THE HAND-BOOK ' - OP HOUSEHOLD SCIENCE. A POPULAR ACCODN'J' OF HEAT, LIGHT, AIR, ALIMENT, AND CLEANSING, THEIR SCIENTIFIC PRINCIPLES AND D03IESTIC APPLICATIONS. WITH NXJMEROTTS ILLTJSTEATIVE DIAGEAMS. ADAPTED FOR ACADEMIES, SEMINARIES, AND SCHOOLS. EDWARD t^YOUMANS, JlUTHOE OF "tnk class-book op chemistry," "chemical atlas " and " chaet," "alcohol and the constitution of man." NEW YORK: D. APPLETON & CO., 346 & 348 BROADWAY. CINCINNATI : RICKEY, MALLORY & COMPANY, 1860. 74951 Enteekd according to Act of IJongrcss, in the year 1867, by D. APPLETON &, CO.. In the Clerk's Office of the District Court of the United States for the Southern District of New York. CONTENTS PART I.— HEAT. rAOB PREFACE, 7 INTRODUCTION, 11 I. Sources and Distribution of Tberesteial Heat, .... 17 II. Influence 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 by moving Matter, .... 36 Vn. 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 op Chimneys, ... 55 XI. Apparatus op "Warming, 60 1. Open fireplaces 62 2. Stoves, 67 8. Hot-air arrangements, 70 PART II.— LIGHT. I. Nature of Light — Law op its Diffusion, 76 II. Reflection op Light, _ . . 79 [II. Transmission and Refraction op Light, 82 rV. Theory of Light — Wave movements in Nature, . . . , 84 V. Composition and mutual relation op Colors, . • . . . .88 VI. Practical sugobstions in combining Colors, .... 102 IV CONTENTS. VII. PnoDUCTioN OP Artificial Light. 1. The Chemistry of Illumination, .... . 105 2. Illumination by means of Solids, .... 108 3. Illumination by means of Liquids, 112 4. Illumination by means of Gases, lit 5. Measurement of Light, 13A VIII. STRUCTUnE AND OPTICAL POWERS OF THE EtE, . . ' . . . 126 IX. Optical defects of Vision — Spectacles, 131 X. InjCRIOCS ACTION OF ARTIFICIAL LiGHT, 137 XI. Management op Artificial Light, 149 PART m.— AIR. I. Properties and composition of the Atmosphere, .... 150 II. Effects of the constituents of Air. 1. Nitrogen, . 164 2. Oxygen, 154 3. Moisture, 157 4. Carbonic acid, 161 6. Ozone and electricity, 164 III. Condition op Air provided by Nature, 165 IV. SoCRCEa OF IMPURE AlR IN DWELLINGS, 168 V. Morbid and fatal effects of imfcre Air, 174 VI. Rate of contamination within doors, 181 VII. Air in Motion — Currents — Draughts, 185 VIII. Arrangements for Ventilation, 198 PART IV.— ALIMENT. I. Source of Aliments — Order of the subject 206 II. General properties of Alimentary Substances. 1. Principles containing no Nitrogen. A Water, ... 207 B The Starches, 21$ C The Sugars 21» D The Gums, 229 E The Oils, 22> P The Vegetable Acids 225 2. Principles containing Nitrogen. A Vegetable and Animal Albumen, 227 B Vegetable and Animal Casein 228 C Vegetable and Animal Fibrin 223 D Gelatin, 230 CONTENTS. V PAGB 8 Compound Aliments — Vegetable Foods. A The Grains, 231 B Leguminous Seeds, 241 C Fruits, 243 D Leaves, Leafstalks, etc., 244 E Eoots, Tubers, Bulbs and Shoots, 245 4. Compound Aliments — Animal Foods. A Constituents of Meat, 243 B Production and composition of Milk, .... 250 in. CuLixAUY Changes op Alimextart Substances. 1. Combining the elements of Bread, 256 2. Bread raised by Fermentation, 259 262 . 267 271 . 274 277 . 281 285 . 287 8. Properties and action of Yeast, . 4. Raising Bread without Fermentation, 5. Alterations produced in baking Bread, 6. Influence 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 Beverages. 1. Properties and preparation of Tea, 289 2. Properties and preparation of Coffee, 293 3. Cocoa and Chocolate, 298 V. Preseevation of Alimentart Substances. 1. Causes of their Changeableness, 300 2. Preservation by exclusion of Air, 302 3. Preservation at Low Temperatures, ' 306 4. Preservation by Drying, 809 5. Preservation by Antiseptics 311 6. Preservation of Milk, Butter, and Cheese, . . . 314 VI. Materials of Culinart and Table Utensils, 313 VII. PuTSIOLOGICAL EFFECTS OF FoOD. 1. Basis of the demand for Aliment, 324 2. Digestion — Changes of food in the Mouth, .... 330 3. Digestion — Changes of food in the Stomach, . . . 335 4. Digestion — Changes of food in the Intestines, . . . 344 5. Final destination of Foods, 347 6. Production of Bodily Warmth, 853 7 J'roduction of Bodily Strength, 360 VI COimSNTi. PAOI 8. Mind, Body, and Aliment, 864 9. Influence of Special Substances. A Saline Matters, 369 B Liquid Aliments, 874 C Solid Aliments 383 10. Nutritive value of Foods, 392 11. The Vegetarian Question, 402 12. Considerations of Diet, 403 PART v.— CLEANSING. I. Pbincipal Cleansing Agents, 422 II. Cleansing of Textile Articles, 428 m. Cleansiko of the Person, 431 IV. Cleansing of the Air, 436 V. Poisons, 441 APPENDIX 443 QUESTIONS .... ... ... 445 INDEX ... , , . . 466 PKEFACE. A DESIRE 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 imiversal; their applications are special and peculiar. There are general laws of Hght, 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. Diffei'ent colors, when brought together, alter and modify each other according to a simple and beautiful laAv ; 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 Vm PEEFACE. 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 liis medical education ; but for the same reasons of life and death, the inhabitants of houses are concerned to vmderstand 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 application. 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 ; first^ to present such facts and principles as have the directest bearing upon household phenomena ; and, second^ to bring into prominence many important things not foimd 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 eflects ; we have accordingly dwelt upon these points with something of the fulness which their impox'tance demands. So with heat, light, 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. "NVe have spared no pams to give the latest and most authentic results. ^Uthough the vol- ume is to a great extent self-explanatory, and adapted for family and general reading, yet in the proper order of school PEEFACK IX Study it will find its most appropriate place after a course of elementary lessons in chemistry 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 difiiculty, 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 w^e would enjoy the thoughts of science we require to learn at least a portion of the language in whicli alone these thoughts are conveyed. The new objects and relations must be named, or they camiot 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 famiharized in 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 nature 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 X FBEFACE. suitable statement. Exemption from errors can hardly be expected in a work of this kind — errors of oversight and eiTors 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 reliable presenta- tion of the subjects considered. The Author desires to acknowledge his indebtedness to his sister, Eliza A. Yousiajns, for constant and invalua- ble aid in the preparation of the work, not only in various experimental oj^erations incident to its progress, but also m several parts of its hterary execution. To his friend Mr. Richard II. Manning, who, though engaged in absorbing mercantile pursuits, has yet found time for thought in the di- rection of science and its applications, his thanks are due for valuable suggestions and important manuscript corrections. If the Avork 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 Yoiik, August, 1857. IKTEODUCTION. When a work is presented, claiming place in a systematic course of school 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 influence upon the mind of the student? In this twofold connexion there are some thoughts to which we solicit the reader's earnest and considerate attention. 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 Sib Henky "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 world." 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 daily 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 imderstand- XU INTBODUCnON. ing and reason, ho should yet have contrived to maintain so dense and perfect an ignorance of himself and the familiar objects by which he is surrounded. That exact knowledge of the ways of nature which puts her powers at human command, and bears 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 jn-eliminary 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 realm of abstraction, farthest removed from the vulgarities of mere matter — the discovery of mathematical principles. The earliest 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. CoPEKNicTjs 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 Eumfoed 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 modern science, the discovery of oxygen gas by Peiestlt, and the earliest analysis of the air we breathe. Chemistry, which is the name given to the first serious grappling 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, agricultural, 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 metaphysical vacuities, gradually closed Avith the pliysical world, and now finds its last and highest inquest into the material conditions of man's daily life. The course of knowledge has been expansive, iis will as pro- gressive; from narrow views to universal principles; from empty speculations to world-wide utilities; from the pleasure of a few to INTBODUCTION. XIU 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 aU 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 mfluence upon the schenu of popular education. It is its first duty to communicate that infor- mation Avhich can be reduced to daily practice, and yield the largest measure of positive good. If recent inquiry has opened new ti'easures of available truth, it is bound to take charge of them for the general benefit. It must report the advance of knowledge, and Jieep 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 afford 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 intrinsic 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 life 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. XIV INTRODUCTION. Shall the thousand matters of mere distant and carious concernment bo suftcred to hold precedence of the solemn verities of being which are Avoven into the contexture of familiar life ? The physical agents w'liich perpetually surround, and act upon, and within us, heat, light, air, and aliment, are liable to perversion through ignorance,so as to produce sufFcring, disease, and death; or they are capable through knowledge of promoting health, strength, and enjoyment. What higher warrant can bo asked that their laws and effects shall becon)e 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 Avithout 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 appai'cntly less cared for in these respects than the inferior animals. Nevertheless, such is tho divine ordination. Xcitlier our Bonses, instincts, nor uninstructed faculties are suflBcient 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 tho properties nor the presence of the most deadly agents. The breathing medium may be laden with noxious gases to the peril of life, and tho senses tail to detect the dan- ger. Hunger and tliirst impel us instinctively to eat and drink, but they fail to inform us of the nutritive value of alimentary substances or their dietetical fitness to our varying requirements. For all tliose 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 evil. 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 tho matter of ventilation. Gas- lighting was a groat advance on the methods of artificial illumination, but there came witli it augmented contamination of the breathing medium and new dangers to the eyes. Against these and similar in- cidental mischiefs — ' residues of evil ' that accumulate against the pre- dominating good, there is no other protection than intellect, instructed INTRODUCTION. XV in the material conditions which influence our health and life, for these, and kindred considerations of practical moment to all who oc- cupy dwellings and assume civilized relations, we urge the study of household science as an essential part of general education. It deserves to bo better understood, that the highest value of science is derived from its power of advancing tlie public good. It is more and more to be consecrated to human improvement, as a sublime re- generative agency. Working 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 np 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.' Fron) XVI INTRODUCnOW. this authoritative moral demand science cannot be exempted. The power it confers is to bo held and used as power is exercised by God himself, for purposes 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, fiict and law. To tlie i)oetic 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 ia 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 the 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 multiplies its materials, and boundlessly amplifies its scope ? Can that bo 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 the 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 affords the most exhilarating, as well as the healthiest and purest of intellectual enjoy- ments? Nor should we forgot 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 rNTRODUCmON. XVll rainda with the richest materials of thought, enlarging our capacitiea of benign exertion, and rising to a more intimate communion with the spirit of the Great Maker of all. But beyond 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 metliod to wliich it accustoms the mind is too little available in gi'appling 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 therefoi'e 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 musu 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 — induc- tion. That the whele is greater than a part, or that two parallel lines will 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- XVm INTRODUCTION. stead of beginning with llio fticts, and carefully evolving the general laws. The splendid achievements of modern science are the fruit uf the inductive method. This should he 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, cxiltivates order in their classification, and develops the reason tlirough 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 rciy 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 departments of thought, where, after the utmost labor, there still remain doubt, dimness, uncertaintj' 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, witli 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 shall best prepare it for varied and serviceable intellec- tual duty in the practical affairs of life. There is still another thought in this connection which it is im- portant should be expressed. It has been too ranch the policy of the past so to train the mind as to enslave, rather than to arouse it. Edu- cation, from the earliest time, has been under tlie patronage of civil and ecclesiastical desj)otisms, whose necessary policy has been the re- pression of free thought. The state of mind for ever insisted on has been that of submissive • acceptance of authority. Instead of laying open the limitations, uncertainties, and conflicts of knowledge, which arise from its progressive nature, the spirit of the general teaching Las been that all things are settled, and that wisdom has reached its last fulfilment. Instead of encouraging bold inquiry, and inciting to noble conquest, the effect has 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 INTRODUCTION. XIX of tilings has been deeply disturbed. The introduction of Re- 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 degi-ee, corrected by a frank admission of the incompleteness of much of our knowl- edge; by showing that it is necessarily imperfect, and that the only just and honest course often involves reservation of opinion and suspension of judgment. Tliis 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 tliat 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 difficult 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 arc, 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 >: XX INTRODUCTION. one who is early instructed in an uncertain science snoh 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, will 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 Avork 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 bo 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 ahall 9peak of the possibilities that are waiting for him in the future i THE HAND-BOOK OF HOUSEHOLD SCIENCE. PART FIEST. HEAT. I. SOURCES AND DISTRIBUTION OF TERRESTRIAL HEAT. 1. Nature of our Knowledge concerning 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 both 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 diflferent feelings by moving in opposite directions, and which makes the diflference be- tween summer and winter, nobody has yet discovered. It is named Tieat. Some have conjectured it to be a kind of material fluid, exceed- ingly subtle and ethereal, having no weight, existing difiused through- ,out aU things, and capable of combining with every known species of matter ; and this supposed fluid has received the name of caloric. Others think heat is not a material thing, but merely motion : either waves, or undulations produced in a universal ether, or a very rapid vibration, or trembling 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 understand nothing, and are acquainted only with its effects: — our information is limited to its behavior. It resides in matter, mores through it, and is capable of variously changing its conditions. It is an agent producing the most wonderful results every Avhere around and even within us ; — a force of such tremendous energy, such far-reachiug, all-pervading influence, — that we may almost venture to say it has been appointed to take control of the material universe ; 18 SOFECES OF TERBESTEIAL HEAT. while in the plan of the Creator, it is so disciplined to the eternal re« straints of law, as to become the gentle minister of universal benefi- cence. 2. To what Extent the Earth is wanned by the Sun. Heat comes from the sun to the earth in streams or rays associated with light. It has been ascertained by careful measurement, that the quantity of solar heat which foils upon a square foot of the earth's surface in a year would be sufiicient to melt 5400 lbs, weiglit 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 around 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. If 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 suflBcient to melt it in the course of a year. This quantity of heat would melt a shell of ice enveloping the sun's sxirface 38.G 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 gi*ate having fifteen hundred thousand miles of fire-surface heated seven times hotter than our fiercest blast furnaces. 3. 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 aU directions from his surface, the earth receives but a small frac- tion. But it is neither lost nor wasted ; ho 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 fiUed. And what the sun docs, 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 eartli 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. rrs UNEQUAL DISTRIBUTION. 10 It results from the researches of Potjillet, that the starry spaces fur- nish heat enough iu 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 Avhole 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. Lardner.) 4, Heat ancqually Distributed upon 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 fi-ost 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 50 degrees ; and at Labrador (less than a thousand miles fm-ther 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. Dublin for example, though between eight and nine hundred miles further 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 Kome, it has also the winter of Copenhagen. ■ II.— INFLUENCE OF HEAT UPON THE LIVING "WORLD, 5. It Controls the Distribntion of Vegetable Life. — It is this variable quantity of heat received at different places and seasons, which deter- mines 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 still colder regions, these again give way to others of a hardier nature, or which are capable of 20 IITFLUENCE OF HBAT UPON THE LIVING WORLD. 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 tliem- 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, pine?, 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 Segalates the Distribntion of Animals. — It is the same also with animal life. Different 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- dines. 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 wf 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 Infloences Man's Physical DcTClopment.— Xor 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- powcrl'ul influence of heat. " The intense cold, dwarfs and deforms the inhabitant of the polar regions. Stunted, squat, large-beaded, fish- featured, short-limbed and stiff-jointed, he resembles iu many points the wolves and bears in whoso skins ho wraps himself. As he ap- oroachcs the sunny south, his stature expands, his limbs acquire shape IT AFFECTS MIND AND CHAEACTEB. 21 and proportion, and his features are ameliorated. In the genial region, he is beheld with that perfect conformation, that freedom of action and intellectual expression, in which grace and beauty consist." 8. Extremes of Dress in Diflferent 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 woollens and furs, fox-skins, sheep-skins, wolf-skins, and bear-skins, until 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 intelligent appreciation on his many- coated panoply against king Death." 9. Temperature and Character. — The effect of cold is to benumb the body and blunt the sensibility ; while warmth opens the avenues ot 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 sterility 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- zling, 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- 22 INFLUENCE OP HEAT UPON THE LIVING WORLD. being. It is within a narrow range of climate tliat great men have been born. In the earth's southern hemisphere, as yet, not one has appeared ; and in the northern, they come only within certain paral- lels of latitude. I am not speaking of that class of men, who in all ages and in every country, have risen to an ephemeral elevation, and have sunk again into their native insignificance so soon as the causes which have forced them from obscurity cease, but of that other class of whom God makes but one in a century, and gives him a power of enchantment over his felloAvs, so that by a word, or even by a look, he can electrify, and guide, and govern mankind." — (Dr. Deapeh.) 10. laflacnce of the Sapply of Foel.— The abundance or scarcity of the supply of fuel, as it controls the amount of artificial heat, exerts a power- ful influence upon the condition of the people in various ways ; indeed, it may involve the health and personal comfort of whole nations, to such 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 dull. The diminutive Laplander spends his long and dreary winter in a hut heated by a smoky lamp of putrid oil ; an arrangement which afficts 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 hearth. 11. Temperature and Langnaget — AEBurmroT 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, sonoroui elocution. 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 it? 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 heat, and the methods by which it may be produced IT INFLUENCES THE DIMENSIONS OE BODIES. 23 and regulated. Ho 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. III.— MEASUREMENT OF HEAT. THE THERMOMETER. 13. Heat tends to Equal Diffasion. — We have said that heat is a force, or energy, existing everywhere throughout nature. Every kind of matter which we know contains heat, but all objects do not contain equal quantities of it. If left to follow its own law, heat would dis- tribute itself through all the matter around, until 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 furniture. 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 balance 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, — robbing one substance of it and storing it up in another ; in short, its motion, and the effects it produces, which enable us 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 aecumnlating in Bodies, enlarges 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 point of 24 MEASITBEMEKT OF HSAT. pints of water, taken at the freezing point, would expand into twenty- four by being heated to boiling. The difference in the heat of the seasons affects sensibly the bulk of liquors. In the height of summer, Fio. 1. spirits will measure five per cent, more than in the depth of winter. (Graham.) "When 180 degrees of heat arc added to iron, 1000 cubic inches become 1045; 1000 cubic inches of air become 13G5. 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. From this point, either upward or downward, it enlarges ; and CTtatest at freezing, or 32°, the expansion amounts to about "■"^ ^' Jth of its bulk. Ice therefore floats upon the surface of water. The ■wisdom of this exception is seen, when wo reflect, that if it sank as fast as it is formed, whole bodies of water •would be changed to solid ice. IG. Relation between Heat and Expansion. — In the same manner, all the objects about us are changed in tlieir 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 cjdled impoTiderahU. 17. Principle and Constrnttion 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 fine aperture or hole tlirough 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 filled 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 ice, and a mark is made SCALES OF THERMOMETERS. 25 Fahrenheit's Scale. Fig. 2. 2120 1220 32° Zero. Centigrade Scide. lOOO 60O Zero. upon the tube at the top of the mercurial column. This pcint of molting ice is the same as that at which water freezes, and is hence called ih.Q freezing point. The tube is then removed, and dipped into boiling water. The heat passes from the Avater, 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 loiling point of watei: 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 through these 180 spaces is precisely the same quantity that changed the water from the freezing to the boiling point ; so that we may say that the water in this case received 180 degrees of heat. If we mix a pound of water at the boiling point with another pound at the freezing point, the result will be a medium ; and if the thermometer is plunged into it, the mercury will stand at the ninetieth space — that is, it contains 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 Thermometers are Gradnatcd 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 degrees 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 fell 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, notight or zero he counted up to the freezing point of water, which was 32°, and Thermometer. 86 MEASUBEMSNT OF BEIT. adding this to the 180 above, he got 212 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 Reaumur'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 Bpace. 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 quajitity. But wo must not suppose that the thermometer indicates quantities of heat in any absolute sense. For example, if we dip a gill 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 wo cannot thence infer that the absolute quantity of heat is as great in the gill 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, Ave 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. "Wo shall sliortly see that there are certain conditions of heat which the thermometer totally fails to recognize. 20. Importance ofthe 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 tlie maintenance of health, it wUl 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 THEEMOMETERS AND THEIR ESTDICATIONS. 2"? and tube may be drawn out of the frame, bo 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. Tagliabue, 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 cholera) 67* Mean temperature at the equator 81* Heat of the blood 98* Beef 8 tallow melts 100* Mutton tallow melts 106* Highest temperature of human body (in tetanus or lockjaw) .... 110* Stearine melts Ill" Spermaceti melts 112'' Temperature of hot bath llC-lSO* Phosphorus inflames, Friction matches ignite 120* Tea and coffee usually drank . . ISO'-WO" 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 820°-400° Sulphur ignites 560° Heat of the common fire 1000' IV. RADIATION OF HEAT AND ITS EFFECTS. 22. Heat passing throngli Bodies. — Heat in motion around us is con- stantly passing through some substance, or from one material body to another. But all substances do not behave alike toward it. They do not all 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 transmit 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 tcinperaiuroM, see Appendix, A. 28 EADIATION AND ITS EFFECTS. Badiation of heat. 28. Decrease in the Foree of Dcat-rays. — "When heat radiates from any source, as the sun, a stove, an open lire, or flarae, it pas-scs from each point in all directions Fig. 3 ; it spreads out or diverges as it F'o- 8. passes away so as to become weaker and much / less intense. It decreases in power at a regular / yy numerical rate, as seen in Fig. 4. It is commonly //y^''',,' 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 dbtance of two feet from it, we receive a certain amount of heat, and then we step back 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 ?hown 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 Fio- 4- is, a surface, which is the way it is practically emitted, it does not decrease at so rapid a rate. 24. Different kinds of neat.— "We all know that some substan- ces Avill 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 Showing the rate nt which radiant heat is without obstruction ; but water, diffused and weakened. ^^.j^j^^ ^^ ^^^^-^^^ ^^^^^,^ ^j^^ ^^ sage of light, has very little power to transmit TIbat. Rays of light, passing through water, are strained 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 Bolar 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 wo place a plate of glass and of rock-salt before a hot stove, the dark heat, w ill pass freely through the salt, but not through the glass. The glass is, therefore, opaque to heat (if wo may borrow the language of light), while salt is transparent to it, and is hence called the glass of heat. CIKCUMSTANCES CONTEOLLING IT. 29 Meloni has shown that if the quantity of dark, radiant heat transmit- ted through air, bo 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 whieh docs not go throngli is Absorbed. — 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, ai-e said to bo alsorbecl by it. Thus, fine window-glass transmits only 49 heat rays in a hundred, the remaining 51 being cibsorled 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 oflt' its heat. As it cools, the radiation becomes slower and slower. But all subtances at the same temperature, do not throAV out their heat alike. The condi- tion of surfaces exerts a powerful control over radiation. Eough, uneven surfaces radiate freely, whUe smooth, polished surfaces ofier a barrier to heal, which greatly hinders its escape. Metals, as their sur- faces are capable of the highest polish, are the worst radiators. Ac- cording to Meloni, surfaces 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 will 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-blackgd surface, as 100, clean bright lead is 19, while if tarnished, it is 45. If the actual radiating surface is metallic, it matters little what substance is imder it. Glass covered with gold-leaf, is re- duced in its radiating power to the condition of a polished metal. If the bright, planished, metallic surface 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. Etjmford took two similar brass cylinders, cov- ered one with a tight investment of linen, and left the other naked • he then filled each with hot water, and found that the same amount of 30 BADIATION AND ITS EFFECTS. heat which was thrown off by tho covered cylinder in 36| minates required 55 ininntes to radiate from the naked cylinder. 27. How Polishing affects Surfaces. — Dr. Lahdner says " the diminu- tion of radiating power, ^yhich ordinarily accompanies increased polish of surface, is not a consequence of the polish in itself, but of the in- creased density of the outer surface^ produced by the act of polishing; and the effect of roughening is to bo 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 bo of polished metal, or have bright metallic covers, which Avill 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 beat 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 Iieat 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 facility. 30. Heat tlirown off from Bodies. — Radiant heat striking upon bodies, if it is not permitted to pass instantly through them in straight lines, is either abso^hed 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 will reflect tho heat rays and itself remain quite cold. As heat cannot get out through a bright surface, so it cannot get in through it. All the heat that is thrown upon such a body, is either reflected or absorbed ; that whicli is not disposed of one way goes the other. If half of it is absorbed, the other half will be reflected. Glass absorbs 90 percent, and reflects 10, while polished silver reflects 97 per cent, and absorbs but 8. A good obsorbing surface is a bad reflecting surface, and a good reflector is a THEOKY OF HEAT-EXCHANGES. 31 bad absorber. So a good radiating surface absorbs well and reflects badly, -wbile a bad radiating surface 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 beat 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 Surface inflaences the admission of Heat. — We have seen (29) that color has no influence over radiating surfaces ; but the power which bodies possess of obsorMng heat, depends very much upon color. Feaxklr; 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 still less, and the white hardly at all, which showed that it absorbed least heat. Hence, by scattering soot over snow, its melting may be hastened : it will 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, will mature or ripen eaiiier 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. 82. Exchanges of Heat— it escapes from all Substances. — 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. Rays 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 9.dwly, and thus returns a portion to the hotter ball ; so that there is an exchange estab- lished. But if a ball of ice at 52° be placed beside the cannon-ball at 32 RADIATION AND ITS EFFECTS. Exchanges of licat ; it radiates from bodies at all temper- atarcs. 100°, the same thing takes place, only in u less intense degree; and if Fio. 5. an ice-ball from the Arctic region at 100" below the freezing point, ^vere jjlaccd be- side another at 32°, ex- actly the same thing would occur. Thu3 all bodies are constantly interchanging heat and tending to equalization. 33. Starlight Klgbts colder than clondy Ones.— The various objects upon the earth's surface, are not only continually radiating their heat to each other, but also upward through the air into space. If there be clouds above, they throw it back again to the earth's surfocc ; 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 sink 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 Prodaccd. — The cause of dew was not understood untU lately. Many were persuaded that it came out of the earth; Avhile others thought it fell as a fine rain from the elevated regions of the atmosphere. The alchemists regarded it as an exudation 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(28G). "When, therefore, the air is suflSciently cooled, its moisture is condensed, and appears as drops of Avater. These are often seen in summer days upon the outside of the pitcher of cold water ; improp crly called the siceating 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 air in contact with them, IT EXPLAINS THE CAUSE OP DEW. 33 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 10" 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 Avith dew, while bad radiators remain dry. Grass, for example, is an excellent radiatoi", 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 bo 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, in both cases being the same. Farmers very well know that nights with heavy dews are very cold ; but the cold is the caicse, 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. Exclianges of Heat may preyent Dew. — 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 littl? 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 any way from exposure to the sky, are, to that extent, guarded from dew. 37. Frost Caused in tbe same way as Dew. — As a certam 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 and grain of autumn. Ilerc, ngain, all circumstances which oppose radiation, prevent the cooling. Vegetables, sheltered by trees, suffer less than 34 CONDUCTION OP HBAT. those not so protected. A thin covering of cloth or straw, preserves plants, as may also fires that fill the air with smoke. V. CONDUCTION OF HEAT AND ITS EFFECTS. 88. neat creeps slowly through some Bodies. — If we place one erul 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 pass 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. G. If now heat is applied ' to one end of the wire, it Tlie balls drop successively as the heat moves i n j. i 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 wc can fuse the end of a glass rod in a lamp, although holding it Avithin 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 lad conductors. In general, the denser a body is, — that is, the closer are its particles, — the better does it conduct heat ; wJiile 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. Rumford's Scale of Conductors. — Rumford 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 tliey are called, — affurd the best barriers to heat, and they are employed when it is desired to confine it. In winter, nature protects thfi earth and crops from excessive cold, by a layer of non- EPFKCrrS OF NON-CONDUCTING SUBSTANCES. 35 conducting snow. Tlie birds, she protects 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, nian 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. While they promote warmth in winter, by retaining the heat generated by fires within, they are favorable to coolness in summer, by excluding the external heat. Hutohin^son 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 G2, 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 Avinter, but if wetted, they convey heat much better. 42. ]Von-condacting properties of Air. — Air is one of the most perfect non-conductors; Rumfoed thinks it is the best of all. Tlie 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, chaff, &c., are good non-conductors of heat. Sawdust is an excellent bar to heat ; it should not be too laucli 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. IVon-condacting Properties of Clothing. — Winter apparel is made of non-conducting woollen fabrics, which prevent the escape of heat from the body. Cotton carries oflf 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- 86 CONVEYANCE OF HEAT. ton.* The liigli non-conducting i)Ower of the woollens, is showD by the common practice of preserving ice in hot weather, by siraplj' wrapping it in flannel. 44. Onr Sensations of Heat depend npon Condnction. — 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 tbe 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 maimer. If the hand bo placed npon 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 Air at 250° or 300° may be endured. Sir Joseph Bajtks went into a room, heated to 2G0°, and remained there a considerable time without incon- venience. The particles of air arc 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 ouce, the amount of heat that they can impart is comparatively small. VI. HEAT CONVEYED BY MOVING MATTER. 45. It is carried by Particles in Motion. — Tlie 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 Fi<'- "• 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 tcmi)erature of tlie water will be but lit- tle elevated in a long time. The conduction of heat is not influenced by the position of tho 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 (Iocs not conduct "^ . the heat downwards. been conducted, it would have travelled as readily down the water column as upward. Yet all understand that * Linen is also best for dressing local Inttanimations, because Its fibres are round and Bmooth, and therefore, less irritating. The fibres of cotton arc flat and angular, and of Woollen, rough and jagged, and consequcntlj-, unfit for this purpose (795). ITS TKANSPOETATION BY WATEK. 37 a large amount of water may be heated by a small fire, if the heat be apphed 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 flask Avith water, and dropping into it a few small pieces of sohd litmus (» cheap^ Hue coloring sul- 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 acquu-ed from the litmus, is seen rising to the surface of the liquid, when it bends over in 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 Eig. 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 tiling takes place when air 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 Currents produced in water warmmg rooms. by boiling. Fig. 8. YII. VAEIOUS PROPERTIES AND EFFECTS OF HEAT. 47. Heat added to Solids, liqaefics them. — Xot only is the size of bodies influenced by heat, but also their state^ or form. As heat enters a solid body, its particles are forced asunder, until at length they lose their cohesive hold of each other, and fall 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 liquefied by any amount of heat yet applied. Some solids, at a given point of temperature, enter 38 VARIOUS EFFECTS OF UEAT. suddenly iuto tho 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 different 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°, sulphur 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 solidifies. Take away the heat from Avater until it falls to 32°, and it becomes solid water, or ice. If kept per- fectly still, 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 raetal— 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 water generates steam. The heat which converts solids iuto liquids, is called caloric oi fluidity^ and as gases are known as elastic fluids, the heat which changes liquids to gases is called caloric 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 all 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 will raise the temperature of a pound of spirita of turpentine 50'^ in ten minutes, it will 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 will heat a pound of mercury through a certain number of degrees in a certain time, it will take 30 flames of tho same heating power, to raise a pound of water through the same range of temjierature in the same period ; to raise it through the same number of degrees, therefore, water requires thirty times WATER HOLDS LARGE QUANTITIES OF IT. 39 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 liave different capa'Cities for heat : and, as each substance seems to take a peculiar or particular quantity for itself, that quantity is said to he 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 amonnt 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 tardily 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 all 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 regulated. 51. Why Water is so cooling when drnnk. — 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 40 VAEIOUS EFFECTS OF HEAT. compressed, water is squeezed out ; but, wliea it expands again, it will again imbibe the 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 ita heat is driven out of its concealment, the iron becomes hot. By suddenly condensing the air as in the instrument called the fire-syringe, J, in which a close fitting piston is driven down a tube (Fig. [Xl^q 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 broiight it out. As we cannot find it by [f ■J^^HtI *^'*^ ordinary test, wo 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 t Air condenser. , , ,. c j.t i} i. • ii, true explanation ot the tacts in the case. 53. How mach Concealed Dcat Water holds. — Whenever a solid is clianged to a liquid, a certain amount of heat disappears — goes into the latent state. If Ave 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 \\\> 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 ico 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 different solids in entering upon the liquid condition STABILITY OF FORMS PKESERVED. 41 13 variable, but a certain amount disappears ia 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 Svill 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 bo sufficient to raise more than 80 pounds of ice- cold Avater up to boiling. 64. Beneficial Effects of this Law. — ^This law of the latent heat of liquidity, operates admirably to preserve the forms 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 33°, 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 sink 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 uumersing the cream or other liquid to be frozen (contained in a thin metallic vessel,) into the cold brine, produced by the melting of the ice and salt. A convenient method of freezing a little water 42 VARIOUS EFFECTS OF HEAT. without tbo uso of ice, is to drench powdered sulphate of soda (glaubcr's sah) with muriatic 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 solid to a liquid ah- sorls heat, the change of that liquid back again to the solid state, must liberate it. If the liquefyiug 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 wanning. 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, evaporjjtion constantly takes place from the surface of ice and snow. The ice upon the window often passes off as vapor, without taking on the intermediate 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 fost 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 exi)elled by heating. As the temperature increases, larger bubbles are formed at the bottom of the vessel, which rise a little way, and arc then crushed in and dis- appear. These bubbles consist of vaporized water, or steam, which ii« CONDITIONS WHICH INFLUENCE BOILING. 43 formed in the hottest part of the 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 boiling or ebullition. 59. Inflaenee 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 conseoyence of the oil having no attraction for the water, 60. Measnring tlie Pressure of the Air. — Aii* has weight like visible ponderable matter, and presses down upon the surface of water the eame as upon the ground. The pressure of the air is measured by a barometer^ 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 vai-ious 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 Vacuum, place of no preeaure. . B.E Barometer tube. 44 VARIOUS EFFECTS OF HEAT, certain quantity of air to press down upon the cartli, in gv^ing up a iiiouutaiu we leave nmch 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 wo rise higher. 61. Inflnenco of Air-pressure Dpon Boiling.— It is reported by travel- lers that, upon high mountains, meat cannot be cooked by the common method of boiling. 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 eft'ect. The boiling point thus fluctuates with the barometric colunm : the natural variations of atmospheric pressure, at the same level, make a difference of 4.V de- grees in the boiling jioint of Avater. 02. Employment of tlic Prineipie in Bcflning 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 boiling 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 boils away at a low temperature, leaving the sugar crj-stals 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 itsclj\ 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 tlian 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); alcoliol, 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 surfoce 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 tlio 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 ITS RELATION TO BOILING. 45 contact with the iron, and is at once exploded into vapoi*. 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 rcqnired to maintain Boiling, — If a liquid be con- fined in a sufficiently strong vessel, so that its vapor cannot escape, it may bo 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 bailing point, the fire may be at once reduced. Attention to this fact would save fuel in many culinary operations. 66. Doable 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 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 filled 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 bath : opening to introduce water. 46 VARIOUS EFFECTS OP HEAT. and so become diftused through it. We do not, therefore, heat it by conduction, but by currents produced within it (46), which distribute and commingle the heat throngliout its mass. It cools in the same way. As the particles at the surface or sides lose their heat, 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 oflf 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 tlie vapor, for it may all 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 Sj times as long to evaporate a pound of water, as it does to raise it from freezing to boiling ; it therefore receives 5^ times as much heat. If, tlierefore, 180° were required to boil 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 water, 1000° of heat must of course be concealed in it. The latent heat of steam is tlien 1000° ; when condensed, it surrenders that 1000° of heat. The condensation of a pound of steam will raise 51 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). Whei'ever condensed, it liberates large quantities of boat. C9. 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 dry ones, are colder. Evaporation dissipates the heat which fulls upon tlicm. The heat poured down from the sun in torrid regions would be intolerable, ITS RELATION TO EVAPORATION. 41 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 bodily 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 still 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. Th§ 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 au\ YO. Reason of " blowing 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 tho 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 which it strikes. If we desire to warm any thing with the breath, as cold hands, for example, we open the mouth and impel upon it the warm air from the lungs without disturbance from compression. 48 rXFLUENCE OP UEAT UPOX THE BODY. VIII.— PHYSIOLOGICAL EFFECTS OF UEAT. 71. Local Inflaencc of Ilcat upon the Body. — It has been noticed that tlie 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 Avarmth is occasioned by an expansion of the vessels of the skin, and the liquids wliich 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-diska arc enabled to enter tubes which would not previously admit tliem. The temperature rises, and there is a slight swelling 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. Medicinalor alterative stimulnnts 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 efiects 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 the cooling influence of surface evaporation (G9), but this power of the system cannot bo taxed with impunity. The rush of the circulation to the surface, and the increased transjjiration 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 falls. The pre- EFFECTS OF SUDDEN CHANGES — FUEL. 45; 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. — (Peeeiba.) 73. Consequences of sudden Changes.— But the worst effect of exces- sive heat, is not always the immediate stimulation, and consequent ex- haustion which it induces ; it is the sudden exposure to various de- grees of cold which often follows, when the system is in a relaxed and depressed condition, that accomplishes the most serious mischief, lay- ing the train 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 05° 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. IX. ARTIFICIAL HEAT— PROPERTIES OP FUEL. Y4. Artificial heat may be produced in various ways, but the com- mon method is by combustion^ which is a chemical operation carried on in the air. All the heat which we generate for household purpo- ses, 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, on 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 the air. The nitrogen dilutes and weakens it, thus restraining its ac- tivity. 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 ; that 3 50 PROPERTIES OP FUEL. depends upon the other elements : hence, the more oxygen, the lesa 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 gaseom carbon. At the intensest white heat, where nearly every other substance melts, or dissipates into vapor, carbon remains fixed. It is the solidifying clement of fuel, and it is this property which makes our fires stationary. 76. Hydrogen, and its Office 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 cambined with fuel, it is condensed down into a solid state, but in the act of burning, it is released, and escapes into the gaseous form. It therefore iur/is in motion^ audit is this which produces flame. 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, oxj-gen has powerful attractions, and combines with them, produciug 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 combustion, or kindle the fire. 78. Products of Combustion. — When tlic combustive process has commenced, two things take place ; the fuel disappears, and the air is changed. Tlie substance of fuel is not destroyed, it only clianges its shape, takes on the invisible form, aud mounts into the air. Oxygen combines with carbon, both elements disappear, and a new product ITS CHEMICAL CONSTITUENTS. 61 results — carbonic acid gas (293). As carbouic acid is tlius given off every where by combustion, it is a constant and universal constituent of the atmosphere. It forms l-2000tli of the air, and would increase in quantity, but it is constantly 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. Facl is changed before it is barned. — 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 2f 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 ^o 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. 52 PROPERTIES OP PUHi. Suppose that 100 pounds of wood contain 30 of Avalcr, they have then but 70 of true coinbustive material. When burned, 1 i)Ound 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 -f'^ 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 jield equal amounts of heat. According to the careful experiments of Mr. Maeous Bxjix, the rela- tive heating values of equal bulks {cords) of several American woods, are expressed as follows; — shell-bark hickory being taken as 100. 100 Yellow Oak . . GO 95 Hard Maplo . 60 81 Whit© Elm . . 69 77 IJed Cedar 56 75 Wild Cherry . 55 73 Yellow rino 64 72 Soft Maplo . . 