COfflCLL^RlffCiiiTT Cornell University Library The original of tliis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924074241112 THE HAND-BOOK 07 HOUSEHOLD SCIENCE. IL POPULAB ACCODKT OP HEAT, LIGHT, AIR, ALIMENT, AND CLEANSING, IS THEIR SCIENTIFIC PRINCIPLES AND DOMESTIC APPLICATIONS. WITH mraiEEOUS ILLTJSTEATrVB DIAGBAMS. BT EDWARD L. YOUMAKSjM.D., AUTHOB OP **THK OliAflS-BOOK OF 0HBMI8TET," "-OUBMIOAI* ATLAS," "CnABT," &C. NEW YORK: D. APPLETON & 00., 443 & 445 BEOADWAY. tOHDON: 16 LITTLE BRITAIN. 1864. Gktsbsd according to Act of Congress, in the year 185T, by r>. APPLETON & CO, In tlio Clerk's Office of tlie District Gonrt of tlie United States for the flonthem District of New York. An edition of the present work has been issued, arranged with Questions for the use of Academies, Semi- naries, and Schools. CONTENTS PABT I.— HEAT. n.aa PREFACE, 7 INTEODUCTION, ,11 I. SouBCES AND DisTEiBnnoir of Tsbbestbiai. Heat, .... 17 n. InrnrENCB of Heat upon the Liteiq World, .... 19 III. MEASUBBUEin' OF Hbat — The Thebuoue'ceb, 23 rV. Kadiation akd its Effects, 27 v. CoNDncTioN OF Heat, and its Effects, 84 VI. Heat cosvetkd bt motinq Matter, .... 86 yn. Yarious fbofebties and effects of. Heat,. ... 37 VJXl. Phtsiological effects of Heat, . 48 IX. Artificial Heat — Peopeeties of Pdel, 49 X. AiE-cuEEEirrs — ^Action and hanagehent of Chiunets, ... 55 XL AfFABATUS of 'WABHINa, 60 1. Open fireplaces, 62 2. Stoves 67 3. Hot-air arrangemeats, 70 PABT n.— LIGHT. I. Katdeb of Light — Law of its Diffusion, 76 IL Beflection of Light, 79 [II. Transhission and Befbaction of Light, 82 rV. Theoet of Light — ^Wate movements in Nathee, .... 84 y. Composition and mutual belation of Colobs, 88 VI. Practical suggestions in combining Colobs, .... 103 IV CONTENTS. PAOS VII. 1'eodtiction of Abtifioial Light. 1. The Chemistry of Illumination, .... .105 2. Illumination by means of Solids, .... 108 3. Illumination by means of Liquids, 112 i. Illumination by means of Gases, 115 5. Measurement of Light, 1^ VIII. Structure and Optical powers of the Etb, 126 IX. Optical defects op Vision — Spectacles 131 X. Injceious action of Artificial Light, 137 XI. Managembht of Artificial Light, 1*6 PART m.— AIR. I. Properties and composition of the Atmosphere, .... 150 II. Effects op the constituents of Air. 1. Nitrogen, 164 2. Oxygen 15* 3. Moisture, 157 4. Carbonic acid 161 5. Ozone and electricity, 1*4 III. Condition of Air peotided bt Nature 165 IV. Sources op impure Air in Dwellings, 168 V. Morbid and fatal effects of impure Air, 174 VI. Rate of contamination within doors, 181 VII. Air in Motion — Currents — ^Draughts, 185 VIII. Arrangements foe Ventilation 193 PART IV.— ALIMENT. I. Source of Aliments — Obder of the subject, 206 II. GrENEBAL PROPERTIES OF ALIMENTARY SUBSTANCES. 1. Principles containing no Nitrogen. A Water, ... 20V B The Starches, 21* C The Sugars 2ie D The Gums, 223 B The Oil^ 223 F The Vegetable Acids, 22? 2. Principles containing Nitrogen. A Vegetable and Animal Albumen, 227 B Vegetable and Animal Casein, 228 C Vegetable and Animal Fibrin, 228 D Gelatin, 230 CONTENTS. \ t. Compound Aliments — ^Vegetable Foods. A The Grains, 231 B Leguminous Seeds, 241 C Fruits, 243 D Leaves, Leafstalks, etc., 244 E Boots, Tubers, Bulbs and Shoots, 245 4. Oompound Aliments — ^Animal Foods. A Constituents of Meat, 248 B Production and composition of Milk, .... 250 IIL Oolh^abt Changes of Aliuentabt Scbstancbs. 1. Combining the elements of Bread, 256 2. Bread raised by Fermentation, 259 3. Properties and action of Yeast, 262 4. Baising Bread without Fermentation, 267 5. Alterations produced in baking Bread, .... 271 6. Influence of foreign substances upon Bread, .... 274 7. Vegetable Foods changed by boiling,. .... 277 8. How cooking changes Meat 281 9. Preparation and properties of Butter, .... 285 10. Preparation and properties of Cheese 287 rV. Common Bevebages. 1. Properties and preparation of Tea, 289 2. Properties and preparation of Coffee, 293 3. Cocoa and Chocolate, 298 V. PbESEETATION op At.TMBNTABT SnBSTANCES. 1. Causes of their Changeableness, 300 3. Preservation by exclusion of Air, 302 3. Preservation at Low Temperatures, 306 4. Preservation by Drying, 309 5. Preservation by Antiseptics, 311 6. Preservation of Milk, Butter, and Cheese, ... 314 VI. Mateeials of Culinabt AND Table Utensils, 318 VII. Phtsiologioal effects op 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, 847 6. Production of Bodily Warmth, 853 7 Prodnctioh of Bodily Strength, 360 1 VI CONTENTS. PAQX 8. Mind, Body, and Aliment, ... ... 364 9. Influence of Special Substances. A Saline Matters, 369 B Liquid Aliments, 374 C SoUd Aliments 383 10. Nutritive value of Foods, 392 11. The Vegetarian Question, 402 12. Considerations of Diet, ....... 408 PART v.— CLEANSING. L Peincipai. Clbausing Agents, 422 IL Cleansins of Textile Abtioles, 428 IIL Cleansing of the Person, 431 IV. Cleansing op the Aie, 436 V. Poisons, 441 APPENDIX, 443 INDEX, . 445 PREFACE. A DEsntB to prepare a better statement than has hitherto been offered, of the bearings of science upon the economy of the household, has led to the following work. The' purpose has been, to condense •within the limits of a convenient manual the largest possible amount of interesting and valuable scien- tific information of those agents, materials, and operations in which we have a concern, chiefly as dwellers in houses. The subjects are treated somewhat in an elementary way, but with constant reference to their domestic and practical relations. Principles are universal; their applications are special and peculiar. There are general laws of light, heat, and air, but they may be studied in various connections. There are many things about them which a person, as a resi- dent of a house, cares little to know ; while there are others in which he has a profound interest. To consider these, we assume to be the province of household science. The question of moisture in the air, for example, is one of universal scien tific interest to meteorologists ; but it has also a special and vital import for the occupants of stove and furnace heated rooms. Different colors, when brought together, alter and modify each other according to a simple and beautiful law : and the Painter, the Decorator, and the Dyer, have each 2 technical interest in the principle ; but hardly more than the Lady at her toilette or engaged ia furnishing her house. Thi Agrici4turi8t is interested in the composition of food, as a prochicer; the Householder equally, as a consiomer. The VIU PKBFACB. Doctor must know the constituents of air and its action upon tlie Uving system for professional purposes, and lie studies these matters as parts of Ms medical education ; but for the same reasons of Ufe and death, the inhahitaats of houses are concerned to understand the same things. These examples illustrate the leading conception of the present work. Its preparation has been attended with grave difficulties. Of course, a volume of this compass can present only a compend of the subjects it considers. Heat, Ught, air, and aUment are topics of large extent, wide and complex in their principles, which are of boundless apph" cation, "We do not profess to have treated them with any completeness, but only to have brought distinctly forward those aspects which have been formerly too much neglected. In deciding what to state, and what to omit, we have been guided by two rules ; 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 found in common books nor included in the ordinary range of school study. As elementary principles may be found fuUy treated elsewhere, we have been brief ia their statement, thus gaining opportunity for important hints and views not generally acces- sible. Our chemistries are deficient in information of the composition and properties of food, while the physiological class-books are equally meagre in statements of its effects ; we have accordingly dwelt upon these points with something of the fiilness which their importance demands. So with heat, hght, and air. It is hoped that the following pages wiQ vindicate the fidelity with which we have labored to enrich the yolume with new and valuable facts and suggestions, not pro- curable in our family manuals or school class-books. Many of the subjects presented have recently undergone searching investigation. They are rapidly progressive ; facts are multi- plying, and views widening. "We have spared no pains to give the latest and most authentic results. Although the vol- ume is to a great extent self-explanatory, and adapted for fenuly and general reading, yet in the proper order of school PKEFACB. rX 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 difficulty, and requires to be managed as best we can. In works designed for general use they should be avoided as far as possible, and yet it is out of the question to think of escaping them entirely. If we would enjoy the thoughts of science we require to learn at least a portion of the language in which alone these thoughts are conveyed. The new objects and relations must be named, or they cannot be described and considered. We have studiously avoided obstructing the course of the common reader with many technical words, yet there are some which it was impossible to omit. The terms carbon, oxygen, hydrogen, nitrogen, carbonic acid, and some others, though hardly yet familiarized 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, — irom 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 PREFACE. BuitaMe statement. Exemption from errors can hardly be expected in a work of this kind — errors of oversight and errors of judgment. Besides, many of its questions are in an unsettled state and involve conflicting views. Tet the utmost care has heen 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. Youmans, for constant and invalua- ble aid in the preparation of the work, not only in various experimental operations incident to its progress, but also^in several parts of its literary execution. To his friend Mr. RiCHAED H. Manning, who, though engaged in absorbing mercantile pursuits, has yet foimd 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 work shall serve, in however small a degree, to ex- cite thought, to give additional interest to household phe- nomena, and awaken a stronger desire for domestic improve- ment, the labor of its preparation will not have been performed in vain. New Yobk, Augmt, 1867. INTRODUCTION. When a work is presented, claiming place in a systematic conrse of school study, two questions at once arise in the mind of the discrimi- nating educator : ji/rit, what is the nature, rank, and value of the knowledge it imparts? and, second, what wiH be its general influence upon the mind of the student? In this twofold connexion there are some thoughts to which we solicit fhe 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-hoxise and home," says Snt Henet "Wotton, " is the theatre of his hospitality, the seat of self-fruition, the com- fortablest part of his own life, the noblest of his son's inheritance, a kind of private princedom ; nay, to the possessors thereof an epitome of the whole 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 conrse 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 understand- xu rNTEODucnoir. ing and reason, he should yet have contrived to maintain so dense and perfect an ignorance of himself and the familiar objects by which ha 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 tiniversal 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 preliminary 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 speculaticn. 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, CoPEENicus struck out the grand law of celestial circulation before Hakvet discovered that of the blood. The genius of Fewton flashed an immortal light upon the mechanism of the universe, many years before EuMroED 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 Peiestly, 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 with the physical 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, as well as pro- gressive; from narrow views to universal principles; from empty speculations to world-wide utilities ; from the pleasure of a few to rNTEODuonoN. xiii the advantage of the many ; from utter ignorance and contempt of nature, to the revelation of aU-emhracing laws, and a beautiful and harmonious order in the commonest objects and operations of daily- experience. To tho- truth of this general statement, the existence of the present boot may be taken as a strong attestation. The mass ol its facts and principles are the result of recent investigation. A hundred years ago such a work would have been, in aU its essentia] features, a blank impossibility; indeed, it had lacked its richest mate rials if prepared for the last generation. These facts should not be without their influence upon the schemt of popular education. It is its first duty to communicate that infor- mation which can be reduced to daUy practice, and yield the largest measure of positive good. If recent inquiry has opened new treasures of available truth, it is bound to take charge of them for the general benefit. It must report the advance of knowledge, and Keep- pace with the progress of the human mind, or it is false to its trust. The subjects of study should be so modified and extended as to afibrd the largest advantage, intellectual and practical, of the labors of the great expounders of nature, — especially in those departments where knowl- edge can be made most useful and improving. A rational and com- prehensive, plan of education for aE classes, which shall be based upon man's intrinsic and essential wants, and promptly avaU 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 Bupereminent designation of ' educated.' There are many things, unquestionably, which it would be most desirable to study : but opportunity is brie^ 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 shaU 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 INTEODirCTION. Shall the thousand matters of mere distant and curious concernment be suiFered to hold precedence of the solemn verities of being which are woven into the contexture of familiar life ? The physical agents which perpetually surround, and act upon, and within us, heat, light, air, and aliment, are liable to perversion through ignorance,so as to produce suflfering, disease, and death; or they are capable through knowledge of promoting health, strength, and enjoyment. What higher warrant can be asked that their laws and effects shall become subjects of general and earnest study. It may seem strange that in regard to the vital interests of life and health, man should be left without the natural guidance of instinct, and be driven to the necessity of reflection and study ; that he for whom the earth seems made should be apparently less cared for in these respects than the inferior animals. Nevertheless, such is the divine ordination. Neither our senses, instincts, nor uninstructed faculties are snfiBoient guides to good, or guards from evil, in even the ordinary conditions of the civilized state. Things which most deeply affect our welfare, the senses fail to appreciate. They can neither discern the properties nor the presence of the most deadly agents. The breathing medium may be laden with noxious gases to the perU of life, and the senses fail to detect the dan- ger. Hunger and thirst impel us instinctively to eat and drink, but they fail to inform us of the nutritive value of alimentary substances or their dietetioal fitness to our varying requirements. For all those things which are independent of man's will. Providence has taken abundant care to provide ; while in the domain of voluntary action, blind instinct is replaced by rational forecast. Whatever may have been those original conditions of bare animal existence which some yet sigh for, as the 'true state of nature,' we are far removed from them now. They have been successively disturbed as, generation after generation, intelligent ingenuity has been exercised to gain con- trol of natural forces for the securing of comforts and luxuries, and to liberate man from the privations and drudgeries of the uncivilized condition. But unmingled good seems not permitted ; the benefits are alloyed with 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 the matter of ventilation. Gas- lighting was a great advance on the methods of artificial illumination but there came with it augmented contamination of the breathing medium and new dangers to the eyes. Against these and similar in- cidental mischiefs — ' residues of evil ' that accumulate against the pre- flominating good, there is no other protection than intellect, instructed INTEODUCTION, XV in the material conditions whioli inflnence our health and life, for these, and kindred . considerations of practical mojnent to all -who oc- cnpy dwellings and assume civilized relations, we urge the study of household science as an essential part of general education. It deserves to he hetter understood, that the highest value of science is derived from its power of advancing the public good. It is more and more to be consecrated to human improvement, as a sublime re- generative agency. 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 fuUy accepted in this relation is hardly surprising. The work of presenting scientiSc 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 flnds"^n 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 suooegsful 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 alle^ance 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 prodiices, we cannot accept. The view seems narrow and illiberal, and is not inspired of human sym- pathy. It took origin in times when the improvement of man's con- dition, his general education and elevation, were not dreamed of It came from the ancient philosophy, which was not a dispensation of pop- ular beneficence, an all-diffusive, ennobling agency in society, but con- fessed its highest aim to be a personal advantage, shut up in the indi- vidual soul. It was not radiant and outflowing like the sun, but drew all things inward, engulfing them in a malstrom of selfishness. The baneful ethics of this philosophy have given place to the higher and more generous inculcations of Christianity, which lays upon hu- man nature its broad and eternal requu-ement, 'to do good.' From XVI INTEODirCnOS'. this authoritative moral demand science cannot be exempted. The power it confers is to be held and used as power is exercised by God himself, for 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, fact and law. To the poetic day-dreamer it may be an affair of sentiment, an ' illusion,' or a ' vapor,' but to the mass of mankind, life is a solid, unmistakable reality, that wiH not dissolve into mist and cannot be conjured out of its qualities. As such, we would deal with it in education, giving prominence to those forms of knowledge which will work the largest practical alleviations and most substantial improvement throughout the community. But it is wisely designed that those studies which may become in the highest degree useful are also first in intellectual interest. It is a grievous mis- take to suppose that the study of natural science martyrizes the more ethereal faculties of the soul, and dooms the rest to painful toil among 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 be restrictive of mental sweep, which unlocks the mysteries of the universe and pioneers its way far into the councils of Omniscience ? "Who was it that lifted the veil, and disclosed a new world of exquisite order and beauty in all the commonest and vulgar- est forms of matter, below the former reach of eye or thought? "Who was it that dissipated the fabulous 'firmament,' which primeval igno- rance had mounted over its central and stationary earth ; set the world in motion, and unfolded a plan of the heavens, so appalling in ampli-' tude that imagination itself falters -in the survey? Who was it that first read the handwriting at 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 forget its elevating tendencies; for in con- templating the varied scheme of being around, its beauties, harmonies, •adaptations, and purposes of profoundest wisdom, the thoughts ascend in unspeakable admiration to the infinite Source of truth and light. We should educate and elevate our nature by these studies^ storing our iNTEODtrcrioir. xvii minds with the richest materials of thought," enlarging our capacities of benign exertion, and rising to a more intimate communion with the spirit of the Great Meier of all. But beyond these considerations, physical science has another claim npon the Instructor, in the kind and extent of the mental discipline it affords. The study of mathematics has a conceded value in this rela- tion, being eminently favorable to precision and persistence of the mental operations — ^to steadfast concentration of thought upon ab- stract and difficult subjects. But we hope not to incur the charge of educational heresy,by expressing the opinion, that its training is some- what defective — is neither sufficiently comprehensive, nor altogether of the right kind. Its influence is limited to certain faculties only, and the method to which it accustoms the mind is too little available in grappling with the practical problems of life. The starting-point of the mathematician is certain universal truths of consciousness, intui- tive axioms — assumed without proof, because they are self-evident, and therefore incapable of proof. From these, by various operations and chains of reasoning, he proceeds to work out special applications. Hia direction is from generals to particulars — it is inferential — deductive. But when we come to deal with the phenomena of the external world, and the actualities of daily experience, this plan fails, and we are driven to the very reverse method. In the phenomenal world we are without the eternal principles, settled and assumed at the outset ; these become themselves the objects of investigation ; they have to be established, and we must begin with particulars, special inquiries, experimental investigations, the observation of facts, and from these we cautiously proceed to general truths — to universal principles. The process is an ascent from particulars — generalization — inditc- tion. That the whsle 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 oimdueUon — ^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- XVUl INTRODUCTIOK stead of beginning with tlie facts, and carefully evolving the general laws. The splendid achievements of modern science are the fruit of the inductive method. This should be largely joined with the mathe- matical to secure a full and harmonious mental discipline. It edu- cates the attention by establishing habits of accurate observation, strengthens the judgment, teaches the supremacy of facts, cultivates order in their classiScation, and develops the reason through the es- tablishment of general principles. It is claimed, as an advantage of mathematics, that it deals with certainties,' and, raising the mind above the confusions and insecurities of imperfect knowledge, habituates it to the demand of absolute truth. That benefits may arise from this exalted state of intellectual requirement, we are far from doubting, and are conscious of the danger of resting satisfied with any thing short of perfect certitude, where that can be attained. But here again there is possibility of error. Mathematical standards and pro- cesses are totally inapplicable in the thousand-fold contingencies of common experience ; and the mind which is deeply imbued with its spirit, is little attracted to those departments of thonght, where, after the utmost labor, there still remain doubt, dimness, uncertainty and entanglement. And yet, such is precisely the practical field in which our minds must daily work. The mental discipline we need, there- fore, is not merely a narrow deductive training of the faculties of cal- culation, with their inflexible demand for exactitudes ; but such a sys- tematic and symmetric exercise of its several powers as shall render it pliant and adaptive, and train it in that class of intellectual opera- tions which shaU best prepare it for varied and serviceable intellec- tual duty in the practical affairs of life. There is stUl another thought in this connection which it is im- portant should be expressed. It has been too much 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 the patronage of civil and ecclesiastical despotisms, 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 has been that aU 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 IHTEODUCnON. XIX of things has heen deeply disturhed. 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 stiU retains much of its ancient spirit, is yet largely scholastic and arbitrarily authoritative. We believe that this evil may be, to a considerable degree, corrected by a frank admission of the incompleteness of much of our knowl- edge; by showing that it is necessarily imperfect, and that the only just and honest course often involves reservation of opinion and suspension of judgment. This may be consonant neither with the teacher's pride nor fhe pupil's ambition, nevertheless it is imperatively demanded. We need to acquire more humility of mind and a sincerer reverence for truth ; to understand that much which passes for knowledge is unsettled, and that we should be constant learners through life. The active influences of society, as well as the school-room, teach far other lessons. We are com- mitted in early childhood to blind partisanships, — political and religious, — and drive on through life in the unquestioning and unscru- pulous advocacy of doctrines which* are quite as likely to be false as true, and are perhaps utterly incapable of honest definitive adjustment. Science inculcates a different spirit, which is most forcibly illustrated in those branches where absolute certainty of conclusion is difficult of attainment. Mr. Pa&et has urged the salutary influence of the study of physiology in this relation. He says, " It is a great hindrance to the progress of truth, that some men will hold with equal tenacity things that are, and things that are not, proved ; and even things that, from their very nature, do not admit of proof. They seem to think (and ordinary education might be pleaded as justifying the thought) that a plain 'yes' or 'no' can be answered to every question that can be plainly asked ; and that every thing thus answered is to be maintained ' as a point of conscience. I need not adduce instances of this error, while its mischiefs are manifested every where in the wrongs done by premature and tenacious, judgments. I am aware that these are faults of the temper, not less than of the judgment ; but we know how much the temper is influenced by the character of our studies ; and I think if any one were to be free from this over-zeal of opinion, it should be XX rNTEODUCHON. one who is early instructed in.an uncertain science sucli 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 (he 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 work of discovery and improvemMit 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 ia destined, and which will be hastened by nothing so much as a more general kindling of the minds of the young with enthusiasm for science. The harvest awaits the reapers — ^how strange that man should have neglected it so long. Fuel, air, water, and the metals, as we see them acting together, now, in the living, laboring steam-engine, have been waiting from the foundation of the world for a chance to relieve man of the worst drudgeries of toil. Long and fruitlessly did the sunbeam court the opportunity of leaving upon the earth permanent impressions of the things he revealed ; while the lightning, though seemingly a lawless and rollicking spirit of the skies, was yet impatient to be pressed into the quiet and useful service of man. Can there be a doubt that other powers and forces, equally potent and marvellous, await the discipline of human genius ? Not in vain was man called upon, at the very morning of creation, to 'subdue the earth.' Already has he justified the bestowment of the viceroyal honor : who shall speak of the possibilities that are waiting for him in the future 1 THE HMD-BOOK OF HOUSEHOLD SCIENCE. PART FIEST. HEAT. I. SOURCES AND DISTEIBUTION OP TERRESTEIAL HEAT. 1. Nature of our Knowledge eonceming Heat. — ^When we place the hand upon a stove with a fire in it, a feeling of warmth is experienced, while if it be made to touch ice, there is a sensation of cold. The im- pressions are supposed to be 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 different feelings by moving in opposite directions, and which makes the difference be- tween summer and winter, nobody has yet discovered. It is named lieat. Some have conjectured it to be a kind of material fluid, exceed- ingly subtle and ethereal, having no weight, existing diffused through- out all things, and capable of combining with every known species of matter ; and this supposed fluid has received the name of caloric. Others 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, moves through it, and is capable of variously changing its conditions. It is an agent producing the most wohderfnl results every where around and even withiu us ; — a force of such tremendous energy, such far-reaching, all-pervading influence, — ^that we may almost venture to say it has been appointed to take control of the material universe ; 18 SOUECES 01" TEEEBSTEIAL HEAT. while in the plan of the Creator, it is so disciplined io the eternal re- straints of law, as to become the gentle minister of universal benefi- cence. 2. To what Extent the Earth Is warmed 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 falls upon a square foot of the earth's surface in a year would be suflBcient to melt 5400 lbs. weight of ice ; and as a cubic foot of ice weighs 54 lbs., the heat thus annually received would melt a column of it 100 feet high, or a shell of ice enveloping our globe 100 feet thick. As the sun turns 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 suflScient to melt it in the course of a year. This quantity of heat would melt a shell of ice enveloping the sun's surface 38.6 feet thick in a minute, or 10.6 miles in thickness in a year. "We are, therefore, warmed by heat-rays shot through a hundred million miles of space, from a vast self-revolving grate having fifteen hundred thousand miles of fire-surface heated seven times hotter than our fiercest blast furnaces. 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 ; he not only warms the earth, but assists to warm the universe. Our globe catches a trifiing 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 does, all the other stars and planets are also doing. A mighty system of exchanges (32)* is estab- lished among the bodies of space, by which each radiates heat to all the rest, and receives it in turn from all the rest, according to the measure of its endowments. The whole stellar universe thus contrib- utes to our warmth. It is a startling fact, that if the earth were de- pendent alone upon the sun for heat, it would not get enough to make the existence of animal and vegetable life possible upon its surface. * Tliese nombers refer to paragraphs. rrs tnsEQUAi, disteibdtion. 10 It results from the researches of Pothllst, that the starry spaces fur- nish heat enough in the course of a year to melt a crust of ice upon the earth 83 feet thick, almost as much as is supplied by the sun. This may appear strange, when we consider how immeasurably small must be the amount of heat received from any one of these distant bodies. But the surprise vanishes, when we remember that the whole firmament of heaven is so thickly sown with stars, that ia some places thousands are crowded together within a space no greater than that occupied by the fuU moon. (Dr. Laednbe.) 4. Heat onequallr Distribnted upon the Eartb. — The quantity of heat which the earth receives from the sun is very unequal at different times and places. The earth turns around every day ; it is globular in form, and is constantly changing the position of its surface in rela- tion to the sun, as it travels about him in its annual circuit. The con- sequence is, that we receive more heat during the day than at night ; more at the equator than toward the poles ; more in summer than in win- ter. "We are all aware that the temperature may fall from blood heat at mid-day, to the point of frost or freezing at night ; and while at the equator they have a temperature averaging, the year round, 81-5 degrees, at 'Kew York (less than 3,000 miles north), the average annual heat falls to 50 degrees ; and at Labrador (less than a thousand miles further north), the average temperature of the year sinks below freez- iag. 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 dififerent seasons: thus while New York' has the summer of Eome, it has also the winter of Copenhagen. n.— INFLUENCE OP HEAT UPON THE LIVING WORLD. 5. It Controls the Distribution of Vegetable Lifei — ^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 stOl colder regions, these again give way to others of a hardier nature, or which are capable of 20 iKFLxnarcE or heat xtbon the LiviNa 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 helts of varying vegetation, which are, as it were, definitely marked off by the different quantities of heat which they receive. " In the tropics we see the palms, which give so striking a characteristic to the forests, the broad- leaved bananas, and the great climbing plants, which throw them- selves from stem to stem, like the rigging of a ship. Next follows a zone described as that of evergreen woods, in which the orange and the citron come to perfection. Beyond this, another of deciduous trees — the oak, the chestnut, and the fruit trees with which, in this climate, we are so well acquainted ; and here the great climbers of the tropics are replaced by the hop and the ivy. StUl further advanc- ing, we pass through a belt of conifers — ^flrs, larches, pines, and other needle-leaved trees — and these, leading through a range of birches, which become more and more stunted, introduce us to a region of mosses and saxifrages, but which at length has neither tree nor shrab ; and finally, as the perpetual polar ices are reached, the red snow algae is the last trace of vegetable organization." 6. Heat Eegnlates the Distribution 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- clines. Some are adapted to the alternations of winter and summer by changes of their clothing ; and others, as birds, are pursued from region to region by the advancing temperatures. Animals whose con- stitutions are conformed to one condition of heat, if transported to another, suffer and perish : while the lion is confined \o his torrid desert ^f 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 Development.— Nor does man fur- nish an exception to these controlling effects of temperature. The striking peculiarities of physical appearance and endowment, exhibited by different tribes and communities of men, is well known ; and it has long been understood that, much of these differences is due to the aU- powerful influence of heat. " The intense cold, dwarfs and deforms the inhabitant of the polar regions. Stunted, squat, large-headed, fish- featured, short-limbed and stiff-jointed, he resembles in many points the wolves and bears in whose skins he wraps himself. As he ap- proaches the sunny south, his stature expands, his limbs acquire shape IT AFFECTS MIND AND CHAEAOL'EB. 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 Different Localities.— The remarkable contrasts of temperature which different races experience, is well illustrated by theu- 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 aftei- layer of woollens and fura, 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. Kaste obseryes, " 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. Temperatnre and Character.— The effect of cold is to benumb the . body and blunt the sensibility ; while warmth opens the avenues of sensation, and increases the susceptibility to external impressions. Thus, the intensity with which the outward world acts upon the inward through the sensory channels, is regulated by temperature. In cold countries the passions are torpid and sluggish, and man is plodding, austere, stolid, and unfeeling. With the barrenness of the earth, there is 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, dehghting in the gorgeous, the daz- zling, and the marvellous. In the medium heat of temperate dimates, 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 oi the imagination. By comparing the efifeots 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, hut even on our bodily well- . 22 INi'LUJilNCE OF HEAT UPON THE UTING WORLD, being. It is mtliin a narrow range of climate that great men hava been born. In the earth's southern hemisphere, as yet, not one has appeared ; and ia 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 fellows, so that by a word, or even by a look, he can electrify, and guide, and govern mankind." — (Dr. Deapee.) 10. Inflnence of the Supply of Fuel. — 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 fael 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 afflicts the whole nation with blear eyes. Scarcity of fuel has not been without its effect in forming the manners of the polished Parisians, by transfer- ring to the theatre and the caf6 those attractions, which, in countries where fuel is common and cheap, belong essentially to the domestic hearth. 11. TemperatiiTe and Langnage. — Aebttthnot 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 aniiong the northern nations, was owing to their reluctance to open their mouths wide in cold air, which made their speech abound in consonants. From a contrary cause, the inhabitants of warm climates formed a softer language, and one abounding in vowels. The Greeks, inhaling air of a happy medium, were celebrated for speaking with the wide-open mouth and a sweet-toned, sonorous elocution. 12. Man may Make Us own Climate. — So controlling is this agent, and yet man comes into the world defenceless from its invasions; provided with no natural means of protection from its disturbing and destructive influence. But in the exercise of that intelligence which gives him command over nature, he has studied the laws, properties, and effects of heat, and the methods by which it may be produced IT ESTLUENCES THE DIMBNSIONS OF BODIES. 23 and.regulated. He has devised the means of creating an artificial and portable climate, and thus of releasing himself, in a great measure, from the vicissitudes of temperature. "We are to regard the production and control of artificial climate, as an art involving the development and expansion of mind and body, the preservation of health and the prolongation of life. Such has been the thought expended upon this subject, and so important the results to the •well-being of man, that we may almost venture to measure the civilization of a people, by the per- fection of its plans and contrivances for the management of heat. m.— MEASUEEMENT OF HEAT. THE THERMOMETER. 13. Heat tends to Equal Diffnsloii. — ^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 eqnal 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 aeqnainted 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 halanee of heat, causing it to leave some bodies, and accumulate in others in xmusual 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 qiumtity of it which a body possesses ? 15. Heat aeenmidating In Bodies, enlarges thenii — ^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 yaM-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 24 MEAStrEEMEaST .OF HEAT. 212' pints of water, taken at the freezing point, woflld 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. (Gteaham.) When 180 degrees of heat are added to iron, 1000 cubic inches become 1045 ; 1000 cubic inches of air become 1865. 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 greattest at freezing, or 32°, the expansion amounts to about ensi y. ,^j^ ^^ ^^ bulk. Icc therefore floats upon the surface of water. The wisdom of this exception is seen, when we reflect, that if it sank as fast as it is formed, whole bodies of water would be changed to solid ice. 16. fielatioa between Heat and Expansion. — ^In the same manner, all the objects about us are changed in their dimensions as heat enters or leaves them. Different substances expand differently by tlie 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 smaU ; we should not be aware of it without careful measurement. The same proportion of heat causes liquids, such as water, alcohol, and mercury, to vary in bulk more than solids ; while heat added to gases, or airs, produces a much greater expansion than it does in liquids. Although heat thus causes bodies to occupy, more space and become larger, yet it does not make them heavier. The same substance weighs exactly the same, no matter how cold or how hot it is ; -hence heat is called imponderable. IT. Principle and Constrnction of the Thermometer.— If, then, when a substance receives a certain quantity of heat, it undergoes a certain amount of enlargement, we can use that enlargement as a measure of the heat ; and this is what is done by the thermometer or heat-meas- urer. A common thermometer is a small glass tube, with a fine aperture or hole through it, like that in a pipe stem, and a hollow bulb on one end of it fig. 2. This bulb and part of the tube is fiUed with the liquid metal mercury. By suitable means, the air is removed from the empty part of the tube, and its open end sealed up. The bulb is then dipped into water containing ice, and a mark is made SCALES OB" THEEMOMBTEES. 25 apon the tube at the top of the mercurial column. This point of melting ice is the same as that at which water freezes, and is hence called the freezing point. The tube is then fm. 2. removed, and dipped into boUtng water. The heat passes from the water, through the glass, into the mercury, which rapidly expands and rises through the naiTow bore. It passes up a considerable distance, wid 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 toiling point of water. The distance upon the tube between these two points is then marked off into 180 spaces, which are called degrees, and marked (°). Now, it is clear that the amount of heat which runs the mercury up 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 boUing point with another pound at tlfe freezing point, the result will be a medium ; and if the thermometer is plunged into it, the mercury wiU stand at the ninetieth • space— 7-that is, it contains 90 degrees of heat according to this scale of meaa- nrement. And so, by dipping the thermometer into any vessel of water, we ascertain how much heat it contains. 18. How Thermometers are Graduated or Ilarkedi— But this is nofr the way that the scale of the common thermometer ia actually marked. Its inventor, Fahbenheit, instead of beginnmg to count his degrees upward from the freezing point, thought it woul3. 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 mertfnry had fallen', in the same way as above, he got 32 additional spaces or degrees. Calling this point of least heat or greatest cold he could get, nought or zero he counted up to the freezing point of water, which was 32°, and 2 Thermoineter. 26 MEASUEEMENT OF HEAT. 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 Eeaumur's thermometer, the same space is 'divided into 80 degrees. Degrees below zero are marked with the minus sign, thus — . It deserves to be remarked, that the glass tube expands by heat as well as the mercury, but by no means to so great a degree. And besides, there being a considerable quantity of mercury in the bulb, it requires but a very small expansion of it to push the quicksilver up the narrow tube, through a perceptible space. 19. Exactly what the Thermometer indicatest — 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 qua/ntity. But we 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 we cannot thence infer that the absolute quantity of heat is as great in the gOl of water as in the gallon. The thermometer shows us simply the degree of in- tensity of the heat in its mercury ; and as this constantly tends to the same point as that of surrounding bodies, we take its degree to be their degree. If the thermometer suspended in a room stands at 70°, we say the room is at 70°, because heat tends to equalization. If by opening windows or doors the thermometer falls to 60°, we say the room has lost 1>0° of heat, — speaking of it as a measured quantity. The insti-ument indicates variable degrees of intensity, which are con- verted into expressions of quantity. We shall shortly see that there are certain conditions of heat which the thermometer totally fails to recognize. 20. Impoitancc of the Domestic use of the Thermometer. — As the ques tion of temperature is one of daily and hourly interest, not only of the utmost importance in conducting numerous household operations, but of the highest moment in relation to the maintenance of health it win at once be seen that a thermometer is indispensable. Every family should have oije, 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 THEEM0MEEEE3 AUD THEIR INDICATIONS. 27 and tube may be' drawn out of the frame, so that the bulb can be im- mersed in a liquid, if required. They must be gradually warmed before dipping in hot liquids to prevent fracture of the glass, and of course need to be handled with much care. Their scales extend no higher than the boiling point of water. There is usually some departure from the accurate standard in the indications of the cheaper class of instru- ments. Mr. Taouabttb, a prominent maker of this city, states that these variations rarely exceed from 1 to 2 degrees. 21. Interesting Facts of Temperatnie. — ^We group together a few points of temperature of familiar interest.* Best temperatnie for a room GS'-eS* Lowest temperature of Jiaman body (In Asiatic cliolera) 67' Kean temperature at the equator 81* Heat of the blood 98* Beef s taUow melts 100* MattoQ tallow jnelts 106' Highest temperature of bimian body (in tetanos or lockjaw) .... 110* Btearine melts Ill* Spermaceti melts 112* Temperatnre of hot bath 110"-180* Phosphorus inflames. Friction matches ignite 120* Tea and coffee nsnally drank . . 180'-14O* Butter melts 180*-140* Coagulation of albumen 145* Scalding heat . . , • . . . 150* Wax melts 155" Milk boils •.'... 199* Bnlphnr melts 226° Cane sugar melts 820* Baking temperature of the oven 820°-40a* Sulphur ignites 660* Heat of the common Are 1000* IT. RADIATION OP HEAT AND ITS EFFECTS. 22. Heat passing thiongli 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 ftirther list of temperalu]'e». see Appendix, A. RADIATION AND ITS EFFECTS. 23. Decrease ia the Foree of Heat-rays. — ^When heat radiates from any source, as the sun, a stove, an open Are, or flame, it passes from each point in all directions Fig. 3 ; it spreads out or diverges as it FxG. 8. / V \^ Badiution of heat. passes away so as to become weaker and much less intense. It decreases in power at a regular numerical rate; as seen in Fig. 4. It is commonly said that the intensity of radiant heat decreases inversely as the square of the distance ; that is, if in standing before the fire at a distance of two feet from it, we receive a certain amount of heat, and then we step 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 shown in Fig. 4. But this state- ment is only true when we consider the heat as passing from a single point. When it flows from an infinite number of adjacent points, — ^that I'lQ- 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 Heat. — We aU know that some substan- ces will let light pass through them, and others will stop it. It is just so with heat : but the same substances which transmit light, do not always transmit heat. Air allows both to pass without obstruction; but water, which so freely allows the pas- sage of light, has very little power to transmit heat. Eays of light, passing through water, are strained of nearly all their heat. But there seems to be a difierence in the source and nature of the heat itself, as to its power of getting through various bodies. Glass allows solar heat to go through it, but not artificial heat. A pane of glass held between the sun and one's face will not protect it from the Keat ; but it may be used as a fire-screen. If we place a plate of ijlass and of rock-salt before a hot stove, the dark heat, will pass treely through the salt, but not through the glass. The glass is, therefore, opaque to heat (if we may borrow the language of light), while salt is iranspm-ent to it, and is hence called the fflass of heat. Showing the rate at which radiant heat is diffused and weakened. CIECUMSTANCE3 CONTEOLLmG IT. 29 Meloni has shown that if the quantity of dark, radiant heat transmit- ted through air, be expressed by 100, the quantity transmitted through an equal thickness of a plate of rock-salt wiU be 92; flint glass, 67; crown glass, 49 ; alum, 12 ; water, 11. 25. Heat whicli does not go tbiongli 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, are said to be absorbed by it. Thus, fine window-glass transmits only 49 heat rays in a hundred, the remaining 61 being absorbed 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 EadiatioUf — The power of a body to emit or radiate heat, depends first, upon the quantity which it contains. Other things being the same, the higher its temperature compared with the sur- rounding medium, the more rapidly will it throw off its heat. As it cools, the radiation becomes slower and slower. But all subtances at the same temperature, do not throw out their heat alike. The condi- tion of surfaces eyerts a powerful control over radiation. Kough, uneven surfaces radiate freely, while smooth, polished surfaces offer a barrier to heat, which greatly hinders its escape. Metals, as their sur- faces are capable of the highest polish, are the worst radiators. Ac- cording to Meloni, 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. Lesub has shown that, compared with a smoke-blacked surface, as 100, clean bright lead is 19, while if tarnished, it is 46. If the actual radiating surface is metallic, it matters little what substance is under it. Glass covered with gold-leaf, is re- duced in its radiating power to the condition of a polished metal. 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. Ettmeoed 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 BPPBCTS. heat which was thrown off by the covered cylinder in 36 J minutea- ,required 56 minutes to radiate from the naked cylinder. 27. How Polishing alTects Surfaces.— Dr. LAEDiraE says " the diminu- tion of radiating power, which ordinarily accompanies increased polish of surface, is not a consequence of the polish in itself, hut of the in- creased density of the outer surface, produced by the act of polishing; and the effect of roughening is to be ascribed to the removal of the outer and denser coating." 