiot air, as it is termed, has re- 
cently come into very general use. In this case the heater is not situ- 
ated in the apartments to he warmed ; hot air being conveyed from it 
through air-flues to the rooms (fig. 19). The most common plan is a 

hot-air furnace. It is construct- 
^^' ' ed of iron, and usually lined with 

fire-brick for burning anthracite, 
and has a flue connecting it with 
the chimney, to remove smoke. 
It is enclosed in a case of iron or 
brick- work, with an interval of 
space between, forming an air- 
chamber. Air is introduced into 
this chamber, either directly 
from the room, or by means 
of a conduit, from without 
the buUding. The furnace is 
situated in the cellar or base- 
ment, and the entering air heat- 
ed to the required temperature, 
by contact with the hot iron, 
escapes upward from the air- 
chamber through tin tubes, 
which distribute it to aU parts 
of the dwelling. It enters the 
room through apertures called 
registers, which may be opened 
or closed at pleasure. This 
method is commended by its 
economy of space, the heating 
machine being excluded from 
the occupied apartments ; fuel 
is also consumed more completely, and with better economy, in a 
single furnace, than if burned in several stoves or grates. A disad- 
vantage however, is, that the power of the furnace being gauged by 
the requirements of a certain sized building, or number of apartments, 
it is not easily accommodated to a fluctuating demand for heat. 

125. DUTosiou of Hot Air tlirongh tlie Apartmcut.— There are serious 

Manner of warming by Hot- Air Furnaces. 


disadvantages attending the entrance of hot air in large streams 
through registers in the floor. If it be very hot, it will ascend directly 
to the ceiling, without imparting its heat to bodies around. In a 
church, heated by two large hot-air stoves, delivering the air through 
two large openings in the floor, we have found a difference, after the 
heating process has been going on three hours, of more than 20° be- 
tween the temperature near the ceiling and that of the floor. In some 
public buildings, a stratum of air has been observed at the height of 
20 or 30 feet from the floor, with a temperature above that of boihng 
water, while below it has been disagreeably cool. In private houses, 
with the hot-air furnaces, now in general use, air is usually introduced 
at a high temperature. It rises directly to the ceiling, spreads out 
upon it, and on reaching the walls, descends by them and the windows, 
more rapidly by the latter (337), until it reaches the floor, along which 
it is diflFased toward the register, when a part is again drawn into the 
ascending current. Hence wo see that those assembling just around 
the register, and not over it, are in the coldest part of the room. 
That this is the case, we have also proved by the thermometer ; while 
the air, midway between the floor and ceiling, in a moderate-sized 
sitting-room, was at 74°, that near the register, was but 68°. — ("Wy- 
MAN.) Even in a room heated by a stove, or any other apparatus 
placed within it, and upon the floor, the air is found, after a time, to 
arrange itself in horizontal layers, the temperatures of which decrease 
from above downwards. In an experiment to ascertain the temper- 
ature in a room 21 feet high, the following indications were obtained. 

Level of floor, 65° 10. 5 80" 

2. 1 foot, 6T° 12. 6 81° 

4 2 " TO* 14. 7 86° 

6. 3 " T2° 16. 8 90° 

8.4 " 75° 19 94° 

126. How we are wanned in Hot-air Rooms. — "We are to remember 
that after all, it is less the contact of heated air which warms us in hot- 
air apartments, than other agencies. We may enter a room in which 
the atmosphere is at 70°, or even higher, and yet be chilly. Great 
amounts of air contain but httle heat. The quantity of heat that will 
raise 1 cubic foot of water 1 degree, would be so diffused as to raise 2,850 
cubic feet of air one degree. — (Ajsnott.) From the amount of air that 
comes in contact with our bodies, therefore, we cannot get suflacient 
heat to warm us rapidly. If the walls, floors, and furniture of the 
room are cold, though the air be warm, the individual radiates heat 
to them, and is compensated by none in return ; while if they are 



■warm, they become constant sources of radiant warmth. Hot air may 
also become a direct source of cold if it be dry. K we moisten the 
bulb of a thermometer, and expose it to the rays of a fire, it receives 
the heat and rises ; but when moistened and exposed to the action of 
warm, dry air, it will sink down several degrees, caused by the evap- 
oration which carries off heat. In the same manner, over-dry air may 
promote cooling by increasing bodily evaporation. "We shall refer to 
the effects of hot air again. 

127. Heating by Hot Water.— We have seen how water is put in 
motion by heat ; the accompanying figure shows the working of the 

Fig. 20. principle. As the lamp heats the water on one side 

of the tube, it expands and ascends, the colder 
water coming forward from below to take its place, 
which establishes a circulation. As the hot water 
passes round the circuit, it gradually parts with its 
heat through the tube to the surrounding air. The 
great specific heat of water (49) by which it holds a 
large quantity of caloric, adapts it weU for the 
transportation of this agent ; and, as it parts with 
its large portion of heat but slowly, it is the most 
constant and equable of all sources of warmth. We 
have already referred to the significant fact that 
when the heat of a cubic foot of water is imparted 
to air, whatever be the number of degrees through 
Circulation of water. ^i^[q]^ the water falls, it will raise through the 
same number of degrees 2,850 cubic feet of air. 

128. Two forms of Hot Water apparatus. — There are two methods of 
warming houses by hot water. In one the mechanism is placed in 
the cellar or basement, and heats air which is conveyed upward to 
warm the apartments above, as in the case of furnaces. In this form 
of the mechanism, the pipes do not ascend to any considerable height 
above the boiler ; but, in the other plan, a system of small tubes is 
distributed through the house, being laid along to fit any form and 
succession of rooms and passages, or they are coiled into heaps in 
various situations, and impart their heat by direct radiation. There 
is a difference in the degi'ee of heat in these two plans. Water 
exj)osed to fire, as we have seen, rises in temperature to the boiling 
point and goes no higher, but this varies with depth and pressure. 
In those arrangements, therefore, which are confined below, the water 
hardly rises above the temperature of 212° ; while, in those which 
extend through the dwelling, it ascends many degrees higher. A 


good hot-water arrangement, from its constancy and regularity of 
action, and when not heated above 200° or 212°, affords one of the 
most agreeable modes of heating a dwelling, although it is at present 
80 expensive as to place it beyond popular reach. 

129. Steam Apparatas for Warming. — As steam contains a large 
amount of heat (68), it becomes an available means of its transmission. 
If admitted into any vessel not so hot as itself, it is rapidly condensed, 
and at the same time gives its heat to the vessel, which may then 
diffuse it in the space around. A system of tubes ascending from a 
hoUer may be so arranged as to warm the air which is thrown into 
the room through a register, or they may be wound into coils as in 
the previous case (128), and dispense their heat by radiation. The 
pipes are so placed, that the water from the condensed steam flows 
back to the boiler, or the hot water may be drawn off into vessels 
which are made to contribute to the heating effect. This mode of 
heating requires a temperature always at 212° for the formation of 
steam, and often much higher to drive forward the condensed water 
and clear the pipes. A serious drawback to this mode of heating is 
that the apparatus often emits a disagreeable rattling or clacking 
sound, owing to the condensation within the pipes and the sudden 
movements of steam and water. There is also a fundamental objec- 
tion to the method of warming rooms by heat radiated from coils of 
pipes, whether they be heated by steam or hot water. In respect of 
the condition of the air, this is the worst of all methods of heating, 
for it makes no provision whatever for exchange of air. All the 
other heating arrangements involve more or less necessary ventilation, 
but radiating pipes afford none at all. 

130. Risk of Fire by these methods of Warming.— It has been supposed 
that the employment of hot water, hot air, and steam pipes, as a 
means of heating buildings, cuts off the common sources of danger 
from fires, and is entirely safe. This is a serious error. Iron pipes 
liable to be heated to 400°, are often placed in close contact with 
floors skirting boards and wooden supports, which a much lower 
degree of heat may suffice to ignite. By the long-continued applica- 
tion of heat, not much above that of boiling water, wood becomes so 
baked and charred that it may take fire without the application of a 
light. A considerable time may be required to produce this change, 
BO that a fire may actually be " hindling upon a mail's premises for 
years," The circular rim supporting a still which was used in the 
preparation of some medicament that required a temperature of only 
300°, was found to have charred a circle at least a quarter of an inch 



deep in the wood beneath it in less than six months. There are nu- 
merous cases of buildings fired by these forms of heating apparatus. 

131. Origin of Fires. — The Secretary of a London Fire Insurance 
office stated that the introduction of lucifer matches caused them an 
annual loss of $50,000. Of 127 fires caused by matches, 80 were 
produced by their going off" from heat ; children playing with them, 
45 ; rat gnawing matches, 1 ; jackdaw playing with them, 1. "Wax 
matches are run away with by rats and mice, taken into their holes 
and ignited by gnawing. These facts point to the indispensableness 
of match-safes. In London, during a period of nine years, the pro- 
portion of fires regularly increased from 1.96, at 9 o'clock, A. M., the 
time at which all households might be considered to be about, to 3.44 
at 1 o'clock, P. M ; 3.55 at 5 P. M., and 8.15 at 10 P. M., which is just 
at the time that fires are left to themselves. 

132. Benefits and Drawbacks of tlie various methods of Heating. — Each 
plan of warming presents its special claims to attention, and vaunts its 
peculiar benefits. Modifications of every scheme are numerous, and 
stiU multiplying. As a result of this inventive activity, there is a 
gradual but certain improvement. The aim of inventors has hitherto 
been mainly to secure economical results ; a laudable purpose, if not 
pursued at the sacrifice of health. As people generally become 
better informed respecting the principles and laws which influence the 
comfort and well-beiag of daily life, improvements will be demanded 
in this direction also. Meantime, each method is to be accepted with 
its imperfections, though we are not to forget that in their working 
results much must depend upon proper and judicious management. 
We recapitulate and contrast the chief advantages and disadvantages 
of the various methods of heating. Some of the points referred to, 
particularly those which relate to ventilation, have not been previ- 
ously noticed, and will be considered when speaking of air. 


They promote ventilation — afford a They are uncleanly — ^require frequent 

cheerful fireside iniJnence — warm objects, attention — are not economical — are apt to 

without disturbing the condition of the air strain the eyes — heat apartments unequally 

— and may furnish warm air from without — are liable to smoke. 


They cost but little — are portable — are They afford no ventilation — if not of 

quickly heated— and consume fuel eco- heavy metal-plates, they quickly lose thoir 
nomically heat — ^yield fluctuating temperatures — are 

liable to overheat the air — are liable to 
leakage of gases— and are not cleanly. 




They are out of the way and save space They are liable to scorch the air— cannot 

— are cleanly — giye but little trouble — may be easily adapted to heat more or less space 

afford abundant ventilation — need waste — are liable to leakage of foul gases — and 

but little heat — and warm the whole house, they dry and parch the air if copious moist- 
ure is not supplied. 



They do not burn or scorch the air — They aro expensive in first cost — if 
give excellent ventilation — do not waste adapted for an average range of tempera- 
heat — and they warm the whole house, ture, they may fail in extreme cold weather 
These remarks do not apply to those which (as may also furnaces) — and may give a dry 
heat rooms by radiation from coils of pipe and parched air if moisture be not supplied. 




132. How the oatward and inward Worlds Commonicate. — We sit at 

the window, and have report of the world without. That intelligent 
consciousness which has residence in the chambers of the brain, holds 
intimate communion with the external universe, by means of a com- 
pound system of telegraphing and daguerreotyping, as much superior 
in perfection to the devices of art, as the works of the Most High 
transcend the achievements of man. We lift the curtains of vision, 
and a thousand objects, at a thousand distances, of numberless forms 
and clad in all the colors of beauty, are instantaneously signalled to 
the conscious agent within. Each point of all visible surfaces darts 
tidings of its existence and place, so that millions upon millions of de- 
spatches which no man can number, enter the eye each moment. A 
landscape of many square leagues sends the mysterious emanation, 
which, entering the camera-box of the eye, daguerreotypes itself upon 
the retina vrith the fidelity of the Infinite. Fresh chemicals are 
brought every instant, by the little arteries, to preserve the sensitive- 
ness of the nerve-plate, while those that have been used and spent, 
are promptly conveyed away by the veins. As impressions are thus 
continuously formed, they are transmitted, jjerhaps by a true electric 
agency, along the line of the optic nerve, to be registered in the brain, 
and placed in charge of memory. By the magic play of these 
wonderful agents and mechanisms, the world without is translated 
within, and the thinking and knowing faculty is brought, as it were, 
into immediate contact with the boundless universe. Let us inquire 
further then, into the nature and properties of this luminous principle, 
and how we are related to, and aifected by it. 

133. Exhilarating Agency of Light. — Light is a stimulus to the ner- 
vous system, and through that, exerts an influence in awakening and 


quickening tlie mind. The nerves of sense, the brain and intel- 
lect, have their periods of repose and action. The withdrawal of 
light from the theatre of eifort is the most favorable condition, as well 
as the general signal, for rest ; while its reappearance stirs us again 
to activity. There is something ia darkness soothing, depressing, 
quieting ; while hght, on the contrary, excites and arouses. It is com- 
mon to see this illustrated socially ; — a company assembled in an apart- 
ment dimly lighted, will be dull, somnolent and stupid ; but let the 
room be brightly illuminated, and the spirits rise, thought is enlivened, 
and conversation proceeds with increased animation. " Most delicate 
and mysterious is the relation which our bodies bear to the passing 
light! How our feelings, and even our appearance change with every 
change of the sky ! "When the sun shiaes, the blood flows freely, and 
the spirits are hght and buoyant. "When gloom overspreads the heav- 
ens, dulness and sober thoughts possess the mind. The energy is 
greater, the body is actually stronger, in the bright light of day, while 
the health is manifestly promoted, digestion hastened, and the color 
made to play on the cheek, when the rays of sunshine are allowed 
freely to sport around us." 

134. Ancient Conceptions of Light.— Light is that agent which reveals 
the external world to the sense of sight. The ancients believed it to 
be something born with us — an attribute or appendage of the eye. 
They thought that the rays of light were set into the organ of vision, 
and reached or extended away from it, so that we see in the same man- 
ner as a cat feels by the whiskers which grow upon its face, — ^by a 
kind of touching or feeling process. 

135. Newton's View of its Nature.— Modern science regards light as 
an agent, or force, originating in luminous bodies, and flowing away 
from them constantly and with great rapidity, in all directions. But 
how ? The human mind is never satisfied with the mere appearances 
of things. It demands a deeper insight into their nature, — an explana- 
tion of their causes. The first scientific attempt to explain the nature 
of light, and the cause of vision, likened the sense of sight to that 
of smell. We know that to excite the sensation of smell, material 
particles, emanating from the odorous body, pass through the air and 
are brought into contact with the olfactory nerve of the nose. It was 
supposed that light affects the eye as odors do the nose ; that it con- 
sists of particles of amazing minuteness, which are shot from the lu- 
minous source, and entering the eye, strike directly upon the optic 
nerve, and thus awaken vision. This was the view of Newton, but 
it is now considered untenable and is generally rejected. It is at pres- 


ent thought that light is motion rather than matter, and that the eye 
is influenced by a mode of action resembling that of the ear rather 
than that of the nose. We omit further reference to this question 
here, as the analogy wiU be more fuUy traced when we come to speak 
of colors (150). 

136. Light loses Intensity as it is Diffased. — The rays of light proceed- 
ing from any source, a candle for example, spread out or diverge, as we 
notice nightly. As light thus diffuses from its source, the same quan- 
tity occupies more and more space, and it becomes rapidly weaker or 
less intense. This takes place at a regular rate. Its power decreases 
from each point of emission, in the same proportion that the space 
through which it is diifused increases, exactly as occurs in the case of 
radiant heat ; and this is as the square of the distance. The light 
which at one foot from a candle occupies a given space, and has a 
given intensity, at two feet is diffused through four times the space, 
and has but one fourth the intensity ; at three feet it spreads through 
nine times the space, and therefore has but one-ninth the intensity ; 
following the law of radiant heat, as is shown in Fig. 21. If we are 
reading at a distance of three feet from a lamp, by removing the book 
one foot nearer to it, more than double the quantity of light wiU fall 
Fi<^- 21. upon the page ; and if we carry 

it a foot closer, we shall have 
nine times the amount of light 
to read by that we did at firpt. 
This effect, however, may be 
modified by the light reflected 
back from the walls, and which 
is always more, the whiter they 
are. Whitewashed walls and 
light-colored paper economize 
light, or give it greater effect 
than dark walls, which absorb or waste it. 

137. How Bodies receive the Luminous Principle. — When light falls 
upon various kinds of matter, they behave toward it very differently. 
Some throw it back {reflection) ; some let it pass through them {trans- 
mission) ; some swallow it up or extinguish it {absorption) ; and some, 
as it were, split it to pieces {decomposition). All bodies, according to 
their nature and properties, affect light in one or more of these modes, 
producing that infinite variety of appearances which the universe 
presents to the" eye. 





138. Those bodies which will not allow the light to pass through 
them, are called opaque. When the rays of light strike an opaque 
body, a portion of them, according to the quahty of the surface, is 
absorbed, and the remainder are thrown back into the medium through 
which they came. This recoil, or return of the rays, is called reflec- 
tion of light. 

139. The Law of Reflected Light.— "When a ray of light strikes per- 
pendicularly, or at right angles, upon a reflecting surface, it is thrown 
back in exactly the same path or line. If a &, Fig. 22, be a ray of 
light falling perpendicularly upon a reflecting Fig. 22. 
surface, it will be thrown back in the same 
direction 5 a. But if the ray fall upon such 
a surface in a slanting or oblique manner, it 
glances off or is reflected, at exactly the same 
angle, as shown by the arrows. The angle 
of rebound is equal to the angle of striking ; * 

or, as it ia commonly said, — the angle op eefleotion is equal to 


looking-glass upon a table, in a dark room. Let a ray of light, 
entering through a hole in a window shutter, strike upon its re- 
flecting surface, it will be thrown off at an equal angle, and both the 
incident and reflected rays wiU be made visible by the particles of dust 
floating in the room. 

140. How Reflected Light is scattered.— Parallel rays fallmg upon a 
plane eurface, are reflected parallel, as shown in Fig. 23 ; but sepa- 
rating rays falling upon such a surface are reflected divergently, or 
scattered. The beams of light from a candle Fig. 24 diverge before 
falling upon a mirror ; and as each single ray makes 
the angle of incidence equal to that of reflection, it 
is clear that the rays must continue to diverge when 
they are reflected, as in the dotted lines in the 
figure. Thus when a burning candle is placed before a looking-glass, 
its diverging rays strike the mirror surface, and being reflected in 
divergent lines, are dispersed through the room. 

141. The Image in the Looking-glass.— A highly polished metallic 
smface, called a speculum^ is the most perfect reflector. Mirrors, 
or looking-glasses, consist of glass plates coated with metal. It is 

Fig. 23. 



Fig. 24. 

Fia. 25. 

not the glass, in looking-glasses, that reflects the light, hnt the 
metallic coating behind it. K we place any illuminated object before 
a plane mirror, rays of light pass from all points of 
its sm-face, and convey an image of it to the mirror. 
But the polished surface does not retain the image ; 
it reflects or throws it back, so that the eye per- 
ceives it. The light which enters the eye comes 
from the real object, which appears behind the 
glass, because the angle or bend in the ray is not 
recognized. The light from an object may be re- 
flected many times, and make a great number of short 
turns, but it will seem as if the rays came straight 
from the object, and it wUl always appear in the 
direction in which the last reflection comes to the 
eye. This will cause the image to appear as far 
behind the glass as the object is before it, as 
the accompanying diagram (Fig. 25) shows. A 
perfectly plane surface reflects ob- 
jects in their natural sizes and propor- 
tions ; but if the form of the reflecting 
surface be altered, made hollow {con- 
cave)^ or rounded {convex)^ they cause 
the image to appear larger or smaller 
than the objects ; or the image is dis- 
torted in various ways, according to 
the figure of the surface. "We see this 
linaje constantly illustrated in the images of 
the face, formed by the bright metallic 
looking-glass. surfaces of domestic utensils. 

142. A perfect Reflecting Surface would be luvisible.— If the surface 
of an opaque body could be perfectly polished, it would perfectly 
reflect all objects placed before it, so that the images would appear as 
bright as the realities; but, in such a case, the reflecting surface 
would be itself invisihle, and an observer looking at it could see 
nothing but reflected images. If a large looking-glass, with such a 
surface, were placed at the side of a room, it would look like an 
opening into another room precisely similar, and an observer would 
be prevented from attempting to walk through such an apparent 
opening, by meeting his image as he approached it. If the surfaces 
of all bodies had this property of reflecting light, they would be 
invisible, and nothing could be seen but the hghts, or sources of illumi- 


How the image appears behind the 


nation, and their multiplied images. Upon the earth's surface nothing 
would be visible but the reflected images of the sun and stars, and in 
a room, nothing except the spectres of the artificial lights, thrown 
back by one universal looking-glass. But perfect polish is impossible ; 
there are no surfaces which in this manner reflect all the light. 

143. Itt what manner Light makes objects Visible. — It is by reflected 
light that nearly every object is seen, No surfaces are perfectly flat ; 
they may appear so, but, when closely examined, they are found to 
consist of an infinite number of minute planes, inclined to each other 
at all possible angles, and therefore, receiving and reflecting the light 
in aU possible directions. K a ray is let into a dark room, and falls 
upon a bright metallic surface, a brilliant spot of light will be seen 
from certain points, but the reflecting surface will be almost invisible 
in other directions, and the room will remain dark. If, now, a sheet 
of white paper be substituted for the mirror, it can be seen in all 
directions, and will slightly illuminate the apartment. The surface 
of the paper scatters the light every way, producing an irregular 
reflection. It is this scattered and diffused light which makes the 
surfaces of objects visible. Thus light irregularly reflected exhibits to 
us real objects^ while light regularly reflected discloses only semblances 
and images. "We see the image in a looking-glass, by light regularly 
reflected ; we see the surface of the glass itself, by the light scattered 
by the minute inequalities of its surface. This irregularly reflected 
light diverges from each point of every visible surface in all direc- 
tions, so that the object may be seen from whatever point of view we 
look at it, provided other light does not interfere (144). It followa 
the law of radiation, that is, it flows from each point as a focus, but 
it does not conform to the principle of regular reflection, which has 
just been noticed. The direction of the reflected rays is independent 
of each of tJie incident rays. In this manner light is radiated from 
surface to surface, so that in the immediate absence of any original 
luminous fountain, there is a reverberation of light from object to 
object, through an endless series of reflections, so that we hav"^ 
general and equal illumination. 

144. Management of Light in hanging Pictures. — ^The foregoing prin- 
ciples are variously applicable ; hanging pictures upon the walls of 
rooms may be taken as an illustration. As it is irregularly reflected 
light that reveals to us the picture, it should be so placed that from 
the most natural point of observation that light reaches the eye, and 
not regularly reflected light. If the light fall upon a picture from a 
window on one side of it, and we stand upon the other side, as at & (Fig. 





Fia. 27. 

26), the eje is filled witli the glare of the regularly 
reflected light, while the picture itself can hardly 
be seen. In such a case, the true position of the 
observer is perpendicular to the plane of the picture, 
as at a in the figure. As pictures are often sus- 
pended higher than the eye, they require to be 
inclined forward, and the degree of their inclination 
should depend upon their height and the distance 
of the point at which they may be best observed. 
They should be inclined until the line of vision is 
perpendicular to the vertical plane of the picture. "With the eye at a 
and the picture at l (Fig. 27), its proper inclination would be to c ; 

but if it were elevated to <Z, it should 
fall forward to e. "We will farther re- 
mark that pictures should be placed as 
nearly as possible in the same relation 
to light as when they were painted; 
that is, if the shadows fall to the right, 
the illumination should come from the 
left to produce harmonious effects. 

145. Light scattered by the Atmosphere. 
— ^By this kind of irregular reflection, 
the atmosphere diffuses and disperses 
the light, — each particle of air acting as 
a luminous centre, radiates light in every 
direction. If it were not for this, the sun's light would only enter 
those spaces which are directly open to his rays, so that, shining 
through the window of an apartment, that portion only where the 
beams passed would be enlightened, and the rest of the room would 
remain totally dark. This secondary radiation occasions the mild and 
softened light which we experience when the heavens are screened 
with clouds, instead of the intense and often painful glare of a cloud- 
less summer day. In the same manner the atmospheric particles 
scatter the rays and diffuse a subdued illumination at morning and 
evening twilight, while the sun is below the horizon. 


146. When light falls upon transparent objects, as air, water, glass, 
it passes through or is said to be transmitted. Bodies vary greatly 
in this power of passing the light, or transparency. The metals are 
least transparent, or most opaque, yet they are not entirelv so ; thin 



gold leaf, for example, transmits a greerdsli light. Nor are there any 
bodies which transmit all the light ; the most transparent detain or 
absorb a part of it. A considerable portion of the sun's light is ab- 
sorbed in the atmosphere ; it does not reach the earth ; and it has 
been calculated that if the atmospheric ocean were TOO miles deep, the 
solar light would not pass through it, and the earth would be in dark- 
ness. The purest water of a depth of seven feet, absorbs one half the 
light which falls upon it, and of 700 feet depth, extinguishes it. 

147. Fracture or Refraction of the Rays. — "When light passes from 
one substance to another of a different density, as from air to water, 
it is liable to be turned out of its straight course. If it pass from one 
medium to another in a line perpendicular to its surface, as a & (Fig. 

28), it will not be diverted ; but if it fall at an angle, 
as at c d^ it wUl not continue straight to (Z, but will be 
as it were broken or refracted and proceed to c. If 
[ the refracting medium have parallel surfaces, the ray 
on leaving it is again bent back to its original course, 
as is shown in the figure. For this reason common 
window panes, which consist of plates of glass with 
parallel surfaces, unless they contain flaws, produce no 
distortion in the appearance of the objects seen through them. When 
light passes obliquely from a rarer to a denser medium, as from air to 
water, it is turned toward a perpendicular ; when from a denser to a 
rarer medium, as from water or glass to air, it is turned /rom a per- 
pendicular, as shown in Fig. 28. 

148. How Refractiou may be shown. — A stick, with half its length 
placed obliquely in water, appears bent at the surface ; this is because 
the rays are bent, so that those which come from that portion of the 
stick which is in the water, show it in a false place. Put a coin in 
any opaque dish upon a table, and step back, until the edge of the 
vessel just hides it from view. Now, if water be carefully poured in, 
without disturbing its position, the coin will become visible (Fig. 29) ; 

the rays of light coming from it, which before 
passed above the eyes of the observer, are 
now, as they come into the air, bent down- 
ward /rom the perpendicular. Bodies possess 
different degrees of refractive power. When 
we look through a mass of water, as in a pond 
or stream, the rays are so altered that it 
appears only thi'ee-quarters as deep as it really 
is. Cases of drowning have happened through ignorance of this 

Fig. 20. 



Fig. so. 

Fis. Si. 

illusion. The degree to whicli any substance bends the light from its 
straight course is called its index of refraction. Each transparent 
body has its refracting index, which is one of the properties by which 
it may be known. 

149. Effect of Lenses upon Light.— This power which bodies have, of 
bending hght from its straight course, 
is employed when we desire to gather 
it to a point or focus, or to concentrate 
it ; or when it is wished to disperse and 
difiuse it. Pieces of glass, cut or ground 
into various shapes, are commonly used 
for this purpose, and are called lenses- 
A plane convex lens (Fig. 30), or a 
double convex lens (Fig. 31), collect 
the rays of light; while a plane-con- 
cave lens (Fig. 32), or a double-concave 
lens (Fig. 33), separate them, or spread 
them out into a greater space. Com- 
mon spectacle glasses are examples of 
these forms of lenses (248). 


Fig. 33. 




150. Light not Matter but Motion. — Thus far we have considered light 
as if it were simple, without inquiring if it be reaUy so, or compounded 
of difierent elements. There is another way in which the objects of 
nature receive and dispose of it, which brings us to the question of 
composition, and the subject of color. But what is color ? and what 
is light, in nature and essence ? Or what opinion has been formed of it, 
by those who have thought upon the subject most deeply? In its 
cause and mode of movement, light is believed to resemble sound ; 
it is propagated, not by moving particles of matter, but by impulses 
of motion, wliich progress unaccompanied by any material substances. 
Let us note how wave-motions take place, and the known extent of 
theu' occurrence in nature. 

151. Visible Ware Motions in Nature. — If we fasten one end of a cord, 
and holding the other strained tight, move the hand sharply up and 
down, or from side to side, icares will be formed, wliich proceed along 
the string. The real motion, in this case, is at riglit angles to the di- 
rection of the string, the apparent motion is forward. The particles 


composing the cord make excursions right and left, or up and down, 
■which gives rise to forward wave-impulses. All have noticed what 
takes place in a field of grain when the wind blows. A succession of 
waves appear to pass over the field ; but it is not the grain that moves 
along over the ground ; every staUc keeps its place, and only bows its 
head. Yet wave-motions are seen to flow successively forward. If 
we toss a stone into perfectly still water, the surface wiU be thrown 
into agitation, and waves will pass rapidly from the point where it 
struck, outward, in all directions. The water in this case does not 
move forward any more than the grain did. This is proved by the 
circumstance that any objects which may be seen floating upon the 
water are not carried along by the advancing waves, but only move 
up and down in their places. Thus, particles of water, moving verti- 
cally, cause wave-motions to travel horizontally. 

152. Sound the result of Waves in the Air. — Air is the medium which 
conveys sound to the ear. If a bell be rung in a vacuum, we cannot 
hear it. The air in some way transmits or convoys the sound from 
point to point. How is it done ? There is no passage of air-particles, 
no current or breeze moving from the sounding body to the ear ; the 
atmospheric medium is thrown into vibratory motion, and it is air- 
waves only which move forward. We all know that sonorous bodies 
vibrate when struck, and that sound results. A harp-string, when 
struck by the fingers, swings rapidly backward and forward for a 
certain time, producing a sound as long as the vibration lasts. A 
piece of steel wire, or a pin held between the teeth, utters a sound 
as often as the free end is inflected. By touching the teeth with the 
prongs of an excited tuning-fork, we can feel the vibrations. Sound 
is thus not only motion, but it is moratory motion, and its transmission 
to the ear is due to the flight of air-waves, which, striking against the 
auditory drum, communicate sensations of sound to the brain through 
the auditory nerve. 

153. Upon what the diflferences of Sound depend. — If sounds are thus 
caused by vibrations, it would seem that the quality of sound should 
depend upon the quality of the vibrations ; which is the fact. The 
first distinction among sounds is into high and low, or acute and 
grave ; it is a difierence of pitch. Slow vibrations produce grav'_> 
sounds of a low pitch. In the case of strings, for example, the larger 
they are the heavier they are, and the looser they are the slower are 
their vibrations, and the deeper are their sounds; while, on the other 
hand, the shorter, lighter, and tighter they are the quicker are their 
vibrations, and the higher and sharper the sounds they give. Each 


sound, therefore, that can be made, is the result of a certain numher 
of air vibrations, and to that pitch of sound always belongs that num- 
ber. Sataet contrived a machine by which the number of pulsations 
which belong to each tone has been determined by actual experiment. 
A thin plate of metal was struck by each tooth of a revolving cogged 
wheel, the motion of which was easily measured. In this way he de- 
termined the exact number of vibrations in the tones forming the 
usual musical scale. 

154. Harmonic Ratios of the Musical Scale.-- It was found, experimen- 
tally, that the orchestra pitch note A, of the treble cleff, is produced 
by 853 vibrations per second. The number of pulsations in each note 
of the octave is as follows : 

Katio of Haemonio Sounds. 
^ D E F q A B I c I 


No. of Vibrations 512, 576, 640, 682, 768, 853, 960 1024, 

Intervals 64, 64, 42, 86, 85, 107, 64. 

It will be seen that in the highest note of this scale there are just 
twice as many vibrations as in the lowest ; the interval which they 
comprise is called an octave. The difference between the number of 
pulsations in any note, and the same note in the octave above, is as 1 to 2. 
Hence, by halving the numbers of any scale we obtain the numerical 
value of the octave below; while by doubling them we have the 
number of vibrations made by the notes in the scale above. The 
lowest note of a seven octave piano is made by 32 vibrations in a sec- 
ond, and the highest by 7,680. Two tones having exactly the same 
number of vibrations are said to be in unison. When their numbers 
are not the same, but are in some simple relation, a concord is pro- 
duced. If one has twice as many as the other an octave results, which 
is the most pleasing of all concords. The simpler the numerical ratio 
between the vibrations which generate a sound, or the air-waves 
which reach the ear, the more perfect and sweet the concord. When 
the difference is such that the proportion cannot readily be recognized 
by the ear, discord is the result. The whole phenomena of music thus 
resolve themselves into certain harmonious numerical ratios among 
air-waves, by which impressions are produced in a certain exact order, 
upon a mathematically constituted organ — the brain. 


155. Light and Colors result from Wave Motion. — As all sound and 
music are thus due to measured wave movements in the air, it is 
thought also that light has a similar origin. This view assumes, that 
throughout the universe there exists a subtle, aU-pervading and in- 
finitely elastic ether^ and that vision is the result of vibrations or wave 
movements sent thraugh this ether, from the source of light to the 
nerve of the eye ; and as different musical sounds are produced by 
varying rates of vibration in the air, so it is suspected that different 
colors are due to the different rates of vibration in the luminous ether, 
and philosophers have gone so far as even to measure the wave-lengths 
of the different elements of light. By wave-length is meant the dis- 
tance from the top or crest of one wave to that of the next ; and it 
is inferred from certain interesting experiments made by Newton, that 
the length of waves, although exceedingly small, differs in the different 
colors, red being largest and violet smallest. In an inch length of a 
ray of red light there are 37,640 vibrations; in an inch of yeUow 
light, 44,000; and in an inch of the violet ray, 59,756. K the minute- 
ness of the wave excite surprise, it may be replied that this is by no 
means the strongest illustration of the smallness of the scale upon 
which nature's works are often constructed. Indeed, in this case it 
has been even outstripped by art. M. IsTobeet, of France, has ruled 
lines upon glass, for microscopical test-purposes, but the -.j-xsto <^f ^^ 
inch apart.* 

156. Vibrations per second of the Inminons Ether. — But the demon- 
strations of science carry us into far profounder regions of wonder. 
The speed of light has been measured ; the velocity with which it 
moves is in round numbers 200,000 miles per second. That is, when 
we look at any thing, an agent or force sent from the illuminated body 
streams into the eye at the rate of 200,000 mUes in a second. Know- 
ing the rate at which light moves, and the number of waves in an 
inch for any particular color, it is easy to ascertain the number of 
vibrations made by each in a second. In two hundred thousand mUes 
there are a thousand millions of feet, and, therefore, twelve thousand 
millions of inches. In each of these inches there are forty thousand 
waves of red light. In the whole length of the red ray, therefore, 
there are four hundred and eighty millions of millions of waves. 
Now as this ray enters the eye in one second, and the retina 
pulsates once for each of these waves, we arrive at the astonishing 
conclusion, that where we behold a red object the membrane of the 
eye trembles at the rate of four hundred and eighty millions of mil- 
lions of times between every two ticks of a common clock. Of yellow 

* See Appendix B. 


light five hundred and thirty-five millions of millions of waves enter 
the eye, and beat against the nerve of vision in the sixtieth part of a 
minute ; "if a single second of time he divided into a million of equal 
parts, a vrave of violet light trembles or pulsates in that inconceivably 
short interval seven hundred and twenty-seven millions of times." 
"Vision is undoubtedly the result of something done within the eye, 
the effect of an active external agent, and the reaction of the mechan- 
ism ; the chemical constituents of nervous matter, — perhaps the atoms 
of carbon or phosphorus are in some way changed or influenced by 
nerve impulses in infinitely rapid succession, the sensations of vision 
and color being the consequence. If it be objected that the foregoing 
statements are incredible, we reply that they are generally accepted 
by the most sober and cautious scientific thinkers. But they are really 
no more strange or impossible than many other of the miracles of being 
which science is constantly unfolding around us. We should observe 
a due modesty in criticising and assigning limits to the wonders and 
perfections of God's works. Dismissing the more purely theoretic or 
explanatory aspect of the subject, we now proceed to notice those 
properties and relations of colors which are the result of actual ex- 


157. White Light taken to pieces. — If a ray of common white light 

be admitted, through a small aperture, into a dark room, and be made 

to strike upon a triangular piece 

of glass (j>rism)^ the white ray 

disappears ; it is turned from its 

course, and there falls upon the 

opposite wall an oblong colored 

image called the solar spectrum. 

It consists of seven bright colors, 

always found in a certain order, 

a 4.- e v<- r 1,+ • + -NT r 1 ^s showu in Fig. 34: but they 

Separation of white ii^at into Newton s seven ° ' •' 

prismatic colors. pass into each other gradually, so 

that it is difficult to tell where one ceases and another begins. New- 
ton assumed, as the result of this experiment, that white light is, a 
compound principle, consisting of these seven colors, which he called 
primary, and taught that all other colors whatever are the result of 
various commixtures of these. For convenience of representing the 
relations of colors, we may represent white light by a circle, and the 



Fia. 35. 

colors wliicli compose it by divisions of the enclosed space. In that 
case the seven primaries of Newtox will be shown as in Fig. 35. 

158. Newton's explanation of Colored Surfaces. 
— White light falls upon objects, and thej ap- 

)ear colored : how is this ? Newton replied : 
oodles have not only the power of reflecting 
and transmitting light, but they can also de- 
compose and absorb it. A body appears 
white because it reflects back to the eye the 
white light that falls upon it, unaltered. When 
white light falls upon a surface and it appears 
'blacky it is absorbed and lost in the substance, 
and therefore does not return to make an impression upon the eye. 
But the blackest surfaces do not really absorb all the light, for then 
they would be invisible, and appear like dark cavities, presenting no 
surface. If the surface appears colored, it is because the white light 
is split up, or decomposed, one part being absorbed and lost, whUe 
the other is reflected to the eye, so that the object appears of the re- 
flected color. For example, grass absorbs all colors but green, which 
it reflects to the eye ; and in the same way the sky absorbs all but 
blue, and reflects that to the eye. Difierent surfaces reflect the pri- 
mary colors mixed in aU manner of ways, and hence the endless 
modifications of color that meet the eye. 

159. Bttt three Primary ColorSt — A more simplified view of the com- 
position of colors has been propounded by Sir D. Beewstee, and 
generally received. He considers 
that instead of seven, there are 
but three elementary colors, red, 
yellow, and blue, and that the 
others are compounds of these. 
We cannot produce red, yellow, 
or blue, by the mixture of any 
other colors ; but we can pro- 
duce aU others by the various com- 
binations of these three. Beews- 
tee maintains, that even the colors 
of the spectrum are not absolutely 
pure, but that each of the three 
exists throughout its whole extent, although greatly in excess at the 
diflferent points where they are visible. Blue, yellow and red being 
primaries, violet, indigo, green and orange are' secondaries derived 



FiQ. 8T. 

from them. The separation of the impure or compound colors from 
the spectrum, leaving the three from which 
they are derived, is illustrated in Fig. 36. 
Orange is derived from the mixture of red 
and yellow ; green from yellow and blue ; 
and indigo and violet from blue and red. So 
that we have white hght at last composed 
only of the three colors, as represented in 
Fig. 37. 

160. What are Complementary Colors. — The eflfect of a colored surface 
is to decompose the white light which falls upon it, reflecting one 
portion, and absorbing or extinguishing the rest. "We do not see any 

colored surface, except 
by the seperation of the 
light which falls upon it 
into two colored parts, 
the one visible, the other 
absorbed. Now it is evi- 
dent that the rays ab- 
sorbed, added to those 
Avhich are reflected,make 
up the ordinary light. 
Hence, whatever be the color reflected, that which is not reflected, 
and which is, therefore, wanting to complete the full set of colors which 

form white, and make 
out the full complement, 
is called the com^ple- 
mentar y colov. The part 
absorbed, or which does 
not appear, is the com- 
plementary of the color 
seen. This may be made 
perfectly clear by the 
circular diagram. If we 
look, for example, upon a red surface supposed to be presented in 
Fig. 38, yellow and blue are seen to be the colors necessary to com- 
plete it to white ; they are therefore the complement of red ; but 
yellow and blue form green, as shown in Fig. 39, which is therefore 
the true complement of red, that which it lacks to make white. If we 
look upon a yellow surface (Fig. 40), blue and red are deficient ; blue 

Fig. 41. 


and red produce violet, therefore violet is the complementary of yel- 
low, as seen in Fig. 41. ^.^^ ^2. Fig. 43. 
Again, we look upon 
blue (Fig. 42) ; red aad 
yellow are required to 
complete the circle into 
whiteness ; but red and 
yellow make orange, 
therefore orange is the 
complement of blue, as 
is shown in Fig. 43. 

161. Tints and Shades, Tones and Scales. — These terms have formerly 
been employed in the most loose and indefinite way ; they have, how- 
ever, now acquired a kind of scientific precision. The tones of a color 
are those aspects which it presents when altered from its maximum 
of brightness or highest intensity, by mixing with it either white or 
black : if we take the purest and brightest red as a standard, say car- 
mine, and mingle various proportions of black with it, we of course 
darken it and get deeper tones of red. If we mingle white with it, 
we lighten it and get lighter tones of red. By the addition of black 
the red is said to be shaded^ by the addition of white it is tinted. 
Each color, in this case, is a tone of red, and the whole series of tones 
constitute a scale — ^the red scale. It may consist of ten, twenty, or 
fifty tones, according to the quantities of black and white successively 
added. In the same manner we make tones of orange and get an 
orange scale, tones of blue and get a blue scale, and so each color has 
its scale, in which it moves in two directions, from its normal or 
standard point, towards black and towards white. 

162. Wliatare Hues? — ^A hue is the result of the movement of a 
color, not in the direction of black or white, but of some other color 
out of its scale. If a little blue be mingled with red so as to change 
it slightly, the red still predominating, a hue of red is produced. So 
if blue be tinged in a similar manner by any color, hues of blue re- 
sult. In the same way are produced hues of orange, yellow, violet, 
green, &g. 

163. Chevreul's scheme for showing the relation of Colors. — A plan has 
been suggested by M.. Cheveettl, of France, for representing the com- 
position and relations of colors, in an extremely simple and effective 
way. It clears the mist from the subject, and not only discloses it in 
a beautiful order, but is very valuable for practical purposes. It is 
represented by the diagram (Fig. 44). The outer circle represents 



black, the centre white. The radial lines passing from the centre to 
the circumference represent scales of color, each dot indicating a tone. 
Each scale comprises ten tones. Take the red scale for example. The 
larger dot at h represents the place of its normal, or type of the purest 
red ; from that point toward the circumference it is shaded down to 
black, and in the other direction it is tinted up to white. The same 




Plan of CHEVEErL's Cheomatio Ciboles, illustrating the principle of complementary 
colors, tints, shades, tones, hues, and scales. 

with yellow ; its normal is at a, and that of blue at c. From these three 
primaries all the rest are derived. Midway between yellow and blue is 
the scale of green, which results from their combination in equal pro- 
portions, half blue and half yellow. Midway between green and blue 
is a scale that we might call a greenish blue. It is only one-quarter 
of the distance from blue to yeUow, and therefore is three-quarters 


"blue, and one-quarter yellow, — a hue of blue. Space or distance 
represents proportions of color. It will be seen that colors may be 
altered in two ways, that is, may move in two directions — along their 
scales, by admixture with white or black, producing tones^ and out of 
their scales, in the direction of the circles, producing hues. The dia- 
gram represents twelve scales, with ten tones on each scale, giving 
an arrangement of 120 colors, each having a definite, known compo- 
sition. With 24 scales, and 24 tones on each scale, we should have a 
scheme of 576 colors. 

164. Making a Chart with the real Colors. — An instructive exercise is 
to produce such a chromatic chart with the actual colors. Make a 
circle upon paper a foot in diameter, designed for twelve scales of ten 
or twelve tones. From a box of paints select carmine for the normal 
red, gamboge for the normal yellow, and Prussian blue for the normal 
blue. By mixing the blue and red with a pencil brush in equal pro- 
portions, the violet is produced, and by varying the proportions all 
the hues between blue and red are obtained. By mixing blue and 
yellow, green, greenish-yellow and yellowish-green are made ; and by 
mingling red and yellow, orange, orange -yellow and yellow-orange 
are made. Thus all the hues are obtained. By mixing each with 
black and white, increasing the proportion of black regularly as you 
proceed outwards, and white as you go inwards, the scales will be 
formed. Familiar colors would at once locate themselves upon such 
a chart, so that we should understand their exact composition. For 
example, the crimson will be found near the red, but in the direction 
of blue, that is, it is red slightly blued, while scarlet is red, moved 
slightly in the opposite direction, toward yellow. So indigo is blue 
just started toward red. 

165. — How the Diagram shows Complementary Colors. — We determine 
the complementary of any color in a moment, by a glance at the sys- 
tem of circles. For example, we want the complementary color of 
red ; this is formed by the union of blue and yellow, producing green. 
Green, therefore, which is the complement of red, is placed exactly 
opposite to it on the diagram. So, opposite blue we see its comple- 
ment orange, and opposite yellow, violet, which is its complement, and 
also the contrary ; the complement of green is red ; of orange, blue ; 
of violet, yellow. So of all the scales, no matter how many are 
formed, their complements are seen on exactly opposite lines of the 
circle. The. complement of red-orange is observed to be blue- 
green ; of a reddish-violet, it is greenish-yellow, and so on round the 
whole circle. We may even say that the complement of black is 


white, and of -white, black, — of a deep tone on one side, it will be a 
light tone on the other. Thus the complementary color of a deep 
tone of green will be a correspondingly light tone of red ; of a light 
tone of violet, it will be a deep tone of yellow. By means of the dia- 
gram, therefore, the complementary of any of the one hundred and 
twenty colors can be found by any one in an instant ; a fact of much 
practical importance, as we shall soon have occasion to see. 

166. — What is meant by Complementary Contrast. — By a glance at the 
diagram it will be seen that the complementary of any color is its 
exact opposite. It is the color which differs from it the most possi- 
ble ; therefore it is in strongest contrast to it. Complementary colors 
are, hence, contrasted colors, and their relation is commonly indicated 
by the term complementary contrast. 

167. Lnmlnons and sombre Colors. — It will be noticed that the three 
normals (Fig. 44) of red, yellow, and blue (represented by the larger 
dots), are not all located at equal distances from the circumference 
or centre. The reason of this is obvious. Yellow is a light, and blue 
a dark color. The natural position of yellow, therefore, at its height 
of intensity, is nearer to the white than to the black, and the natural 
position of bright blue is much nearer to the black than to the white, 
while red is intermediate. For this reason it requires more tones to 
shade yellow down to black than it does blue, and more also to tint 
blue up to white than it does yellow. Colors are thus divisible into 
luminous and somlre. Those into which yellow enters most largely, 
belong to the first class, and those consisting mainly of blue, to the 
second, red forming a medium color. 

168. Grays and Browns ; Pure and Broken Colors. — Grays resiilt from 
the simple mixture of black and white. Browns are the result of 
mixing black with the various colors. The deeper tones of all the 
scales upon the diagram are browns. A color which has no black in 
it is said to be pure^ while the addition of black produces a l)roTcen 
color. The browns are therefore all broken colors. A color may be 
broken, however, without directly adding black ; the three primaries 
mixed in certain proportions produce this effect. If a little blue, for 
example, be added to orange, it neutralizes a pprtion of the yeUow 
and red, breaking the color and starting it towards black. 

169. No Colors perfectly pure. — We must guard against the error of 
supposing that in practice we meet with any such thing as a pure or 
perfect color. Even those of the spectrum or rainbow are not per- 
fect ; Beewster has shown that the very brightest is contaminated by 
others. But when we leave the spectrum, and begin to deal with the 


commoner aspects of colors, paints, dyes, &c,, their imperfections be- 
come mucli more obvious. We are to regard a red surface as reflect- 
ing to the eye, not a simple and perfect red, but along with the red a 
certain portion of the other colors of the spectrum, which have the 
eflfect of weakening and lowering the red. The true statement is, that 
the sensation of red is the result only of the predominance of that 
color. It is the same with all the colors we see ; others are more or 
Jess mixed with them, which impair their brightness. 

170. How Colors mntnally improve each other. — The action of colors 
upon each other is not a matter of hap-hazard, and although it was 
long inexphcable, and half suspected to be a field where nature ca- 
priciously refused to be curbed by rules, yet science has at length dis- 
covered the reign of law in the domain of colors. Some combinations 
of colors are pleasing to the eye, and others disagreeable ; some are 
harmonious, and others discordant. The harmonies of color are of 
several kinds, but the fundamental and most important one is the har- 
mony of complementary contrast. If a purchaser be shown succes- 
sively a dozen pieces of bright-red cloth by a shopkeeper, those last 
seen will be declared much inferior in intensity of color to the first, 
such being the actual appearance which they present to the purchaser's 
eye. If now the buyer's attention be directed by the merchant to 
green stuffs, they wiU appear extremely bright, unnaturally so ; and 
if the eye recur again to the reds, they will look much finer than 
before. Eed and green viewed in this way have the mutual effect of 
improving each other. It is the same if the two colors be placed side 
by side and observed together ; they will so heighten each other's in- 
tensity as to appear much brighter and purer than when they are 
viewed separately, that is, when the eye cannot be directed from one 
to the other. If now we take yellow and violet, or blue and orange, 
or violet-red and yeUow-green, and observe them in the same manner, 
we shall get the same result ; their brOliancy and clearness will be 
mutually heightened. But these colors are complementaries of each 
other; complementaries then, when viewed together, improve each 
other. They are the most opposite or contrasted, and therefore the 
pleasing effect they produce upon the eye is denominated Harmony of 
Complementary Contrast. These effects are experimental facts which 
may be verified by any one. Take six circular pieces of paper, say 
an inch and a half in diameter, and color them respectively red, orange, 
yellow, blue, green, and violet. Place each one separately on a sheet 
of white paper, and then, with a thin wash of color, tint the white 
paper around each circle with its complementary color, gradually 


weaker and weaker as the tint recedes from the colored circle. If 
now the red circle be placed upon the sheet that is colored green, it 
will be made to appear greener ; so if the green circle be placed upon 
the reddened sheet, the latter color wUl be at once brightened. It wUl 
be found upon trial, that each color when viewed with its comple- 
mentary, increases its intensity or improves it. "We get by such exper- 
iments two kinds of result ; first, a successive change where one color 
is viewed after another ; and, second, a simultaneous change when 
both colors are seen at once and together. Both these effects require 
to be explained, and first of successive contrast. 

171. Colors exert an inflnence npon the Eye. — Colors appear to exist 
upon the surfaces of external objects, but we must not forget that 
their real seat is in the eye itself ; that is, external bodies so modify 
the light, that it produces within the eye different effects, which we 
name colors. Colors are sensations, or nerve-impressions, the result 
of something accomplished within the optic organism. Thus we say 
snow is white, and blood is red ; meaning thereby that snow so influ- 
ences the light, that it originates within the organ of vision a sensa- 
tional effect which we style white ; while blood so modifies the light 
falling upon the nerve of the eye as to cause the perception of red. 
As color thus finally resolves itself into different modes of affecting 
tJie eye J we might naturally expect that both the agent and its organ 
would react upon each other, — colors producing changes in the eye, 
and the eye producing changes in colors, more or less considerable, 
according to circumstances. The eye being a part of the bodily sys- 
tem, and governed by general physiological laws, is subject to the 
same vicissitudes of varying activity, acute and blunted susceptibility, 
as other parts. We shall now notice the change that takes place, only 
so far as colors are themselves affected ; deferring to another place an 
examination of the influence of colored light upon the eye in refer- 
ence to its health (253). 

172. Daration of Impressions npon the Retina. — ^Impressions continue 
upon the nerve of the eye about one-sixth of a second after the object 
is removed. For this reason, a torch whirled swiftly roimd appears 
as a continuous streak or ribbon of fire. But the eye continues to be 
affected for a much longer time ; although it is not, as we might at 
first suppose, by a feeble, lingering impression left upon it, which 
gradually fades out after the object is withdrawn from sight. If there 
were a continuance of the perception of an object after its removal, 
the effect of viewing another object would be the mixture of two 
colors. For example, if a bright blue object were seen, and then the 


eye suddenly directed to a red, the effect would be a perception of a 
mixture of the two, or violet, and this would remain until the first 
impression, or blue, faded away from the retina, after which the red 
object alone would be perceived. But such is not the case. 

173. The Eye loses its sensibility to Colors, and demands tMr Comple- 
mentaries. — The influence of any color upon the eye is to diminish or 
deaden its sensibility to that color ; it gets fatigued in looking at one 
color for some time, so that it appears less bright. If, for example, 
the gaze be directed for a time upon a bright red object, that part of 
the retina upon which the image is impressed, becomes exhausted by 
the action of the red color, and partially blinded to its brightness ; 
just as the ear may be deafened for a moment by an overpowering 
sound. But the effect does not stop here. If the eye be averted from 
the red and directed to white, the red contained in the white will not 
produce its natural effect, whUe the balance of the colors in white, 
blue, and yellow, make their proper impression upon the eye, pro- 
ducing green. Thus the eye, dulled to one color, has a tendency to 
see its complementary. If we place a red wafer upon a sheet of white 
paper, and fix the gaze upon it steadfastly for some time, and then toss 
it off, we shall see a spectral image of the wafer upon the paper, hut it 
will te green. The wafer so extinguished the sensibility to red upon 
a certain portion of the retina, that when it was removed, the eye 
saw the white, minus the red, that is, green. In like manner, if the 
eye be impressed with green, it loses its sensibility for it, so as again 
to decompose white and see red. If blue is observed, the impressi- 
bility of the nerve of sight is lowered for that color, so that white 
light is seen without its blue, and orange appears, which is the com- 
plementary of blue. In like manner the observance of yellow creates 
a tendency to see violet, and in the same way the effect of any color 
whatever, is to dispose the eye to see its complement. If we gaze at 
the sun at sunrise, when of a ruddy appearance in consequence of his 
rays being strained of their blue and yellow as they pass through the 
damp atmosphere near the ground, an image wUl be generated by the 
eye formed of these missing rays, and, therefore, green. When he 
has ascended higher and become of an orange yellow color, the image 
will be dark violet. It is well known that in looking at the sun 
through colored glasses at the time of an eclipse, spectres of the solar 
disk are sometimes produced which continue for a time before the eye. 
The color of these is always complementary to the color of the glass 
through which the sun was viewed. 

174. Simaltaneons contrast of Colors. — But colors placed side by side, 



exert upon eacii other, simultaneoudi/, an influence that can hardly be 
accounted for by the theory which explains successive contrast. The 
effect is of the same kind, — contrasted colors are augmented in bright- 
ness, but it results from the equal action of both colors upon the eye 
at the same time. It has been stated that surfaces reflect to the 
eye rays of other colors beside those which appear. No surface can 
so perfectly analyze the white light which falls upon it, as to absorb 
all of one color, and reflect all of another. It appears of the color 
of the predominating ray, though more or less of the remaining colors 
of white light are reflected also, and diminish its purity. We look 
upon a red ; it is not perfect, because other colors not red, but the 
opposite of red, are mingled with it and reduce its effect. We gaze 
separately upon green ; it is vitiated by rays coming from it that are 
not green, but its opposite. Now if we could clear away or destroy 
these vitiating rays, we should improve both colors, and this is ac- 
tually done by placing them side by side. The reducing colors, which 
are active when the surfaces are viewed separately, seem to be, in 
some way, neutralized when they are brought together, and the com- 
plementary of each is thrown upon the other. 

175. How associated Colors injure each other. — If certain combina- 
tions of color alter each other for the better, it is easy to see how 
other combinations must act in other ways for the worse. If the 
mutual effect of colors most contrasted be to intensify and exalt each 
other, it follows that if those most nearly alike are associated to- 
gether, they will vitiate and injure each other. What the exact effect 
wiLl be, may be seen at once by inspecting the chromatic diagram. 
The complement of violet is yellow. If violet be associated with 
yellow, therefore, the only effect it can produce is to make it yellower ; 
but suppose it be placed beside other colors, the result must be a ten- 
dency to yellow them all. Violet placed beside green drives it out of 
its scale (see diagram) toward yeUow. It was hah" yellow before, but 
the effect of violet is to increase the proportion of this element, and 
thus produce a new hue of yellowish-green. If violet be placed 
beside orange, which is also half yellow, it is moved out of its scale 
in the same direction as before toward yellow, a hue of yellowish 
orange being produced. As orange and green are already half yeUow, 
it is obvious that the effect of adding to them a little more yellow will 
not be so marked as when this color is cast upon those which do not 
contain it. Violet, beside blue, stains it of a greenish hue ; while 
beside red it changes it to scarlet. By tracing these effects out upon 
the diagram we at once get at the general law of the mutual influence 



Fig. 45. 

of colors. A color placed beside another tends to make that color as 
different as possible from itself. In the case of violet just alluded to, 
by reference to the diagram it will be seen that the color naturally 
farthest from it, by its very constitution indeed exactly opposite to it, 
is yellow. Now if bright violet be placed beside the yellow scale, it 
will drive every tone of that scale one or two steps back, away from 
itself, by making them all still yellower, and you will notice that the 
effect of violet upon the other colors, by throwing yellow upon them, 
is to start every one of them away from itself in the direction of its 
antagonist, which is the yellow. If traced out it wiU be seen that the 
effect of any other color is precisely the same. The complementary 
of any color thrown upon another renders it more unlike, or increases 
the difference between them. 

176. Contrast of Tone. — The effect of viewing white and black to- 
gether is to heighten the contrast between them, and so with the in- 
termediate tones of a scale of white and black. The accompanying 
wood-cut (Fig. 45) affords an im- 
perfect illustration of this effect. 
It consists of five bands, shaded 
successively deeper and deeper 
from left to right. As the eye 
glances at the scale, the bands 
appear darker at their left bor- 
ders and lighter at their right. 
But this appearance is an effect 
of contrast ; for if we take two 
slips of paper with straight edges, 
and cover all the diagram but 
any single band, its surface will be seen to be perfectly uniform. When 
viewed together, however, there is a heightening of the real differences, 
the light tones seem lighter and the dark tones darker, almost as if 
the intention was to represent fluting. It is so with the different 
tones of any color which has been shaded with black or tinted with 
white. If we place two different tones of the same color together, 
they always alter each other's intensity ; dark tones making adjacent 
light ones appear still lighter, and light ones making dark tones seem 
still darker. This is, perhaps, because the absence of light in the 
dark color renders the eye more sensitive to the white light of the 
lighter color, and on the contrary the dark color appears darker, be- 
cause the white light of the lighter color destroys the effect of the 
small amount of white light reflected by the other. Thus if we place 

Illustrating the effect of contrast of tone. 


a dark red beside a light rose-color, or a deep yellow iu contact "witli 
a straw-color, they will, as it were, push each other further apart, the 
light tones in both cases appearing lighter, and the deep ones deeper, 
so as to deceive the eye in regard to the real depths of their colors. 
Thus for tones as well as hues the law of Cheteetjx holds good. " In 
the case where the eye sees at the same time two contiguous colors., they 
will appear as dissimilar as possiile, ioth in their optical composition 
and the height of their tone^ 

177. Harmonies of Analogy. — The employment of glaring or intense 
colors in many cases, as often in dress, is not admissible by the rules 
of cultivated taste. It is chiefly among the rude and nncultured 
that we remark a passion for gaudy and flaunting colors. With the 
progress of a refined civilization there is a tendency to the employ- 
ment of more subdued colors in personal and household decoration. 
Not by any means that good taste requires the total rejection of bright 
colors, but only that they be used with skill and discretion — ^be ameli- 
orated by combination, so as not to produce staring and stunning effects, 
or strong and deep contrasts which often offend the eye. Harmonies of 
complementary contrast are to be first and chiefly sought in chromatic 
arrangements ; but these are comparatively limited, and in the demand 
for variety, othei" concords are found, which, although less striking, 
often give beautiful results. In studying the best arrangement of 
colors to produce a harmonious grouping, regard must be had to the 
kind of effect required, whether lively, medium or sombre. In one 
case, bold striking contrasts will be sought, in another mild ones ; and 
again, rejecting contrasts altogther, we may get an agreeable effect by 
grouping together similar or analogous colors. Harmonies of analogy 
may be produced in three ways. First^i we may arrange the different 
tones of a single scale in a series, beginning with white and terminating 
with brown black, leaving as nearly as possible equal intervals be- 
tween them. This will produce a pleasing result. The greater the 
number of tones the finer will be the effect. Second, we may asso- 
ciate together the hues of adjacent scales, all of the same tone, and 
often produce an agreeable analogy. But sometimes colors of near 
scales mutually injure each other, as blue and violet ; the complemen- 
tary of blue, which is orange, being thrown upon violet gives it a 
faded and blackened appearance ; while tlie complementary of violet, 
which is yellow, falling upon blue turns it to green. Sometimes when 
one color is injured we may sacrifice it to give prominence or relief to 
another. Tliird, a pleasing harmony of analogy is produced by view- 
ing groupings of various colors through a colored medium that casts 


its own peculiar hue over tlie whole, as when we view a carpet in 
light that comes through a stained glass window. 

178. Circumstances which disturb the influence of Colors. — Various con- 
ditions exert a modifying effect upon the mutual action of colors. 
The result may he greatly influenced by the shape of the object, and 
the manner of its exposure to light. The surface of a red curtain, 
for example, hung in folds, appears of different hues, the parts most 
exposed to the light being changed in the direction of scarlet, while 
those more protected from it are shaded so as to approach a crimson. 
The condition of surfaces is also important. When they are glossy 
their colors affect each other much less, and a bad association may be 
concealed or overlooked where the elegance of symmetry of the 
object, or the light and shade are so related, or our ideas are in some 
way so associated with it as to draw the attention from the ill effects 
of the colors. It is often thus that flowers present bad associations, 
yet our feeling concerning them is such that we are not offended as 
when we see the same upon flat unglossed surfaces. The flower of the 
sweet pea, for instance, gives us the alliance of red and violet, which 
mutually injure each other, though the green leaves set off the red 
and help the result. 

179. Effect of associating Colors with White. — All colors appear 
brighter and deeper when associated with white, because its superior 
brilliancy renders the eye insensible to the white light which accom- 
panies and weakens the color. At the same time the white is tar- 
nished by the complementary of the color falling upon it. "White is 
BO intense that in all its arrangements with color, except perhaps light 
tones of yellow, there will be contrast. It may often be interposed 
with advantage between colors which injure each other. All the pris- 
matic colors gain by grouping them with white, but not in an equal 
degree, for the height of tone of the color makes a decided difference 
in the result. The deep tones of blue, red, green, and violet, contrast 
too strongly with white, while the light tones of the same colors form 
with it the pleasantest contrasts we can obtain. Orange, the most 
brilliant of the colors, is almost too intense with white, while the 
deeper tones of yellow appear well with it. 

180. Effect of associating Colors with Black and Gray. — Black is agree- 
able if associated with almost any color. With their light tones it 
contrasts well, making them appear lighter, and being itself darkened, 
while their sombre complementaries thrown upon the black scarcely 
affect it as its surface reflects so feebly. With the deep tones of the 
Bcales it forms harmonies of analogy, although their luminous com- 


plementaries, especially those of blue and violet when falling upon 
black, deprive it of its vigor, and tend to make it look faded. Gray 
being intermediate between black and white, it is used where white 
gives too strong a contrast, and black makes the combination too 
sombre, as with orange and violet, green and blue, green and violet. 


181. Articles of Dress. — A recollection of the foregoing principles 
may enable us to avoid gross errors in combining colors. Thus a lady 
would hardly trim a violet bonnet with blue flowers, or an orange 
with yellow ribbon, while she would do well to trim a yellow bonnet 
with violet or blue, and a gi-een one with rose-red or white, and to 
follow the same general rule in arranging the colors of a dress. We 
are not to overlook the effect of contrast of tone as well as color. A 
black coat that is much worn, will appear well in summer in contrast 
with white pantaloons ; but if put on over new black pants, it will 
appear older, rustier, and more threadbare than it really is. Stains 
upon garments are less apparent where there is considerable difference 
among the colors of the various articles of apparel, than where they 
are more uniform, the contrast among the colors rendering that be- 
tween the stain and the surrounding cloth less conspicuous. Colored 
articles of dress produce a deceptive effect in reference to the size of 
the wearer. The influence of dark or black colors is to make the per- 
son wearing them seem smaller, while white or light dresses causes the 
figure to appear larger than the real size. Large figures or patterns 
upon dresses and horizontal stripes make the person look short, while 
narrow vertical stripes on a dress cause the wearer to seem taller. 

182. Inflncnce of Colors npoa the Complexion. — Any colored objects, 
as bonnet trimmings or draperies, in the vicinity of the counteiyjnce, 
change its color ; but clearly to trace that change we must know what 
the cast of complexion is. This varies infinitely, but we recognize 
two general sorts, light and dark, or Monde and Irunette. In the 
blondes or fair-complexi(?ued the color of the hair is a mixture of red, 
yellow, and brown, resulting in a pale orange brown. The skin is 
lighter, containing little orange, but with variable tinges of light red. 
The blue eye of the blonde is complementary to the orange of the 
hair. In brunettes the hair is black, and the skin dark, or of an 
orange tint. The red of the brunette is deeper or less rosy than that 
of the blonde. Now the same colors affect these two styles of com- 
plexion very differently. A green setting in bonnet or dress throws 


its complement of red upon the face. If the complexion be pale and 
deficient in ruddy freshness, or admits of having its rose-tint a little 
heightened, the green will improve it, though it should be delicate in 
order to preserve harmony of tone. But green changes the orange 
hue of the brunette into a disagreeable brick-red. If any green at all 
be used, in such case it should be dark. For the orange complexion 
of brunette the best color is yeUow. Its complementary, violet, neu- 
tralizes the yellow of the orange and leaves the red, thus increasing 
the freshness of the complexion. If the sMn be more yellow than 
orange, the complementary violet falling upon it changes it to a duU 
paUid white. Blue imparts its complementary orange, which im- 
proves the yellow hair of the blondes, and enriches white complexions 
■ and light flesh tints. Blue is therefore the standard color for a 
blonde, as yeUow is for a brunette. But blue injures the brunette by 
deepening the orange, which was before too deep. Violet yellows the 
skin, and is inadmissible except where its tone is so deep as to whiten 
the complexion by contrast. Eose-red, by throwing green upon the 
complexion, impairs its freshness. Eed is objectionable, unless it be 
sufiiciently dark to whiten the face by contrast of tone. Orange 
makes light complexions blue, yellow ones green, and whitens the 
brunette. White, if without lustre, has a pleasant efiect with light 
complexions ; but dark or bad complexions are made worse by its 
strong contrast. Fluted laces are not liable to this objection, for they 
reflect the hght in such a way as to produce the same effect as gray. 
Black adjacent to the countenance makes it lighter. 

183. Arrangement of Flowers in a Bouquet. — In grouping flowers, com- 
plementary colors as far as possible should be placed side by side, blue 
with orange, yellow with violet-red, and rose with the green leaves. 
On the contrary we should avoid combining pink with scarlet or 
crimson ; orange with orange-yeUow ; yellow with greenish-yeUow ; 
blue with violet or violet-blue ; red with orange, or pink with violet. 
If these are to be inserted in the same nosegay, white should be inter- 
posed between them, as it prevents colors from acting injuriously upon 
each other while it heightens their tone. 

184. Best colors for Paper Hangings. — ^Dark paper for the waUs is bad, 
because it absorbs too much light, and the room is not sufficiently 
luminous : this is especially true of rooms with a northern aspect 
where the sun never enters, for such apartments paper of the lightest 
tints should be used. "We have seen that the complementaries of red 
and violet are bad for the complexion (181), red and violet are there- 
fore objectionable as wall colors. Orange and orange yeUow are 


fatiguing to the eye. Among the simple colors light blue, light green 
(314), and yellow, seem fittest for hangings. Yellow is lively, and ac- 
cords well with dark furniture and brunette complexions, but it hardly 
appears well with gilding. Light green is favorable to pale skins, 
deficient in rose, and suits with mahogany furniture. Light blue goes 
well with mahogany, is excellent with gilding, and improves blonde 
complexions. White and light gray, with velvet patterns the same 
color as the ground, are well adapted to a wall to be decorated with 
pictm-es. In selecting a 'border we should seek for contrast, so that 
it may appear, as it were, detached from the hangings with which it 
is associated. If there is a double border, an interior one of flowers 
and an exterior one, the last must be deep in color and much smaller. 
Yellow hangings shoiild be bordered with violet and blue mixed with 
white. Green will take any hue of red as a border. White hangings 
should have orange and yellow. Gray uniform hangings admit of 
borders of all colors, but no strong contrasts of tone ; gilt borders do 
well with them. If the gray be colored, the border should be com- 
plementary. The neutral tints of paper, drabs, stones, &c., are par- 
ticularly appropi'iate for picture-galleries, — they produce good effects 
in other rooms with weU chosen borders and mouldings. 

185. Pictures, Frames, and Gilding. — ^As the picture itself is the valu- 
able object upon which we wish to fix attention, it is not in good taste 
to divert or distract it by gaudy and conspicuous surroundings and 
ornaments ; hence simple framings, just enough to isolate or separate 
the picture, are preferable. Gilt frames will do with large oil-pictures, 
particularly if there is no gilding represented in the picture. Gilt 
frames also answer well for black engravings and lithographs, but a 
little margin of white should be left around the subject. Black 
frames, by their strong contrast of tone, tend to lighten the aspect of 
the picture, and often spoil a good engraving by taking the vigor from 
its dark colors. Gray frames are good, especially if the picture have 
a leading color, and the gray be slightly tinged with its complementary. 
As a rule, neither the frame nor the border within it should ever be 
suffered by their brightness, color, or ornaments, to injure the colors, 
shadows, or lights of the picture. The best ground for gilt ornaments 
is blue, because its complementary intensifies the color of the orna- 
ments ; hence shrewd shopkeepers who sell gilt articles line their show- 
cases with blue. A bright green ground reddens and improves gilt 
objects. Eed and orange pervert the gilt tint, and black lightens and 
weakens it (144). 

186. Assortment of Colors for Fnrnitnre. — In determining the colors 


to be used in furnishing a room, the amount of light is an important 
consideration ; dark colors, as dark blue, crimson, &c., require much 
light to be seen distinctly. Eed curtains redden the transmitted light 
of day, and impart this color to the countenances it falls upon. But 
by artificial or reflected light, red curtains and fm-niture dispose the 
eye to see green in the countenances of people in the room, while 
green curtains make the countenances rosy. Chairs and sofas, when 
complementary to the paper upon the wall, are most favorable to dis- 
tinct vision ; but for collective effect, when we desire to present the room 
as a unit, bold and complementary contrasts are iuadmissible, as they 
fix the attention too much upon distinct and separate objects. It is 
better, therefore, in arranging for chairs and hangings to seek contrast 
of scales, or hues and harmonies of analogy. In trimming chairs and 
sofas, vivid reds should never be used with mahogany, for they are so 
bright that the mahogany loses its beauty, and looks no better than 
oak or black walnut. Crimson velvet is often used with mahogany 
because of its durability ; but the colors are so nearly allied, that a 
strip of green or black galloon should be used as a border to the stuff, 
or a narrow cord of golden yellow with gilt nails. Green or green 
grays are best suited to trim mahogany and red-colored woods. In 
using differently colored woods we can assort the colors of their trim- 
mings according to the rule previously laid down. The carpet should 
be selected with reference to the other furniture of the room. K 
mahogany is used, the carpet should not have a predominance of red, 
scarlet, or orange in it. If the furniture exhibit various and vivid 
colors, the pattern of the carpet should be simple and sober, as green 
and black for example, whUe if the furniture is plain the carpet may 
be gay. 

1. The Chemistet of Illtjmination. 

187. Natural and Artificial Light. — As respects its sources, light is o ' 
two kinds, natural light, or that which comes from the sun, moon 
and stars ; and artificial light, or that which man obtains at will by 
various means. Artificial light may be procured by electricity, gal- 
vanism, and phosphorescence ; but the ordinary method is by tliat 
kind of chemical action which is termed comdustion, the nature of 
which has been explained when speaking of heat. 

188. Light emitted by ignited Bodies. — AU solid substances shine 
when sufficiently heated. The temperature at which they become 



luminous, according to Dr, Deapee, "wlio has lately investigated the 
subject, is 977° F. He enclosed a number of different substances 
with a mass of platinum in a gun barrel ; upon heating and looking 
down the tube, he saw that they all commenced to shine at the same 
moment, and this, even though, as in the case of lead, the melted con- 
dition had been assumed. The color of light emitted from ignited 
substances was found to depend upon the degree to which they were 
heated. Dr. Draper showed that as the temperature rises, the 
colored rays appear in the order of their refrangibility, first red, then 
orange, yellow, green, blue, indigo and violet, are emitted in succes- 
sion. At 2130° all these colors are produced, and from their commix- 
ture the substance appears white-hot. The same Investigator also 
found, that as the temperature of an ignited solid rises, the intensity 
of the light increases very rapidly ; platinum at 2600° emitting almost 
forty times as much light as at 1900°. 

189. All onr illnmination comes from bnrning Gas — The foregoing ex- 
periments were made upon solid substances, but their results do not 
hold true for gases. These require to be heated to a much higher 
temperature before beginning to shine ; and when they do become 
luminous they emit but a feeble light. If we hold a piece of fine iron 
wire in the hot air which streams up above a lamp flame it wUl 
quickly become red, showing that a degree of heat which makes the 
metal shine does not make the air luminous. And yet all ordinary 
illumination comes from the combustion of gases. "We use those ma- 
terials for lighting, which in burning produce flame ; and flame is 
burning gas. All substances which can be used for light must be 
capable of conversion into the gaseous state. The process is essentially 
the same, whether we burn the illuminating gas which is brought to 
our dwellings in underground pipes, or the liquid oil, or solid sperma- 
ceti. In the first instance the gas is manufactured on a large scale 
from solid bituminous coal or resin ; in the latter cases the liquid oil 
and solid tallow or wax are converted into gas at the time of hurning. 
In all cases the light proceeds from a rising stream of gaseous matter 
which is lighter than the air, and therefore tends to ascend. 

190. What takes place in the Lnminons Flame. — The materials used 
for illumination contain hydrogen and carbon, and the gas they yield 
consists of these elements more or less pure. Hydrogen, as we have 
before stated, is the lightest and most ethereal of all substances (76). 
Tlie gas which gives rise to flame in illumination is therefore com- 
pound — a hydro-carbon. In burning, the oxygen of the air combines 
with these two elements, but it is not attracted to them equally. It 



Fi&. 46. 

Fig. 47. 

seizes upon the hydrogen first, burning it with an intense heat, and 
the production of water. As the hydrogen combines with oxygen, it 
abandons the carbon, which is thus set free 
in a pure state. F ow pure carbon is always 
a solid. As the hydrogen leaves it, therefore, 
it is set free in the form of exceedingly mi- 
nute solid particles in the midst of the heated 
space, — those heated to redness, yellowness, 
or whiteness, become luminous, and are the 
real sources of the light. The carbon par- 
ticles remain suspended in the flame but for an instant ; they are 
themselves quickly burned and converted into carbonic acid.* 

191. How these facts may be shown. — If we hold a piece of clean 
cold glass a short distance above a candle flame (Fig. 46), a fine dew 
will be seen deposited upon it, which is the water generated within 
the flame. If a piece of white 
earthen be lowered over the 
flame the combustion is in- 
terrupted, and the uncon- 
sumed particles of carbon are 
deposited upon the white 
surface, thus proving that 
they exist free in the flame. 
K an inverted tumbler be 
held above a flame, so that 
the rising current may enter 
it (Fig. 47), and then it be 
closed with a card, set down, and a little clear lime-water poured into 
it and shaken, it will become milky from the combination of the car- 
bonic acid with the lime, which shows that the former substance was 
generated within the flame. 

192. Admirable simpUcity of the Laws of lUnmination.— There is a 
wonderful simplicity and beauty in this chemistry of iUumination. 
The same active prmciple of the air which animates the living body 
and nourishes the fires which warm us, is also the awakener of light. 
All artificial illumination that we employ is due to the chemical energy 
of oxygen gas. The hydro-carbon compounds, upon which oxygen 
acts, are not only universal as life itself, being produced in all kinds 

* See the author's Atlas of Chemistry and Chemical Chart of Colored Diagrams, 
iUustrating combustion and illmnination. 


of plants and animals, but the very crust of the glohe is stored with 
endless accumulations of them. The hydrogen combines with and 
condenses a much larger amount of oxygen than any other element, 
and consequently produces a great heat. But the burning of these 
pure gases, although the heat is so high, hardly creates a perceptible 
light. To get illumination, solid matter is required. Accordingly the 
lightest and most subtle of aU gases, hydrogen, is associated with car- 
bon, the most refractory of aU solids, which remains fixed without 
melting or vaporizing at the intensest heat whicli art can produce. 
These carbon atoms are set free, and shining brilliantly for an instant 
pass to the verge of the flame, and there unite with atmospheric 
oxygen, forming carbonic acid gas. The two products of combustion — 
vapor of water and carbonic acid — are both entirely transparent and 
invisible, so that although constantly formed within and around the 
flame, they do not eclipse or obscure it, but let the light pass freely 
in all directions. If oxygen were equally attracted to hydrogen and 
carbon, so as to burn them both at once, no solid particles would be 
liberated in the flame, and consequently there could be no light. It 
is the successive combustion which takes place, — first the hydrogen 
burning and then the carbon, which gives rise to the luminous eflfect. 

193. Threefold form of Ulnminatiiig Substances. — The modes of burn- 
ing illuminating materials are various, depending upon their forms and 
properties. If capable of being used in a solid condition, they are 
moulded into a cylindrical or rod-like shape, and are called candles. 
If liquid, they are consumed from suitable vessels known as lamps; 
and if gases, they are simply jetted from minute orifices, by pressure 
upon the gaseous fountains. There are several things with respect to 
each of those methods of illumination which it is important to under- 

2. Illtjminatioit by means of Solids. 

194. Adaptation of Tallow for Candles. — Tliose fatty and waxy bodies, 
which are sufficiently hai'd and solid to be handled, are worked into 
candles. They are made from tallow, stearine, spermaceti, and wax. 
There has been no way devised for burning those softer, fatty and 
greasy bodies which lie between the liquid oils and these firmer sub- 
stances. Tallow derived from beeves or sheep is most universally 
employed for candles. If they are mixed there should not be too 
great a proportion of mutton tallow or suet, as this contains a peculiar 
principle called Mixin^ Avhich causes ii sometimes to give a disagree- 
able smell, especially in hot weather. When of the best quality tallow 


is white, firm and brittle. Alum is often put witli it to harden it. 
The bad quality of tallow candles is chiefiy owing to their adulteration 
with hog's fat and cheap soft grease, which makes them smell, gutter 
and smoke. Good tallow candles will resist decomposition for two 
years, and are better after being preserved six or eight months. They 
should be kept from the atmosphere, and may be well preserved by 
being covered with bran. The place for their preservation should be 
cool and dry, as dampness mildews and damages them. Light turns 
them yellow. 

195. Candles made from Stearic Acid. — The fats and oils are believed 
to consist of acids combined with a base ; at all events they are capa- 
ble of being decomposed and separated into those substances. The 
common base which exists in all fats and oils is, when set free, a sweet 
liquid called glycerin. The substances combined with it are stearic 
acid, margaric acid, and oleic acid. Stearic acid, combined with 
glycerin, forms stearin. Margaric acid, with glycerin, yields mar- 
garin ; and oleic acid, with glycerin, produces olein. Oleic acid, or 
olein, is the more liquid portion of oleaginous bodies ; it predominates 
in the fluid oils. Stearic acid, on the contrary, abounds in the hard 
fats and tallows ; it is their chief solidifying element. Margaric acid 
is less solid, being intermediate between stearic and oleic acids. The 
intermixture of these, in various proportions, gives rise to all the 
various grades of softness and solidity which the endless oU and fat 
tribe exhibit. Tallow contains seventy to seventy-five per cent, of 
stearic acid, and olive oil but twenty-five. Candles were at first made 
from stearin, and were much superior to tallow ; but they are now 
manufactured from stearic acid, which is more infusible. This sub- 
stance does not feel greasy to the touch, and is firm, dry, and brittle. 
It makes hard and briUiant candles, which are considered nearly equal 
to wax. 

196. Spermaceti and Wax. — Spermaceti is a kind of stearine existing 
in the oil taken from cavities in the skulls of certain species of whales. 
It is manufactured into candles, which are of a beautiful silvery white 
aspect, translucent like alabaster, and having a high lustre. The wax 
of which bees construct their honeycomb is also used for candles. It 
is purified and bleached to a pure white. It burns with a clear and 
beautiful light, and is the most expensive material employed for illu- 
mination. Owing to its high price it is often adulterated, "White 
lead, oxide of zinc, chalk, plaster, and other earthy bodies may be 
detected by boiling the wax in water, when these substances will 
separate and faU to the bottom. If starch or flour has been used, they 



Fig. 48. 

may be detected by boiling and adding a solution of iodine, •wMcli 
will yield a beautiful blue color, the test for starcb. Yellow bees'-wax 
is often adulterated with resin, pea and bean meal, and many other 
substances. The former may be detected by the smell, and the latter 
by the iodine solution. 

197. Structare of Candles— Office of the Wick. — The common burning 
candle affords a beautiful illustration of the general principles of illu- 
mination. If we should attempt to burn solid taUow or wax in the 
lamp to produce light, it would be found very difficult to set it on fire, 
as it would melt away long before it could ignite. But if at length 
made to burn, a much larger amount of the combustible would be on 
fire than the air would perfectly consume ; there would therefore be 
a thick smoky flame instead of a clear white light. Some contrivance 

is hence needed to avoid this result and regulate the com- 
bustion, and this is secured by placing cotton fibres within 
the combustible, which form the wicTc. These fibres are 
placed parallel in the axis or centre of the candle. "When 
the wick which protrudes at one end is set fire to, it ra- 
diates heat downwards, so as to melt the material of the 
candle, and form a hollow cup filled with the liquid com- 
bustible around the wick-fibres (Fig. 48). The flame is 
fed from this cup or cistern by the wick, which draws or 
sucks up the oily liquid exactly as a sponge or towel 
draws up water, by what is called the force of capillary 

attraction, or the attraction of small tubes for liquids. 

from^the"dstern ^^ this case the spaces between the fibres act as tubes, 
of oil below. ^^^ attract upward the liquid fat or wax. 

198. The hnraing Caadle a miniature Gas-Factory. — "We thus see that 
the caidle is a kind of lamp which constantly melts its own combus- 
tible. From the reservoir the wick draws up the liquid material to 
the centre of the flame. Here, in the midst of a high heat, and cut 

off from the air, it undergoes another change 
exactly as if it were enclosed and heated in 
the gasmaker's retort, — it is converted into 
gas. The candle-flame is not a solid cone of 
fire. If we lower a piece of wire-gauze or 
broken wiadow-glass over the flame (Fig. 49), 
we shall see that the interior is dark, and that 
what we regard as the flame is really but a 
thin, hollow, luminous shell of fire surrounding 
This space is filled with the hydro-carbon gas 

Fig. 49. 

The candle-flame hollow. 

the dark inner space. 


manufactured from the liquid tallow, stearine, spermaceti, or wax, 
drawn up by the wick. This may be directly shown. If one end of a 
glass tube, having a bore ^ of an inch, be introduced into a candle-flame, 
as seen in Fig. 50, the gas will be conveyed away r a 50 

through it, and may be lit at the other end, thus 
exhibiting a miniature gas manufactory, pipe and 
jet. "When a candle is blown out, gaseous pro- 
ducts of distilled and burnt tallow continue to 
rise, emitting a disgusting odor, and the candle 
may be re-lit by applying a light to the smoky 
stream of combustible gas which will convey 
the flame back to the wick. It is the hydro- 
carbon gas that is really burnt and produces the 
light, the hydrogen and carbon being successively 
consumed, as we have seen, at the surface, or The interior of the candle- 
where the air comes in contact with the gas. ^^^ ® ^^ ^^' 

199. Interfereace of the Wick with Light. — As the candle consumes 
downward, the wick of course rises into the flame. In a short time 
it becomes so much lengthened as to interrupt the combustion and 
interfere with the light. Particles of unconsumed carbon are gradu- 
ally deposited upon the wick, forming a large spongy snuff which 
nearly extinguishes the light. Peclet found that if the intensity of 
the light from a freshly snuffed candle be represented at 100, if left 
without being snuffed, its brightness is reduced in 4 minutes to 92, in 
10 minutes to 41, in 20 minutes to 32, and in 40 minutes to 14, al- 
though the consumption of the candle remained the same. Rumfoed 
found that the brilliancy of an unsnuffed candle was reduced f in 29 
minutes. To prevent this annoyance and the necessity of frequent 
snuffing, wicks are sometimes so plaited and twisted, or are so slender 
that they bend over to the side of the flame, and coming in contact 
with the air are consumed (Fig. 48). This however is only practicable 
with the more infusible candles, stearine, wax, and spermaceti. Tallow 
melts so easily, that if the wick were bent over, the candle would melt 
down on that side and burn badly. 