64 70 Chestnut . 52 C9 Yellow Poplar . 62 65 Butternut . 61 65 White Birch . . 48 63 White Pine 43 Shell-bark Hickory Pignut Hickory White Oak White Ash Dogwood Scrub Oak Witch Hazel Apple tree . Ked Oak White Beech . Black Walnut Black Birch 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 var}' 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. Why Soft and Hard Woods bnrn 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 produce less flaTse, 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 BUKNING OF WOOD AND COAL. 6Z woody fibre, or lignin, from all kinds of wood, lias 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 weigJits) 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 FacK — 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, hydrogen is set free, and there is produced a small amount of flame. Being very light and porous, and its vacancies being filled with condensed oxygon, (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 i)ure 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 difficult in the grate to keep the whole mass of coal in a state of vivid redness, as the t4 PKOPEBllES OP FUEL. air conveys away so much heat from the surface of the fire as to coo. it down below the point of combustion (114). Anthracite burns without flame, smoke, or soot, although with sulphurous vapors, wliich, when the draught is imperfect, or when burned in a stove, are liable to accumulate in the room, to tlie serious detriment of its inmates. Tlie 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. 87. Combnstlon of Bitaminons Coal. — When the great natural process of underground charring is less advanced, the coals are hituminons\ 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' bitummous coal, and in burning, they soften or melt down into a cake, {caTcing 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 iron 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 small proportion of sulphurous vapor, and the common carbonaceous constituents of smoke (103). Its heat is much less violent than that of anthracite. 88. Lignite or Bromi Coal is thatVariety which seems to have been least charred, and stih retains the woody structure; its combur^ive value is low. 89. Heating Efllsets 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 will raise from tlie freezing to the boiling point, 73 pounds of water. One pound of min- eral coal will heat 60 pounds of water tlirough 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 eflJect ; and besides, tlie circumstances under Avhich the fuel is bnrncd, wliether it he in a stove or fire-place, makes considerable difference in the residt. 90. Amoant of Air required to consanie Fuel. — As the weight of air ASCENT OF AIB THEOUGH CHIMNEYS. 56 necessary to burn fuel is vastly greater than the fuel itself, and as air is exceedingly light, it will 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 18 cubic feet of space, the pound of charcoal wiU requii-e 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 hinders Combustion. — 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). X.-AIRCUREENTS— ACTION AND MANAGEMENT OF CHDINEYS. 92. Cause of the Chimney 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 a. flue or chimney. 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 66 ACTION AND MANAGEMENT OF CHIMNEYS. di'aught depends upou the velocity of the rising current, and tliat again upon the difference of weight between tlie 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 ho its ascensional force. All high chimney stacks, with large channels, containing highly rarilied air, produce roaring draughts ; while if they be short and narrow, and their temperature low, the draught is proportionally enfeebled. Friction against the sides of tie 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 bo increased. If it be narrowed at top, the smoke and hot air will be discharged above with more force, and lience 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 smoke. 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 shaft 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 ol air at a high temperature, by which its volume is so much increased, that, although the velocity may be very great, the quantity^ Avhcu reduced to the temperature of the atmosphere, is less than at a lower temperature. — Wtmax. ^ 94. UTinds eause Chimneys to Smoke. — A high building, or a tree standing close to a chimney and overtopping it^ often disturbs its draught. The wind passing over these objects, falls down like water over a dam, and stops the ascending current so that smoke is forced back into the room ; or the wind may strike against the higher i^bject, and, rebounding, form eddies, and thus beat down the smoke. "When chimneys arc not thus commanded by eminences in the vicinity, gnsta f air may still interfere with their draught. To prevent this, tlicy DISTURBANCES OF THE DEAUGUT. 51 are often mounted with turmaps, cowls, or ejectors (354) wliioh are so constructed that the effect 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. 96. New and Damp Chimneys. — "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 Dranglits. — 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 still more favorable warna 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 eacli otlier. — 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. la degree of heat, throws it promptly into movement. We are apt to forget the exceeding delicacy 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 will over- come that in the shorter, and create a downward current in the latter; or if two tubes of equal length, united 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 thirfl 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 diflficult, if not impossible ; for though currents may be commenced in both routes, one quickly neutralizes the other, and but a single flue is used. 68 ACTION AND MANAGEMENT OF CniMNEYS. Fio. 14. 98. One Chimney overiJowerinR another. — When tliero are two tirc-placus in a room, or in rooma communicating by open doors, a fire in the one may burn A'ery ■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 dilficulty may be remedied by opening a door or window, so as to supply both fires with the necessary air. The same effect 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 ctrong kitchen fire may over- power all the other chimneys in the house and cause them to smoke. 99. Upper and lower Fines — 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 au 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 ) 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 mnch Air. — Too largo 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 dilficulty is a deficiency of air to supply the DEFICIENCY OF AIR-SUPPLT. 59 II 11 draught. • "Want of a copious and regular supply of air is by far the most common cause of smoky chimneys. However well constructed and aiTauged 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 fiq. 15. 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. Fbanklin's plan was to set the door open until the fire burned properly, then gradually close it until 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 will 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 opening shall be inade. 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 inmates, a thin shelf is to be placed below it, sloping Ing^smokef '^^^^ upwards, which would direct the air toward the ceiling. The modes of introducing air will be noticed in another place (351). 102. Draaghts through a Room,— Currents of air throagh a room, as from door to door, or window to window, when open, may coun- teract tlae 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 room. 103. Visible Elements of Smoke. — Smoke consists of all the dust and visible particles of the fuel which escape unburnt, 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 flue, or, swept upward by the air current, is carried to a greater or lesser height, and finally falls again to tho 00 APPARATUS OB' ^V ARMING. cartl). Tims all that is visible of sinoko is really heavier than au which may be shown by placing a lighted candle in the receiver of an air-i)uini>. By then exhausting the air, the flame is extinguished ; and the stream of smoke that continues to pour from the wick, falls Vu) 16 "'' t^'® pump-plate, as is seen in Fig. 10, 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 duo 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 coustitneDts 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 from 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. XI.— APPARATUS OF WARMING. 105. The vai'ious devices for warming are to bo 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 will be assigned to it, and the heating contrivances will then be reconsidered in respect of their atmospherio influences. 106. How Rooms 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 SOURCES OF THE LOSS OF HEAT. 61 by the external air. Glass is a bad conductor of heat, yet the plates used are so thin as to oppose but a very slight barrier to its escape ; on tlie other hand, it is an excellent absorber and radiator, — so that, in fact, it permits the escape of heat almost as readily as plates of iron of equal thickness. The loss of heat in winter, by single windows, is enormous. Three-fourths or 75 per cent, of the heat which escapes through the glass, would be saved by double windoAvs, 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 tlirough crevices and imperfect joinings of windows and doors, while cold air rushes in to supply its place. Heat also escapes through walls, floors, and ceilings, 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 the scale adopted. Much heat, besides, is conveyed away by the cur- rents necessary to maintain combustion. To renew the heat thus rapidly lost in these various ways, different arrangements have been resorted to, which wiU now be noticed. 107. OnrBodieshelpto Warm the Rooms. — In estimating the sources of heat in apartments, we must not overlook that generated in our own systems. The heat 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, the 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 head 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 lec- 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 witli the t^aybreak of the new civili- C2 APPARATUS OF WARMING. zatiou that succeeded the dark ages. Previously to that time, houses Avere hcjited as Iceland huts are now, — by aa open fire in tlie middle of tlic 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 lieat. They kept fires in open pans called braziers. 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 waljs most exposed were painted black, to prevent the visible eft'ects 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 aw^ay. 1.— OPEN FIRE-PLACES. 109. Strnctnrc and ImproTemcnts. — 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 (jamhs) and large enough to contain several persons, who were provided with seats inside the jambs. These fire-places were enormously wasteful of fuel, and were 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, th ? 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 fall, — 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. Count Rumford states that the proper angle for the positions of jaiubs is 135 degrees Avith the back of the fire-place. 110. now the open Fire-place warms the Room.— 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- OPEN FIKE-PLACES WASTE HEAT. 63 place. It strikes upon the walls, ceiling, floor, and furniture of the room ; a portion of it is reflected iu various directions, and the rest is absorbed. The objects which receive it are warmed, 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 will be hot, while 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. The opea 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 ^, of the whole amount produced. As a general result, those combustibles which burnt with the least flame yielded the most radiant heat. As the radiant heat is tlius 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 15-16ths of all the heat generated, ascended the chimney and was lost. It is probable that in the best constructed fire-place, from 1-2 to 8-4ths of all the heat is thus wasted. The fire-place is greatly improved in economy and heating efficiency 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 the ordiaary one, and leaving a vacant space between them, into which 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, it answers admirably. Even a flue made of some thin Fig IT Air from with- ont warmed by thfJ flre-place. 64 ArrAKAiTs of waemixg. luuterhil, and i-ontaiiicd in the chimney, the lower extremity coin municating -\vilh the external air, and tlie upper with the ri>om (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 Stove. — Dr. Feanklin contrived a heating apparatus of cast iron, which he called the Pennsylvania fire-place^ but which is generally known as the FranMin stove. It offers 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 fire 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 without. 113. Coal Grates. — 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 cliim- ney is sufficient to carry oflf the smoke. The coal-grate is a more economical contrivance for warming than the larger Avood 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 i>lace of the escaping Avarm 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 bo 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 Rlmford first pointed out, there should be as little metal about a grate as i>ossible, 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 Combustion In the Grate. — The form of the grato COMBUSTION IK GRATES. 65 eliould be such as to expose tlie largest surfoce 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 bo 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 &nd perfect combustion, all 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 wiU be sufiicient 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 will be found most economical. 115. Different kinds of Grate— Tho modifications and variations of the fii'c-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. Tlie 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 librarj 66 APPARATUS OP WAKMING. and bedroom alternately. In Golson's stove-grate, the fire is contained in an urn or vase-shaped grating, and is surrounded by a circular re- flector which throws the rays, both of heat and light, into the room in parallel lines. Coal-grates are also constructed on the principle of the double fire-place, by which warmed air is introduced into the room from without. Dr. rKA>TKi.ix devised an ingenious grate called the circular firc-ca^e. 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 thfeir smolce having to pass through the fire above them, was en- tirely consumed. 116, Arnott's new Grate. — Dr. Aknott has recently constructed a hew 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 beneath. 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 affords 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, wo can no more advantageottsly convert it to heating purposes than wo 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 dull 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 hums its smohe, but that it Intrns iritJtout smoke. The aim should be, so to conduct the first combustion that smoke shall he preventeJ. 117. Grates shonid not be set too low. — As the open fire warms by radiation, it should be so placed as to fiivor this mode of diffusing heat. The tendency of currents of heated air to rise, secures suflBciently the warmth of the upper portion of the room, so that the main object of EPFECrr OF TOO LOW FIRES. 67 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 abo've the horizon. If a in (fig. 18), represent a radiating point or fire in a room, and & e the floor, it will be seen that no heat-rays faU 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 u \ the persons forming the fireside cir- cle are placed. Striking proof of the •^^ facts here set forth, is obtained by laying thermometers on the fioors of rooms with low fires, and with BimUar 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 wanned 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 Avood 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 flue 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 APPABArUS OF WAJRMINO. materials are most common in Gennany and Russia, 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, Avhich are subject to rapid variations of temperature. 120. Sclf-rcgnlating 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. Arxott 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 rc ore readily than solids, a well constructed regulator of this kind woUd be more sensitive and prompt in action than one of metal. 121. Alr-tlght Stores. — The so called air-tight stoves are very common. They are designed to admit the air in small and regulated quantities, so jis to produce a slow and protracted combustion. Tliis 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. Ube found that while 85 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 ticelve hours, but little over half that quantity of water was evaporated. As has been previou!?ly stated, to evolve the largest amount of heat from fuel it nmst bo burned rapidly, and with a supply of air suflicient to oiirry t])e oxidation at once to its highest i)oint, 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 thoir heat before entering the chimney, there remains noth- POINTS SECUKED BY THE BEST STOVES. 69 ing to be desired on the score of economy. It is evideit that all the heat has been retained in the room, and in this case the stove becomes the most efficient heating apparatus. 122. Effect of Elbows in StoTcpipcs. — 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 tJie 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 qualities of a Stove. — The desirable points to be secured in the construction and management of stoves, are, first, 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 ; tJiird, enclosure of the fire-space, with slow conductors, as fire-brick or stone ; fourth, a high temperature, attained l^y the rapid and perfect combustion of the fuel ; and fifth, to bring aU the heated products of the combustion in contact with the largest possible alsorh- 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 our modern stoves. 10 APPARATUS OF WABMING. 8. HOT-AIR ARRANGEMENTS. 124. Uot-alr Furnaces. — Heating by hot 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 be 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 constrnct- ' ■ ' 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 building. 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 all 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 Manner of warming by IIot-Air Furnaces^ 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, tliat the power of the furnace being gauged by the requirements of a certain sized building, or number of apartinents, it is not easily accommodated to a fluctuating demand for heat. 125. Diffaslon of Hot Air throngli the Apartment.— There are serioua DISTEIBUnON OF HEAT IN THE AIR OF ROOMS. Vl 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 difierence, 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 boiUng 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 difinsed 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 registei-, 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, 67' 12. 6 81- 4. 2 " TO* 14. 7 80° 6. 8 " 72* 16. 8 90° 8.4 " 75* 19 94° 126. How we are warmed in Hot-air Booms. — "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 little heat. The quantity of heat that will raise 1 cubic foot of water 1 degree, Avould be so diff'used as to raise 2,850 cubic feet of air one degree. — (Abnott.) From the amount of air that comes in contact with our bodies, therefore, we cannot get sufficient 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 72 APPABATU8 OP WAIWnNG. warm, thoj'' beconio constant sources of radiant warmtli. Hot air may also become a direct source of cold if it be dry. If -vve moisten the bulb of a tlierinonieter, 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 Fio. 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 well 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 which 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 ditTerenco in the degree of heat in these two plans. Water exposed 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 Circnlation of water. STEAM-HEAT — DAJfGER OP FIRE. 73 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 60 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 boiler 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 wdiich 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 t4ie 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 au', 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 hoards and wooden supports, which a much lower degree of heat may suflice 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 applicatioa-x)f a light. A considerable time may be required to produce this change, 60 that a fire may actually be " Icindling upon a maii's j9re??»5<38 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 1A APPARATUS OP ■WARMING. 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. — Tlie Secretary of a London Fire Insurance ofiSce stated tliat 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 oflF 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 Drawbacl^s of tlie rarions 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 still 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-being 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 bo considered when speaking of air. ADVANTAGES OF OPEN FIRE-PLACES. DISADVANTAGES OF OPEN FIRE-PLACES. They promote ventilation — afford a They are uncleanly — require frequent cheerful fireside influence — 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. ADVANTAGES OF STOVES. DISADVANTAGES OF STOVES. 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 their homioally heat — yield fluctuating tcnipcratures— are liable to overheat the air — are liable to leakage of gases — and nre not cleanly. HOT-WATKB APPARATUS. ^6 ADVANTAGES OF HOT-AIR FURNACES. They are out of the way and save space —are cleanly — give but little trouble — may afford abundant ventilation — need waste out little heat — and warm the whole house. DISADVANTAGES OP HOT-AIR FURNACES. They are liable to scorch the air— cannot be easily adapted to heat more or less space — are liable to leakage of foul gases — and they dry and parch the air if copious moist- ure is not supplied. ADVANTAGES OF HOT-WATER APPARATUS. They do not burn or scorch the air — give excellent ventilation — do not waste heat — and they warm the whole house. These remarks do not apply to those which heat rooms by radiation from coils of pipe (129). DISADVANTAGES OF HOT-WATER APPARATUS. They arc expensive in first cost — if adapted for an average range of tempera- ture, they may fail in extreme cold weather (as may also furnaces) — and may give a dry and parched air if moisture be not supplied. PAET SECOND LIGHT. I. NATURE OF LIGHT— LAW OF ITS DIFFUSION. 182. now the outward and inward Worlds Commnnitate. — 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 with 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, perhaps 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 farther then, into the nature and properties of this luminous principle, and how we are related to, and afiocted by it. 183. Exhilarating Agency of Light.— Light is a stimulus to the ner- eous system, and through that, exerts an influence in awakening and OLDER NOTIONS OP ITS NATURE. 77 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 effort is the most favorable condition, as well as the general signal, for rest ; while its reappearance stirs us again to activity. There is something in darkness soothing, depi-essing, quieting ; while light, 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 1 When the sun shines, the blood flows freely, and the spirits are light 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." 1 34. 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 Natnre. — 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- •78 HOW LIGHT IS DIFFUSED. 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. "Wo omit farther reference to this question here, as the analogy ■will be more fully traced ^Yhen we come to speak of colors (150). 13G. Light loses Intensity as It Is Dlffased. — The rays of light proceed- ing from any source, a candle for example, spread out or diverge, as "we notice nightly. As light thus diflfuses 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 -lecnmes from each point of emission, in the same proportion that the space through which it is ditfused 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 will fall Fio. 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 fir.=t. 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 Avaste it. 137. How Bodies receive the Lnminons Principle. — "When light falls upon various kinds of matter, they behave toward it very ditTerently. Some throw it back {reflection) ; some let it pass through them {tram- mmion) ; 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, aftect light in one or more of these modes, producing that infinite variety of appearances which the universe presents to the eye. ITS KELATIOX TO SURFACES. V9 £.(fl6etin!r II. KEFLECTION OP LIGHT. 138. Those Lodies 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 quality 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 5, Fig. 22, be a ray of light falling perpendicularly upon a reflecting Fig. 22. surface, it will be thrown back in the same direction & 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 is commonly said, — the angle of eefleotion is equal to THE ANGLE OF INOIDENCE, THE EEFLEOTED BAY 13 ON THE OPPOSITE SIDE OF THE PERPEKDICtTLAE, AND THE PEBPENDICULAE, THE INCIDENT AND THE EEFLEOTED EATS AEE ALL IN THE SAME PLANE. PlaCe a looking-glass upon a table, in a dark room. Let a ray of light, entering through a hole in a window slmtter, strike upon its re- flecting surface, it will be thrown off at an equal angle, and both the incident and reflected rays wUl be made visible by the particles of dmit floating in the room. 140. How Reflected Light is scattered. — Parallel rays falling upon a plane surface, 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 ; aid 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 divergmg 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 metalHc surface, called a speculum, is the most perfect reflector. Mirrors, or looking-glasses, consist of glass plates coated with metal. It ia Fig. 23. 80 rKODucrioN op images. FlO. 24. Fig. 25. uot tlio glass, iu looking-glasses, that reflects the light, but the metallic coating behind it. If we place any illuminated object before a plane mirror, rays of light pass from all points of its surface, and convey an image of it to the mirror. But the polished surface docs not retain the image ; it reflects or throws it back, so that the eye per- ceives it. The light Avbich enters tlie eye comes from the real object, Avhicli 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 will 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 luutjf constantly illustrated in the images of the face, formed by the bright metallic lookiny-giass. surfiices of domestic utensils. 142. A perfect Ucflectlng Surface would be Invisible.— If the surface of an opaque body could be perfecthj 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 invisible, and an observer looking at it could see nothing but reflected images. If a large looking-glass, with such a sui-ftice, 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 notliing could be seen but the lights, or sources of illumi- Ctjhc& How the imn^o appcirs behind the TWO KINDS OF REFLECTED LIGHT. 81 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. In 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. If a ray is let into a dark room, and falls upon a bright metallic surface, a brilliant spot of hght will be seen fi-om certain points, but the reflecting surface will be almost invisible in other directions, and the room will remain dark. If, now, a sheet of Avhite 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 follows 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 the incident rays. In this manner light is radiated from surface to surface, bo 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 have 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 tha*A-om 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 b (Fig. 4* 82 RKLATION OP PICTUKES TO LIGHT. Window Fio. 27. Fio. 2«. 26), tlio eye is filled with the glare of the regularlj 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 bo 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 Z> (Fig. 27), its proper inclination would be to c ; but if it were elevated to tZ, it should fall forward to e. We will further 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 diff"uses 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 bo enlightened, and the rest of the room would remain totally dark. This secondary radiation occasions tho mild and softened light which we experience when the heavens are screened Avith clouds, instead of tho intense and often painful glare of a cloud- less summer day. In the same manner tho atmospheric particles scatter the rays and diffuse a subdued illumination at morning and evening twilight, while the sun is below the horizon. III.— TRANSMISSION AND REFRACTION OF LIGHT. 146. "When light fulls upon transparent objects, as air, water, glass, it passes through or is said to bo transmitted. Bodies varj- greatly in this power of passing the light, or transparency. Tho metals are least transparent, or most opaque, yet they are not entirelv so ; thin LIGHT EEFRACTED OR BROKEN, 83 gold leaf, for example, transmits a greenish 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 baa been calculated that if the atmospheric ocean were 700 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« Fio 28 ^^'^' ^* ^^^^ "*^* ^® diverted ; but if it fall at an angle, as at c fZ, it will not continue straight to d^ 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 ^e 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 Refraction 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 Ught 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 three-quarters as deep as it reaUy is. Cases of drowning have happened through ignorance of thi» 84 WAVE THEOKY OF LIGHT. Fio. 80. Plane-convex Lens. Fig. 82. Fig. 81. illusion. The degree to which any substance bends the light from it.- Btraight course is called its hidex of refraction. Each transparent body has its refracting index, which is one of the proi)crtie3 by which it may be known. 149. Effect of Lenses npon Light.— This power which bodies have, of bending light from its straight course, is employed when we desire to gather it to a point or focus, or to concentrate it ; or Avhen it is wished to disperse and diffuse 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 tliem, or spread them out into a greater space. Com- mon spectacle glasses are examples of these forms of lenses (248). Double-convex Lons. Fig. 8.3. Plane-concave Lens. Double-concave Lens. IV. THEORY OF LIGHT— WAVE MOVEMENTS IN NATURE. 150. Light not Matter lint Motion. — Thus far we have considered light as if it Avcre simple, without inquiring if it be roaUy so, or compounded of diftereut 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 i)articles of matter, but by impulses of motion, Avhich progress unaccompanied by any material substances. Let us note how wave-motions take place, and the known extent of their occnrrenco in nature. 151. Visible Wave Motions inXatnrc. — 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, waves Avill be formed, wliich proceed along the string. The real motion, in this case, is at right angles to the di- rection of the string, the apparent motion is forward. The particles SOUND PRODUCED BY AIR-WAVES. 86 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 stalk keeps its place, and only bows its head. Yet wave-motions are seen to flow successively forward. If we toss a stone into perfectly stiU water, the surface will 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- calli/, 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 01 an excited tuning-fork, we can feel the vibrations. Sound is thus not only motion, but it is vibratory 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 dififerenecs 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; wliich is the fact. The first distinction among sounds is into high and low, or acute and grave ; it is a difference of pitch. Slow vibrations produce grave sounds of a low pitch. In the case of strings, for example, the larger they are the heavier tliey 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 86 WAVB-THEOBY OP LIGHT. sound, therefore, that can be made, is the result of a certain nnmher of air vibrations, and to that pitch of sound always belongs that num- ber. Savakt 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. Ilarinonic Ratios of the Musical Scale. — It was found, experimen- tally, that the orchestra pitch note A, of the treble cleflf, is produced by 853 vibrations per second. The number of pulsations in each note of IJie octavo is as follows : Ratio of Harmonic Sounds. p. D E F G A B ! C i No. of Vibrations 512, 576, 640, 6S2, 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 arc 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 numeric.il 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 liir-waves, by which impressions are produced in a certain exact order, npon a mathematically constituted organ — the brain. SCALE OF THE LUMINOUS VIBRATIONS. 87 155. Light and Colors result from Wrtc 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 suhtle, all-pervading and in- finitely elastic etJier^ and that vision is the result of vibrations or wave movements sent through 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 yellow light, 44,000 ; and in an inch of the violet ray, 59,756. If 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. Nobeet, of France, has ruled lines upon glass, for microscopical test-purposes, but the Tfyg-g^ of an inch apart.* 15>3. Vibrations per second of the luminous Ether. — But the deinon- 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 acy thing, an agent or force sent fi-om the illuminated body streams into the eye at the rate of 200,000 miles in a second. Know- ing the rate at which light moves, and the number of waves in an inoli for any particular color, it is easy to ascertain the number of vibrations made by each in a second. In two hundred thousand miles 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 fovr hundred and eighty millions of mil' lions of times between every two ticks of a common clock. Of yellow * See Appendix B. R8 COMPOSITION AND MUTUAL INFLUENCE OF COLORS. light five Imndred 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 wave 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 eflect 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- amination. v.— COMPOSITION AND MUTUAL INFLUENCE OF COLORS. 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 (prism), the white ray r^^ disappears ; it is turned from its course, and there foils upon the opposite wall an oblong colored image called the solar spectrum. It consists of seven bright colors, '"^^^ always found in a certain order, Separation of ^hitoliffht into Newton's seven "3 ^^'O'^'" i'^ ^'S- 34; but they 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 wliite light is a compound principle, c(^nsisting of these seven colors, whicli he called primari/, and tauglit that all other colors whatever are tlie result «f various commixtures of these. For convenience of representing the relations of colors, wo may represent white light by a circle, and the NUMBER OF PRIMARIES. 89 FiQ. 85. colors which 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 cxplaaatioa of Colored Surfaces. —White light falls upon objects, and they ap- jear colored : how is this ? Newtok replied : Dodiei 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 hlacTc^ it is absorl)ed 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, while 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. Different surfaces reflect the pri- mary colors mixed in all manner of ways, and hence the endless modifications of color that meet the eye. 159. Bat three Primary Colors. — A more simplified vierir of the com- position of colors has been propounded by Sir D. Brewstee, 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. Wo 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. Brews- ter 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 diflTerent points Avhere they are visible. Blue, yellow and red being r^^;rr,«r;->a vinlAt indisTO. ereen and orange are secondaries derived Fig. 36. 90 REr.ATIOX AXD MUTUAL IXFLUENCE OF COLORS. from them. The separation of the impure or compound colors from Yia. 87. the spectrum, leaving the tlirce from which they are derived, is illustrated in Fig. 86. 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 Ave have white light at last composed only of the three colors, as represented in Fig. 37. 160. Wliat are Complementary Colors. — The effect 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 Fig. 33. Fro. 89. 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 which 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 comple- Rei \ / \ \ ''nentari/ color. The part absorbed, or which does ; niit appear, is the com- / plementary of the color seen . This m ay be made perfectly clear by the circular diagram. If we jook, 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. 89, which is therefore the true complement of red, that which it lacks to make white. If we Vook upon a yellow surface (Fig. 40), blue and red are deficient ; blue A. NEW SYSTEM OF ARRANGING THEM. 91 Fig. 4-2. and red produce violet, therefore violet is the r.oinplementary of yel- low, as seen in Fig. 41. Again, we look upon blue (Fig. 42) ; red and yellow are required to complete the circle into whiteness ; hut 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, noAv 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 sJiaded, 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. What are 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 tiaged in a similar manner by any color, hues of blue re- sult. In the same way are produced hues of orange, yellow, violet, green, &c. 163. ChcvTcnPs scheme for showing the relation of Colors. — A plan has been suggested by M. Cheveeul, of France, for representing the com- position and relations of colors, in an extremely simple and eflEectivo 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 02 EELATION AND MUTUAL IKFLVESCli OF COLOKS. black, the centre white. The radial lines passing froni the centre to the circumference represent scales of color, eacli dot indicating a tune. 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 ELIOW Orange RED Plan of CirevEEUL's Chkomatio Circles, illnstrattng the principle of complomcntary 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 bhie is the scale of green, which results from their combination in eqnal pro- portions, half blue and half yellow. Midway between preen and blue is a scale that we might call a greenish blue. It is only one-quarter of the distance from blue to yellow, and therefore is three-quarters HOW THEY MAY BE EXHrBITED. 93 blue, and one-quarter yellow, — a hue of blue. Space or distance represents i)roportions 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. Famihar 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 94 RELATION AND MUTUAL INFLUENCE OF COLORS. wliite, 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 Avill 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 sonibre. 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 ; Pnrc and Broken Colors. — Grays result 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 pttre^ while the addition of black produces a Irol-en color. The browns arc 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 portion of the yellow and red, breaking the color and starting it towards black. 169. Xo Colors perfectly pore. — We must guard against the error of supposing that in practice wo meet with any such thing as a pure or perfect color. Even those of the spectrum or rainbow are not per- fect ; Bbkwster has shown that the very brightest is contaminated by others. But when we leave the spectrum, and begin to deal with the KFFECrS OP COMPLEJIENTARIES. 95 commouer aspects of colors, paints, dyes, &c., their imperfections be- come much 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 effect 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 less mixed with them, which impair their brightness. 170. How Colors mntaally improve each other. — The action of colors upon each other is not a matter of hap-hazard, and although it was long inexplicable, 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 Tiar- 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 will appear extremely bright, unnaturally so ; and if the eye recur again to the reds, they will look much finer than before. Red 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 yellow-green, and observe them in the same manner, we shall get the same result ; their briUianoy and clearness wiU 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 9Q RELATION AND MUTUAL INFLUENCE OF COLORS. ■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 xipon the reddened sheet, the latter color will be at once brightened. It will 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 simultaneotts 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 inflaenre upon the Eyct — 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 Avhich wo style w7iite ; 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 the eye, 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 genei'al 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. Duratlou of Impressions upon 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 round appears as a continuous streak or ribbon of fire. But the eye continues to be affected for a much longer time ; althougli it is not, as we miglit 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 THsr APFEcrr each other through the eye. 97 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 seusibility to Colors, and demands tlieir Comple- mentariest — The influence of any color upon the eye is to diminish or deaden its sensibihty 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, while 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, lut it toill be 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, viinus the I'ed, 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 tJiat 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 will be generated by the eye formed of these missing rays, and, therefore, green. AVhen 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 tlirough colored glasses at the time of an eclipse, spectres of the solar disk are sometimes produced Avhich continue for a time before the eye. Tlie color of these is always complementary to the color of the glass tlirough which the sun was viewed. 1 74. Simaltaneons contrast of Colors. — But colors placed side by side, 5 98 RELATION AKD MUTUAL INFLUENCE OP COI-OES. exert upon each other, siimiUaneotisly^ an inQuence that can hardl} ba 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 t?ie same time. It has been stated that surfaces reflect to the eye rays of other colors beside those which appear. No surface can 60 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 Avhen they are brought together, and the com- plementary of each is thrown upon the other. 175. How associated Colors injure eacli otiier. — 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 tlie 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 yellow. It was half yellow before, bat the effect of violet is to increase the proportion of this element, and thus produce a new hue of yellowish-green. If violet bo 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 yellow, 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 HOW THEY ARE CHANGED BY CONTRAST. 99 Fig. 45. of colors. A color placed beside another tends to make tliat color as different as possible from itself. la 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 will 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 Touc. — 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, . . o. ', ,, ,, T , , Illustrating the effect of contrnst of tone. 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 hghter, 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 email amount of white liglit reflected by the other. Thus if we place tirc. 100 RELATION AND MUTUAL INFLUENCE OF COLORS. a dark red beside a light rose-color, or a deep yellow ia contact with a straw-color, they will, as it were, push each other further apart, the light tones in both cases appearing ligliter, and the deep ones deeper, 80 as to deceive the eye in regard to the real depths of their colors. Thns for tones as well as hues the law of Ciietkeul holds good. " In the case cohere the eye sees at the same time two contiguous colors, they teill appear as dissimilar as possible, both in their optical composition and the height of their tone^ 177. Harmonics 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 uncultured that we remark a passion for gaudy and flaunting colors. "With tho 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 eflfects, or strong and deep contrasts which often offend the eye. llarmonies of complementary contrast are to be first and chiefly sought in chromatic arrangements ; but these are comparatively limited, and in the demand for variety, other 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 Avays. I'irst, we may arrange the different tones of a single scale in a series, beginning witli 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 bo the effect. Second, wo may asso- ciate together the hues of adjacent scales, all of tho same tone, and often produce an agreeable analogy. But sometimes colors of near scales mutually injure each other, as blue and violet ; tho complemen- tary of blue, which is orange, being thrown upon violet gives it a faded and blackened appearance ; while the 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. I7nrd, a pleasing harmony of analogy is produced by view- ing groupings of various colors through a colored medium that casta EFFECTS OF DIFFERENT GKOUPINGS. 101 its own peculiar Ime over the whole, as when we view a carpet ic 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 be 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- I^anies and weakens the color. At the same time the white is tar- nished by the complementary of the color falling upon it. "White is so 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- 102 PRACriCAL SUGM3ESTI0NS IN COMBINING COLOKS. plomentaries, 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 wlicre white gives too strong a contrast, and black makes the combination too sombre, as with orange and violet, green and blue, green and violet. VI.— PRACTICAL SUGGESTIONS IN COMBINING COLORS. 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, Avhile she would do well to trim a yellow bonnet with violet or blue, and a green one with rose-red or white, and to follow the same general rule in arrangiug 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 Avhere they arc 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, Avhile 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. Influence of Colors upon the Complexion. — Any colored objects, as bonnet trimmings or draperies, in the vicinity of the countenance, 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 hloiide and hrunette. In the blondes or fixir-complexioued 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 aflect these two styles of com- plexion very diflcrently. A green setting in bonnet or dress throws HOW THEY AFFECT THE COMPLEXION. 103 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 yellow. Its complementary, violet, neu- tralizes the yellow of the orange and leaves the red, thus increasing the freshness of the complexion. If the skin be more yeUow than orange, the complementary violet falling upon it changes it to a duU pallid 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 yellow 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. Ked is objectionable, unless it be sufficiently 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 effect 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 light 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 Avith violet-red, and rose with the green leaves. On the contrary we snould avoid combining pink with scarlet or crimson ; orange with t)range-yellow ; yellow with greenish-yellow ; 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 walls 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 waU colors. Orange and orange yellow are 104 rKACTICAL SUGGESTIONS IN COMBLNING C0L0K9. fatiguing to tbe eye. Among tlic simi»lc colors light blue, liglit green (314), nnd yellow, 6cem 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 Avith 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 pictures. In selecting a lorder we should seek for contrast, so that it may appear, as it were, detached from tbe 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 should be bordered with violet and blue mixed with white. Green will take any line 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 appropriate for picture-galleries, — they produce good efiecta in other rooms with well chosen borders and mouldings. 185. PIctares, Frames, and Gilding. — As the i)icture 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 1^ 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 sufl^ered 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. Red and orange pervert the gilt tint, and black lightens and weakens it (144). 186. Assortmcut of Colors for Fnrnltnre. — In determining the colors COMBINATIONS IN HOUSE-FUENISHING. 105 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 i-edden the transmitted light of day, and imjjart this color to the countenances it falls upon. But by artificial or reflected light, red curtains and furniture dispose the eye to see gi-een in the countenances of people in the room, Avhile green curtains make the countenances rosy. Chairs and sofas, when complementary to the paper upon the Avail, are most favorable to dis- tinct vision ; but for collective effect, Avhen we desire to present the room as a unit, bold and complementary contrasts are inadmissible, 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 sofjxs, vivid reds should never be used Avith 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 narroAV cord of golden yellow Avith gilt nails. Green or green grays are best suited to trim mahogany and red-colored Avoods. In using differently colored woods Ave 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. If 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, while if the furniture is plain the carpet may be gay. VII.— PRODUCTION OF ARTIFICIAL LIGHT. 1. The Chemistry of Illtjmination. 187. Jiataral and Artificial Light. — As respects its sources, light is of 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 that kind of chemical action which is termed cornbustion^ the nature of which has been explained when speaking of heat. 188. Light emitted by ignited Bodies. — All solid substances shine when suflSciently heated. The temperature at which they become 5* 106 PBODUCriOX OF ARTIFICIAL UGHT. luminous, according to Dr. Dbaper, wlio has lately investigated tlie subject, is 977° F. lie enclosed a number of diflferent 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 einitted 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-Jwt. 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 our illamination comes from burning Gas — Tlie foregoing ex- periments were made upon solid substances, but their results do not hold time 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 will 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, Oi' solid sperma- ceti. In tlie 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 burning. In all cases the light proceeds from a rising stream of gaseous mattei which is lighter than the air, and therefore tends to ascend. 190. What takes place la 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 CHEMISTRY OF ILLUMINATION. 10^ Fig. 46. Fig. 47, seizes upon the hydrogen first, burning it with an intense heat, and the production of water. As the hydrogen combines with osygen, it abandons the carbon, which is thus set free in a pure state. Now pure carbon is always a solid. As the hydi'ogen leaves it, therefore, it is sot 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 imtant; thiey are themselves quickly burned and converted into carbonic acid.* 191. How these facts may Lc 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 uncou- sumed particles of carbon are deposited upon the white surface, thus proving that they exist free in the flame. If 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 Illnmination.— There is a wonderful simpUcity and beauty in this chemistry of illumination. The same active principle 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^ Illustrating combustion and illumination 108 PRODUCTION OF AKTIFICIAL LIGHT. of i)lants and animals, but the very crust of the globe 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 l)ure 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 all gases, hydrogen, is associated with car- bon, the most refractory of all solids, which remains fixed without melting or vaporizing at the intensest heat which 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 atmosi>heric 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 tho flame, they do not eclipse or obscure it, but let tho 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 ba 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 effect. 193. Threefold form of lllnminating 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- stand. 2. Illcmination by means of Solids. 1 91:. Adaptation of Tallow for Candles. — Those fatty and waxy bodies, v.liich are sufiiciently hard 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 bo too gi-eat a proportion of mutton tallow or suet, as this contains a peculiar principle called liircin, which causes it sometimes to give a disagree- able smell, especially in hot weather. When of the best quality tallow ILLUMINATION BY MEANS OF SOLIDS. 