28. Best Diode of Conflnlng and Retaining Heat. — These principles show us howjaest to enclose and retain heat when we wish to prevent waste from radiation. Glass, porcelain, and stone ware surfaces, radiate freely : vessels of these materials are not the best to preserve foods and fluids hot at table. They should either be of polished metal, or have bright metalhc covers, which will confine the heat. Bright tea- urns and coffee-pots are best to retain their contents liot ; and a tea- kettle keeps hot water much more effectually if clean and bright, than if covered with soot, though it is much harder to boil. Pipes intended to convey heat should be bright and smooth, while those designed to radiate or expend it, should be rough. For the same reason, polished stoves and stove-pipes are less useful in warming rooms than tho'se with rougher surfaces. 29. Color of Surfaces does not influence Radiation, — ^It is very generally supposed that the color of a substance influences the escape of heat from it. But the experiments of Dr. Bache have shown that this is a popular fallacy. He has proved that color exerts no control on the radiation of non-luminous heat, or such as is unaccompanied with light. A body will emit heat from a white or black surface with equal facUity. 30. Heat thrown off from Bodies.— Radiant heat striking upon bodies, if it is not permitted to pass instantly through them in straight lines, is either abson^led 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 the 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 which is not disposed of one way goes the other. If half of it is absorbed, the other half will be reflected. Glass absorbs 90 per cent, and reflects 10 while polished silver reflects 97 per cent, and absorbs but 3. A good absorbing surface is a bad reflecting surface, and a good reflector is. a THEORY OF HBAT-BXCHANGBS. 31 bad absorber. So a good radiating surface absorbs well and reflects badly, wbUe a bad radiating surface absorbs badly but reflects well. The density, or polish, of a surface controls tbe admission as well as the escape of radiant heat. Two kinds of heat may thus pass in straight lines from a body — radiant heat and reflected heat. The former comes from within, and therefore cools it ; the latter strikes against it, and rebounds without either warming or cooling it. 31. Color of Surface inflnences the admission of Heat. — We have seen (29) that color has no influence over radiating surfaces ; but the power which bodies possess of absorbing heat, depends very much upon color. FEAHlnjir spread differently colored pieces of cloth upon snow iu the sunshine. That of the black color sunk farthest below the surface ; which showed that it melted the most snow, and consequently received most heat. The blue piece sunk to a less depth, the brown stiU less, and the white hardly at aU, which showed that it absorbed least heat. Hence, by scattering soot over snow, its melting may be hastened : it 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 earlier than if against light-colored walls, because, for the same reason, they are warmer. So, also, in the matter of clothing, white -throws off the solar heat, while black absorbs it. 32. Exchanges of Heat — It escapes from aU 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 otAj possessing the power of radiation, but as actu- ally exercising it. Kays 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 wiU 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 o2° be placed beside the cannon-ball at 32 EADIATION AND ITS EFFECTS. 100°, the same thing takes place,only in a less intense degree; and if Pis. 5. an ice-hall from the Arctic region at 100° belo-w the freezing point, were placed he- side another at 82°, ex- actly the same thing woidd occur. Thus all bodies are constantly Exchanges of lest; it radiates ftom bodies at all temper- interchanging heat and "'"^°' .tending to equaliife,tion. 33. StarUght Jfights colder than clondyOnes. — 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 bact again to the earth's surface ; but if the sky is cloudless, the heat streams away into space, and there is none retnmed. 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 Frodnced. — The cause of dew was not understood until lately. Many were persuaded that it came out of the earth; while others thought it fell as a fine rain from the elevated regions of the atmosphere. The alchemists regarded it as an 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 (ow,less(286). When, therefore, the air is suflBciently cooled, its moisture is condensed, and appears as drops of water. These are often seen in summer" day i3 upon the outside of the pitcher of cold water ; improp erly called the sweating of the pitcher. The moisture that is seen trickling down the window-pane in winter, is condensed from the vapor of the air in the room, by the outward escape of heat from the glass, and the consequent cooling of the air in contact with it inside. When, therefore, by nightly radiation, any objects upon the earth's Burfaoe have become so cold as to cool the air in contact with theru rr EXPLAINS THE CAUSE OF 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. 35. 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 Ls formed upon them. Good radiators become covered with dew, whUe bad radiators remaiu dry. Grass, for example, is an excellent radiator, and it receives dew copiously, while under the same circumstances, stones, being bad radiators, are not moistened. Dew is deposited from a stratum of air only a few inches thick, which is condensed by contact with the cold body. If, however, that stratum of air ia moved away before it gets suflEiciently cooled, no dew will be formed. Hence, when the air is in motion, as on windy nights, there is no dew. Fall of temperature always precedes the formation of dew, and the greater the fall, the heavier the dews ; the quantity of moist- ure in the atmosphere, in both cases being the same. Farmers very well know that nights with heavy dews are very cold ; but the cold is the eaiise, not the effect, of the dew. The moister the air is, with the same descent of temperature, the more dew falls. Thus, arid deserts are dewless, notwithstanding the intense nightly radiation. 36. Exchanges of Heat may prevent Dew. — We have noticed Peevost's theory of the exchanges of heat, by which, all bodies are assumed tp radiate heat to each other constantly (32). This explains why little or no dew is found under trees. "While the grass radiates upward, the foliage radiates downward, and thus.checks cooling. For this reason, no dew is precipitated on cloudy nights. As objects radiate upward, the clouds radiate back again, and prevent the falling of the tempera- ture. More dew falls upon the summits'of mountains, where objects are most open to the sky, than in valleys, where the angle of radiation or access to the open heavens is- much less. Objects protected in any way from exposure to the sky, are, to that extent, guarded from dew. 37. Frost Caused In the same way as Dew. — As a certain amount of cooling, deposits moisture from the air, more still, freezes it ; and hence, frost or frozen dew. This extreme cooling is often hurtful to vegetation, and during the serene nights of spring, tender plants are often killed, as is frequently the case with immature fruits and grain of autumn. Here, again, all circumstances which oppose radiation, prevent the cooling. Vegetables, sheltered by trees, suffer less than 34 CONDUCTION OF HEAT. those not so protected. A thin covering of cloth or straw, preseryea plants, as may also fires that fill the air with smoke. V. CONDUCTION OF HEAT AND ITS EFFECTS. 38. Heat creeps slowly tlirongh some Bodies. — If we place one end of a bar of metal in a fire, that end becomes hotter than the other parts of the bar. Bnt this effect is only temporary ; the heat will gradually pass through it, being communicated from particle to particle, until f lo. 6. the other extremity beconies heated. This is easily shown by taking several marbles, and sticking them to an u'on or copper wire with wax Tig. I w 6. 'If now heat is applied to one end of the wire, it The balls drop snccessively as the heat mores in, i -, , i along the rod. gradually travels along, the wax is melted, and the marbles drop off successively. The heat in this case is conducted by the metal. S9. Different Snlistances conduct at different Rates. — ^Heat diffuses in this manner, at very unequal speed through different substances. If we hold one end of a nail in a candle flame, it soon gets so hot as to burn the fingers ; while we can fuse the end of a glass rod in a lamp, although holding it within an inch of the melting extremity. Iron thus conducts heat much better than glass. Those substances through which heat is diffused most rapidly, are called good conductors, while those through which it passes slowly, are l>ad conductors. In general, the denser a body is, — that is, the closer are its particles, — the better does it conduct heat; -wliile the more porous, soft, loose and spongy^ it is, the lower is its oauduoting power. The metals, therefore, are the best conductors, while bodies of a fibrous nature, such as hair, wool, feathers, and down, are the worst conductors of heat. 40. Enmford's Scale of Condnctors. — Kumeoed 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. Condncting Power of Bnlldii^ Materials. — Bad conductors, — rum- conaiictors, as they are called, — afford the best barriers to heat, and they are employed when it is desired to confine it. In winter, nature protects the earth and crops from excessive cold, by a layer of non- EFFECTS OF NON-CONDUCmfG SUBSTANCES. 35 conducting snow. The birds, she prorbects by feathery and downy plu- mage ; quadrupeds, by hair, wool, fur ; — and even the trees, by porous, non-conducting bark. In the management of heat, man finds the variation in the conducting powers of bodies, of the highest import- ance. In building houses, the worst conductors are the best materials for the walls. "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. Hutchinson examined some building materials, and ascertained their conducting powers to be as follows, omitting fractions. (Slate being taken as 100.) Marble 75 to 58, fire brick 62, stock brick 60, oak wood 34, lath and plaster 25, plaster of Paris 20, plaster and sand 18. The hard woods conduct better than soft, and green woods better than dry. Dry straw, leaves, &c., are good non-conductors, and are used to cover tender plants in winter, but if wetted, they convey heat much better. 43. Kon-eondaeting properties of Air. — Air is one of the most perfect non-conductors; Euicfoed thinks it is the best of all. The conduct- ing power of air, however, is greatly increased by moisture. If we represent the power of common dry air to conduct heat, by 80, its power, when loaded with moistore, 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, chaflF, &o., are good non-conductors of heat. Sawdust is an excellent bar to heat ; it should not be too much pressed together, as then, the particles, being in too close con- tact, conduct better : — nor too loose, as the air circulates through it, and thus conveys the heat. A layer of air between double windows, checks the escape of heat, but we do not, in such a case, avail our- selves of its perfect non-conducting power, otherwise we might use it to enclose ice-houses, &c. It is easily set in motion (97), and thus becomes a ready transporter of heat. Loose, porous bodies are filled with it, and they act as non-conductors by preventing its motion. 43. Tfon-condncflng Properties of Clotiiing. — "Winter apparel is made of non-conducting woollen fabrics, which prevent the escape of heat from the body. Cotton carries off 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- 36 C0!NTETA1TCE 01" TTEAT , ton.* The high non-conducting power of the woollens, is shown by the common practice of preserving ice in hot weather, by simply wrapping it in flannel. 44. Oar Sensations of Heat depend npon Condnetion.— The sense of touch is an unreliable guide to the degree of heat, because substances are so diverse in conducting power. The badly conducting carpet feels warmer to the naked feet than the better conducting oilcloth, because the latter will carry away the heat faster from the skin, al- though both are at exactly the same temperature. This influence of conduction over sensation, as also the remarkable difference of con- ducting power among solids, liquids, and gases, may be shown in a forcible manner. If the hand be placed upon metal at 120° it will be burned, owing to the rapidity with which the heat enters the flesh. "Water will'not scald, provided the hand be kept in it without motion, till it reaches the temperature of 150° ; while the contact of dir at 250° or 300° may be endured. Sir Joseph Banes went into a room, heated to 260°, and remained there a considerable time without incon- venience. The particles of air are so far asunder, that the heat crosses their inter-spaces with difiSculty ; and as but few of them can come in contact with the body at once, the amount of heat that they can impart is comparatively smaU. VI. HEAT CONVEYED BY MOVING MATTER. 45. It is carried l»y Particles in Slotion. — The freedom with which the particles of liquids and gases move among each other, is another source of the motion of heat. Water conducts heat but very imperfectly. If a glass tube filled with water, be inclined over a lamp, so that the ^"'' "'• flame is applied at the upper end Fig. 7, the water will boil at the top of -the column, but below the point where the flame is applied, the temperature of the water wiU be but lit- tle elevated in a long time. The conduction of heat is not -influenced by the position of the body along which it passes. It moves through a conductor as swiftly downward as upward. The water does not oondnot <"^ borizoutally. Had the heat, in this case, the heat downwards. been conducted^ it woiild have travelled as readilj down the water column as upward. Yet all understand that * Linen is also "best for dressing local inflammations, because its fibres are round and Bmooth, and therefore, less irritating. The fibres of cotton are flat and angular, and of woollen, rough and jagged, and consequently, unfit for this purpose (T95). ITS TEANSPOETATION BY VATEK. 37 a large amount of water may be heated by a small fire, if the heat be applied at the bottom. The cause of this is, that the lower layer of water in the vessel, being warmed, expands, becomes lighter, and for the same reason that a cork would rise, ascends through the mass of liquid above. Its place is taken by the colder liquid, which in turn warms, expands and ascends ; and thus currents are formed, by which the heat is conveyed upward, and diffused through the mass. This mode of heat movement is hence called convection of heat. 46. How the Water-currents may be slioim. — The circulation thus pro- duced by ascending and descending currents, may be beautifully seen by nearly filling a pretty large glass flask with water, and dropping into it a few small pieces of solid litmus (a cheap, Hue coloring sub- stance), which sink through the liquid. On applying heat to the bot- tom of the vessel by a small lamp, a central current of water, made visible by the blue tint it has acquired from the litmus, is seen rising to the surface of the liquid, when it bends over 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 thing takes place when air is heated ; it expands, becomes lighter, rises in currents, . and carries "Vith it the heat. We shall refer to this principle again, when speaking of the contrivances for Curronts produced in watoi warnsting rooms. by toiling. Fio. 8. Til. TABIOTJS PEOPEETIES AND EFFECTS OF HEAT. 47. Heat added to Solids, liquefies thenii — Not 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 VAKIOtrS EFFECTS OF HEAT. suddenly into the liquid state, and others pass gradually through an intermediate stage of pastiness or softening. 48. Melting Points.— That degree of temperature which is required to melt a suhstance, is called its melting or fusing point. The com- mon temperature of the air is suflSoient 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 water until it falls to 32°, and it becomes solid water, or ice. If kept per- fectly stiU, it may be lowered below 32° before the atoms lock to- gether into the crystalline or congealed state ; but if the water is jarred or agitated, crystalline ice results at that temperature. Heat taken from mercmy until it faUs to 39° below zero, causes it to harden into a solid, ringing metal— freezes it. - 180° of heat taken from alco- hol, do not freeze, but make it thick and oUy. 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 into liquids, is called caloric of fluidity, and as gases are known as elastic flnids, the heat which changes liquids to gases is called caloric of eloLstieity. 49. What is meant l>y SpecJ^c Heat. — If we take equal weights of different substances, and expose them to the same sources of heat, they do not aU receive it with equal readiness ; in the same length of time some will be much more warmed than others. If a lamp flamo of a given size wiU raise the temperature of a pound of spirits 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 wiH 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 wiU take 30 flames of the same heating power, to raise a pound of water through the same range of temperatiire in the same period ; to raise it through the same number of degrees, therefore, water requires thirty time.") WATEB HOLDS LAEGB QTJANTITEES 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 have different capacities for heat : and, as eacli substance seems to take a peculiar or particular quantity for itself, that quantity is said to be its ' specific ' heat. The specific heat of water is greater than that of any other substance. In ascending from a given lower to a higher point, it takes into itself or swallows up more heat than any other body ; and in coohng 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 33.82. 50. Why Water was made to bold a large amount of Heat. — ^When we consider the extent to which water is distributed upon the earth, we see the wisdom of the arrangement by which it is made to hold a large amount of heat, and the necessity that it should slowly receive, and 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 dinnk, — ^It is because water is capahle of receiving so much heat, that it is better adapted than any other snbstanc? 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 aU substances. For the same reason, a hottlo of hot water will keep the feet warm much longer than a hot stone or block. 52. Concealed or latent Heat. — ^AU 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, somethiug as water is held in a sponge— lodged in its cavities or pores. If a wet sponge is 40 VAEIOtrS EFFECTS OF HEAT. compressed, water is squeezed out ; but, when it expands again, it win again imbibe tie 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 anvU, its particles are forced closer together, and its heat is driven out of its concealment, the iron becomes hot. By suddenly condensing the air as in the instrument called the flre-syringe, _ in which a close fitting piston is driven down a tube (Fig; [X^ 9), the condensed air gives out so much heat as to set fire to tinder. ITow, before condensing the iron, or the air, in these cases, they appeared cold, the thermometer de- tected in them no heat; yet they contained heat, and condensation brought it out. As we cannot find it by the ordinary test, we infer that it was concealed or latent in the iron and air. Heat is capable, therefore, of be- coming lost or hidden in bodies, and then of again re-appeariflg under proper circumstances. We call this latent heat, because we must caU it something, and the term is convenient : but we are probably very far from a Air condenser. . / , , . j j.t, j; i ■ it, true explanation of the facts m the case. 53. How much Concealed Heat Water holdst — ^Whenever a solid is changed to a liquid, a certain amount of heat disappears — goes into the latent state. If we take a lump of ice at zero, fix a thermometer in it, and expose it to a source of heat, the mercury in the thermo- meter will be seen to gradually rise up to 82 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 stUl, 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 82°, and an ounce of water at 174°, and add them together, the ice will melt and we shall have two ounces of water at 32°. The ounce of hot water, therefore, parted with 142° of its heat, which has disap- peared in melting the ice. 142° is thus the latent heat of fusion of ice, which is hidden in the resulting water. The quantity of latent Ueat absorbed by difierent solids in entering upon the liquid condition STABILITT OF FOEMS PEESEEVKD. ^ 41 is variable, but a certain amount disappears in aU cases. Thus, if a mass of lead be heated to 594°, it will then become stationai-y, although the addition of heat is continued ; but the moment the temperature ceases to rise, it wiU begin to fuse, and the temperature wiU continue steadily at 594° until the last particle of lead has been melted, when it will again begin to rise. Those who have attempted to procure hot water from snow for culinary purposes, know by the delay of the result the great loss of heat which is involved. The heat necessary simply to melt 100 pounds of ice, without raising its temperature a single degree, would be sufScient to raise more than 80 pounds of ice- cold water up to boiling. 54. Beneficial Effects of this taw. — ^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 32°, the addition of one degree of heat would raise it to 33°, and thus throw it into the liquid form, all the accumulated snows of winter might be turned almost in an hour into floods of water, by which whole countries would be inundated. But so large a quantity of heat is requii'ed 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 Artiflcial 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 sur^unding bodies of the heat necessary to its fluidity. Ices for the table are made in summer by mixing together pounded ice and salt, and immersing the cream or other liquid to be frozen (contained in a thin metallio vessel,) into the cold brine, produced by the melting of the ice and salt. A convenient method of freezing a little water 42 VAEIOUS EFFECTS OF UEAT. without the use of ice, is to drench powdered stilphate of sodfi (glauber's Bait) 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. 66. Freezing liberates Heat. — If the change of a solid to a liquid ab- sorbs heat, the change of that liquid back again to the solid state, must liberate it. If the liquefying process swallows up heat, the solidifying process must produce the contrary effect — set it free again. As the thawing of snow and ice in spring, is delayed by the large amount of heat that must be stored away in the forming water, so the freezing processes of autumn are delayed, and the warm season prolonged, by the large quantities of heat that escape into the air by the changing of water to ice. The same principle is made available to prevent the freezing of vegetables, fruits, &c., in cellars during intense cold weather. Pails or tubs of water are introduced, which, in freezing, give out sufficient heat to raise the temperature of the room several degrees. Freezing is thus made a means of warming. 37. Evaporation of Water. — ^Water, at the surface, is constantly changing iato invisible vapor, and rising into the air, which is called evaporation. It goes on at all temperatures, no matter how cold the water is : indeed, evaporation constantly takes place from the surface of ice and snow. The ice upon the window often passes off as vapor, without taking on the 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 fast as the air becomes loaded with moisture, it is re- moved and drier air takes its place. Extent of surface also facilitates evaporation. The same quantity of water will disappear much quicker in shallow pans, than in deep vessels. 58. What occurs in Boiling.— When water is gradually heated in a vessel, minute bubbles may be seen slowly to rise through it. These consist of an-, which is diffused thr"ough all natural waters, to the ex- tent of about four per cent., and which is partially expellea by heating. As the temperature increases, larger bubbles are formed at the bottom of the vessel, which rise a little way, and are then crushed in and dis- appear. These bubbles consist of vaporized water, or steam which ia CONDITIONS WHICH INFLUENCE BOILING. 43 formed iu 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 &e just before bolKng, 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. Inflnenec of the vessel in Boiling.— Different liquids boU 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 conseguence of the oU having no attraction for the water. 60. Measnringthe Pressure of the iir. — Air has weight like visible ponderable matter, and presses down upon the surface of water the same as upon the ground. The pressure of the air is measured by a barometer, which is simply a glass tube about Fm. lo. a yard long, closed at one end, filled with mercury, and then inverted with its open end in a vessel of mercury, as shown in Fig. 10. The liquid metal in the tube, is thus balanced against the air outside, and falls to a point upon the scale, which exactly indi- cates the pressure of the air. A column of atmosphere from the ground to its upper limit, is about as heavy as a column of mer- cury 30 inches high. We represent in the figure, but a single column of air pressing down upon the mercury; but we must re- member that its surface is completely cov- ered by such columns of air. Of course, the empty space or vacuum in the upper part of the tube permits the mer- cury to rise ^and fall without disturbance. From various causes the weight of the atmosphere varies ; when it is heavier, it presses harder upon the mercury, and drives it up ; when it is lighter, the mercury falls. The ordinary fluctuations of atmospheric pressure, cause the mercury to play along a scale of some two inches. As there is only a Barometer tube. 44 VABIOUS EFFECTS OF HEAT. certaiu quantity of air to press down upon the earth, in gciDg up a mountain we leave much of it below us : of course, what remains above, is lighter, and presses with less weight. Hence, in ascending a mountain, the mercury in the barometer sinks in proportion as we rise higher. 61. Influence of Air-pressure upon Boiling. — ^It is reported by travel- lers that, upon high mountains, meat cannot be cooked by the common method of hoUing. The reason is, that the boULng water is not hot enough ; and the reason of that is that the pressure of the air being partially taken off, the water finds less resistance to rising into vapor, "and a lower degree of heat produces the effect. The boiling point thus fluctuates with the barometric column : the natural variations of atmospheric pressure, at the same level, make a difference of 4| de- grees in the boiling point of water. 62. Employment of the Frinelple In Befining 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 boUs away at a low _ temperature, leaving the sugar crystals perfect. 63. Dlevatlon of the Boiling Point. — If the weight of air pressing upon a liquid affects its boiling point, for the same reason the weight of the liquid itself, must affect it. When salts are dissolved in water, they render it heavier, and its boUing point is always raised. Some salts, however, raise it more than others. Water saturated with com- mon salt (100 water to 30 salt), boils at 224° ; saturated- with nitrate of potash ( 100 water to 74 salt), it boils at 238° ; with chloride ot calcium, at 264°. Ether boils at 96° (plood Jieat) ; alcohol, at 174° ; turpentine, at 316° ; mercury, at 662°. The viscidity of a liquid, or the glutinous coherence of its particles is opposed to its free ebullition. 64. Spheroidal state of Water.— Water in contact with highly heated metallic surfaces does not boU or vaporize. AU may have noticed it dancing or darting about in globules upon a hot stove. The reason offered why a globule does not evaporate from a red-hot surface is, that a stratum of steam is formed under it, which props it up, so that it is not really in contact with the iron ; and steam being a noncon- ductor, cuts off also the heat. Water enters upon the spheroidal state between 288° and 340° of the hot surface : but when the temper- ttture falls, the steam no longer sustains the drop ; it is brought into ITS EELATION TO BOILING. 45 contact with the iron, and is at once exploded into vapor. This prin- ciple is made available in the laundry in judging of the degree of heat. The temperature of the smoothing-iron is determined by its effects upon a drop of saliva let faJl upon it. K 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. 66. But little Heat required to maintaia Boiling, — If a liquid he con- fined in a sufficiently strong vessel, so that its vapor cannot escape, it may be heated to any desked point of temperature ; though at high heats, vapors acqtiire such an expansive and explosive energy as to Durst 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 win maintain it there just as well as more. Water boiling violently, is not a particle hotter than that which boils moderately. When water is brought to the boiling point, the fire may be at once reduced. Attention to this fact would save fuel in many culinary operations. 66. Double Vessels to Regulate Heatt — If we have a substance which, placed directly over the fire, would receive an indefinite quantity of heat, but which we desire to raise only to a Fio. ii. certain temperature, we place it in a vessel surrounded by another vessel ; the outer one heing filled with a liquid which boUs 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 mternal vessel. Section of a culinary bath: a ■,ia^ iiiwi xic^ ^0.3^ opening to introrluce water. 67. Why Puddings, Pies, ic, 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. 46 VABIOUS B] — Chimneys in the north end of a house, exposed to cold winds, often draw much less perfectly than those on other sides, or in the stiU more favorable warm interior of a building. The air in a chimney in the north or shaded side of a house is liable to cool in summer, so as to have a doymward, 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 the tops of those fhat are drawing downwards, it is sucked in with the current and fills the room below. 97. Cnrrents eonnteracting each other. — We have seen that it is only when the atmosphere is of a perfectly uniform temperature that it is perfectly still ; the slightest inequality in its Fio. la degree of heat, throws it'promptly into movement. Wg 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 third tube, admitting a limited supply of air. It is sometimes attempted to make a current proceeding from a fire, traverse two flues, which join again before discharging their smoke into the air. But this is difficult, if not impossible ; for though currents may be commenced in 'both routes, one quickly neutralizes the other, and but a single flue is used. 18 ACTION AITD MANAGEMENT OE CHIMNErS. Fio. 14. 98. One Chimney overpowering another. — ^When there are two fire-places in a room, or in rooms commmiicating by open doors, a Are in the one may burn very well by itself; but, if we attempt to light fires in both, the rooms are filled with smoke. The stronger burning fire draws upon the shaft of the weaker for a supply of air, and of course brings the smoke down with it. This difficulty may be remedied by opening a door or window, so as to supply both fires with the necessary air. The same eifect may take place, even though the two rooms be separated by a partition, when they communi- cate atmospTierically 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 uppe^ room is turned into the chimney of a lower room. If a fire is kindled in an upper room when there is none below, the cold air in the main shaft rises, and, mixing with the warm air, dilutes it, and thus checks or obstructs the ascent ] while if the lower fire only be kindled, the cold air from the upper fine 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 ia both fire-places or to dose one with a fireboard. 100. Admission of too mnch Air. — Too large openings in fire-places often occasion smoke by admitting so much air from the room as to cool the upward current, and thus impair its ascensional force. If the fire-place be too high or capacious, or its throat too large, the air is drawn from a large space, or it may pass round behind the fire by way of the jambs on both sides ; the current is thus impeded, and the flame, which should be drawn backward, rises directly against the mantel-bar and escapes into the room. The fire-place should be so constructed as to compel all the air which enters it, to pass through or close to the fire. 101. Admission of too little AIti — It is well known that a smoky ahimney is often relieved by opening a window or outer door ; where this is the case, the difficulty is a deficiency of air to supply the DEFICIENCY OF AIK-SUPl'LT. 59 Fig. 15. draught. "Want of a copious and regular supply of air is by far the most common cause of smoky chimneys. However well constructed and arranged may be the flues and fire-places, if they are not supplied with a proper amount of air they will inevitably smoke. Of course if the room be nearly air-tight, there is no air to supply a current, and there will he no current, for as much air as escapes through the chimney must be constantly fiimished from some other source. In such a case, tlie smoke not being carried off will diffuse through the room. There may even be a double current in the chimney, one upwards from the fii-e 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 he brought in under these circumstances. Dr. "Ft? a T nrr.Tis r'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, nntil the necessary supply was admitted. Suppose now the opening to he 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 made. It has been proposed to cut a crevice in the upper part of the window-frame ; and, to prevent the cold air from falling down in a cataract upon the heads of the . 'Donblo cmrent mmates, a thin shelf is to be placed below it, slopmg ing smoke. upwards, which wouW direct the air toward the ceiling. The modes of introducing air wUl be noticed in another place (351). 102. Dranghts throngli a Room. — Currents of air through a room, as from door to door, or window to window, when open, may coun- teract the chimney draught ; or a door in the same side of the room with the chimney may, when suddenly opened or shut, whisk a cur- rent across the fire-place, to be followed by a puff of smoke into the 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 the 60 APPAEATUS OF WAEMiya earth. Thus all that is visible of smoke is really heavier than air, which may be showii by placing a lighted candle in the receiver of an air-pump. By then exhausting the air, the flame is extinguished ; and the stream of smoke that continues to pour from the wick, falls Fig. 16. ^^ *^® pump-plate, as is seen in Fig. 16, because there is no air to support it. Often, in days when the wea- ther is said to be ' close' we notice that the smoke floats away from the chimney-top and falls instead of I'ising; 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 Tiemy, which prevents smoke from rising, is quite erroneous. The visibility of smoke is not entirely due to sooty exhalations. "Watery vapor is a large product of com- bustion, and, when the air is warm and dry, it remains dissolved and invisible ; but, when it is cold or saturated with moisture, it wiU absorb no more, and that which rises from the chimney appears as a vapor-oloud, and thus adds greatly to the apparent bulk of the smoke. 104. Other constitaents of Smokei — Smoke contains many sub- stances beside the carbonaceous dust, which vary with the conditions of combustion and the kind of fuel used. Ooal 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.— APPAEATUS OP 'WAEMING. 105. The various devices for warming are to be considered in a twofold relation, as generating heat and affecting the breathing quali- ties of the air. These topics are often treated together ; but, as we desire to present the subject of air and breathing with the utmost distinctness, a separate part vriH be assigned to it, and the heating contrivances will then be reconsidered ia respect of their atmospheric influences. 106. How Rooms lose Heat. — ^Apartments lose their heat at a rate proportional to the excess of their temperature above the externa] 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 lieat, yet the plates used are so thin as to oppose but a very slight barrier to its escape ; on the 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 en(Jrmous. . Three-foiu'ths or 75 per cent, of the heat which escapes through the glass, would be saved by double windows, whether of two sashes or of double panes only half an inch apart in the same sash. Heat is also lost by leakage of warm rarefied air through crevices and imperfect joinings of windows and doors, while cold air rushes in to supply its place. Heat also escapes through walls, floors, and 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 will now be noticed, 107. Our Bodies help to 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. Aneicnt Method of Warming. — The chunney is a modern device, coming into use only 500 or 600 years ago, with the mariner's compass, the printing press, inineral coal, and that array of capital inventions and discoveries which appeared with the caybreak of the new civili- 62 APPARATUS OP -WAEMING. zatiou that, succeeded the dark ages. Previously to that time, housei ■were heated as Iceland huts are now, — by an open fire in the middle of the apartment, the smoke escaping by the door, or passing out through apertures in the roof, made for this purpose. The Greeks and Eomans had advanced no further than this in the domestic manage- ment of heat. They kept fires in open pans called Iraziers; Those of the Romans were elegant bronze tripods, supported by carved im- ages with a round dish above for the fire. A small vase below con- tained perfumes, odorous gums, and aromatic spices, which were used to mask the disagreeable odor of the combustive products. The por- tion of the walls most exposed were painted black, to prevent the visible effects of smoke ; and the rooms occupied in winter had plain cornices and no carved work or mouldings, so that the sojt might be easily cleared away. 1.— OPEN FIRE-PLACES. 109. Strnetnre and ImproTements. — 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 (jomibs) 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, the fire was advanced to a more favorable position for heating the room. Rays of heat, like those of light, when they strike on an object, are reflected at the same angle as that at which they 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. Coustt Rukfoed states that the proper angle for the positions of jambs is 135 degrees with the back of the fire-place. 110. How tlie open Fire-place warms the Koom. — 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- OPEK ITBE-PLACES WASTE HEAT. 63 place. It strikes upon tlie walls, ceiling, floor, and furniture of the room ; a portion of it is reflected in various directions, and the rest is absorbed. The objects which receive it are 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 conckietion, but they immediately rise into the chimney, and are, therefore, of no nse in heating the room. As a flre- 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 wiU 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 Jine 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 open Fire not Economical. Fuel gives out its heat in two ways, by radiation and by immediate contact. Peolbt has shown, by ingenious experiments, that the radiated heat from wood was i ; from charcoal and hard coal about i, 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 thus the smaller quantity, the arrangements in which it alone is employed are by no means economical ; yet the open fire-place heats entirely by radiation, and is therefore the most wasteful of all the arrangements for heating. It is said that in the earlier flre-places T-Sths, and KuMEOED says 15-1 6ths 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 3-4ths 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 U/ the ordinary 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 re^ster above. This is an excellent plan ; it is ^^^ executed with various modifications, but, if well done, out warmed by om it answers admirably. Even a fine made of some thin ^^v^^^- Fia IT tf 64 APPAEATtrS OF WAEMING. material, and oontained in the chimney, the lower extremity com municating with the external air, and the upper with the room (Fig. 17), answers a most useful purposg. Heat is saved; ahnndance of air is fm-nished to the room without unpleasant draughts, while a common cause of smoke is avoided (101). 112. Franklin Stovei — ^Dr. Feanklin contrived a heating apparatus of cast iron, which he called the Pennsylvania fire-pla/ie, hut which is generally known as the FrcmMin stove. It oflfers 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 fir^-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 stiU another source of warmth in the hot air brought in from without. 113. Coal GrateSi — ^As coal contains more combustible matter in the same space than wood, and produces a more intense heat, a much smaller fire-place answers for it. A very narrow throat in the chim- ney is suflScient to carry off the smoke. The coal-grate is a more economical contrivance for warming than the larger wood fire-place, chiefly because it lessens the current of air which enters the flue. In the wood fire-place a copious stream of warm air passes up the chim- ney, which takes no part in combustion, but carries off with it much heat, the place of the escaping warm air being supplied by cold air from without. The coal-grate is closed, like the. fire-place, on tliree sides, the front consisting of metallic bars or grates, which, while they confine the coal, suffer the heat to radiate between them into the room. The sides and back of the grate should be formed of fire-brick, soap-stone, or some slowly-conducting substance, and not of iron, which conducts away the heat so fast as to deaden the combustion — for a fire may be effectually extinguished by contact of a good con- ducting solid body. For this reason, as Rdmfoed first pointed out, there should be as little metal about a grate as possible, the bars being made as slender and as wide apart as practicable, so as to inter- cept the fewest radiations from the burning surface. 114. Conditions of Comtastion in the Grate.— The form of the grate COMBUSTION m GRATES. 65 eliould be such as to expose the largest surface of incandescent coal to the apartment. If it has a circular front, there will be not only more surface, but the heat may then be radiated in all directions ; yet, if too great a surface is exposed to air, in extreme cold weather it carries off the heat faster than combustion renews it ; and the coal, if it be anthracite, grows black upon the exposed side and burns feebly. The art of burning fnel to the best advantage in open grates, is to main- tain the whole mass in a state of bright incandescence, by preventing all unnecessary obstruction of heat, either by contact of surrounding metal, or currents of cold air flowing over the fire. It is very difficult, however, to expose a large fire-surface to the atmosphere, and at the same time properly regulate the quantity of air admitted. It is pos- sible for fuel to smoulder away and entirely disappear with the pro- duction of very little sensible heat. To be burned with economy, therefore, it must be burned rapidly under the most favorable condi- tions of vivid combustion. The heat absorbed by the fuel, the sur- rounding solids, or the rising vapor, is of course not available, but only the excess which is emitted into the room. To cause this lively and perfect combustion, all the air which comes in contact with the fuel mnst 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 oflF 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 the 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. I^ 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 will be sufficient to intercept and decompose the cold air which rises through the wide spaces. If the coal be not large, perhaps a depth of four or five inches wDl be found most economical. 115. Different kinds of Grate— The modifications and variations of the fire-place and coal-grate are innumerable : and the multiplied de- vices which are continually pressed upon phbhc attention, are, many of them, but reproductions of old plans. The use of a simple iron plate for a fire-back, has been employed to warm an adjoining room situated behind the fire-place. For the same purpose grates have been hung upon pivots, so as to revolve, and thus warm two rooms, as libraij 66 APPARATUS OP WABMING. 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 doable fire-place, by which warmed air is introduced into the room from without. Dr. Feanelin devised an ingehious grate called the circular fire-cage. It was so hung as to allow it to revolve. The coal was ignited, as usual, at the bottom, and when the combustion was well advanced, the cage was turned over so as to bring the fire at the top By this means, the fresh coals at the bottom were gradually ignited, and their smoJce having to pass through the fire above them, was en- tirely consumed. 116. Arnott's new GTate> — Dr. Aenott has recently constructed a new grate, in which the same benefit — the consumption of smoke, is secured. The bottom of the grate is a movable piston, which may be made to fall a considerable distance below the lower grate bar. A large charge of coals is then introduced, which rests upon the piston and fills the grate. They are lighted at the top, so that the heat passes downward and consumes the smoke as it is formed below. As the coals waste away at the top, the piston may be raised by the poker used as a bar, and thus fresh coal is supplied to the fire from ieneath. When the first charge is consumed and the piston is raised to the bot- tom of the grate, a broad, flat shovel is pushed in upon the piston which supports the burning coals, and 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, we can no more advantageously convert it to heating purposes than we can the smoke of a badly burning candle to the purposes of lighting. When anoke escapes from the ill-adjusted fiame 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 iums its smoJee, but that it hurm without smohe. The aim should be, so to conduct the first combustion that smoke shall be prevented. 117. Grates should not be set too low.— As the open fire warms by radiation, it should be so placed as to favor this mode of diffusing heat. The tendency of currents of heated air to rise, secures sufficiently the vrarmth of the upper portion of the room, so that the main object of EPEECT OF TOO LOW FIEEB. 67 the grate should be to heat the floor. If the fire is situated very low, the radiation will be considerable upon the heaxth, while but few heat- rays will strike further back upon the floor. They will pass nearly parallel along the carpet or floor, just as the solar rays, at sunrise, dart along the surface of the earth. If, however, the fire be raised, its downward radiations strike upon the floor and carpet at some -dis- tance back, with sufficient force to warm them, just as the sun's rays are more powerful when he shines from a considerable distance above the horizon. If a in (flg. 18), represent a radiating point or fire in a room, and 5 c the floor, it will be seen _, ,„ /I 11 . 1 .1 FWJ. 18. that no heat-rays fall upon it ; while if the floor be at d e, it wfll 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 flre must spread over it, and chiefly between the middle of the room and the grate, where the feet of « | the persons forming the fireside cir- cle are placed. Striking proof of the ^^ fects here set forth, is obtained by laying thermometers on the floors of rooms with low fires, and with similar rooms with fires as usual of old, at a height of about 15 or 16 inches above the hearths. The temperature in the upper parts of all these being the same, the carpets in the rooms with low fires are colder by several degrees than in the others." 2.-ST0TES. 118. How Booms are warmed liy 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 fnel, which may be either wood or coal. The heat generated within is communicated, first to the matal, 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. Bilek, £artlienware, and Porcelain Stoves.— Stoves made of these 68 APPABATUS OP WAEMIKa. materials are most common in Germany and Kussia. They are gen- erally made to project into tlie room from one side, like a chest of drawers or a sideboard ; the door for the flre being sometimes in an adjoining apartment. These stoves heait more slowly, and conse- quently give out their warmth for a longer time than those made of iron, which are subject to rapid variations of temperature. 120. Self-regulating Stores. — ^These are stoves to which are appended contrivances for regnlating the draught. The principle employed is the expansion of bodies by heat, and their contraction by cold. A bar of brass or copper is so attached to the stove, that when the heat within increases, it lengthens ; it then moves a lever and closes the aperture which admits the draught. This checks the fire, and causes the bar slowly to cool ; it now contracts, and again opens the aper- ture of draught. Dr. Aenott produced the same result by means of a column of air contained within a tube acting upon mercury which • moved a valve, and thus controlled the air-aperture. As the addition and subtraction of heat cause gases to change their bulk m ore readily than solids, a well constructed regulator of this kind woTild be more sensitive and prompt in action than one of metal. 