200. Influence of the melting point. — Tallow melts at 100°, spermaceti 
at 112°, stearine at 120°, stearic acid at 167°, and bleached wax at 
155°. Candles made from those materials which are most infusible of 
course melt slowest ; the liquid which is formed in the cup being smaller 
in quantity may be drawn upward to the flame with a smaller wick. 
Hence the wicks of wax and spermaceti candles are smaller than those 
used for taUow. A slender wick in a tallow candle would melt the 


combustible faster than it could consume it, the liquid would overfill 
and overflow the cup, which takes place in what is called the guttering 
of candles. For this reason candles of softer materials require larger 


201. Argand's great ImproTemcnt, — Lamps are vessels of various 
forms and appearances for burning light- producing substances in the 
liquid condition. They generally have wicks to feed the flame, which 
may be either solid round masses of fibre like those of the candle, or 
fibres arranged flatwise so as to produce a long thin flame, or they 
may be circular. Dr. Feanklust showed that two small wicks placed 
in two candles and burnt side by side, will give more light than if they 
were combined and placed in one candle, as there is a greater burning 
surface ; hence the advantage of spreading the wick-fibres out, and 
using them in some other form than condensed in a solid mass. Very 
large wicks of this kind convert the oil into gas faster than the air can 
completely burn it, and the consequence is that the flame smokes. To 
remedy this evil, the most important improvement yet made in lamps 
was contrived in the year 1789 by Ami Aegand of Geneva, and since 
called after him the " Argand Burner." He made the wick hollow, 
so as to burn in a ring or circle, and thus admitted a current of air to 
the inside of the flame, by which the central core of dark nnburnt 
gases is avoided, and a double burning surface secured. By means of 
sheet-iron chimneys set above the flame (which were soon replaced by 
those of glass), a strong upward draught of air was secured, which 
heightened the combustion and greatly intensified the light. The 
wick was raised and depressed either by means of cogwork {racTc and 
pinion) or by a screw ; the supply of oil is thus regulated to that of 
the air, and smoking prevented. An important advantage gained by 
the Argand burner is the great steadiness of the light caused by the 
chimney. "When a draught of air strikes an unprotected flame, its 
force and cooling influence check the combustion,* and produce flicker- 
ing and smoke. In Argand burners, on the contrary, the supply of 
air is self-regulated, and the cylinder prevents any interruption of the 
flame by outside currents, 

202, Improvement upon the Argand Burner, — The cylinder that Ae- 
GAND employed was straight, or had vertical sides. This allowed a 
much larger amount of air to rise within it than could take part in 
the combustion, and this excess had the partial effect of cooling the 
flame. M. Lange, a Frenchman, improved the form of the chimney- 


tube, by contracting its size and constructing it with a shoulder at 
such a point (JFig. 51 i), that the rising air striking against it was de- 
flected inward and thrown directly upon the flame. This had a power- 
ful efiect in increasing the combustion and heightening the intensity 
of the light. Another improvement consisted in mounting a button 
just above the circular opening within the burner, so that the current 
of air that comes up from within, will be deflected outwards, as shown 
in fig. 54 a, and thus strike directly upon the inner surface of the 
flame. The main point to be considered in the structure ^^^ ^^^ 
and management of lamps upon the Argand principle, or 
with chimneys, is the relation between the current of air 
and the flow of oil. This is controlled by the movable 
wick, the movable button, and the width and height of 
the chimney. As chimneys of glass only can be used, ^---J I _g 
they are apt to be made large to lessen the liability to <^^ 
fracture, though the danger is generally overrated. As i,™ 

a consequence more air is conducted to the flame than is 
demanded for vivid combustion, while the excess, by rapidly convey- 
ing away the heat, lowers the temperature of the flame, and thus 
diminishes its luminous intensity. Dashing a surplus of air against 
the flame is also unfavorable to that successive combustion which is 
essential to illumination (192). 

203. Points to be secured iu the structure of Lamps. — ^Lamps are made 
in a great variety of ways suited to burn different kinds of oily matter, 
and adapted to avoid, as far as possible, certain difficulties which are 
incident to this mode of lighting. The distance from the burning 
part of the wick to the surface of the reservoir from which the oil is 
derived should remain unchanged, so that an equal quantity of oil 
may be drawn up at all times, and the reservoir should be so shaped 
and placed that its shadow will occasion the least inconvenience. If 
the wick is supplied from a reservoir below, it is obvious that just in 
proportion as that is exhausted, the distance from its surface to the 
flame is increased ; the wick-fibres elevate less oil, and the light grows 
faint and dim. To remedy this, the reservoir in some cases is made 
to have a large surface of oil that will fall but little distance, although 
a considerable amount is withdi-awn. To avoid the objectionable 
shade thrown by such a large cistern close to the wick, the astral 
lamp had its reservoir constructed in the form of a narrow circular 
vessel or ring, which threw but a small shadow. The sinumbra lamps 
had this ring so shaped and mounted as to produce still less shade. 
Sometimes there is a fountain of oil placed on one side higher than 


the wick, "witli a self-acting arrangemeiit by which the reservoir is fed 
from it, and its height constantly maintained at the same point. The 
shadow cast, in this case, upon one side, is objectionable, and limits its 
use to that of a study lamp (Fig. 67). In the Oaecel lamp, or mechani- 
cal lamp, clockwork is applied to pump up the oil through tubes in a 
constant stream to the wick, thus keeping it thoroughly soaked, while 
the excess of the oil drops back into the cistern, which is situated so 
far below as to cast no shade. It is moved by a spring, and wound 
up like a clock. It runs sis or eight hours, maintaining a constant and 
equal flow of oil, and a bright and steady flame. These lamps are ex- 
cellent, but expensive, costing from fifteen to seventy-five doUars, and 
requiring mach care. 

204, Hot-Oi! Lamps. — One great obstacle to the use of lamps lies ia 
the viscidity, or thickness and consequent sluggish supply of the oil to 
the wick ; this becomes a very serious difficulty with common lamps 
during the winter. Dr. Uee made some experiments to ascertain the 
relative viscidity or fluidity of different liquids, and of the same liquids 
at different temperatures. He introduced 2,000 water-grain measures 
of the liquid to be tested in a cup, and then drew it off with a glass 
syphon of \ inch bore, having the inner leg 3, and the outer one 3j 
inches long. If the weight or specific gravity of two liquids, and 
their consequent pressure upon the syphon were the same, their dif- 
ference of viscidity would be determined by the different time they 
would require to flow off through the tube. He found that 2,000 
grain-measures of water at 60° ran off through the syphon in 73 sec- 
onds ; but when heated to 180°, they ran off in 61 seconds. OU of 
turpentine and sperm oil have very nearly the same specific gravity ; 
yet 2,000 grain-measures of oil of turpentine ran off in 95 seconds, 
while that quantity of sperm oil took 2,700 seconds, being in the ratio 
of 1 to 28| ; so that the fluidity of od of turpentine is 28^ times greater 
than that of sperm oil. Sperm oil, when heated to 265°, ran off in 
300 seconds, or one-ninth of the time it took at a temperature of 64°. 
Hence lamps have been advantageously constructed to heat the oU 
before burning, either by means of a copper tube which receives heat 
from the flame, and conducts it downward to the reservoir, or stiU 
better by means of a cistern placed above the flame. Paekee's Eng- 
lish Economic Lamp has its oil heated in this latter way, and is said 
to perform admirably. 

205. Compositlou of Oils. — The oils in general use in these lamps are 
those derived from fish, chiefly whales, and known as sperm-oU and 
train-oil. Lard-oil is also much employed. It is the more oily portion 


of hogs'-fat separated by artificial means. The chemical composition 
of these oils is quite similar to that of the harder substances which 
are wrought into candles. Sperm-oil consists in 100 parts — of carbon 
78, hydrogen 12, and oxygen 10 ; mutton tallow, of carbon 'J'S'IO, 
hydrogen 11*70, and oxygen 2'30 ; wax, of carbon 80'4, hydrogen 
11'3, and oxygen 8'3. 

206, Properties of Spirits of Turpentine or Campliene. — In addition to 
these substances a new class of compounds, the basis of which is de- 
rived from the turpentine of the pine tree, have latterly come into use. 
By distillation of the turpentine pitch, it is separated into a thin trans- 
parent liquid, spirits of turpentine or oil of turpentine, and a hard 
brittle residue known as common resin. The crude spirits of turpen- 
tine when rectified, that is, separated as completely as possible from 
resinous matter by repeated distillation, is burnt in lamps under the 
name of camphene. It differs from the substances just mentioned in 
its extreme liquidity (being, as we have seen, 28^ times more fluid 
than sperm oil) ; in its powerful pungent odor, and in chemical compo- 
sition, as it contains no oxygen, and consists of 88'46 parts in a hun- 
dred of carbon to 11*54 of hydrogen, and is therefore called Tiydro- 
carion. Oil of turpentine is also much more highly inflammable, and 
is volatile and explosive. 

207. Conditions required for its Combustion. — Oil of turpentine is a 
superior illuminating substance, but it contains so large a proportion 
of carbon, that if burned in the ordinary way, it smokes excessively. 
Lamps designed to burn it require to be so constructed as to supply to 
the flame a large and powerful draught of air, to effect the complete 
combustion of its elements. Camphene burns with a flame very much 
whiter and brighter than any of the substances we have yet noticed, 
and which displays the natural colors of objects, as flowers or pictures 
in their true tints, much more perfectly than the light of candles and 
oil lamps. Although more luminous, the camphene flame is smaller 
than the oil flame. This is explained by the fact that camphene con- 
sists entirely of carbon and hydrogen, whUe the fat oils contain 10 
per cent, of oxygen. This oxygen, already existing in the oil, neu- 
tralizes a portion of its carbon and hydrogen, so that there is really 
but 85 or 86 per cent, of hydro-carbon to sustain the combustion ; and 
not only this, but the other 15 per cent, of incombustible matter acts 
to hinder the combustion. On the other hand, the oil of turpentine 
consists of pure combustible matter, burns entirely, and contains 
nothing to retard the activity of the burning process. A hundred 
parts of fat-oil consume only 287 parts of atmospheric oxygen, while 


100 parts of camphene consume 328 of oxygen. From its extreme 
fluidity, the oil of turpentine is also supplied copiously and constantly 
to the flame by the simple capillary or sucking action of the wick. 

208. Why Camphene soon spoils. — Camphene, if exposed to the air, 
cannot be preserved pure. It belongs to a , class of bodies known as 
essential oils, which by combination with oxygen are changed into 
substances of a resinous nature. Under the influence of oxygen, oU 
of turpentine undergoes this change, and becomes deteriorated by 
solid resinous impurities. When employed for illumination, therefore, 
it should be procured in small quantities fresh from the manufacturer. 

209. Nature and properties of Bnrning Fluids. — There is another 
method by which oil of turpentine may be employed for illumination, 
which is generally much preferred, as it avoids the liability and trou- 
ble of smoke. It consists in mixing it with alcohol, so as to form 
what is known as lurning fluid. Alcohol burned alone produces only 
a feeble bluish-white light, as it is deficient in the necessary quantity 
of carbon. It has the opposite defect of oU of turpentine, as that has 
too much carbon ; the alcohol has an excess of hydrogen. By mixing 
them, a compound is formed which supplies the deficiencies of both, 
yields a good light, and may be burned in lamps of the simplest con- 
struction. These mixtures are commonly burned with wicks, but 
there is a lamp so made that the liquid is vaporized by the heat of the 
burner, and escaping in jets through minute orifices, is burned without 
a wick, like common illuminating gas. Owing to the large propor- 
tion of expensive alcohol which must be used in making it, and which 
gives but vei-y little light, burning fluid is a very costly source of illu- 
mination (230). 

210. In what way Burning Fluids are Explosive. — Both alcohol and oil 
of turpentine are very volatile ; that is, when exposed to the air or 
not confined, they rapidly evaporate or rise into the gaseous state. In 
a lamp reservoir containing burning fluid, as it is gradually consumed, 
vapor rises from its surface and flUs the upper space. In all vessels, 
whether lamps, cans, or jugs, if but partially fllled with fluid, the re- 
maining space is occupied with its vapor, which may or may not be 
mixed with air. Or when exposed to the air in open vessels, vapor 
rises and charges the atmosphere immediately above. Now the liquid 
oil of turpentine and alcohol are both inflnitely more inflammable than 
the fat oUs. These cannot be set fire to at common temperatures ; 
they must be heated very hot before they will catch fire. But the 
more volatile liquids, on the contrary, wiU take fire at any time 
when exposed, though cold, and burn with great violence. But the 


case is made much, -worse on account of the invisible vapor which they 
exhale. This mixes with the air, and at the approach of the slightest 
spark or flame, ignites explosively. "When pure hydrogen is mixed 
with the air and ignited, it explodes with a sharp report like a pistol ; 
the cause is the sudden combination of the hydrogen with the oxygen 
of the air. Now when vapor of turpentine or alcohol, or any volatile 
hydro-carbon is mingled with air and fired, an explosion takes place 
in the same way. 

211. Conditions under wMch Explosions Oficur. — The burning fluid 
itself^ although excessively inflammable, is not explosive. It does not 
go off like gunpowder when set on fire, nor with a sudden noise or 
report, such as its vapor produces. But it is always accompanied by 
the invisible treacherous gas which catches fire at a distance, and this 
ignites the fluid. Most accidents that occur with these compounds 
result from attempts to fill or replenish lamps while they are lit, or 
where there is a light near by. The vapor of the opened lamp, jug or 
can, is fired ; it explodes with more or less violence and concussion, 
setting the liquid on fire, and perhaps scattering it upon the clothing 
of the person present, who is severely or fatally burned, while the 
house is very liable to be set on fire. If the lamp have a screw cap 
and be perfectly tight, heat may be conducted downwards from the 
flame through the metal, and increase the evaporation. There being 
no vent but through the interstices of the wick-threads, if these are 
close, the pressure wiU increase and force out the fluid and vapor so 
as to burn irregularly, and sometimes occasion little explosions in the 
flame. If the wick is loose, and the lamp be agitated so as to dash 
the liquid against the hot screw-cap, vapor is suddenly formed, and 
being pressed out the flame streams up, often producing alarm. If the 
pressure become too great, and there be no vent, the lamp may ex- 
plode. Dr. Hats says, it is a uniform result of numerous trials con- 
nected with experiments on closed lamps, that no lamp is safe which 
has a closed cap, unless there are openings for the escape of vapor. 
It would be wise to substitute metallic lamps for those of glass, on 
account of the danger of fracture. "When these substances are em- 
ployed for light, they should not be committed to the charge of those 
ignorant of their properties ; and it is the only safe rule, when they 
are used in ordinary lamps, never to open any vessel containing them 
when there are lights burning near by. 

212. How Burning Fluids may be used with safety — ^IVewell's Lamps. — 
The advantage which these liquids have over oils and candles in re- 
spect of simplicity, cleanliness, and greater brilliancy of light, makes 



Fig. 52. 

it eminently desirable that some safe way be devised to consume them. 
This has been done by Mr. John Newell, by applying to them the 
principle of Davy's Safety Lamp. Hydro-carbon gases are often 
generated in coal mines, and when mixed with common air, are 
exploded by the lamp which the miners use. By surrounding these 
lamps with fine wire-gauze, they could be lit and carried into the dan- 
gerous mixtures without exploding them. The inside of the gauze 
would be filled with burning gas, but the fine wire texture has the 
efifect of cooling the flame, so that it cannot pass through and ignite 
the gases outside. Hence, by ingeniously mounting his lamps with 
this gauze, Mr. Newell prevents the possibility of explosion from 
camphene and burning fluids. The can also for containing the fluid 
has a sheet of the gauze inserted under the lid, and another fixed in 
the spout. These do not prevent pouring; but if vapor or fiuid 
escaping through them were lit, the flame could not enter the 

213. Eerosene Oil as an Illamiiiator. — This is a 
product of the distillation of bituminous coal, 
and has come lately into use as a source of 
light. It is rich in carbon, and requires to be 
burned in peculiar lamps adapted to its properties. 
It produces a bright and beautiful light, which 
we have used with much satisfaction. It does not 
vaporize, and is therefore not explosive. The 
proprietors make large claims on the score of its 
economy (230), and are entitled to credit for hav- 
ing prepared a variety of elegant lamps for burning 
it. Fig. 52 represents one of their style of parlor 
lamps. The cistern is narrow, and so far below 
the wick as to cast but little shadow. When not 
burning, the oil emits a kind of empyreumatic gas- 
odor, to which many object ; but the smell is net 
perceived during combustion. 

214. Liglit from Sylvic Oil. — This is a cheap oil 
from resin. It gives a vivid light, but it contains 
so much carbon that it is difficult to burn it with- 
out smoking ; this may, however, be done with 

ArgandLamp for Kero- Pi'^'P^^i' care in Van Bensohoten's lamp. 
Bene Oil. 


4. Illttmcstation by Gases. 

215, Conditions of the Gas Mannfacture. — The last source of illumi- 
nation to be noticed is gas^ which gives the cheapest and brightest of 
all the generally employed artificial lights. It has come into use en- 
tirely within the present century, and has been very widely adopted 
in cities. It was first employed in London in 1802, and its use has 
extended until 408,000 tons of coal have been consumed in a single 
year by the establishments of that city alone ; producing four thou- 
sand millions of cubic feet of gas, and yielding an amount of light 
equal to that which would be produced by eight thousand millions of 
tallow candles, of six to the pound. How wonderful, that sunbeams 
absorbed by vegetation in the primordial ages of the earth's history, 
and buried in its depths as vegetable fossils through immeasurable eras 
of time, until system upon system of slowly -formed rocks have been 
piled above, should come forth at last at the disenchanting beck of 
science, and turn the night of civilized man into day. 

216. Materials used for making it. — Gas is chiefly produced from the 
bituminous varieties of coal (87), those which are rich in the pitchy 
elements containing hydrogen. It is also made from tar, resin, oils, 
fats, and wood. 

21Y. Products of the distillation of Coal. — If coal is used, it is placed 
in tight cast-iron vessels called retorts, which are fixed in furnaces and 
heated to redness by an external fire. The high heat decomposes the 
enclosed coal, productag numerous gaseous and liquid compounds. 
The principal products of this destructive distillation are coTce, or the 
solid residue of the coal, a black oily liquid known as coal-tar ; water 
or steam, various compounds of ammonia, among others that with 
sulphuroiis acid, sulphuretted Tiydrogen, carbonic acid and carbonic 
oxide, light carburetted hydrogen, heavy carburetted hydrogen or 
defiant gas, and a small proportion of vapor of sulphur et of carbon. 
There are also variable traces of many other substances. 

218. Purification of the Gas. — This heterogeneous mixture is totally 
unfit for illuminating purposes until purified. The liquid and gaseous 
products, as they are set free, flow out from the retort through a tube 
into a receiver caUed the hydraulic main, in which the liquid products 
of the distillation — coal-tar and ammoniacal liquor — are to a great 
extent separated from the gaseous products. But being hot they still 
retain various matters in a vaporous state, which would be deposited 
and clog the pipes ; these are still farther separated by passing through 
the condenser, which consists of iron tubes surrounded by cold water. 


The gas is then passed through a mixture of lime and water (milk of 
lime), or tlirough layers of damp slacked lime, which absorb the car- 
bonic acid and sulphuretted hydrogen. It is then sometimes freely 
washed with water, which removes all its ammonia, when it passes 
into a large receiving vessel, the gasometer^ from whence it is dis- 
tributed in pipes to the places where it is to be consumed. 

219. Compositioii of Iliuminating Gas. — This is very variable, but it 
mainly consists of olefiant gas, light carburetted hydrogen, carbonic 
oxide, with free nitrogen and hydrogen, and sometimes other substan- 
ces in small amounts. It takes its value from the proportion of olefiant 
gas which it contains, as this is the chief light-producing compound. 
Olefiant gas consists of 86"21 per cent, carbon to 14-79 per cent, hy- 
drogen. Several other substances which burn with much light are 
liable to be associated with olefiant gas, as Butylene, Propylene, vapor 
of Benzole and Naphtha. Olefiant gas burns with a vrhite and re- 
markably luminous flame ; but it would hardly answer to burn it alone, 
as its proportion of carbon is so large, that if the combustion were at 
all imperfect, there would be liability to smoke. Light carburetted 
hydrogen is the same as the marsh gas, which is generated in the 
organic mud of stagnant pools, and rises upward in bubbles. It con- 
tains less carbon, and is richer in hydrogen ; its composition being 75 
per cent, of the former to 25 of the latter. It burns with a dim yel- 
low flame, giving but little light. Carbonic oxide and hydrogen both 
burn with a faint blue, hardly luminous flame. Mtrogen takes no 
part in the burning process, except to hinder it by diluting the gas, an 
eflfect which is also produced by both carbonic, oxide, and hydrogen. 
The gas that comes off from a charge of good coals consists, when the 
retort is first raised to a vivid cherry-red heat, of 18 per cent, of ole- 
fiant gas, 82-5 carburetted hydrogen, 3-2 carbonic oxide, and 1*3 of 
nitrogen. After five hours the gas that continued to escape gave 7 
per cent, of olefiant gas, 56 of carburetted hydrogen, 11 of carbonic 
oxide, 21*3 of hydrogen, and 4'7 of nitrogen. Towards the end of the 
operation, or after about ten hours, it contained 20 parts of carburetted 
hydrogen, 10 parts of carbonic oxide, 60 of hydrogen, and 10 of nitro- 
gen. The best gas therefore is that which is produced first. 

220. Gas derived from other sources. — Crude and refuse oil, which is 
unfit for burning, is sometimes converted into gas. It is made to 
trickle into a retort, containing fragments of coke or bricks heated to 
redness. The oil, as it falls upon these fragments, is instantly decom- 
posed and changed to gas. It contains no sulphur products, and needs 
no purification. It is very rich in olefiant gas, and has double the 



Fig. 53. 

illuminating power of the best coal gas, and treble that of ordinary 
coal gas. Eesin also, by being melted and treated in a similar way, 
yields a highly illuminating gas. But in point of economy, neither oil 
nor resin can compete with coal as a source of light. A pound of coal 
yields from three to four cubic feet of gas ; a pound of oil, 15 cubic 
feet ; of tar, 12 ; and of resin, 10. 

221, How Gas is measured. — Gas is sold by the cubic foot, or by the 
thousand cubic feet. From the underground pipes (mains) that run 
through the street, a pipe branches off leading to the dwelling to be 
illuminated. Before being distributed through the house the gas is 
made to pass through a self-acting instrument called a meter^ which 
both measures and records the quantity consumed in a dwelling. The 
meter consists of an outer stationary cylindrical case, enclosing an 
inner and smaller cylinder which revolves upon its axis. Both cylin- 
ders are closed at the ends, water-tight and gas-tight. The inner one 
is divided into four compartments with crooked partitions, and the 
gaspipe passes into its centre or axis, and, turning up at the end, de- 
livers to them its contents successively. The meter is kept about two- 
thirds filled with water, which the gas 
constantly displaces as the cylinder turns. 
The principle will be understood by the 
aid of the diagram (Fig. 53), which ex- 
hibits the meter as if seen endwise, with 
the ends of the drums removed. A A A A 
is the outer cylinder ; B B B B the four 
compartments of the inner one ; c is the 
gaspipe supplying one of the apartments. 
As it enters the partition E rises, and the 
water passes out at the slit Z>, into the 
space between the two cylinders. The in- 
ternal one revolves from left to right, the 
gas passing in the direction of the arrows, 

first displacing the water and filling the compartments, and then 
passing out into the space between the two drums, where it is con- 
veyed away by a tube not shown in the figure. The revolving drum 
is connected with clockwork, which shows by an index the number 
of revolutions made, and the capacity of the compartments being 
known, the quantity of gas which passes through is correctly deter- 
mined. The meter reports the amount of gas that actually passes 
through it ; but its indications are by no means to be taken as infalli- 
ble proofs of honesty on the part of the gas company. Their tempta- 

Meter for measuring the flow of 


tion is, to put on pressure and crowd more gas through than is neces- 
sary, or than can be burned with economy, for increased consumption 
of gas does not at all involve a corresponding increase of light (222). 
Nor do meters afford any indication whatever in reference to the 
quality of the gas ; the companies control this, and may do quite as 
they please, the customer being unprotected. "We do not intimate, 
however, that the gas-companies ever yield to the evil temptations 
with which they are beset. 

222. How Gas is 'biirned. — From the fountain of distribution — the 
gasometer — the gas flows away through the branching system of tubes 
under the influence of pressure. "When little openings are made in 
the pipes, this pressure drives out the gas in jets or streams, and it is 
these which produce the light when ignited. The orifices are from 
■^-gih to the -s^ih of an inch in diameter. Eecent experiments by the 
French tend to show that wider openings are more economical with 
the best kinds of gas. The openings are made in various ways. A 
circle of them round a large central orifice forms an Argand burner 
(201). Two holes drilled obliquely, so that the flames cross each other, 
produce what is called a swallow-tail jet. A slit gives a continuous 
sheet of flame, called a iat-wing jet. Other flgures are also produced, 
as the '■^fan-jet,'''' '■'■fish-tail jet^''"' &c. The quality of light depends much 
upon the mode of burning as well as the composition of the gas ; a 
good article may be spoiled by mismanagement. Its illuminating 
power is impan-ed when burned too rapidly to allow the separation 
and ignition of the carbon particles (190). The order of the combus- 
tion, upon which aU illumination depends, is destroyed, by excess of 
air, as when we move a lighted candle rapidly through the atmosphere, 
the hydrogen and carbon are both burned at once, and we get only a 
feeble blue flame. This occurs when gas issues with considerable ve- 
locity from a minute orifice, and by expansion gets intimately mixed 
with a large proportion of air. When the current of gas does not 
ignite at a considerable distance (several lines) from the aperture, 
and then burns with a faint blue flame, the gas-stream is too rapid, it 
is improperly mingled with the air and consumes wastefuUy, — that is, 
to the luyer. If chimneys are used, and the draught becomes too 
strong, for the same reason the light almost vanishes, yielding only a 
dull blue flame. On the other hand, too smaU a draught of air is 
equally injurious, not only from incomplete combustion which causes 
the flame to smoke, but also because the highest illuminating power 
of the flame is obtained only when the carbon atoms are heated to 
whiteness, which requires a considerable amount of air. We have 


before seen how rapidly light is evolved by the addition of small 
quantities of heat at high temperatures (188). 

223. Influence of the length of the Flame. — The dimensions of the gas- 
flame may be controlled with perfect facility by simply turning a stop- 
cock, although its extent depends upon the width of the orifice and 
the amount of pressure. It was found that if the light from a flame 
2 inches long were represented at 100, at 3 inches it became 109, at 
4 inches 131, at 5 inches 150, at 6 inches 160, with an equal consump- 
tion of gas in each case. 

224. How mach, Gas-bnrning contaminates the AiTi-^The active source 
of light in this kind of illumination, as has been stated, is defiant gas 
and other compounds abounding in carbon. But these could not be 
burned alone even if it were possible to procure them. A diluting 
material is therefore necessary to give the flame sufficient bulk, and 
separate the particles of carbon so far asunder as to prevent the risk 
of imperfect combustion and smoke. Now the three substances found 
in gas — light carburetted hydrogen, carbonic oxide, and free hydro- 
gen — are all equally well adapted for this purpose. So far as light is 
concerned, it is of little consequence which of these is associated with 
the oleflant gas. But in other respects this becomes a matter of im- 
portance. The two objections most commonly urged against the use 
of gas in our apartments are, firsts the heat which it communicates to 
the air ; and, second^ the contamination of it by carbonic acid. Now, in 
these particulars, the three diluting substances have very different in- 
fluences. One cubic foot of hght carburetted hydrogen consumes in 
its combustion two cubic feet of oxygen, and generates one cubic foot 
of carbonic acid, — a portion of the oxygen being consumed in the for- 
mation of water with hydrogen. This produces a suflQcient amount 
of heat, according to Dr. Feanxland, to raise 2,500 feet of air from 
60° to 80"8°, while a cubic foot of hydrogen burned under the same 
circumstances produces no carbonic acid, and yields heat capable of 
raising 2,500 cubic feet of air 60° to 66"4°. One cubic foot of carbonic 
oxide consumes in burning half a cubic foot of oxygen, and generates 
one cubic foot of carbonic acid. The light carburetted hydrogen, 
therefore, is the worst diluent and hydrogen the best, as it produces 
no carbonic acid, and excites least heat. We saw that at different 
stages of heating, the coals in the retort yielded at one time a gas, rich 
in illuminating constituents, and at another time a gas deficient in 
these, but rich in hydrogen (216). Advantage has been taken of this 
fact to mingle the products of the retorts at different stages of heat- 
ing, by which the olefiant gas is diluted with hydrogen, and a mixture 

124 PEODucnoNS op aeteficial light. 

produced of superior illuminating qualities and the least injurious 

225. Disadvantages of Gas-lighting.^ — The chief obstacle to the use of 
gas-lights in private houses is, that the burners are stationary, and 
cannot be placed in positions available for all purposes. Candles and 
lamps ai-e movable, but a gas-light, even where iiexible india-rubber 
tubes are used, is more or less a fixture. The burners being usually 
situated high for general illumination, and calculated for giving more 
light than is required for one or two persons, cannot be reduced to the 
limits of the strictest economy of consumption. Hence, although gas 
is the cheapest of all sources of illumination, this apparent necessity 
for consuming it in large quantities prevents the real saving that might 
otherwise be expected. "We have just spoken of the effects of burning 
gas upon the air, and shall notice it again, as also the prejudices against 
its use (275). 

226. Care of Gas-fixtures. — Air, when mixed with gas, exerts upon 
it a slow change, tending to produce fluid and soUd bituminous bodies 
by oxidation. Now if air gets access to the tubes and mingles with 
the gas, as it does constantly between the burner and the stop-cock, 
when the gas is not burning, the pipe becomes coated and obstructed, 
and hence requires periodical cleaning, which should be done with in- 
struments that ought to be furnished gratuitously by the gas com- 
panies. Gas of high value contains six per cent, of its volume in 
vapor, which can become fluid in the pipes when they are exposed to 
the temperature of freezing water. Hence depressions in the pipes 
soon collect fluids, unless they decline towards instead oi from the 
meter, and the flow of gas to the burner is irregular, producing fluc- 
tuation or what is called 'jumping' of the flame. When the burners 
are long out of use, as sometimes in summer, the pipes are liable to 
become deranged and clogged, and as gas acts on and solidifies all oily 
and lubricrating substances hitherto used, the keys of stop-cocks of1;en 
become fixed. — Hays. The ventilation of gas-burners will be de- 
scribed when treating of air (360). 

5. Measueement of Light. 

227. Can Light be Measured 1 — It is sometimes of importance to de- 
termine the cost of light produced in different ways and from different 
materials. There is no method known by which light can be directly 
measured ; that is, we have no mode of estimating the absolute quan- 
tity of light emitted by a flame, but we can ascertain how much more 



Fig. 54. 

or less light one flame produces than another, and thus arrive at useful 
comparative results. All flames are not equally bright, — of two flames 
of equal size, one may be much more brilliant and emit more light 
than the other. Wo do not judge of the intensities of diff"erent lights 
by direct comparison, but by the comparison of their shadows, on the 
principle that the greater the flluminating power of the hght the 
deeper is the shadow which it casts. 

228. How Light is Measured. — Before a piece of board, covered with 
unglazed white paper at a distance of two or three inches, let an iron 
rod be placed which has been previously blackened by holding it in 
the candle. Now if it is desired to cotnpare two lights, they are to 
be placed opposite the 
board at the same 
height, and each will 
cast a shadow upon 
the paper as illustra- 
ted in Fig. 54. The 
lights should be so sit- 
uated that the shad- 
ows will fall close to 
each other, and the 
stronger flame should 
be so far removed, or 
the weaker idvauopd I'l'otometer or contrivance for measuring the intensity of ligM. 

that both shadows will appear equally deep. To ascertain their 
luminous intensities we measure the difierence from their centres to 
the shadow : if these are equal, their illuminating powers are equal ; 
but if one casts an equal shadow at a greater distance than the other, 
its light must be more intense, or its illuminating power greater. The 
difference in the degrees of light is not proportional to the distances 
of the luminaries from their shadows, but to the squares of these dis- 
tances, in accordance with the law of radiation before explained (136). 
If one light at two feet, and another at six, give equal shadows, their 
difference is not as six to two, but as the square of 6, which is 36 to 
the square of 2, which is 4 ; that is, 36 to 4, or 9 to 1. The luminary 
at 6 feet gives nine times as much light as the one at 2 feet. 

229. We liave no unit for measuring Light. — This plan, modified in va- 
rious ways, affords a ready means of comparing the relative amount 
of light emitted by two flames. But we have not been able yet to 
reap the practical advantages which this success at first appears to 
promise. If we can measure light, why not establish the exact iUumi- 


nating values of the various lighting materials, so that we may know 
precisely how far a dollar will go in buying light when the substances 
are at given prices. Something has been done in this way, but we 
have no results that command implicit trust. The composition of the 
materials is variable, and the same materials in different trials give 
different results. "We are without an accepted unit to serve as a stand- 
ard for a scale of values. It has been proposed to make the sperma- 
ceti candle (6 to the lb.), burning 120 grains to. the hour, the unit of 
measure. If this were satisfactory, we could compare other lighting 
materials with it. A burner consuming a certain amount of gas per 
hour would equal a given number of candles, and any variation in its 
quality would be easily detected. "We should speak of it as 10 candle- 
gas, 15 candle-gas, and 20 candle-gas, according to its gi*ade, and so 
of the various illuminating substances. But these candles have been 
found to burn variably, and do not perfectly answer. Some unit wiU 
probably be fixed upon by which the comparative values of lighting 
materials may be determined and expressed. 

230. Photometric Bcsnlts of Ure and Kent.. — Dr. Fee gives the follow- 
ing as the cost of an equal amount of light per hour from several 
sources, according to his experiments. 


Carcel Lamp, -with Sperm Oil IJ 

Wax Candles 6 

Spermaceti Candles 5i 

Stearic Acid Candles 4i 

Moulded Tallow Candles 2^ 

E, N. Kent, of the U. S. Assay OflBce, experimented on various 
lighting materials with the following results : 

Retail price of Cost of an equal 

Matei-ials. Lamp osed. Oil per gallon, amount of light. 

Kerosene Oil Kerosene $1 00 $4 10 

Camphene Camphene 63 4 85 

Sylvic Oil Pvosin Oil 50 6 05 

Eape Seed Oil Mechanical 1 50 9 00 

Whale Oil Solar 1 00 12 00 

Lard Oil Solar 1 25 IT 00 

Sperm Oil Solar 2 25 26 00 

Burning Fluid Large Wick 8T 29 00 


231. Value of the sense of Vision. — The eye is perhaps the most im- 
portant organ of sense. By it the mind is put into the widest com- 
munication with the external world. Although it may be said that 
this organ only recognizes light and colors, yet through it we become 
acquainted with the forms, magnitudes, motions, distances, directions 
and positions of all objects, whether immediately around us, or re- 


motely distributed tlirougli tlie distant universe. In its adaptation to 
the agent whicli is designed to act upon it, the eye is a miracle of 
beauty and wise design. For this reason alone we might well afford 
to devote a little space to it ; but when we consider that it is an organ 
of exquisite delicacy, and greatly liable to abuse from the domestic 
mismanagement of Hght, as well as other causes, and remember how 
tedious and distressing are its disorders, and what a lamentable life- 
disaster is its loss, it becomes of the first importance to assist in diffus- 
ing any suggestions that may lead to its better care. Our previous 
study of light and colors will moreover aid us materially in forming 
correct ideas upon the subject. 

232. Sclerotic Coat and Cornea, and their uses. — ^When the eye is re- 
moved from its socket and dissected, it is found to consist of several 
coats. The outer one forms the wMfe of the eye ; it is a tough, re- 
sisting membrane, and serves both to sustain the delicate parts within, 
and also to give insertion to those outer muscles which roll the eye- 
ball. It is called the sclerotie coat^ or briefly tJie sclerotic. As light 
is to enter the eye, and as, from the nature of the organ, it could not 
be admitted through a hole, it became necessary to have a wuidow in 
the eye-ball. In the front part of the globe there is a circular open- 
ing in the sclerotic, which is closed by a thin and perfectly transparent 
membrane called the cornea, the front window of the structure. The 
cornea bulges out somewhat like a watch-glass ; that is, it is more 
convex than the general surface of the eye-ball, as may be felt through 
the closed lid. It covers that portion of the eye which is colored, and 
is attached round the edge of the colored part to the sclerotic coat, 
with which it is continuous. The cornea is very hard, tough and 
horn-like, the word being derived from the Latin cornu, which signi- 
fies horn. The general arrangement of the parts we are describing is 
shown in the accompanying view of the section of the eye (Fig. 55). 

233. The Iris and Pnpil, and their uses. — Behind the cornea 
there is a small space or chamber filled with a perfectly clear and col- 
orless liquid, which consists chiefly of pure water, and is called the 
aqueous humor. This chamber is divided by a thin partition known 
as the iris, in the centre of which there is a circular aperture called 
the pupil. The pupil is simply, therefore, a hole through the iris ; it 
is the round black spot which we see surrounded by a colored ring. 
That colored ring is the iris. It is black behind, and on the front 
or visible side, it is of different colors in different individuals. The 
color of the iris is observed to be, in some measure, connected with 
the color of the hair. The iris has the remarkable property of con- 




Ch Of Old 




tracting and dilating under the influence of light, by which the pupil 
is enlarged and diminished. If the light he strong, the iris contracts 
and reduces the size of the pupil, so as to esclude a portion of the 

light ; if the light be weak, the iris 
expands so that more light is ad- 
mitted. This moderates and equal- 
izes the illumination of the organ, 
the delicate sensibility of whicb 
might otherwise be injured. The 
play of this mechanism may easily 
^^^^ be seen by bringing a candle near to 
neni'e ~~^ the eye while gazing upon its im- 

Eelation and names of the several parts age in a looking-glass. These move- 

^^' ments are involuntary, the eye reg- 

ulating the quantity of light it will receive, independent of the choice 
of the mind. 

234. Crystalline Lens and Vitreous Hnmor. — Behind the little chamber, 
of which we have spoken, and bounding it on the back side, is a sub- 
stance in the form of a double convex lens, called the crystalline lens. 
It is situated immediately behind the pupil, very near it, is a little 
larger than that opening, and is very convex, its thickness being al- 
most equal to its diameter. It is supported by a ring of muscles called 
the ciliary process. The crystalline has about the consistence of hard 
jelly, and is purer and more transparent than the finest rock-crystal. 
It is this part which becomes diseased in cataract. The space behind 
the crystalline lens constitutes the main body of the eyeball, and 
is filled with a clear gelatinous fluid, very much resembling the white 
of es,g^ and called, from its apparent similarity to melted glass, the 
mtreous humor. 

235. The Choroid Coat, and how it is Colored. — There is a second coat, 
lining the interior of the sclerotic, which consists of minute vessels, 
arteries, and veins, closely internetted, and is called the choroid. It 
extends around to the cornea, and supports the ciliaiy process. The 
inside of the choroid is covered with a slimy matter of an intensely 
black color, called the figmentum nigrum (blaclc pigment). This 
gives to the interior of the eye a jet-black surface, which absorbs and 
stifles the light, so as effectually to prevent reflection. 

236. Optic Nerve and Retina. — At the back part of the eye, the scle- 
rotic coat is formed into a tube which leads inwards to the brain. 
This tube contains the optic nerve. As it enters the globe, it spreads 
out over the inner surface of the choroid, in the form of a most deli- 



Fig. 56. 

cate network of nervous filaments, called, from its reticulated struc- 
ture, the retina. The retina is therefore the extended and diffused 
optic nerve. In dissection it is easily separated from the choroid. It 
is absolutely transparent, so that light and colors penetrate and pass 
through it perfectly, and therefore fall upon the dark surface beneath. 
To prevent the delicate and transparent nerve tissues of the retina 
from being stained by the black pigment, a very thin film is interposed 
between them called JacoVs membrane. 

237. How Vision is Produced. — From every object which we see, 
rays of light pass into the eye, penetrating the successive transparent 
media, the cornea, the aqueous humor, the crystalline lens, and the 
vitreous humor, and falling upon the retina, form there an image of 
the visible object, the impression of which is carried by the optic 
nerve to the brain. 
The diagram (Fig. 
66) shows how, in 
the perfect eye, the 
image is made to 
fall accurately upon 
the retina. It is 
seen to be inverted. 
The pictures in the 
eye, of everything 
we behold, are upside down, although there is no confusion, and we 
are unconscious of it. "We have said that the image is formed upon 
the retina, and this is the common mode of expression, but that is 
perfectly transparent, so that the colored image is formed, not proper- 
ly ti2:>c>?i it^ but upon the black surface of the choroid coat behind it. 
It is maintained that the retinal membrane is affected by the colored 
image in the same manner that the sense of touch is affected by ex- 
ternal objects. It is supposed to touch or feel, as it were, the image 
on the choroid, and transmit the impression to the brain, something 
in the same way that the hand of a blind person transmits to the or- 
gan of consciousness, the form of an object which it touches. This 
view seems to be confirmed by the fact, that at that portion of the 
retina where the optic nerve enters the eyeball, which therefore has 
not the black choroid behind, it is insensible, and produces no per- 
ception. It has been proved by experiment that images made to fall 
upon that spot, are instantaneously extinguished. 

238. Wonderful Minuteness and Distinctness of tlie Images.— Nothing 
is more calculated to awaken our astonishment than the perfect dis- 


How the Images are formed in the perfect Eye. 


tinctness of the pictures upon tlie retina, compared with their magni- 
tude. The diameter of the picture of the full moon upon the retina 
is but the 2I0 P^^* of an inch, and the entire surface of the picture is 
less than the ^-aWo P^^* ^^ ^ square inch. And yet we are able to 
perceive portions of the moon's disc, whose images upon the retina are 
no more than the 15,000,000th part of a square inch. The figure of a 
man 70 inches high, seen at a distance of 40 feet, produces an image 
upon the retina the height of which is about the yV part of an inch. 
The face of such an image is included within a circle whose diameter 
is about Yz *^f ^-^^ height, and therefore occupies on the retina a cir- 
cle whose diameter is about ^\ part of an inch ; nevertheless, within 
this circle, the eyes, nose, and lineaments are distinctly seen. The 
diameter of the eye is about —^ that of the face, and therefore, though 
perfectly visible, does not occupy upon the retina a space exceeding 
the l-4,000,000th of a square inch. If the retina be the canvas on 
which this exquisite miniature is delineated, how infinitely delicate 
must be its structure, to receive and transmit details so minute, with 
such wondrous precision ; and if, according to the opinion of some, 
the perception of these details be obtained by the retina feeling the 
image formed upon the choroid, how exquisitely sensitive must be its 
touch. (Lardnee.) 

239. Adaptation of the Eye to Intensities of Light. — The susceptibility 
of the eye under great variations of intensity in the light which en- 
ters it, is most wonderful. We can read a book either by the light of 
the sun or of the moon, yet sunlight is more than a quarter of a mil- 
lion times more brilliant than moonlight. "The direct light of the 
sun has been estimated to be equal to that of 5,570 wax candles of 
moderate size, supposed to be placed at the distance of one foot from 
the object. That of the moon is probably only equal to the light of 
one candle at a distance of twelve feet, hence the light of the sun is 
more than 300,000 times greater than that of the moon." "WoUaston 
estimated the light from Sirius, one of the largest fixed stars, as twenty 
thousand million times less than that of the sun. 

240. Conditions of the System aflfect the Eye. — The eye is thus an opti- 
cal contrivance which challenges our wonder continually for the ex- 
quisite beauty and perfection of its parts. Yet we must not forget 
that it is a living organ of the body made up of vessels, membranes, 
muscles and nerves, and nourished by the vital blood-stream like any 
other organ. It is therefore liable to be influenced in numberless 
ways by conditions of the system. When in use, it acts, expends force, 
exhausts itself and becomes fatigued. Dr. Wharton Jones remarks : 


" Much exertion of the eyes operates more prejudicially to the sight 
under some circumstances than under others. Exertion of the sight 
is especially prejudicial immediately after a full meal; after the use of 
spirituous drinks ; while smoking ; when the body is in a recumbent or 
stooping posture, when dressed in tight clothing, especially a tight 
neckcloth ; tight corsets ; and even tight boots or shoes ; in close and 
Ul-ventilated apartments lit with gas ; after bodily fatigue ; during men- 
tal distress ; late at night when sleepy ; after a sleepless night ; while 
the bowels are much confined ; during convalescence from debilitating 
illness. Though during recovery from severe disease the eyes cannot 
bear much exertion, yet, for want of other employment, it is not un- 
common for convalescents to read even more than when in health. 
Many persons have much injured then* sight in this way. Young 
growing persons, at the age of puberty, persons of weakly constitu- 
tions, are incapable of supporting much exertion of the eyes without 
injury to the sight." Sudden suppression of the perspiratory action 
of the skin, or any cause which determines a pressure of blood to the 
head, is also liable to afi'ect the eyes injuriously, 

241, Beading and Writing. — In this reading age, with such strong 
and insidious temptations to overuse and bad management of the eyes, 
it may be well to make some suggestions concerning this mode of 
exercising vision. The closer the eye is confined to the page, the 
more of course it is strained, Novel reading is worse than science, 
history, or any grave subjects, because in the first instance we read 
fast and uninterruptedly, while in the latter cases thinking alternates 
with the use of the eyes in reading. Eeading from a broad page with 
the lines long and the print small, is very tiresome, as it is difiicult 
for the eye always to take up the next line. "Writing down our own 
thoughts is easy for the sight ; but copying is hard, as we have both 
to read and write, and look backward and forward in addition. 
Eeading when in motion, as in riding or walking, or in the brightness 
of sunshine, or under a tree, where from the motion of the leaves by 
the wind lights and shadows fly over the page, are all severe upon the 
eyes, and liable to injure them. But perhaps the most serious mischief 
to which we are exposed in reading, comes from the bad quality of 
artificial light, which we shall notice particularly farther on. 


243. Limits of perfect Vision. — The transparent portions of the eye, 
the cornea and included humors, act as lenses (149), which bend or 
refract the light from its straight course as it passes through them, 



Fig. 57. 

bringing it to a point or focus at the back of the eye. TVTiere the 
vision is perfect, the rays are so bent that the image, in its utmost 
distinctness of outline and color, falls exactly upon the retina, as shown 
in rig. 56. If the eye were a fixed or rigid mechanism, as if made 
of glass, only objects at certain precise distances would come to a 
point upon the retina, all others would produce their images either 
before or behind it, and thus give rise to imperfect vision. But the 
organ possesses a power of adjustment by which objects at different 
distances may be seen clearly. How this occurs ia not understood. 
Perhaps the crystalline lens is capable of slightly varying in position 
and curvature. The limits of perfect vision in the normal eye vary 
somewhat in different persons ; but in general they may be put down 
as between nine and fifteen inches. 

243. Cause of Far-sightedness. — -The eye is a system of lenses beau- 
tifully arranged to bend light to a point. But its bending or con- 
vergent powers may be too MgTi or too low^ 
producing imperfect vision in either case. 
This converging or refractive power de- 
pends upon the curvature of the lenses. 
The rounder they are, the stronger they are ; 
the flatter they are, the weaker they become. 
"^%i^v ■^^ persons advance in life, there is a ten- 
dency to loss of fluids, which fill and dis- 
tend the body, and a consequent shrinking 
of the flesh and wrinkling of the skin. Th( 
Far-sighted Eye^^witli flattened ^y^ participates in this natural change of 
tissue, its contents seem to shrink, and the 
cornea becomes flattened or loses something of its convexity, appear- 
ing as shown in Fig. 5Y. This -pvodnces far-sightedjiess, in which per- 
sons can see objects distinctly only when they are at a very consider- 
able distance from 
the eye, such as 
holding the book 
at arm's length in 
reading. In this 
state of the eye 
the rays tend to a 
focus at a point 

behind the retina, 
Far-siKhted Eye — the focal point thrown too far back. , . -, ,■■ 

° ■' ^ on which, there- 

fore, they strike in a scattered state, forming an indistinct image. In 

Fig. 58. 


Fig. 58 the object a has its focal point thrown back to 5, making a 
confused picture upon the retina at c. The further an object is from 
us, the less divergent or more parallel are the rays coming from it ; 
and the less divergent are the rays vyhich enter the eye, the easier are 
they brought to a focus by it. This is the reason that to the far- 
sighted, distant objects are distinct, and near ones confused. The far- 
sighted see minute objects indistinctly at every distance, because when 
near they are out of focus, and when remote from the eye, they do not 
reflect sufficient light to make a strong impression. They hence strive 
to increase the light upon the object, as we often see when attempting 
to read by candlelight, they place the candle between the book and 
the eye, and both at arm's length. It is but rarely that eyes recover 
naturally from this defect, yet much may be done to preserve the 
sight by care. When the eyes begin to fall, all over-exertion, as 
minute work or reading by badly arranged artificial light, should 
be avoided. As soon as the eyes begin to feel fatigued or hot they 
should have rest. 

244. How Glasses help the Far-sighted. — The remedy for this defect 
is convex lenses, which are so selected and adapted to the eye as ex- 
actly to compensate for the want of refracting power in the organ 
itself. These len- -^^^ 5g_ 

ses gather the rays 
to a point at vari- 
ous distances de- 
pending upon their 
curvature. The 
greater the curve, 
the nearer the fo- 
cus and the higher 
the power • while Far-sighted Eye corrected by double convex glasses, 

with less curvature, and a more distant focus, there is lower power. 
The refractive power of a glass is expressed by the distance of its 
focal point in inches. A 10-inch glass, or a No. 10, collects the rays 
to a point at a distance of 10 inches, a No. 5 at 5 inches, and a No. 
20 at 20 inches. The higher numbers express the lower powers, and 
the lower numbers the higher powers. Fig. 59 shows the far-sighted 
eye, with its internal focus, properly adjusted by a convex glass. 

245. Management of far-sighted Eyes. — "When the sight begins to fail, 
and glasses are sought, those of the lowest power, which wiU bring 
objects within the desired distance, should be chosen. But they 
should be comfortable and not cause headache, nor strain or fatigue 



the eyes ; if they do this, they are too convex. If practicable, it is 
well to get two or three pairs from the optician, as nearly correct as 
possible, and try them leisurely at home before deciding which to take. 
If the eyes only see clearly at a wry great distance, the No. of the 
glass required will be the same as the number of inches at which it is 
desired to read. But the moderately far-sighted do not require such 
strong glasses. If they can see small objects distinctly at 20 niches 
distance, for example, and wish to be able to read at 12, the power of 
the desired glass may be obtained by multiplying the two distances to- 
gether, and dividing the product, 240, by the difference between them, 
viz. 8 ; the quotient, 30, is the focal length in inches of the glasses re- 
quired. The intensity of the light influences the power of the glasses 
used ; it is commonly found that those a degree more convex are re- 
quired by artificial light, than by daylight. Many suppose that glasses 
of certain focal lengths correspond to certain ages, but no rule of this 
kind is safe. The nearest average relation between the age and the 
focal length of the convex glass is as follows: 

Age in Tears 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90. 

Focal Length in Inches...... 86, 30, 24, 20 16, 14, 12, 10, 9, 8, T. 

246. Near-sightedness. — This is the opposite defect; the cornea is 
too rounded and prominent, as shown iu Fig. 60. The rays of light 
which fall upon it are consequently too powerfully refracted, and ar- 
riving at a focus before reaching the ret- 
ina, cross, and are in a scattered state 
when they do fall upon it, as illustrated 
in Fig. 61, where a is the object, 5 the 
focus, and g the confused rays falling 
upon the retina. In this condition of 
vision, persons can see objects with per- 
fect distinctness only when they are at a 
short distance from the eyes ; if they 
_ bring minute objects closer than ten 

Near-sighted Eye, with its Protrud- inches they are usually accounted near- 
ing ornea. sighted. By bringing the object nearer 

it is distinctly seen, because the rays of light from it which enter the 
eyes, being more divergent than when it was distant, are not so soon 
brought to a focus. The near-sighted eye retains its power of adjust- 
ment to distances ; the nearest distance may be from 2 to 4 inches, 
while the greatest is from 6 to 12. Short-sighted people see minute 
objects more distinctly than other people, because from their nearness 

Fig. 60. 



Fig. 61. 

they are viewed under a larger angle and in stronger light. They can 
see better than others with a weak light, and hence can read small 
print with a feeble illumination. To persons who are occupied with 
minute objects, short-sightedness, unless extreme, is rather an advan- 
tage, as they can 
observe all the 
details of their 
work very ac- 
curately, while 
for distant vis- 
ion they can get 
ready help from 
glasses. Yet if 
an eye be at first 

Near-sighted Eye, the focus falling too far forward. 

perfect, the constant employment of it upon small objects tends to 
produce near-sightedness, which is hence a common defect of vision 
among the educated classes, and those who do much minute work. 
On the contrary, the habitual exercise of the eyes upon distant objects 
improves their power in that direction. If young persons have a ten* 
dency to nearness of sight, and are designed for vocations in which 
lengthened vision is required, they should avoid much exertion of 
the eyes on small objects, and exercise them frequently in scenes in 
the open country. It is an error that the near-sighted acquire perfect 
vision as they advance in life. "We often see old people who are com- 
pelled to use near-sighted glasses ; indeed, this state of the eyes some- 
times occurs in old persons whose vision was previously at the usual 

247. Management of Near-siglitedncss. — Concave glasses extend the 
vision of the near-sighted by separating or diverging the rays of light 
before they enter 
the eye, so that 
they may be less 
quickly brought 
to a focus, and 
the image formed 
further back, as 
shown in Fig. 62. 
The powers of 

. J? j.T^ " Near-sighted Eye, corrected by double concave glass. 

near-sighted are expressed in a manner contrary to those for the far- 
sighted (245). They are numbered 1, 2, 3, &c., No. 1 having the 

Fig. 62. 


smallest convexity and the smallest power, and being therefore adapted 
for those that are least near-sighted. In selecting glasses, the near- 
sighted should choose the lowest or weakest powers that will answer 
the purpose, and the best plan is to make trial of a series, as was sug- 
gested to the far-sighted. If the glasses make objects appear very- 
bright, or glaring, or small, or produce fatigue, strain, or dizziness and 
confusion of vision after being laid aside, they are too concave. If 
glasses are wanted for reading or to behold near objects, the power of 
the required glass may be determined as foUows : Let a person multi- 
ply the distance at which he is able to read easily with the naked eye, 
say four inches, by the distance at which he wishes to read, say 12 
inches, and divide the product, 48, by the difference between the two, 
which is 8 ; the quotient, 6, is the focal length of the glasses required. 
The far-sighted have to change their glasses as the sight progressively 
fails, but near-sightedness usually continues much the same through 
the greater part of life, so that the same glass gives assistance a much 
longer time. It is well for both the far-sighted and near-sighted to 
employ glasses of various grades for different purposes. Thus the 
near-sighted need glasses adapted to distant objects, and as they are 
much inclined to stoop in reading and writing, they might remove the 
eye further from the page by using glasses of slight concavity. ISTear- 
sigbtedness may be occasioned by other causes than the one just no- 
ticed. There may be a declining sensibility of the retina, which makes 
it necessary to bring objects nearer to the eye ; this is called nervoits 
sTiort-sightedness, and although objects are seen better close by, yet 
they are not seen so distinctly as in true or optical short-sightedness. 
Such persons seek strong light, to get a more vivid impression, and use 
convex glasses to increase the light upon the retina. This use of glasses 
is perilous (266). Short-sightedness is sometimes a symptom of com- 
mencing cataract. This disease is not, as is commonly supposed, 
something growing over the sight on the outside of the ball. It is a 
change in the crj'stalline lens, by which it loses its transparency, and 
becomes more or less opaque, so as to confuse, scatter, or stop the 
light, and destroy the distinctness of the image. Children often shorten 
their vision at school by stooping over their desks and poring over 
bad print, combrued with the debihtating action of extreme heat and 
bad air, a result which should be carefully guarded against by parents 
and teachers. 

248. Important Suggestions in selecting Spectacles. — "Whatever be the 
defects of vision which spectacles are designed to remedy, there are 
certain points which should always be observed, both by the maker in 


mounting the glasses, and by the buyer in selecting the frames. It ia 

essential that the lenses be so framed that their axes shall be exactly 

parallel, so as to couacide with the axes of vision when the eyes look 

straight forward. Frames are often made so light and flexible as 

readily to bend in clasping the head, so that the glasses cease to be in 

the same plan, and then- axes lose their parallelism. This is shown in 

Fig. 63, where the axes of the len- 

ses, c (?, instead of comciding with 

the axes of vision, a &, are altered in | / 

their direction, and become conver- :; 

gent. Again, the most perfect vision Y''''~°'''''''f=^aaag B-__-a ,»g 

with spectacles is produced when the / / i 

eye looks through the centre, or in / / ■ 

the direction of the axis of the \ ^ h 

lens. Where the eye turns from the I 

axial centre of the glass, and looks I j 

obliquely through it, the view is less \ / 

clear and perfect. For this reason \ / 

persons wearing spectacles general- \ - / 

ly turn the head, where those with- Tie axes of the glasses, c <f, should coin- 
'' ' cide with the axes of vision, a o. 

out them generally turn the eye. 

The distance between the centres of the lenses should be exactly equal 
to the distance between the centres of the pupils. As the clearest vision 
is through the centres of the glasses, the eyes wiU have a constant 
tendency to look in that direction. Hence, if the lenses be too far 
apart, the eyes, in striving to accommodate themselves, will acquire a 
tendency to an outsquint ; whUe if the glasses are too near together, 
there will be, for a similar reason, a tendency to an insquint. The 
frames should not only correctly adjust the glasses, but should main- 
tain them firmly and steadily before the eye. The lenses should be 
free from veins or small bubbles, be ground to an exact curvature, and 
be perfectly polished and free from flare, or what is technically called 
curdling. "What are called 'pebble-glasses,' or 'pebbles,' are some- 
times used ; they are cut from Brazilian rock-crystal, and have the ad- 
vantage of being more transparent than glass ; they are also much 
harder, do not scratch, take a higher polish, and consequently trans- 
mit more light. 


249. Artificial Light not White, but Colored.— Artiflcial light differs 
from daylight in composition ; it is colored, while dayhght is of a pure 


■wMte. We have seen that white light is a compound, consisting of 
three simple colors, red, yellow, and blue (159). There is no means 
of positively determining the proportion in which these colors combine 
to produce white, although it is commonly stated to be, red 5, yellow 
8, blue 8. Whatever may be the measured quantities in which they 
combine, we know that any disturbance of those quantities destroys 
whiteness and produces a colored light. Now our common artificial 
lights are not really white ; they appear so from want of a pure white 
to contrast with them. They are more or less deficient in blue, and 
consequently appear of the tints which result from a mixture of what 
remain, yellow and red ; these combined produce orange, so that arti- 
ficial luminaries produce in a greater or less degree yellow or orange- 
colored light. 

250. How the fact may be shown. — To become assured of this fact, 
it is only necessary to observe both daylight and candlelight under 
circumstances favorable for comparison, which may be done in the 
following manner. If a lighted candle be placed in a bos, with a 
round hole cut in one side so that the rays may pass through and form 
a luminous circle on a sheet of white paper ; and if then a second 
luminous circle be formed on another part of the paper by a beam of 
daylight admitted through an opening in a closed window-shutter, the 
orange- yellow tint of the candlelight, contrasted with the whiteness 
of the other circle, will then be strikingly apparent. 

251. Order of deviation of different Lights from Whiteness. — ^The red- 
colored light is produced by the slowest and most imperfect combus- 
tion (188) ; as the burning becomes intenser orange and yellow appear, 
and lastly, at the highest temperature, blue, which by mingling with 
the other colors produces whiteness. The different illuminating sub- 
stances yield lights of various tints, from a dingy red up to white, ac- 
cording to their composition and the various circumstances of combus- 
tion which we have noticed. Dr. J. Hunter arranges the lights of 
illuminating substances as degenerating from whiteness nearly in the 
following order. Oil-gas, naphtha ; sperm oil ; coal-gas from the 
best coal ; wax, spermaceti, and stearine candles ; vegetable oils ; 
moulded tallow candles ; coal-gas from inferior coal ; coarse oil and 
dipped tallow candles. Oamphene and kerosene oil wUl probably 
rank with the best gas, and a good quality of burning fluid with 
spermaceti candles. 

252. Alteration in Colors seen by Artificial Light. — It is well known that 
colors appear differently when illuminated artificially than when seen 
by daylight. This is a necessary consequence of the difference in the 


rays wMch fall upon them. As sunlight contains a large proportion 
■of hlue rays, and artificial light an excess of yellow rays, they must 
inevitably influence the color of surfaces in a different manner. In 
artificial light green has a yellow hue, and blue turns green from the 
excess of the yellow rays ; dark blue becomes purple and nearly black ; 
orange, by reflecting its own constitutent rays, appears very bright ; 
yellow appears white, from there being no really white light to con- 
trast it with, and red has a tawny color from the excess of yellow ; at 
the same time all the colors except the orange are much impaired in 
brilliancy, and many of the deeper shades become quite black and 
sombre, from there not being any pure white light reflected from their 
surfaces, as in daylight, when even the gravest colors have a remark- 
able degree of clearness and purity. Of course the appearance of 
colors by artiflcial light will depend directly upon its quality. The 
whiter and purer and nearer to daylight it is, the more bright and 
natural will they be ; whUe the more colored and dingy the light, the 
more chromatic disturbance and perversion will it produce. 

253. How Artificial LlgM affects the Eyes. — But the eye itself is 
affected by the use of artificial light, as is shown by the following 
simple experiment, suggested by Dr. James Hunter. " Tie up the 
left eye, and with the other look steadily and closely for about a 
minute at some small object placed upon a sheet of white paper, and 
strongly illuminated with ordinary daylight, but not exposed to the 
direct rays of the sun ; then uncover the left eye and look at some 
distant white object or surface, such as the celling of the room, first 
with the left eye and then with the right. It wiU be found that there 
is not much difference in its appearance as seen by one eye or by 
the other, though in general it will be a very little brighter to the left 
eye. After this, darken the room by closing the shutters, tie up the 
left eye again, and then with the right one look at the same object 
placed on a sheet of white paper as formerly, but illuminated by a 
large tallow candle or oU lamp, so that it shall be seen as distinctly as 
it was in daylight. Keep the right eye fixed on this object for about 
a minute, so as to examine it closely and narrowly, then extinguish 
the candle or lamp, open the shutters, and uncover the left eye. 
"When both eyes are now turned to the ceiling, it wiU appear some- 
what dim and indistinct ; and on looking at it first with the one eye, 
and then with the other, the difference will be very remarkable. To 
the left eye, which had not been exposed to the action of the artificial 
light, it wiU appear unchanged, or sometimes of a pale yeUowish- 
white color ; but to the right eye it will be very dim and of a darh 


hlue or purple color. The effect produced npon the right eye in this 
experiment soon goes oif ; and though it always takes place to a cer- 
tain extent when artificial light is used, it is not much observed, 
because as both eyes are equally affected, the contrast is not very 
striking. But if any one will read or write by candlelight for some 
hours with one eye closed, he will be rendered fully sensible of its 
very injurious action, when he afterwards compares the state of one 
eye with that of the other. 

254. Explanation of these eflTects. — We shall understand these effects 
by recalling what has been said of complementary colors (173). "When 
the nerve of vision is exposed to a colored light, it is unequally excited. 
The equilibrium of its action seems to be disturbed. It becomes less 
sensitive to the observed color, and when the eye is afterwards turned 
to white objects, they do not appear white but tinged with the com- 
plementary to the one seen first. The continued action of one color 
seems to paralyze the retina to its influence, and produce an unnatural 
sensibility to the other colors, which, combined with that, compose 
white light. In the preceding experiment, the eye, stimulated by 
candlelight, in which orange-yellow is in excess, temporarily lost its 
power of discerning white, and saw in it only the complementary of 
orange-yellow, blue or dark violet. 

255. How this may injnre the Retinai — Now the effect of this over- 
stimulating the nerves of vision through excess of red and yellow 
r^s, on the jjart of those who use their eyes much by artificial light, 
is often to produce at certain points of the retina a total insensibility 
to those rays. The consequence of this is, that in daylight dark films 
of a blue or purple color, which are complementary to the orange or 
yellow color of the artificial light, appear before the eyes. The pecu- 
liar color of these films is not very obvious, unless they are seen in 
contrast with a yellow or orange surface, and over them they appear 
very sombre and almost black ; because, in the peculiar state of the 
eye that gives rise to their appearance, there always coexists a certain 
degree of diminished sensibility to all the rays composing white 

256. Popular recognition of the effect of different Colors. — There is a 
difference in the effect of different colors upon the eye, which is 
generally recognized and variously expressed. Thus blue is said to be 
a very soft, cool, retiring color ; green is cool, though less so than 
blue ; yellow is warmer and advancing ; orange still Avarmer, and red, 
fiery^i JiarsTi^ and exciting. This agrees with the view which regards 
blue and green as least hurtful, and yellow, orange and red as more 


irritating and injurious to tlie eyes. An explanation of these different 
effects is found in the wave theory of light and colors, which has 
been previously noticed (155). Vibrations of the red ray are larger 
and more forcible than those of the yellow, and the yellow than those 
of the blue, just as the large and slow heavings of a swell upon the 
ocean are more violent and irresistible than the smaller and quicker 

257. Heat aceompanying Colors — The above current phrases in refer- 
ence to the coolness and warmth of color, correspond perfectly with 
the distribution of measured heat among the several colors of the 
spectrum. We all know that heat is associated with light ; but it is 
not equally associated with each color that composes the light. 
When the colors of the sunbeam are separated and spread out as in 
the spectrum, it is found that the heat is least intense at the blue, and 
constantly increases through the green, yellow, orange, and is most 
intense in the red color. Thus Englefield found that while the blue 
rays were at a temperature of 66°, the yellow were at 62°, and the 
red at 72°. Thus the orange and red of common artificial light are 
actually more fiery and exciting than the absent blue rays. This ac 
companying heat is apt to be much more injurious in artificial than in 
natural light. The sun's rays are seldom, if ever, allowed to fall 
directly on a near object on which the eyes are to be employed for 
any length of time, without having previously undergone repeated 
reflections from the atmosphere and clouds, or from the surface of the 
ground and walls and furniture of the apartment, which absorb a 
great portion of their accompanying heat. But owing to the non- 
diffused and concentrated character of artificial light, the rays must 
be generally allowed to fall directly on the object looked at, from 
which they are reflected to the eye along with nearly the whole of 
their accompanying heat. 

258. The Lnminons Matter being imperfect, more must l»e used. — The 
luminous effect, or as it is termed the defining power of light, that 
quality by which we are enabled to see minute objects with the most 
distinctness and ease, is much less in artificial light than in the white 
light of day. This lower defining power of orange-colored light 
makes it necessary to increase the amount of the inferior rays ; we 
attempt to compensate for deficient quality by excess in quantity. In 
reading by daylight the black ink is strongly contrasted with the pure 
Ivhite paper ; but by artificial light, as the paper has an orange or yel- 
low hue, the contrast is not so marked, and so to aid vision, the quantity 
of light is increased. In severe, long-continued, and nightly exercise, 

142 kstjurious action of aetificial light. 

as in reading, writing, sewing, type-setting, &c., the injurious conse- 
quences of impure light are apt to be heightened by its excessive use, 

259. Carbonic Acid affects the Eyes. — Sunlight does not poison the 
air, artificial light does. In proportion to its brilliancy and abundance, 
the insidious narcotic agent, carbonic acid gas, is generated and set 
free. The effects of breathing this substance wiQ be described when 
treating of the air and ventilation (293) ; but it may be remarked, that 
by its special influence in deranging and disordering the nerves, it is 
fitted to concur with those influences which impair the action of the 

260. Unsteadiness of Artificial Light Injnrions. — Sunlight never wavers 
or flickers ; its action upon the eye is equable and unvarying. But in 
artificial illumination, as it is impossible perfectly to regulate the sup- 
ply of air and of combustible material, the light is fiickering and un- 
steady. The glass chimney of the Argand burner, however, produces 
the most constant and unchanging flame. The bad effects of these 
sudden and continual alterations in the brightness of artificial light, 
may be shown by supposing that a minute object can be seen in light 
of 8, 9 or 10 degrees of intensity, but that the intermediate degree of 9 
is best .Now if sunlight be used, as it flows in a perfectly uniform man- 
ner without sudden variations, the retina and pupil adapt themselves 
to its quantity, and the eye may be long used without fatigue. But if 
artificial light of 9 degrees be used, it may at one moment rise to 10, 
and at the next fall to 8 degrees, from the fiickering of the fiame, so 
that the retina and pupil have not time to accommodate themselves to 
the change, and a degree of temporary blindness or impaired distinct- 
ness of vision, results, which is very straining and fatiguing to the 
eye. To remedy this, the light is increased in intensity. If it be 
raised, say to 14 degrees, then it may be reduced to 13 or rise to 15 
degrees, without immediate inconvenience to the eye ; there being 
abundance of light, its variations are less sensible. This relief, how- 
ever, is fraught with iiltimate danger ; for the retina is too much 
excited by this increase of one-half in the quantity of light admitted 
to it ; and this state of excitement is but the prelude to an opposite 
state, in which the sensibility to light is greatly, and perhaps perma- 
nently diminished (265). Unsteadiness of the object viewed, if the 
eye be long and closely directed to it, is a source of injury. It is thus 
that much reading in railroad cars, where the trembling or incessant 
movement of the print keeps the image in constant motion upon the 
retina, has a bad influence upon the eye. 

261. All Light iiyarions but that from the objects viewed. — The distinct- 


ness of vision is interfered with, and the eyes made to suffer by an- 
other important circumstance — tlie admission of light into the eye 
from other sources than objects to which sight is directed ; in other 
words, the introduction of extraneous light into the eye. Impres- 
sions upon the retina may be diminished and obliterated by other 
rays falling upon it, which excite the nerve more strongly. The moon 
at night, as we all know, produces a vivid impression upon the nerve 
of visual sense. It produces precisely the same impression in the 
daytime, but then the luminous image is extinguished by the over- 
powering light of the sun, so that we are not conscious of it. "Wlien 
we are using the eyes upon any object, all light which enters them, 
except from that object^ is injurious ; that is, it has a blinding effect. 
This is shown by the greater clearness of objects seen through a tube, 
where aU the diffused and side-light is excluded, on the same principle 
that persons see stars from the bottom of a weU in the daytime.* Or it 
may be shown in another way. Let a person stand before a gas-light 
in such a position, that in reading a book a considerable number of 
the direct rays from the flame shall enter the eye. Let him then 
cautiously reduce the light by turning the stop-cock until the letters 
can be no longer distinguished. If he now shade his eye by inter- 
posing his hand or a screen, so as to cut off the direct rays, the words 
will again become visible, and again disappear when the hand or 
screen is removed. This proves that when the eye is protected from 
the direct rays, small objects can be seen with less light, and conse- 
quently with less injury to the nerve of vision. 

262. PreTalence of this source of injury. — Upon this point Dr. Hun- 
tee remarks : " Though the injurious action of artificial light, in con- 
sequence of its improper position, can be easily obviated ; it is aston- 
ishing how little it is attended to, and how generally it is in operation. 
For the express purpose of satisfying myself on this point, I have 
visited a great many workshops, printing-houses, tailors' rooms, and 
other places, and in almost every instance I found the artificial lights 
placed close to, and directly opposite the eyes of those engaged in fine 
work, requiring the excessive exertion of the sight, and frequently the 
mischief was increased by concave metallic reflectors, placed behind 
instead of around the light. Now that gaslight is so generally em- 
ployed, its improper position is a most serious evil : for as its intensity 
can be so easily increased in proportion as the sensibility of the eye 
becomes impaired, few persons, particularly those who are igno- 
rant of the harm they are doing, can resist the temptation to use a 

♦ Humboldt, however, questions if stars are ever thus seen. 


stronger and stronger light, till at last their eight ia permanently 
weakened or even quite destroyed." 

263. Bad Light may inflame the Eyes. — The continued action of im- 
proper light upon the eye is liable to inflame it. The first symptom 
is a reddening of the lining membrane of the eyelids, which in health 
is of a white or pale rose-color. This may be observed by gently 
drawing down the lower lid, when its surface will be seen injected 
with blood and of a deep red color. At first there may be but little 
uneasiness in the daytime, but at night, when the eyes are employed 
on objects illuminated by a candje, they become hot, watery, and 
irritable, the lids feeling dry, stifi", and itchy, and causing the patient 
constantly to rub them. The dryness, after a time, may give place to 
a copious flow of burning tears, which suffuse the eyes, and pour over 
and scald the cheek. Sometimes there is an excess of gummy and 
adhesive secretions, which dry at night and glue together the lids so 
hard as to require long bathing with warm water before they can be 
opened. If this incipient inflammation be unchecked, it may increase 
and run on to various forms of disorganization, or it may take the 
shape of a chronic or unmanageable afiection of the eyes without pro- 
ducing blindness. 

264. Unnatural increase in the sensibility of the Retina* — In the preced- 
ing case, the disease is located in the external or image-forming por- 
tions of the eye, but the bad management of artificial light is apt to 
engender a far more dangerous and intractable form of disease, which 
fixes itself upon the image-feeling parts — the retina and optic nerve. 
The excessive use of impure light, by its unequal action, excites and 
stimulates the nerves of vision, producing an unusual irritability to 
light, and a low degree of inflammation of the retina. Moderate light 
becomes unpleasant, and the individual, after looking steadily at some 
object for a few minutes and then closing the eyes, or putting out the 
light, appears to see still before him quite a distinct representation or 
image of the object, which may last for two or three minutes, and be 
variously colored or pass through a succession of colors. It moves, 
but its motions are in opposite directions to those of his eye, for it 
passes upwards when he looks downwards, and sinks downwards when 
he rolls his eyeballs upwards. It is caused by the morbidly increased 
sensibility of the retina, which retains the impressions of light for a 
greater length of time than when it is in a healthy condition. This 
state of the eye is accompanied often during the daytime by a dull, 
heavy feeling in the forehead, hardly amounting to pain, but causing 
the patient frequently to pass his hand across his brow, and ia read- 


ing or writing at night, there is an unpleasant sense of distension in 
the or hits, with an increased flow of tears and frequent twittering or 
quivering of the eyelids. BriUiant flashes of fire are seen, particu- 
larly when the eye is touched, on lying down, and after reading, writ- 
ing, or sewing for some time by artificial light. 

265. Decrease in nervons sensibility— Appearance of dark films. — This 
condition of excessive irritability may continue for months, and then 
be followed by others totally different, and indicating a diminished 
sensibility of the nerves of vision. This is evinced by the appearance 
of dark spots or films floating in the air. At first but one film appears 
before each eye, which is seen only for a moment, and then darts away, 
shortly to reappear. But afterward their number is increased, they 
appear oftener, are larger, darker, more opaque, and continue longer 
visible than at first. They sometimes look like cobwebs, or flakes of 
soot, or bunches of fur-down. They often resemble large-sized leaden 
shot, or minute and transparent globules, looking lite drops of oil upon 
the surface of water, and, connected with each other like the links of 
a chain, float slowly through the air. These appearances are known 
by the doctors as musece wUtantes; they are probably connected with 
morbid conditions of the nerves, but how we do not know. 

266. Paralysis of the nerve of vision — imanrosis. — These appearances, 
in their less marked form, are quite common, many eyes being subject 
to them, and they may occur for a long time without getting worse, 
and unaccompanied by positive disease. But when they appear as a 
dense, opaque, stationary film, which interrupts and obscures vision, 
the symptoms become very alarming ; there is danger of palsy of the 
retina producing nervous blindness, or amaurosis. To the casual ob- 
server, the eye, under the influence of this malady, appears perfectly 
well, there being no external evidence of disease. But when once 
seated, its effects may be seen in the irregular shape of the pupil, 
which loses its roundness while the motions of the iris under the in- 
fluence of varying light, become sluggish and imperfect, or are alto- 
gether lost. Objects appear clouded in a thick mist, and the air some- 
times seems filled with sparkling, glittering points. In the final 
stages of amaurosis the pupil is very much dilated, the sight is impaired 
or quite gone, and the eye has a lustreless, dead appearance. As the 
disease advances pain ceases, the light, instead of being disagreeable, 
as at first, can hardly be procured of sufiicient intensity. The patient 
resorts to spectacles of a high magnifying power, which condense a 
great quantity of light upon the palsied nerve of vision ; these may 
afford transient aid, but do ultimate injm-y. This disease may require 



from a few months to several years to run its course, but amaurotic 
blindness is regarded as incurable. 

267. Who are most subject to amaurotic disease. — Amaurosis may arise 
from otber causes than the improper use of artificial light, but Dr. 
Elliott states that nearly two-thirds of aU the cases of this disease 
which are met with in practice, occur in those who use their eyes 
much by artificial light, such as literary men, students, compositors, 
tailors, seamstresses, shoemakers, engravers, stokers, glass-blowers, 
&c. He also remarks that some individuals ai'e more liable than others 
to sufier from the injurious action of artificial light, particularly those 
of a fair complexion and with gray or light blue eyes. 


268. Effect of gronnd glass Shades.— "We have stated (261) that all 
light which is more intense than that coming from the object viewed, 
dazzles the eye and weakens the impression of the object, causing it 
to appear less clear and distinct. To cut off these blinding rays from 
the flame itself, translucent screens of groimd glass, called shades^ globe- 
shaped, or of any other desirable figure, are made to surround the lu- 
minary, and have the efiect of deadening the light in a surprising man- 
ner. The outline of the fiame disappears, while the rays of light come 
from the surface of the globe, which thus appears self-luminous, and 
emits a difi'used and softened light. As the rays cross each other at 
aU points, and are scattered in all directions, objects near by throw 
only short, indistinct shadows, and there is a general and equal illumi- 
nation. These shades should be used whenever it is desired to reveal 
to the best advantage the objects of a room, but where the vision is to 
be specially exerted upon particular things, their use is unfavorable, 
as by diffusion there is considerable loss of light. Objection has been 
made to the employment of ground glass and semi-transparent white 
ware shades, on the ground that by scattering the light they expand 
the impression over a larger surface of the retina ; but as the image en- 
larges in area, it diminishes in intensity, which is desirable, unless the 
eye is constantly engaged in the scrutiny of minute objects. 

269. How to collect the Light — Eeflectors. — It is apparent that the ra- 
diation of light in all directions, is favorable to the equal illumination of 
objects distributed in all parts of the room. But when we desire to 
view closely minute objects, as in reading, writing, sewing, &c., it is 
necessary to concentrate upon the point of observation the light which 
would be otherwise wasted by general diffusion. To collect the rays, 



and direct them to tlie part where they are required, (50oir<il shades or 
reflectors, of tin, paper, or some other opaque substance, acd usuall,- 
pohshed or whitened on the inside, are made to surround tho flame, 
These not only protect the eyes from the glaring rays, but direct down 
wards that which would escape in other directions and be lost. 

270. Blue Shades to supply the missing rays. — To remedy the defect* 
which arise from the bad composition of artificial light, several expe- 
dients have been suggested. It is proposed to surround the flame with 
a conical shade, the inner side of which is sky-blue. As the light that 
passes upward, falls upon this surface, its red and yellow colors are 
absorbed, and the few blue rays which it contained, being thrown 
downward by the sloping sides of the reflector, mtagle with the 
orange light, proceeding directly from the flame, and improve the bad 
color by imparting to it a higher degree of whiteness. As in this 
case a portion of the reddish yellow rays are absorbed, there is a loss 
of light. If a common white reflector is used, more luminous matter 
is thrown down than with the blue shade, and a stronger illumination 
is produced. But, with a blue reflector, although there is less bril- 
liancy, the light is whiter, purer, and has a higher defining power, 
while it is cooler, more agreeable, and less injurious to the eyes.* 

271. Structare and moonting of these Shades. — Shades of bristol-board, 
or strong paper, or sUk, may be made by 
any one. The material is to be cut into 
the shape exhibited in Fig. 64, and then 
the edges, a a and 5 5, are to be united 
to each other, which gives rise to the 
conical structure shown in Fig. 65. This 
may be mounted upon a wire frame, 
which is to be hooked on to the glass 
chimney, or ground shade, or in the ab- 
sence of these, a wire framework may be supported by the body of 
the lamp. If the reflector be made of metal, as tin or copper, it may 
be sustained either in the way described or by a three-branched sup- 
port, screwed on to the burner. Eeflectors are 
adapted to candles by attaching to the candlestick 
an upright brass rod, on which the reflector slides, 
being fixed at any point by a thumb-screw. This 
is shown in Fig. 66. 

272. How blue Reflectors should be colored. — The 
most pure and michangeable blue color is ultramarine, and this is best 

Fig. 64 

Fig. 65. 

• E. V. HAUGirworT, of 490 Broadway, N. T., furnishes these shades. 




Candlestick with, 

adapted for painting the inner surface of shades. Prnssian-hlue de-' 
composes and turns green by exposure to the heat, and other coloring 
matters are hable to fade or change. The colored 
surface should be smooth, but without gloss or var- 
nish, the surface appearing dead, or, as it is techni- 
cally termed, ' flat.' 

273. Artificial Light wMt«ned by absorption. — Blue, 
transparent media absorb the yellow and red rays, 
and transmit only those of blue. If the glass chim- 
ney of a lamp be tinted lightly and evenly with a 
mixture of ultramarine and mastic varnish, the of- 
fensive orange will be separated from the light as it 
passes through, but at the expense of its brilliancy; 
there will be much less of luminous matter. But if 
a polished tin or silvered reflector be employed to 
collect the rays, it will throw downward a beautiful 
soft white light. If the light from a luminary which 
is surmounted by a white or polished reflector (Fig. 
61) be made to pass through a glass globe filled with 
water which has been slightly blued, its color will be 
improved, while to compensate for the loss of luminous matter ab- 
sorbed, the spherical form of 
the water-bottle wUl serve to 
converge or gather the rays so 
as greatly to increase their Hlu- 
miaating power, at the point 
upon which they fall. Mello- 
Ni has proved that when the 
rays of artificial light are passed 
through even a very thin stra- 
tum of water, their heatiug 
power is diminished by eighty- 
nine per cent., but with little 
increase in the temperature of 
the water, in consequence of its 
great capacity for heat (49). 
The water-globe thus transmits 
a cooler as weU as a whiter and 
purer light. Lamp-globes made 
of glass, slightly blued in its composition, would be very desirable. 
274. Colored glasses for Spectacles. — The indiscriminate use of these 

Whitening the rays and straining them of 
their heat. 


is altogether objectionable. They place the eyes in very unnatural 
conditions as regards the light, and if their employment is persisted in, 
it impairs their sensibility to the true relations of color, and otherwise 
injures them, as we have just seen that artificial colored light is able 
to do (253). If we look through a glass of any color, the effect is, that 
when it is withdrawn, the eye sees all objects tinged by its comple- 
mentary. As the colored glass cuts off a large quantity of light, its 
removal produces a sudden and injurious impression. Faint blue 
glasses may be serviceable in using artificial light. Colored glasses 
absorb and accumulate the heat so as in many cases to be disagreea- 
ble. Their bad effects are more marked, as it is for ' weak' eyes that 
they are generally commended. They may, at times, be of service to 
protect the eye from an intense glare, as of snow or the surface of 
water in sunshine. Gray glasses, or what is called a ' neutral tint, ' 
that is no particular color, are perhaps best ; they should not be of too 
dark a shade. 

275. Is Gas-liglit injnrions 1 — There is a prejudice against gas-light, 
as being the most injurious form of artificial illumiDation. As against 
the proper and well-regulated use of gas, this prejudice is entirely 
groundless, but there can be little doubt that from its abuse and bad 
management it is really doing more mischief than any other kind of 
light ; its very excellencies are turned to bad account ; its extreme 
cheapness, compared with other sources of illumination, naturally leads 
to its use in excessive quantities ; floods of light are poured forth, so 
that persons may read and sew for hours together in the remotest cor- 
ners of the room. The air is heated by the excessive combustion, and 
poisoned by large quantities of carbonic acid, which there are no means 
of removing. The eye is unprotected from the glare by screen or shade ; 
extraneous light is freely admitted, which obscures the impression and 
strains the nerve of vision, and in proportion as the sensibihty of the 
eye is impaired, stronger light is used, which gives temporary relief, 
but with danger of ultimate and permanent injury to the sight. On 
the other hand, good, well purified gas, judiciously controlled in ac- 
cordance with the hints we have given, and others to be offered in the 
next part, is perfectly harmless (360). 




276. Part it plays in the scheme of Nature* — It is impossible to con- 
template the wonderful properties of the atmosphere without a feeling 
of profound amazement. Whether we regard it as the grand medium 
of water circulation, through which rivers of vapor lifted from the 
oceans are carried landward, to be condensed and channel their way 
back again to the sea ; or as the scene of tumultuous storms, generating 
the lightnings within its bosom, and taking voice in the reverberating 
thunders ; whether as hanging the landscape with gorgeous cloud- 
pictures, or as the vehicle through which aU melody and beauty and 
fragrance are conveyed to the portals of sense — it is alike strange and 
interesting. But when we glance at its deeper mysteries, those inti- 
mate relations to life which have been disclosed to modern science ; 
when we consider that the vegetable kingdom not only has the same 
chemical composition as the air, but in its mass is actually derived 
from it ; that the whole architecture and physiology of trees, shrubs, 
and plants, are conformed to atmospheric nutrition, so that in literal 
truth the forests are but embodied and solidified air, the subject rises 
to a still higher interest. And more startling yet is the surprise when 
we recollect not only that the materials of our own bodily structures, 
derived from vegetation, have the same atmospheric origin ; but that 
active life, the vital union of body and spirit, and all the powers and 
susceptibilities of our earthly being are only maintained by the action 
of air in our systems ; — air which we inhale incessantly, day and night, 
from birth to death. There is an awful life-import in these never- 
ceasing rhythmic movements of inspiration and expiration, this tidal 
flux and reflux of the gaseous ocean through animal mechanisms. 
Shall we question that it is for an exalted purpose ? Science has many 


things to say of the relations of air to life, but it can add nothing to 
the simple grandeur of the primeval statement, that the Creator 
"breathed into his nostrils the breath of life, and man became a 
living soul." 