109 is white, firm and bi-ittle. Alum is often put with it to harden it. The bad quality of tallow candles is chiefly owing to their adulteration with hog's tat 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 tm'ns 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, margarie acid, and oleic acid. Stearic acid, combined with glycerin, forms stearin. Margarie 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. Margarie 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 whicii the endless oil 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 am": brilliant 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 fall to the bottom. If starch or flour has been used, they 110 PRODUCTION OF ARTIFICIAL UQHT. Fio. 4S. may be detected by boiling and adding a solution of iodine, which will yield a beautiful blue color, the test for starch. Yellow bees'-wax is often adulterated with resin, pea and bean meal, and many othei substances. The former may be detected by the smell, and the latter by the iodine solution. 197. Strnctnre of Candles— Office of the Wick. — The common burning .audle affords a beautiful illustration of the general principles of illu- mination. If we should attempt to bum solid tallow or wax in the lamp to produce light, it would be found very diflScult 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 tire 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 wiclc. 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. rrtmi'tiie'ci'stcrn ^^ this case the spaces between the fibres act as tubes, of oil below, jj^j attract upward the liquid fat or wax. 198. The barnin^ Candle a niiniatare Gas-Factory. — We thus see that the ca'idle is a kind of lamp which constantly melts its own combus- tible. From the reservoir the wick draws up tlie 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 window-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 gaa Fio. 49. The candle-flame hollow. the dark inner space. ILLUMINATION BY MEANS OF SOLIDS. Ill niannfactured from the liquid tallow, stearine, spermaceti, or was, drawn up by the wick. This may be directly shown. If one end of a glass tube, having a bore I- of an inch, be introduced into a candle-flame, as seen in Fig. 50, the gas will be conveyed away 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 / m. w- ^^m^ \\w\ may be re-lit by applying a light to the smoky 1 ^j ]itf//i stream of combustible gas which will convey ^!^~^ ^^f/,, 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- , . 1 • • J. i. ■ xi ii flame filled with gas. where the air comes m contact with the gas. 199. Interference 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 gi-adu- ally deposited upon the wick, forming a large spongy snuflF 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. Kumfoed foi'iad that the brilliancy of an unsnuffed candle was reduced 4 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. Inflacnte 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 tallow. A slender wick in a tallow candle would melt the 112 rEODUcnoN of artificial light. combustible faster than it could consume it, the liquid would overfill and overtlow the cup, which takes place in what is called the guttering of candles. For this reason candles of softer materials require larger wicks. 3. Illuminatiox by means of Liqcids. 201, Argand's great ImproTcmcnt. — 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 bo circular. Dr. Feanklix showed that two small wicks plac!•• MOISTURE. 183 328. Air Tltlatcd by Illaminating Proeesses. — The case is diffei-ent 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 wHJiin the room. A candle (six to the pound) will 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 *Jiat time (224). 329. Influence of Moisture upon the qnantity 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 will 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 wUl be about 23 grains per minute. Now 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 60° contains 4*5 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 will become saturated by the addition of 217 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- uact with the system ; and this necessarily involves large provision for change of air. 184 KATE OP CONTAMINATION WITHIN DOORS. 330. Air vitiated by one person In a minnte. — These sonrces of impuritj are capable of measurement in their rate of effect, but 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 J 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 efSuvia 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. Reid 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). 331. Influence 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 will be spoiled much quicker. Twelve persoas 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 gingle hour. Two persons sleeping in a close bedroom 10 feet square by 8 high, will render all its air unfit for respiration in less than two hours. In actual practice, the cases are not quite so bad as this, foi with the utmost perfection of carpentry there will be cracks for the jiassage 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 sufficient air for the agreeable and whole- some use of their occupants. This must bo attained in another way. MOTIVE POWER IN VENTILATION. 185 832. Infflnence of Plants npon 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 their 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 kept, 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. Ilence, 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 humidity. VII.— AIR IN MOTION— CURRENTS— DRAUGHTS. 333. Two methods of pnrifying the Air. — Pure air may be secured in two ways : first and most perfectly by the removal of the vitiated at- mosphere of the apartment, and its replacement by fresh 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. Tho air may also bo more or less perfectly cleansed by means of substances which absorb, decompose and destroy its noxious ingredients. This is the chemical 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-engines 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. 186 AIR IN MOTION — CURRENTS — DRAUGHTS. Fio. 72. 335. Carrcnts of Air iu Close Apartmeats. — 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 curient. If a candle be lit in the middle of a room (Tig. 72) where the doors, windows and flues are closed, and the air is motionless, a set of currents will 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 direction 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 bo 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. All local disturbances of temperature tend to produce simi- lar efi^ects, 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. 336. Nataral YMitilatlon of the Person. — The warmth of the human body imparts itself to the layer of surrounding air, expands it, and Fio. 78. DOWNWARD CURRENTS IN WINTER FROM WINDOWS. 187 Fig. T4. causes a rising current (107). 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 bead. 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 will add much complexity to the movements of the air, and to a small extent counteract the stove-currents. 337. Windows, though tight, prodace Currents. — Windows, in cold weather, though entirely tight, so that no air passes their crevices, are always sources of descending currents 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 winter, 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. The Air of rooms arranged in strata. — But the effect of currents is not to cause a perfect intermixture witli uniformity in the condition ot 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. 188 AIR IN MOnON — CUERENTS — DRAUGHTS. 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 sometimes 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 ])art of the room contains also the impure air which has been generated within it. The breath which escapes from the lungs, 20° or S0° 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 current* 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 air being below and the worst above. In a room having a fireplace, the cold air may enter at the top and bottom of a Avindow, fall 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 communica- tion has been opened be- tween a room and the outer air, therefore currents will 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. Car- Fio. 76. Fio. 76. 50' -60- -50- 60" Conditions in which openings in rooms do not produce exchange of air. TNTEECHANGES THROUGH WrNDOWS AND DOOES. 189 rents cannot be produced unless their causes are brought into action. If a room bo opened below, and the temperature within be higher than that without, as represented in Fig. Y6, the 'outer, heavier air, pressing harder than that within, will confine it, no movement will take place, and the strata will 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. Currents between rooms and external Air. — 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 rimning as " the arrows show (Fig. 77), 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 the cold, hea- vy air with- out flows in, as shown in Fig. 78. If Fig. 77. ^^ 6rf / 50° J -»- y Fio. 78. N N \ CO" \ V / 50- Conditions in which openings in rooms 'produce exchange of air. 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 coonter-enrrents 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 190 AIR IN MOTION — CUERENTS — ^DBAUGHTS. Fio. 79. Effect of separating the air currents. Fig. 80. exchange does not take place. Yet, if a slip of paper be inserted in the moutli of the bottle or lamp-glass, as seen in Fig. 79, thus dividing 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 suflSciently large, the currents pass without diflBculty, as is easily illustrated. If the door of a warm apartment be opened, and a candle placed near it on the floor, the flame will 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 bo rcarmer 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. Cnrrents throogb Windows. — Draughts through windows and doors are often not efiectual 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 diflferent, and in a manner opposite to that of the door. When the air is cold without and warm witliin, and the Avindow opened above and below, the apartment is emptied and refilled as in Fig. 81. If the external air is warm and that within cool, all 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. INTEBCHANGES THROUGH WINDOWS AKD DOORS. 191 Fis. 81. Condition in which the air escapes above. 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 cnrrcnts 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 effect will be simply a general cooling without any necessarily injurious eflfects. But if the draught faU only upon some one part of the body, it is liable 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, in 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 Fig, Conditions in which the air escapes below. 192 ARRANGEMENTS FOB VENTILATION. very extensive and its velocity hardly perceptible. Of course we can- not have ventilation without movement of air, but the motion should be 80 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, will 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. (Wtman.) 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 wo are accustomed to it, the safer we are in the vicissitudes of changing weather. VIII.— AKRANGEMENTS FOR VENTILATION. 344. The opcu 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, whicli 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 ACmON OF FIEKPLACES AlTD STOVES. 193 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 eflfected in the structure of the fireplace to secure the greater economy of fuel — the contraction of its dimensions ami the lowering of the chimney-piece, by diminishing 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 byStOTCS. — 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 aftbrd the least ventilation of all our means of heating. They . take little more air than just sufiicient to consume the fuel, and that is withdrawn from the pui-er 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. Euttan, of Coburg, C. W., has devised a plan of heating and ventilatiug, strongly recommended by those who have used it, although we have had no opportunity of seeing its operation. He locates his 'air-warmer' in the hall, 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 witli 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 (3G2). 846. Ventilation by Hot-Air ArrangementSt — Sources of warmth be- 9 194 AEEANGEMENTS FOB VENTILATION. como the 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 tlirough 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 bo projected into the room horizontally or at different points, so as to be well diftused (125). It should always be derived from perfectly pure sources, and never used a second time. But the chief difficulty 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 snpply of Moistnre. — 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. Reid states, tbat 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 auhsequently 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 bo 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. Jamks, No. 77 White street. Now York, nas largo provision for ovaporation, which the proprietors offer to increase to any extent that individuals may demand. HEATING COlSTErVANCES THAT BEST EFFECT IT. 195 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-sliaped 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. 848. Best method of Warming and Ventilation. — If we would have tho pleasantest mode of warming and ventilating a dwelling-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 draughts 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 tho 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. — ^Wymabt. Yet it can only be had by very few ; for the mass of the people it is entirely out of the question from expen- siveness. 349. Supply of Air by loose Joinings, Crevices, &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. No provision is made for the entrance and exit of air. The use of doors to rooms is for the admissiqn 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 afibrd a kind of imperfect accidental ventilation, which, by effecting the purpose in a partial 196 AERANGEMENTS FOE VENTILATION'. degree, has prevented mankind from discovering the want of any thing better. 850. Four points to be secured in Vcntilatiooi — Tliat ventilation may be complete, and do for us its best service, four things must be at- tended to. First. Pare 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 ia 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 introdncing pare 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 Avill 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 Avay is to lower the top window sash, although the stream of cold air which presses in and is both unpleas- ant and unsafe, falb to the floor and glides to the stove or fireplace without being sufficiently 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, INTRODUCTION OP AIR INTO DWELLINGS. 19Y Fig. 83. taken from cellars or basements, or what is still worse, used over and over again. If there be local sources of impurity in the vicinity, 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 w^ooden boxes, is admitted into the room at various points. There may bo an air passage made along behind the base of 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 tbe 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 JcZow 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 ; C is a pipe or flue, through which a stream of cold condensed air falls constantly, as shown by the course of Emcrsoii''s Injector. 196 AKRANGEMENTS FOR VENTILATIO>. Lyman's cold air flue. the arrows; i>, a wire gauze box filled witli 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 while writing ; over beds, to cool the air while sleeping ; and over cradles, to furnish pure air for sick children (341). 353. The astendhig Current most Natnral. — We have noticed that by a beautiful provision of nature, xenti- lation of the person 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 Eljectors. — 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 wo 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, when the wind Motes, by surmount- ing it with Emerson's Ejector (Fig. 85), and as the air is almost con- stantly in mure or less rapid motion, tliis arrangement becomes very Bcrviceablo. 855. Opening into the Chimney — Arnott's Valve. — But the force of ABNOrr'S SELF-ACTING VALVE. 199 Fig. 85. cliaiijiht ill the chimney is after all to be the main reliance in convey- iug 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 sufficient 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 vrith 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. Abnott 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 bo noisy but that it is made to strike against soft ^^^^,___ leather. A modification of this valve Amott's Yaive. consists of a square piece of wire gauze set in the opening, with a cur- tain of oiled silk susj^nded 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 m fire-boards used to close the fronts of chimneys. 356. Importance of Arnott's Valre. — The value of this valve to the public can hardly be exaggerated. Mr. Tredgold expressed what many have felt, when he said that all the plans he had seen or read ot for drawing off 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 tuserted, may Fig, 200 AREANGiafENTS FOE VENTILATIOTf. be manngecl Avith trifling care, and drains the room effectively 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 suflBciently 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. Chimney Curreiits inSninnier. — 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 bo 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 will be a draught through it, and it may be devoted ex- clusively to ventilation. It would seem that sucb 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 aa 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 will not be tolerated, and if it is too much warmed, as compared with the air of the room, it will rise immediately to the ceiling and escape tlirough tlie 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 Avhero we SPECIAL DEMANDS OP TIIE BEDKOOM. 201 spend nearly half of our 4ives, in its general condition and manage- ment is the opprobrium of civilization. No place in the house should bo more copiously supplied with air to guard us against the injurious agencies to which 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 Avhich bedg 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 efiects 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 ill 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 -p ^ g,. 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-bnmcrs. — 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 quaUties 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. Faka- DAY adopted the following successful plan to ventilate gas-burners 202 AEKANGJiMIiNTS FOB VKNTILATION. lie placed a metallic tube about an iucb in diameter over tbe lamp- glass, dipping down into it (Fig. 87) one or two inches, and connect- ing by its oilier extremity with a flue. But this was thought to be an ungraceful appendage to the chandelier, and has not come into use. lie devised another, by which the tube carrying olF the products Oi combustion, returned parallel with the supply pipe, but we have not seen it. There is report also of a still more elegant and successful Englisli contrivance, but it cannot yet be found in this country. 361. Vontllatlon 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 Avith 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 ceUar to the top of the building, mounted with an ejecting cowl, answers a good purpose. Some go for abolishing cellars altogether.* 362. Ventilation should be provided for in Bnildln?, — There can be little question that the whole policy of warming and ventilating dwellings is yet in an unsettled and transition state, although this aftbrds 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 would condemn cellars and basements entirely, tbe common plan of build- ing, in their absence, must be 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 wbich becomes, on a smaller scale, the source of noxious emanations. ITnder-floor space sho\ild be abolished as well as cellars and basements. The plan that I have adopted with the most satisfactory sncccss, 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 flllod 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 communication 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 anim.al can get a lodgment in your lower story. By adopting this plan, your house will bo dry and cleanly ; the atmosphere of your ground floor will be fresh and pure ; you will bo entirely relieved fronj that steady drain upon life, which is i)roduced by basements and cellars, — and if you ajipropriato the ground- floor to purposes of storerooms, kitchen, iVc, you will find that the dry apartments thus constructed are infinitely superior to the old basements and cellars. And if you plact your sitting and sleeping rooms on the second and third floors you will bo as thoroughly exempt from local miasma. as Architecture cad make you."— Dr. Uucuanan. WUY THEY ARE NOT UNIVERSAL. 203 Provision should be made for ventilation in the first construction of dwellings, as it may then be effectually and cheaply accomplished. The introduction of adequato 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 structural 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 profoundly imconscious 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 within twenty years that Liebeg 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 auimals. 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. 863. Ventilatloii involves necessary loss of Heat. — The real practical difficulty in ventilation is its cost. Although the atmosphere is every one's property, and is the cheapest of all 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 vaost 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 204 AERANGEMENTS FOR ViamLATION. air, but they are not yet reduced to practice. Until that is done, heat must continue to be lost by ventilation, just in proportion to its extent. Uence, as was before remarked, ventilation may bo classed with food and apparel, and it becomes a question of how much can bo afforded. But there is this important difference, that Avhile economy in tho 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 tho worst evils of scarce and expensive fuel is, that the poorer cla-sses feel compelled to keep their rooms as tight as possible to prevent tlie escape of warm air and the consequent waste of heat. PART FOURTH. ALIMENT. I.— SOURCE OF ALDIENTS— ORDER OP THE SUBJECT. 364. View of the origin of Foods. — The ground thus far traversftd has furnished 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. Rocks, 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 Sttn, 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 hundred millions of miles through the amplitudes of space, take effect upon the chemical atoms of the earth's surface — its gases, waters, minerals, and combine them into nutritive, life-sus- taining compounds. The vegetable world is the laboratory where 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 Dodily fabric, originated in plants, under the direct agency of the sun« 206 SOURCE OP ALIMENTS — ORDER OP THE SUDJECT. beam. The vegetable leaf is the crucihlc of vitality, the consecrated mechanism appointed to receive the life-forces wliicli God is per- l)etnally i)ouring tlirough his imiverse. In partaking of the bounties of the table, arc we not, then, consummating a purpose to which planetary systems are subservient ? 'W^ rcjtair 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 gro\\i;h 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. Wo direct attention first to the general properties of foods, as we find them already produced and presented for preparation and use. 365. How Foods may be 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 vls alimentary principles^ — simple aliments, nnd proximate jirin- ciples. These are not the ultimate elements, carbon, oxygen, hydro- den, nitrogen, sulphur, &c., but are formed by combinations of these. They diflfer from each other in properties, exist in very diflierent proportions in various kinds of food, and are capable of being sepa- rated from each other and examined iudependently. These require to be first considered. Next in order we shall speak of the products which these simple principles form when nnited together. Thus starch, sugar, gluten, «&c., are simple aliments; while grain, roots, meats, &c., are made up of them, and are therefore called comjyound 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 tlie changes Avhich they undergo in culinary management. The principles involved in various modes of preserving alimentary substances will next bo described, and the subject closed by an examination of their physiological efiects and nutritive powers. WATER — ITS SOLVENT PKOPEKTIES. 207 360. Division of Alimentary Principles. — The simple alimentary prin- ciples are separated into two important divisions, based on their com- position ; first, the noii'nitrogcnotis 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, oil, and vegetable acids ; while 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 — icater, 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. II.— GENERAL PROPERTIES OF ALDIENTARY SUBSTANCES. 1. Peinciples Containing- no Niteogen. A.— Water. 867. Solyent Powers of Water, — One of the most important proper- ties of water is its wonderful power of dissolving many solids ; that is, when placed Avithin it they lose their solid form, disappear, and be- come difi'used 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 ot 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 aliTce 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, lleat influences the solvent powers of Avater, most generally increasing it ; thus, boiling water will dissolve 17 times as much saltpetre as ice 208 GENERAL PROPERTIES OF ALIMENTARY SUBSTANCES. water. Tliis it seeras to do by repelliug the particles of tbe solid body from each other, thus assisting the water to insinuate iti?elf among them, by whicli its action is helped. But there are exceptions to the rule, of which lime is au example ; sixty-six gallons of water at 32° dissolves one lb. of lime, but it takes 75 gallons at G0°, or 128 at 212°, to produce the same effect, so that ice-cold water dissolves twice as jnucli lime as boiling water. 3G8. How best to hasten Solotion. — Solids should be crushed or pulverized, to expose tlie 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 tliis 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. Solatioa of Gases — Soda-water — Water also dissolves or absorbs various gases, some more and some less. It may take 780 times its bulk of ammonia, an equal bulk of carbonic acid, or ^'3 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 pressm'O 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. Tlie 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, 870. Different 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 Avater. The substances which it takes up are numerous, and differ under various circumstances and conditions, and as these foreign substances or impurities which the THE GASES DISSOLVED IN WATEE. 209 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. Raln-Tvater aad Snow-water. — Rain-water is the least contami- nated of all natural waters, yet it is by no means perfectly pure. As it falls 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 impure. 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 ot water there is 33 per cent. The animals which dweU in water absorb this oxygen by breathing, just as land animals do from the air, whUe 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 will 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, &>om mud and decayed leaves, the decomposing bodies of dead ani- 210 GENERAL PBOPEETIES OP ALIMENTARY SUBSTANCES. inals, and a variety of other causes, waters are liable to conta /A ganic impurities, or those vestiges of living structures ■wliicl are capable of decomposition and putrefactive change. The effect of this organic matter may he 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 distilled water, when in a short time, if the weathei be warm, it will begin to smell oflonsively. This kind of contamina- tion may bo cither suspended mechanically in water as solid particles, or it may be dissolved in it so that the water shall still have an appear- ance of purity. 374. The living InbabitaDts 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 ai*e nourished upon the dead organic matter which the Avater 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 hind 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 will appear. This may bo shown by diffusing a little 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 will swarm with animalcula in a few days ; if, on the contrary, it bo slightly acid, vegetable forms will be princi- pally originated. It is important to notice also that the alkaline solution will run rapidly into putrefaction, and yield a putrescent smell, Avhilo the acid fluid will scarcely alter at all, and emit no unpleasant odor. It is lienco obvious that these two kinds of water have difterent 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. 875. I'se of living beings in Impure Water. — The presence of living tribes in impure water, fulfils a wise and beneficent purpose. If the largo amount of organic matter present in many waters could be re- moved only by tlic common process of putrefaction, and the forma- tion of injurious comi)Ounds and offensive gases, immense mischief would bo the consequence. To obviate tins, nature has ordained that some of the organic matter of impure water, in place of undergoing decomposition, shall bo imbibed by living beings, and these dying that others shall take their place and fidfil the same important oflace. The M1NEEAI< MATTER DISSOLVED BY WATER. 211 living races thus exert a preservative influence upon water, although this is more especially true of aquatic vegetation. 376. Water dissolrcs variable qnantities of Mineral Matter. — Eain 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 Ihe surface of the bed until it finds an opening or crevice, tlirough 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 Avith, 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 j'j- 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. Kinds 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 all 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 hme, 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. 212 GENERAL PROPERTIES OP ALIMENTARY SUBSTANCES. 378. Hard and Soft Water. — Tho presence in water of these dis- solved mineral substances, though in extremely small proportion, pro- dnces 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 liard and soft is usually coimccted with its cleansing qualities and its behavior towards soap, which wo shall consider in another place. It is also important dietetically (533). 379. Water la contact with Lead. — There has been much coiitradic- 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 Avaters ? Dr. Cubistisox said those wliich 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 tlian soft in their action upon lead. It may be remarked that water can act upon lead, cor- roding it Avithout becoming itself actively poisonous, if the compound formed be insoluble ; it is only when the lead is dmohed 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 hydi*ated 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 tho water much carbonic acid, a bicarbonate 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 hi 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 tho storage of hard water uuder tho 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 SOFT -VTATER — STARCH. 213 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 wiU 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 (CIO), are coming much into use instead of lead for the conveyance of water. 380. Sapply of Soft Water. — ^Wells and springs are often inacessible, or the water furnished is bad. In such cases the heavens furnish an unfaiUng resource, which, with AveU-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 6|- gallons, so that we get 18 J 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.-Tbc Starcbcs. 381. AVlience obtained, 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- _, gg table kingdom in much greater quantity than any otlier 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 linen cloth with clean water, a milky liquid passes through containing „ .• a. ^ ^ , , ° Separating Starch from flour by wasliing. wheat starch, which grad- ually settles to the bottom of the vessel. If raw potatoes are 214 GENERAL PROPERTIES OP ALIMENTARY SUBSTANCES. grated, and the pulp treated in a similar manner, potato starch u separated. 882. Proportions ia Tarlons substances. — The variable proportion of starch in different articles of food is as follows, in decreasing order : Slarch p«r e«nt. Eice flour 84 to 85 Indian corn 7T to 80 Oatmeal 70 to SO Wheat flour 89 to 77 Barley flour 67 to 70 Rye flour 50 to 61 Buckwheat J>2 Pea and bean meal 42 to 43 Potatoes, containing 78 to 78 water, 13 to 15 383. StarcJi Grains — tUelr size. — Starch consists of exceedingly small rounded grains. They cannot bo 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 arc largest, while those of wheat and rice are much smaller (Fig. 89), and those of turnips and parsnips still smaller, varying all the way from Fig. 89. ... ^ ^ ^^J Starch-grains of potatoes. Starch-grains of plantain. Starch-grains of rlco. the 1 -300th to 1-1 0,000th of an inch in diameter. Assuming the grains of wheat starch to bo l-lOOOth of an inch in diameter, a thou- sarkd million of them would bo contained in a cubic inch of space. 384. Their Appearance and Strnctnre. — Viewed under a higli 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 ineinbranes, like the coats DIFFERENT VAEHrnES OP STARCH. 215 of an onion. The grains of potato starcli are ovoid or egg-sliaped. 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 diy, 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, by 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 palm 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 all 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 vai-iety 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 arroio-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-root. — 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. Corn Starch, — 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 efiect the separation. The starch is freed from the glutinous, oily and ligneous elements of the seed, by the aid of alkaline solutions, and by grinding 21 G GENEIIAL PROPEKTIES OF ALIMENTAET SUBSTANCES. and bolting tho corn in a wot 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 tlio system will bo considered under these topics (516). 389. Chemical 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 tho composition of this substance may bo given as simply char- coal and Avater. 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— The Sug;ars. 390. Proportion in varions Substances. — 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 tho 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 : Vet cent, of Sugar. Juico of Sugar cane 12 to 18 Beet root 6 to 9 Wheat flour 4 to 8 Barley incal 64 Oat meaL 4"8 Cow's milk S'8 Eye meal 8-2 Peas 2 Indian corn 1*5 Kico •« There are several varieties of sugar, but wo are practically concerned with but two, cano sugar and grape sugar. 391. Grape Sugar or Frnit Sugar. — The white sweet grains of raisins or dried grapes take tho name of grape sugar. Most other fruits, however, as apples, pears, plums, figs, cherries, peaches, gooseberries, currants, «fec., 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. 892. Sugar Artificially Produced. — If starch bo boiled for some time in water wliich has been soured by adding to it one or two per cent, of sulphuric acid, tho solution gradually acquires a sweet taste. If, PRODUCTIOSr AND COMPOSITION OF HONEY. 217 now, by suitable means, the acid be neutralized and removed, and the Bohition 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 it's 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. Honey. — 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 returns to the hive and disgorges it into a previously prepared cell of the honeycomb, which it then caps over by a thin covering of wax. 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 cuUender 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. 894. Properties and Composition. — Honey, in difierent 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 svarms ; and whUe some regions are renowned for the exquisite and unrivalled flavor 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 10 218 GENERAL PEOPEETEES OP ALIMENTAEY SUBSTANCES. 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 Sngar — Its Sources. — Our common sugar is obtained, as is ■well known, from the sugar-cane. Eleven-twelfths of all 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, tnrnips and melons, from green corn-stalks, and the miripe seeds of grain, is identical in essential properties with that of the sugar-cane, and they are all distinguished as cane sugar. 896. Cane and Grape Sugars, different 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 grape sngar, while 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 Sngars, chemical differences. — Sugar, like starch, consists only of carbon and water ; but these two sugars differ in the proportion of these elements. While 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 combined 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 tufts. 898. Difference of solubility and sweetening powers. — Pure cane sugar remains perfectly di-y aud unchanged in the air, while grape sugar PRODUCTION OF COAESE SUGAR. 219 attracts atraospLerio 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 rapidly changed ; the acid of vinegar being generated ; — twenty minutes is, in many cases, suflScient 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 gramclates, 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 Irotcn 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, 220 GENERAL PROPERTIES OP ALIMEISTART SUBSTANCES. Fig or "wJiicli may have been introduced into the granulating vessels by careless management. 401. Brown Sngar nndergoes 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 Avhich a portion of cane sugar is converted into grape sugar. Dr. IIassall, perhaps the highest authority in matters pertaining to alimentary im- purities, states that nearly all samples of brown sugar contain also grape sngar, 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 Sagar. — "VVe had occasion, when speaking of water, to correct that common impression of the ill-in- formed, that swarms of animalcula) 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 all animal structures, from the largest to the smallest contain nitrogen, one of the conditions of the exist- ence of animalculeo 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 ofters nourishment to these beings, and accordingly they are commonly found in- fested with minute insects called augar-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 animalcula) 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 Bugar-mite, as scon upon a frafnncnt of cane, magnifled 130 diameters. MOLASSES — SUGAE-EEFINING. 221 the bottom, mixed T?itli cane-fragments, grit, and dirt. Tlie mite is visible to the naked 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 Composition 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 saccTiarates. 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 uncrystaUized in purifying and refining brown sugar. 404. Refined Sogar. — 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 boihng 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 transpai-ent solid, like glass. "When threads are suspended in the sugar solution, crystals of extreme hardness collect upon them, which are known as roclc-candy. The cause of whiteness in refined sugar is that the crystals are small, cofi- 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 fi-equently 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- 222 GENERAL PEOPEETTES OF AUMENTAET SUBSTANCES. rious are tlic vegetable and animal coloring matters, bnt 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 : ( Oxi J Bis I Bis ■I Oxido of lead {red lead). Keds J Bisulphurct of mercnry (vermilion). Bisulphuret of arsenic (red orpimenC). Gamboge. Yellows. . . •{ Chromato of lead (chrome yellow). Sulphuret of arsenic (yellow orpimtnf). Ferrocyanide of iron (Pruasian blue). Cobalt. Blues i Bmalt (glass of cobalt). f Carbonlto of copper (verdiier). {_ Ultramarine. Diacetate of copper (verdigrit). Greens -i^ Arscnito of copper (emerald green . Carbonate of copper (mineral green). WniTES Carbonate of lead (white lead). PuKPLEs Formed by combining blues and reds. I From an examination of 101 samples of London confectioneiy, Dr. Bassall found that 59 samples of yellow were colored with cTiromate of lead and 11 with ganiboge. That of the reds 61 were colored with cochineal., 12 with red lead., and 6 with vermilion. Of the blues, one sample was colored by indigo, 22 by Prussian hlue, and 15 by ultra- marine. Of the greens 10 were colored by a mixture of chromate oj lead and Prussian Hue, 1 with carbonate of copper^ and 9 with arsen- ite of copper. These colors were variously combined in the different cases, as many as from three to seven colors occurring in the same parcel, including three or four poisons. 406. Their dangerons and fatal Effects. — The Dr. remarks: "It may bo 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 cumulatire, that is, they are liable to accumulate in the system, little 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 GUMS AND OILS, 223 many that are employed in sugar confectionery. How much more in- jurious, then, must the consumption of sugar thus painted prove when these pigments are actually received into the stomach," D.— The 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 swells 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 Gnm. — When common starch is heated to 300 degrees in an oven, or boiled 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 Gmu 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, E.— The 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 fixed oils; and, 2d, such as will vanish from paper, under such circumstances leaving no permanent stain, and there- fore called volatile oils. The former is a universal and important element of diet, the latter presents itself chiefly among condiments, and will be there considered. 411, Sources and Forms of Oily Bodies. — Oil is largely procured both from plants and animals, and from both sources it is chemically the same thing. It exists in many parts of vegetables, but is chiefly etored up in their seeds, from many of which it is obtained by pressure 224 GENERAL PEOPERTIES OF ALIMENTARY SUBSTANCES. in largo quantities. In animal bodies it is deposited in the sacks or cavities of cellular tissue, and becomes accumulated in large quanti- ties in difterent parts of the body. Oils and fats are chemically iden- tical, differing only in consistence^ and this quality 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 j)alm oil, is with us boIiOl palm hutter. Those oils, however, which at ordinary temperatures are not perfectly fluid, but have what is called an oily consistence, become much thinner aud completely liquid when heated. 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 : Tolk of Egg 28-75 per cent. Ordinary Meat (Likbig) 14-03 " Indian Corn 9- " Oatmeal (husk excluded) 6* " Cow'eMilk 818 " Eye Flour 85 " "Wheat Flour 1 to 2 " Barley Meal 2* " Potatoes (dried) 1" " Rico -3 " Buckwheat '4 " il3. Its Composition. — Oleaginous bodies are distinguished froir. 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 aro, composed almost entirely of hydrogen and carbon, with but a small proportion of oxygen. The composition of hogs-lard, as given by Cheveeul, 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 fire-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 bo decomposed into several acid and basic principles (195). THE ACIDS FOUND IN FRUITS. 226 F.— Tlie Vegetable Acids. 414. Combiuatioa and Composition. — The sourness of fruits and suc- culent vegetables is due to various acids produced in the plant, and ffhich they contain usually in quite small 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 (G91). 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 tnem 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 in 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 fhiit, 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 Bold in the crystalhne 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 effer- 10* 226 GENERAL PROPERTIES OP ALIMENTARY SUBSTANCES. vescing, 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 half a pint of water. 418. Oxallc-Aeld — ^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, Avhich they much resemble. 419. YcgctaWe Jelly, Peetinc or Pectlc-Acld.-r-This is obtained from 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 oxj^gen. Vegetable jelly is thought not to exist exactly as such in the plant- juices, but to bo 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 spo-'ed. It differs from animal jelly 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, cellular-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. (Pekeira .) 420. Acetic Atld, or Viucgar. — The acid in most general use for dief etical purposes is the acetic, or acid of vinegar, which we obtain b THB ALBTJMINOUS PRINCIPLES. 227 fennentation (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 Avay of yeast to start the operation. There accimaulates 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, atiirst, undergo the vinous change producing cider and wine, and the process continued converts them both into vinegar {cider-vinegar and wine-vinegar), which arc prized, on account of the fruity aroma which accompanies them. 2. — Peinoiples Coittainino ISTitkogen. A.— Vegetable and. Animal Albumen. 421. It exists in both organized Kingdoms. — "We are all familiar with albumen or Avhite of eggs, and recollect the remarkable change it un- dergoes by heat, being coagulated or altered from a transparent liquid to an opacjue, white, brittle solid. This substance exists in small pro- portions dissolved in the juices of plants. If such juices are clarified and then boiled, 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 Eegnault, 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 peculiar animal juices, in the glands, nerves, brain, and around the muscular fibres of flesh. 422. Composition of Albumen. — In composition, albumen differs widely from the alim^ts 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 cai'bon, 189 of hydrogen, 68 of oxygen, 27 of nitrogen, and 2 of sulphur. The albumen of eggs, however, contains a slightly larger proportion 228 GENERAL PROPERTIES OF ALIiEENTARY SUBSTAKCES. of sulphur. Vegetable and animal albumen are essentially the same thing in properties and composition, dilicring no more upon analysis tliau two samples from the same source. 423. General Properties of Albnmen. — It exists in two states — soluble and insoluble, or coagulated. The coagulation is efiFected by simple heat ; but there is much confusion of statement among different writers as to the point of temperature at which it solidifies. 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 107°. "When excessively diluted, no turbidity can bo produced by a less heat than 194°, and it will only separate in solid masses after it has been boiled a considerable time. As a general rule, albumen coagulates Avith 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. B.— Vegretable and Animal Casein. 424. Sonrce and Composition. — The water in which flour has been washed or diffused, as in sepai-ating 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 with the curd of milk, which is known as animal casein, and is the chief ingredient of cheese. The identity of vegetable auu animal casein is weU 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 tlio people. The composition of vegeta- ble and animal casein is nearly if not quite identical with that of albumen (422). C— Vcg^ctablc and Animal Fibrin. 425. The Blood and Vegetable Juices. — When blood is drawn from FIBRIN AND GLUTEN, 229 Fia. 91. Fibres of lean meat magnified. the living bod}*, in a shoi't time it clots ; that is, a net- work of fibres is formed within it. These fibres consist of animal Jibrin^ Avhich 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 fibrin. The accompanying diagram (Fig. 91) shows its structure as seen under the microscope. The paral- lel fibres have cross markings, wrinkles, or strife. By the contraction of a muscle in the li\ang animal the strife are made to approach each other, become less distinct, and the fibre increases considerably in breadth and thickness. 426. Gluten. — 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 different in the proportion of these constituents ; rye "■ gluten, for example, con- sists largely of casein, and has less of the tenacious fibrinous princi* pie. By acting upon crude gluten with different solvent agents, it is separated into four principles as follows ; Fig. 92. 230 GENERAL PEOPERTIES OF ALIMENT AEY SUBSTANCES. Vegetable fibrin 72 percent. Gluten 20 Casein (muclne) .* 4 " Oil 3T " Starch Accidental), small quantity Total 99-7 " 427. Aolmal Fibrin. — The muscles or lean meat of animals are prin- cipally composed of tins substance, its proportionate quantity being greatest in flesh that is dark-colored, aud 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-transparent, though all 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 tbe Nitro^enons Principles. — Wliatever 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 aui- malculse. We shall consider these substances again (678). D.— Gelatin. 429. ItsSonrtes, 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 iu 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 DIFFERENT NAMES OF THE NITBOGENOUS PEINCIPLES. 231 used dictetically. Isingla«s 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. Four parts of isinglass convert 100 of water into a trem- bling jelly. Gelatin is also extracted from calves' feet, in forming calves footjelhj^ and calves' heads are also employed to furnish jelly in mak- ing mocic Uirtle 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 coifee 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 alimentai'y 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 ofmitrition; they are also called nutritive principles, x\x& flesh- forming and blood-mahing substances. Mulder 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 ^ro^cJTi, and hence the group has been called jpro^em or pro- tcinaceous compounds. Mulder's peculiar views are abandoned, but his terms are still 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, 232 GENEBAL PROPERTIES OF ALIMENTARY BUBSTANCE8. from many causes, as variety of seed, climate, soil, kiad of fertilizera, seed, time of harvest, &c. We give five analyses. Water Gluten Vau(JUelin. Dumas. Bbck. Flinty Wheat 12-00 14-60 56-50 8-50 4-90 2-80 Soft Wheat 10-00 12-00 62-00 7-40 5-80 1-20 Flinty Wheat. 12-00 14-55 56-50 8-48 4-90 2-80 Soft Wheat. Oencsue Wheat 10-00 12-00 62-00 7-86 5-81 1-29 12-40 11-46 70-20 ^6-20 Starch Sugar Gum Bran Total 98-80 98-40 98-73 98-46 99-20 433. 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 be^n noticed (420), is of the first importance in examining the grains. From an analysis of six samples of wheat, made by VArQUELiir, we get an aver- age of ll'lS per cent, of gluten ; Dumas, from three samples obtain- ed an average of 12-50 per cent. ; and Dr. Lewis C. Beck, Avho 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. Beok — that of washing away the starch by a stream of Avater (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. IIoesford 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 Qaality of the Gluten of Wlieat. — 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. THE GLUTEN AND WATER OF WHEAT. 233 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 beconaes 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 fltted 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 aftgr long boiling, withoirC either running into a mass or falling to pieces. 436. Water in Wheat. — The wheat grain consists of a solidifled veg- etable mUk. As the grain ripens, evaporation of water takes place, and the milk condenses into a hard mass. Wheat ripened under the hot sun of this dry 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. 234 GENERAL PBOPERTIES OF ALIMENT A.EY SUBSTANCES. 437. Grinding of Grain. — Grain ia converted into flonr by being ground between two horizontal stones, the upper of whicli revolves, while the lower is stationary. The mill-stones (buhr-stones) are com- posed of a peculiar bard 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 ioin or fit. From the centre outwards, they approach closer together, so that the grain is first coarsely crushed, and then cut finer and f ner 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 xmiform powder, composed of equal sized particles, but consists of parts which have been differently affected by the grinding process. Some are coarser, and others finer, 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 partSy fine flour, coarse flour, bran, &c. 438. Structure of tlie Grains. — Wlien 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 othei-s, rough, thick, and opaque ; in some light- colored, in others dark ; in some tough, in others brittle ; and in some it peels or flakes off readily imder 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 interdiflusion of these elements throughout tho body of tho seed, yet, upon dissection, they are each found in excess in the i)arts indicated. 439. Anatomy of Grains Illnstratcd. — An idea may be gathered of this distribution of substances throughout tho cereal seeds, by tho accom- STRUCTURE OF THE CEREAL GRAINS. 