121. Air-tigM Stores. — The so called air-tight stoves are very common. They are designed to admit the air in small and regulated quantities, so as to produce a slow and protracted combustion. This mode of generating heat is less economical than is generally supposed. To become most perfectly available, heat must be set free at certain rates of speed. The compounds formed by combustion at a low tem- perature, generate much less heat than those which result from quick burning. Indeed, in the low, smothered combustion, the fuel under- goes a kind of dry distillation, producing carburetted hydrogen gases which escape into the chimney as unburnt volatile fuel, and are of course lost. These gases are inflammable, and when mixed with air, often cause explosions in air-tight stoves. Dr. Ubb found that while 3A pounds of coke evaporated 4i pounds of water, from a cop- per pan, when burned in a single hour, yet that when the same amount was burned in tweUe hov/rs, but Uttle over half that quantity of water was evaporated. As has been previously stated, to evolve the largest amount of heat from fuel it must be burned rapidly, and with a supply of air sufficient to carry the oxidation at once to its highest point, by the production of carbonic acid and water. Where the fuel is quickly and completely burned, and the hot, escaping gases are made to traverse a snflBcient length of pipe to have parted with nearly all their heat before entering the chimney, there remains notb- POINTS SKCUEED- 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 e£Scient heating apparatus. 122. Effect of Elbows In Stovepipes. — The heating action of the sheet- iron flue or stovepipe, is derived from the hot current of air ■within it. In proportion therefore as it contributes to the •warmth of the room, this current of escaping air is cooled. That this cooling of air within the pipe takes place rapidly, may be shown by the difference of tem- perature at its connection with the stove, and where it enters the chimney. The cooling takes place of course from without inwards ; the outer stratum of the hot air current which is in contact with the pipe cools faster than the interior portion, so that the centre of the current is the hottest. Now it is well known that the effect of elbow- joints in a pipe, is to make the same length of it much more efScacious In warming a room, than it would be if straight. The cause of this is, that the heated air, in making abrupt turns, stiikes against the sides with suflScient 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 unparted. It also checks the rapidity of the current. As radi- ation proceeds muoh 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 contcmis, than the hotter parts' of the pipe. There wUl, 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, Jirst, ready contriv- ances for regulating the draught ; second, accurate fitting in the joinings, doors, dampers, and valves, to prevent the leakage of foul gases into the room ; third, enclosure of the flre-spaoe, with slow conductors, as fire-brick or stone ; fov/rth, a high temperature, attained by the rapid and perfect combustion of the fuel ; and jvfth, to bring all. the heated products of the combustion in contact with the la/rgest possible absorl- ing and radiating metallic swrfaee, 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 infiuence. 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 APPAEATUS OB" WASMISG. S. aOT-AIK ARRANGEMENTS. 124. Hot-!dr Furnaces.— Heating by Jwt air, as it is termed, has re cently come into very general use. In this case the heater is not situ- ated in the apartments to he warmed ; hot air heing conveyed from it through air-flues to the rooms (fig. 19). The most common plan is a hot-air furnace. It is construct- ^'®- ^'' ed of iron, and usually lined with £re-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 airr chamber. Au- is introduced into this chamber, either directly from the room, or by means of a conduit, from without the building. The furnace ia 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 dweUing. It enters the room through apertures called registers, which may be opened or closed at pleasure. This method is commended by its economy of space, the heating machine being excluded from the occupied apartments; fuel is also consumed more completely, and with better economy, in a single furnace, than if burned in several stoves or gi-ates. A disad- vantage however, is, that the power of the furnace being gauged by the requirements of a certain sized building, or number of apartments, it ia not easUy accommodated to a fluctuating demand for heat. 125. Diffnsion of Hot Air throngli the Apartment. — There are serious Manner of warming by Hot- Air Furnaces. DISTEIBtmON OP HEAT IN THE AIE OP BOOMS. 71 disadvantages attending the entrance of hot air in large streams through registers in the floor. K 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, deUvering the air thi'ough two large openings in the floor, we have found a difference, after the heating process has been going on three hours, of more than 20° be- tween the temperature near the ceiling and that of the floor. In some public buildings, a stratum of air has been observed at the height of 20 or 30 feet from the floor, with a temperature above that of boiling water, whUe below it has been disagreeably cool. In private houses, with the hot-air fornaces, 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 diffused toward the register, when a part is again drawn into the ascending current. Hence wo see that those assembling just a/round 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 ; whUe the air, midway between the floor and ceiling, in a moderate-sized sitting-room, was at 74°, that near the register, was but 68°. — (Wy- MAif.) 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. a " 70' 14. 7 86' 6. 8 " 72' 16. 8 90' 8.4 " 15' 19. 94' 126. How we are warmed in Hot-air Eooms. — 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 cMlly. Great amounts of air contain but little heat. The quantity of heat that will raise 1 cubic foot of water 1 degree, would be so diffused as to raise 3,850 cubic feet of air one degree.— (Aenott.) 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 APPABATUS OF WAKMUSTG. warm, they become constant sources of radiant warmth. Hot air may also become a direct source of cold if it be dry. If we moisten the bulb of a thermometer, and expose it to the rays of a fire, it receives the heat and rises ; but when moistened and exposed to the action of warm, dry air, it will sink down several degrees, caused by the evap- oration which carries off heat. In the same manner, over-dry air may promote cooling by increasing bodily evaporation. We shall refer to the effects of hot air again. IST'. 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 CircnMionot water, ^t^jp^j the water falls, it will raise through the same number of degrees 2,830 cubic feet of air. 128. Two forms of Hot Water apparatus. — There are two methods of warming houses by hot water. In one the meJchanism 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 smaU tubes is distributed through the house, being laid along to fit any form and succession of rooms and passages, or they are coiled into heaps in various situations, and impart their heat by direct radiation. There is a difference in the 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 STEAM-HEAT — DAifGEK OP PIEB. 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, althongh it is at present so expensive as to place it beyond popular reach. 129. Steam Apparatns 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 boUer, or the hot water may be drawn off into vessels which are made to contribute to the heating effect. This mode of heating requires a temperature always at 212° for the formation of steam, and often much higher to drive forward the condensed water and clear the pipes. A serious drawback to this mode of heating is that the apparatus often emits a disagreeable rattling or clacking sound, owing to the condensation within the pipes and the sudden movements of steam and water. There is also a fundamental objec- tion to the method of warming rooms by heat radiated from coils of pipes, whether they be heated by steam or hot water. In respect of the condition of the air, this is liie worst of all methods of heating, for it makes no provision whatever for exchange of air. AU the other heating arrangements involve more or less necessary ventilation, but radiating pipes afford none at alL 130. Bisk of Fire by these methods of Warming. — ^It has been supposed that the employment of hot water, hot air, and steam pipes, as a means of heating buildings, cuts off the common sources of danger from fires, and is entirely safe. This is a serious error. Iron pipes liable to be heated to 400°, are often placed in close contact with floors skirting boards and wooden supports, which a much lower degree of heat may saflSce 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 applicatioaof a light. A considerable time may be required to produce this change, so that a fire may actually be " MndUng vpon a man's premises for years." The circular rim supporting a still which was used in the preparation of some medicament that required a temperature of only 800°, was found to have charred a circle at least a quarter of an inch 4 74 APPAEAT0S OF WABMING. deep in the wood beneath it in less than six months. There are nu- merous cases of buildings fired by these forms of heating apparatus. 131. Origin of Fires. — The Secretary of a London Fire Insurance cfiSce stated that the introduction of lucifer matches caused them an annual loss of $50,000. Of 127 fires caused by matches, 80 were produced by their going off from heat ; children playing with them, 45 ; rat gnawing matches, 1 ; jackdaw playing with them, 1. "Wax matches are run away with by rats and mice, taken into their holes and ignited by gnawing. These facts point to the indispensablenesa 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 8.1S at 10 P. M., which is just at the time that fires are left to themselves. 132. Benefits and Drawbacks of tbe Tarions metbods 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 weU-being of daily life, improvements wiU 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 ventUation, have not been previ- ously noticed, and will be considered when speaking of air. ADVANTAOES OF OPEN PIKE-PLACES. DISADVANTAGES OF OPEN FIRE-PLACES. They promote Tentilation — afford a They are uncleanly — require ireqnent heerfol fireside inQnence — 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 ttom 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 bomioally heat — ^yleld fluctuating temperatures — are liable to overheat the air— are liable to leakage of gases— and are not cleanly. HOT-WATEE APPAKATUS. ^6 AOTANTASES OF HOT-AIK TUBNACES. They are out of the way and save space —are cleanly— give bnt little troable— may afford abnndant yentllation — need waste Dnt little heat — aud warm the whole house. DISADTANTAOES OF 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- nre is sot supplied. ADTABTAGES OF HOT-WATER APPARATUS. They do not bum or scorch the (rir — 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 firom coils of pipe (IM). DISADVANTAGES OF HOT-WATER APPARATUS. They aia expensive in first cost — if adapted for an average range of tempera- ture, they may fail in extreme cold weather (as may also ftimaces) — and may give a dry and parched air if moisture be not supplied. PAET SECOND LIGHT. I. NATUEE OF LIGHT— LAW OP ITS DIFFUSION. 1S2. How tlie outward and inward Worlds Commnnicate. — We sit at the Tnndow, and have report of the world without. That intelligent consciousness which has residence in the ohamhers of the hrain, 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 ohemicak 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 v6ins. 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 affected by it. 133. Exhilarating Agency of Light.— Light is a stimulus to the ner- rous system, and through that, exerts an influence in awakening and OLDER NOTIONS OF ITS NATUKE. 77 quickening the mind. The nerves of sense, the hrain 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, depressing, quieting ; while Hght, on the contrary, excites and arouses. It is com- mon to see this illustrated socially ;— a company assembled in an apart- ment dimly lighted, will he dull, somnolent and stupid ; hut let the , room he 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 eveiy change of the sky I "When the sun shines, the blood flows freely, and the spirits are light and buoyant. When gloom overspreads the heav- ens, dnlness 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 sunshuie are allowed freely to sport around us." 134. Aneient 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 Mnd of touching or feeling process. 135. Newton's View of its Natniet — 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- 7£ HOW LIGHT IS DIETirSED. ent thought that light is moUon rather than matter, and that the eye is influenced by a mode of action resembling that of the ear rather than that of the nose.'' We omit further reference to this question here, as the analogy mil be more fully traced when we come to speak of colors (150). 136. Light loses Intensity as It Is DUTosed. — The rays of light proceed- ing from any source, a candle for example, spread out or diverge, as we notice nightly. As light thus diffuses from its source, the same quan- tity occupies more and more space, and it becomes rapidly weaker or less intense. This takes place at a regular rate. Its power decreases from each point of emission, in the same proportion that the space through which it is diffused 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 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 first. This effect, -however, may be modified by the light reflected back from the walls, and which is always more, the whiter they are. Whitewashed walls and light-colored paper economize light, or give it greater effect than dark walls, which absorb or waste it. 137. How Bodies receive the Lnminons Principle. — When light falls upon various kinds of matter, they behave toward it very differently. Some throw it back (reflection) ; some let it pass through them (trans- mission) ; some swallow it up or extinguish it (absorption) ; and some, as it were, split it to pieces (decomposition). All bodies, according to their nature and properties, affect light in one or more of these modes, producing that infinite variety of appearances which the universe presents to the eye. Fio. 21. ITS RELATION TO SUKPACES. 79 II. EEFLECTION OF LIGHT. 188. Those bodies which will not allow the light to pass through them, are called opaque. "When the rays of light strike an opaque body, a portion of them, according to the 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 fiq. 22. surface, it will be thrown back in the same direction 5 a. But if the ray fall upon such a surface in a slanting or oblique manner, it glances off or is reflected, at exactly the same angle, as Shown by the arrows. The angle of rebound is equal to the angle of striking; or, as it is commonly said, — thb aitglb of eeflbotion is equal to TB3! ANGLE OF INOIDBirOB, THE EBFLEOTBD EAT IS ON THE OPPOSITE SIDE OF THE PBEPBNBIOTJXAE, AND THE PEEPENDICULAE, THE INCIDENT AND THE KEFLEOTED EATS ABE 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 ^shutter, strike upon its re- flecting surface, it will be thrown off at an equal angle, and both the incident and reflected rays will be made visible by the particles of dust floating in the room. 140. How Reflected Ught is scattered. — Parallel rays falling upon a plane eurface, are reflected parallel, as shown in Kg. 23 ; but sepa- rating rays falling upon such a surface are reflected divergently, or scattered. The beams of light from a candle Fig. 24 diverge before falling upon a mirror ; and as each single ray makes the angle of incidence eqnal to that of reflection, it is clear that the rays must continue to diverge when they are reflected, as in the dotted lines in the figure. Thus when a burning candle is placed before a looking-glass, its diverging rays strike the mirror surface, and- being reflected in divergent lines, are dispersed through the room. 141. The Image ia the Looking-glass.— A highly polished metallic surface, called a speculum, is the most perfect reflector. Mirrors, or looking-glasses, consist of glass plates coated with metal. It is Fis. 80 PEODtrcnon op images. ria. 24. Fia. 25. not the glass, in looking-glasses, that reflects the light, but the metallic coating behind it. If we place any illuminated object before a plane miiTor, rays of light pass from all points of its surface, and convey an image of it to the mirror. But the polished surface does not retain the image ; it reflects or throws it back, so that the eye per- ceives it. The light which enters the eye comes from the real object, which appears behind the glass, because the angle or bend in the ray is not recognized. The light from an object may be re- flected many times, and make a great number of short turns, but it will seem as if the rays came straight from the object, and it will always appear in the direction in which the last re/lection 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 (Kg. 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 (eon- c(me\ 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 X i the figure of the surface. We see this lAage constantly illustrated in the images of „ ,, . V T,- J 4.T, the face, formed by the bright metallic How the image appears beUnd the ' •' ° looking-glass. — surfaces of domestic utensils. 142. A perfect Eefleeting Surface would be Invisible. — If the surface of an opaque body could be perfectly polished, it would perfectly reflect all objects placed before it, so that the images would appear as bright as the realities; but, in such a case, the reflecting surface woidd be itself invisible, and an observer looking at it could see nothing but reflected images. If a large looking-glass, with such a surface, were placed at the side of a room, it would look like an opening into another room precisely similar, and an observer would be prevented from attempting to walk through such an apparent opening, by meeting his image as he approached it. K the surfaces of all bodies had this property of reflecting light, they would be Invisible, and nothing could be seen but the lights, or sources of Ulumi ] TWO KENDS OF EEFLECTED 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 olgects 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 all possible directions. K a ray is let into a dark room, and falls upon a bright metallic sm-face, a brilliant spot of light will be seen from certain points, but the reflecting surface will be almost invisible in other directions, and the room will remain dark. If, now, a sheet of white paper be substituted for the mirror, it can be seen in all directions, and will slightly illuminate the apartment. The surface of the paper scatters the light every way, producing an i/rregula/r 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 mch of the incident rwys. In this manner light is radiated from surface to surfece, so that in the immediate absence of any original luminous fountain, there is a reverberation of light from object to object, through an endless series of reflections, so that we have general and equal illumination. 144. Management of Light in hanging Fietmcs. — ^The foregoing prin- ciples are variously applicable ; hanging pictures upon the walls of rooms may be taken as an illustration. As it is irregularly reflected light that reveals to us the picture, it should be.so placed that from the most natural point of observation that light reaches the eye, and not regularly reflected light. If the light fall upon a picture from a window on one side of it, and we stand upon the other side, as at 6 (Fig. 4* 82 EBLATION OF PICTITEES TO LIGHT. Fio. ! WintZeu Fio. 2T. 26), the eye is filled with the .glare of the regularly reflected light, while the picture itself can hardly be seen. In such a case, the true position of the observer is perpendicular to the plane of the picture, as at a in the figure. As pictures are often sus- pended higher than the eye, they require to be inclined forward, and the degree of their inclination should depend npon 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 I (Fig. 27), its proper inclination would be to c ; but if it were elevated to d, 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. Ligbt scattered It; tlie Atmosphere. — ^By this kind of irregular reflection, the atmosphere diffuses and disperses the light, — each particle of air acting as a luminous centre, radiates light in every direction. If it were not for this, the sun's light would only enter those spaces which are directly open to his rays, so that, shining through the window of an apartment, that portion only where the beams passed would be enlightened, and the rest of the room would remain totally dark. This secondary radiation occasions the mild and softened light which we experience when the heavens are screened with clouds, instead of the intense and often painful glare of a cloud- less summer day. In the same manner the atmospheric particles scatter the rays and diffuse a subdued illumination at morning and evening twilight, whUe the sun is below the horizon. m.— TRANSMISSION AND BEFEACTION OP LIGHT. 146. When light falls upon transparent objects, as air, water, glass, it passes through or is said to be transmitted. Bodies vary greatly in this power of passing the light, or lyranspwremy. The metals are least transparent, or most opaque, yet they are not entirely so ; thin LIGHT EBFEACTED OB 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 has been calculated that if the atmospheric ocean were 700 mUes 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 Sefraetton of the Bays. — Whea. hght 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, asai (Fig. Fio 28. ^^-^' ^* ^"^ "^"^ ^® diverted ; but if it fall at an angle, as&tcd, it will not continue straight to d, but will be as it were broken or refrcusted and proceed to c. If [ the refracting medium have parallel surfaces, the ray on leaving it is f^ain bent back to its original course, I as is shown in the figure. For this reason common window panes, which consist of plates of glass with parallel surfaces, unless they contain flaws, produce no distortion in the appearance of the objects seen through them. "When light passes obliquely from a rarer to a denser medium, as from air to water, it is turned toward a perpendicular ; when from a denser to a rarer medium, as from water or glass to air, it is turned //-om a per- pendicular, as shown in Fig. 28. 148. How Eefraetion may be shoviii — ^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, untU the edge of the vessel just hides it from view. Now, if water be carefully poured in, without disturbing its position, the coin wiH become visible (Fig. 29) , the rays of light coming from it, which before ji, ' ' passed above the eyes of the observer, are »\. now, as they come into the air, bent down- ward /rowi 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 really is. Oases of drowning have happened through ignorance of thw 84 ■WAVE THEOET OP LIGHT. illusion. The degree to which any substance bends the light from its straight course is called its indem of refraction. Each transparent, body has its refracting index, which is one of the properties by which it may be known. 149. EfTeet of Lenses upon tight. — This power which bodies have, of , Fis. Fia. 81. Plane-convex Lens. Fia. S2. Double-oonTex Lens. FiQ. 8S. Plane-concaTe Lens. Double-concave Lene, bending light from its straight course, is employed when we desire to gather it to a point or focus, or to concentrate it ; or when it is wished to disperse and 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 them, or spread them out into a greater space. Com- mon spectacle glasses are examples of these forms of lenses (248). IT. THEOET OP LIGHT— WATE MOTEMENTS IN NATURE. 150. liigbt not Matter Irat Motion. — Thus far we have considered light as if it were simple, without inquiring if it be really so, or compounded of different elements. There is another way in which the objects of nature receive and dispose of it, which brings us to the question of composition, and the subject of color. But what is color ? and what is light, in nature and essence ? Or what opinion has been formed of it, by those who have thought upon the subject most deeply ? In its cause and mode of movement, light is believed to resemble sound ; it is propagated, not by moving particles of matter, but by impulses of motion, which progress unaccompanied by any material substances. Let us note how wave-motions take place, and the known extent of their occurrence in nature. 151. Visible Wave Motions in Nature. — If we fasten one end of a cord, and holding the other strained tight, move the hand sharply up and down, or from side to side, wmes will be formed, which proceed along the strhig. The real motion, in this case, is at right angles to the di- rection of the string, the appwrent motion is forward. The particles SOUITD PEODUCKD BY AIE-WATES. 85 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 still water, the surface wUl be thrown into agitation, and waves will pass rapidly from the point where it struck, outward, in all dkections. The water in this case does not move forward any more than the grain did. This is proved by the circumstance that any objects which may be seen floating upon the water are not carried along by the advancing waves, but only move up and down in their places. Thus, particles of water, moving verti cally, cause wave-motions to travel Tiorisontally. 152. Sonnd the resnlt of Waves in tbe AlTt — 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 fi:om the sounding body to the ear ; the atmospheric medium is thrown into vibratory motion, and it is air- waves only which move forward. "We all know that sonorous bodies vibrate when struck, and that sound results. A harp-string, when struck by the fingers, swings rapidly backward and forward for a certain time, producing a sound as long as the vibration lasts. A piece of steel wire, or a pin held between the teeth, utters a sound as often as the free end is inflected. By touching the teeth with the prongs of an excited tuning-fork, we can feel the vibrations. Sound is thus not only motion, but it \& vibratory raotvm, and its transrpission to the ear is due to the flight of air-waves, which, striking against the auditory drum, communicate sensations of sound to the brain througL the auditory nerve. 153. Ppon what the differences of Sonnd depend. — ^If sounds are thus caused by vibrations, it would seem that the quality of sound should depend upon the quality of the vibrations; which is the fact. The first distinction among sounds is into high and low, or acute and grave ; it is a 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 they are, and the looser they are the slower are their vibrations, and the deeper are their sounds; while, on the other hand, the shorter, lighter, and tighter they are the quicker are their vibrations, and the higher and sharper the sounds they give. Eac)* 86 WAVE-THBOET OF LIGHT. Bound, therefore, that can be made, is the result of a certain number of air vibrations, and to that pitch of sound always bfelongs that num- ber. Sataet contrived a machine by which the number of pulsations which belong to each tone has been determined by actual experiment. A thin plate of metal was struck by each tooth of a revolving cogged wheel, the motion of which was easily measured. In this way he de- termined the exact number of vibrations in the tones forming the usual musical scale. 154. Harmonic Ratios of tbe Mnsical 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 the octave is as follows : Ratio or Haemonio Soitnbs. O D E F q A B I C I m -3— 3- S No. of Vibrations 512, 5T6, 640, 682, 768, 853, 960 1024, Intervals 64, 64, 42, 86, 86, lOT, 64. It wiU 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 ootcme. The difference between the number of ptflsations in any note, and the same note in the octave above, is as 1 to 2. Hence, by halving the numbers Of any scale we obtain the numerical value of the octave below; while by doubling them we have the number of vibrations made by the notes in the scale above. The lowest note of a seven octave piano is made by 32 vibrations in a sec- ond, and the highest by 7,680. Two tones having exactly the same number of vibrations are said to be in unison. When their numbers are not the same, but are in some simple relation, a concord is pro- duced. If one has twice as many as the other an octme results, which is the most pleasing of aU concords. The simpler the numerical ratio between the vibrations which generate a sound, or the air-waves which reach the ear, the more perfect and sweet the concord. When the difference is such that the proportion cannot readily be recognized by the ear, discord is the result. The whole phenomena of music thus resolve themselves into certain harmonious numerical ratios among Rir- waves, by which impressions are produced in a certain exact order upon a mathematically constituted organ — ^the brain. SCAIB OF THE LUMINOXTS TIBBATIOITS. 87 165. Light and Colors resnlt from WaTe Ilotloii. — ^As all sound and music are thus due to measured wave movements in the air, it is thought also that liglit has a similar ori^. This view assumes, that throughout the universe there exists a subtle, all-pervading and in- finitely elastic ether, 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 nieant 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 Nbwtoit, 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. K the minute- ness of the wave excite surprise, it may be replied that this is by no means the strongest illustration of the smallness of the scale upon which nature's works are often constructed. Indeed, in this case it has been even outstripped by art. M. Nobeet, of France, has ruled lines upon glass, for microscopical test-purposes, but the Tf^Jinr "f an inch apart.* 153. Vibrations per second of the Inminons Etiier, — But the demon- strations of science carry us into far profounder regions of wonder. The speed of light has been measured ; the velocity with which it moves is in round numbers 200,000 mUes per second. That is, when we look at any thing, an agent or force sent from the iUnminated 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 inch for any particular color, it is easy to ascertain the number of vibrations made by each in a second. In two hundred thotlsand 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 oi four htmoh'ed and eighty millions of mil- iums of times between every two ticks of a common clock. Of yellow * Seo Appendix iJ. 88 COMPOSITION AKD MUTUAL rNTXtTENCE OF COLOES. light five himdred and thirty-fiye 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 be 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 effect of an active external agent, and the reaction of the mechan- ism; the chemical constituents of nervous matter, — ^perhaps the atoms of carbon or phosphorus are in some way changed or influenced by nerve impulses in infinitely rapid succession, the sensations of vision and color being the consequence. If it be objected that the foregoing statements are incredible, we reply that they are generally accepted by the most sober and cautious scientific thinkers. But they are really no more strange or impossible than many other of the miracles of being which science is constantly unfolding around us. "We should observe a due modesty in criticising and assigning limits to the wonders and perfections of God's works. Dismissing the more purely theoretic or explanatory aspect of the subject, we now proceed to notice those properties and relations of colors which are the result of actual ex- amination. v.— COMPOSITION AND MUTUAL INFLUENCE OP COLOES. 167. White light taken to pieces. — If a ray of common white Mght be admitted, through a small aperture, into a dark room, and be made j,jg g^ to strike upon a triangular piece of glass (prism), the white ray disappears ; it is turned from its course, and there falls upon the opposite wall an oblong colored image called the solar spectrum. It consists of seven bright colors, always found in a certain order. Separation of white light into Newton's seven ^^ ^^°^^ ™ ^ig- 34; hut they prismatic colors. pass jnto each other gradually, so that it is difficult to tell where one ceases and another begins. Nbw- Tou assumed, as the result of this experiment, that white light is a compound principle, consisting of these seven colors, which he called primari/, and taught that all other colors whatever are the result af various commixtures of these. For convenience of representing the relations of colors, we may represent white light by a circle, and the NUMBEE OB" PEIMAErBS. 89 Fia. 85. colors wMch compose it by divisions of the enclosed space. In that case the seven primaries of Newton will be shown as in Pig. 85. 158. NeTTton's explanatioa of Colored Snifaecs. — ^White light falls upon objects, and they ap- jear colored : how is this ? Newton replied : Dodies 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 hlaei;, it is absorbed and lost in the substance, and therefore does not return to make an impression upon the eye. But the blackest surfaces do not really absorb all the light, for then they would be invisible, and appear like dark cavities, presenting no surface. K the surface appears colored, it is because the white light is split up, or decomposed, one part being absorbed and lost, whUe the other is reflected to the eye, so that the object appears of the re- flected color. For example, grass absorbs all colors but green, which it reflects to the eye ; and in the same way the sky absorbs all but blue, and reflects tJiat to the eye. Different surfaces reflect the pri- mary colors mused in aU manner of ways, and hence the endless modifications of color that meet the eye. 159. But tliree Primary Colors. — ^A more simplified vieo- of the com- position of colors has been propounded by Sir D. Bbewstee, and generally received. He considers ^^^ ^g that instead of seven, there are but three elementary colors, red, yellow, and blue, and that the others are compounds of these. TVe cannot produce red, yellow, or blue, by the mixture of any other colors ; but we cam pro- duce all others by the various com- binations of these three. Bbbws- -\ TEB 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 different points where they are visible. Blue, yellow and red being primaries, violet, indigo, green and orange are secondaries derived 90 JEEIATION AND MUTUAl INFLUENCE OF COLOES. Fio. ST. Fio. 83. i"ra. 39. from them. The separation of the impure or compoimd colors from the spectrum, leaving the three from which they are derived, is illustrated in Fig. 36. Orange is derived from the mixture of red and yellow; green from yellow and blue; and indigo and violet from blue and red. So that we have white light at last composed only Of the three colors, as represented in Fig. 87. 160. Wliat are Complemontary 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 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 fuU set of colors which form white, and make ■ out the full complement, is called the comple- menta/ry aoloT. The part absorbed, or which does not appear, is the com- plementary of the color seen. This may be made perfectly clear by the circular diagram. If we lOok, for example, upon a red surface supposed to be presented in Fig. 38, yellow and blue are seen to be the colors necessary to com- plete it to white ; they are therefore the . complement of red ; but yellow and blue form green, as shown in Fig. 39, which is therefore the true complement of red, that which it lacks to make white. If we W)ok upon a yellow surface (Fig. 40), blue and red are deficient ; blue Tia. 40. EiG. 41. A NEW SYSTEM OP AEBAKGrtTG THEM. 91 and red produce violet, therefore violet is the complementary of yel- low, as seen in Fig. 41. ^^^ ^,^ j,^^ ^ ^ain, 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. 4S. 161. "nuts and Shades, Tones and Scales. — ^These terms have formerly been employed in the most loose and indefinite way ; they have, how- ever, now acquired a kind of scientific precision. The tones of a color are those aspects which it presents when altered from its maximum of brightness or highest intensity, by mixing with it either white or black : if we take the purest and brightest red as a standard, say car- mine, and mingle various proportions of black with it, we of course darken it and get deeper tones of red. If we mingle white with it, we lighten it and get lighter tones of red. By the addition of black the red is said to he shaded, by the addition of white it is tinted. Each color, in this case, is a tone of red, and the whole series of tones constitute a scale — ^the red scale. It may consist of ten, twenty, or fifty tones, according to the quantities of black and white successively added. In the same manner we make tones of orange and get an orange scale, tones of blue and get a blue scale, and so each color has its scale, in which it moves in two directions, from its normal or standard point, towards black and towards white. 162. What are Hnest — 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 Lf blue be tinged in a similar manner by any color, hues of blue re- sult. In the same way are produced hues of orange, yellow, violet, green, &c. 163. Cherrenl's scheme for showing the relation of Colors. — ^A plan has been suggested by M. Oheveeux, of France, for representing the com- position and relations of colors, in an extremely simple and effective way. It clears the mist from the subject, and not only discloses it in a beautiful order, but is very valuable for practical purposes. It is represented by the diagram (Fig. 44), The outer' circle represents 92 RELATION AND MUTUAL INFLUENCE OP COLOBS. black, the centre white. The radial lines passing from the centre to the circumference represent scales of color, each dot indicating a tone. Each scale comprises ten tones. Take the red scale for example. The larger dot at A 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 B£D Plan of CHETBism's Chsoiutto Cieolks, lUuBtratbig tie principle of complementary colorB, tints, shades, tones, hnes, and scales. with yellow ; its normal is at a, and that of blue at c. From these three primaries aU the rest are derived. Midway between yellow and blue is the scale of green, which results from their combination in equal pro- portions, half blue and half yellow. Midway between green and blue is a scale that we might call a greenish blue. It is only one-quarter of the distance from blue to yellow, and therefore is three-quarters HOW THET MAY BE EXHIBrrED. 93 blue, and one-quarter yello-w-, — a hue of blue. Space or distance represents proportions of color. It will be seen that colors may be altered in two ways, that is, may move in two directions — along their scales, by admixture with white or black, producing tones, and out of their scales, in the direction of the circles, producing hvss. 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 tlie 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 bine. 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-yeDow 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 yon go inwards, the scales will be formed. Familiar colors would at once locate themselves upon such a chart, so that we should understand their exact composition. For example, the crimson will be found near the red, but in the direction of blue, that is, it is red slightly blued, while scarlet is red, moved slightly in the opposite direction, toward yellow. So indigo is blue just started toward red. 165. — How tlte Diagram sliowg 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, prqduoing 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 it» complement, and also the contrary ; the complement of green is red ; of orange, blue ; of violet, yeUow. 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. Ve may even say that the complement of black ia 94 EELATION AND MUTUAL IITFLUENCE OF COLOKS. white, and of white, black, — of a deep lone on one side, it will be a light tone on the other. Thus the complementary color of a deep tone of green will he 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 hnndred and twenty colors can be found by any one in an instant.; a fact of much practical importance, as we shall soon have occasion fe) see. 166. — ^Wlat is meant by GomplementaTy Contrast. — ^By a glance at the diagram it will he 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 (Kg. 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, whUe 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 Ivmiruyas and sombre. Those into which yellow enters most largely, belong to the first class, and those consisting mainly of blue, to the second, red forming a medmm color. 168. Grays and Browns ; Fnre 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 pv/re, while the addition of black produces a IroTcen color. The browns are therefore all broken colors. A color may be broken, however, without directly adding black ; the three primaries mixed in certain proportions produce this effect. If a little bine, for example, be added to orange, it neutralizes a portion of the yellow and red, breaking the color and starting it towards black. 169. No Colors perfectly pnre. — We must guard against the error of supposing that in practice we meet with any such thing as a pure or perfect color. Even those of the spectrum or rainbow are not per- fect ; Beewstee has shown that the very brightest is contaminated by others. But when we leave the spectrum, and begin to deal with the EFFECTS OF COMPLEMENTAEIES. 95 commoner aspects of colore, paints, dyes, &o., their imperfections be- come mucli more obvious. We are to regard a red surface as reflect- ing to the eye, not a simple and perfect red, but along with the red a certain portion of the other colors of the spectrum, which have the effect of weakening and lowering the red. The true statement is, that the sensation of red is the result only of the predomirumee of that color. It is the same with all the colors we see ; others are more or less mixed with them, whichimpair their brightness. 170. How Colors mntnally Improve each other. — ^The action of colors npon 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 har- mowy 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. Ked and' green viewed in this way have the mutual effect of improving e^ch- other. It is the same if the two colors be placed side by side and observed together ; they wiU 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 tod orange, or violet-red and yellow-green, and observe them in the same manner, we shall get the same result ; their briUiancy and clearness wiU be mutually heightened. But these colors are eomplementaries of each other; eomplementaries 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 Mormon^ of Complementary GonPrast. These effects are COTerimental facts which may be verified by any one. Take six circul» 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 96 EEIATION Am) MUTUAL INFLUBNCE OF COLOES. weaker and weaker as the tint recedes from the colored circle. If now the red circle be placed upon the sheet that is colored green, it will be made to appear greener ; so if the green circle be placed upon the reddened sheet, the latter color 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 simultaneous change when both colors are seen at once and together. Both these effects require to be explained, and first of successive contrast. 171. Colors exert an influence npon the Eye. — Colors appear to exist upon the surfaces of external objects, but we must not forget that their real seat is in the eye itself; that is, external bodies so modify the light, that it produces within the eye different effects, which we name colors. Colors are sensations, or nerve-impressions, the result of something accomplished within the optic organism. Thus we say snow is white, and blood is red ; meaning thereby that snow so influ- ences the light, that it originates within the organ of vision a sensa- tional effect which we style white ; while blood so modifies the light falling upon the nerve of the eye as to cause the perception of red. As color thus finally resolves itself into different modes of affecting 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 general physiological laws, is subject to the same vicissitudes of varying activity, acute and blunted susceptibility, as other parts. "We shall now notice the change that takes place, only so far as colors are themselves affected ; deferring to another place an examination of the influence of colored light upon the eye in refer- ence to its health (253). 172. Duration of Impressions upon the Setlna. — ^Impressions continue npon 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 ; although it is not, as we might at first suppose, by a fefble, lingering inipression' left npon 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. Por example, if a bright blue object were seen, and then the THEr AFFECT EACH OTHER TUKOUGH THE EYE. 97 eye suddenly directed to a red, the eflfeot would be a perception of a mixture of the two, or violet, and this would remain until the first impression, or blue, faded away from the retina, after which the red object alone would be perceived. But such is not the case. 173. The Eye loses its sensibility to Colors, and demands their Comple- mentaries. — ^The influence of any color upon the eye is to diminish or deaden its sensibility to that color ; it gets fatigued in looking at one color for some time, so that it appears less bright. If, for example, the gaze be directed for a time upon a bright red object, that part of the retina upon which the image is impressed, becomes exhausted by the action of the red color, and partially blinded to its brightness ; just as the ear may be deafened, for a moment by an overpowering sound. But the effect does not stop here. If the eye be averted from the red and directed to white, the red contained in the white will not produce its natural effect, 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 ofi^ we shall see a spectral image of the wafer upon the paper, 5tti it will te green. The wafer so extinguished the sensibility to red upon a certain portion of the retina, that when it was removed, the eye saw the white, minus the red, that is, green. In like manner, if the eye be impressed with green, it loses its sensibility for it, so as again to decompose white and see red. If blue is observed, the impressi- bility of the nerve of sight is lowered for that color, so that white light is seen without its blue, and orange appears, which is the com- plementary of blue. In like manner the observance of yellow creates a tendency to see violet, and in the same way the effect of any color whatever, is to dispose the eye to see its complement. If we gaze at the sun at sunrise, when of a ruddy appearance in consequence of his rays being strained of their blue and yellow as they pass through the damp atmosphere near the ground, an image will be generated by the eye formed of these missing rays, and, therefore, green. When he has ascended higher and become of an orange yellow color, the image will be dark violet. It is well known that in. looking at the sun through colored glasses at the time of an eclipse, spectres of the sokr disk are sometimes produced which continue for a time before the eye. The color of these is always complementary to the color of the glass through which the sun was viewed. 174. Slmnltaneons contrast of Colors. — But colors placed side by side, 5 98 EELATION AND MUTUAL INPLUEJS^CK OF COLOES. exert upon eacli other, simultaneously, an influence that c&n hardly be accounted for by the theory which explains successive contrast. The effect is of the same kind,-^-contrasted colors are augmented in bright- ness, but it results from the equal action of both colors upon the eye at the same time. It has been stated that surfaces reflect to the eye rays of other colors beside those which appear. No surface can so perfectly analyze the white light which falls upon it, as to absorb all of one color, and reflect all of another. It appears of the color of the predominating ray, though more or less of the remaining colors of white light are reflected also, and diminish its purity. "We look upon a red ; it is not perfect, because other colors not red, but the opposite of red, are mingled with it and reduce its effect. We gaze separately upon green ; it is vitiated by rays coming frota it that are not green, but its opposite. Now if we could clear away or destroy these vitiating rays, we should improve both colors, and this is ac- tually done by placing them side by side. The reducing colors, which are active when the surfaces are viewed separately, seem to be, in some way, neutralized when they are brought together, and the com- plementary of each is thrown upon the other. 176. How associated Colors injnie each other. — ^If certain combina- tions of color alter each other for the better, it is easy to see how other combinations must act in other ways for the worse. If the mutual effect of colors most contrasted be to intensify and exalt each other, it follows that if those most nearly alike are associated to- gether, they will vitiate and injure each other. What the exact effect wUl be, may be seen at once by inspecting the chromatic diagram. The complement of violet is yeUow. 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, but the effect of violet is to increase the proportion of this element, and thus produce a new hue of yellowish-green. If violet be placed beside orange, which is also half yellow, it is moved out of its scale in the same direction , as before toward yellow, a hue of yellowish orange being produced. As orange-and green are already half 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 AEE CHANGED BY CONTEAST. 99 of colors. A color placed beside another tends to make that color as different as possible from itself. In the case of violet just alluded to, by reference to the diagram it will be seen that the color naturally farthest from it, by its very constitution indeed exactly opposite to it, is yellow. Now if bright violet be placed beside the yellow scale, it will drive every tone of that scale one or two steps back, away from itself, by making them all stiU yellower, and you wiU 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 Tone. — The effect of viewing white and black to- gether is to heighten the contrast between them, and so with the in- termediate tones of a scale of white and black. The accompanying wood-cut (Fig. 45) affords an im- perfect illustration of this effp"* It consists of five bands, shai I successively deeper and d^e| from left to right. As the ' glances at the scale, the ba I appear darker at their left I ders and lighter at their ri^ But this appearance is an efi of contrast ; for if we take t slips of paper with straight edges, and cover all the dia^am but Fio. 45. lllustratiiig the effect of contrast of tone. 