277. Air a material reality — Its pressure. — The atmosphere is so thin 
and invisible, and so totally unlike the objects that present themselves 
to our most impressible senses, that we are half inclined to forget that 
it is a reality, and are too apt to think of it as being mere empty space. 
Yet it consists of ponderable matter, and is heavy, just like the solid 
resisting objects which we see and handle, and it presses down upon 
the ground with a force propoi-tional to its weight. Upon every 
square inch of the earth's surface there rests about 15 lbs. of air. 
Upon the body of a medium-sized man, having a surface of 2,000 
square inches, the atmosphere exerts an external crushing force of 
30,000 lbs. But there is air also within the system which exerts an 
equal outward pressure, and thus prevents injury. The pressure of 
air upon the body is not the same at aU times. There are tides in it, 
just as there are in the ocean, great atmospheric waves which regu- 
larly sweep over the earth and cause the weight of the atmosphere to 
vary. Winds and storms produce similar effects. These variations in 
atmospheric pressure are measured by the barometer (60), and they 
are so considerable that a man's body may sometimes have from one 
to two thousand pounds more pressure upon it than at others. Of 
com-se, as the pressure upon the air increases from above, more of it 
is crowded into the same space, and it becomes more dense. The 
maximum height of the barometric column, therefore, corresponds to 
the greatest density of the air, and a low condition of the mercury to 
rarity of the air. 

278. Weiglit of varions masses of Air, — As the air is thus ponderable, 
it is desirable to obtain definite ideas of the proportion between its 
bulk and weight. A cubic foot of air weighs 538*1 grains, or some- 
thing more than an ounce. 13 "06 cubic feet weigh 1 lb. About 65 
cubic feet of aii" furnish 1 lb. of oxygen. An apartment 8 feet high, 
12 wide, and 13 long, contains about 100 lbs. of air ; and a room 40 
feet square and 18 feet high contains about a ton. The atmosphere is 
estimated to be 45 or 50 miles high, but the great mass of it lies close 
to the earth, as it grows very rapidly thinner and rarer in ascending 
from the earth's surface. Indeed if it were all the way up of the 
same density as that which we breathe, it would be only about five 
miles deep, just sufficient to cover the highest mountains. 

279. Effects of varyii^ pressure <rf tlie Air. — ^Every variation of at- 


mospheric pressure must decidedly influence the state of the body, 
modifying, as it were, the tension of tlie whole fahri«, affecting the 
pores of the skin, the cells of the luugs, and the circulations within 
the system. The constitutions of many invalids, especially the asth- 
matic and consumptive, are undoubtedly much influenced by changes 
of atmospheric density. As the barometer falls and the air becomes 
lighter, the tendency to evaporation from all surfaces, and the amount 
of expansion in all the more compressible tissues increases. As the 
lungs have a constant capacity, and consequently receive the same 
bulk of air at all times, it is clear that the quantity taken into these 
organs to act upon the blood will vary with its density, there being of 
course more matter in a chest-full of dense air than in a chest-full of 
light air. Such changes, which powerfully influence the general rate 
of action within the system, must affect the mind as well as the body, 
and assist to explain the fact that "persons are often joyful, sullen, 
sprightly, hopeful and despairing, according to the weather, while 
there are days in which the faculties of memory, imagination and 
judgment, are more acute and vigorous than others." Every alter- 
ation of an inch in the mercury of the barometer adds or removes a 
weight of 1,080 lbs. from the average weight which a man of common 
stature sustains. The effects of sudden alterations of this pressure, as 
when the barometer is subject to rapid and extreme variations, often 
appear in the shape of headache and apoplexy (779). Yet in this, as 
in numerous other cases, it is remarkable to what different states the 
system can habituate itself. Saussttee, at the summit of Mont Blanc, 
had scarcely sufficient strength to consult his instruments ; while at 
heights scarcely inferior. South American girls wiU dance all night. 
The influence of fluctuating pressure of the air is of great importance 
to the inhabitants of low, swampy, malarious districts of country. 
The amount of exhalation and effluvia which rise from the ground 
depends much upon atmospheric pressure. When the air is heavy, 
these substances are, as it were, confined to their sources, that is, they 
are liberated at the slowest rate ; but as the barometer falls the pres- 
sure is taken off, and the miasmatic emanations rise much more 
freely (301). 

280. Of what the Air is composed. — ^Now we can study all about at- 
mospheric pressure, and many other things concerning the air, without 
ever asking what it is made of; but before we can know why it 
is that animals breathe, we must understand its chemical properties. 
We have referred to the constituents of air in connection with the 
subject of combustion (74) ; we are now to examine its composition 



and endo-wments more fully in relation to life. The atmosphere con- 
sists of four substances, — a pair of elements^ nitrogen and oxygen, 
and a pair of compounds^ carbonic acid gas and vapor of water. Dry 
air contains by weight very nearly 77 per cent, of nitrogen to 23 of 
oxygen. The proportion of moisture in the atmosphere varies with 
the temperature ; when saturated at 60°, it contains about 1 per cent., 
and it has an average of about l-2000th of carbonic acid. These pro- 
portions are thrown into visible form by the diagram (Tig. 68). In 
addition to these definite and stable elements, of which the atmosphere 
ia universally composed, various gaseous exhalations from the earth 

Nitrogen, or the diluUng constituent 
of the Air. 

Oxygen, or the active constituent of 
the Air, 

Moisture, or the variable constituent 
of the Air. 

Carbonic Acid, or the poisonous con- 
stituent of the Air. 

The areas of blackened surface represent the rela- 
tive proportions by weight of the constituents of 
the Air. 

constantly enter it, though so minutely as generally to elude detection 
and identification. LiEBia has shown that a trace of ammonia is 
always present in it (299). 

281. Intermktnre, or diffasioa of Gases. — These gases have different 
weights. The oxygen is slightly heavier than the nitrogen ; the watery 
vapor is much lighter than either, and the carbonic acid about half as 
heavy again as the air itself It might seem, then, that if they were 
mingled together they would gradually separate and arrange them- 
selves in distinct layers, the heaviest at the bottom and the lighter 
above. Some works on ventilation have actually stated such to be 
the case, and that when we breathe out vapor of water and carbonic 
acid, the former rises while the latter descends. One of them re- 
Tiarks : "were these different portions of air as they come from the 


lungs, of different colors, we should, in a perfectly still atmosphere, 
see the stream divided, part of it falling and part ascending." This, 
of course, is not true. If such were the fact, if gases tended to 
arrange themselves in the order of their gravities, and there were no 
universal and inflexible law to prevent it, the carbonic acid of the air 
might slowly sink to the earth, and form a deadly stratum 10 or 15 
feet deep over its entire surface, or fill up aU its valleys with treacherous 
invisible lakes of aerial poison. But such is not the tendency of 
things. Gases brought together, no matter what their different 
weights or varying proportions, diffuse throughout each other so as 
to become perfectly and equally commingled. Heavy gases wiU rise 
up to mix with lighter ones, and lighter gases descend to mingle with 
those that are heavier. As a consequence of this important law, the 
proportions of the atmospheric gases to each other are kept extremely 
miiform, being scarcely, if at aU, influenced by season, climate, wind, 
weather, or even the salubrity of the air. How benign and admirable 
is this provision of nature, by which, without being aware of it, we 
are relieved at every instant of a deadly though invisible poison, the 
process continuing as well during sleep as while awake, and taking 
place as perfectly for the unconscious babe as for the matured man. 
This great law secures the unity of the atmosphere. Its ingredients 
are perfectly mingled and equally diffused throughout each other, but 
not chemically combined, so that in breathing, although we separate 
the constituents of the air, we do not have to chemically decompose 
it. When we speak of air we mean the mass of commingled gases 
acting together ; yet as each constituent preserves its identity, and 
produces its peculiar effects, it is necessary to consider them 



282. This gas seems to take no active part in breathing; it 
passes out of the body as it entered it, without being changed. A 
fire cannot be kindled in it, and an animal breathing it quickly dies, 
though not from any positive noxious effect which it produces, but 
rather from want of something else. Nitrogen is a negative or inert 
substance, its chief use being to dilute or temper the other active in- 
gredients of the air to a proper degree of strength. 

2. OXTGEN-. 

283. How the System Is ebarged with Oxygen. — Of the wonderful in- 



Fig. 69. 

fluence of this agent we can here speak bnt briefly, as the subject will 
have to be considered again more fully in treating of the action of 
foods. "We have noticed that oxygen is the active agent in combus- 
tion, so it is also in breathing. It is on account of what it does in our 
system that we respire the atmosphere. The air enters the lungs 
through the windpipe and bronchial tubes or air passages, as seen in 
Fig. 69. It fills and distends the numberless little cavities or air-cells, 
which are enclosed by these membranes, and overspread with the finest 
network of capillary blood-vessels. Oxygen then penetrates or passes 
through the delicate membrane and enters the blood, imparting to 
it a bright crimson color, and rushing forward with it through what 
is called the pulmonary vein (Fig. 70) to the heart. It is estimated that 
the lungs contain, on an average, 220 cubic inches of air, with an 
inner membrane surface of 440 
square feet, nearly thirty times 
greater than the whole exterior of 
the body.* This vast extension of 
surface is to secure the largest and 
most perfect opportunity of action 
and reaction between the air and 
blood. From the heart the blood 
passes by the arteries to aU portions 
of the body. These arteries divide 
and subdivide until they are reduced 
in size to the finest hairlike tubes, 
which are densely interlaced through- 
out all the tissues of the body. 
The arterial channels thus represent 
streams of oxygen flowing from the 
lung fountains to every portion of 
the system. In this way each mi- 
nute part of the living fabric is in 
direct communication with the ex- 
ternal air, that it may receive from 
it the agent upon which it imme- 
diately depends for the performance 
of its vital offices. This system of 

arterial currents, bearing oxygen /rom the air to every portion of the 
system, implies a set of counter-currents to drain off the poisons gen- 
erated within the body, back into the air. This is the duty of the veins 
OP venous system. In the accompanying diagram (Fig. 70), the fine 

* Dr. Addison estimates the number of air-cells in the two Inngs at 1,744,000,000, 
«nd the extent of the membrane at 1,500 square feet. 


Human Lung. 
a the larynx; 6 wirxipipe ; e c o bron- 
chial tubes or air passages ; e lung. 



vessels at the top represent the lungs, and those at the bottom the 
capillaries of the whole body. The double circulation is shown, and 
how the heart is related to it. The vessels on the right side represent 
the arteries carrying blood charged with oxygen, and those on the left 
side, the veins, conveying carbonic acid. 

Fig. 70. 
Lesser or Pulmonary Circulation. 


Eight Auricle. 

Eight Ventricle. 

Vena Cava. 


Left Auricle. 

Left Ventricle. 

- Aorta. 

Greater or Systemic Circulation. 

284. What Oxygen does In the hody. — The purpose of this incessant 
inflowing stream of oxygen, is to carry forward the great operations 
of the vital economy. Oxygen has a wide range of chemical attrac- 
tions, and combines with other elements with intense energy. It is 
the ever-laboring, tireless Hercules of the atmosphere. As it kin- 
dles and maintains the combustion of our fires, so it does our bodily 
vitality. The muscles are called into action through decomposition 
by oxygen, and as with the muscles in the manifestation of mechani- 
cal force, so with the brain in the exercise of intellectual power. This 


organ is on an average only about ^ the -weiglit of the whole body, 
yet it receives from jth to -j^th of the entire oxygenated stream from 
the Imigs and heart. A torrent of oxygen is thus poured incessantly 
into the material apparatus of thought to carry forward certain physio- 
logical changes upon which thinking depends. If the arterial stream 
be cut off from a muscle, it is paralyzed ; if it be stopped from the brain, 
unconsciousness occurs instantaneously. In proportion to the activity 
of muscle is its demand for the destructive agent ; in proportion also 
to the activity of the mind is the brainward flow of arterial blood. 

285. Eflfccts of varying the quantity of respired Oxygen. — If an animal 
be deprived of this gas, it dies at once. If man undertake to breathe 
a less proportion than that naturally contained in the air, the effect is 
a depression of all the powers of the constitution, physical and mental, 
to an extent corresponding with the deficiency. If the natural amoun"t 
be increased, there is augmented activity of all the bodily functions, 
the life-forces are exalted, and the vital operations are driven at a 
preternatural speed. If pure oxygen is respired, the over action and 
fever become so great that life ceases in a short time. Nitrous oxide 
(laughing gas) is a compound rich in oxygen, and when presented to 
the blood it absorbs a much larger proportion of it than of pure oxygen. 
Hence, when this gas is breathed, the blood drinks it up rapidly, and 
the system becomes so saturated with it as to produce the most remark- 
able effects. The muscular energy is so aroused that the inhaler is 
often impelled to extraordinary feats of exertion, and the intellectual 
powers are excited to a delirious activity. 


286. How mncli moistnre the Air contains. — The third constant ingre 
dient of the air is moisture, derived from evaporation upon the earth's 
surface. The quantity which the air wiU hold depends upon its tem- 
perature, and hence fluctuates greatly. At zero a cubic foot of aii 
will hold but •18 of a grain of watery vapor ; at 32° it wiU contain 2'35 
grs.; at 40°, 3-06; at 50°, 4-24; at 60°, 5-82; at 70°, 7*94; at 80°, 
10-78; at 90°, 14-38; at 100°, 19'12 grains, and as the temperature 
goes higher still, the capacity for moisture also increases (308). After 
the air has imbibed its due quantity of vapor, at a given temperature, 
it is then said to be saturated, and wiU receive no more unless the heat 
be increased. To better appreciate how rapidly the capacity for moist- 
ure augments, as the temperature ascends, we will state the propor- 
tions in another form. A quantity of air absolutely saturated at 32°, 


holds in solution an amount of vapor equal to the ^fo part of its 
weight; at 59°, ^V; at 86°, ^\; at 113°, ^V; and at 140°, ~,\. 

287. Conditions of the drying power of the Air. — If, when the air is 
saturated, its temperature falls, a portion of its moisture is precipitated, 
that is, it does not remain dissolved, but appears in drops of dew. 
Thus a cubic foot of air, saturated at 90°, if cooled 10° would deposit 
3 -5 grains of water. Until it is saturated, air is constantly absorbing 
moisture from all sources whence it can procure it. A cubic foot 
of air at 90°, and containing but 8 grains of moisture, is capable of 
absorbing 6*3 more, and this is the measure of its drying power. 
Watery vapor is lighter than the air, and when mingled with it in- 
creases its levity in a degree proportional to its temperature. This is 
one of the causes of the ascent of breath expired by the lungs, at the 
temperature of the body. In drying-rooms and laundries, if the open- 
ings for the escape of hot air be at the bottom, as the air gets saturated 
with vapor it becomes lighter, and rising, fills the room and stops 
the evaporation. If the opening be at top the loaded air rises and 
escapes, and the drying wiU be observed to commence at the bottom. 

288. Moisture lathe Air of Rooms— Dew-point. — It has been explained 
that the temperature at which air is saturated, and begins to condense 
its moisture in drops, is called the dew-point (34). "When air contains 
so much moisture that its temperature needs to decline but little be- 
fore water appears, the dew-point is said to be high ; when it must 
lose much heat before drops are produced, its dew-point is low. Air, 
with a high dew-point, is therefore moist, while that with a low dew- 
point is always thirsty and drying. A simple means of finding out 
the dew-point, and ascertaining the drying power of the air, is as 
follows : — Note the temperature of the air by a thermometer, taking 
care that the instrument is not influenced by the radiation of any 
heated body in its vicinity. Then introduce it into a glass of water 
and gradually add a little ice, carefully watching for the first ap- 
pearance of moisture on the outside of the tumbler. The tempera- 
ture at which the deposit commences is the dew-point ; and the 
difference between it and the temperature of the air, expresses its 
drying power. If the air is at 60° and moisture begins to be con- 
densed at 40° its drying power is 20 degrees. Mason's hygrometer 
is a little instrument which indicates the dew-point without trouble. 
It has two thermometers, one of which gives the temperature of 
the air, and the bulb of the other, connected constantly with a 
reservoir of evaporating liquid, is kept cooled, and gives the dew- 
point ; so that the amount of humidity in the air is seen at a glance 


by comparing the two scales ; — cost, from 3 to 5 dollars. From obser- 
vations made at ■Washington through June, July, August, and Sep- 
tember, from 9 to 3 o'clock of the day, the dew-point was, on an 
average, 11° below the temperature of the air, and sometimes more 
than 20° below. The air is always dampest near the ground; a 
difference in height of 60 feet, in the same exposure, has been known 
to make a difference of 10^ degrees in the dew-point. In our houses, 
we are to imitate as far as possible the external conditions of the air. 
As the temperature of freshly drawn well water is about 50°, a vessel 
containing it should receive a deposit of moisture when brought into 
our rooms, if they have a temperature above 65°. It is very rare that 
any such deposit is seen in apartments heated by a hot-air furnace, 
even if a considerable quantity of water is evaporated. 

289. How doable Windows affect the moistnre of Eooms. — Glass sky- 
lights often drip moisture upon those below, and we see it copiously 
condensed in winter upon the windows and trickling down the panes. 
This is often mistaken for a symptom of abundant humidity in the air, 
but it may occur when the air is extremely dry. "When, as often 
occurs, air within a room is at 70° or 80°, while just outside the 
window-glass it is down to freezing, or below ; the inner layer of au* 
next the glass will rapidly deposit its water, and then falling to the 
floor will be succeeded by other air (337), so that the window acts as 
a perpetual drain upon the moisture of the apartment. It is often 
impossible to maintain the air properly humid on this account. Peo- 
ple are misled by this copious deposit of dew upon the glass, and it is 
hard to convince them that the air is deficient in moisture when they 
can see it condensed upon the windows. We have referred to double 
windows as a means of saving h^eat, and we might have added that 
they are equally serviceable in summer to exclude its excess of heat ; 
the enclosed air acting just as well to bar out the heat of the warm 
season, as to confine it within, in cold weather.* But double win- 
dows also prevent the deposit and loss of moisture from the air in 
rooms, and in this respect they are most useful. Glass is not essential 
to their construction, where we require only a diffused light ; white 
cotton cloth stretched upon a suitable frame and rendered impervious 
to air by linseed oil or other preparation, will answer equally as well 
for preserving heat, and be much less expensive. 

290. Rate of Eraporation. — ^When dry air is exposed to a source of 
moisture, a considerable time must elapse before it will become satu- 

* If double windows are to be retained in summer, tbey cannot be used for airways, 
lis single windows are made to do; there must be independent means of ventilation. 


rated. The diffusion of vapor into hot air is much more rapid than 
into that which is lolder, but it is not at all instantaneous. Mr. 
Daniell observed, that a few cubic inches of dry air, continued to 
expand by the absorption of humidity for an hour or two, when ex- 
posed to water at the temperature of the surrounding air. In cold 
regions there is much less moisture in the air than in hot, and less 
in winter than in summer. It is also subject to a regular diurnal 
variation. As the sun warms the air during the day, evaporation is 
increased, and the humid element rises into the atmosphere ; but as it 
declines toward evening, cooling begins, and at night the watery vapor 
again falls, and is deposited upon the earth. "We are not to infer that 
because there is an absence of rain, therefore the air is dry ; on the 
contrary, in long droughts the air is often heavily charged with mois- 

291. How moist Air aflfects the System. — The skin relieves the System 
of moisture in two ways ; by insensible perspiration, and by sweating. 
Under common circumstances, the loss is six times greater by the 
former than by the latter process. The skin, as well as the lungs, is 
an excreting organ ; it contains, packed away, some 28 miles of micro- 
scopic tubing, arranged to drain the system of its noxious matters, 
carbonic acid, &c., which, if retained in the body, become quickly in- 
jurious. The perspiration given off in this climate amounts to 20 oz. per 
day, and in hot countries to twice that quantity. But air which is al- 
ready saturated with moisture refuses to receive the perspiration which 
is offered to it from the skin and lungs ; the sewerage of the system 
is dammed up. Much of the oppression and languor that even the 
robust sometimes feel in close and sultry days, is due to the obstruc- 
tion of the insensible perspiration by an atmosphere surcharged with 
humidity. Not only are waste matters generated in the system thus 
unduly retained, but malarious poisons introduced through the lungs 
by respiration, are prevented from escaping ; which would lead us to 
anticipate a greater prevalence of epidemic diseases in damp than in 
dry districts. Sucli is the fact, as we notice in Cholera, which follows 
the banks of rivers, and revels in damp, low situations. Moisture 
joined with warmth is most baneful to the system. The American 
Medical Association report that during the remarkable prevalence of 
Sun-stroke in the city of Few York in the summer of 1853, which al- 
most amounted to an epidemic, the heat of the atmosphere was ac- 
companied by great humidity, the dew-point reaching the extraordi- 
nary height of 84°. In Buffalo, in the summer of 1854, the progress 
of cholera to its height was accompanied by a steady increase in at- 


mospheric humidity. Air whicli is warm and moist, has a relaxing and 
weakening influence upon the body. The siroco is invariably charged 
with moisture, and its effects upon the animal economy illustrate but 
in an exaggerated degree the influence of damp warm weather. When 
it blows with any strength, the dew-point is seldom more than four or 
five degrees below the temperature of the air. The higher its tempera- 
ture, the more distressing its effects, owing to the little evaporation it 
produces. This, connected with its humidity, is the principal cause of 
all its pecuUarities — of the oppressive heat — of the perspiration with 
which the body is bathed — of its relaxing and debilitating effects on 
the system, and its lowering and dispiriting effects upon the mind. 
— Wtma]!?. Damp air at the same temperature as dry air has a more 
powerful cooling effect, producing a peculiar penetrating chilling feel- 
ing, with paleness and shivering, painfully known to New England 
invalids as accompanying the east winds of spring. 

292. Effects of dry Air. — Dry air favors evaporation. By promoting 
rapid transpiration from the pores of the skin, it braces the bodily 
energies and induces exhilaration of the spirits. Cold dry air is 
invigorating and reddens the skin, with none of the distressing symp- 
toms of cold moist air. If very dry, it not only accelerates perspira- 
tion, but desiccates and parches the surface, and deprives the lining 
membrane of the throat and mouth of its moisture so rapidly as to pro- 
duce an uncomfortable dryness, or even inflammation. Dry climates 
which quicken evaporation, are best adapted for relaxed and languid 
constitutions with profuse secretion, as those afiQicted with humid 
asthma, and chronic catarrh with copious expectoration. The Ha/r- 
mattan, a dry wind from the scorching sands of Africa, withers, 
shrivels, and warps every thing in its course. The eyes, lips, and 
palate become dry and painful. Yet it seems to neutralize certain 
conditions of disease. "Its first breath cures intermittent fevers. 
Epidemic fevers disappear at its coming, and smaU-pox infection 
becomes incommunicable." 

4. Oaebonio Aoid. 

293. Physiological effects of Carltonic Acid. — The fourth constant in- 
gredient of the atmosphere is carbonic acid ; a transparent, tasteless, 
inodorous gas. It takes no useful part in respiration, indeed it exists 
in the air in so small a proportion that its effects upon the system are 
inappreciable. Its sources are the combustion of burning bodies, fer- 
mentation and decay, the respiration of animals ; and it is also gener- 
ated within the earth, and poured into the air in vast quantities from 


volcanoes, springs, &c. It may be set free more rapidly than it will 
dissolve away into air ; it then accumulates, as sometimes in weUs, 
cellars, rooms, «&c. and becomes dangerous. "When breathed pure, it 
causes suffocation by spasmodically closing up the glottis of the throat. 
When mixed with air in small quantities, it is admitted to the lungs, 
and then acts as a rapid narcotic poison. The symptoms of poisoning 
by carbonic acid gas are throbbing headache, vdth a feeling of fulness 
and tightness across the temples, giddiness, palpitation of the heart, the 
ideas get confused and the memory falls. A buzzing noise in the ears 
is next experienced, vision is impaired, and there is strong tendency to 
sleep. The pulse falls, respiration is slow and labored, the skin cold 
and livid, and convulsions and delirium are followed by death. This 
gas has been often employed as a means of suicide. A Son of the 
eminent French chemist, Bertholet, under the influence of mental de- 
pression, retired to a small room, locked the door, closed up every 
crevice which might admit fresh air, carried wi'iting materials to a table 
on which he placed a seconds watch, and then seated himself before 
it, described his sensations, and was found dead upon the floor.* 

294. Effects ia small qnaatities. — The proportion of carbonic acid ne- 
cessary to produce a poisonous atmosphere is very small ; so much so 
that in attempts at suicide by burning charcoal in an open room, the 
people who entered it have found the air quite respirable, although the 
persons sought were in a state of deep insensibility {coma). From 5 
to 8 per cent, of carbonic acid in the au" renders it dangerous to 
breathe, 10 to 12 makes it speedily destructive to life. The natural 
quantity in the air is so small that it may be multiplied 20 times before 
it rises to 1 per cent. Air containing one per cent, of this gas is 
soporific, depressing, takes from the mind its cutting edge, tends to 
produce headache, and is most injurious. That proportion of carbonic 
acid which nature has placed in the atmosphere, we assume to be 

* " I light my farnace, aBil place my candle and lamp on the table with, my watch. It 
is now 15 minutes past ten. The charcoal lights with difficulty. I have placed a funnel 
on each furnace to aid the action of the fire. 20 minutes past ten. The funnels fall : I 
replace them ; this does not go to my satisfaction. The pulse is calm, and beats as usual. 
10 h. 30. A thick vapor spreads itself by degrees in the chamber. My candle seems 
ready to go out. My lamp does better. A violent headache commences. My eyes are 
filled with tears ; I have a general uneasiness. 10 h. 40. My candle is extinguished, the 
lamp still burns. The temples beat as if the veins would burst. I am sleepy. I suffer 
horribly at the stomach ; the pulse beats 40 per min. 10. 50. I am suffocated. Strange 
ideas present themselves to my mind. I can hardly breathe. I shall not live long. I 
have symptoms of madness. lOh. 60. [Here, he confounds the hours with the minutes.] 
I can hardly write ; my vision is disturbed ; my lamp flickers ; I did not believe we suf- 
fered 60 much in dying. 10 h. 62 m. [Hero were some illegible characters]." 


entirely inoffensive, but the more it is increased beyond that amount, 
the less it is fitted for respiration. Precisely so with the body. Car- 
bonic acid is continually generated within it and continually poured 
out from the lungs into the air ; a certain amount in the blood is com- 
patible with health, but if that quantity be slightly increased, it at 
once begins to act as a poison. Any cause, therefore, which hinders 
the escape of this gas from the lungs, tends to accumulate it in the 
blood and produce injury, and this is exactly the effect, if there be 
considerable carbonic acid in the air we breathe. Its exhalation from 
the lungs is retarded if the outer air already contains more than its 
usual amount of carbonic acid. 

295. Why then does the Air contain Carbonic Acid? — But if this gas be 
useless, or positively detrimental in animal respiration, why is it made 
a constant and essential ingredient of the atmosphere ? The plan of 
nature requires it. As it is formed in all animal bodies, and breathed 
out into the air, and also by all combustions, its presence there is un- 
avoidable, while it is the great source of nom'ishment to the whole 
vegetable world, which drinks it in through innumerable pores in every 
green leaf, and thus keeps the proportion down to the point of safety 
for animals. 

296. Effect of these Ingredients combined. — Such are the constant con- 
stituents of the air, and such, so far as it has been possible to determine 
it, is their separate influence upon man. The effects of the atmosphere 
we breathe are the resultant of these agents acting together. "We see 
that it exerts an all-controlling influence upon the human constitution. 
To say that it is useful or important, gives us no adequate conception 
of the facts ; it is the first condition of vital activity — what the stream 
is to the water-wheel or fire to the steam-engine — ^the immediate im- 
pelling power of life. Any one of its elements breathed alone would 
be fatal ; any other proportions than those in which they are com- 
mingled would be dangerous or deadly. Its elements taken alone are 
poisonous and excoriating, but properly mingled and neutralized, how 
bland, how balmy, how innocent they become. Pressing upon us with 
the weight of tons, bathing the sensitive breathing passages — distend- 
ing the filmy membranes of the air cells, flashing through into the 
blood and swept forwai'd to the inmost depths of the system, corroding 
and consuming in its progress the living parts — and yet with such 
marvellous delicacy are aU these things accomplished, that we remain 
profoundly unconscious of them. Unspeakable indeed are these har- 
monies of life and being, and how adorable the Power, Wisdom and 
Love from which they emanate. 

164 effects of the constituents of air. 

5. Ozone and Eleoteioitt. 

297. Ozone in the Air. — Our view of the properties of the atmo- 
sphere would be incomplete without reference to these agencies. At- 
tention has latterly been drawn to the interesting and significant fact 
that the chemical elements are capable of existing in different states, 
with widely different pi-operties and powers. We see this in the case of 
carbon, which assumes several states, as charcoal, lampblack, diamond. 
Sulphur, phosphorus, and indeed many of the other elements are found 
capable of this change of state, wiich is -known as allotropism. It has 
been discovered also that the remarkable element oxygenhas its double 
condition, its ordinary state and another of extreme activity, in which 
it seems to acquire new energies ; in this heightened form of action it 
is called ozone. It may be readily changed from the common to the 
superactive state, acquiring bleaching and oxidizing energies which it 
had not before. Ozone is extensively formed in the atmosphere, by the 
operations of nature, although under precisely what circumstances we do 
not know. It is found more abundantly in some locahties than in 
others, and may be generally recognized in air which has swept over 
the ocean, although usually absent in that which has traversed large 
tracts of land. There has been much speculation as to how the air is 
affected by its presence, in relation to health and disease. It is said 
that when present in excess diseases of the lungs, especially influenza, 
prevail ; when deficient, fevers and all those diseases which are sup- 
posed to depend upon a kind of fermentation in the blood are com- 
mon, — it being thought that ozone oxidizes or burns away the exciting 
fermentable matter, thus acting as a purifying agent. It has been 
stated that in cholera ozone is entirely absent from the air. 

298. Atmospheric Electricity. — "I cannot tell," says Dr. Faraday, 
" whether there are two fluids of electricity, or any fluid at all ;" such 
is our profound uncertainty in relation to this mysterious agent. Yet 
it is commonly assumed to be a subtle fluid, distributed through all 
substances, and lying buried beneath their surfaces in a condition of 
equilibrium, or rest. Various causes may disturb this state, producing 
electrical excitement^ when the fluid is supposed to accumulate in 
some substances to excess, which are then said to be positively electri- 
fied, — while in others it is deficient, and these are negatively electrified. 
Some substances, as the metals, allow electricity to pass through them 
freely ; these are called good conductors; others refuse it a ready passage, 
and are termed non-conductors^ as silk, glass, air. "When from any cause 
excitement has taken place, and a body has been charged with electri- 


city, or robbed of it to a certain degree, there is an escape ; if a good 
conductor be presented to it, it flows off quietly ; if a bad conductor, it 
dashes through it, producing fire, light sound, and perhaps violent 
rupture {disruptive discharge). The friction of unlike bodies against 
each other creates electrical excitement. If we slide rapidly over a 
carpet, the body becomes so excited that it may yield a spark which 
will light the gas. The friction of masses of air, of different temper- 
atures, or containing different degrees of moisture, by rubbing against 
each other, or grinding against the earth, developes electricity. So, 
also, does evaporation. If a saucer of water be suspended by non- 
conducting silk cords (insulated)^ evaporation goes on as usual at first, 
but is soon checked. It gives off positively electric vapor, while the 
saucer remains negatively electrified. If it be connected with the 
ground by a conductor, active evaporation is resumed. Combustion 
produces electricity ; the escaping carbonic acid being positive, while 
the burning body is negative ; the vapor of the expired breath is also 
positive. The air is generally electrified positively, especially in clear 
■weather ; but during the fall of rain, fogs, snow, and storms, it may be 
negative. The electricity of the atmosphere appears to have a daily 
ebb and fiow, like the tides of the sea, twice in every 24 hours. It is 
feeble at sunrise, increases in intensity during the forenoon, declines 
again in the afternoon, until about two hours before sunset ; it then 
advances until perhaps two hours after sunset, and again diminishes 
until morning. It has become fashionable, latterly, to offer electricity 
in explanation of all obscurities, material and spiritual. Beyond doubt 
it is profoundly involved in the phenomena of our being, but we as 
yet understand but httle about it. In connection with the air, we can 
only say, that when it is clear, and electricity is rapidly developed, the 
spirits are more buoyant, and the feelings more agreeable, than when 
the atmosphere is in the opposite state. 


299. Impurities of the external Air.— There are natural causes which 
tend to make the atmosphere impure, but they act with variable in- 
tensity in different localities. Animal respiration and combustion exert 
a contaminating influence upon the atmosphere, but considering its 
vast mass, the general effect is but trifling, and besides is perfectly 
neutralized by growing vegetation, which evermore absorbs from the 
air carbonic acid, and returns to it pure oxygen in the daytime. The 
decay of organic matter, vegetable and animal, generates numer- 


ous substances which are prejudicial to health. Liebig has lately 
shown that ammonia from these sources is continually present in 
the air. Its quantity is so minute that it cannot be directly de- 
tected, but it may be traced in rainwater, having been washed 
out of the air in its descent (371). The exhalations and eflBuvia 
arising from active decomposition in wet lands, swamps, marshes, 
&c., especially in hot seasons and locahties, are prolific sources 
of disease. Minute microscopic germs, both vegetable and animal, 
exist in the atmosphere, and the course of winds has been tracked 
across oceans by the peculiar organic dust which they carried. 
Not only do plants and flowers exhale continually their peculiar fra- 
grances, but even mineral matters and earths have also their odors, which 
rise and mingle with the air. Indeed, we must conceive of the air as 
the grand reservoir into which all volatile matters escape. Professor 
Gbaham contends that malarious and contagious bodies are not strictly 
gaseous, but are highly organized particles of fixed or sohd matter, 
which find their way into the atmosphere, like the pollen of flowers, 
and remahi for a time suspended in it. The inconceivable minuteness 
of exhalations difiiised through the air, which are yet sufficiently 
active to impress the senses, is forcibly illustrated by the foIlo"\ving 
fact, which we give on the authority of Dr. Oaepentee. " A grain 
of musk has been kept freely exposed to the air of a room, of which 
the doors and wiadows were constantly open for a period of ten years, 
during all which time the air, though constantly changed, was com- 
pletely impregnated with the odor of musk ; and yet, at the end of 
that time, the particle was found not to have sensibly dimhiished in 

300. Effects of Exposnre, Foliage, aad Soil. — The salubrity of the ex- 
ternal air is influenced by elevation, trees, and soU. The exposed hUl- 
top ensures atmospheric purity. It is often surprising what effect 
a small difference in the elevation has upon the healthfulness of a par- 
ticular spot. A rise of 16 feet within 300 yards has been known to 
produce an entire change from a relaxing to a bracing air. The lower 
place was completely enveloped in foliage and without drainage, while 
the higher was comparatively free from trees, and besides, had a good 
fall for surface-water and sewerage. Dense foliage around a dwelling 
may be injurious, by causing dampness and stagnation of air, especially 
if the situation be protected from winds. If the ground be loaded 
Avith putrefy' ng matter and soaked with refuse water, the air above it 
cannot be pure. The ground below and around the dwelling should 
be dry. A soil absorbent and retentive of moisture, always damp, is 


unfit to live on nnless thorougHy drained. Sand or gravelly ground 
is best, provided it be not locked in by a surrounding clay basin, with 
no outlet for the rainfall. 

301. Cause of the unwholcsomeness of Night Air. — There is ground for 
the common belief that night air is less healthful than that of the day. 
It is known that the deadly tropical fevers affect persons almost only 
during the night. Yet the poisonous miasms from the rotting substan- 
ces of the ground vrhich cause those fevers, is produced much faster 
during the intense heat of the day than in the colder night. But in 
the daytime, under the hot tropical sun, the air heated by contact 
with the burning ground expands and rises in an upward current, thus 
dUuting and carrying away the poisonous malaria as fast as it is set 
free. The invisible seeds of peStUence, as they ripen in the festering 
earth, are lifted and dispersed in the daytime by solar heat ; but as no 
such force is at work at night, they then accumulate and condense in 
the lower layer of the atmosphere. Now although fatal fever poison 
may not be generated, yet decomposition of vegetable matter yielding 
products which are detrimental to health take place every where upon 
the surface of the ground ; and though dissipated during the day, they 
are concentrated and confined so close to the earth at night as to affect 
the breathing stratum of the air. 

302. Upper Rooms least affected by Night Air. — It will hence be seen 
that the different stories of a house are differently related to this 
source of injury : the upper ones being situated above the xmwhole- 
some zone, are most eligible for sleeping chambers, while the ground- 
floor is more directly exposed to the danger. Dr. Kxjsh states, that 
during the prevalence of yeUow fever in Philadelphia, those who oc- 
cupied apartments in the third story were far less liable to attack than 
those who resided lower. Low one-story houses, in which the inhab- 
itants sleep but three or four feet from the ground, and are therefore 
directly exposed to the terrestrial exhalations, must be considered 
more objectionable than loftisr sleeping apartments. Sleeping in low 
rooms is perhaps worse in the city than in the country. 

303. The Atmosphere Self-purifying. — In aU healthy localities the pro- 
portion of impurities is so small that their effect is imperceptible. 
When noxious exhalations are set free from any source, they are dif- 
fused through the vast volume of the atmosphere, so as not to be 
detectable by the most refined means of chemistry. The law of 
gaseous diffusion, aided by winds and storms, secures dispersion and 
universal intermixture. Oxygen finally takes effect upon these baneful 
emanations, destroying and burning them as truly as if they had been 


consumed in a furnace. The atmosphere thus secures its own puri- 
fication on the grandest scale, and its vital relation to animal life re- 
mains undisturbed. 

304. Air within Doors. — But when we enter a dwelling the case is 
altered. It is as if the boundless atmosphere had ceased to exist, or 
had been contracted within the walls of the apartment we occupy. 
Causes of impurity now become a matter of serious consideration. 
They are capable of affecting, in the most injurious manner, the little 
stock of air in which we are confined ; and it is therefore, on every 
account, important that we have a clear idea of the nature and extent 
of the common causes which vitiate the air of our dwellings. 


305. Breathing and Gomhastion. — By breathing, the burning of fuel 
and combustion for light, large quantities of oxygen are removed from 
the air, while at the same time carbonic acid in nearly equal bulk 
takes its place. In the case of fuel, if the combustion is perfect, the 
air that has been changed is immediately removed up chimney by the 
draught. But not so in respiration and illumination ; the air spoiled 
by these processes remains in the room, unless removed by special 
ventilating arrangements. 

306. Leakage of bad Gases from Heating Apparatus. — While, in point 
of economy, stoves are most advantageous sources of heat, yet in their 
effects upon the air they are perhaps the worst. We saw that in the 
stoves called air-tight^ the burning is carried on in such a way that 
peculiar gaseous products are generated (121). These are liable to 
leak through the crevices and joinings into the room. Carbonic oxide 
gas is formed under these circumstances, and recent experiments have 
shown that it is a much more deadly poison than carbonic acid. The 
slow, half-smothered burning of these stoves requires a feeble draught, 
which does not favor the rapid removal of injurious fumes. Besides, 
carbonic acid being about half as heavy again as common au', must be 
heated 250° above the surrounding medium to become equally light, 
and still higher before it will ascend the pipe or fine. If the com- 
bustion of the fuel is not vivid, and the draught brisk, there will be 
regurgitation of this gaseous poison into the apartment. Dr. Uee 
says, " I have recently performed some careful experiments upon this 
subject, and find that when the fuel is burning so slowly as not to heat 
the iron surface above 250° or 300°, there is a constant deflux of car- 
Ionic acid into the room.'''' Probably all stoves, from their imperfect 


fittings, are liable to this bad result. Hot-air farnaces, also, have the 
same defect. They are cast in many pieces, and however perfect the 
joinings may be at first, they cannot long be kept air-tight, m conse- 
quence of the unequal contraction and expansion of the different parts 
under great alterations of heat. Combustion products are hence 
liable to mingle with the stream of air sent into the room, 

307. Air aflFected by Hot-irou Surfaces. — But if stoves become a source 
of contamination to the air at low temperatures, neither are they free 
from this objection when made hotter ; at high heats (and they are 
often red-hot), they seriously injure it in other ways. It is well known 
that iron highly heated causes disagreeable effects upon the air of 
rooms, producing a sensation ascribed to hurnt air^ but the nature of this 
change is not fully understood. The common method of explaining it, 
that the iron decomposes the air and robs it of oxygen, is in no degree 
satisfactory, as the quantity of oxygen thus removed must be extremely 
small, and besides, a portion of this very small amount comes from 
the decomposition of atmospheric moisture, its hydrogen being set 
free. The minute particles of dust, myriads of which fill the air, as 
seen when a ray of light is admitted into a darkened room, and which 
consist of aU kinds of vegetable and animal matters, settle upon the 
hot stove, and are roasted or burnt with the escape of gaseous impu- 
rities. In the stove metal itself there is always, beside the cast-iron, 
more or less carbon, sulphur, phosphorus and arsenic, and it is possible 
that the smell of air, passed over it in the red-hot state, may be owing 
to the volatilization or escape of some of these ; because it is to be re- 
membered that a quantity of noxious efl3uvia, too small to be seized 
and measured by chemical means, may yet affect the sense of smell 
and the pulmonary organs. 

308. Composition of Air altered by Iieating it. — It is a capital advan- 
tage of the methods of warming by fireplaces and grates — simple ra- 
diation — that they do not heat the air : it remains cool while the 
heat rays dart through it to warm any objects upon which they fall. 
The sun pours his floods of heat through the atmosphere without 
warming it a particle. Air is made to be hreathed^ and we again dis- 
cover Providential Wisdom in the arrangement by which the sun 
warms us, without disturbing, in the slightest degree, the respiratory 
medium. But if we heat the air itself^ we at once destroy the natural 
equilibrium of its composition, and so change its properties that it be- 
comes more or less unpleasant and prejudicial to health. "We have 
noticed the bad effects upon the system of dry heated air, and it was 
shown that the state of dryness does not depend upon the actual 





1 , flO , 2l0 , 3|0 , 4 


1 6 


810 1 910 1 10 

00° ^ 
60° i 

82° g 


1 1 1 1 1 



















The length of the bars indicates the relative propor- 
tions of moisture that a cubic foot of air will hold at 
the different temperatures. 

amount of moisture present, but upon the temperature. Witli the 
same quantity of aque- 
ous vapor^ it will be 
moist and humid at a 
low temperature, while 100 
at a high one it will be 
parched and greedy of 
water. The accompa- 
nying diagram (Fig. 71) 
exhibits the relative 
amount of moisture that 
air contains when satur- 
ated at the temperatures 
mentioned. Suppose that air at 32° be heated to 100° (and it often is 
much higher), and be then thrown into the room. The difference in 
the length of the bars opposite these two numbers expresses its de- 
ficiency of moisture, and hence its drying and parching power. Air 
thus changed is apt to produce unpleasant feelings and painful sensa- 
tions iu the chest, which are often attributed to too great heat. " In 
very dry air the insensible perspiration will be increased, and as it is 
a true evaporation it will generate cold proportional to its amount 
(69). Those parts of the body which are most msulated ia the air, 
and furthest from the heart, will feel this refrigerating influence most 
powerfully ; hence that coldness of the hands and feet so often expe- 
rienced. The brain being screened by the skuU from this evaporating 
influence, will remain relatively hot, and wiU get surcharged besides 
with the fluids which are expelled from the extremities, by the con- 
traction of the blood-vessels caused by cold." In close rooms, not 
well ventilated, stoves exert this baneful influence upon the air in an 
eminent degree. This objection lies against Jieated air, no matter how 
heated. Stoves and air-furnaces, with their red-hot surfaces, are un- 
doubtedly worse for the air than hot-water apparatus, which never 
Bcorch it ; yet they, too, may pour into our apartments a withering 
blast of air at 150°, which may be potent for mischief. The only way 
that hot-air can be made healthful and desirable is by an effectual plan 
of artificial evaporation, which will be noticed among the means of 
preserving atmospheric purity (347). 

309. CotttaminatioE of Air from the Hnman Being. — It is a common 
belief that the human system is distinguished by its vital power of re- 
sisting, during life, the physical agents which would destroy it ; but 
that after death it is abandoned to these forces, and falls quickly into 


putrefaction. This is an error. Under the influence of physica] 
agency decomposition is constantly going on throughout the body, and 
is indeed the fundamental condition of its life (624). There is the 
same decay and chemical decomposition taking place in the animal 
fabric during life as after death ; the difference being, that in the dead 
body the decomposing changes speedily spread throughout the mass, 
while in the living system they are limited and regulated, and pro- 
vision is made for the incessant and swift expulsion of those effete 
and poisonous products of change, which if retained within the organ- 
ism for but the shortest time, would destroy it. Streams of subtile 
and almost intangible putrescent matter are, all through life, exhaling 
from each living animal body into the air. The fluid thrown from the 
lungs and skin is not pure water. It not only holds in solution car- 
bonic acid, but it contains also animal matter^ the exact nature of 
which has not been determined. From recent inquiries, it appears to 
be an albuminous substance in a state of decomposition. If the fluid 
be kept in a closed vessel, and be exposed to an elevated temperature, 
a very evident putrid odor is exhaled by it. Leblano states that the 
odor of the air at the top of the ventilator of a crowded room, is of 
so obnoxious a character that it is dangerous to be exposed to it, even 
for a short time. If this air be passed through pure water, the water 
soon exhibits aU the phenomena of putrefactive fermentation. 

310. Dr. Faraday's Testimony apou this point. — " Air feels unpleasant 
in the breathing cavities including the mouth and nostrils, not merely 
from the absence of oxygen, the presence of carbonic acid, or the ele- 
vation of the temperature, tut from other causes depending on matters 
communicated to it from the human heing, I think an individual may 
find a decided difference in his feelings when making part of a large 
company, from what he does when one of a small number of persons, 
and yet the thermometer give the same indication. "When I am one 
of a large number of persons, I feel an oppressive sensation of closeness, 
notwithstanding the temperature may be about 60° or 65°, which I 
do not feel in a small company at the same temperature, and which I 
cannot refer altogether to the absorption of oxygen, or the inhalation 
of carbonic acid, and probably depends upon the effluvia from the many 
present ; but with me it is much diminished by a lowering of the tem- 
perature, and the sensations become m.ore like those occurring in a 
small company." 

311. Air of Bedrooms.— The escape of offensive matters from the liv- 
ing person becomes most obvious when from the pure air we enter an 
nnventilated bedroom in the morning, where one or two have slept 


the night before. Every one must have experienced the sickening and 
disgusting odor upon going into such a room, though its occupants 
themselves do not recognize it. The nose, although an organ of ex- 
quisite sensibility, and capable of perceiving the presence of offensive 
matters where the most delicate chemical tests faD, is nevertheless 
easily blunted, and what at the first impression feels pre-eminently dis- 
gusting, quickly becomes inoffensive. Two persons occupying a bed for 
eight hours, impart to the sheets by insensible perspiration, and to the 
air by breathing, a pound of watery vapor charged with latent animal 
poison. Where the air in other inhabited rooms is not often changed, 
the water of exhalation thus loaded with impurities, condenses upon 
the furniture, windows, and walls, dampening their surfaces and run- 
ning down in unwholesome streams. 

312. Pnrity the Intention of Nature. — Yet we are not to regard the 
human body as necessarily impure, or a focus of repulsive emanations. 
The infinite care of the Creator is seen nowhere more conspicuously 
than in the admirable provision made for the removal of waste matters 
from the system, the form in which they are expelled, and the prompt 
and certain means by which nature is ready to make them inoffensive 
and innq?ious. " The skin is not only," as Biohat eloquently observes, 
" a sensitive limit placed on the boundaries of man's soul, with which 
external forms constantly come in contact to establish the connections 
of his animal life, and thus bind his existence to all that surrounds 
him ; " it is at the same time throughout its whole extent densely 
crowded with pores, through which the waste substances of the system 
momentarily escape in an insensible and inoffensive form, to be at once 
dissolved and lost in the air if this result le alloxced. It is not by the 
natural and necessary working of the vital machinery that the air is 
poisoned, but by its artificial confinement and the accumulation of 
deleterious substances. If evil results, man alone is responsible. 

313. Other sources of Impurity. — Gaseous exhalations of every sort 
escape from the kitchen, and are diffused through the house as their 
odors attest, and the darkening of walls and wood-work painted with 
white lead shows that poisonous sulphuretted hydrogen from some 
source has been thrown into the air, its sulphur combining with the 
lead and forming black sulphuret of lead.* From the imperfect com- 
bustion of oil and tallow for lighting, and the defective burning of gas 
jets there arise emanations often most injurious to health. The vapor 
of a smoky lamp, if disengaged in small quantities, and the fumes of 
the burning snuff of a candle, may fill the room with disgusting odors 

♦ White zinc paint does not tlius turn black. 


and excite severe headache. It may be well here to correct the com- 
mon fallacy that cold air is therefore pure, and that apartments need 
less ventilation in winter than in summer. People confound coolness 
with freshness, and disagreeable warmth with chemical impurity; 
whereas these properties have necessarily nothing to do with each 
other. Cold air may be ii-respirable from contamination and warm air 
entirely pure. 

314. Poisonons Colors on Paper Hangings. — Attention has lately been 
called to the poisonous influence of green paper hangings upon the air. 
Cases are mentioned of children poisoned by chewing green colored 
hanging paper, and of persons sickened by breathing air in rooms in 
which certain green papers have been mounted. The basis of the bright 
green colors used for staining paper-hangings is the poisonous arsenite 
of copper^ a combination of arsenic and copper. This, however, is not 
volatile, and does not create poisonous fumes or vapors, unless perhaps 
by being dusted fine particles are loosened and set afloat in the air. 
Nevertheless, though it do not vaporize and get into our systems 
through the lungs, arsenite of copper is a deadly poison, and when 
spread over paper-hangings, utterly spoils them/br dietetical purposes, 
either for children or adults. Professor Johnson, of New Haven, states 
that the most beautiful of all green pigments is the aeeto-arsenite of 
copper^ and that this compound, in damp weather and humid situations, 
exhales deadly poisonous vapors supposed to contain arsenuretted 
hydrogen. This gentleman has given an account of a family poi- 
soned by sleeping in a room where the paper was colored with this 

815. Fonl Air generated in Cellars. — The air in our houses is also liable 
to contamination from various organic decompositions, if vigilant 
precaution is not taken to prevent it. Cellars are commonly con- 
verted into reservoirs of pernicious airs, by the reprehensible custom 
of using them as receptacles for the most perishable products. But 
even where large masses of organic matter are not left to undergo 
putrefactive decay, and generate unwholesome miasms, serious injury 
is liable to occur from the damp and stagnant air of basements and 
cellars. It is not necessary that the lower spaces of a house should 
be half filled with rotting garbage to generate foul air. The surface 
of the earth is filled with decomposable substances, and whenever air 
is confined in any spot in contact with the ground, or any changeable 
organic matter, it becomes saturated with various exhalations which 
are detrimental to health. If air is to be confined, unless it is so 
sealed up as to touch nothing but dry, glassy or mineral substances, 


it will certainly degenerate. Even dry rooms and closets in the upper 
part of tlie house, become mouldy and musty to a most disagreeable 
extent, if not often aired. To be pure and healthy, air requires con- 
tinual circulation; but cellars are very rarely either ventilated or 
made absolutely dry by water-proof walls or floors. They are usually 
damp, cold, uncleanly, and mouldy. " The noxious air generated in 
cellars, basements, and under-floor spaces, reaches the inhabitants of 
upper apartments in so small quantities, that instead of producing 
any marked and sudden process of disease, it operates rather as a 
steady tax upon their income of health ; so uniform in its depressing 
effects as not to be appreciated. Yet many an invalid, who fancies 
himself improved by a change of air, in going to another residence, 
is really relieved by escaping the mouldy atmosphere which comes 
from beneath his own ground-floor." * 


316. Sources of danger in Breathing — The constituent of the atmo- 
sphere are mingled in such perfect proportions, that its temper is ex- 
actly suited to the necessities of the healthy system ; any alteration 
in its composition, therefore, however slight, must result in physi- 
ological disturbance. So direct is the access that respiration aflDords 
to the inmost recesses of the body, that any gas mingled with the re- 
spired air, is at once admitted, and takes prompt control of the system. 
When aliment is taken into the stomach, it is submitted to a long 
process of preparation and sifting, before it can gain admission to the 
blood, those parts which are useless or obnoxious being rejected; 

* " The reports of the Eegistrar-Genera of England disclose to us some very startling 
facts in reference to the slow influences of different states of air in affecting length of 
life. If any one were to select from among all the different occupations the healthiest 
men of a nation, he would probably choose the farmers and the butchers. Both arc- 
usually stout in frame, and ruddy in complexion. Both are actively employed, have 
plenty of exercise and abundance of food. In one point, therefore, their circumstances 
widely differ. The farmer breathes the pure air of the country ; the butcher inhales the 
atmosphere of the shambles and the slaughter-house, tainted with putrefying animal 
effluvia. The result is an instructive lesson as to the value of pure air. The rate of deaths 
stated among the farmers, between the ages of 45 and 55, was 11'99 per thousand 
(annually). The butchers at the same age died at 231 per thousand, so that their mor- 
tality is about double that of the farmers. These two classes, indeed, occupy nearly the 
extremes of the table of mortality. The farmer is the healthiest man on the list, while 
there is but one worse off than the butcher — the innkeeper. Any one who knows how 
large a proportion of taverns are mere grogshops, reeking with impurities and environed 
in filth, will not be surprised that the mortality among this class ascends to 2S'84 in the 


but the Inngs exercise no sucli protective or selective power, they 
cannot guard the system by straining the air, or barring out its in- 
jurious gases. Besides, air both pure and impure is alike transparent 
and invisible, so that the eye cannot detect the difference. The 
causes of vitiation are also gradual and insidious in their action, 
so that their effects steal imperceptibly over the system. Unlike 
heat, deleterious air announces its presence by no sensation ; indeed, 
its effects are of that stupefying kind that makes a person insensible 
to them. A bedroom, as we before remarked, may be so foul from 
loathsome exhalations, as to nauseate a person who enters it from the 
pure air, and yet its inmates will feel quite unconscious of any thing 
disagreeable. Without intelligent and thoughtful precaution, there- 
fore, we are constantly liable to the evil effects of foul air, and to im- 
minent danger from various forms of disease. 

317. The System prepared to receive Contagion. — Eespiration of im- 
pure air, is a prolific source of disease, which appears in numerous 
forms and all degrees of malignity. The effect of breathing a con- 
fined and unrenewed atmosphere, is not only to taint the air, but by a 
double influence, to taint also the blood. It is an office of oxygen in 
the body, as we have seen, to throw the products of waste into a 
soluble state that they may be readily excreted, but if its quantity be 
diminished in the air, this work is imperfectly performed in the body ; 
and the vital current is encumbered with putrescent matter. The 
increase of carbonic acid in the air, by offering a barrier to exhalation 
from the lungs, conspires to the same result. Accumulation of these 
morbid products in the blood, greatly heightens its susceptibility of 
being acted upon by atmospheric malaria, the causes of epidemics. 
The blood is supposed, under these circumstances, to acquire a fer- 
mentable state, forming, as it were, a ready prepared soil for the seeds 
of infection. Atmospheric malaria seem not capable alone of producing 
epidemic disease. From those in real robust health, with perfect 
sanative surroundings, the arrows of contagion rebound harmless. 
The miasmatic poison mmt jindL some morbidity in the system to co- 
operate with, — some unhealthy condition induced by intemperence or 
debauchery, bad food or drink, bodily exhaustion, mental depression, 
or the discomforts of poverty — upon which it may take effect. But 
of all these predisposing agencies, none invite the stalking spectre of 
pestilence with so free and deadly a hospitality, as corrupt, con- 
taminated air. 

318. Blnstration in the case of Cholera. — Of the tendency of an at- 
mosphere charged with the emanations of the human body, to favor 


the spread of contagious disease, the illustrations that might be quoted 
are innumerable. Take an instance of cholera, for example. It is 
■well known to those who have had the largest opportunities of study- 
ing the conditions which predispose to this malady, that overcroioding 
is among the most potent. In the autumn of 1849, a sudden and 
violent outbreak of cholera occurred in the workhouse of the town 
of Taunton (England), no case of cholera having previously existed, 
and none subsequently presenting itself among the inhabitants of 
the town, though there was considerable diarrhoea. The building 
was badly constructed, and the ventilation deficient ; but this was 
especially the case with the school-rooms, there leing only about 68 
cubic feet of air for each girl, and even less for the boys. On Nov. 3d 
one of the inmates was attacked with the disease ; in ten minutes 
from the time of the seizure, the sufferer passed into a state of hope- 
less collapse. "Within the space of 48 hours, from the first attack, 42 
cases and 19 deaths took place; and in the course of one week, 60 
of the inmates, or nearly 22 per cent, of the entire number were 
carried off; whilst almost every one of the survivors suffered more 
or less, from cholera or diarrhoea. Among the fatal cases were those 
of 25 g iris and 9 boys, and the comparative immunity of the latter, not- 
withstanding the yet more limited dimensions of their school-room, 
affords a remarkable confirmation of the principle we are indicating, 
for we learn that " although good and otedient in other respects, the 
hoys could not ie Tcept from hreaMng the windoics,^'' so that many of 
them probably owed their lives to the better ventilation thus established. 
In the jail of the same town, in which every prisoner was allowed 
from 800 to 900 cubic feet of air, and this continually renewed by an 
effcient system of ventilation, there was not the slightest indication 
of the epidemic influence. (Dr. Oaepeisttee.) It is in confined spaces 
thus charged with putrescent bodily exhalations, that pestilence revels ; 
they resemble in fatality those localities where the air is poisoned 
by effluvia from foul drains, sewer-vents, slaughter-houses, and manure 

319. Fevers originate ia Impure Air. — As with cholera, so also with 
fevers ; foul air not only augments their malignity, but also calls them 
into existence. "Writers on pestilence, observes Dr. Geiscom, note two 
distinct species of virus applied to the body, through the medium of the 
air. First, that arising from the putrefaction of dead animal and vege- 
table matter — the accumulations of filth around dwellings and in cities, 
and the exhalations of swamps, grave-yards, and sewers, called marsh 
miasm. This is supposed to give rise to yeUow, remittent, bilious, 

rr PEODUCES fevees and sceofula. 177 

and intermittent fevers, dysentery, and perhaps also cholera. And 
second, exhalations from the human body, confined and accumulated 
in ill -ventilated habitations, sometimes termed typhoid miasm, and 
which usually gives origin to common typhus and low nervous fevers. 
It . would thus appear, that the very type and character of febrile 
disease is determined by the Hiid of impurity which is breathed. 
Prof. Smith, of New York, says, "Let us suppose the circumstances 
in which typhus originates, to occur in summer, such as the crowd- 
ing of individuals into small apartments badly ventilated, and ren- 
dered offensive by personal and domestic filth ; these causes would 
obviously produce typhus in its ordinary form. But, suppose there 
exist at the same time, those exhalations which occasion plague, and 
yellow fever, or remittent and intermittent fevers; tinder such cir- 
cumstances we would not expect to see any one of those diseases fully 
and distinctly formed, but a disease of a new and modified character. 
It is, therefore, beyond probability that a few deleterious gases are 
quite sufficient to produce an infinite variety of pestilential and con- 
tagious maladies." 

320. Scrofnla, or Struma, the consequence of Impure Air. — There is a 
diseased condition of body known as scrofulous or strumous, which 
manifests itself in various forms, and in all parts of the system. It 
seems to be a result of deficient nutrition ; that is, not a want of 
material for nutricious purposes, but a failure of power to produce 
healthy and perfect tissue from the elements of food. Various causes 
have been assigned as tending to produce scrofulous habits of body, 
such as hereditary tendency, bad diet, depressing passions, too late, 
too early, or in-and-in marriages, sedentaiy occupations, want of ex- 
ercise, deficient clothing, bad water, &c., and these, under different cir- 
cumstances, may each contribute to the result ; but imperfect respira- 
tion is probably the most efficient and universal cause. An eminent 
French Physician, * who has made this subject a matter of extensive 
study, says, "Invariably it will be found on examination, that a truly 
scrofulous disease is caused by a vitiated air, and it is not always neces- 
sary that there should have been a prolonged stay in such an atmosphere. 
Often a few hours each day is sufficient, and it is thus that persons may 
live in the most healthy country, pass the greater part of the day in 
the open air, and yet become scrofulous, because of sleeping in a 
confined place, where the air has not been renewed." The same ob- 
server goes further, and affirms that the repeated respiration of the 
same atmosphere, is a primary and efficient cause of scrofula, and 

* M. Baudoloqub. 


that, " if there be entirely pure air, there may be bad food, bad cloth- 
ing, and want of personal cleanliness, but that scrofulous disease can- 
not exist." In 1832, at Norwood School in England, where there 
were 600 pupils, scrofula broke out extensively among the children, 
and carried oflE" great numbers. This was ascribed to bad and inef- 
ficient food. Dr. Arnott was employed to investigate the matter, and 
immediately decided that the food "was most abundant and good," 
assigning " defective ventilation, and consequent atmospheric im- 
purity " as the true cause. 

321. Consnmptioa indaced by Impure Air. — When scrofula localizes 
itself in the lungs, there \s pulmonary or tubercular consumption. The 
essence of the nutritive process consists in the vital transformation of 
albumen (678) into fibrin and organized tissue. Now the tubercles 
which in this disease make their appearance in the pulmonary 
organs, consist of crude, coagulated, half organized masses of albumen 
— the abortive products of incomplete nutrition. In this manner, 
bad air, by producing the strumous condition, becomes a cause of con- 
sumption. It seems natural to expect that the organs with which 
the foreign gaseous ingredients of the atmosphere come more im- 
mediately into contact, and whose blood-vessels they must enter on 
their passage into the system, should feel, in a distinctive manner, 
their noxious influence ; and this expectation is strengthened by 
observation, and experiment upon both men and animals. It has 
been observed that when individuals habitually breathe impure air, 
and are exposed to the other debilitating causes which must always 
influence, more or less, the inhabitants of dark ill-ventilated dwellings, 
scrofula, and consumption, as one of its forms, are very apt to be 

322. State of the Air influences Infant Mortality. — The same malign in- 
fluence of the air of unventilated rooms is seen in the mortality of 
infants. That the new-born and tender child should be infinitely sus- 
ceptible to the influence of contaminated air is what we might well 
expect. We are, therefore, not surprised, that in the foul and stifling 
air of Iceland habitations, two out of three of all the children should 
die before twelve days old. Opportunities have been afibrded in hos- 
pitals, to compare the effects of pure and vitiated air, and it has been 
invariably found that a neglect of atmospheric conditions was accom- 
panied by high rates of infant mortality, which promptly disappeared 
with the introduction of efficient ventilation. " On the imagination of 
mothers, educated as well as ignorant, the feeling still seems to be 
Btereotyped, that the free, pure, unadulterated air of heaven falls upon 


the brow of infancy as the poppies of eternal sleep, and enters the 
lungs and circulates as a deadly poison ; and still the ' shawls and 
blankets,' sleeping and awake, are pretty generally employed to de- 
prive the objects of the most rapturous paternal solicitude, of what 
was originally breathed into the nostrUs of the great archetype of the 
human race as the ' breath of life.' " 

323. Bad Air nndernunes the Vital Powers. — And yet the fatal effects 
of mephitic air are by no means confined to those terrible maladies, 
Cholera, Fevers, Consumption, and Infantine disease, by which the 
earth is ravaged ; by undermining the health it paves the way for aU 
kinds of disorders. The human system is armed with a wonderful 
protective or conservative power, by which it is able to resist the in- 
vasion of morbific agencies. Indeed, this power of resisting disease is 
perhaps a more correct measure of the real vigor of the body than its 
outward appearance of health. Individuals may often continue for 
years to breathe a most unwholesome atmosphere without apparent 
ill-effects ; and when at last they yield, and are prostrated, or carried 
off by some sudden disease, the result is attributed to the more ob- 
vious cause, the long course of preparation for it by subtle and insidi- 
ous poisoning being entirely overlooked. The mass of mankind refuse 
to recognize the action of silent, unseen causes. Our youth in the 
morning of their days, and men in the meridian of their strength, 
pass abruptly away, and we wiU be satisfied with no solution of the 
problem which refers the mournful result to reprehensible human 
agency.* " The action of contaminated confined air has been shown, 
to be the most potent and insidious of mortiferous agencies. Any ad- 
dition to the natural atmosphere that we breathe must be a deterio- 
ration, and absolutely noxious in a greater or less degree ; and health 

* " It is evident that the depressing effects of foul air are not confined to those cases In 
which the immediate results of its poison are seen. Because it requires a given quan- 
tity of carbonic acid in the air to exhibit decided effects, it does not follow that a much 
lower proportion does not seriously impair the vital energies, and especially the power 
of resisting disease. We are firmly convinced that many a case of scarlet fever or of 
measles proves fatal on account of an unperceived depression of the little sufferer's 
Btrength by previous continued exposure to an atmosphere tainted with carbonic acid 
and other exhalations from his own lungs. We know that all diseases of low grade, such 
as typhoid and typhus fever, prevail to a very great extent in ill ventilated houses ; we 
know that an epidemic inflammation of the eyes has been frightfully prevalent in the 
Irish work-houses, and that it has been traced to imperfect ventilation, the eye-disease 
being merely the index of the general depression of the vital powers ; we know, too, 
that in one of the Trans-Atlantic Hospitals, the mortality went down from forty in a 
thousand to nine, upon the adoption of a proper system of ventilation, and that it rose 
again to 24 on the subsequent abandonment of that system. These are only illustra- 
tions ; hosts of similar facts could be cited from the records of medical science." 


would immediately suffer, did not some vital conservative principle 
accommodate our functions to circumstances and situation. But this 
seems to get weaker from exertion. The more we draw on it, the less 
balance it leaves in our favor. The vital power, which in a more 
natural state would carry the body to seventy or eighty years, is pre- 
maturely exhausted, and like the gnomon shadow, whose motion no 
eye can perceive, but whose arrival at a certain point in a definite time 
is inevitable, the latent malaria, which year after year seems to inflict 
no perceptible injury, is yet hurrying the bulk of mankind, with un- 
deviating, silent, accelerating rapidity, to an unripe grave. It should 
never be overlooked, that by breathing pent-up effete air, all the ad- 
vantages of an abundance of fuel, and every blessing of a genial sky 
are utterly thrown away, and though the habitation were on the hill- 
top, fanned by the sweetest bi'eezes of heaven, it would become the 
focus of contagious and loathsome disease, and of death in its most 
appaUing aspect. On the other hand, even in the confined quarters oi 
a crowded city, rife in malaria, and where pestilence is striking whole 
families and classes, ventilation and warmth, with cleanliness, thei? 
usual attendant, like the sprinklings on the lintels and door-posts of-- 
the Ilebrew dwellings, stand as a sign for the destroying angel, as hs 
passes over, to stay his hand, for in the warm, fresh-aired chamber 
none may be smitten." — (Beenan.) 

324. Morbid Mental Effects of Bad Air. — Dr. Robeetson remarks- 
" The health, the mental and bodily functions, the spirit, temper, dis- 
position, the correctness of the judgment and brilliancy of the imagin- 
ation depend directly upon pure air." This is strongly put, but it is not 
an overstatement. As the inflowing stream of air is the imminent and 
instant condition of physical life, so it is the immediate material agent 
charged with the exalted function of establishing and maintaining the 
connection of mind and body. It is air acting definitely and quauti- 
tively through the bodily mechanism, that sustains the order and ac- 
tivity of the mind's faculties. Mind is thus physiologically condi- 
tioned, and one of the mighty tasks to which science must gird itself in 
the future is to work oxit the analysis of these conditions. Mr. Paget, 
the eminent English physiologist, remarks : " The health of the mind, 
so far as it is within our own control, is subject to the same laws as is 
the health of the body. For the brain, the organ of the mind, grows, 
and is maintained according to the same methods of nutrition as every 
other part of the body ; it is supplied by the same blood, and through 
the blood, like any other part, may be affected for good or ill by the 
various physical influences to which it is exposed. But I will not 


dwell on this more than to assert, as safely deducible from physiology, 
that no scheme of instruction or of legislation can avail for the im- 
provement of the human mind, which does not provide with equal 
care for the weU-being of the human body. Deprive men of fresh air 
and pure water, of the light of heaven, and of suflBcient food and rest, 
and as surely as their bodies will become dwarfed, and pallid, and dis- 
eased, so surely will their minds degenerate in intellectual and moral 
power." The immediate effect of breathing impure air is to cloud the 
mind's clearness, to dull its sharpness, and depress its energy. All the 
mental movements are clogged, each faculty suffering restraint and 
perversion. The wings of the imagination are clipped, reason loses its 
keenness of penetration, and the judgment its acuteness of discernment 
and perspicacity. When we breathe bad air, the impressibility of the 
mind is diminished ; if we undertake to study, we can neither under- 
stand so clearly, nor remember so well as if the air were pure. So- 
cially we become less interesting, the spirits fall, conversation flags, 
dulness supervenes, we get impatient and irritable, and there is too 
often a resort in these circumstances to artificial exhilarants, and stim- 
ulants to afford relief, which would be better secured by freshness and 
purity of the atmosphere. 


325. Oxygen withdrawn by Respiration. — Any scheme for the removal 
of foul air from an apartment, and the introduction of fresh air in its 
place, involves the previous inquiry, how rapidly ought this change to 
be made ? Our next question, then, is at what rate does the air in 
dweUings become contaminated ? The amount of air taken into the 
system by different ii.dividuals, varies greatly according to age, capa- 
city of lungs, rate of exercise, and many other circumstances. Hence 
there is much discordance in the results of inquiries made by different 
physiologists. The disagreement is also much owing to the difficulties 
attending this kind of experimenting. If we take as the basis of our 
calculation Coathtupe's estimate, the lowest that we can find, we shall 
assume as an average, that there are 20 respirations in a minute, and 
at each respiration, 16 cubic inches of air pass in and out of the lungs. 
This is equal to 320 cubic inches per minute, 19,200 per hour, 460,800 
cubic inches or 266 1 cubic feet per day of 24 hours. Yieroedt makes the 
quantity 306f cubic feet, ScHAULiifa 361 cubic feet ; and YALENTra- as 
high as 398| cubic feet per day. As ^ of the air is oxygen, there will be 
four cubic inches of this gas taken into the lungs at each inspiration. Of 


this quantity, very nearly one half is absorbed and enters the blood. 
We may safely assume that 35 per cent, of the oxygen is thus absorbed 
at each breath, or 7 per cent, of the entire air. The quantity of oxygen 
consumed will be 22 to 24 cubic inches per minute, 1344 cubic inches or 
3-4ths of a cubic foot per hour, and 18"6 cubic feet per day. A person, 
therefore, robs of all its oxygen nearly four cubic feet of air per hour, 
and diminishes its natural quantity 5 per cent, in 80 cubic feet per 
hour, or li cubic feet per minute. 

326. Proportioa of Carbonic Acid exhaled by Respiration. — ^When carbon 
is completely burned in pure oxygen, the carbonic acid gas produced 
occupies exactly the space that the oxygen did before burning. If all 
the oxygen absorbed by respiration was converted into carbonic acid 
in the system, the volume of this compound gas restored to the air 
would be exactly equivalent to the oxygen withdrawn. But a portion 
of oxygen unites with hydrogen and sulphur, forming water and sul- 
phm-ic acid, while a small part of the carbonic acid generated within 
the body escapes into the air through the pores of the skin. The con- 
sequence is, that the bulk or volume of carbonic acid expelled from 
the lungs is not quite equal to that of the oxygen absorbed. Assuming 
the quantity of carbonic acid in the expired air to be 5 per cent., it 
will be one hundred times greater than the natural amount in the at- 
mosphere (280). A person, therefore, by breathing adds 1 per cent, 
of carbonic acid to 55^ cubic feet of air in an hour, or would vitiate 
to this extent nearly one cubic foot in a minute. 

327. Oxygen withdrawn by Combustion. — The amount of combustion 
varies so widely with the kind of fuel used, the mode of burning it, 
the quantity of heat required, and other circumstances, that we can 
approach nothing like an average estimate of its influence upon the 
air in a given time. It is known with certainty how much oxygen 
given weights of the different fuels require for combustion, but the 
amount withdrawn from the air of a room depends entirely upon the 
rapidity with which it is consumed. A pound of mineral coal requires 
the oxygen of 120 cubic feet of air to burn it (90). If five pounds 
are consumed in an hour, at least 600 cubic feet of air must be re- 
moved from the room. Combustion of fuel, however, does not, like 
respiration, decompose the air, separating the life-sustaining element, 
and leaving the residue in the apartment. If properly conducted, it 
removes the air from the room unchanged, and having decomposed it 
in the fire, dismisses the contaminated product through the flue. Very 
often, however, when fires get low and draughts feeble, there is a re- 
fluence of foul gases into the apartment (121). 


328. Air Titiated by Eluminating Processes. — The case is different when 
combustion is employed for illuminating purposes, as in the burning 
of candles, oil, and gas ; these, like the body in respiration, alter the 
air within the room. A candle (six to the pound) wiU consume one- 
third of the oxygen from 10 cubic feet of air per hour, while oil 
lamps with large burners will change in the same way 70 feet per hour. 
As the degree of change in the air corresponds with the amount of 
light evolved, it is plain that gas-illumination alters the air most 
rapidly. A cubic foot of coal-gas consumes from 2 to 2|- cubic feet of 
oxygen, and produces 1 to 2 cubic feet of carbonic acid. Thus every 
cubic foot of gas burned imparts to the atmosphere 1 cubic foot of 
carbonic acid, and charges 100 cubic feet with 1 per cent, of it, making 
it unfit to breathe. A burner which consumes 4 cubic feet of gas 
per hour, spoils the breathing qualities of 400 cubic feet of air in 
that time (224). 

329. Inflaence of Moisture upon the quantity of Air required. — It has 
been noticed that air which is either very dry, or very moist and 
damp, is disagreeable and unwholesome. It should not contain so 
little moisture as to dry and stimulate the skin ; nor so much that it 
wiU not readily receive the insensible perspiration which constantly 
flows to the surface. The amount of watery vapor emitted from the 
body has been stated at from 20 to 40 ounces per day. Estimates 
upon this point vary. If one of each sex be taken, the mean exhala- 
tion win be about 23 grains per minute. ITow let us suppose the air 
of a room to be at 70°, and that it has to be cooled 20° before it 
begins to deposit moisture, that is, its dew-point is at 50°. The cubic 
foot of air at 50° contains 4'6 grains of moisture, and at 70° it will 
hold 8*4 grains, so that it is capable of dissolving 3*9, or nearly 4 grs. 
of water. Of air in this state, it will require about 6 cubic feet per 
minute to dissolve and remove the insensible perspiration from the 
skin. If the dew-point be lower, the air will take up more water, and 
less of it will be required to evaporate the moisture of the body. 
But if the dew-point be higher, the air will receive less moisture, and 
the system will require a larger supply. If the dew-point is at 60° 
and the temperature of the air at 70°, a cubic foot of it wUl become 
saturated by the addition of 2*17 grains, so that 10 feet per minute 
would hardly carry off the cutaneous exhalation. To be pleasant, air 
must not be deficient in moisture ; if it be nearly saturated, it can im- 
bibe but little, and consequently much of it must be brought in con- 
tact with the system ; and this necessarily involves large provision for 
change of air. 


330. Air vitiated by one person in a niinnte. — These sources of impurity 
are capable of measurement in their rate of effect, hut there are other 
influences so irregular in action that the results they produce cannot 
be estimated. The whole quantity of air tainted by emanations from 
the person, and which requires removal, is variously stated by different 
authorities at from 3^ to 10 cubic feet per minute. We are of opinion, 
that for the restoration of its lost oxygen, the removal of carbonic 
acid, insensible perspiration, and the peculiar effluvia of the living 
body, there are required, at the lowest estimate, 4 cubic feet of air 
in a minute, or 240 per hour. But this may be much too low. 
It is evident that the nearer the air breathed within doors, approaches 
in purity and freshness to the free and open atmosphere, the better 
will it conduce to health, strength, and length of life. As far as pos- 
sible we ought not to limit ourselves to that supply which the consti- 
tution can bear or tolerate, but to that amount which will sustain the 
highest state of health for the longest time. And yet, as Dr. Eeid 
remarks, the question of the amount of air to be supplied may be con- 
sidered in some respects in an economical point of view, in the same 
manner as the table any one can afford to sustain, the house in which 
he may dwell, or the clothing he may put on. Although pure air is 
the most abundant of all things, yet in our plans of living it is by no 
means free of cost (363), 

381. InHncnce of size of Apartments, — The smaller an occupied room, 
the sooner, of course, will the stock of pure air contained in it be ex- 
hausted and replaced by foul air. Three persons sitting in a tight 
room 8 feet high, and 12 by 14 square, will vitiate all its air in two 
hours. If they use lights, the air wiU be spoiled much quicker. 
Twelve persons sitting in a parlor 16 by 20 and 9 feet high, will make 
its air unbreathable without the assistance of either fire or lights in a . 
single hour. Two persons sleeping in a close bedroom 10 feet square 
by 8 high, wiU render all its air unfit for respiration in less than two 
hours. In actual practice, the cases are not quite so bad as this, for 
with the utmost perfection of carpentry there will be cracks for the 
passage of air, though perhaps in small quantities ; and the opening 
and closing of doors cause intermixture and currents, and this some- 
what delays the result. Where the rooms are capacious, the reservoirs 
of air are more slowly contaminated, and if no means are taken to 
remove the foul air and introduce that which is pure, large-sized rooms 
are of the utmost importance. But no apartments of ordinary or prac- 
ticable dimensions will enclose sufl&cient air for the agreeable and whole- 
some use of their occupants. This must be attained in another way. 


332. Influence of Plants upon the Air of Rooms. — The general action 
of plants upon the air is antagonist to that of animals. In the day- 
time, under the influence of light, they absorb carbonic acid from the 
atmosphere by then* leaves, decompose it, and return pure oxygen to 
the air, thus tending by a double action to purify it. The rate at 
which these changes occur corresponds with the activity of growth. 
The plant, however, derives a portion of its carbonic acid from the 
soil, especially if it be rich, in decomposing organic matter, like the 
garden mould of flower-pots. Compared with the ordinary rate of 
contamination in occupied apartments, the purifying effect of the few 
green plants usually kejDt, is but small. In the absence of light, the 
peculiar actions of the leaves are suspended, nay, reversed; they 
now rather absorb oxygen, and give off carbonic acid, like ourselves. 
Hence, in sleeping-rooms, their tendency would be to impurity of the 
air, though the action is probably very slight. As respects moisture 
plants are also like animals, constantly exhaling it through the pores 
of their leaves. According to Hale's experiment, a sunflower weigh- 
ing 3 lbs. exhaled from its leaves 30 ounces of water in a day. Plants 
may therefore be a useful means of supplying dry air with the requisite 


333. Two methods of purifying the Air. — Pure air may be secured iu 
two ways : first and most perfectly by the removal of the vitiated at- 
mosphere of the apartment, and its replacement by fi-esh air from out 
of doors. This is the mechanical method, and is known as venti- 
lation^ — a term derived from the Latin word signifying wind. The 
air may also be more or less perfectly cleansed by means of substances 
which absorb, decompose and destroy its noxious ingredients. This 
is the cJiemical method. It is useful only under certain circumstances, 
and is not applicable in common cases (802). 

334. Motive Power employed.— As ventilation consists in the move- 
ment of masses of air, it implies some kind of moving force. On a 
large scale, as for public buildings, revolving fans, pumps, bellows, &c., 
driven by steam-engmes or water-power, have been used to impart 
movement to air. But these contrivances are impracticable for 
dwellings. Wind power is often used as an aid in ventUation, but its 
unsteadiness prevents us from depending upon it. The force gener- 
ally resorted to in private residences to secure exchange of air 
is heat. 



Fig. 72. 

335. Currents of Air In Close Apartments. — Changes of temperature 
externally give rise to unceasing commotions in the air — breezes, 
"winds, and hurricanes. The same thing occurs within doors ; any 
portion of air heated becomes lighter and causes an ascending current ; 

any portion cooled becomes denser 
and causes a descending current. 
If a candle be lit in the middle 
of a room (Fig. 72) where the 
doors, windows and flues are 
closed, and the air is motionless, 
a set of currents wiU rise in the 
centre of the room, spread out 
near the wall, to its sides, then 
descend and return along the floor 
to the centre again. The arrows 
in the diagram show the direction 
of the currents in a section of the 
apartment. Fig. 73 shows the 
dkection of the currents along the floor, that is, on a plan, as it 
is termed. If the arrows (Fig. 73) were reversed, they would show 
the course of the currents at the top of the room. If a lump of ice 
be substituted for the candle, currents are again produced, but they 
are exactly reversed in direction (352). The air descends from the 

cold ice, and the currents on the 
floor run outwards. In each of these 
cases, the currents above and below 
are opposite. AU local disturbances 
of temperature tend to produce simi- 
lar effects, although the currents are 
commonly much interrupted by dis- 
turbing forces. Of course several 
lights would occasion several cur- 
rents, which would mutually inter- 
fere with each other. A stove in 
the centre of the room produces just 
such a movement of air as we have 
seen established by the candle ; but 
if placed at one side, the hot-air ascends on that side and descends on 
the opposite. 

836. Natural Ventilation of the Person. — The warmth of the human 
body imparts itself to the layer of surrounding air, expands it, and 

Fig. 73. 


Fig. 74 

causes a rising current (lOY). "When the temperature of the room is 
65°, the body is 33° warmer, while 4° added to the circumjacent air 
will cause it to ascend and escape above the head. The simple 
presence of an individual in a room is therefore sufficient to throw 
the air into movement and cause currents. The body thus acts pre- 
cisely in the same way as a stove, and the presence of persons dis- 
tributed through a room wUl add much complexity to the movements 
of the air, and to a small extent counteract the stove-currents. 

337. Windows, thoagb tight, produce Currents. — Windows, in cold 
weather, though entirely tight, so that no air passes their crevices, are 
always sources of descending curfents of air, with a corresponding 
ascending movement (Fig. 74). When between the internal warm air 
and the external cold air there is only one thin film of window-glass, 
the heat escapes through it so fast that the air within is rapidly 
cooled, condensed, and becomes heavier, so that a sheet of it is con- 
stantly falling to the floor. This cascade 
of cold air is frequently so sensible in 
winter that persons are apt to suppose 
it comes from some opening about the 
window. These winter window currents 
are often most injurious. If there be 
draughts through the room, produced by 
a fire or any other cause, they throw the 
window current out of its direction more 
or less to one side, so as frequently to 
fall upon persons who suppose them- 
selves to be safely away from any such 
source of discomfort. Large windows 
in public rooms, in vsdnter, should on 
this account be carefully avoided, as the 
cataract of cold air which they pour down upon the body is a fre- 
quent cause of rheumatism, colds, and inflammations. Such sheets of 
air often fall with mischievous effect upon sleepers, where beds are 
placed near windows. It may be remarked that in summer these 
currents are reversed; the heat, passing from without through the 
window glass, rarefies the air in contact with it, which rises so that the 
current passes in a contrary direction (289). 

338. Tlie Air of rooms arranged in strata. — But the effect of currents 
is not to cause a perfect intermixture with uniformity in the condition 
of the air throughout the room. Indeed, the very cause that gives 
rise to them is the tendency of cold air to fall into the lower place, 

Currents produced in winter by 
single windows. 



while it presses upward that which is warm and lighter. Hence, not- 
withstanding its constant motion, the air is in fact arranged in layers 
or strata, according to its temperature, the hotter air collecting near 
the ceiling, and the layers decreasing in temperature downwards as 
was previously stated (125). The difference of these temperatures is 
Bometimes so considerable that flies will continue to liv;e in one stratum 
which would perish in another. Now the warm and rarefied air which 
rises to the upper part of the room contains also the impure air which 
has been generated within it. The breath which escapes fi'om the 
lungs, 20° or 30° warmer than the surrounding air, slowly rises above 
the head, while ascending currents from the body carry upward all 
its exhalations (334). So also the heated poisonous products of illu- 
mination mount rapidly to the ceiling. The effect of currents is, to a 
certain extent, to diffuse the foul gases throughout the apartment, but 
chemical tests show the same stratification of impurities that the 
thermometer indicated in regard to heat, the best ah* being below and 
the worst above. In a room having a fireplace, the cold air may enter at 
the top and bottom of a window, faU towards the floor and move 
along near it to the flue, where it is discharged. In its progress, it 
may even blow strongly upon a bed made on the floor, while all the 
air above, enveloping a bedstead of ordinary height, remains loaded 
with carbonic acid and aqueous vapor. In all ordinary rooms the 
floor is swept by draughts of cold air, and is unfit for a sleeping place, 
especially if the apartments have open fireplaces. 

339. Simple openings do not produce Currents. — If an apartment be 
opened to the external air, various movements are liable to occur, or 

there will be 
no motion at 
all, according 
to circum- 
stances. It 
by no means 
follows that 
because a 
tion has been 
opened be- 
tween a room 

and the outer air, therefore currents wiU set in and an active inter- 
change take place. Air will not leap out of a bottle because we ex- 
tract the cork, nor out of a window simply because we open it. Cur- 

FiG. 75. 

Fig. T6. 





Conditions in which openings in rooms do not produce 
eschanire of air. 



Fig. 77. 