235 panying section of a grain of rye highly ^^^ ^ magnified (Fig 93) : a represents the outer - . _ "— "cSl investing seed-coat, consisting of three 5^^'';^^'^^^^^^cdc: c , rows of cells ; i, an inner membrane or :H^Is£S^££S^r;^ i» seed-coat, composed of a single layer of y^-^vj^^vv^^wj- cells ; c, a layer of cells containing gluten. ^^^^M^^lig^^/i,^^ These three form the bran ; d, cells con- '^ taining starch grains in the interior of the seed. Fig. 94 represents a cell 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 ^^P grain is mainly composed, is crushed most completely. As the particles of these substances, therefore, are of |f)^S|i!;iK different sizes, they may be separated by a bolting cloth, ''"'^ ^ having different degrees of fineness of texture. The ^i^^pl product is divided by the miller according to custom or fancy, four or five grades being often established, which, of com*se, 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 adlierent matter of the grain, by which its com- / '^y^ ('((^^ position will be made to fluctuate. Johnston V. . / states, that in good wheat the husky portion amounts to between 14 and 16 per cent, of its V^5^^^\^ whole weight. The same authority found six wheats to yield bran of an average composition, as follows : Water 131 Nitrogenized matter 19'S Oil 4T Husk, and a little starch 65"6 Baline matter (ash) ; 7"8 100 236 GENERAL PROPERTIES OF ALIMENTARY SUBSTANCES. 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 wheat, helps to protect it against the penetration of moisture, and enables it to bo washed (which ought al- ways to be done before grinding), without wetting the inner part of the grain. 442. White and dark-colored Flours. — In separating flour into dif- ferent grades, the finest and whitest will contain the largest quantity of starch, Avhile 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 sejjarates 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 witli 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 bo kneaded, and which may be drawn out into long strips, or thinly flattened Avithout 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 still 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 Floor. — Wheaten flour becomes whiter with age, but it is at the expense of gradual deterioration of flavor, sweetness, and nutritive quality. Bekgs 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. Mrr- CHERLicii and Keocker showed that wheat in which sugar was proved to be absent before sending it to the mill, yielded, after being ground, i per cent, of it. Starch was thus transformed into sugar, which coidd not be done otherwise than through the mternal action of the gluten fuded by air and superabundant moisture (473). The mutual action of the gluten, and the natural moisture of the flour, seem often capa- THE GRA.INS — WHEAT. 237 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 miller 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 finest 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 milk, 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 childi-en (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 sufficient to show the excellent qualities of the farina, whetl^er as a simple diet for invalids, or as an excellent food for the healthy." 446. What Minerals exist in Wheat. — When wheat is burned, there is left about 2 per cent, of ash, w^hich consists of various mineral in- gredients. An average of 32 of the most recent and reliable analyses gives the leading constituents, as follows: Phosphoric acid 46 per cent., (nearly half its weight,) potash 29*97, soda 3"30, magnesia 3*35, sulphuric acid '33, oxide of iron •79, and common salt "09. Phos- 238 GENERAL PROPERTIES OF ALIMENTARY SUBSTANCES. phoric acid is the characteristic and predomLnant 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 are distributed as follows. We give the average: — fine flour 1-08 per cent, next grade 3-8, coarser still 6-2, bran 7"2. The ash of bran contains considerable silica. 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 pbysio- logical effects of food (690). 447. Properties and Composition of Rye. — This grain ranks next to wheat in bread-making and nutritive qualities. It produces & larger pro- portion of bi'an 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. Boussingault obtain- ed from the grain of rye 24 per cent, of bran, and 76 of flour. lie separated by drying 17 per cent, of moisture, and the dry flour gave of Rye (Boi-sstNOAULT). Bye (Fooqailb). Gluten, albumen, &c 105 Nitrogenous matters 8-790 Starch WO Starch and dextrin 65-538 Gum 110 Fatty matters 1-999 Fatty matter 85 Lignin 6-8S3 Sugar 8-0 Mineral matters 1-T72 Epidermis and salts 00 Water 15-580 Loss 2-0 A sample of rye dried in Prof. JonxBTON's laboratory, lost 14'50 per cent, of water. Uorsfokd examined four sample-; of European rye, THE GRAINS — ^INDIAN CORN — OATS. 239 and obtained an average of 14 per cent, of water, and 13*79 per cent. nitrogenous compounds. 4i8. Indian Com or Qlaize. — This grain is distinguished chemically by containing a larger proportion of oily or fatty matter than any other. It u quite rich in nitrogenous constituents, though less so than wheat. Its peculiar protein element takes the name of sem (from zea maize, the botanic name of Indian corn) ; it is not of a glutinous, adhesive nature, and hence maize flour or meal will not make a dough, or fer- mented bread. It is prepared in several forms. Its composition is given as follows : Maixe (Paykn). Yellow Maiie (Foggaile). Starch 67 '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 3-968 Celulose 590 Mineral 1-440 Saltsorashes 1-25 Water 13-4T2 100-00 HoESFOBD 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 hominy 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 diflBcult 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, rangiog 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, beino; first in its proportion of the nitrogen- ous element. It is also distinguished by its large quantity of fat oi oil, ranging in this particular next to Indian corn. The following table gives the result of an analysis of French oats, by Boussingault, and the average of four samples of Scotch oats, by Prof. Norton. 240 GENERAL PROrERTIES OF ALIMENTARY SUBSTANCES. (Cocssingault). (N'oeiok). starch ; 461 Starch 65-10 Sugar 60 Sugar 249 Gum 8-3 Gum S'SZ Oil 6T Oil 6-55 Avenln.. ) Avcnin 16"50 Albumen V 13-7 Albumen, 142 Gluten..) Gluten 1-6T Hnsk, ash, and loss 23-7 Epidermis 3-17 Alkaline, salt, and loss l'S4 100-0 99-9C Norton'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"9G per cent, of protein compounds, the specimens ranging from 14 to 22 per cent. Prof. IIoesfokd 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 he mixed with water, it does not form a dough like Avheat 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 bai'ley is represented as follows : Fine Barley Mekl (Johnston). Barley (Poooailk), laUr. Starch 68 Nitrogenous matters 10"655 Fatty matter 2 Starch and dextrin 60-880 Gluten, albumen, &c 14 Fatty matters 2-884 Water..... 14 Lijrnin 8779 Ash 2 Mineral substances 2-628 Water 15-229 100 Einhof's analysis represents it as containing 4*62 of gum and 5*21 of sugar. Its husk or bran forms ft-om 10 to 18 per cent, of its weight. GRAINS — ^LEGUMINOUS SEEDS. 241 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 hulled or pot-barley^ and is used for making broth. After a considerable portion more of the kernel has been ground ofi", the rounded and polished grains are known &^ pearl-barley. 451. Elce 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 corn, and less than half that of oats. Analysis gives the following results : Rice (Paykn). Rice (Pogsaile). Starch 86-7 Starch, dextrin, sugar 74-470 Gluten, &c 7"5 Nitrogenous matters 7'SOO Fatty matter 0-8 Fatty matters 2-235 Sugarandgum O'S Mineral -326 Epidermis (skin) 8-4 Lignin 8-345 Salinematter (ash) 0-9 Water 17-730 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. Baekwbeat. — ^The composition of this grain has not been satis- factorily elucidated; there remains considerable discrepancy in the results of its analysis. Zexneok 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 1512 Starch 65-05 Protein 584 B.— Liegumiuous Seeds. 453. Composition of Peas. — Seeds obtained from pods are called leguminous. Of this class we are only concerned with peas and 11 242 GENEKAIi PBOPEBTIBS OP ALIMENTAET SUBSTANCES. beans. They resemble niucb in composition tlie cereal grains, bu*^ are more highly nutritive ; indeed, they afford the most concentrated form of vegetable nourishment. The roasted chick-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. Acco'd- ing to HoESFORD and Keockke : A Table Pea yielded : A Field Pea gave : Albumen and casein 2S-02 Albumen and casein 29-18 Storch 88-81 Starch 66-28 Gum 28-50 Gum 66-28 Skin 7-65 Skin 6-11 Ash 8-18 Ash 2-79 According to Pogoaile, field peas that had been deprived of 9*5^ ( envelope, contained : Kitrogenous matters 21-670 Starch, dextrin, and sugar 67-650 Fatty matters 1-920 Lignin 8-318 Mineral 2-802 Water , 12-740 He found also in very soft green peas : Nitrogenous matters 88-85 Older than the above 84-17 IJipened 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 diflScult 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 difieren- ences of fiavor and softness when cooked, and they probably diflfer equally in composition. We have before stated, that in consequence of its abundance of casein, the Chinese make it up into a kind of vegetable cheese (424). 454. Compositioa of Beans. — The composition of beans varies but little from tlmt of peas. The authorities above cited (Horsfobd and Kbooker) give the following results : LEGUMINOUS SEEDS — FRUITS. 243 Beaoa (HoRsroBo nnd Krockeb). Table Bean. Large White B«aa. Vegetable casein and albumen 28'54 29-31 Starch 8750 6617 Gum 29-20 66-17 Skin 411 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-prodncing material in Peas and Beans. — Bj reference to the preceding analytical results, it wiU 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 Fkesinius' analyses of the nsh of Three analyses of the ash of beans gave the peas gave : following average result : Potash 39-51 Potash 29-62 Soda 8-98 Soda 13-31 Lime 5-91 Lime 6-11 Magnesia 6-48 Magnesia 8-95 Oxideofiron 1-05 Oxide of iron 0-98 Phosphoric acid 34-50 Phosphoric acid 4*84 Common salt 8-71 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, pectine, 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 imperfect. 457. Composition of Apples. — Every one will understand that the 244 GENERAL PROPEETTES OP ALIMENTARY SUBSTANCES. various sorts of apples differ much 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, O'lG of casein, 1"4 of albumen, 8-1 of dextrine, 8-3 of sugar, 0-3 of malic acid, 82-G6 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 Sallsbuet's examination. Talman Sweeting. Greening. Swarr Apple. Roxbary Ruuet. Englith Rntwt, "Water 81-52 82-85 84-75 81-35 79-21 Dry Matter.. 18.48 17-15 1525 18-65 20-79 Muakmelon. Cocamb«r. 90-93 96-36 9-01 8-63 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 : Walennelon. Water 94-89 Dry Matter. 610 The dry matter of melons contains quite a large percentage of albumen, casein, sugar, and dextrin, with a small quantity of acid. D.— licaves, Lieaf-Stalks, &c. 458. Many kinds of leaves abound in principles adapted for animai 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 Joukstox 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 tliey 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." LEATES, tEAP-STAXKS, EOOTS, ETC. 246 Tbo cabbage and cauliflower lose in drying more tban 90 per cent, of water ; and tbe dried residue, according to Peeeika, is remarkably ricb in sulphur as well as nitrogen. Tbe plant decays quickly, and gives out a strong odor of putrefaction, owing to its nitrogenous and sulpliurous compounds. Decayed cabbage leaves should therefore not be allowed to remain in cellars, or lie about in the vicinity of dwellings. 460. Lcltace 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 rhubarb, ased. 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 : Rhnbarb Stalke. Celery. Vegetable Oyater. Water 89-50 88-22 84-46 DryMatter 10-50 11-TT 15-54 Ash 1-13 Half the dry matter consists of malic, tartaric, and oxalic acids, with fibre, sugar, albumen, and casein. £.— Boots, TuberS) Bulbs and Sboots. 461. Compositioa of Potatoes — ^Water. — This is the most widely culti- vated and important for dietetical purposes of all 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, nnripe 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. KdETE 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 the fol- lowing results. Greatest proportion of water in young potatoes, 82 per cent. ; largest proportion in full grown potatoes, 68*6 per cent. 246 GENEEAL PROPEETIES OP ALIMENTAEY SUBSTANCES. Ho gives the mean of 51 determinations upon potatoes of all ages — aa water 76 per cent, dry matter 24. 462. Starch in Potatoes. — A large part of the solid matter in potatoes consists of starch. Joitnston 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 (Jiminishes by keeping. Payen found the same variety to yield of starch in October 17-2 per cent February IS'S per cent November 168 " 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 all 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. IIoesfokd, by a more accurate method, foimd the percentage of these compounds in the dry matter of potatoes to be — in white potatoes 9-96 per cent, in blue 7-66 per cent. Ho 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 Boussingault also found the proportion of the protein compounds to diminish the longer the potato is kept. 464. Woody Fibre, Sugar, Gum. — Tlio proportion of fibre in the potato varies from IJ to 10 per cent., and may be said to average about 3. The fatty matter is also variable, but may bo stated at about 1 per cent. Sugar in the natural state about 3-3, gum 0-55, or in the dry condition, sugar 13-47, gum 2-25. 465. Average Composition of Solid or Dry Matter of Potato. — This ia summed up by Professor Johnston in round numbers as follows : THJE POTATO AND ONION, 24? Starch 64 Sugar and gam 15 Protein compounds b ^ Fat 1 Fibre 11 Total 100 The dry potato, therefore, is about equal in 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 formerly 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 follows : Potash 55-75 Soda. 1-86 Magnesia 5-28 Lime 207 Phosphoric acid 12-57 Sulphuric acid 13-64 Silica 4-2S 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- nesia. 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 oil, the same that gives its powerful odor to the garlic. The con- stituents of the onion are thus stated by Peebiea : Volatile oil, Woody fibre, Uncrystallizable sugar, Pectic and phosphoric acid. Gum, Phosphate and carbonate of lime, Vegetable albumen. Iron. 467. Beets. — The varieties of beets of course difier in composition, .but they all contain much sugar. Their nutritive qualities are not well determined. Beetroot is represented as containing 81 per cent 248 GENERAL PEOPEKTIES OF ALIMENT AEY SUBSrANCES. of water, 10-20 of sugar, and 2-03 of nitrogenous matter. In tho long blood-beet there is 89-09 per cent, of water, and 10-90 of dry matter. 466. Turnips, Carrots, Parsnips. — Chemistry has liitberto cast bat 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 18* Mangel-wurzel 15 Carrot 14 The dry substance of these roots is much 'ower 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 Compound*. The dried potato 8 per cent. Yellow turnip 9} do. Mangel-wur2el 15i do. The nitrogenous matter of dried mangel-wurzel being nearly twice as great as in the dried potato. In the carrot the proportion of water is 85-78, and dry matter 14-22. According to Ceome, the parsnip contains — Starch 1-8 Albumen 2-1 Gum 6-1 Sugar 6-5 Fibre 61 Water 794 Total 10000 4. COMPOTTirD AUMKNTS — AuiMAL FoOD. A.— Constituents of meat. 469. — ^Various parts of animal bodies contribute materials for diet; the flesh and fat chiefly, but nearly fJl other portions, blood, intestines, membranes, bone?, 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 Flesli-meat. — This is generally understood to sig- nify the muscular or lean parts of cattle, surrounded by fat, and con- taining more or less bone. Tho muscles consist of fibrin ; tliey are separated into bundles by membranes, and into larger separate masses by cellular tissues, in which fat is deposited. Tho fleshy mass is pene- COKSTITUENTS OF MEAT. 249 trated hy 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. Bbande, is as foUows : Water. Albumea and Fibrin. Qelatin, Total solid matter. Beef 74 20 6 26 Veal 76 19 6 25 Mutton 71 22 7 29 Pork 76 19 5 24 Chicken 73 20 7 27 Cod 79 14 7 21 These results give an average of very nearly 75 per cent, water. LiEBio assumes it at H, with 26 per cent, of dry matter. The ratio of water in meat, fowl, and fish, is quite uniform, ranging from 70 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, while swine are often fed until the animal becomes one morbid and unwieldy mass of fat. The pure muscular flesh of ordi- nary meat, with all 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. Jnice 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 the 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 fixiid, 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 Jcreatine and Tcreatinine^ nitro- genous compounds, which may be crystallized. The quantity yielded U* 260 GENERAL PROPERTIES OF ALIMENTARY SUBSTANCES. is variable in different kinds of flesh, but in all is extremely small Kreatine is a neutral or indifferent substance, while kreatinine is a powerful organic base, of a similar nature with theine 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 solidified blood. About half the weight of bones is mineral matter, lime combined with phosphoric acid, forming phosphate of lime — the substauce that we have seen to abound so greatly in the ash of grains. The other half of bones is gelatin, 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, cartilage, and membrane, yield much gelatin. The tongue and heart are muscular organs, agreeing in dietetical proper- ties with lean flesh. Bracconnot's analysis of the liver gives 68 per cent, of water, and 26 of nitrogenous matter; it also contains oil. The Irain is a nervous mass, containing 80 per cent, water, some al- bumen, and much of a peculiar phosphoric oily acid. The stomacTia of ruminating animals which yield tripe, are principally composed of fibrin, albumen, and water. 473. Composition of I^gs. — The eggshell is a compoxmd 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 16 or 20 per cent, of albumen. The yolk is water and albumen, but contains, also, a largo proportion (two-thirds of the dried yolk) of a bright yellow oil, containing sulphur and phosphoric compounds. A common-sized hen's-cgg 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 (salta) 1-5 Total 100 R.— Production and Composition of Milk. 474. What It Contains. — This familiar liquid consists of oil or butter engar, casein or the cheesy principle, and salts, with a largo proportion of water. The sugar, casein, and salts are dissolved in the wate' PEODUCmON AND COMPOSITION OF MILK. 251 while the butter is not, but exists diiFused through the liquid in the form of numberkss extremely minute globules. They cannot be seen by the naked eye. When the light falls upon them they diffuse it in all 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 Heney and Chevalier: Cow. Woman. Casein 4-48 1-52 Butter 818 3-55 Milksugar 4-47 6-50 Salts -60 0-45 Water 8702 8798 The following are Hadleen's results : — The second column is tho average of two analyses. Cow'i MUk. Woman's Milk.* Butter 3 2-35J Sugar of milk and salts soluble In alcohol 4*6 3.75 Casein and insoluble salts 5*1 2-90 Water 878 90-50 476. Circnmstances Inflnencing tlie Quality of Blilk. — ^Both the quantity and quality of mUk 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 R. 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 between 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.) 262 GEXERAL PKOPERTIES OF ALIltENTAEY SUBSTANCT-S. milk rich in casoin. It appeared from Thomson's observations, that the prcxluco of milk of a cow, with uniform diet, gradually diminished, and increased again by a cliange of diet. It is well known that a cow fed upon one pasture will yield more cheese, Avhile upon another it will give more butter. Hence the jiractice 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 milk ; 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 mUk. 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 wild onions grow, there will 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 clovei*. 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 calTlng. — The colostrum, or first milk which the cow gives for several days after the birth of her young, differs from normal mUk. Gbegoey 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 Ayton : Quart* p«r da;. Quarto. First 60 days 24 or In all 1200 Second " 20 " " 1000 Third " 14 " " 700 Fourth " , 8 " " 400 Fiftli " 8 " " 400 Sixth " 6 " " 800 and at the end of ten months, they become nearly or altogether dry, 478. Time of year, age aad condition of the animal. — In spring, milk is finest and most abundant. Moist and temperate climates and scasijns 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, whUe hot weather PEoDUCriON AND COMPOSITION OF MILK. 253 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 quality of the milk. 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. — (Johnston.) 479. Production and Composition of Cream. — We have stated that butter exists in milk, 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 beco:^es perfectly clear by the complete separation of these globules. Hence, cream may be viewed as milk rich in 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 oil-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 the 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 hours standing. Milk is, there- fore, sometimes skimmed twice, and made to yield two qualities of but- ter. The deeper the milk, the greater the difficulty with which the 254 GENERAL PROPERTIES OF ALIMENTARY SUBSTANCES. oily matter ascends through it ; hence, it is customary to set the milk aside in sliallow pans, so that it may not be 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. 7(^7n^era^^/re 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 oil, greatly retards their sepa- ration. Hence it is said, that from 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, milk may bo perfectly creamed In 86 hours when the temperature of the air is 60* F. "24 " " " 50' « 18 to 20 " " " 68* » 10 to 12 " " " 71* 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. — (Spkengel.) 481. Milk Creams before it is taken from tUe 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 hollow spaces or reservoirs which diijtend 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, Avhile 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 afteriiigs, abounds in cream. Professor An- derson 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 t^e advantage of this 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 PBODUCTION AND COMPOSITION OP MILK. 256 ^^^-t«< by keeping the milk in separate portions as it is drawn, and setting these aside to throw up 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 fiq. ge. quantity of cream that may be separated, but much delays the operation which, in hot weather, when milk soon sours, is objectionable. 482. Determiiung the value 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- cijic gravity^ is determined by the hydrometer (Fig. 96). A tin or glass cylinder is fiUed with milk to be tested, and the hydrometer, a glass bulb with a stem above, is placed Hydrometer. in it ; the lighter the milk, the deeper it sinks ; the hea\'ier it is, the higher it floats. A scale is marked upon the stem, which indicates at once how far the weight of the milk 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 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. The tube being filled with milk to the top space, is suffered to stand until the Lactometer. Fig. 97. * Made by Tagliabtte, of New York. 266 CULINARY CUANGES OF ALIMENTARY SUBSTANCES. 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 milk 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 8 Phosphate of lime 2-81 lbs. 8-44 1 19. Phosphate of magnesia. 0'42 " 0'64 " Phosphate of peroxide of iron O-OT " 0'07 " Chloride of potassium 1'44 " 1'88 " Chloride of sodium 024 " 0a4 " Free soda 042 " 0-45 " Total 4-90 6-77 III.— CULINARY CHANGES OF ALIMENTARY SUBSTANCES. 1. CoiEBIXIN'O THE ELEMENTS OF BkEAD. 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 Avater, or in va- rious ways and degrees, is the chief agent of culinary traTisformations. Another proper object of cooking is the preparation of palatable dishes, * The narober given hy 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. COMBINING THE ELEMENTS OP BRT2AD. 257 from the crude, tasteless, or even offensive substances furnished 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 aire 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 ieat 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 will occupy our first and principal attention. 485. Water absorbed ia making Dongh. — The addition of much water to flour 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 ofllce 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. K 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 in making the dough. Thus — Dryflonr 56 ) Water in flour naturally lOJ- ) Water added in baking 88J 100 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 quahty. The amount with which they will combine is sup- posed to depend upon the proportion of gluten. In dry seasons flour 258 CULINARY CHANGES OF ALIMENTARY SUBSTANCES. Will bear more water than in wet, and a thorough process of kneading will also cause the dongh 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 Tcneading the dough, and is generally performed with the bands. 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 inte- 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- continued. 487. Bread from plain Flonr 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 diflS- cult of digestion. If baked a'-: a still higher heat, and afterward sub- jected to prolonged drying, we have the common s1iii>-'bread or sea- hiscuit, which is made in thin cakes and never in largo loaves, and which is very dry, hard, and diflicult 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 eliaracters, — suflicient 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 BREAD RAISED BY PEBMENTATION. 259 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. By 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. Various methods are employed for this nur- pose, which will now be noticed ; and first of fermentation : 2. — ^Bkead Eaised by Feementation. 488. Substances capable of Patrcsccnce. — 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 slight disturbing forces easily overturn them. Oxygen of the aii* 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 pi-operties 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, putrejiable substances. 489. The Patrefactive change Contagions. — The other class of aliments, 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, oi oil, are 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 prodnce upon the other class, they take a new name, and are called fei'ments. The communication of that con- dition of change from one class to the other, is called fermentation^ and the substances acted upon are nariied fermentable compounds. Thus, if some sugar be dissolved in water, and a portion of putrefying dough, meat, or white of egg be added to \t, fermentation sets in; that is, the change is communicated to the sugar, the balance of its affini- ties is destroyed, and two new substances — one alcohol, containing all 260 CULINAET CHANQES OF ALIMENTAET SUBSTANCES. the hydrogen of tho sugar, and the other carhonic acid, containing two-thirds of its oxygen — are produced. 490. Conditions of Fermentationt — When matter capable 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 vpon, 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 70° 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 drying, by exposure of it to a boiling heat, and by various chemical substances, as volatile oils, sul- phurous acid, &G. 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 vinous or alcoholic fermentation. If this be not checked, the process is liable to run on to another stage ; tho 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. Tliere 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. Dongli raised by Spontaneous Fermentation. — Now dough, as it con- tains both gluten and sugar, Avhcn moistened is capable of fermentation without adding any other substance. If simple flour and water bo mixed and set aside in a warm place, after the lapse of several hours it will exhibit 8}Tnptoms of internal chemical action, becoming sour from the formation of lactic acid,Avhilo minute bubbles appear, which are ow- ing to a gas set free within the dough. The changes are irregular and un« BREAD RAISED BY FERMENTATION". 261 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 baked 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 "svater, 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. What makes the Dongh rise ? — 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 suflficiently 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. 262 CULrNAET CHANGES OF ALIMENTARY SUBSTANCES. 494. Raising Dongli by Leaveii. — But the mode of raising dough by spontaneous fermentation (492) is not sufficiently prompt and conve- nient ; we require some readier means of establishing immediate de- composition. If we take a piece of dough which has been kept suflS- 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 bo 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, while 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 skill to produce a good result. Leaven is but little used in this country, bread be- ing almost universally raised by means of yeast. 3. Peoperties Am) Action of Yeast. 495. Prodaction of Brewer's Yeast. — 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. Ilcnce, 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 {siceet-worf) 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 bo seen to rise from all parts of the liquid ; a ring of froth, PEOPEKTTES AKD ACTION OF YEAST. 263 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 bubbles of gas {carbonic 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 httle pointed heaps, which become brownish on the surface and edges ; the yeast gradually thickening 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 from 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 i\iat it is a true plant belonging to the Fungus tribe. Under a powerful magni- fier, it is seen to consist of munberless 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 off from each other, as shown in Figs, 98 and 99, The little grains from which they ^(^rT\% ,.fpfD spring or germinate are shown, and how they rv-<-'^r-:>^LZ^ 0> multiply by budding. They are of amazing ^^~rQ^2©3 ^ minuteness, a single cubic inch of yeast, free llferj "^ 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 thoy stance to join with the sugar, in producing ^Sl "o^/sfeftaTa'pfi alcohol and carbonic acid. Liebig supposes "<'™ ^^^i' interior. the effect to be dynamic^ that is, produced by an impulse of force ; the 264 CULINABT CHANGES OP ALIMENTARY SUBSTANCES. Fw. 99. motions of the atoms of tbo decomposing ferment, being communi- cated to the atoms of sugar, set these also in motion, by which the SQgar structure is, as it were, jarred and shaken to jneces, its atoms falling into new arrangements and forming new substances. 497. Domestie 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 will, after the third day, begin to emit a little gas, and to exhale an exceeding disagreeable sour odor. After the lapse of some (5)^©iEv' time this smell disappears ; the gas evolved is greatly increased, and is accompanied witli 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, and the temperature kept up by iti^^tlTe'.tL'^UX-s'f^w^"'"^^ 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. PEOPERTIES AND ACnON OF YEAST. 285 499. Action of Hops in Yeast-making. — Hop-flowers contain about 8 percent, 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 called 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 how 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-thirds 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 cui-ious 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. Liebig remarks that simple pressure diminishes the power of yeast to excite 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, untU it becomes an inch or two in thickness. When thoroughly dried, it can be preserved in bottles or canisters. Yeast is also commonly preserved by adding to it maize meal, and making it into a dough which is wrought into cakes and drie^. 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, boQ 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 3^ lbs. of rye flour. Next day, thoroughly mix in 7 lbs. of Indian meal, forming a stiff dough ; knead it well, roll 12 266 CULINARY CnANGES OF ALIMENTABT SUBSTANCES. 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 tasto 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 oflE" 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 tbroAving 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 Yeast— how eorreeted. — 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. Dongh raised by Yeast. — IIow fermentation lightens dough, has been shown (493). Yeast produces these changes promptly and effec- tually. It is mixed Avith 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 \ifalU, 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 pcrho.ps 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 bo so feeble as to EAISING BREAD •WITHOUT FERMENTATION. 267 produce acid (476), or it may be too active and rapid, if too much or too strong yeast has 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 Avith the fingers moistened with an alkaline solution. 505. The Sngar of Flow all decomposed in Dough. — It is at the ex- pense of sugar destroyed that fermented bread is raised, but liow much sugar is thus decomposed is variously stated, and depends upon the activity and continuance of fermentatipn. Expei-iments would seem to show, that all the sugar present is rai'ely, if ever, destroyed. The raised dough and bread both contain sugar, often nearly as much as the flour before it Avas used. This is explained by remembering that one of the effects of fermentation is to change starch to sugar. 50G. How mnch Alcohol is produced in 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 GO cubic inches, 20 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. RAisi:Na Bread without Ferjientatiou. 507. Objectioas to raising by Ferment. — Two or three objections have been nrged against raising bread by fermentation. Firsts the loss of 268 CULmART CHANGES OP ALIMENTAEY SUBSTANCES. a portion of the sugar of the flour which is decomposed ; this loss, how- ever, is triflinf^, and the objection futile. It is said, secondly^ that aa a destruction or incipient rotting process Ims been established in the dough, bread made from it cannot be healthful. This is oi\\y fancy, experience i« wanting to show that well-made fermented bread is in- 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 w.e 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, rises 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. 609. 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. Pereira indicates the following proportions : rionr 1 lb. Bicarbonate of soda 40 grains. Cold water, or any liquid necessary \ pint. Hydrochloric 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 will 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 effects. The changes that take place are thus shown. We begin with — RAISING BBEAD WITHOUT PEEMEKTATION. 269 Carboxic acid; (gas,) Water ; (liquid,) and Common salt : Bicarbonate op soda: ) , „„, (solid,) ^a P^uMf' °""''°(™0""' 3 Plough, Brea& is also raised with soda powders ; — tartaric acid, and bicar- bonate of soda, which are the active ingredients in effervescing draughts. The cliauges are these Bicarbonate of soda; ) __„j„„„ C Carbonic acid; (solid,) and ( PF°^^f ' ) (gas,) and Tartaric acid; I j„„„u i Tartrate op soda; (solid,) 3 ^""g'^' ( (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 like cream of tartar — gently aperient. Preparations which are known as egg-powder, iahing-powder, and custard-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 difficulty with these powders, is to get them in perfect neutrahzing 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. Sesqniearbonate of Ammonia. — The perfect theoretic conditions of raising bread without fei-ment 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. Thus — (solid,) \ P^duces. Ammonia ; Bicarbonate op Ammonia ; (ga^,) Carbonic acid, (eras.) 270 CUUITAET CHANGES OF ALHEETNTAET SUBSTANCES. 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 Clicmlcals ased. — The class of substances thus introduced in the bread are not nutritive but me- dicinal^ and exert a disturbing action upon the healthy organism. And although their occasional and cautious employment may perhaps be tolei-ated, on the ground of convenience, yet Ave 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 bi-ead, 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 la 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 Avithout 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, challc, 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 licarhonate 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 Substances and E^s. — 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 ALTEEATIOirs PRODUCED IN BAKING BREAD. 2'71 heat causes the disengagement of elastic vapor from the water and fatty matter, which, being diffused between the numerous layers of dough, causes them to swell up, producing the flaky or puffy appearance which is seen in pastry. This kind 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 Avith it air bubbles, which are expanded in baking. From its glairy, tenacious consistence when mixed with dough or pudding, it encloses globUes of gas or steam, which are generated by fermentation or heat. In this way eggs contribute to the lightness of baked articles. 513. Raising 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 milk, 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. Colquhoitn 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, \ oz. carbonate of magnesia, \ oz. of tartaiic acid, with the requisite molasses, butter, and aroraatica. 5. Alteeations Peodtjoed ix Bakiiig Beead. 514. Temperature of the Ovcnt — 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 will rise to 212°. This heat is suflScient to 2V2 CULINAKY CHANGES OF ALIM£NTABT 8UBKTANCE8. carry on the inner 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 bo 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 350° 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 ov turns black, the heat is too great. 515. Heat causes a loss of Weight. — The loaf loses a portion of its Aveight 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 bo of a certain weight, this loss must be calculated upon and a proportionate amount of additional flour used. Peeohtl 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 six 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 oflF, as is shown by the spirituous odor yielded in the baking process. 517. Chemical Changes in producing the Cmst. — The heat of the oven falling upon the surfsice 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 ruptured (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 fonnation 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 prodncing the Crumb. — As the temperature within the loaf docs 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 ALTERATIONS PRODUCED IN BAKING BREAD. 273 the yeasty 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 wiU 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 ceU 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. Qnalities 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 will 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 12* 214: CULINARY CHANGES OF ALIMKNTAKY SUBSTANCES. equally disseminated; nor should the crust be bitter and black, but of an aromatic agreeable flavor. " If the yeast be so dilTused 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 bo raised and made as light as a sponge before the acetous feriuentation 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." — (GuAnAM.) 6. Influence of Foreign Substances upon Beead. 521. fommou Salt, Alnm, kt, — 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 ((597). Alum has exactly the same effect on bread as common salt, but in a much more marked degree. A small quantity of it will bring up a bad flour to the whiteness of the best sort, and will 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- pJiate of copper, (blue vitriol), in exceedingly minute proportions, exerts a striking influence upon bread in the same manner as alum. Carhonate 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. Davt. INFLUENCE OF FOREIGN SUBSTANCES UPON BREAD. 275 recommeiided 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. Lieblg recommends Lime-water in Bread. — However it is to be lamented, it is nevertheless a fact, that enormous quantities of flour, more or less deteriorated, are purchased iu 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 alcue, 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 iu a high degree a water-absorbing substance, so much so that it attracts and combines with the moisture of the air, and is thus injured. This can only be avoided by artificial drying and protecting thoroughly from the air. The effect 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 flour. 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-600tli 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 all who have 276 CULINARY CHANGES OF ALIMENTARY SUBSTANCES. eaten it for any length of time to any other." — (Liebio.) The use of lime-water removes all acidity from the dough, and also somewhat augments the pro])()rti(jn of Avater 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 suffices 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, Avith this artificially added the cereal grains still contain less of it than peas and beans. Indeed, Liebig hsjs sug- gested that experience may yet prove the cereal grains to be incapable of perfect nutrition, on account of their small proportion of the bono forming element. 525. Different kinds of Bread. — Rice 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. liye makes a dark-colored bread, and is capable of being fermented and raised m 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 Avarm. 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 bo acted upon by heat in the baking process than Avheat or rye. If ground wheat be unbolted, that is, if its bran be not separated, wheat wcaZ or Graham Jloiirrcsuhs, from which Graham or dyspepsia bread is produced. It is made in the same general way as other Avheaten bread, but requires a little peculiar man- agement. Upon this point Mr. Graham remarks : " The wheat meal, and especially if it is ground coarsely, swells considerably in the dough, and therefore the dough should not at first be made quite so stiff a.s 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 wheat 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 VEGETABLE FOODS CHANGED BY BOILING. 277 In which 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. 520. 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 cerealine, 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 irown color also of the bread, are due to cerealine. He says cerealine ferment wiU make a brown bread of the whitest flour, whereas, if it be neutralized, a wJiite hread can ie made from a dark fiour containing iran. He grinds wheat so as to separate it into about 74 per cent, of fine flour, 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 chanoed by Boiling. 527. Its General Effects. — Boiling differs from baking in several re-r 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 readUy masticated, more easily pen- etrated by the saliva and juices of the stomach, and hence more 2/8 CULINAKY CIIANQES OP ALIMENTARY SUBSTANCES. promptly and perfectly digested. Perhaps v>'g may hero most con- veniently consider the specific effects of heat upon tlic 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. Wo 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, «fec., &c. We are hardly justified in ranking woody fibre, as Pekeira 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 tlie more pure. Yet woody fibre seems capable, by tlie joint action of heat and chemical agencies, of being converted into nutritive matter. If old linen or cotton i-ags, 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 dexfrin, and then into grape sugar. By such modes of treat- ment old rags may be made to yield moi'e than their weight of sugar. But weah solutions of acid or alkali do not produce any such effect. Nor will strong vinegar. We may therefore assume that woody fibre remains totally unchanged by exposure to culinary agencies and ope- rations. Professor Autexeieth, 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. AVe are not aware that his experiments have been confirmed, wliile it is suspected that whatever nutritive value his bread may have possessed, was due to starch associated with the wood. 529. Changes of Sngar. — Sugar, dissolved in cold water, or boiled to a sirup, has very diflferent 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 850°, it loses the property of crystallizing when redissolved in Avatcr, 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 VEGETABLK FOODS CUAXGED DY UOILING. 279 Fig. 100. only very soluble in water, but also very absorbent of it (deliquescent)^ turns of a decj) 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 saccJiaraies. 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 up 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 liilum. If one of these gi-ains 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 resisteut at that point. But under the joint action of heat and water, the grains break up difl'er- ently. Their membranes are torn apart, or exfoliated by internal swelling, as shown in Fig. 101. 531. Changes of Starcli. — Starch is but slightly acted *hroiigb''its uiium.^ upon by cold water. When heated with water it does not dissolve ; but the grains swell, forming a viscid mucilaginous 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 pomt, and sweU 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 Avith the microscope, it wiU 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. Starch grain ruptured by boll- 280 CULINARY CHANGES OF ALIMENTARY SUBSTANCES. By being boiled in water for a considerable time, it nndergoes tbe 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 arc 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 . lialf, of starch. When examined by the Fio. 102. microscope, the tissue cf 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. 103, 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 Starch grains of potato them, baking them, or browning the surface, dries 01 mg. ^^ ^j^^ starch into a hard, lialf-charcoaily 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 wliich is free from dissolved mineral matter, makes its way into, or is imbibed by organized tissues, with much more readiness and focility than hard water. It also exerts a more powerful solvent or extractive action, and thus is a better vehicle for conveying alimentary sub- Fio. 103. HOW COOKING CHANGES MEAT. 281 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 effect 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 principles. 8. How Cooking changes Meat. 534. Action of Heat upon the Constitnents of Flesh.. — K 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 effect 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 aliumen to the solid condition ; altering remarkably all 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 suflicient 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 282 CULINARY CHANGES OF ALIMENTARY SUBSTANCES. 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 ai"e 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. Proiierties of the Liquid and Solid parts of Flesli. — 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 ':'.onstituents 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 hquid 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 dried, 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 In Cooking. — 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, loiling, roastirig, and 'baking. During these operations, frcsli beef and mutton, when moderately fat, lose on an average about as follows: In boiling. In baking. In roasting. 4 lbs. of beef lose lib. 1 lb. 8 ozs. 1 lb. 5 ozs. 4 lbs. of mutton lose 14 ozs. 1 lb. 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 meltod out dm-ing these two methods of cooking. 537. Best method of cooking "(Jeat— 'n preparing meat for the table, HOW COOKING CHANGES MEAT. 283 WO sliall discover it to be most desirable that the ingredients of its juice should remain in it; and this will depend much upon the method of culinary procedure. If the piece of meat be in- troduced into the "water when hrishly 'boiling^ 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 tlie coloring matter of the blood coagulates. As in boiling, 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 liquid. 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. 284 CULINARY CHANGES OP ALIAiENTAEY SUBSTANCES. 640. Sonp, Beef-tea, Matton-broth, &c. — In tlio i)reparation of these our object is the reverse of tliat which has just been considered. "We dfisiro to take the nutritive and savory principles out of the nieat, and get them into a liquid or soluble 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, "which 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 bo 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 OAvn 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 homy, 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 Avhat 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 effected 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 j)lace (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 compJetest 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 Strengthening the Slek. — In certain maladies (as typhus fever, for example, at particular stages), the greatest difficulty met with by the physician, lies in incomplete digestion, or inability ]>romptly to reinforce the exhausted and bankrupt blood. To meet this difficulty Liebio prepared, as follows, a nutritive liquid, which has been used at Munich with the best results. Take half a lb. ot'jyer- Jectli/ frenh meat (beef or chicken), cut it in small ]>iecos, 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, stx'ain through a common hair sieve, letting it pass PEEPAE4.TI0N AND PEOPERTIES OP BUTTEE, 285 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 water must be used, and refrigeration with ice will guard sgainst decomposition. 9. Prepaeation and Peopekties of Buttek. 642. Action 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 boil 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 tlie firm consistence of churned butter. 543. Butter separated meclianically. — 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 fi'om under the cover, or when the churn is opened. 544. Rate of Motion in Churning. — 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 sound from a low and smooth to a harsh tone is 286 CULINARY CHANGES OF ALIMENTAEY SUBSTANCES. observed. It may tlien bo again slightly increased, until the butter begins 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 hurnt^ 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 bo produced in from 10 minutes to 3 oreven 5 hours. Dr. Muspratt assigns from 45 minutes to an hour as the best time for cream, while Prof. Arrox states for cream an hour and a half, and for whole milk from two to three hours. Dickessox says it is no matter if we are six hours in churnii.g sweet milk. It is, however, the well established result of experimentj 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. Wo have had frequent occasion to notice the controlling influence of temperature over the changes of matterj and we find it again illustrated here. Cream, when put into the churn, should never be warmer 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 tho first importance, so tliat 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 Ls 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. Composition and properties of Bntter. — 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, lutyric acid, combined with oxide of lipyle. 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 difterent surface when cut from fat or grease. This granular quality results from tho peculiar mode of its production, which is by tho 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 PREPARATION AND PROPERTIES OP CHEESE. 287 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, :5 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. Pbeparation and Propketies of Cheese. 547. Spontaneons Curdling 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 eflfect upon the milk sugar, converting it into lactic acid, which causes the sourness of milk. When sufiicient 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 witli 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 eftect in precisely the same way, that is, an acid substance is employed to neutralize the soda of the milk, by which the casein assumes the coagulated state. Almost any acid will have the eflfect 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. 288 CULINAEY CHANGES OF ALIMENTARY SUBSTANCES. 549. Artificial Curdling with Rennet. — The salted and dried stomach of the uinvcaued calf, lamb, or pig, is called rennet. If a small piece of this be soaked iu water for a time, and the infusion bo 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 stomacli 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 duo 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 is 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 largo portion of oil and a trace of sugar of milk, with some water ; and second, the whey 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, while 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 cheeso are influenced by a great number of circumstances. Pure casein makes a cheeso poor, hard, and liorny. 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 wo 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 irhole milk 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 PROPERTIES AND PREPARATION OF TEA. 289 richer. All the conditions which influence the properties of the milk itself (334) affect also the quality of the cheese. The heat, in curd- ling, should not he 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 from the curd, while too much rennet makes the curd tough, and otherwise affects disagreeably the subsequent changes and flavor of 4he 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 skilful 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). IV.