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 anff 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 stiU lighter, and hght ones making dark tones seem StiU darker. This is, perhaps, because the absence of light in the dai-k color renders the eye more sensitive to the white light of the lighter color, and on the contrary the dark color appears darker, be- cause the white light of the lighter color destroys the effect of the small amount of white light reflected by the other. Thus if we place 100 EELATIOir AUD MUTUAL INFLUIiNCB OF COLOES. a dark red beside a ligM 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 lighter, and the deep ones deeper, so as to deceive the eye in regard to the real depths of their- colors. Thus for tones as well as hues the law of Ohbvketjl holds good. " In the ease where the eye sees at the same time two contiguous colors, they mil appear as dissimilar as possible, both in their optical composition and the height of their tone." 177. Harmonies of inalogyi — 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 imcnltured that we remark a passion for gaudy and flaunting colors. With the progress of a reflned civilization there is a tendency to the employ- ment of more subdued colors in personal and household decoration. Not by any means that good taste requires the total rejection of bright colors, but only that they be used with skill and discretion — ^be ameli- orated by combination, so as not to produce staring and stunning effects, or strong and deep contrasts which often oflTend the eye. Harmonies of complementary contrast are to be first and chiefly sought in chromatic arrangements ; but these are comparatively limited,, and in the demand for variety, other concords are found, whicli, althongh 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. Ha/rmonies of analogy may be produced in three ways. First, we may arrange the different tones of a single scale in a series, beginning with white and terminating with brown black, leaving as nearly as possible equal intervals be- tween them. This will produce a pleasing result. The greater the number of tones the finer will be the effect. Second, we may asso- ciate together the hues of adjacent scales, all of the same tone, and often produce an agreeable analogy. But sometimes colors of near scales mutually injure each other, as blue and violet ; the complemen- tary of blue, which is orange, being thrown upon violet gives it a faded and blackened appearance ; while 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. Third, a pleasing harmony of analogy is produced by view- ing groupings of various colors through a colored medium that casts EFFECTS OF'DIFFEEENT GEOUPINGS. 101 its own peculiar hne over the whole, as when we view a carpet ir light that comes through a stained glass window. 178. Circmnstaiiees wMeb distarb tbe inflnenee of Colors. — Various con ditions exert a modifying effect upon the mutual action of colors. The result may he greatly influenced hy the shape of the object, and the manner of its exposure to light. The surfece of a red curtain, for example, hung iu 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 Ul effects of the colors. It is often thus that flowers present bad associations, yet our feeling concerning them is such that we are not offended as when we see the same upon flat unglossed surfaces. The flower of the sweet pea, for instance, gives us the alliance of red and violet, which mutually injure each other, though the green leaves set off the red and help the result.' 179. Effect of associating Colors with White. — ^All colors appear brighter and deeper when associated with white, because its superior brilliancy renders the eye insensible to the white light which accom- panies and weakens the color. At the same time the white is tar- nished by the complementary of the color falling upon it. White is BO intense that in all its arrangements with color, except perhaps light tones of yellow, there will be contrast. It may often he 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 scales it forma harmonies of analogy, although their luminous com- 102 PEACTICAL SUGGESTIONS DT COMBINING COLOES. plementaries, especially those of blue and violet when falling upon black, deprive it of its vigor, and tend to make it look faded. Gray being intermediate between black and white, it is used where white gives too strong a contrast, and black makes the combination too sombre, as with orange and violet, green and blue, green and violet, VI.— PRACTICAL SUGGESTIONS IN COMBINING COLOES. Igl. Articles of Dress. — ^A recollection of the foregoing principles may enable us to avoid gross errors in combining colors. Thus a lady would hardly trim a violet bonnet with blue flowers, or an orange with yellow ribbon, while she would do well to trim a yellow bonnet with violet or blue, and a green one with rose-red or white, and to follow the same general rule in arranging the colors of a dress. 'W^e 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 reaUy is. Stains upon garments are less apparent where there is considerable difference among the colors of the various articles of apparel, than where they are more uniform, the contrast among the colors rendering that be- tween the stain and the surrounding cloth less conspicuous. Colored articles of dress produce a deceptive effect in reference to the size of the wearer. The influence of dark or black colors is to make the per- son wearing them seem smaller, while white or light dresses causes the figure to appear larger than the real size. Large figures or patterns upon dresses and horizontal stripes make the person look short, whUe narrow vertical stripes on a dress cause the wearer to seem taller. 182. luflnence 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 Monde and trwneite. In the blondes or fair-complexiOTied the color of the hair is a mixture of red, yellow, and brown, resulting in a pale orange brown. The skin is lighter, containing little orange, but with variable tinges of light red. The blue eye of the blonde is complementary to the orange of the hair. In brunettes the hair is black, and the skin dark, or of an orange tint. The red of the brunette is deeper or less rosy than that of the blonde. Now the same colors affect these two styles of com- plexion very differently. A green setting in bonnet or dress throws HOW THEY ATFUCT THE COMPLEXION. 103 its complement of red upon the face. K 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 he delicate in order to preserve harmony of tone. But green changes the orange hue of the brimette into a disagreeable brick-red. If any green at aU 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 sMn be more yellow than orange, the complementary violet faUing-npon it changes it to a dull 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 yeUows 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. Red 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 hght in such a way as to produce the same effect as gray. Black adjacent to the countenance makes it hghter. 183. Arrangement of Flowers in a Eonqnet. — In grouping flowers, com- plementary colors as far as possible should be placed side by side, blue with orange, yeUow with violet-red, and rose with the green leaves. On the contrary we snould avoid combining pink with scarlet or crimson ; orange with orange-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 wall colors. Orange and orange yellow are 104 PEACTICAL SUGGESTIONS IN COMBINING COLOUa. fatiguing to the eye. Among the simple colors light blue, light green (314), and yellow, seem fittest for hangings. Yellow is lively, and ac- cords well with dark furniture and brunette complexions, but it hardly appears well with gilding. Light green is favorable to pale skins, deficient in rose, and suits with mahogany furniture. Light blue goes well with mahogany, is excellent with gilding, and improves blonde complexions. White and light gray, with velvet patterns the same color as the ground, are well adapted to a wall to be decorated with pictures. In selecting a harder we shonld seek for contrast, so that it may appear, as it were, detached from the hangings with which it is associated. If there is a double border, an interior one of flowers and an exterior one, the last must be deep in color and much smaller. Tellow hangings should be bordered with violet and blue mixed with white. Green wiU take any hue of I'ed as a border. White hangings should have orange and yellow. Gray uniforin 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 effects in other rooms with well chosen borders and mouldings. 185. Pictures, Frames, and Gilding. — ^As the picture itself Is the valu- able object upon which we wish to fix attention, it is not in good taste to divert or distract it by gaudy and conspicuous surroundings and ornaments ; hence simple framings, just enough to isolate or separate the picture, are preferable. Gilt frames wiU 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 he left around the subject. Black frames, by their strong contrast of tone, tend to lighten the aspect of the picture, and often spoil a good engraving by taking the vigor from its dark colors. Gray frames are good, especially if the picture have a leading color, and the gray be slightly tinged with its complementary. As a rule, neither the frame nor the border within it should ever be suffered by their brightness, color, or ornaments, to injure the colors, shadows, or lights of the picture. The best ground for gilt ornaments is blue, because its complementary intensifies the color of the orna- ments ; hence shrewd shopkeepers who sell gilt articles line their show- cases with blue. A bright green ground reddens and improves gilt objects. Red and orange pervert the gilt tiat, and black lightens and weakens it (144). 186. AssortiiMait of Colors for Fnrnitiire. — In determining the colors COMBINATIONS IN HOUSB-FUKNISHING. 105 to be used in furnisMng a room, the amount of light is an important consideration ; dark colors, as dark blue, crimson, &o., require much light to be seen distinctly. Ked curtains redden the transmitted light of day, and impart this color to the countenances it falls upon. But by artificial or reflected light, red curtains and furniture dispose the eye to see green in the countenances of people in the room, while green curtains make the countenances rosy. Chairs and sofas, when complementary to the paper upon the wall, are most favorable to dis- tinct vision ; but for collective effect, when we desire to present the room as a unit, bold and complementary contrasts are 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 sofas, vivid reds should never be used with mahogany, for they are so bright that the mahogany loses its beauty, and looks no better than oak or black walnut. Crimson velvet is often used with mahogany because of its durability ; but the colors are so nearly allied, that a strip of green or black galloon should be used as a border to the stuff, or a narrow cord of golden yellow with gilt nails. Green or green grays are best suited to trim mahogany and red-colored woods. In using differently colored woods we can assort the colors of their trim- mings according to the rule previously laid down. The carpet should be selected with reference to the other furniture of the room. If mahogany is used, the carpet should not have a predominance of red, scarlet, or orange in it. K 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. ' vn.— PRODUCTION OF ABTIFICIAL LIGHT. 1. The Chemistet op Illumination. 187. Natural and Artificial JUgliti — As respects its sources, light is of two kinds, natmral light, or that which comes from the sun, moon and stars ; and artificial light, or that which man obtains at wiU 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 combustion, the nature of which has been explained when speaking of heat. 188. Light emitted by ignited Bodies. — All solid substances shine when sufficiently heated. The temperature at which they become 5* 106 PEODUCTION OP AETITICIAl LIGHT. luminotis, according to Dr. Dbapbe, who has lately investigated tlia subject, is 97T° F. He enclosed a number of different substances ■with a mass of platinum in a gun barrel ; upon heating and looking down the tube, he saw that they all commenced to shine at the same moment, and this, even though, as in the case of lead, the melted con- dition had been assumed. The color of light emitted from ignited substances was found to depend upon the degree to which they were heated. Dr. Dkapeb 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- tm-e the substance appears wMte-Jiot. 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 OUT Ulninination comes from bmning Gas. — The foregoing ex- periments were made "upon solid substances, but their results do not hold true for gases. These require to be heated to a much higher temperature before beginning to shine ; and when they do become luminous they emit but a feeble light. If we hold a piece of fine iron wire in the hot air which streams up above a lamp flame it wiU. quickly become red, showing that a degree of heat which makes the metal shine does not make the air luminous. And yet all ordinary illumination comes from the combustion of gases. "We use those ma- terials for lighting, which in burning produce flame ; and flame is burning gas. All substances which can be used for light must be capable of conversion into the gaseous state. The process is essentially the same, whether we burn the illuminating gas which is brought to our dwellings in underground pipes, or the liquid oil, or solid sperma- ceti. In the first instance the gas is manufactured on a large scale from solid bituminous coal or resin ; in the latter cases the liquid oil and solid tallow or wax are converted into gas at the time of turning. In aU cases the light proceeds from a rising stream of gaseous matter which is hghter than the air, and therefore tends to ascend. 190. What takes place in the Lnminons Flame. — The materials used for illumination contain hydrogen and carbon, and the gas they yield "consists of these elements more or less pure. Hydrogen, as we have before stated, is the lightest and most ethereal of aU substances (T6). The gas which gives rise to flame in illumination is theref6re 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. 101? Fie. 46. Fio. 47. seiaes upon the hydrogen first, burning it with an intense heat, aad the production of water. As the hydrogen combines with oxygen, it abandons the carbon, which is thus set free in a pure state. Now pure carbon is always a solid. As the hydrogen leaves it, therefore, it w set free in the form of exceedingly mi- nute solid particles in the midst of the heated space, — ^those heated to redness, yellowness, or whiteness, become luminous, and are the real sources of the light. The carbon par- ticles remain suspended in the flame but for an instant; they are themselves quickly burned and converted into carbonic acid.* 191. How these facts may be shown. — If we hold a piece of clean cold glass a short distance above a candle flame (Fig. 46), a fine dew will be seen deposited upon it, which is the water generated within the flame. If a piece of white earthen be lowered over the flame the combustion is in- terrupted, and the uncon- sumed particles of carbon are deposited upon the white surface, thus proving that they exist free in the flame. 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. AdmiraWe simplicity of the laws of lUnmination.— There is a wonderful simphcity 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. AH artificial iUnmination 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 Biagrame^ Illustrating combustion and iUnmination. 108 PEODircnON op AKTrFICIAl LIGHT. of plants and animals, but the very crast of the glohe is stored with endless accumnlations of them. The hydrogen combines with and condenses a much larger amount of oxygen than any other element, and consequently produces a great heat. But the burning of these pure gases, although the heat is so high, hardly creates a perceptible light. To get illumination, solid matter is required. Accordingly the lightest and most subtle of all gases, hydrogen, is associated with car- bon, the most refractory of aU 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 atmospheric oxygen, forming carbonic acid gas. The two products of combustion — vapor of water and carbonic acid — are both entirely transparent and invisible, so that although constantly formed within and around tha flame, they do not eclipse or obscure it, but let the light pass freely in all directions. If oxygen were equally attracted to hydrogen and carbon, so as to burn them both at once, no solid particles would ba liberated in the flame, and consequently there could be no light. It is the suceesswe combustion which takes place, — ^flrst the hydrogen burning and then the carbon, which gives rise to the luminous effect. 193. Threefold form of Illnmlnating 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. iLLUMItfATIOIf BY MEANS OF SoLIDS. 194. Adaptation of Tallow for Candles. — Those fatty and waxy bodies, which are sufficiently 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 be too gi-eat a proportion of mutton tallow or suet, as this contains a peculiar principle called Mrcin, which causes it sometimes to give a disagree- able smell, especially in hot weather. When of the best quality tallow niUMINATION BY MEANS OP SOLIDS. 109 b -wMte, firm and brittle. Alum is often put with it to harden it. The had quality of tallow candles is chiefly owing to their adulteration with hog's fat and cheap soft grease, which makes them smell, gutter and smoke. Good tallow candles will resist decomposition for two years, and are better after being preserved six or eight months. They should be kept from the atmosphere, and may be well preserved by being covered with bran. The place for their preservation should be cool and diy, as dampness mildews and damages them. Light turns them yellow. 195. Candles made from Stearic Acidi — 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, marga/ric acid, and oleic acid. Stearic acid, combined with glycerin, forms stearin. Margaric acid, with glycerin, yields mar- garin ; and oleic acid, with glycerin, produces olein. Oleic acid, or olein, is the more liquid portion of oleaginous bodies ; it predominates in the fluid oUs. Stearic acid, on the contrary, abounds in the hard fats and tallows ; it is their chief solidifying element. Margaric acid is less sohd, being intermediate between stearic and oleic acids. The intermixture of these, in various proportions, gives rise to all the various grades of softness and solidity which the endless oil and fat tribe exhibit. Tallow contains seventy to seventy-flve 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 anr, 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 iUu- raination. 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 PEODUCnON OF ARTIFICIAL LIGHT. Fio. 48. may be detected by boiling and adding a solution of iodine, ■wHch wiU yield a beautiful blue color, the teat for starch. Yellow bees'- wax is often adulterated with resin, pea and bean meal, and many other substances. The former may be detected by the smell, and the latter by the iodine solution. 197. Strncture of Candles— Office of the Wick. — The common burning .andle 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 vei'y difficult to set it on Are, as it would melt away long before it could ignite. But if at length made to burn, a much larger amount of the combustible would be on fire than the air would perfectly consume ; there would therefore be a thick smoky flame instead of a clear white light. Some contrivance is hence needed to avoid this result and regulate the com- bustion, and this is secured by placing cotton fibres within the combustible, which form the meh. These fibres are placed parallel in the axis or centre of the candle. When the wick which protrudes at one end is set fire to, it ra- diates heat downwards, so as to melt the material of the candle, and form a hollow cup filled with the liquid com- bustible around the wick-fibres (Fig. 48). The "flame is fed from this cup or cistern by the wick, which draws or sucks up the oily liquid exactly as a sponge or towel draws up water, by what is called the force of capillary attraction, or the attraction of small tubes for liquids. from'uiedstern ^^ this case the spaces between the fibres act as tubes, of oil below. ^^^ attract upward the liquid fat or wax. 198. The burning Candle a miniature Gas-Factory. — ^We thus see that the candle is a kind of lamp which constantly melts its own combus- tible. From the reservoir the wick draws up the liquid material to the centre of the flame. Here, in the midst of a high heat, and cut off from the air, it undergoes another change exactly as if it were enclosed and heated in the gasmaker's retort, — ^it is converted into gas. The candle-flame is not a solid cone of fire. If we lower a piece of wire-gauze or broken 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 gas Fio. 49. The candle-flame hollow. the dark inner space. m-UMmATION BY MEANS OP SOUDS. Ill manufactured from the liquid tallow, stearine, spennaoeti, or -wax, drawn up by the wick. This may be directly shown. If one end of a glass tube, having a bore J of anindi, be introduced into a candle-flame, as seen in Kg. 50, the gas wiU 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 may be re-lit by applying a light to the smoky stream of combustible gas which will convey the flame back to the wick. It is the hydro- carbon gas that is really burnt and produces the light, the hydrogen and carbon being successively consumed, as we have seen, at the surface, or The interior of the candie- where the air comes in contact with the gas. ° ° ^' ^""' 199. iDterference of the Wiek with Light. — As the candle consumes downward, the wick of course rises into the flame. In a short time it becomes so much lengthened as to interrupt the combustion and interfere with the light. Particles of unconsumed carbon are gradu- ally deposited upon the wick, forming a large spongy snuff which nearly extinguishes the light. Peolbt 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. Etjmtobd forbid that the brilliancy of an nnsnuffed candle was reduced | in 29 minutes. To prevent this annoyance and the necessity of frequent snuffing, wicks are sometimes so plaited and twisted, or are so slender that they bend over to the side of the flame, and coming in contact with the air are consumed (Fig. 48). This however is only practicable with the more infusible candles, stearine, wax, and spermaceti. Tallow melts so easily, that if the wick were bent over, the candle would melt down on that side and burn badly. 200. Influence of the melting point. — Tallow melts at 100°, spermaceti at 112°, stearine at 120°, stearic acid at 167°, and bleached wax at 155°. Candles made from those materials which are most infusible of course melt slowest ; the liquid which is formed in the cup being smaller in quantity may be drawn upward to the flame with a smaller wick. Hence the wicks of wax and spermaceti candles are smaller than those used for tallow. A slender wick in a tallow candle would melt the 112 PEODUCnON OP AEHPICIAI, LIGHT, combustible faster than it could consume it, the liquid would overfill and overflow the cup, which takes place in what is called the guttering' of candles. For this reason candles of softer materials require larger wicks. 3. iLLtrMHrATIOlT BY MEANS OF LiQmDS. 201. Irgand's great Improvement. — ^Lamps are vessels of various forms and appearances for burning light-producing, substances in the liquid condition. They generally have wicks to feed the flame, which may be either solid round masses of fibre like those of the candle, or fibres arranged flatwise so as to produce a long thin flame, or they may be circular. Dr. FEAmsxiN showed that two small wicks placed in two candles and burnt side by side, will give more light than if they were combined and placed in one candle, as there is a greater burning surface ; hence the advantage of spreading the wick-fibres out, and using them in some other form than condensed in a solid mass. Very large wicks of this kind convert the oil into gas faster than the air can completely burn it, and the consequence is that the flame smokes. To remedy this evil, the most important improvement yet made in lamps was contrived in the year 1T89 by Ami As^usm of Geneva, and since called after him the " Argand Burner." He made the wick hoUow, so as to burn in a ring or circle, and thus admitted a current of air to the inside of the flame, by which the central core of dark unbumt gases is avoided, and a double burning surface secured. By means of sheet-iron chimneys set above the flame (which were soon replaced by those of glass), a strong upward draught of air was secured, which heightened the combustion and greatly intensified the light. The wick was raised and depressed either by means of cogwork {rack and pinion) or by a screw ; the supply of oil is thus regulated to that of the air, and smoking prevented. An important advantage gained by the Argand burner is the great steadiness of the light caused by the chimney. When a draught of air strikes an unprotected flame, its force and cooling influence check the combustion, and produce flicker- ing and smoke. ' In Argand burners, on the contrary, the supply of air is self-regulated, and the cylinder prevents any interruption of the flame by outside currents. 202. Improvement upon the Argand Burner. — The cylinder that Ae- GAND employed was straight, or had vertical sides. This allowed a much larger amount of air to rise within it than could take part in the combustion, and this excess had the partial eflfect of cooUng the flame. M. Lange, a Frenchman, improved the form of the chimney- ILLTTMIXATION BY MEANS 01" UtQinDS. 113 tube, by contracting its size and constructing it with a shoulder at such a point (^g. 51 S), that the rising air striking against it was de- flected inward and thrown directly upon the flame. This had a power- ful efiect in increasing the combustion and heightening the intensity of the light. Another improvement consisted in mounting a button just above the circular opening within the burner, so that the current of air that comes up fi-om within, wiU be deflected outwards, as shown in fig. 54 a, and thus strike dh-ectly upon the inner surface of the flame. The main point to be considered in the structure _, and management of lamps upon the Argand principle, or with chimneys, is the relation between the current of air and the flow of oil. This is controlled by the movable wick, the movable button, and the width and height of the chimney. As chimneys of glass only can be used, ik^ they are apt to be made large to lessen the liability to fracture, though the danger is generally overrated. As a consequence more air is conducted to the flame than is demanded for vivid combustion, while the excess, by rapidly convey- ing away the heat, lowers the temperature of the flame, and thus diminishes its luminous intensity. Dashing a surplus of air against the flame is also unfavorable to that successvee combustion which is essential to illumination (192). 203. Points to be secured in the stmctiire of Lamps. — ^Lamps are made in a great variety of ways suited to burn different kinds of oily matter, and adapted to avoid, as far as possible, certain difiBculties which are incident to this mode of lighting. The distance from the burning part of the wick to the surface 6f the reservoir from which the oil is derived should remain unchanged, so that an equal quantity of oil may be drawn up at all times, and the reservoir should be so shaped and placed that its shadow will occasion the least inconvenience. If the wick is supplied from a reservoir below, it is obvious that just in proportion as that is exhausted, the distance from its surface to the flame is increased ; the wick-fibres elevate less oil, and the light grows faint and dim. To remedy this, the reservoir in some cases is made to have a large surface of oil that will fall but little distance, although a considerable amount is withdrawn. To avoid the objectionable shade thrown by such a large cistern close to the wick, the astral lamp had its reservoir constructed in the form of a narrow circular vessel or ring, which threw but a smaU shadow. The sinurribra lamps had this ring so shaped and mounted as to produce stiU less shade. Bometimes there is a fountain of oil placed on one side higher than 114 PEODUCnON OF AETIFICIAl LIGHT. the wick, with a self-acting arrangement by which the reservoir is fed from it, and its height constantly maintained at the same point. The shadow cast, in this case, upon one side, is objectionable, and limits its use to that of a study lamp (Fig. 67). In the Oakoel lamp, or meoTumi- cal lamp, clockwork is applied to pump up the oil through tubes in a constant stream to the wick, thus keeping it thoroughly soaied, while the excess of the oil drops back into the cistern, which is situated so far below as to oast no shade. It is moved by a spring, and wound up like a clock. It runs six or eight hours, maintaining a constant and equal flow of oil, and a bright and steady flame. These lamps are ex- cellent, but expensive, costing from fifteen to seventy-five dollars, and requiring much care. 204. Hot-Oil Lamps. — One great obstacle to the use of lamps Hes in the viscidity, or thickness and consequent sluggish supply of the oil to the wick ; this becomes a very serious difficulty with common lamps during the winter. Dr. Uee made some experiments to ascertain the relative viscidity or fluidity of different liquids, and of the same liquids at different temperatures. He inti'oduced 2,000 water-grain measures of the liquid to be tested in a cup, and then drew it off with a glass syphon of \ inch bore, having the inner leg 3, and the outer one &^ inches long. If the weight or specific gravity of two liquids, and their consequent pressure upon the syphon, were the same, their dif- ference of viscidity would be determined by the different time they would require to flow off through the tube. He found that 2,000 grain-measures of water at 60° ran off through the syphon in 73 sec- onds ; but when heated to 180°, they ran off in 61 seconds. Oil of turpentine and sperm oil have very nearly the same specific gravity ; yet 2,000 grain-measures of oil of turpentine ran off in 95 seconds, while that quantity of sperm oil took 2,700 seconds, being in the ratio of 1 to 285 ; so that the fluidity of oil of turpentine -is 28 J times greater than that of sperm oil. Sperm oil, when heated to 265°, ran off in SOO seconds, or one-ninth of the time it took at a temperature of 64°. Hence lamps have been, advantageously constructed to heat the oil before burning, either by means of a copper tube which receives heat from the flame, and conducts it downward to the reservoir,. or stil] better by means of a cistern placed above the flame. Paekee's Eng- lish Economic Lamp has its oil heated in this latter way, and is said to perform admirably. 205. Composition of OilSi — ^The oils in general use in these lamps are those derived from fish, chiefly whales, and known as sperm-oil and train-oil. Lard-oE is also much employed. It is the more oUy portion ILLTJMIN'ATrOIir BY MEANS OF LIQUIDS. 115 of hogs'-fat separated by artificial means. The chemical composition of tliese oils is quite similar to jihat of the harder substances which are Trrought into candles. Sperm-oil consists in 100 parts — of carbon 78, hydrogen 12, and oxygen 10 ; mutton tallow, of carbon 78-10, hydrogen 11-70, and oxygen 2-30 ; wax, of carbon SO-d, hydrogen 11-3, and oxygen 8-8. 206. Properties of Spirits of TnrpeBtine or Caraplienei — ^In addition to these substances a new class of compounds, the basis of which is de- rived from the turpentine of the pine tree, have latterly come into use. By distillation of the turpentine pitch, it is separated into a thin trans- parent liquid, spirits of turpentine or oil of turpentine, and a hard brittle residue knowr as common resin. The crude spirits of turpen- tine when rectified, tiiat is, separated as completely as possible from resinous matter by repeated distillation, is burnt in lamps under the name of camphene. It difiers from the substances just mentioned in its extreme liquidity (being, as we have seen, 28J times more fluid than sperm oU) ; in its. powerful pungent odor, and in chemical compo- sition, as it contains no oxygen, and consists of 88-46 parts in a hun- dred of carbon to 11-54 of hydrogen, and is therefore called hydro- carbon. Oil of turpentine is also much more highly inflammable, and is volatile and explosive. 207. Conditions required for its Combostlon. — Oil of turpentine is a superior Uluminatiag substance, but it contains so large a proportion of carbon, that if burned in the ordinary way, it smokes excessively. Lamps designed to burn it require to be so constructed as to supply to the flame a large and powerful draught of air, to effect the complete combustion of its elements. Camphene burns with a flame very much whiter and brighter than any of the substances we have yet noticed, and which displays the natural colors of objects, as flowers or pictures in their true tints, much more perfectly than the light of candles and oil lamps. Although more luminous, the camphene flame is smaller than the oil flame. This is explained by the fact that camphene con- sists entirely of carbon and hydrogen, while the fat oils contain 10 per cent, of oxygen. This oxygen, already existing in the oil, neu- tralizes a portion of its carbon and hydrogen, so that there is really but 85 or 86 per cent, of hydro-carbon to sustain the combustion ; and not only this, but the other 15 per cent, of incombustible matter acts to hinder the combustion. On the other hand, the oil of turpentine consists of pure combustible matter, burns entirely, and contains nothing to retard the activity of the burning process. A hundred parts of fat-oil consume only 287 parts of atmospheric oxygen, while 116 PEODUCnONS OF AETrPICIAL LIGHT. 100 parts of camphene consume 328 of oxygen. From its extreme fluidity, the oil of turpentine is also supplied copiously and constantly to the flame by the simple capillary or sucking action of the wick. 208. Why Campliene soon spoilsi — Camphene, if exposed to the air, cannot be preserved pure. It belongs to a class of bodies known as essential oils, which by combination with oxygen are changed into substances of a resinous nature. Under the influence o£ oxygen, oil of turpentine undergoes this change, and becomes deteriorated by solid resinous impurities. When employed for illumination, therefore vt should be procured in small quantities fresh from the manufacturer. 209. Nature and properties of Burning Flnids. — There is anothei method by which oil of turpentine may be employed for illumination, which is generally much preferred, as it avoids the liability and trou- ble of smoke. It consists in mixing it with alcohol, so as to form what is known as "burning fluid,. Alcohol burned alone produces only a feeble bluish-white light, as it is deficient in the necessary quantity of carbon. It has the opposite defect of oil of turpentine, as that has too much carbon ; the alcohol has an excess of hydrogen. By mixing them, a compound is formed which supplies the deficiencies of both, yields a good light, and may be burned in lamps of the simplest con- struction. These mixtures are commonly burned with wicks, but there is a lamp so made that the liquid is vaporized by the heat of the burner, and escaping in jets through minute orifices, is burned without a wick, like common illuminating gas. Owing to the large propor- tion of expensive alcohol which must be used in making it, and which gives but very little light, burning fluid is a very costly source of illu- mination (230). 210. In what way Bomlng FInlds are Explosivei — ^Both alcohol and oil of turpentine are very volatile ; that is, when exposed to the air oi not confined, they rapidly evaporate or rise into the gaseous state. In a lamp reservoir containing burning fluid, as it is gradually consumed, vapor rises from its surface and flUs the upper space. In all vessels, whether lamps, cans, or jugs, if but partially filled with fluid, the re- maiaing space is occupied with its vapor, which may or may not be mixed with air. Or when exposed to the air in open vessels, vapor rises and charges the atmosphere immediately above. Now the liquid oil of turpentine and alcohol are both infinitely more inflammable than the fat oils. These cannot be set fire to at common temperatures ; they must be heated very hot before they will catch fire. But the more volatile liquids, on the contrary, will take fire at any time when exposed, though cold, and bum with great violence. But the ILLUMINATION BY MEANS OF LIQUIDS. 117 ease is made much worse on account of the invisible vapor which they exhale. This mixes with the air, and at the approach of the slightest spark or flame, ignites explosively. "When pure hydrogen is mixed with the air and ignited, it explodes with a sharp report like a pistol ; the cause is the sudden combination of the hydrdgen with the oxygen of the air. Now when vapor of turpentine or alcohol, or any volatile hydro-carboB is mingled with air and fired, an explosion takes place in the same way. 211. Conditions nnder wMeh Explosions oeeiiT.~-The burning fluid iUelf, although excessively inflammable, is not explosive. It does not go off like gunpowder when set on fire, nor with a sudden noise or report, such as its vapor produces. But it is always accompanied by the invisible treacherous gas which catches fire at a distance, and this ignites the fluid. Most accidents that occur with these compounds result from attempts to fill or replenish lamps while they are . lit, or where there is a light near by. The vapor of the opened lamp, jug or can, is fired ; it explodes with more or less violence and concussion, setting the liquid on fire, and perhaps" scattering it upon the clothing of the person present, who is severely or fatally burned, while the house is very liable to be set on fire. If the lamp have a screw cap and be perfectly tight, heat may be conducted downwards from the flame through the metal, and increase the evaporation. There being no vent but through the interstices of the wick-threads, if these are dose, the pressure will increase and, force out the fluid and vapor so as to burn irregularly, and sometimes occasion little explosions in tho flame. K the wick is loose, and the lamp be agitated so as to dash the liquid against the hot screw-cap, vapor is suddenly formed, and being pressed out the flame streams up, often producing alarm. If the pressure become too great, and there be no vent, the lamp may ex- plode. Dr. Hays says, it is a uniform result of numerous trials con- nected with experiments on closed lamps, that no lamp is safe which has a closed cap, unless there are openings for the escape of vapor. It would be wise to substitute metallic lamps for those of glass, on account of the danger of fracture. "When these substances are em- ployed for light, they should not be committed to the charge of those ignorant of their properties ; and it is the only safe rule, when they are used in ordinary lamps, never to open any vessel containing them when there are lights burning near by. 213. How Bnming Flnids may lie nsed with safety — ^tfewell's Lamps. — The advantage which these liquids have over oils and candles in re- spect of simplicity, cleanliness, and greater brilliancy of light, makes 118 PEODUCnON OF AETTPICLil LIGHT. it eminently desirable that some safe way be devised to consume them. This has been done by Mr. John Newell, by applying to them the principle of Davt's Safety Lamp. Hydro-carbon gases are often generated in coal mines, and when mixed with common air, are exploded by the lamp which the miners nse. By surrounding these lamps with fine wire-gauze, they could be lit and carried into the dan- gerous mixtures without exploding them. The inside of the gauze would be filled with burning gas, but the fine wire texture has the effect of cooling the flame, so that it cannot pass through and ignite the gases outside. Hence, by ingeniously mounting his lamps with this gauze, Mr. Newell prevents the possibility of explosion from camphene and burning fluids. The can also for containing the fluid has a sheet of the gauze inserted under the lid, and another fixed in the spout. These do not prevent pouring; but if vapor or fiuid escaping through them were lit, the fiame could not enter the Fia. 52. 218. Kerosene Oil as an ninmiaatori — This is a product of the distillation of bituminous coal, and has come lately into use as a source of light. It is rich in carbon, and requires to be burned in peculiar lamps adapted to its properties. It produces a bright and beautiful light, which we have used with much satisfaction. It does not vaporize, and is therefore not explosive. The proprietors make large claims on the score of its economy (230), and are entitled to credit for hav- ing prepared a variety of elegant lamps for burning it. Pig. 52 represents one of their style of parlor lamps. The cistern is narrow, and so far below the wick as to cast but little shadow. When not burning, the oil emits a kind of empyreumatio gas- odor, to which many object ; but the smell is net perceived during- combustion. 214. Light from SyMe Oil. — This is a cheap oil from resin. It gives a vivid light, but it contains so much carbon that it is difficult to burn it with- out smoking; this may, however, be done with Arga^ampfor Kero- P^oper care in Van Bensohoten's lamp. Bene Oil. IIXtTMINATION BY MEANS OF GASES. 119 4. iLLtTMnTATIOir BY GASBS. 215. Conditions of the Gas Slannfaetme. — The last source of illimii- nation to be noticed is gas, which gives the cheapest and brightest of all the generally employed artificial lights. It has come into use en- tirely within the present century, and has been very widely adopted in cities. It was first employed in London in 1802, and its use has extended until 408,000 tons of coal have been consumed in a single year by the establishments of that city alone ; producing four thou- sand millions of cubic feet of gas, and yielding an amount of light equal to that which would be produced by eight thousand millions of tallow candles, of six to the pound. How wonderful, that sunbeams absorbed by vegetation in the primordial ages of the earth's history, and buried in its depths as vegetable fossils through immeasurable eras of time, until system upon system, of slowly-formed rocks have been piled above, should come forth at last at' the disenchanting beck of , science, and turn the night of civilized man into day. 216. Materials used for making iti — Gas is chiefly produced from the bituminous varieties of coal (87), those which are rich in the pitchy elements containing hydrogen. It is also made from tar, resin, oils, fats, and wood. 217. Frodnets of the dlstUlation of Coal. — ^If coal is used, it is placed in tight cast-iron vessels called retorts, which are fixed in furnaces and heated to redness by an external fire. The high heat decomposes the enclosed coal, producing numerous gaseous and liquid compounds. The principal products of this destructive distillation are coJie, or the solid residue of the coal, a black oUy Uqnid known as coal-ta/r ; water or steam, various cempounds of ammonia, among others that with gulphuro'm acid, sulphuretted Tiyd/rogen, ca/rlonie acid and earhonic oxide, UgJit cariuretted hydrogen, heaay ea/rbv/retted hyd/rogen or olefiant gas, and a small proportion of vapor of sulphuret of carton. There are also variable traces of many other substances. Z18. Purification of the Gas. — ^This heterogeneous mixture is totally unfit for illuminating purposes nntU purified. The liquid and gaseous products, as they are set free, flow out from the retort through a tube into a receiver called the hyd/roMlic main, in which the liquid products of the distillation — coal-tar and ammoniacal liquor — are to a great extent separated from the gaseous products. But being hot they still retain various matters in a vaporous state, which would be deposited and clog the pipes ; these are still farther separated by passing through the condenser, which consists of iron tubes surrounded by cold water. 120 PEODUCTION OF AETITICIAL LIGHT. The gas is then passed through a mixture of lime and water (milk of lime), or through layers of damp slacked lime, which absorb the car- bonic acid and sulphuretted hydrogen. It is then sometimes freely washed with water, which removes all its ammonia, when it passes into a large receiving vessel, the gasometer, from whence it is dis- tributed in pipes to the places where it is to be consumed. 219. Gomposition of niDmiiiatii^ Gas. — This is very variable, but it mainly consists of olefiant gas, light carburetted hydrogen, carbonic oxide, with free nitrogen and hydrogen, and sometimes other substan- ces in small amounts. It takes its value from the proportion of olefiant gas which it contains, as this is the chief light-producing compound. Olefiant gas consists of 86'21 per cent, carbon to 14'79 per cent, hy- drogen. Several other substances which bum with much light are liable to be associated with olefiant gas, as Butylene, Propylene, vapor of Benzole and Naphtha. Olefiant gas burns with a white and re- markably luminous flame ; but it would hardly answer to burn it alone, as its proportion of carbon is so large, that if the combustion were at all imperfect, there would be liability to smoke. -Light carburetted hydrogen is the same as the marsh gas, which is generated in the organic mud of stagnant pools, and rises upward in bubbles. It con- tains less carbon, and is richer in hydrogen ; its composition being 75 per cent, of the former to 25 of the latter. It burns with a dim yel- low flame, giving but little light. Carbonic oxide and hydrogen both burn with a faint blue, hardly luminous flame. Nitrogen takes no part in the burning process, except to hinder it by diluting the gas, an effect which is also produced by both carbonic, oxide, and hydi-ogen. The gas that comes off from a charge of good coals consists, when the retort is first raised to a vivid cherry-red heat, of 13 per cent, of ole- fiant gas, 82"5 carburetted hydrogen, 3'2 carbonic oxide, and 1-3 of nitrogen. After five hours the gas that continued to escape gave 7 per cent, of olefiant gas, 56 of carburetted hydrogen, 11 of carbonic oxide, 21 '3 of hydrogen, and 47 of nitrogen. Towards the end of the operation, or after about ten hours, it contained 20 parts of carburetted hydrogen, 10 parts of carbonic oxide, 60 of hydrogen, and 10 of nitro- gen. The best gas therefore is that which is produced first. 220. Gas derived from other sources. — Crude and refuse oil, which is unfit for burning, is sometimes converted into gas. It is made to trickle into a retort, containing fragments of coke or bricks heated to redness. The oD, as it falls upon these fragments, is instantly decom- posed and changed to gas. It contains no sulphur products, and needs uo purification. It is very rich in olefiant gas, and has double the rLLtrMINA.TION BY MEANS OF GAS. 121 illnminating power of the best coal gas, and treble that of ordinary coal gas. Kesin also, by being melted and treated in a similar way, yields a highly illuminating gas. But in point of economy, neither oil nor resin can compete with coal as a source of light, A pound of coal yields from three to four cubic feet of gas ; a pound of oil, 15 cubic feet ; of tar, 12 ; and of resin, 10. 221. How Gas is measured. — Gas is sold by the cubic foot, or by the thousand cubic feet. From the underground pipes (maim) that run through the street, a pipe branches off leading to the dwelling to be illaminated. Before being distributed through the house the gas is made to pass through a self-acting instrument called a meter, which both measures and records the quantity consumed in a dwelling. The meter consists of an outer stationary cylindrical case, enclosing an inner and smaller cylinder which revolves upon its axis. Both cylin- ders are closed at the ends, water-tight and gas-tight. The inner one is divided into four compartments with crooked partitions, and the gaspipe passes into its centre or axis, and, turning up at the end, do- livers to them its contents successively. The meter is Icept about two- thirds flUed with water, which the gas „ .„ constantly displaces as the cylinder turns. The principle wUl be understood by the aid of the diagram (Fig. 53), which ex- hibits the meter as if seen endwise, with the ends of the drums removed. A A A A is the outer cylinder ; B B B B the four compartments of the inner one ; c is the gaspipe supplying one of the apartments. As it enters the partition E rises, and the water passes out at the slit B, into the space between the two cylinders. The in- temal one revolves from left to right, the M«*«' "" '^"'^^^^ t^« "«' "' gas passing in the direction of the arrows, first displacing the water and filling the compartments, and then passing out into the space between the two drums, where it is con- veyed away by a tube not shown in the figure. The revolving drum is connected with clockwork, which shows by an index the number of revolutions made, and the capacity of the compartments being known, the quantity of gas which passes through is correctly deter- mined. The meter reports the amount of gas that actually passes through it ; but its indications are by no means to be taken as mfalli- Dle proofs of honesty on the part of the gas company. Thei/r tempta- 6 122 PEODUCTIONS OF ARTIFICIAL LIGHT. tion is, to put on pressure and crowd more gas through than is neces* sary, or than can be burned with economy, for increased consumption of gas does not at all involve a correspdnding increase of light (222). Nor do meters afford any indication whatever in reference to the quality of the gas ; the companies control this, aq4 ™*y tlo quite as they please, the customer being unprotected. "We do not intimate, however, that the gas-companies ever yield to the evil temptations with which they are beset. 222. How Gas Is liiirned. — From the fountain of distribution — ^the gasometer — the gas flows away through the branching system of tubes under the influence of pressure. When little openings are made in the pipes, this pressure drives out-the gas iu jets or streams, and it is these which produce the light when ignited. The orifices are from 5jth to the jVtl' of ^^ \n.