Fia. 78. 

rents cannot be produced unless their causes are brought into action. 
If a room be opened below, and the temperature within be higher 
than that without, as represented in Fig. Y5, the outer, heavier air, 
pressing harder than that withio, will confine it, no movement wiU 
take place, and the strata wUl retain their relative positions undis- 
turbed, as in the figure ; or, if the room be opened above, and the 
external air be warmer than the internal (Fig. 76), the lighter air with- 
out cannot press down to displace the inner, heavier air, which re- 
mains without movement or disturbance of its arrangement. 

340. Ciirreiits between rooms and external Am — If there be an open- 
ing at the lower part of a room, and the external air be warmer 
than that within, interchange takes place, the outward air displacing 
that within by currents running as the arrows show (Fig. Y7), the 
heavier air within falling or flowing out. If the opening be above, 
and it be 
warmer in- 
side than 
out, the light 
air inside 
wiU escape 
upward, and 
vy air with- 
out flows in, 
as shown in 
Fig. 78. If 

there be but a single opening to a room, although all other condi- 
tions are favorable for a change, yet the counter currents meeting in 
the passage conflict, and to a certain extent obstruct each other. 
There should, therefore, be separate openings for currents of ingress 
and egress. 

341. Friction of counter-cnrrents of Air. — The importance of having 
two independent openings to an apartment, if we desire to secure a 
change of air, is shown by the following simple experiment : Take a bot- 
tle with the bottom removed, or a lamp chimney (Fig 79), place under it 
a short piece of burning candle in a shallow dish of water, so that no 
air can get in from below ; now, although the stopper be removed so 
that the inside of the bottle has direct communication with the outer 
air, the candle will go out. Although there is a tendency of the 
burnt air to escape and of the fresh air to rush in, yet they cannot 
pass each other at the open mouth ; the currents conflict and the 

Conditions in which openings in rooms produce exchange of air. 



Fig. T9. 

Fig. 80. 

exchange does not take place. Yet, if a slip of paper be inserted in 
the mouth of the bottle or lamp-glass, as seen in Fig. 79, thus dividmg 
it into two distinct apertures, the lit candle will con- 
tinue to burn. The foul air will pass out on one side 
of the pasteboard and the pure air enter on the 
other, as may be shown by the smoke from the snuff 
of a candle held near ; it will be drawn in on one side 
and carried up on the other. The purity of the air 
within is thus secured. "When the opening, how- 
ever, is sufficiently large, the currents pass without 
difficulty, as is easily illustrated. If the door of a 
warm apartment be opened, and a candle placed 
^toe\S:%uwent°^ ^^ar it on the floor, the flame wiU be blown in- 
wards ; if it be raised nearly to the top of the door 
it will be blown outward, as illustrated in Fig. 80. The warm air 
flows out at the higher openings. If the air of the room be warmer 

than that without, it enters by all the 
crevices near the bottom, and escapes 
. by those near the top, and the reverse 
if it be colder. 

342. Currents throngli Windows. — 
Draughts through windows and doors 
are often not effectual in removing all 
the air of rooms. In the case just 
.instanced (Fig. 80), of the open door, 
the cold air below enters and expels 
^an equal portion of the warmer air, 
' but only that will flow out which lies 
below the level of the door-top. The 
mass of air above this level will not 
be displaced. If, however, the temperature of the room were at 60°, 
and that of the outer air at 70°, an open door would evacuate the 
room entirely of its airy contents ; the colder air in the room tending 
to fall would pour out at the bottom, and the warm air enter at the 
top to take its place. If a window be situated in the upper part of 
the room and opened, its action is different, and in a manner opposite 
to that of the door. "When the air is cold without and wann within, 
and the window opened above and below, the apartment is emptied 
and refilled as in Fig. 81. If the external air is warm and that within 
cool, aU above the window sill is removed (Fig. 82), but the cold air 
below that level continues undisturbed. By thus imderstanding the 

Counter-currents in the doorway. 



Fig. 81. 

Condition in wliich the air escapes 

conditions of inflow and outflow, we are enabled to regulate windows 
having both sashes movable, and which are often valuable for venti- 
lating private rooms. Although the interference of other causes is 
liable to modify, and perhaps often 
confuse and divert these movements, 
yet they are quite sufficient to show 
that the motion and rest of air are 
controlled by laws as definite and reg- 
ular as those which govern the mo- 
tion and rest of water. Though infi- 
nitely more light, mobile, and easily 
agitated, yet it is never thrown into 
commotion except by adequate and ap- 
preciable causes. 

343. How cnrrents of Air affect the Sys- 
tem. — The sensations produced upon 
the body by gently-moving currents of 
air in proper conditions of temperature and moisture are extremely 
agreeable, but in many cases streams of air directed against the per- 
son become most injurious. Air at low temperatures of course has a 
cooling efiect. We lose no more heat by radiation in moving air than 
in still air, but by conduction we lose heat 
in proportion to the velocity of the cur- 
rent or the number of particles which 
come in contact with the body. The cur- 
rent also drives the cold air through the 
clothing, displacing the warm air which 
was entangled in its pores. Increased 
evaporation, proportional to the dryness 
and speed of the air, is also a further 
source of cold. If the whole surface of 
the body is exposed to the current, the 
eflfect will be simply a general cooling 
without any necessarily injurious effects. 
But if the draught fall only upon some 
one part of the body, it is hable to produce serious mischief, disturb- 
ing the circulation and producing febrile movements, which may be 
directed to the part exposed to the draught or even to remote organs, 
iu either case often laying the foundation for serious and fatal disease. 
This point should be particularly considered in introducing air in sum- 
mer which has been artificially cooled (352) ; its diffusion should be 


Conditions in which the air 
escapes below. 


very extensive and its velocity hardly perceptible. Of course we can- 
not have ventilation without movement of air, but the motion should 
be so moderated that we are not aware of it, and is always to be con- 
sidered in connection with the two important conditions of tempera- 
ture and moisture. We have made several trials to determine the ve- 
locity which, as a general rule, with a proper regard to other condi- 
tions, wiU not be found unpleasant, and give as the result about two 
feet per second. It is evidently no greater than that with which we 
should pass through still air when walking with the same velocity. 
(Wyman.) Yet it is important that we be exposed to currents. Few 
things are more favorable to taking cold than the confined and stag- 
nant air of unventilated apartments. Just in proportion as we habit- 
uate ourselves to such still, stagnant air, do we become sensitive to at- 
mospheric changes, against which it is impossible perfectly to protect 
ourselves on going out. The effect of a free internal circulation of air 
in our rooms is therefore most salutary ; the more we are accustomed 
to it, the safer we are in the vicissitudes of changing weather. 


344. The open Fireplace. — The mechanical expedients for securing 
exchange of air in dwellings are numerous, but they are chiefly con- 
nected with arrangements for heating. Wherever there is active com- 
bustion in stove or fireplace, there must be a stream of air passing 
out of the room through the chimney. If the room be absolutely 
tight, so that no air can enter it, none will ascend, and if the fire be 
kindled the chimney will smoke. A draught through a chimney im- 
plies openings somewhere for air to enter the room, and thus there is 
some ventilation as a matter of necessity. In noticing the heating ef- 
fect of the fireplace, we saw that the open space above the fire con- 
veys away a large amount of warmed air from the room, which took 
no part in the combustion and wasted much heat. But this fault was 
an advantage in respect of ventilation. The magnitude of the open 
space above the fire represents the ventilating capacity of the chim- 
ney. But it is from the air below the level of the mantel — the purest 
in the apartment — that the fireplace is supplied. Only so much of 
the foul imprisoned air above as gradually cools and descends, be- 
ing swept into the chimney. When the weather is quite cold, the 
briskness of the fire that is demanded, occasions a powerful draught 
and produces annoying currents. So powerful were these draughts in 
old times, that they were compelled to use a settle, a long bench with 


a high •wooden back, to protect the body from currents and retain the 
radiant heat in order to keep warm. " It would be well for those who 
question the importance of ventilation, because our forefathers lived 
to a good old age without even understanding the meaning of the 
word, to remember their fireplaces, the kind of dwellings they occu- 
pied, and the quantity of air which must have passed through their 
houses." It cannot be doubted that the changes which have of late 
years been effected in the structure of the fireplace to secure the 
greater economy of fuel — ^the contraction of its dimensions and the 
lowering of the chimney-piece, by dimiaishing the amount of air that 
was forced through the room to fill the capacious chimney, and by 
bringing the foul-air space down more completely within the zone of 
respiration — have been altogether unfavorable ; although, even in their 
newer construction, open fires may be considered as affording a toler- 
able amount of ventilation. Fresh air is well secured by the double 
fireplace, which warms and introduces into the room a steady stream 
of air from without. (111.) 

345. Ventilation by Stoves. — As respects the condition of the air, the 
exchange of even the low and contracted fireplace for the close and 
stifling stove, has been eminently promotive of discomfort and disease. 
Stoves afford the least ventilation of all our means of heating. They 
take little more air than just sufficient to consume the fuel, and that 
is withdrawn from the purer portion near the floor. In most cases of 
the use of stoves, no provision whatever is made for the removal of 
bad air. They may be made subservient to ventilation in several 
ways ; first, by allowing air to pass through tubes in the body of the 
stove ; second, by admitting it between the stove and an external 
casing ; and third, by simply allowing it to strike upon the external 
surface of the stove. In either case the entering air will be warmed, 
rise toward the ceiling, and afterward gradually descend as the air 
below is drawn off, producing a downward ventilation through the 
whole apartment. Mr. Exjttan, of Coburg, 0. "W., has devised a plan 
of heating and ventilating, strongly recommended by those who have 
used it, although we have had no opportunity of seeing its operation. 
He locates his 'au'-warmer' in the haU, or where required, brings in 
the air from below, heats and transmits it through the building. For 
the best working of his arrangement it is important that the house be 
built with reference to it ; indeed, he insists that the general failure to 
ventilate is because the architects fail to provide the necessary lungs 
in the original construction of dwellings (362). 

846. Ventilation by Hot-Air ArrangenientSi — Sources of warmth be- 


come tlie most effective means of ventilation when air itself is made 
the vehicle for conveying heat into the room, as in the use of hot- 
water apparatus, furnaces, &c. The hot current enters through a 
register, or guarded opening, and streams up at once to the ceiling ; 
and by diffusion through the apartment, displaces the air already 
present, which must find escape somewhere, and thus the renewal of 
the breathing medium is constantly secured. Apartments warmed in 
this manner require a chimney or other place by which air may escape. 
The fireplace answers perfectly ; but under the impression that rooms 
heated by air-currents require no channel of escape, houses have been 
constructed with no flues at all. The air ought to be projected into 
the room horizontally or at different points, so as to be weU diffused 
(125). It should always be derived from perfectly pure sources, and 
never used a second time. But the chief difificulty and danger, as 
before noticed, is to be found in that condition of the air itself, which 
results from its being suddenly heated (305). 

347. The supply of Moisture. — The provision for supplying moisture 
by evaporation is rarely any thing like adequate, a supply of 35 cubic 
feet of air per minute introduced at the temperature of freezing and 
heated to 90", is capable of taking up an ounce of water per minute, 
or four pounds in an hour. Dr. Eeid states, that in ventilating the 
English House of Commons, when it was crowded, he often exposed 
the air furnished to 5,000 feet of evaporating surface, to impart the 
necessary moisture, and sulsequently made the air flow through jets 
of water. The artificial supply of moisture to air in the exact quan- 
tity required, involves grave difficulties. The common method of 
supplying humidity by simmering water in an open vessel, is glaringly 
insufficient. A pan of water is placed in a furnace,* but of the torrent 
of air that rushes through, how little is brought into contact with the 
water. We place a vessel upon a stove with a few square inches of 
water-surface, and fancy all is right, but the air may still be parching 
dry. Where air in cold weather is introduced, suddenly rarefied by 
heat, and actively changing, we have little conception of the amount 
of moisture which must be artificially added to give to it soft and 
balmy qualities. The best thing to be done of course is, to obtain the 
largest possible evaporating surface. To accomplish this, a piece of 
linen or cotton cloth dipped in a vessel of water, may be hung in folds 
from any convenient framework or support. The cloth, by sponging 

* Walker's furnace, manufactured by S. B. Jameb, No. T7 White street, New Yort, 
Has large provision for evaporation, whlcli the proprietors offer to increase to any 
extent that individuals may demand. 


up the water is always wet, and gives out its moisture to the air. If 
previously dipped into a solution of potash, which is very absorbent 
of water, it continues more perfectly wet. If it be unsightly, the sus- 
pended cloth may be concealed from view by any graceful screen, as 
by a tower-shaped cover of porcelain, open above and below to admit 
the passage of air. "Where hot-air is used, it may even become neces- 
sary to mingle with it the vapor of boiling water. 

348. Best method of Warming and Ventilation. — If we would have the 
pleasantest mode of warming and ventilating a dwell ing-house, with- 
out regard to trouble or expense, we should certainly combine the 
open fireplace with air-heating apparatus, which should never exceed 
in temperature 212°. The first is desirable for its pleasant light and 
radiant heat, while the second gives to the entries and chambers a 
mild atmosphere, which prevents cold di'aughts from open doors, and 
at the same time, through an opening in each apartment, moderately 
warms it, and likewise supplies air for the ventilation going on by the 
fireplace. The fireplace also has its influence upon the introduction 
of the warmed air. The heat of the chimney establishes a current 
which draws from the air-heating apparatus a large supply of air at a 
lower temperature than would otherwise enter the apartment. We 
know of no single apparatus which warms and ventilates a dwelling- 
house in so healthy and comfortable a manner as is accomplished by 
this combination. — Wtman. Yet it can only be had by very few ; for 
the mass of the people it is entirely out of the question from expen- 

349. Supply of Air by loose Joinings, CrcTices, &c. — Hot-air con- 
trivances of any kind, although coming more into use, especially in 
cities, are by no means general. Grates and stoves are the nearly 
universal sources of heat, and the latter of these cannot be said to 
ventilate at all. Fo provision is made for the entrance and exit of 
air. The use of doors to rooms is for the admission of their occu- 
pants, windows are for the entrance of light, and it would certainly 
seem, both from its importance and peculiar properties, that air also 
is entitled to an entrance of its own. Yet in most cases we treat the 
air as if it had no business in our dwellings. It has to avail itself of 
the mechanics' botch-work or the chance shrinkages of time, and 
creep through any crevices and wind-chinks that there may happen 
to be, or dodge in and out at the casual opening of windows and 
doors. These cracks and loose joinings afford a kind of imperfect 
accidental ventilation, which, by effecting the purpose in a partial 


degree, has prevented mankind from discovering the vrant of any 
thing better. 

350. Fonr points to be secured in Ventilation. — Tliat ventilation may 
be complete, and do for us its best service, four things must be at- 
tended to. 

First. Pure air must be introduced. 

Second. The foul air must be removed. 

Third. The supply must be sufficiently copious. 

Fourth. There must be no offensive currents. 

Now as things usually are, none of these points are certainly se- 
cured. There is no constant and regulated supply of air, this being 
left entirely to chance. There is no provision for the exit of the 
vitiated gases. All the air that is drawn off from the apartment is 
taken from its lower and purer portion by the draughts of the stove 
and fireplace, while that which should escape stagnates above. The 
quantity furnished is therefore variable and usually stinted, while in- 
jurious draughts are notoriously common. Independent and effective 
methods of changing the air, by which these enumerated benefits may 
be gained, are on every account desirable. 

851. Modes of iBtrodncing pure Air from without. — In summer the 
free opening of doors and windows ensures a supply of air. It is a 
good plan to have light door-frames fitted to the outer entrances, and 
covered with wirecloth or some loose fabric, as millinet, through 
which the air will pass readily, but in a diffused manner. In winter 
the air should always, if possible, be warmed before being thrown 
into the apartment. For introducing more fresh air than accidental 
fissures will admit, the readiest way is to lower the top window sash, 
although the stream of cold air which presses in and is both unpleas- 
ant and unsafe, falls to the floor and glides to the stove or fireplace 
without being suflficiently commingled with the general atmosphere to 
serve the purpose of ventilation. It becomes a mere feeder of the fire. 
To disperse cold currents of air from above, a plate of zinc perforated 
with numerous holes is made to replace the pane of glass furthest from 
the fireplace and in the upper row of the window. Louvres made 
either of tin, zinc or glass, with horizontal openings and slats like 
Venetian blinds, are also substituted for window panes. A small tin 
wheel or whirligig, which revolves and scatters the inflowing current, 
is sometimes mounted in the window ; it is often noisy and rattling. 
In arranging openings for the entrance of air, several circumstances 
are to be borne in mind. The air should always be fresh from with- 
out and not, as is too often done where hot-air furnaces are used, 



taken from cellars or basements, or what is still worse, used over and 
over again. If there be local sources of impurity in the Adcinity, 
apertures should not be placed favorably to its admission. "Where 
dust is an annoyance, or from any cause there is contamination of air 
near the ground, the supply may be brought from the top of the house. 
Openings are made under the caves, or in some eligible place near the 
summit, leading to channels left in the walls, called fresh-air venti- 
ducts^ which pass down and open into the room in any convenient 
manner. The prevailing direction of the wind should also be noticed, 
as it is desirable to command its aid as far as possible ia forcing air 
into the building. Emeeson's injector (Fig. 83) causes a downward 
current from whatever quarter the wind may 
blow upon it. All outer apertures should be 
guarded with valves. Air entering them and 
led along proper passages, either in tin tubes 
or air-tight wooden boxes, is admitted into 
the room at various points. There may be 
an air passage made along behind the base or 
mop-board, communicating with the room by 
innumerable minute openings, through which 
the air passes. Or the inflowing currents 
may be received through registers or made to 
rise through small apertures in the floor. 

352. The downward Current.— Air once breathed must not be again 
brought within the sphere of respiration, but should it be removed 
downward or upward ? The air thrown from the lungs escapes hori- 
zontally from the mouth and downward from the nostrils ; it may 
then be swept without difficulty by the ventilating current in either 
direction. In cases where hot air is thrown into the room, it first rises 
to the ceiling, and then, as it is gradually cooled, falls, and is mainly 
drawn off by the fireplace below the plane of respiration. This is in 
effect a downward current, but it is hardly strong enough to carry the 
breath down with it. It ascends, is diluted by the upper air, and fall- 
ing again is liable to be reinhaled. A descending current of air arti- 
ficially cooled has been employed for ventilation ; in fact, rooms can 
be as effectually ventilated in summer by the aid of coolers placed 
above them, as they are in winter by the heater lelow them. Lyman's 
ventilator (Fig. 84), consists of a reservoir of ice — A^ the bottom of 
which is an open grate ; ^ is a gutter to catch the water from 
the melting ice ; {7 is a pipe or flue, through which a stream of 
cold condensed air falls constantly, as shown by the course of 

Emerson's Injector. 



Fig. 84. 


the arrows; I), a wire gauze box filled with char 

coal, which prevents the waste of ice by radiation, 

and disinfects and purifies the descending air. The 

force of the current depends on the length of the cold 

air flue and its temperature, compared with the outer 

air. In hot weather the breeze continues quite brisk. 

This arrangement, on a small scale, has been mounted 

on secretaries, to secure a cool and refreshing air whUe 

writing ; over beds, to cool the air while sleeping ; 

and over cradles, to furnish pure air for sick children 


353. The ascending Cnrrent most IVatnrali — We have 

T , 1^ • noticed that by a beautiful provision of nature, venti- 
liyman s cold air ■' ^ ' 

flue. lation of the ferson is constantly taking place. The 

exquisite mechanism of the human system would have been created to 
little purpose if it had been left to smother in its own poison. A gentle 
and insensible current constantly rises from the body, which carries 
all that might be injurious into the higher spaces. Vitiated air would 
thus constantly escape from us if it could. But in our houses we de- 
feat the benign intentions of nature by enclosing the spaces above us, 
so that the detrimental gases accumulate in the upper half of the 
room, surrounding the head and corrupting the respiratory fountain. 
It is thus evident that if we desire to aid nature in her plans, we must 
remove or puncture the air-tight covers of our apartments, so that the 
ascent and complete escape of foul air shall not be obstructed. 

354. Ventiducts and Ejectors. — Openings for the escape of these bad 
gases above are indispensable. Each room fifteen feet square, for the 
accommodation of six or eight individuals, should have a flue for the 
escape of foul air, either in the chimney or elsewhere, of at least 100 
inches area. A bedroom should have an outlet of nearly the same 
dimensions. But in practice a serious difficulty is encountered here. 
If we make an opening out from the top of the room, either by low- 
ering the top sash of a window or by carrying up a duct through the 
roof, instead of the foul air escaping through them, a flood of cold air 
rushes in from without. Tubes or ventiducts, connecting the room 
with the top of the house, may be made to act exhaustively, and drain 
the apartment of its polluted air, wTien the wind blows, by surmount- 
ing it with Emerson's Ejector (Fig. 85), and as the air is almost con- 
stantly in more or less rapid motion, this arrangement becomes very 

355. Opening into the Chimney— Arnott's Valve. — But the force of 




draught in the chunney is after all to be the main reliance in convey- 
ing away foul air. Its necessary action is that of a drawing or suck- 
ing pump, which exhausts the room of large quantities of air. As the 
velocity of smoke in a chimney with a good fire is estimated to be 
from 3 to 4 feet per second, its exhaustive power is amply suflBcient 
to make it serve the secondary purpose of a ventilating flue. Hence, 
if we make a hole into the chimney, by knock- 
ing out two or three bricks near the ceiling, the 
foul gases will rush in, and mingling with the 
ascending current will escape. Yet these ven- 
tilating chimney openings are liable to the se- 
rious and even fatal objection, that when from 
any cause the current in the chimney is inter- 
rupted, smoke is driven into the room. An 
ordinary register, requiring personal attendance 
to open and close it, would be of no service. To Emerson's Ejector, 
remedy this inconvenience. Dr. Aenott has contrived a self-acting sus- 
pension valve. It is so placed in the aperture, and so mounted, that a cur- 
rent of air passing into the chimney opens it, while a current in the con- 
trary direction closes it. It is so delicately suspended that the slight- 
est breath of air presses it back, while 
any regurgitation of the chimney current 
shuts it, and thus prevents the backward 
flow of smoke into the room. It is shown 
in Fig. 86. Owing to the unsteadiness of 
the currents, the valve is constantly vibrat- 
ing or trembling, and would be noisy but j 
that it is made to strike against soft 
leather. A modification of this valve Arnott's Vaive. 

consists of a square piece of wire gauze set in the opening, with a cur- 
tain of oiled silk susj-ended behind it. The current into the chimney 
pushes back the pendant flap, while a reversed current drives it against 
the gauze, and thus closes the aperture against the admission of fire- 
fumes and smoke. These are easily placed in fire-boards used to close 
the fronts of chimneys. 

356. Importance of Aruott's Valve. — The value of this valve to the 
public can hardly be exaggerated. Mr. Teedgold expressed what 
many have felt, when he said that all the plans he had seen or read ol 
for drawing oS the air from the top of a room are objectionable, either 
from being wholly inefficient or from causing the chimney to smoke. 
This valve first meets the difficulty. It is cheap, easily inserted, may 



be managed with trifling care, and drains the room eflfectively of its 
gaseous pollutions. In the thousands of stifling, stove-heated rooms, 
where palor of countenance, headache, and nervousness, bear painful 
witness to the perverted and poisoned state of the air, this simple me- 
chanical contrivance might bring happy relief. It is much used in 
England, but has not been made sufiiciently known in this country. 
We have inquired for it in vain at many establishments. It is manu- 
factured by S. B. James & Co., 77 "White street — ^price, $2 50 to $5, 
according to size. If the orifice in the chimney be deemed unsightly, 
it may be screened from view by placing a picture before it. 

357. CMmney Currents in Sammer. — The air in the chimney is usually 
somewhat warmer than the external air, even when there is no fire, 
and this will occasion a slight draught, so that if there be an aperture 
in the upper part of the room into the flue, and the fireplace be 
closed, the vitiated air above will be removed. This exhaustive ac- 
tion of the chimney without fire, is aided by winds blowing across its 
top, which exert a slight suction influence, or tendency to form a 
vacuum within it. This effect of the wind will be much increased if 
the chimney be mounted with an ejector (354). A slight fire in a fire- 
place, even when not wanted for warmth, is often desirable for ven- 
tilation. Lamps have been sometimes introduced into flues for the 
purpose of exciting currents. 

358. An additional Ventilating Fine. — If an extra flue be constructed 
adjoining the chimney, warmed by it and opening into the top of the 
room, there wiU be a draught through it, and it may be devoted ex- 
clusively to ventilation. It would seem that such a secondary flue 
would not be liable to refluent smoke, and might have connected 
tubes extending to remote rooms, thus effectually ventilating the 
whole building. But practically such shafts do not well succeed. 
Double outlets in the same apartment rarely work satisfactorily. The 
chimney is liable to convert the extra flue into a feeder of the fire, 
and thus, if it be of the same height as the chimney, to suck back the 
smoke into the room. " Such cases have occurred, and the ventilating 
flue has been closed in consequence. This evil can be remedied by 
providing a free supply of air for both air and smoke flues. But the 
air which enters must be warmed, or it wiU not be tolerated, and if it 
is too much warmed, as compared with the air of the room, it wiU 
rise immediately to the ceiling and escape through the ventilator, and, 
not mingling with the air of the room, it will greatly diminish or en- 
tirely prevent any change of air where most wanted." 

359. Ventilation of Bedrooms. — The bedroom, the place where wo 


spend nearly lialf of our lives, in its general condition and manage- 
ment is the opprobrium of civilization. No place in the house should 
be more copiously supplied with air to guard us against the injurious 
agencies to vs^hich we are nightly exposed. The materials of which 
bedding is composed have a strong tendency to attract moisture from 
the air and become damp. Not only are the textile fibres highly hy- 
groscopic, or absorbent of atmospheric moisture, but the coldness of 
rooms in which beds are usually placed, favors the deposit of moisture 
when the air is charged with it. They are also saturated with bodily 
perspiration. Beds should, therefore, be often and thoroughly aired. 
Their injurious effects when damp are much more dangerous than 
those of wet clothes. As the body is at rest while we sleep, there is 
no exercise to warm the surface and throw off the Ul effect, as can be 
done with damp clothes. Moreover, as the vital activity is depressed 
during the state of slumber, the system is more open to the malign in- 
fluence of cold or other causes. Many and fatal diseases, inflamma- 
tions, rheumatisms, catarrhs, asthmas, paralysis and consumption, are 
induced by a want of precaution in this particular. Yet with all these 
demands for capacious drying air-space, bedrooms are apt to be scan- 
dalously small and low, damp and unwholesome. They do not usually 
contain fireplaces to drain off the bad air, and the lack of all ventila- 
tion is made worse by the popular dread of draughts, which prevents 
the opening of windows. There is urgent necessity for the adoption 
of some means of relieving them. Opening the window 
above and below is very serviceable; lowering the upper 
sash, with an opening over the door, and currents in halls> 
also gives relief. But if the bedroom have no fireplace, it 
should be connected by tubes with the chimney flue, the 
aperture being guarded by an Arnott's valve. 

360. Ventilating Gas-bnincrs. — As we before remarked, the 
common mismanagement of gas is a forcible illustration of 
the effect of ignorance or thoughtlessness, in often turning 
the best things to the worst account. Gaslight is cheap, 
brilliant and convenient, the very qualities we want ; and so 
we turn it on and enjoy the flood of light. But bad air and 
headache supervene, and then gas-lighting is condemned, 
though the real fault is lack of ventilation. The use of gas- 
light greatly heightens the necessity for effective change of air ; it 
generates poison exactly in proportion to its brilliancy. Dr. Faea- 
DAT adopted the following successful plan to ventUate gas-burners 


He placed a metallic tube about an incb in diameter over tbe lamp- 
glass, dipping down into it (Fig. 87) one or two inches, and connect- 
ing by its other extremity with a flue. But this was thought to be an 
ungraceful appendage to the chandelier, and has not come into use. 
He devised another, by which the tube carrying off the products of 
combustion, returned parallel with the supply pipe, but we have not 
seen it. There is report also of a stiU more elegant and successful 
English contrivance, but it cannot yet be found in this country. 

361. Ventilation of Cellars. — It was seen that cellars are fountains 
of offensive air, which ascends through crevices in the floor, doors, 
windows, and stairways, often infecting the upper apartments with 
the noxious cellar atmosphere. If cellars are to be tolerated under 
our houses, they should be thoroughly ventilated. Perhaps the best 
plan is to extend a flue from the chimney down into the cellar, by 
which the fire-draught above shall constantly drain it. A tube or 
passage from the cellar to the top of the building, mounted with an 
ejecting cowl, answers a good purpose. Some go for abolishing cellars 

362. Ventilation should be provided for in Bnilding. — There can be 
little question that the whole policy of warming and ventilating 
dwellings is yet in an unsettled and transition state, although this 
affords no apology for neglecting the subject. Much is known, and a 
great deal may be done about it to promote health and preserve life. 

* " While I woDld condemn cellars and basements entirely, the common plan of build- 
ing, in their absence, must bo condemned also. The house being built above the surface 
of the earth, a space is left between the lower floor and the ground, which is even closer 
and darker than a cellar, and which becomes, on a smaller scale, the source of noxious 
emanations. Under-floor space should be abolished as well as cellars and basements. 
The plan that I have adopted with the most satisfactory success, to avoid all these evils, 
is the following : Let the house be built entirely above the ground ; let the lower floor 
be built upon the surface of the earth, at least as high as the surrounding soil. If filled 
up with any clean material a few inches above the surrounding earth, it would be better. 
A proper foundation being prepared, make your first floor by a pavement of brick, laid 
in hydraulic cement, upon the surface of the ground. Let the same be extended into 
your walls, so as to cut off the walls of your house with water-proof cement, from all 
communicatiou with the moisture of the surrounding earth. Upon this foundation build 
according to your fancy. Your lower floor will be perfectly dry — impenetrable to moist- 
ure and to vermin ; not a single animal can get a lodgment in your lower story. By 
adopting this plan, your house will be dry and cleanly ; the atmosphere of your ground- 
floor will be fresh and pure ; you will be entirely relieved from that steady drain upon 
life, which is produced by basements and cellars, — and if you appropriate the ground- 
floor to purposes of storerooms, kitchen, &c., you will find that the dry apartments thus 
constructed are infinitely superior to tlie old basements and cellars. And if you placi 
your sitting and sleeping rooms on the second and third floors, you will be as thoroughly 
exempt from local miasma as Architecture can make you." — Dr. Buchanan. 


Provision should be made for ventilation in the first construction of 
dwellings, as it may then be efiectually and cheaply accomplished. 
The introduction of adequate arrangements, after the building is 
finished, is costly and difiicult. The necessity is absolute for including 
ventilating provisions in houses as well as those for heat. Architects 
and Builders should make them a primary and essential element of 
their stractural arrangements, and design in accordance with the prin- 
ciples of ventilation as an established art. It is to be regretted that 
too many in those professions to which a careless public commits its 
interests in this particular, are prof&undly unconscious of the just 
claims of the subject, and totally unqualified to deal with it properly. 
This is hardly a matter of surprise when we recollect how recent it is 
that science has thrown its light upon the physiological relations of 
air. It is almost within the memory of men still living that oxygen 
gas was first discovered^ and it is withia twenty years that Liebeo an- 
nounced the last constant ingredient of the atmosphere (280). Archi- 
tecture on the contrary rose to the dignity of a regular art thousands 
of years ago, when men had little more intelligent understanding of 
the real import of the breathing process than the inferior animals. 
"We have therefore little cause for amazement when a book appears 
upon the subject of Architecture, of more than a thousand pages, and 
dispatches the whole matter of ventilation in ten lines — and that, too, 
with a sneer. Our buildings are hence commonly erected with less 
reference to healthful comfort than outside show, and ventilation is 
too much looked upon as a mere matter of tin tubes and knocking 
out bricks, that may be attended to at any time when it may be 
thought necessary. 

363. Ventilatiott involves necessary loss of Heat. — The real practical 
difliculty in ventilation is its cost. Although the atmosphere is every 
one's property, and is the cheapest of aU things, yet a supply of pure 
air in dwellings is by no means free of expense. To ensure ventilation 
we must have motion of air, and to produce motion demands force, 
which is a marketable commodity. Whatever will produce available 
force has value in it. "Whether it be fans and pumps driven by steam- 
engines, or upward currents set in motion by naked fire, in both cases 
there is expenditure of fuel. It is true we may use the fire that must 
be kindled to produce warmth, and thus secure the additional result 
of ventilation, apparently without additional cost. But in most cases 
foul air is also warm air, and in escaping conveys away its heat, which 
is thus lost. Contrivances have been proposed, by which the outflow- 
ing warm air may be made to impart its heat to the incoming cold 


air, but tliey are not yet reduced to practice. Until that is done, heat 
must continue to be lost by ventilation, just in proportion to its extent. 
Hence, as was before remarked, ventilation may be classed with food 
and apparel, and it becomes a question of how much can be afforded. 
But there is this important difference, that whUe economy in the 
latter — a plain table and coarse clothing — are at least equally favorable 
to health with more expensive styles of eating and dressing, economy 
of ventilation on the contrary, that is, any cheapening or deterioration 
of the vital medium of breathing, is injurious to health. One of the 
worst evils of scarce and expensive fuel is, that the poorer classes feel 
compelled to keep their rooms as tight as possible to prevent the 
escape of warm air and the consequent waste of heat. 




364. Yiew of the origin of Foods. — The ground thus far traversfid has 
farnislied abundant illustration of the close alliance between man and 
the material universe, and of his subjection to physical influences ; but 
we are now to see that he is composed of exactly the same materials 
as the solid globe upon which he dwells. Eocks, corroded by the 
agencies of time and crumbled into soils, join with the ethereal ele- 
ments of the atmosphere, to furnish the substances of which the 
living body is composed. But rocks, soils, and air are not food. They 
are unorganized, lifeless matter ; and can neither nourish the body, 
nor have they the power of uniting themselves together into nutritive 
compounds. The forces which play upon terrestrial atoms, throwing 
them into movement, arranging them into vital groups, and endowing 
them with the capability of becoming parts of animal systems, are 
shot down from the heavens. The impulses of organization and 
growth are not inherent powers of our earth, residing in air and soil. 
In the plan of the universe the Sun, a star among the stellar systems, 
is the architect of living forms, the builder of terrestrial organization, 
the grand fountain of vitality. His rays are streams of force, which, 
after travelling a hundi'ed millions of miles through the amplitudes 
of space, take effect upon the chemical atoms of the earth's surface — 
its gases, waters, miaerals, and combine them into nutritive, life-sus- 
taining compounds. The vegetable world is the laboratory wher« 
this subtle chemistry is carried forward, and matter takes on the 
properties of organization. Such is the ultimate source of all our 
food. The solid materials which we perpetually incorporate into the 
bodily fabric, originated in plants, under the direct agency of the sun- 


beam. The vegetable leaf is the crucible of vitality, the consecrated 
mechanism appointed to receive the life-forces which God is per- 
petually pouring through his universe. In partaking of the bounties 
of the table, are we not, then, consummating a purpose to which 
planetary systems are subservient ? We repair the failing textures of 
animal life, but it is with tissues woven in a loom of invisible airs by 
the flying shuttles of light. That a single grain of wheat may be 
ripened — that its constituent starch, gluten and sugar may be per- 
fected, this ponderous orb must shoot along the ecliptic at the rate 
of 68,000 miles per hour, from Taurus to Libra, whirling perpetually 
upon its axis as it flies, that all parts may receive alike the vitalizing 
radiations. When therefore we contemplate the grandeur of the 
operations by which the Creator accomplishes the problem of life in 
this state of being, the subject of foods rises to a transcendent interest. 
The consideration of these questions, however, the forces that control 
vegetable groAvth and give rise to organic compounds, pertains to 
chemistry and vegetable physiology ; neither our plan nor our space 
will allow us to consider them here. We direct attention flrst to the 
general properties of foods, as we find them already produced and 
presented for preparation and use. 

365. How Foods may te considered. — A systematic presentation of 
the subject of aliments, that shall be quite free from scientific objec- 
tion, appears in the present state of knowledge to be impossible. We 
shall adopt an arrangement which aims only to be simple and popular. 
All articles of diet are composed of certain substances, which are 
known a.?, alimentary principles^ — simple aliments, ajid proximate prin- 
ciples. These are not the ultimate elements, carbon, oxygen, hydro- 
den, nitrogen, sulphur, &c., but are formed by combinations of tliese. 
They differ from each other in properties, exist in very different 
proportions in various kinds of food, and are capable of being sepa- 
rated from each other and examined independently. These require to 
be first considered. ISText in order we shall speak of the products 
which these simple principles form when united together. Thus 
starch, sugar, gluten, &c., are simple aliments; while grain, roots, 
meats, &c., are made up of them, and are therefore called compound 
aliments. We shall give the composition of these, and as much of 
their history and preparation as may be necessary to understand their 
properties, and then trace the changes which they undergo in culinary 
management. The principles involved in various modes of preserving 
alimentary substances will next be described, and the subject closed 
by an examination of their physiological effects and nutritive powers. 


366. Division of Alimentary Principles. — The simple alimentary prin- 
ciples are separated into two important divisions, based on their com- 
position ; first, the non-nitrogenous aliments, or those containing no 
nitrogen in their composition ; and second, the nitrogenous aliments, 
or those which do contain this element. The first group consists of 
starch, sugar, gum, oO, and vegetable acids ; whUe the second com- 
prise albumen, fibrin, gluten, casein. Of these two classes the first 
is simpler in composition and much more abundant in nature than the 
other class ; we shall hence consider them first. There is, however, 
another alimentary substance of peculiar properties, and of the first 
importance — water, which cannot be ranked strictly with either group. 
It is not a product of vegetable growth, but is rather a kind of univer- 
sal medium or instrument of all sorts of organic changes. As the 
most abundant and indispensable of all the principles of diet, it claims 
our first attention. 


A.— "Water. 

867. Solvent Powers of Water. — One of the most important proper- 
ties of water is its wonderful power of dissolving many solids ; that 
is, when placed within it they lose their solid form, disappear, and be- 
come diffused through the liquid. Such a combination is called solu- 
tion. It is the result of a mutual attraction between the liquid and 
the solid, and it becomes weaker between the two substances as this 
attraction is satisfied. The action of water upon soluble substances is 
very powerful at first, but as solution proceeds the action gradually de- 
creases, until the water will dissolve no more; it is then said to be 
saturated. Water saturated with one substance, may lose a portion of 
its power to dissolve others, or its solvent energy may sometimes be 
increased ; this depends upon the compound which it contains in solu- 
tion. "With some substances it combines in all proportions, and never 
gets saturated. Water does not dissolve all substances ; if a fragment 
of glass and a piece of salt be put into it, the glass will be unchanged, 
while the salt will vanish and become liquid. Nor does it dissolve 
alike all that it acts upon ; a pound of cold water will dissolve two 
pounds of sugar, while it will take up not over six ounces of common 
salt, two and a half of alum, and not more than eight grains of lime. 
Heat influences the solvent powers of water, most generally increasing 
it ; thus, boiling water will dissolve 17 times as much saltpetre as ice 


water. This it seems to do by repelling the particles of the solid body 
from eacb other, thus assisting the water to insinuate itself among 
them, by which its action is helped. But there are exceptions to the 
rule, of which lime is an example ; sixty-six gallons of water at 32° 
dissolves one lb. of lime, but it takes 75 gallons at 60°, or 128 at 212°, 
to produce the same effect, so that ice-cold water dissolves twice as 
much lime as boiling water. 

368. How test to hasten Solution. — Solids should be crushed or 
pulverized, to expose the largest surface to the action of the solvent 
liquid. Substances which in the lump would remain for days undis- 
solved, when reduced to powder are liquefied in a short time. When 
a solid, as common salt or alum, is placed in a vessel of water to dis- 
solve, it rests at the bottom. The water surrounding it becomes sat- 
urated, and being heavier, remains also at the bottom, so that the solu- 
tion proceeds very slowly. By stirring, the action is hastened, but this 
takes up much time. The best plan is to suspend the salt in a colan- 
der, basket, or coarse bag, at the surface of the liquid. As the parti- 
cles of water take up the particles of salt, they become heavier and 
sink ; other particles take their places, dissolve more of the salt, and 
sink in turn, so that the action of a constant current of liquid is kept 
up on the suspended crystals, and always at that portion most capable 
of dissolving them. 

369. Solution of Gases — Soda-water. — Water also dissolves or absorbs 
vai'ious gases, some more and some less. It may take 780 times its 
bulk of ammonia, an equal bulk of carbonic acid, or Jj its bulk of 
oxygen. The quantity is, however, controlled by heat and pressure ; 
heat acts to expel the gases, so that as the temperature rises, the water 
will hold less and less, while with increased pressure, on the contrary, 
it will receive an increased amount. Soda-water is thus by pressure 
overcharged with carbonic acid gas, which escapes with violent effer- 
vescence when the pressure is withdrawn. The effect is the same, 
whether the gas is forced into the water from without, or generated in 
a tight bottle or other vessel, as is the case with fermented liquors. 
The gas gradually produced is dissolved by the water, which, escaping 
when the cork is withdrawn or the vessel unclosed, produces the foam- 
ing and briskness of the liquor. 

370. DiflTerent varieties of Water. — In nature water comes in contact 
with a great number of substances which it dissolves, so that there is 
consequently no perfectly pure, natural water. The substances which 
it takes up are numerous, and differ under various circumstances and 
conditions, and as these foreign substances or impurities which the 


■water acquires, communicate their properties to the liquid, it results 
that there are many varieties of natural water, as for example, spring- 
water, river-water, sea-water, rain-water, &c. 

371 . Rain-water and Snow-water. — Rain-water is the least contami- 
nated of all natural waters, yet it is by no means perfectly pure. As 
it faUs through the air, it absorbs oxygen, nitrogen, carbonic acid 
and ammonia, with which it comes in contact, and it also washes out 
of the atmosphere whatever impurities it may happen to contain. 
Thus, in the vicinity of the ocean, the air contains a trace of common 
salt ; in the neighborhood of cities, various saline, organic, and gaseous 
impurities, while dust is raised from the ground and scattered through 
it by winds, and these are all rinsed out of the air by rains. The 
water which falls first after a period of drought, when contaminations 
have accumulated in the air for some time, is most impm-e. Rain fall- 
ing in the country, away from houses, and at the close of protracted 
storms, is the purest water that nature provides. It differs from dis- 
tilled water only in being aerated^ that is, charged with the natural 
gases of the air. Falling near houses, it collects the smoky exhala- 
tions, and flowing over the roofs it carries down the deposited soot, 
dust, &c. "Water from melted snow is purer than rain-water, as it de- 
scends through the air in a solid form, incapable of absorbing atmos- 
pheric gases. When melted, the water which it produces is insipid 
from their absence, and should be exposed for a day or two to the at- 
mosphere, that it may absorb them. 

372. The Gases contained in Water. There is an atmosphere diffused 
through all natural waters. It is richer in oxygen than is the upper 
atmosphere ; in the latter there is but 23 per cent., while in the air of 
water there is 33 per cent. The animals which dwell in water absorb 
this oxygen by breathing, just as land animals do from the air, while 
water-plants in the same manner live on the carbonic acid it contains. 
These absorbed gases also influence its taste, giving it a brisk and 
agreeable flavor. If it is boiled they are driven off, and the liquid be- 
comes flat and mawkish. The presence of as much oxygen as water 
wiU hold, improves it as a beverage, as this gas is necessary to the ac- 
tive performance of several of the most important vital functions. 
Water that is quite cold contains more oxygen than that which has 
been made warm in any way, as by exposure to the sun or the warmth 
of a close room, which causes a portion of it to escape. 

373. Organic Contaminations of Water. — From the dust and insects 
of the air, the wash of the ground and the drainage of residences, 
from mud and decayed leaves, the decomposing bodies of dead ani- 


mals, and a variety of other causes, waters are liable to contain or- 
ganic impurities, or those vestiges of liviag structures which are 
capable of decomposition and putrefactive change. The effect of this 
organic matter may be shown by taking a little of the sediment that 
has accumulated at the bottom of a cistern, and placing it in a bottle 
of perfectly pure distUled water, when in a short time, if the weather 
be warm, it wiU begin to smell offensively. This kind of contamina- 
tion may be either suspended mechanically in water as solid particles, 
or it may be dissolved in it so that the water shall stUl have an appear- 
ance of purity. 

374. The lining Inbaltitants of Water. — Under certain favorable con- 
ditions of warmth, access of air, light, &c., countless numbers of living 
beings, both plants and animals, make their appearance in water. 
They are nourished upon the dead organic matter which the water 
may happen to contain, and belong either to the animal kingdom as 
animalcula or infusoria, or are of a vegetable nature, as fungi. 
There are other conditions which influence the Tcind of life which ap- 
pears in water. If the liquid be slightly alkaline, animalcula will be 
produced, while if it be a little acid, fungi or microscopic plants wUl 
appear. This maybe shown by diffusing ahttle white of egg through 
water in a wine glass, and keeping it in a warm place. If it be made 
in a small degree alkaline, it wiU swarm with animalcula in a few days ; 
if, on the contrary, it be slightly acid, vegetable forms will be princi- 
pally originated. It is important to notice also that the alkaline solution 
wiU run rapidly into putrefaction, and yield a putrescent smell, while 
the acid fluid will scarcely alter at all, and emit no unpleasant odor. 
It is hence obvious that these two kinds of water have different rela- 
tions to human health, the slightly acid being more favorable to it 
than alkaline waters. These living inhabitants are never found in 
freshly fallen rain-water, caught at a distance from houses, nor in 
spring or well-water, but they more or less abound in cistern water, 
reservoir water, and marsh, pond, and river waters. 

375. Use of living beings in impnre Water. — The presence of living 
tribes in impure water, fulfils a wise and beneficent purpose. If the 
large amount of organic matter present in many waters could be re- 
moved only by the common process of putrefaction, and the forma- 
tion of injurious compounds and offensive gases, immense mischief 
would be the consequence. To obviate this, nature has ordained that 
some of the organic matter of impure water, in place of undergoing 
decomposition, shall be imbibed by living beings, and these dying that 
others shall take their place and fulfil the same important office. The 


living races thus exert a preservative influence upon water, although 
this is more especially true of aquatic vegetation, 

376. Water dissolves variable quantities of Mineral Matter. — Rain 
which falls upon high ground filters through the porous soil and strata 
of the earth until stopped by impenetrable clay or rock; it then passes 
along the surface of the bed until it finds an opening or crevice, 
through which it is forced up to the surface of the ground, producing 
a spring. Water which has thus leached through the mineral mate- 
rials of the earth, dissolves such portions of its soluble materials as it 
meets with, and carries them down to the lower levels, so that they 
ultimately collect in the sea. The amount of mineral matter thus dis- 
solved is extremely various. The water of the river Loka, in North- 
ern Sweden, which flows over impervious, insoluble granite, contains 
only Jg of a grain of mineral matter in a gallon weighing 70,000 
grains. Common well-waters, spring- water and river-water, contain 
from 5 to 60 grains in a gallon, but generally, in waters of average 
purity, which are employed for domestic purposes, there are not pres- 
ent more than 20 or 30 grains of mineral matter to the gallon. When 
the dissolved substances accumulate untU they can be tasted, a mineral 
water results. The celebrated Congress water, at Saratoga, contains 
611 grains to the gallon. Ocean water has as much as 2,500 grains of 
saline substances, and the water of the Dead Sea the enormous quan- 
tity of 20,000 grains in the gallon. Of the two natural waters — those 
of the river Loka and the Dead Sea — the latter contains 400,000 times 
more saline matter than the former, 

377. Rinds of Mineral Matter dissolved by Water. — The mineral sub- 
stances dissolved in spring and well waters, are chiefly iron, soda, 
magnesia and lime, combined with carbonic and sulphuric acids, and 
forming salts^ which are compounds of acids with alkalies or bases ; 
sulphates and carbonates, together with chloride of sodium or common 
salt. Iron, mixed with carbonic and sulphuric acids, is present in 
most waters which percolate through the ground; soda and magnesia 
also often exist in these waters, but their most universal and important 
ingredient is lime. This exists in almost aU soils in combination with 
carbonic acid as carbonate of lime, or powdered limestone, and it is 
also very common in the shape of sulphate of lime, or plaster. Most 
of these substances are soluble in pure water, but this is not the case 
with the widely diffused carbonate of lime. The power of dissolving 
this substance depends upon the presence of free carbonic acid con- 
tained within in the water. If charged with this gas, water becomes 
a solvent of limestone. 


378. Hard and Soft Water. — The presence in water of these dis- 
solved mineral substances, though in extremely small proportion, pro- 
duces important changes in its properties. Compounds of lime and 
magnesia give it hardness^ while rain and snow-water, and that from 
some springs which are free from these mineral matters, are called 
soft. This distinction of waters into hard and soft is usually connected 
with its cleansing qualities and its behavior towards soap, which we 
shah consider in another place. It is also important dietetically (533), 

379. Water in contact with Lead. — There has been much contradic- 
tion among scientific men in regard to the effects of storing water in 
leaden vessels, or transmitting it through leaden pipes. It was known 
that some kinds of water would corrode or dissolve the lead and be- 
come poisonous ; but what waters ? Dr. Oheistison said those which 
were soft^ while hard waters would form a crust in the interior surface 
of the lead, and thus protect it from corrosion. But later experi- 
menters declare hard waters to be even worse than soft in their action 
upon lead. It may be remarked that water can act upon lead, cor- 
roding it without becoming itself actively poisonous, if the compound 
formed be insoUible ; it is only when the lead is dissolved that the 
water containing it becomes dangerous. When ordinary water is 
placed in contact with lead, the free oxygen it contains combines with 
the metal, forming oxide of lead ; water immediately unites with that 
producing hydrated oxide of lead, which is nearly insoluble in water. 
There is also more or less carbonic acid existing in all natural waters ; 
this combines with the oxide of lead, forming carbonate of lead, 
which is also highly insoluble. But if there be in the water mucJi 
carbonic acid, a hicarbonate of lead is formed, which is very soluble, 
and therefore remains dissolved in the water. Hence waters which 
abound in free carbonic acid, as aiso those which contain bi carbonates 
of lime, magnesia, and potash, are most liable to become poisoned by 
lead. Water containing common salt acts upon this metal, forming a 
soluble, poisonous chloride of lead. On the other hand, water con- 
taining sulphates and phosphates is but little injured, these salts exert- 
ing a protective influence on the lead. "From a review therefore of 
the whole of the arguments and experiments now advanced, respect- 
ing the action of different waters on lead, we deduce the following 
general conclusions : That while very soft water cannot be stored for 
a lengthened period, with impunity, in leaden vessels, the danger of 
the storage of hard water under the same circumstances is in most 
cases much greater. This danger, however,-is to be estimated neither 
by the qualities of hardness or softness, but altogether depends upon 



the chemical constitution of each different kind of water ; thus, if this 
be ever so soft, and contain free carbonic acid, its action on lead will 
be great ; whereas if it be hard from the presence of sulphates and 
phosphates principally, and contain but few bicarbonates, &c., little 
or no solution of the lead will result." — Dr. Hassall. Water is 
powerfully corrosive of iron when conveyed through this metal in 
pipes, but the compounds formed are not injurious. Galvanized iron 
pipes, which have received a coating of tin (610), are coming much 
into use instead of lead for the conveyance of water. 

380. Supply of Soft Water, — Wells and springs are often inacessible, 
or the water furnished is bad. In such cases the heavens furnish an 
unfailing resource, which, with well-constructed cisterns, filters, and 
ice, leave little to be desired in the way of aqueous luxury. Taking 
the annual rainfall at 36 inches, we have 3 cubic feet of water falling 
upon a square foot of surface in a year. A cubic foot contains 61- 
gallons, BO that we get 18J gallons upon each surface foot annually. 
A house 25 by 40 has a thousand feet of surface, and collects nearly 
19,000 gallons of water annually, which if stored in cisterns of suf- 
ficient capacity, will furnish more than 50 gallons per day throughout 
the year. 

B.— Tbe Starcbes. 

381. Whence oI)tained, and how separated. — Starch, when pure, is 
seen to be a fine snow-white glistening powder. It is found univer- 
sally distributed in the vege- 
table kingdom in much 
greater quantity than any 
other substance formed by 
plants for food. It exists 
in grain, peas and beans ; in 
all kinds of seeds ; in roots, 
as potatoes and carrots, and 
in the stem, pith, bark, and 
fruit of many plants. When 
wheat flour is mixed up into 
a dough, and washed (Fig. 
88), on a Unen cloth with 
clean water, a milky liquid * O ii k^ ||| 

passes through containing ^ . „ , „ , , 

, , , , ^ Separating Starch from flour by Tvashmg. 

wheat starch, which grad- 
ually settles to the bottom of the vessel. If raw potatoes are 


grated, and the pulp treated in a similar manner, potato starcli is 

882. Proportions in Tarions substances. — The variable proportion of 
starch in different articles of food is as follows, in decreasing order : 

starcli per eent* 

Eice flour 84 to 85 

Indian corn 77 to 80 

Oatmeal 70 to 80 

Wheat flour 39 to 77 

Barleyflonr 67 to 70 

Kye flour 50 to 61 

Buckwheat 52 

Pea and bean meal 42 to 43 

Potatoes, containing 73 to 78 water, 13 to 15 

383. Starch Grains — their size. — Starch consists of exceedingly small 
rounded grains. They cannot be distinctly seen with the naked 
eye, and are so extremely minute that the finest wheat flour, which 
has been ground to an impalpable dust, contains its starch grains 
mostly unbroken and perfect. The granules of potato starch aro 
largest, while those of wheat and rice are much smaller (Fig. 89), end 
those of turnips and parsnips still smaller, varying all the way from 

Fig. 89. 

starch-grains of potatoes. Starch-grains of plantain. Starch-grains of rico. 

the l-300th to l-10,000th of an inch in diameter. Assuming tho 
grains of wheat starch to be 1-lOOOth of an inch in diameter, a thou- 
sand million of them would be contained in a cubic inch of space. 

384. Their Appearance and Structure. — Viewed under a high mag- 
nifier, starch grains from various sources exhibit marked peculiarities 
in form as well as in size. Several kinds have a ringed or grooved 
aspect, as seen in Fig. 89, which appearance is explained by the fact 
that they consist of concentric layers or membranes, like the coats 


cf an onion. The grains of potato starch are ovoid or egg-shaped. 
Many of the grains of pea starch are hollowed or concave in the direc- 
tion of their length, while wheat starch consists of dull, flattened, 
lens-shaped grains, sticking together when not perfectly dry, on 
which account the wheat starch of commerce always comes in loose 
lumps. Thus each variety of starch-grain has some peculiar appear- 
ance of its own, hy which the practical microscopist is enabled to 
identify it. He can hence detect adulterations of the more valuable 
with the cheaper varieties, as wheaten flour or maranta arrow-root 
with potato starch. 

385. Sago Starch is procured from the pith of several varieties of 
the pahn tree. It comes in various forms. Sago meal or flour is a 
whitish powder. Pearl-sago, the kind in general use for domestic 
purposes, consists of small pinkish or yellowish grains, about the size 
of a pin's head. Common or brown sago consists of much larger 
grains, which are of a brownish white color, each grain being brownish 
on one side and whitish on the other. As aU. the kinds of sago contain 
coloring matters, they are considered inferior to those varieties of 
starch, as arrow-root and tapioca, which are perfectly white. 

386. Tapioca is a variety of starch which comes from South Ameri- 
ca, and is obtained from the root of a plant containing a poisonous 
milky juice. When it appears as a white powder, it is called Brazil- 
ian arrow-root. The term tapioca is commonly applied to that form 
of it which appears in small irregular lumps, caused by its having 
been dried on hot plates, and then broken up into fragments. 

387. Arrow-roct. — A root growing in the West Indies (the Maranta 
arundinacea), contained a juice supposed to be capable of counter- 
acting the effects of wounds inflicted by poisonous arrows. This root 
yielded a starch which took the name of maranta arrow-root. But 
afterward starches from other plants which had a resemblance to 
maranta starch, took also the name of arrow-roots. Thus there is 
Tahiti arrow-root, Manihot arrow-root, from the plant which yields 
tapioca, and potato arrow-root, or British arrow-root, as it is some- 
times called. Maranta arrow-root, which is a very pure white starchy 
powder, is the most prized of all the varieties, but it is often adulter- 
ated with other and cheaper kinds. 

388. Com Starcb. — This is a preparation of the starch of Indian 
corn, which has been separated as perfectly as possible from the other 
constituents of the grain. Chemical means are used to effect the 
separation. The starch is freed from the glutinous, oily and hgneous 
elements of the seed, by the aid of alkaline solutions, and by grinding 


and bolting the corn in a wet condition. The grain is reported to 
yield from 30 to 35 per cent, of pure starch, which bears a general 
price, about one-third greater than wheaten flour. The culinary 
changes of starch and its effects upon the system will be considered 
under these topics (516). 

389. CIiemLcal Composition. — Starch consists of three elements, — 
carbon or charcoal, oxygen, and hydrogen. The two latter are found 
in starch in exactly the same proportions that they exist in water, so 
that the composition of this substance may be given as simply char- 
coal and water. A compound atom of starch consists of twelve atoms 
of carbon, combined with ten of oxygen and ten of hydrogen, or 
twelve atoms of carbon to ten of water. 

C— Tlie Sug'ars. 

390. Proportion in varions Snlistances. — This is the sweet principle 
of food, and is produced by both plants and animals. It exists in 
milk, and it has lately been shown that it is generated in the animal 
liver. But our supplies come entirely from the vegetable world, 
where it is produced in great abundance, both in the sap and juices 
of plants, and stored up in their fruits and seeds. The following is 
the proportion of sugar obtainable from various sources : 

Per cent, of Sugar. 

Juice of Sugar cane 12 to 18 

Beet root 5 to 9 

Wheat flour 4 to 8 

Barley meal 5'3 

Oat meal 4'8 

Cow's milk 8-3 

Eye meal 3-2 

Peas 2 

Indian corn ^ 1"5 

Rice -2 

There are several varieties of sugar, but we are practically concerned 
with but two, cane sugar and grape sugar. 

391. Grape Sngar or Fruit Sugar. — The white sweet grains of raisins 
or dried grapes take the name of grape sugar. Most other fruits, 
however, as apples, pears, plums, figs, cherries, peaches, gooseberries, 
currants, &c., grow sweet in ripening, which is owing to the same 
kind of sugar which exists in the grape. It may be readily extracted 
from fruits, but this is rarely done. 

392. Sugar Artificially Produced. — If starch be boiled for some time 
in water which has been soured by adding to it one or two per cent. 
of sulphuric acid, the solution gradually acquires a sweet taste. If, 


now, by suitable means, the acid be neutralized and removed, and the 
solution boiled down, it yields a rich sirup or a solid sugar. This 
comes from the transformation of starch ; the acid taking no direct 
part in the change, but only inducing it by its presence. Potatoes 
treated in this way, it is said, will produce ten per cent, of their weight 
of sugar. But what is still more singular, the fibre of wood may also 
be converted into sugar. Paper, raw cotton, flax, linen and cotton 
rags, and even sawdust, may be changed to sugar by the same agency. 
The boiling with acid must, however, in this case, be continued longer, 
as the woody matter has first to be changed to starch before it be- 
comes sugar. This product, known as starch sugar^ has the same 
nature and properties as grape sugar. 

393. Hoaey. — This is obtained by bees from the juices found in the 
nectaries, or honey-cups of flowers. They collect it in the crop, or 
honey-bag, which is an enlargement of the gullet, and when filled is 
about the size of a pea. Laden with its sweet treasure, the insect 
retm-ns to the hive and disgorges it into a previously prepared cell of 
the honeycomb, which it then caps over by a thin covering of was. 
To procure it in the purest liquid form, and of the best flavor, the 
plan is to unseal the cells by removing a slice from the surface of the 
comb, after which it is laid upon a cullender to drain. It is some- 
times warmed, to facilitate the flowing, but this is said to injure the 
delicacy of its flavor. It is more commonly pressed. This increases 
the quantity, and saves time ; but it is then contaminated by traces 
of wax, and fouled by the juices of crushed bee-maggots, which may 
happen to be in the comb. 

394. Properties and Composition. — Honey, in different localities, differ- 
ent seasons, and from different flowers, varies very much in color, flavor, 
and fragrance. That from clover, or from highly fragrant flowers, is far 
superior to that from buckwheat ; spring-made honey is better than 
that produced in autumn. Virgin honey, or that made from bees 
that never swarmed, is finer than that yielded by older swarms ; and 
while some regions are renowned for the exquisite and imrivalled 
fiavor of their honeys, that made in some other places is actually 
poisonous. "We can hardly suppose honey to be a simple vegetable 
liquid. It probably undergoes some change in the body of the insect 
by the action of the juices of the mouth and crop, as when bees are 
fed upon common sugar alone they produce honey. Honey is an in- 
tensely sweet sirup, varying in color from nearly white to a yellowish 
brown. It consists of two sorts of sugar. One of these remains always 
in a liquid or sirupy condition, and the other is liable to crystallize or 


change to solid grains {granulate)^ this is grape sugar. The lightest 
colored and most valuable honeys contain the most of it, and hence 
are most liable to granulate and grow thick. Honey contains an 
acid, and aromatic principles, which together with its uncrystallizable 
sweet part, are not very well understood. 

395. Cane Sugar — ^its Sources, — Our common sugar is obtained, as is 
weU known, from the sugar-cane. Eleven-twelfths of aU the sugar 
of commerce has this origin. That which is procured from the as- 
cending sap of the maple, the descending sap of the birch, and also 
from the walnut and other trees ; from the juice of beets, carrots, 
turnips and melons, from green corn-stalks, and the unripe seeds of 
grain, is identical in essential properties with that of the sugar-cane, 
and they are all distinguished as cane sugar. 

396. Cane and Grape Sugars, diflferent conditions of origin. — It is neces- 
sary to understand clearly the difference between cane sugar and grape 
sugar. "We have seen that the agency of acids is employed to convert 
starch into grape sugar, and they have the same effect upon cane 
sugar. This change takes place even in the interior of growing 
plants. Those plants and fruits which possess sour or acid juices, yield 
gi-ape sugar, whUe those which contain little or no acid in their saps, 
contain generally cane sugar. Grape sugar may be produced by art, 
while cane sugar cannot. 

397. Cane and Grape Sugars, clienucal differences. — Sugar, like starch, 
consists only of carbon and water ; but these two sugars differ in the 
proportion of these elements, WhUe cane sugar contains twelve 
atoms of carbon to eleven of water, grape sugar contains twelve atoms 
of carbon to fourteen of water. Grape sugar is therefore less rich in 
carbon than cane sugar, and cane sugar may be transformed into 
grape sugar by the addition of chemically combtaed water. It is an 
essential property of sugar, that under the action of ferments, they are 
decomposed ; converted into carbonic acid and alcohol. Grape sugar 
is most prone to this change ; and cane sugar, before it can undergo 
fermentation, must be first changed into grape sugar. Cane sugar 
passes into the solid state much more readily than grape sugar, taking 
on the form of clear, well defined crystals of a constant figure ; grape 
sugar, on the contrary, crystallizes reluctantly and imperfectly, with- 
out constancy or form. Crystals of cane sugar are regular six-sided 
figures, while those of grape sugar are ill-defined, needle-shaped 

898. Difference of solubility and sweetening powers. — Pure cane sugar 
remains perfectly dry and unchanged in the air, while grape sugar 


attracts atmospheric moisture, becoming mealy and damp. Yet cane 

sugar dissolves in water mucli more readily than grape sugar. While 
a pound of cold "water will dissolve three pounds of the former, it will 
take up but two-thirds of a pound of the latter. Cane sugar will, 
therefore, make a much thicker and stronger sirup than grape sugar, 
dissolving also more freely in the juices of the mouth, (a property 
upon which taste depends). Cane sugar possesses a higher sweetening 
power than the other variety. Powdered grape sugar has a floury 
taste when placed upon the tongue, and very gradually becomes 
sweet and gummy or mucilaginous as it dissolves. Two parts by 
weight of cane sugar are considered to go as far in sweetening as 
five of grape sugar. To make them economically equal, therefore, 
five pounds of grape sugar should cost only as much as two of cane 
sugar ; and hence the mingling of grape with cane sugar is a serious 
deterioration of it. 

399. How Raw, or Brown Sugar is produced. — The sugar of commerce 
appears in various forms, and is sold at various prices. It is impor- 
tant to inquire into the source of these differences which involves a 
reference to the manufacture. Cane-juice contains vegetable albu- 
men, a substance which has a strong tendency to fermentation (488), 
hence, when left to itself in warm climates, it is rajjidly changed ; the 
acid of vinegar being generated ; — twenty minutes is, in many cases, 
sufficient to produce this effect. To neutralize any acid that may be 
thus formed, and partially to clarify the crude juice, lime, which has a 
powerful attraction for organic matter, is added. The juice is then 
boiled, the water being evaporated away until a sirup is produced. 
The liquid is then drawn off into shallow vessels and stirred. As it 
cools the sugar granulates, or appears in the form of small irregular 
grains or crystals, which are kept from uniting together by some of 
the sirup (which has been so altered by the heat that it refuses to 
crystallize), and is known as molasses. The product is then placed in 
suitable circumstances to drain, when a large portion of the molasses 
flows away, and is collected in separate vessels. The sugar, packed in 
hogsheads, is then sent to the market as raw or muscovado, or as it is 
more commonly known, as 'brown sugar. 

400. Of what Brown Sugar consists. — The article when packed by 
the sugar-boiler, consists of sugar more or less browned and dampened 
by molasses, according to the completeness of the draining and dry- 
ing process. It contains more or less vegetable albumen, lime from 
the added lime-water, minute fragments of crushed cane-stalks, often 
in considerable quantity, with grit or sand from the unwashed canes, 


or which may have been introduced into the granulating vessels by 
careless management. 

401. Brown Sngar undergoes a slow fermentation, — We have stated 
that albumen is a very changeable substance, and by its own decompo- 
sition, when in contact with sugar, tends to alter that also. Cane 
sugar, it transforms into grape sugar. Hence, in nearly all raw sugars, 
there is an incipient, slow fermentation going forward, by which a 
portion of cane sugar is converted into grape sugar. Dr. Hassall, 
perhaps the highest authority in matters pertaining to alimentary im- 
purities, states that nearly aU samples of brown sugar contain also 
grape sugar, and that its proportion is greater where there is most 
vegetable albumen. This change, of course, just according to its ex- 
tent, lowers the value of brown sugar. 

402. Living contaminations of Brown Sugar. — We had occasion, when 
speaking of water, to correct that common impression of the iU-in- 
formed, that swarms of animalcules are present In every thing we eat 
and drink. On the contrary, they exist only in certain circumstan- 
ces, and when they do occur, of course impair the value of food for 
dietetical use. As aU animal structures, from the largest to the 

^ „„ smallest contain nitrogen, one 

Fig. 90. PIT 

of the conditions of the exist- 
ence of animalculse is the pres- 
ence of nitrogeneous matter 
upon which to feed. Now pure 
sugar contains no nitrogen, and 
therefore cannot sustain animal 
life. But in brown, coarse 
sugars the existence of vegeta- 
ble albumen offers nourishment 
to these beings, and accordingly 
they are commonly found in- 
fested with minute insects called 
sugar-mites. In general, the 
more the sugar is contaminated 
with albumen, the more numer- 
ous are these disgusting insects. 
They may be detected in the 
less pure sugars by dissolving two or three tea-spoonfuls in a large 
wine-glass of tepid water. After standing at rest an hour or two, the 
animalculfB will be found, some on the surface of the liquid, some ad- 
hering to the sides of the glass, and some in the dark sediment at 

Sugar-mlte, as seen iipon a fragment of cane, 
magnified 130 diameters. 


the bottom, mixed with cane-fragments, grit, and dirt. The mite is 
visible to the nalied eye, as a mere speck ; the microscope, however, 
exhibits its appearance, and history, from the egg state to the per- 
fectly developed animal, which is represented in Fig. 90. 

403. Properties and Compositioa of Molasses. — Common molasses is a 
dense brown liquid, the drainage of the brown sugar manufacture. It 
contains a portion of sugar that has been burnt and darkened in boil- 
ing ; another part that has been so changed to the mucilaginous state, 
by boiling, that it does not crystallize, together with a quantity of 
crystallizable sugar. It is strongly absorbent of water ; indeed, many 
kinds of raw sugar melt into sirup when exposed to the air. Chemi- 
cally considered sugar is an acid substance, and combines with bases, 
as potash, soda, magnesia, to form salts called saceharates. Molasses 
contains a portion of saccharine matter, combined with the lime used 
in the sugar manufacture (399) ; also with small quantities of the alka- 
lies. Molasses itself is also acidulous. It has a peculiar strong taste, 
which Cadet states may be removed by boiling for half an hour with 
pulverized charcoal. Sugar-house molasses and sirups are the residue 
which remains uncrystallized in purifying and refining brown sugar. 

404. Refined Sngan — To cleanse it of impurities and improve it in 
color and taste, crude sugar is refined. It is melted and has mingled 
with it a small portion of albumen (ox-blood), which clears it of me- 
chanical contaminations. The sirup is then filtered through a bed of 
animal charcoal (burnt bones crushed), by which it is decolorized, and 
lastly, it is crystallized, by boiling at a low temperature in vacuum- 
pans, in which the atmospheric pressure is removed (62). The discol- 
oring and darkening principle in the various grades of sugar is the 
molasses which has not been removed, but which remains in the crys- 
tallized mass. 

405. Sugar-candy and how it is Colored. — "When the pure sugar is melted 
or dissolved, it forms a clear liquid, and when allowed to cool or dry 
without disturbance, it crystallizes into a transparent solid, like glass. 
When threads are suspended in the sugar solution, crystals of extreme 
hardness collect upon them, which are known as rock-candy. The 
cause of whiteness in refined sugar is that the crystals are small, con- 
fused, and irregular. To make candy white, the sugar, while cooling, 
is agitated and worked (pulled)^ which breaks up the crystals and ren- 
ders the mass opaque. Candy is commonly adulterated with flour, 
and frequently with chalk. Various colors are given to sugar-confec- 
tionery by adding paints and dies expressly for the purpose. Some of 
these are harmless and others poisonous. Those which are least inju- 


rious are the vegetable and animal coloring matters, but these neither 
form so brilliant colors nor are they so lasting as the mineral com- 
pounds, which are far the most deadly. The following are the chief 
coloring substances used by confectioners to beautify their sugar 
preparations : 

( Oxide of lead (red lead). 

Eeds J Bisulplmret of mercury {DermiUon). 

( Bisulpliuret of arsenic (red orpimenf). 

I Gamboge. 

Yellotts. . . •< Chromate of lead (chrome yellow). 

( Sulphuret of arsenic (yelloio orpiTntnt). 

( Ferrocyanide of iron (Prussian dlue). 

I Cobalt. 

Bltjes J. Smalt (fflass of codalf). 

> Carbonate of copper (verdiier). 

I. Ultramarine. 

( Diacetate of copper (verdigris). 

Greens ■< Arsenite of copper (emerald green . 

( Carbonate of copper (mineral green). 

Whites Carbonate of lead (white lead). 

PuEPLEB Formed by combining blues and reds. 

From an examination of 101 samples of London confectionery, Dr. 
Hassall found that 59 samples of yellow were colored with chromate 
of lead and 11 with gamboge. That of the reds 61 were colored with 
cocTiineal.! 12 with red lead., and 6 with vermilion. Of the blues, one 
sample was colored by indigo, 22 by Prussian Hue, and 15 by ultra- 
marine. Of the greens 10 were colored by a mixture of chromate of 
lead and Prussian dlue, 1 with carbonate of copper, and 9 with arsen- 
ite of copper. These colors were variously combined in the diiferent 
cases, as many as from three to seven colors occurring in the same 
parcel, including three or four poisons. 

406. Their daEgerons and fatal Effects. — The Dr. remarks: "It may 
be alleged by some that these substances are employed in quantities 
too inconsiderable to prove injurious, but this is certainly not so, for 
the quantity used, as is amply indicated in many cases by the eye 
alone, is often very large, and sufficient, as is proved by numberless re- 
corded and continually recurring instances, to occasion disease and 
death. It should be remembered, too, that these preparations of lead, 
mercury, copper, and arsenic, are what are termed cumulative, that is, 
they are liable to accumulate in the system, httle by little, until at 
length the full effect of the poisons become manifested. Injurious con- 
sequences have been known to result from merely moistening wafers 
with the tongue ; now the ingredients used for coloring these include 


many that are employed in engar confectionery. How mucli more in- 
jurious, then, must the consumption of sugar thus painted prove when 
these pigments are actually received into the stomach." 

D.— Tlie Gums. 

407. Properties of the Gums. — The juices of many plants contain 
substances which ooze out through the bark, forming rounded trans- 
parent masses of gum, as we often see upon cherry, plum, peach and 
apple trees. The gums differ considerably in properties. Cherry-tree 
gum is insoluble in cold water, but dissolves readily in boiling water, 
while gum-arabic dissolves in cold water, and gum-tragacanth dissolves 
in neither, but only sweUs up into a kind of mucilage. The solutions 
of gums are clear and tasteless, and have a glutinous and sticky nature, 
which adapts them for paste. 

408. Artificial Gum. — "When common starch is heated to 300 degrees 
in an oven, or boUed in water made sour by a little sulphuric acid, it 
is so altered as to dissolve in cold water, forming a clear, viscid solu- 
tion. The substance thus produced from the starch has the properties 
of gum, and is known as dextrine. 

409. How Gum is Composed. — In chemical composition, gum and 
dextrine do not differ from starch; they consist of 12 atoms of 
carbon combined with 10 of water. Gum exists in grains, and many 
vegetables, and hence is a widely-diffused element of food, although it 
does not occur in large quantities. Its dietetical value, as shown by 
its composition, is the same as starch and sugar, and hence it is 
grouped with the saccharine alimentary principle. 

£.— Tbe Oils. 

410. Distinction between Volatile and Fixed Oils. — Oils are of two 
classes : 1st, those which, when smeared upon paper, produce a stain 
or grease spot, which does not disappear by time or warmth, and 
hence called Jixed oils; and, 2d, such as wiU vanish from paper, 
under such circumstances leaving no permanent stain, and there- 
fore called volatile oils. The former is a xmiversal and important 
element of diet, the latter presents itself chiefly among condiments, 
and wiU be there considered. 

411. Sonrces and Forms of Oily Bodies. — Oil is largely procured both 
from plants and animals, and from both sources it is chemically the 
same thmg. It exists in many parts of vegetables, but is chiefly 
stored up in their seeds, from many of which it is obtained by pressure 


in large quantities. In animal bodies it is deposited in the sacks or 
cavities of cellular tissue, and becomes accumulated in large quanti- 
ties in different parts of the body. Oils and fats are chemically iden- 
tical, differing only inconsistence, and this quaUty depends upon tem- 
perature. Lowering the temperature of a liquid oil sufficiently, 
changes it to a solid, while raising that of a solid tallow converts it 
into a flowing oil. That which, in the hot climate of Africa, is liquid 
palm oil, is with us solid ^aZm 'butter. Those oils, however, which at 
ordinary temperatures are not perfectly fluid, but have what is called 
an oily consistence, become much thinner and completely liquid when 

412. Proportion of Oil in Articles of Diet. — The proportion of oily 
matter from many sources is variable, as in the case of meat, which 
may more or less abound in fat. Nor has its amount in many vege- 
tables been determined with sufficient certainty. The following are 
the quantities given by the later authorities : ' 

Yolk of Egg 28-75 per cent. 

Ordinary Meat (Libbig) 14-03 " 

Indian Corn 9' " 

Oatmeal (husk excluded) 6" " 

CoVe Milk 3-13 " 

Eye Flour 8-5 " 

Wheat Flour 1 to 2 " 

Barley Meal 2- " 

Potatoes (dried) 1* " 

Eico "8 " 

Buckwheat "4 " 

^13. Its Composition. — Oleaginous bodies are distinguished from 
all the other alimentary principles, by their chemical composition, and 
the resulting properties. They resemble the preceding substances 
which we have been considering in containing three elements, carbon, 
hydrogen and oxygen ; but they differ from all of them in this im- 
portant respect, that they are composed almost entirely of hydrogen 
and carbon, with but a small proportion of oxygen. The composition 
of hogs-lard, as given by Oheveeul, may be taken as an example of 
the general structure of this alimentary group. It consists of carbon 
79, hydrogen 11, oxygen 10 parts in a hundred. We have seen that 
hydrogen and carbon are the active flre-producing elements of fuel 
(80). As the oils are so rich in these, they rank high as combus- 
tibles, burning with great intensity, and yielding much heat. It has 
been also noticed that oils may be decomposed into several acid and 
basic principles (196). 


F.— The Vegetable Acids. 

414. Combination and Composition, — The sourness of fruits and suc- 
culent vegetables is due to various acids produced in the plant, and 
which they contain usually in quite smaU proportions. They exist in 
two states : 1st, as pure acids, or free, when they are strongest ; and, 
2d, combined with bases, as potash, lime, &c., by which they are 
partially neutralized, and thus rendered less pungent to the taste. In 
this case they exist as acid salts (691). The vegetable acid group con- 
sists of but three elements, carbon, oxygen, and hyorogen, like the 
starch and oil groups, but it is distinguishable from them by contain- 
ing but a small share of hydrogen and a large proportion of oxygen. 
The composition of the different vegetable acids is quite variable, but 
they all agree in possessing less hydrogen and more oxygen than any 
other class of organic alimentary principles. Their nutritive value is 
very low. 

415. Acid of Apples — Malic-Acid, — This is the peculiar acid of apples, 
and it is also found la numerous other fruits. Thus, it exists free in 
pears, quinces, plums, peaches, cherries, gooseberries, currants, straw- 
berries, raspberries, blackberries, elderberries, pineapples, grapes, 
tomatoes, and several other fruits. It exists very abundantly in green 
apples, causing their extreme acidity, and diminishes as they ripen. 
The wild crab-apple is much richer in malic-acid than the cultivated 
fruit, and generally speaking, in proportion as we obtain sweetness by 
culture, we deprive the apple of its malic-acid. No use is made of 
this acid in the separate state. 

416. Acid of Lemons — Citric- Acid — Gives their sourness to the lemon, 
orange, citron, and cranberry. Mixed with malic-acid, it exists also 
in the gooseberry, red-currant, strawberry, raspberry, and cherry. 
Citric-acid is separated from lemon juice, and sold in the form of crys- 
tals, which may be at any time redissolved in water, and by flavoring 
with a little essence of lemon, an artificial lemon juice is produced, 
which is used like the natural juice in the preparation of refreshing 
and cooling beverages. 

417. Acid of Grapes — ^Tartaric-Acid, — This acid in the free state ex- 
ists in the grape, and is found besides in some other fruits. It also 
exists abundantly in the grape in combination with potash, as acid, 
tartrate of potash, or cream-of-tartar. Tartaric-acid is prepared and 
sold in the crystalline form as a cheap substitute for citric-acid, or 
lemon juice. It does not absorb moisture when exposed to the air 
like citric-acid, but is inferior to it in flavor. The commercial efter- 



veacing, or soda powders^ consist of 30 grains of bicarbonate of soda, 
contained in a blue paper, and 25 grains of tartaric acid, in a white 
paper, to be dissolved in balf a pint of water. 

418. Oxalic-Acid — ^Exists in sorrel, and also in the garden rhubarb 
or pie-plant, combined with and partially neutralized by potash or 
lime. It is a prompt and mortal poison when pure, and fatal results 
frequently occur from mistaking its crystals for those of Epsom salts, 
which they much resemble. 

419. YcgetaWe Jelly, Pectine or Pectic-Acid. — This is obtained fi*om 
the juice of apples, pears, quinces, currants, raspberries, and many 
other fruits ; also, from turnips, carrots, beets, and other roots. It is 
composed similarly to the vegetable acids, having an excess of oxygen. 
Vegetable jelly is thought not to exist exactly as siich in the plant- 
juices, but to be produced from another substance in the process of its 
separation. The substance from which it is obtained is soluble in the 
vegetable juices, but the jelly itself is scarcely soluble in cold water. 
Boiling water dissolves it, but it coagulates again as the water cools. 
It is commonly prepared by mixing sugar with the juice, and suffering 
it to stand for some time in the sun, by which a portion of the water 
is evaporated ; or it may be boiled a short time. But when long 
boiled, it loses the property of gelatinizing by cooling, and becomes of 
a mucilaginous or gummy nature. This is the reason that in making 
currant or any other vegetable jelly, when the quantity of sugar is not 
sufficient to absorb aU the water, and consequently it becomes neces- 
sary to concentrate the liquor by long boiling, the mixture often loses 
its peculiar gelatinous properties, and the jelly is of course spoiled. 
It differs from animal jeUy in containing no nitrogen, and although 
readily digestible, it is supposed to be but slightly nutritive. Isinglass 
is often added to promote the stiffening of vegetable jellies, and sugar 
also has a similar effect. They form cooling and agreeable articles of 
diet for those sick with fevers and inflammatory complaints. Jams 
consist of vegetable pulps preserved with sugar. They are very simi- 
lar in their uses and effects to the fruit-jellies, from which they prin- 
cipally differ in containing a quantity of insoluble, and therefore indi- 
gestible ligneous matter (or vegetable membranes, ceUular-tissue and 
sometimes seeds), which in the healthy state of the system contribute 
by their mechanical stimulus to promote the action of the bowels, but 
in irritable conditions of the alimentary canal, sometimes prove injuri- 
ous. (Pereiea.) 

420. Acetic Acid, or Vinegar. — The acid in most general use for diet- 
etical purposes is the acetic, or acid of vinegar, which we obtain by 


fermentation (491). Good strong vinegar contains about four per cent. 
of the pure acid. Vinegar may be easily made at any time by adding 
ferment, or yeast, to water sweetened with sugar or molasses, or any 
sweet vegetable juice, and exposing the whole for a reasonable time to 
the air in a warm place. Vinegar itself added to the mixture will act 
in the way of yeast to start the operation. There accumulates in old 
vinegar a thick, ropy matter, called mother^ because it is capable of 
producing the acetous change in a sugary solution. It consists, like 
yeast, of vegetable cells (496). The juices of most fruits contain all 
the elements necessary for fermentation and souring. Apple and grape 
juice, at first, undergo the vinous change producing cider and wine, and 
the process continued converts them both into vinegar (cider-vinega/r 
and wine-vinegar), which are prized, on account of the fruity aroma 
which accompanies them. 

A.— Vegetable amd Animal Albumen. 

421. It exists in both organized Kingdoms. — We are aU familiar with 
albumen or white of eggs, and recollect the remarkable change it un- 
dergoes by heat, being coagulated or altered from a transparent liquid 
to an opaque, white, brittle solid. This substance exists in smaJl pro- 
portions dissolved in the juices of plants. If such juices are clarified 
and then boUed, the albumen coagulates in thin flakes, and may be 
separated from the liquid. The same substance exists also in small 
quantities, laid up dry and solid in seeds and grains, but its exact pro- 
portion in various parts of plants has not been ascertained. Albumen 
exists also in animals, and is a much more abundant constituent of 
these than of plants. It constitutes, according to EEG^yfAirxT, about 19 
per cent, of healthy human blood, and is therefore found in large 
quantities in all parts of the system. It exists in the pecuhar animal 
juices, in the glands, nerves, brain, and around the muscular fibres of 

422. Composition of Aibnmen. — In composition, albumen differs widely 
from the aliments we have considered ; it contains not only the ali- 
ments they contain — carbon, oxygen, and hydrogen, — but in addition, 
a large proportion of nitrogen, and also a minute amount of sulphur. 
The chemical structure is thus complex. The result of the latest 
analysis is, that a compound atom of albumen consists of 216 carbon, 
189 of hydrogen, 68 of oxygen, 27 of nitrogen, and 2 of sulphur. 
The albumen of eggs, however, contains a slightly larger proportion 


of sulpliTir. Vegetable and animal albumen are essentially the same 
thing in properties and composition, differing no more upon analysis 
than two samples from the same source. 

423. General Properties of Albnmen. — It exists in two states — soluble 
and insoluble, or coagulated. The coagulation is effected by simple 
heat ; but there is much confusion of statement among different writers 
as to the point of temperature at which it sohdifies. This depends 
upon circumstances. A moderately strong solution of pure albumen 
in water becomes turbid at 140°, and completely insoluble at 145°, and 
separates in flakes at 167°. When excessively diluted, no turbidity 
can be produced by a less heat than 194°, and it will only separate in 
solid masses after it has been boUed a considerable time. As a general 
rule, albumen coagulates with greater difficulty in proportion to the 
quantity of water in which it is dissolved. Coagulated albumen 
refuses to dissolve in cold water, merely swelling up in it. There are 
many substances which, if mixed with it, coagulate albumen when 
cold, as alcohol and corrosive sublimate, the mineral acids, and many 
salts, while the presence of alkalies hinders its coagulation. The 
change of coagulation does not alter or disturb its composition. 

SS.— Veg'dal>le and Animal Casein. 

424. Sonrce and CompositioDi — The water in which flour has beea 
washed or difl^used, as in separating starch, contains a small portion 
of a dissolved substance, which is coagulated by the addition of an 
acid, and may be then separated. It is called vegetable casein^ and is 
found in the largest proportion in peas and beans, constituting from 
20 to 28 per cent, of their weight. This substance is identical in 
properties Avith the curd of mUk, which is known as animal casein, 
and is the chief ingredient of cheese. The identity of vegetable and 
animal casein is well illustrated by the fact that the Chinese make a 
real cheese from peas. They are boiled to a thin paste, passed through 
a sieve, and coagulated by a solution of gypsum. The curd is treated 
like that formed in milk by rennet. The solid part is pressed out, 
salted, and wrought into cheese in moulds. This cheese gradually 
acquires the smell and taste of milk cheese ; and when fresh, is a 
favorite article of food with the people. The composition of vegeta- 
ble and animal casein is nearly if not quite identical with that of 
albumen (422). 