— COmiON BEVERAGES. 1. Peopeexies and Pkepaeation of Tea. 551. The Tea Shrob. — 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 differmt varieties of Tea. — Many varieties of tea of all grades of quality are known in market. These differences depend iwst 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. TJdrd, 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. 553. Dlflference between Green and Black Teas. — All the different varieties of tea are classed as either green or llach "What constitutes 13 290 COilMON BEVERAGES. the real diflference between these two sorts has long been a matter of doubt. It was at first supposed that they came from totally difFerenl 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 : GEEKN TEA. BLACK TEA. 1. Coltivated in manured soils. 1. Grown chiefly on tho slopes of hiUa 2. Leaves are steamed, withered and and ledges of mountains. roasted almost immediately after gather- 2. Allowed to be spread out in the air Ing. for some time after they are gathered. 8. They are dried quickly after the 3. They are tossed about until they be- rolling process ; the whole operation being come soft and flaccid, brief and simple. 4 They are now roasted for a few min- utes, and rolled. 6. They are exposed to tho 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 tho 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 tho fresh leaves, it being well known to collectors of plants, tliat many which inevitably turn black when simply dried, preserve their green color brilliant and permanent, when they are killed by steam, previously to drying. Tho 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 system. 554. Varieties of Green and Black Tea. — The most important teas of commerce may bo thus arranged, beginning with the lowest qualities. Annexed is an approximative scale of the prices per pound paid for them in Canton. Green Tea*. BUck Tcu. Twangay IS to 27 cts. Bohca 12 to 13 cts. nyson Skin 18 to 80 " Congou 22 to 25 " Young Hyson 27 to 40 " Campoi 22 to 80 " Hyson 40 to 60 " Souchong 20 to 85 " Imperial 45 to 63 " Caper 20 to 40 " Gunpowder 45 to 60 " Pekoe 85 to 75 " PEOPERTIES AND PEEPAIUTION OF TEA. 291 Twangay is tlie coarsest and most inferior of the green teas. The Hysons are of a better quality, and are more Avidely used. The word ' Hyson ' is derived from Hee-chun, the name of a celebrated Chinese tea-maker. Hyson-shin 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. BoTiea is the poorest and cheapest of the black teas, and tiikes 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. Caper comes in little balls or grains, made up in the form of capers. Pehoe 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 PeJcoe, 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. Compositioa 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 painful 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. Stentiouse 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. 292 COMMON BEVERAGES. This substance is a powerful 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 const! tnents are com- municated 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 cat 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 suflBciently 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 will 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 tJiein being no longer held in solution, is precipitated and rises, forming a skin upon the surface. 557. What remains In the Gronnds, or residue. — 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, so 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 PROPERT/JiS AND PREPARATION OF COFFEE. 293 cent. Peugot 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 in the market yield very different proportions of soluble matter. Teas prepared from young leaves furnish more soluble matter than the older leaves ; whUo 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 boiling 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 nutritious. 558. Adulterations of Tea. — Teas of all 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, tiwmeric, gypsum, and China-clay. With these ingredients they glaze or face the surface of the leaves, to such an ex- tent, that it is affirmed we never 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 caU 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, (fee, 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 Peepaeation 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, 294 COMMON BEVERAGSS. varies from 10 to 30 feet; but it is iisuall}' pruned down to 5 or 6 feet, to increase the crop of fruit. All are familiar with 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 Java and BaU Indian coffees are larger and of a paler yellow, while Ceylon, West Indian, and Srasnlian coffees are of a bluish or greenish gray tint. 661. 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 Payen, is as follows ; "Water 13 Gum and Sugar 15*50 Gluten 18 Cafein 00-75 Fat and Volatile Oil 13 Tannic Acid 6 Woody Fibre 84 Ash 6-75 Dr. Stbnhoxtse states that it contains 8 per cent, of cane sugar. Cof- fee, it will be seen, contains tannin, the same astringent principle as 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 tcgetalle alkali, with the same composition and properties as thein of tea. A direct analysis of the two substances gave the following result : Corbon. Nllrogm. Hjrdroffen. Oijrgon. Thein 501 290 52 15-7 Cafein 49-8 28-8 51 IC'S 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 PBOPKBTIES AND PEEPAEATION OF COFFEE. 295 in the raw or natural state ; like tea, it is first altered by heat or roasted. Fio, 104, 562. Effects of roasting Coffee. — ^ ' -, The operation of roasting, j^roduces 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 full solvent effect upon them. Roasting 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). If now we place a fragment or section of roasted cof- fee under a magnifier, it will be observed that these drops of oil 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 and highly esteemed aroma for 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 unroasted coffee-berries magnified, showin? tlie size and form of tlie cells, and the drops of oil contained in their cavities. Fi&. 105. Appearance of roasted coffee berries. 206 COMMON B£VJ£IiAG£S. sets a portion of tbe cafein free from its combination with tannic acid, and ovapoi-ates it. The temperature is sufficiently 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 brown, loses in weight, 16 per cent., and gains in bulk, 30 per cent. To a chestnut hrown, it loses 20 per cent, in weight, and gains 50 in bulk. To a dark Irotcn, it loses 25 per cent, of weight, and gains 50 in bulk. 563. nints concerning the Boasting Processi — The roasting of coffee is an operation of considerable nicety ; more, perhaps, depending upon it than upon tlie 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 tecommended that the coffee be first dried in an open pan over a gentle fire, until it becomes yellow. It should then be scorched iu 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 ia 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 astring^acy 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 npoa 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.— (Ei.lis.) liut it is differ- ent after tlio coffee is roasted and ground. Its flavoring ingredients have a tendency to escape, and il should therefore bo confined in ves- PBOPERTIKS AND PREPARATION OF COFFEE. 297 eels 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 Avhole ship-load of coffee. — (Noesianbt.) 665. Mode of Preparing the Beverage. — 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 fiour 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 ; boiling ^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 Avhole of the water to be used be diAdded 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 will 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. Adalterations of Coflfec. — Groimd coffee is very extensively adulterated. Various substances are employed for this purpose, as 13* 298 COMMON BEVEBAGES. roasted peas, beans, and corn, and dried and roasted roots, such as tar- nips, carrots, potatoes, &c. But the most common adulterant is cJiiccory, 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, anjl 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 as much, the temptation is strong to crowd it into ground coliee. So common has the use of chiccory with cofiee, 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 bow one fraud opens the door to another, it is found that pure chiccory is almost as difficult 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 boiling 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 oillne:tural or uncooked state ; being in a kind of pulpy, half-dissolved condition, they are ready to take prompt effect upon the pappilfe of the mouth. But the same property of fi-uits 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 cellars where the necessary warmth for inducing decay is not attained. Sometimes fruit, as many varieties of apple;;, 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 whea perfectly dry, at a time when the stalk separates easily from the spur. Apples and pears should have their stalks or " stems " separated from BY DRYING. 309 the tree, and not from themselves. The utmost care should be 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 pi-eventing the evaporation of the juices. Apples have been preserved 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 album^. The preservation is here due to the joint in- fluence of exclusion of air, and a low and uniform temperature. A presertatory for fruit, or kind of refrigerator on a large scale, has been devised by Mr. Paekee. The fruit, picked carefully 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. 4. Preseetation by DRYiNa. 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. TJnripe potatoes and unripe apples removed from the parent stock shrivel, shrink, and perish. These effects 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 810 PRESERVATION OF ALIMENTARY SUBSTANCES. kind of disorganization of the alimentary body, its largest constitnenl 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 insoluble. 589. Preserving Saccnlent Vegetables. — These, if exposed to the air,_ evaporate their moisture, wilt, 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. Habsall 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 difiBcult 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." BY ANTISEPTIC AGENTS. 311 5. Pke8eevation by Antiseptics. 590. fiemarkable properties of common Salt. — Antiseptics are op- pcsers 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, cJdorine, and the other a bright silvery-looking metal, sodium (Tience 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 with more than five hundred times its bulk of the heavy gas, yet the compound formed occupies less space fis. los. than the solid sodium alojie did before the union. No known mechanical force 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 rock 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- ^^,>-„ ;.. +!,„ ^i:;i /•„ « j. iv How crystals of common salt are pears in the sohd form, 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. Eesulting from evapoi-ation, 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 812 PRESERVATION OF ALIMENTARY SUBSTANCES. poon form, which are joined to tlio first at its four upper edges, con- stituting a frame above the first Httle 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 tlie same way gives the appearance shown in Fig 111. The consequence of this arrangement is that the crystjils 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 Jioppcr-shaped (Fig. 112). 591. Sources and Pnriflcation of Salt. — Salt is obtained from three sources ; first, it is dug from the earth in mines, in large masses, like transparent stones {rock salt) ; second, it is procured by evaporating eea-water {bay salt) ; and, thh'd, by boiling down the liquid of brine springs. It differs very much, in purity, from dilTerent 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 bo 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, rccrystallized and ground. 592. Uow 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 BY ANTISEPTIC AGEKTS. 313 meat. The salt robs the meat of one-third or one-half the water of ita 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 different 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 flbre 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. Pekeira thinks that the separation of water is not sufiicient alone to account for its preservative action, but that it umst produce some further unexplained eflect 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, really abstracts the juice offlesli 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 from its impurities, lime and magnesia. These are decomposed by the phos- pliorio 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 13 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 purpose. 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 sauerkraut from cabbages, and in salting cu- cumbers. The brine with which both vegetables are sm-rounded is found strongly impregnated with both lactic and butyric acids. 595. Preservation by Sagar. — This is chiefly employed to preserve 14 814 PKJESKBVATION OF ALIMENTABY SUBSTANCES. fruits. Many employ both engar and molasses for the preservation of meat; sometimes alone, but more commonly united with salt. Tha 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, however, very prone to change ; they require to be of a thick or sirupy consist- ence. EInapp 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 suflBcient to induce incipient decomposition, by diluting the upper layers of sugar. The eflfect of the acids of fruits is gradually to convert the cane sugar into uncrystallizable and more fer- mentable grape sugar. 596. Preserving 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 obstructs 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 will not putrefy, even in the heat of summer. Or if exposed in a close box to the vapor of creosote, the eifect is the same, though in both cases the amount producing the result is extremely small. The preservative effect of smoke-drying is partly duo 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. Preservation of Milk, Butter, axd Cheese. 597. Modes of preserving Milk. — 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, the milk be tightly bottled, and MILK, BUTTER, AND CHEESE. 315 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 curd 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 mUk 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 again dissolved in water. Aldeii's concentrated milk 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. Unpnrilied Butter quickly spoils. — Butter when taken from the chum 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. Cheveetjl 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. Butter Purified by Mechanical Working. — It is obvious, therefore, 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 soap), 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 Butter by Washing. — Some join washing with 810 PRESKBVATION OF ALIMENTAEY SUBSTANCES. mechanical working, to separate the buttermilk. It is objected to this, first, that water removes or impairs the fine aroma of tiie butter, and. tecond, that it exposes the particles of butter to the injurious action of air much more than mechanical working. On the other hand, it ia 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. If 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. Speengkl states that the butter absorbs the lime, and is unpleasantly affected by it. A. B. Dickinson 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. Tliat it does alter and spoil 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 oily substance itself, develops a series of acids, the hutyric, 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. Aetion of Air npon Bntter. — 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 margaric acid. This is, however, a first step of decomposition, which, when once begun, may rapidly extend to the production of variona offensive substances. "When, therefore, butter is much exposed to the MILK, BUTTER, AlH) CHEESE. 817 air it is certain to acquire a surface rancidity, which, without pene- trating into the interior, is yet snfficient to injure its flavor. It is in- dispensable to its effectual 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 ofiice 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 j)ound 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 will 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 plate. The influence of temperature is shown by the fact that in certain locali- ties of France, especially at Koquefort, there are subterranean caverns which rent and are sold at enormous sums for the purpose of keeping 318 MATERIALS OP CULINAEY AND TABLE UTENSIIfi. and maturing checso. These natural rock-cellars are maintained, bj 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 EggSt — When i ewly laid, eggs are almost per- fectly fuU. 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 Avater 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 bo done by dipping them in melted suet, olive oil, milk of lime, solution of gum arable, or cover- ing them with any air-proof varnish. They are then packed in bran, meal, salt, ashes, or charcoal powder. REArrMUE is said to have coated eggs with spirit varnish, and produced chickens from them after two years, when the varnish was carefully removed. VI.— MATERIALS OF CULINARY AND TABLE UTENSILS. 606. It seems important in this place to offer 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. Itcnslls 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 will even VESSELS Oi-' IKON XHD TIN. 319 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 simjAj oxid& 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 styptic taste. Fortunately, however, most of these compounds, although ob- jectionable, are 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. Thei'e 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 metallic surface, but become evenly coated with a hard, thin trust of a dark brown color, forming a soi*t 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 nncertain and unsatisfactory, and besides it is inapplicable 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 hloch 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 food. 610. Adaptation of Tin to Cnlinary Purposes. — Tin, in its metallic Btate, 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- 320 MATERIALS OF CULINABY AND TABLE UTENSILS. 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. Peoust showed that a tin platter, Avhich had been in use two years, lost only four grains of its original weiglit, 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 y^y 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. Pereiba 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 it domes- tic economy. 611. Zinc Vessels ObjectionaWc. — 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 in contact with Food. — This metal suflfers 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. All kinds of fatty and oily matter have the property of acting upon copper and generatfhg poisonous combinations. Sugar also forms a compound with oxide of copper, — the sacharate of copper. 618. 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, Ac., and cooks often throw a penny-piece into a pot of boiling greens to . COPPER AND ENAMELLED VESSELS. 321 intensify tbeir 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, oil, 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. Protection 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. Mitohel 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 iron 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. Uee 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. 14* 322 MATERIALS OF CTJLINAET AND TABLE UTENSILS. 616. Earthenwnr* 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 sufficiently firm and stifi', 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 eontalning 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 witli 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 difficult, and hence the ware more expensive. Lead glazing can be d(^ tected by its remarkably smooth, lustrous surface, resembling varnish ; while the salt glaze, on the contrary, has less lustre, anci 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, avo 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 bo touched to the broken surface, it will adhere, showing the porous and absorbent n;iture of the material. Is'ow it often hap- EABTHEN AND POECELAIN WAKE. 32S pens that the shell of glaze and the body which it encloses, are not affected 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 crated. 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 afforded them a large experience in the porcelain manufacture. This ware was first made in China, and is still known as China-ware. But, after long and diflScult 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 Jaaolin, 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 afford 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 all 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 oil. 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 824 PHYSIOLOGICAL EFFECTS OP FOOD. adopted, the heat is estimated to run up to 21,000 degrees of the Fahrenlieit scale. The color of porcelain is milk-white, without any tinge of blue. The qualities which give it pre-eminence among tha 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 Avhen 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 materiaU 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 broken Porcelain. — Various cements are in use for producing adhesion between fragments of broken porcelain and glass. A very strong cement for common earthenware is made by boiling slices of skim-uiilk 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. Shtllac dis- solved in 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 bo aided by heating the fragments to be joined. VII.— PHYSIOLOGICAL EFFECTS OF FOOD, 1. Basis of the Demand fob Aliment. 621. Creation a Continuous Work^ — TVe 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 perxietual creation. Ilad our earth been formed of an eternal adamant, subject to no vicissitudes of change through all the cycles of duration, wo might perhaps well refer to the act of bringuig it into existence, as especially illustrative of creative power. But where all BASIS OP THE DEMAND FOB ALIMENT. 325 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 phenomena 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 bread." 622. Onr Systems capable of being 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 discovex*ed; 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 vses of its parts were at once understood. The whole scope and drift of past inquiry, and all the considerations which cluster around the sxibject, 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 326 PHYSIOLOGICAL EFFECTS OF FOOD. 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 have 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 grovm 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 tlie 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, susceptibility, and force, originate in atomic transformations taking place in his BASIS OP THE DEMAND FOR ALIMEliT. 327 system. As each part is brought into action, its particles perish and are replaced by others ; and thus 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 which the vital changes proeeed*. — But very few persons liave any correct conception of the rate at which change goes on in their bodies. The average amount "f 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 standai-d of 140 lbs, as the weight of the body, the amount of oxygen consumed daily is nearly 2]- lbs., which results from breathing about 25 or 80 hogsheads of air ; the quantity of water is nearly 4yV 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 longs, 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. — (Johnston.) 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. Chambees.) At the same time there escapes from the lungs nearly 2 lbs. of carbonic acid and li of watery vapor. The sHn 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 ^8 PHTSIOLOGICAL EPPECTS OP POOD. 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 illnstration of these cbaoges. — 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 Parr, of England, lived to the ago of 152 years. If wc take the twelve years of his childhood, and double them over upon the succeeding twelve years of his youth, we shall 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. Pare, 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 Avas 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 miles. 626. Bclation between Waste and Snpply. — 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 unifi)rm 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 ivfanaj, childhood and youth, the reception BASIS OF THE DEMAND FOR ALIMENT. 329 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 lil'o 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- phosis) that it has undergone is oxidation, or a true 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 iu 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 fullest 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 bo arrested but for a few moments, suffocation and death follow. 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 iu the plan of our being the bodily requirement for food were left to the determination of reason, the purposes of nature would S30 PHYBIOLOGICAL EFFECTS OF FOOD. 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 thirst, which are independent of reason or wiU, cannot be dislodged while life lasts, and whose duty it is to proclaim that further nourishment is required for bodily 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- satisfactory. 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 in a cer- tain natural and successive order, which will next be noticed. 2. FiEST Stage of Digestion — CnAXGES of Food in the Mouth. G29. The great oluect of Digestion. — The prepared food upon our tables is in the form of crude, unmixed, and chiefly solid masses. Various vegetables, bi'eads, 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 all the parts, and produce all the peculiar liquids or secretions of the body. It circulates rapidly through every portion of the system, bearing all the constituents that can be required, whUe 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, while 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 witli facility through the minutest vessels. Now, it is obvious that the food before us must be profoundly cliangod before it can be- come blood. No one element of diet contains all the necessary ma- DiaESTION — CHANGES IN THE MOUTH. 331 terials for this purpose ; the various articles must, therefore, be mixed. Some of the elements of food are incapable 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. 630, BedaciBg Mechanism of the Montht — The food, liquefied or soft- ened, or Tvith 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 difierences are illustrated by Fig. 113, which represents half the lower jaw. A shows two of the front or ... i .-I 111-. Illustration of the diflferent kinds of Teeth. cuttmg teeth, called tncisors ; . 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 hicuspids 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 will 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, cw«pi« signifies the point of a spear; oanie, dog; mo2a,amill; incisor anything which cuts." 882 PHYSIOLOGICAL EFFECTS OF FOOD Fio. 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 ^gmsmsgL ^y^mri'mm ^°^ ^'^^^' ^^ streams out abundantly X^ mMS3SSt—^Kmlfl^B~a under the stimulation of spices, and continues to flow after the meal is concluded ; the secretion also goes on during sleep. 632. Properties. — The saliva is a clear, slightly bluish, glairy juice, readily frothing. It contains less than one per cent, of saline matter, and in health is always alkaline. It Salivary glands; a nnrotid, isubmaxil- contains also an organic principle larj-, c sublingual. named pti/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 differ- ent salivas poured out by three pairs of glands. Parotid saliva is thin and watery, so as to bo readily incorporated with tlie food by the teeth ; it also contains much lime. Submaxillary saliva is so thick and glutinous that it may be readily drawn out into tlireads. 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 iiiediuin 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 DIGESTION CHANGES IN THE MOUTH. 333 pure starch be chewed for a short time, it will become sweet ; a por- tioij of it has undergone a chemical trant-formation, 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, fibrous nature, needs more mastication than vegetable. Meat and albuminous substances require to l,e 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). 634. Importance of thorongh 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 ill-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 falee relation to nature, as 834 PHYSIOLOGICAL EFFECTS OF FOOD. to imagine that they exalt the spiritual attributes of their being by casting contempt upon the physical. Such are inclined to regar4 the act of eating as a very animal and materializing operation, and any considerations of the Awoy 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 "his 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 suflBcient 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." 035. Effect of profase 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 office 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 eflect 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 ealine substances in the saliva is increased, and that, so far as that DIGESTION — CHANGES IN THE STOMACH. 335 Section of the human stomach : a esophagus ; 5 c cardiac orifice ; d e greater curvature ; / g lesser curvature ; h class of bodies is concerned, the salivary glands act vicariouslj lor the kidneys, and the mouth is thus partially converted into t, urinary aqueduct." — (Dr. Dkapee.) 3, Second Stage of Digestion — Change of Food in the {>jcmaoh. 636. Figure and Dimensions of the Organ. — Having underg me more or less perfectly the changes which appertain to the mouth, the food Lsswallovred, 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 /,iU the right side of the body, and its lesser end at the left. That por- tion where the esoph- Py^"^"" '"^'^°^<' ' ^^ duodenum ; k bile duct, agus enters it, is termed the cardiac region (because it is in the vicin- ity of the Tcear 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. Aa 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. Layers of 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 rims lengthways, and the other crossways, 336 PHT8I0L0GICAL EFFECTS OF FOOD. or around the orj^an. By moans of tliese 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 {mucons mem- hrane) lines its internal surface. It is a soft, velvet-like membrane, 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. Motions 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. Maktin, a Canadian soldier, whose stomach was opened by a gunshot wound in the side, and healed up leaving a permanent orifice {gastric 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 mouthful), 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 ? C39. Miaate arrangements for Stomach Digestion. — Before considering what takes place in the 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 vSSinB^^ the microscope to see it. Magnified about 70 ^^Sj^Mj^j^ diameters the mucous membrane exhibits the honey- ^^SStSn/^/ combed appearance seen in Fig. 116. Into these "•^^^^^IR* reticulated spaces, there open little cup-shaped J^SS^ cavities called stomach follicles, which are about It^^ 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 DIGESTION — CHANGES IN THE STOMACH. 337 Fia. lir. like pallsadiiig, 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. 117, represents the se- creting follicles in the stomach of a dog after twelve hours' abstinence ; «, from the middle re- gion of the stomach ; 5, 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 effect this directly ; another agency, — that of cells (496) , — 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. Recurring 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 swell nntil they are driven up in crowds into the hand or larger cavity, and hav- ing reached their full maturity, are pushed out at the surface, burst, and deliver their contents into the stomach. 641. The periodic snpply 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 numbers, and yield large amounts of fluid. During fasting, no full-grown cells escape ; the tubes collapse, and an opportunity is allowed for the production of a new stock of germs or cell-grains. If this be so, it must follow that we cannot with impunity interfere with 15 338 PHYSIOLOGICAL EFFECTS OP FOOD. tliat which 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 quickly 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 as certainly, that continual or irregular eating is wholly contrary to the economy of the human stomach. — (Paget.) 648. Properties of Gastric 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 rolled 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 Stomach 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 diflerences 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 diflfcrent 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 effect only upon the non-nitrogenoua principles. Upon proceeding to the stomach we find new conditions — an acid liiniicl replaces the alkaline — the changes that commenced in the mouth are partially or totally suspended, the non-nitrogenous com- DIGESTION — CHANGES IN THE STOMACH. 339 pounds remain unaltered, the gastric fluid taking effect only upon nitrogenous substances. 645. Actioa 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 little ' 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 liquid form. These are the results of an arti- Jicial gastric juice, but they are exactly the same in hind 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- tical. 646. What is the Digestive Ferment Sabstance 1 — There has been much controversy about pepsin ; what is it ? A substance in the gastric fluid discovered by ScnwAH 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 calfs stomach (rennet). When proper means are taken to separate and dry it, it appears as a y6llow gummy mass. Its potency for digestive pur- poses was proved by Wasmann, who showed that a solution containing only l-60,000th part, if slightly acidulated, dissolves coagulated albumen in six or eight hours. Liebig is, however, disinclined to regard pepsin as a peculiar digestive agent. He maintains that the fermentative change of digestion is duo to minute parts of the mucous membrane of the stomach, separated and in a state of decomposition. The surface of that membrane is lined 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 tiO PHYSIOLOGICAL EFFECTS OF F001>» membraue. This epitbelium, acted on by the oxygen swallowed in the frothy saliva, excites tlie 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 thaa Solatiou. — It was formerly thought that digestion was simply solution, or change of alimeutary matter to the liquid state ; but late investigations iufoi'm us that nu- tritive substances are more than dissolved, they are really altered in properties. The nitrogenous matters are not only dissolved, but are 60 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 solid 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 still further change, by Avhich they continue soluble. Casein in milk, and liquid albumen are already dissolved Avhen 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 capability 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 pxirpose in passing through it. The nitrogenous matters are not chemically altered, except perhaps by combining with water. 648. Action of SallTa in tlie 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. Uut acids and alkalies cannot get on together. They either kill each other, or if one is the strongest or most abundant, it destroys the other, though not without injury to itself. Ilence, whenever the saliva DIGESTION — CHANGES IN THE STOMACH. 341 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 iirst upon the food where it comes in contact with the bedewed coats of the stomach, while the saliva, in- corporated within, is allowed a little time for- 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 supplied in due quantity, the saliva, acting upon the contents of the stomach, will generate the required substitute. 649. Quantity of Gastrie Juice secreted. — There has been, and indeed there still 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 will 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, Bidder and Schmidt 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. Gexhste- 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 342 PHYSIOLOGICAL EFFECTS OF FOOD. formerly believed. What goes forward in the stomachy although of great importance, afibrds but a partial view of the "whole operation. Dr. BEATJiiONT made an admirable series of observations upon this oi'gan, and did much to advance the inquiry. Yet the value of hia 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 ia 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. Dufat, announcing the first laws of electricity, in 1737, stood much nearer Thales, of ancient Greece, rubbing his piece of amber, than to Prof. Morse, 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 80 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. Regarding 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 will be the more digestible which has 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 ti7n€ 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. W© subjoin an abstract. DIGESTION CHANGES IN THE STOMACH. 343 MEAN TIMES OF CHTMIFICATION OF FOOD. Rice Pig's feet, Bonsed. . . Tripe, soused Trout, salmon, fresh, Apples, sweet, mellow Venison, steak Sago Apples, sour, mellow Cabbage with vinegar Codfish, cured, dry . . . Eggs, fresh Liver, beefs, fresh Milk Tapioca Milk Turkey, wild " domesticated Potatoes, Irish Parsnips Pig, sucking Meat hashed with j vegetables ) Lamb, fresh Goose Cake, sponge Cabbage-head Beans, pod Custard Chicken, full-grown . . Apples, sour, hard. . . . Oysters, fresh Bass, striped, fresh . . . Beef, fresh, lean, rare " steak Corn cake Dumpling, apple Eggs, fresh Mutton, fresh Preparation. Time. h.m. Boiled 1 — Boiled 1 — Boiled 1 — Boiled 1 80 Fried 1 30 Pvaw 1 30 Broiled . . . 1 85 Boiled 1 45 Eaw 2- Kaw 2 — Boiled..... 2 — Kaw 2 — Broiled. . . . 2 — Boiled 2 — Boiled.... 2 — Eaw 2 15 Boasted... 2 18 Boiled 2 25 Boasted . . . 2 30 Baked 2 30 Boiled .... 2 80 Boasted . . . 2 SO "Warmed. . . 2 30 Broiled. . . . 2 30 Boasted . . . 2 30 Baked 2 30 Kaw 2 30 Boiled .... 2 30 Baked 2 45 Fricasseed. 2 45 Kaw ■' 2 50 Eaw 2 55 Broiled 3 — Koasted. .. 8 — Broiled.... 3 — Baked 3 — Boiled 3 — Coiled soft. 3 — Broiled 3 — Boiled.... 3 — Pork, recently salted. . Soup, chicken Oysters, fresh Pork, recently salted . Pork steak Corn bread Mutton, fresh Carrot, oransre Sausage, fresli Beef, fresh, lean, dry.. Bread, wheat, fresh. . . Butter Cheese, old, strong Eggs, fresh Flounder, fresh Oysters, fresh Potatoes, Irish Soup, mutton " oyster Turnip, flat Beets 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 Tendon Preparation. Time. h. m. Eaw 8 — Boiled.... 8 — Eoasted.. . 3 15 Broiled.... 8 15 Broiled 8 15 Baked 3 15 Eoasted... 8 15 Boiled .... 3 15 Broiled 3 20 Eoasted . . . 3 M Baked 8 80 Melted 3 30 Eaw 3 30 Hard boil'd 3 30 Fried 3 30 Fried 3 30 Stewed . . . 3 30 Boiled 3 SO Boiled .... 3 30 Boiled .... 3 30 Boiled.... 3 30 Boiled 3 45 Boiled.... 3 45 Fried 4 — Boiled .... 4 — Eoasted.. . 4 — Broiled . . . 4 — Boiled .... 4 — Boiled.... 4 — Fried 4 — Boiled.... 4 15 Fried 4 15 Boiled .... 4 80 Eoasted.. . 4 30 Boiled....' 4 80 Boiled .... 4 30 Fried 4 30 Eoasted . . . 5 15 Boiled .... 5 30 Boiled .... 5 30 651. Absorption from the Stomach. — The power possessed by liquids and gases of penetrating and passing through 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 344 PHYSIOLOGICAL EFFECTS OF FOOD. is proved by tho fact that wlien the outlet to the stomach is closed bj 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 tho 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, whUe the unabsorbed matters gradually ooze through the valvular opening that leads into the intestine. 4. TniED STAGE OF DIGESTION — ChANOES OF FoOD IN TUB INTESTINES. G52, Digestive Juices of the Intestinal Tube. — The partially digested food dismissed from the stomach enters the duodenum, the first por- Fia. 118. i B- Lnrge intotinea Append » of _,- COCIUB Spleen SmaU ioteatbiM Small iiitesUnra Digestive tnict in man. DIGESTION CHANQKS IN THE INTESTINES. 345 tion of the intestinal tract {small intestine). This is a tube about 20 feet in lengtli, 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 bile, and the other from the pancreas, yielding 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. C53. Cbanges 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 all 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 all 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 15* 346 PUTSIOLOGICAL EFFECTS OF FOOD. intestinal coats. They were formerly supposed to be open at their ex- tremities, hut they are now seen to present fine, blunt ends to tlie in- testinal cavity, llow 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 oU. These veseels are gathered into knots (glmuls), 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 tlie bloodvessels into the lacteals, is gradually olianged to fibrin, the liquid acquiring the power of clotting or coag- ulating. 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 tho food itself is influential. Some aliments have a relaxing effect, and others are of a binding nature, or tend to constipation, and they difi'er 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, milk, 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 : THOSE OF A CONSTIPATING TENDENCY. THOSE OF A LAXATIVE TENDENCY. Bread and cakes, from fine whcaten 'Wheaten bread and cakes from nn- flour; rice, beans, peas, meats, eggs, tea, bolted flour, ryo bread, corn bread, raw •IcohoUc drinks. sugar, (from the molas4«?s it contains,) fruits, raw and cooked, and generally substances abounding In ligneous matter.as skins, cores, hasks, bran, Ac its final destination. 347 5. Final Destination of Foods. 656. Digested alimentary matter enters the circulation and becomes BLOOD. This fluid is contained in a system of vessels, whicli 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 in 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 ago, 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 ovai)orated 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, orasli 57 " Blood 100 " 658. Blood Discs, Globules, or Cells. — To the naked eye blood appears of a red color, but under the microscope it is seen as a transparent, watei-y 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 bo 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 independent individual, which runs a definite career, is born, grows, performs its oflfices, and ,,^;«sfc ^ dies like the most perfect being, though the phy- *^ ^^ © /!^ A Biologist tells us that twenty miUions of them ._ perish at every beat of the pulse. Figs. 119 and 120, from a work of Dr. Hassall, represent different aspects of the blood discs, as seen under CJL^-^ the microscope. The physiology of the blood \J in its details is curious and most interesting, but /p\ we have no space to consider it here, and it is „ , v, . , , , ' Human red blood globules, not necessary to the general view we propose sho-wing their natural form to give of the final influence of food upon the brought^foily'^Stofocul. *° system. 348 PHYSIOLOGICAL EFFECTS OF FOOD. G59. Graud purpose of the Ilaman Body. — The living man is yre- Bcutcd to our consideration as an engine of power — a being capable of producing etTocts. 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 supremo 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 jg no evidence that in the course of events upon into rolls, like adherent ■,••■, ^ • i pieces of money. the eai'th, there IS either the creation or destruc- tion of a single atom of matter, so it is believed that in no absolute sense is force either created or destroyed. It changes states, disappears, and remains latent or reappears in ditTerent 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- tain definite causes. It is desirable to understand, as far as wo may bo able, the conditions of its production. 660. Food prodaced by the aetion of Forces. — The stream of aliment which flows 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 incUned to depart. These three substances constitute the chief nourishment of the vegetahle 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 thcimeltes, nor can they bo separated and re-arranged without an enormous expenditure of ITS FINAL DESTINATION. 849 power. Man Avith 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. Nor 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 npon. Carbonic acid is only decomposed in the leaf during the daytime by the power of light ; the efifect 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 liave been forced from a lower into a higher combination in plants, and in their new state they represent the amount 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 living 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 establish the possible conditions of terrestrial life (3^ 661. How Food produces Animal Force, — ^Food represents force, but it is force in a state of .equilibrium 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 350 PHYSIOLOGICAL EFFKCrS OF FOOD. sisted ia forcing carbon and hydrogoa 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 scries of decompo- 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 deocmposition of ali- ment, under the iniluence of inspired oxygen, bodily force originates. "\Vo sec every day that steam power results from the destruction of fuel 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 l)Ower 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 build up the bodily fabric, but it only continues in that state transiently; it is all finally decomposed and dissevered into the simplest inorganic forms. 662. Dcstrnctlve 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 limb, a muscle, or the brain, bo 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, wo quickly discover the peculiar agency of oxygen. He loses weight at every breath. Inspired oxygen, borne by the arterial 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, dehrium supervenes, and there is an end of life. AVe call this starvation ; it is a conditim in which "atmos- pheric oxygen acts like a sword, which gradually but irresistibly pen- ITS FINAL DESTINATION. 351 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 fotal inroading effects of oxygen. 66S. Combnstiou within the Body. — The term combtcstion 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 forwart at all degrees of speed, the effects being less intense the slower it proceeds. The changes that go on in the body are the same as those 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 in the body is, there- fore, a real burning ; a slow, silent, regulated combustion. 664. All Foods not equally Combnstible. — 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 — those 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 all be consumed together. Accordingly the non-nitrogenous bodies, sugar, starch, oil, are easy of combustion ; while the albuminous compounds are burned with much greater difficulty ; 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 352 PHYSIOLOGICAL EFFECTS OP FOOD. 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 economy. C65. NitrogCE Lowers the Combnstibllity 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 lefea 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 jjliosphuret of nitrogen only ignites at a red heat, and in oxygen gas, but docs 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.) 66G. Ileat-prodnclng and Tlssnc-maklng Foods. — In considering the final uses of foods, we are to ])rescrve the distinction with which w© began. The non-nitrogenous aliments, by their ready attraction for oxygen, seem devoted to simple combustion in the system, with only Jio evolution of heat ; while the albuminous compounds are devoted PBODUCmON OP BODILY AVAEilTH. 353 to the production of tissue. The first class is hence called the heat- producing, calorijient, 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 ceUs 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 LiEBia. 6. PBODtrOTION OF BODILY "WaeMTH. 667, Constant Temperature 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 all 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- 354 PHYSIOLOGICAL EFFECTS OF FOOD. 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 hut 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 outward 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 cooling 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 Avhich 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 produces Heat. — To keep the system up to the standard point, notwithstanding this rapid and constant loss, there must be an active and unremitting source withui. Heat-force cannot bo created out of nothing ; it must have a definite and adequate cause. PRODUCTION OF BODILY WARMTH. 855 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 oxygen 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. — (Johnston.) 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 is due to oxidation in the system, isstrikingly 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 all 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 burn on such mountain tops ; the air is 356 PHYSIOLOGICAL EFFECTS OF FOOD. too thin and rare to support tlicra ; and so these conihnstions which go on at a measured rate in the interior of tlie 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 arc breathing a compressed and condensed atmosphere. — (Dr. Draper.) 671. How the unequal demands for neat «re met. — The steady main- tenance of bodily 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 occupies 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 oils head the list ; they consist almost entirely of the two highly combustible elements, carbon and hydrogen, containing from 77 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 fot, 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 23 lbs. of starch, or 7-ys 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 stai)lcs 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 calorifyiug power, is found to be very insuflB- «ient in the arctic regions for the maintenance of animal heat •f PRODUCTION OP BODILY WAEMTH. 357 All breads are, however, not alike in this respect, for the Hudson's Bay Traders have found, according to Sir John •Richaedson, that Indian corn bread, which contains about nine per cent, of oil, 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 frozen 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 I call 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. Regulation 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 effected 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. Duriug the heat of 358 PHYSIOLOGICAL ErFECrS OF FOOD. Bummer, much water evaporates from tlio skin, and a correspondinglj 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 stovos have been devised which adjust their own 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. C73. Douses 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 and 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 imited very soon produce exhaustion. A starving man is soon frozen to death." 674. Times of Life wlicn 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 mortality becomes less apparent, so that at the age of from 25 to 30 years, the diftorence between the summer and winter mortality is very slight. Yet this difterence reappears 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 PEODTJCnON OP BODILY WARMTH. 359 chill.' Tho Brussels statistics show that the mortality between 60 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- uary 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 dally changes of Temperature. — The heat of inani- mate objects, as stones, trees, &c., rises and falls with the daily varia- tions of temperature. The living body would do the same thing if it did not produce its own heat independently. If we disturb the calo- 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 moi*e 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 daily 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 treaTc fast, as it is significantly termed, but we do no more ; postponing the taking of the chief supply until 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 the systematic rise and fixl? 860 PHYSIOLOGICAL EFFECTS OF FOOD. of temperature atteudlug on the maxima and minima of daily heat. The light breakfast has a preparatory reference to noonday, the solid dinner to midnight." 7. Peoduction op Bodily Strength. 676. Amoant of mechanieal 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 boiler, 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 elfects 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 jjurposes 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 hundred 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 esthnated force of 13 lbs., while 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 forma of voluntary physical exercise, labor, amusement, «&c. 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. Smeatox states, that working with his arms he can produce an effect equal to PEODUCnON OP BODILY STRENGTH. 361 raising 370 lbs. ten feet high, or 3,700 lbs. one foot high in a minute for eight hours in the da^' . 