(^ in diameter. Recent experiments by the French tend to show that wider openings are more economical with the best kinds of gas. The openings are made in various ways. A circle of them round a large central orifice forms an Argand burner (201). Two holes drilled obliquely, so that the flames cross each other, produce what is called a swallow-tail jet. A slit gives a continuous sheet of flame, called a iat-wing jet. Other figures are also produced, as the "fan-jet" "flsh-tail jet," &o. The quality of light depends much upon the mode of burning as well as the composition of the gas ; a good article may be spoiled by mismanagement. Its illuminating power is impaired when burned too rapidly to allow the separation and ignition of the carbon particles (190). The order of the combus- tion, upon which all illumination depends, is destroyed, by excess of aii:, as when we move a lighted candle rapidly through the atmosphere, the hydrogen and carbon are both burned at once, and we get only a feeble blue flame. This occurs when gas issues with considerable ve- locity from a minute orifice, and by expansion gets intimately mixed with a large proportion of air. When the current of gas does not ignite at a considerable distance (several lines) from the aperture, and then hums with a faint blue flame, the gas-stream iS too rapid, it is improperly mingled with the air and consumes wastefuUy, — that is, to the Iwyer. If chimneys are used, and the di-aught becomes too strong, for the same reasdn the light almost vanishes, yielding only a dull blue flame. On the other hand, too small a draught of air is equally injurious, not only from incomplete combustion which causes the flame to smoke, but also because the highest illuminating power of the "flame is obtained only when the carbon atoms are heated to whiteness, which requires a considerable amount of air. We have ILLUMINATION BY MEANS OV GAS, 123 before seen how rapidly light is evolved hy the addition of small quantities of heat at high temperatures (188). 223. Inflacnce of the length of the Flame. — ^The dimensions of the gas- flame may be controlled with perfect facility by simply turning a stop- cock, although its extent depends upon the width of the orifice and the amount of pressure. It was found that if the hght from a flame 2 inches long were represented at 100, at 3 inches it became 109, at 4 inches 131, at 5 inches 150, at 6 inches 160, witA an equal consump- tion o/ gas in each, case. 224. How mneh, Gas-bimung contaminates the Air. — ^The active source of light in this kind of illumination, as has been stated, is oleflant gas and other compounds abounding in carbon. But these could not be burned alone eTen if it were possible to procure them. A diluting material is therefore necessary to give the flame sufiBcient bulk, and separate the particles of carbon so far asunder as to prevent the risk of imperfect combustion and smoke. Now the three substances found in gas — flight carburetted hydrogen, carbonic oxide, and free hydro- gen — are all equally well adapted for this purpose. So far as liffht is concerned, it is of little consequence which of these is associated with the oleflant gas. But in other respects this becomes a matter of im- portance. The two objections most commonly urged against the use of gas in our apartments sa:6,Jirst, the heat which it communicates to the air; and, gecojwZ, the contamination of it by carbonic acid. Now, in these particulars, the three diluting substances have very different in- fluences. One cubic foot of light carburetted hydrogen consumes in its combustion two cubic feet of oxygen, and generates one cubic foot of carbonic acid, — a portion of the oxygen being consumed in the for- mation of water with hydrogen. This produces a suflBoient amount of heat, according to Dr. Feaheland, to raise 2,500 feet of air from 60° to 80'8°, while a cubic foot of hydrogen burned under the same circumstances produces no carbonic acid, and yields heat capable of raising 2,500 cubic feet of air 60° to 66-4°. One cubic foot of carbonic oxide consumes in burning half a cubic foot of oxygen, and generates one cubic foot of carbonic acid. The light carburetted hydrogen, therefore, is the worst diluent and hydrogen the best, as it produces no carbonic acid, and excites least heat. We saw that at different stages of heating, the coals in the retort yielded at one time a gas, rich in illuminating constituents, and at another time a gas deficient in these, but rich in hydrogen (216). Advantage has been taken of this fact to mingle the products of the retorts at different stages of heat- ing, by which the defiant gas is diluted with hydrogen, and a mixture 124 PEODUCTIONS or AETTFICIAIi LIGHT. produced of superior illuminating qualities and the least injurious effects. 226. Disadvantages of Gas-lighting.' — The chief obstacle to the use of gas-lights in private houses is, that the burners are stationary, and cannot be placed in positions available for all purposes. Candles and lamps are movable, but a gas-light, even where flexible india-rubber tubes are used, is more or less a fixture. The burners being usually situated high for general illumination, and calculated for giving more light than is required for one or two persons, cannot be reduced to the limits of the strictest economy of consumption. Hence, although gas is the cheapest of all sources of illumination, this apparent necessity for consuming it in large quantities prevents the real saving that might otherwise be expected. We have just spoken of the effects of burning gas upon the air, and shall notice it again, as also the prejudices against its use (275). 226. Care of Gas-fixtnres. — ^Air, when mixed with gas, exerts upon it a slow change, tending to produce fluid and solid bituminous bodies by oxidation. Now if air gets access to the tubes and mingles with the gas, as it does constantly between the burner and the stop-cock, when the gas is not burning, the pipe becomes coated and obstructed, and hence requires periodical cleaning, which should be done with in- struments that ought to be furnished gratuitously by the gas com- panies. Gas of high value contains six per cent, of its volume in vapor, which can become fluid in the pipes when they are exposed to the temperature of freezing water. Hence depressions in the pipes soon collect fluids, unless they decline towa/rds instead of from the meter, and the flow of gas to the burner is irregular, producing fluc- tuation or what is called 'jumping' of the flame. "When the burners are long out of use, as sometimes in summer, the pipes are liable to become deranged and clogged, and as gas acts on and solidifies all oily and lubricrating substances hitherto used, the keys of stop-cocks often become fixed. — Hays. The veijtilation of gas-burners wiU be de- scribed when treating of air (360). 6. Measuebment or Light. 227. Can Light he Jneasnred I — ^It is sometimes of importance to de termine the cost of light produced in different ways and from different materials. There is no method known by which light can be directly measured ; that is, we have no mode of estimating the absolute quan- tity of light emitted by a flame, but we can ascertain how much mora MODE OF ITS MEASUEBMENT. 125 Fio. 64. or less light one flame produces than another, and thus arrive at nseful eomparative results. All flames are not equally hright, — of two flames of equal size, one may be much more brilliant and emit more light than the other. Wo do not judge of the intensities of different lights by direct comparison, but by the comparison of their shadows, on the principle that the greater the illuminating power of the light the deeper is the shadow which it oasts. 228. How Ligbt Is Measured. — Before a piece of board, covered with nnglazed white paper at a distance of two or three inches, let an iron rod be placed which has been previously blackened by holding it in the candle. Now if it is desired to compare two lights, they are to be placed opposite the board at the same height, and each wiU cast a shadow upon the paper as illustra- ted in Fig. 54. The lights should be so sit- uated that the shad- ows will fall close to each other, and the stronger flame should be so far removed, or tlip weatpr advaTipetl ^l'ot<>™«t«'<>r''<"'t'lT*'"'6'*>'™°''"™^°St'''9'°'6''sitjr of light that both shadows will appear equally deep. To ascertain their luminous intensities we measure the difference from their centres to the shadow : if these are equal, their illuminating powers are equal ; but if one casts an equal' shadow at a greater distance than the other, its light must be more iatense, or its illuminating power greater. The difference in the degrees of light is not proportional to the distances of the luminaries from their shadows, but to the squa/re» of these dis- tances, in accordance with the law of radiation before explained (136). If one light at two feet, and another at six, give equal shadows, their difference is not as six to two, but as the square of 6, 'vAich is 36 to the square of 2, which is 4 ; that is, 36 to 4, or 9 to 1. The luminary at 6 feet gives nine times as much light as the one at 2 feet. 229. We have ao unit for measnriiig Light — This plan, modified in va- rious ways, affords a ready means of comparing the relative amount of light emitted by two flames. But we have not been able yet to reap the practical advantages which this success at first appears to promise. If we can measure light, why not establish the exact iUumi- 126 STKUCTUISE AJSD OPTICAL POWERS OF THE EYE. nating values of the various lighting materials, so that we may kuo-ff precisely how far a dollar will go in buying light when the substances are at given prices. Something has been done in this way, but we have no results that command implicit trust. The composition of the materials is variable, and the same materials in dififerent trials give different results. We are without an accepted unit to serve as a stand- ard for a scale of values. It has been proposed to make the sperma- ceti candle (6 to the lb.), burning 120 grains to the hour, the unit of measure. If this were satisfactory, we could compare other lighting materials with it. A burner consuming a certain amount of gas per hour would equal a given number of candled, and any variation in its quality would be easily detected. We should speak of it as lO.candle- gas, 15 candle-gas, and 20 candle-gas, according to its gi-ade, and so of the various illuminating substances. But these candles have been found to burn variably, and do not perfectly answer. Some unit will probably be fixed upon by which the comparative values of lighting materials may be determined and expressed. 230. Photometric Results of Uro andKenti. — ^Dr. Uee gives the follow- ing as the cost of an equal amount of light per hour from several sources, according to his experiments. Fence. Carcel Lamp, "with Sperm Oil 1} Wax Candles 6 Spermaceti Candles 5i Stearic Acid Candles 4i Moulded Tallow Candles 2} E. N. Kent, of the TJ. S. Assay Office, experimented on various lighting materials with the following results : Retail price of Cost of an equal Materiali, Lamp used. Oil per gallon. amount of light. Kerosene Oil Kerosene. $1 00 $4 10 Camphene .*. Gamphene 63 4 85 SylTioOil EosinOil 60 6 05 Eape Seed Oil Mechanical 1 69 9 00 Whale Oil Solar _ 1 00 12 00 Lard Oil Solar 1 25 IT 00 Sperm Oil Solar 2 25 26 00 Earning Fluid Large Wick 87 29 00 • Tin.— STRUCTURE AND OPTICAL POWERS OF THE EYE. 231. Value of the sense of Vision. — The eye is perhaps the most im- portant organ of sense. By it the mind is put into the widest com- munication with the external world. Although it may be said that this organ only recognizes light and colors, yet through it we become acquainted with the forms, magnitudes, motions, distances, directions and positions of aU objects, whether immediately around us, or re- THE lEIS AND PUPIL, AND THEIR USES. 12V motely distributed tlirougli the distant universe. In its adaptation to the agent which is designed to act upon it, the eye is a miracle of beauty and wise design. For this reason alone we might well afford' to devote a little space to it ; but when we consider that it is an organ of exquisite delicacy, and greatly liable to abuse from the domestic mismanagement of light, as well as other causes, and remember how tedious and distressing are its disorders, and what a lamentable life- disaster is its loss, it becomes of the first importance to assist in diffus- ing any suggestions that may lead to its better care. Our previous study of light and colors will moreover aid us materially in forming oorrect ideas upon the subject. 232. Sclerotic Coat and Cornea, and their nses. — ^When the eye is re- moved from its socket and dissected, it is found to consist of several coats. The outer one forms the white of the eye; it is a tough, re- sisting membrane, and serves both to sustain the delicate parts within, and also to give insertion to those outer muscles which roll the eye- ball. It is called the sclerotic coat, or briefly the sclerotic. As light is to enter the eye, and as, from the nature of the organ, it could not be admitted through a hole, it became necessary to have a window in the eye-ball. In the front part of the globe there is a circular open- ing in the sclerotic, which is closed by a thin and perfectly transparent membrane called the cornea, the front window of the structure. The cornea bulges out somewhat like a watch-glass ; that is, it is more convex than the general surface of the eye-ball, Si maybe felt through the closed lid. It covers that portion of the eye ^hich is colored, and is attached round the edge of the colored. part to the sclerotic coat, with which it is continuous. The cornea is very hard, tough and horn-like, the word being derived fi-om the Latin cornu, which signi- fies horn. The general arrangement of the parts we are describing is shown in the accompanying view of the section of the eye (Fig. 55). 233. The Iris and Pnpil, and their uses. — Behind the cornea there is a small space or chamber filled with a perfectly clear and col- orless liquid, which consists chiefly of pure water, and is called the aqueom humor. This chamber is divided by a thin partition known as the iris, in the centre of which there is a circular aperture called the pupiL The pupil is simply, therefore, a hole through the hris ; it is the round black spot which we see surrounded by a colored ring. That colored ring is the iris. It is black behind, and on the front or visible side, it is of different colors in different individuals. The color of the ii-is is observed to be, in some measure, connected with the color of the hair. The iris has the remarkable property of con- 128 STEUCTCTEB AOT) OPTICAl POWEES OF THE EYE. Tie. 55. Oi/sbillineXcns Vtlremt ChoroXi > coat tracting and dilating under tlie influence of light, by which the pupil is enlarged and diminished. If the light be strong, tha iris contracts and reduces the size of the pupil, so as to exclude a portion of the light ; if the light be weak, the iria expands so that more light is ad- mitted. This moderates and equal- izes the illumination of the organ, the delicate sensibility of which might otherwise be injured. The play of this mechanism may easily be seen by bringing a candle near to , nea-e ^ the eye while gazing upon its im- S'eleynlie coaT , t i • i rrii • Eelation and names of the several parts agem a looking-gjass. Ihesemove- of tte Eye. ments are inroluntary, the eye reg- ulating the quantity of light it will receive, independent of the choice of the mind. 234. Crystalline Lens and Vltreons Hnmor. — ^Behind the little chamber, of which we have spoken, and bounding it on the back side, is a sub- stance in the form of a double convex lens, called the crystalline lens. It is situated immediately behind the pupil, very near it, is a little larger than that opening, and is very convex, its thickness being al- most equal to its diameter. It is supported by a ring of muscles called the ciliary proaesi. The crystalline has about the consistence of hard jelly, and is purer and more transparent than the finest rock-crystal. It is this part which becomes diseased in cataract. The space behind the crystalline lens constitutes the main body of the eyeball, and is filled with a clear gelatinous fluid, very much resembling the white of egg, and called, from its apparent similarity to melted glass, the mtreous humor. 285. Tbe Choroid Coat, and how it Is Colored. — There is a second coat, lining the interior of the sclerotic, which consists of minute vessels, arteries, and veins, closely internetted, and is called the choroid. It extends around to the cornea, and supports the ciliary process. The inside of the choroid is covered with a slimy matter of an intensely black color, called the pigmentvm, nigrum (blcuik pigment). This gives to the interior of the eye a jet-black surface, which absorbs and stifles the light, so as effectually to prevent reflection. 236. Optic Jferye and Retina. — ^At the back part of the eye, the scle- rotic coat is formed into a tube which leads inwards to the brain. This tube contains the optic nerve. As it enters the globe, it spreads out over the inner surface of the choroid, in the form of a most deli- Fis. 5«. THE EETniTA SUPPOSED TO FEEL THE PICTtlEE. 129 cate network of nervous filaments, called, from its reticulated struc- ture, the retina. The retina is therefore the extended and diffused optic nerve. In dissection it is easily separated from the choroid. It is absolutely transparent, so that light and colors penetrate and pass through it perfectly, and therefore fall upon the dark surface beneath. To prevent the delicate and transparent nerve tissues of the retina from being stained by the black pigment, a very thin film is interposed between them called JaeoVs membrane. 237. How Vision Is Produced.— From every object which we see, rays of light pass into the eye, penetrating the successive transparent media, the cornea, the aqueous humor, the crystalline lens, and the vitreous humor, and falling upon the retina, form there an image of the visible object, the impression of which is carried by the optic nerve to the brain. The diagram (Pig. 56) shows how, in the perfect eye, the image is made to fall accurately upon the retina. It is seen to be inverted. The pictures in the eye, of everything we behold, are upside down, although there is no confusion, and we are unconscious of it. "We have said that the image is formed upon the retina, and this is the common mode of expression, but that is perfectly transparent, so that the colored image is formed, not proper- ly upon it, but upon the black surface of the choroid coat behind it. It is maintained that the retinal membrane is affected by the colored image in the same manner that the sense of touch is affected by ex- ternal objects. It is supposed to touch or feel, as it were, the image on the choroid, and transmit the impression to the brain, something in liie same way that the hand of a blind person transmits to the or- gan of consciousness, the form of an object which it touches. This view seems to be confirmed by the fact, that at that portion of the retina where the optic nerve enters the eyeball, which therefore has not the black choroid behind, it is insensible, and produces no per- ception. It has been proved by experiment that images made to fall upon that spot, are instantaneously extinguished. 238. Wonderfnl Minntcness and Distinctness of the Images.— N^othing is more calculated to awaken our astonishment than the perfect dis- 6* How the Images are formed in tlie perfect Eye. 130 STEUCTUEE AND OPTICAL POWBES OP THE ETB, tinctness of the pictures upon the retina, compared with their magni- tude. The diameter of the picture of the full moon upon the retina is hut the -^^ part of an inch, and the entire surface of the picture is less than the Siirs V^^ of * square inch. And yet we are "able to perceive portions of the moon's disc, whose images upon the retina are no more than the 15,000,000th part of a square inch. The figure of a man 70 inches high, seen at a distance of 40 feet, produces an image upon the retina the height of which is about the yV part of an inch. The face of such an image is included within a circle whose diam'eter is about 1^ of the height, and therefore occupies on the retina a cir- cle whose diameter is about ^\ part of an inch ; nevertheless, within this circle, the eyes, nose, and lineaments are distinctly seen. The diameter of the eye is about ^ that of the face, and therefore, though perfectly visible, does not occupy upon the retina a space exceediug the l-4,000,000th of a square inch. If the retina be the canvas on which this exquisite miniature is delineated, how infinitely delicate must be its structure, to receive and transmit details so minute, with such wondrous precision ; and if, according to the opinion of some, the perception of these details be obtained by the retina feeling the image formed upon the choroid, how exquisitely sensitive must be its touch. (Laednee.) 239. Adaptation of the Eye to Intensities of Lighti — The susceptibility of the eye under great variations of intensity in the light which en- ters it, is most wonderful. Ve can read a book either by the light of the sun or of the moon, yet sunlight is more than a quarter pf a mil- lion times more briUiant than moonlight. " The direct light of the sun has been estimated to be equal to that of 5,570 wax candles of moderate size, supposed to be placed at the distance of one foot from the object. That of the moon is probably only equal to the light of one candle at a distance of twelve feet, hence the light of the sun is more than 300,000 times greater than that of the moon." "WoUaston estimated the light from Sirius, one of the largest fixed stars, as twenty thousand million times less than that of the sun. 240. CondlHons of tbo System aifect the Eye. — The eye is thus an opti- cal contrivance which challenges our wonder continually for the ex- quisite beauty and perfection of its parts. Tet we must not forget that it is a living organ of the body made np of vessels, membranes, muscles and nerves, and nourished by the vital blood-stream like any other organ. It is therefore liable to be influenced in numberless ways by conditions of the system. When in use, it acts, expends force, exhausts itself and becomes fatigued. Dr. Whaetoit Jones remarks : STATES OF THE BODY APFECTIKG THE EYES. 131 ' Much exertion of the eyes operates more prejudicially to the sight under some ou'cumstances than under others. Exertion of the sight is especially prejudicial immediately after a fiiU meal; after the use of spirituous drinks ; while smoking ; when the hody is in a reoumhent or stooping posture, when dressed in tight clothing, especially a tight neckcloth ; tight corsets ; and even tight hoots or shoes ; in close and ill-ventilated apartmentslit with gas ; after hodUy fatigue ; during men- tal distress ; late at night when sleepy ; after a sleepless night ; while the bowels are much confined ; during convalescence from debilitating iUness. Though during recovery from severe disease the eyes cannot bear much exertion, yet, for want of other employment, it is not un- common for convalescents to read even more than when in health. Many persons have much injured their sight in this way. Young growing persons, at the age of puberty, persons of weakly constitu- tions, -are incapable of supporting much exertion of the eyes without injury to the sight." Sudden suppression of the perspiratcry action of the skin, or any cause which determines a pressure of blood to the head, is also liable to affect the eyes injuriously. 241. Reading and Writingt — In this reading age, with such strong and insidious temptations to overuse and bad management of the eyes, it may be well to make some suggestions concerning this mode of exercising vision. The closer the eye is confined to the page, the more of course it is strained. Novel reading is worse than science, history, or any grave subjects, because in the first instance we read fast and uninterrnptedly, while in the latter cases thinking alternates with the use of the eyes in reading. Eeading from a broad page with the lines long and the print small, is very tiresome, as it is difficult for the eye always to take up the next line. "Writing down our own thoughts is easy for the sight ; but copying is hard, as we have both to read and write, and look backward and forward in addition, Eeading when in motion, as in riding or walking, or in the brightness of sunshine, or under a tree, where from the motion of the leaves by the wind lights and shadows fly over the page, are all severe upon the eyes, and liable to injure them. But perhaps the most serious mischief to which we are exposed in reading, comes from the bad quality of artificial light, which we shall notice particularly further on. IX.— OPTICAL DEMICTS OF VISION— SPECTACLES. 242. Limits of perfect Vision. — The transparent portions of the eye, the cornea and included humors, act as lenses (149), which bend or refract the light from its straight course as it passes through them, 132 OPnCAl DEFECTS OF VISIOK — SPECTACLES. Fio. 5T. bringing it to a point or focus at the back of the eye. Where the vision is perfect, the rays are so bent that the image, in its utmost distinctness of outhne and color, falis exactly upon the retina, as shown in Fig. 56. If the eye were a fixed or ri^d mechanism, as if made of glass, only objects at certain precise distances would come to a point upon the retina, all others would produce their images either before or behind it, and thus give rise to imperfect vision. But the organ possesses a power of adjustment by which objects at different distances may be seen clearly. How this occurs is not understood. Perhaps the crystalline lens is capable of slightly varying in position and curvature. The limits of perfect vision in the normal eye vary somewhat in different persons^ but in general they may be put down as between nine and fifteen inches. 243. Cause of Far-sigbtedness. — The eye is a system of lenses beau- tifully arranged to bend light to a point. But its bending or con- vergent powers may be too Tiigli or too low, producing imperfect vision in either case. This converging or refractive power de- pends upon the curvature of the lenses The rounder they are, the stronger they are ; the flatter they are, the weaker they become. As persons advance in life, there is a ten- dency to loss of fluids, which fill and dis- fend the body, and a consequent shrinking of the flesh and wrinkling of the skin. Th< Far-sighted Eye with flattened gyg participates in this natural change of tissue, its contents seem to shiink, and the cornea becomes flattened or loses something of its convexity, appear- ing as shown in Fig. 67. This ^Todmaesfa/r-sigJitedness, in which per- sons can see objects distinctly only when they are at a very consider- able distance from the eye, such as holding the book at arm's length in reading. In this state of the eye the rays tend to a focus at a point behind the retina, on which, there- fore, they strike in a scattered state, forming an indistinct image. In Fie. ss. Far-sighted Eye — ^the focal point thrown too far hack. COEKEOTION 01" PAE-SIGHTED EYES. 133 Fig. 58 the object a has its focal point thrown back to J, making a confused picture upon the retina at c. The further an object is from ns, the less divergent or more parallel are the rays coming from it; and the less divergent are the rays which enter the eye, the easier are they brOnght to a focns by it. This is the reason that to the far- sighted, distant objects are distinct, and near ones confused. The far- sighted see minute objects indistinctly at every distance, because when near they are out of focus, and when remote from the eye, they do not reflect sufficient light to make a strong impression. They hence strive to increase the light upon the object, as we often see when attempting to read by candlelight, they place the candle between the book and the eye, and both at arm's length. It is but rarely that eyes recover naturally from this defect, yet much may be done to preserve the sight by care. When the eyes begin to fail, all over-exertion, as minute work or reading by badly arranged artificial light, should be avoided. As soon as the eyes begin to feel fatigued or hot they should have rest. 244. How Glasses help the Far-sighted. — The remedy for this defect is convex lenses, which are so selected and adapted to the eye as ex- actly to compensate for the want of refracting power in the organ itself. These len- Fio. 69. ses gather the rays to a point at vari- ous distances de- pendingnpon their curvature. The greater the curve, the nearer the fo- cus and the higher the power • while rar-sighted Eye corrected by double convex glaeees. with less curvature, and a more distant focus, there is lower power. The refractive power of a glass is expressed by the distance of its focal point in inches. A 10-inch glass, or a No. 10, coUeots the rays to a point at a distance of 10 inches, a No. 5 at 5 inches, and a No. 20 at 20 inches. The higher numbers express the lower powers, and the lower numbers the higher powers. Fig. 69 shows the far-sighted eye, with its internal focus, prot)erly adjusted by a convex glass. 245. Maaagement of. far-sighted Eyes. — When the sight begins to fail, and glasses are sought, those of the lowest power, which will bring objects within the desired distance, should be chosen. But they should be comfortable and not cause headache, nor strain or fatigue 134 OPTICAL DEFECTS OF VISION — SPECTACLES. the eyes ; if they do this, they are too convex. If practicable, it is well to get two or three pairs from the optician, as nearly correct as possible, and try them leisurely at home before deciding which to take. If the eyes only see clearly at a 'oery great distance, the No. of the glass required will be the same as the number of inches at which it is desired to read. But the moderately far-sighted do not require such strong glasses. If they can see small objects distinctly at 20 inches distance, for example, and wish to be able to read at 12, the power of the desired glass may be obtained by multiplying the two distances to- gether, and dividing the product, 240, by the difference between them, viz. 8 ; the quotient, 30, is the focal length in inches of the glasses re- quired. The intensity of the light influences the power of the glasses used ; it is commonly found that those a degree more convex are re- quired by artificial light, than by daylight. Many suppose that glasses of certain focal lengths correspond to certain ages, but no rule of this kind is safe. The nearest average relation between the age and the focal length of the convex glass is as follows : Age in Tears "....40, 45, 50, 55, 60, 65, TO, T5, 80, 85, 90. Focal Length In Indies 8^ 80, 24, 20 16, 14, 12, 10, 9, 8, 7. 246. Vcar-sightedness. — This is the opposite defect; the cornea is too rounded and prominent, as shown in Fig. 60. The rays of light which fall upon it are consequently too powerfully' refracted, and ar- riving at a focus before reaching the ret- ina, cross, and are in a scattered state when they do fall upon it, as illustrated in rig. 61, where a is the object, 6 the focus, and c the confused rays falling upon the retina. In this condition of vision, persons can see objects with per- fect distinctness only when they are at a short distance from the eyes ; if they bring minute objects closer than ten Near-sighte'd Eye, with its Protrnd- inches they are usually accounted near- mg ornea. sighted. By bringing the object nearer it is distinctly seen, because the rays of light from it which enter the eyes, being more divergent than whea it was distant, are not so soon brought to a focus. The near-sighted eye retains its power of adjust- ment to distances ; the nearest distance may be from 2 to 4 inches, while the greatest is from 6 to 12. Short-sighted people see minute objects more distinctly than other people, because from their nearness FlQ. 60. Near-sighted Eye, the focus filing too ikr forward. COEEKCnON OF NEAE-SIGHTEDNESS. 136 they are viewed under a larger angle and in stronger liglit. They can see better than others with a weak hght, and hence can read small print with a feeble iUumination. To persons who are occupied with minute objects, short-sightedness, unless extreme, is rather an advan- tage, as they can j^g_ 6i_ observe all the details of their work very ac- curately, while for distant vis- ion they can get ready help from glasses. Yet if an eye be at first perfect, the constant employment of it upon small objects tends to produce near-sightedness, which is hence a common defect of vision among the educated classes, and those who do much minute work. On the contrary, the habitual exercise of the eyes upon distant objects improves their power in that direction. If young persons have aten-- dency to nearness of sight, and are designed for vocations in which lengthened vision is required, they should avoid much exertion of the eyes on small objects, and exercise thein frequently in scenes in the open country. It is an error that the near-sighted acquire perfect vision as they advance in life. We often see old people who are com- pelled to use near-sighted glasses ; indeed, this state of the eyes some- times occurs in old persons whose vision was previously at the usual distance. 247. Jlfmagement of Near-sightedness. — Concave glasses extend the vision of the near-sighted by separating or diverging the rays of light before they enter ^^ ^^ the eye, so that they may be less quickly brought to a focus, and the image formed further back, as shown in Pig. 62. ^ Near-sighted Eye, corrected by double concaTe glass. glasses for the near-sighted are expressed in a manner contrary to those for the far- sighted (245). They are numbered 1, 2, 3, &c., No. 1 having the 136 OPTICAI, DEFECTS OP VISION — SPECTACLES. smallest convexity and the smallest power, and being therefore adapted for those that are least near-sighted. In selecting glasses, the near sighted should choose the lowest or weakest powers that will answer the purpose, and the best plan is to make trial of a series, as was sug- gested to the far-sighted. If the glasses make objects appear very bright, or glaring, or small, or produce fatigue, strain, or dizziness and confusion of vision after being laid aside, they are too concave. If glasses are wanted for reading or to behold near objects, the power of the required glass may be determined as follows : Let a person multi- ply the distance at which he is able to read easily with the naked eye, say four inches, by the distance at which he wishes to read, say 12 inches, and divide the product, 48, by the difference between the two, which is 8 ; the quotient, 6, is the focal length of the glasses required. The far-sighted have to change their glasses as the sight progressively fails, but near-sightedness usually continues much the same through the greater part of life, so that the same glass gives assistance a much longer time. It is well for both the far-sighted and near-sighted to employ glasses of various grades for different purposes. Thus the near-sighted need glasses adapted to distant objects, and as they are much inclined to stoop in reading and writing, they might remove the eye further from the page by using glasses of slight concavity. Near- sigh tedness may be occasioned by other causes than the one just no- ticed. There may be a declining sensibility of the retina, which makes it necessary to bring objects nearer to the eye ; this is called nervous sTwrt-aightedness, and although objects are seen better close by, yet they are not seen so distinctly as in true or optical short-sightedness. Such persons seek strong light, to get a more vivid impression, and use convex glasses to increase the light upon the retiua. This us6 of glasses is perilous (266). Short-sightedness is sometimes a symptom of com- mencing cataract. This disease is not, as is commonly supposed, something growing over the sight on the outside of the ball. It is a change in the crj'stalline lens, by which it loses its transparency, and becomes more or less opaque, so as to confuse, scatter, or stop the light, and destroy the distinctness of the image. Children often shorten their vision at school by stooping over their desks and poring over bad print, combined with the debilitating action of extreme heat and bad air, a result which should be carefully guarded against by parents and teachers. 248. Important Suggestions in selecting Spectacles. — Whatever be the defects of vision which spectacles are designed to remedy, there are certain points which should always be observed, both by the maker in SUGGBSHOITS COKCBKNING SPECTACai^S. 131 monntmg the glasses, and by the buyer in selecting the frames. It is essential that the lenses be so framed that their axes shall he exactly parallel, so as to coincide with the axes of vision when the eyes look straight forward. Frames are often made so light and flexible as readily to bend in clasping the head, so that the glasses cease to be in the same plan, and their axes lose their parallelism. This is shown in Fig. 63, where the axes of the len- ses, c d, instead of coinciding with " " . the axes of vision, a 5, are altered in \ i their direction, and become conver- gent. Again,,the most perfect vision with spectacles is produced when the eye looks through the centre, or in the direction of the axis of the lens. Where the eye turns from the axial centre of the glass, and looks obliquely through it, the view is less clear and perfect. For this reason persons wearing spectacles general- ly turn the head, where those with- The axes of the glasses, o y daylight. This is a necessary consequence of the difference in the ITS KFFBCTS UPON THE EYBS. 139 rays which fall upon them. As sunlight contains a large proportion of Hue rays, .and artificial light an excess of yellow rays, they roust inevitably influence the color of surfaces in a different manner. In artificial light green has a yellow hue, and blue turns green from the excess of the yellow rays ; dark blue becomes purple and nearly black ; orange, by reflecting its own constitntent rays, appears very bright ; yellow appears white, from there being no really white light to con- trast it -with, and red has a tawny color from the excess of yellow ; at the same time all the colors except the orange are much impaired in brUlianoy, and many of the deeper shades become quite black and sombre, from there not being any pure white light reflected from their surfaces, as in daylight, when even the gravest colors have a remark- able degree of clearness and purity. Of course the appearance of colors by artificial light will depend directly upon its quality. The whiter and purer and nearer to daylight it is, the more bright and natural will they be ; while the more' colored and dingy the light, the more chromatic disturbance and perversion wiU it produce. 253. How litificial Light affects the Eyes. — But the eye itself is affected by the use of artificial light, as is shown by the following simple experiment, suggested by Dr. James Httntee. "Tie up the left eye, and with the other look steadily and closely for about a minute at some small object placed upon a sheet of white paper, and strongly illnminated with ordinary daylight, but not exposed to the direct rays of the sun ; then uncover the left* eye and look at some distant white object or surface, such as the ceiling of the room, first with the left eye and then with the right. It will be found that there is not much difference in its appearance as seen by one eye or by the other, though in general it will be a veiy little brighter to the left eye. After this, darken the room by closing the shutters, tie up the left eye again, and then with the right one look at the same object placed on a sheet of white paper as formerly, but illuminated by a large tallow candle or oil lamp, so that it shall be seen as distinctly as it was in daylight. Keep the right eye fixed on this object for about a minute, so as to examine it closely and narrowly, then extinguish the candle or lamp, open the shutters, and uncover the left eye. When both eyes are now turned to the ceiling, it will appear some- what dim and indistinct ; and on looking at it first with the one eye, and then with the other, the difference will be very remarkable. To the left eye, which had not been exposed to the action of the artificial light, it will appear unchanged, or sometimes of a pale yellowish- "vhite color ; but to the right eye it will be very dim and of a dm-'k 140 iNJUEioxrs AcrnoN of aettficial light. llite or purple color. The effect produced upon the right eye in this experiment soon goes off; and though it always takes place to a cer- tain extent when artificial light is used, it is not much observed, because as both eyes are equally affected, the contrast is not very striking. But if any one wiU read or write by candlelight for some hours with one eye closed, he wiU be rendered fully sensible of its very injurious action, when he afterwards compares the state of one eye with that of the other. 254. Explanation of these effects. — We shall understand these effects by recalling what has been said of complementary colors (173). When the nerve of vision is exposed to a colored light, it is unequally excited. The equilibrium of its action seems to be disturbed. It becomes less sensitive to the observed color, and when the eye is afterwards turned to white objects, they do not appear white but tinged with the com- plementary to the one seen first. The continued action of one color seems to paralyze the retina to its influence, and produce an unnatural sensibility to the other colors, which, combined with that, compose white light. In the preceding experiment, the eye, stimulated by candlelight, in which orange-yellow is in excess, temporarily lost its power of discerning white, and saw in it only the complementary of orange-yellow, blue or dark violet. 255. How this may Injure the Ketina. — ^Now the effect of this over- stimulating the nerves of vision through excess of red and yeUow rays, on the part of those who use their eyes much by artificial light, is often to produce at certain points of the retina a total insensibility to those rays. The consequence of this is, that in daylight dark films of a blue or purple color, which are complementary to the orange or yellow color of the artificial light, appear before the eyes. The pecu- liar color of these films is not very obvious, unless they are seen in contrast with a yellow or orange surface, and over them they appear very sombre and almost black ; because, in the peculiar state of the eye that gives rise to their appearance, there always coexists a certain degree of diminished sensibility to aU the rays composing white light. 256. Popular recognition of the effect of different Colors. — There is a difference in the effect of different colors upon the eye, which is generally recognized and variously expressed. Thus blue is said to be a very soft, cool, retiring color ; green is cool, though less so than blue ; yellow is warmer and adnxmeing ; orange still warmer, and red, fiery, Tiarsh, and exciting. This agrees with the view which regards blue and green as least hurtful, and yeUow, orange and red as more ITS ASSOCIATED HEAT. 141 irritating and injurious to the eyes. An explanation of these different effects is found in the wave theory of light and colors, which has been previously noticed (155). Vibrations of the red ray are larger and more forcible than those of the yellow, and the yellow than those of the blue, just as the large and slow heavings of a swell upon the ocean are more violent and irresistible than the smaller and quicker ripple- waves. 257. Heat aceompanying Colors. — The above current phrases in refer- ence to the coolness and warmth of color, correspond perfectly with the distribution of measured heat among the several colors of the spectrum. "We all know that heat is associated with light ; but it is not equally associated with each color that composes the light. When the colors of the sunbeam are separated and spread out as ic the spectrum, it is found that the heat is least intense at the blue, and constantly increases through the green, yellow, orange, and is most intense in the red color. Thus Englbfield found that while the blue rays were at a temperature of 66°, the yellow were at 62°, and the red at 72°. Thus the orange and red of common artificial light are actually more fiery and exciting than the absent blue rays. This ac companying heat is apt to be much more injurious in artificial than in natural light. The sun's rays are seldom, if ever, aEowed to fall directly on a near object on which the eyes are to be employed for any length of time, without having previously undergone repeated reflections from the atmosphere ^d clouds, or from the surface of the ground and walls and furniture of the apartment, which absorb a great portion of their accompanying heat. But owing to the non- diffused and concentrated character of artificial light, the rays must be generally allowed to fall directly on the object looked at, from which they are reflected to the eye along with nearly the whole of their accompanying heat. -«. 258. The Lnmlnons Matter being imperfect, more mnst be used. — The luminous effect, or as it is termed, the defining power of light, that quality by which we are enabled to see minute objects with the most distinctness and ease, is much less in artificial light than in the white light of day. This lower defining power of orange-colored light makes it necessary to increase the amount of the inferior rays ; we attempt to compensate for deficient qtuiKty by excess in quantity. In reading by daylight the black ink is strongly contrasted with the pure white paper ; but by artificial light, as the paper has an orange or yel- low hue, the contrast is not so marked, and so to aid vision, the quantity of light is increased. In severe,- long-continued, and nightly exercise, 142 INJUEIOUS ACTION OP AETlFICLiL LIGHT. as in reading, writing, sewing, type-setting, &c., the injurious conse- quences of impure light are apt to be heightened by its excessive use. 259. Carbonic Acid affects the Eyes. — Sunlight does not poison the air, artificial light does. In proportion to its brilliancy and abundance, the insidious narcotic agent, carbonic acid gas, is generated and set free. The effects of breathing this substance will be described when treating of the air and ventilation (293) ; but it may be remarked, that by its special influence in deranging and disordering the nerves, it is fitted to concur with those influences which impair the action of the retina. ~ 260. Cnsteadlaess of Artiflcial Light injnriong^ — Sunlight never wavers or flickers ; its action upon the eye is equable and unvarying. But in artiflcial illumination, as it is impossible perfectly to regulate the sup- ply of air and of combustible material, the light is flickering and un- steady. The glass chimney of the Argand burner, however, produces the most constant and unchanging flame. The bad effects of these sudden and continual alterations in the brightness of artificial light, may be shown by supposing that a minute object can be seen in light of 8, 9 or 10 degrees of intensity, but that the intermediate degree of 9 is best .Now if sunlight be used, as it flows in a perfectly uniform man- ner without sudden variations,' the retina and pupil adapt themselves to its quantity, and the eye may be long used without fatigue. But if .artificial light of 9 degrees he used, it may at one moment rise to 10, and at the next fall to 8 degrees, from the flickering of the flame, so that the retina and pupil have not time to accommodate themselves to the change, and a degree of temporary blindness or impaired distinct- ness of vision, results, which is very straining and fatiguing to the eye. To remedy this, the light is increased in intensity. If it be raised, say to 14 degrees, then it may be reduced to IS or rise to 15 degrees, without immediate inconvenience to the eye; there being abundance of light, its variations are less sensible. This relief, how- ever, is fraught with ultimate danger ; for the retina is too much excited by this increase of one-half in the quantity of light admitted to it ; and this state of excitement is but the prelude to an opposite state, in which the sensibility to light is greatly, and perhaps perma- nently diminished (265). Unsteadiness of the object view«d, if the eye be long and closely directed to it, is a source of injury. It is thus that much reading in railroad cars, where the trembling or incessant movement of the print keeps the image in constant motion upon tha retina, has a bad influence upon the eye. 261. ill Light ii(jiirions1iiit that from the objects viewed. — The distinct- THE EYE BLINDED BY EXTEANEOUS EATS. 143 ness of vision is interfered with, and the eyes made to suffer by an- other important circumstance — the admission of light into the eye from other sources than objects to which sight is directed ; in other words, the introduction of extraneous light into the eye. Impres- sions upon the retina may be diminished and obliterated by other rays falling upon it, which excite the nerve more strongly. The moon at night, as we all know, produces a vivid impression upon the nerve of visual sense. It produces precisely the same impression in the daytime, but then the luminous image is extinguished by the over- powering light of the sun, so that we are not conscious of it. When we are using the eyes upon any object, all light which enters them, except from that object, is injurious ; that is, it has a blinding effect. This is shown by the greater clearness of objects seen throngh a tube, where all the diffused and side-light is excluded, on the same principle that persons see stars from the bottom of a well in the daytime.* Or it may be shown in another way. Let a person stand before a gas-light in such a position, that in reading a book a considerable number of the direct rays from the flame shall enter the eye. Let him then cautiously reduce the light by turning the stop-cock until the letters can be no longer distinguished., If he now shade his eye by inter- posing his hand or a screen, so as to cut off the direct rays, the words wiU again become visible, and again disappear when the hand or screen is removed. This proves that when the eye is protected from the direct rays, small objects can be seen with less light, aftd conse- quently with less injury to the nerve of vision. 262. Prevalence of this soniee of injury. — Upon this point Dr. Htjn- TEE remarks : " Though the injurious action of artificial light, in con- sequence of its improper position, can be easily obviated ; it is aston- . ishing how little it is attended to, and how generally it is in operation. For the express purpose of satisfying myself on this point, I have visited a great many workshops, printing-houses, tailors' rooms, and other places, and in almost every instance I found the artiiicial lights placed close to, and directly opposite the eyes of those engaged in fine work, requiring the excessive exertion of the sight, and frequently the mischief was increased by concave metallic reflectors, placed behind instead of around the light. Now that gaslight is so generally em- ployed, its improper position is a most serious evil ; for as its intensity can be so easily increased in proportion as the sensibility of the eye becomes impaired, few persons, particularly those who are igno- rant of the harm they are doing, can resist the temptation to use a • HcMBOiDT, however, questions if stars are ever thus seen. 144 rNJUEIOUS ACTION 01" AETIFICIAL LIGHT. stronger and stronger light, till at last their sight is permanently weakened or even quite destroyed." 