C— "Vegetable and Animal Fibrin. 

425. The Blood and Vegetable Jiiic«s. — When blood is drawn from 



Fig. 91. 

Fibres of lean meat magnified. 

the living body, in a short time it clots ; that is, a net-work of fibres is 
formed within it. These fibres consist of animal fibrin, which was 
dissolved in the blood, and then took on the solid form {spontaneous 
coagulation). Vegetable juices, as those expressed from turnips, car- 
rots, beets, &c,, also contain the same kind of matter which they deposit 
on standing, that is, it spontaneously coagulates^ and this is known 
as vegetable fibrin. If a piece of 
lean beef be long washed in clean 
water, its red color, which is due to 
blood, gradually disappears, and a 
mass of white fibrous tissue re- 
mains, which is known as animal v^ 
fibrin. The accompanying diagram 
(Fig. 91) shows its structure as seen 
under the microscope. The paral- 
lel fibres have cross markings, wrinkles, or striaa. By the contraction 
of a muscle in the living animal the stri« are made to approach each 
other, become less distinct, and the fibre increases considerably in 
breadth and thickness. 

426. Glnten. — If wheat flour be made into a dough, and then 
kneaded on a sieve or piece of muslin under a stream of water 
(Fig. 92), its starch is 
washed away, and there 
remains a gray, elastic, 
tough substance, almost 
resembling a piece of ani- 
mal skin in appearance. 
"When dried it has a glue- 
like aspect, and hence its 
name, gluten. "When thus 
produced, it consists chiefly 
of vegetable fibrin ; but it 
contains also a little oil, 
with albumen and casein. 
That from other grains is 
dilferent in the proportion 
of these constituents ; rye 
gluten, for example, con- 
sists largely of casern, and has less of the tenacious fibrmous princi- 
ple. By acting upon crude gluten with different solvent agents, it 
is separated into four principles as follows : 

Fig. 92. 


Vegetable fibrin 72 per cent 

Gluten 20 " 

Casein (mucine) 4 " 

Oil 87 « 

Starch (accidental), small quantity 

Total 99-7 " 

427. Animal Fibrin, — The muscles or lean meat of animals are prin- 
cipally composed of this substance, its proportionate quantity being 
greatest in flesh that is dark-colored, and belongs to animals that have 
attained their full growth. Its characters vary somewhat in different 
animals, and in the same animal at different ages. Its color is vari- 
able ; in beef and mutton it is red ; in pigeons and many kinds of 
game it is brownish ; pink in veal, salmon color in pork ; in fish, white 
or semi-trausparent, though aU animals yield it on various colors. 
When washed free from blood and other foreign substances, pure 
fibrin is white and opaque, but darkens by drying. 

428. Properties of the Sitrogenons Principles. — Whatever their form or 
source, these substances are identical in composition, a fact of great 
importance in connection with animal nutrition. They present varia- 
tions of aspect and physical properties, and different solubilities, albu- 
men and casein being soluble in water, while the others are not ; and 
while fibrin coagulates or solidifies spontaneously, albumen is altered 
in the same manner by heat, and casein by acids. It is possible tliat 
some of these conditions may be influenced by the mineral phosphates 
which these substances contain in variable amount, but this point is 
not yet determined. These substances are decomposed by heat, and 
exhale a pungent odor like that of burnt feathers. They may be long 
preserved when dried, or even in the moist state when cut off from 
the atmosphere ; but in contact with air and moisture they quickly 
decompose, putrefy, and call into existence a host of microscopic ani- 
malculae. We shaU consider these substances again (678). 

D.— Gelatin. 

429. Its Sonrces, Properties and Uses. — There exists in the bone, carti- 
lages and various membranes of animal bodies, a principle rich in ni- 
trogen, called gelatin. It is not identical in composition with the ni- 
trogenous class which we have been considering, nor is it like them 
produced in the vegetable kingdom ; but it is supposed to be derived 
from them in the animal system. It dissolves in hot water, and when 

cooled, forms a white jelly. It is the universal principle of animal 
jellies. Common glue consists of gelatin, but in this form it is not 


used dietetically. Isinglass is a preparation of gelatin in various forms 
to be used as food. It is mainly procured from the air-bag or bladder 
of fishes. Tour parts of isinglass convert 100 of water into a trem- 
bling jelly. Gelatin is also extracted from calves' feet, in forming calves' 
foot jelly ^ and calves' heads are also employed to furnish jelly in mak- 
ing mock turtle soup. Gelatin is used not only to produce jellies, but 
to thicken and enrich gravies and sauces, and also as a clarifying or 
' fining ' agent to clear coffee or other mixtures. 

430. Different Names applied to these Substances. — The recent rapid 
progress of organic chemistry, has brought this class of substances for- 
ward into new and highly interesting dietetical relations, and there 
has been a confusion in the terms applied to them, which, though 
perhaps inevitable, is at first very embarrassing to unscientific readers. 
As they all contain nitrogen^ they are called nitrogenous alimentary 
principles ; and as one of the names of nitrogen is azote, they are call- 
ed azotized compounds. As they have all (except gelatin) the same 
composition as albumen, and are convertible into it, they are often 
called albuminous substances. As they form the material from which 
the body is nourished and built up, Liebig named them plastic ele- 
ments of nutrition ; they are also called nutritive principles, the^esA- 
forming and blood-malcing substances. Muldee supposed that a com- 
mon principle could be separated from all of them by getting rid of 
sulphur, (of which they contain variable traces,) and he called this 
principle ^rc»^^w, and hence the group has been gs^qH protein or pro- 
tcinaceotis compoxmds. Mitlder's peculiar views are abandoned, but 
his terms are stUl in current use. 

3. Compound Aliments. — Vegetable Foods. 

431. Our common articles of diet consist of the alimentary princi- 
ples which have just been noticed, combined together and forming 
what are known as compound aliments. They are naturally divided 
into vegetable foods and animal foods ; of the former first. 

A.— The Grains. 

432. Composition of Wheat. — We begin with wheat, the prince of 
gi'ains. It consists of gluten, starch, sugar, gum, oil, husk, and water, 
with salts that are left as ash when it is burned. It is maintained by 

• some that there is really no sugar present in the ripe grain, especially 
in wheat, but that it is produced by the action of air and water upon 
the starch during the process of bread making, or analysis. The 
proportion of constituents in wheat is liable to considerable variation. 


from many causes, as variety of seed, climate, soil, kind of fertilizers, 
seed, time of harvest, &c. We give five analyses. 






























433. Proportion of Gluten in Wheat. — It will be shown when we come 
to speak of the physiological influence of foods, that the most valuable 
portion, the strictly nutritious part, is that containing nitrogen, and 
that therefore 'gluten,' the properties of which have been noticed 
(426), is of the first importance in examining the grains. From an 
analysis of six samples of wheat, made by VAUQUELiisr, we get an aver- 
age of 11"18 per cent, of gluten ; Dumas, from three samples obtain- 
ed an average of 12 '50 per cent. ; and Dr. Lewis 0. Beck, -who made 
an investigation of the subject, at the direction of the Federal Govern- 
ment, and of 33 samples of wheat, gathered from all parts of the coun- 
try, procured an average of 11 "72 per cent, of this constituent, the 
specimens ranging from 9*85 to 15'25 per cent. The mode of exam- 
ination, however, adopted by Dr. Beck — that of washing away the 
starch by a stream of water (426) — is not the most accurate. A por- 
tion of albumen and casein, with small particles of gluten, are carried 
away by the stream — which would make the remaining quantity an 
under-statement of the true proportion of nitrogenous matter. This 
loss is assumed to be compensated for by the oil retained in the gluten, 
and the result is thus to a certain degree guessed at. Hoesfoed pro- 
ceeded more accurately, by making an ultimate analysis of the wheat, 
and calculating the amount of nitrogenous matter by the quantity of 
nitrogen finally obtained. Six samples of wheat thus treated, yielded 
15 -14 per cent, of gluten. Quantities of gluten are mentioned by 
Davy and Boussingalt as high as 20 or 30, and even 35 per cent., but 
these are probably erroneous over-statements. For general purposes 
we may adopt Dr. Beck's results — 11-72 of gluten, or in even num- 
bers 12 per cent. 

434. Quality of the Glnten of Wheat. — But not only do wheats differ 
in the proportion of gluten, but also in its quality. In some it is more 
tough and fibrous, or ' sounder ' and ' stronger, ' than in others. 


Moreover, any injury or damage that flour may sustain, is most 
promptly manifested by a change in the gluten ; it is both reduced in 
quantity and diminished in tenacity. Flour dealers and bakers deter- 
mine the quality of flours by making a few grains into a paste with 
water, when its value is judged of by the tenacity of the dough, the 
length to which it may be drawn into a thread, or the extent to which 
it may be spread out into a thin sheet. M. Boland has invented an 
instrument for determining the quality of gluten. A little cup-shaped 
copper vessel, which will contain about 210 grains of fresh gluten, is 
secured to a copper cylinder of three -fourths inch diameter and six 
inches long. It is then heated to about 420° in an oil bath. The 
gluten swells, and according to its rise in the tube so is its quality. 
Good flours furnish a gluten which will augment to four or five times 
its original bulk, while bad flours yield a gluten which does not swell, 
but becomes viscous and nearly fluid, adhering to the sides of the tube, 
and giving off occasionally a disagreeable odor, whilst that of good 
flour merely suggests the smell of hot bread. — (Mitchell.) 

435. Macaroni and Vermicelli are pastes formed from wheaten flour, 
and made to take various shapes by being passed through holes in me- 
tallic plates. Those flours are best adapted for this preparation which 
make the toughest paste ; those, therefore, which are richest in gluten, 
and where this element is of the best quality. The wheat of southern 
or warm climates is said to abound most in gluten, and hence to be 
better fitted for this production. Our chief supplies of macaroni are 
from Italy. The English have attempted the manufacture by separat- 
ing the gluten of one flour and incorporating it into another. Their 
success has been but indifferent, nor have we succeeded satisfactorily 
with it in this country. The best macaroni should retain its form, and 
only swell after long boiling, without either running into a mass or 
falling to pieces. 

436. Water ia Wlieat. — The wheat grain consists of a solidified veg- 
etable mUk. As the grain ripens, evaporation of water takes place, 
and the mUk condenses into a hard mass. Wheat ripened under the 
hot sun of this diy climate evaporates much of its water, and dries 
harder, with a tendency to shrivel in the berry ; while in the cooler 
and damper climate of England longer time is allowed for ripening, 
and evaporation is slower, so that the same variety of English wheat 
presents a larger and plumper berry than if grown In this country. 
Dr. Beck's examination gave an average of 12-78 per cent, of water, 
the range being from 11-75 to 14-05. Different wheats, however, are 
stated to vary in their natural proportion of water so widely as from 
5 to 20 per cent. 


437. Grinding of Grain. — Grain is converted into flour by being 
ground between two horizontal stones, the upper of which revolves, 
while the lower is stationary. The mill-stones (buhr-stones) are com- 
posed of a peculiar hard and porous sand-stone, so that the working 
surfaces consist of an infinite number of minute cutting edges. There 
is an opening in the centre of the upper revolving stone through 
which the grains are dropped. The lower stone is convex and the 
upper one is concave, so as to match it ; but they do not perfectly 
join or fit. From the centre outwards, they approach closer together, 
so that the grain is first coarsely crushed, and then cut finer and finer 
as it is carried to the circumference by the centre-flying (centrifugal) 
force. The crushed grain, as it leaves the stones, is not an absolutely 
uniform powder, composed of equal sized particles, but consists of 
parts which have been diff'erently aff'ected by the grinding process. 
Some are coarser, and others flner, so that it becomes possible to 
separate them. The ground mass is therefore conveyed away and 
bolted ; that is, passed through a succession of sieves, and separated 
into several parts, fine flour, coarse flour, bran, &c. 

438. Stractnre of the Grains. — When we consider wheat or other grain 
with reference to its grinding and sifting capabilities, the proportion 
and quality of its separated products, several things require notice in 
regard to the structure of the kernel or berry. Each grain consists of 
a farinaceous body, enclosed in a membranous husk or skin. This 
husky envelope varies in properties ; in some wheat it is thin, smooth, 
and translucent ; in others, rough, thick, and opaque ; in some fight- 
colored, in others dark ; in some tough, in others brittle ; and in some 
it peels or flakes off readily under the stones, and in others it is very 
adherent to the kernel. The other elements of the seed, albumen, glu- 
ten, starch, and oil, and the salts which it leaves as ash when burned 
(446), are not equally distributed throughout its mass. Immediately 
beneath the incrusting husk, is a layer of matter of rather a darkish 
color, and not very easily reduced to an impalpable powder. It is 
rich in gluten, and contains oil, which exists in minute drops enclosed 
in cells. Underneath this is the heart of the seed, which is whiter 
and more readily crumbles to a fine dust. This part consists more 
purely of starch, and forms the finest and whitest flour. There is 
a certain degree of interdiffusion of these elements throughout the 
body of the seed, yet, upon dissection, they are each found in excess 
in the parts indicated. 

439. Anatomy of Grains Illnstratcd. — An idea may be gathered of this 
distribution of substances throughout the cereal seeds, by the accom- 



panying section of a grain of rye highly ^^^ ^^ 

magnified (Fig 93) : a represents the outer _; - -_. "^'^ — - 

investing seed-coat, consisting of three s?C^]£f -— ^^'C i^oc n 
rows of cells; &, an inner membrane or cS'^j," ' '^TiBliMIB'' 
seed-coat, composed of a single layer of te^^45%)^^^^^^^^^^ 
cells ; c, a layer of cells containing gluten. ^^^M^^i^^^&l^ 
These three form the bran ; d, cells con- j^^^^^^Kl^^^^Jf^ 
tainiug starch grains in the interior of ^^^li^\^/^^^M'^^ 
the seed. Fig. 94 represents a ceU con- 
taining starch, more highly magnified, and Fig. 95, the appearance of 
the grains of rye starch viewed by a still stronger power. 

440. Parts Separable by Sifting. — These several portions oppose un- 
equal resistance to the pulverizing force of the mill- 
stones. The outer fibrous portion which forms the bulk 
of bran is least afiected ; the tough coherent gluten is 
divided stiU finer, while the brittle starch, of which the yC^v 
grain is mainly composed, is crushed most completely. |">pS| 
As the particles of these substances, therefore, are of Iji^^jiP'fiS!) 
different sizes, they may be separated by a bolting cloth, 
having different degrees of fineness of texture. The 
product is divided by the miUer according to custom or 
fancy, fom* or five grades being often established, which, of course, 
vary much in composition and properties. 

441. Properties and Composition of Bran. — ^From what has been said 
of the husk, it will appear that the quantity of bran yielded by differ- 
ent wheats, is liable to variation (438). As the 

husk is detached with different degrees of ease, it 

is evident that it may carry with it more or less 

adherent matter of the grain, by which its com- ,;. '-/-x-i^ wvv 

position will be made to fluctuate. Johnstoit '^^'^^^ 

states, that in good wheat the husky portion 

amounts to between 14 and 16 per cent, of its it((fl^ 

whole weight. The same authority found six 

wheats to yield bran of an average composition, 

as follows : 

Water 13-1 

Nitrogenized matter 19'3 

OU 4T 

Husk, and a little starch 55-6 

Saline matter (ash) 7-3 



This discloses the nitrogenous matter, the oil, and the salts, in larger 
proportion than they exist in the interior of the seed. The excess 
of oil existing in the husks of Avheat, helps to protect it against the 
penetration of moisture, and enables it to be washed (which ought al- 
ways to be done before grindiug), without wetting the inner part of 
the grain. 

442. White and dark-colored Flonrs. — In separating flour into dif- 
ferent grades, the finest and whitest will contain the largest quantity 
of starch, while the coarser will more abound in gluten, and present 
a darker color. From the soft wheats the bran peels off readily under 
the stones, and separates perfectly in bolting; and as these varie- 
ties contain least gluten, they yield the whitest or superfine flours. 
But the outer coating clings so closely to the hard or flinty sorts, that 
much of it is ground up finely with the flour, imparting to it a dark 
color, an effect which is also heightened by the larger proportion of 
gluten existing in the harder kinds. It is thus apparent that white- 
ness is not an indication of nutritive value of flour, but rather the 
reverse. "We may add here, that flour of the first quality holds 
together in a mass when squeezed by the hand, and shows impressions 
of the fingers and even the marks of the skin much longer than when 
it is of inferior grade. The dough made with it is gluey, ductile, 
and elastic, easy to be kneaded, and which may be drawn out into 
long strips, or thinly flattened without breaking. 

443. Loss of Weight by Evaporation. — "When wheat is kept for several 
months, it loses water by evaporation, becomes denser, and one or 
two pounds a bushel heavier. "When ground it gets hot, and stiU 
more of its moisture is evaporated, so that the flour and bran, 
although twice as bulky as the wheat, weigh some two or three per 
cent. less. 

444. Injnrions changes in Flour. — ^Wheaten flour becomes whiter 
with age, but it is at the expense of gradual deterioration of flavor, 
sweetness, and nutritive quality. Beegs kept various samples of 
flour, and found that the second and third qualities, which contained 
most gluten^ were completely spoiled, after keeping only nine months, 
though preserved in casks in a cool, airy, and dry warehouse. Mit- 
CHERLicn and Keockee showed that wheat in which sugar was proved 
to be absent before sending it to the miU, yielded, after being ground, 
4 per cent, of it. Starch was thus transformed into sugar, which could 
not be done otherwise than through the internal action of the gluten 
aided by air and superabundant moisture (4Y3). The mutual action 
of the gluten, and the natural moisture of the flour, seem often capa- 


ble, at common temperatures, of slowly bringing about this injurious 
change. But when the flour comes out hot from the friction of the 
stones, and is left to cool gradually in large heaps, decomposition quickly 
sets in, starch is changed to sugar, and perhaps sugar to alcohol, and 
even alcohol to vinegar ; so that the process advances rapidly to the 
souring stage. This action always takes place in the middle of the 
heap first, and proceeds towards the surface, the air enveloped in 
the flour, and the heat produced by chemical action, favoring the 
change most in the centre. Flour, as soon as ground, should therefore 
be conveyed to properly- constructed chambers, and quickly cooled, or 
if it be desired to preserve it for some time, it should be dried at a 
low heat. The amount of damaged flour thrown into the market is 
immense. Large quantities of it are due to careless and imperfect 
cooling, by which chemical changes are commenced, which time con- 
tinues. Sometimes, to separate the bran most perfectly and procure 
the whitest flour, the miUer moistens the grain previously to grinding ; 
but if such flour is packed in barrels or sacks without artificial drying, 
it rapidly moulds and sours. From these considerations, we infer 
the desirableness of procuring flour for household use, freshly ground, 
and frequently from the mill, where that is practicable. 

445. Farina. — A wheaten preparation under this name has come 
recently into general use, the same formerly known as 'pearled 
wheat.' It consists of the inner portion of the kernel of the flnest 
wheat, freed from bran and crushed into grains, {granulated,) the fine 
floury dust and smaller particles being all removed. In cooking, it 
absorbs much water or mUk, and forms an easily-digestible prepara- 
tion, readily permeable by the juices of the stomach. In consequence 
of containing nitrogenous matter, it is greatly superior in nutritive 
power to cornstarch, arrowroot, tapioca, as a diet for invalids and 
children (746). Prof. J. 0. Booth of Philadelphia, analyzed Hecker's 
Farina with the following results: Starch 60'4, nitrogenous matter 
11"6, gum 2-9, sugar 2'41, bran 2-1, water 9'9. Professor Booth re- 
marks : " The analysis is sufiicient to show the excellent qualities of 
the farina, whether as a simple diet for invalids, or as an excellent 
food for the healthy." 

446. What Minerals exist in Wheatt — "When wheat is burned, there 
is left about 2 per cent, of ash, which consists of various mineral in- 
gredients. An average of 32 of the most recent and reliable analyses 
gives the leading constituents, as foUows: Phosphoric acid 46 per 
cent., (nearly half its weight,) potash 29'97, soda 3-30, magnesia 3*35, 
Bulphuric acid '33, oxide of iron '79, and common salt -09. Phoa- 


phoric acid is the characteristic and predominant element, potash and 
magnesia occurring next in the order of quantity. These mineral sub- 
stances are unequally diffused throughout the seed. Johnston has 
shown by an analysis of six samples of wheat, the ground product of 
which was divided into four qualities, that the mineral substances ai'e 
distributed as follows. "We give the average: — ^fine flour 1*08 per cent, 
next grade 3*8, coarser still 5-2, bran 7*2. The ash of bran contains 
considerable sUica. The presence of these mineral substances is far 
from accidental, as was formerly supposed ; we shall point out some 
of their important uses in the system when considering the physio- 
logical effects of food (690). 

447. Properties and Compositton of RyCi — This graia ranks next to 
wheat in bread-making and nutritive qualities. It produces a larger pro- 
portion of bran than wheat, yielding less flour, and that of a decidedly 
darker color. It contains more sugar than wheat, which accounts for 
the sweet taste which is peculiar to new rye-bread. Its husk has an 
aromatic and slightly acidulous flavor, which renders it agreeable to the 
palate. The bran should not, therefore, be entirely separated from 
the flour ; for if the grain be ground fine and divested entirely of the 
husk, the bread will be deprived of much of its pleasant taste. The 
gluten of rye flour, although sufficiently tenacious to make good bread, 
is less tough and fibrous than that of wheat. Indeed it is more prop- 
erly a kind of casein (424), or 'soluble gluten,' for when rye dough 
is washed with water, instead of remaining together in an adherent 
mass, its gluten diffuses itself throughout the liquid. Rye is generally 
stated to be less rich in the nutritive nitrogenous constituents than 
wheat. It has not been so thoroughly examined as that grain, but the 
analyses that have been made would seem to show that it is very 
little, if at all, inferior to it in nutritive power. Botjssikgatjlt obtain- 
ed from the grain of rye 24 per cent, of bran, and 76 of flour. He 
separated by drying 17 per cent, of moisture, and the dry flour gave of 

Eye (Bocssinqadlt). Rye (Poggaile). 

Gluten, albumen, &c 10'5 Nitrogenous matters 8'790 

Starch 64'0 Starcli and dextrin 65'533 

Gum 11-0 Fatty matters 1-992 

Fatty matter 8"5 Lignin 68S3 

Sugar 3-0 Mineral matters 1'772 

Epidermis and salts C'O "Water 15'530 

Loss 2-0 

A sample of rye di'ied in Prof. Johnston's laboratory, lost 14"50 per 
cent, of water. Hoksfoed examined four samples of European rye, 


and obtained an average of 14 per cent, of water, and 13*79 per cent, 
nitrogenous compounds. 

448, Indian Cora or Maize. — This grain is distinguished chemically by 
containing a larger proportion of oily or fatty matter than any other. 
It is quite rich in nitrogenous constituents, though less so than wheat. 
Its peculiar protein element takes the name of zein (from zea maize, 
the botanic name of Indian corn) ; it is not of a glutinous, adhesive 
nature, and hence maize flour or meal wiU not make a dough, or fer- 
mented bread. It is prepared in several forms. Its composition is 
given as follows : 

Maize (Payen), Yellow Maize (Fosgxilb), 

Starch fi7"55 Nitrogenous matters 9-905 

Gluten or zea 12-50 Starch, dextrin, sugar 64-535 

Dextrin or gum 4-00 Fatty matter 6-6S0 

Fatty matter 8-80 Lignin and coloring matter 8-968 

Celulose 5-90 Mineral 1-440 

Saltscrashes 1-25 Water 13-472 


HoESFOED obtained 13*65 of nitrogenous matter from maize meal, and 
14'66 from maize grain. Samp is Indian corn divested of its outside 
skin or bran, and of its germinal eye, the grain being left whole or 
nearly so. In Tiominy each grain is broken up into a number of small- 
er pieces. The meal of Indian corn, in consequence of its excess of 
oily matter, attracts much oxygen from the air, and is hence very 
prone to change, and does not keep well. This is the serious draw- 
back of this most valuable grain ; though cheap, nutritive and health- 
ful, it is difficult to transport and preserve its meal, especially in warm 
seasons or climates. 

449, Oats. — This grain is not employed to any considerable extent 
as an article of diet for man, in this country. The oat varies greatly 
in weight, ranging from 30 to 40 lbs. per bushel. In grinding, 30 lbs. 
give 16 of meal and 14 of husk, while a bushel weighing 40 lbs. yields 
23 lbs, 6 oz. of meal and 16 lbs. 10 oz. of husk — the largest proportion 
of bran yielded by any grain, yet different varieties give different re- 
sults. Oat flour stands before all other grains in point of nutritive or 
flesh-producing power, being first in its proportion of the nitrogen- 
ous element. It is also distinguished by its large quantity of fat or 
oil, ranging in this particular next to Indian corn. The following 
table gives the result of an analysis of Prench oats, by Boussingaitlt, 
and the average of four samples of Scotch oats, by Prof. Norton. 


(Boussingault). (Noktou). 

starch 46-1 Starch 65-10 

Sugar 6-0 Sugar 2-49 

Gum 8-S Gum 2-22 

Oil 6-7 Oil 6-55 

ATenin.. \ Avenin 16-50 

Albumen I 13-7 Albumen, 1-42 

Gluten . . ) Gluten 1-67 

Husk, ash, and loss 23-7 Epidermis 2-17 

Alkaline, salt, and loss 1-84 



Noeton's analysis, the most accurate we have, thus gives 19*59 per 
cent, of nitrogenous compounds. Again, from nine samples of dry 
oats he obtained 16"96 per cent, of protein compounds, the specimens 
ranging from 14 to 22 per cent. Prof. Hoesfoed obtained from three 
samples an average of 12-83 per cent, water, and 16*59 protein con- 
stituents. From the dried grain he got 21*5 per cent, of these com- 
pounds. If oatmeal be mixed with water, it does not form a dough 
like wheat flour, and if it be washed upon a sieve, nearly the whole 
will be carried through, only the coarse parts of the meal remaining 
behind. The chief portion of the nitrogenized matter of the oat re- 
sembles casein more than gluten, and has received the name of avenin 
(from avena, the oat). Oatmeal, the ground and sifted flour of the 
grain, is not so white as wheaten flour, and has a somewhat bitterish 
taste. Under the husk of the oat there is a thin cuticle or integu- 
ment, surrounding the central part, which is ground up with the meal, 
and not being sifted out, gives it a rough and harsh taste, and although 
the oatmeal gruel be strained, still a quantity of the sharp fragments 
of cuticle escape through the strainer. Grits, or groats, are oats in 
which the outer husk and cuticle are ground off and removed, so that 
grit gruel is 'smoother,' as it is termed. It is chiefly made into 
cakes, porridge, and gruel. 

450. Barley. — The composition of barley is represented as follows : 

Fine Barley Meal (Johnston). Barley (Poggaile), later. 

Starch 68 Nitrogenous matters 10-655 

Fatty matter 2 Starch and dextrin 60-330 

Gluten, albumen, &c 14 Fatty matters 2-384 

Water 14 Lignin 8779 

Ash 2 Mineral substances 2-623 

Water 15-229 


Einhof's analysis represents it as containing 4*62 of gum and 5*21 of 
sugar. Its husk or bran forms from 10 to 18 per cent, of its weight. 


The composition of barley has not been very carefully examined. It 
is reported to contain a good share of nitrogenous matter, but of what 
nature is not known. It is deficient in true gluten and behaves like 
oatmeal when washed with water. When stripped of its husk or 
outer skin by a mill, it is called Tiulled or pot-larleij^ and is used for 
making broth. After a considerable portion more of the kernel has been 
ground off", the rounded and polished grains are known as pearl-iarley. 

451. Rice is remarkable for being richest in starch and most de- 
ficient in oil of all the cultivated grains. Its flesh -producing elements 
are low, much lower than wheat or Indian com, and less than half 
that of oats. Analysis gives the following results : 

Rice (Paten). Rice (Poggaile). 

Starch 86-T Starch, dextrin, sugar T4-4T0 

Gluten, &c 7'5 Nitrogenous matters T-SOO 

Fatty matter 0'8 Fatty matters 2-235 

Sugar and gum 0'5 Mineral -SZS 

Epidermis (skin) 3'4 Lignin 3-345 

Saline matter (ash) 0-9 "Water lT-730 

Prof. Johnston found five varieties to contain an average of 13"4 per 
cent, of water and but •41, that is less than half of one per cent, of 
ash. Mr. Hoesfoed separated from some rice 15 "14 per cent, of water, 
and 6'27 per cent, of nitrogenous matter in its ordinary state, and 7.4 
per cent, in its dry state. It is usually presented to us in market 
hulled, or freed from its husk, and is used whole, being but rarely 
ground into flour. 

452. Buckwheat. — The composition of this grain has not been satis- 
factorily elucidated; there remains considerable discrepancy in the 
results of its analysis. Zenneok found that in the dry state it con- 
sisted of — 

Husk 26-9 

Gluten, &c 10-7 

Starch 52-3 

Sugar and gum 8-3 

Fatty matter 0-4 

The gluten is here supposed to be estimated too high. Hoesfoed ob- 
tained from buckwheat flour in the natural state (that is, not dried) : 

"Water 15-12 

Starch 65-05 

Protein 584 

B.— liCg-iiininous Seeds. 

453. Composition of Peas.— Seeds obtained from pods are called 
leguminom. Of this class we are only concerned with peas and 



beans. They resemble much in composition the cereal grains, but are 
more highly nutritive ; indeed, they afford the most concentrated form 
of vegetable nourishment. The roasted cMclc-pea of the East is con- 
sidered to be more capable of sustaining life, weight for weight, than 
any other kind of food ; hence, it is preferred by travellers about to 
cross the deserts, as the least bulky and heavy form of diet. Accord- 
ing to HoESFOED and Keookee : 

A Table Pea yielded : A Field Pea gave ! 

Albumen and casein 28-03 Albumen and casein 29-18 

Starch 88-81 Starch 66-23 

Gum 28-50 Gum 66-23 

Skin 7-65 Skin 6-11 

Ash 8-18 Ash 2-79 

According to PooaAiLE, field peas that had been deprived of 9*50 of 
envelope, contained : 

Nitrogenous matters 21-670 

Starch, dextrin, and sugar 57-650 

Fatty matters 1-920 

Lignin 8-218 

Mineral 2-802 

Water 12-740 

He found also in very soft green peas : 

Nitrogenous matters 38-35 

Older than the above 34-17 

Eipened 27-72 

Prof. Johnston states that the proportion of nitrogenous, or flesh- 
forming matter, in both peas and beans, is on an average about 24 per 
cent., and of oil about two per cent. The nitrogenous element of 
peas and beans is not glutinous, and consists chiefly of vegetable 
casein. They are hence incapable of making bread. From their 
high proportion of nitrogenous constituents, peas and beans are ex- 
tremely nutritious, ranking first among concentrated strength-impart- 
ing foods. They are considered difficult of digestion, and of a con- 
stipating quality, which requires to be corrected by admixture with 
other kinds of food. The varieties are numerous, with wide differen- 
ences of flavor and softness when cooked, and they probably differ 
equally in composition. "We have before stated, that in consequence 
of its fibundance of casein, the Chinese make it up into a kind of 
vegetable cheese (424). 

454. Composition of Beans. — The composition of beans varies but 
little from that of peas. The authorities above cited (Hoesfoed and 
Keookkr) give tbe following results ; 


Beans (Hoksfoed and Keockek). Table Bean. Large White Bean. 

Vegetable casein and albumen 2S-54 29-31 

Starcb ST-50 66-lT 

Gum 29-20 66-lT 

Skin 4-11 4-41 

Ash 4-38 4-01 

The peas and beans in this analysis were dried at 212°, and lost an 
average of 15.53 per cent, of moisture. 

455. Bone-prodacittg material in Peas and Beans. — By reference to the 
preceding analytical results, it wUl be seen that the ash, or mineral 
constituents of peas and beans, from which the earthy part of bones 
is derived, is considerable, but larger in beans than in peas. 

Will and Fkesinids' analyses of the ash o£ Three analyses of the ash of beans gave the 
peas gave : following average result : 

Potash 89-51 Potash 29-62 

Soda 3-98 Soda 13-31 

Lime 5-91 Lime 6-11 

Magnesia 6-48 Magnesia 8-95 

Oxide of iron 1-05 Oxide of iron 0-98 

Phosphoric acid 34-50 Phosphoric acid 4-84 

Common salt 3-Tl Chlorine 1*18 

Sulphuric acid 4-91 Sulphuric acid 1-43 

Silica 5-34 

C— Fruits. 

456. Their General Composition. — Although fruits are extensively 
used as articles of diet, yet as staple sources of nutrition they bear no 
comparison to the grains. They consist of pulpy masses, which are 
nearly all water, and are prized far more for those properties which 
relate them to the taste than for nourishing or strengthening power. 
They generally consist of from 75 to 95 per cent, water, from 1 to 15 
or 20 per cent, fruit sugar, organic acids in variable proportions (414) 
in combination chiefly with lime and potash, pectiae, or the jelly- 
producing principle, ligneous skins and cores, with peculiar aromatic 
and coloring principles of infinite shades of diversity. The unripe 
fruits contain a larger proportion of water and acid, and a less amount 
of sugar than the natural fruits. As they contain so great a proportion 
of watery juices, they are very prone to change, and thus exhibit little 
constancy of composition. From this circumstance, and the number- 
less varieties of fruits that are catalogued, and also from the fact that 
comparatively little attention has been given to this branch of organic 
chemistry, our knowledge of the exact composition of fruits is very 

457. Composition of Apples.— Every one will understand that the 


various sorts of apples differ mucli in composition, yet in an average 
condition 100 lbs. of fresh apples contain about 3-2 lbs. of fibre, 0*2 
lbs. of gluten, fat, and wax, 016 of casein, 1-4 of albumen, 3-1 of 
dextrine, 8-3 of sugar, 0-3 of malic acid, 82-66 of water. Besides the 
above mentioned bodies, the apple contains a small quantity of tannic 
and gallic acid — ^most in the russets. To these acids apples owe their 
astringency of taste, and the blackening iron or steel instruments used 
to cut them. The following is the proportion of water and dry matter 
in several varieties of apples, according to Sallsbuey's examination. 

Talman Sweeting. 


Swarr Apple. 

Roxbury Russet. 

Englisli Ruaaet. 

Water 81-52 





Dry Matter.. 18.48 











The percentage of ash in the apple is small, yet it is rich in phosphoric 
and sulphuric acids, potash, and soda. The proportions of water and 
dry matter have also been determined in the following substances : 


Water 94-89 

Dry Matter 5-10 

The dry matter of melons contains quite a large percentage of albumen, 
casein, sugar, and dextrin, with a small quantity of acid. 

©.— Licaves, JLeaf-Stalks^ &c. 

458. Many kinds of leaves abound in principles adapted for animal 
nutrition, as is shown by the extent to which cattle are grown, sus- 
tained and fattened upon the grasses, Man makes use of leaves in his 
diet to but a limited extent. Professor Johnston remarks, "leaves 
are generally rich in gluten ; many of them, however, contain other 
substances in smaller quantity associated with the gluten, which are 
unpleasant to the taste, or act injuriously upon the general health, and 
therefore render them unfit for human food. Dried tea-leaves, for 
example, contain about 25 per cent, of gluten ; and therefore if they 
could be eaten with relish and digested readily, they would prove as 
strengthening as beans or peas." 

459. The Cabbage. — The same authority says of this vegetable : " It 
is especially nutritious. The dried leaf contains, according to my 
analysis, from thirty to thirty-five per cent, of gluten ; and is in this 
respect, therefore, more nutritious than any other vegetable food 
which is consumed to a large extent by men and animals. I know, 
indeed, of only two exceptions, — the mushroom, which in its dry mat- 
ter contains sometimes as much as 56 per cent, of gluten, and the 
dried cauliflower in which the gluten rises, as high as 64 per cent." 


The cabbage and cauliflower lose in drying more than 90 per cent, of 
water ; and the dried residue, according to Peeeiea, is remarkably- 
rich in sulphur as well as nitrogen. The plant decays quickly, and 
gives out a strong odor of putrefaction, owing to its nitrogenous and 
sulphurous compounds. Decayed cabbage leaves should therefore 
not be allowed to remain in cellars, or lie about in the vicinity of 

460. Lcttnco Leaves are much used at table as a salad. The young 
leaves contain a bland, cooling juice ; but as the plant advances, its 
milky juice becomes bitter, and is found to contain opium. In this 
stage it has a slight tendency to promote sleep. The water-cress^ leaves 
of white mustard and of common cress, probably owe their pungency 
to a minute portion of sulphurized volatile oil, analogous to that found 
in horseradish. The stalks of many kinds of leaves, as spinach, 
turnip-tops, potato-tops, cowslips, &c., are used as greens, but their 
peculiar characters have not been ascertained. The stalks of rhubarh, 
used for pies, puddings, &c., like apples and gooseberries, contain 
much malic and oxalic acid in combination with lime and potash. 
The proportion of water, dry matter, and ash, in the rhubarb stalk, 
celery, and vegetable oyster, is as follows : 

Rhubarb Stalks. Celery. Vegetable Oyster. 

■Water 89-50 88-22 84-46 

Dry Matter 10-50 11-77 15-54 

Ash 1-13 

Half the dry matter consists of malic, tartaric, and oxalic acids, with 
fibre, sugar, albumen, and casein. 

£.— Roots, Tubers, Bulbs and Sboots. 

461. Composition of Potatoes — Wsiter. — This is the most widely culti- 
vated and important for dietetical purposes of aU the root tribe, and 
has been more carefully examined than any other. Like fruits and 
leaves its leading constituent is water, which composes about three- 
quarters of its weight. Young, unripe potatoes contain more water 
than those fully grown, and it has been found that the ' rose ' end of 
the potato, or that part from which the young shoots spring, contains 
more water than the ' heel ' or part by which it is attached to the 
rootlet. KoETE examined 55 varieties of potato and found them to 
contain 75 per cent, of water and 25 of solid matter. Professor 
Johnston gathered from 27 analyses made in his laboratory tlie fol- 
lowing results. Greatest proportion of water in young potatoes, 82 
per cent. ; largest proportion in fuU grown potatoes, 68"6 per cent. 


He gives the mean of 51 determinations upon potatoes of all ages — as 
water 76 per cent, dry matter 24. 

462. Starch in Potatoes. — A large part of the solid matter in potatoes 
consists of starch. Johnston states as the results of numerous expe- 
riments, that the proportion is in the natural state 64-20 per cent. 
Siemens ascertained the proportion of starch in 66 varieties to range 
between 19'25 and 11*16 per cent. ; the average being 15'98. These 
proportions, however, vary with the kind of potato, soil, season, 
and other circumstances. The heel end usually contains more starch 
than the rose end. The weight of potatoes and their proportion of 
starch diminishes by keeping. Paten found the same variety to yield 
of starch in 

October 17'2 per cent. February 15"2 per cent. 

Kovember 16-8 " March 15 " 

December 15-6 " April 14-5 " 

January 15'5 

Other experiments would seem to show that there is rather an increase 
after digging ; but aU examinations agree, that as vegetation becomes 
active in the spring, the buds begin to grow at the expense of the 
starch contained in the tuber, and hence at this season potatoes are 
less mealy, and not so much esteemed for table use. 

463. Flesh-prodacing constituents of Potatoes. — The potato contains a 
considerable proportion of nitrogenous matter in the threefold form 
of albumen, casein, and gluten, as it exists in the grains. They exist 
dissolved in its juices. There is more of the casein than of the other 
elements. Johnston gives the average of these constituents at l-4th 
per cent, in the natural state, and 5-8th.per cent, when freed from 
water. But he acknowledges his mode of separating them to be liable 
to error, so that the figures are probably too low. Hoesfoed, by a 
more accurate method, found the percentage of these compounds 
in the dry matter of potatoes to be — in white potatoes 9 "9 6 per 
cent., in blue 7*66 per cent. He found also that not only is the pro- 
portion different in different varieties, but that it is greater in young 
potatoes than in old ; and Botjssingaxjlt also found the proportion of 
the protein compounds to diminish the longer the potato is kept. 

464. Woody Fibre, Sugar, Gum. — The proportion of fibre in the 
potato varies from 1\ to 10 per cent., and may be said to average 
about 3. The fatty matter is also variable, but may be stated at about 
1 per cent. Sugar in the natural state about 3 '3, gum 0"55, or in the 
dry condition, sugar 1347, gum 2 "25. 

465. Average Composition of Solid or Dry Matter of Potato. — This is 
summed up by Professor Johnston in round numbers as follows : 


etarch 64 

Sugar and gum 15 

Protein compounds e 9 

Fat 1 

Fibre 11 

Total 100 

The dry potato, therefore, is about equal iu nutritive value to rice, and 
is not far behind the average of our finer varieties of wheaten flour. 
The juice of potatoes is acid ; it was fornaerly supposed to contain 
citric acid, but it is now ascertained to be due to malic acid, and per- 
haps the sulphuric and phosphoric found in the ash. Potatoes also 
contain a small portion of asparagin, the peculiar principle of asparagus. 
When potatoes are freed from their large excess of water, so as to 
bring them into just comparison with the grains in composition, they 
are found to contain quite a large percentage of mineral matter left as 
ash — the average of six determinations giving 3 '92 per cent. The 
constituents of these six samples give an average as foUows : 

Potash 5575 

Soda 1-86 

Magnesia 5*28 

Lime ,... 207 

Phosphoric acid 12-57 

Sulphuric acid 13-64 

Silica 4-23 

Peroxide of iron 0-52 

Common salt » 7-01 

The carbonic acid, which was from 6 to 12 per cent., was deducted. 
The mineral matter of the potato seems to be thus distinguished from 
that of the grains by its large proportion of potash, sulphuric acid, 
and common salt, and its lesser quantity of phosphoric acid and mag- 

466. The Onion,' — This bulbous root abounds in nitrogenous matter; 
when dried, it has been found to yield from 25 to 30 per cent. It 
is therefore highly nutritive. It contains a strong-smelling sulphur- 
ized oU, the same tliat gives its powerful odor to the garlic. The con- 
stituents of the onion are thus stated by Peeeiea : 

VolatUe oil, Woody fibre, 

Uncrystallizable sugar, Pectic and phosphoric acid, 

G-um, Phosphate and carbonate of lime, 

Vegetable albumen, Iron. 

467. Beets, — The varieties of beets of course differ in composition, 
but they all contain much sugar. Their nutritive qualities are not 
well determined. Beetroot is represented as containing 81 per cent 


of water, 10"20 of sugar, and 2'03 of nitrogenous matter. In tlie long 
blood-beet tbere is 89"09 per cent, of water, and 10"90 of dry matter. 
468. Turnips, Carrots, ParsnipSi — Chemistry has hitherto cast but 
an uncertain light upon the composition of this class of substances. It 
appears from the best determinations, that the proportion of solid mat- 
ter in several roots is as follows : 

White Turnips lOJ 

Yellow do IBi 

Mangel-wurzel 15 

Carrot 14 

The dry substance of these roots is much lower than that of the pota- 
to, which ranges at 25 per cent. Yet the flesh-forming constituents 
of dried turnips much exceed those of the potato, as the following com- 
parison shows. 

Protein Compounds. 

The dried potato 8 per cent. 

Yellow turnip 9J do. 

Mangel-wurzel l&J do. 

The nitrogenous matter of di'ied mangel-wurzel being nearly twice 
as great as in the dried potato. In the carrot the proportion of water 
is 85 "YB, and dry jnatter 14'22. According to Oeome, the parsnip 
contains — 

starch 1-8 

Albumen 21 

Gum 61 

Sugar 5'5 

Fibre 51 

Water T9-4 

Total lOO'OO 

4. CoMPOTiN"D Aliments — Animal Food. 
A.— Constituents of WLea,t. 

469. — ^Various parts of animal bodies contribute materials for diet ; 
the flesh and fat chiefly, but nearly aU other portions, blood, intestines, 
membranes, bones, and skin, more or less. The staple constituents 
of animal food are fibrin, albumen, gelatin, fat, salts, and water, and 
in the case of milk, casein and sugar. 

470. Composition of Flcsh-mcat.— This is generally unders'^ood to sig- 
nify the muscular or lean parts of cattle, surrounded by fat, and con- 
taining more or less bone. The muscles consist of fibrin ; they are 
separated into bundles by membranes, and into larger separate masses 
by cellular tissues, in which fat is deposited. The fleshy mass is pene- 


trated by a network of blood-vessels and nerves, and the whole is dis- 
tended by water, which composes about three-fourths of the weight 
of the meat. The composition of the muscular flesh of different ani- 
mals, according to Mr. Beande, is as follows : 

Water. Albumen and Fibrin. Gelatin. Total solid matter. 

Beef 74 20 6 26 

Veal 75 19 6 25 

Mutton 71 22 T 29 

Pork 76 19 5 24 

Chicken 73 20 T 27 

Cod 79 14 7 21 

These results give an average of very nearly 75 per cent, water. 
LiEBiG assumes it at T4, with 26 per cent, of dry matter. The ratio of 
water in meat, fowl, and fish, is quite uniform, ranging from YO to 80 
per cent., but the proportion of the other constituents, muscular fibre, 
fat, and bone, exhibits the widest possible diversity. In some animals, 
more especially wild ones, as deer, &c., there may be hardly a traco 
of oily matter, whUe swine are often fed until the animal becomes one 
morbid and unwieldy mass of fat. The pure muscular flesh of ordi- 
nary meat, with aU its visible fat separated, is assumed by Knapp and 
LiEBiG to contain still about 8 per cent, of fat. In beef and mutton, 
such as is met with in our markets, from a third to a fourth of the 
whole dead weight generally consists of fat. — (Johnston.) 

471. Juice of Flesh. — The true color of the fibrin of meat is white, 
yet flesh is most commonly of a reddish color (flesh-color). This is due 
to a certain portion of the coloring matter of the blood, by which it is 
stained. Yet the liquid of meat is not blood ; when that has been 
withdrawn from the animal, and the blood-vessels are empty, there 
remains diffused through the muscular mass a peculiar liquid, known 
as the juice of flesh. It consists of the water of flesh, containing about 
5 per cent, of dissolved substances, one-half of which is albumen, and 
tlie other half is composed of several compounds, not yet examined. 
The juice of flesh may be separated by finely mincing the meat, soak- 
ing it in water, and pressing it. The solid residue which remains after 
all the soluble matter has been thus removed, is tasteless, inodorous, 
and white like fish. The separated juice is uniformly and strongly 
acid, from the presence of lactic and phoshporic acids, hence it is in 
the opposite state to that of the blood, which is invariably alkaline. 
The juice of flesh contains the savory principles which give taste to 
meat, and which cause it to differ in different animals. It also con- 
tains two remarkable substances, called Tcreatine and Tcreatinine^ nitro- 
genous compounds, which may be crystallized. The quantity yielded 



is variable in different kinds of flesh, but in all is extremely small. 
Kreatine is a neutral or indifferent substance, wbile kreatinine is a 
powerful organic base, of a similar nature witb tbeine and cafeine of tea 
and coffee. 

472. Blood, Bones, and Internal Organs. — ^The leading constituents of 
blood are the same as flesh ; it contains only some three per cent, more 
of water. Its nitrogenous matter, however, is chiefly liquid albu- 
men. Blood has been called liquid flesh, and flesh sohdified blood. 
About half the weight of bones is mineral matter, lime combined 
with phosphoric acid, forming phosphate of lime — ^the substance that 
we have seen to abound so greatly in the ash of grains. The other 
half of bones is gelatm, the thickening principle of .soups (glue). It 
is sometimes partially extracted for this purpose by boiling. Marrow 
is a fatty substance, enclosed in very fine cellular tissue within the 
bone. Skin, cartUage, and membrane, yield much gelatin. The 
tongue and heart are muscular organs, agreeing in dietetical proper- 
ties with lean flesh. Beacoonnot's analysis of the liver gives 68 per 
cent, of water, and 26 of nitrogenous matter; it also contains oU. 
The Irain is a nervous mass, containing 80 per cent, water, some al- 
bumen, and much of a peculiar phosphoric oily acid. The stomacM 
of ruminating animals which yield tripe, are principally composed of 
fibrin, albumen, and water. 

473. Composition of Eggs. — The eggshell is a compound of lime, not 
the phosphate as exists in bones, but chiefly carbonate of lime. It is 
porous, so as to admit of air for the wants of the young animal in 
hatching, and usually weighs about one-tenth of the entire egg. The 
white of egg consists of water containing 15 or 20 per cent, of albumen. 
The yolk is water and albumen, but contains, also, a large proportion 
(two-thirds of the dried yolk) of a bright yellow oil, containing sulphur 
and phosphoric compounds. A common-sized hen's-egg weighs about 
a thousand grains, of which the shell weighs 100, the white 600, and 
the yolk 300. The composition of its contents is : 

Water 74 

Albumen 14 

Fat 10-5 

Ash (salts) 1-5 

Total 100 

B.— Production and Composition of Milk. 

474. What it Contains. — This familiar liquid consists of oil or butter, 
sugar, casein or the cheesy principle, and salts, with a large proportion 
of water. The sugar, casein, and salts are dissolved in the water. 


while the butter is not, hut exists diffused through the Kquid in the 
form of numberless extremely minute globules. They cannot be seen 
by the naked eye. "When the liglit falls upon them they diffuse it in 
aU directions, so that the mass appear opaque and white. Viewed 
by a microscope, the globules appear floating in a transparent liquid. 
In respect of its sugar, casein, and salts, milk is a solution; but with 
reference to its oily part, it is an emulsion. It is heavier than water 
in the proportion of about 103 to 100, although it differs considerably 
in specific gravity. When first drawn it is slightly alkaline and has a 
sweetish taste, which is due to the sugar of milk. 

475. Proportion of its Elements. — This is variable. It generally con- 
tains about 86 per cent, water, 4 to 7 of casein, 3 "5 to 5 '5 of butter, 
and 3 to 5-5 of sugar of milk and salts. The following are analyses 
by Henet and Ohevaliee : 

Cow. Woman. 

Casein 4-4S 1-52 

Butter 313 8-55 

Milksugar 4-47 6-50 

Salts -60 0-45 

Water 8T-02 8T-98 

The following are Hadlein's results : — The second column is thai 
average of two analyses. 

Cow's Milk, Woman's Milk.* 

Butter 8 2-351 

Sugar of milk and salts soluble In alcohol 4-6 8.75 

Casein and insoluble salts 5-1 2-90 

Water 87-3 90-50 

476. Circnmstances Influencing the Quality of Milk. — ^Both the quantity 
and quahty of milk are influenced by various conditions apper- 
taining to the animal. Its food exerts a powerful control in this 
respect. Green succulent food is more favorable to the production of 
milk than dry, and E. D. Thomson's experiments go to show that of 
dry food, the richest in nitrogenous matter best promotes the milk 
secretion. Platfaie was led, by his brief experiments, to conclude 
that food low in nitrogenous matters (as potatoes) yielded a large 
quantity of milk which was rich in butter, and that quiet {stall feed^ 
ing) had the same effect, whilst cows grazing in the open air upon 
poor pasture, and consequently obliged to take much exercise, yielded 

* The milk of -women from 15 to 20 years of age, contains more solid constituents 
than of women bet-ween 30 and 40. Women with dark hair also give a richer milk than 
-women with light hair. In acute diseases the sugar decreases one-fourth, and the curd 
increases one-fourth ; -while in chronic affections the butter increases one-fourth, and 
the casein slightly diminishes. In both classes of diseases the proportion of saline matter 
diminishes. — (Johnston.) 


milk rich in casein. It appeared from Thomson's observations, that 
the produce of miLk of a cow, with uniform diet, gradually diminished, 
and increased again by a change of diet. It is well known that a cow 
fed upon one pasture will yield more cheese, while upon another it 
will give more butter. Hence the practice in dairy districts of al- 
lowing the animal to roam over a wide extent of pasture to seek out 
for itself the kind of herbage necessary to the production of the richest 
mUk ; hence, also, the propriety of adding artificial food to that de- 
rived from grazing. Plants and weeds found scattered in many 
pastures are apt to affect, injuriously, the quality and taste of the milk. 
Butter is especially liable to be deteriorated in this way. An observ- 
ing dairy -manager remarks as follows : " If a cow be fed on ruta-baga, 
her butter and milk partake of that flavor. If she feeds on pastures 
where leeks, garlicks, and wUd onions gi-ow, there wUl be a still more 
offensive flavor. If she feeds in pastures where she can get a bite of 
brier leaves, beech or apple-tree leaves, or any thing of the kind, it 
injuriously affects the flavor of the butter though not to the same 
extent, and would scarcely be perceptible for immediate use. So 
with red clover. Butter made from cows fed on red clover is good 
when first made, but when laid down in packages, six months or a 
year, it seems to have lost all its flavor, and generally becomes more 
or less rancid as the clover on which the cow fed was of rank and 
rapid growth." — (A. B. Dickinson.) 

477. Distance from the time of calving. — The colostrum^ or first milk 
which the cow gi^es for several days after the birth of her young, 
differs from normal mUk. Geegory states that it contains from 15 to 
25 per cent, of albumen, with less casein, butter, and sugar of milk 
A much larger quantity of milk is yielded in the first two month? 
after calving, than at the subsequent periods ; the decrease is stated 
as follows, according to Atton : 

Quarts per day, Qimrta. 

. First 50 days 24 or in all 1200 

Second " 

Third " 

Fourth " 

Fifth " 

Sixth " 

and at the end of ten months, they become nearly or altogether dry. 

478. Time of year, age and condition of the animal. — In spring, milk is 
finest and most abundant. Moist and temperate climates and seasons 
are favorable to its production. In dry seasons the quantity is less, 
but the quality is richer. Sprengel states that cool weather favors 
the production of cheese and sugar in the milk, while hot weather 

20 " 

" 1000 

14 " 

" 700 

8 " 

" 400 

8 " 

" 400 

6 " 

" 800 


increases the product of butter. The poorer the apparent condi- 
tion of the cow, good food being given, the richer, in general, is the 
milk ; but it becomes sensibly poorer when she shows a tendency to 
fatten, A state of comparative repose is favorable to all the impor- 
tant functions of a healthy animal. Any thing which frets, disturbs, 
torments, or renders her uneasy, affects these functions, and among 
other results, lessens the quantity, or changes the quahty of the mUk. 
Such is observed to be the case when the cow has been newly de- 
prived of her calf — when she is taken from her companions in the 
pasture-field — when her usual place in the cow-house is changed — 
when she is kept long in the stall after spring has arrived — when she 
is hunted in the field, or tormented by insects, or when any other 
circumstance occurs by which irritation or restlessness is caused, 
either of a temporary or of a permanent character. — (JoffisrsTow.) 

479. Prodaction and Composition of Cream. — "We have stated that 
butter exists in mUk, as a fatty emulsion ; that is, not dissolved, but 
floating as exceedingly minute globules throughout the watery mass. 
These butter globules are lighter than water, and hence, when the 
milk is suffered to stand undisturbed, they slowly rise to the sur- 
face, forming cream. The oil-globules of cream do not coalesce or 
run together, they are always separated from each other, and sur- 
rounded by the soluble ingredients of milk ; while at the same time, 
the body of the milk never becomes perfectly clear by the complete 
separation of these globules. Hence, cream may be viewed as milk 
rich ia butter, and skimmed milk as containing little butter. It is 
supposed by some, that the butter particles are in some way invested 
or enclosed with casein ; at all events, a quantity of cheesy matter 
rises with the oU-globules. Its proportion in cream depends upon the 
richness of the milk, and upon the temperature at which it is kept 
during the rising of the cream. In cool weather, the fatty matter will 
bring up with it a larger quantity of the curd, and form a thicker cream. 

480. Conditions of tlie Formation of Cream. — The globules of butter 
being extremely minute, and but slightly lighter than the surround- 
ing liquid, which is at the same time somewhat viscid or thick, they 
of course ascend but slowly to the surface. The larger globules of 
butter, which rise with greater ease, mount first to the surface. If 
the first layer of cream, consisting of these largest particles, be taken 
off after 6 or 12 hours, it affords a richer, fresher, and more palatable 
butter than if collected after 24 or 30 hom-s standing. Milk is, there- 
fore, sometimes skimmed twice, and made to yield two quahties of but- 
ter. The deeper the milk, the greater the difficulty with which the 


oily matter ascends througli it ; hence, it is customary to set the milk 
aside in shallow pans, so that it may not he more than two or three 
inches in depth ; hence, if it is desired to prevent the formation of cream, 
the milk should be kept in deep vessels. Temperature powerfully in- 
fluences the formation of cream, or the rapidity with which it rises. 
Heat, by increasing the thinness and limpidity of the liquid, and the 
lightness of the oil-globules, favors their ready ascent ; while cold, by 
thickening the liquid, and solidifying the oU, greatly retards their sepa- 
ration. Hence it is said, that fi-om the same milk an equal quantity of 
cream may be extracted, in a much shorter time during warm than dur- 
ing cold weather ; that, for example, mUk may be perfectly creamed 

In 36 hours when the temperature of the air is 50° F. 

"24 " " " 55° 

" 18 to 20 " " " 68° 

" 10 to 12 " " " 7r 

while at a temperature of 34° to 37° (two to five degrees above freez- 
ing), milk may be kept for three weeks, without throwing up any 
notable quantity of cream. — (Speengel.) 

481. Blilk Creams before it is taken from the Cow, — This spontaneous 
tendency of milk to separate itself mechanically into two sorts or 
qualities, explains the remarkable difference in the richness of milk 
withdrawn at different stages of the milking process. The glands in 
the teats of the animals, which secrete the milk, are vessels interlaced 
with each other in such a way as to form hoUow spaces or -reservoirs 
which distend as the milk is secreted. In these reservoirs the same 
thing takes place as occurs in an open vessel, and with still more 
facility as the temperature is up to blood heat (98°) — the rich creamy 
portion rises above, while the poorer milk falls below. Hence that 
which is first drawn is of an inferior quality, while that which is last 
drawn, the strippings or afterings^ abounds in cream. Professor An- 
DEESON states, that compared with the first milk the same measure of 
the last will give at least eight, and often sixteen times as much cream. 
The later experiments of Reiset show, that where the milkings are 11 
or 12 hours apart, the quantity of butter in the last drawn milk is 
from three to twelve times greater than that obtained from the first 
drawn milk. Where the milkings were more often, the difference 
became less. As milk before being taken from the cow is already 
partially separated — its richer from its poorer parts — the dairy man- 
ager should take advantage of tliis circumstance, and not commingle 
in the same vessel the already half-creamed milk, if the object is the 
separation of butter. It has been shown that more cream is obtained 




by keeping the milk in separate portions as it is drawn, and setting 

these aside to throw np their cream in separate vessels, than when 

the whole milking is mixed together. Moreover, the intimate mixture 

of the richer and poorer portions not only reduces the fig. 96. 

quantity of cream that may be separated, but much delays 

the operation which, in hot weather, when mUk soon 

sours, is objectionable. ^=^ltp 

482. Determining the valne of Milk. — Its value is propor- 
tional to the amount of its solid alimentary constituents, 
and is liable to variation, according to circumstances. If 
butter is to be manufactured from it, that is most valuable 
which contains most oily matter ; if cheese is desired, 
then that which contains most casein. Milk is heavier 
than water, and the richer it is the heaver it is ; hence it 
has been attempted to make the latter quality a guide 
to the former. Its weight compared with water, or spe- 
cific gravity^ is determined by the hydrometer (Tig. 96). A A — 
tin or glass cylinder is filled with milk to be tested, and — 
the hydrometer, a glass bulb with a stem above, is placed ^ ''**™^ °'"' 
in it ; the lighter the milk, the deeper it sinks ; the heavier it is, the 
higher it floats. A scale is marked upon 
the stem, which indicates at once how 
far the weight of the mUk rises above 
pure water. Yet the results of the instru- 
ment are to be received with caution. 
Milks, though pure, differ naturally in 
specific gravity ; while it is easy to add 
adulterating substances that shall in- 
crease their weight, thus causing the (^M^^s. J [^T 

hydrometer to report them rich. Yet 
as giving an important indication it has 
value, and with experience and judgment, 
may be made useful.* An instrument 
called the lactometer (milk measurer) 
has been used to determine the propor- 
tion of cream. It consists of a glass 
tube ten or twelve inches long, marked 

off and numbered into a hundred spaces. [ --all ""^^ ^ -Jl 

The tube being filled with milk to the \ ^ 

top space, is suffered to stand until the Lactometer. 

Fig. 97. 

* Made by Tagliabcte, of Now York, 


cream rises to the surface, when its per cent, proportion is at once 
seen. It will answer if only the upper portion of the tube be marked 
as shown in Fig. 97. The percentage of cream, that is, the thickness 
of its stratum at the top of the tube, varies considerably. "We have 
found the average to be 8|- per cent., although samples are liable to 
range much above and below this number.* If the milk has been 
mixed, say with one-third water, the cream will fall to 6, if with one- 
half, it may fall to 5 per cent. 

483. Mineral Matter in Milk. — The proportion of salts in mUk 
averages about half per cent. ; that is, 200 lbs. when dried and burned 
will yield 1 lb. of ash. The composition of this ash is shown by the 
analysis of Haidlein, who obtained from 1000 lbs. of milk 

1 s 

Phosphate of lime 2-31 lbs. 8-44 lbs. 

Phosphate of magnesia 0'42 " 0"64 " 

Phosphate of peroxide of iron 007 " O'OT " 

Chloride of potassium 1-44 " 1-83 " 

Chloride of sodium 0-24 " 0-34 " 

Free soda 0-42 " 0-45 " 

Total 4-90 6-T7 

1. Combining the Elements of Beead. 

484. General Objects of Culinary Art. — We have seen that the ma- 
terials employed as human food consist of various organized substances 
derived from the vegetable and animal kingdoms, grains, roots, stalks, 
leaves, flowers and fruit, with flesh, fat, milk, eggs, &c. &c. But few of 
these substances are best adapted for food in the condition in which they 
occur naturally. They are either too hard, too tough, insipid or injuri- 
ous, and require to undergo various changes before they can be properly 
digested. Most foods, therefore, must be subjected to processes of 
manufacture or cookery before being eaten. In their culinary prep- 
aration, numerous mechanical and chemical alterations are effect- 
ed, in various ways; but the changes are chiefly wrought by means of 
water and heat. "Water softens some substances, dissolves others, some- 
times extracts injurious principles, and serves an important purpose 
in bringing materials into such a relation that they may act chemically 
upon each other. Heat, applied through the medium of water, or in va- 
rious ways and degrees, is the chief agent of culinary transformations. 
Another proper object of cooking is the preparation of palatable dishes, 

* The number given by the lactometer will, from the nature of the case, be somewhat 
under the truth, as the butter globules do not all ascend through the long column of milk. 


from tlie crude, tasteless, or even offensive substances fumislied by 
nature. This involves, not only the alterations produced by water and 
heat, but the admixture of various sapid and flavoring ingredients, 
■which increase the savory qualities of food. The cereal grains, con- 
verted into flour and meal, are to be prepared for mastication, mixture 
with the saliva, and stomach digestion. This end is best accomplished 
by converting them into bread, while at the same time they assume a 
portable and convenient form, and are capable of being preserved for 
a considerable time. Bread is made, as is well known, by first incor- 
porating water with the flour, and making it into dough, and then by 
various means causing it to rise, that is, to expand into a light, spongy 
mass, when, after being moulded into loaves, it is finally submitted to 
the action of heat in an oven, or baked. "We shall consider the suc- 
cessive steps of this important process, in the order of their occurrence ; 
and as the flour of wheat is the staple article in this country for the 
manufacture of bread, it wiU occupy our first and principal attention. 
485. Water absorbed iu making Dongh. — The addition of laauch water 
to fiour forms a thick liquid, called batter ; more flour admixed stiffens 
it to a sticky paste, and still more worked through it produces a firm 
dough. The water thus added to flour does not remain loosely associ- 
ated with it, but enters into intimate combination with its constitu- 
ents, forming a compound, and is not all evaporated or expelled by 
the subsequent high heat of baking. In the dough, the liquid performs 
its usual office of bringing the ingredients into that closer contact which 
is favorable to chemical activity. As water is thus made to become a 
permanent part of solid bread, it is important to understand in what 
proportion, and under what conditions, its absorption takes place. 
Baked bread that has been removed from the oven from 2 to 40 hours, 
loses, by thorough drying at 220,° from 43 to 45 per cent, of its 
weight, or an average of 44 per cent. If we assume the flour to con- 
tain naturally 16 per cent, of water, 10^ lbs. of the 44 that was lost 
belonged to the flour itself, while 33|- lbs. were artificially added m 
making the dough. Thus — 

Dryflo^r 56 ) 

Water in flour naturally lOJ j ^ 

Water added in baking 83^^ 


Ten pounds of flour would thus absorb 5 lbs. of water, and yield 15 
lbs. of bread. The best flours absorb more water than those of infe- 
rior quality. The amount with which they will combine is sup- 
posed to depend upon the proportion of gluten. In dry seasons flour 


will bear more water than in wet, and a thorough process of kneading 
will also cause the dough to absorb a larger quantity without becoming 
the less stiff on that account. Certain substances added to flour aug- 
ment its property of combining with water (521). 

486. Effects of the Kneading Process. — The purpose of water inter- 
mingled with flour is to combine with and hydrate the starch, to dis- 
solve the sugar and albumen, and to moisten the minute particles of 
dry gluten, so as to cause them to cement together, and thus bind the 
whole into a coherent mass. But, as only a certain limited quantity 
of water can be employed to produce these results, it is obvious that 
it must be carefully and thoroughly worked throughout the flour — this 
is called hieading the dough, and is generally performed with the 
hands. The process is laborious, and attempts have been often made 
to accomplish it by machinery, but hitherto without success. Flours 
differ so much in their dough-making properties, that judgment is re- 
quired in managing them. As the eye cannot penetrate into the ulte- 
rior of the- doughy mass to ascertain its condition, we have no guide 
equal to the sense of touch. Differences of consistence, foreign sub- 
stances, dry lumps of flour, are readily distinguished by the hand of 
the kneader, who is also by feeling able to control the gradual and 
perfect admixture of water, yeast, and flour, better than any machine 
yet devised. Much of the excellence of bread depends upon the 
thoroughness of the kneading, the reasons of which will soon be 
apparent. At first the dough is very adhesive, and clings to the fin- 
gers, but it becomes less so the longer the kneading is continued, and 
when the fist upon being withdrawn leaves its perfect impression in 
the dough, none of it adhering to the hand, the operation may be dis- 

487. Bread from plain Flour and Water. — ^When dough, made by 
simply working up flour and water, is dried at common temperatures, 
a cake is produced, not very hard, but which is raw, insipid, and indi- 
gestible. If baked at 212° (ordinary steam heat), a portion of the 
starch becomes soluble, but the cake is dense, compact, and very diffi- 
cult of digestion. If baked at a still higher heat, and afterward sub- 
jected to prolonged drying, we have the common sMp-lread or sea- 
lisGuit, which is made in thin cakes and never in large loaves, and 
which is very dry, hard, and difficult to masticate, although it has an 
agreeable taste, derived from the roasting of the surface of the dough. 
Bread prepared in this manner lacks two essential characters, — sufficient 
softness to be readily crushed in the mouth or chewed, and a looseness 
of texture or sponginess by which a large surface is exposed to the 


action of the digestive juices in the stomach. To impart these quali- 
ties to bread, the dough is subjected to certain operations before bak- 
ing, which are technically called raising. The capability of being 
raised is due to the gluten. JBy the mechanical operation of kneading, 
the glutinous parts of the flour are rendered so elastic that the mass 
of dough is capable of expanding to twice or thrice its bulk without 
cracking or breaking. Yarious methods are employed for this nur- 
pose, which will now be noticed ; and first of fermentation : 

2. — ^Beead Raised by Feementation. 

488. Substances capable of Putrescence. — ^It is a remarkable property 
of the nitrogenous alimentary principles, that when in a moist state, 
and exposed to atmospheric oxygen, they speedily enter upon a state of 
change or rapid decay. They are of very complex composition (422), 
the attractions of their atoms being so delicately adjusted that 
Blight disturbing forces easily overturn them. Oxygen of the air 
seizes upon the loosely held atoms, breaks up the chemical fabric, and 
produces from its ruins a new class of substances — the gaseous pro- 
ducts of putrefaction. Thus, it is well known that flesh, blood, milk, 
cheese, dough, bread, all of which are rich in nitrogenous substances, 
will preserve their properties in the air only a short time, but pass 
into a state of putrescence, becoming sour and nauseous, and sending 
forth offensive exhalations. This change is called putrefaction, and 
the compounds which are liable to it, putrefiable substances. 

489. The Putrefactive change Contagious. — The other class of alunents, 
the non-nitrogenous, are in this respect of a very different nature. 
They contain fewer atoms, lack the fickle element nitrogen, and have 
a simpler and firmer composition. "When pure starch, gum, sugar, or 
oil, ai'e exposed to the air in a moistened state, they exhibit little ten- 
dency to change, and give rise to none of the effects of putrefaction. 
Yet if placed in contact with putrefying substances, the change proves 
contagious; they catch it, and are themselves decomposed and de- 
stroyed. Hence, when the putrefiable substances are considered, with 
reference to the effects they produce upon the other class, they take a 
new name, and are cai^Qdi ferments. The communication of that con- 
dition of change from one class to the other, is called fermentation^ 
and the substances acted upon are named fermentable compounds. 
Thus, if some sugar be dissolved in water, and a portion of putrefying 
dough, meat, or white of egg be added to it, fermentation sets in; that 
is, the change is commimicated to the sugar, the balance of its affini- 
ties is destroyed, and two new substances— one alcohol, containing all 


the hydrogen of the sugar, and the other carhonic acid, contaming 
two-thirds of its oxygen — are produced. 

490. Conditions of Fermentation. — When matter capahle of putre- 
faction begins to change, decomposition rapidly spreads throughout 
the mass. If a small portion of putrefying substance be added to a 
large quantity, in which it has not commenced, the change extends 
until the whole becomes alike affected. But it is not so in fermenta- 
tion. The sugar cannot catch the infection and then go on decompos- 
ing itself. It can only break up into new compounds as it is acted, 
upon, and when the limited quantity of ferment made use of is ex- 
hausted, or spent, the effect ceases, no matter what the amount of 
fermentable matter present. Two parts by weight of ferment decom- 
pose no more than one hundred of sugar. Temperature controls the 
rate or activity of fermentation. At 32° no action takes place; at 45° 
it proceeds slowly ; at Y0° to 86°, which is the proper range of warmth, 
it goes on rapidly. The operation may be stopped by the exhaustion 
of either the ferment or the sugar, by di-ying, by exposure of it to a 
boiling heat, and by various chemical substances, as volatile oUs, sul- 
phurous acid, &c. 

491. Different kinds of Fermentation. — "When nitrogenous matters 
are just beginning to decompose, the action is too feeble to establish 
the true alcoholic fermentation in solutions of sugar. Yet even in this 
early stage they can change the sugar, not breaking it to pieces so com- 
pletely, but splitting each of its atoms into two equal atoms of lactic 
acid, the sour principle of milk. This process is called the lactic acid 
fermentation, while that in which alcohol is produced is the mno^ls or 
alcoholic fermentation. If this be not checked, the process is liable to 
run on to another stage ; the ferment is capable of attacking the alco- 
hol itself, and converting it to acetic acid, the active principle of vine- 
gar. This is the acetous fermentation. There are several conditions 
of this acetous change. First, a spirituous or alcoholic solution ; second, 
a temperature from 80° to 90° ; third, a ferment to give impulse to 
the change ; and, fourth, access of air, as oxygen is rapidly absorbed 
in the process, combining with and oxidizing the alcohol. 

492. Dougli raised by Spontaneous Fermentation. — Now dough, as it con- 
tains both gluten and sugar, when moistened is capable of fermentation 
without adding any other substance. If simple flour and water be 
mixed and set aside in a warm place, after the lapse of several hours it 
will exhibit symptoms of internal chemical action, becoming soiu- from 
the formation of lactic acid, while miaute bubbles appear, which are ow- 
ing to a gas set free within the dough. The changes are irregular and un- 


certain, according to the proportion and condition of the constituents 
of the flour. They also proceed with greater or less rapidity at the 
surface or in the interior, accordingly as the parts are exposed to the 
cooling and oxidating influence of the air. Bread haked from such 
dough, is sour, heavy, and altogether bad. Yet the true vinous fer- 
mentation may be spontaneously established in the dough, by taking 
measures to quicken the action. If a small portion of flour and water 
be mixed to the consistency of batter (its half-fluid state being favor- 
able to rapid chemical change), and the mixture be placed in a jar or 
pitcher and set in a vessel of water, kept at a temperature from 100° 
to 110°, in the course of five or six hours decomposition will have set 
in, with a copious production of gas bubbles, which may be seen by 
the appearance of the batter when stirred. If this be now mixed and 
kneaded with a large mass of dough, moulded into loaves and set 
aside for an hour or two in a warm place, the dough will swell, or ' rise ' 
to a much larger bulk ; and when baked, will yield a light spongy bread. 
A little salt is usually added at first, which promotes the fermenta- 
tion, and hence, bread raised in this manner is called 'salt raised 
bread.' Milk is often used for mixing the flour, instead of water ; 
the product is then called ' milk-emptyings bread.' 

493. Wliat makes the Dongh rise 1 — The cause of the rising is the 
vinous fermentation produced by the spontaneous change of the gluten 
or albumen which acts upon the sugar, breaking it up into alcohol and 
carbonic acid gas. If the fermentation is regular and equal, the knead- 
ing and intermixture thorough, and the dough kept sufiiciently and 
uniformly warm, the production of gas will take place evenly through- 
out the dough, so that the bread when cut will exhibit numberless 
minute cavities or pores, equally distributed throughout. For its capa- 
bility of being raised, dough depends upon the elastic and extensible 
properties of its gluten, which is developed by the admixture of water 
with flour. Hence the proper quantity of water is that which im- 
parts to the gluten the greatest tenacity; an excess of it lowering 
the adhesiveness of the glutinous particles. The toughness of the 
gluten prevents the small bubbles of gas from uniting into larger ones, 
or from rising to the surface. Being caught the instant they are pro- 
duced, and expanding in the exact spot where they are generated, they 
swell or raise the dough. All rising of bread depends upon this prin- 
ciple — the liberation of a gas evenly throughout the glutinous dough. 
No matter what the mode of fermentation, or what the substances or 
agents employed instead of it, they all bring about the result in the 
same way. 


494. Raising Dongh by Leayen, — But the mode of raising dough by 
spontaneous fermentation (492) is not suiEciently prompt and conve- 
nient ; we require some readier means of establishing immediate de- 
composition. If Tve take a piece of dough which has been kept suffi- 
ciently long to ferment and turn sour, and then knead it up thoroughly 
with a large lump of fresh dough, the whole of the latter will shortly 
enter into a uniform state of fermentation ; and if a little of this be re- 
served for the next baking, it may be worked into a fresh mass of dough, 
and in this way, active fermentation may be induced at any time. 
Fermenting dough thus used is called leaven. It may be made from 
any sort of flour, and is improved by the addition of pea and bean 
meal, which ferment easily. When properly made, leaven may be 
kept weeks or mouths fit for use, and by adding a portion of dough 
to the leaven, as large as that reserved for the bread-maker, the 
stock of leaven is always kept up. Although leaven when added 
to dough, awakens the true alcoholic fermentation, yet being in a sour 
state, it produces a portion of lactic acid, and often acetic acid ; the 
latter being mostly driven off in the process of baking, whUe the 
former remains in the bread. Hence, bread made with leaven always 
has a distinctly sour taste, partly caused by the acid of the leaven it- 
self, and partly by the sour fermentation which it induces in the 
dough. It is difficult to manage, and requires much skUl to produce 
a good result. Leaven is but little used in this country, bread be- 
ing almost universally raised by means of yeast. 

3. Peopeeties and Action of Yeast. 

495. Production of Brewer's Teast. — When grains are placed in the 
proper conditions of germination, that is, moistened and exposed to 
atmospheric oxygen at the proper temperature, a portion of their glu- 
ten is changed to the state of ferment, and acquires the property of 
transforming starch into sugar. Hence, seeds in germinating become 
sweet. Barley placed in these conditions, begins to germinate, swells, 
softens, and turns sweet ; it is then heated and dried, by which the 
process is stopped. The barley is then called malt. It is next crushed 
or ground and infused {mashed) in water at 160° so as to extract all 
the soluble matter it contains. The liquid {sweet-wort) is then boiled 
to coagulate the excess of vegetable albumen. Hops are added, to 
impart a bitter taste to the product (beer), and also to regulate the 
subsequent fermentation. The cooled wort is then run into the fer- 
menting vat, and yeast is added. " In three or four hours, bubbles of 
gas will be seen to rise from all parts of the liquid ; a ring of froth, 


forming at first around its edge, gradually increases and spreads till it 
meets in the centre, and the whole surface becomes covered with a 
white creamy foam. The hubbies of gas (carhoniG acid) then rise and 
break in such numbers, that they emit a low hissing sound, and the 
white foam of yeast continues to increase in thickness, breaking 
into little pointed heaps, which become brownish on the surface and 
edges ; the yeast gradually thickenilig until it forms a tough, viscid 
crust." Although a portion of the yeast was spent in the operation, 
yet a much larger quantity has been produced from the nitrogenous 
matter of the grain in the solution. 

496. Appearance of Yeast — It is a Plant. — Yeast, as usually procured 
from the brewer, is a yellowish gray or fawn-colored frothy liquid, 
of a bitter taste, and which shrinks in a few hours into one-fourth 
the space it occupied at first. "When fresh, it is in constant move- 
ment, and bubbles of gas escape frorn it. When dried it loses 70 per 
cent, of its weight, becomes solid, horny-looking, half- transparent, and 
breaks readily into gray or reddish fragments. The nature of yeast 
was for a long time matter of doubt and speculation, but the micro- 
scope has at length cleared up the question, and showed t^^at it is a 
true plant belonging to the Fungus tribe. Under a powerful magni- 
fier, it is seen to consist of numberless minute rounded or oval bodies, 
which are true vegetable cells. Each little globule consists of an en- 
veloping skin or membrane, containing a liquid within. Such cells 
are the minute agencies by which all vegetable growth is affected. 
The leaves and pulpy parts of plants are built up of them, as a wall 
is built of bricks. All the numberless substances produced by plants, 
are generated within these little bodies. They grow or expand from 
the minutest microscopic points and seem to 
bud oif fi'om each other, as shown in Figs. 98 
and 99. The little grains from which they 
spring or germinate are shown, and how they 
multiply by budding. They are of amazing 
minuteness, a single cubic inch of yeast, free 
from adhering matter, containing as many 
as eleven hundred and fifty-two millions 
of them. In what manner yeast acts to 
decompose sugar is not known. The yeast 
is destroyed or expends itself in producing 
the effect, yet it furnishes none of its sub- Teast cells, showing how tiiey 
stance to join with the sugar, in producing SSJ 'o^r t't "esc'apini 
alcohol and carbonic acid. Liebig supposes *^°°^ ^^^^ interior. 
the efiect to be dynamic^ that is, produced by an impulse of force ; the 



motions of the atoms of the decomposing ferment, being commnni- 
cated to the atoms of sugar, set these also in motion, by which the 
sugar structure is, as it were, jarred and shaken to pieces, its atoms 
falling into new arrangements and forming new substances, 

497, Domestic preparation of Yeast — ^Fowne's method. — But, as 
many have no access to breweries, it is desirable to know how 
to make yeast at home. If common wheaten flour be mixed 
with water to a thick paste, and 
exposed slightly covered, and 
left to spontaneous change in a 
moderately warm place, it wUl, 
after the thu-d day, begin to 
emit a little gas, and to exhale 
an exceeding disagreeable sour 
odor. After the lapse of some 
time this smell disappears ; the 
gas evolved is greatly increased, 
and is accompanied with a dis- 
tinct agreeable vinous odor ; this 
will happen about the sixth or 
seventh day, and the substance 
is then in a state to excite fer- 
mentation. An infusion of crush- 
ed malt (wort) is then boiled 
with hops, and when cooled to 
90° or 100°, the altered dough, 
above described, after being 
thoroughly mixed with a little 
lukewarm water, is added to it, 

, ,T. , , 14., V „ A developed yeast plant, the numbers indi- 

and the temperature kept up by eating the successive stages of growth, 
placing the vessel in a warm situ- 
ation. After a few hours fermentation commences, and when that is 
complete, and the liquid clear, a large quantity of excellent yeast is 
formed at the bottom. 

498. Yeast from Potatoes.— Boil half a dozen potatoes in three or 
four quarts of water, with a couple of handfuls of hops placed in a 
bag. Mash the potatoes and mix with the water, adding and stirring 
in a little salt, molasses and flour, until it is of a battery consistence. 
Then mix in a couple of spoonfuls of active yeast. Place before the 
fire, when it will soon begin to ferment. In a cool place it may 
be kept for weeks. 


499. Action of Hops in Teast-making. — Hop-flowers contain about 8 
per cent, of a brownish yellow bitter volatile oil, upon which its pecu- 
liar odor depends. The hop has been long known for its soporific or 
sleep-producing properties, which are supposed to be duo to this 
volatile narcotic oil. When dry hop-flowers are beat, rubbed and 
sifted, they yield about 8 per cent, of fine yellow dust — an aromatic 
resin, which has an agreeable odor, and a bitter taste. "When taken 
internally it has a soothing, tranquillizing, sleep-provoking influence. 
It is caUed lupulin. Hops also contain a considerable proportion of 
another strong bitter principle, which is said not to be narcotic. In 
brewing, the chief use of hops is to impart an agreeable bitterness to 
the beer, but it also has the effect of arresting or checking fermenta- 
tion before all the sugar is converted into alcohol, and then prevent- 
ing the production of acid. It is also well-known that in the domestic 
preparation of yeast, hops serve to prevent the mixture from souring, 
though Jiow this is affected we cannot tell. 

500. Yeast preserved by drying. — The liquid, or active yeast, is liable 
to turn sour and spoil in warm weather, losing its properties and im- 
parting to bread a most disagreeable flavor. Drying has therefore 
been resorted to, as a means of preserving it. On a large scale, it is 
pressed in bags and dried at a gentle heat, until it loses two-tbirds of 
its weight of water, leaving a granular or powdery substance, which, 
if packed and kept from the air and quite dry, may be preserved a 
long time. It is curious that mechanical injury kills or destroys yeast. 
Falls, bruises, a rough handling spoils it, so that great care is required 
to remove it from place to place. LiEBia remarks that simple pressure 
diminishes the power of yeast to escite the vinous fermentation. 
Yeast is also preserved by dipping twigs in it and drying them in the 
air. Or it may be worked round with a whisk untU it becomes 
thin, and then spread with a brush over a piece of clean wood and 
dried. Successive coats may be thus applied, until it becomes an inch 
or two in thickness. "When thoroughly dried, it can be preserved in 
bottles or canisters. Yeast is also commonly^-eserved by adding to it 
maize meal, and making it into a dough which is wrought into cakes 
and dried. They may be kept for months and are ready for use at 
any time, by crumbling down and soaking a few hours in warm water. 
We add minuter directions for making yeast-cakes. Eub three ounces 
of fresh hops until they are separated, boil half an hour in a gallon of 
water, and strain the liquid through a fine sieve into an earthen vessel. 
While hot, stir in briskly 3i lbs. of rye flour. Next day, thoroughly 
mix in 7 lbs. of Indian meal, forming a stiff dough ; knead it well, roll 



it out a third or half an inch thick, cut into cakes and dry in the sun, 
turning every day and protecting from wet. If preserved perfectly 
from damp they will keep long. 

501. Bitterness of Yeast— how corrected. — Yeast is often so bitter as to 
communicate a most disagreeable taste to bread. This may be de- 
rived from an excess of hops. To rectify this, mix with the yeast a 
considerable quantity of water, and set it by to rest for some hours, 
when the thickest part will fall to the bottom. Pour off the water 
which will have extracted a part of the bitter principle, and use only 
the stiff portion that has fallen to the bottom. But yeast sometimes 
acquires a bitter taste from keeping, which is quite independent of that 
derived from the hops. One method of remedying this, consists in 
throwing into the yeast a few clean coals freshly taken from the fire, 
but allowed to cool a little on the surface. The operation appears to 
depend in principle upon the power of freshly burnt charcoal to ab- 
sorb gases and remove offensive odors (811). 

502. Acidity of Teast— how corrected, — In country places, where it is 
customary to keep yeast for some time, and especially during the 
warmth of summer, it is very liable to sour. In such case, it may 
be restored to sweetness, by adding a little carbonate of soda or car- 
bonate of magnesia, only so much being used as may be necessary to 
neutralize the acidity. 

503. Dough raised by Yeast. — How fermentation lightens dough, has 
been shown (493). Yeast produces these changes promptly and effec- 
tually. It is mixed with a suitable portion of water, flour, and salt, 
to form a stiff batter, which is placed near the fire for an hour or two, 
covered with a cloth. This is called setting the sponge. An active fer- 
mentation is commenced, and the carbonic acid formed in the viscid 
mass, causes it to swell up to twice its original size. If not then quickly 
used iifalls^ that is, the accumulated gas within escapes, and the dough 
collapses. Yet after a time it may again rise, and even fall a second 
time and rise again. This, however, is not allowed. When it has fully 
risen, much more flour is thoroughly kneaded with the sponge, and 
the dough is left for perhaps an hour and a half, when it rises again. 
It is then again kneaded and divided into pieces of the proper size foi 
loaves. The loaves should be moulded with care, as too much hand- 
ling is apt to cause the escape of the enclosed gas, and make the 
bread heavy. 