677. Tissues destroyed in 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 M ater 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 ai'e 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 incessant 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. Chossat 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 Johnstox says : " An animal when fasting will 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. Destination 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 {clot) is removed from blood, the watery serum or plasma remains, containing albumen, which coagulates like white of egg by heat. Albnmen is the universal starting point of animal nutri- tion i it is the hquid basis of tissue and bodily development through- out the entire animal kingdom. We see this strikingly 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 16 362 PHYSIOLOGICAL EFFECTS OF FOOD. the porous shell, uuder the influence therefore of the same conditions which accompany respiration, all the tissues, membranes 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 bodily parts in strength and integrity, and to be finally destroyed for the development of power. 679. Action of Oxygen upon the Tlssnes. — 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, moreover, 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 efiect. 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 ali- ments become heat-producers. It is not to bo 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. Rel&tlod between Waste and Supply. — If an organ or part be the PEODUCnON OF BODILY STRENGTH. 363 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 precisely 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 nuti'ition. That portion of the mechanism which is independent of voluntary control, is thus self-sustaining. Still, 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 effort 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 effort 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 tissnc ehanges. — 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 cTiech it. Common salt, for example, and an excess of water, act as hasteners 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- 364 PHYSIOLOGICAL EFFECTS OP FOOD. clines in weight with more rapidity tlian 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 effects, may be 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. Chambers 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 retardec^ 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, Avhich 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. Still, we are to be cautious about theoretically prejudging any substance ; whether it be beneficial or injurious is as- certainable only by careful observation and experience of its effects. 8. Mind, Body, and Aliment. 682. Mind bronght 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 corresponds 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 will-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 Will 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 effected, 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 nature of this MIKD, BODY, AND ALIMENT. 365 union, Juno it is accomplished, we know nothing, but 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 all the avenues of sense, along the nerve routes to the cen- tral seat of consciousness, the brain ; while 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 arrested, 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, 70 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 arrangementj but we cannot explain it. 684. Caa we measure Brain and Bfcrre waste ? — The appropriation of certain specific parts to certain purposes, is the basal fact of physiolo- gy. A part may indeed perform several ofl5ces, 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 par^ therefore, does its appropriate work ; and as it has a special composi- tion, its metamorphosis gives rise to peculiar products. Muscular de- 866 PHYSIOLOGICAL EFFECTS OF FOOD. composition must hence yield one set of substances, and nerve-waste another. It has been attempted to identify tliese 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 affirm that it may also come from unassimilated 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 tlio 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 sind extiansts tlie Body. — That all forms of mental exertion have a wearing, exhausting effect 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 tthe 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 BO imperfectly as to produce morbid and unsound tissue, which can only bo restored to the healthy state by long mental tranquillity and cessation of effort. 686. The Phosphatie constltnents of Brain. — "We have spoken of the phosphates as special products of brain and nerve waste. That phos- MIND, BODY, AND ALIMENT. 367 phorns, 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 the 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 smd light. It is also capable of existing in two states ; its ordinary active condition and a passive or inert state, in which it seems paralyzed or asleep, and exhibits no affinity for oxygen. The solar rays have the power of throwing it from tlie 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 compounds, 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'Heeitier'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 peint of view Dr. Moleshott leaps at once to the conclusion, 'no phosphorus, no thought;' LrEBio, however, denies point-blauc that elementary phosphorus has ever been found in nervous matter. He gays, " 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 oUy matters of nerve tissue, which are hence called ' phosphorized fats.' 687. Arc there special Brain Natriments. — 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, milk, oysters, &c. Such advice has no justification in well de- termined facts. "We are not authorized by science to prescribe a diet 368 PUYSIOLOGICAL EFFJECTS OF FOOD. specially or peculiarly constructed to promote brain nutrition and pro tract mental exercise. But whilo it would seem as if care had been taken to secure these high results in the universal constitution of food, still it is certainly in accordance with analogy, that s|>ecific aliments should be adapted, or at all events lest adapted, to produce certain kinds of eflfect 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 Brain-workers.— Yet the diet of the literary, of artists, and those who devote themselves to intellectual labor, is by no means imimportant, 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 still 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. INFLUENCE OP SPECIAL SUBSTANCES. 369 689. Mea seek for Brain Excitants. — Althougli specific brain nutri- ents and thought-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 powerfully, although somewhat differently, upon the nervous system, and thus directly afiect the state of the mind and feelings. "We here touch upon the myste- rious world problem of narcotism; but its discussion, though of absoib- 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). 9. Infltjenoe of Special Substances. A.— Saline Matters. 690. The Ash 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, m 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 alTcalies 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 16* 370 PHTSIOLOGICAi EFFECTS OF FOOD. alkaline. If the acid be stronger, or there be a donble or treble dos« of it combining Avith 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 alkaline 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 cai'bonic 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 in 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 percent. 692. The Ashes of the Food are Assimilated. — 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 otliers, to contribute to special local nutrition. Thus phosphate of lime is selected to promote the growth of bones, whUe 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 the blood, and the black coloring matter within the eye. C93. The Blood Alkaline, and wliy ? — 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 foct of the digestive juices; one is always acid, and the other alkaline, and their peculiar powers depend ujion these properties. So with the blood. It contains potash, soda, lime, mag- ESTFLUBNCB OF SPECIAL SUBSTANCES. 371 nesia, oxido 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 facility 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 all. 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 well 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 all possess at the ordinary temperature of the air, or at that of the body. — (Cheveeul.) The alkalies of the blood exert a precisely similar action, increasing the combustibility of the respiratory foods. 694. Flesh and its Juices, 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 alkaline 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 tlic System. — The properties of commercial or common salt, have been noticed when speaking of its preservative powers (590). "We may now consider its action in the system. It is 372 PHYSIOLOGICAL EFFECTS OF FOOD. a largo and constant ingredient of the blood, forming nearly sixty pel cent, of its ash. It exists also in other fluids of the body, but is not, perhaps, a constituent of tlie 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 as 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 efiected 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 well as the soda of the alkaline blood, are chiefly 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 flows 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 of potassium is another salt of apparently quite similar properties. Yet in their physiological effects, they are so difitrent, 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. Common 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 wo obtain it both in the solid food Ave consume and in the water wo 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 moi'o than vegetable ; though the parts which most abound in this ingredient, — the blood and carti- lages — are not commonly used for food. Of vegetable foods, seeds contain the least amount of common salt, roots vary in their quantity. INFLUENCE OF SPECIAL BUBSTANCES. 372 turnips having hardly a trace. Yet much 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 eflfect 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 ali ments are abstracted (593). Potatoes, and vegetables rich in potash are excellent antiscorlutics — 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 tinges, 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 ; while in others, no such result followed. Yet the amount supplied naturaUy 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 diet. 374 PHYSIOLOGICAL EFFECTS OF FOOD. 698. Carbonates of Soda and Potash. — The exclusive employment of these substances in extemporising light bread (509), makes a reference to their pliysiological action necessary. Carbonate of potash in its crude shape, appears &spearki«h; in its more purified form it isaaleratus. 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 alkaline or burning property, which belongs to free potash and soda ; lot 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 wo 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. T.bese changes do take place to a certain extent, and the saline oompounda formed, are much less powerful and noxious than the unneutralized alkalies ; their effects are moderately laxative. Yet, in tlie common use of these substances, as we have stated, the alkali is not all ex- tinguished ; much of it enters the system in its active form. Pure, strong potash, is a poAverful corrosive poison ; disorganizing the Btomach, 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 ia 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.— liiquid Aliments. 699. Physiologleal importance of Water. — Water is the most abundant compound in the body, constituting 80 per cent, of the blood, and 76 per cent, of the whole system, — in importance to life it ranks next to oxygen of respiration. An adult man 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 idiraeuts (366). It is the simple and universal beverage furnished by nature, for all living beings, and exists in greater or less proportion, as we have INPLtrENCK OF SPECIAL SUBSTANCES. 375 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, while 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 the 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, all 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 smaU 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 all ; on the contrary, it is one of its leading offices to combine the elements which the plant separated, and thns 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 npon 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, bile, gastric and pancreatic fluid, saliva, mucus, tears, perspiration, and all other pectdiar liquids of the body, are simply water, containing various substances in solution. In- deed, the final result of the whole digestive process is to liquefy the aliments, or dissolve them in water. The eflfect of taking liquids is of course to dilute the bodily fluids, just in proportion to the amount 376 PUYSIOLOGICAL EFFECTS OF FOOD. taken. TIio first efFect will be a dilution 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. Wo know that excessive eating is usually accompanied fty a copious use 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 enforcing moderate eating. Dr. Chambeks, of London, asserts that, " A moderate meal is certainly easier digested Avhen diluents are taken with it." Again he remarks, " Aqueous fluids jn large quan- tities during meals, burden the stomach with an extra bulk of matter, and, therefore, often cquse 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 all without a much more fluid diet than is usual among heal- thy persons." 703. Water Influences change of Tissae. — Beyond digestion is meta- morphosis of structure, and this is influenced by the amoimt of water drank. Recent 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 sufficient 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 of water, the weight of the body constantly diminished. The excess of water increased the waste, so that the same food would no lougei restore it — the balance inclined on the destructive side. Neither th^ pulse nor respiration were affected, but there was more languor aftei exercise, while tlie sensation of hunger kept pace with the increased metamorphosis of matter. 704. Tea and Coffee. — These are taken in the form of infusions, tht 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 j)eculiar action are thein and cafein, tannic acid and volatile or empyrcumatic oil. nrPLUENCE OF SPECIAL SUBSTANCES. 371 705. Effects of Tea. — Though 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 ingi-edients, 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 Avakefulness. 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 ounce 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, first^ that tea in ordinary 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 insuflicient, 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. Inflacnce of Coffee In Digestion. — The active ingredients of cof- fee are eafein^ 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- 318 PHYSIOLOGICAL EFFECTS OP POOD. ficiently delicate reagents to detect such eflfects, 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.) 707. Lehman on the Influence 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 eff'ects upon the gen- eral system, which it seems difficult to associate together, viz : height- ening vascular and nervous activity, and at the same time protracting the decomposition of the tissues. The cafein and oil both contribute to the same peculiar stimulant effects, by which it rouses the exhaust- ed system and promotes feelings of comfort and cheerfulness. He finds that in retarding the decompositions of the body, it is the em- pyreumatic oil of the beverage that chiefly acts, the cafein only pro- ducing this result when taken in larger than usual proportion. Excess of this oil causes "perspiration, diuresis, quickened motion of the bowels, and augmented activity of understanding, which may indeed, by an increase of doses end in irregular trains of thought, congestions, restlessness, and incapacity for sleep ; and that excess of cafein pro- duces increased action of the heart, rigors, derangement of the renal organs, headache, a peculiar inebriation, and delirium." 708. Chocolate is allied to tea and coffee by its nitrogenous princi- ple (theobromin), but the effect of this substance seems to bo less marked than in the other cases, and has not been clearly traced. It is more nutritive than those drinks from its larger proportion of albu- men and fat, but the excess of the latter substance makes it indigesti- ble and offensive to delicate stomachs. 709. Alcoholic Llqnors. — The common and active principle of spirit- ous liquors is alcohol, obtained from sugar by fermentation. It varies in proportion in the different sorts from 1 to 50 or CO per cent. Liquors contain various accompanying substances, traces of albumen, sugar, acids, volatile oils, ethers, bitter principles produced in the pro- cess of fermentation or distillation, or purposely added to suit the de- mands of taste. The scale of commercial valuation of alcoholic hquora is made to depend, not on the peculiar spirituous principle, which is cheap, but on the attending flavoring ingredients, and various sub- stances which are said to modify the effect of alcohol upon tlie sys- tem. Yet It is the alcoholic principle found in all these mixtures that INFLUENCE OF SPECIAL SUBSTANCES. 379 gives them life, and a common character, and groups them all together under the common title of intoxicating liquoi-s. It has been insisted by some that alcoholic beverages are entitled to rank as food or nutri- ment, but the claim is inadmissible, and moreover, is not urged by the most discriminating physiologists, even those who look "vvith favor upon its general use. 710. They cannot replace Water in the System. — Water is the ap- pointed solvent within the living body. Aided by acids, alkalies, salts, it brings the various solids into the required condition of solution. But alcohol cannot replace water in this duty. Its solvent powers are not the same as those of water. What alcohol dissolves, water may not, and the reverse. Alcohol mixed with water may deprive it of its solvent powers in particular cases. This is precisely what is done when alcoholic liquids are taken into the stomach. They coagulate, and precipitate the pepsin dissolved in the watery gastric juice, and if not quickly absorbed by the stomach into the blood, they would in this way effectually stop digestion. Their action while within the stomach is to disturb and arrest the digestive process. 711. They cannot nonrisli Tissne. — Alcohol contains no nitrogen; it cannot, therefore, be transformed into tissue, nor take part in meta- morphic changes. Its composition forbids the possibility of any such effect, and nobody acquainted with the* rudiments of physiology claims it. 712. Their relation to Animal Heat. — The assumption that alcohol is a respiratory aliment is plausible at the first blush, but conceding the utmost demand — that it undergoes combustion in the body — it is en- tirely impossible to sustain the doctrine. True, alcohol gives rise to Jieat in the system, but so do other agents, whose claim to the charac- ter of foods would be on their face preposterous. The question is, do these liquors produce heat in the manner of foods, or in some unnatu- ral and injurious way. .By reference to Luebig's scale of respirants (743), it will be seen that the strongest spirits drank are inferior, pound for pound, to starch and sugar, and not nearly half so valuable as oily substances for a heat generator. Yet they act in such a rapid, flashy way, as to produce preternatural excitement and irritation in the system. In sustained calorific effect, they are not to be compared with the aliments provided by nature, as is emphatically attested by the concurrent experience of Arctic voyagers exposed to the utmost se- verities of cold. 713. Dr. Bocker's Observations. — This gentleman tested the effects of alcohol in small quantities upon his own person, in a course of skilfully 880 PHYSIOLOGICAL EFFECTS OF FOOD. conducted experiments. lie found that this substance diminishes both the solid and liquid constituents of excretion by the kidneys, that it does not increase perspiration, that it diminishes tlie quantity of carbonic acid exhaled by the lungs, while the quantity of water thrown off by these organs remained unchanged, or, if any thing, was slightly re- duced. The general action, therefore, was that of an arrester of the bodily changes. As carbonic acid is hindered from being freely ex- creted, it accumulates in the blood in poisonous quantities, and thus contributes to the effects of intoxication, 714. Is Its use Physiologically Economical. — The apologists for the general and moderate use of alcoholic beverages, cannot agree among themselves upon any philosophy to suit the case. Dr. Moleshott says, "Alcohol may be considered a savings-box of the tissues. He who eats little and drinks a moderate quantity of spirits, retains as much in the blood and tissues as a person who eats proportionally more, without drinking any beer, wine, or spirits. Clearly, then, it is hard to rob the laborer, who in the sweat of his brow eats but a slen- der meal, of a means by which his deficient food is made to last him a longer time." Upon which Dr. Chambers justly remarks, " This is going rather too far. "When alcohol hmits the consumption of tissue, and so the requirements of the system, while at the same time a man goes on working, it is right to inquire, whence comes his new strength ? It is supplied by something which is not decomposition of tissue ; by what, then ? " Dr. Liebig points out the consequences of that pecu- liar economy by which the laboring man saves his tissue and the food necessary to repair it by the use of liquors. "Spirits, by their action on the nerves, enable the laborer to make up for deficient power (from insuflicient food), at the expense of 1m lody, to consume to-day that quantity which ought naturally to have been employed a day later. He draws, so to speak, a bill on his health which must bo always re- newed, because, for want of means, he cannot take it up ; he con- sumes his capital instead of his interest, and the rqsult is the inetita- hlc banhruptcy of his body.'''' 715. Stimulating effect of the Beverages. — They produce general stim- ulation; the heart's action is increased, tlio circulation quickened, the secretions augmented, the system glows with unusual warmth, and there is a general heightening of the functions. Organs, usually below par from debility, are brought up to the normal tone, while those which are strong and healthy are raised above it. Thus the stomach, if feeble, for example, from deficient gastric secretion, may be aided to pour out a more copious solvent, which promotes digestion, or if it INPLUENCE OE SPECIAL SUBSTANCES, 381 be in full health, it may thus be made to digest more than the body requires. The life of the system is exalted above its standard, which takes place, not by confei-ring additional vitality, but by plying the nervous system with a fiery irritant, which provokes the vital func- tions to a higher rate of action. This is the secret of the fatal fascina- tion of alcohol, and the source of its evil. The excitement it produces is transcient, and is followed by a corresponding depression and drag- ging of all the bodily movements. It enables us to live at an acceler- ated speed to-day, but it is only by plundering to-morrow. By its means we crowd into a short period of intense exhilaration, the feel- ings, emotions, thoughts, and experiences, which the Author of oi:r nature designed should be distributed more equally through the pass- ing time. We cannot doubt that God has graduated the flow of these life-currents, in accordance with the profoundest harmonies of being, and the highest results of beneficence. By habitually resorting to this potent stimulant, man violates the Providential Order of his con- stitution, loses the voluntary regulation and control of his conduct, in- augurates the reign of appetite and passion, and reaps the penal con- sequences in multiform suffering and sorrow, — for nature always vindicates herself at last.* 71 G. Effects of Milk. — This is the food prepared by nature for the complete nourishment of the infant. It is easily digestible, but con- stipating. There is a difference, however, in different kinds of milk. Cow's milk is richer in butter, or oil, than human milk, or asses' milk, and for this reason often disagrees with delicate stomachs. By sMm- minff, however, cow's milk is made to approach human milk in quality. It still, however, contains nearly all the cheese, the sugar of milk, the salts, and some butter. It is therefore scarcely less nutritious than new milk, but from its loss of butter is less fattening, and has a lower power of sustaining, through respiration, the temperature of the body. Physicians order milk when they are desirous of affording stimulus or excitement. It is also recommended as a good diet for children, especially in scrofulous complaints. ■ 717. Properties and effects of Soaps. — The soluble extract of various animal and vegetable substances, obtained by boiling or steeping, forms ♦ " When, by habit, the stimulant has become a necessity, an enervating relaxation in- fallibly follows, as sometimes mournfully illustrated by less prudent literary men. The stimulant ceases to excite — the debilitated organs have already been indebted to it for all the activity it can give. In this case the victim continues to seek his refuge, until dangerous diseases of the stomach cripple the digestive powers ; with the decay of the digestive organs, the formation of blood and nutrition are disturbed ; and with the di- gestion vanish clearness of thought, acuteness of the senses, and the elasticity of the muscles."— (MOLESHOTT.) 882 PHYSIOLOGICAL EFFECTS OF FOOD. 6oaps. They aro made from a great number of materials, and thoif effects, of coin-se, depend upon the substances they contain. The infu- sion of meat, which has been described (471), is easily digestible, nourishing, and well adapted to restore the exhausted strength of in- valids. The substance which has played the most important part in soups, is gelatin^ the glue-principle obtained from bones, tendons, car- tilages, and membranes. It is this element in soup, procured by long boiling of animal substances, which causes it to coagulate and thicken (gelatinize) in cooling, and thus conveys to the uninstructed, the im- pression of strength and richness. Gelatin is the principle of animal jellies — calves' feet, blanc-mange, &c. It is an exclusive animal pro- duct, und never found in plants, — pectin being the vegetable jelly principle. Gelatin is a nitrogenous compound, but not of the protein type. It is regarded as a product of the partial decomposition of al- buminous bodies in the system, but is not capable of replacing them when taken as aliment. It is questioned, indeed, if gelatin, taken as such in food, is even capable of nourishing the gelatinous tissues. It is digestible in the stomach along with other nitrogenous matters, and finally contributes slightly, by its destruction to bodily warmth, thus ranking as a respirant of low power. But even this small duty is not performed without detriment, for while the true respiifants burn com- pletely away, gelatin loads the blood with its incombustible and nox- ious residues. The French attempted to feed the inmates of their hos- pitals on gelatinous extract of bones ; murmurs arose, and a commis- sion was appointed, with Magexdik at its head, to investigate the matter ; the conclusion of which was, that giving the poor gelatin, was just equivalent to giving them nothing at all. The use of gelatin as a nutritive or invigorating substance may be regarded as given up. The utmost claim now put forth for it is, that, mixed with other food, it makes it go further ; " but at the same time we must be careful that it is not used in excess, as it is apt not only to weaken the individual by its insuflSciency as an article of diet, but causes also diarrhoea, whether by acting as a foreign body, or by some spontaneous decom- position. Hence the unwholesomeness, to healthy stomachs, of dishes containing a great quantity of gelatin, such as mock-turtle soup, calves' foot jelly, &c. At the same time, to invalids they often fulfil very inportant indications. In the first place they dilute nutritious matter, 8o as to render it capable of being absorbed ; then again perhaps they line the irritable membranes with a sluny coat, and it is not impossi- ble that in some cases they are beneficial because not nutritious, con- stituting, in fact, an agreeable mode of abstaining from food." INTLUENCE OP SPECIAL SUBSTANCES 383 C— Solid Aliments. Y18. Starcb, as we have seen, consists of hard, highly organized grains, enclosed in a firm envelope, so that in the raw state they defy the action of the digestive organs. Thorough cooking of starch, to break its grains, is therefore indispensable. We remember that the digestion of starch, altered by culinary heat, begins in the mouth by intermixture with saliva. Its changes in the stomach depend upon such previous intermixture. This explains why it is that those in whom the action of the salivary glands has been impaired (as tobacco smokers, often), complain that starchy food lays like a weight on the stomach. Starch prepared in the form of slops for invalids, as arrow- root, sago, &c., is apt to be swallowed without provoking the salivary flow, which prevents its prompt change ; hence starchy matter in the solid form, as bread or potatoes, which require mastication, is likely to be best digested. Starch is mainly changed in the system to sugar, perhaps some of it becomes dextrine and lactic acid. 719. Sugar. — Of the behavior of this substance in the system, we know very little positively. A portion of it is absorbed through the veins into the circulation, and then burned away for the production of heat. But it contributes to other objects also. Another part is turned into lactic acid, which may assist stomach digestion, and serve other important uses. Physiologists are now agreed that sugar is ca- pable of conversion into fat in the body. To effect this change, it is only necessary to remove its oxygen, the remaining hydrogen and car- bon furnishing the constituents of oil. A deficiency of oxygen in the system is a necessary condition of the accumulation of fat, as an ex- cess of this agent would consume the elements, and thus prevent their deposition. Sugar is of an acid nature, and combines with lime and the alkalies. There is an old opinion, that sugar, when eaten freely, attacks the teeth, corrupting them, and spoiling their color ; and re- cent French experiments are quoted confirming this view. Dr. Pereiea declares the opinion totally unfounded, saying that no peo« pie on earth have finer teeth than .the negroes of Jamaica, who per- haps use sugar most liberally. " It is probable that this erroneous no- tion has been propagated by frugal housewives, in order to deter chil- dren from indulging in an expensive luxury. Their fondness for sac- charine substances may be regarded as a natural instinct ; since nature, by placing it in milk, evidently intended it to form part of their nour- ishment during the first period of their existence. Instead, therefore, of repressing this appetite for sugar, it ought rather to be gratified in moderation. 384 PHYSIOLOGICAL EFFECIS OF FOOD. 720. Gum, in composition, resembles sugar and starch, and, there- fore, would seem to bo devoted iu the system to the same final pur- pose — the production of heat ; but there is no evidence that it is absorbed into the blood, nor indeed satisfactory proof that it accom- plishes any alimentary purpose in the system. 721. Supply of Oily Snbstanees. — These are furnished to the system mingled by nature with nearly all the food we take. Milk contains three or four per cent, of it, wheat about one per cent., rye 1*75, corn 8 or 9, ordinary meats abound in it, while in butter, gravies, and fat meat, we have it concentrated and almost pure. The roots, as potatoes, beets, &c., contain the smallest proportion of it. The system is thus largely furnished with fat, ready prepared ; and moreover, when its supply is deficient, it has the power of producing it out of other ali- mentary principles, sugar, starch, and perhaps even nitrogenous sub- stances. The physiological services rendered by the fats are manifold and most important. In digestion and absorption, they undergo little or no change. We may consider their uses under a twofold aspect ; first, when laid up in the body, in a passive state ; and, second, as par- ticipating in the active changes of the system. 722. The aecomalated Fat of the Body. — The necessity of some sub- stance adapted to fill and occupy the interspaces that must occur be- tween bones, muscles, and vessels, is obvious. There is hence extended across these vacancies a fine tissue of cells filled with fat. But as un- impeded motion is required in all regions of the system, the matter built into these openings and fissures to connect the working parts must be of a nature to facilitate movement. The lubricating, anti- friction properties of the oils answer this requirement perfectly ; and this effect becomes the more apparent when wo consider that the oily matter of the living body is kept by its heat, either entirely fluid, or nearly so. Masses of fat tissue are interposed among the muscular bundles of the heart to promote the ease, freedom and regularity ol their movements. The eye, with its retinue of muscles and nerves, is bedded in it ; it fills up the interstices of the intestinal cavity, to aid the peristaltic motion of the bowels ; layers of it are placed on tho soles of the feet and between the bones of the joints, where it serves similar purposes — that of pads and cushions to break the effect of shocks, and tho mechanical violence to which the body is constantly liable. 13es;ides, deposited in the layer of cellular tissue, under the skin, it relieves abrupt inequalities of the surface, and rounds the out- line into curves of grace and beauty, as we notice most conspicuously in women and children. " The fat which smooths the bony cornera INFLUENCE OF SPECIAL SUBSTANCES. 385 and angles, and the narrow muscles of the face, is the cosmetic em- ployed by nature to stamp the human countenance with the incom- parable impress which exalts it far above all the lower animals." Fat in a fluid state is also a tiery had conductor of heat, so that the layer of it which nature provides under the skin answers an important pur- pose in protecting the body from the effects of extreme heat and cold, and sudden changes of temperature. Finally, in the course of our experience upon this water-drenched planet, It is often desirable that wo should be able to swim, and this is only made possible by tlie extreme lightness of the fatty parts of the body. Were the fat con- tained in our systems as heavy as water, swimming would be imprac- ticable ; besides entailing upon the muscles the increased labor of moving the more weighty limbs and body under ordinary circum- stances. 723. Behavior of Fats in the Stomach.^^We have seen that fats are not digested in the stomach, but are reduced to a fine state of emulsion in the intestines, so as to be capable of absorption. But it has been found that their presence is essential to stomach digestion. Lehman ascertained " that a certain, though small quantity of fat, was indis- pensable to the solution of nitrogenous articles of food during the process of gastric digestion." Elsassee observed in experiments on artifical digestion, that the solution of articles used as food is consider- ably accelerated by means of fat. It has been found in the case of dogs with artificial openings in their stomachs, that flesh which had been designedly deprived of fat laid longer in the stomach, and there- fore required a longer period for its change than the same substances when mixed or impregnated with a little fat. Yet on the other hand excess of fat exerts an injurious action, especially in persons of weak digestion. Fat in small amount is thus necessary to digestion ; in the considerable proportion which the system requires, it ought not to derange the gastric apparatus ; but that it is actually a powerful dis- turber of digestion, in very numerous cases, is well understood. It is probable that those principles which -are designed to be dissolved in the stomach, may be so enclosed and pervaded with fat as to cut off the access of the solvent juice, and thus greatly hinder solution. The way in which fat is distributed among the muscular fibres of meat, for example, is one thing that makes it more or less easily soluble by stomachs deficient in gastric juice. " Mutton owes its good character for digestibility to the little fat there is among its close-grained fibres, while the flesh of the ox is infiltrated with oleaginous matter through- out. The oil envelops the fibres when in the stomach, prevents their IV 886 PHYSIOLOGICAL EFFECTS OF FOOD. being permeated by the gastric secretion, and so renders beef indiges- tible to all but robust persons, Tlio absence of fat in fish, and in poultry, is one great cause of their easy digestibility in the stomach, though their ultimate fibre is less easily soluble than that of red meat. Meat or fish "fried or otherwise dressed "with grease is thereby ren- dered less digestible to weak stomachs, though to those whose gastric juice is suflBciently plentiful to wash away the oily envelope and pene- trate the muscular fibre, it is wholesome. — (Cuambebs.) Even the healthy stomach often recoils at certain combinations of fat, starch and gluten, as in the instance of the oily meats of nuts, filberts, almonds, walnuts, &c. Y24. Cooking luflaences the Digestibility of Fats. — ^The effect of cook- ing upon fatty substances is generally to render them less agreeable to the stomach, especially if the organ be weak. When speaking of butter, we noticed the complex composition of fats and their liability to be decomposed into various offensive substances. Heat effects these changes rapidly, and to an extent proportional to its in- tensity. In some, as butter, the bare act of melting produces an un- favorable alteration, which the morbidly delicate stomach detects. In fi^ng, the temperature runs high, tending to decomposition and the ^/eduction of various acrid and irritant fatty acids. Fatty matters thus changed, or oven predisposed to change, are liable to become rancid by the fermenting action of the stomach, producing heartburn and nausea. This explains why cakes are less healthy and digestible than bread. The large proportion of butter, cream, and eggs, (the yoUcs being rich in oil,) which are usually contained in cakes, and the changes they undergo at the high heat of baking, impairs their diges- tibility. Dr. Peeeiea remarks : " Fixed oil or fat is more difficult of digestion, and more obnoxious to the stomach, than any other ali- mentary principle. Indeed, in some more or less obvious or concealed form, I believe it will be found the offending ingredient in nine-tenths of the dishes which disturb weak stomachs. Many dyspeptics, who have most religiously avoided the use of oil or fat in its obvious or ordinary state, (as fat meat, man-ow, butter, and oil,) unwittingly em- ploy it in some more concealed form, as yolk of eggs, livers of animals, rich cheese, fried dishes, buttered toasts, suet puddings, &c." Dr. CuAMBERS says : " Fatty food can be taken without pain by gastric invalids, very closely in proportion as it is fresh, and without rancidity. New made butter often agrees, when the empyreumatic fat in baked meat makes it utterly indigestible. If there is much emaciation, it is right to try several forms of oleaginous food in each case, to see if one INPLUKNCB OF SPECIAL SUBSTAJifCES. 387 cannot be found capable of supplying nutriment to the failing adipose tissue." 725. Belation of the Fats to Nutrition. — Tlie fats are ranked as respi- ratory aliments, but it would be a great mistake to suppose that after absorption from the intestinal passage into the blood they are simply burned away for heat ; before their destruction they serve other and capital uses in the body. Fat is an essential constituent of the brain and nervous system ; it is thus one of the prime material substances destined to establish communication between mind and matter. It has also been lately maintained that fatty substances have an essential share in the tissue-making process. They do not furnish the material, and we do not know how they act ; but it is agreed that their pres- ence is necessary to the formation of cells and the growth of the bodily structure. Thus, in point of fact, oleaginous substances, though at the head of respiratory aliments, are indispensable to nutrition. 726. Oicaginons Diet and Coosamption. — Masses of crude unorganized matter containing coagulated albumen and half-formed cells, and called tubercles^ are sometimes found in the lungs, producing tubercular consumption. The immediate cause of the disease is an abortive or perverted nuti-ition, tubercle being produced instead of true tissue. The seeds of consumption are most generally sown in the system in youth, when there is a double demand upon nuti-ition, for current waste and steady growth. There is, however, sufficient nitrogenous matter present to nourish the structures ; some other condition must therefore be wanting. It has been lately maintained that the faulty nutrition which results in tubercle, is caused by a deficiency of oily substances, and therefore such of these bodies as are easiest digested and absorbed have been indicated as remedies. Cod Liver Oil has come into use for this purpose. Dr. Hughes Bennett, who first in- troduced this oil to the notice of the English and American public, states that butchers, cooks, oilmen, tanners, and others who are con- stantly coming in contact with fatty matter, are less liable than others to tubercular disease ; and Dr. Simpson has observed that children and young persons employed in wool factories, where large quanties of oil are daily used, are generally exempt from scrofula and pulmonary con- sumption. These facts would indicate that even absorption of fatty matter through the skin may powerfully influence nutrition. Dr. Bennett says that, to prevent consumption during youth, indulgence in indigestible articles of food should be avoided, especially pastry, unripe fruit, salted provisions, and acid drinks, while the habit of eating a certain quantity of fat should be encouraged, and, if neces- 388 PHYSIOLOGICAL EFFECTS OP FOOD. sary, rendered imperative. Dr. Carpenter observes : There is a strong tendency, and increasing reason to believe that a deficiency of ole- aginous matter, in a state fit for appropriation by tlic nutritive processes, is a fertile source of diseased action, especially that of a tuberculous character ; and that the habitual use of it in larger pro- portion would operate favorably in the prevention of such maladies, as cod liver oil unquestionably does in their cure. A most remark- able example of this is presented in the population of Ireland, which, notwithstanding the concurrence of every one of the circumstances usually considered favorable to the scrofulous condition, enjoys a most remarkable immunity from it, without any other assignable cause than the peculiarly oleaginous character of the diet usually em- ployed. Dr. HooKEE, in a report on the diet of the sick, says : 1st. Of all persons between the ages of 15 and 22 years, more than one- fifth eat no fat meat ; 2d. That of persons at the age of 45, all except- ing less than one in fifty, habitually use fat meat ; 3d. Of those who have abstained, a few acquire an appetite for it and live to a good old age, while the great proportion die of consumption before 45 ; 4th. Of persons dying of consumption between the ages of 15 and 45, nine-tenths at least have never used fat meat. 727. Effects of Undue Proportions of Alimentary Principles. — The di- gestion and final use of the nitrogenous principles have been explained. "When taken in too great quantity, they charge the system with im- perfectly assimilated compounds and Avrongly-changed products of de- composition, which are not promptly expelled, and which produce a gouty state of the constitution, besides influencing the course of other diseases. The excess of oily substances in the food tends to increase the proportion of fat in the body. If more is taken than can be stored up, or consumed by oxidation, and thrown from the skin and lunga, the burden of disposing of it falls upon the liver, the blood becomes charged with the elements of bile, and a hiliom condition of the sys- tem results. The rheumatic state of the body, like the gouty, is sup- posed to be connected with mal-assirailation ; but rather with a de- ficiency of albumen and an excess of lactic acid, derived from a rich, starchy, and saccharine diet. A deficiency of oleaginous substances tends, as wo have just seen, to produce the scrofulous state, and a lack of fruits and fresh vegetables engenders the scorlutic condition of body, or scurvjj. 728. Flesh Meats. — Having considered the action of the constitu- ents of flesh, little needs to be added here concerning their combined eflfect. The less the fibre of meat has been dried or altered by cook- INPLUENCE OP SPECIAL SUBSTANCES. 389 ing, the more juicy and abounding in soluble albumen, and the less its fat has been changed from the condition of perfect freshness, either by heat or other causes, the more digestible it is. The flesh of young animals contains less fibrin than that of old ones, biit more soluble al- bumen and gelatin, and is hence more tender. This preponderance of gelatin explains why the broth of veal and lamb coagulates sooner in cuoling than that of beef and mutton. Albumen is usually considered the most digestible form of nitrogenous matter. But as the acids of the stomach coagulate it before digestion, it does not appear that liquid albumen is more digestible than that partially coagulated. Eggs boiled, not too hard, are therefore quite as digestible as if taken raw. 729. Preparations of Flour. — Of the products of grain and flour which we get in multifarious shapes, baked and boiled, it may be said, their digestibility depends first and mainly upon their condition as respects lightness or heaviness. The porous and spongy state, as in good bread, is most favorable to the penetration and action of the di- gestive juices, while glutinous masses in a dense compact condition, especially if charged with fat, are the torment of weak stomachs, re- quiring the strongest digestive powers for their reduction. It is very difficult to preserve the loose and open texture of flour-paste, or dough in boiling, and hence pastry, dumplings, &c., are very rarely light or digestible. Dr. Paeis remarks, " All pastry is an abomina- tion. I verily believe that one-half at least of the cases of indiges- tion which occur after dinner-parties, may be traced to this cause. The most digestible pudding is that made with bread or biscuit and boiled flour ; latter puddings are not so easily digested, and suet pud- ding is to be considered the most mischievous to invalids in the whole catalogue." Dr. Lee observes, " It is doubtful whether there is any way of boiling wheat dough so as to render it fit for food ; it wiU al- ways be crude, and heavy, and impermeable to the gastric juice. Our best puddings are those made of rice, bread, sago, or Indian meal baked. Boiled Indian puddings are not very indigestible, and are far preferable to those of wheat." 730. Coarse and Fine Bread. — As respects the final or nutritive effects of ground grains, it makes every difference whether they be bolted or unbolted. "We have stated the composition of flour from the interior of the seed, and the whole flour, which includes the bran (441). The fine or bolted flour has less of the fibre-buUding gluten, and is therefore less nourishing and strengthening. The unbolted sorts, and even the dark-colored sorts, through which finely-pulver- ized bran is diffused, are more digestible ; the fibrous or ligneous par- 390 PHYSIOLOGICAL EFFECTS OF FOOD. tides act as a kind of mechanical divisor, separating and dilating the highly-concentrated food, rendering the mass looser and more pene- trable to the solvent liquids, and submitting it more gradually to the membranous absorbing surface. The ground grain, or Avoody fibre, mingled with the flour, together Avith the adhering oil, are further ser- viceable by promoting the action of the intestines. Bread from fine flour is constipating, while that from whole flour has an aperient ten- dency, although it is not purgative. Unquestionably, coarse bread is much superior to fine for maintaining the free and regidated action of the boweis, and Mr. Graham insists strongly, as the result of large ob- servation, that coarse bread is corrective, not onh' of undue consti- pating tendencies, but also of morbid and chronic laxity ; though at first it may seem to aggravate the symptoms, yet the final result is de- clared to be most decidedly beneficial. Besides, in the fine flour wo miss the full proportion of the elements of bone and tooth nutrition, the essential mineral phosphates. The nourishment of the bony parts must be deficient, having less volume, solidity, and strength, with a diet of fine bread than with the coarser varieties. We have sacrificed several most important qualities, and gamed on]j tcTiitencss, We trifle with the first conditions of health to gratify a fancy of the eye. 731. Beans and Peas. — The digestibility of these is much dependent upon their preparation. When old and hard, and cooked with their husks and shells, and more especially if boiled in hard water, which prevents the softening and solution of their nitrogenous matter, they are apt to be very indigestible and heating, occasioning flatulence and sometimes colic. When boiled in soft water, the nutritive principle softens, partially dissolves, and becomes more digestible if the husks are separated by passing through a hair sieve. Soup is, therefore, the best form in which dried beans and peas can be taken. 732. Vegetables. — The healthful and indispensable influence of fresh vegetables in diet is undoubted. They are rich in valuable saline sub- stances, essential to the system, and probably act by these as antiscor- hutics, — preventives, and remedies of scurvy. They of course vary in digestibility, according to the proportion of their constituents, and the thorough softening and decomposing eflect of culinary heat. Most esculent vegetables abound in indigestible ligneous tissues, which pro- voke intestinal movement, and thus incline to produce aperient eflA.'cts, Leaves and young shoots contain organic acids ; thus, asparagus and the whole cabbage tribe contain acid of aj)ples, or malic acid ; rheu- barb, n)alic and oxalic acid ; white cabbage converted into sour krout ferments and yields large quantities of lactic acid. These acids may INFLUENCE OF SPECIAL SUBSTANCES. 891 contribute to stomach-digestion, promoting tlie solution of the more nutritive aliments. In the case of fruits, which are still richer in acids, this effect is more marked. 733. Edible Boots, of which the potato ranks first, are superior in dietetic importance to the vegetables just referred to. Besides their chief constituents, water, starch, and albumen, potatoes contain malic acid and asparagin, a nitrogenous substance existing also in asparagus. Potatoes are rich in all the mineral ingredients required by our bodies, and are of permanent value against scurvy ; they especially abound in potash. Turnips contain no soda, but little iron, and considerable potash. Onions have a peculiar volatile oil which is not assimilated or destroyed by the body, but escapes through the lungs, contaminating the breath. Y34. Fruit. — The delicious and refreshing taste of fruits is caused by a combination of sweets and sours, sugars and acids. The sour taste predominates in the green fruit, for although the quantity of acid in- creases as the fruit ripens, yet the sugar increases so much faster, that there is a gradual sweetening as the fruit matures. In ripe fruits the acids are enveloped in sugar, just as in stewed fruit they are in the vegetable jelly, produced by stewing. In stewed and prepared fruit, the sugar and jelly cover, or, as it were, mask the acids and salts, and thus check their irritating action upon the interior coating of the di- gestive passage. The following suggestions of Liebig concerning the value of apples, afford us hints of the utility of fruits generally. " The importance of apples as food has not hitherto been sufficiently estimated or understood. Besides contributing a large propertion of sugar, mucilage, and other nutritive compounds in the form of food, they contain such a fine combination of vegetable acids, extractive substances, and aromatic principles, with the nutritive matter, as to act powerfully in the capacity of refrigerants, tonics, and antiseptics, and when freely used, at the season of ripeness, by rural laborers and others, they prevent debility, strengthen digestion, correct the putre- factive tendencies of nitrogenous food, avert scurvy, and probably maintain and strengthen the power of productive labor." 735. Seasoning Agents, or Con^jnents. — Substances taken in small quantities for the purpose of flavoring, and rendering foods palatable, are called condiments. Few or none, however, are merely limited to this effect ; they serve other purposes besides ministering to the taste. Sugar, oil, acids, and common salt, have been described as aliments, but they are also employed as condiments. 736. Cliecse. — We may regard cheese as an aliment when consider- 392 PHYSIOLOGICAL EFFECTS OF FOOD. ing it as composed simply of casein and fat, to be digested and ab- sorbed. Thus regarded, it is a highly concentrated food, difficult of digestion. But it is also used in small quantities in a condimentary waj', and may thus possess active properties in relation to digestion. Old, changed, and mouldy cheese has long had the reputation of being a digester^ that is, of assisting in some manner tlie action of ihe stom- ach, and for this purpose it is often taken in trifling quantities after a meal. Being in a state of decomposition, it is capable, when mingled with the contents of the stomach, of exciting fermentation, and thus of assisting the process. Of course, if the cheese be fresh, or not in the mouldy, putrefactive condition, it can be expected to produce no such result. 