263. Bad Light may Inflame the Eyes. — The continued action of im- pToper light upon the eye is liable to inflame it. The first symptom is a reddening of the lining membrane of the eyelids, which in health is of a white or pale rose-color. This may be observed by gently drawing down the lower lid, when its surface will be seen injected with blood and of a deep red color. At first there may be but little uneasiness in the daytime, but at night, when the eyes are employed on objects illuminated by a candle, they becomfe hot, watery, and irritable, the 'lids feeling dry, stiff, and itchy, and cansing the patient constantly to rub them. The dryness, after a time, may give place to a copious flow of burning tears, which suffuse the eyes, and pour over and scald the cheek. Sometimes there is an excess of gummy and adhesive secretions, which dry at night and glue together the lids so hard as to require long bathing with warm water before they can be opened. If this incipient inflammation be unchecked, it may increase and run on to various forms of disorganization, or it may take the shape of a chronic or unmanageable affection of the eyes without pro- ducing blindness. 264. UnnatnTal increase in the sensibility of the Betina. — In the preced- ing case, the disease is located in the external or image-forrrmig por- tions of the eye, but the bad management of artificial light is apt to engendei' a far more dangerous and intractable form of disease, which fixes itself upon the image-feeting parts — the retina and optic nerve. The excessive use of impure light, by its unequal action, excites and stimulates the nerves of vision, producing an unusual irritability to light, and a low degree of inflammation of the retina. Moderate light becomes unpleasant, and the individual, after looking steadily at some , object for a few minutes and then closing the eyes, or putting out the light, appears to see stUl before him quite a distinct representation or image of the object, which may last for two or three minutes, and be variously colored or pass through a succession of colors. It moves, but its motions are in opposite directions to those of his eye, for it passes upwards when he looks downwards, and sinks downwards when he rolls his eyeballs upwards. It is caused by the morbidly increased sensibility of the retina, which retains the impressions of light for a greater length of time than when it is in a healthy condition. This state of the eye is accompanied often during the daytime by a dull, heavy feeling in the forehead, hardly amounting to pain, but causing the patient frequently to pass his hand across his brow, and in read- rrs MOEBID KPPECTS UPON THE EETllfA. 145 ing or writing at night, there is an unpleasant sense of distension in the orbits, with an increased flow of tears and frequent twittering or quivering of the eyelids. BrlUiant flashes of Are are seen, particu- larly when the eye is touched, on lying down, and after reading, writ- ing, or sewing for some time by artificial light. 265. Decrease in nervoDS sensibility— Appearance of dark films. — This condition of excessive irritability may continue for months, and then be followed by others totally different, and indicating a dimiaished sensibility of the nerves of vision. This is evinced by the appearance of dark spots or films floating in the air. At first but one film appears before each eye, which is seen only for a moment, and then darts away, shortly to reappear. But afterward their number is increased, they appear oftener, are larger, darker, more opaque, and continue longer visible than at first. They sometimes look like cobwebs, or flakes of soot, or bunches of far-down. They often resemble large-sized leaden shot, or minute and transparent globules, looking like drops of oil upon the surface of water, and, connected with each other like the links of a chain, float slowly through the air. These appearances are known by the doctors as rmmeo^ voUtantes; they are probably connected with morbid conditions of the nerves, but how we do not know. 266. Paraly^ of the nerve of vision— Amaurosis. — ^These appearances, in their less marked form, are quite common, many eyes being subject to them, and they may occur for a long time without getting worse, and unaccompanied by positive disease. But when they appear as a dense, opaque, stationary film, which interrupts and obscures vision, the symptoms become very alarming; there is danger of palsy of the retina producing nervous blindness, or cmiaurosis. To the casual ob- server, the eye, under the influence of this malady, appears perfectly weD, there being no external evidence of disease. But when once seated, its effects may be seen in the irregular shape of the pupil, which loses its roundness while the motions of the iris under the in- fluence of varying light, become sluggish and imperfect, or are alto- gether lost. Objects appear clouded in a thick mist, and the air some- times seems flUed with sparkling, glittering points.^ In the flnal stages of amaurosis the pupil is very much dilated, the sight is impaired or quite gone, and the eye has a lustreless, dead appearance. As the disease advances pain ceases, the light, instead of being disagreeable, as at first, can hardly be procured of suflBcient intensity. The patient resorts to spectacles of a high magnifying power, which condense a great quantity of light upon the palsied nerve of vision ; these may afford transient aid, but do ultimate injury. This disease may require r 146 MANAGESrENT OF AKTIFICIAl LIGHT. '. from a few months to several years to run its course, but amaurotio blindness is regarded as incurable. 267. Who are most snliject to amanrotic disease. — Amaurosis may arise from other causes than the improper use of artificial light, but Dr. Elliott states that nearly two-thirds of aU the cases of this disease which are met with in practice, occur in those who use their eyes much by artificial light, such as literary men, students, compositors, tailors, seamstresses, shoemakers, engravers, stokers, glass-blowers, &c. He also remarks that some individuals are more liable than others to suffer from the injurious action of artificial light, particularly those of a fair complexion and with gray or light blue eyes. XI.— MANAGEMENT OP AETIFICUL LIGHT. 268. Effect of ground glass Shades.— We have stated (261) that all light which is more intense than that coming from the object viewed, dazzles the eye and weakens the impression of the object, causing it to appear less clear and distinct. To out off these blinding rays from the flame itself, translucent screens of ground glass, caHed. shades, globe^ shaped, or of any other desirable figure, are made to surround the lu- minary, and have the effect of deadening the light in a surprising man- ner. The outline of the flame disappears, while the rays of light come from the surface of the globe, which thus appears self-luminous, and emits a diffused and softened light. As the rays cross each other at all points, and are scattered in all directions, objects near by throw only short, indistinct shadows, and there is a general and equal illumi- nation. These shades should be used whenever it is desired to reveal to the best advantage the objects of a room, but where the vision is to be specially exerted upon particular things, their use is unfavorable, as by diffusion there is considerable loss of light. Objection has been made to the employment of ground glass and semi-transparent white ware shades, on the ground that by scattering the light they expand the impression over a larger surface of the retina ; but as the image en- larges in area, it diminishes in intensity, which is desirable, unless the eye is constantly engaged in the scrutiny of minute objects. 269. How to collect the Light— Eeflectors.— It is apparent that the ra- diation of light in all directions, is favorable to the equal illumination of objects distributed in all parts of the room. But when we desire to view closely minute objects, as in reading, writing, sewing, &c., it is necessary to concentrate upon the point of observation the light which would be otherwise wasted by general diffusion. To collect the rays, EMPLOTMBNT OF SHADES. 147 and direct them to the part where they are required, oonioal shades or reflectors, of tin, paper, or some other opaque substance, and usually polished or whitened on the inside, are made to surround the flame. These not only protect the eyes from the glaijngrays, but direct down- wards that which would escape in other directions and be lost. 270. Blue Shades to snpply the missing rays. — To remedy the defects which arise from the bad composition of artificial light, several expe- dients have been suggested. It is proposed to surround the flame with a conical shade, the inner side of which is sky-blue. Aa the light that passes upward, falls upon this surface, its red and yellow colors are absorbed, and the few blue rays which it contained, being thrown downward by the sloping sides of the reflector, mingle with the orange light, proceeding directly from the flame, and improve the bad color by imparting to it a higher degree of whiteness. As in this case a portion of the reddish yellow rays are absorbed, there is a loss of light. If a common white reflector is used, more luminous matter is thrown down than with the blue shade, and a stronger illumination is produced. But, with a blue reflector, although there is less bril- liancy, the light is whiter, purer, and has a higher defining power, while it is cooler, more agreeable, and less injurious to the eyes.* 271. Stmetiire and moimUng of these Shades. — Shades of bristol-board, or strong paper, or silk, may be made by any one. The material is to be cut into the shape exhibited in Fig. 64, and then the edges, a a and J S, are to be united to each other, which gives rise to the conical structure shown in Fig. 65. This may be mounted upon a wire frame, which is to be hooked on to the glass chimney,or ground shade, or in lihe ab- sence of these, a wire framework may be supported by the body of the lamp. If the reflector be made of metal, as tin or copper, it may be sustained either in the way described or by a three-branched sup- port, screwed on to the burner. Keflectors are !■ o es adapted to candles by attaching to the candlestick an upright brass rod, on which the reflector slides, being fixed at any point by a thumb-screw. This is shown in Fig. 66. 272. How blae Reflectors shonld be colored. — ^The most pure and unchangeable blue color is -ultramarine, and this is best • E. V. HAvoHWonr, of 490 Broadway, N. T., famishes those shades. 148 MANAGEMENT OP AEHFICIAL LIGHT. adapted for painting the inner surface of shades. Prussian-blue de- composes and turns green by exposui-e to tiie heat, and other coloring matters are liable to fade or change. The colored surface should be smooth, but without gloss or var- nish, the surface appearing dead, or, as it is techni- cally termed, ' flat.' 278. Artificial Ligbt whitened by absorptioiii — ^Blue, transparent media absorb the yellow and red rays, and transmit only those of blue. If the glass chim- ney of a lamp be tinted lightly and evenly with a mixture of ultramarine and mastic varnish, the of- fensive orange will be separated from the light as it passes through, but at the expense of its brilliancy ; there will be much less of luminous matter. But if a poUshed tin or silvered reflector be employed to collect the rays, it will throw downward a beautiful soft white light. If the light from a luminary which is surmounted by a white or polished reflector (Fig. Candlestick witii 67) be made to pass through a glass globe fiUed with ahade. tyater which has been slightly blued, its color wiU be improved, while to compensate for the loss of luminous matter ab- Fig. 6T. WUtenlng the rays and straining them of their heat sorbed, the spherical form of the water-bottle will serve to converge or gather the rays so as greatly to increase their illu- minating power, at the point upon which they fall. Mbllo- Hi has proved that when the rays of artificial light are passed through even a very thin stra- tum of water, their heating power is diminished by eighty- nine per cent., but with little increase in the temperature of the water, in consequence of its great capacity for heat (49). The water-globe thus transmits a cooler as well as a whiter and purer light. Lamp-globes made of glass, slightly blued in its composition, would be very desirable. 274. ColOTed glasses for Spectacles. — ^The indiscriminate use of these COLOEED GLASSES — MISUSE OF GAS. 149 is altogether objectionable. They place the eyes in very unnataral conditions as regards the light, and if their employment is persisted in, it impairs their sensibility to the true relations of color, and otherwise injures them, as we have just seen that artiflcial colored light is able to do (253). If we look through a glass of any color, the effect is, that when it is withdrawn, the eye sees all objects tinged by its comple- mentary. As the colored glass cuts off a large quantity of light, its removal produces a sudden and injurious impression. Taint blue glasses may be serviceable in using artificial light. Colored glasses absorb and accumulate the heat so as in many cases to be disagreea- ble. Their bad effects are more marked, as it is for ' weak' eyes that they are generally commended. They may, at times, be of service to protect the eye from an intense glare, as of snow or the surface of water in sunshine. Gray glasses, or what is called a ' neutral tint, ' that is no particular color, are perhaps best ; they should not be of too dark a shade. 275. Is Gas-light iojiirions 7 — There is a prejudice against gas-light, as being the most injurious form of artificial illumination. As against the proper and well-regulated use of gas, this prejudice is entirely groundless, but there can be little doubt that from its abuse and bad management it is really doing more mischief than any other kind of light ; its very excellencies are turned to bad account ; its extreme cheapness, compared with other sources of illumination, naturally leads to its use in excessive quantities; floods of light are poured forth, so that persons may read and sew for hours together in the remotest cor- ners of the room. The air is heated by the excessive combustion, and poisoned by large quantities of carbonic acid, which there are no means of removing. The eye is unprotected from the glare by screen or shade ; extraneous light is freely admitted, which obscures the impression and strains the nerve of vision, and in proportion as the sensibility of the eye is impaired, stronger light is used, which gives temporary relief, but with danger of ultimate and permanent injury' to the sight. On the other hand, good, well purified gas, judiciously controlled in ac- cordance with the hints we have given, and others to be offered in the next part, is perfectly harmless (360). PAET THIKD. AIR. I.— PROPERTIES AND COMPOSITION Oi- THE ATMOSPHERE. 276. Part it plays in the scbeme of Nature. — It is impossible to con- template the wonderful properties of the atmosphere without a feeling of profound amazement. Whether we regard it as the grand medium of water circulation, through which rivers of vapor lifted from the oceans are cai'ried landward, to he coijdensed and channel their way back again to the sea ; or as the scene of tumultuous storms, generating the lightnings within its bosom, and taking voice in the reverberating thunders; whether as hanging the landscape with gorgeous cloud- pictures, or as the vehicle through which all melody and beauty and fragrance are conveyed to the portals of sense — it is alike strange and interesting. But when we glance at its deeper mysteries, those inti- mate relations to life which have been disclosed to modern science ; when we consider that the vegetable kingdom not only has the same chemical composition as the air, but in its mass is actuaJly derived from it ; that the whole architecture and physiology of trees, shrubs, and plants, are conformed to atmospheric nutrition, so that in literal truth the forests are but embodied and solidified air, the subject rises to a stOl higher interest. And more startling yet is the surprise when we r'ecoUect not only that the materials of our own bodily structures, derived from vegetation, have the same atmospheric origin ; but that active life, the vital union of body and spirit, and all the powers and susceptibilities of our earthly being are only maintained by the action of air in our systems ; — air which we inhale incessantly, day and night, flrom birth to death. There is an awful life-import in these never- ceasing rhythmic movements of inspiration and expiration, this tidal flux and reflux of the gaseous ocean through animal mechanisms. Shall we question that it is for an exalted purpose ? Science has many rr conrsisTs of pondeeable matiee. 151 things to say of the relations of air to life, but it can add nothing to the simple grandeur of the primeval statement, that the Creator " breathed into his nostrils the breath of life, and man became a living soul." 277. Air a material reality— Its pressure. — The atmosphere is so thin and invisible, and so totally unlike the objects that present themselves to our most impressible senses, that we are half inclined to forget that it is a reality, and are too apt to think of it as being mere empty space. Yet it consists of ponderable matter,, and is heavy, just like the solid resisting objects which we see and handle, and it presses down upon the ground with a force proportional to its weight. Upon every 6C[uare inch of the earth's surface there rests about 15 lbs. of air. Upon the body of a medium-sized man, having a surface of 2,000 square inches, the atmosphere exerts an external crushing force of 30,000 lbs. But there is air also within the system which exerts an equal outward pressure, and thus prevents injury. The pressure of air upon the body is not the same at all times. There are tides in it, just as there are in the ocean, great atmospheric waves which regu- larly sweep ovei*the earth and causa the weight of the atmosphere to vary. "Winds and storms produce similar eflfects. These variations in atmospheric pressure are measured by the barometer (60), and they are so considerable that a man's body may sometimes have from one to two thousand pounds more pressure upon it than at others. Of course, as the pressure upon the air increases from above, more of it is crowded into the same space, and it becomes more mpo^tion RELATIVE PEOPOETION OF IIS CONSTITUENTS. 153 and endowments more fully in relation to life. The atmosphere con- sists of fom- substances, — a pair of elements, nitrogen and oxygen, and a pair of compounds, carbonic acid gas and vapor of water. Dry air contains by, weight very nearly V7 per cent, of nitrogen to 23 of oxygen. The proportion of moisture in the atmosphere varies with the temperature ; when saturated at 60°, it contains about 1 per cent., and it has an average of about l-2000th of carbonic acid. These pro- portions are thrown into visible form by the diagram (Fig. 68). In addition to these definite and stable elements, of which the atmosphere is universally composed, various gaseous exhalations from tJie earth Nitrogen, or the (Mluting constituent of the Air. Oxygen, or the adioe constituent of the Air. Moisture, or the variable constituent of tho Air. Carbonic Acid, or the poisonous con- stitnent of me Air. The areas of blackened surface represent the rela- tive proportion^ by weight of the constituents of the Air. constantly enter it, though so minutely as generally to elude detection and identification. Liebig has shown that a trace of ammonia is always present in it (299). 281. Intermlxtiire, or diffaslon of Gases. — These gases have different weights. The oxygen is slightly heavier than the nitrogen ; the watery vapor is much lighter than either, and the carbonic acid about half as heavy again as the air itself. It might seem, then, that if they were mingled together -they would gradually separate and arrange them- selves in distinct layers, the heaviest at the bottom and the lighter above. Some works on ventilation have actually stated such to be the case, and that when we breathe out vapor of water and carbonic acid, the former rises while the latter descends. One of them re- marks : *' were these different portions of air as they come from the 154 EFFECTS or THE CONSTTTXTENTS OB" AIE. lungs, of different colors, we should, in a perfectly still atmosphere, see the stream divided, part of it falling and part ascending." This, of course, is not true. If such were the fact, if gases tended to arrange themselves in the order of their gravities, and there were no universal and inflexible law to prevent it, the carbonic acid of the air might slowly sink to the earth, and form a deadly stratum 10 or 15 feet deep over its entire surface, or fill up all its valleys with treacherous invisible lakes of aerial poison. But such is not the tendency of things. Gases brought together, no matter what their different weights or varying proportions, diffuse throughout each other so as to become perfectly and equally commingled. Heavy gases will rise up to mix with lighter ones, and lighter gases descend to mingle with those that are heavier. As a consequence of this important law, the proportions of the atmospheric gases to each other are kept extremely uniform, being scarcely, if at all, influenced by season, climate, wind, weather, or even the salubrity of the air. How benign and admirable is this provision of nature, by which, without being aware of it, we are relieved at every instant of a deadly though invisible poison, the process continuing as well during sleep as while awake, and taking place as perfectly for the unconscious babe as for the matured man. This great law secures the unity of the atmosphere. Its ingi-edients are perfectly mingled and equally diffused throughout each other, but not chemically combined, so -that in breathing, although we separate the constituents of the air, we do not have to chemically decompose it. "When we speak of air we mean the mass of commingled gases acting together ; yet as each constituent preserves its identity, and produces its peculiar effects, it is necessary to consider them separately. II.— EFFECTS OF TEE CONSTITUENTS OP AIE. 1. IflTEOOBN. 282. This gas seems to take no active part in breathing; it passes out of the body as it entered it, without being changed. A fire cannot be kindled in it, and an animal breathing it quickly dies, though not from any positive noxious effect which it produces, but rather from want of something else. Nitrogen is a negative or inert substance, its chief use being to dilute or temper the other active in- gredients of the air to a proper degree of strength. 2. OxTGBsr. 283. How the System is eharged with Oxygen. — Of the wonderful in- OXYGEN — HO"W IT ENTBES THE SYSTEM. 155 fiuence of tiiis agent we can here speak but briefly, as the subject will have to be considered again more fully in treating of the action of foods. We have noticed that oxygen is the active agent in combus- tion, so it is also in breathing. It is on account of what it does in our system that we respire the atmosphere. The air enters the lungs through the windpipe and bronchial tubes or air passages, as" seen in Fig. 69. It fills and distends the numberless little cavities or air-cells, which are enclosed by these membranes, and overspread with the finest network of capillary blood-vessels. Oxygen then penetrates or passes through the delicate membrane and enters the blood, imparting to it a bright crimson color, and rushing forward with it through what is called the pulmonary vein (Fig. 70) to the heart. It is estimated that the lungs contain, on an average, 220 cubic inches of air, with an inner membrane surface of 440 square feet, nearly thirty times greater than the whole exterior of the body.* This vast extension of surface is to secure the largest and most perfect opportunity of action and reaction between the air and blood. From the heart the blood passes by the artefles to all portions of the body. These arteries divide and subdivide until they are reduced in size to the finest hairlike tubes, which are densely interlaced through- out aU the tissues of the body. ^ ^ The arterial channels thus represent streams of oxygen flowing from the lung fountains to every portion of the system. In this way each mi- nute part of the living fabric is in direct communication with the ex- ternal air, that it may receive from it the agent upon which it imme- diately depends for the performance of its vital oflBces. This system of ' arterial currents, bearing oxygenfrom the air to every portion of the system, implies a set of counter-currents to drain off the poisons gen- erated within the body, back into the air. This is the duty of the veins or venous system. In the aocompaiiying diagram (Fig. 70), the fine Human Lung. a the larynx; I windpipe ohlal tubes or air passages ceo bron- e lung. * Dr. ADDKOif estimates the n»mber of air-cells in the two lungs at 1,744,000,000, and the extent of iJie membrane at 1,500 square feet. 156 EFFECTS OF THE CONSTTTUBNTS OF AIE. vessels at the top represent the lungs, and those at the bottom the capillaries of the whole body. The double circulation is shown, and how the heart is related to it. The vessels on the right side represent the arteries carrying blood charged with oxygen, and those on th* left side, the veins, conveying carbonic acid. Fio. 70. Lessor or Fulmonaiy CiTCnlation. Pulmonary Artery. Heart. Bight Auricle. Bight Ventricle. Vena Cava. Pulmonary Vein. — . — Left Auricle. Left Ventricle. Aorta. Greater or Systemic Circulation. 284. Wlat Oxygen does in the body. — The purpose of this incessant inflowing stream of oxygen, is to carry forward the great operations of the vital economy. Oxygen has a wide- range of chemical attrac- tions, and combines with other elements with intense energy. It is the ever-laboring, tireless Hercules of the atmosphere. As it kin- dles and maintains the combustion of our fires, so it does onr bodily vitality. The muscles are called into action through decomposition by oxygen, and as with the muscles in the manifestation of mechani- cal force, so with the brain in the exercise of intellectual power. This nnmijDNCE of oxygen — ^moistuee. 15^ organ is on an average only about 3^ the weight of the whole body, yet it receives from ^th to y^th of the entire oxygenated stream from the lungs and heart. A torrent of oxygen is thus poured incessantly into the material apparatus of thought to carry forward certain physio- logical changes upon which thinking depends. If the arterial stream be cut off from a muscle, it is paralyzed ; if it be stopped from the brain, nnconsciousness occurs instantaneously. In proportion to- the activity of muscle is its demand for the destructive agent ; in proportion also to the activity of the mind is the brainward flow of arterial blood. 285. Effects of varying tbe qnantlty of respired Oxygen. — ^If an animal be deprived of this gas, it dies at once. If man undertake to breathe 1 less proportion than that naturally contained in the air. the effect is depre^on of all the powers of the constitution, physical and mental, to an extent corresponding with the deficiency. If the natural amount be increased, there is augmented activity of all the bodily functions, the life-forces are exalted, and the vital operations are driven at a pretematm-al speed. If pure oxygen is respired, the over action and fever become so great that life ceases in a short time. Nitrons oxide (laughing gas) is a compound rich in oxygen, and when presented to the blood it absorbs a much larger proportion of it than of pure oxygen. Hence, when this gas is breathed, the blood drinks it up rapidly, and the system becomes so saturated with it as to produce the most remark- able effects. The muscular energy is so aroused that the inhaler is often impelled to extraordinary feats of exertion, and the intellectual powers are excited to a delirious activity. 3. MOIBTDBE. 286. How niiicli moisture the iir contains. — ^The third constant ingre dient of the air is moisture, derived from evaporation upon the earth'a surface. The quantity which the air will hold depends upon its tem- ' perature, and hence fluctuates greatly. At zero a cubic foot of aii will hold but -18 of a grain of watery vapor ; at 32° it will contain 2-35 grs.; at 40°, 3-06; at 60°, 4-24; at 60°, 6-82; at 70°, 7-94 ; at 80°, 10-T3 ; at 90°, 14-38; at 100°, 19-12 grains, and as the temperature goes higher still, the capacity for moisture also increases (308). After the air has imbibed its due quantity of vapor, at a given temperatui'e, it is then said to be saturated, and will receive no more unless the Aeat be increased. To better appreciate how rapidly the capacity for moist- ure augments, as the temperature ascends, we will state the propor- tions in another form. A quantity of air absolutely saturated at 32°, 158 EFFECTS OF THE CONSTITUENTS OF AIE. holds in solution an amount of vapor equal to the j^^ part of its weight; at 59°, ,V; a* 86°, ^\; at 113°, ^\; and at 140°, -L. 287. €onditlons of the drjing power of the Air, — If, when the air is saturated, its temperature falls, a portion of its moisture is precipitated, that is, it does not remain dissolved, hut appears in drops of dew. Thus a cubic foot of air, saturated at 90°, if cooled 10° would deposit 8-5 grains of water. UntU it is saturated, air is constantly absorbing moisture from all sources whence it can procure it. A cubic foot of air at 90°, and containing but 8 grains of moisture, is capable of absorbing 6'3 more, and this is the measure of its drying power. Watery vapor is lighter than the air, and when mingled with it in- creases its levity in a degree proportional to its temperature. This is one of the causes of the ascent of breath expired by the lungs, at the temperature of the body. In drying-rooms and laundries, if the open- ings for the escape of hot air be at the bottom, as the air gets saturated with vapor it becomes lighter, and rising, fills the room and stops the evaporation. If the opening be at top the loaded air rises and escapes, and the drying will be observed to commence at the bottom. 288. Moistnre intbeiir of Booms— Dew-point. — ^It has been explained that the temperature at which air is saturated, and begins to condense its moistnre in drops, is called the dew-point (34). When air contains so much moisture that its temperature needs to dechne but little be- fore water appears, the dew-point is said to be high; when it must lose much heat before drops are produced, its dew-point is low. Air, with a high dew-point, is therefore moist, while that with a low dew- point is always thirsty and drying. A simple means of finding out the dew-point, and ascertaining the drying power of the air, is as follows : — Note the temperature of the air by a thermometer, taking care that the instrument is not influenced by the radiation of any heated body in its vicinity. Then introduce it into a glass of water and gradually add a little ice, carefully watching for the first ap- pearance of moisture on the outside of the tumbler. The tempera- ture at which the deposit commences is the dew-point ; and the difference between it and the temperature of the air, expresses its drying power. If the air is at 60° and moisture begins to be con- densed at 40° its drying power is 20 degrees. Mason's hygrometer is a little instrument which indicates the dew-point without trouble. It has two thermometers, one of which gives the temperature of the air, and the bulb of the other, connected constantly with a reservoir of evaporating liquid, is kept cooled, and gives the dew- point; so that the amount of humidity in the air is seen at a glance MOISTURE — ITS PEESEEVATION IK THE BOOM. 159 by comparing the two scales ; — cost, from 3 to 5 dollaxs. From obser- vations made at "Washington through June,- July, August, and Sep- tember, from 9 to 3 o'clock of the day, the dew-point was, on an average, 11° below the temperature of the air, and sometimes more than 20° below. The air is always dampest near the ground; a difference in height of 60 feet, in the same exposure, has been known to make a difference of lOJ degrees in the dew-point. In our houses, we are to imitate as far as possible the external conditions of the air. As the temperature of freshly drawn well water is about 50°, a vessel containing it should receive a deposit of moisture when brought into our rooms, if they have a temperature above 65°. It is very rare that any such deposit is seen in apartments heated by a hot-air furnace, «ven if a considerable quantity of water is evaporated. 289. How donble Windows affect the moistnie of Booms. — Glass sky- lights often drip moisture upon those below, and we see it copiously condensed in winter upon the windows and trickling down the panes. This is often mistaken for a symptom of abundant humidity in the air, but it may occur when the air is extremely dry. When, as often occurs, air within a room is at "70° or 80°, while just outside the window-glass it is down to freezing, or below ; the inner layer of air next the glass wfll rapidly deposit its water, and then falling to the floor wiU be succeeded by other air (337), so that the window acts as a perpetual drain upon the moisture of the apartment. It is often impossible to maintain the air properly humid on this accoxmt. ■ Peo- ple are misled by this copious deposit of dew upon the glass, and it is hard to convince them that the air is deficient in moisture when they can see it condensed upon the windows. We have referred to double windows as a means of saving heat, and we might have added that they are equally serviceable in summer to exclude its excess of heat ; the enclosed air acting just as well to bar out the heat of the warm season, as to confine it within, in cold weather.* But double win- dows also prevent the deposit and loss of moisture from the air in rooms, and in this respect they are most useful. Glass is not essential to their construction, where we require only a diffused light ; white cotton cloth stretched upon a suitable frame and rendered impervious to air by linseed oil or other preparation, will answer equally as well for preserving heat, and be much less expensive. 290. Kate of Evaporation. — When dry air is exposed to a source of moisture, a considerable time must elapse before it will become satu- * If double TTindowB are to be retained in summer, they cannot be used for airways, as single windows are made to do ; there must be independent means of ventilation. 160 EI-FECrS OF THE CONSTErOENTS OE AIB. rated. The diffusion of vapor into hot air is much more rapid tlian into that which is tolder, hut it is not at all instantaneous. Mr. Daniell observed, that a few cubic iaches of dry air, continued to expand by the absorption of humidity for an hour or two, when ex- posed to water at the temperature of the surrounding air. In cold regions there is much less moisture in the air than in hot, and less in winter than in summer. It is also subject to a regular diurnal variation. As the sun warms the air during the day, evaporation is increased, and the humid element rises into the atmosphere ; but as it declines toward evening, cooling begins, and at night the watery vapor again falls, and is deposited upon the earth. "We are not to infer that because there is an absence of rain, therefore the air is dry ; on the contrary, in long droughts the air is often heavily charged with mois- ture. 291. How moist Air affects the System, — The skin relieves the System of moisture in two ways ; by insensible perspiration, and by sweating. Under common circumstances, the loss is six times greater by the former than by the latter process. The skin, as well as the lungs, is an excreting organ ; it contains, packed away, some 28 miles of micro- scopic tubing, arranged to drain the system of its noxious matters, carbonic acid, &c., which, if retained in the body, become quickly in- jurious. The perspiration given off in this climate amounts to 20 oz. per day, and in hot countries to twice that quantity. But air which is al- ready saturated with moisture refuses to receive the perspiration which is offered to it from the skin and lungs ; the sewerage of the system is dammed up. Much of the oppression and languor that even the robust sometimes feel in close and sultry days, is due to the obsti-uc- tion of the insensible perspiration by an atmosphere surcharged with humidity. Not only are waste matters generated in the system thus unduly retained, but malarious poisons introduced through the limgs by respiration, are prevented from escaping ; which would lead us to anticipate a greater prevalence of epidemic diseases in damp than in dry districts. Such is the fact, as we notice in Cholera, which follows the banks of rivers, and revels in damp, low situations. Moisture joined with warmth is most baneful to the system. The American Medical Association report that during the remarkable prevalence of Sun-stroke in the city of New York in the summer of 1853, which al- most amoimted to an epidemic, the heat of the atmosphere was ac- companied by great humidity, the dew-point reaching the extraordi- nary height of 84°. In Buffalo, in the summer of 1854, the progress of cholera to its height was accompanied by a steady increase in at- MOISTITBE — CAEBONIC ACID. 161 mospherio humidity. Air -wljioh is warm and moist, has a relaxing and weakening influence upon the body. The siroco is invariably charged with moisture, and its effects upon the animal economy illustrate but in an exaggerated degree the influence of damp warm weather. "When it blows with any strength, the dew-point is seldom more than four or five degrees below the temperature of the air. The higher its temperar tnre, the more distressing its effects, owing to the little evaporation it produces. This, connected with its humidity, is the principal cause of all its peculiarities— of the oppressive heat — of the perspiration with which the body is bathed — of its relaxing and debilitating effects on the system, and its lowering and dispiriting effects upon the mind. — Wtmah. Damp air at the same temperature as dry air has a more powerful cooling effect, producing a peculiar penetrating chilling feel- ing, with paleness and shivering, painfully known to New England invalids as accompanying the east winds of spring. 292. Effects of dry Air. — ^Dry air favors evaporation. By promoting rapid transpiration from the pores of the skin, it braces the bodily energies and induces exhilaration of the spirits. Gold dry air is invigorating and reddens the skin, with none of the distressing symp- toms of cold moist air. If very dry, it not only accelerates perspira- tion, but desiccates and parches the surface, and deprives the lining membrane of the throat and mouth of its moisture so rapidly as to pro- duce an uncomfortable dryness, or even inflammation. Dry climates which quicken evaporation, are best adapted for relaxed and languid constitutions with profuse secretion, as those aflSicted with humid asthma, and chronic catarrh with copious expectoration. The Hwr- mattan, a dry wind from the scorching sands of Africa, withers, shrivels, and warps every thing in its course. The eyes, lips, and palate become dry and painful. Yet it seems to neutralize certain conditions of disease. "Its first breath cures intermittent fevers. Epidemic fevers disappear at its coming, and smaE-pox infection be- comes inoommnnicable." 4 Oaebonic Acid. 293. Physiologital effects of Carltonle Acid. — ^The fourth constant in- gredient of the atmosphere is carbonic acid ; a transparent, tasteless, inodorous gas. It takes no useful part in respiration, indeed it exists in the air in so small a proportion that its effects upon the system are inappreciable. Its sources are the combustion of burning bodies, fer- mentation and decay, the respiration of animals ; and it is also gener- ated within the earth, and poured into the air in vast quantities from 162 EFKECTS OF .THE CONSTITUENTS OP AIK. volcanoes, springs, &c. It may be set free more rapidly than it wil dissolve away into air ; it then accumulates, as sometimes in wells, cellars, rooms, &o. and becomes dangerous. When breathed pure, it . causes suffocation by spasmodically closing up the glottis of the throat. When mixed with air in small quantities, it is admitted to the lungs, and then acts as a rapid narcotic poison. The symptoms of poisoning by carbonic acid gas are throbbing headache, with a feeling of fulness and tightness across the temples, giddiness, palpitation of the heart, the ideas get confused and the memory fails. A buzzing noise in the ears is next experienced, vision is impaired, and there is strong tendency to sleep. The pulse falls, respiration is slow and labored, the skin cold and livid, and convulsions and delirium are followed by death. This gas has been often employed as a means of suicide. A Son of the eminent French chemist, Bbrtholet, under the influence of mental de- pression, retired to a small room, locked the door, closed up every crevice which might admit fresh air, carried writing materials to a table on which he placed a seconds watch, and then seated himself before it, described his sensations, and was found dead upon the floor.* 294. Effects in small quantities. — The proportion of carbonic acid ne- cessary to produce a poisonous atmosphere is very small; so much so that in attempts at suicide by burning charcoal in an open room, the people who entered it have found the air quite respirable, although the persons sought were in a state of deep insensibility (coma). From 6 to 8 per cent, of carbonic acid in the air renders it dangerous to breathe, 10 to 12 makes it speedily destructive to life. The natural quantity in the air is so small that it may be multiplied 20 times before it rises to 1 per cent. Air containing one per cent, of this gas is soporific, depressing, takes from the mind its cutting edge, tends to produce headache, and is most injurious. That proportion of carbonic acid which nature has placed in the atmosphere, we assume to be * " I light my furnace, and place my candle and lamp on the table with my watch. It is now 15 minutes past ten. The charcoal lights with diflBculty. I have placed a funnel on each furnace to aid the action of the fire. 20 minutes past ten. The funnels fall : I replace them ; this does not go to my satisfaction. The pulse is calm, and beats as usual. 10 h. SO. A thick vapor spreads itself by degrees In the chamber. My candle seems ready to go out. My lamp does better. A violent headache commences. My eyes are filled with tears ; I have a general uneasiness. 10 II. 40. My candle is extinguished, the lamp still burns. The temples beat as if the veins would burst. I am sleepy. I suffer horribly at the stomach ; the pulse beata 40 per min. 10. 50. I am suffocated. Strange ideas present themselves to my mind, I can hardly breathe. I shall not live long. I have symptoms of madness. 10 h, 60. [Here, he confounds the hours with the minutes.] I can hardly write; my vision is disturbed; my lamp flickers; I did not believe wo suf- fered so much in dying. 10 h. 62 m. [Hero were some illegible characters]." THEIE HAEMONIOUS AlilX) BENEFICENT ACTION. 163 entii^Iy inoffensive, but the more it is increased beyond that amount, the less it is fitted for respiration. Pi-ecisely so with the body. Car- bonic acid is continually generated within it and continually poured out from the lungs into the air ; a certain amount in the blood is com- patible with health, but if that quantity be slightly increased, it at once begins to act as a poison. Any cause, therefore, which hinders the escape of this gas from the lungs, tends to accumulate it in the blood and produce injury, and this is exactly the effect, if there be considerable carbonic acid in the air we breathe. Its exhalation from the lungs is retarded if the outer air already contains more than its osual amount of carbonic acid. 295. Why then does the Air contain Carbonic Aeidt — ^But if this gas be useless, or positively detrimental in animal respiration, why is it made a constant and essential ingredient of the atmosphere ? The plan of nature requires it. As it is formed in aU animal bodies, and breathed out into the air, and also by all combustions, its presence there is un- avoidable, whUe it is the great source of nourishment to the whole vegetable world, which drinks it in through innumerable pores in every green leaf, and thus keeps the proportion down to the point of safety for animals. 296. Effect of these Ingredients eomhlned. — Such are the constant con- stituents of the air, and such, so far as it has been possible to determine it, is their separate influence upon man. The effects of the atmosphere we breathe are the resultant of these agents acting together. We see that it exerts an all-controlling influence upon the human constitution. To say that it is useful or important, gives us no adequate conception of the facts ; it is the first condition of vital activity — what the stream is to the water-wheel or fire to the steam-engine — ^the immediate im- pelling power of life. Ajay one of its elements breathed alone would be fatal ; any other proportions than those in which they are com- mingled "would be dangerous or deadly. Its elements taken alone are poisonous and excoriating, but properly mingled and neutra]i?ed, how bland, how balmy, how innocent they become. Pressing upon us with the weight of tons, bathing the sensitive breathing passages — distend- ing the filmy membranes of the air cells, flashing through into the blood and swept forward to the inmost depths of the system, corroding and consuming in its progress the living parts — and yet with such marvellous delicacy are all these things accomplished, that we remain profoundly unconscious of them. Unspeakable indeed are these har- monies of life and being, and how adorable the Power, Wisdom and Love firom which they emanate. 164 EFFECTS GE THE CONSTITUENTS 01" AlB. 5. OZONB AND ElEOTEIOITT. 297. Ozone in the Air. — Our view of the properties of ttie atmo- sphere would be incomplete without reference to these agencies. At- tention has latterly been drawn to the interestiag and significant fact, that the chemical elements are capable of existing in different states, with widely different properties and powers. We see this in the case of carbon, which assumes several states, as charcoal, lampblack, diamond. Sulphur, phosphorus, and indeed many of the other elements are found capable of this change of state, wiich is known as alhtropism. It has been discovered also that the remarkable element oxygen has its double condition, its ordinary state and another of extreme activity, in which it seems to acquire new energies ; in this heightened form of action it is called ozone. It may be readily changed from the common to the superactive state, acquiring bleaching and oxidizing energies which it had not before. Ozone is extensively formed in the atmosphere, by the operations of nature, although under precisely what circumstances we do not know. It is found more abundantly in some localities than in others, and may be generally recognized in air which has swept over the ocean, although usually absent in that which has traversed large tracts of land. There has been much speculation as to how the air is affected by its presence, in relation to health and disease. It is said that when present in excess diseases of the lungs, especially influenza, prevail ; when deficient, fevers and all those diseases which are sup- posed to depend upon a kind of fermentation in the blood are com- mon, — it being thought that ozone oxidizes or burns away the exciting fermentable matter, thus acting as a purifying agent. It has been stated that in cholera ozone is entirely absent from the air. 298. Atmospherle Eleetrleity. — "I cannot tell," says Dr. Faraday, " whether there are two fluids of electricity, or any fluid at all ;" such is our profound uncertainty in relation to this mysterious agent. ' Yet it is commonly assumed to be a subtle fluid, distributed through all substances, and lying buried beneath their surfaces in a condition of equihbrium, or rest. Various causes may disturb this state, producing electrical excitement, when the fluid is supposed to accumulate in some substances to excess, which are then said to be positively electri- fied, — ^while in others it is deficient, and these are negatively electrified. Some substances, as the metals, allow electricity to pass through them freely, these axe oalleA good conductors; others refuse it a ready passage, and are termed non-conductors, as sUk, glass, air. "When from any cause excitement has taken place, and a body has been charged with electri- ELECTEICITY — AXMOSPIIEEIC CONTAMINATIONS. 165 city, or robbed of it to a certain degree, there is an escape ; if a good conductor be presented to it, it flows off quietly; if a bad conductor, it dashes through it, producing fire, light sound, and perhaps violent rupture {disruptive discMrge). The friction of unlike bodies against each other creates electrical excitement. If we slide rapidly over a carpet, the body becomes so excited that it may yield a spark which ■will light the gas. The friction of masses of air, of different temper- atures, or containing different degrees of moisture, by rubbing against each other, or grinding against the earth, developes electricity. So, also, does evaporation. If a saucer of water be suspended by non- conducting silk cords (insulated), evaporation goes on as usual at first, but is soon checked. It gives off positively electric vapor, while the saucer remains negatively electrified. If it be connected with the ground by a conductor, active evaporation is resumed. Combustion produces electricity ; the escaping carbonic acid being positive, while the bm-ning body is negative ; the vapor of the expired breath is also positive. The air is generally electrified positively, especially in clear weather ; but during the fall of rain, fogs, snow, and storms, it may be negative. The electricity of the atmosphere appears to have a daily ebb and flow, like the tides of the sea, twice in every 24 hours. It is feeble at sufirise, increases in intensity during the forenoon, declines again in the afternoon, until about two hours before sunset ; it then advances until perhaps two hours after sunset, and again diminishes until morning. It has become fashionable, latterly, to offer electricity in explanation of all obscurities, material and spiritual. Beyond doubt it is profoundly involved in the phenomena of our being, but we as yet understand but little about it. In connection with the air, we can only say, that when it is clear, and electricity is rapidly developed, the spirits are more buoyant, and the feelings more agreeable, than when the atmosphere is in the opposite state. III.