504. Correction of Acidity in Dongh. — Dough is frequently sour 
from an acid condition of the flour. It may be in this condition from 
a sour state of the yeast, or the fermentation may be so feeble as to 


produce acid (476), or it may be too active and rapid, if too much or 
too strong yeast lias been used ; or in hot weather when the dough is 
liable to sour by running into the acetous fermentation. If the diffi- 
culty is too sluggish a change, it should be hastened by securing the 
most favorable warmth. If, on the contrary, it is too violent, it may be 
checked by uncovering the dough, and exposing it to the air in a cool 
place. If the dough be already sour, it may be sweetened by alkaline 
substances. Carbonate of soda will answer this purpose. Carbonate 
of ammonia is perhaps better, as it is a volatile salt, and is raised in 
vapor and expelled by the heat of the oven (510). If too much be used, 
a portion of the excess is driven off by the heat, and in escaping assists 
in making the bread lighter. Caution should, however, be employed 
to use no more alkali than is really necessary to neutralize the acid. 
"When the acidity is but slight, it may be rectified by simply kneading 
the dough with the fingers moistened with an alkaline solution. 

505. The Sugar of Flour all decomposed in Dough. — It is at the ex- 
pense of sugar destroyed that fermented bread is raised, but how much 
sugar is thus decomposed is variously stated, and depends upon the 
activity and continuance of fermentation. Experiments would seem 
to show, that all the sugar present is rarely, if ever, destroyed. 
The raised dough and bread both contain sugar, often nearly as much 
as the flour before it was used. This is explained by remembering 
that one of the effects of fermentation is to change starch to sugar. 

506. How much Alcohol is produced iu Bread. — Of course the quantity 
of alcohol and carbonic acid generated in bread is in exact proportion 
to the amount of sugar destroyed, which, as we have said, is by no 
means constant. In an experiment, a pound of bread occupied a space 
of 60 cubic inches, 26 of which were solid bread, and 34, cell-cavi- 
ties; consequently 34 cubic inches of carbonic acid of the heat of the 
oven were generated to raise it, which implied the production of about 
15 grains of alcohol, or less than one-quarter of one per cent, of the 
weight of bread. It has been attempted to save this alcohol, which 
is vaporized and driven off into the air by the baking heat, but the 
product obtained was found to be so small as not to pay cost. It is 
also a current statement, that alcohol exists in the bread, contributing 
to its nutritive qualities. "We have never found it there, and never 
saw a chemical analysis of bread that enumerated it as a constituent. 

4. Kaising Bkead withotjt Fermentation. 

507. Objections to raising by Ferment. — Two or three objections have 
been urged against raising bread by fermentation. First, the loss of 


a portion of the sugar of tlie flour which is decomposed ; this loss, how- 
ever, is trifling, and the objection futile. It is said, secondly, that as 
a destruction or incipient rotting process has been established in the 
dough, bread made from it cannot be healthful. This is only /ancy, 
experience is wanting to show that well-made fermented bread is ia- 
jurious. Thirdly, it is said that the fermenting process is not only- 
uncertain, but slow, and requires more time than it is often convenient 
to allow. There is such force in this latter objection, that means have 
been sought to replace fermentation by some quicker and readier 
method of raising the dough. 

508. How it is done without Ferment. — As the lightening and expan- 
sion of the dough are caused by gas generated within it, it would seem 
that we may adopt any means to produce such a result. It is com- 
monly done in two ways ; either by mixing chemical substances 
with the flour, which, when brought into contact and wet, act 
upon each other so as to set free a gas, or by introducing into the 
dough a volatile solid substance, which, by the heat of baking, ri^es 
into the state of gas. In the first case, substances are used which set 
free carbonic acid ; in the second case, a compound of ammonia. 

509. Raising Bread with Chemical Substances. — Bicarbonate of soda and 
hydrochloric acid are used for raising bread. The soda is mixed inti- 
mately with the flour, and the acid is added to the water requisite to 
form dough. Peeeiea indicates the following proportions : 

Flour 1 lb. 

Bicarbonate of soda 40 grains. 

Cold water, or any liquid necessary ■§■ pint. 

Hydrocliloric acid 50 drops. 

The soda and flour being mixed, the acidulated water is added gradu- 
ally, with rapid stirring, so as to mix speedily. Divide into two loaves, 
and put into a hot oven immediately. The acid combining with the 
soda, sets free its carbonic acid, which distends the dough. Both the 
acid and the alkali disappear, are destroyed, and the new sub- 
stance formed by their union is chloride of sodium, or common salt; 
so that this means of raising bread answers also to salt it. If the in- 
gredients be pure, the proportions proper, and the mixture perfect, no 
other substance will remain in the bread. If the acid be in excess, there 
wUl be sourness ; and if there be too much alkali, or if it be not en- 
tirely neutralized, unsightly yellow stains in the bread crumb will be 
apparent, accompanied by the peculiar, hot, bitter, alkaline taste, and 
various injurious efiects. The changes that take place are thus shown. 
"We begin with — 


Bicarbonate of soda; J ^ , 
{solid,) and r .^^l^> 

Carbonic acid; 

Water ; 

{liquid,) and 
Common salt ; 


Bread is also raised "with soda powders ; — tartaric acid, and bicar- 
bonate of soda, ■which are the active ingredients in effervescing draughts. 
The changes are these 

Bicarbonate of soda; ^ ■^y.r.A^^a C Carbonic acid; 

{solid,) and ( P[° the } (^«^') '^""^ 

Tartaric acid; ( ^„ „i, ) Tartrate of soda; 

{solid,) ) ^°'^S'^> ( {solid.) 

Cream of tartar, consisting of tartaric acid combined with and partly 
neutralized by potash, is also used with soda, one being mixed with 
flour, and the other dissolved in water. Double the quantity of cream 
of tartar to soda is commonly used, but of tartaric acid only an equal, 
or slightly less quantity. In these cases tartrate of soda is formed in 
the bread, which, in its action upon the system, is hke cream of tartar 
— gently aperient. Preparations which are known as egg-powder, 
baking-powder, and ctista/)'d-powders, consist of bicarbonate of soda and 
tartaric acid, mixed with wheat flour or starch, and colored yellow 
with turmeric, or even poisonous chromate of lead. The diflicnlty Avith 
these powders, is to get them in perfect neutralizing proportions. 
This may be ascertained by dissolving them in water ; the mixture 
should be neutral to the taste, and produce no effervescence by 
adding either alkali or acid. Sour milk, or buttermilk, are often used 
with soda or saleratus. In these cases the lactic acid they contain 
combines with the alkali, forming lactate of soda, or potash, and set- 
ting carbonic acid free, which lightens the dough, just as in all the 
other instances. 

510. Sesquicarbonate of Ammonia. — The perfect theoretic conditions 
of raising bread without ferment would be, to find a solid substance 
which could be introduced into the flour, but which would entirely es- 
cape as a gas during baking, raising the bread, and leaving no trace of 
its presence. Carbonate of ammonia complies with the first of these 
conditions ; it is a solid which, under the influence of heat, is decom- 
posed entirely into gases. Tlius — 

Sesquicarbonate of 

in baking 

Ammonia; l m "^J^mg 

(solid \ i produces, 


Ammonia ; 

Bicarbonate op 
Ammonia ; 

Carbonic acid, 



Yet practically these gases do not all escape in baking ; a portion of 
them is apt to remain, communicating a disagreeable hartshorn flavor. 
All these methods have one common and serious disadvantage — the 
gas is set free too suddenly to produce the best effect. Alum and car- 
bonate of ammonia are sometimes used ; they act more slowly, but 
leave an unwholesome residue of alumina and sulphate of ammonia in 
the bread. 

511. Important Cantion in reference to the Chemicals used. — The class 
of substances thus introduced in the bread are not nutritive but me- 
dicinal, and esert a disturbing action upon the healthy organism. 
And although their occasional and cautious employment may perhaps 
be tolerated, on the ground of convenience, yet we consider their ha- 
bitual use as highly injudicious and unwise. This is the best that can 
be said of the chemical substances used to raise bread, even when 
pure, but as commonly obtained they are apt to be contaminated with 
impurities more objectionable still. For example, the commercial mu- 
riatic acid which is commonly employed along with bicarbonate of 
soda, is always most impure — often containing chlorine, chloride of 
iron, sulphurous acid, and even arsenic, so that the chemist never uses 
it without a tedious process of purification for his purposes, which are 
of far less importance than its employment in diet. "While common 
commercial hydrochloric acid sells for 3 cents per pound wholesale, 
the purified article is sold for 35. Tartaric acid is apt to contain lime, 
and is frequently adulterated with cream of tartar, which is sold at 
half the price, and greatly reduces its efficacy ; while cream of tar- 
tar is variously mixed with alum, chalk, bisulphate of potash, tartrate 
of lime, and even sand. Sesquicarbonate of ammonia is liable by ex- 
posure to air to lose a portion of its ammonia. It is hence seen that 
the substances we employ are not only liable to injure by ingredients 
which they may conceal, but that their irregular composition must 
often more or less defeat the end for which they are intended. "We 
may suggest that, in the absence of tests, the best practical defence is 
to purchase these materials of the druggist rather than the grocer. If 
soda is desired, call for the licarionate of soda ; it contains a double 
charge of carbonic acid, and is purest. Soda-saleratus is only the 
crude, impure carbonate — soda-ash. The cream of tartar should appear 
white and pure, and not of a yellowish tinge (698). 

512. Raising Dongh with Oily Snbstanccs and Eggs. — If dough be mixed 
with butter or lard, rolled out into a thin sheet, and covered with a 
thin layer of the oily matter, then folded, rolled and recoated from 2 
to 10 times, and the sheet thus produced be submitted to the oven, the 


heat causes the disengagement of elastic vapor from the water and 
fatty matter, which, heiag diffused between the numerous layers of 
dough, causes them to swell up, producing the flaky or puffy appearance 
which is seen in pastry. This kiad of lightness must not be confound- 
ed with that produced by the other methods described ; for, although 
the layers are partially separated, yet the substance of each stratum 
is dense and hard of digestion. The albumen of eggs, when smartly 
beaten, becomes frothy and swells, by entangling much air in its 
meshes. If then mixed with dough, it conveys with it air bubbles, 
which are expanded in baking. From its glairy, tenacious consistence 
when mixed with dough or pudding, it encloses globules of gas or 
steam, which are generated by fermentation or heat. In this way egga 
contribute to the lightness of baked articles. 

513. Kaising Gingerbread. — Gingerbread usually contains so much 
molasses that it cannot be fermented by yeast. But the molasses is of 
itself always acidulous, and takes effect upon the saleratus, setting 
free carbonic acid gas. Sour mUk, buttermilk, and cream, are also 
used, which act in the same way upon the carbonate of soda or potash, 
and thus inflate the dough. Dr. Colquhoxtn has found that carbonate 
of magnesia and tartaric acid may replace the saleratus (and alum 
also, which is sometimes used), affording a gingerbread more agreeable 
and wholesome than the common. His proportions are, 1 lb. of flour, 
■i oz. carbonate of magnesia, \ oz. of tartaric acid, with the requisite 
molasses, butter, and aromatics. 

5, AxTEEATioNS Peodtjoed ht Bakin& Beead. 

514. Temperature of the Oyen.— Bread is usually baked by heat radi- 
ated or conducted from the brick walls or iron plates of which ovens 
are made. The oven should be so constructed that the heat may be 
equal in its different parts, and remain constant for a considerable 
time. If the heat be insufiicient, the bread will be soft, wet, and 
pasty ; if on the other hand the heat be too great at first, a thick, 
burnt crust is produced, forming a non-conducting carbonaceous cov- 
ering to the loaf, which prevents the heat from penetrating to the 
Interior. Hence a burnt outside is often accompanied by half-raw 
dough within. If, however, the temperature be proper, the heat 
passes to the interior of the loaf and produces the necessary changes 
before the outside becomes thickly crusted. If we cut open a well 
baked loaf, immediately from the oven, and bury the bulb of a ther- 
mometer in the crumb, it wiU rise to 212°. This heat is sufficient to 


carry on the iimer chemical changes of baking, and it is obvious that 
the heat cannot rise above this point so long as the loaf continues 
moist (65.) Bread might be baked at a temperature of 212° (by 
steam), but then it would lack that indispensable part, the crust. The 
baking temperature of the oven ranges from 360° to 450° or 500°, and 
bakers have various means of judging about it. If fresh flour strewn 
upon the oven bottom turns brown, the heat is right, if it chars or 
turns black, the heat is too great. 

515. Heat causes a loss of Weight. — The loaf loses a portion of its 
weight by evaporation. The quantity thus lost depends chiefly upon 
the size and form of the loaf. If it be small or thin, it will part with 
more water in proportion than if of cubical shape. Something de- 
pends upon the quality of the flour and the consistence of the dough. 
"Various experiments would seem to show that bread parts with from 
one-sixth to one-tenth of its weight in baking. In those places where 
bread is required by law to be of a certain weight, this loss must be 
calculated upon and a proportionate amount of additional flour used. 
Peechtl states from experiment that loaves which, after baking and 
drying, weigh one pound, require that an extra weight be taken, in 
dough, of six ounces ; if the loaves are to weigh three pounds, twelve 
ounces additional must be taken, and if sis pounds, sixteen ounces. 

516. How Heat enlarges the Loaf. — When the loaf is exposed to the 
heat of the oven, it swells to about twice its size. This is owing to 
the expansion of the carbonic acid gas contained in its porous spaces, 
the conversion of water into steam, and the vaporizing of alcohol, 
which also rises into the gaseous form and is driven off, as is shown 
by the spirituous odor yielded in the baking process. 

517. Chemical Changes in prodneing the Crust. — The heat of the oven 
falling upon the surface of the loaf causes first the rapid evaporation 
of its water, and then begins to produce a disorganization of the 
dough. The starch-grains are ruptui-ed (530) and its substance con- 
verted into gum; as the roasting continues chemical decomposition 
goes on, and organic matter is produced of a brown color, an agreeable 
bitter taste, and soluble in water, which has received the name of 
assamar. The formation of hard crusts on the loaf may be prevented 
by baking it in a covered tin, or, it is said, by rubbing a little melted 
lard over it after it is shaped and before it is set down to rise. 

518. Chemical Changes in producing the Crumb. — As the temperature 
within the loaf does not rise above 212°, no changes can go on there 
except such as are produced by the heat of the aqueous vapor. This 
is sufficient to stop the fermentation, destroy the bitter principle of 


the yeast, and kill the yeast plant. In baking about one-fourteenth of 
the starch is converted into gum, the rest is not chemically altered, as 
may be shown by moistening a little bread-crumb and touching it with 
solution of iodine, when the blue color will prove the presence of 
starch. The gluten, although not decomposed, is disunited, losing its 
tough, adhesive qualities. The gluten and starch-paste are intimately 
mixed, but they do not unite to form a chemical compound. 

519. Moisture contained in Bread. — In newly-baked bread the crust 
is dry and crisp, while the crumb is soft and moist, but after a short 
time this condition of things is quite reversed. The brown products 
of the roasting process attract moisture and the crust gets daily softer, 
while the crumb becomes dry. Bread, two or three days old, loses 
its softness, becoming hard and crumbly. But this apparent dry- 
ness is not caused by evaporation or loss of water, for it may be 
shown by careful weighing that stale bread contains almost exactly 
the same proportion of water as new bread that has become com- 
pletely cold. The change to dryness seems to be one of combination 
going on among the atoms of water and bread. That the moisture 
has only passed into a state of concealment may be shown by exposing 
a stale loaf in a closely covered tin for half-an-hour to a boiling heat, 
when it will again have the appearance of new bread. The quantity 
of water which well-baked wheaten bread contains amounts, on an 
average, to about 45 per cent. The bread we eat is, therefore, nearly 
one-half water. It is, in fact, both meat and drink together. One of 
the reasons why bread retains so much water is, that during the 
baking a portion of the starch is converted into gum, which holds 
water more strongly than starch does. A second is, that the gluten 
of flour when once thoroughly wet is very difficult to dry again, and 
that it forms a tenacious coating round every little hollow cell in the 
bread, which coating does not readily allow the gas contained in the 
cell to escape, or the water to dry up and pass off in vapor ; and a 
third reason is, that the dry crust which forms round the bread in 
baking is nearly impervious to water, and, like the skin of the potato 
we bake in the oven or in the hot cinders, prevents the moisture from 
escaping. — (Johnston.) 

520. Qualities of Good Bread, — In baking bread, it is desirable to 
avoid the evils of hardness on the one hand and pastiness on the other, 
nor should it be sour, dense, or heavy. It should be thoroughly and 
uniformly kneaded, so that the carbonic acid wiU not be liberated in 
excess in any one place, forming large hollows and detaching the 
crumb from the crust. The vesicles should be numerous, small, and 



equally disseminated ; nor should the crust be bitter and black, but of 
an aromatic agreeable flavor. " If the yeast be so diffused throughout 
the whole mass as that a suitable portion of it will act on each and 
every particle of the saccharine matter at the same time, and if the 
dough be of such consistency and temperature as not to admit of too 
rapid a fermentation, then each minute portion of saccharine matter 
throughout the whole mass will, in the process of fermentation, pro- 
duce its little volume of air, which will form its little cell, about 
the size of a pin's head and smaller, and this will take place so nearly 
at the same time in every part of the dough, that the whole will be 
raised and made as light as a sponge before the acetous fermentation 
takes place in any part. And then, if it be properly moulded and baked, 
it will make the most beautiful and delicious bread, perfectly light and 
sweet, without the use of any alkali, and with all the gluten and nearly 
all the starch of the meal remaining unchanged by fermentation." — 


521. Common Salt, ilum, &c. — It has been found that certain mineral 
substances influence in a remarkable degree the aspect and properties 
of bread, causing that made of inferior flour to resemble, in appear- 
ance, bread made from the best quality. Common salt produces this 
effect in a decided degree. It whitens the bread and causes it to 
absorb and retain a larger amount of water than the flour would 
otherwise hold. In consequence of this influence and under cover of 
the fact, that salt is a generally admitted element of diet, it is often 
introduced into bread more freely than is consistent with health (697). 
Alum has exactly the same effect on bread as common salt, but in a 
much more marked degree. A small quantity of it wUl bring up a 
bad flour to the whiteness of the best sort, and wiU enable it to hold 
an extra dose of water. It is much used for this purpose, and the 
baker who employs it not only practises upon the consumer a double 
imposition, but drugs him with a highly injurious mineral into the 
bargain. Mitchell detected in ten four-pound loaves 819 grains of 
alum, the quantity in each loaf ranging from 34 to 116 grains. Sul- 
phate of copper (blue vitriol), in exceedingly minute proportions, 
exerts a striking influence upon bread in the same manner as alum. 
Carlonate of magnesia has a similar effect, and its use in so large 
quantities as from 20 to 40 grains to the pound of flour has been re- 
commended on scientific authority.* This substance has been also 

* Dr. C. Davy. 


recommended for correcting acidity in yeast, dough, &c., instead of 
soda, and because it is less powerfully alkaline. But from its diffi- 
cultly soluble earthy nature, it tends to accumulate in the system in 
the highly objectionable shape of concretions and deposits. 

522. Lieliig recommends Lime-water in Breadi — However it is to be 
lamented, it is nevertheless a fact, that enormous quantities of flour, 
more or less deteriorated, are purchased in the markets of this country ; 
and if there be any method of improving its condition by means that 
are not essentially injurious, they are certainly most desirable. Indeed, 
it is well known that flour is injured by time alcne, so that freshly 
ground flower is always more prized than that which is several months 
old. The scientific reason is apparent. Vegetable gluten in contact 
with water becomes chemically changed, and loses its peculiar tough 
elastic properties. As these are essential to bread-making, flour that 
has been altered in this way necessarily makes a bad dough, Now, 
flour is ia a high degree a water-absorbing substance, so much so that 
it attracts and combines with the moisture of the air, and is thus 
injm-ed. This can only be avoided by artificial drying and protecting 
thoroughly from the air. The eflect of the substances noticed in the 
previous paragraph is to combine with the gluten thus partially 
changed, and in a measure to restore its lost properties. Upon inves- 
tigating this subject, Liebig found that lime-water is capable of pro- 
ducing this effect, and thus of greatly improving old, or low grade 

523. How Lime-water Bread is prepared. — To make lime-water 
chemists usually employ water that has been distilled; very pure 
soft water, as clean rain water, may, however, be used. Mix a quarter 
of a pound of slacked lime in a gallon of such cold water in stoppered 
bottles or vessels kept tight from the air. The mass of the lime falls 
to the bottom, leaving the liquid above, which has dissolved l-600th 
its weight of lime, clear and transparent. This is to be poured off 
when required for use and replaced by pure water. Liebig recom- 
mends 5 lbs. or pints of lime-water to every 19 lbs. of flour, although 
this quantity of lime-water does not suffice for mixing the bread, 
and of course common water must be added, as much as is requisite. 
" If the lime-water be mixed with flour intended for the dough, and 
then the yeast added, fermentation progresses in the same manner as 
in the absence of lime-water. If at the proper time more flour be 
added to the risen or fermented dough, and the whole formed into 
loaves and baked as usual, a sweet, beautiful, fine-grained elastic 
bread is obtained of exquisite taste, which is preferred by aU who have 



eaten it for any length of time to any other." — (Liebig.) The use of 
lime-water removes all acidity from the dough, and also somewhat 
augments the proportion of water ahsorbed. 

524. Its Physiological claims. — The quantity of lime introduced into 
the system by the use of this bread, is by no means large. A pound 
of lime-water sufl&ces for 4 lbs. of flour, which with the common water 
added, yields 6 lbs. of bread ; and as the pound of lime-water contains 
but l-600th of lime, with this artificially added the cereal grains 
still contain less of it than peas and beans. Indeed, Liebig ha-s sug- 
gested that expex'ience may yet prove the cereal grains to be incapable 
of perfect nutrition, on account of their small proportion of the bone- 
forming element. 

525. Different kinds of Bread. — Eice flour added to wheaten flour 
enables it to take up an increased quantity of water. Boiled and 
mashed potatoes mixed with the dough cause the bread to retain 
moisture, and prevent it from drying and crumbling. Rye makes a 
dark-colored bread, and is capable of being fermented and raised in 
the same manner as wheat. It retains its freshness and moisture 
longer than wheat. An admixture of rye flour, with that of wheat, 
decidedly improves the latter in this respect. Indian corn bread is 
much used in this country. Mixed with wheat and rye, a dough is 
produced capable of fermentation, but pure maize meal cannot be fer- 
mented so as to form a light bread. Its gluten lacks the tenacious 
quality necessary to produce the regular cell-structure. It is most 
commonly used in the form of cakes, made to a certain degree light 
by eggs or sour milk and saleratus, and is generally eaten warm. 
Indian corn is ground into meal of various degrees of coarseness, but 
is never made so fine as wheaten flour. Bread or cakes from maize 
require a considerably longer time to be acted upon by heat in the 
baking process than wheat or rye. If ground wheat be unbolted, that 
is, if its bran be not separated, wheat meal or Graham flour results, from 
which Graham or dyspepsia bread is produced. It is made in the same 
general way as other wheaten bread, but requires a little peculiar man- 
agement. IJpon this point Mr. Geaham remarks : " The wheat meal, 
and especially if it is ground coarsel}^, swells considerably in the 
dough, and therefore the dough should not at first be made quite so 
stiff as that made of superfine flour; and when it is raised, if it is 
found too soft to mould well, a little more meal may be added." It 
should be remarked that dough made of Avheat meal will take on the 
acetous fermentation, or become sour sooner than that made of fine 
flour. It requires a hotter oven, and to be baked longer. Puddings 


in whicli flour is an ingredient are changed by the baking process in 
the same way as bread. They are usually mixed with milk instead 
of water, and made thinner than dough. Yeast is not used to raise 
them, eggs being commonly employed for this purpose, and sometimes 
other substances. 

526. White and Brown Bread— A new French Plan. — ^M. Moueies, of 
Paris, has announced some new views of bread making, theoretic and 
practical, upon which a commission of the French Academy has just 
reported favorably. He claims the discovery of a nitrogenous sub- 
stance called eerealine, which is a very active ferment, rendering 
starch soluble, altering gluten to a brown substance, and actively pro- 
ducing lactic acid instead of carbonic acid and alcohol. It resides 
near the surface of the wheat-grain, so that in grinding, it is nearly all 
separated in the bran, leaving but little in the white flour. M. Mou- 
eies states that in bread made from unbolted flour, the tendency to 
sourness, the softness, crumbliness, and want of firmness of the crumb, 
and the 'brown color also of the bread, are due to cerealine. He says 
cerealine ferment wHl make a brown bread of the whitest flour, 
whereas, if it be neutralized, a white bread can le made from a darh 
flour containing bran. He grinds wheat so as to separate it into about 
Y4 per cent, of fine fiour, 16 of brown meal, and 10 of bran. The 
brown meal is then so acted on by yeast as to neutralize the cerealine. 
The product in a liquid form is used to mix white flour into dough, 
which is baked as usual. The claims of this method are, a larger 
economy of ground products, making a white bread from dark mate- 
rials, preventing the liability to acidity, and a yield of the finest, 
lightest, and sweetest bread, comprising the largest portion of farina- 
ceous materials. 

7. — Vegetable Foods changed by Boiling. 

527. Its General Effects.— Boiling dificrs from baking in several re- 
spects. First, the heat never rises above the boiling point, and the 
changes of course are such only as may be produced by that tempera- 
ture. Second, the food is surrounded by a powerful solvent, which 
more or less completely extracts certain constituents of the food. Veg- 
etable acids, sugar, gum existing in the organic matter, and gum 
formed from starch, with vegetable albumen, are all soluble in water, 
and by boiling are partially removed. The tougher parts are made 
tender, the hard parts softened, and the connections of the fibres and 
tissues loosened, so as to be more readily masticated, more easily pen- 
etrated by the saliva and juices of the stomach, and hence more 


promptly and perfectly digested. Perhaps we may here most con- 
veniently consider the specific effects of heat npon the chief constitu- 
ents of which vegetable foods are composed. 

528. Changes of Woody Fibre. — A constituent more or less abundant 
of all vegetable substances is woody fibre. We find it in the husk or 
bran of grains, the membrane covering beans and peas, the vessels of 
leaves and leaf-stalks, the skin of potatoes, the peel and core of apples 
and pears, the kernels of nuts, and the peel of cucumbers, melons, &c., 
&c. "We are hardly justified in ranking woody fibre, as Peeeiea has 
done, among aliments. Indeed, he remarks, " although I have placed 
ligneous matter among the alimentary principles, yet I confess I am 
by no means satisfied that it is capable of yielding nutriment to man." 
Yet it is important to understand how it may be affected by the heat 
of culinary operations. Boiling in water does not dissolve it ; but 
by dissolving various substances with which it is associated, it only 
renders it the more pure. Yet woody fibre seems capable, by the joint 
action of heat and chemical agencies, of being converted into nutritive 
matter. If old linen or cotton rags, paper, or fine sawdust, be boiled 
in a strong solution of alkali, or moistened with pretty strong sulphu- 
ric acid, the woody substance is changed, being converted first into 
gum or dextrin, and then into grape sugar. By such modes of treat- 
ment old rags may be made to yield more than their weight of sugar. 
But weak solutions of acid or alkali do not produce any such effect. 
For will strong vinegar. TVe may therefore assume that woody fibre 
remains totally unchanged by exposure to culinary agencies and ope- 
rations. Professor AuTE^rrjETH, of Tubingen, announced some years 
since, a method of preparing bread from wood-powder or wood-flour, 
which was changed into nutritive matter by successive heatings in an 
oven. "We are not aware that his experiments have been confirmed, 
while it is suspected that whatever nutritive value his bread may have 
possessed, was due to starch associated with the wood. 

529. Changes of Sugar. — Sugar, dissolved in cold water, or boiled 
to a sirup, has very diflerent properties, as is well known to those 
who feed it to bees in winter. In the first case, the warmth of the 
hive will dry up the water and leave the sugar in hard crystals which 
the bees cannot take ; but by boiling, the water and sugar become so 
intimately united that the mixture does not become dry, but retains 
the consistence of sirup. If melted sugar be kept for some time at 
350°, it loses the property of crystallizing when redissolved in water, 
its properties being in some way deeply altered. If dry sugar be 
heated to a little above 400°, it loses the sugar taste and becomes not 



Fia. 100. 

only very soluble in water, but also very absorbent of it {deliquescent)') 
turns of a deep brown color, and is used to stain liquids of a dark red, 
or wine color, under the name of caramel. Sugar itself is slightly 
acid, and forms compounds with bases which are of a salt nature, and 
known as saccharates. Caramel is more decidedly acid, and if the 
sugar be heated still higher it is converted into still stronger acid pro- 
ducts with inflammable gases. 

530. Breaking np of the Starch Grains. — The structure of starch grains 
has been described (384). They consist of layers or coats arranged 
concentrically around a point called the Mlum. If 
one of these grains be strongly compressed between 
two plates of glass it breaks apart into several pieces, 
as seen in Fig. 100, and all the planes of rupture 
generally pass through the hilum as if the substance 
were less resistent at that point. But under the joint 
action of heat and water, the grains break up differ- 
ently. Their membranes are torn apart, or exfoliated 
by internal swelling, as shown in Fig. 101. 

531. Changes of Starch. — Starch is but slightly acted througTits hUum.^ 
upon by cold water. "When heated with water it 

does not dissolve ; but the grains swell, forming a viscid mucUaginous 
mass, a kind of stiff, half opaque jelly. When starch is diluted with 
twelve or fifteen times its weight of water, 
the temperature of which is slowly raised, 
all the grains burst on approaching the 
boiling point, and swell to such a degree as 
to occupy nearly the whole volume of the 
liquid, forming a gelatinous paste. If a 
pint of hot water be poured on a table- 
spoonful of arrow-root starch, it imme- 
diately loses its whitenes and opacity, be- 
comes transparent, and the entire matter °' 
passes into the condition of a thick jelly. If a little of this be diffused 
through cold water and examined with the microscope, it will be seen 
that the starch grains are greatly altered. They have increased to 
twenty or thirty times their original size ; the concentric lines are 
obliterated (384) ; the membrane of the grain is ruptured, and its inte- 
rior matter has escaped. A cold jelly of starch and water, left to stand, 
either closed or exposed to the air, gradually changes, first into gum 
(dextrin), and then into sugar. The process, however, is slow, and 
months must elapse before the whole of the starch is thus transformed. 

Fig. 101. 

starch grain ruptured by boil- 


By being boiled in water for a considerable time, it undergoes the 
same change, and if the water be acidulous the change is quickened. 
When dry starch is gradually heated to a temperature not exceeding 
300°, it slowly changes, acquires a yellow or brownish tint, and be- 
comes entirely soluble in cold water. It is changed to dextrin or 
gum (British gum). 

532. How Potatoes are changed by Cooking. — By referring to the 
statement of the composition of potatoes (461), we shall notice that 
a pound contains about three-quarters of a pound of watery juice, to 
two ounces, or two and a half, of starch. "When examined by the 
Yia. 102. microscope, the tissue of the potato is found 

to consist of a mass of cells, containing starch 
grains. Each cell contains some 10 or 12 
grains, loosely situated, as shown in Fig. 102, 
and surrounded by the potato juice, which 
contains albumen. If potatoes be of good 
quality, they boil dry, or mealy ^ as it is term- 
ed. But their water or juice does not sepa- 
rate, or boil out. It is absorbed by the starch 
Starch grains of potato before grains, which form a compound with it, and 
°' swell up so as completely to fill, and even 

burst the cells, as seen in Fig. 108. The albumen at the same time 
coagulates, so as to form irregular fibres, which are seen among the 
starch grains. When the juice of the potato is 
only partially absorbed by the starch, it is said to be 
watery, waxy, or doughy. Potatoes by boiling in 
water do not form a jelly, like common starch, be- 
cause the starch grains in the tubers are protected, 
partly by the coats of the cells in which they are 
contained, and partly by the coagulated albumen. 
"Potatoes steamed or roasted — or if boiled, mash- 
ed so as to extract all hard lumps, are in the best 
condition for digestion. Frying them, toasting 
Btarch grains of potato them, baking them, or broAvning the surface, dries 
ater oi ing. ^^ ^^^ starch into a hard, half-charcoally mass, 
which, except in most powerful stomachs, must act as a foreign body." 
533. Quality of the Water for Culinary Pnrposes. — Soft water, or that 
which is free from dissolved mineral matter, makes its way into, or is 
imbibed by organized tissues, with much more readiness and facility 
than hard water. It also exerts a more powerful solvent or extractive 
action, and thus is a better vehicle for conveying alimentary sub- 

FiG. 108. 


stances into the living system. In culinary operations where the 
object is to soften the texture of animal and vegetable matter, or to 
extract from it and present in a liquid form some of its valuable parts, 
as in making soups, broths, stews, or infusions, as of tea or coffee, soft 
water is the best. But there are cases in which the solvent action of 
soft water is too great, as sometimes upon green vegetables, which it 
makes too tender, destroying the firmness that is essential to the 
preservation of their juices, which are dissolved and extracted, making 
the substance proportionately tasteless. In those cases, therefore, 
when we do not desire to dissolve out the contents of a structure, but 
to preserve it firm and entire, hard water is better than soft. To pre- 
vent this over-dissolving action, common salt is often added to soft 
water, which hardens it. This fact also explains why it is impossible 
to correct and restore the flavor in vegetables that have been boiled 
in soft water by afterwards salting them. It is weU known that peas 
and beans do not boil soft in hard water. This is owing to the efiect 
which salts of lime, especially the sulphate or gypsum, exert in hard- 
ening or coagulating casein which abounds in these seeds. Onions 
furnish a good example of the influence of quality in water. If boiled 
in pure soft water, they are almost entirely destitute of taste ; though 
when cooked in salted water, they possess in addition to the pleasant 
saline taste, a peculiar sweetness, and a strong aroma ; and they also 
contain more soluble matter than when cooked in pure water. The 
salt hinders the solution and evaporation of the soluble and flavoring 

8. How CooKiNa changes Meat. 

534. Action of Heat upon the Constitncnts of Flesh.. — If the pure fibrin 
of meat is exposed to a moderate heat, it parts with a large portion of 
its water, which it held like a sponge, and loses the power of taking 
it up again. It consequently shrivels and shrinks. If the heat be 
carried high, further decomposition and charring take place. The eflfect 
of boiling upon fibrin, is not to make it more tender, but to increase its 
hardness and toughness. A low degree of heat changes liquid albumen 
to the solid condition ; altering remarkably aU its physical properties. 
It neither dissolves in water, hot nor cold, and is impenetrable to it. 
If diffused through one or two hundred times its weight of water, it 
coagulates, forming fine fibrous meshes throughout the liquid sufficient 
to entangle any mechanical substances that may be floating in it, and 
bring them to the surface or carry them to the bottom. In this way 
albumen is used as a clarifying agent. If its proportion be much 


larger, the entire water may combine with it and pass into the solid 
state. The egg, for example, contains 74 per cent, of water and 10 of 
oil, yet its contents are all solidified by boiling through the action of 
14 per cent, of pure albumen. Fat is liquefied, of course, by the action 
of heat, and at a high temperature it is resolved into various acid and 
acrid bodies. The effect of heat upon flesh in the mass, has been in- 
vestigated by LiEBiG, with his usual acuteness and with highly inter- 
esting and practical results. 

535. Properties of the Liquid and Solid parts of Flesh. — When mus- 
cular flesh or lean meat is chopped fine, and steeped or leached with 
cold water, there remains a solid residue consisting of the muscular 
fibres, tissues, vessels, &c. If this be boiled, it is tasteless, or indeed 
slightly nauseating ; it cannot be masticated, and even dogs reject it. 
All the savory constituents of the flesh were contained in its juice ; 
and were entirely removed by cold water. The watery infusion thus 
obtained, is tinged red by some of the coloring matter of the blood. 
~ If it be boiled, this coloring matter separates, leaving the liquid clear 
and of a pale yellowish color. This liquid has the aromatic taste, 
and all the properties of soup made by boiling the flesh. When 
evaporated and di-ied, a soft brown mass amounting to 12 or 15 per 
cent, of the weight of the original dry flesh is obtained, having an 
intense flavor of roast meat. This extract of flesh is soluble in cold 
water, and when dissolved in about 32 parts of hot water, with salt, 
it gives to this water the taste and all the properties of an excellent 
soup. The liquid extract retains the peculiar taste of the flesh from 
which it was derived; so that if we add the concentrated juice of 
venison or fowl to exhausted beef, the latter at once acquires a venison 
or fowl taste, 

536, Loss of Weight ia Cookiag. — The first effect of applying a 
strong heat to a piece of fresh meat, is to cause the fibres to contract, 
to squeeze out a portion of the juice, and partially to close the pores so 
as to prevent the escape of more. Heat is applied to meats chiefly in 
three ways, 'boiling^ roasting^ and laTcing. During these operations, 
fresh beef and mutton, when moderately fat, lose on an average 
about as follows : 

In boiling. In baking. In roasting. 

4 lbs. of beef lose 1 lb. 1 lb. 3 ozs, 1 lb. 5 ozs. 

41bs. of mutton lose 14 ozs. lib. 4 ozs. 1 lb, 6 ozs. 

The greater loss in baking and roasting, arises chiefly from the greater 
quantity of water evaporated, and of fat which is melted out during 
these two methods of cooking. 

537. Best method of cooking Meat. — In preparing meat for the table, 


we sliall discover it to be most desirable that the ingredients 
of its juice should remain in it; and this wiU depend much upon 
the method of culinary procedure. If the piece of meat be in- 
troduced into the water when IrisMy foiling, the albumen at its 
surface, and to a certain depth inward, is immediately coagulated; 
thus enclosing the mass in a crust or shell which neither permits its 
juice to flow out, nor the external water to penetrate within, to dis- 
solve, dilute, and weaken it. The greater part of the sapid consti- 
tuents of the meat are thus retained, rendering it juicy and well- 
flavored. It should be boiled for only a few minutes, and then kept 
for some time at a temperature from 158° to 165°. Meat is under- 
done or bloody, when it has been heated throughout only to the 
temperature of coagulating albumen (140°) ; it is quite done or cooked, 
when it has been heated through its whole mass to 158° or 165°, at 
which temperature the coloring matter of the blood coagulates. As 
in boUing, so in baking or roasting ; for whether the meat be sur- 
rounded by water, or in an oven, as soon as the water-proof coating 
is formed around it, the further changes are effected alike in both 
cases, by internal vapor or steam. In roasting or baking, therefore, the 
fire should be at first made quite hot, until the surface pores are com- 
pletely plugged, and the albuminous crust formed. Hence, a beef- 
steak, or mutton-chop, is done quickly over a smart fire that the richly- 
flavored natural juices may be retained. 

539, Objection to the common method. — The fibrin of meat, in its 
natural state, is surrounded by an albuminous hquid. In coagulating, 
it becomes firm and hard, but at the same time, brittle and tender. 
If the albumen be coagulated within the meat, it forms a protective 
sheath around the fibres, and thus prevents them from being shrivelled, 
toughened, and hardened by boiling. This explains why the flesh of 
young animals, which is richer in albumen than that of old ones, is 
also more tender. If the meat be placed in cold water, and the 
temperature slowly raised to boiling, a portion of the savory and 
nutritive juices is dissolved out, and the meat becomes proportion- 
ally poorer for the loss. At the same time the fibres lose more or 
less of their shortness, or tenderness, and become tough. The smaller 
or thinner the piece of fiesh is, the greater is its loss of savory con- 
stituents. If, in baking, the meat be exposed to a slow fire, its pores 
remain open, there is a constant escape of juice from within, and the 
flesh becomes dry and unsavory.* 

* The flesh of old animals often yields no more than 1 or 2 per cent, of albumen, that 
of young animals as much as 14 per cent — Liebig. 


540. Soup, Beef-tea, Mntton-broth, &c. — In the i)reparation of these 
our object is the reverse of that which has just been considered. We 
desire to take the nutritive and savory principles out of the meat, and 
get them into a hquid or sokible form. To obtain a liquid extract of 
meat, in the form of soup, broth, or tea, the flesh is finely chopped 
and placed in cold water^ vphich is then slowly heated and kept boiling 
for a few minutes, when it is strained and pressed. In this manner 
we obtain the very strongest and best flavored soup which can be 
made from flesh. " When one pound of lean beef, free of fat, and sepa- 
rated from the bones, in the finely-divided state in which it is used for 
beef-sausages or mince-meat, is uniformly mixed with its own weight 
of cold water, slowly heated to boiling, and the liquid after boiling 
briskly for a minute or two is strained through a towel from the coag- 
ulated albumen and fibrin, now become hard and horny, we obtain an 
equal weight of the most aromatic soup of such strength as cannot be 
obtained, even by boiling for hours, from a piece of flesh." — (Liebig.) 
To make the best article, it is desirable not to boil it long, as the ef- 
fect is to coagulate and render insoluble that which was extracted by 
cold water, and which should have remained dissolved in the soup. It 
is obvious from what has been said, that a piece of meat introduced 
undivided into boiling water, is in the most unfavorable condition pos- 
sible for making good soup. It is customary in soup-making to pro- 
tract the boiling for the purpose of thickening and apparently enrich^ 
ing the soup. This is efiected by the gelatin, which is gradually 
extracted from the tissues, bones, and other parts, but in a nutritive 
point of view this ingredient is a fiction, as will be shown in the proper 
place (717). Soup-making is a kind of analysis of alimentary sub- 
stances used in its preparation — a part is taken, and a residue usually 
rejected. Yet it is clear that we shall have the completest nourish- 
ment by taking both parts, as the fibre of meat and the softened beans 
and peas of their respective soups. 

541. A new Broth for Strengtliening the Sict. — In certain maladies (as 
typhus fever, for example, at particular stages), the greatest difiiculty 
met with by the physician, lies in incomplete digestion, or inability 
promptly to reinforce the exhausted and bankrupt blood. To meet 
this difficulty Liebig prepared, as follows, a nutritive liquid, which 
has been used at Munich with the best results. Take half a lb. o^ per- 
fectly fresh meat (beef or chicken), cut it in small pieces, add to it Ij 
lb. of distilled (pure soft) water, with four drops of muriatic acid, and 
half a drachm of common salt ; mix the whole well together, and after 
standing an hour, strain through a common hair sieve, letting it pass 


without pressing or squeezing. The portion passing through first be- 
ing cloudy, it is again poured through the sieve, and this process is 
repeated until it becomes perfectly clear. Upon the residue of meat 
remaining in the sieve, half a pound of distilled water is poured in 
small portions. In this manner a pound of cold extract of meat is ob- 
tained, of a red color, and pleasant meat-broth taste. It must not be 
heated, and is administered cold, by the cupful, according to the pa- 
tient's inclination. It is difficult to make it in summer, on account of 
its liability to ferment and change. Perfectly cold vrater must be 
used, and refrigeration with ice wiU guard against decomposition, 

9. Peepaeation and Peopeeties of Buttee. ii^ 

542. Actiou of Heat npon Milk and Cream. — The gradual heating of 
milk facilitates the rising of its cream. The oil globules are broken, 
liquefied, run together, and ascend to the upper part of the vessel. 
There is always a trace of albumen in milk ; when boiled this is coag- 
ulated and rises to the surface with oil globules, and forms there a 
pelicle or skin, which is increased by evaporation. The layer thus 
formed prevents the escape of steam, causing the liquid to boU over 
if the vessel is not removed from the fire. If cream be heated for 
some time nearly to boiling, its fat-globules melt together and collect 
upon the surface, as a fluid oil. When this is cooled it forms a very 
pure butter, which will keep long without being salted or becoming 
rancid, but has neither the fine flavor nor the firm consistence of 
churned butter. 

543. Butter separated mechanically. — If either milk or cream be beat- 
en or agitated mechanically for a time, the oil globules coalesce and 
form a mass of butter. It is believed that each little fat-globe is en- 
closed in a thin film of casein, which is ruptured by agitation. How- 
ever this may be, the oil-cells have sufficient resistance to require 
considerable mechanical violence to break them up, which is effected 
by churning. During this operation oxygen is absorbed from the air, 
the temperature rises, the cream or mUk, if not already acid, turns 
sour, and gases are set free, which escape from under the cover, or 
when the churn is opened. 

544. Rate of Motion in Chnrnuig. — In churning cream, which is usu 
ally thick and uneven, the agitation should at first be slow, until it has 
become completely broken into a uniform mass. As it becomes thin- 
ner the motion is easier and may be slightly increased, and continued 
until a change in the §opnd from a low and smooth to a harsh tone is 


observed. It may then be again slightly increased, nntil the bntter 
Degins to form, when it is collected or 'gathered' by a slower move- 
ment. If the rate of motion in churning is too rapid, the cream is 
liable, especially at high temperatures, or in hot weather, to lurbt^ as 
it is called, while the butter is soft, frothy and bad. 

545. Time and Temperature. — "With different churns, and at dif- 
ferent rates of speed, butter may be produced in from 10 minutes to 3 
or even 5 hours. Dr. Muspeatt assigns from 45 minutes to an hour as 
the best time for cream, while Prof. Ayton states for cream an hour 
and a half, and for whole milk from two to three hours. Dickenson 
says it is no matter if we are six hours in churning sweet milk. It 
is, however, the well established result of experiment, that the more 
quickly milk or cream is churned, the paler, softer, and poorer is the 
butter. It is said also that in over-churning, that is, when the opera- 
tion is too long continued after the butter is produced, it is apt to 
be softened and lightened in color, although the quantity may be 
somewhat increased. We have had frequent occasion to notice the 
controlling influence of temperature over the changes of matter, and 
we find it again illustrated here. Cream, when put into the churn, 
should never be wai'mer than 53° to 55°. It rises during churning 
from 4° to 10°. Johnston states that when the whole milk is churned, 
it should be raised to 65°. The careful regulation of the temperature 
is of the first importance, so that a thermometer is indispensable to 
the proper management of the operation. Some churns have them 
attached, which is an excellent plan. The temperature of the cream 
is increased or diminished by mixing with hot or cold water, but many 
strenuously object to this. In some churns there is an outer chamber 
or vessel, which is separated from the cream by a thin sheet of metal, 
through which heat or cold readily passes from water contained in the 
chamber. This is a good arrangement, although the metal commonly 
used {zinc) is not quite free from objection (611). 

546. Compositiou and properties of Butter. — The mass of butter is a 
tasteless and inodorous fat ; its pleasant aromatic flavor being due to 
a compound existing in it in very small quantity, namely, hutyric acid, 
combined with oxide of li2Jyle. First quality butter has a pleasant 
peculiar aroma, is of a fine orange-yellow color, solid, and of a waxy 
or grained texture, exposing a different surface when cut from fat or 
grease. This granular quality results from the peculiar mode of its 
production, which is by the mechanical coherence of minute butter- 
particles or grains. Were butter separated like lard, by melting, it 
would not present this appearance. Between good ordinary butter 


and a first-rate article there is a wide difference ; the former is com- 
mon, the latter is but rarely seen. Cream and butter are both highly- 
absorbent of unpleasant odors, and are extremely susceptible of taint 
from this cause. The air of the dairy -house must be " sweet as that 
wafted from the rose itself. A common farm cellar with meat, fish, 
and vegetables, would spoil the best package of butter ever made in 
sixty days." The cows should be kept on rich, tender, high-flavored 
grasses, — timothy, white clover, blue grass, red-top, with which the 
ground is to be thickly swarded over to protect it from sun and 
drouth. May, June and September are the best months, July and 
August being too hot ; while after frost appears, the grass becomes 
insipid and bitter, and will not yield butter of the best quality. 
Almost every kind of butter, however, is good when newly made. 
The vital considerations of its manufacture are connected with its 
quality of keeping, which will be noticed when we reach the subject 
of preservation (599). 

10. Peepaeation and Peopeeties of Cheese. 

547. Spontaneons Cnrdling of Milk. — When milk is left to itself for a 
time, which is shorter in warm or stormy weather, it sours and 
curdles, that is, its casein changes from the dissolved to the solid state. 
This is brought about by a series of interesting and beautiful changes 
originating in the unceasing activity of atmospheric oxygen. Casein, 
in itself, is insoluble in water. But it is of an acid nature, and is ca- 
pable of combining with potash or soda, and forming a compound 
which dissolves in water. Soda is the alkali which holds the casein 
of milk in solution. Now when fresh milk is exposed to the air, its 
oxygen acting upon a portion of the nitrogenous casein, changes it to 
a ferment ; and this takes effect upon the milk sugar, converting it 
into lactic acid, which causes the sourness of milk. "When sufficient 
of the lactic acid is thus formed, it seizes upon the soda, takes it away 
from the casein, and forms lactate of soda. The casein thus set free 
shrinks in bulk, and gathers into an insoluble, curdy mass, the opera- 
tion being aided by a gentle warmth. 

548. Artificial Curdling with Acids. — In making cheese the milk is 
curdled artificially, and in different countries various substances are 
used for this purpose. But they all produce the effect in precisely the 
same way, that is, an acid substance is employed to neutrahze the 
soda of the milk, by which the casein assumes the coagulated state. 
Almost any acid will have the effect of curdling milk. Muriatic acid, 
weakened with water, vinegar, tartaric acid, cream of tartar, lemon 
juice, and sour milk, are each used for the purpose. 


549. Artificial Cardling with Rennetf — The salted and dried stomacli 
of the unweaned calf, lamb, or pig, is called rennet. If a small piece 
of this be soaked in water for a time, and the infusion be mixed with 
milk at a temperature of 90° or 95°, curdling shortly takes place. It 
was once supposed that it is the acid of the gastric juice of the stomach 
which produces the change ; but this cannot be, as the membrane acts 
with equal promptitude, though it has been thoroughly washed free 
from every thing of an acid nature. The change is due to the action 
of the animal matter itself. It is said that the rennet should never be 
■used unless ten or twelve months old. During this period, by exposure 
to the air, a portion of the membrane has undergone decay and become 
soluble in water. This decomposing animal matter acts upon the 
sugar of milk, changing it to lactic acid, which produces curdling ex- 
actly as in spontaneous coagulation (547). There is much about the 
action of rennet that is not yet explained. Its condition seems to 
exert a decided influence on the quality of the cheese. The result im- 
probably much influenced by the state of decay of the animal matter, 
as the decomposition may be so far advanced as to induce putrefaction 
in the milk. 

550. Conditions of the preparation of Cheese. — By the action of curd- 
ling agents the milk is divided into two parts ; first the curd, com- 
prising all the casein, a large portion of oil and a ti-ace of sugar of 
milk, with some water ; and second, the wJiey or fluid part containing 
the bulk of water, the sugar of milk, and a small but variable propor- 
tion of oily matter. Of the saline matter in milk, the phosphates of 
lime and magnesia exist in the curd, vvhile the remaining salts are 
found in the whey. The curd, separated from the whey and prepared 
in various ways, and then pressed, forms cheese. The properties of 
cheese are influenced by a great number of circumstances. Pure 
casein makes a cheese poor, hard, and horny. The admixture of the 
oil or cream of the milk enriches it in proportion to its quantity. The 
most inferior cheeses therefore are made from milk that has been re- 
peatedly skimmed and deprived of all its oil, while the richest cheeses 
are those made directly from cream (cream cheeses), and which hence 
contain an excess of oily matter. Between these extremities there 
are all grades of quality, which depend upon the proportion of the 
constituents. Thus if we use the new milk of the morning, mixed 
with the previous evening's milk that has been deprived of its cream, 
we get a cheese of a certain quality ; if we use the tcTiole milJc of the 
previous night, the cheese will of course be better ; and if we use only 
the cream of the previous evening's milk, the cheese will be still 


richer. All tlie conditions wliicli influence the properties of the milk 
itself (334) affect also the quality of the cheese. The heat, in curd- 
ling, should not be too high, as it is apt to give excessive oiliness to 
the fatty portion of the milk. A thermometer affords more reliable 
indications than the sense of feeling. As soon as coagulation is com- 
plete, the curd should be separated, as the longer it stands the harder 
and tougher it is. Much judgment is required to know the proper 
quantity of rennet to be used ; if there is too little, the process is too 
slow, and time is given for the butter to separate itself fi'om the curd, 
while too much rennet makes the curd tough, and otherwise affects 
disagreeably the subsequent changes and flavor of the cheese. The 
mode of separating the curd from the whey, its subsequent prepara- 
tion, and the degree and duration of the pressure applied, together 
with a great variety of other circumstances known to the skUfuI 
cheese-maker, have a powerful influence upon the quality of the arti- 
cle produced. We shall refer to cheese again when speaking of preser- 
vation (604). 

1. Peopeeties and Peepaeation op Tea. 

551. The Tea Shrub, — Tea consists of the prepared leaves of the 
tea-plant, a hardy shrub which grows from 3 to 6 feet high, chiefly in 
China. The plant is propagated from the seed, and matures in from 
two to three years, yielding usually three crops of leaves each season. 
"When a year old, the young bushes are planted out in rows 3 or 4 
feet apart, and being cropped down so as to grow thick and bushy, the 
tea-field resembles a garden of gooseberry bushes. The leaves are 
picked by hand in May and June, and the plant yields leaves from 
four to six seasons. 

552. What causes different Tarieties of Tea. — Many varieties of tea of 
all grades of quality are known in market. These differences depend 
first upon the soil, climate, culture, &c., of the locality where it is 
grown. Second^ upon the time of picking ; the young unexpanded 
leaves that are gathered first being tender and delicate, while the sec- 
ond and third gatherings are more bitter, tough, and woody. Tliird^ 
the mode of treatment or preparation, which consists in drying, roast- 
ing, and rolling in the hand, by which the leaves acquire their twisted 
appearance, and finally sifting and winnowing. The methods of hand- 
ling are various, and much depends upon them. 

558. Difference between Green and Black Teas. — All the different 
varieties of tea are classed as either green or hlach. What constitutes 




1. Cultivated in manured soils. 

2. Leaves are steamed, 'witliered and 
roasted almost immediately after gather- 

8. They are dried quickly after the 
rolling process ; the whole operation being 
brief and simple. 

the real difference between these two sorts has long been a matter of 
doubt. It was at first supposed that they came from totally different 
species of plants ; but the latest accounts agree that they are both de- 
rived from the same plant, the difference being in conditions of growth 
and modes of dealing with the leaves. They may be thus contrasted : 


L Grown chiefly on the slopes of hiUs 
and ledges of mountains. 

2. Allowed to be spread out in the air 
for some time after they are gathered. 

8. They are tossed about until they be- 
come soft and flaccid. 

4. They are now roasted for a few min- 
utes, and rolled. 

5. They are exposed to the air for a few 
hours in a soft moist state. 

6. Lastly, they are dried slowly over 
charcoal fires. 

It is by lengthened exposure to the air in the process of drying, ac- 
companied perhaps by a slight heating and fermentation that the dark 
color and distinguishing flavor are given to the black teas of com- 
merce. The oxygen of the atmosphere acts rapidly upon the juice of 
the leaf during this exposure, and changes chemically the peculiar 
substances they contain, so as to impart to the entire leaf the dark 
hue it finally acquires. The precise nature of these changes has not 
been chemically investigated. — (Johnston.) The unchanging green 
color of green teas is produced, says Knapp, by employing steam to 
wither the fresh leaves, it being well known to collectors of plants, 
that many which inevitably turn black when simply dried, preserve 
their green color brilliant and permanent, when they are killed by 
steam, previously to drying. The same authority remarks, that green 
tea gives up much less of its juice in the drying process ; a circum- 
stance which fully explains its more energetic action upon the nervous 

554. Varieties of Green and Black Tea. — The most important teas of 
commerce may be thus arranged, beginning with the lowest qualities. 
Annexed is an approximative scale of the prices per pound paid for 
them in Canton. 

Green Teas. 

Twangay 18 to 27 cts. 

Hyson Skin 18 to 80 " 

Young Hyson 27 to 40 " 

Hyson 40 to 56 " 

Imperial 45 to 58 " 

Gunpowder 45 to 60 " 

BlBck Teas. 

Bohea 12 to 18 eta. 

Congou 22 to 25 " 

Campoi 22 to 30 " 

Souchong 20 to 85 " 

Caper 20 to 40 " 

Pekoe 85 to 75 " 


Ticangay is the coarsest and most inferior of the green teas. The 
Hysons are of a better quality, and are more widely used. The word 
' Hyson ' is derived from Hee-chun, the name of a celebrated Chinese 
tea-maker. Hyson-skin is composed of the light, inferior leaves, sepa- 
rated from Hyson by winnowing. Young-Hyson^ Hyson, and Impe- 
rial, consist of the second and third crops; while Gunpowder, the 
finest of the green teas, consists of the first leaves, or leaf-buds, of 
the vernal crop. It is called 'gunpowder,' from the fancied resem- 
blance of its small rounded leaves to gunpowder grains. Bohea is the 
poorest and cheapest of the black teas, and takes its name from being 
largely produced on the Bohea mountains ; Congou, from cong-fou, 
' made with care,' and Souchong, from se-ou-chong, " a very little 
sort," are better varieties. Gaper comes in little balls or grains, made 
up in the form of capers. Pekoe is the best of all the black teas, and 
corresponds to gunpowder among green teas. The word ' Pekoe,' or 
Pak-Ho, means ' white down,' and is applied to the first downy leaves 
of the spring growth. It is often called the Flowery Pekoe, which is 
erroneously supposed to refer to the blossom of the tea-plant ; but the 
tea flower itself has little fragrance, and although sometimes used in 
China, is not imported. 

555. Composition of Tea. — The analysis of tea shows it to be com- 
posed of four principal constituents. First, an aromatic, volatile oil, 
which produces the peculiar odor and flavor. It is of a citron yellow 
color, floats on water, and when exposed to the air is quickly convert- 
ed into a solid resin by atmospheric oxygen. It has such a powerful 
taste, that when placed on the tongue it spreads over the entire throat, 
and exerts a painfal action upon the nerves. It does not exist in the 
fresh or natural leaves, but is produced during the roasting process. 
A hundred pounds of tea yield only a single pound of the oil. Second, 
tea contains a peculiar principle called thein, a substance rich in nitro- 
gen, and classed among 'vegetable alkalies. Stenhottse states that or- 
dinary tea contains about two per cent, of thein; but Peligot has 
found as much as 6 per cent, in certain green teas, although this quan- 
tity is very unusual. Thein has a slightly bitter taste, no smell, and 
dissolves in hot water. An infusion of tea, therefore, contains dis- 
solved thein : and if the leaves be of good quality, an ounce will yield 
about 10 grains. Third, tannin or tannic acid, a substance so named 
because it is the ingredient in oak and hemlock bark, which combines 
with leather in the operation of tanning. If a compound of iron (sul- 
phate of iron — copperas, for example), be introduced into an infusion of 
tea, it turns it to an inky blackness, by precipitating its tannic acid. 


This substance is a po-werful astringent, and gives to tea its astringent 
taste and properties. It forms from 12 to 18 per cent, of the weight 
of tea. When tea is steeped, the three foregoing constituents are com- 
Jmunicated to the water; they hence give its active properties to the 
ordinary beverage. But tea leaves contain, fourthly, another constit- 
uent, namely, gluten — which, not being dissolved by hot water, is 
usually lost with the dregs or grounds. The proportion of this sub- 
stance is stated to be as high as 25 per cent., so that the leaves, after 
exhaustion by steeping, are still highly nutritive. In some localities 
it is customary to eat them. 

556. How Tea is best made. — The Chinese method is to throw some 
tea into a cup, and pour boiling water over it ; they cover the cup 
with a shallow saucer, and let it rest for some time. After it has 
stood sufficiently long, they pour the clear liquid into a saucer, and 
drink it hot. Various methods are pursued in different countries, but 
a knowledge of the composition and properties of tea is the best guide 
in preparing its infusion. It is desirable to obtain from the leaves the 
largest possible amount of matter which water wiU extract, and retain 
them in the liquid. The thein of tea is in combination with tannic acid, 
forming a compound which requires boiling water to dissolve it. But, 
on the other hand, the aromatic oil of tea is volatile, so that the boil- 
ing tends to drive it off with the steam into the air. If lukewarm 
water is used, the most important element of tea, its thein, is not ob- 
tained ; while, by boiling, its fragrant aroma is wasted. The plan to 
be pursued, therefore, is to pour boiling water upon the tea, in close 
vessels, so that its active ingredients may be dissolved, and at the same 
time the volatile oil retained in the mixture. In cooling, a good de- 
coction of tea becomes slightly turbid, the tannate of thein being no 
longer held in solution, is precipitated and rises, forming a skin upon 
the surface, 

557. What remains in the Grounds, or residne. — If tea be steeped in 
water below the boiling temperature, an infusion is obtained, having 
the peculiar tea-taste, but the thein is not obtained ; a second infusion 
of the leaves with boiling will extract the thein, and tannic acid, 
60 that, although it may be less fragrant, it will be more active. The 
leaves which have been used of course vary in composition, according 
to the completeness of the first exhaustion. By the common method 
of extraction, the entire quantity of thein is never dissolved, about 
one-third being left in the leaves. Mulder found hot water to ex- 
tract from six specimens of black tea, from 28 to 38 per cent, of their 
weight ; of the same number of kinds of green tea, from 34 to 46 per 


cent. Peligot procured from black tea an average of 38 per cent., 
and from green, 43 per cent. Yet the quantities are by no means con- 
stant, as different samples of the same color and name ia the market 
yield very different proportions of soluble matter. Teas prepared from 
young leaves furnish more soluble matter than the older leaves ; while 
green teas give more of light-colored, and black of dark-colored ingre- 
dients. The gluten, in which tea leaves are rich, is not dissolved by 
boding water ; but water made slightly alkaline dissolves gluten. It 
has therefore been recommended that a little soda be added to the 
water, which would have the effect of making the tea slightly more 

558. Adulterations of Tea. — Teas of aU sorts are liable to the grossest 
adulterations. The green teas are extensively stained or painted by 
the Chinese, to heighten their green color. For this purpose they use 
Prussian blue, indigo, turmeric, gypsum, and Ohina-clay. With these 
ingredients they glaze or face the surface of the leaves, to such an ex- 
tent, that it is affirmed we nevier get pure green tea. Other leaves are 
also often mixed with those of the tea-plant, by the Chinese. In Eng- 
land, the leaves of the sloe and thorn are much mixed with tea. The 
Chinese also make a crude and worthless preparation of sweepings, 
dust, sand, leaves, and various impurities of the tea warehouses, cement- 
ed with gum or rice-water, which they honestly call lie-tea^ and employ 
it extensively to mix with other teas. In England, exhausted leaves 
are bought up, their astringent property restored by the addition of 
catachu (a concentrated tanning extract), and colored with black lead, 
logwood, &c., are sold again as genuine tea. Another fraud of great 
prevalence consists in mixing inferior qualities of tea with the better 
sorts, and cheating the purchaser by selling the compound at the price 
of the best article. To detect indigo or Prussian blue in tea, let a por- 
tion of it be shaken with cold water and thrown upon a bit of thin 
muslin, the fine coloring matter will pass through the muslin, and 
settle to the bottom of the water. When the water is poured off, the 
blue matter may be treated with a solution of chloride of lime. If it 
is bleached, the coloring matter is indigo. If potash makes it brown, 
and afterwards a few drops of sulphuric acid make it blue again, it is 
Prussian blue. — (Johnston-.) 

2. Peopeeties and Preparation of Coffee. 

559. The Coffee Tree and its Seeds. — Coffee is the product of a plant, 
grown extensively in warm climates. The natural height of the tree, 


varies from 10 to 30 feet ; but it is usually pruned down to 5 or 6 feet, 
to increase the crop of fruit. All are familiar -witli the structure 
of coffee seeds ; they are of an oblong figure, convex on one side, 
and flat, with a little straight furrow, on the other. They are en- 
closed in a pulpy berry of a red color, which resembles a cherry, and 
are situated within it with their flat sides together, and invested by a 
tough membrane called the parchment. The seeds are separated by 
fermenting the berries, crushing them under heavy rollers, drying, 
grinding, and winnowing. 

560. Varieties of Coffee. — The best coffee is the Arabian; that 
grown in the province of Mocha {Mocha coffee) is of the finest quality. 
It may be known by having a smaller and rounder berry than any 
other, and likewise, a more agreeable smell and taste. It is of a dark 
yellow color. The Ja'oa and Ea^st Indian coffees are larger and of a 
paler yeUow, while Ceylon^ West Indian, and Brazilian coffees are of 
a bluish or greenish gray tint. 

561. Composition of Coffee. — The raw coffee, as it comes to market, 
is but slightly aromatic ; its odor is faint, while its taste is moderately 
bitter and astringent. In this state its composition, according to 
Paten, is as foUows : 

Water 12 

Gum and Sugar 15'50 

Gluten 13 

Cafein 00T5 

Fat and Volatile Oil 13 

Tannic Acid 5 

Woody Fibre 34 

Ash 6-75 

Dr. Stenhouse states that it contains 8 per cent, of cane sugar. Oof- 
fee, it vrill be seen, contains tannin, the same astringent principle aa 
tea, but in much smaller proportion ; and the substance itself is of 
a somewhat different chemical nature. They both contain much 
gluten ; but the most remarkable point of similarity between tea and 
coffee, is found in the fact, that the cafein of coffee is a vegetable 
alhali, with the same composition and properties as thein of tea. A 
direct analysis of the two substances gave the following result : 

Carbon. Nitrogen, Hydrogen,- Oiygen, 

Thein 50-1 29-0 5-2 15T 

Cafein 49-8 28-8 5-1 16-2 

The proportion of cafein in coffee is probably somewhat higher 
than the preceding analysis indicates. It is of course variable ; but 
is about half that of thein in tea (555). Coffee, however, is not used 



Fia. 104 

in the raw or natural state; like tea, it is first altered by heat or 

562, Effects of roasting Coffee.— 

The operation of roasting, produces 
several important changes in coffee. 
In the first place, the raw coffee- 
berries are so tough and horny, 
that it is very difficult to grind, and 
pulverize them sufficiently fine, that 
water may exert its fuU solvent 
effect upon them. Boasting ren- 
ders them yielding and brittle, 
so that they may be more readily 
ground ; while, at the same time, it 
increases the amount of matter so- 
luble in hot water. If we examine 
the raw coffee seed with the micro- 
scope, it will be found to consist of 
an assemblage of cells, in the cavi- 
ties of which are seen small drops 
of the aromatic volatile oil of cof- 
fee. This appearance is shown in 
(Fig. 104). K now we place a 
fragment or section of roasted cof- 
fee under a magnifier, it wUl be 
observed that these drops of oD. 
in the cells are no longer visible 
(Fig, 105). They have, in part, 
been dissipated by the heat, and 
in part, become more generally dif- 
fused throughout the mass of the 
seed; a portion being driven to the 
surface. It is obvious, that roasting 
produces certain chemical changes 
in coffee, which alter its flavor and 

taste, and bring out the peculiar 'Oi'^^^^^^^ 
and highly esteemed aroma for YJ'ts 

^ i . 1 ,■,. 1 • T i." • T. Appearance of roasted coffee berries. 

which this beverage is distinguish- 

ed. Johnston states that the peculiar aromatic principle which gives 
flavor to coffee, exists in extremely minute quantity, (one part in fifty 
thousand,) and is generated in the roasting process. The heat also 

Appearance of nnroasted coffee-berries 
magnified, showing the size and form of 
the cells, and the drops of oil contained in 
their cavities. 

FiQ. 105. 


sets a portion of the cafein free from its combination with tannic 
acid, and evaporates it. The temperature is suflSciently high to de- 
compose the sugar, and change it to brown, burnt sugar, or caramel. 
Coffee darkens in color during roasting, swells much in bulk, and 
loses a considerable portion of its weight, by evaporation of its water 
and loss of other constituents. Coffee roasted to a reddish Irown, 
loses in weight, 15 per cent., and gains in bulk, 30 per cent. To a 
chestnut trown, it loses 20 per cent, in weight, and gains 50 in 
bulk. To a darTc irown, it loses 25 per cent, of weight, and gains 
50 in bulk. 

563. Hints concerning the Eoasting Process. — The roasting of coffee 
is an operation of considerable nicety; more, perhaps, depending 
upon it than upon the variety of the article itself. Coffee is roasted 
by the dealers, in hollow iron cylinders or globes, which are kept 
revolving over a fire. As the first effect is the evaporation of a consid- 
erable amount of water, if the vessel be close this is retained, and the 
coffee roasted in an atmosphere of its own steam. This is not thought 
to be the best plan, and if the operation be carried on at home, it is 
recommended that the coffee be first dried in an open pan over a 
gentle fire, until it becomes yellow. It should then be scorched in 
a covered vessel, to prevent the escape of the aroma ; taking care, 
by proper agitation, to prevent any portion from being burnt ; as a 
few charred grains communicate a bad odor to the rest. It is impor- 
tant that just the right temperature should be attained and kept. If 
the heat be too low, the aromatic flavor is not fully produced, and if 
it be too high, the rich oily matter is dissipated, leaving only the 
bitterness and astringency of the charred seeds. The operation should 
be continued until the coffee acquires a deep cinnamon or chestnut 
color, and an oily appearance, and the peculiar fragrance of the roasted 
coffee is sufficiently strong. It may then be taken from the fire, 
and allowed to cool without exposure to the air, that the aromatic 
vapor may condense and be retained by the roasted grains. Coffee is 
very apt to be over-roasted, and even a slight excess of heat greatly 
injures its properties. 

564. Effects of Time upon Coffee. — Coffee berries undergo a change 
called ripening, by keeping; that is, they improve in flavor. The 
Arabian coffee ripens in three years, and it is said that in ten or a 
dozen years the inferior American coffees become as good, and acquire 
as high a flavor as any brought from Turkey. — (Ellis.) But it is differ- 
ent after the coffee is roasted and ground. Its flavoring ingredients 
have a tendency to escape, and it should therefore be confined in ves- 


sels closed from the air. It should not be exposed to foreign or dis- 
agreeable odors, as it has a power of imbibing bad exhalations, by 
which it is often injured. Many cargoes of coffee have been spoiled 
from having been shipped ■with, or even put into vessels which had 
previously been freighted with sugar. A few bags of pepper are suffi- 
cient to spoil a whole ship-load of coffee. — (Noemandt.) 

565. Mode of Preparing the Bercrage. — To prepare the coffee, it 
should be roasted and ground just before using, no more being ground 
at a time than is wanted immediately. Of course the finer it is re- 
duced the stronger will be the extract from a given weight of coffee, 
one-fourth more soluble matter being obtained from coffee ground to 
the fineness of flour than from the ordinary coarse powder (Knapp). 
If a cup of good coffee be placed upon a table, boiling hot, it will fill 
the room with its fragrance. Its most valuable portion is thus liable 
to be exhaled and lost. Hence the same difficulty is encountered as 
in tea making ; boUing dissipates the much-prized aroma ; but a high 
heat is necessary to extract the other important ingredients of the 
coffee. It should therefore be steeped rather than boiled, an infusion, 
and not a decoction being made. Some make it a rule not to suffer 
the coffee to boil, but only to bring it just to the boiling point. Yet, a 
few minutes' boiling undoubtedly increases the quantity of the dis- 
solved, bitter, exhilarating principle. Dr. Donovan recommends that 
the whole of the water to be used be divided into two parts, one half 
to be put on the fire with the coffee, and, as soon as the liquor boUs, 
taken off, allowed to subside for a few seconds, and then poured off as 
clear as it wiU run. Immediately the remaining half of the water, at 
a boiling heat, is to be poured on the grounds ; the coffee pot is to be 
placed on the fire and kept boiling three minutes, and after a few mo- 
ments' settling, the clear part is to be poured off and mingled with the 
first. The mixture now contains a large share of the qualities of the 
coffee, both aromatic and bitter. 

566. Alkaline Water for Coffee-making. — It is observed, that some 
natural waters give a stronger and better flavored coffee than others, 
and this has been traced as in Prague, to the presence of alkaline mat- 
ter in those which give the most agreeable infusion. Hence, to obtain 
a more uniformly strong and well-flavored coffee, it is recommended 
to add a little soda to the water with which the infusion is made. 
About forty grains of dry, or twice as much of crystallized carbonate 
of soda, are sufficient for a pound of coffee. — (Johnston.) 

567. Adulterations of Coffee. — Ground coffee is very extensively 
adulterated. Various substances are employed for this purpose, as 



roasted peas, beans, and corn, and dried and roasted roots, sucli as tur- 
nips, carrots, potatoes, &c. But the most common adulterant is cUccory, 
a plant of the dandelion tribe, which has a large, white parsnip-like 
root, abounding in a bitter juice. The root is mashed, sliced, dried, 
and roasted with about two per cent, of lard, until it is of a chocolate 
color. A little roasted chiccory gives as dark a color and as bitter a 
taste to water, as a great deal of coffee ; and, costing only about one- 
third ae much, the temptation is strong to crowd it into ground coffee. 
So common has the use of chiccory with coffee, become, that it has, 
in fact, created a taste for a solution of unmingled chiccory, as a bever- 
age, although it is destitute of any thing corresponding to the cafein, 
or exhilarating principle of coffee. As an illustration of the extent of 
adulteration, and how one fraud opens the door to another, it is found 
that pure chiccory is almost as diflBcult to be met with in market as 
unadulterated coffee. Venetian red is employed to impart to it a true 
coffee color, while brick dust is used by the painter to cheapen and 
modify the shade of his Venetian red. 

568. How the Cheats in Coffee may be Detected. — When cold water is 
poured upon coffee the liquid acquires color only very slowly, and it 
does not become very deep after prolonged soaking; even when 
boding water is employed, the infusion, although somewhat deeper, 
still remains clear and transparent. "When, however, cold water is 
poured upon roasted and ground chiccory root, it quickly becomes of 
a deep brown, and in a short time is quite opaque ; with boiling water 
the result is still more prompt and marked. We may therefore detect 
chiccory in a suspected sample of coffee by placing a little in cold 
water. If it be pure the water will remain uncolored ; if chiccory be 
present it will be strongly discolored. It may be remarked, however, 
that if the coffee should be adulterated with burnt sugar, it will pro- 
duce a similar coloration of the water. It may be further noticed that 
particles of coffee float upon water, and, owing to their oiliness, are 
not melted, while chiccory absorbs water and sinks. The admixture 
of burnt and ground beans, peas, and grain, is not so readily shown. 
The most certain method of detecting these is by microscopic exami- 

3. CoooA AND Chocolate. 

569. Source and Composition of Cacao Seeds. — These beverages are 
prepared from the cacao beans, which are derived from a fruit resem- 
bling a short, thick cucumber, grown upon the small cacao tree of the 
West Indies, Mexico, and South America. The beans are enclosed in 


rows, in a rose-colored, spongy substance, like that of tlie wateianelon. 
When shelled out of this fleshy part, they are surrounded by a thin 
skin or husk, which forms about 11 per cent, of their weight. The 
cacao bean is brittle, of a dark brown color internally, cuts like a rich 
nut, and has a slightly astringent, but decidedly bitter taste. In pre- 
paring it for use, it is roasted, in the same way as coffee, until the 
aroma is fully developed. The bean is now more brittle, lighter 
brown in color, and less astringent and bitter than before. The fol- 
lowing is its composition, according to Lampadius : 

Fatty matter, 53-16 

Albuminous brown matter, containing the aroma of the bean, 16-70 

Starch, 10-91 

Gum, 7-75 

Lignin, -90 

Eed coloring matter, 2-01 

Water, 5-20 

Lobs, 3-43 

The largest constituent is a fatty substance, called 'butter of cacao^ of 
the consistence of tallow, white, of a mild, agreeable taste, and not 
apt to turn rancid by keeping. Cacao beans have also been found to 
contain a substance, in minute proportion, not included in this analysis, 
called theobromine a nitrogenous body, similar in nature and properties 
to thein, of tea, and cafeine of coffee. 

570. Forms of Preparation. — It is prepared in three ways. First. 
The whole bean, after roasting, is beat into a paste in a hot mortar, or 
ground between hot rollers. This paste, mixed with starch, sugar, &c., 
forms common cocoa, sold under various names, as ' rich cocoa, ' 
' flake cocoa,' ' soluble cocoa,' &c. These are often greatly injured 
from the admixture of earthy and other matters, which adhere to the 
husk of the beans. Second. The bean is deprived of its husk, and then 
crushed into fragments. These form commercial cocoa nibs, the purest 
state ia which cocoa can be obtained from the retail dealer. Third. 
The bean, when sheUed, is ground at once into a paste by means of 
hot roUers, mixed with sugar, and seasoned with vanilla, and some- 
times with cinnamon and cloves. This paste forms chocolate. — 

571. How these preparations are v&tA,— First, the chocolate is made 
up into sweet cakes, sugar confectionery, &c., and is eaten in the solid 
state as a nutritious article of diet, containing in a small compass much 
strength-sustaining capability. Second, the chocolate or cocoa is 
scraped into powder and mixed with boiling water, and boiling milk, 
when it makes a beverage somewhat thick, but agreeable to the pal- 


ate, refreshing to tlie spirits, and highly nutritious. Third, the nihs are 
boiled in water, with which they form a dark brown decoction, which, 
like coflfee, is poured off the iasoluble part of the bean. "With sugar 
and milk this forms an agreeable drink, better adapted for persons of 
weak digestion than the entire bean. The husk is usually ground up 
with the ordinary cocoas, but it is always separated in the manufac- 
ture of the purer chocolates. 

572. Adnlteration of Chocolate. — Pure or genuine chocolate should 
dissolve in the mouth without grittiness, and leave a peculiar sensation 
of freshness, and after boiling it with water, the emulsion should not 
form a jelly when cold ; if it does, starch or flour is present. Many 
of the preparations of the cocoa-nut, sold under the name of chocolate 
powder, consist of a most disgusting mixture of bad or musty cocoa- 
nuts, with their shells, coarse sugar of the very lowest quality, ground 
with potato starch, old sea-biscuits, coarse branny flour, animal fats 
(generally tallow). I have known cocoa-powder made of potato 
starch moistened with a decoction of cocoa-nut shells and sweetened 
with molasses ; chocolate, made of the same materials, with the ad- 
dition of tallow and ochre, a coarse paint. I have also met with 
chocolate in which brick-dust, or red ochre, had been introduced to 
the extent of 12 per cent. — (Noemandt.) The temptation to fraud in 
these preparations seems to be as irresistible as in the case of ground 
coffee. There is no easy means of detection short of refined micro- 
scopic and chemical examination, so that the only practicable means of 
self-defence for the purchaser, is to deal only with traders of unques- 
tionable integrity, where such can be found. 

1. Causes of their Changeableness. 

573. Why is it Necessary that Foods should he Perishable ? — As in the 

plan of nature the production of force depends upon change of matter, 
and as the fundamental purpose of animal life is the evolution of pow- 
er, it is apparent that matter which is to act as food, must be capable 
of ready and rapid transformation. This inherent facility of change, 
by which alimentary substances are conformed to the deep require- 
ments of the animal economy, renders them extremely transient and 
perishable. If they are designed for change loitMn the body, they 
must be subject to change without. In order that the gluten of flour, 
for example, may pass readily through the successive changes of the 
animal organism, being converted first into blood, then into muscular 


fibre, and then decomposed for the development of contractile force, it is 
necessary that this substance should be so loosely buUt up, the attrac- 
tions amongst its atoms should be so feeble, that slight causes become 
capable of breaking down its chemical structure. 

5T4. Change of Nntrient Matter withiu and without the Body. — ^It was 
formerly taught that the living body is the domain of a peculiar vi- 
tal power, which suspends the ordinary destructive play of chemical 
aflBnities and physical forces, but that at death the vital energy ceases, 
and those forces resume their natural activity, causing the speedy dis- 
organization of the inanimate organism. But this is hardly correct. 
The vital force, or whatever we may name the presiding agency of 
the living system, does not suspend physical and chemical laws, but 
only regulates, and as it were uses them. "We have already seen that 
strictly chemical changes go on constantly in the body, and shall 
shortly have occasion to notice their extent (624). They are of the 
same kind {oxidations)^ are carried on by the same agent (atmospheric 
air), and yield the same final products (carbonic acid, water and am- 
monia), in both conditions. In the living fabric the decompositions 
are measured ; while in the lifeless body they are uncontrolled, and 
quickly spread through the entire organic mass. 

575. Conditions of the Perishableness of Foods. — Alimentary substances 
are by no means alike changeable ; some keep longer than others un- 
der the same circumstances. There are certain specific causes of or- 
ganic decomposition, and accordingly as these act conjointly, or with 
variable intensity, is the rate of putrefactive change. In chemical 
composition, vegetable and animal substances are much more compli- 
cated than mineral compounds, and hence they are less permanent. 
Generally, mineral substances are combined in the simplest and 
most stable way, containing but few atoms, and consisting of pairs of 
elements, with nothing to disturb their direct attraction for each other. 
On the contrary, organized substances, in some cases, contain several 
himdred atoms, and consist of three, four or five different elements, 
joined by complex afiinities into delicate and fragile combinations. 
We have seen, in speaking of fermentation, that albuminous substan- 
ces are, from this cause, most changeable, and are universally present 
in substances designed for food. Water is a large constituent of 
all alimentary bodies, in their natural state, and is highly promotive 
of chemical changes; indeed, it is indispensable to them. Tem- 
perature exerts an all-controlling influence — warmth favoring, and 
cold retarding, or arresting, these transformations. The atmospheric 
medium, which is in contact with every thing, contains an element 


whicli is the ever-active and eternal enemy of organization. The in- 
satiable hunger of oxygen gas for the elements of organic substances, 
is a universal cause of decomposition — it is the omnipresent destroyer, 
consuming alike the li ving and the dead (662). Putrefactive decay may 
also be prevented by certain chemical substances which are used for the 
purpose. A knowledge of the laws and conditions of organic decom- 
position, has led to various practical methods of controlling it, which 
constitute the art of preserving. 

2. Peeseevation by Exolttsion of Aie. 

576. Oxygen as an exciter of decay, — Other conditions being favor- 
able, that is, moisture being present and a proper temperature, access 
of air starts decomposition, — it is the prime mover of the destructive 
processes. We have already noticed its mode of action, in speaking of 
fermentation (488). In the case of vegetables, as potatoes and apples, 
for example, if the air is excluded from their interior, they remain 
for a considerable time sound. But if we cut them, the oxygen 
quickly attacks the exposed surface and turns it brown, indicating the 
incipient stage of decay. When the surface of fruits and vegetables 
is injured, so that their juices come in direct contact with the air, the 
effect is at once seen. If an apple is bruised, the injured spot imme- 
diately turns dark, and decomposition gradually spreads from that 
point, until the whole apple becomes rotten. The juice of the ripe 
grape, while protected from air by an unbroken skin, remains sweet 
and scarcely changes ; it may be dried and converted into a raisin, 
its sweetness remaining. If it be crushed under mercury, and the 
juice be collected in a glass completely filled with mercury, so as to 
prevent all contact of air, it will remain unchanged for several days. 
But if air be once admitted, as by perforating the grape-skin with a 
needlo's point, fermentation commences almost instantaneously, and the 
juice is soon entirely changed. The same is true of all animal fluids. 
Milk, while in the udder of the healthy cow undergoes no change, 
but in contact with air, its properties are soon totally altered — it is 
soured and coagulated (547). When life has been destroyed by bodily 
wounds, decomposition spreads from them ; or if the animal have not 
died by violence, the changes may begin ioternally in those parts, 
such as the lungs, which are in contact with the air. 

577. Changes begun by Oxygen may proceed without it. — ^It is by no 
means necessary, in all cases, that air should be in constant contact 
with the changing substance; the decomposition once commenced, 


may contintie, thougli the oxygen be entirely excluded. Milk, if once 
exposed to the air, coagulates and sours, though sealed up in air-tight 
vessels. Grape juice, though oxygen be completely cut off, ferments, 
generates gases, and often explodes the bottles in which it is confined. 
The impulse of disorganization being given, decomposition goes on 
without further external aid. To explain this, we must suppose that 
the atoms of the changing substance were at first in a kind of rest or 
equilibrium, without mutual activity, and that by the invasion of oxy- 
gen, this equilibrium has been disturbed, so that the elements of the 
substance begin to act and re-act upon each other, giving rise to new 
products. In this way, a state of change commenced by merely jost- 
ling a few surface atoms through contact of oxygen, is propagated by 
intestinal action throughout the entire mass. 

578. How changes begun by Oxygen may be stopped. — "The property 
of organic substances to pass into a state of fermentation and decay 
in contact with atmospheric air, and in consequence to transmit these 
states of change to other organized substances, is annihilated, in all 
cases without exception^ l)y heating to the hoiling points — ^Liebio. 
The substance most prone to be affected by air-contact, is hquid albu- 
men ; and this by boiling is solidified, and so altered in properties, as 
to lose its peculiar susceptibihty of transmutation. The boiling cer- 
tainly obhterates the effect that oxygen has produced, and as the 
atoms of matter have no inherent power to put themselves in motion, 
and cannot change place unless influenced by some external cause, it 
is obvious that the nutritive substance will remain unaltered if the 
air is Jcept excluded. These facts indicate the most certain, manage- 
able, and perfect method of preserving alimentary substances. By 
simply boating to the boiling point, which produces no other change 
than that of partial cooking, and afterward protecting from the air, 
alimentary substances, both animal and vegetable, may be preserved 
in their natural condition entirely unchanged in both flavor and pro- 
perties, for an indefinite period. This plan was first brought into 
general notice by M. Appeet of France, in 1809. He preserved all 
kinds of fruits, vegetables, meats, soups, &c., in glass bottles. His prac- 
tical methods, however, were crude and unsatisfactory, and have been 
superseded by others. Captain Ross presented the society of arts with 
a box from the house of Gamble and Daekin (London), which con- 
tained cooked provisions sixteen years old, and that were in a state of 
perfect preservation. The details of the preparation on a large scale, 
as practised chiefly for marine consumption, we have no space here 
to describe. The vegetables, meats, poultry, &c., are cooked precisely 


in the same maBner as for immediate consumption, and then sealed 
up in boxes and canisters which do rot contain a particle of air. 