737. Aincgar, in small quantities, by augmenting the acidity of the stomach, may help digestion, assisting the solution of albumen, gluten, and fibrin. It does not, however, dissolve the legumin of peas and beans, but rather precipitates it from solution. An idea has i)revailed that the free use of vinegar promotes leanness. Ilowever the fact may be, the experiment of reducing corpulence in this way is fraught with the danger of estabUshing deeply-rooted disease (775). 738. Spices, &c. — A class of substances rich in pungent oils, — horse- radish, mustard, pepper, cloves, and various spices, are in extensive request as condiments. These oils produce a heating, irritating effect upon the organs of taste, and the stomach ; upon entering the blood, they increase the circulation, and give rise to stimulation. " Con- diments, particularly those of the spicy kind, are not essential to the process of digestion, in a healthy state of the system. They afford no nutrition. Though they may assist the action of a debilitated stom- ach for a time, their continual use never fails to produce a weakness of that organ. They affect it as alcohol or other stimulants do — the present relief afforded is at the expense oi future suffering. Salt and vinegar are exceptions, and are not obnoxious to this charge, when used in moderation." — (Dr. Beaumont.) 10. NuTBiTiTE Value of Foods. 739. Limitation of tlie Nntrltive Powers. — It is to be expected that substances dillering so widely as those which constitute food — sub- stances of such various composition — some containing nitrogen, whilo others are free from it, some containing sulphur, others none, some an excess of carbon, others the reverse — must serve very ditlerent pur- poses in tic economy. Each has its siiecial work to do, while their duties are not interchangeable. A certain degree oi variety is thus rra NUTEinvE vaxue. 393 the fundamental requirement of the system ; and accordingly we find that where nature herself has prepared the food, as in the case of the mother's milk for her young, it is always of a mixed nature, embracing alimentary principles of very different composition. We have no shadow of evidence that the living body possesses the power of converting one element into another ; it cannot transmute hydrogen into nitrogen, or carbon into phosphorus ; if it lack an element, it must suffer the inconvenience of deficiency. As regards the conver- sion of one compound into another, the system has a limited faculty of this kind in a certain direction ; it can effect some changes, as we have seen ; it cannot effect others. It can destroy compounds by a progressive series of changes, each descending step being a new sub- stance, but it cannot work upward in a formative direction, — tliat is the office of plants. The materials necessary to form a compound may be present in the body without any power whatever to produce it. The dissevered constituents of used-up tissue, exist in the blood, but it is entirely incapable of reconverting them into tissue. Nor has the body the power of transmuting the respiratory group of aliments into the albuminous, or of enabling the former to replace the latter, in the exigencies of the animal economy. It cannot make starch do the work of gluten. " That none of the non-nitrogenous substances can be made capable, by metamorphosis or combination within the animal body of taking the place of the nitrogenous or plastic compounds, may now be regarded as one of the most certain facts in physiology ; the concurrent evidence of experiment and observation tending to the conclusion, that in plants alone can any production of nitrogenous compounds take place. If animals be fed exclusively on saccharine or oleaginous substances of any kind, or in any combination whatever, they speedily perish with symptoms of starvation." — (Dr. Caepentee.) As the system has no mysterious energy to change what it will and as it will, its action being absolutely limited, it follows that its nutritive supplies must be adapted to its wants. 740. Mixed Diet Indispensable. — Our diet thus requires to be of a mixed nature, comprehending such a variety of materials as to supply the whole range of bodily wants, and moreover, should be varied with the varying circumstances of growth, bodily and mental exercise, tem- perature, and numerous changing requirements of the system. Hence the impossibility of prescribing any thing like precise and invariable rules in reference to the quantity and proportions of alimentary sub- stances. We now call attention to the comparative values of nutritive substances, in certain important respects, as based upon composition, 11* 394 PHYSIOLOGICAL EPTBCTS OP FOOD. and experience of tlieir effects. We shall have occasion to note both agreement and discordance, in many particulars, between general habits and the indications of science. 741. Proportions of Solid Matter and Water. — The following scheme, Fig. 121, illustrates the ])roportion of solid matter and water contained in the principal articles of diet. They were dried at 212 ; the results are averages of statements by the best authorities. The length of the bars represent the proportion of dry solid matter in 100 parts, the remain- der of the hundred indicated by the scale being water. The preva- FiG. 121. PBOPOETION OF SOLID MATTKH AND WATEE ET FOODS. Wheat, Peas. Eice, IJyo, Beans, Corn. "Wheat Bread. Mutton. Chicken. Lean Bec£ Eggs. Veal. Potatoes. Pork. Cod. Blood. Trout. Apples. Carrots. /■■■ Beets. BP Milk. ^ Oysters. pH Musktnclon. BH Cabbage, ft^ Turnips. ■■' ■Watermelon. ■■" Cucumbers. B' 100 The length of the bars represents upon the scale, the percentage proportion of solid mat- ter in the various articles of diet, opposite to which they are placed. lence of the aqueous element in diet, is thus strikingly apparent. Most of the articles contain 75 per cent, water ; some much more. The grains are driest, but in being reduced to bread they become more than half water, and even then we take additional liquids freely while eating it. "Water is essential to food, but to make the best statement of its nutritive value, we must throw this constituent out of the ac- ITS NUTRITIVE VALT7E. 395 count, and regard only the dry matter. But the quantity of solid sub- stance left, is no guide to its nutritive effect ; potatoes and lean beef have the same proportion of water, but they are certainly widely apart in imtritive power. 742. IIow far we can measure Nutritive Values. — A full view of the nutritive value of foods, requires us to take into account all their effects ; but we are as yet far from being prepared to do this on any systematic or comparative scale. The nearest approach to a state- ment that can be ventured, is by classifying foods in reference to the two great leading purposes which they serve in the system — forma- tion of tissue, and production of heat — the proportion of the nutritive to the caloriQent principles. This division, although fundamentally true, and capable of being embodied in a valuable shape, we take with its qualifications ; for as has been stated, the respiratory principles contribute also to nutrition, Avhile the albuminous may produce heat (666). 743. Different values of the Respiratory Principles, — The albuminous substances are identical in composition, and have equal nutritive powers; whether in the form of gluten, fibrin, casein or albumen, EKLATIVE POWEES OF THE nEAT-PEOmJCES'a PKINCIPLE3 OF FOOD. Fig. 122. 10 20. SO pr^ — ' ' ' Fat Starch. Cane Sugar. Grape Sugar. Spirits, 50 per ct. Alcohol. Lean Flesh, The relative lengths of the bars illustrate the comparative amount of heat produced in the system by equal weights of the substances mentioned. they are replacable in nutritive effect. Not so, however, with the calorifient principles; their heat-giving powers are very unequal. The preceding diagram (Fig. 122), exhibits the relative proportions of heat produced by equal weights of the substances mentioned. It will be thus seen that 10 parts of fat go as far as 24 of starch in generating heat. This is Liebig's estimate. He calculates the oil as starch, by multiplying it by 2*4. Thus the 9 per cent, of oil in Indian 396 PHYSIOLOGICAL EFFECTS OF FOOD. corn, would be equal to adding 22 per cent, to its real amount of ctarcli. In this way, the nutritive and calorifient powers of foods are readily brought into comparison. It appears from this estimate of Linnir., that the strongest spirits are not only incomparably iufcrioi to the oils, in heat-producing power, but also rank decidedly below starch and sugar (712). When we renieiiiber that alcohol is derived from sugar by a destructive process, in which half the saccharine sub- stance is lost, and that the product obtained is still below sugar on the heat-making scale ; it is clear, that the use of alcohol as a respira- tory substance, is any thing but good economy. 744. Bad Economy of an exclusive Meat Diet. — It is seen by the fore- going scale, that lean meat is tlic feeblest of all respirants If it is to be employed, not only for nutrition, but to produce heat, an enormous quantity of it must be consumed. As the largest alimentar} demand of the system is for carbon and hydrogen to support respiration, the nitrogenous principles being low in these elements, afford the least economical diet that can be adopted. Thus it has been calculated, tliat since lifteen lbs. of flesh contain no more carbon than four lbs. oi starch, a savage with one carcass and an equal weight of starch, could support life for the same length of time, during which another, restricted to animal food, would require five such carcasses in order tc produce the carbon necessary for ref^piration. The mixture of the nitro- genous and non-nitrogenous compounds, (gluten and starch,) that exist in wheat flour, seems to be just that which is most generally useful to man ; and hence we see the explanation of the fact, that from very early ages, bread has been regarded as the ' staflf of life.' 745. Eqnllibrinm of Valaes Disturbed. — When the due proportion demanded by our physiological welfixro, is struck, between the nutri- tive and respiratory principles, they may be regarded as of equal values ; that is, they are both, in their just relative amounts, equally necessary, and a diminution of either produces injury. But under ordinary circumstances, the nitrogenous matters are most diflicult to obtain. They exhaust the soil most, and the tendency of cropping is to reduce their proportion in equal weights of alimentary products. They represent animal power, are more complex and highly organized, arc less easily produced, and more destructible than the other group. The value of foods, therefore, under ordinary circumstances, rises and falls mainly in correspondence with the 'proportion of these constit- uents. But in case of famine, or arrest of production, these conditions are reversed. Crops of green roots and vegetables, the immediate and principal soupces of respiratory food, in the shape of starch, sugar, ITS NUTRITIVE VAXUE. 397 ducing principles. !0_i2aj, 30_, 40 and oil, are cut off. "We fall back upon the animal world, but this is chiefly a grand store of nitrogenous matter, without its due proportion of other constituents. The balance being thus lost, respiratory food rises in demand and value. 74:6. Proportioa of Nutritive to Calorificnt Principles. — The following scheme represents approximately the values, nutritive and calorifient — building materials and fuel — of various articles of food. It must be received as only a general or outline expression of the facts. Different samples of the same food vary in composition ; an average is the best result that can be obtained. Fig. 123. OOMPAEATIVK SCALE OF THE NUTRITIVE AND EESPIKATOET VALUES OF VARIOUS AETICLE3 OF FOOD, Natritive or tissue- Cttlori6cnt or hent-pro- forming principles. *Vcal. Ilaro. Dried Beef. Eggs. Beef. Beans. Peas. Fat Mutton. Pork. Cow's Milk. Humau Milk. Wheat Flour. Eye Flour. White Potatoes. Indian Corn. Turnips- Blue Potatoes. Eice. BucKwheat Flour. Arrow-root, sa go, tapioca, corn-starch •] I represents, by the relative length of the bars, the proportion of nitrogenous to the igenous principles in each article given, the latter being all reduced to the value of This scheme i non-nitrogenous i , ^ , starch. The upper part of the scale represents those foods which are highest in proper nutri- tive power, and lowest in heat-producing effect, while the lower portion exhibits those which are lowest in nutritive, but highest in calorifying effect. ♦The authorities for the above scale are as follows, in numerical order, counting from the top downward: ], 2, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 17, 18, 19 (Libbig); 8, 4, 16 (Prof: Johk 8T0N) ; 20 (Prof. K. D. Thompson) ; 15 (Author). 398 PHYSIOLOGICAL EFFECTS OF FOOD. The point to Avhich wo called attention in the previous paragraph must not be forgotten, or the scheme will certainly mislead us. The calorifient principles are reduced to the expression for starch, so that wherever fats are involved, the respiratory equivalent appears higher than the quantities furnished by analysis would otherwise war- rant. Thus, if we take the weight of the casein of milk to represent its nutritive power, and the combined weights of the sugar and butter to represent the respiratory effect, we shall get a result different from that in the table, 10 of nutritive, to 18 or 20 of respiratory food. LiEBiG says in substance, in connection with tins statement, that the relative proportions of the nutritive constituents :n milk, to its butter and milk-sugar, that of the plastic matter of flesh to its fat, and of the albuminous substance of grain, potatoes, peas and beans to their starch, are not constant. They vary in milk with the food ; fattened flesh contains more fat than that which is lean ; and the difference be- tween the two kinds of potato shows how great may be the variation in different varieties of the same plant. But the above may be re- garded as average numbers lying between the opposite extremes in each case. "We may consider as constant the following results, namely, that peas, beans, and lentils contain for one part by weight of plastic matter, between two and three of non-nitrogenous matter ranked as starch ; that grains, such as wheat, rye, and oats, contain be- tween five and six parts, potatoes from eight to eleven parts, and rice and buckwheat from twelve to thirteen parts of the latter, to one of the former. 747. Nntritive Powers of Milk. — The above scheme is rich in sug- gestions. The starting point of all inquiries into the nutritive quali- ties of foods is milk. It is the only complete or typical aliment fitted to nourish the entire body ; the only dietetic prescription that nature has furnished to fill the full circle of bodily wants. The water is there in large proportion to supply the necessary liquids, the mineral salts, to build the bony framework, the casein to form the tissues, and but- ter and sugar to sustain the bodily warmth. Not only does it contain every thing the system requires, but in proportions exquisitely adapted to the demands of peculiar and varjring conditions. It is the appointed diet of the infant, the chief business of which is to grow. Its diet must, therefore, not only be adjusted to meet its current waste, but it requires to be especially rich in the structure-making constituents, and such is the fact. The weight of the nitrogenous curd to the butter and sugar, is as high as 1, to 2 or 3. But see how admirably nature modifies these proportions to suit special occasions. Of all the yomig INFLUENCE OP SPECIAL SUBSTANCES. 399 of the animal world, none lead eo quiescent a life, or advance so slow- ly to maturity, as does the human infant. The young of other ani' ranis more quickly develop, and are called upon to put forth exertion much earlier. Hence the milk of these animals, as for example the cow, is richer in the curdy, or building and strength-giving principle than human milk. 748. Wheat resemMes Milk and Blood. — Wheat, by universal consent, ranks first in nutritive value among grains. It abounds in the valua- ble elements which the body requires — mineral matter for bones, glu- ten for tissue, starch for respiration. Its deficiencies are water and oil ; the former we supply in converting it into bread, and the latter by the universal custom of using butter with it when eaten. Another great advantage of wheat is, that its gluten is pre-eminently of that quality which yields the lightest and most digestible bread. The near- ness of wheat flour in chemical composition to milk and blood, is shown in the following analytical statement : Mour. Blood. MUJc Fibrin, Fibrin, Albumen, Albumen, Albumen, Casein, Casein, Casein, Gluten, on and starch, Coloring matter. Fats and oils. Butter, Sugar, Chloride of potassium, Chloride of sodium, Sugar, Milk-sugar. Phosphate of soda, " " lime, Ditto. Ditto. " " magnesia, " " iron. . 749. How Wheaten preparations meet the losses of the System. — The attempt has been made to determine the daily consumption in the sys- tem of nutritive and respiratory matter. The problem is most diffi- cult, and the results thus far only average and approximative. It is as- sumed that the waste of tissue is about a grain a minute, or 62 grains per hour, or somewhat more than 3 oz. per day. Poggaile states that the researches of the last 20 years have shown that an adult la- boring man consumes each day between 11 and 12 ounces of heat-pro- ducing principles, and about 4j ounces (dry) of nitrogenous matters, charged with the regeneration of the tissues ; that his nourishment is not complete unless it is formed of one part nitrogenous matter and four parts respiratory. Bexeke, from an examination of the diet scales of various educational, invalid, and penal establishments in Lon- don, obtains the result that the nitrogenous should be to the non-nitro- 400 rHTSIOLOGICAL EFFECTS OF FOOD. j^onous as one to five. Fkeeiohs calculates that the daily consump tion should be 2'17 ounces avoirdupois of uitrogenous, and 15'54 ounces of non-nitrogenous food, that is, about as one to seven. Wheat aver- ages, perhaps, one to five. But starch is a bulivy form of re8i>iratorj aliment, and hence it is only by the use of very considerable quanti- ties of bread, that enough of this ingredient can be procured to sus- tain the temperature. IJutter, a more concentrated heat-producer, comes in to assist in relieving this difficulty, and as wheat is almost entirely destitute of oil, it is highly probable that butter is also in- stinctively added to promote its digestion. 750. Variations in KotritiTe Value of Wheat. — The proportion of nu- tritive to respiratory principles in wheat, fluctuates much, which of course, affects its value correspondingly. Flour containing 9 per cent, of gluten must give rise to very different physiological effects from that containing 18 per cent. The large proportion Avill produce the blood constituents most copiously, and yield most strength. Yet, as we liave repeatedly stated, commercial and nutritive values, so far from coinciding, actually antagonize. Instead of the increasing pro- portion of nitrogenous compounds being any indication of the price which will be paid for wheat, it is quite the reverse. "We prize and estimate flour directly in proportion to its whiteness, which is gener- ally in inverse ratio to the proportion of its gluten. TTe give most for the wheat that will nourish least. As the chief object of the farmer is to produce an article which will command the highest 7«arlr^ price, he has no inducement to cultivate grains rich in albuminous com- pounds, but a double motive for the contrary course ; those which are deficient in these elements exhaust the soil less and bring most money. 751. nigh Nntritire Power of coarse Bread. — In the seventeenth century, Vaubax estimated the annual consumption of a man at near- ly 712 pounds of wheat, a quantity which now nearly suffices for two men ; and by the improvements in mills, there arc now gained to the population immense masses of nutritious matter, of the annual value of many millions, which were formerly used for animals ; the bran may be far more easily replaced by other food not in the least adapted for the use of man. The high value of bran for food has been long ago pointed out. Wheat does not contain above 2 per cent, of indi- gestible, woody fibre, and a perfect mill should not yield more than that proportion of bran, but practically, the best mills always sepa- rate, even now, from 12 to 20 per cent. (10 per cent, coarse bran, 7 fine bran, 3 bran flour) ; and the ordinary mills produce as much as 25 oer cent, of bran, containing 60 or 70 per cent, of the most nutritious ITS NUTRITIVE VALUE. 401 constituents of tho flour. By baking bread with unbolted flour, the mass of it may be increased from one-sixth to one-fifth, and the price of it lowered by the difference between the price of the bran as fodder for cattle, and that of the four gained by not bolting it. The separation of the bran from the flour by bolting is a matter of luxury, and injurious rather than beneficial as regards the nutritive power of the bread — (Liebig). 752. Aliments may he corrected by Intermrxtnre. — Lean flesh is the most concentrated form of nutriment, is easily digested, and quickly converted again into muscle. Yet, though a most perfect nutriment, it is least fitted to meet the complete demands of the system. It is not a complementary food, like wheat, answering to the double re- quirements of the body ; its deficiency of resjiiratory matter makes it necessary to consume with it fats and gravies, or else join it with those substances at the opposite extremity of the scale, rice, potatoes, vegetables, &c., which abound in calorifying matter, but are deficient in the nutritive. On the other hand, if we attempt to live exclusively on rice, potatoes, or vegetables, in order to procure suflicient of the flesh-producing ingredients, we must consume an enormous bulk of respiratory matter, so much more than is needed, as to produce de- formity and disorder of the system. It is easy to see, however, by reference to the preceding scale, that we can make such combinations of dietetical articles, as shall compensate for natural deficiencies. In- deed, the due admixture of these difi'erent principles of food, is a vital and immanent necessity, which, if disregarded, makes itself quickly felt in physiological derangement, so that man's instincts have sufficed to guard him in many cases against broad departures from the proper and healthy course. In aU countries we notice dietetical adjustments tending to the same physiological end. In the coarsest and crudest diet of barbarous tribes, or the high-wrought luxuries of the refined, the same instinctive cravings are ever regarded — the same purpose of nature is always in view. Potatoes and vegetables, with beef, mutton, and pork, are almost universal combinations. Beans and peas, which are the most highly concentrated vegetable nutriments, are associated with fat pork, in the well-known dishes — 'pork and beans,' 'pork and peas pudding,' and the extreme oiliness of ham or bacon is cor- rected by the highly nutritive egg (ham and eggs). So also milk and eggs are cooked with rice, and butter is added to bread, which is de- ficient in oily matter. In Ireland, where potatoes form the staple ol diet, and there is a deficiency of meat, they attempt a compensation by mingling with the potatoes boiled cabbage, which is ricli in nitro- 402 PHYSIOLOGICAL EFFECTTS OF FOOD. genous matter, with perhaps a little meat, making a dish known as kol< cannon. Rico is also a staple article of food through vast regions. It is very deficient as a nutriment, containing but little nitrogenous, fatty or saline matter. It forms an nnsubstantial diet, cannot bo substituted for meat and dry vegetables in soldiers' rations — and must always be combined with nitrogenous principles. Hence, whenever they can bo obtained, milk, fish and meat are added to it ; and even with the ut- most procurable quantity of these substances, it is questionable wheth- er the natives of rice-eating countries do not owe much of their lack of spirit and power to defective diet. 753. Diet required by Cbildren. — "We are remindcvl agam, by refer- ence to the preceding scale of equivalents, of the ill- adaptation of rice, sago, arrow-root, corn-starch, «&c., as diet for children. Milk, rich in nutrient matters, is their typical food. They require nitrogenous sub- stances, for the double purpose of present waste and growth. "When fed on the substances just mentioned, which lack both nitrogenous and mineral substances, fat may indeed accumulate, but the frame is weak and rickety, from small muscles and softness of bones. Children should have a full supply of blood-producing food — even bread contains too little for them — milk or flesh should be added. But whether fed on bread and milk, or meat and bread, there is apt to occur a deficiency of phosphate of lime, from the rapid formation of bone. But as meat, eggs and milk contain an excess of phosphoric acid, there being not enough lime to convert it all into phosphate, lime itself is a good ad- dition to the food of young children. It may be given in the form of lime-water, which the peasants of Germany give to their children with the best results, while the children greedily take it, guided by instinct. — (Geegoey.) 11. Thb Veqktabian Question. 754. The points In Controversy. — Strenuous objection to the use of animal diet has been made by many, and pure vegetable products com- mended as the best food of man. The controversy has been between the advocates of a mixed diet, of vegetable and animal substances, on tlie one hand, and the partisans of an exclusive vegetable diet, on the other ; the point of contention being the dietetical fitness of animal 'bod. The vegetarians, however, as a school, do not entirely proscribe animal diet. They generally admit tlie uso of eggs, milk, butter, and cheese, but repudiate fiesh. Mr. (JitAnAM recognizes the inconsistency of this course witli tlie true vegetarian tlicory, and regards the use of ihose substances with disfavor, tolerating them, as it might be, under THE VEGBTAKIAN QUESTION. 403 protest. The quarrel is an old and embittered one, and has been made to involve all sorts of considerations. "We epitomize and con- trast below, some of the arguments and objections which are most commonly started in the course of this discussion. ADVOCATES OF VEGETABLE DIET. Flesh diet involves the barbarous and unfeeling practice of destroying sentient life. In a state of primitive nature, man lived on vegetable products, fruits, and grains of the earth. Whatever may be true concerning the natural dietetic character of man, there is neither now on earth, nor has there been for many centuries, any portion of the hu- man race, which has lived in all respects so perfectly in a state of nature, as to af- ford us an opportunity to study man's true natural history and dietetic habits. .Ana- tomically, and in strict propriety, man must be regarded as an extinct species, that is, he has become so artificial in his dietetic habits, that they afford no evidence of his natural dietetic character. Man's al- imentar}' organs, if placed before us, afford no clear and determinate indications of his true dietetic character — his natural habits in this respect are wholly unknown, ex- cept as matter of history and tradition. — (Stlvestek Graham.) Vegetables afford the pure, first princi- ples of nature ; while animal products are drossy, corrupted, second-hand residues, from which the finer and subtler essences have been, as it were, exhaled and lost. ADVOCATES OF MIXED DIET. So does the necessary clearance of house- hold pests, and the insects and vermin in- jurious to the farm and garden. It is in- volved in the fundamental oixier of nature. If so, it was because he knew no better ; he is a progressive being, designed to be civilized, and improve his condition in numberless ways. The anatomical structure of man proves his adaptation to a mixed diet. The her- bivorous animals are enabled by numerous and variously-formed teeth to gnaw and grind, and by a longer digestive canal, and larger salivary glands, to digest substances which could not be sufficiently reduced by the differently structured and sharper teeth of carnivorous animals, nor dissolved by their smaller salivary glands, and shorter intestinal canal. In the structure of man's stomach and intestines, teeth and jaw- bones, salivary glands, and muscles of mas- tication, we find a medium between these extremes, which points to a compromise in his diet, and indicates that he was designed to use both forms of food. There is no proof of any such difference ; the foundation of our being is laid in ani- mal nutrition ; the infant in the early stages of its life, is exclusively nourished by its mother's blood and milk. It is ordered, at all events, that we shall not hegin our ca- reer as vegetarians, — a pretty distinct prov- idential hint t The meat of diseased animals being eaten, is liable to Introduce the same diseases, or others, into the human system. Animal diet excites and inflames the ani- xasH passions and propensities, favoring cru- Diseased meat is of course unwholesome, dangerous, and to be rejected ; but so are diseased grains, and damaged flour ; both •are liable to engender disease. But does not the carnivorous animal cat flesh because it is ferocious, that is, because 404 PHYSIOLOGICAL ETTECTS OF FOOD. elty and ferocity of disposition, as seen In the Creator has Implanted in tlthelnstlncto tho carnivora; whilo vegetable food pro- necessary to its acquirement of the food duces mildness and docility of disposition for which its orf^anization is destined; and (687). that the herb and grain eaters arc without this eavago nature, because they have no occasion for it, being Intended to derive their food from tho produce of the soil. But if wo admit that the habitual diet reacts upon, and tends to Iccep up the respective pro- pensities of these two classes, still there is nothing in vegetable food that necessarily induces mildness and docility. The ferocity of wild bulls, boars, bnffalos, &c., is well known. Our domesticated animals are not in their natural state, an active source of ex- citement and danger being removed, in the general mutilation of the males. "Wo can- not see the least ground for tho conviction, that a man, in good average health, with no plethoric excitability, will be in the least changed for the better by relinquishing his slice of mutton and potatoes for its equivalent in wheat-flour, or an omelet and custard-pnd- ding. And if the effect of universal vegetarianism were to be, to reduce the character of all mankind to the insipidity of said omelet, and the blandness of custard-pudding, we, for our part, should not like tho world half so well as we do now. A very excellent lady, who had kept a school for nearly half a century, said — ' I never liked the girls who were brought to mc with "very good characters" from their parents; they had cither no energy, or were very sly ; give mo the naughty children ; there is something in them to work upon, and a promise of future activity.' The emotions and propensities are the sources of all action, and if these be tamed down to tho vegetarian standard, we appre- hend that, neither will the better parts of human nature be called into energetic opera- tion by their own activity; nor will the worse call forth that energy for their repression, which is often the foundation of what is noblest in human character." — (Dr. Cabpentek.) Into the general question, as thus opened, wo do not propose to en- ter ; but simply to call attention to a few chemical and physiological facts, which appear to have been established, and which may enable us, perhaps, better to comprehend the present conditions, and more strict- ly scientific aspects of the subject. 755. Restricted Scope of Animal Transformations. — "We recall at this point tho statement repeatedly made, that the animal system is not to be viewed as capable of creating or fabricating the compound sub- stances which it employs in nutrition. Recent organic chemistry has profoundly modified the older views of this matter. In the ab- sence of all accurate information, the animal system was looked upon as endowed with unlimited and mysterious powers of transforma- tion; but we now understand that those powers are definite, and limited within a narrow range. It is not strange that, in tlie absence of exact knowledge, but little could be discovered in common between herbage and dried leaves of grass consumed by an ox, and the blood and texture of its body. But chemistry teaches us now that the very identical material of blood and tissue is i)repared in the vegetable, and that the office of the animal is chiefly limited to extracting and col- lecting it from its multifarious vegetable food; it can only appropri- ate pre-existing compounds. THE VEGETARIAN QUESTION. 406 756. Vegetable and Animal Principles the same. — We have furthei* seen that there is a remarkable identity of alimentary principles, whether derived from plants or animals. Vegetable and animal fats have the same substantial composition — are alike divisible into liquid and solid parts, with similar properties. And so the nitrogenous principles, vegetable and animal, are remarkable for their chemical similarity — in composition, the proportion of their elements, external properties, and modes and products of decomposition, vegetable albumen resem- bles animal albumen, and the same with casein and fibrin. The veg- etable principles, by simple digestive soluticm, are converted into blood and flesh, without decomposition, just as mineral substances may be dissolved and separated, again and again, without affecting their chem- ical integrity or essential properties. "Whether we go to the vegetable or animal world, therefore, we get the same nutritive principles, and we arrive at this twofold conclusion : that, while we may procure every thing adequate to complete and healthful sustenance from the vegetable kingdom, where it is all first fabricated ; on the other hand, we find substantially the same principles in the animal world, with only modifications of form, concentration, and solubility. It would seem from this point of view, that we may confine ourselves without detriment to the former source of aliment, or resort without injury to the latter. 757. Peenliar influence of Flesli Diet. — Yet there are important dif- ferences between vegetable and animal food ; in what do they con- sist? LiEBiQ observes, "Bread and flesh, or vegetable and animal food act in the same way with reference to those functions, which are common to man and animals ; they form in the living body the same products. Bread contains in its composition, in the fonn of vegetable albumen and vegetable fibrin, two of the chief constituents of flesh, and in its incombustible constituents, the salts, which are indispensa- ble for blood-making, of the same quality and in the same proportion as flesh. But flesh contains, besides these, a number of substances which are entirely wanting in vegetable food ; and on these peculiar constituents of flesli depend certain efiects by which it is essentially distinguished." Keference is here made to the peculiar constituents of flesh-juice which have been mentioned (471). Flesh is thus a com- plex product, containing peculiar principles, — a result of all the diges- tive and preparatiye actions of an animal organism ; and as the purpose of food is to re-produce flesh, it is evident that no dietetical preparation can eflfect this so perfectly, so rapidly, or with so little physiological labor as meat itself. Flesh is nearest to blood, and flesh 406 PHYSIOLOGICAL EFFECTS OF FOOD. of all aliments is most easily converted into both. The ingestion of flesh augments the proportion of fibrin in the blood, and increases the activity of nutrition. The heart being a tissue of muscular fibres, is more fully nourished ; the activity of the circulation is consequently increased. The excitation of this activity, observed after a copious meul of venison, is due not only to the abundance of albuminous mat- ters contained in the • venison, but also, probably, to its proportion- ately large quantity of kreatin. Highly animalized diet exalts the density and solid constituents of the blood, and increases the number of its corpuscles or globules; but does not augment the proportion of its albumen. This re-enforcement of the blood by con^ sumption of flesh, in heightening the general power of the system, of course, strengthens the passions and propensities. For this reason the term stimulating has been applied to flesh-diet. From its greater concentration, it is easier to over-eat with animal than with vegetable diet. As excessive alimentation is a universal danger, the vegetarian is most protected, though by no means safe ; for it is very easy to slide into excess upon a vegetable regimen, especially if eggs, milk, butter, and cheese bo freely used, as is very apt to be the case.* 758. Mineral Jlattcrs Replaceable In the two Diets. — But while vegetable and animal food yield precisely the same organic principles to the blood, tliey do not furnish to it identical mineral constituents, as was stated before. The phosphoric acid which appears in the blood in com- bination with the alkalies forming phosphates, when animal food is consumed, is replaced by carbonic acid, and the carbonates when we change to a diet of vegetables, and fruits. Bread gives rise to phos- phoric acid like flesh. We called attention to this most extraordinary fact — that a powerful, fixed, mineral acid, and a feeble, volatile, or- ♦ "The influence of diet over muscular fibre, is an important social question; for thews and sinews have always ruled the world, in peace and in war. In a proportion quite equal to brains. Indeed, it is a question which the present writer Is disposed to answer in the affirmative, whether nationally muscular and mental energy do not always run in couples und whether the flrst is not the cause of the second. It does not appear that any diet, so Ihoro bo plenty of it, is incapable of fitting a man to get through his daily work in a fufthion; but the best specimens of the species in their several sorts, hunters, agricul- turists, or citizens, are those nations who get most flesh-meat A collateral advantage of a moat diet to a nation is the dittlculty of obtaining it ; for tho truth, probably, is that the mode of procuring food has as great an influence over mind, manners, and muscles, as the nature of tho food itself. He that is satisfied with what ho can pick up, ready grown, degenerates either into a starved New Hollander, where food is deficient, or into an ttfeminato creature like the old inhabitants of the W est Indies, where it is abund.int ; while a civilized people with ' a care for their meat and diet,' will have thought about It, labored for it steadily, advanced science, and ransacked nature, to improve it, and ob- tained their reward in the search itself.' " — (Dr. Cuambkrs). THE VEGBTAEIAN QUESTION. 407 ganic acid, deport themselves alike, and produce exactly the same effects, in that most delicate and changeable of all chemical prepara- tions — the blood of the living body. "We can hardly suppose that these widely dissimilar substances would have been made so perfectly interchangeable under these circumstances, except to provide for the possibility of a mixed and variable diet. 759. Indications from the Saliva. — Attention has been called to the saliva, as affording a possible test of the kind of food adapted to different aunnals. Human saliva is much more powerful in its action than that of carnivorous animals, as the dog. This evidently points to a diet abounding in starch as proper for man, while the contrary is clearly indicated in reference to the dog. 760. Relative Economy of Vegetable and Animal Diet. — If the question present itself as one of economy on the largest scale, that is, under which diet the greatest number of human beings can be sustained on a given area, we must decide at once in favor of the vegetarian policy. All animals are organisms for the destruction of nutritive matter. "When an animal is slaughtered, it affords a mass of nutritive material ; but it is only a residue, — a small remaining part after life-long waste and destruction of food. The body of the ox represents, perhaps, thou- sands of bushels of grains and roots which it has consumed. If we ob- tained from him force, in the shape of work done, the loss was not total ; otherwise, a few hundred weights of beef is our sole equivalent for the destruction of many tons of vegetable food. The amount of nutritive material procurable upon a given surface of the earth, is de- finite and limited, and the inferior animals are machines for its de- struction ; in consuming them, we take what happens to remain, and besides the previous necessary loss, the nutriment we get comes in the worst possible shape in point of economy (744). If grains, legu- minous seeds, fruits, and roots, are cultivated — nutriments adapted to the sustenance of men ; and the lower animals be dispensed with, the conditions are provided for the largest human population. The great superiority of agricultural communities in numbers and power, over the hunting and flesh-consuming races, is thus obvious. The case was pithily put by a North American Chief, who, according to the French traveller Cre vigour, addressed his tribe as follows : "Do you not see the whites living upon seeds, while we eat flesh? That the flesh requires more than thirty moons to grow up, and is then often scarce ? That each of the wonderful seeds they sow in the earth, returns them a hundred fold ? That the flesh on which we subsist has four legs to escape from us, while we can use but two to pursue and 408 PnTSIOLOGICAL EFFECTS OP FOOD. capture it? That the gi-ains remain wliere the whites sow them, and grow ? That winter, -which with us is the time for laborious hunting, to them is a period of rest ? For these reasons have they so many children and live longer than Ave do. I say, therefore, unto every one that will hear me, that before the cedars of our village shall have died down -with age, and the maple trees of the valley shall have ceased to give us sugar, the race of the little corn-sowers, ■will have extermi- nated the race of flesh-eaters, provided their huntsmen do not them- selves become sowers." 761. Diversities of Diet among diflTerent Nations. — The adaptability of the human constitution to widely different dietetic conditions, is re- markable. "We find among the races distributed over the globe, the pure vegetarians, — some subsisting upon soft fruits, others upon hard grains, others upon succulent herbage, and others again upon tough fibrous roots. On the other hand, there are the exclusive animal feeders, some consuming flesh, others fish, others fowl, and others even insects ; — some devour their food raw, others cook it ; some take it as soon as it has ceased to live, and others wait till it turns putres- cent. Thus the diet of one locality would become loathsome and fiital in another. It has been aflSrmed that this dietetic pliancy of man, by which he is enabled to live upon the most strangely diverse forms of aliment, is a wise providential design to secure the diffusion of the human race, and the most extended occupancy of the earth. But though this be admitted, it brings us no nearer to a settlement of the question, " What form of diet is best suited to the full and harmonious and highest development of man's nature ? " that is one of the large and serious problems to which science will address itself in the future. 12. CONSIDEBATIONS OF DiBT. 762. "We conclude the subject of the physiological action of foods with some general and practical suggestions concerning diet, partly in recapitulation and partly supplemental. 763. Tlie demand for Food variable. — By recalling the purposes to which food is applied, wo perceive how changeable must be the de- mand for it. It is the source of power, and therefore, with the alter- nations of exercise and rest, its requirement rises and falls. It is the source of warmth, and therefore the quantity we need must vary with our protection from cold. Any cooling of the body increases the appetite, and compels us to eat more than usual. Again, the necessity for food is complicated with the conditions of breathing. The waste CONSIDERATIONS OF DIET. 409 of matter in the body stands in close relation to the oxygen it con- sumes, and this varies with capacity of the lungs, atmospheric purity and density, and therefore influences the quantity of food necessary to restore the bodily loss. A Manchester manufacturer ventilated his Aveaviug mill, when forthwith the appetites of the operatives were sharpened, and as their wages would just support them, they made formal complaint of the change, and demanded an advance of com- pensation. Thus the multiplex and ever-varying conditions of tem- perature, air, and exercise, joined with the diverse influences of age, sex, constitution, temperament, and habit, conspire to determine the necessity for food in each special case. 764. Diversities In Digestion and Diet. — There are also wide differ- ences among different persons in point of ability to digest and assim- ilate food. We meet with one class — types of robust health, with sound, vigorous systems, accustomed to much exercise in the open air, and who take all kinds of food, caring only that tliere shall be enough. They never suffer the slightest inconvenience from what they eat, and seem- indeed to be unconscious of having any stomach or visceral organs. All discriminations among aliments, as digestible and indi- gestible, with suggestions and precautions concerning diet, fall upon the ears of such as without signification. On the other hand, we behold the dismal group of dyspeptics, horribly conscious of their digestive arrangements, and to whom the whole world of aliment is turned into a perennial fountain of misery. Between these two ex- tremes there ai'e all degrees of digestive power and gastric suscepti- bility. Again we notice great diversities in plans of diet among those with healthy digestions. This state of things makes difficulty in fixing upon terms to describe different sorts of diet. Low diet, for ex- am2)le, is applied to a combination of food that yields less blood and strength than usual, while a high or generous diet tends to produce a contrary effect. But it is obvious that a diet which would be, to all intents and purposes, low and spare^ to a hearty meat-eater, might be high and generoiis to a strict vegetarian. To be able, therefore, to pronounce any particular diet abstemious or fall, we must understand the preceding dietetic habits. 765. Daily requirement of Food — These facts make it apparent, thai all rules of diet are necessarily so general as to be of little service, until modified to suit the peculiar circumstances of each individual. Instead of blindly submitting ourselves to any scheme of dietetic directions, we should exercise an independent judgment, studying carefully our own constitutional peculiarities, analyzing our conditions, 18 410 PHYSIOLOGICAL EFFECTS OF FOOD. and freely revising all rules before reducing them to personal practice. We cannot fix the precise quantity of food required to be consumed. Where men are dealt with systematically in large numbers, as the inmates of hospitals, soldiers, &c., it becomes necessary to establish diet scales, that is, to apportion to each person his due allowance of food by weight and measure. The following is the diet scale of the U. S. Navy : Three days in the week ; — pork, 16 oz. ; beans or peas, 7 oz. ; biscuit, 14 oz. ; pickles or cranberries, 1 oz. ; sugar, 2 oz. ; tea, I oz. ;=40| oz. Two days in the week; — ^beef, 16 oz.; flour, 8 oz. ; dried fruit, 4 oz. ; biscuit, 14 oz. ; tea and sugar, 2| oz. ; pickles or cranberries, 1 oz. ;=45| oz. Two days iri the week; — beef, 16 oz. ; rice, 8 oz. ; butter, 2 oz. ; cheese, 2 oz. ; biscuit, 14 oz. ; tea and sugar, 2} oz. ; pickles or cranberries, 1 oz.=45f oz. These numbers are valuable as near expressions of the wants of large bodies of men, under given circumstances ; but they are of small service as dietetical guides to individuals. 766. Regulating the Appetite. — We are left, therefore, in this matter entirely to individual discretion. Nature's guide is the appetite, but we must be cautious not to misinterpret its indications. In what hunger exactly consists we cannot tell. But the feeling seems to depend less upon the immediate state of the stomach (in respect of fulness or emptiness), than upon conditions of the general system, llenco the swallowing of food, although an immediate relief of hunger, does not at once extinguish the appetite. If therefore we eat slowly, prolonging the meal with deliberate and thorough mastication (634), time is given for the system to become conscious, as it were, of the progress of the supply, while the sense of quiescent satisfaction indi- cates that sufficient food has been taken, and that we should ceaso eating. If, on the other hand, wo neglect these monitions, bolting the aJiuientary mass, and driving on to repletion, we incur the double evil of over-eating, and of taking our food in a crude, half-prepared state. To obtain that command of appetite which shall enable us to abstain before we reach satiety, is every way most desirable, both as a means of preserving health, and of regaining it when lost. 767. Frequency and times of Eating. — Systematic recurrence is the order of nature, observed every where, alike in the timing of melo- dious sounds, the rhythmic beats of the heart, the measured respirations, the coming and going of light, the ocean's ebb and flow, seasonal revo* lutions and planetary periodicities. The arrangement of regular times for meals, harmonizes, therefore, with the universal policy of nature, and is, moreover, of the highest social convenience. Yet it is impos* CONSIDEBATIONS OP DIET. 411 sible to subject all to the same regulations of time. Dr. Combe re- marks : " The grand rule in fixing the number and periods of our meals is, to proportion them to the real wants of the system, as modi- fied by age, sex, health, and manner of life, and as indicated by the true returns of appetite." As the blood is usually most impoverished after the eight or ten hours' fast of the night, breakfast should be early (768). The stomach is usually vacated of its nutritive contents in about four hours after eating, but it may be an hour or two later before the blood begins to caU upon it for a renewed supply. Persons engaged in active labor, in which bodily expenditure is rapid, of course require to eat more often than the indolent and the sedentary ; and children need nourishment oftener than adults. But too long absti- nence, especially if the digestive power be not strong, sharpens the appetite, so that there arises danger of excessive eating. Some avoid luncheon for fear of 'spoiling the dinner,' whereas the thing they most need is to have it spoiled. Where the intervals between the meals are so long as to produce pressing hunger, something should be taken between them to stay the appetite and prevent over-eating. Late and hearty suppers are to be reprobated. Active digestion and sleep mutually disturb each other, as at night the exhalation of car- bonic acid is slowest, and tissue changes most retarded, the overloaded blood is not relieved, and invades the repose of the brain, producing heavy, disordered dreams, and nightmare, followed by headache and iU-humor in the morning. StUl there is the opposite extreme, of sit- ting up late, and going to bed wearied, hungry, and with an ' inde- finable sense of sinking,' followed by restless, unrefreshing sleep. • A little light nourishment in such cases, may prevent these unpleasant effects. Custom lias fixed the daily number of meals at from three to five ; probably three is the smallest number that consists with well- sustained vigor of the system ; four or five may be unobjectionable, the amount of nourishment taken each time being less. The essential thing is, regularity in each case, in order that the digestive glands may have time to prepare their secretions (641). 768. Rest before Meals. — We should not take our meals when tired out, or much fatigued. The stomach participates with the other parts of the system in the exhaustion, and is thus unfitted for the perform- ance of its proper and active duties. If there has been severe exer- cise, either of body or mind, a short interval should be allowed for repose, or half an hour may be appropriated to any light occupation, such as dressing, before sitting down to dinner. It is questionable if much exercise before breakfast be generally proper. When we rise in 412 PHYSIOLOGICAL EPPECTrS OP FOOD. the morning, the system has passed the longest interval without food, and is at the lowest dinrnal point of weakness from want of nourish- ment. It is well understood that the body is more susceptible to the morbid influence of colds, miasms, and all noxious agencies, in the morning before eating, than at any other time; and those exposed to the open air before getting any thing to eat, in aguish regions, are in- finitely more liable to be affected than those who have been fortified by a comfortable breakfast. Cases may be quoted, undoubtedly, in which early exercise has produced no injurious results — perhaps even the contrary. Yet in most instances, especially if the constitution be not strong, breakfast should follow shortly after rising and dressing, before serious tasks are attempted. Dr. Combe justly observes, that in "boarding schools for the young and growing, who require i)lenty of sustenance, and are often obliged to rise early, an early breakfast is almost an indispensable condition of health." 769. State of Mind daring Meals. — We have before seen how^ mental and passional excitement disturb appetite and digestion (685). The brain and stomach are profoundly sympathetic. Morbid states of the stomach often so disturb the brain as to throw a pall of gloom over the mind, or destroy its equanimity, as we often see in dyspeptics, ■while any mental tension or discord interrupts the gastric functions. Food has been rejected from the stomach, unaltered, several hours after it was taken, under the dread of an impending surgical opera- tion. During meals, therefore, every thing like intense mental exercise should be avoided, yet the mind ought to be lightly occupied, as in cheerful, exhilarating conversation upon passing topics. A flow of sprightly or sportive talk, that may agreeably engage the attention, and thus protract the meal, is not only most pleasant at table, but is of solid physiological service. This explains an observation of Dr. Chambers. " It is very common to hear bachelors complain that when they dine in company, their dinner gives them no trouble ; they swal- low all sorts of imprudent food, and feel no more of it, while a soli- tary meal at their club, on the plainest meat, is digested with diffi- culty and pain." 770. Exercise after Meals. — "When any portion of the body is strongly exercised, the whole system is taxed to sustain it. There is an unu- sual determination of blood to the excited part, with, of course, a cor- responding deficiency in other parts. The case of the two dogs is well known, both of which had taken a hearty meal, one being then left at rest and the other put upon the chase. After a short time they were both killed, when digestion was found far advanced in the one at rest, CONSIDERATIONS OF DIET. 413 wMle it vras not even begun in the other. The vital force required to promote digestion was diverted entirely to the muscular and nervous systems. There is some conflict of opinion as respects the propriety of exercise after a hearty meal, such as dinner. Dr. Beaumont says, " From numerous trials, I am persuaded that moderate exercise con- duces considerably to healthy and rapid digestion. The discovery was the result of accident, and contrary to preconceived opinions." Dr. Combe, on the other hand, observes " that active exercise immediately after a full meal, such as is generally taken for dinner, is prejudicial to its digestion, seems to be proved by daily and unequivocal experi- ence." "We conclude that physiological indications, the widest expe- rience, and the analogies of nature, concur to suggest rest for a time, or very gentle exercise, as most advisable.