— CONDITION OF AIR PROVIDED BY NATURE. 299. Impwities of the external Air. — There are natural causes which tend to make the atmosphere impnre, but they act with variable in- tensity in different localities. Animal respiration and combustion exert a contaminating influence upon the atmosphere, but considering its vast mass, the general effect is but trifling, and besides is perfectly neutralized by growing vegetation, which evermore absorbs from the air carbonic acid, and returns to it pure oxygen in the daytime. The decay of organic matter, vegetable and animal, generates numer- 166 CONDITION OP ATE PEOVIDED BY NATUEE. ous substances which are prejudicial to health. Libbig Las lately shown that ammonia from these sources is continually present in the air. Its quantity is so minute that it cannot he directly de- tected, hut it may be traced in rainwater, having been washed out of the air in its descent (371). The exhalations and efSuvia arising from active decomposition in wet lands, swamps, marshes, &c., especially in hot seasons and localities, are prolific sources of disease. Minute microscopic germs, both vegetable and animal, exist in the atmosphere, and the course of winds has been tracked across oceans by the peculiar organic dust which they carried. Not only do plants and flowers exhale continually their peculiar fra- grances, but even mineral matters and earths have also their odors, which rise and mingle with the air. Indeed, we must conceive of the air as the grand reservoir into which all volatile matters escape. Professor Geaham contends that malarious and contagious bodies are not strictly gaseous, but are highly organized particles of fixed or solid matter, which find their way into the atmosphere, like the pollen of flowers, and remain for a time suspended in it. The inconceivable minuteness of exhalations diflnised through the air, which are yet sufficiently active to impress the senses, is forcibly illustrated by the following fact, which we give on the authority of Dr. Oaepbntee* '' A grain of musk has been kept freely exposed to the air of a room, of which the doors and windows were constantly open for a period of ten years, during aU which time the air, though constantly changed, was com- pletely impregnated with the odor^ of musk ; and yet, at the end of that time, the particle was found not to have sensibly diininished in weight." 300. Effects of Exposnre, Foliage, and Soil. — ^The salubrity of the ex- ternal air is influenced by elevation, trees, and soU. The exposed hill- top ensures atmospheric purity. It is often surprising what efiect a small difiference in the elevation has upon the healthfulness of a par- ticular spot. A rise of 16 feet within 300 yards has been known to produce an entire change from a relaxing to a bracing air. The lower place was completely enveloped in foliage and without drainage, while the higher was comparatively free from trees, and besides, had a good fall for surface-water and sewerage. Dense foliage around a dwelling may be injurious, by causing dampness and stagnation of air, especially if the situation be protected from winds. If the ground be loaded with putrefying matter and soaked with refuse water, the air above it cannot be pure. The ground below and around the dwelling should be ^ry. A soU absorbent and retentive of moisture, always damp, is IMPlTErnES mEAE THE GROUND AT NIGHT. 167 nnflt to live on xinless thorongUy drained. Sand or gravelly gvovrnd is best, provided it be not locked iq t>y a surrounding clay basin, -with no outlet for the rainfall. 301. Canse of the luiwliolesomeness of NlgM Air. — There is ground for the common belief that night air is less healthful than that of the day. It is known that the deadly tropical fevers affect persons almost only during the night. Yet the poisonous miasms from the rotting Bubstan> ces of the ground which cause those fevers, is produced much faster during the intense heat of the day than in the colder night. But in the daytime, under the hot tropical sun, the air heated by contact with the burning ground expands and rises in an upward current, thus diluting and carrying away the poisonous malaria as fast as it is set free. The invisible seeds of pestilence, as they ripen in the festering earth, are lifted and dispersed in the daytime by solar heat ; but as no such force is at work at night, they then accumulate and condense in the lower layer of the atmosphere. Now although fatal fever poison may not be generated, yet decomposition of vegetable matter yielding products which are detrimental to health take place every where upon the surface of the ground ; and though. dissipated during the day, they are concentrated and confined so close to the earth at night as to affect the breathing stratum of the air. 302. Upper Rooms least affected by Nigbt iiri — ^It will hence be seen that the different stories of a house are differently related to this source of injury : the upper ones being situated above the unwhole- some zone, are most eligible for sleeping chambers, whUe the ground- floor is more directly exposed to the danger. Dr. Etjsh states, that during the prevalence of yellow fever in Philadelphia, those who oc- cupied apartments in the third story were far less liable to attack than those who resided lower. Low one-story houses, in which the inhab- itants sleep but three or four feet from the ground, and are therefore directly exposed to the terrestrial exhalations, must be considered more objectionable than loftier sleeping apartments. Sleeping in low rooms is perhaps worse in the city than in the country. 303. The Atmosphere Self-purifying. — In all healthy localities the pro- portion of impunities is so small that their effect is imperceptible. When noxious exhalations are set free from any source, they are dif- fused through the vast volume of the atmosphere, so as not to be detectable by the most refined means of chemistry. The law of g.-vseous diffusion, aided by winds and storms, secures dispersion and universal intermixture. Oxygen finally takes effect upon these baneful emanations, destroying and burning them as truly as if they had been M8 SOURCES OP IMPUEB AIE IN DWELLINGS. consumed in a furnace. The atmosphere thus secures its own puri- fication on the grandest scale, and its vital relation to animal life re- mains undisturbed. 804. Air within Doors. — But when we enter a dwelling the case is altered. It is as if the boundless atmosphere had ceased to exist, or had been contracted within the walls of the apartment we occupy. Causes of impurity now become a matter of serious consideration. They are capable of affecting, in the most injurious manner, the little stock of air in which we are confined ; and it is therefore, on every account, important that we have a clear idea of the nature and extent of the common causes which vitiate the air of our dwellings. IV.— SOUECES OP IMPTJEE AIR IJT DWELLINGS. 305. Breathing and Comlinstion.-— By breathing, the burning of fttel and combustion for light, large quantities of oxygen are removed from the air, while at the same time carbonic acid in nearly equal bnlt takes its place. In the case of fuel, if the combustion is perfect, the air that has been changed is immediately removed up chimney by the draught. But not so in respiration and illumination ; the air spoiled by these processes remains in the room, unless removed by special ventilating arrangements. 806. Leakage of bad Gases from Beating Apparatus. — While, in point of economy, stoves are most advantageous sources of heat, yet in their effects upon the air they are perhaps the worst. We saw that in the stoves called air-tight, the burning is carried on in such a way that peculiar gaseous products are generated (121). These are liable to leak through the crevices and joinings into the room. Carbonic oxide gas is formed under these circumstances, and recent experiments have shown that it is a much more deadly poison than carbonic acid. The slow, half-smothered burning of these stoves requires a feeble draught, which does not favor the rapid removal of injurious fumes. Besides, carbonic acid being about half as heavy again as common air, must be heated 250° above the surrounding medium to become equally light, and stm higher before it will ascend the pipe or flue. If the com- bustion of the fuel is not vivid, and the draught brisk, there will be regurgitation of this gaseous poison into the apartment. Dr. Ueb says, " I have recently performed some careful experiments upon this subject, and find that when the fuel is burning so slowly as not to heat the iron surface above 250° or 300°, there is a constant deflux of car- Ionic acid into the room." Probably all stoves, from theu' imperfect HOW AlE IS AITEBED BY HEAT. 169 fittings, ai-e liable to this bad result. Hot-air furnaces, also, have the same defect. They are cast in many pieces, and however perfect the joinings may be at first, they cannot long be kept air-tight, m conse- quence of the unequal contraction and expansion of the different parts under great alterations of heat. Combustion products are hence liable to mingle with the stream of air sent into the room. 307. Air affected liy Hot-iron Snrfaees. — But if stoves become a source of contamination to the air at low temperatures, neither are they free from this objection when made hotter ; at high heats (and they are often red-hot), they seriously injure it in other ways. It is weU known that iron highly heated causes disagreeable effects upon the air of rooms, producing a sensation ascribed to lurnt air, but the nature of this change is not fiiUy understood. The common method of explaining it, that the iron decomposes the air and robs it of oxygen, is in no degree satisfactory, as the quantity of oxygen thus removed must be extremely small, and besides, a portion of this very small amount comes from the decomposition of atmospheric moisture, its hydrogen being set free. The minute particles of dust, myriads of which fill the air, as seen when a ray of light is admitted into a darkened room, and which consist of all kinds of vegetable and animal matters, settle upon the hot stove, and are roasted or burnt with the escape of gaseous impu- rities. In the stove metal itself there is always, beside the cast-iron, more or less carbon, sulphur, phosphorus and arsenic, and it is possible that the smell of air, passed over it in the red-hot state, maybe owing to the volatilization or escape of some of these ; because it is to be re- membered that a quantity of noxious effluvia, too small to be seized and measured by chemical means, may ye.t affect the sense of smell and the pulmonary organs. 308. Cemposltion of Air altered by heating iti — ^It is a capital advan- tage of the methods of warming by fireplaces and grates — simple ra- diation — that they do not heat the air : it remains cool while the heat rays dcurt through it to warm any objects upon which they fall. The sun pours his floods of heat through the atmosphere without warming it a particle. Air is made to be breathed, and we again dis- cover Providential Wisdom in the arrangement by which the sun warms us, without disturbing, in the slightest degree, the respiratory medium. But if we heat the air itself, we at once destroy the natural equilibrium of its composition, and so change its properties that it be- comes more or less unpleasant and prejudicial to health. We have noticed the bad effects upon the system of dry heated air, and it was shown that the state of dryness does not depend upon the actual 8 170 SOUECES OF IMPUEE AIE IN DWELLINGS. amount of moisture present, but upon the t&mpm-atnire. same quantity of aque- "With tha Fio. n. The length of the hara indicates the relative propor- tions of moisture that a cubic foot of air will hold at the different temperatures. oiu vapor, it will be. moist and humid at a low temperature, while at a high one it will be parched and greedy of water. The accompa- nying diagram (Kg. 71) exhibits the relative amount of moisture that air contains when satur- ated at the temperatures mentioned. Suppose that air at 32° be heated to 100° (and it often is much higher), and he then thrown into the room. The difference in the length of the bars opposite these two numbers expresses its de- ficiency of moisture, and hence its drying and parching power. Air thus changed is apt to produce unpleasant feelings and painful sensa- tions in the chest, which are often attributed to too great heat. " In very dry air the insensibje perspiration will bQ increased, and as it is a true evaporation it will generate cold proportional to its amount (69). Those parts of the body which are most insulated in the air, • and furthest from the heart, will feel this^ refrigerating influence most powerfully ; hence that coldness of the hands and feet so often expe- rienced. The brain being screened by the skuU from this evaporating influence, will remain relatively hot, and wiU get surcharged besides with the fluids which are expelled from the extremities, by the con- traction of the blood-vessels' caused by cold." In close rooms, not well vehtUated, stoves exert this baneful influence upon the air in an eminent degree. This objection lies against heated aw, no matter how heated. Stoves and air-furnaces, with their red-hot surfaces, are un- doubtedly worse for the air than hot-water apparatus, which never Boorch it ; yet they, too, may pour into our apartments a withering blast of air at 150°, which may be potent for mischief. The only way that hot-air can be made healthful and desirable is by an effectual plan of artiflcial evaporation, which will be noticed among the means of preserving atmospheric purity (347). 309. Contamination of iir from the Human Being. — It is a common belief that the human system is distinguished by its vital power of re- sisting, during life, the physical agents which would destroy it ; but that after death it is abandoned to these forces, and falls quickly into EXHALATIONS FBOM THE LIVING BODY. 171 pntrefaotion. This is an error. Under the influence of physical agency decomposition is constantly going on throughout the body, and is indeed the fundamental condition of its life (624). There is the same decay and chemical decomposition taking place in the animal fabric during life as after death ; the dlQerence beiug, that in the dead body the decomposing changes speedily spread throughout the mass, whUe in the living system they are limited and regulated, and pro- vision is made for the incessant and swift expulsion of those effete and poisonous products of change, which if retained within the organ- ism for but the shortest time, would destroy it. Streams of subtile and almost intangible putrescent matter are, all through life, exhaling from each living animal body into the air. The fluid thrown from the lungs and skin is not pure water. It not only holds in solution car- bonic acid,, but it contains also animal matter, the exact nature of which has not been determined. From recent inquiries, it appears to be an albuminous substance in a state of decomposition. If the fluid be kept in a closed vessel, and be exposed to an elevated temperature, a very evident putrid odor is exhaled by it. Leblano states that the odor of the air at the top of the ventilator of a crowded room, is of so obnoxious a character that it is dangerous to be exposed to it, even for a short time. If this air be passed through pure water, the water soon exhibits all the phenomena of putrefactive ferinentation. 310. Dr. Faraday's Testimony npoa this point. — " Air feels unpleasant in the breathing cavities including the mouth and nostrils, not merely from the absence of oxygen, the presence of carbonic acid, or the ele- vation of the temperature, hut from other causes depending on matters communicated to it from the human teing. I think an individual may find a decided difference in his feelings when making part of a large company, from what he does when one of a small number of persons, and yet the thermometer give the same indication. When I am one of a large number of persons, I feel an oppressive sensation of closeness, notwithstanding the temperature may be about 60° or 65°, which I do not feel in a small company at the same temperature, and which I cannot refer altogether to the absorption of oxygen, or the inhalation of carbonic acid, and prohahlj depends upon the effluvia from the many present ; but with me it is much diminished by a lowering of the tem- perature, and the sensations become more like those occurring in a smaU company." 311. Air of Bedrooms. — ^The escape of offensive matters from the liv- ing person becomes most obvious when from the pure air we enter an nnventUated bedroom la the morning, where one or two have slept 11 2 SOUECES OF IMPUEE AIR IN DWELLINGS. the night before. Every one must have experienced the sickening and disgusting odor upon going into such a room, though its occupants themselves do not recognize it. The nose, although an organ of ex- quisite sensibility, and capable of perceiving the presence' of offensive matters where the most delicate chemical tests fail, is nevertheless easily blunted, and what at the first impression feels pre-eminently dis- gusting, quickly becomes inoffensive. Two persons occupying a bed for eight hours, impart to the sheets by insensible perspiration, and to the air by breathing, a pound of watery vapor charged with latent animal poison. Where the air in other inhabited rooms is not often changed, the water of exhalation thus loaded with impurities, condenses upon the furniture, windows, and walls, dampening their surfaces and run- ning down in unwholesome streams. 312. Purity the Intention of Natnre. — ^Tet we are not to regard the human body as necessarily impure, or a focus of repulsive emanations. The infinite care of the Creator is seen nowhere more conspicuously than in the admirable provision made for the removal of waste matters from the system, the form in which they are expelled, and the prompt and certain means by which nature is ready to niake them inoffensive and innoxious. " The skin is not only," as Biohat eloquently observes, " a sensitive limit placed on the boundaries of man's soul, with which external forms constantly come in contact to establish the connections of his animal life, and thus bind his existence to all that surrounds him ; " it is at the same time throughout its whole extent densely crowded with pores, through which the waste substances of the system momentarily escape in an insensible and inoffensive form, to be at once dissolved and lost in the air if this result he allowed. It is not by the natural and necessary working of the vital machinery that the air is poisoned, but by its artificial confinement and the accumulation of deleterious substances. If evil results, man alone is responsible. 318. Other sources of Impniity. — Gaseous exhalations of every sort escape from the kitchen, and are diffused through the house as their odors attest, and the darkening of walls and wood-work painted with white lead shows that poisonous sulphuretted hydrogen from some source has been thrown into the air, its sulphur combining with the lead and forming black sulphnret of lead.* From the imperfect com- bustion of oil and tallow for lighting, and the defective burning of gas jets there arise emanations often most injnrious to health. The vapor of a smoky lamp, if disengaged in small quantities, and the fumes of the burning snuff of a candle, may fiU the room with disgusting odors * White zinc paint does not thns turn black. HfFLUENCE OF CELLAES AHD BASEMENTS. 173 and excite severe headache. It may be well here to correct the com- mon fallacy that cold air is therefore pure, and that apartments need less ventilation in winter than in summer. People confomid coolness with freshness, and disagreeable warmth with chemical impm'ity ; whereas these properties have necessarily nothing to do with each other. Cold air may be irrespirable from contamination and warm air entirely pure. 314. Poisonous Colors on Paper Hangings.— Attention has lately been called to the poisonons influence of green paper hangings upon the air. Cases are mentioned of children poisoned by chewing green colored hanging paper, and of persons sickened by breathing air in rooms in which certain green papers have been mounted. The basis of the bright green colors used for staining paper-hangings is the poisonous a/raenite of copper, a combination of arsenic and copper. This, however, is not volatile, and does not create poisonous fumes or vapors, unless perhaps by being dusted fine particles are loosened and set afloat in the air. Nevertheless, though it do not vaporize and get into our systems through the lungs, arsenite of copper is a deadly poison, and when spread over paper-hangings, utterly spoils them^r dietetieal purposes, either for children or adults. Professor JoHNSoif , of New Haven, states that the most beautiful of all green pigments is the aceto-arsenite of copper, and that this compound, in damp weather and humid situations, exhales deadly poisonous vapors supposed to contain arsenuretted hydrogen. This gentleman has given an account of a family poi- soned by sleeping in a room where the paper was colored with this pigmeiit. 313. Foul Air generated In Cellars. — The air in our houses is also liable to contamination from various organic decompositions, if vigUant precaution is not taken to prevent it. Cellars are commonly con- verted into reservoirs of pernicious airs, by the reprehensible custom of using them as receptacles for the most perishable products. But even where large masses of organic matter are not left to undergo putrefactive decay, and generate unwholesome miasms, serious injury is liable to occur from the damp and stagnant air of basements and cellars. It is not necessary that the lower spaces of a house should be half flUed with rotting garbage to generate foul air. The surface of the earth is filled with decomposable substances, and whenever air is confined in any spot in contact with the ground, or any changeable organic matter, it becomes saturated with various exhalations which are detrimental to health. If air is to be confined, unless it is so sealed up as to touch nothing but dry, glassy or mineral substances. 11 i HOEBID AND FATAi EFFECTS OF IMPUEE AIE. it will certainly degenerate. Even dry rooms and closets in the nppei part of the house, become mouldy and musty to a most disagreeable extent, if not often aired. To be pure and healthy, air requires con- tinual circulation; but cellars are very rarely either ventilated or made absolutely dry by water-proof walls or floors. They are usually damp, cold, uncleanly, and mouldy. "The noxious air generated in cellars, basements, and under-floor spaces, reaches the inhabitants of upper apartments in so small quantities, that instead of producing any marked and sudden process of disease, it operates rather as a steady tax upon their income of health ; so uniform in its depressing effects as not to be appreciated. Yet many an invalid, who fancies himself improved by a change of air, in going to another residence, is really relieved by escaping the mouldy atmosphere which comes from beneath his own ground-floor." * V. MORBID AND FATAL EFFECTS OF IMPURE AIR. 316. Sources of danger in BreatUng — The constituent, of the atmo- sphere are mingled in such perfect proportions, that its temper is ex- actly suited to the necessities of the healthy system ; any alteration in its composition, therefore, however slight, must result in physi- ological disturbance. So direct is the access that respiration affords to the inmost recesses of the body, that any gas mingled with the re- spired air, is at once admitted, and takes prompt control of the system. When aliment is taken into the stomach, it is submitted to a long process of preparation and sifting, before it can gain admission to the blood, those parts which are useless or obnoxious being rejected; * " The reports of the Registrar-Genera, of England disclose to ns some very startling facts in reference to the slo^^ influences of different states of air in affecting length of life. If any one were to select from among all the different occupations the healthiest men of a nation, he would probably choose the farmers and the butchers. Both arc- usually stout in frame, and ruddy in complexion. Both are actively employed, have plenty of exercise and abundance of food. In one point, therefore, their- circumstances ■widely differ. The farmer breathes the pure air of the country ; the butcher inhales the atmosphere of the shambles and the slaughter-house, tainted "with putrefying animal effluvia. The result is an instructive lesson as to the value of pure air. The rate of deaths stated among the farmers, between the ages of 45 and 55, was 11-99 per thousand ^annually). The butchers at the same age died at 23-1 per thousand, so that their mor- tality is about double that of the farmers. These two classes, Indeed, occupy nearly the extremes of the table of mortality. The farmer is the healthiest man on the list, while there is but one worse off than the butcher — the innkeeper. Any one who knows how large a proportion of taverns are mere grogshops, reeking with impurities and environed in filth, -will not be surprised that the mortality among this class ascends to 28'34 in the Jiousand." IT PEEPAEBS THE WAY FOE PESTILENCE. 1^5 bnt tho Jungs exercise no sucli protective or selective power, they cannot guard the system by straining the air, or barring out its in- jurious gases. Besides, air both pure and impure is alike transparent and invisible, so that the eye cannot detect the difference. The causes of vitiation are also gradual and insidious in their action, so that their effects steal imperceptibly over the system. UnUke heat, deleterious air announces its presence by no sensation ; indeed, its effects are of that stupefying kind that makes a person insensible to them. A bedroom, as we before remarked, may be so foul from V)athsome exhalations, as to nauseate a person who enters it from the pure air, and yet its inmates will feel quite unconscious of any thing disagreeable. "Without intelligent and thoughtful precaution, there- fore, we are constantly liable to the evil effects of foul air, and to im- minent danger from various forms of disease. 317. The System prepared to receive Contagion, — Eespiration of im- pure air, is a prolific source of disease, which appears in numerous forms and all degrees of mialignity. The effect of breathing a con- fined and unrenewed atmosphere, is not only to taint the air, but by a double influence, to taint also the blood. It is an office of oxygen in the body, as we^ have seen, to throw the products of waste into a soluble state that they may be readily excreted, bnt if its quantity be diminished in the air, this work is imperfectly performed in the body ; and the vital current is encumbered with putrescent matter. ■ The increase of carbonic acid in the air, by offering a barrier to exhalation from the lungs, conspires to the same result. Accumulation of these morbid products in the blood, greatly heightens its susceptibility of being act«d upon by atmospheric malaria, the causes of epidemics. The blood is supposed, under these circumstances, to acquire a fer- mentable state, forming, as it were, a ready prepared soil for the seeds of infection. Atmospheric malaiia seem not capable alone of producing epidemic disease. From those in real robust health, with perfect sanative surroundings, the arrows of contagion rebound harmless. The miasmatic poison rmist find some morbidity in the system to co- operate with, — some unhealthy condition induced by intemperence or debauchery, bad food or drink, bodily exhaustion, mental depression, or the discomforts of poverty — upon which it may take effect. But of all these predisposing agencies, none invite the stalking ■spectre of pestilence with so free and deadly a hospitality, as corrupt, con taminated air. 318. Ulnstration in the case of Cholera, — Of the tendency of an at- mosphere charged with the emanations of the human body^ to favor 116 MOEBTD AKD FATAL EFFECTS OF mPUBB AIE, the spread of contagious disease, the illustrations that might he quoted are inaumerahle. Take an instance of cholera, for example. It is well known to those who have had the largest opportunities of study- ing the conditions which predispose to this malady, that overcrowding is among the most potent. In the autumn of 1849, a sudden and violent outbreak of cholera occurred in the workhouse of the town of Taunton (England), no case of cholera having previously existed, and none subsequently presenting itself among fhe inhabitants of the town, though there was considerable diarrhoea. The building was badly constructed, and the ventilation deficient ; but this was especially the case with the school-rooms, there ieing ordy about 68 cuMcfeet of air for each girl, and even less for the boys. On Nov. 3d one of the inmates was attacked with the disease ; in ten minutes from the time of the seizure, the sufferer passed into a state of hope- less collapse. Within the space of 48 hours, from the first attack, 42 cases and 19 deaths took place; and in the course of one week, 60 of the inmates, or nearly 23 per cent, of the entire number were carried off; whilst almost levery one of the survivors suffered more or less, from cholera or diarrhoea. Among the fatal cases were those of 25 girls and 9 boys, and the comparative immunity of the latter, not- withstanding the yet more limited dimensions of their school-room, affords a remarkable confirmation of the principle we are indicating, for we learn that " although good amd obedient in other respects, the hoys could not be hept from breaHng the windows," so that many of them probably owed their lives to the better ventilation thus established. . In the jaU of the same town, in which every prisoner was allowed from 800 to 900 cubic feet of air, and this contiaually renewed by an effcient system of ventilation, there was not the slightest indication of the epidemic influence. (Dr. Oaepbntee.) It is in confined spaces thus charged with putrescent bodily exhalations, that pestilence revels ; they resemble in fatality those localities where the air is poisoned by effluvia from foul drains, sewer- vents, slaughter-houses, and manure manufactories. 319. Fevers originate in Impure ilt. —As with cholera, so also with fevers ; foul air not only augments their malignity, but also calls them into existence. Writers on pestilence, observes Dr. Geisoom, note two distinct species of virus applied to the body, through the medium of the air. First, that arising from the putrefaction of dead animal and vege- table matter — the accumulations of filth around dweUings and in cities, and the exhalations of swamps, grave-yards, and sewers, called marsh miasm. This is supposed to give rise to yellow, remittent, bilious, IT PEODUCES FEVBES AND SCROFDXA. 17V and intermittent fevers, dysentery, and perhaps also cholera. And second, exhalations from the human hody, confined and accumulated in ill-ventilated habitations, sometimes termed typhoid miasm, and which usually gives origin to common typhus and low nervous fevers. It would thus appear, that the very type and character of febrile disease is determined by the Icind of impurity which is breathed. Prof. Smith, of New York, says, " Let us suppose the circumstances in which typhus originates, to occur in summer, such as the crowd- ing of individuals into small apartments badly ventilated, and ren- dered ofiensive by personal and domestic filth ; these causes would obviously produce typhus in its ordinary form. But, suppose there exist at the same time, those exhalations which occasion plague, and yellow fever, or remittent and intermittent fevers; under such cir- cumstances we would not expect to see any one of those diseases fully and distinctly formed, but a disease of a new and modified character. It is, therefore, beyond probability that a few deleterious gases are quite sufficient to produce an infinite variety of pestilential and con- tagious maladies." 320. Scrofula, or Struma, the conseqneneeof Impnie Air. — There is a diseased condition of body known as scrofulous or strumous, which manifests itself in various forms, and in all parts of the system. It seems to be a result of deficient nutrition; that is, not a want of material for nutriciovis purposes, but a failure of power to produce healthy and perfect tissue from the elements of food. Various causes have been assigned as tending to produce scrofulous habits of body, such as hereditary tendency, bad diet, depressing passions, too late, too early, or in-and-in marriages, sedentary occupations, want of ex- ercise, deficient clothing, bad water, &c., and these, under diflferent cir- cumstances, may each contribute to the result ; but imperfect respira- tion is probably the most efficient and universal cause. An eminent French Physician, " who has made this subject a matter of extensive study, says, " Invariably it will be found on examination, that a truly scrofulous disease is caused by a vitiated air, and it is not always neces- sary that there should have been a prolonged stay in such an atmosphere. Often a few hours each day is sufficient, and it is thus that persons may live in the most healthy country, pass the greater part of the day in the open air, and yet become scrofulous, because of sleeping in a confined place, where the air has not been renewed." The same ob- server goes further, and affirms that the repeated respiration of the same atmosphere, is a primary and efficient cause of scrofula, and * M. Bauiioloqite. 8* 178 MOEBID A2 FATAL EFFECTS OF IMPUEE AIE. that, " if there he entirely pure air, there may be bad food, bad cloth- ing, and -want of personal cleanliness, but that scrofulous disease can- not exist." In 1832, at Norwood School in England, where there ■were 600 pupils, scrofula broke out extensively among the children, and carried off great numbers. This was ascribed to bad and inef- ficient food. Dr. Amott was employed to investigate the matter, and immediately decided that the food "was most abundant and good," assigning "defective ventilation, and consequent atmospheric im- purity " as the true cause. 321. Consnmption indnced l>y Impure Air. — When scrofula localizes itself in the lungs, there \%pulmona/ry or tubercular consumption. The essence of the nutritive process consists in the vital transformation of albumen (678) into fibrin and organized tissue. Now the tubercles which in this disease make their appearance in the pulmonary organs, consist of crude, coagulated, half organized masses of albumen — the abortive products of incomplete nutrition. In this manner, bad air, by producing the strumous condition, becomes a cause of con- sumption. It seems natural to expect that the organs with which the foreign gaseous ingredients of the atmosphere come more im- mediately into contact, and whose blood-vessels they must enter on their passage into the system, should feel, in a distinctive manner, their noxious influence ; and this expectation is strengthened by observation, and experiment upon both men and animals. It has been observed that when individuals habitually breathe impure air, and are exposed to the other debilitating causes which must always influence, more or less, the inhabitants of dark iU- ventilated dwellings, scrofula, and consumption, as one of its forms, are very apt to be engendered. 322. State of the Air inilnenccs Infant Mortality. — The same malign in- fluence of the air of unventilated rooms is seen in the mortality of infants. That the new-horn and tender child should be infinitely sus- ceptible to the influence of contaminated air is what we might well expect. We are, therefore, not surprised, that in the foul and stifling air of Iceland habitations, two out of three of aU the children should die before twelve days old. Opportunities have been afforded in hos- pitals, to compare the effects of pure and vitiated air, and it has been invariably found that a neglect of atmospheric conditions was accom- panied by high rates of infant mortality, which promptly disappeared with the introduction of eflBcient ventilation. " On the imagination of mothers, educated as well as ignorant, the feeling stiU seems to be stereotyped, that the fr^e, pure, unadulterated air of heaven falls upon rr BREAKS DOWN CONSTITDTIONAI, VIGOE. 179 the broTi? of infancy as the poppies of eternal sleep, and enters the lungs and circulates as a deadly poison; and still the 'Shawls and blankets,' sleeping and awake, are pretty generally employed to de- prive the objects of the most rapturous paternal solicitude, of what was originally breathed into the nostrils of the great archetype of the human race as the 'breath of life.' " 323. Bad Air nndeTmines the Vital Powers, — And yet the fatal effects of mephitio air are by no means confined to those terrible maladies, Cholera, Fevers, Consumption, and Infantine disease, by which the earth is ravaged ; by undermining the health it paves the way for all kinds of disorders. The human system is armed with a wonderful protective or conservative power, by which it is able to resist the in- vasion of morbific agencies. Indeed, this power of resisting disease is perhaps a more correct measure of the real vigor of the body than its outward appearance of health. Individuals may often continue for years to breathe a most unwholesome atmosphere without apparent ill-effects ; and when at last they yield, and are prostrated, or carried off by some sudden disease, the result is attributed to the more ob- vious cause, the long course of preparation for it by subtle and insidi- ous poisoning being entirely ovei-looked. The mass of mankind refuse to recognize the action of silent, unseen causes. Our youth in the morning of their days, and men in the meridian of their strength, pass abruptly away, and we will be satisfied with no solution of the problem which refers the mournful result to reprehensible human agency.* " The action of contaminated confined air has been shown to be the most potent and insidious of mortiferous agencies. Any ad- dition to the natural atmosphere that we breathe must be a deterio- ration, and absolutely noxious in a greater or less degree ; and health * " It is evident that the depressing effects of foni air are not confined to those cases In ■which the immediate results of its poison are seen. Because it requires a given quan- tity of carbonic acid in the air to exhibit decided effects, it does not follow that a much lower proportion does not seriously impair the vital energies, and especially the power of resisting disease. We are firmly convinced that many a case of scarlet fever or of measles proves fatal on account of an unperceived depression of the little sufferer^s strength by previous continued exposure to an atmosphere tainted with carbonic acid and other exhalations from his own Innga. "We know that all diseases of low grade, such as typhoid and typhus fever, prevail to a very great extent in ill ventilated houses ; we know that an epidemic inflammation of the eyes has been frightfully prevalent in the Irish work-houses, and that it has been traced to imperfect ventilation, the eye-disease being merely the index of the general depression of the vital powers ; we know, too, that in one of the Trans-Atlantic Hospitals, the mortality went down from forty in a thousand to nine, upon the adoption of a proper system of ventilation, and that it rose again to 24 on the subsequent abandonment of that system. These are only illiistra- tions ; hosts of similar feots could be cited from the records of medical science." 180 MOEBID AND FATAl EFFECTS OF IMPUEE AIE, would immediately suffer, did not some vital conservative principle accommodate our functions to circumstances and situation. But this seems to get weaker from exertion. The more we draw on it, the less balance it leaves in our favor. The vital power, which in a more natural state would carry the body to seventy or eighty years, is pre- maturely exhausted, and like the gnomon shadow, whose motion no eye can perceive, but whose arrival at a certain point in a definite time is inevitable, the latent malaria, which year after year seems to inflict no perceptible injury, is yet hurrying the bulk of mankind, with un- deviating, silent, accelerating rapidity, to an unripe grave. It should never be overlooked, that by breathing pent-np effete air, aU the ad- vantages of an abundance of fuel, and every blessing of a genial sky are utterly thrown away, and though the habitation were on the hill- top, fanned by the sweetest breezes of heaven, it would become the focus of contagious and loathsome disease, and of death in its most appalling aspect. On the other hand, even in the confined quarters oi a crowded city, rife in malaria, and where pestilence is striking whole families and classes, ventilation and warmth, with cleanliness, theii usual attendant, like the sprinklings on the lintels and door-post* en' the Hebrew dwellings, stand as a sign for the destroying angel, as h« passes over, to stay his hand, for in the warm, fresh-aired chamber none may be smitten." — (Beenan.) 324. Morbid Mental Effects of Bad Air. — Dr. Eobeetsos remarks- " The health, the mental and bodily functions, the spirit, temper, dis- position, the correctness of the judgment and brUliancy of the imagin- ation depend dii'ectly upon pure air." This is strongly put, but it is not an overstatement. As the inflowing stream of air is the inuninent and instant condition of physical life, so it is the immediate material agent charged with the exalted function of establishing and maintaining the connection of mind and body. It is air acting definitely and quanti- tively through the bodily mechanism, that sustains the order and ac- tivity of the mind's faculties. Mind is thus physiologically condi- tioned, and one of the mighty tasks to which science must gird itself in the future is to work out the analysis of these conditions. Mr. Paget, the eminent English physiologist, remarks : " The health of the mind, so far as it is withia our own control, is subject to the same laws as is the health of the body. For the brain, the organ of the mind, grows, and is maintained according to the same methods of nutrition as every other part of the body ; it is supplied by the same blood, and through the blood, like any other part, may be affected for good or ill by the various physical influences to which it is exposed. But I will not MENTAI, DISTUEBAlfCK ASD DEPEESSION. 185 dwell on tMs more than to assert, as safely dedncible from physiology, that no scheme of instruction or of legislation can avail for the im- provement of the human mind, ■which does not provide with equal care for the well-being of the human body. Deprive men of fresh air and pure water, of the light of heaven, and of sufiBcient food and rest, and as surely as their bodies will become dwarfed, and pallid, and dis- eased, so surely will their minda degenerate in intellectual and moral power." The immediate effect of breathing impure air is to cloud the mind's clearness, to dull its sharpness, and depress its energy. All the mental movements are clogged, each faculty suffering restraint and perversion. The wings of the imagination are clipped, reason loses its keenness of penetration, and the judgment its acnteness of discernment and perspicacity. When we breathe bad air, the impressibility of the mind is diminished ; if we undertaie to study, we can neither under- stand so clearly, nor remember so well as if the air were pure. So- cially we become less interesting, the spirits fall, conversation flags, dulness supervenes, we get impatient and irritable, and there is too often a resort in these ch-cumstances to artificial exhilarants, and stim- ulants to afford reUef, which would be better secured by freshness and purity of the atmosphere. VI.— RATE OF CONTAMINATION WITHIN DOORS. 325. Oxygen irithdrawn by Respiration. — ^Any scheme for the removal of foul air from an apartment, and the introduction of fresh air in its place, involves the previous inquiry, how rapidly ought this change to be made ? Our next question, then, is at what rate does the air in dwellings become contaminated ? The amount of air taken into the system by different ii.dividuals, varies greatly according to age, capa- city of lungs, rate of exercise, and many other circumstances. Hence there is much discordance in the results of inquiries made by different physiologists. The disagreement is also much owing to the difficulties attending this kind of experimenting. If we take as the basis of our calculation Ooathfpe's estimate, the lowest that we can find, we shall assume as an average, that there are 20 respirations in a minute, and at aach respiration, 16 cubic inches of air pass in and out of the lungs. This is equal to 320 cubic inches per minute, 19,200 per hour, 460,800 cubic inches or 266| cubic feet per day of 24 hours. Yibeoedt makes the quantity 306f cubic feet, Sohaeling 361 cubic feet ; and Valemtin as high as 398| cubic feet per day. As J of the air is oxygen, there will be 'bur cubic inches of this gas taken into the lungs at each inspiration. Of 182 BATE OF CONTAMINATION WITHIN DOOES. this quantity, very nearly one half is absorbed and enters the blood. "We may safely assume that 35 per cent, of the oxygen is thus absorbed at each breath, or 7 per cent, of the entire air. The quantity of oxygen consumed will be 22 to 34 cubic inches per minute, 1344 cubic inches or 8-4ths of a cubic foot per hour, and 18'6 cubic feet per day. A person, therefore, robs of all its oxygen nearly four cubic feet of air per hour, and diminishes its natural quantity 5 per cent, in 80 cubic feet per hour, or 1\ cubic feet per minute. 326. Proportion of Carbonic Add exluiled hy Respiration. — "When carbon • is completely burned in pure oxygen, the carbonic acid gas produced occupies exactly the space that the oxygen did before burning. If aU the oxygen absorbed by respiration was converted into carbonic .acid in the system, the volume of this compound gas restored to the air would be exactly equivalent to the oxygen withdrawn. But a portion of oxygen unites with hydrogen and sulphur, forming water and sul- phuric acid, while a small part of the carbonic acid generated within the body escapes into the air through the pores of the skin. T^he con- sequence is, that the bulk or volume of carbonic acid expelled from the lungs is not quite equal to that of the oxygen absorbed. Assuming the quantity of carbonic acid in the expired air to be 5 per cent., it will be one hundred times greater than the natural amount in the at- mosphere (280). A person, therefore, by breathing adds 1 per cent, of carbonic acid to 55^ cubic feet of air in an hour, or would vitiate to this extent nearly one cubic foot in a minute. 327. Oxygen withdrawn by Combnstion. — The amount of combustion varies so widely with the kind of fuel used, the mode of burning it, the quantity of heat required, and other circumstances, that we can approach nothing like an average ■ estimate of its influence upon the air in a given time. It is known with certainty how much oxygen given weights of the different fuels require for combustion, but the amount withdrawn from the air of a room depends entirely upon the rapidity with which it is consumed. A pound of mineral coal requires the oxygen of 120 cubic feet of air to burn it (90). If five pounds are consumed in an hour, at least 600 cubic feet of air must be re- moved from the room. Combustion of fuel, however, does not, like respiration, decompose the air, separating the life-sustaining element, and leaving the residue in the apartment. If properly conducted, it removes the air from the room unchanged, and having decomposed it in the fire, dismisses the contaminated product through the flue. "V"ery olLen, however, when fires get low and draughts feeble, there is a re- fluence of foul gases into the apartment (121). BY LIGHTING AITD I.0S.5 OF MOISTUEE. 183 828. Air vitiated l»y ninminating Processes. — The case is different when combustion is employed for illuminating purposes, as in the burning of candles, oil, and gas ; these, like the body in respiration, alter the Mr wUMn 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 thfe air most rapidly. A cubic foot of coal-gas consumes from 2 to 2i cubic feet of oxygen, and produces 1 to 2 cubic feet of carbonic acid. Thus every cubic foot of gas burned imparts to the atmosphere 1 cubic foot of carbonic acid, and charges 100 cubic feet with 1 per cent, of it, making it unfit to breathe. A burner which consumes 4 cubic feet of gas per hour, spoils the breathing qualities of 400 cubic feet of air in that time (224). 829. Influence of Moisture npon tbe quantity of ilr reqnlred. — ^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 diy 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. K one of each sex be taken, the mean exhala- tion win 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 50° 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 wiU 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 dewpoint is at 60° and the temperature of the air at 70°, a cubic foot of it will become saturated by the addition of 2"17 grains, so that 10 feet per minute would hardly carry off the cutaneous exhalation. To be pleasant, air must not be deficient in moisture ; if it be nearly saturated, it can im- bibe but little, and consequently much of it must be brought in con- tact with the system ; and this necessarily involves large provision for •jhange of air. 184 BATE OF CONTASnNATIOlT WITHIN DOOES. 330. Air Tltiatcd by one peison in a minntc. — ^These somces of impurit j are capable of measurement in tlieir 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|^ to 10 cubic feet per minute. We are of opinion, that for the restoration of its lost oxygen, the removal of carbonic acid, insensible perspiration, and the peculiar effluvia of the living body, there are required, at the lowest estimate, 4 cubic feet of air in a minute, or 240 per hour. But this may be much too low. It is evident that the nearer the air breathed within doors, approaches in purity and freshness to the free and open atmosphere, the better win it conduce to health, strength, and length of life. As far as pos- sible we ought not to limit ourselves to that supply which the consti- tution can bear or tolerate, but to that amount which will sustain the highest state of health for the longest time. And yet, as Dr. Eeid remarks, the question of the amount of air to be supplied may be con- sidered in some respects in an economical point of view, in the same manner as the table any one can afford to sustain, the house in which he may dwell, or the clothing he may put on. Although pure air is the most abundant of all things, yet in our plans of living it is by no means free of cost (363). 