579. Domestic preservation in air-tiglit Tessels. — ^The preservation of 
delicate fruit and vegetables in air-tight cans, has now become quite 
generally a household operation, and there can be no doubt that as 
people acquire experience in the process, they will employ it much 
more extensively. Of this process Prof. Liebig remarks, "The pre- 
pared aliments are enclosed in canisters of tinned iron plate (609), 
the covers are soldered air-tight, and the canisters exposed to the 
temperature of boiling water. When this degree of heat has pene- 
trated to the centre of the contents, which it requires about three or 
four hours to acomplish, the aliments have acquired a stability which 
one may almost say is eternal. When the canister is opened, after 
the lapse of several years, the contents appear just as if they were only 
recently enclosed. The color, taste, and smell of the meat, are com- 
pletely unaltered. This valuable method of preparing food, has been 
adopted by many persons in my neighborhood, and has enabled our 
housewives to adorn their tables with green vegetables in the midst 
of winter, and with dishes at all times which otherwise could be ob- 
tained only at particular seasons." 

580. Canisters closed by soldering. — Perfectly tight tin canisters of 
almost any convenient shape are provided, and the article to be pre- 
served, sometimes raw, but generally cooked, is placed within it, and 
the lid soldered down. The lid, is however, perforated with a small 
aperture or pin-hole. The canister is then placed in boiling water, and 
the moisture within is converted into steam which drives out the air. 
The boiling is continued as long as may be required totally or partially 
to cook the contents of the can, which is then withdrawn, and the 
pin-hole closed with solder. This is an operation of considerable 
nicety. The heat drives out not only air contained in the canister, 
but also a jet of steam. The solderer, therefore, lets fall a few drops 
of cold water on the tin around the aperture, producing a momentary 
condensation of the steam, during which the pin-hole is dexterously 
closed. The delicacy and success of the operation, consists in carry- 
ing the condensation only so far as just to arrest the jet of steam, and 
in closing the opening at the instant. After the canister is closed, 
it is again exposed with its contents for a short period to a boiling 

581. Spratt's self-sealing Cans. — In many cases a tinsmith may not 
be near, and the soldering operation for closing the canisters will be 
quite certain to fail in the hands of the inexperienced. To obviate 



Fig. 106. 

this difficulty, other arrangements have been contrived. Speatt's 
cans* are oblong tin cylinders (Fig. 106), holding from a quart to a 
gallon, which are closed with a screw acting upon a ring or ' com- 
press ' of india-rubber, and then hermetically sealed with beeswax. 
The closure is simple and effectual, and can be managed with a little 
care by any body. The articles being introduced into the can, the cap 
is screwed down tightly with the fingers^ and the can submerged in a 
boiler of cold water, which is then raised 
to boiling. After boiling a sufficient time 
they are withdrawn, the caps unscrewed^ 
and the cans left open for one minute. If \ 
the previous boiling has been thorough, 
steam wiU escape freely. If it does not 
so escape, the boiling must be repeated. 
The cap is then screwed down, this time 
very tightly, with a wrench provided^ and 
the can introduced into the water and 
boiled a second time. On withdrawing it 
again melted beeswax is poured into a 
little channel or groove, which makes the 
sealing perfect, if the cap fits and is tightly 
screwed down. In all cases there are at 
least two boilings. The second might be 
thought unnecessary, but it is not. The vessel must be opened, that 
the steam may drive out the air, and there is always the possibility 
that a trace may be left. If so, during the second boiling the oxygen 
will be entirely converted into carbonic acid, which is innoxious. As 
the results of large experience the times required for the boiling are 
as follows : 

First boiling. Second boiling. 

Berries of all kinds 15 minutes. 5 minutes. 

Cherries or currants 15 « 5 « 

Khubarb 15 « 6 « 

Peaches 20 " 5 " 

Plums 20 " 10 " 

Quinces, pears or apples 45 " 15 « 

Tomatoes 80 " 15 " 

Asparagus 60 " 80 " 

Green peas, corn or beans 8 hours. 3 hours. 

582. Suggestions concerning the use of the Cans.— None but perfectly 
fresh sound fruit shoiild be put up in the above manner. It is recom- 

Spratt's Self-sealing Can. 

* Manufactured by Wells & Pbovost, New York, 


mended that peaches, quinces, pears and apples be peeled, and the 
seeds removed before preserving, as seeds and peel embitter and other- 
wise injure the flavor. Peach stones contain traces of Prussic acid, a 
powerful poison, which, if the fruit be preserved whole, is liable to be 
diffused through it. Fruits are preserved either with or without 
sugar ; if without, a quarter of a pint of water should be poured over 
every quart of fruit while in the can. If the fruit is to be sweetened, 
make a sirup, and pour on it in the can, until it is nearly full. A 
sirup for summer fruits is made by adding a pound of crushed sugar 
to a pint of water, and boiling two minutes. Very acid fruits, such 
as quinces and plums, require a stronger sirup, say li lb. sugar to a 
pint of water. If the cans are not perfectly tight when the steam 
condenses vnthin, forming a vacuum, the external pressure of the air 
may drive the soft beeswax in through the crevice. Aliments well 
put up wiU keep in a room at any temperature ; if the cans bulge, it 
is a sign of development of gas by internal decomposition, and their 
contents wiU not keep. 

3. Peeseevation at low Tempeeatuees. 

583. Influence of Temperature. — Degrees of temperature exert an 
absolute control over the duration of alimentary compounds. At 32° 
their juices are congealed, and they remain totally unchanged. At a 
few degrees above the freezing point changes are very slow. As we 
ascend the scale, the conditions of mutation become more favorable, 
except in the case of albumen, which is rendered more enduring by 
the heat of coagulation. In all other cases decomposition proceeds 
more rapidly as warmth increases, until the point of quick disorgani- 
zation, charring, and active combustion is reached. 

584. Freezing as a means of Preserving. — Congelation, therefore, may 
be resorted to as a means of preservation, chemical action being im- 
possible where the substance is reduced to a solid state. Eemarkable 
cases are on record in which the bodies of animals have been disen- 
tombed from masses of ice, in such a state of preservation that the 
flesh was flt to support nutrition, although they had been wrapped in 
ice for such a vast period that the race to which they belonged had 
become extinct. It is customary in many regions to preserve fresh 
meat by freezing it, and packing in snow. Some object that the 
flavor of meat is injured by freezing ; but the Enssians, on the con- 
trary, insist that it is improved. Great care is necessary in thawing 
all frozen aliments, whether meat, fish, or vegetables. It should be 
done slowly, and the best way is by immersion in very cold water. 



A shell of ice will be formed around them, as we have often seen in 
' taking the frost out of apples ; ' — the water in contact with the sur- 
face being frozen into a scale, by parting with its heat to thaw the 
frozen apple within. If thawed too rapidly, as by placing them in a 
warm room or in hot water, the taste is impaired, and the composition 
of the substance so affected that putrefaction is rapidly brought on. 
One of the effects of freezing and thawing potatoes and some fruits, 
is to increase the amount of sugar, as shown by their sweeter taste. 

585. Low Temperatures above Freezing — Refrigerators. — We command 
^ow temperatures by cellars, and the use of ice. Excavations made 
below the surface of the ground have a temperature common to the 
surrounding strata of earth, which is cooler the deeper we go for 
nearly a hundred feet. The temperature is also very constant, the 
extremes of winter and summer being both excluded. The temper- 
ature of good cellars (40° to 60°), is below the range most favorable 
to putrefaction (60° to 100°). By the use of ice in the ice-house 
or refrigerator, the temperature 

may be kept down to within 5° ^^®- ^^^ 

or 10° of freezing. At these 
points changes proceed slowly, so 
that meat admits of being kept at 
this degree of coolness for a con- 
siderable time. It is said that 
meat should never be suffered to 
touch ice, as it is toughened and 
otherwise injured. The refriger- 
ator is commonly a rude, shelved 
box. If opening at top, it is 
troublesome of access and difficult 
to make its space available. If it 
have doors at the sides, the cold 
air flows out every time it is 
opened ; and if the ice is placed 
at the bottom, there is no circu- 
lation of air or means of cooling 
the upper space. A. S. Lyman, of K Y., has obviated these defects by 
a newly devised arrangement (Fig. 107). The ice is placed in an upper 
chamber over a grate opening to the flue a, through which, ice-cold 
air constantly falls. The body of the refrigerator is occupied by three 
drawers, I e d, c being represented as partially withdrawn. The cold 
air fills these di-awers, and as it becomes slightly warmer is pressed 

Lyman's Bureau EeMgorator. 


upward in the direction of the arrows, and re-cooled by contact with 
the ice. It descends again through the flue, the temperature of the 
whole refrigerator being thus kept down nearly to freezing. The 
waste water is caught at g. The arrangement of drawers makes the 
whole space available, and is as convenient as a common bureau. 
When one is partially withdrawn, as at e, the air in, it being heavier 
than that of the room, does not escape, while the circulation of air con- 
tinues within. There is also a twofold means of purifying the air. 
At f there is a filter consisting of a wire-gauze box, through which 
the air passes and is disinfected. "When it comes in contact with the 
ice, it is condensed and its moisture deposited, so that it has a real dry- 
ing effect upon the articles to be preserved. The water constantly form- 
ing by the melting ice is highly absorbent of the gases set free by de- 
composing food, so that these impurities are constantly washed out of 
the air in its progress. The charcoal filter, in effect, divides the space 
into two refrigerators ; _ thus preventing articles in one from smelling or 
tasting of those in the other. Cars are constructed upon this prin- 
ciple, in which meat is transported from the Western States to New 
York in summer. 

586. Keeping Frnits at low Temperatares. — The most important fact 
relating to the composition of fruits is the large proportion of water 
they all contain, and which constitutes the bulk of their peculiar 
juices. From three-fourths to nine-tenths of them being liquid, we 
are to regard them as consisting of a small amount of solid matter 
diffused through from four to ten times their bulk of water. This con- 
dition is eminently favorable to the action of fruits upon the organs 
of taste in their njLtural or uncooked state ; being in a kind of pulpy, 
half-dissolved condition, they are ready to take prompt effect upon 
the pappilsa of the mouth. But the same property of fruits which 
adapts them so perfectly to our gustatory enjoyment, shortens the 
time when they can be so employed. Their abounding moisture 
"favors decomposition, and they are hence perishable and short-lived. 
Yet by proper management fruits may be long preserved in a fresh 
and perfect state. Vegetables and juicy fruits, as apples and pears, 
can be preserved for months in ceEars where the necessary warmth 
for inducing decay is not attained. Sometimes fruit, as many varieties 
of apples, are not really ripened at the time of gathering, but undergo 
a slow change during the winter months, their acid principle being 
converted into sugar. To be best preserved fruit should be picked when 
perfectly dry, at a time when the stalk separates easily from the spur. 
Apples and pears should have their stalks or " stems " separated from 



the tree^ and not from themselves. The utmost care should he ob- 
served to prevent bruises or contusions ; some have implements for 
collecting the most valuable kinds of fruit, so as not to touch it with 
the hand. The most delicate kinds do not bear handling or wiping, 
as this rubs off the bloom which, when allowed to dry on some fruits, 
constitutes a natural varnish, closing up the pores and preventing the 
evaporation of the juices. Apples have been presei-ved a year in a 
fine fresh condition, by keeping them in an atmosphere within ten 
degrees of the freezing point. Constancy of temperature is important, 
as alternations of heat and cold, by contracting and expanding the 
juices, seem to favor chemical changes. Grapes, cherries, currants, 
gooseberries, and other soft fruits have been preserved for use in win- 
ter by gathering them when not too ripe, and when very dry putting 
them unbruised into dry bottles, which are afterwards well corked, 
and then buried in the earth. The efficiency of this method of pre- 
serving is increased by immersing the bottles containing the fruit for 
a few minutes previously to corking, in hot water, which coagulates 
the vegetable albumen. The preservation is here due to the joint in- 
fluence of exclusion of air, and a low and uniform temperature. A 
preservatory for fruit, or kind of refrigerator on a large scale, has been 
devised by Mr. Paekee. The fruit, picked carefuUy and unbruised, is 
conveyed at once to the preservatory, where the temperature is 
down nearly to freezing. The plan requires that ice be supplied the 
previous winter. 


587. Retention of Water in Fruits and Vegetables. — ^As nature places 
water in large quantities in organic bodies, in many cases she 
takes due precautions to keep it there. Unripe potatoes and unripe 
apples removed from the parent stock shrivel, shrink, and perish. 
These eifects result from the porous condition of the immature skin, 
which permits the water within to escape by evaporation. " But 
when ripe this porous covering has become chemically changed into a 
thin impervious coating of corh^ through which water can scarcely 
pass, and by which, therefore, it is confined within for months to- 
gether. It is this cork layer which enables the potato to keep the 
winter through, and the winter pear and winter apple to be brought 
to table in spring of their full dimensions." — (Johnston). 

588. Loss of Water as a means of Preservation. — Yet as organic sub- 
stances may be kept by solidifying the water, that is, freezing them, 
they may also be preserved by withdrawing it. Both vegetable and 
animal substances are extensively preserved in this way. Drying is a 


kind of disorganization of the alimentary body, its largest constitnent 
being removed ; yet, in this case, the lost ingredient may be added 
again, and the substance brought into a condition more or less re- 
sembling the natural state. Drying is effected either by simple 
exposure to the sun and air, or by artificial heat of a higher intensity, 
applied in various ways. Both methods are quite practicable, but 
have their disadvantages. Drying in the air is necessarily a slow pro- 
cess, so that there is danger of moulding and fermentation ; the sub- 
stances require to be made small or thin, and as the air itself is moist, 
the drying can never be complete, but only reaches a certain point, 
and then fluctuates with the varying atmospheric dampness. On the 
other hand, when artificial heat is employed, as in kiln-drying in close 
apartments, it is obvious that the foods are liable to be much altered 
in their nature. The starch may be dissolved, or altered to gum ; the 
sugar browned and changed to caramel, acquiring a bitter, disagree- 
able taste, if the heat of the drying chamber be too high ; while if the 
temperature be not higher than 140°, the albumen may be dried so as 
to dissolve again in water ; if higher, it is coagulated, and remains 

589. Preserviiig Succulent Vegetables. — These, if exposed to the air, 
evaporate their moisture, wUt, and lose their crispness and freshness. 
A damp cool place is best to prevent these changes for a time. Many 
are kept soundly during winter by burying in the earth. M. Masson, 
head gardener to the Horticultural Society of Paris, has described a 
mode of preserving succulent vegetables by drying and compression. 
He prepares cabbage, cauliflower, potatoes, spinach, endive, celery, 
parsley, &c., in such a manner that they keep for any length of time, 
and when soaked in water resume much of their original freshness 
and taste. They are chiefly prepared for marine consumption. The 
packages of dried vegetables are covered with tinfoil. Dr. Hassall 
speaks of a specimen of dried cabbage as follows : " On opening the 
package the contents, which formed a solid cake, were seen to consist 
of fragments of leaves of a yellowish color, interspersed here and 
there with some that were green. In this state it was difficult to de- 
termine what the nature of the vegetable was. Soaked in hot water 
for about half an hour, it gradually underwent a great expansion, so 
that it acquired several times its former bulk. "When examined, it 
was evident at a moment's glance that the vegetable consisted of the 
sliced leaves of the white-hearted garden cabbage, presenting the ap- 
pearance and color, and possessing the taste and smell, to a remarkable 
extent, of the vegetable in its recent state." 


5. Peeseevation by Antiseptics. 

590. Remarkable properties of common Salt. — Antiseptics are op- 
posers of putrefaction. Certain bodies when added to organized 
substances, possess the power of resisting or preventing their putre- 
factive decomposition ; they are numerous, and act in various ways. 
Those used for preserving aliments are salt-petre, sugar, alcohol, 
creosote, vinegar, oil, and common salt. However ' common ' this 
last substance may be, we shall nevertheless be interested in giving it a 
moment's attention. Though mild and pleasant to the taste, it is 
composed of two elements, one a yellowish green, suffocating, poison- 
ous gas, cMori?ie, and the other a bright silvery-looking metal, sodium 
(hence the chemical name of the substance chloride of sodium). 
"When these two elements are brought together, they unite spontane- 
ously ; and yet so prodigous is the force with which they combine, so 
enormous the condensation of matter, that although the sodium unites 
vrith more than five hundred times its bulk of the heavy gas, yet the 
compound formed occupies less space fio. los. 

than the solid sodium alone did before 
the union. No known mechanical forc6 
could have accomplished this, yet it re- 
sults from the agency of chemical af- 
finity (Faeeaday). If a lump of com- 
mon salt, (it occurs in large masses in 
the shape of rod salt,) be cut into the 
form of a thin plate, and held before a 
fire, it does not stop the heat-rays, but 
has the singular property of permitting - — ^ 
them to dart through it, as light does 
through glass — it is the glass of heat. A 
hundred lbs. of water, hot or cold, dis- 
solve 37 of salt, forming a saturated so- 
lution or the strongest brine. When the 
briny solution evaporates, the salt reap- 

■r^^^^r, 4^ +i^« r,^T;A -f^,.™ „_ i IT How crystals of common salt are 

pears m the solid lorm, or crystauizes. formed. 

Its crystals are cube shaped ; if the evaporation takes place slowly 
they are large, but if it be rapid, they are small, and formed in a 
curious manner. Eesultmg from evaporation, they are naturally 
formed at the surface of the liquid, and present the appearance of little 
floating cubes, as shown in (Fig. 108), where the solid crystal is up- 
borne or floats in a little depression of the fluid surface. New crystals 


soon form, which are joined to the first at its four upper edges, con- 
stituting a frame above the first little cube (Fig.. 109). As the whole 
descends into the fluid, new crystals are grouped around the first 
frame constituting a second {Fig. 110). Another set added in the 
same way gives the appearance shown in Fig 111. The consequence 
of this arrangement is that the crystals are grouped into hollow, four- 
sided pyramids, the walls of which have the appearance of steps, be- 
cause the rows of small crystals retreat from each other. This mode 
of grouping is called Jiopper-sTiaped (Fig. 112). 

591. Sources and Purification of Salt. — Salt is obtained from three 
sources ; first^ it is dug from the earth in mines, in large masses, like 
transparent stones (roc^ salt) ; second, it is procured by evaporating 
sea-water (bay salt) ; and, third, by boiling down the liquid of brine 
springs. It differs very much, in purity, from diflferent sources, being 
in many cases contaminated by salts of calcium and magnesium, which 
render it bitter. Pure salt, in damp weather, attracts water from the 
atmosphere, and becomes moist, but parts with it again when the 
weather becomes dry. But the chlorides of calcium and magnesium 
are much more absorbent of water, and hence, if the salt is damp and 
moist when the air is dry, we may infer that a large proportion 
of these substances is present in it. Salt, for certain culinary pur- 
poses, as for salting butter, should be perfectly pure. Its bitter in- 
gredients are more readily soluble in water than is the salt itself; 
hence, by pouring two or three quarts of boiling water upon ten or 
twenty lbs. of salt, stirring the whole well now and then for a couple 
of hours, and afterwards straining it through a clean cloth, the ob- 
noxious substances may be carried away in solution. Among the 
purest, is that called Liverpool salt, which is an English rock-salt dug 
from the mines ; dissolved, recrystallized and ground. 

592. How salt preserves meat. — Salt is more widely used than any 
other agent in conserving provisions, especially meats. It is well 
known that when fresh meat is sprinkled with dry salt, it is found 
after a few days swimming in brine, although not a drop of water 
has been added. If meat be placed in brine it grows lighter, while 
the quantity of liquid is increased. The explanation of this is, 
that water has a stronger attraction for salt than it has for flesh. 
Fresh meat contains three-fourths of its weight of water, which is 
held in it as it is in a sponge. Dry salt will extract a large part of 
this water, dissolving in it and forming a saline liquid or brine. In 
this case, the water of the meat is divided into two parts ; one is taken 
up by the salt to form brine, while the other is kept back by the 


meat. The salt robs the meat of one-third or one-half the water of its 
juice. Salting is therefore only an indirect mode of drying ; the chief 
cause, perhaps, of the preservation of the meat, being, that there is 
not sufficient water left in it to allow putrefaction. The surrounding 
brine does not answer this purpose, as it does not act upon the meat ; its 
relation to flesh being totally dififerent to that of fresh water. If fresh 
water be applied to a piece of dry meat, it is seen to have a strong 
attraction for it, but if we use even a weak solution of salt, it flows 
over it wetting it but very imperfectly. 

593. How meat is injured by salting. — The separation of water from 
the fibre of meat shrinks, hardens, and consequently renders it less di- 
gestible. It is quite probable, also, that the salt, in some way not yet 
understood, combines with the fibre itself, ^hus altering injuriously 
its nutritive properties. Peeeiea thinks that the separation of water 
is not sufficient alone to account for its preservative action, but that 
it must produce some further unexplained effect upon the muscular 
tissue. The main and well-established injury of salting, however, is 
caused by the loss from the meat of valuable constituents, which escape 
along with the water which the salt withdraws. It has been shown 
that the most influential constituents of meat are dissolved in its juice 
(471). The salt, therefore, reaUy abstracts the juice of flesh with its 
albumen, kreatine, and valuable salts ; in fact, the brine is found to 
contain the chief soup-forming elements of meat. Salting, therefore, 
exhausts meat far more than simple boiling, and as the brine is not 
consumed, but thrown away, the loss is still greater In salting meat, 
however, there happens to be a slight advantage resulting fi*om its 
impurities, lime and magnesia. These are decomposed by the phos- 
phoric acid of the juice of flesh, and precipitated upon the surface, 
forming a white crust, which may often be observed upon salt meat ; 
this constituent, therefore, is not separated in the brine. Saltpetre 
has a preservative effect, probably in the same way as common salt, 
but it is not so powerful, and unlike salt produces a reddening of the 
animal fibres. A little of it is often used along with salt for this 

594. Salting Vegetables.— These may be preserved by salt, as well as 
flesh, but it is not so commonly done. In salting vegetables, however, 
a fermentation ensues, which gives rise to lactic acid. This is the 
case in the preparation of sauerTcraut from cabbages, and in salting cu- 
cumbers. The brine with which both vegetables are surrounded is 
found strongly impregnated with both lactic and butyric acids. 

595. Preservation by Sugar. — This is chiefly employed to preserve 


fruits. Many employ both sugar and molasses for the preservation of 
meat ; sometimes alone, but more commonly united with salt. The 
principle of preserving by means of sugar is probably similar to that 
of salting. In the case of fruits, the sugar penetrates withiu, changing 
the juices to a sirup, and diminishing their tendency to fermentation 
or decomposition. "Weak or dilute solutions of sugar are, hovpever, 
very prone to change ; they require to be of a thick or sirupy consist- 
ence. Knapp states that the drops of water which condense from 
the state of vapor on the sides of the vessels in which the preserves 
are placed, are often sufficient to induce incipient decomposition, by 
diluting the upper layers of sugar. The effect of the acids of fruits is 
gradually to convert the cane sugar into uncrystaUizable and more fer- 
mentable grape sugar, 

596. PreserTing by Alcohol and other substances. — Strong alcoholic li- 
quors are used to prevent decomposition in both vegetable and animal 
bodies. They penetrate the substance, combine with its juices, and 
as the organic tissues have less attraction for the spirituous mixture, 
it escapes ; and the tissues themselves shrink and harden in the same 
way as when salted. Alcohol also obstmots change by seizing upon 
atmospheric oxygen, in virtue of its superior attraction for that gas, 
and thus preventing it from acting upon the substance to be preserved. 
Vinegar is much used for preserving, but how it acts has not been ex- 
plained. Spices exert the same influence. Creosote, a pungent com- 
pound existing in common smoke, and which starts the tears when 
the smoke enters the eyes, is a powerful antiseptic, or preventor of 
putrefaction. Meat dipped for a short time in a solution of it wOl not 
putrefy, even in the heat of summer. Or if exposed in a close box to 
the vapor of creosote, the effect is the same, though in both cases the 
amount producing the result is extremely small. The preservative 
effect of smoke-drying is partly due to creosote, which gives to the 
meat its peculiar smoky taste, and partly to desiccation. Oil is but 
little employed in saving alimentary substances — two kinds of fish, 
anchovies and sardines, are preserved in it. Charcoal has always been 
ranked as an antiseptic or arrester of putrefaction ; but it has been 
lately shown that it is rather promotive of decomposition. How this 
is, will be explained in another place (811). 

6. Peeseevation of Milk, Buttee, and Cheese. 

597. Modes of preserving Blilk. — The cause of the souring of milk 
we have seen to be the action of oxygen upon its casein, which alters 
the sugar to acid (547). If, therefore, tlie milk be tightly bottled, and 


then boiled, the fermentative power of the curdy matter is destroyed, 
and it may be kept sweet for several months. When, however, the 
milk is again exposed to the air, the cm-d resumes its power of acting 
upon sugar, and acid is again formed. "When milk is kept at a 
low temperature, the cold retards its changes. If the vessels contain- 
ing it are placed in a running stream of cool water, or in a place cooled 
by ice, it will remain cool for several days. Milk may also be pre- 
vented from souring, even in warm weather, by adding to it a little 
soda or magnesia. The alkali destroyes the acid as fast as it is pro- 
duced, and the liquid remains sweet. The small quantity of lactate 
of soda or magnesia which is formed, is but slightly objectionable. If 
milk be evaporated to dryness, at a gentle heat, with constant stirring, 
it forms a pasty mass, which may be long kept, and which reproduces 
milk when agaia dissolved in water. Alderi's concentrated milh is a 
solidified pasty preparation, made by evaporating milk, with sugar, 
and affords an excellent substitute for fresh milk, in. many cases, when 
dissolved in water. 

598. Unpnrifled Butter qnickly spoils. — Butter when taken from the 
churn contains more or less of all the ingredients of milk, water, casein, 
sugar, lactic acid, which exist in the form of buttermilk, diffused 
through the oily mass. Oheveetjl states that fresh butter yields 16 
per cent, of these ingredients, chiefly water, and 74 of pure fat. In 
this state butter cannot be kept at all. Active decomposition takes 
place almost at once, the butter acquires a bad odor, and a strong dis- 
agreeable taste. Tlie casein passes into incipent putrescence, generat- 
ing offensive compounds, from both the sugar and oily matter. 

599. Bntter Pnrifled by Mechanical Worldng. — It is obvious, theyefore, 
that in order to preserve butter, it must first be freed from its butter- 
milk, which is done by working it, over and over, and pressing or 
squeezing it, which causes the liquid slowly to ooze out and flow away. 
The working or kneading is done with a wooden ladle, or a simple 
machine adapted to the purpose, or else by the naked hand. It is ob- 
jected that the employment of the hand is apt to taint the butter by 
its perspiration ; but while it is admitted that moist hands should never 
do the work, many urge that those which are naturally cool and dry, 
and made clean by washing in warm water and oatmeal {not soaj))^ 
and then rinsed in cold water, will remove the sour milk from the 
butter more effectually than any instrument whatever, without in the 
least degree injuring it. Overworking softens butter, renders it oily, 
and obliterates the grain. 

600. Preparation of Batter by Washing. — Some join washing with 


mechanical working, to separate the buttermilk. It is objected to this, 
first, that water removes or impairs the fine aroma of the butter, and, 
second, that it exposes the particles of butter to the injurious action 
of air much more than mechanical working. On the other hand, it is 
alleged that without water we cannot completely remove the ferment- 
ing matter, the smallest portion of which, if left in the butter, ulti- 
mately injures it. K water be used, it is of the utmost consequence to 
guard against its impurities. It is liable to contain organic substances, 
vegetable or animal matter, in solution, invisible, yet commonly pres- 
ent, even in spring water. These the butter is sure to extract, and 
their only effect can be to injure it. The calcareous waters of lime- 
stone districts are declared to be unfit for washing butter. Speengel 
states that the butter absorbs the lime, and is unpleasantly affected by 
it. A. B. DioKiNsoii is of opinion that the best butter cannot be 
made where hard water is used to wash it ; he employs only the soft- 
est and purest for this purpose. 

601. Cause of Rancidity in Bntter. — Pure oil has little spontaneous 
tendency to change. If lard, for example, be obtained in a condition 
of purity, it may be kept sweet for a long time without salt, when 
protected from the air. That it does alter and spoU in many cases, is 
owing to traces of nitrogenous matter, animal membranes, fibres, &c., 
which have not been entirely separated from it. These pass into de- 
composition, and carry along the surrounding oily substance. So with 
butter ; when pure, and cut off from the air, it may be long kept with- 
out adding any preservative substance. But a trifling amount of curd 
left in it is sufficient to infect the whole mass. It is decomposed, and 
acting in the way of ferment upon the sugar and oUy substance itself, 
develops a series of acids, the tutyric, which is highly disagreeable 
and offensive, and the capric and caproic acids, which have a stron g 
sour odor of perspiration. The butter is then said to be rancid. 
In general, the more casein is left in butter, the greater is its tendency 
to rancidity. 

602. Action of Air npon Butter. — The fat of butter is chiefly composed 
of margarin, which is its main solidifying constituent, and abounds 
also in human fat. It is associated with a more oily part, olein. 
Now, air acts not only upon the curdy principle, causing its putres- 
cence; but its oxygen is also rapidly absorbed by the oleic acid. One 
of the effects of this absorption may be to harden it, or convert it into 
mai'garic acid. This is, however, a first step of decomposition, which, 
when once begun, may rapidly extend to the production of various 
offensive substances. When, therefore, butter is much exposed to the 


air it is certain to acquire a surface rancidity, which, without pene- 
trating into the interior, is yet sufficient to injure its flavor. It is in- 
dispensable to its eflfectual preservation that the air be entirely ex- 
cluded from it. Hence, in packing butter, the cask or firkin should 
be perfectly air tight. Care should be taken that no cavities or spaces 
are left. If portions of butter are successively added, the surface 
should be either removed or raised up in furrows, that the new portion 
may be thoroughly mixed with it, or it should be kept covered with 
brine, and the vessel ought not to be finally closed until the butter has 
ceased shrinking, and the vacancies that have arisen between the but- 
ter and vessel's sides are carefully closed. 

603. Substances used to preserve Butter. — Salt, added to butter, per- 
forms the twofold office of flavoring and preserving it. The salt be- 
comes dissolved in the water contained in it, and forms a brine, a 
portion of which flows away, while the butter shrinks and becomes 
more solid. Salt preserves butter by preventing its casein from chang- 
ing ; hence the more of this substance is left in it the more need of 
salt. The quantity used is variable, from one to six drachms to the 
pound of butter. It is objected to salt that it masks the true flavor 
of butter, especially if it be not of the purest quality (591). Salt- 
petre will preserve butter ; but it is less active than common salt, 
and some think its flavor agreeable. Sugar is sometimes added to aid 
in preservation, and to compensate for the loss of the sugar of milk. 
Honey has been also used for the same purpose, at the rate of an 
ounce to the pound of butter. Some employ salt, saltpetre, and sugar 
all together. From an examination of upwards of forty samples of 
English butter, Hassall found the proportion of water in them to 
vary from 10 to 20, and even 30 per cent., and the proportion of salt 
from one to six or seven per cent. A simple method of ascertaining 
the quantity of water in butter is, to melt it and put it in a small bottle 
near the fire for an hour. The water and salt wUl separate and sink 
to the bottom. 

604. Changes of Cheese by Time. — Cheese requires time to develop 
its peculiar flavor, or ripen. A slow fermentation takes place within, 
which differs much according to the variety of circumstances con- 
nected with its preparation, and the degree and steadiness of the tempe- 
rature at which it is kept. The fermentation, which is gentle and pro- 
longed at a low temperature, becomes too rapid in a warm, moist place. 
The influence of temperature is shown by the fact that in certain locaU- 
ties of France, especially at Eoquefort, there are subterranean caverns 
which rent and are sold at enormous sums for the purpose of keeping 


and maturing cheese. These natural rock-cellars are maintained, by 
gentle circulation of air, at 41° to 42°. The nature of the changes 
that cheese undergoes has not been clearly traced. It is known that 
the casein becomes so altered as to dissolve in water. The salt intro- 
duced to preserve it is said to be decomposed ; the oily matter gets 
rancid, as may be shown by extracting it with ether ; and peculiar 
volatile acids and aromatic compounds are produced. Cheese of poor 
or inferior flavor, it is said, may be inoculated with the peculiar fer- 
mentation of a better cheese, by inserting a plug or cylinder of the 
latter into a hole made to the heart of the former. To prevent the 
attacks of insects the cheese should be brushed, rubbed with brine or 
salt, and smeared over with sweet oil, the shelves on which they rest 
being often washed with boiling water. 

605. Preservation of Eggs. — When t ewly laid, eggs are almost per- 
fectly full. But the shell is porous, and the watery portion of its 
contents begins to evaporate through its pores the moment it is ex- 
posed to the air, so that the eggs become lighter every day. As the 
water escapes outward through the pores of the shell air passes inward 
and takes its place, and the amount of air that accumulates within de- 
pends, of course, upon the extent of the loss by perspiration. Eggs 
which we have preserved for upward of a year, packed in salt, small 
ends downwards, lost from 25 to 50 per cent, of their weight, and did 
not putrefy. As the moisture evaporated the white became thick 
and adhesive, and the upper part was filled with air. To preserve 
the interior of the egg in its natural state, it is necessary to seal up 
the pores of the shell air-tight. This may be done by dipping them in 
melted suet, olive oil, milk of lime, solution of gum arabic, or cover- 
ing them with any air-proof varnish. They are then packed in bran, 
meal, salt, ashes, or charcoal powder. Eeatjmtje is said to have coated 
eggs with spirit varnish, and produced chickens from them after two 
years, when the varnish was carefully removed. 


606. It seems important in this place to ofier some observations 
pertaining to our ordinary kitchen and table utensils. We speak of 
the chemical properties of their materials rather than of their mechan- 
ical structure. 

607. Utensils of Iron. — Iron is much employed for vessels in kitchen 
operations. The chief objection to it springs from its powerful attrac- 
tion for oxygen, which it obtains from the atmosphere. It wiU even 


decompose water to get it. In consequence of this strong tendency to 
oxidation, its surface becomes corroded and roughened by a coating of 
rust, which is simply oxide of iron. The rust combines with various 
substances contained in food, and forms compounds which discolor the 
articles cooked in iron vessels, and often impart an irony or stj-ptic 
taste. Fortunately, however, most of these compounds, although ob- 
jectionable, ai'e not actively poisonous ; yet, sulphate of iron (copperas) 
and some other mineral salts of iron, are so. Cast iron is much less 
liable to rust than malleable, or wrought iron. There is one mode of 
managing cast iron vessels, by which the disagreeable effects of rust 
may be much diminished, if not quite prevented. If the inside of 
stew-pans, boilers, and kettles be simply washed and rinsed out with 
warm water, and wiped with a soft cloth instead of being scoured with 
sand or polishing materials, the vessel will not expose a clean metalho 
surface, but become evenly coated with a hard, thin jsrust of a dark 
brown color, forming a sort of enamel. If this coating be allowed, to 
remain, it will gradually consolidate and at last become so hard as to 
take a tolerable polish. The thin film of rust thus prevents deeper 
rusting and at the same time remains undissolved by culinary liquids. 

609. Protection of Iron by Tin. — As such protection, however, in- 
volves care and consideration, it is uncertain and unsatisfactory, and 
besides it is inapphcable to vessels of thin or sheet iron, A better 
method is that of coating over the iron with metallic tin, which has 
come into universal use in the form of tin-ware. The sheet tin which 
is so widely employed for household utensils is made by dipping pol- 
ished sheet iron in vats of melted tin. Tin itself is a metal some- 
what harder than lead, but is never used for culinary vessels. What 
is called dlocTs tin is generally supposed to consist of the pure metal. 
This is an error. It is only tinned iron plate, better planished, stouter, 
and heavier than ordinary. All tin ware, therefore, is only iron plate 
coated or protected by tin : yet, practically, it is the metallic tin only 
that we are concerned with, as that alone comes in contact with our 

610. Adaptation of Tin to Culinary Purposes. — Tin, in its metallic 
state, seems to have no injurious effect upon the animal system, for it 
is often given medicinally in considerable doses, in the form of powder 
and filings. It is frequently melted off from the sides of sauce-pans or 
other vessels in globules, and is thus liable to be swallowed, a circum- 
stance which need occasion no alarm. The attraction of tin for oxy- 
gen is feeble, and it therefore oxidizes or rusts very slowly. Strong 
acids, as vinegar or lemon juice, boiled in tin-coated vessels, may dis- 


solve a minute portion of the metal, forming salts of oxide of tin, 
but the quantity will be so extremely small that it need excite little 
apprehension. It is a question among toxicologists whether its oxide 
be poisonous. Pkotjst showed that a tin platter, which had been in 
use two years, lost only four grains of its original weight, and probably 
the greater part of this loss was caused by abrasion with whiting, sand, 
or other sharp substances during cleansing. If half of it had been 
taken into the system dissolved, it would have amounted only to -^-^ of 
a grain per day, a quantity too trifling to do much harm, even if it were 
a strong poison. Common tin, however, is contaminated with traces 
of arsenic, copper, and lead, which are more liable to be acted upon 
by organic acids and vegetables containing sulphur, as onions, greens, 
&c. Peeeiea remarks that acid, fatty, saline, and even albuminous 
substances may occasion colic and vomiting by having remained for 
some time in tin vessels. Still, tin is unquestionably the safest and 
most wholesome metal that it is found practicable to employ 11 domes- 
tic economy. 

611. Zinc Vessels Objectionable. — Zinc is rarely employed as a mate- 
rial for culinary vessels. In many cases it would be unsafe, as a poi- 
sonous oxide slowly forms upon its surface. It has been recommended 
for milk pans on the ground that milk would remain longer sweet in 
them, and hence, more cream arise. But whatever power of keeping 
milk sweet zinc possesses, it can only be caused by neutralizing the 
acid of milk with oxide of zinc, thus forming in the liquid a poisonous 
lactate of zinc. 

612. Behavior of Copper ia contact with Food. — This metal suffers 
very little change in dry air, but in a moist atmosphere oxygen unites 
with it, forming oxide of copper ; and carbonic acid of the air, combin- 
ing with that substance, forms carbonate of copper, of a green color. 
Copper is easily acted on by the acid of vinegar, forming verdigris, 
or the acetate of copper, which is an energetic poison. Other vegeta- 
ble acids form poisonous salts with it in the same way. Common salt 
is decomposed by contact with metallic copper during oxidation, the 
poisonous chloride of copper being formed. AU kinds of fatty and 
oUy matter have the property of acting upon copper and generating 
poisonous combinations. Sugar also forms a compound with oxide of 
copper, — the sacharate of copper. 

613. Test. — As the salts of copper are of a green color, vessels of 
this metal have a tendency to stain their contents green. They are 
sometimes employed purposely to deepen the green of pickles, &c., 
and cooks often throw a penny-piece into a pot of boiling greens to 


intensify their color. A simple test for copper in solution is, to plunge 
into the suspected liquid a plate of polished iron, (a knife blade, for 
example,) when in a short time, (from five minutes to as many hours,) 
it will become coated with metallic copper. The solution ought to be 
only very slightly acid. Now, as acid, oU, or salt, is found in almost 
every article of diet, it is clear that this metal, unprotected, is quite 
unfit for vessels designed to hold food. 

614. Protectiou of Copper Utensils. — Yet copper has several advan- 
tages as a material for culinary utensils. It is but slowly oxidized, and 
hence does not corrode deep, scale, become thin, and finally fall into 
holes as iron vessels are liable to do. Besides, copper is a better con- 
ductor of heat than iron or tin plate, and consequently heats more 
promptly and with less fuel, and as it wears long, and the metal when 
old bears a comparatively high price, its employment, in the long run, 
is unquestionably economical. Copper vessels ought never to be used, 
however, without being thoroughly protected by a coating of tin and 
when this begins to wear off they should be at once recoated, which the 
copper or tin-smith can do at any time. It has been stated that a small 
patch of tin upon the surface of a copper vessel would entirely prevent 
the oxidation of the latter by galvanic influence ; but Mr. Mitchel has 
shown by experiment that such is not the fact, and that the only 
safeguard is in covering completely the entire copper surface. Brass 
is an alloy of zinc and copper, and although less liable to oxidize, is 
nevertheless unsafe. Kettles of brass are often employed in preparing 
sauces, sweetmeats, &c., but this ought never to be done unless they 
are scrupulously clean and polished, and hot mixtures should not be 
allowed to cool or remain in them. 

615. Enamelled Ironware Vessels. — It would seem that no one mate- 
rial possesses all the qualities desirable to form cooking vessels. 
Some of the metals are strong and resist heat ; but, as we have seen, 
various kinds of food corrode them. Earthenware, on the contrary, 
if well made, resists chemical action, but is fractured by slight blows 
and the careless application of heat. An attempt has been made to 
combine the advantages of both by enamelling the interior of ii'on ves- 
sels with a kind of vitreous or earthenware glaze. Various cooking 
vessels, as saucepans, boilers, and the like, have been prepared in this 
manner, and answer an admirable purpose. Dr. Fee remarks, I con- 
sider such a manufacture to be one of the greatest improvements 
recently introduced into domestic economy, such vessels being remark- 
ably clean, salubrious, and adapted to the delicate culinary opera- 
tions of boiling, stewing, making of jellies, preserves, &c. 



616. Earthenware Vessels — Glazing. — Vessels of earthenware are in 
universal household use. They are made, as is well known, of clay 
and sand, of various degrees of purity, witk other ingredients, forming 
a plastic mass, which is moulded into all required shapes, and hardened 
by baking in a hot furnace. The ware, as it thus comes from the 
baking process, is porous, and absorbs water. To give it a smooth, 
glossy, water-resisting surface, it is subjected to the operation of glaz- 
ing. This is effected in two ways; first, when the stoneware has at- 
tained a very high temperature, a few handfuls of damp sea-salt are 
thrown into the furnace. The salt volatilizes, the vapor is decomposed, 
the hydrochloric acid escaping ; while the soda, diffused over the sur- 
face of the ware, combines with its silica, and glosses over the pieces 
with a smooth, hard varnish. Another mode by which the desired 
artificial surface is given to earthenware, is by taking it from the fire 
when it has become sufiiciently firm and stiff, immersing it in a pre- 
pared liquid, and restoring it again to the furnace, where by the action 
of heat a vitreous or glassy coating is formed. 

617. Earthenware Glaze eontaining Lead. — The preparations employed 
for glazing common earthenware, are chiefly combinations of lead 
with the alkalies, producing vitreous or glassy compounds. It is 
known that lead enters largely into many kinds of glass ; it imparts to 
them great brilliancy -and beauty, but makes them soft, so that they 
are easily scratched, and liable to be attacked by strong chemical sub- 
stances. Lead glaze upon earthenware is also subject to the same 
objection. It is tender and can be scraped off with a knife, so that 
the plates soon become marred and roughened. They also soon black- 
en, or darken, when in contact with sulphurized substances. Cooking 
eggs or fish in these vessels gives them a brownish tinge. If less lead 
be used, the glaze becomes less fusible, the process of applying it more 
difiicult, and hence the ware more expensive. Lead glazing can be de- 
tected by its remarkably smooth, lustrous surface, resembling varnish ; 
while the salt glaze, on the contrary, has less lustre, and the vessel has 
not so fine an appearance, all the asperities of the clay beneath being 
perfectly visible. Fatty matters, and the acids of fruits, exert a solvent 
action on oxide of lead combined in lead glaze, especially where the 
chemical energy is increased by a boiling temperature. 

618. Other defects of Earthenware Glaze. — If a piece of earthenware 
be broken, we may observe upon the freshly fractured edge, the thin 
coating of glaze which has been fused on to the body of the ware. If 
the tongue be touched to tlie broken surface, it will adhere, showing 
the porous and absorbent nature of the material. Eow it often hap- 


pens that the shell of glaze and the body which it encloses, are not 
aflfected in the same way by changes of temperature. They expand 
and contract unequally when heated and cooled, the consequence be- 
ing, that the glaze breaks or starts, and the surface of the plate, sau- 
cer, or vessel, becomes covered with a network of cracks. Ware in 
such a condition is said to be crazed. Through these cracks liquid or- 
ganic matters are liable to be absorbed, which make the articles un- 
cleanly and impure. Glaze that does not crack is often too soft. To 
determine this, drop a small quantity of ink upon it, and dry before 
the fire, and then wash it thoroughly ; if the glaze be too soft, an in- 
delible brown stain wiU remain. 

619. How Porcelain-ware is made. — This is the purest and most per- 
fect product of the plastic art. "We are indebted for several suggestions 
concerning its processes to Messrs. Haviland, of this city, whose ex- 
tensive establishment in France has aflfbrded them a large experience 
in the porcelain manufacture. This ware was first made in China, and is 
stiQ known as China-ware. But, after long and difllcult experience, the 
manufacture has at length become so perfected in Europe as greatly 
to surpass the Chinese in elegance, and hence but little is now import- 
ed from that country. True porcelain consists of two essentially dif- 
ferent constituents, one of which is an infusible, plastic, white clay, 
called Molin, or China-clay, and the other an infusible but not plastic 
substance, called the Jlux, which is composed of the mineral felspar. 
Kaolin alone would afibrd a porous, opaque body ; the flux, however, 
softens in the heat of the baking furnace, and penetrates as a vitreous 
or glassy matter the whole body of the clay, completely filling up the 
pores, and covering aU the surface ; it binds the whole together into 
a dense impenetrable mass. Porcelain-ware is translucent, or permits 
the partial passage of light, which is due to the clay body being satu- 
rated as it were with glass, as transparent paper is permeated with 
on. The material is moulded with great care and nicety into the de- 
sired forms, and then, placed in cases of clay made expressly to hold 
and protect them, are put into the kiln or furnace, and subjected to 
an intense heat for 15 or 20 hours. The articles are then withdrawn 
and dipped into a glaze composed of felspar, of the same nature as 
the flux, and which never contains either lead or tin. The ware is 
then returned to the furnace and subjected to the most intense white 
heat that art can produce, for 10 or 20 hours longer. The glaze is 
thus melted into the flux, so that the porcelain has a uniform body, as 
we see when it is broken. There is no accurate mode of measuring 
the very high temperatures produced in these kilns, but by the method 


adopted, tlie heat is estimated to run up to 21,000 degrees of the 
Fahrenheit scale. The color of porcelain is milk-white, without any 
tinge of blue. The quaUties which give it pre-eminence among the 
clay wares, are the entire absence of porosity, the intimate union of 
the glaze with the mass, and the indestructibleness of the glazed sur- 
face under the knife, or when exposed to changes of temperature, and 
various chemical agencies. The production of the naked porcelain- 
ware in its present perfection, is one of the most signal triumphs of 
inventive ingenuity and perseverance, which the history of domestic 
improvement affords. But when we observe the beautiful and deli- 
cate colors with which porcelain is now ornamented, we are aston- 
ished at the resources of art. The paints or pigments with which ex- 
quisite pictures are made upon it, consist of colored glass, stained of 
various hues by metallic oxides. The coloring materials require to be 
fire-proof, as they are pamted upon the ware, and then melted into the 
flux or glaze by the heat of the furnace. 

620. Repairing brokeu Porcelain. — Various cements are in use for 
producing adhesion between fragments of broken porcelain and glass. 
A very strong cement for common earthenAvare is made by boiling 
slices of skim-milk cheese with water into a paste, and then grinding 
it with newly slaked lime in a mortar. "White of egg will cause a 
quite strong adhesion, where the objects are not exposed to moisture. 
It is however improved by mixture with slaked lime. Shellac dis- 
solved iu alcohol or in a solution of borax, forms a pretty good ce- 
ment. Various excellent cements are to be procured, ready prepared, 
of the dealers. In their anxiety to unite the fragments strongly, per- 
sons are apt to defeat their purpose by applying the cement too thick- 
ly, whereas the least possible quantity should be used, so as to bring 
the edges most closely together. This may be aided by heating the 
fragments to be joined. 

1. Basis of the Demand eoe Aliment. 

621. Creation a Continuous Work. — We are accustomed to conceive 
of the creation of man as a dim miraculous event of the most ancient 
time, half-forgetting that God's scheme of managing the living world 
is one oi perj^etual creation. Had our earth been formed of an eternal 
adamant, subject to no vicissitudes of change through all the cycles of 
duration, we might perhaps well refer to the act of bringing it into 
existence, as especially illustrative of creative power. But where all 


is changing, transitory, and incessantly dissolving away, so that noth- 
ing remains immutable, but God's conception of being, which the 
whole universe is for ever hastening to realize, we cannot escape the 
conviction of his immediate, living, omnipresent, constructive agency. 
Tlie truth is, we are hourly and momentarily created, and it is impos- 
sible to imagine in what respect the first act of formative power was 
more wonderful or glorious, or afforded any more conspicuous display 
of omnipotent wisdom, than that august procession of phenortiena by 
which man, and the entire living world, are now and continually 
called into being. Those material atoms which are to-day interposed 
between us and destruction, are recent from chaos, — they were but 
yesterday formless dust of the earth, corroded and pulverized rocks, 
or fleeting and viewless gases of the air. These, through the vast 
enginery of astronomic systems, whose impulses of movement spring 
directly from the Almighty Will, have entered a world of organic or- 
der, are wrought into new states, and made capable of nourishing the 
animal body. The mingled gases and mineral dust, have become 
vital aliment. The test-miracle which the Tempter of old demanded 
as evidence of Godlike Power, is disclosed to the eye of science, as a 
result of natural laws, for in the most literal sense, " stones are made 

622. Our Systems capable of beiug understood. — That it was designed 
for us to understand what goes on within the body, we are not at 
liberty to doubt. Instead of being the theatre of a mysterious power 
which defies investigation, we find the living system acting under 
allegiance to invariable laws, and entirely amenable to investigation. 
The whole course of physiological discovery has consisted in showing 
that the human constitution is an embodiment and illustration of 
reason. The victory of research is to understand a thing ; that is, to 
bring it into agreement with reason. The mechanism of the eye was 
a mystery, until its optical adaptations and purposes were discovered ; 
that is, the reason of its construction. The heart was an object of 
mere curious wonder and superstitious speculation, until the circula- 
tion was discovered, when the reasonable uses of its parts were at 
once understood. The whole scope and drift of past inquiry, and all 
the considerations which cluster around the subject, lead us to expect 
and demand a rational explanation of living processes. " Not many 
years ago, the most acute and distinguished physicans regarded the 
stomach as the abode of a conjurer; who, if respectfully treated, and 
in good humor, can change thistles, hay, roots, fruits, and seeds, 
into blood and flesh; but when angry, despises, or spoils the best 


food." Chemistry has dispelled these crude fancies, and enabled us 
to understand how such marvellous transformations occur. We are 
getting daily clews to the profounder secrets of the organism ; know- 
ledge is here as rapidly progressive as in any other department of 
science. In this connection Dr. Draper remarks, " Since it is given 
us to know our own existence, and be conscious of our own individu- 
ality, we may rest assured that we h&ve what is in reality a far more 
wonderful power, the capacity of comprehending all the conditions 
of our life. God has formed our understanding to grasp all these 
things. For my own part, I have no sympathy with those who say of 
this or that physiological problem, it is above our reason. My faith 
in the power of the intellect of man, is profound. Far from suppos- 
ing that there are many things in the structure and functions of the 
body which we can never comprehend, I believe there is nothing in it 
that we shall not at last explain. Then, and not till then, will man 
be a perfect monument of the wisdom and power of his Maker, a 
created being knowing his own existence, and capable of explain- 
ing it." 

623. The living System a theatre of change. — The body of the grown 
man presents to us the same unaltered aspect of form and size, for 
long periods of time. "With the exception of furrows deepening in 
the countenance, an adult man may seem hardly to alter for half a 
hundred years. But this appearance is altogether illusory ; for with 
apparent bodily identity, there has really been an active and rapid 
change, daily and nightly, hourly and momently, an incessant waste 
and renewal of all the corporeal parts. A waterfall is permanent, and 
may present the same aspect of identity, and unchangeableness from 
generation to generation ; but who does not know that it is certainly 
made up of particles in a state of swift transition ; the cataract is 
only a form resulting from the definite course which the changing 
particles pursue. The flame of a lamp presents to us for a long time 
the same appearance ; but its constancy of aspect is caused by a cease- 
less change in the place and condition of the chemical atoms which 
carry on combustion. Just so with man ; he appears an unchanged 
being endowed with permanent attributes of power and activity, but 
he is really only an unvarying form, whose constituent particles are 
for ever changing. As the roar, spray, and mechanical power of the 
falling water are due to changes among the aqueous particles ; 
and the heat and light of the flame are due to changes among com- 
bustible atoms ; so man's endowments of bodily activity, susceptibilitj', 
and force, originate in atomic transformations taking place in his 


system. As each part is brought into action, its particles perish and 
are replaced by others ; and thns destruction and renovation in the 
vital economy are indissolubly connected, and proceed together. It is 
said, with reference to the casualties to which man is every where 
exposed, that "in the midst of life we are in death," but physiologi- 
cally, this is a still profounder truth ; we begin to die as soon as we 
begin to live. 

624. Rate at wMch the vital changes proeeedt — But very few persons 
have any correct conception of the rate at which change goes on in 
their bodies. The average amount of matter taken into the system 
daily, under given circumstances, has been determined with a con- 
siderable degree of precision. From the army and navy diet-scales of 
France and England, which of course are based upon the recognized 
necessities of large numbers of men in active life, it is found that 
about 2^ lbs. avoirdupois of dry food per day are required for each 
Individual ; of this about three-quarters are vegetable and the rest 
animal. Assuming a standard of 140 lbs. as the weight of the body, 
the amount of oxygen consumed daily is nearly 2j lbs., which results 
from breathing about 25 or 80 hogsheads of air ; the quantity of 
water is nearly 4j-'o- lbs. for the same time. The weight of the entire 
blood of a full-grown man varies from 20 to 30 pounds; of this, the 
lungs, in a state of health, contain about half a pound. The heart 
beats, on an average, 60 or 70 times in a minute. Every beat sends 
forward two ounces of the fluid. It rushes on, at the rate of 150 ft. 
in a minute, the whole blood passing through the lungs every two 
minutes and a half, or twenty times in an hour. In periods of great 
exertion the rapidity with which the blood flows is much increased, 
so that the whole of it sometimes circulates in less than a single 
minute. — (Joh^tston.) According to these data, all the blood in the 
body, travels through the circulatory route 600 or 700 times in a day, 
or a total movement through the heart of 10,000 or 12,000 lbs. of 
blood in 24 hours. To assist in carrying forward the several bodily 
changes, various juices are poured out each day, according to the latest 
estimates, as follows : gastric juice, 14 to 16 lbs. ; bile, 3 to 4 lbs. ; pan- 
creatic juice, |- lb. ; intestinal juice, ^ lb. — (Dr. Ohambees.) At the 
same time there escapes from the lungs nearly 2 lbs. of cai'lonic acid 
and li oi watery vapor. The shin loses by perspiration 2^ lbs. of water, 
and there escape in other directions about 2i lbs. of matter. In the 
course of a year, the amount of solid food consumed is upwards of 800 
lbs. ; the quantity of oxygen is about the same, and that of water taken 
in various forms, is estimated at 1,500 lbs., or all together a ton and a 


half of matter, solid, liquid, and gaseous, is ingested annually. We 
thus see that the adult, of a half a century, has shifted the substance 
of his corporeal being more than a thousand times. 

625. A striking illustration of these clianges. — ^Let us take a signal 
example, which, although not falling within the limits of ordinary ex- 
perience, yet actually occurred in the course of nature. Thomas Pare, 
of England, lived to the age of 152 years. If we take the twelve 
years of his childhood, and double them over upon the succeeding 
twelve years of his youth, we shaU have 140 years of adult life, or 
twice the common allotment of man. Applying to his case then the 
established physiological constants, we get the following startling 
results of the amount of possible change in matter produced in the 
lifetime of a single man. He drank upwards of a hundred tons of 
water, ate nearly sixty tons of solid food, and absorbed from the air 
one hundred and twelve thousand lbs. of oxygen gas to act upon that 
food. There are fifteen lbs. weight of air resting upon every square 
inch of the earth's surface ; of this one-fifth is oxygen, there being 
therefore 3 lbs. of oxygen over every square inch of the earth, extending 
to the top of the atmosphere. The daily consumption by respiration 
is 2 lbs. Pake, therefore, consumed all the oxygen over a surface of 
236 square feet of ground to the very summit of the earth's atmos- 
phere, and generated noxious gases enough to contaminate and render 
unfit for breathing ten times that space, or poison a column of air 45 
miles high, having a base of nearly 2,400 square feet. If we may 
indulge in a somewhat violent supposition that the whole blood which 
was actually driven through his heart during that long period could 
have been accumulated and measured as one mass, by forming a pro- 
cession of vehicles, each taking a ton and occupying two rods of space, 
such a procession would have attained the enormous length of 2,000 

626. Relation between Waste and Supply. — Such is the ground of our 
daily requirement for food. The annual supply of 3,000 lbs. of mattei 
to the body is demanded, because in the yearly exercise of its powers 
and functions 3,000 lbs. of matter have been used up or spent. It 
cannot be maintained for a moment that the bodily system possesses 
any power of producing or creating a single particle of the matter 
which it uses ; it must receive every thing from without, and maintain 
its uniform condition of weight by striking an exact balance between 
waste and supply, receipt and expenditure. There are two periods in 
the natural life of man when the balance between these antagonizing 
forces is overturned ; in infancy, childhood and youth, the reception 


of matter prevails over its loss, and the body steadily augments in 
weight ; in old age reparation does not keep pace with decay, and the 
bodily weight gradually declines. In the intervening period of adult 
life these antagonizing forces are maintained with but little variation 
in a state of constant equilibrium. In all the deepest recesses of the 
body, in every springing muscle, and conducting nerve and connecting 
tissue, and even the thinking brain, myriads of atoms are continually 
passing into the condition of death, while by the profoundest law of 
physiological life an exactly equal number are constantly introduced 
to replace them, each of its proper kind and in its appropriate place. 

626. Practical inference from these facts. — As thus the living being is 
the result and representative of change on a prodigious scale, the 
question of the course, rate, and regulation of those changes must be 
controlling and fundamental. Matter is introduced into the system in 
one condition and escapes from it in another ; the change [metamor- 
plioda) that it has undergone is oxidation, or a ti'ue burning. The 
solid aliment is all combustible, oxygen is the agent which burns or 
destroys the food by uniting with it, and water the medium which 
brings them into proper relation to act on one another. Hence the 
life, activity, and multiform endowments of the organism, originate 
in the chemical action and reaction of prepared matter, borrowed 
temporarily from the outward world to be quickly restored to it again. 
And as the supply of nutritive matter is effected through our own 
voluntary agency ; as we select, mingle and prepare the nutritive mate- 
rials, and control the times, frequency, quantity and condition in which 
they shall be taken, and influence their physiological results in num- 
berless ways, it is clear that our practice, whatever it may be, must 
exert a direct and powerful influence upon the whole being ; its states 
of feeling, conditions of action, health, and disease. It is desirable 
therefore to gain the fuUest possible understanding of the subject. 

627. Beneficent use of Hanger and Thirst. — It will be seen from the 
nature of the case, that the necessities of the system for matter from 
without, are pressing and momentous. If the inflowing tide of gases 
be arrested but for a few moments, suffocation and death foUow. If 
the liquid and solid aliments be withheld, indescribable agonies shortly 
ensue, and in a few days the extinction of life. There is, therefore, 
an irresistible life-demand for the supply of nutriment which cannot 
be put off upon peril of existence, while the cost of nutritive matter 
is laborious struggle and exertion, both of body and mind. Now it is 
plain, that if in the plan of our being the bodily requirement for food 
were left to the determination of reason, the purposes of nature would 


be liable to continual defeat from indolence, carelessness or urgency 
of occupations. The Divine Architect has therefore wisely intrenched 
in the system two monitors, hunger and thirsty which are independent 
of reason or will, cannot be dislodged while life lasts, and whose duty 
it is to proclaim that further nourishment is required for bodUy sup- 
port. And beside the sensations of hunger and thirst, imperative as 
they are, there is attached to their proper indulgence a degree of 
pleasure which never fails to insure attention to their demands. In 
what hunger and thirst consist, what state of the stomach or vessels 
produces them, or how the general nutritive wants of the sys- 
tem get expressed in feeling or sensation, we do not know ; several 
explanations have been offered upon this point, but they are all un- 

628. Impelled by the demands of the constitution food is procured, 
and in several ways, which have been described, prepared for use. 
"When taken into the system it is subject to various changes iu a cer- 
tain natural and successive order, which will next be noticed. 

2. FiEST Staoe of Digestion — Changes of Food in the Mouth. 

629. The great ol«ect of Digestion, — The prepared food upon our tables 
is in the form of crude, unmixed, and chiefly solid masses. Various 
vegetables, breads, meats, butter, each with its peculiar constituents 
and properties, are ready for use. Their physiological purpose is to 
make blood, the source upon which the whole system draws for what- 
ever it requires. The blood contains every thing necessary to form aU 
the parts, and produce aU the peculiar hquids or secretions of the 
body. It circulates rapidly through every portion of the system, 
bearing all the constituents that can be required, while each part is 
endowed with the special power of withdrawing from the current as 
it passes along, just those particular constituents that it may require ; 
compounds of lime for bones and teeth, sulphurized compounds for the 
muscles, and phosphorized for the nerves, whUe various parts separate 
the liquids of secretion — the glands of the mouth attracting out the 
substances necessary to form saliva, those of the eyes the elements of 
tears, the coats of the stomach, gastric juice, and the liver, bile. The 
blood is a magazine of materials comprehensive enough for every want 
of the body, and all brought to a perfectly fluid condition, so as to 
flow with facility through the minutest vessels. Now, it is obvious 
that the food before us must be profoundly changed before it can be- 
come blood. No one element of diet contains all the necessary ma- 



terials for this purpose ; the various articles must, therefore, he mixed. 
Some of the elements of food are incapahle of forming blood ; these 
require to be separated, and the entire nutritive portion brought into 
a state of perfect liquidity. To effect these important changes in food 
is the great purpose of digestion, which presents itself to our conside- 
ration in three distinct stages, commencing with transformations pro- 
duced in the mouth. 

680. Redacing Slecbanism of the Mouth. — The food, liquefied or soft- 
ened, or with its texture relaxed, loosened, or made spongy by culi- 
nary methods, is reduced to small pieces by table instruments, and 
thus transferred to the mouth. An ingenious cutting and grinding 
mechanism here awaits it, to complete the mechanical operation of 
crushing and reducing. It consists of a double system of teeth, 
planted firmly in the jaws, and made to work against each other by a 
set of powerful muscles. The 
teeth are so shaped and placed 
as to combine cutting, crushing 
and grinding, through vertical 
and side movements of the low- 
er jaw. The teeth are 32 in 
number, and their differences 
are illustrated by Fig. 113, which 
represents half the lower jaw. 
A shows two of the front or 
cutting teeth, called incisors; 
B the cuspid., canine, or dog tooth, so called from being large in the 
dog and carnivorous animals, and used by them to seize and tear their 
food ; G the ticuspids or double-speared, from their resemblance to a 
double-headed canine tooth ; and D the molars, double-rooted, with 
broad, irregular, grinding surfaces.* 

631. Conditions of the flow of Saliva. — But no amount of mechani- 
cal action alone wUl convert solid aliment into the fluid state. If the 
food is to be dissolved, there must be a solvent or liquid to bring about 
the solution. It is the office of the saliva or spittle to commence this 
work. The saliva is separated from the blood and poured into the 
mouth by three pairs of glands (Fig. 114). The rate at which it is 
secreted varies at different times and under different circumstances. 
The sight, or even the thought of dinner may fill the mouth with it, 
while continued mental attention to other subjects, or a state of anxi- 

*" In Latin, cuspis signifies the point of a spear ; cants, dog ; mola, a mill ; incisor 
anything which cuts." 

Illustration of the different kinds of Teeth. 



Fig. 114. 

ety, will dry it up. The movements of the mouth, as in speaking, 
reading, or singing, excite its flow, but it is most copiously furnished 
at times of eating, by the contact and pressure of food during masti- 
cation. Hence, the glands on that side of the mouth which is most 

used in mastication, secrete more than 
the others. The nature of the food 
causes the quantity furnished at meals 
to vary exceedingly ; hard, dry ali- 
ments provoking a much greater dis- 
charge than those which are moist 
and soft. It streams out abundantly 
under the stimulation of spices, and 
continues to flow after the meal is 
concluded ; the secretion also goes on 

^^JT^V/I |i wr 632. Properties.— The saliva is a 

^k *'^ f f I f\i' clear, slightly bluish, glairy juice, 

It ^1 \ ^ I readily frothing. It contains less 

\ H ^ ^^^'^ ^^® P®^" cent, of saline matter, 

' *l and in health is always alkaline. It 

Salivary glands; a parotid, 6 submaxil- contains also an organic principle 
lary, c sublingual. named ptj/alin, an albuminous sub- 

stance which acts as a strong ferment. The tartar which collects 
on the teeth is the residue left by evaporation of the water of the sa- 
liva, and consists of earthy salts, cemented together by animal matter. 
The salivary juice of the mouth is, however, a mixture of three difl:er- 
ent salivas poured out by three pairs of glands. Parotid saliva is thin 
and watery, so as to be readily incorporated with the food by the 
teeth ; it also contains much lime. Submaxillary saliva is so thick 
and glutinous that it may be readily drawn out into threads. It is 
supposed to facilitate swallowing by affording a sort of anti-friction 
coating to the masticated food. The sublingual saliva is more limpid, 
resembling the parotid. 

633. Uses of Saliva. — Saliva serves not only to moisten and lubri- 
cate the mouth, and wet the aliment, so that it may assume a pasty or 
pulpy condition, but it is an indispensable medium for the sense of 
taste, as every thing is tasteless which the saliva cannot dissolve. By 
its frothy quality it embroils globules of air, and thus serves to convey 
oxygen into the stomach, where it probably plays a part in promoting 
the transformations. But beyond these important effects, the saliva 
actually begins the operation of digestion in the mouth. If a little 


pnre starch be chewed for a short time, it will become sweet ; a por- 
tion of it has undergone a chemical transformation, and been con- 
verted into sugar. By its joint alkaline and fermentative powers, 
saliva produces an almost instantaneous effect upon starch, changing 
it first into sugar, and in a little longer time converting the sugar into 
lactic acid. This important change seems to be effected, not by any 
one of the salivary secretions, but is due to their combined action. 
Saliva exerts no solvent influence upon the nitrogenous aliments. It 
will thus be noticed that the first chemical attack, at the very thresh- 
old of the digestive passage, is made upon that alimentary principle 
which abounds most of all in our food (382). We furthermore draw a 
practical inference opposed to the current opinion which assumes that 
animal food, from its tough, fibroas nature, needs more mastication 
than vegetable. Meat and albuminous substances require to be thor- 
oughly disunited and subdivided in order that each particle may be 
brought into contact with the secreting membrane of the stomach, 
while bread, and substances which abound in starch, have not only to 
be reduced fine, but to be well imbued with the salivary liquid. In 
animal food, it is possible to supply the place of mastication by the use 
of implements in the kitchen and at the table ; but culinary science 
cannot compound an artificial saliva to be mixed with starchy food, so 
as to save the trouble of chewing it. The changing of this substance 
from a solid to a liquid form, as in gruel and sago slops, so that they 
are swallowed without being delayed in the mouth and mingled with 
its secretions, is unfavorable to digestion, especially if the stomach be 
not vigorous. The best condition in which starch can be taken is 
where the outer membrane has been ruptured by heat, and the mass 
made light, as in well-baked bread and mealy potatoes (532). 

684. Importance of thorough Mastication. — ^The mechanism of insali- 
vation has been inserted in the mouth for a definite and important 
purpose, and as the act of mastication is under the control of the will, 
it is very easy to defeat that purpose. If the food be imperfectly 
chewed, and hastily swallowed, or as the phrase goes, ' bolted,' the 
aliment passes into the stomach crude and iU-prepared, and the whole 
digestive function is just so far imperfect and enfeebled. It is of much 
consequence that meals should not be precipitated, but that proper 
time should be allowed to perform that portion of the digestive opera- 
tion, which falls so directly under voluntary control. Besides thought- 
lessness, and business pressure which pleads want of time, there is an- 
other cause of inattention to this matter which deserves notice. Many 
persons have placed themselves in such a false relation to nature, as 


to imagine that they exalt the spiritual attributes of their being by 
casting contempt upon the physical. Such are inclined to regard the 
act of eating as a very animal and materializing operation, and any 
considerations of the way it should be conducted, are apt to weigh 
but lightly upon their minds. This view is false, and leads to conse- 
quences practically mischievous. Dr. Combe remarks, — " Due mastica- 
tion being thus essential to healthy digestion, the Creator, as if to insure 
its being adequately performed, has kindly so arranged that the very 
act of mastication should lead to the gratification of taste — the mouth 
being the seat of that sensation. That this gratification of taste was 
intended, becomes obvious when we reflect that even in eating, nature 
makes it our interest to give attention to the process in whica we are 
for the time engaged. It is well known, for example, that when food 
is presented to a hungry man, whose mind is concentrated on the in- 
dulgence of liis appetite, the saliva begins to flow unbidden, and what 
he eats is consumed with a peculiar relish. "Whereas, if food be pre- 
sented to an individual who has fasted equally long, but whose soul is 
absorbed in some great undertaking or deep emotion, it will be swallow- 
ed almost without mastication, and without sufficient admixture with 
the saliva — now deficient in quantity — and consequently lie on the 
stomach for hours unchanged. A certain degree of attention to taste 
and the pleasures of appetite is, therefore, both reasonable and bene- 
ficial ; and it is only when these are abused that we oppose the inten- 
tion of nature." 

635. Effect of profuse Spitting, — The salivary juices are parts of a 
great water circulation of secretion and absorption. They are poured 
into the mouth, not to le cast out, but to do a specific work, and then 
pass into the stomach and be again absorbed. If they are habitually 
ejected by spitting, the object of nature is contravened, and the sys- 
tem drained of that which it was not intended to lose. In such case 
the order of bodily functions is reversed, and the mouth is converted 
into an organ of excretion. It is the oflBce of the kidneys and urinary 
ducts to convey away a large part of the superfluous water, and all 
the waste salts that require to be expelled from the body ; but if a 
drain be established at the mouth, the effect is to relieve those parts 
of a portion of their labor. " When the impure habit of profuse spit- 
ting is indulged in, it is interesting to remark the reflected effect which 
takes place in the reduced quantity of the urinal excretion, and an in- 
stinctive desire for water, a kind of perpetual thirst. It is probable 
that, under these disgusting circumstances, the percentage amount of 
saline substances in the saliva is increased, and that, so far as that 



class of bodies is concerned, the salivary glands act vicariously for the 
kidneys, and the mouth is thus partially converted into a urinary 
aqueduct."— (Dr. Dkapee.) 

3. Second SiAaE of Digestiok— Change of Food m the Stomach. 

636. Figure and Dimensions of the Organ. — Having undergone more 
or less perfectly the changes which appertain to the mouth, the food 
is swallowed, and pass- Fig. 115. 

ing down the esopha- 
gus, or gullet, enters 
the stomach. This or- 
gan is a pouch-shaped 
enlargement of the di- 
gestive tube, having 
the form shown in Fig. 
115. The larger ex- 
tremity is situated at /ji 
the right side of the 
body, and its lesser end 
at the left. 

tion where the esoph- 
agus enters it, is termed the cardiac region (because it is in the vicin- 
ity of the Jcear or heart) ; the other extremity, where the contents of 
the stomach escape into the intestine, is known as the pyloric region 
(from pylorus^ a gate-keeper). The capacity of the human stomach 
of course varies considerably, but on an average, it wiU hold when 
moderately distended about three pints. As a general rule, it is larger 
among those who live upon coarse, bulky diet. In different animals 
the size of the stomach varies exceedingly, according to the concen- 
tration of the food upon which they live. Thus in the flesh-eating 
animals it is very small, only a slight enlargement of the esophagal 
tube ; while in those which feed upon herbage, it is distended into 
an enormous cavity, or rather into several, as in the ruminants, cows, 
sheep, &c. 

637. Layersof the Stomach. — The walls of the stomach consist of 
three membranous coats. The outer layer is a smooth, glistening, 
whitish membrane (serous membrane), lining the abdomen, and cover- 
ing all the internal organs, which it strengthens, and by its smoothness 
and constant moisture, permits them to move upon each other with- 
out irritation. The middle coat consists of two layers of muscular 
fibres or bands, one of which runs lengthways, and the other crossways, 

„, Section of the human stomacli : a esophagus ; & c cardiac 

i Jiat por- orifice ; d e greater curvature ; / g lesser curvature ; h 
pyloric orifice ; ij duodenum ; h bile duct.. 


or around the organ. By means of these muscles the stomach may 
contract its dimensions in all directions, so as to adapt its capacity to 
the amount of its contents. They also give to the organ its constant 
motion during digestion. The third layer of the stomach {mucous mem- 
hrane) lines its internal surface. It is a soft, velvet-like memhrane, 
of a pale pink color, in health, and of much greater extent than the 
outer coats, by which it is thrown into folds or wrinkles. It is con- 
stantly covered with a thin, transparent, viscid mucus. 

638. Motious of the Stomach. — The food upon which operations have 
been commenced in the mouth, is passed into the stomach, but it is 
not permitted to rest. By the successive contraction and relaxation of 
its muscular bands, the stomach imparts to its contents a constant 
churning, or revolving motion. In the celebrated case of St. 
Maktest, a Canadian soldier, whose stomach was opened by a gunshot 
wound in the side, and healed up leaving a permanent orifice (gastrie 
fistula), Dr. Beaumont made numerous observations of digestive 
phenomena. He thus describes the movements of food within the or- 
gan. " After passing the esophagal ring it moves from right to left along 
the small arch ; then through the large curvature from left to right. The 
bolus (swallowed mouthfiU), as it enters the cardiac, turns to the left, 
descends into the splenic extremity (large extremity near the spleen), 
and follows the great curvature towards the pyloric end. It then re- 
turns in the course of the smaller curvature, performing similar revolu- 
tions. These revolutions are completed in from one to three minutes. 
They are slower at first, than after digestion is considerably ad- 
vanced." The motion is not absolutely constant, but continues for a 
few minutes at a time. If the food remains in the stomach three 
hours it travels round and round through this circuit two or three 
hundred times : — to what purpose? 

639. Minute arrangements for Stomsich Digestion. — Before considering 
what takes place in tlie stomach, we must have a closer view of its 

mechanism. The lining layer of this organ is curi- 

J-^ ' ously and admirably constructed, though it requires 

^^^gote^ the microscope to see it. Magnified about 70 

•WBroWSIJ^S: ^i^^sters the mucous membrane exhibits the honey- 

-a^^^^.^M^/ combed appearance seen in Fig. 116. Into these 

reticulated spaces, there open little cup-shaped 

cavities called stomach follicles, which are about 

1*200 of an inch in diameter. They are closely 

packed together in the mucous membrane, so that 

when it is cut through, and viewed with the microscope, it looks 



Fig, 117. 

like palisading, or like little flasks or test-tubes close packed and up- 
right ; many thousands of these upright cylindrical cavities being 
set in a square inch of surface. They are of different depths in 
different parts of the stomach, and they terminate at the bottom in 
minute closed tubes. The arrangement has been 
likened to a little glove, the hand of which opens 
into the stomach, while the fingers are buried in 
the tissue beneath. Fig. 11 '7, represents the se- 
creting foUicles in the stomacJi of a dog after 
twelve hours' abstinence ; a, from the middle re- 
gion of the stomach ; &, from near the pylorus ; c d, 
the mouths opening upon the surface, e /, the closed 
tubes imbedded in the membrane below. The walls 
of these cavities are webbed over with a tissue of 
most delicate bloodvessels, carrying streams of blood 
— a network of veins surrounds their outlets upon 
the surface of the membrane, while nerves innu- 
merable pervade the whole arrangement. 

640. Use of these little pocket-shaped vessels. — ^What, now, is the 
purpose served by these interesting little contrivances ? It is to 
separate from the blood the digestive fluid of the stomach. But they 
do not eflect this directly ; another agency, — that of cells (49 6), — is 
called into play. The gastric juice does not simply ooze or distil 
from the blood into the stomach. It is manufactured by a determi- 
nate process. "For each minutest microscopic drop of it, a cell of 
complex structure must be developed, grow, burst and be dissolved." 
At the bottom of the cavities, in the little tubulai' roots, the seeds or 
germs of cells arise in immense numbers. Eecurring to the simile of 
the glove, within each finger, at the tip and upon its sides, the cells 
take origin, and, nourished by the blood, multiply and sweU untU 
they are driven up in crowds into the hand or larger cavity, and hav- 
ing reached their fuU maturity, are pushed out at the surface, burst, 
and deliver their contents into the stomach. 

641. The periodic supply of Food. — The digestive principles are thus 
a product of cell-action, and into their preparation there enters the 
element of time. Though short-lived, a certain period must elapse 
for their production. During digestion the cells are perfected in in- 
credible munbers, and yield large amounts of fluid. During fasting, 
no fall-grown cells escape ; the tubes collapse, and an opportunity is 
allowed for the production of a new stock of germs or ceU-grains. If 
this be 60, it must follow that we cannot with impunity interfere with 



that whicli seems a natural rule, of allowing certain intervals between 
the several times of eating. Every act of digestion involves the con- 
sumption of some of these cells ; on every contact of food some must 
quipkly perfect themselves, and yield up their contents ; and without 
doubt, the design of that periodical taking of food, which is natural to 
our race, is, that in the intervals, there may be time for the production 
of the cells that are to be consumed in the next succeeding acts of di- 
gestion. We can, indeed, state no constant rule as to the time re- 
quired for such constructions ; it probably varies according to age, the 
kind of food, the general activity or indolence of life, and above all, ac- 
cording to habit ; but it may be certainly held, that when the times 
are set, they cannot with impunity be often interfered with ; and aa 
certainly, that continual or irregular eating is wholly contrary to the 
economy of the human stomach. — (Paget.) 

648. Properties of Qistric Juice. — The digestive juice of the stomach 
is a colorless, inodorous, slightly viscid fluid, which when removed 
from the organ, retains its active properties for a long time, if kept 
excluded from the air. A boiling heat destroys its activity, but freez- 
ing does not. In a healthy state, it is always distinctly sour, which is 
caused by an uncombined acid, usually the hydrochloric, but some- 
times lactic acid. With its acid principle, the gastric juice also con- 
tains a peculiar albuminous body called ' pepsin ' or ' ferment sub- 
stance.' If the juice be evaporated to dryness, this pepsin constitutes 
three-fourths of the solid residue. As the food is roUed round in the 
stomach, it is incorporated with this juice, and changes gradually to 
a pulpy semi-fluid mass. Digestion is fully under way in an hour 
after the meal is taken, and is usually finished in about four. 

644. Limit of Stomacli Digestion. — Recent physiological investigations 
have exploded the opinion long entertained, that the stomach is the 
exclusive or principal seat of digestive changes. In tracing the 
properties of foods, we had occasion to divide them into two great 
classes based upon fundamental differences in chemical composition — 
the nitrogenous and the non-nitrogenous aliments. We find this dis- 
tinction recognized by nature in arranging her plan of digestion. So 
different are these two kinds of aliments that they require totally 
different agents to dissolve them, — nay, solvent fluids of entirely 
opposite characters. We have seen that digestion began in the mouth 
with an alkaline liquid, and took eflfect only upon the non-nitrogenou3 
principles. Upon proceeding to the stomach we find new conditions — 
an acid liquid replaces the alkaline — the changes that commenced in 
the mouth are partially or totally suspended, the non-nitrogenous com- 


pounds remain unaltered, the gastric fluid taking effect only upon 
nitrogenous substances. 

645, Action of the Acid and Ferment. — If coagulated white of egg 
be placed in water acidulated with hydrochloric acid, no solvent 
action takes place at common temperatures for a long time. If the 
temperature be raised to 150°, a slow dissolving effect begins, which 
is much increased at the boiling heat. But if a Httle ' pepsin-' be 
added to the liquid the solution goes on actively, so that the pepsin, 
as it were, replaces the effect of a high temperature. An ounce of 
water mixed with twelve drops of hydrochloric acid and one grain 
of pepsin, will completely dissolve the white of an egg in two hours 
at the temperature of the stomach (100°). It acts in the same manner 
on cheese, flesh, vegetable gluten, and the whole nitrogenous group, 
changing them to the Uquid form. These are the results of an arti- 
ficial gastric juice, but they are esa^itly the same in Tcind as those 
which take place in the stomach. Drs. Bidder and Schmidt, whose 
researches upon digestion are the most recent and extensive, have 
shown that gastric juice withdrawn from the stomach and placed in 
vials, produces upon food precisely the same alterations as occur in 
the stomach, only much more slowly. In consequence of the motions 
of the stomach turning the aliment round and round, and the flow of 
the secretions which constantly washes away the dissolved parts and 
exposes fresh surfaces, the action proceeds about five times faster 
within the body than without, but the nature of the results is iden- 

646. What is the Digestive Ferment Substance 1 — There has been much 
controversy about pepsin ; what is it ? A substance in the gastrio 
fluid discovered by Sohwan a few years ago, and supposed to be a 
peculiar principle specially prepared for digestive purposes. It may 
be obtained from gastric juice, or by soaking the membrane of a calf's 
stomach {rennet). "When proper means are taken to separate and dry 
it, it appears as a yellow gummy mass. Its potency for digestive pur- 
poses was proved by "Wasmann, Avho showed that a solution containing 
only l-60,000th part, if slightly acidulated, dissolves coagulated albumen 
in six or eight hours. Liebig- is, however, disinchned to regard pepsin 
as a peculiar digestive agent. He maintains that the fermentative 
change of digestion is due to minute parts of the mucous membrane of 
the stomach, separated and in a state of decomposition. The surface 6f 
that membrane is Uned with what is called epithelium^ composed of 
exceedingly thin filmy cells ; and physiologists have discovered, that 
during digestion it separates completely from the other layers of the 


membrane. This epithelium, acted on by the oxygen swallowed in 
the frothy saliva, excites the digestive fermentation attributed to 
pepsin. It may be remarked that this stomach fermentation cannot 
change the starch of food into alcohol and carbonic acid, nor give rise 
to gases, although in morbid conditions of the organ other fermenta- 
tions may arise in the alimentary mass. 

647. Gastric Digestion sometliing more than Solution. — ^It was formerly 
thought that digestion was simply solution, or change of alimentary 
matter to the liquid state ; but late investigations inform us that nu- 
tritive substances are more than dissolved, they are really altered in 
properties. The nitrogenous matters are not only dissolved, but are 
so modified as to remain dissolved. In ordinary solution a solid body 
is changed to a liquid by the action of another liquid or solvent ; but 
when the solvent is removed the dissolved substance again resumes its 
sohd condition. Not so, however, in gastric digestion ; the digestive 
fluid dissolves albumen, fibrin, casein ; but as it cannot accompany them 
to maintain them in this state, it impresses upon them a stiU further 
change, by which they continue soluble. Casein in milk, and liquid 
albumen are already dissolved when swallowed ; but they are not 
digested, and the first act of the stomach is to coagulate or solidify 
both. They are then dissolved again, and so altered as to retain the new 
condition under circumstances which would have been before impos- 
sible ; while their capabihty of being absorbed, so as to pass into the 
blood, is greatly increased. The term '■peptone ' has been given to 
nitrogenous matters changed in this way ; thus albumen produces 
an albumen-peptone ; fibrin, a fibrin-peptone ; and casein, a casein- 
peptone, — substances which have lost the power of coagulating or 
setting into a jelly as they did when dissolved before. It has been 
found that oil plays a part in the changes by which the peptones are 
produced ; so that, although oily matters are certainly not themselves 
digested in the stomach, they are made to serve a useful purpose in 
passing through it. The nitrogenous matters are not chemically 
altered, except perhaps by combining with water. 

648. Action of Saliva in the Stomach. — The alkaline saliva attacks 
the sugar and starch in the mouth, and has the power of rapidly 
changing the starch into sugar, and that into lactic acid. But the 
food tarries only a few moments in the mouth ; charged with its alka- 
line solvent, it descends into the acid region of the stomach. But 
acids and alkalies cannot get on together. They either kill each 
other, or if one is the sti'ongest or most abundant, it destroys the 
other, though not without injury to itself. Hence, whenever the saliva 


and gastric juice come into contact, the former will be neutralized by 
the excess of the latter, and a stop put to its action. Yet this does 
not occur instantaneously, as the food is swallowed. The effect of the 
gastric juice is superficial, acting at nrst upon the food where it comes 
in contact with the bedewed coats of the stomach, whUe the saliva, in- 
corporated within, is allowed a little time foi- action. In this limited 
sense there may be two digestions going on in the stomach, although 
gastric digestion speedily overpowers and suspends the salivary. It 
is interesting to remark that lactic acid may replace hydrochloric in 
stomach digestion, and that if from any cause the latter is not suppUed 
in due quantity, the saliva, acting upon the contents of the stomach, 
will generate the required substitute. 