* There is clearly a de- pression of the general functions of the body, with a tendency to slug- gishness and repose. Inclination to rest after eating, seems to be a uni- versal instinct of the animal kingdom. To those who are drowsy and • " Beading has been too much overlooked of late as a bodily exercise, and the benefit has been doubted, because of the awkward manner in which it is done. Look at a Greek or Roman representation of a man speaking or reading ; he is standing np, or sit- ting back with the chest thrown well forward and dilated, the nostrils open, and the shoulders flatter and more erect than when walking. The artist's model evidently has the lungs filled with air, and the diaphragm at rest, so that full play is given to the elas- tic cartilages of the ribs. The man is rolling out his words really dare, as CBLStrs has it, comfortably to himself, and agreeably to his hearers. Observe as a contrast many a modern reader or orator ; his constrained attitude recalls rather the architectural incon- gruities of Gothic art, expressing, perhaps, the earnestness and self-denial which that style may be held to indicate, but certainly not wholesome ease. The head is bent for- ward, a stiff neck-cloth compresses the windpipe, the lungs are emptied, and the words are squeezed out by an effort of the diaphragm and abdominal muscles, which makes the listener fancy he can almost hear them creak with the strain. They are used at an enor- mous mechanical disadvantage, and the nervous energy of the whole trunk is foolishly exhausted. Hence, reading and preaching, instead of being a relief to gastric derange- ment, are nowadays found actually to produce it. The clergyman's sore throat and dyspepsia have often been traced to their professional work, and that which might have been a cure has become an aggravation. There was, some years ago, a quack in the Isle of Wight, who used to treat clergymen very successfully, under a promise of secrecy. His method was simply to teach them to keep the chest inflated, by breathing in only through the nose, and to allow it to empty itself by the elasticity of the cartilages as the patient spoke. This plan entails the habit of straightening the windpipe, sitting or standing upright, and throwing the shoulders back; in fact, of assuming the attitude which I have described as a model for the reader, and is for that reason found practically beneficial. If patients can sing, they possess a part of the Materia Medica very valuable to their digestion. They will seldom require the hints above given, for most leading masters have found the necessity for teaching their pupils a rational attitude, and the or- dinary time for exercising the art is the hour after the meal that most requires attention. It is striking how rarely powerful singers suffer from gastric derangement."— (Db. Cham BEBS.) 414 PHTSIOLOGICAI, EFFECTS OF FOOD. inclined to take their siesta, or after-dinner nap, we may suggest that it is better to sleep upright in a chair than to repose on a sofa or bed. In the former position the sleep is generally short, and never very pro- found ; but when the whole body is recumbent and the stomach full, the sleep is heavy, prolonged, and unrcfreshing. 771. Effects of Excessive Eating.— The consequences of uncontrolled indulgence of the appetite manifest themselves variously. The imme- diate result of over-eating is lethargy, heaviness, and tendency to sleep. The effect of persisting in the habit will depend upon numer- ous circumstances. In a healthy system, with good digestion and much active out-of-door exercise, bad results may not folloAv from the freest use of plain food. In other conditions the burden may fall upon the overworked digestive organs, which are irritated by the presence of the excess of food which they cannot appropriate. If digestion be strong, an excess of nutriment may be projected into the blood, over- loading the circulation. If food is not expended in force, the natural alternative is its accumulation in the system, increasing the volume of muscle and tissue, and swelling the deposit of fat. Degeneracy of the sti'uctures, mal-assimilation of nutritive material, increased pronenesa to derangement and diseased action, and various unhealthy conditions, may be induced by the habitual employment of too much food. It is either transmuted into fat and flesh, or into pain and disease. Yet it is very common to charge upon quantity/ the evils that flow from qual- ity/ in diet. Injury may spring from hearty indulgence in a rich, con- centrated, and various diet, which would not flow from the most lib- eral use of plain and simple food. ' Dine upon one dish, and in that consult your taste,' is an excellent motto. 772. Effects of InsnfDcient Nutrition. — The blood is the stock of ma- terial on hand, from which the supplies of the constantly wasting sys- tem are withdrawn, and this stock is but small. It contains dissolved only about one-eighth of the dry matter of the body, so that the strength can be sustained only a very short time without external sup- plies. Yet when food is withheld, life holds its ground against exten- sive changes. An animal does not die of starvation till it has lost two- fifths of its weight and more than a third of its heat. Yet, so impor- tant is the prompt and regular ingestion of aliment, to keep tlie sys- tem up to the par of its activity, that even transient interruptions pro- duce serious disturbance. As the demand for nourishment is the prime necessity of our being, taking precedence of all other needs, if the supply be suspended, the clamors of the system for food rise at once %bove all other wants. Until hunger is appeased, there is disquiet ; the CONSIDERATIONS OP DIET. 415 mind traverses witli less than its usual freedom, the temper is more easily started, and sleep falls to invigorate as usual. There was shrewd, practical wisdom in the warning of Cardinal De Eetz to politicians, never to risk an important motion before a popular assemblage, how- ever proper or wise it might be, just before dinner. Of the effects of insuflicient food Moleshott speaks as follows : " There is another in- Btinct by which the vigor of the mind is vanquished in a more melan- choly way. Hunger desolates head and heart. Though the craving foi' nutriment may be lessened to a surprising degree y Snlplmroiis Acid. — "When sulphur is burned in the open air, oxygen combines with it, producing sulphurous acid gas. It has a noxious odor, and if largely mingled with the air, is injurious to health. It is an active chemical agent, much used for bleaching, as may be illustrated by holding over a burning sulphur match, a red rose, which is immediately whitened. "Woollen, silk, and other garments are bleached by it. It is of a strongly acid nature and combines with alkaline vapors of the air, while it decomposes and de- stroys otlier substances, as sulphuretted and phosphuretted hydrogen. When an apartment is fumigated by burning sulphur, it is necessary to leave it ; it corrodes metiils. 809. Other Sabstances nsed for Disinfection. — Chloride of iron is a CHABCOAL HASTENS CHANGE OF MATTER. 43 ft cheap and efficient disinfectant, though it imparts a brown or bluish stain wherever its sohition falls. Chloride of zinc is equally efficient, but more expensive. Sulphate of iron (copperas or green vitriol) has strong disinfecting power. Either of these substances dissolved in water, (one, two, or three lbs. to the pailful,) thrown into vaults, cess- pools, or gutters, or over any foul masses of fermenting matter, exert not only a disinfecting and deodorizing action, but partially arrest putrefactive change. Acetate and nitrate of lead are strong disin- fectants. These substances are all solids. They do not assume tho gaseous form, but act, dissolved in water, by fixation of nc xious sub- stances as they arc set free. 810. Effects of Charcoal. — It is well known that charcoal is a power- ful deodorizer. Strewn over heaps of decomposing filth, or the bodies of dead animals, it prevents the escape of effluvia. Tainted meat sur- rounded with it, becomes sweetened. Foul water strained through it is purified. Placed in shallow trays in apartments where the air is ofiensive, it quickly restores it to sweetness, and even purges the putrid air of dissecting rooms. Charcoal has also a powerful attraction for coloring substances, and is used for bleaching sirups, liquors, &c., by filtration through it. 811. Mode of Action of Charcoal. — Charcoal produces these efiects in a particular manner, unhke any substance that has been noticed! Most, if not all porous solids, have the power of absorbing and con- densing gases within their minute interior spaces. Charcoal is ex- ceedingly porous, and has this property pre-eminently. A cubic inch of freshly burned, light, wood charcoal, will absorb nearly 100 inches of gaseous ammonia ; 50 or 60 of sulphuretted hydrogen, and nearly 10 of oxygen. The charcoals are not aU alike in efficacy. Animal charcoal — from charred animal substances — and peat charcoal, are both superior in absorbing and condensing power to wood charcoal. But how d oes this substance produce its effects ? It was formerly supposed, simply by sponging up the deleterious gases and retaining them in its pores. But later inquiries have thrown light upon this matter, and we now understand that by means of this mechanical condensation, charcoal becomes a powerful agent of destructive change. Chemical action is hastened in proportion to the nearness with which the atoms can be brought together. In the pores of the coal they are forced into such close proximity, as rapidly to augment the chemical changes. The condensed oxygen seizes upon the other gases present, producing new compounds, oxidized products. In this way ammonia is changed to nitric acid, and sulphuretted hydrogen to sulphuric acid. 440 CLEANSING THB AIB. In this way, charcoal promotes oxidation, so that instead of being ac antiseptic or preventer of change, it is really an accelerator of decom- position.* Tliis active property of hastening decomposition has been made medically available in the form of poultice, to corrode away sloughing and gangrenous flesh in malignant wounds and sores. Dr. Bird, in his work on the medical uses of charcoal, quotes several cases : Ave give one. " A man was admitted to St. Mary's hospital with a slough- ing sore upon bis leg. A poultice of this kind was put on, and in six hours the dead portion was reduced in size fully one-quarter. At the same time, the poultice thus made, effectually prevents any odor or putrefying exhalations proceeding from the slough and pervading tlio apartment." Dr. Stenhouse, who, in 1855, first drew distinct atten- tion to the fact, that charcoal is rather a hastener of decomposition than an antiseptic, has contrived ventilating arrangements in which the air of dwellings is filtered through charcoal. He has also a brcath-lilter or respirator, consisting of a hollow case of fine flexible Avire-gauze, which is mounted upon the face, as shown in Fig. 130. It is filled with coarsely powdered charcoal, so that all the air that enters the lungs is strained of its impurities. Charcoal is thus strongly commended as a disinfectant. It has many advantages over the preparations of chlorine, as it neither injures the texture of substances, nor corrodes metals, nor discharges the color of fabrics by contact, nor gives off dis- agreeable fumes. It is never in anj application or use, poisonous or danger- ous, but is entirely innocent, and in only one solitary instance can it become pernicious, and that is when it ceases to become charcoal, and is burnt in a perfectly closed room. Fio. 180. ♦ "I took the body of an English torrior, weight about ten lbs., placed It on a stone floor in a small apartment, and lightly covered it with charcoal; although the weather was very warm, not the slightest odor could be detected. By some accident the charcoal was disturbed, and a largo portion of the m.iss was loft uncovered ; in spito of this the circunijacent charcoal was sufficient to prevent any offensive stench. Upon seeing this, I left the body completely uncovered, merely surrounding it with the deodorizing agent; this again prevented any disagreeable smell. Having determined this fact, I a;ain cov- ered the carcass. In less than a fortnight not a pirticlo of flesh remained upon tho bones, which were picked perfectly clean, an i were of a snowy whiteness."— (Bikd oj« CUAKCOIU) POISONS, Am) THEIE ANTIDOTES. 441 v.— POISONS. 812. Poisous and Poisoaing. — Poisons are divided into three classes according to the way they act upon the system. Acrid or irritant poisons directly corrode or destroy the tissues with which they come in contact, and cause intense pain, but do not suspend consciousness. Strong acids, and alkalies, and indeed all poisonous metallic substances, belong to this class. I^arcotic poisons are such as produce stupor, as opium, carbonic acid. N'aj'coto-aerids, as tobacco, alcohol^ «&c., act both as acrids and narcotics. Some of these poisons may be arrested or neutralized in the system before producing fatal results, if measures are promptly taken, but no time is to be lost. Whatever is done, must be done at once ; the delay necessary to ransack books for anti- dotes, or to get a physician, may cost the victim's life. If severe pain in the stomach, vomiting, purging, &c., come on after a meal, poisoning is to be suspected. Something may be gathered from the demeanor of the poisoned individual, and a knowledge of circumstances. A person who has swallowed poison, by way of suicide, will be apt to be more silent about it than one who has taken it accidentally or to whom it has been administered purposely. 813. Resources in case of Poisoning. — ^If the vial or vessel from which the poison Avas taken be accessible, or if there be discolored spots upon the dress, and if on applying the tongue to either there is sourness, we infer that the poison is acid. In this case, or if it be known that an acid has been swallowed, chalk or whiting, mixed with milk, should be given copiously. If these are not at hand, plaster torn from the wall, or soap, may be substituted. Alkalies are given as an- tidotes to acids, and the reverse. Thus, poisoning by oxalic or sul- phuric acids may be remedied by soda or saleratus, while poisoning by pearlash would be arrested by vinegar. So if lime get into the eyes, it may be dissolved and washed out by moderately strong vinegar. The antidote for corrosive sublimate is eggs; for sugar of lead, epsora salts. If other or unknown poisons have been taken, the stomach should be freed of its contents as speedily as possible by an emetic, the readiest and best being a teaspoonful of mustard stinted up with warm water, its action being promoted by copious draughts of the latter. The poison called arsenic or ratsbane is not the metal arsenic, but the oxide of arsenic — a white, slightly sweetish insoluble powder. Being destitute of any decided taste, it is eminently fitted for the pur- pose of the poisoner, as it may be mingled with food without easy detection. Bat while this circumstance is fitted to tempt the mur- 19* 442 AKSENIC POISONING. derer, there follows anotlier which is fraught with sure retribution No poison is so ready and certain of detection as arsenic. And not only this, bnt " it is as indestructible as adamant. The corpse may decay ; the coffin fall to dust ; hundreds or thousands of years may pass, but underneath the mound of earth, in the spot where the corpse was laid, there is the arsenic." The best antidote to this poison is the hydrated sesquioxideof iron, which coiobines with it, forming an inert compound ; in the absence of this, milk, sugar, eggs, &c., may be given, and an emetic should be administered as quickly as possible to relieve the stomach of its contents : it must be prompt to be available. APPENDIX. A. ADDITIONAL LIST OF TEMPEEATUEE8. of; Lowest artificial cold 187° below zero, or 219° below freezing water Carbonic acid freezes 148° below zero, or 180° below freezing water. Lowest natural temperature at Yakutsk, in Siberia, 84° below zero. Estimated mean temperature of the North Pole, 13° below zero. Salt water of specific gravity 1-104, and oil of turpentine freezes, Wino freezes, ...... Jilood freezes, ...... Milk freezes, ...... Water freezes, '. ..... Alcohol boils In a Tacuum, .... Mean winter temperature of England, Temperature of hybernating animals, . . . Mean winter temperature "at Kome, Mean annual temperature at Toronto, . Putrefaction begins, ...... Cultivation of the vine begins at a mean annual temperature Mean annual temperature of New York, . Mean annual temperature at Eome, Cultivation of the vine ends. Water boils in a vacuum, .... Temperature of glow-worm and cricket, 8iIk-wonn hatches — temperature of germination, Tepid bath begins, ..... Acetous fermentation, ..... Putrefaction rapid, ..... Tepid bath ends, — warm bath begins, . Temperature in man — ^blood heat, . Warm bath ends, — vapor bath begins, . Cold-blooded animals die, .... Vapor bath ends, ...... Temperature in a boat In Upper Egypt, . Steamboat's engine-room (West Indies), Starch converted to sugar, .... Finland vapor bath, ..... Alcohol (specific gravity '794) boils, Water boils at the summit of Mont Blanc (15,860 ft, elevation), Water boils at an elevation of a mile, Water boils at the sea-level, ..... 14« 20" 25"* 30° 82' 86» 87.8" 88° 41° 48° 50° 50° 54° 69° 65° T2» 74° 77° 86° 95° 98° 99° 106° 180° 188° 155° 160° 170° 174° 182° 202° 212° 444 ArrEXDix. Syrup, 52 per cent, sugar, boils, ...... 216' Water of tlie Dead Sea boils, ...... 223° Syrup, 80 per cent, sugar, boils, ...... 264" Gypsum converted to plaster, ...... 291° B. We append an illustration of the astonishing scale of minuteness upon wliich even art has found it practicable to conduct her operations. Within a circle of but one-thirtieth of an inch in diameter — a mere visible dot, as we see in the figure, M. Fuomext, by an exquisite mechanical I contrivance, executed an elaborate piece of writing and engraving. | • Of course no result was visible to the naked eye ; but when the I work was placed under a compound microscope, its details came out, as we see in fig. 131, which is a transcript of the magnified view. With what marvellous accuracy were those infinitesimal movements performed. Fio. 181. QUESTIONS. PART I.— HEAT. Page IT.-l. SOURCES AND DISTRIBUTION OF TERRESTRIAL HEAT. 1 What is heat? What of its essence or nature? "What is stated of its importance? 2. How inucli heat docs the earth receive from the sun annually ? How do we ascertain the total amount of heat thrown off from the sun, and how much is it? 3. Is there any loss of solar heat? What may reasonably be inferred about the celestial movements of heat? "What are the results oi FouleVs researches? 4. "Why are unequal quantities of heat received from the sun at different places? What examples are given of the un- equal diffusion of heat ? Page 19.— II. INFLUENCE OF HEAT UPON THE LIVING WORLD. 5. What controls the distribution of plants upon the earth ? How do we see this cx- emplifled? 6. In passing from the equator to the arctic regions, what do we observe in relation to animals? Why is this? Are all animals equally subject to this influence? 7. Does temperature affect man also? How in the polar regions? How in the tropics? 8. How docs the dress of the West Indian contrast with that of the Greenlander ? What does Dr. Kane observe on this subject? 9. What is the effect of cold and warmth upon the animal body ? What controls the intensity of the action of external nature upon the senses ? What is the character of the people in cold countries ? In hot ? In temperate ? What is s.-iid concerning the appearance of great men upon the earth? 10. How may the scarcity of fuel affect national character? To what may the polished manners of the P-arisians be referred ? 11. What has been suggested concerning the relation of climate to language ? 12. In the absence of a natural defence from heat and cold, how does man shield himself? What is said of the art of producing artificial climate ? Page 2-3.— III. MEASUREMENT OF HEAT. 13. What is meant by the equilibrium of heat? Give an example. 14. What condi- tion must precede the tendency of heat to an equilibrium ? How are we enabled to be- come acquainted with it? 15. Howdoesheataflfect the bulk of bodies? Mentionsomo familiar examples. 16. What is said of the expansion of different substances by heat? What forms of matter exp.ind le.Tst ? What most ? Why is heat said to be imponderable ? 17. What is the principle of the thermometer? What is the freezing point? Boiling point? What are degi'ces ? IS. How is the scale of the common thermometer obtained ? How does it differ from the centigrade scale? From Reaumer's? 19. What does the word thermometer mean ? What mistake must wo avoid ? What docs it actually show us? 20. Why should the thermometer be in constant use in the family? 21. What points of temperature are given in the table ? 446 QUESTIOXS. Paoe 27.— IV. RADIATION OF IIEAT. 22. What is radiant heat? Arc all bodies radiators? Give an example. tS. Is the decrease In the force of heat as you recede from its source the same in all cases ? What Is the rate of decrease as you pass from a radiant point? Is it different with asu rfacc? 24. Wliat is said of the transparency of bodies to light and heat ? How do solar and arti- ficial light ditfor ? Mention the degree of transparency of various substances compared with air? 25. To what is the heating power proportional ? Why is not the air warmed by the direct rays of the sun? 26. When do bodies part with their heat most rapidly T What other circumstance affects radiation, and how ? What are the best radiators ? The worst? Give examples. How may the radiating power of a metallic surface be in- creased? Describe Kumford's experiment. 27. How does Di. Lardner explain the action of polished surfaces? 28. What vessels are best to keep their contents warm? What is said of tea-kettles, and pipes and stoves for warming rooms ? 29. What is said of the effect of color ? 80. What is reflected heat ? Why cannot a good reflector be warmed? IIow does the absorbing compare with the reflecting power in glass? How in polished silver? What is the difference between radiant and reflected heat? 81. Does color influence absorption? Describe Franklin's experiment What is the effect of a dark soil? Dark walls for grapes ? Dark clothing? 32. Do all bodies radiate heat? Explain Fig. 5. 83. Why are starlight nights colder than cloudy ones ? 84. What were the old ideas of the cause of dew? How does Dr. Wells explain it? What common phenomena are explained in the same way? What is meant by dew-point? 85. Why is dew more copious on some bodies than others? Why is there no dew on windy nights? What relation is there between cold nights and heavy dews? 36. Why is there no dew under trees? On cloudy nights? In valleys? 87. What is frost? What pre- cautions may be taken to prevent Injury from frost? Page 84.— V. CONDUCTION OF HEAT. 88. Explain Fig. 6. 89. What is said of the different conducting power of different sub vtanccs ? What bodies are the best conductors ? What are the worst ? 40. What is Eumford's table ? 41. How has nature protected the earth and animals from excessive cold ? What advantage have non-conducting materials in the walls of houses ? What is the comparative conducting power of the leading building materials ? 42. What is the difference in conducting power between moist and dry air? Why aro saw-dust, tan- bark, r's. table, 343. Bedrooms, air of, 171 ; ventilation of; 201. Beets 247. Beverages, 2S9. Blood, constituents of, 250, 347; globules, 347; alkaline, 370. Boiling, culinary changes by, 277. Boiling point, elevation of, 44. Bran, composition of, 235. Brain, measure of its change, 805; phos- phatic constituents of, 866; has its special nutriments. 867 ; excitants, 369. Braziers, 61, 62. Bread, from plain flour and water, 258 ; fer- mented, 2.59 ; objections to fermented, 207 ; unfermented, 268 ; raised by chemi- cals, 269, 270 ; heat of baking, 271 ; loss of weight in baking, 272 ; changes in tho crust, 272 ; in tho crumb, 272 ; moisture in, 278; good, 278; influence of salt on, 274; alum, 274; effects of lime water, 275; different kinds of, 276; white and brown, 277 ; coarse and fine, effects of, 389. Broth for the sick, 284. Buckwheat, composition of, 241. Burning fluids, composition of, 116; how explosive, 116 ; conditions of accident from, 117; how used with safety, 117. Butter, separation, of, 285; composition and [(roperties of, 2S6; cause of its change- ubleness, 315; cause of rancidity, 810; ac- tion of air upon, 316; subst:mces used t» preserve, 817. INDEX. 467 Cabbage, nutritive properties of, 244. Camphene, 115; combustion of, 115 ; why it spoils, 115. Candles, 108 ; stearic acid, 109 ; tallow, 109 ; spermaceti and wax, 109 ; structure of, 110; office of wick, 110; how it burns, 110; snulHng of, 111; shade for, 14S. Carbon, office in fuel, 49; heating effects of, 51. Carbonic acid, 161 ; physiological effects of, 162; in small quantities, 162; case of sui- cide by, 16'.i; necessity for, in air, 168; exhaled by respiration, 182. Carrots, 248. Casein, composition of, 228. Cataract, 136. Cellars, foul air in, 173. Changes in the living system, 326 ; rate of, 827; equaUzation of bodily, 362 ; hasten- ing and retarding, 363. Charcoal, as fuel, 53 ; as a disinfectant, 489 ; mode of its action, 439; respirator, 440. Cheese, preparation of, 288; changes by time, 817 ; influence in digestion, 391. Chevreul, 91. Chimneys, draught of, 55 ; causes of smoky, 56, 57, 58, 59 ; currents in summer, 200.- ■Jhocolate, 298 ; adulterations, 300 ; effects, 378. Cholera and foul air, 175. Dhuming, 285. Citric acid, 225. Cleansing, principles involved in, 422 ; by alkaline substances, 425; of textile arti- cles, 428; cottons, linens, and woollens, 429 ; of spots and stains, 430 ; agents for, 480 ; of the person, 431 ; of the skin, 483 ; of the face, 434; of the teeth, 485; of the air, 430. Climate, artificial, 22. Coal, mineral, 53, 54. Cocoa, composition, 298 ; preparation, 299 ; how used, 299. Coffee, varieties, 294; composition, 294; effects of roasting, 295; effects of time upon, 296 ; mode of preparation, 297 ; adul- teration, 297; how detected, 298; Lehman f on the effects of, 878. Cold, when most fatal, 858. Color, influence upon radiation, 80; upon absorption, 31 ; Newton's theory ot, 89 ; Brewster's theory, 89; complementary, 90 ; tints and tones of, 91 ; chromatic cir- cles, 92 ; contrast of, 97 ; miitually inju- rious. 98 ; contrast of tone, 99 ; harmonies of, 100 ; circumstances influencing, 101 ; associated with white, black, gray, 101 ; combining, 102 ; influence of, upon com- plexion, 102 ; arrangement of flowers, 103 ; paper-hangings, 103 ; furniture, 105 ; popu- lar recognition of the effects of, 140 ; asso- ciated heat of, 141. Combustion, products of, 50; air hinders, 55 ; within the body, 851. Common salt transparent to heat, 28; effect upon bread, 274; uses of, in the system, 371; contained in food, 372 ; mode of crys- tallization, 311 ; purification of, 812 ; how it preserves meat, 312; how it injures meat, 318 ; too little and too much, 377. Complexion, 102. Condiments, 891. Contagion and foul air, 175. Corn starch, 215. Cream, production of, 258. Culinary art, objects of, 256. Culinary utensils, 818 ; of iron, 813 ; of tin, 319; zinc, 320; copper, 320, 321; enam- elled ironware, 321 ; earthenware, 322 ; Porcelain ware, 823. D Dentifrices, 435. Dew, cause of, 32 ; dew-point, 158. Diet, for brain-workers, 368 ; mixed indis- pensable, 398 ; exclusive meat, bad econ- omy, 396 ; required by children, 402 ; of flesh, influence o^ 405 ; mineral matters replacable in, 406 ; economy of vegetable and animal, 407 ; diversities of, 408, 409 ; scale of U. S. Navy, 410, and the capacity of exertion, 415 ; order and variety in, 416, and corpulence, 417 ; of infancy, 417, 418; of childhood and youth, 419; of middle life, 420 ; of advanced life, 420. Diffusion of gases, 153. Digestion, object of, 830; in stomach, 888; extent of gastric, 340 ; influence of coffee on, 377. Dirt, composition of, 428. Disguising bad smells, 486. Disinfectants, 487 ; quicklime, 437 ; chlorine, 487; chloride of lime, 438; sulphurous acid, 438 : charcoal, 439. Double windows, 159. Dough, water absorbed by, 257 ; effects of kneading, 258 ; what makes it rise, 261 ; raising by leaven, 262; raised by yeast, 266 ; acidity in, 266 ; sugar in, 267 ; alco- hol in, 267 ; raised vrith esgs, 270. Dress, 21, 35 ; colors of, 102." E Ebullition, 42 ; effects of pressure upon, 44 Eggs, composition of, 250; preservation of, 318. Electricity, atmospheric, 164. Emerson's injector, 197 ; ejector, 198. Ether, luminous, vibrations of, 87. Evaporation, 42 ; cooling efl'ects of, 46 ; rate of, 159. Eye, sensibility to colors, 97 ; parts of, 127, 128 ; minuteness of images in, 129 ; adap- tation to light, 130 ; affected by conditions of the system, 130 ; influence of reading and writing upon, 181 ; cause of far-sight- ed, 132; remedy of far-sightedness, 133; cause of near-sighted, 134 ; remedy of near-sighted, 135 ; cataract in, 136 ; influ- ence of carbonic acid upon, 142 ; bad light inflames, 144. Faraday, Dr., 171. Fats, see Oils. Farina, 237. Farina kettle, 45. Fermentation, 200 ; conditions of, 260 ; dlf ferent kinds of, 260 ; spontaneous, 260. Fibrin, 228. 468 INDEX. Fire, kindling of, 50; risk of, 73; origin of, 74. Fireplace, form of, 62 ; action of, 62; econ- omy of, 63; ventilation by, 192. Flame, cause of, 50; illunination from, 106; hollowness of, 110; length of, in gas burn- ins, 123. flesh, composition of, 24S ; juico of, 249 ; action of heat upon, 281 ; changes by cooking, 282; loss of weight in, 282; best plan of cooking, 283 ; common method objectionable, 2S3; its juices acid, 371; digestion of, 388. Flour, white and dark, 236; evaporation from, 230 ; changes in, 236 ; eliects of its preparations, 889. Foods, why perishable, 300 ; conditions of perishableness, 301 ; effects of, may be un- derstood, 325; periodic supply of, 887; digestibility of, 341, 342, 343; changes in mouth, 330 ; in stomacli, 385 ; in intes- tines, 844 ; constipating and laxative, 346; final destination of, 847 ; produced by forces, 343; produces animal force, 349; unequal combustibility of, 351 ; heat-pro- ducing and tis.sue-maklng, 352 ; replaced by houses and clothing, 358; ash elements of, 369 ; demand for variable, 408 ; daily requirement of, 409. Force, production of, destroys tissue, 361. Freezing, artificial, 41 ; heat produced by, 42. Frost, cause of, 3.3. Fruits, composition of, 243 ; dietetic effects of, 391. Fuel, influence of, 22 ; composition of, 49 ; heating effects of, 54 Furniture, colors of, 104. G Gas fi.xtures, 124. Gas, illumination by, 119; sources of, 119 ; composition of, 120; purification of, 119; various sources of, 120 ; measurement of, 121; how burned, 122; contaminations of air, by burning of, 128; disadvantages of lighting by, 124 ; fixtures of, 124; is light- ing by,'injurious, 149. Gas meter, 121. Gastric juice, 83S; its acid and ferment, 339; quantity of, 341. Gelatin, 230. Gingerbread, 271. Glass, opaque to heat, 23. Gluten, 229 ; quality of, 232. Glycerine, 109. Gr.iin, grinding of, 234; structure of, 284; sifting of, 285. Grates, 04; combustion in, 64; Circular, 66 ; Arnott's, 66 ; height of, 67. Oum, artificial, 223; composition of, 223; physiological ctt'ects of, 384. H Heat, from the sun, IS; from the stars, 18; distribution of, 19; influence on vegeta- tion, 19; distribution of animal, 20; in- fluences man's development, 20; relation to character, 21; diffusion of, 2:J; equi- librium of, 23; expansion of, 23; weight of, 24 ; radiation of, 27, 29, 80 ; transmis- sion of, 28; absorption of, 29; exchanges of, 81 ; conduction of, 34; convection of, 86; circulation of, 87; capacity for, 38; latent, 39, 40, 41, 46; influence on the body, 4S; loss of, in room», 60; source of in rooms, 01 ; amount of bodily, produced, 860. Heating arraDgemcnts compared, 74. Honey, 217. Hot-air furnace, 70 ; ventilation by, 198. Hot-water apparatus, 72. Human body, purpose of, 348 ; constant temperature of, 353; how it loses heat, 854; how it produces heat, 354; resources against cold, 356 ; force e.xerted by, 860 ; limited action over food, 892 ; its restricted transforming power, 404. Hunger, use of, 829. Hydrogen, its oflice in fi'el, 50; heating powers of, 51. Hydrometer, 255. Illumination, artificial, 105 ; by ignition, 106 ; from burning gas, 106 ; simplicity of the laws of, 107; by means of solids, 108; by liquids, 112 ; by gases, 119. Impure air, and contagion, 175 ; cholera and, 175; fevers and, 176; scrofula and, 177; consumption and, 178; infant mortality and, 178 ; undermines the health, 179 ; morbid mental effects of, ISO. Indian corn, 239. Intestines, juices of, 844; changes in, 345; absorption from, 845. Jelly, vegetable, 226. Kneading, effects of, 258. Lactometer, 255. Lamps, 112 ; structure of, 118 ; astral, 113 ; Carcel, 114; sinumbra, 113; hot oil, 114: NeweU's 117 ; study, 148. Language, 22. Lead, vessels for water, 212. Leaves, nutritive properties of, 244. Lenses, 84. Lettuce, 245. Light, exhilarating effects of, 76 ; theory of, 77 ; diffusion of, 7S ; reflection of, 79, 80 ; scattered by air, 82; transmission of, 82 ; refraction of, 82 ; wave theory of, 87 ; arti- ficial, 105 ; ft'om ignition, 105 ; measure- ment of, 124 ; results of Ure and Kent, 126 ; color of artificial, 187; injurious action of artificial, 137. Liquefaction, 87. Liquors, alcoholic, 878 ; cannot replace wa- ter in the system, 879, and animal heat, 379; Bocker'8 observations, 379; not eco nomical, 8S ; stimulating effect, 380. Looking-glass, 79. Lyman's cold-air flue, 193 ; refrigerftto)' 801 Macaroni, 288. Malaria, 166. U INDEX. 469 Malic acid, 225. Margaric acid, 109. Marjiarine, 109. Mastication, importance of, 383. Meals, frequency in times of, 410 ; rest be- fore, 411 ; state of mind during, 412 ; ex- ercise after, 412 ; effects of excess at, 414. Melting points, 33, 111. Milk, composition of, 250; qualities of, 251, 252; cream of, 253; value of, 255; mineral matter in, 256; spontaneous curdling of, 287; curdlini; with acids, 237; -with ren- net, 23S ; preserving, 814 ; etfects of, 381. Mind, relation of, to matter, 864; its action destroys the nerves, 365 ; wears the body, 866. Moisture, in air, 157; in the air of rooms, 15S ; amount required in air, 1S3 ; the supply of, 194. Molasses. 221. M. Mouries, 277. Musical sounds, 85; scale, SO. N Night-air, 167. Nitrogen, 154 ; lowers the combustibility of food, 352. Nitrogenous principles, properties of, 230 ; names of, 231 ; destination of, 361. Non-nitrogenou8 principles, different values of, 395. Nutrition, effects of, insuiHcient, 414. Nutritive values, 395; scale of, 397; equi- librium of, 396; milk, .398; wheat, 399; aiiaptations of wheat, 899 ; coai-se bread, 400. O Oats, 289. Oils, proximate composition of, 109, 114; fluidity of, 114; kerosene, 118; sylvic, 118; volatile and fixed, 223; sources of, 223 ; proportion of in articles of diet, 224 ; ultimate composition of, 224; supply of, in diet, 3S4; accumulation of, 384; in stomach, 385; digestibility of, 886; rela- tion of to nutrition, 387 ; to consumption, Oleaic acid, 109. Oleaine, 109. Onions, 247. Oxygen, 49, 154 ; how it enters the system, 155 ; what it does in the body, 156 ; etfect of varying the quantity of, respired, 157 ; consumed by respiration, 181 ; consumed by combustion, 182; an exciter of decay, 302; destructive agency of, 350; action of, upon tissues, 362. Oxalic acid, 226. Ozone, 164. P Paper-hangings, colors of, 103; poisonous colors on, 173. Parr, Thomas, 328. Parsnips, 248. Pectic acid, 226. Peas, composition, 241 ; digestibility of, 390 Photometer, 125. Pictures, hanging of, 81 ; frames of, 104. Poisons, used to color candy, 222 ; how di- vided, 441 • how managed, 441. Potatoes, composition of, 245 ; water in, 245; starch in, 246; nutritive part of, 240; dry matter of, 246 ; ash of, 247 ; changed by cookincr, 280. Potash, 374. Preservation, by exclusion of air, 302 ; Ap. pert's method, 303; in canisters, 304; In Bpratt's cans, 305 ; at low temperatures, 306 ; by freezing, 306 ; in refrigerators, 807 ; fruits, 308 ; by drying, 309 ; by anti- septics, 311 ; by sugar, 313 ; by alcoliol, 814. Putrefaction, 269. Reflectors, 146 ; blue, 147. Kotina, Image formed upon, 129; loss of sen- sibility of, 144; paralysis of, 145. Eice, composition of, 241. Koots edible, dietetic effects of, 891. liye, anatomy of; 235 ; compositioji of, 288. Sago, 215. Saliva, flow of, 331 ; properties of, 332; uses of, 832 ; action in stomach, 340. Salts, 369. Shades, ground glass, 146 ; blue, 147 ; struc- ture and mounting of, 147. Simultaneous contrast of colors, 97. Skin, structure of, 431 ; impurities of, 432 ; cleansing of, 433. Smoke, 59, 00. Soap, how made, 425; hard and soft, 426; wate^ in, 426; varieties of, 427; its re- action with water, 428. Soda, 374. Solution, 208. Sound, transmission of, 85. Soup, preparation and properties of, 284 ; effects of, 381. Spectacles, 181 ; for the far-sighted, 133 ; for the near-sighted, 135; snggostious In selecting, 136 ; management, 137 ; pebble- glass, 137 ; colored gl.osses for, 148. Spectrum, 88. Specific heat, 83. Spermaceti, 109. Spitting, ett'ects of, 834. Starch, separation of, 218; proportion of, 214; grains, 214; sago, 215; tapioca, 215; arrow-root, 215; corn-starch, 215; com- position, 216 ; culinary changes of, 279 ; physiological effects oli 383. Steam, M-arming by, 73. Stearine, 109. Stearic acid, 109. Stomach, figure of, 835; layers of, 885; mo- tions of, 336 ; follicles of, 380 ; absorption from, 846. Stovepipe, 09. Stove, I'ranklin, 64; self-regulating, 63; air- tight, 68 ; best, 69 ; ventilation by, 193. Sugar, proportion from various sources, 210 ; artificially produced, 216 ; honey, 217 ; cane, 218; grape, 218; sweetening power, 218; production of brown, 219; compo- sition of brown, 219 ; fermentation of brown, 220 ; contaminations of brown, 220 ; refined, 221 ; candy, 221 ; culinary changes of, 278 ; as a preserver, 818 ; phy siological effects of, 883; refining of, 44, 470 INDEX. •fnptoca, 215. Tartaric acid, 225. Tea, 2S9; tiie slirub, 2S9; varieties, 289; fjreen and blaclc, 290 ; composition of, 291 ; how best made, 292 ; grounds. 292 ; adul- teration, 293 ; phy.siological effects of, 877. Tooth, .•J21 ; cloansins of,4;». Toriiporature, facts of, 27 ; of body constant, ;i5:{ ; regulation of bodily, 357 ; diet and daily changes of, 359. Therinoineter, 23, 24, 25, 26. Turpentine, spirits of, 115. Turnips, 248. Vegetables, influence of, in diet, 890. Vegetarian question, 402 ; statements of, contra-sted, 403, 404. Ventiducts, 19S. Vermicelli, 233. Vinegar, effects of, 892. Vision, conditions of, 76; value of the sense of, 126 ; how produced, 129 ; mechanism of, 128 ; optical defects of, 131 ; limits of porfrnt, 131 ; paralysis of the nerve of^ 145. Ventilation, of the person, 186; arrange- ments for, 192 ; by the fireplace, 192 ; by stoves, 193 ; by hot-air .irrangeuionts, 193 ; points to be secured in, 196 ; downward current in, 197 ; ascending current in, 198 ; by an additional flue, 200 ; of gas-burners, 20l ; of cellars, 202 ; should be provided for in building, 202 : involves loss of beat. w ■Warming by steam, 73 ; by hot water, 72 and ventilation best method of, 195. AVanning of rooms by air, 71. "Waste and supply, 228. AVater, its relations to heat, .39 ; evaporation of, 42 ; boiling of, 42, 43 ; spheroidal state of 44 ; solvent powers of 207 ; to hasten solution, 20S ; its dissolved gases, 20S, 209 ; varieties of, 208; rain and snow, 209 ; or- ganic contaminations of, 209 ; living in- habitants of, 210 ; their use, 210 ; its min- eral matter, 211; hard and soft, 212; in contact with lead, 212 ; supply of rain, 213 : for culinary uses, 280 ; physiological effects of, 874, 375 ; influences digestion, 875; change of tissue, 376; proportions of in foods, 894; as a cleansing agent, 422; filtration of, 423 ; its dissolved impurities, 424. Wave movements, &4. Wax, 109. "Wheat, composition of, 232 ; gluten in, 233 water in, 233; mineral matter in, 237 nutritive value of, 399. "Wood, water in, 51 ; heating value of, 52 soft and hard, 52. "Woody fibre, 278. Y Yeast, brewer's, 262 ; a plant, 263 ; domestic preparation of, 264; hops in, 266; drying of, 265 ; bitterness of, 266 ; acidity oL 266. Works on Chemistry. Class-book of Chemistry. BY E. L. YOUMANS. 12mo. 340 pages. Price 75 cents. Every page of this book bears evidence of the author's superior .ibility of perfectly conforming his style to the capacity of youth. This is a merit rarely possessed by the authors of scientific school- books, and will be appreciated by every discriminating teacher. While Chemistry is almost universally regarded by students as a dry and repulsive study (owing to the rigid and technical manner in which it is presented), Mr. Youmans' work will be found pre- eminent in clearness and simplicity of diction, by which the subject is made at once interesting and attractive. It is especially commended by the eminently practical manner in which each subject is presented. Its illustrations are dravra largely from the phenomena of daily experience, and the interest of the pupil is speedily 3,wakened by the consideration that Chemistry is not a matter belonging exclu- sively to physicians and professors. From Peof. Wm. II. Bigelow. The eminently practical character of the Class-book, treating o»' the familiar ap- plications of the science, is, in my opinion, its chief excellence, and gives it a value fiir superior to any other work now before the public. From David Stme, A. M., formerly Principal of the Math. Dept. and Lecturer in 2<'itt. Philosophy, C/iemistry, and Physiology, in Columbia College. Mr. Youmans : Dear Sir, — I have carefully examined your Class-Book on Chem- istry, and, in ray opinion, it is better adapted for use in schools and academies than any other work on the subject that has fallen under my observation. 1 hope that the success of your Class-Book will be proportionate to its merits, and that your etforts to ditfuse the knowledge of Chemistry will bo duly appreciated by the friends of education. From Peof. J. Mulligan, Principal of Young Ladies' School, New Tori: "We have a largo number of school-books for the purpose of giving elementary instruction in Chemistry — possessing various kinds and various degrees of merit ; but of all which I have examined, I should prefer the Class-Book of Chemistry, as the most perspicuous in stylo and method, and as containing the happiest selection of what is most interesting, and most practically valuable in the vast field of chemical science. From the N. Y. Commercial Advertiser. Either for schools or for general reading, we know of no elementary work on Chemistry which in every respect pleases ns so much as this. From, the Scientific American. Buch a book, in the present state of chemical science, was demanded; but to pre. sent the subject in such a clear, comprehensive manner, in a work of the size bafore us, is more than we expected. The author has happily succeeded in clothing his ideas in plain language— true eloquence — so as to render tho subject both interesting and easily comprehended. The number of men who can write on science and writo clearly, is small ; but our author is among that number. Works on Chemistry. Chemical Atlas: OS. THE CHEMISTRY OF FAMILIAR OBJECTS. ExiftBinxG trnt gkneeal prixciples op the science in a sep.ies ok beautiftjllt COLORED DiAGKAMS, AND ACCOMPAXIKD BV EXPLASATOUV FjSSATS, EMUUACINC THE LATEST VIEWS OF THE BUBJECIS ILLUSTRATED. DESIGNED FOR TUB USE OF STUDENTS IN ALL 8CU00LS WHERE CURMISTBY IS TAUGUT. • BY EDWARD L. YOUMANS. Large Quarto. 105 pages. Price S2. The Atlas iss a reproduction (in book form), and a continuation of the mode of exhibiting: cliemical facts and phenomena adopted in the author's " Chemical Chart." The application of the diagrams is here much extended, occupying thirteen plates, printed in sixteen colors, and accompanied by 100 quarto pages of beautifully'- printed explanatory letter-press. It is a chart in a portable and convenient form, containing many of the latest views of the science which are not found in the text-books. It is designed as an additional aid to teachers and pupils, to be used in connection with the author's Class-Book, or as a review, and for individuals who are studying alone. It is intended to accompany the author's Class-book of Chemis- try, but it may be employed with convenience and advantage in connection with any of the school text-books on the subject. From the Home Journal Ilore wo have scicnco in pictures— Chemistry in diasrams — eye-dissections of all tlie CDininon forms of matter around us; tlic clieinical composition and properties of all f:iniiliarol)iects illustrated to the most impressibleof our senses by the aid of colors, 'i liis is a beautiful book, and as useful as it is beautiful. Mr. Youmans has hit upon a happy method of simplifying and brinsrin;; out the profoundcst abstractions of sci- ence, so that they fall within tlio clear comprehension of children. From Vie Utica. Morning ITirald. An excellent ide.o, well carried out. The style is lucid and happy, the definitions concise and clear, and the illustrations felicitous and appropriate. From the Lawrence Sentinel. We have devoted some little time in looking over this Atlas, and comparina; its rilative merits with similar treatises heretofore published, and feel bound to accord to it the highest degree of approbation and favor. From Life fl/uMraf/'d. Tliis method of usin? the eye in education, thonch not the royal road to know- l.'ilf.'.', is really the peojde's railroad— a means of saving both tim'o and labor. This work is worth for actual instruction in common schools far more than a set of appar- atus, which the teacher might not be able to nse, while cverv one can teach from the Atlas. \V(! pronounce it, without e.vception, the best popular work on Chemistry in the English language. From the IVetc 5'orX- Trihune. Mr. Toumans Is not a mere routine teacher of his favorite Rcienco; ho has hit f.pon novel and elTective methods for tlie Illustration of its principles. In his writ- ings, as well as liis lectures, ho is distinguished for the comprehensive order of his statements, liis symmetrical arrangement of scientific farts, and the happy manner in which he aiTa B. Bogess, Professor of Cliemistry in the University of Pennsylvania. We cordially subscribe to the opinion of Professor Draper concerning the valuo to beginners of Mr. Youmaus' Chemical Chart. JOHN TOEEET, Professor of Chemistry in the College of Physicians <& Surgeons, 2^. Y, WM. n. ELLET, Late Professor of Cliemistry in Columbia College, S. C. JAMES B. EOGEES, Professor of Chemistry irithe University of Pennsylvania. From BENJAiirtJ Silliman, LL. D., Professor of Cliemistry in Yale College. I have hastily examined Mr. Youmans' New Chemical Diagrams or Chart of chcmicnl combinations by the union of the elementa iu atomic proportions. Tha design appears to bo an excellent one. Familiar Science. The Haiid-Book of Household Science. A POrULAR ACCOUNT OF Heat, Ligut, Aik, Aliment, and Cleansino, in their SciExnno PEiNciPLia AND Domestic Aitlications. . BY EDWARD L. YOUMANS. 12mo. Illustrated. 470 pages. Price $126. This work has been prepared to meet a long-acknowledged want in our schools. There is a strong and growing demand for that kind of knowledge which can be made available in the daily opera- tions of familiar life. Various books have been prepared which cross the field of domestic science at different points, but this is the first work that traverses and occupies the whole ground. Hardly a page can be opened to that does does not convey information in- teresting and valuable to every person who dwells in a house. The work will be found not only of high practical utility, but captivat- ing to the student, and unequalled in the interest of its recitations. Extract from the Preface. " The purpose has been to condense within the limits of a convenient manual the hirgest possible amount of intcrestinfij and valuable scientific inlbrniation of those as;ents, materials, and operations in which wo have a concern chiefly as dwellers in houses. "The subjects are treated somewhat in an elemcntaiy 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 ligiit, heat, and air, but they may be studied in various connections. There are many things about them which aperson, a.s a resident of a house, cares little to know, while there are others in which lie has a profound in- terest. To consider these, we assume to be the province of household sci- ence. The question of moisture in the air, for example, is one of universal Bcientific interest to meteorologists ; but it has also a special and vital im- port for the occupants of stove and furnace-heated rooms. Ditfurent 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 laily at her toilet, or engaged in furnishing her house. The agriculturist is interested in the composition of food as a producer ; the householder equally as a con- sumer. The doctor must know the constituents of air and its action upon the living system for professional purposes, and lie 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 cxamplca illustrate the loading conception of the present work." Natural Science. Class-Book of Physiology. BY B. N. COMINGS, M. D., PBOFESSOR OF PHYSIOLOGY, CHEMISTRY, AND NATURAL niSTOEY, IN CONNECTICUT STATE NORMAL SCHOOL. 12nio. 324 pages. Price $1. KEVISED EDITION, WITH AN APPENDIX. Professor Comings' thorough acquaintance with every depart- ment of Physiology, and his long experience as a teacher of that science, qualify him in an eminent degree for preparing an accurate and useful text-book on the subject. He has lost no opportunity of introducing practical instructions in the principles of hygiene, thus not only making the pupil acquainted with the wondrous workmanship of his own frame, but showing him how to preserve it in a sound and healthy state. Avoiding technical terms, as far as possible, he has brought the subject fully within the comprehen- sion of the young, and has clothed it with unusual interest, by ju- dicious references to the comparative physiology of the inferior ani- mals. Pictorial illustrations have been freely introduced, wherever it was thought they could aid or interest the student. Physiology cannot but be considered, by every intelligent and reflecting mind, an exceedingly interesting and necessary study. It makes us acquainted with the structure and uses of the organs of life, and the laws by which we may keep them active and vigorous for the longest period. The publishers would respectfully urge its importance on such teachers as have not heretofore made it a regu- lar branch in their institutions ; and would solicit, at the hands of all, an impartial examination of what is pronounced by good judges, " the best elementary text-book" on the science. From M. Y. Brown, Principal of Webster ScJiool, JVeio Haven. " I have used Comings' Class-Book of Physiology for nearly two school terms in the First Department of my school. I am happy to say that I regard it the bext text-book ou this important branch with which I have any acquaintance. The subjects are systematically arranjrcd ; the principles, facts, and illustrations are clearly and fully represented to the pupil. I find that liis introduction of Comparative Anatomy and Physics, tends greatly to increase the interest of the pupil in this most important and necessary study. I therefore can cheerfully recommend this admirable work to my fellow-teachers as one of rare excellence, and hope it may take the rank it deserves as a text- book upon this subject."' From Abraham Powelson, Jr., Teacher, J>rooH>/n., Keto TorTc. "After a very careful examination of the Class-Book of Physiology, by Comings, I tan freely say that I consider it a performance of superior excel- lence. It embodies a fund of information surpassing in importance and va- riety that of any other work of the kind which has come imdcr my notice." Natural Science. Analytical Class-Book of Botany. BY FRANCES H. GREEN. PAltT 1.-ELEMENT8 OP VEGETABLE STEPCTCKF. AND PHYSIOLOGY. PAET II.— SYSTEM- ATIC BOTANY. TO -WlllCn 18 ADDED A CCMPENDIOl'S FLOK.V OF THE NOKTUERN AND MIDDLE STATES ; WITH DESCRIPTIONS OF MORE THAN ONE THOUSAND DU'FER- ENT SPKCIES: BY Jo8. W. CoNGUON. niostrated Quarto. 228 Pages. Price $1 50. Primary Class-Book of Botany. Composed from the first tart of the analytical class-book, and designed for the use of common bchools and families. niostrated Qaarto. 102 Pages. Price 75 Cents. The style is simple, concise, and intelligible ; and what has for- merly been considered dark and forbidding, is here rendered both clear and interesting. The whole life of the plant, beginning with the formation of the first cell, is portrayed with that vivid and quickening power which invests it with the interest of a real biog- raphy. Here we find not merely a dry assemblage of dry facts, but the plant seems to unfold itself, part by part, with a kind of individual life and character. The work is illustrated with 400 well-executed wood-cuts. Most of these arc arranged in 29 plate-pages, which are designed to be used for regular exercises and recitations, the same as maps in geog- raphy. They furnish a recapitulation of the Lessons of tlie Text in a new form, and addressed to another sense, thus awakening the most lively and permanent impressions. Part II. is distinguished by the simplicity and directness of the whole structure, the clearness of the synopsis, the comprehensive- ness and popular character of the descriptions, the nice distinctions observed between nearly allied species, and the high degree of cer- tainty and perfection in the peculiar form of analj-sis. The descrip- tions of the Natural Orders arc illustrated by fifty elegant wood- cuts, drawn from nature. LEMy'08