649. Qaantity of Gastric Juice secreted. — There has been, and indeed 
there stUl is, much doubt upon this point ; but it is now generally con- 
ceded that former estimates ranged much too low. The hourly de- 
struction of fibrin throughout the system, in average muscular action, 
has been assumed at 62 grains, and it has been found that 20 
parts of gastric juice are needed to dissolve one part of dry nitro- 
genous matter. To digest this quantity only, some 60 or 70 ounces 
of the fluid would be required. It is obvious that the natural quanti- 
ty must much exceed this, as a considerable portion vsdU be neutralized 
by the saliva, and much inevitably escapes into the intestines. But 
observation indicates quantities greatly higher than any calculated re- 
sults. In the case of dogs, Biddee and Schimxdt found from experi- 
ment the proportion to be one-tenth of their weight. This proportion 
applied to man would give a daily secretion of 14 lbs. Dr. GEUira- 
WALDT has however quite recently had an opportunity of determining 
the quantity yielded by the human body, in the case of a stout, healthy 
peasant girl, weighing 120 lbs., who had a fistulous opening in her 
stomach, from childhood, that did not in the least degree interfere 
with her general health. His experiments gave the astonishing result 
of 31 lbs. of the gastric secretion in 24 hours, or one-fourth the weight 
of the body. Making every possible allowance for error in these in- 
vestigations, we must conclude that the quantity of digestive fluid 
poured out each day must, at any rate, be very large. 

650. Digestibility of Foods. — By this we understand their capability of 
yielding to the action of the digestive forces, the joint result of seve- 
ral distinct chemical agents fitted to act upon special constituents of 
the food, and brought into play throughout the whole alimentary 
tract. Digestion is therefore an affair of many conditions, and its re- 
sults are by no means capable of being so simply stated as has been 


formerly believed. What goes forward in the stomachy although of 
great importance, affords but a partial view of the whole operation. 
Dr. Beaumont made an admirable series of observations upon this 
organ, and did much to advance the inquiry. Yet the value of his 
observations was diminished by the imperfect knowledge of his time, 
for we see him constantly misled by the conviction that there is but 
one digestive agent, the gastric juice, and but one digestion, that in 
the stomach. "We speak of his time, as if he might have lived long ago. 
Measuring the time by the course of investigation, he did live long 
ago. The history of science has a chronology of deeds, and marks off 
time by what has been accomplished. Dtjfat, announcing the first laws 
of electricity, in 1737, stood much nearer Thales, of ancient Greece, 
rubbing his piece of amber, than to Prof. Moese, patenting the electro- 
magnetic telegraph, in 1837. Within a quarter of a century, organic 
and animal chemistry have risen to the position of separate and in- 
dependent branches of science ; and it is hardly an exaggeration to say 
that more has been done to elucidate the subject of digestion in the 30 
years that have elapsed since Dr. Beaumont began his experiments, 
than was accomplished by all the physiologists who preceded him, 
though we are far enough yet from any thing like a clearing up of the 
subject. Eegarding digestion comprehensively, as the blood-forming 
function, we are to take into account not only the solubility of ali- 
ments, but their conformability to the blood. If two substances are 
dissolved with equal ease, that wiU be the more digestible which haa 
the greatest similarity to some constituent of the blood. Gum, for 
example, is much more easily dissolved than fat, yet the latter is a 
constant constituent of blood, while the former is never found there. 
Gum, to be made available, must pass through a series of transforma- 
tions, — sugar, lactic acid, butyric acid, while fat passes into the circu- 
lation without decomposition. " If the conformity of two alimentary 
principles with the constituents of the blood is equal, the more soluble 
is the more digestible. Soluble albumen and fibrin stand equally near 
to the blood, both being contained in it ; as the soluble albumen is 
however more readily dissolved in the digestive juices than fibrin, the 
digestion of the latter is more difficult." We thus see that the diges- 
tibility of foods is not the mere matter of the time of solution in the 
stomach that has been generally supposed, but involves much more. 
Meanwhile, Dr, Beaumont's statements of the periods which various 
alimentary substances require to break down into chyme in the 
stomach, may be serviceable, if received with due restrictions. We 
subjoin an abstract. 





Pig's feet, sotised 

Tripe, soused 

Trout, salmon, fresh. 

Apples, sweet, mellow 
Venison, steak 

Apples, sour, mellow. 
Cabbage with vinegar 
Codfisii, cured, dry 

Eggs, fresh 

Liver, beefs, fresh. 




Turkey, wild 

" domesticated 

Potatoes, Irish 


Pig, sucking 

Meat hashed with ) 

vegetables j 

Lamb, fresh 


Cake, sponge 


Beans, pod 


Chicken, full-grown . . 
Apples, sour, hard. . . . 

Oysters, fresh 

Bass, striped, fresh . . . 
Beef; fresh, lean, rare 

Corn cake 

Dumpling, apple. 

Eggs, fresh 

Mutton, fresh.... 



h. m. 








1 SO 


1 80 


1 80 

Broiled . . . 

1 35 


1 45 


2 — 


2 — 

Boiled. .... 

2 — 


2 — 


2 — 


2 — 

Boiled .... 

2 — 


2 15 


2 18 


2 25 

Eoasted . . . 

2 30 


2 30 

Boiled .... 

2 80 


2 80 

"Warmed. . . 

2 80 

Broiled. . . . 

2 30 

Eoasted . . . 

2 30 


2 30 


2 30 

Boiled .... 

2 30 

Baked. .... 

2 45 


2 46 

Eaw J 

2 50 


2 55 


3 — 

Eoasted. .. 

3 — 


3 — 


8 — 


3 — 

Boiled soft. 

3 — 


3 — 

Boiled .... 

3 _ 

Pork, recently salted. . 

Soup, chicken 

Oysters, fresh 

Pork, recently salted . 

Pork steak 

Corn bread 

Mutton, fresh 

Carrot, orange 

Sausage, fresh 

Beef, fresh, lean, dry. . 
Bread, wheat, fresh. . . 


Cheese, old, strong 

!^gs, fresh 

Flounder, fresh 

Oysters, fresh 

Potatoes, Irish 

Soup, mutton 

" oyster 

Turnip, flat 


Corn, green, & beans. . 

Beef, fresh, lean 

Fowls, domestic 

Veal, fresh 

Soup, beef, vegeta- ( 
bles, and bread ( 

Salmon, salted 

Heart, animal 

Beef, old, hard, salted 
Pork, recently salted . 
Cabbage, with vinegar 

Ducks, wild 

Pork, recently salted . 

Suet, mutton 

Veal, fresh 

Pork, fat and lean .... 

Suet, beef fresh 





h. m, 
3 — 

Boiled .... 

3 — 


3 15 

Broiled. . . . 

3 15 


3 15 


8 15 


3 15 

Boiled .... 

3 15 


3 20 

Eoasted . . . 

8 M) 


3 80 


8 80 


8 80 

Hard boird 

3 80 


8 80 


8 80 

Stewed . . . 

3 30 


8 30 


3 30 


3 30 


8 30 

Boiled .... 

8 45 

Boiled .... 

8 45 


4 — 


4 — 

Eoasted.. . 

4 — 

Broiled . . . 

4 — 

Boiled .... 

4 — 

Boiled .... 

4 — 


4 — 

Boiled .... 

4 15 


4 15 


4 30 

Eoasted.. . 

4 80 

Boiled .... 

4 80 

Boiled .... 

4 80 


4 80 

Eoasted.. . 

5 15 

Boiled .... 

5 30 

Boiled .... 

5 80 

651. Absorption from the Stomacb. — The power possessed by liquids 
and gases of penetrating and passing througti membranes, is of the 
highest physiological importance ; indeed it is one of the primary 
conditions of life. The little cell, the starting-point of organization, 
is a closed bag — without an aperture. All its nourishment must 
therefore pass through its membranous wall. So also with the perfect 
animal body. Currents and tides of juices are constantly setting this 
way and that, through the membranous sides of vessels. The liquefied 
food is destined to pass into the blood, but there is no open door 
or passage by which it can get there, and so it enters the circu- 
lating vessels by striking at once through their sides. In this way, 
water drank is absorbed by the minute veins distributed over the sur- 
face of the stomach, and enters the circulatory current directly. This 



is proved by the fact that when the outlet to the stomach is closed by 
tying the pyloric extremity, water which has been swallowed rapidly 
disappears from the organ, and medicines taken produce their effects 
upon the system almost as promptly as under natural circumstances. 
In the same way portions of sugar, lactic acid and digested nitro- 
genous substances, which are dissolved in water, pass into the blood 
by absorption through the stomach veins. The contents of the stomach 
thus leave it in two directions, — a portion is absorbed through the 
coats of the organ, while the unabsorbed matters gradually ooze 
through the valvular opening that leads into the intestine. 

4. Thied stage op Digestion — Changes of Food in the Intestines. 

652. Digestiye Jniees of the IntvCiinal Tube. — The partially digested 
food dismissed from the stomach enters the duodenum, the first por- 

FiG. 118. 

Gan bladder 

Iiarge intestinea 

Append ra of 


Small ictestinM 

Small intostineg 

Digestive tract in man. 


tion of the intestinal tract (small intestine). This is a tube about 20 
feet in length, with a surface of some 3,500 square inches, and is the 
organ designed for finishing the digestive process. The general 
scheme of the digestive tract in man is exhibited in Fig. 118. Into 
the duodenum, and but a few inches from the valve of entrance, two 
small tubes {ducts) open, one leading from the liver and pouring in 
&i?e, and the other from the pancreas, jieldiag pancreatic juice, the 
quantity of the former being much greater than of the latter. Both 
of these liquids are strongly alkaline from the presence of soda. The 
pancreatic juice much resembles saliva in properties; indeed the 
pancreas itself is so like the salivary glands as to be grouped with 
them. From the walls of the intestine there is also poured out a 
fluid called the intestinal juice. It is secreted in small but variable 
quantities, and is alkaline like the other secretions. 

653. Changes in the Intestinal Passage. — "We find that the alkaline 
digestion of the mouth is now resumed. The starch is attacked ener- 
getically and rapidly changed into sugar, and that to lactic acid. The 
oily substances hitherto untouched by the digestive agents are now 
acted upon, not perfectly dissolved like the other alimentary matter, 
but reduced to the condition of an emulsion, its particles being very 
finely divided and rendered capable of absorption. It is believed that 
the Pancreatic juice is the efficient or principal agent in producing 
these changes ; although the bile undoubtedly contributes to the efiect 
in some way not yet understood. As undigested albuminous matter 
is constantly liable to escape through the pyloric gateway into the in- 
testines, it seems required that they should be capable, upon emer- 
gency, of completing the unfinished work, and such really appears to be 
the case. Although the secretions poured into the intestine are aU 
distinctly alkaline, yet they convert sugar so actively into lactic acid, 
that the intestinal mass quickly becomes acidulous, — strongly so, as it 
advances to the lower portion. The conditions are thus afforded for 
the digestion of nitrogenous matters in the intestines, which is known 
often to take place, although their ordinary function is admitted to be 
digestion of non-nitrogenous substances, starch, sugar, and fat. 

654. Absorption from the Intestine. — The nutriment being finely dis- 
solved, is absorbed through the coats of the intestine, but not aU in 
the same manner. Those substances which are completely dissolved 
in water, are taken up by the veins, which are profusely distributed 
over the intestinal surface, while the oily and fatty matters, which are 
not so perfectly dissolved, are taken up by a special arrangement of 
vessels, called the lacteals, which are extremely fine tubes arising in the 



intestinal coats. They -were fonnerly supposed to be open at tlaeir ex- 
tremities, but they are now seen to present fine, blunt ends to the in- 
testinal cavity. How oily substances get entrance into these tubes is 
an old physiological puzzle. The membrane is moist, and water repels 
oil ; how then can it be imbibed ? Yet it constantly flows through. 
The thing is accomplished by the agency of cells, which are produced 
in vast numbers during lacteal absorption. These contain the oil, and 
bursting, deliver it to the absorbent vessels. The liquid which enters 
the lacteals is white, milk-like, and rich in oil. These veseels are 
gathered into knots (glands), so as to be greatly prolonged without 
consuming space. They finally gather into a tube (thoracic duct), and 
pour their contents into a large vein near the left shoulder. In its 
route, there is a disappearance of the large proportion of oil ; and 
albumen, which either entered from the intestine, or has afterwards 
transuded from the bloodvessels into the lacteals, is gradually 
changed to fibrin, the liquid acquiring the power of clotting or coag- 

655. Constipating and Laxative Foods. — The walls of the alimentary 
canal having absorbed from its contents such parts as are adapted for 
nourishment, there remains an undigested residue which passes at in- 
tervals from the bowels. The conditions of the intestines in reference 
to the retention or ready passage of excrementitious matters, is liable 
to variation from many causes. Amongst these, the nature of the 
food itself is influential. Some aliments have a relaxing effect, and 
others are of a binding nature, or tend to constipation, and they differ 
much in the degree in which these effects are produced. These re- 
sults are not, however, always due to specific active effects produced 
upon the bowels ; for some foods, as meats, eggs, mUk, are considered 
to be binding, because they are completely absorbed, and leave no 
residue to excite the intestines to action. Those aliments are best 
adapted to relieve a costive habit of body which leave much undigested 
refuse to stimulate the intestines to free action. In this relation wo 
may group the most important aliments, according to their reputed 
characters, as follows : 


Bread and cakes, from fine wheaten Wheaten bread and cakes from un- 

flonr; rice, beans, peas, meats, eggs, tea, bolted flour, rye bread, corn bread, raw 
alcoholic drinks. sugar, (from the molasses it contains,) fruits, 

raw and cooked, and generally substances 
abounding in ligneous matter,as skins, cores, 
husks, bran, &c. 


5. Final Destination of Foods. 

656. Digested alimentary matter enters tlie circulation and becomes 
Blood. This fluid is contained in a system of vessels, which extends 
to all parts of the body. It has been aptly called the floating capital 
of the system, lying between absorption and nutrition. Its quantity 
m an average-sized man is estimated at from 20 to 24 lbs. It is whirled 
as a rapid stream incessantly through the body, circulating round and 
round, so as to be brought into relation with all parts (624). 

657. Composition of Blood. — The composition of blood varies slightly 
with age, sex, constitution, and state of health ; it is also liable to acci- 
dental variations, as the supplies to it are periodic and fluctuating, 
while the draught upon it, though constant, is unsteady. It consists 
of about 78 per cent, water and 22 per cent, solid food dissolved in it. 
When evaporated to dryness, the solid matter is found to consist of: 

■ Fibrin Albumen Gelatin 93 per cent. 

Fat, a little sugar, and a trace of starch 2 " 

Saline matter, crash 57 " 

Blood 100 " 

658. Blood Discs, Globnles, or Cells. — To the naked eye blood appears 
of a red color, but under the microscope it is seen as a transparent, 
watery fluid, containing vast numbers of little floating cells or discs, 
which are the grand instruments of change in the sanguinary fluid. 
Their minuteness is amazing; fifty thousand would be required to 
cover the head of a small pin, while in a single drop of blood which 
would remain suspended upon the point of a fine needle, there must 
be as many as three millions. And yet each of these little bodies, 
which dwells down so low in the regions of tenuity that the unas- 
sisted eye cannot discover it, seems to be an li' iia 
independent individual, which runs a definite 
career, is born, grows, performs its offices, and j^f% ^(<% 
dies like the most perfect being, though the phy- ^ ^^ O^/S^ A 
Biologist tells us that twenty millions of them A ' ' 
perish at every beat of the pulse. Figs. 119 and m^ mm 
120, from a work of Dr. Hassall, represent ^®(0!i 
different aspects of the blood discs, as seen under © ^ 
the microscope. The physiology of the blood \J 
in its details is curious and most interesting, but /fs\ 

we have no space to consider it here, and it is _ , , , 

' Human red blood globules, 

not necessary to the general view we propose showing their natural form 
to give of the final influence of food upon the brought^fuHy iut'o^focM^^^ 


659. Grand pnrpose of the Homan Body. — The living man is pre- 
sented to our consideration as an engine of power — a being capable of 
producing effects. The bony framework within is broken into numer- 
ous pieces to admit of free motion. A complicated and extensive ap- 
paratus of contractile muscles is provided for me- 
chanical movement. The nervous system binds 
the whole into a co-operating unity, presided over 
by the brain, which not only regulates and gov- 
erns the animal nature, but is the material seat of 
intellectual power. Altogether, the body dis- 
closes its supreme purpose to be the reception of 
impressions by the senses, and the development 
and expenditure of physical and mental force. 
But force cannot be produced out of nothing. 
The body cannot and does not create it. As there 

Blood discs, seen united ig xxo evidence that in the course of events upon 

into rolls, like adherent '■ 

pieces of money. the earth, there is either the creation or destruc- 

tion of a single atom of matter, so it is beheved 
that in no absolute sense is force either created or destroyed. It 
changes states, disappears, and remains latent or reappears in different 
forms, but its total amount is thought to correspond with the total 
quantity and fixed properties of matter. Power is thus not literally 
generated in the body, but is developed or made active there by cer- 
taia definite causes. It is desirable to understand, as far as we may 
be able, the conditions of its production. 

660. Food produced by the action of Forces.— The stream of aliment 
which fiows into the system from without, consists mainly of carbon, 
oxygen, hydrogen, and nitrogen. These, when left to the undisturbed 
play of their attractions, take the compound form of water, carbonic 
acid, and ammonia, natural and permanent conditions of equilibrium 
from which they are not inclined to depart. These three substances 
constitute the chief nourishment of the vegetable kingdom. Through 
the roots, or by direct absorption from the air, they get admission into 
the vegetable leaf, the crucible of nature, where organized compounds 
originate. They are there decomposed and thrown into new arrange- 
ments, forming new compounds. Simple substances, those having few 
atoms, are destroyed, and the atoms built together into more complex 
substances, with greater numbers of atoms. The changes are from 
the lower to the higher, ascending, constructive. Now carbonic acid, 
"water, and ammonia cannot separate and re-arrange themselves^ nor can 
they be separated and re-aiTanged without an enormous expenditure of 


power. Man with his utmost skill cannot imitate the first step in the 
chemistry of the plant. Every green leaf upon the surface of the re- 
volving globe decomposes carbonic acid every day at the ordinary 
temperatures, setting free the oxygen, a thing which the chemist cannot 
accomplish with all the forces at his command. ISTor are we to sup- 
pose that the leaf itself does it ; that cannot originate force any more 
than the water-wheel or the steam-engine ; it must be acted upon. 
Carbonic acid is only decomposed in the leaf during the daytime by 
the power of light ; the effect is produced by solar radiations. All 
true aliments originate under these circumstances in vegetation. 
Though we consume flesh, we only go by the route of another animal 
back to the plant ; our food is all fabricated there. Animal life begins 
and is sustained by compounds which are the last and highest product 
of the creative energy of plants. The animal is nourished from its 
blood, but it does not in any sense produce it, it only gives it form ; 
the constituents of blood are generated in plants, stored up in their 
seeds, which are the crowning results of vegetable life, and with the 
maturity of which, most plants employed by man, as food, perish. 
Aliments are thus composed of atoms that have been forced from a 
lower into a higher combination in plants, and in their new state they 
represent the amoxmt of force necessary to place them there. The 
particles of sugar, starch, oil, gluten, «&c., are little reservoirs of 
power, resembling bent or coiled springs, which have been wound up 
into organic combination by nothing less than solar enginery. It is 
these materials, dissolved in water, that constitute blood, and with 
which the animal system is kept perpetually charged. The circulating 
medium of the liviog body is of celestial coinage ; it is a dynamic pro- 
duct of astronomic agencies. The energies of the stellar universe it- 
self are brought into requisition to estabUsh the possible conditions of 
terrestrial life (3). 

661. How Food produces Animal Force. — ^Food represents force, but 
it is force in a state of equiUbrium or rest, just like a pond of water 
enclosed on all sides. But if we make an outlet to the pond, its force 
at once becomes active and available. So the quiescent force of food 
is to become active animal power ; but how ? There enters the vital 
current incessantly from the outward world another stream of matter, 
not solid but gaseous, oxygen from the air, which came by the route of 
the lungs. It is the office of this agent to unlock the organic springs 
throughout the vital domain. We have stated before that oxygen is 
an agent of destruction (284) ; it is the foe of the organized state. 
The first step of growth, and the production of food in the leaf, con- 


sisted in forcing carbon and hydrogen out of its grasp ; but in the ani- 
mal fabric it is destined to take possession of them again. The food, 
as we have seen, is not destroyed in digestion, it is only dissolved ; but 
in the blood and tissues it is destined to undergo a series of deeompo- 
sitions, which are marked by the production of compounds richer and 
richer in oxygen, until finally they are thrown from the body loaded 
to their utmost capacity with this substance. The course of changes 
that characterizes the animal is descending, from higher to lower, from 
the complex to the simple, from compounds containing comparatively 
little oxygen to those containing much. In this decomposition of ali- 
ment, under the influence of inspired oxygen, bodily force originates. 
We see every day that steam power results from the destruction of 
fael under the boiler by atmospheric oxygen, and that electric power 
comes from the oxidation or destruction of metal by the liquid in the 
galvanic battery ; but it is equally true that the conditions of human 
power are the oxidation of food and its products in the system. It is 
not from the mere introduction of aliment into the system that we 
obtain strength and nourishment, but from its destruction. A portion 
of food, of course, serves to buUd up the bodily fabric, but it only 
continues in that state transiently; it is aU finally decomposed and 
dissevered into the simplest inorganic forms. 

662. Destructive agency of Oxygen. — The body is built of aliment, 
which gives rise by its destruction to force, but the immediate active 
agent which destroys the body, and thus develops force, is oxygen 
withdrawn from the air. From the moment of birth to the moment 
of death, every living animal is incessantly occupied in introducing 
this element into the body to maintain the conditions of force by its 
constant destructive action. If the current of oxygen flowing toward 
a hmb, a muscle, or the brain, be arrested, those parts instantaneously 
lose their power of action. The body of every animal is kept charged 
with this gas every instant of its active existence. If a man is aban- 
doned to the action of air, that is, if no other matter is taken into 
his system, we quickly discover the peculiar agency of oxygen. He 
loses weight at every breath. Inspired oxygen, borne by the arte:-ial 
current, cuts its destructive way through every minutest part, decom- 
posing the constituents of both blood and tissues. The fat is consumed 
first, then the muscular portions, the body becoming reduced and 
emaciated, yet the waste must proceed if life is to last. The brain is 
attacked, its offices disturbed, delirium supervenes, and there is an end 
of life. "We call this starvation ; it is a conditim in which " atmos- 
pheric oxygeoi acts hke a sword, which gradually but irresistibly pen- 


etrates to the central point of life, and puts an end to its activity." 
— (LiEBiG.) Had food been regularly introduced, it would have 
opposed a constant resistance to that agent, that is, it would have 
offered itself for destruction and for repair, and thus have protected 
the system from the fatal inroading effects of oxygen. 

663. Combustion vrithin the Body. — The term combmtion is com- 
monly applied to that rapid combination of oxygen with other ele- 
ments, by which a high heat is produced, accompanied with light. 
But the essence of the process is, not its rate, but the nature and di- 
rection of the changes. It may go forwarc at aU degrees of speed, 
the effects being less intense the slower it proceeds. The changes that 
go on in the body are the same as tliose in the stove. There is loss of 
oxygen, destruction of combustible matter, oxidized products (car- 
bonic acid and water), and the development of heat, in one case 
rapidly, in the other slowly ; in both cases, in proportion to the amount 
of matter changed. The destruction of aliment iu the body is, there- 
fore, a real burning ; a slow, silent, regulated combustion. 

664. All Foods not equally Combustible. — Foods are destined to be 
burned in the body, but they do not all consume alike. We found it 
necessary, at the outset, to divide the aliments into two great groups, 
based upon their composition — thoso which contain nitrogen, and 
those which do not. "We next found a twofold digestion, in which 
this distinction is recognized ; an acid digestion for nitrogenous mat- 
ters, and an alkaline digestion for the others. And we are now to 
find that this fundamental difference is observed in their final uses, — 
in their relations to oxygen, and modes of destruction. All foods are 
capable of being burned, and are burned ; but there is a wide difference 
in their facility of undergoing this change, and upon that difference 
depends the very existence of the bodily structure. It is clear that if 
certain substances are to be burned in the blood, and others are to es- 
cape from it unburned, the latter must be less combustible than the 
former, or they would aU be consumed together. Accordingly the 
non-nitrogenous bodies, sugar, starch, oil, are easy of combustion ; 
while the albuminous compounds are burned with much greater 
difiiculty ; these latter are drawn out of the blood, and used in the 
construction of all the tissues of the system. The bodily structures, 
which require to have a certain degree of permanence, are built of ni- 
trogenous substances, having a low combustibility. The case is roughly 
represented by what occurs in a common stove. Both the fuel and 
the stove itself are combustible. The iron is capable of being burned 
up, under proper circumstances, as truly as the wood or coal ; and in 


a long time stoves are partially so consumed, or as the phrase is, 
' burned out.' Yet the fuel is so much more easily burned, that the 
iron serves as a structure to retain, enclose, and regulate the combus- 
tion. The difference in capability of burning between the non-nitro- 
genous and the nitrogenous aliments, may not be so great as between 
iron and wood ; yet it is fully sufficient for the purposes of the animal 

665. Nitrogeii Lowers the Comljustibility of Food. — Of all the elements 
of the animal body, nitrogen has the feeblest attraction for oxygen ; 
and what is still more remarkable, it deprives all combustible ele- 
ments with which it combines, to a greater or less extent, of the 
power of combining with oxygen, or of undergoing combustion. Every 
one knows the extreme combustibility of phosphorus, and of hydrogen ; 
but by combining with nitrogen, they produce compounds entirely 
destitute of combustibility and inflammability under the usual circum- 
stances. Phosphorus takes fire at the heat of the body ; while the 
phosphuret of nitrogen only ignites at a red heat, and in oxygen gas, 
but does not continue to burn. Ammonia, a compound of nitrogen 
with hydrogen, contains 75 per cent., by bulk, of the highly combusti- 
ble hydrogen ; but in spite of this large proportion of an element so 
inflammable, ammonia cannot be set on fire at a red heat. Almost all 
compounds of nitrogen are, compared with other bodies, difficultly 
combustible, and are never regarded as fuel, because when they do 
burn, they develop a low degree of heat, not sufficient to raise the 
adjacent parts to the kindling point. So with albuminous principles 
in the blood and tissues ; they are placed so low in the scale of com- 
bustibility, that the other group of aliments is attacked and destroyed 
first. " Without the powerful resistance which the nitrogenous con- 
stituents of the body, in consequence of their peculiar nature as com- 
pounds of nitrogen, oppose, beyond all other parts, to the action of the 
air, animal life could not subsist. Were the albuminous compounds 
as destructible or liable to alteration by the inhaled oxygen, as the 
non-nitrogenous substances, the relatively small quantity of it daily 
supplied to the blood by the digestive organs, would quickly disappear, 
and the slightest disturbance of the digestive functions would, of ne- 
cessity, put an end to life." — (Liebig.) 

666. Heat-prodncing and Tissne-making Foods. — In considering the 
final uses of foods, we are to preserve the distinction with which we 
began. The non-nitrogenous aliments, by their ready attraction for 
oxygen, seem devoted to simple combustion in the system, with only 
the evolution of heat ; while the albuminous compounds are devoted 


to the production of tissue. The first class is hence called the heat- 
producing, calorifi&nt, or respiratory aliments, while the second is 
designated as the tissue-forming, plastic, or nutritive aliments (430). 
This distinction is to he received with due limitation, for on the one 
hand, fat, which stands at the head of the heat-producers, is deposited 
and retained in the cells of the tissues, without being immediately con- 
sumed, and probably serves other important purposes beside produc- 
ing heat (722) ; on the other hand, some nitrogenous substances (as 
gelatin, for example,) do not reproduce tissue, while those which are 
worked up into the structure of the system, in their final dissolution, 
minister also to its warmth. These facts, however, do not disturb the 
general proposition. That it is the chief purpose of sugar, starch, veg- 
etable acids, and fat, to be destroyed in the body for the generation 
of warmth ; while albumen, fibrin, and casein, furnish the material for 
tissue, and in their destruction give rise to mechanical force, or animal 
power, — is a fact of great physiological interest and importance, now 
regarded as established, and which was first distinctly enunciated, il- 
lustrated, and confirmed, by LrEsia. 

6. Peodtjotion of Bodilt Waemts. 

667. Constant Temperatnre of the Body. — The influence of tempera- 
ture over chemical transformations is all-controlling ; they are modified, 
hastened, checked, or stopped, by variations in the degrees of heat. 
The living body is characterized by the multiplicity and rapidity of its 
chemical transmutations. Indeed, the whole circle of life-functions 
is dependent upon the absolute precision of rate with which these vi- 
tal changes take place. A standard and unalterable temperature is 
therefore required for the healthy animal organism, as a fundamental, 
controlling condition of vital movements — a certain fixed degree of 
heat to which aU the vital operations are adjusted. This standard 
temperature of health in man, or blood heat, varies but slightly from 
98°, the world over. Yet the external temperature is constantly 
changing, daily with the appearance and disappearance of the sun, and 
annually with the course of the seasons. We are accustomed to fre- 
quent and rapid transitions of temperature, from 30 to 60 degrees, by 
the alternations of day and night, sudden changes of weather, and by 
passing from warmed apartments into the cold air of winter. The circle 
of the seasons may expose us to a variation of more than a hundred 
degrees, while the extreme limits of temperature to which man is nat- 
urally sometimes subjected in equatorial midsummer, and arctic mid- 


■winter, embrace a stretch of more than 200° of the thermometric scale. 
Yet through all these thermal vicissitudes, the body of man in health 
varies but little from the constant normal of 98°. 

668. How the Body loses Heat. — In view of these facts, it has been 
maintained that the living body possesses some vital, mysterious, in- 
ternal defence against the influence of external agents ; indeed, that it 
is actually emancipated from their effects. But this is wholly errone- 
ous ; the body possesses no such exemption from oatward forces ; it is 
a heated mass, which has the same relation to surrounding objects as 
any other heated mass ; when they are hotter than itself it receives 
heat, when they are colder it loses heat ; and the rate of heating or 
cooHng depends upon the difference between the temperature of the 
body, and that of the surrounding medium. But in nearly all circum- 
stances, the temperature of the body is higher than the objects around. 
It is, therefore, almost constantly parting with its heat. This is done 
in several ways. The food and water which enters the stomach cold, 
are warmed, and in escaping carry away a portion of the heat. The 
air introduced into the lungs by respiration is warmed to the tempera- 
ture of the body, and hence every expired breath conveys away some 
of the bodily warmth. This loss is variable ; as the temperature of 
the outer air is lower, of course more heat is required to warm it. 
The body also parts with its heat by radiation, just like any other ob- 
ject, and much is likewise lost by the contact of cold air with the skin, 
which conducts it away, a loss which is considerable when the air is 
in motion! This rapid carrying away of heat by air-currents, explains 
why it is that our sensations often indicate a more intense cold than 
the thermometer. But, lastly, the body loses heat faster by evapora- 
tion than in any other way. This takes place from the surface of the 
skin, and from the lungs. About 8^ lbs, of water are usually estimated 
to be exhaled in the form of vapor daily, of which one-third escapes 
from the lungs, and two-thirds from the skin, which is stated to have 
28 miles of perspiratory tubing, for water-escape (797). We shall appre- 
ciate the extent of this cooling agency, by recalling what was said of 
the amount of heat swallowed up by vaporization (68). The water of 
the body at 98° receives 114° of sensible heat, and then 1000° of latent 
heat, before it is vaporized ; hence it carries away 1114° of heat from 
the body. 

669. How the Body prodaccs Heat. — To keep the system up to the 
standard point, notwithstanding this rapid and constant loss, there 
must be an active and unremitting source within. Heat-force cannot 
be created out of nothing ; it must have a definite and adequate cause. 


It is by the destruction of food through respiration, that animal heat 
is generated. The main physiological difference between the warm 
and the cold-blooded animals is, that the former breathe actively, 
while the latter do not. It is natural, therefore, to connect together 
the distinctive character of breathing, with the equally distinctive 
character of greater warmth ; to suppose that the incessant breathing 
so necessary to life, is the source of the equally incessant supply of 
heat from within, so necessary also to the continuance of life ; and 
this connection is placed, beyond all doubt, when we attend to the 
physical circumstances by which the change of starch and fat into 
carbonic acid and water is accompanied in the external air. If we 
burn either of these substances in the air or in pure osygen gas, they 
disappear and are entirely transformed into carbonic acid and water. 
This is what takes place also within the body. But in the air, this 
change is accompanied by a disengagement of heat and Hght, or, if it 
take place very slowly, of heat alone without visible light. Within 
the body it must be the same. Heat is given off continuously as the 
starch, sugar and fat of the food,, are changed within the body into 
carbonic acid and water. In this, we find the natural source of animal 
heat. Without this supply of heat, the body would soon become 
cold and stiff. The formation of carbonic acid and water, therefore, 
continually goes on ; and when the food ceases to supply the materials, 
the body of the animal itself is burned away, so to speak, that the 
heat may stUl be kept up. — (JoHS'STOjr.) There are certain periods 
in the history of the plant, as germination and flowering, when oxy- 
gen is absorbed, combines with sugar and starch, and produces car- 
bonic acid and water. In these cases, the temperature of the seed 
and the flower at once rises, and becomes independent of the sur- 
rounding medium. 

670. Effect of breathing rarified Air. — The doctrine, that animal heat 
ia due to oxidation in the system, is strikingly illustrated by what might 
be termed starving the respiration. As cold is felt from want of 
food, so also it is felt from want of air. In ascending high mountains, the 
effect upon the system has been graphically expressed as ' a cold to the 
marrow of the bones,' a difficulty of making muscular exertion is ex- 
perienced ; the strongest man can scarcely take a few steps without 
resting ; the operations of the brain are interfered with ; there is a pro- 
pensity to sleep. The explanation of aU this is very clear. In the 
accustomed volume of air received at each inspiration, there is a less 
quantity of oxygen in proportion as the altitude gained is higher. 
Fires can scarce be made to bum on such mountain tops ; the air is 


too thia and rare to support them ; and so these combustions which 
go on at a measured rate in the interior of the body, are greatly re- 
duced in intensity, and leave a sense of penetrating cold. Such jour- 
neys, moreover, illustrate how completely the action of the muscular 
system, and also of the brain, is dependent on the introduction of air ; 
and under the opposite condition of things, where men descend in 
diving-bells, though surrounded by the chilly influences of the water, 
they experience no corresponding sensation of cold, because they are 
breathing a compressed and condensed atmosphere. — (Dr. Deapee.) 

671. How the unequal demands for Heat are met. — The steady main- 
tenance of bodUy heat being a matter of prime physiological necessity, 
we find it distinctly and largely provided for by a class of foods pre- 
pared in plants and devoted to this purpose. Much the largest por- 
tion of food consumed by herbivorous animals, and generally by man, 
is burned at once in the blood for the production of heat. But there 
are varying demands upon the system at different places and seasons, 
and the provision for these is wise and admirable. First, as the cold 
increases, the atmosphere becomes more dense, the watery vapor is 
reduced to its smallest proportion, and pure air occiapies its place, 
so that breathing furnishes to the body a considerably higher per- 
centage of oxygen in winter than in summer, in the colder regions of 
the north, than in the warmer vicinity of the equator. On the other 
hand, there is an important difference among the heat-producing 
principles of food. They vary widely in calorific power. The fats 
and oUs head the list ; they consist almost entirely of the two 
highly combustible elements, carbon and hydrogen, containing from 
Y7 to 80 per cent, of the former, to 11 or 12 of the latter. Starch 
occurs next in the series, then the sugars, and lastly the vegetable 
acids and lean meat. Liebig states their relative values, or power 
of keeping the body at the same temperature during equal times, as 
follows : To produce the same effect as 100 parts of fat, 240 of starch 
will be required, 249 of cane sugar, 263 of dry grape sugar and milk 
sugar, and 770 of fresh lean flesh. We shall illustrate this point more 
clearly, when we come to speak of the nutritive value of foods (743). 
A pound of fat thus goes as far in heating as 2| lbs. of starch, or 7^ lbs. 
of muscular flesh. In regions of severe cold, men instinctively resort 
to food rich in fatty matters, as the blubber and train oil, which are 
the staples of polar diet. Bread, which consists of starch and gluten, 
and which, therefore, as shown by the above illustration, falls far be- 
low oleaginous matter in calorifying power, is found to be very insuflS- 
cient in the arctic regions for the maintenance of animal heat. 


All breads are, however, not alike in this respect, for the Hudson's 
Bay Traders have found, according to Sir John Riohaedson, that 
Indian corn bread, which contains about nine per cent, of oH, is de- 
cidedly more supporting than wheaten bread. Dr. Kane, in the nar- 
rative of his last arctic expedition, remarks : " Our journeys have 
taught us the wisdom of the Esquimaux appetite, and there are few 
among us who do not relish a slice of raw blubber, or a chunk of 
frozen walrus beef. The liver of a walrus, eaten with little slices 
of his fat, of a verity it is a delicious morsel. The natives of South 
Greenland prepare themselves for a long journey in the cold by a 
course of fi-ozen seal. At Upernavick they do the same with the 
norwhal, which is thought more heat-making than the seal. In. 
Smith's Sound, where the use of raw meats seemed almost inevitable, 
from the modes of living of the people, walrus holds the first rank. 
Certainly, its finely condensed tissue, and delicately permeating fat — 
oh ! caU it not blubber — is the very best kind a man can swallow ; it 
became our constant companion whenever we could get it." On the 
contrary, the inhabitants of warmer regions live largely upon fruits, 
which grow there in abundance, and in which the carbonaceous matter, 
according to Liebig, falls as low as 12 per cent. The demands of ap- 
petite seem to correspond closely with the necessities of the system ; 
for while oranges and bread-fruit would be but poor dietetical stuff 
for an Icelander, the West Indian would hardly accept a dozen tallow 
candles as a breakfast luxury ; but reverse these conditions and both 
are satisfied. A knowledge of the calorifying powers of the various 
elements of food, and of the proportions in which they are found, 
enables us to modify our diet according to the varying temperature of 
the seasons. 

672. Begnlation of Bodily Temperature. — The question naturally arises, 
why is it that when the external temperature is 100° and even higher 
for a considerable time, and the system is constantly generating ad- 
ditional heat, that it does not accumulate, and elevate unduly the 
bodily temperature ? How is it constantly kept down in health to 
the limit of 98° ? This is efifected by the powerful influence of evapo- 
ration from the lungs and skin, already referred to in speaking of the 
way the body loses heat (668). The large amount of water daily 
drank and taken in combination with the food, is used for this pur- 
pose as occasion requires. The lungs exhale vapor quite uniformly, 
but the quantity thrown off from the skin varies with the condition 
af the atmosphere. When the air is hot and dry, evaporation is ac- 
tive, and the cooling effect consequently greater. During the heat of 


summer, mucli water evaporates from the skin, and a correspondingly 
small proportion by the kidneys ; but in the cold of winter there is 
less cutaneous exhalation, the water of the body is not vaporized, but 
chiefly escapes in the liquid form by kidney excretion. As human 
invention has made the steam-engine beautifully automatic and self- 
regulating, and as stoves have been devised which adjust their ov?n 
rate of combustion, and thus equalize the heat, so we find the living 
body endowed with a matchless power of self-adjustment in regard to 
its temperature, by the simplest means. 

673. Houses and Clothing replace Food. — We have seen that the neces- 
sity for the active generation of heat within the body is in proportion 
to the rapidity of its loss. If the conditions favor its escape, more 
must be produced ; if on the other hand the surrounding temperature 
be high, the loss is diminished, and there is less demand for its evo- 
lution in the body. We have also described the various expedients 
by which heat is produced in our dwellings in winter, thus forming 
an artificial summer climate. Clothing also acts to protect the body 
from loss, and enable it to preserve and economize the heat it gen- 
erates. Hence in winter we infold ourselves in thick non-conducting 
apparel. Clothing and household shelter thus replace aliment ; they 
are the equivalents for a certain amount of food. The shelterless a,nd 
thinly clad require large quantities of food during the cold of winter 
to compensate for the rapid loss of heat. They perish with the same 
supply that would be quite sufficient for such as are adequately clothed 
and well-housed. " It is comparatively easy to be temperate in warm 
climates, or to bear hunger for a long time under the equator ; but 
cold and hunger united very soon produce exhaustion. A starving 
man is soon frozen to death." 

674. Times of Life when Cold is most fatal. — The potent influence of 
temperature upon life must, of course, be most strikingly manifested 
where there is least capability of resistance — in infancy and old age. 
During the first months of infant life the external temperature has a 
very marked influence. It was found in Brussels that the average 
infant mortality of the three summer months being 80, that of January 
is nearly 140, and the average of February and March 125. As the 
constitution attains vigor of development, the influence of seasons 
upon mortaUty becomes less api^arent, so that at the age of from 25 
to 30 years, the difference between the summer and winter mortality 
is very slight. Yet this diffference reappeai's at a later period in a 
marked degree. As age advances, the power of producing heat de- 
clines, old people draw near the fire and complain that ' their blood is 


chill.' The Brussels statistics show that the mortality between 50 
and 65 is nearly as great as in early infancy ; and it gradually becomes 
more striking until at the age of 90 and upwards the deaths in Jan- 
nary are 158 for every 74 in July. It has been observed in hospitals 
for the aged, that when the temperature of the rooms they occupy in 
winter sinks two or three degrees below the usual point, by this small 
amount of cooling the death of the oldest and weakest, males as well 
as females, is brought about. They are found lying tranquilly in bed 
without the slightest symptoms of disease, or the usual recognizable 
causes of death. 

675. Diet and the daily changes of Temperature. — The heat of inani- 
mate objects, as stones, trees, &c., rises and falls with the daily varia- 
tions of temperature. The hving body would do the same thing if it 
did not produce its own heat independently. If we disturb the calp- 
rifying process, the body becomes immediately subjected to the muta- 
tions of external heat. In starving animals, this temperature rises 
and falls with the daily rise and nightly fall of the thermometer, and 
this response of the living system to external fluctuations of heat is 
more and more prompt and decided as the heat-producing function is 
more and more depressed. As the system is unequally acted upon by 
the daily assaults of cold, it becomes necessary to make provision 
against the periods of severest pressure. In the ever admirable 
arrangements of Providence, the diurnal time of lowest temperature 
is made to coincide with the time of darkness, when animals resort to 
their various shelters to rest and recruit, and are there most perfectly 
protected from cold. Dr. Deapee has suggested also that the diet of 
civilized man is instinctively regulated with reference to the daUy 
variations of temperature. He says : " In human communities there is 
some reason beyond mere custom which has led to the mode of dis- 
tributing the daily meals. A savage may dispatch his glutinous repast 
and then starve for want of food ; but the more delicate constitution 
of the civilized man demands a perfect adjustment of the supply to 
the wants of the system, and that not only as respects the Mnd, but 
also the time. It seems to be against our instinct to commence the 
morning with a heavy meal. We l)reaTc fast, as it is significantly 
termed, but we do no more ; postponing the taking of the chief supply 
untU. dinner, at the middle or after part of the day. I think there 
are many reasons for supposing, when we recall the time that must 
elapse between the taking of food and the completion of respiratory 
digestion, that this distribution of meals is not so much a matter of 
custom, as an instinctive preparation for flie systematic rise and f^U 


of tomperature attending on the maxima and minima of daily heat. 
The hght breakfast has a preparatory reference to noonday, the solid 
dinner to midnight." 

7. Peodtjotion of Bodily STEEisraTH. 

676. Amount of mecbaiiical force exerted by the Body. — "We have seen 
how the double stream of alimentary and gaseous matter which enters 
the body incessantly gives rise to heat, an agent which we every day 
convert into mechanical power through the medium of the steam engine. 
Sufficient heat is produced in this way annually by an adult man, if it 
were liberated under a boUer, to raise from 25,000 to 30,000 lbs. of 
water from the freezing to the boiling point. But the body also 
generates mechanical force directly, producing effects which present 
themselves to us in a twofold aspect ; those which are involuntary, 
constant, and connected with the maintenance of life, and the volun- 
tary movements which we execute under the direction of the will, 
for multiplied purposes and in numberless forms. That which produces 
movement is force, and there can be no movement without an adequate 
force to impel it. If a load of produce or merchandise is to be trans- 
ported from one place to another, we all understand that force must 
be applied to do it. And so with the human body ; not a particle of 
any of its flowing streams can change place, nor a muscle contract to 
lift the hand or utter a sound, except by the application of force. 
We may form an idea of the amount generated to maintain the invol- 
untary motions essential to life, by recalling for a moment their num- 
ber and extent. "We make about nine millions of separate motions of 
breathing, introducing and expelling seven hundi'ed thousand gallons 
of air in the course of a year. At the same time the heart contracts 
and dilates forty millions of times — each time with an estimated force 
of 13 lbs., whUe the great sanguinary stream that rushes through the 
system is measured by thousands of tons of fluid driven through the 
heart, spread through the lungs, and diffused through the minute ves- 
sels, beside the subordinate currents and side-eddies which traverse 
various portions of the body, and contribute essentially to its action. 
The system not only generates the force indispensable for these effects, 
but also an additional amount which we expend in a thousand forms 
of voluntary physical exercise, labor, amusement, (fee. A good laborer 
is assumed to be able to exert sufficient force (expended as in walking) 
to raise the weight of his body through 10,000 feet in a day. Smeaton 
states, that working with his arms he can produce an effect equal to 


raising SVO lbs. ten feet high, or 3,700 lbs. one foot high in a minute 
for eight hours in the day. 

677. Tissues destroyed la producing Force. — The expenditure of force 
in labor, if not accompanied by a sufficiency of food, rapidly wears 
down the system, — there is a loss of matter proportioned to the 
amount of exertion, and which can only be renewed by a correspond- 
ing quantity of nourishment. The parts brought into action during 
exercise are of course those possessing tenacity, firmness, and strength ; 
that is, the tissues and organized structures. The unorganized parts, 
such as water and fat, which are without texture, have no vital pro- 
perties, and cannot change their place or relative position by any in- 
herent capability. It is the bodily tissues that are called into action, 
and these undergo decomposition or metamorphosis in the exact ratio 
of their active exercise. We have stated that the motions within the 
system are numerous and constant. If we look on a man externally, 
he is never wholly at rest ; even in sleep there is scarcely an organ 
which is not in movement or the seat of incess5,nt motion ; yet the 
destruction of parts is correspondingly active. It may vary perhaps 
in different constitutions, in different parts of the system, and under 
various circumstances, but it goes on at a rate of which we are hardly 
conscious. Ohossat ascertained the waste in various animals to be an 
average of l-24th part of their total weight daily ; and Schmidt deter- 
mined it to be, in the case of the human being, l-23d of the weight. 
Professor Johnston says : " An animal when fasting wiU lose from a 
fourteenth to a twelfth of its whole weight in twenty-four hours. 
The waste proceeds so rapidly that the whole body is now believed 
to be renewed in an average period of not more than thirty days. 

678. Destinatioii of the Nitrogenous Principles. — The basis of animal 
tissue is nitrogen. The muscular masses are identical in composition 
with the nitrogenous principles of food, albumen, casein, gluten. 
Those substances have, by digestion, become soluble; that is, they 
have all assumed the form of albumen, and thus enter the blood. In 
this liquid, whose prime function is to nourish the system, albumen is 
always present in considerable quantity. When the fibrin and red- 
coloring matter {dot) is removed from blood, the watery serum or 
plasma remains, containing albumen, which coagulates like white of 
egg by heat. Albumen is the universal starting point of animal nutri- 
tion ; it is the liquid basis of tissue and bodily development through- 
out the entire animal kingdom. We see this sti-ikingly illustrated by 
what takes place in the bird's egg during incubation. Under the in- 
fluence of warmth, and by the action of oxygen, which enters through 



the porous shell, under the inflaence therefore of the same conditions 
which accompany respiration, all the tissues, memhranes and bones, 
(by the aid of lime from the shell,) are developed. The foundation 
material from which they are all derived is albumen, and it is the 
same with the growth and constant reproduction of our own bodies 
during life. The course of transformation by which albumen is con- 
verted into the various bodily tissues, has not yet been certainly 
traced. But it is now universally agreed that it is the nitrogenous 
principles of food, — those of low combustibility, which are employed 
for the nutrition of animal structures — the reparation of tissue-waste. 
Those substances furnish the instruments of movement, and minister 
directly to the production of mechanical force. Their design is two- 
fold, to form and maintain the bodUy parts in strength and integrity, 
and to be finally destroyed for the development of power. 

679. Action of Oxygen npon the Tissnes. — Oxygen plays the same im- 
portant part in tissue destruction as in the simple development of heat 
by combustion of respiratory food. It is the agent by which the 
moving parts are decomposed and disintegrated. The muscles are 
paralyzed if the supply of arterial blood containing the oxygen which 
is to change them, and the nutritive matter which is to renew them, 
be cut off. On the other hand, if there is rapid muscular exercise 
and consequent waste, the circulation is increased and the breathing 
quickened, by which the supply of oxygen is augmented. The 
changes of the tissues in action are, moreovei*, retrogressive, and 
downwards to simpler and simpler conditions. The products of 
metamorphosis are oxidized, and then made soluble in the blood by 
which they are promptly conveyed away, and thrown out of the body 
by the liquid excretion. It is thus that oxygen, by slow corrosion and 
burning of the constituents of the muscles, gives rise to mechanical 
force. But oxidation is invariably a cause of heat ; decomposition of 
the tissues, therefore, must develop heat at the same time with me- 
chanical effect. Indeed, violent muscular exercise is often resorted to 
in winter as a source of bodily warmth, by increasing the respirations 
and muscular waste. In this subordinate way, the nitrogenous ah- 
ments become h^at-producers. It is not to be supposed that oxygen 
seizes upon all the atoms of tissue indiscriminately, or upon those 
which it finds next before it. There is a wonderful selective power, 
some particles are taken and others left. Those only are seized upon 
which in some unknown way, perhaps under the regulating influence 
of the nervous system, are made ready for change. 

680. Relation between Waste and Supply. — If an organ or part be the 


seat of destructive and reparative changes, and its weight remains in- 
variable, we know that an exact balance is struck between these two 
kinds of transformation. But the processes of destruction and reno- 
vation in the body are not necessarily equal, so that every atom that 
perishes out of the structure is promptly replaced by another. In 
those cases where the system neither gains nor loses weight, the an- 
tagonist forces must of course pi'ecisely compensate each other. Yet, 
even here, the general equilibrium is the result of constant oscillations. 
The involuntary muscles, which play continually, as those of the heart, 
and the muscles engaged in respiration, have an intermitting action. 
The short or momentary period of activity is followed by a corre- 
sponding interval of rest. If the first condition involves destruction, 
the second allows of nutrition. That portion of the mechanism which 
is independent of voluntary control, is thus self-sustaining. StUl, in 
the case of these parts, the equipoise between waste and supply may be 
lost, as in bodily growth when nutrition exceeds decomposition, or in 
deficiency of nutriment, when destruction proceeds at the expense of 
the tissue, which loses weight faster than the food renews it. As re- 
gards the waste and renovation attending voluntary movement, there 
is the same periodicity. Destruction gains upon nutrition during the 
exercise of the day, and what was lost is regained by nutrition during 
rest at night. In sleep, nutrition is at its height while waste falls to its 
minimum. As bodily exertion costs tissue destruction, which can only 
be made good again by albuminous substances, it follows that these will 
be demanded for food, in proportion to the amount of efibrt expended. 
If such food be not adequately supplied, or if from any cause the body 
be incapable of digesting or assimilating it, the apparatus of force begins 
at once to give way, the acting tissues shrink and fail, for human efibrt is 
carnivorous, flesh-consuming. If, on the other hand, the system is main- 
tained at rest, that is, if force is not exerted, the nutriment is not used 
or expended, but is laid up in the body, and serves to increase the mass. 
681. Hastening and retarding tissne changes.— Ingested substances have 
a twofold relation to waste or metamorphosis of the tissues. Some, 
as we have seen, become portions of the animal solids, and then un- 
dergo transformation. Others have the power of modifying or con- 
trolling these changes, without in the same way participating in them. 
Some of these increase metamorphosis, and others chech it. Common 
salt, for example, and an excess of water, act as Jiasteiwrs of tissue 
change, while alcohol and tea act as arresters of metamorphosis. If 
we consume those substances which augment the waste, it is said we 
require a fuller diet to compensate for the extra loss, or the body de- 


clines in weight with more rapidity than otherwise. If we employ the 
arresters of metamorphosis, we are supposed to have tissue, and can 
maintain our usual strength and weight on a more slender diet. That 
certain substances produce these eflfects, may he regarded as establish- 
ed, but it cannot be admitted that they are proper aliments. "We re- 
cognize transformation of the living parts, as the highest and final 
physiological fact, the necessary condition of human activity. Dr. 
Ohambees remarks — " Metamorphosis is life^ or an inseparable part 
of life." Undoubtedly the rates of bodily change are liable to certain 
variations, within limits of health ; but the whole import of the vital 
economy, leads us to connect accelerated and retarded changes with 
variations in the exercise of force, by a fixed organic ordinance. "With 
high activity, a rapid change, and with rest, a minimum of loss is evi- 
dently nature's purpose, and her law. Substances introduced into the 
system, which act upon the tissues, as it were from without, and in- 
terfere with this fundamental relation between rate of exertion and 
rate of change, can be regarded in no other light than as disturbers of 
physiological harmony, StUl, we are to be cautious about theoretically 
prejudging any substance ; whether it be beneficial or injm-ious is as- 
certainable only by careful observation and experience of its effects. 

8. Mind, Body, and Aliment. 

682. Mind brongM into relation with Matter. — In his ultimate destiny, 
we contemplate man as an immortal spirit, but in the Divine arrange- 
ment, that .spirit is to be educated and prepared in nature and time for 
its onward career. Spirit or mind partakes in nothing of the attri- 
butes of matter, but it coiresponds closely to our conception of force. 
The passions are regarded as the mind's motors^ or motive powers. 
The directive or governing element we call will^ or wUl-power. We 
speak constantly of intellectual force, and mental energy, and regard 
the mind as an assemblage of faculties or powers capable of producing 
effects. Indeed, as we consider the Mind or WUl of God to be the all- 
controlling activity of the universe, so the mind of man, created in his 
Maker's image, is perpetually demonstrating an over-mastering con- 
trol of the elements and agencies of nature. As mind is thus designed 
to be developed by action, with the material world for its theatre, it 
must of course be brought into relation with matter. The brain is the 
consecrated part where this inscrutable union is eftected, and the ner- 
vous system is the immediate mechanism which establishes a dynamic 
connection between the spiritual intelligence and the physical creation. 

683. Mental Exercise destroys Nervons Matter. — Of the natui-e of this 


union, how it is accomplished, we know nothing, bnt some of its con- 
ditions are understood. We are certain that the brain and nerves 
wear and waste by exercise, and require renewal, just like all the 
other tissues. Nervous matter in this respect is no exception to the 
general law of the organism. The external universe pours in its im- 
pulses through aU the avenues of sense, along the nerve routes to the cen- 
tral seat of consciousness, the brain ; whUe the mind, exerting itself 
through that organ, and another system of nerves, calls the muscles into 
action, and produces its thousand-fold effects upon external objects. In 
both cases there is decomposition and loss of nerve-substance, and 
there must, therefore, be a nutrition of brain and nerves, as truly as 
of any other part ; nay, more truly, for destruction and renovation 
are perhaps more active in these parts than in any others. Arterial 
blood, with its agent of disorganization (oxygen), and its materials of 
repair, are sent to the brain in a far more copious flood than to any 
other equal portion of the body. Blood-vessels are also distributed 
most abundantly around the nerves, so as to effect their nutrition in a 
perfect manner ; while if the vital stream be checked or ai'rested, the 
nerve loses its power of conducting impressions, and the brain its 
capacity of being acted upon by the mind ; the interruption of the 
blood-stream through this organ producing instantaneous unconscious- 
ness. Besides, the nerve-tissue consists of the most changeable mate- 
rials, "TO to 80 per cent, water, 10 of albumen, and 5 to 8 of a peculiar 
oily or fatty substance, with various salts. It is interesting to re- 
mark, that in starvation the parts are disorganized and consumed in 
the inverse order of their physiological values. First, that which is 
of lowest service, and can be best spared ; the fatty deposits are 
wasted away, then the muscular and cellular tissues, and lastly the 
nervous system, which remains undisturbed and intact until the dis- 
organization of other parts is far advanced. The mind's throne is the 
last part invaded, and the last to be overturned. We are struck with 
the wisdom of this arrangement, but we cannot explain it. 

684. Can we measure Brain and Nerve waste ? — The appropriation of 
certain specific parts to certain purposes, is the basal fact of physiolo- 
gy. A part may indeed perform several oflSces, but they are determi- 
nate and limited, and the different portions cannot change duties ; the 
stomach cannot respire, nor the lungs digest, the mind cannot act di- 
rectly upon the muscular system (only through the intermedium of 
the nerves), nor can the nerves exert mechanical force. Each part, 
therefore, does its appropriate work ; and as it has a special composi- 
tion, its metamorphosis gives rise to peculiar products. Muscular de- 


composition must hence yield one set of substances, and nerve-waste 
another. It has been attempted to identify these products, and thus 
get indications of the amount of change in each part, as a measure of 
the degree of its exercise. But the results yet obtained are probably 
only approaches to the truth. Thus, urea is undoubtedly a result of 
muscular change, and some have regarded its amount in the renal ex- 
cretion as an index to the degree of muscular exercise. But others 
aflBrm that it may also come from unassimUated food, as well as active 
muscle, which casts a doubt over conclusions thus formed. In the 
same way, salts of phosphoric acid have been regarded as the peculiar 
products of brain and nerve waste, and their amount in the kidney 
evacuations, as a measure of the exercise of brain and nerves. From 
the researches of Dr. Bense Jones, it appeared that where there is a 
periodical demand upon the mental powers (as among clergymen, for 
example, in preparation for their Sunday exercises), there is a corre- 
sponding rise in the quantity of alkaline phosphates voided by the renal 
organs. Yet here, too, there is uncertainty, for we are not sure that 
these phosphatic salts may not have other sources also. 

685. The Mind's action wears and cxhansts the Body. — That all forms of 
mental exertion have a wearing, exhausting eflEect upon the body, 
producing hunger, and a requirement for food, is well known. Pure 
intellectual labor, vigorous exercise of the will, active imagination, 
sustained attention, protracted thought, close reasoning, ' the nobler 
enthusiasms, the afflatus of the poet, the ambition of the patriot, the 
abstraction of the scholar,' — the passions and impulses, hope, joy, 
anger, love, suspended expectance, sorrow, anxiety, and ' corroding 
cares,' all tend to produce physical exhaustion, either by increasing 
the destruction of the tissues, or preventing the assimilation of nutri- 
ment. It is true that the stunning effect of an emotion, a surge of 
joy, or a blast of anger, or profound grief, may temporarily overpower 
the sensation of hunger, that is, prevent its being felt, but after a time 
the appetite returns with augmented force. In sleep, the mechanism 
of sense, consciousness, volition, and passion, is at rest, and unhindered 
nutrition makes up for the losses of the waking hours. If the brain 
be overworked, either by long and harassing anxiety, or by severe 
and continued study, it may give way ; that is, its nutrition takes place 
so imperfectly as to produce morbid and unsound tissue, which can 
only be restored to the healthy state by long mental tranquillity and 
cessation of effort. 

686. The Phosphatic constituents of Brain. — We have spoken of the 
phosphates as special products of brain and nerve waste. That phos- 


pliorus, in some state, or combination, is a leading ingredient of nervous 
and cerebral matter, is unquestionable ; and that it stands related in 
some way to tbe fundamental exercise of those parts, will hardly be 
doubted. "We remember that it is a very remarkable element, 
shining in the dark (from which it takes its name), and having a most 
powerful attraction for oxygen, combining with a large amount of it, 
and generating phosphoric acid with intense heat und Hght. It is 
also capable of existing la two states ; its ordinary active condition 
and a passive or inert state, in which it seems paralyzed or asleep, and 
exhibits no aflBnity for oxygen. The solar rays have the power of 
throwing it from the active to the passive form. It has been main- 
tained that in the leaf and by the sun, elementary phosphorus is sepa- 
rated from its compoimds, put in the passive state, rocked to sleep (297), 
is stored up in foods, and thus finds its way into the body, its blood and 
nervous matter, — and that finally, in the exercise of mental and ner- 
vous power, it resumes the active condition, and undergoes oxidation, 
producing phosphoric acid. In L'Heeitiee's analysis of nervous mat- 
ter (quoted by standard physiological authorities); it is stated that the 
proportion of phosphorus in infants is 0'80 parts per 1,000, in youths' 
1"65 (more than double), in adults 1'80, in aged persons 1"00, and in 
idiots 0'85, thus apparently connecting the quantity of this substance 
in the brain with maturity and vigor of mental exercise. From this 
point of view Dr. Moleshott leaps at once to the conclusion, ' no 
phosphorus, no thought ;' Liebig, however, denies point-blauc that 
elementary phosphorus has ever been found in nervotis matter. He 
says, " no evidence is known to science tending to prove that the food 
of man contains phosphorus, as such, in a form analogous to that in 
which sulphur occurs in it. No one has ever yet detected phosphorus 
in any part of the body, of the brain, or of the food, in any other 
form than that of phosphoric acid." As phosphorus and phosphoric 
acid, in their properties, are as wide asunder as the poles of the earth, 
it is highly incorrect to use the terms interchangeably, or (according to 
the statement of Liebig) to apply the term phosphorus in this con- 
nection. It may be remarked that the phosphoric compound is a con- 
stituent of the oily matters of nerve tissue, which are hence called 
' phosphorized fats.' 

687. Are there special Brain NatrimeatSt — On the strength of this 
phosphoric hypothesis, crude suggestions have been volunteered for 
students and thinkers, to take food abounding in phosphorus, as fish, 
eggs, mUk, oysters, &c. Such advice has no justification in weU de- 
termined fact^ "We are not authorized by science to prescribe a diet 


specially or peculiarly constructed to promote brain nutrition and pro- 
tract mental exercise. But while it would seem as if care had been 
taken to secure these high results in the universal constitution of food, 
stUl it is certainly in accordance with analogy, that specific aliments 
should be adapted, or at all events iest adapted, to produce certain 
kinds of effect in the system. Special means for special ends make up 
the unitary scheme of the living economy. The waste produced by 
mental exertion is repaired only by food, but to say by all food alike 
transcends the warrant of science. Professor Liebig remarks, " It is 
certain that three men, one of whom has had a full meal of beef and 
bread, the second cheese or salt fish, and the third potatoes, regard a 
difficulty which presents itself from entirely different points of view. 
The effect of the different articles of food on the brain and nervous 
system is different, according to certain constituents peculiar to each 
of these forms of food. A bear kept in the anatomical department of 
this university, exhibited a very gentle character as long as he was fed 
exclusively on bread. A few days' feeding with flesh rendered him 
savage, prone to bite, and even dangerous to his keeper. The carni- 
vora are, in general, stronger, bolder, and more pugnacious than the 
herbivorous animals on which they prey ; in like manner those nations 
which live on vegetable food differ in disposition from those which 
live chiefly on flesh. The unequal effects of different kinds of food, 
with regard to the bodily and mental functions of man, and the de- 
pendence of these on physiological causes, are indisputable ; but as yet 
the attempt has hardly been made to explain these differences accord- 
ing to the rules of scientific research." 

688. Diet of Braia-workers. — Yet the diet of the literary, of artists, 
and those who devote themselves to intellectual labor, is by no means 
unimportant, and should be carefully conformed to their peculiar cir- 
cumstances. They should avoid the mistake of supposing that, as they 
do not work physically, it is no matter how slight their diet, and the 
perhaps stUl more frequent error, on the other hand, of excessive eat- 
ing, the fruitful cause of dyspepsia, and numerous ailments of the sed- 
entary. The best condition of mind corresponds with the most 
healthy and vigorous state of body. The blood prepared by the di- 
gestive and pulmonary organs, and taking as it were its quality and 
temper from the general state of the system, nourishes the brain and 
influences the mind. That diet and regimen are therefore best for 
thinkers, which maintain the body in the most perfect order. They 
should select nutritious and easily digestible food, avoiding the more 
refractory aliments, leguminous seeds, heavy bread, rich pastry, &c. 


689. Men seek for Brain Excitants. — Althongli specific brain nutri- 
ents and though t-sustainers are not determined among foods, yet sub- 
stances exerting a powerful influence through the brain upon the mind, 
are but too well known. By a kind of ubiquitous instinct, men have 
ransacked nature in quest of agents which are capable of influencing 
their mental and emotive states, and they have found them every 
where. It is estimated that the peculiar narcotic resin of Indian 
hemp (haschish), is chewed and smoked among from two to three hun- 
dred millions of men. The ietel nut is employed in the same way 
among a hundred millions of people ; the use of opium prevails among 
four hundred millions, and of tobacco among eight hundred million 
of the world's inhabitants. These substances act poAverftJly, although 
somewhat diflferently, upon the nervous system, and thus directly affect 
the state of the mind and feelings. "We here touch upon the myste- 
rious world problem of narcotism; but its discussion, though of absorb- 
ing interest, would* be too extensive for our limits, besides being for- 
eign to the present inquiry, which is restricted to the general subject 
of foods. The effects of tea and coffee will be noticed when speaking 
of drinks (704). 

A.— Saline Matters. 

690. Tlie Asli elements of Food essential to Life. — When vegetable sub- 
stances are burned, there remains a small portion of incombustible 
mineral matter. It was formerly thought that this consisted merely 
of contaminations from the soil, which happened to be dissolved by 
water that entered the roots, and was therefore present in the vegeta- 
ble by accident. We now understand that such is far from being the 
fact. The ash-principles of food are indispensable to animal life. In- 
deed, without them neither group of the alimentary substances which 
we have been considering could do its work. It has been found, in 
numerous experiments, made upon the lower animals, that neither 
gluten, casein, albumen, sugar, oil, nor even a mixture of these, when 
deprived as far as possible of their mineral ingredients, are capable of 
sustaining life ; the animal thus fed actually perishes of starvation. 

691. Acids, Alkalies, Salts. — We remember that acids are bodies hav- 
ing the power of turning blue test paper red, and that alJcalies change 
the red to blue. They also combine together, each losing its peculiar 
properties, and produce salts. If the properties of the acid and alkali 
both disappear, the salt produced is neutral^ that is, neither acid nor 



alkaline. If the acid be stronger, or there be a donble or treble dose 
of it combining with the alkali, the compound is still acid, an acid 
salt; or if the alkali be strongest or in excess, it overpowers the acid 
and an alhaline salt results. If a neutral salt be dissolved in water, 
the liquid will be neither acid nor alkaline. If an acid salt be dis- 
solved, the water will be acidulous, and produce all the effects of 
acidity ; if an alkaline salt, the liquid will be alkaline, producing alka- 
line effects. The ash of foods consists of potash, soda, lime, magnesia, 
oxide of iron, sulphuric, carbonic and phosphoric acids, silica and com- 
mon salt. Fruits abound in acid salts, that is, powerful organic acids, 
as oxalic, tartaric, and malic acids, with potash and lime ; the acids be- 
ing in excess. When fruits are burned, the organic acids are consumed 
or converted into carbonic acid, and the salts become carbonates — neu- 
tral carbonates of lime or alkaline carbonates of potash. The quanti- 
ties of salts, alkalies, and alkaline earths contained ia many kitchen 
vegetables are surprising. Celery (dried), contains from 16 to 20 per 
cent., common salad 23 to 24 per cent., and cabbage heads 10 per cent. 

692. Tlie Ashes of the Food are Assimiiated, — When the organic mat- 
ter of food is burned away in the system, a residue of ashes is left, 
just as in open combustion in the air. But they are not cast at once 
from the body as useless, foreign, or waste matters. They have im- 
portant duties to perform as mineral substances, after being set free 
from organized compounds ; and they hence remain dissolved in the 
blood and various juices of the system. Portions of these mineral 
matters are constantly withdrawn from the circulation, some at one 
point and some at others, to contribute to special local nutrition. 
Thus phosphate of lime is selected to promote the growth of bones, 
while the muscles withdraw the phosphates of magnesia and potash ; 
the cartilages appropriate soda in preference to potash ; silica is se- 
lected by the hair, skin, and nails ; while iron is attracted to the red 
coloring matter of tha blood, and the black coloring matter within 
the eye. 

693. The Blood Alkaline, and why ? — But there remains constantly 
dissolved in the blood and animal juices, a proportion of acids, al- 
kalies, and salts, which impart to these liquids either acid or alkaline 
properties. The result, however, is not left to accident. Whether 
a liquid be acid or alkaline is of essential importance in refer- 
ence to the offices it has to perform. We have seen that it is 
the determining fact of the digestive juices ; one is always acid, and 
the other alkaline, and their peculiar powers depend upon these 
properties. So with the blood. It contains potash, soda, lime, mag- 


nesia, oxide of iron, phosphoric acid, and common salt ; yet these are 
so proportioned that soda is in excess, and hence the blood of all animals 
is invariably alkaline. An alkaline condition is indispensable to the 
action of this fluid. Liebig remarks, " The free alkali gives to the 
blood a number of very remarkable properties. By its means the 
chief constituents of the blood are kept in their fluid state, the ex- 
treme facUity with which the blood moves through the minutest ves- 
sels, is due to the small degree of permeability of the walls of these 
vessels for the alkaline fluid. The free alkali acts as a resistance to many 
causes, which, in the absence of the alkali, would coagulate the albu- 
men. The more alkali the blood contains, the higher is the tempera- 
ture at which its albumen coagulates ; and with a certain amount of 
alkali, the blood is no longer coagulated by heat at aU. On the al- 
kali depends a remarkable property of the blood, that of dissolving 
the oxides of iron, which are ingredients of its coloring matter, as 
weU as other metallic oxides so as to form perfectly transparent solu- 
tions." Alkali in the blood also promotes the oxidation of its consti- 
tuents. A number of organic compounds acquire by contact with, or 
in presence of, a free alkali, the power of combining with oxygen 
(burning), which alone they do not at aU possess at the ordinary 
temperature of the air, or at that of the body. — (Cheveettl.) The 
alkalies of the blood exert a precisely similar action, increasing the 
combustibility of the respiratory foods, 

694, Flesh and its Jaices, Acid.— But while alkali is necessary to 
maintain the perfect fluidity and combustive relations of the blood, 
the alkaline state seems unfavorable to nutrition. In the ash of 
muscles, there is an excess of phosphoric acid, and the juice of flesh 
which surrounds the muscles is also acidulous. The blood nourishes 
the flesh-juice, and that the muscles, but an acid medium is indis- 
pensable to the latter change. Taking the whole body together, acids 
predominate, so that if the blood were mingled with the other juice, 
the whole would have an acid character. The chief flesh acids are 
phosphoric and lactic, but how they influence nutrition is not under- 
stood. The remarkable fact of the existence in all parts of the body 
of an alkahne liquid, the blood, and an acid liquid, the juice of flesh, 
separated by very thin membranes, and in contact with muscles and 
nerves, seems to have some relation to the fact now established, of the 
existence of electric currents in the body. 

695. Uses of Salt in the System. — The properties of commercial or 
common salt, have been noticed when speaking of its preservative 
powers (590). We may now con^der its action in the system. It is 


a large and constant ingredient of the blood, forming neariy sixty pei 
cent, of its ash. It exists also in other fluids of the body, hut is not, 
perhaps, a constituent of the solid tissues, except the cartilages. Its 
offices in the system are of the first importance. It increases the so- 
lubility of albuminous matters. Dissolved in the liquids of the ali- 
mentary canal, it carries with it their important principles, preserves 
them fluid through the chyle and blood, then parting from them aa 
they become fixed in the tissues, returns to perform the same round 
again. By decomposition in presence of water, common salt yields 
an acid and an alkali, hydrochloric acid and soda. This separation is 
is effected in the system, indeed there is no other source for the hy- 
drochloric acid of stomach digestion. The considerable quantity of 
soda in the bile and pancreatic juice, which serve for intestinal diges- 
tion, as weU. as the soda of the alkaline blood, are chiefiy derived from 
common salt. A portion comes directly from the food, but by no 
means sufficient for the wants of the body. Yet it is highly probable, 
that in the econony of the system, the same materials are used over 
and over, the acid of the stomach, as it fiows into the intestine, com- 
bining with the soda it finds there, and reproducing common salt, 
which is absorbed into the blood, decomposed, and yielded again to 
the digestive organs. We recollect that common salt consists of 
chlorine and sodium ; it is a chloride of sodium. Chloride oi potassium 
is another salt of apparently quite similar properties. Tet in their 
physiological effects, they are so different, that while chloride of 
sodium exists largely in the blood, it is not present in muscles or juice 
of flesh, chloride of potassium being found there. They seem to have 
distinct and different offices, and are not replaceable. But the chlo- 
rine of the chloride of potassium comes from common salt. It may 
be remarked, that as phosphate of soda exists in the blood, phosphate 
of potash belongs to flesh-juice and muscles. 

696. Commott Salt contained in Food. — Salt escapes from the system 
by the kidneys, intestines, mucus, perspiration, and tears. To re- 
place this constant loss, and maintain the required quantity in the 
body, there must be a proper supply. It is universally diffused in 
nature, so that we obtain it both in the solid food we consume and in 
the water we drink, though not always in quantity sufficient for the 
demands of the system. Yet the proportion we obtain in food is 
variable, animal diet containing more than vegetable ; though the 
parts which most abound in this ingredient, — the blood and cai-ti- 
lages — are not commonly used for food. Of vegetable foods, seeds 
contain the least amount of common salt, roots vary in their quantity, 


turnips having hardly a trace. Yet mucli depends upon its abundance 
in the soil, and even in the atmosphere ; the air near the sea being 
saline from salt vapor. Plants near the sea are richer in soda than 
those grown inland, the latter abounding in potash. When we reflect 
upon the importance of the duties of salt in the organism, and that its 
necessary proportion in the blood is so much larger than in the food, — 
often tenfold greater — and besides, that its quantity is extremely vari- 
able in our aliments, its almost universal use as a condiment, will not 
surprise us. The craving for it is very general — probably instinctive 
— but where it does not exist, we conclude, either that sufficient is 
furnished naturally in the food and drink, or that animals suffer for 
the want of it. The quantity annually consumed by each individual 
in France, has been estimated at 19| lbs ; in England at 22 lbs. 

697. Effects of too little and too much Salt. — From what has been 
said, we see that a due supply of salt is of the first necessity ; its de- 
ficiency in diet can only prove injurious. The most distressing symp- 
toms, ending in death, are stated as the consequence of the protracted 
use of saltless food. The ancient laws of Holland " ordained men to 
be kept on bread alone, unmixed with salt, as the severest punish- 
ment that could be inflicted upon them in their moist climate ; the 
effect was horrible ; — these wretched criminals are said to have been 
devoured by worms engendered in their own stomachs." Taken into 
the system in large quantity (a table spoonful), it excites vomiting ; 
when thrown into the large intestines, it purges. A too free use of 
salt engenders thirst ; in moderate quantities, it increases the appetite 
and aids digestion. A long course of diet on provisions exclusively 
salt-preserved, produces the disease called scurvy. This condition of 
body is believed by some to be due to a deficiency of potash com 
pounds in the system, as in the act of salting, various valuable all 
ments are abstracted (593). Potatoes, and vegetables rich in potash 
are excellent antiscorbutics — correctives of scurvy. Fresh flesh yieldr 
potash to the system unequally ; for in that of the ox, there is three 
times, in that of the fowl, four times, and in that of the pike, five times 
as much potash as soda. Experiments relating to the influence of com- 
mon salt upon animals, have given somewhat discordant results. In 
some cases, it improved their appearance and condition decidedly ; 
whUe in others, no such result followed. Yet the amount supphed 
naturally in the food, in the several instances, was not determined. 
Salt is supposed to be in some way closely allied to the nutritive 
changes, and some think it increases the metamorphosis of the 
body ; so that a free use of it would only be consistent with a liberal 


698. Carbonates of Soda and Potash. — The exclusive employment of 
these substances in extemporising light bread (509), makes a reference 
to their physiological action necessary. Carbonate of potash in its 
crude shape, appears a'spearlasTi; in its more purified form it is saleratus. 
Crude soda is known as sal-soda or soda-saleratus ; refined and cleared 
of its chief impurities, it forms carbonate and bicarbonate of soda. 
All these compounds have the common alkahne or burning property, 
which belongs to free potash and soda ; tut it is lowered or weakened 
by the carbonic acid united with them. The potash compounds are 
the strongest, those of soda being of the same nature but weaker. Yet 
the system, as we have just seen, recognizes essential differences be- 
tween them ; one pertains to the blood and the other to the flesh. 
According to the theory of their general use for raising bread, they 
ought to be neutralized by an acid, muriatic, tartaric, acetic, or lactic, 
thus losing their peculiar properties and becoming salts. These 
changes do take place to a certain extent, and the saline compounds 
formed, are much less powerful and noxious than the unneutralized 
alkalies ; their effects are moderately laxative. Yet, in the common 
use of these substances, as we have stated, the alkali is not aU ex- 
tinguished ; much of it enters the system in its active form. Pure, 
strong potash, is a powerful corrosive poison ; disorganizing the 
stomach, and dissolving its way through its coats, quicker, perhaps, 
than any other poisonous agent. When the alkalies are taken in small 
quantities, as where there is an excess in bread, they disturb healthy 
digestion in the stomach, by neutralizing its necessary acids (643). 
They are sometimes found agreeable as palliatives, where there is 
undue acidity of the stomach ; and, on the other hand, they may be 
of service in the digestion and absorption of fatty substances. It is 
alleged that their continued use tends to reduce the proportion of the 
fibrin in the blood. Cases are stated, where families have been poisoned 
by the excessive employment of saleratus. 

B.— Liiqnid Aliments* 

699. Physiological importance of Water. — "Water is the most abundant 
compound in the body, constituting 80 per cent, of the blood, and 75 
per cent, of the whole system, — in importance to life it ranks next 
to oxygen of respiration. An adult umn takes into his system three- 
quarters of a ton of it in a year. It supplies some of the first condi- 
tions of nutrition, and is, therefore, entitled to head the list of aliments 
(366). It is the simple and universal bevei-age furnished by nature, for 
all living beings, and exists in greater or less proportion, as we have 


seen, in all solid food. Vegetables and meats are, at least, three- 
fourths water ; while bread is about 45 per cent, or nearly one half. 
Athough there is a little water even in the dryest food, yet the demand 
for it is so great, and its consumption so rapid, that our mixed ali- 
ments do not furnish sufficient, whUe the most nutritious, are the most 
provocative of thirst. Hence, we daily drink large quantities of it in 
the free or liquid condition. 

700. Its twofold state in the body. — Water exists in the body, in the 
fluctuating, circulating, liquid condition ; and also fixed as a solid in th« 
tissues. In the liquid state, it subserves the same great purpose :^ 
in the world of commerce, it is an agent of transportation. Its par- 
ticles glide so freely among each other, as easily to be put in motion, 
which makes it a perfect medium of circulation, and transportation of 
atoms. It is the largest constituent of the fleshy parts, serving to 
give them fulness, softness, and pliancy. Water is a vital and essen- 
tial portion of the animal structure, but hardly an organized constitu- 
ent. It is intimately absorbed and held in a peculiar mechanical 
combination, which permits of separation by pressure. " The milk- 
white color of cartilage, the transparency of the cornea, the flexibility 
and elasticity of muscular fibre, and the silky lustre of tendons, aU 
depend on a fixed proportion of water in each case." 

701. Water generated in the Animal System. — Water in large quantities 
is as necessary to plants as to animals ; but it serves an important pur- 
pose in the vegetable world, which it does not, or but to a small de- 
gree, in the animal kingdom. Plants decompose it, and use its ele- 
ments to form their peculiar compounds. The animal possesses this 
power in but a limited way, if at aU ; on the contrary, it is one of its 
leading offices to combine the elements which the plant separated, 
and thus produce water. Hydrogen and oxygen combine continually 
in the combustion of food, so that in reality, a considerably larger 
quantity of water is excreted from the system, than was introduced 
into it in that form. 

702. Influence of Water upon Digestion, — We have referred to the 
remarkable solvent powers of water (367). If we could look into the 
living organism, we should see that its whole scheme is but an illus- 
tration of it. Blood, juice of flesh, bUe, gastric and pancreatic fluid, 
saliva, mucus, tears, perspiration, and aU other peculiar liquids of the 
body, are simply water, containing various substances in solution. In- 
deed, the flnal result of the whole digestive process is to liquefy the 
aliments, or dissolve them in water. The effect of taking Liquids is of 
course to dilute the bodily fluids, just in proportion to the amount 


taken. The first effect "will be a dilation of the gastric juice of the 
stomach, but the water is rapidly absorbed into the blood, which is 
thus made thinner. It has been taught that the effect of swallowing 
much liquid during meals is to lower the digestive power by diluting 
and weakening the gastric juice. This is, however, denied by high 
authority. We know that excessive eating is usually accompanied by 
a copious nse of liquids, so that it is easy to commit the mistake of 
charging the evils of over-eating to the account of over-drinking. In 
such cases abstinence from drinks may be commended as a means 
of enfoscing moderate eating. Dr. Chambees, of ix>ndon, asserts 
that, " A moderate meal is certainly easier digested when diluents 
are taken with it." Again he remarks, " Aqueous fluids in large quan- 
tities during meals, burden the stomach with an extra bulk of matter, 
and, therefore, often cause pain and discomfort, but that they retard 
digestion I do not believe. Indeed, among the sufferers from gastric 
derangements of all kinds, cases frequently occur of those who cannot 
digest at aU without a much more fluid diet than is usual among heal- 
thy persons." 

703. Water iMoenees change of Tissue. — Beyond digestion is meta- 
morphosis of structure, and this is influenced by the amount of water 
drank. Eecent careful experiments by Dr. Bockee, performed upon 
himself, show that the use of any quantity of water above the actual 
demand of thirst, and the essential wants of the system. Increase the 
transformations of the solid parts of the body. He first ascertained 
what quantity of food and drink was just suflicient to satisfy his appe- 
tite and cover the losses of the system. He then found that by con- 
tinuing the same quantity of food, and increasing the proportion ot 
water, the weight of the body constantly dimiuished. The excess 
of water increased the waste, so that the same food would no longei 
restore it — the balance inclined on the destructive side. Neither tht 
pulse nor respiration were affected, but there was more languor aftei 
exercise, while the sensation of hunger kept pace with the increased 
metamorphosis of matter. 

Y04. Tea and Coffee. — These are taken in the form of infusions, the 
composition and preparation of which have been described (551). 
They are allied to foods by whatever nutritive constituents they hap- 
pen to have, which are inconsiderable, and they are distinctly separa- 
ted from them by possessing certain additional qualities which do not 
pertain to nutriment. The ingredients to which tea and coffee owe 
their peculiar action are thein and cafein, tannic acid and volatile or 
empyreumatic oU. 


705. Effects of Tea, — Thotigh tea is so universally employed in diet, 

yet its effects upon the constitution are by no means precisely ascer- 
tained. Its tannic acid gives an astringent taste, and a constipating in- 
fluence in the intestines. It also acts as a diuretic. Thein and vola- 
tile oil of tea are its most active ingredients, producing, perhaps 
jointly, its characteristic effects upon the nervous system. It is 
acknowledged that tea is a brain excitant, that it influences the mind, 
and produces exhilaration and wakefulness. How it effects the men- 
tal faculties, observers have been unable to decide, judging by their 
discrepant statements. If the quantity of thein contained in an oimce 
of good tea (8 or 10 grains), be taken, unpleasant effects come on, the 
pulse becomes more frequent, the heart beats stronger, and there is 
trembling of the body. At the same time the imagination is excited, 
the thoughts wander, visions begin to be seen, and a peculiar state of 
intoxication supervenes; all these symptoms are followed by, and pass 
off in, a deep sleep. Dr. Booker has made several careful sets of ex- 
periments upon his own person to determine the physiological effects 
of tea. He took exact account of the quantity of aliment ingested, of 
the substances excreted, of his own weight, and the general bodily 
sensations. His investigations lead to the conclusion, Jirst, that tea in. 
ordiuary doses has no effect on the amount of carbonic acid expired, 
the frequency of the respirations, or of the pulse ; second, when the 
diet is insufficient, tea limits the loss of weight thereby entailed ; 
third, when the diet is sufficient, the body is more likely to gain weight 
when tea is taken than when not ; fourth, tea diminishes the loss of 
substance in the shape of urea, lessens the solid excretions, and limits 
the loss by perspiration. It is thus claimed that this beverage is an 
enlivener of the mind, a soother of the body, and a lessener of the 
waste of the system. 

706. Influence of Coffee in Digestion. — The active ingredients of cof- 
fee are cafein, which is identical in properties with thein of tea, and 
the peculiar empyreumatic or burnt oil produced in roasting. "By 
the presence of empyreumatic substances, roasted coffee acquires the 
property of checking those processes of solution and decomposition 
which are begun and kept up by ferments. "We know that all em- 
pyreumatic bodies oppose fermentation and putrefaction, and that, for 
example, smoked flesh is less digestible than that which is merely 
salted. Persons of weak or sensitive organs will perceive, if they at- 
tend to it, that a cup of strong coffee after dinner, instantly checks 
digestion ; it is only when the absorption and removal of it has been 
effected, that relief is felt. For strong digestions, which are not suf- 


ficiently delicate reagents to detect such effects, coffee after eating 
serves from the same cause to moderate the activity of the stomach, 
exalted beyond a certain limit by wine and spices. Tea has not the 
same power of checking digestion ; on the contrary, it increases the 
peristaltic motions of the intestines, and this is sometimes shown in 
producing nausea, especially when strong tea is taken by a fasting 
person" — (Liebig.) 

Y07. Lehman oa the inflnenee of Coffee. — "We are indebted also to Pro- 
fessor Lehman for valuable experiments to ascertain the effects of cof- 
fee. He states that coffee produces two leading effects upon the gen- 
eral system, which it seems difficult to associate together, viz : height- 
ening vascular and nervous activity, and at the