331. Inflnence of size of Apartments. — The smaller an occupied room, the sooner, of course, will the stock of pure air contained in it be ex- hausted and replaced by foul air. Three persons sitting in a tight room 8 feet high, and 12 by 14 square, will vitiate all its air in two hours. If they use lights, the air wiU be spoiled much quicker. Twelve persons sitting in a parlor 16 by 20 and 9 feet high, will make its air unbreathable without the assistance of either fire or lights in a single liour. Two persons sleeping in a close bedroom 10 feet square by 8 high, wUl render all its air unfit for respiration in less than two hours. In actual practice, the cases are not quite so bad as this, fol with the utmost perfection of carpentry there wiU be cracks for the passage of air, though, perhaps in small quantities ; and the opening and closing of doors cause intermixture and currents, and this some- what delays the result. "Where the rooms are capacious, the reservoirs of air are more slowly contaminated, and if no means are taken to remove the foul air and introduce that which is pure, large-sized rooms are of the utmost importance. But no apartments of ordinary or prac- tic'able dimensions will enclose sufficient air for the agreeable and whole- some use of their occupants. This must be attained in another way. MOTrVB POWER IN VENTILATION. 185 332. Inflaenee of Plants npon tbe Air of Rooms. — The general action of plants upon tlie air is antagonist to that of animals. In the day time, under the influence of light, they aibsorb carhonic 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. Hence, in sleeping-rooms, their tendency would be to impurity of the air, though the action is probably very slight. As respects moisture plants are also like animals, constantly exhaling it through the pores of iheir leaves. According to Hale's experiment, a sunflower weigh- ing 3 lbs. exhaled from its leaves 80 ounces of water in a day. Plants may therefore be a useful means of supplying dry air with the requisite humidity. Vn.— AIR m MOTION— CDBRENTS— DRAUGHTS. 333. Two methods of purifying the Air. — ^Pure air may be secured iu two ways : first and most perfectly by the removal of the vitiated at- mosphere of the apartment, and its replacement by 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. The air may also be more or less perfectly cleansed by means of substances which absorb, decompose and destroy its noxious ingredients. This is the 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, &o., 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 rtsed as an aid in ventilation, 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 AIE IN MOTION — CtTEEENTS — DEATJGHTS. Fio. 72. 335. Cnrrents of Air in Close Apartments. — Changes of temperature externally give rise to nnceasing 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 curieat. If a candle be lit in the middle of a room (Fig. 72) where the doors, windows and flues are closed, and the air is motionless, a set of cuiTents wiU rise in the centre of the room, spread out near the wall, to its sides, then descend and return along the floor to the centre again. The arrows in the diagram show the direction of the currents in a section of the .apartment. Fig. 73 shows the direction of the currents along the floor, that is, on a plan, as it is termed. If the arrows (Kg. 73) were reversed, they would show the course of the cnrrents at the top of the room. If a lump of ice be substituted for the candle, cm-rents are again produced, but they ai'e exactly reversed in direction (352). The air descends from the cold ice, and the currents on the floor rtm outwards. In each of these cases, the cnrrents above and below are opposite. All local disturbances of temperature tend to produce simi- lar effects, although the currents are commonly much interrupted by dis- turbing forces. Of course several lights would occasion several cur- rents, which would mutually inter- fere with each other. A stove in the centre of the room produces just such a movement of air as we have seen established by the candle ; but if placed at one side, the hot-air ascends on that side and descends on thfe opposite. 336. Ifatnral Ventilation of the Person. — The warmth of the human body imparts itself to the layer of surrounding air, expands it, and Fia. T8. DOWNWARD CUEEENTS IN WINTER FROM WINDOWS. 187 Fio 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 head. The simple presence of an individual in a room is therefore sufficient to throw the air into movement and cause currents. The body thus acts pre- cisely in the same way as a stove, and the presence of persons dis- tributed through a room wiU add much complexity to the movements of the air, and to a small extent counteract the stove-currents. 33T. Windows, thoagh tight, produce Cnrrentg.— 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 remal-ked 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). 388. The Air of rooms arranged in strata. — ^But the effect of currents is not to cause a perfect intermixture with uniformity in the condition of the air throughout the room. Indeed, the very cause that gives rise to them is the tendency of qold air to fall into the lower place, Carrents produced in ■winter by single windows. 188 AlE IN MO'nOIf — CUEEENTS — DEAUGHTS. while it px-esses 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 li-ste in one stratum which would perish in another. Now the warm and rarefied air which rises to the upper part of the room contains also the impure air which has been generated within it. The breath which escapes from the lungs, 20° or 80° warmer than the surrounding air, slowly rises above the head, while ascending currents from the body carry upward all its exhalations (334). So also the heated poisonous products of illu- mination mount rapidly to the ceiling. The effect of currents is, to a certain extent, to diffuse the foul gases throughout the apartment, bat 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 window, fall towards the floor and move along near it to the flne, where it is discharged. In its progress, it may even blow strongly upon a bed made on the floor, whUe 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, etpecially if the wpa/rtmenta lume open fireplaces. 339. Simple openings do not produce Cnrrents. — If an apartment be opened to the external air, various movements are liable to occur, or there will he no motion at all, according to circum- stances. It 50° by no means . follows that because a communica- tion has been opened be- tween a room Fio. T5. Fio. T6. 50° -6tf^ -SO- Condltlons in wMcli openings in rooms do not produce exchange of air. 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. Our- INTEECHANGBS THROUGH WINDOWS AND DOOES. 189 rents cannot be produced unless their eaicaea are brought into action. If a room be opened below, and the temperature within be higher than, that without, as represented in Fig. 76, 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 itr. — If there be an open- ing at the lower part of a room, and the external air be warmer than that within, interchange takes place, the outward air displacing that within by currents running as the arrows show (Fig. 77), the heavier air within falling or flowing out. K the opening be above, and it be Fio. 77. Fio. 78. warmer in- side than out, the light air inside will escape upward, and tLecold,hea- vy air with- out flows in, as shown in Fig. 78. If y ) 6rf / 50° / .eandy and how it is Colored. — When the pure sugar is melted or dissolved, it forms a clear liquid, and when allowed to cool or dry without disturbance, it crystallizes into a transparent solid, like glass. When threads are suspended in the sugar solution, crystals of extreme hardness collect upon them, which are known as rocJc-ccmdy. The cause of whiteness in refined sugar is that the crystals hre small, con- fused, and irregular. To make candy white, the sugar, while cooling, is agitated and worked (pulled), which breaks up the crystals and ren- ders the mass opaque. Candy is coAmonly adulterated with flour, and frequently with chalk. Yarious 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 GENERAI, PEOPBETIES OF ALIMENTAET SUnSSTAlTCES. rions are the vegetable and animal coloring matters, but these neither form so brilliant colors nor are they so lasting as the mineral com- pounds, which are far the most deadly. The following are the chief coloring substances used by confectioners to beautify their sugar preparations : I Oxide of lead (red lead). Ebds J Biflulptiuret of mercury {vermiMori). ( BisulplLuret of arsenic (retZ orpmienty. I Gamboge. Yellows. . . ■< Chromate of lead {chrome yeUov)), \ Sulplniret of &rsQmQ,\ydlow orpimitit), Ferrocyanide^flron {Prtissicm, line). Cobalt. Blues i Smalt (glass of cobalt). Carbonate of copper {^&rdMe/r\ . Ultramarine. ( Diacetate of copper (verdigris). Gkbens -^ Axsenite of copper (emerald green . ( Carbonate of copper (mineral green). Whites Carbonate of lead (white lead). PuKPLES Formed by combining blues and reds. From an examination of 101 samples of London confectionery. Dr. Hassall found that 59 samples of yellow were colored with chromate of lead and 11 with gamboge. That of the reds 61 were colored with eocTtineal, 12 with red lead, and 6 with vermilion. Of the blues, one sample was colored by indigo, 22 by Prussicm blue, and 15 by ultra- marine. Of the greens 10 were colored by a mixture of chromate o/ lead and Fruasian Hue, 1 with ca/rbonate of copper, and 9 with a/rsem ite of copper. These xolors 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 be alleged by some that these substances are employed in quantities too inconsiderable to prove injurious, but this is certainly not so, for the quantity used, as is amply indicated in many cases by the eye alone, is often very large, and suflBcient, as is proved by numberless re- corded and continually recurring instances, to occasion disease and death. It should he remembered, too, that these prepai-ations of lead, mercury, copper, and arsenic, are what are termed cumulative, 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- eequences 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 mucli more ia- jnrious, then, must the consumption of sugar thus painted prove when these pigments are actually received into the stomach." D.— Tbe Gums. . 407. Properties of tie Gimis. — ^The juices of many plants contain suhstances which ooze out through the hark, forming rounded trans- parent masses of gum, as we often see upon cherry, plum, peach and apple trees. The gums differ considerably in properties. Oherry-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. Artifieial Gum. — When common starch is heated to 300 degrees in an oven, or boUed in water made sour by a little sulphuric acid, it is so altered as to dissolve in cold water, forming a clear, viscid solu- tion. The substance thus produced from the starch has the properties of gum, and is known as dextrine. 409. How Gnm 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, i^ the same as starch and sugar, and hence it is grouped with the saccharine alimentary principle. X;.— The Oils. 410. Distinctioii between Tolatile 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 j^ed oils; and, 2d, such as wUl 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, afid from both sources it is chemically the same thing. It exists in many parts of vegetables, but is chiefly stored up in their seeds, from many of which it is obtained by pressure 224 GENEEAI, PEOPEETIES OF AIJMENTAET SUBSTANCES. in large quantities. In animal bodies it is deposited in tlie sacks or cavities of cellular tissue, and becomes accumulated in large quanti- ties in diflPerent parts of the body. Oils and fats are chemically iden- tical, differing only in consistence, and this quality depends upon tem- perature. Lowering lie temperature of a liquid oil sufficiently, changes it to a solid, while raising that of a solid tallow converts it into a flowing oil. That which, in the hot climate of Africa, is liquid palm oil, is with us solid ^asfci hitter. Those oils, however, which at ordinary temperatures are not perfectly fluid, but have what is called an oily consistence, become much thiuner and completely liquid when hea.ted. 412. Proportion of OH la 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 : Tolkof Egg 28-75 per cent Ordinary Meat (Lbbbis) 14-08 " Indian Corn 9* " Oatmeal (husk excluded) 6* *' Cow'sMilk 81S " EyeFIour 8-5 " Wheat Flour ItoZ " BarleyMeal 2- " Potatoes (dried) 1- " Eioe -8 " Buckwheat..; -4 " il3. Its Composition. — Oleaginous bodies are distinguished from all the other alimentary principles, by their chemical composition, and the resulting properties. They resemble the preceding substances which we have been considering in containing three elements, carbon, hydrogen and oxygen ; but they diflfer from all of them in this im- portant respect, that they are composed almost entirely of hydrogen and carbon, with but a small proportion of oxygen. The composition of hogs-lard, as given by Ohbvebui,, may be taken as an example of the general structure of this alimentary group. It consists of carbon 79, hydrogen 11, oxygen 10 parts in a hundred. We have seen that hydrogen and carbon are the active flre-producing elements of fuel (80). As the oils are so rich in these, they rank high as combus- tibles, burning with great intensity, and yielding much heat. It has been also noticed that oils may be decomposed into several acid and basic principles (195). THE ACIDS FOUND IX PEUITS. 226 F.— The Vegetable Acids. 414. Combination and Composition. — ^The sourness of fruits and suc- culent vegetables is due to various acids produced in the plant, and which thej 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, &o., by which they are partially neutralized, and thus rendered less pungent to the taste. In this case they exist as acid salts (691). The vegetable acid group con- sists of but three elements, carbon, oxygen, and hyarogen, like the starch and oil groups, but it is distinguishable from them by contain- ing but a small share of hydrogen and a large proportion of oxygen. The composition of the different vegetable acids is quite variable, but they all agree in possessing less hydrogen and more oxygen than any other class of organic alimentary principles. Their nutritive value is very low, 415. Aeid of Apples— Ualic-Acld. — 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 fruit, and generally speaMng, in proportion as we obtain sweetness by culture, we deprive the apple of its malic-acid. ITo use is made of this acid in the separate state. * 416. Acid of Lemons — Citric- Acid — Gives their sourness to the lemon, orange, citron, and cranberry. Mixed with malic-acid, it exists also in the gooseberry, red-currant, strawberry, raspberry, and cherry. Citric-acid is separated from lemon juice, and sold in the form of crys- tals, which may be at any time redissolved in water, and by flavoring with a little essence of lemon, an artificial lemon juice is produced, which is used like the natural juice in the preparation of refreshing and cooling beverages. 417. Acid of Grapes — ^Tartaric-Acid. — This acid in the free state ex- ists in the grape, and is found besides in some other fruits. It also exists abundantly in the grape in combination with potash, as acid, tartrate of potash, or cream-of-tartar. Tartaric-acid is prepared and sold in the crystalline form as a cheap substitute for citric-acid, or lemon juice. It does not absorb moisture when exposed to the air like citric-acid, but is inferior to it -in flavor. The commercial effer- 10* 226 GENBEAX PEOPBETIES OP ALIMENTAET StJBSTAlTCBS. vesoing, 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. Oxalic-Acld — Exists in sorrel, and also in the garden rhubarb or pie-plant, combined with and partially neutralized by potash or lime. It is a prompt and mortal poison when pure, and fatal results frequently occur from mistaking its crystals for those of Epsom salts, which they much resemble. 419. VegetaWe JeUy, Peetlne or Feetic-lcid. — 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 oxygen. Vegetable jelly is thought not to exist exactly as such in the plant- juices, but to be produced from another substance in the process of its separation. The substance from which it is obtained is soluble in the vegetable juices, but the jelly itself is scarcely soluble in cold water. Boiling water dissolves it, but it coagulates again as the water cools. It is commonly prepared by mixing sugar with the juice, and suffering it to stand for some time in the sun, by which a portion of the water is evaporated ; or it may be boiled a short time. But when long boUed, 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 jeEy, when the quantity of sugar is not sufflcient to absorb all 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-jeUies, 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. — (Peebiea.) 420. Acetic Acid, or Vinegar. — The acid in most general use for diet- etical purposes is the acetic, or acid of vinegar, which we obtain by THB AliBUMINOTTS PEIlfCIPI.ES. 227 fermentation (491). Good strong vinegar contains about four per cent. of the pure acid. Vinegar may be easily made at any time by adding ferment, or yeast, to water sweetened with sugar or molasses, or any sweet vegetable juice, and exposing the whole for a reasonable time to the air in a warm place. Vinegar itself added to the mixture will act in the way of yeast to start the operation. There accumulates in old vinegar a thick, ropy matter, called mother, because it is capable of producing the acetous change in a sugary solution. It consists, like yeast, of vegetable cells (496). The juices of moat fruits contain aU the elements necessary for fermentation and souring. Apple and grape juice, at first, undergo the vinous change producing cider and wine, and the process continued converts them both into vinegar (cider-vinega/r and wine-vinegar), which are prized, on account of the fruity aroma which accompanies them. 2. — ^PEUfciPLES Containing Niteogbn. A>— Teg'eta.ble and Animal A11>nnien> 421. It exists in both organized Eingdoms. — We are all familiar with albumen or white of eggs, and recollect the remarkable change it un- dergoes by heat, being coagulated or altered from a transparent liquid to an opaque, white, brittle solid. This substance exists in 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 Eegnauit, about 19 per cent, of healthy human blood, and is therefore found in large quantities in aU 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 ilbnmeni — ^In composition, albumen differs widely from the aliments we have considered ; it contains not only the ali- ments they contain — carbon, oxygen, and hydrogen, — ^but in addition, a large proportion of nitrogen, and also a minute amount of sulphur. The chemical structure is thus complex. The result of the latest analysis is, that a compound atom of albumen consists of 216 carbon, 189 of hydrogen, 68 of oxygen, 27 of nitrogen, and 2 of sulphur. The albumen of eggs, however, contains a slightly larger proportion 228 GENHEAI, PEOPEETIES OP ALIMBNTAET SUBSTANCES. of sulphur. Vegetable and animal albumen are essentially the same thing in properties and composition, differing no more upon analysis than twq samples from the same source. 423. General Properties of Albnmen, — ^It exists in two states — soluble and insoluble, or coagulated. The coagulation is effected by simple heat ; but there is much confusion of statement among different writers as to the point of temperature at which it solidifies. This depends upon circumstances. A moderately strong solution of pure albumen in water becomes turbid at 140°, and completely insolable at 145°, and separates in flakes at 167°. When excessively dUuted, no turbidity can be 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 with greater difficulty in proportion to the quantity of water in which it is dissolved. Coagulated albumen refuses to dissolve in cold water, merely swelling up in it. There are many substances which, if mixed with it, coagulate albumen when cold, as alcohol and corrosive sublimate, the mineral acids, and many salts, while the presence of alkalies hinders its coagulation. The change of coagulation does not alter or disturb its composition. B.— VegetaUe and Animal Casein. 424. Sonree and Composition. — The water in which flour has beea washed or diffused, as in separating starch, contains a small portion of a dissolved substance, which is coagulated by the addition of an acid, and may be then separated. It is called vegetable casein, and is found in the largest, proportion in peas and beans, constituting \from 20 to 28 per cent, of their weight. This substance is identical in properties with the curd of milk, which is known as animal casein, and is the chief ingredient of cheese. The identity of vegetable and animal casein is well illustrated by the fact that the Chinese make a real cheese from peas. They are boiled to a thin paste, passed through a sieve, and coagulated by a solution of gypsum. The curd is treated like that formed in milk by rennet. The solid part is pressed out, salted, and wrought into cheese in moulds. This cheese gradually acquires the smeE and taste of milk cheese ; and when fresh, is a favorite article of food with the people. The composition of vegeta- ble and animal casein is nearly if not quite identical with that of dbumen (422). C— VegetaMe and Animal Fibrin. 425. The Blood and VegetaWe Juices.— When blood is drawn from riBEIN AND GLUTEN'. 229 Fia. 91. I^lbres of lean meat magnified. the living body, in a short time it elots ; that is, a net-work of fibres is formed -within it. These fibres consist of unimal flbrin, which was dissolved in the blood, and then took on the solid form (apontaneoua 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 striae. By the contraction of a muscle in the living 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 nnder 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, vTith 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 prind- pie. By acting upon crude gluten with different solvent agents, it «B separated into four principles as follows : Fia. 92. 530 GBNEEAI, FEOPEETIES OP ALIMENTARY SUBSTAIfCES. Vegetable ^brin 72 percent. Gluten , 20 " Casein (muclne) 4 " Oil 87 '• Starch (accidental), small quantity Total 99-7 " 42^. Animal Fibrin. — The muscles or lean meat of animals are prin- cipally composed of this suhstance, its proportionate quantity being greatest in flesh that is dark-colored, and belongs to animals that have attained their full growth. Its characters vary somewhat in different animals, and in the same animal at different ages. Its color is vari- able ; in beef and mutton it is red ; in pigeons and many kinds of game it is brownish ; pink in veal, salmon color in pork ; in fish, white or semi-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 the Nitrogenous Principles. — ^Whatever their form or source, these substances are identical in composition, a fact of great importance in connection with animal nutrition. They present varia- tions of aspect and physical properties, and different solubilities, albu- men and casein being soluble in water, while the others are not ; and while fibrin coagulates or solidifies spontaneously, albumen is altered in the same manner by heat, and casein by acids. It is possible that 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 eihale a pungent odor like that of burnt feathers. They may be long preserved when dried, or even in the moist state when cut off from the atmosphere ; but in contact with air and moisture they quickly decompose, putrefy, and call into existence a host of microscopic ani- malculse. We shall consider these substances again (678). D.— Gelatin. 429. Its Sources, Properties and Uses. — There exists in the bone, carti- lages and various membranes of animal bodies, a principle rich in ni- trogen, called gektMn. It is not identical in composition with the ni- trogenous class which we have been considering, nor is it like them produced in the vegetable kingdom ; but it is supposed to be derived from them in the animal system. It dissolves in hot water, and when cooled, forms a white jelly. It is the universal principle of animal jellies. Common glue consists of gelatin, but in this form it is not DUTEEENT NAMES 01" THE" NTTEOGENOUS PEINCIPLES. 231 used dietetically. Isinglass is a preparation of gelatin in various forms to be used as food. It is mainly procured from the air-bag or bladder of fishes. Four parts of isinglass convert 100 of water into a trem- bling jelly. Gelatin is also extracted from calves' feet, in forming eahes foot jelly, and calves' heads are also employed to furnish jelly in mat- ing mock turtle soup. Gelatin is used not only to produce jellies, but to thicken and enrich gravies and sauces, and also as a clarifying or ' fining ' agent to clear coffee or other mixtures. 430. Diffeient Names applied to these SnbstaneeSi — The recent rapid progress- of organic chemistry, has brought this class of substances for- ■ward into new and highly interesting dietetical relations, and there has been a confusion in the terms applied to them, which, though perhaps inevitable, is at first very embarrassing to unscientific readers. As they all contain nitrogen, they are called nitrogenous alimentary principles ; and as one of the names of nitrogen is asote, they are call- ed aeotieed compounds. As they have all (except gelatin) the same composition as albumen, and are convertible into it, they are often called albuminous substances. As they form the material from which the body is nourished and built up, Liebig named them plastic ele- ments of nutrition; they are also called nutritive principles, the.^A- forming and bhod-maTcing substances. Mtjldee 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^eJTi, and hence the group has been called _proiei?i or ^ro- teinaceous compounds. Muidbe's peculiar views are abandoned, but his terms are still in current use. . 3. OoMPOTTND 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 Degetaile foods and animal foods ; of the former first. A.— Xbe Grains. 433. Composlflon ot Wheat — ^We begin with wheat, the prince of grains. 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 GENKEAl PEOPEETIBS OF AlIMENTAJET SUBSTAITCES. from many causes, as variety of seed, climate, boU, kind of fertilizera^ seed, time- of harvest, &c. We give five analyses. 'W'ater TAtTQUELIN. Dumas. Ebck. Plinty Wheat Soft Wheat. riinty Wheat Soft Wheat Genesee Wheat 12-00 14-60 56-60 8-50 4-90 2-80 10-00 12-00 62-00 T-40 5-80 1-20 12-00 14-55 56-50 8-48 4-90 2-80 10-00 12-00 62-00 T-86 5-81 1-29 12-40 11-46 70-20 15-20 Gluten 3ugar Gum Total 98-80 98-40 98-T3 98-46 99-26 ■483. Proportion of Glnten in Wbeat. — ^It wiU 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 (426), is of the first importance in examining the grains. Trom an analysis of six samples of wheat, made by Vattqdelin, we get an aver- age of 11"18 per cent, of gluten; Dumas, from three samples obtain- ed an average of 12'50 per cent. ; and Dr. Lewis 0. Beck, who made an investigation of the subject, at the direction of the Federal Govern- ment, and of 33 samples of wheat, gathered from aU 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. Bkok— that of washing away the starch by a stream of water (426) — ^is not the most accurate. A por- tion of albumen and casein, with small particles of gluten, are carried away by the stream — which would make the remaining quantity an under-statement of the true proportion of nitrogenous matter. This loss is assumed to be compensated for by the oil retained in the gluten, and the result is thus to a certain degree guessed at. Hokseoed 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 Davt and Botjssin&alt as high as 20 or 30, and even 35 per cent., but these are probably erroneous over-statements. For general purposes we may adopt Dr. Beck's results — 11-72 of gluten, or in even num- bers 12 per cent. 434, Quality of the Glaten of Wheat. — But not only do wheats differ in the pi-oportion 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 OP WHEAT. 233 Moreover, any injury or damage that flour may sustain, is most promptly manifested by a cliange 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 iato 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-rfourths 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, whUe bad flours yield a gluten which does not swell, but becomes viscous and nearly fluid, adhering to the sides of the tube, and giving off occasionally a disagreeable odor, whilst that of good flour merely suggests the smell of hot bread. — (Mitohbll.) 435. Macaroni and Vermicelli are pastes formed from wheaten flour, and made to take varipus 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 macaroiii 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 indifferentj nor have we succeeded satisfactorily with it in this country. The best macaroni should retain its form, and only swell after long boiling, withoirt either running into a mass or falling to pieces. 436. Water in Wlieati — The wheat grain consists of a solidified veg- etable milk. 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. Bbok'b 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 froni 5 to 20 per cent. 234 GENERAL PEOPEETIES OF ALIMENTAEY SUBSTANCES. 437. Grinding of Grain.— Grain is converted into flour by being ground between two liorizontal stones, the upper of which revolves, while the lower is stationary. The mill-stones (bnhr-stones) are com- posed of a peculiar hard and porous sand-stone, so that the working surfaces consist of an infinite number of minute cutting edges. There is an opening in the centre of the upper revolving stone through which the grains are dropped. The lower stone is convex and the upper one is concave, so as to match it; but they do not perfectly 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 uniform powder, composed of equal sized particles, but consists of parts which have been difierently afiected 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 parts, fine flour, coarse flour, bran, &c. 438. Strnctnre of the Grains. — When we consider wheat or other grain with reference to its grinding and sifting capabilities, the proportion and quality of its separated products, several things require notice in regard to the structure of the kernel or berry. Each grain consists of a farinaceous body, enclosed in a membranous husk or skin. This husky envelope varies in properties ; in some wheat it is thin, smooth, and translucent ; in others, rough, thick, and opaque ; in some light- colored, in others dark ; in some tough, in others brittle ; and in some it peels or flakes off readily under the stones, and in others it is very adherent to the kernel. The other elements of the seed, albumen, glu- ten, starch, and oil, and the- salts which it leaves as ash when burned (446), are not equally distributed throughout its mass. Immediately beneath the incrusting husk, is a layer of matter of rather a darkish color, and not very easily reduced to an impalpable powder. It is rich in gluten, and contains oil, which exists in minute drops enclosed in cells. Underneath this is the heart of the seed, which is whiter and more readily crumbles to a fine dust. This part consists more purely of starch, and forms the finest and whitest flour. There is a certain degree of interdiffusion of these elements throughout the body of the seed, yet, upon dissection, they are each found in excess in the parts indicated. 439. Anatomy of Grains Ilinstrated. — An idea may be gathered of this distribution of substances throughout the cereal seeds, by the accom- KTEUCrrUKE OF THE CEREAL GRAINS. 233 panying section of a grain of rye highly „ magnified (Fig 93) : a represents the outer _-_;._-' -. . investing seed-coat, consisting of three "^^^isf^g-^^cr^cr^ ^ rows of cells ; i, an inner memhrane or ii fa|| S fe iw jftB|B i | | ^ ^ seed-coat, composed of a single layer of P^^^^^^p^^^PW cells ; c, a layer of cells containing gluten. ^^Hf^Ml^^^wV These three form the bran ; d, cells con- l®^^^n^ffl^^^^^!i taining starch grains in the interior of ^^^^LsJ^s^f^/W^S) the seed. Kgj 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 SUUngt — These several portions oppose un- equal resistance to the pulverizing force of the miE- stones. The outer fibrous portion which forms the bulk of bran is least affected ; the tough coherent gluten is divided stiU finer, while the brittle starch, of which the grain is mainly composed, is crushed most completely. As the particles of these substances, therefore, are of different sizes, they may be separated by a bolting cloth, having different degrees of fineness of texture. The jiss^^'y*^ product is divided by the miller according to custom or ^^^ fancy, four or five grades being often established, which, of course, vary much in composition and properties. 441. Properties and Composition of Bran. — ^From what has been said of the husk, it will appear that the quantity of bran yielded by differ- ent wheats, is liable to variation (488). As the husk is detached with different degrees of ease, it is evident that it may carry with it more or less adherent matter of the grain, by which its com- i; f/xm ■ ^'^^ position will be made to fluctuate. Johnstok ^y^Ms states, that in good wheat the husky portion amounts to between 14 and 16 per cent, of its whole weight. The same authority found six wheats to yield bran of an average composition, as follows: Water 181 Nitrogenized matter 19'3 OU *"7 Hnsk,and a little starch BS-6 Saline matter (asli) ^'^ 100 236 GBNEEAl PEOPEBTTES OF AlIMEIirrAET SUBSTAIfCES. 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 whes^t, helps to protect it against the penetration of moisture, and enables it to be washed (which ought al- ways to be done before grinding), without wetting the inner part of the grain. 442. White and dark-coloied Flonis. — ^In separating flour into dif- ferent grades, the finest and whitest will contain the largest quantity of starch, while the coarser will more abound in gluten, and present a darker color. From the soft wheats the bran peels off readily under the stones, and separates perfectly in bolting; and as these varie- ties contain least gluten, they yield the whitest or superfine flours. But the outer coating clings so closely to the hard or flinty sorts, that much of it is ground up finely with the flour, imparting to it a dark color, an effect which is also heightened by the larger proportion of gluten existing in the harder kinds. It is thus apparent that white- ness is not an indication of nutritive value of flour, but rather the reverse. We may add here, that flour of the first quality holds together in a mass when squeezed by the hand, and shows impressions of the fingers and even the marks of the skin nmeh longer than when it is of inferior grade. The dough made with it is glney, ductile, and elastic, easy to be kneaded, and which may be drawn out into long strips, or thinly flattened without breaking. 443. Loss of Weight by ErapoTation. — ^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. Injniloiis changes in Flour. — Wheaten flour becomes whiter with age, but it is at the expense of gradual deterioration of flavor, sweetness, and nutritive quality. Beegs kept various samples of flour, and found that the second and third qualities, which contained most gluten, were completely spoiled, after keeping only nine months, though preserved in casks in a cool, airy, and dry warehouse. Mit- OHEELioH and Keookeb showed that wheat in which sugar was proved to be absent before sending it to the mill, yielded, after being ground, 4 per cent, of it. Starch was thus transformed into sugar, which could not be done otherwise than through the internal action of the gluten aided by air and superabundant moisture (473). The mutual action of the gluten, and the natural moisture of the flour, seem often capa- THB GRAINS — ^WHEAT, 23? 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. Hour, as soon as ground, should therefore be conveyed to properly- constructed chambers, and quickly cooled, or if it be desired to preserve it for some time, it should be dried at a low heat. The amount of damaged flour thrown into the market is immense. Large quantities of it are due to careless and imperfect cooling, by which chemical changes are commenced, which time con- tinues. Sometimes, to separate the bran most perfectly and procure the whitest flour, the miUer moistens the grain previously to grinding ; but if such flour is packed in barrels or sacks without artificial drying, it rapidly moulds and sours. From these considerations, we infer the' desirableness of procuring flour for household use, freshly ground, and frequently from the mill, where that is practicable. 445. Farina.— -A wheaten preparation under this name has come recently into general use, the same formerly known as 'pearled wheat.' It consists of the inner portion of the kernel of the finest wheat, freed from bran and crushed into grains, (grcmulated,) the fine floury dust and smaller particles being all removed. In cooking, it absorbs much water or milk, and forms an easUy-digestible prepara- tion, readily permeable by the juices of the stomach. In consequence of containing nitrogenous matter, it is greatly superior in nutritive power to cornstarch, arrowroot, tapioca, as a diet for invalids and children (746). Prof. J. 0. Booth of Philadelphia, analyzed Hecker's Farina with the following results: Starch 604, nitrogenous matter 11 -a, gum 2-9, sugar 241, bran 2-1, water 9-9. Professor Booth re- marks; " The analysis is suflBcient to show the excellent qualities of the farina, whether as a simple diet for invalids, or as an excellent food for the healthy." 446. What Minerals exist in Wlieati — ^When wheat is burned, there is left about 2 per cent, of ash, which consists of various mineral in- gredients. An average of 32 of the most recent and reliable analyses g^ves the leading constituents, as follows: Phosphoric acid 46 per cent., (nearly half its weight,) potash 29-97, soda 3-80, magnesia 3-35, sulphuric acid -33, oxide of iron -79, and common salt -09. Phos- 238 QENBEAI, PEOPliETrES OF AUMENTAET SUBSTAJSTCES. phoric acid is the characteristic and predominant element, potasli 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 stiU 6"2, bran 7'3. The ash of bran containe considerable sHioa. The presence of these mineral substances is far from accidental, as was formerly supposed ; we shall point out some of their important uses in the system when considering the physio- logical effects of food (690). 44T. Properties and CompOsitioa of Ryet — This grain ranks next to wheat in bread-making and nutritive qualities. It produces a larger pro- portion of bran than wheat, yielding less flour, and that of a decidedly darker color. It contains more sugar than wheat, which accounts for the sweet taste which is peculiar to new rye-bread. Its husk has an aromatic and slightly acidulous flavor, which renders it agreeable to the palate. The bran should not, therefore, be entirely separated from the flour; for if the grain be ground fine and divested entirely of the husk, the bread wiU 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. Bye 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. BouBsiNQAirLT obtain- ed from the grain of rye 24 per cent, of bran, and 76 of flour. He separated by drying 17 per cent, of moisture, and the dry flour gave of Rye (BouesiNGAULT). Rye (Poqoailb). Glaten, albmnen, &0. 10-5 Nitrogenons matters 8'T90 Starch B^'O Starch and dextrin 65'5S8 Gum 11-0 Fattymatters 1-992 Fattymatter 8-5 gLignin 6-888 Sugar. 8-0 Mineral matters 1-772 Epidermis and salts 6-0 Water 15-580 2-0 A sample of rye dried in Prof. Johjtbton's laboratory, lost 14"50 per cent, of water. Hoesfobd examined four samples of European rye, THE GEAINS — ^INDIAN OOEN — OATS. 239 *iid obtained an average of 14 per cent, of water, and 13*79 per cent, nitrogenons componnds. 4^8. Indian Com or Midze. — This grain is distinguished chemicall;- by containing a larger proportion of oUy or fatty matter than any other. It is quite rich in nitrogenous constituents, though less so than wheat. Its peculiar protein element takes the name of zein (from eea maize, the botanic name of Indian com) ; 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 foUows : Matxe (Faybn). Yellow Maize (Foggails). StaTch 6T'55 Nitrogenous matters 9905 Glnten or zea 12"50 Starch, dextrin, angar 64-635 Dextrin or gum 4-00 Fatty matter 6680 Fattj matter 8*80 Lignin and coloring matter 8-968 Celulose 6-90 Mineral 1-440 Salts or ashes 1-25 Water 18-472 100-00 HoESPOED obtained 13'65 of nitrogenous matter from maize meal, ana 14-66 from maize grain. Samp is Indian corn divested of its outside skin or bran, and of its germinal eye, the grain being left whole or nearly so. In Tiominy each grain is broken up into a number of small- er pieces. The meal of Indian corn, in consequence of its excess of oily matter, attracts much oxygen from the air, and is hence very prone to change, and does not keep well. This is the serious draw- back of this most valuable grain ; though cheap, nutritive and health- ful, it is difficult to transport and preserve its meal, especially in warm seasons or climates. 449. Oats. — This grain is not employed to any considerable extent as an article of diet for man, in this country. The oat varies greatly in weight, ranging from 30 to 40 lbs. per bushel. In grinding, 30 lbs. give 16 of meal and 14 of husk, while a bushel weighing 40 lbs. yields 23 lbs. 6 oz. of meal and 16 lbs. 10 oz. of husk — the largest proportion of bran yielded by any grain, yet different varieties give different re- sults. Oat flour stands before all other grains in point of nutritive or flesh-producing power, being first in its proportion of the nitrogen- ous element. It is also distinguished by its large quantity of fat or oil, ranging in this particular next to Indian corn. The following table gives the result of an analysis of French oats, by Bottssingault, and the average of four samples of Scotch oats, by Prof. Norton. 240 GENERAL PEOPEETIES OF ALIMBNTAET StTBSTAlfCES. (BouisiNaAVLT). (Nortoit). starch 461 Staioli 65-10 Sugar 60 Sugar 2-49 Gum 8-8 Gum 222 Oil 6-r Oil 655 A-venin.. j Avenin 16-50 Albumen J. 13-T Albumen, 1-42 Gluten . . ) Gluten 1-67 Hu£k, aeh, and loss 23-T Epidermis 2-17 100-0 Alkaline, salt, and loss 1-84 Noeton's analysis, the most accurate yire have, thns gives 19'59 per cent of nitrogenous compounds. Again, from nine samples of dry oats ne obtained 16'96 per cent, of protein compounds, the specimens ranging; from 14 to 22 per cent. Prof. Hoesfobd obtained from three samples — lieguminous Seeds. 453. Compositioii of Peas. — Seeds obtained from pods are called Ugiiminou). Of this class we are only concerned with peafl and 11 242 GESTBEAl PEOPEETIBS OF ALIMENTAET SUBSTAH'CES. beans. They resemble muoli in composition the cereal grains,' bn* 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. Aocc»^- ing to HoESFOED and Keookee : A Table Pea yielded : A Field Pea gave : Albumen and casein 28'02 Albumen and casein 29-18 Starch 33'81 Btareb 66-23 Gum 28-50 Gum 66-23 Skin 7-65 Skin '. 6-11 Aflb 3-18 Ash 2-79 According to Poggaij,b, field peas that had been deprived of 9*5(? I envelope, contained : Mtrogenous matters 21-6T0 Starch, dextrin, and sugar 57-650 Fatty matters 1-920 Lignin 3-218 Mineral 2-802 "Water 12-740 He found also in very soft green peas : Hitrogenous matters 88-85 Older than the above 84-17 Eipened 27-72 Prof. JoaNSTON 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 mtrogenous constituents, peas and beans are ex- tremely nutritious, ranking first among concentrated strength-impart- ing foods. They are considered difficult of digestion, and of a con- stipating quality, which requires to be corrected by admixture with other kinds of food. The varieties are numerous, with -wide differen- ences of flavor and softness when cooked, and they probably differ equally in composition. We have before stated, that in consequence of its abundance of casein, the Chinese make it up into a kind of vegetable cheese (424). 464. Composition of Beans. — The composition of beans varies but little from that of peas. The authorities above cited (Hoesfoed and Kkockbr) give the foUowing results: tEGUMIKOUS SEEDS — ^FBUITS. 243 Beaofl (HoBsFosD and Kkockbb). Table Bean. Large White Bean. TegetaUe casein and albnmen 2854 29-81 Starch 8T-50 66-17 Gnm 29-20 66-lT Skin , 4-11 4-41 Ash 4-38 4-01 The peas and beans in this analysis were dried at 212°, and lost an average of 15.53 per cent, of moisture. -455. Bone-pTOdueiiig material in Peas and Beans. — By 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. Wii.1. and Fbesihiub* analyeea of the aeh of Three onBlyaei of the ash of beana gave the peae gave : following average resolt : Potash 89-51 Potash 29-62 Soda 8-98 Soda 18-81 iJme 5-91 Lime 611 Magnesia.... 6-48 Magnesia 8-95 Oxide of iron 1-05 Oxide of iron 0-98 Phosphoric acid 84-50 Phosphoric acid 4-84 Conmionsalt 8-Tl Chlorine 1*18 Sulphuric acid 4-91 Sulphuric acid 1-43 Silica 6-84 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 73 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 fraits 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 GENEEAl PEOPEETIBS OP AUMBNTABT SUBSTAITCES, various sorts of apples differ much in composition, yet iu an average condition 100 lbs. of fresh apples contain about 3-2 lbs. of fibre, 0-2 lbs, of gluten, fat, and wax, 0-16 of casein, 1-4 of alhumen, 3-1 of dextrine, 83 of sugar, 0-3 of malic acid, 82-66 of water. Besides the above mentioned bodies, the apple contains a small quantity of tannic and gaUic 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 Saixsbtjey's examination. Talman Sweeting. Greening. Swsrr Apple. Roxbory BuHiet. Engliili Ruuet. ■Water 81-52 82-85 84-75 81'85 T9-21 Dry Matter.. 18.48 lT-15 16-25 18-65 20-79 Mnskmelon. encumber. 90-98 96-86 9-01 8-68 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 : • Watermelon. ■Water. 94-69 Dry Matter. 510 The dry matter of melons contains quite a large percentage of albumen, casein, sugar, and dextrifl; with a small quantity of acid. O.—liearreSf Tjeat-StaXka, See. 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 Johnston remarks, "leaves are generally rich in gluten ; many of them, however, contain other substances in smaller quantity associated with the gluten, which are unpleasant to the taste, or act injuriously upon the general health, and therefore render them unfit for human food. Dried tea-leaves, for example, contain about 25 per cent.' of gluten ; and therefore if they could be eaten with relish and digested readily, they would prove as strengthening as beans or peas." 459. The CabbagCi — 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." I.EATEB, LEAF-STALKS, BOOTS, ETC. 245 The cabbage and cauliflower lose in drying more than 90 per cent, of water ; and the dried residue, according to Pbbkiea, is remarkably rich in sulphur as well as nitrogen. The plant decays quickly, and gives out a strong odor of putrefaction, owing to its nitrogenous and sulphurous compounds. Decayed cabbage leaves should therefore not be allowed to remain in cellars, or lie about in the vicinity of dwellings. 460. Lettuce Leaves are much used at table as a salad. The young leaves contain a bland, cooling jnice ; 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-cresa, leaves of white miista/rd 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-fops, potato-tops, cowslips, &c., are used as greens, but their pecuUar characters have not been ascertained. The stalks of rhvhairb, used for pies, puddings, &c., like apples and gooseberries, contain much malic and oxalic acid in combination with lime and potash. The proportion of water, dry matter, and ash, in the rhubarb stalk, celery, and vegetable oyster, is as follows : Ehabftrb Stdks. Celery. Vegetable OyBter, Water 89-50 8822 84-46 DryMatter 10-50 11-77 16-64 Ash 1-13 Half the dry matter consists of malic, tartaric, and oxalic acids, with fibre, sugar, albumen, and casein. E.— BootS) Tnbers, Bulbs and Sboots. 461. Composition of Potatoes— Water. — This is the most widely culti- vated and important for dietetical purposes of all the root tribe, and has been more careMIy examined than any other. Like fruits and leaves its leading constituent is water, which composes about three- quarters of its weight. Young, unripe potatoes contain more water than those folly 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. KOetb 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- lo-vring results. Greatest proportion of water in young potatoes, 82 per cent. ; largest proportion in full grown potatoes, 68'6 per cent. 246 GENERAL PEOPEETTES OF AlIMENTAEY SUESTANCES. He gires the mean of 51 determinations upon potatoes of all ages— as water 76 per cent, dry matter 24. 462. Starch in Potatoes.— A large part of the solid matter in potatoes consists of starch. Johnston states as the results of nnmerons expe- riments, that the proportion is in the natural state 64-20 per cent. Siemens ascertained the proportion of starch in 66 varieties to range between 19-25 and 11-16 per cent. ; the average being 15-98. These proportions, however, vary with the kind of potato, soil, season, and other circumstances. The heel end usually contains more starch than the rose end. The weight of potatoes and their proportion of starch diminishes by keeping. Paten found the same variety to yield of starch in October lT-2 percent PEbrnary 15-2 percent November 16-8 " March 15 " December 15-6 " April 14-5 " January 15'S Other experiments would seem to show that there is rather an laerease 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 meaJy, and not so much esteemed for table use. 463. Flesli-prodncing constituents of Potatoes.— The potato contains a considerable proportion of nitrogenous matter in the threefold form of albumen, casein, and gluten, as it exists in the grains. They exist dissolved in its juices. There is more of the casein than of the other elements. Johnston gives the average of these constituents at l-4th per cent, in the natural state, and 5-8th per cent, when freed from water. But he acknowledges his mode of separating them to be liable to error, so that the figures are probably too low. Hoesfoed, by a more accurate method, found the percentage of these compounds in the dry matter of potatoes to be — in white potatoes 9-96 per cent., in blue 7-66 per cent. He found also that not only is the pro- portion different in different varieties, but that it is greater in young potatoes than in old ; and Boussinoatii.t also found the proportion of the protein compounds to diminish the longer the potato is kept. 464. Woody Fibre, Sugar, Gnm. — The proportion of fibre in the potato varies from \\ to 10 per cent., and may be said to average about 3. The fatty matter is also variable, but may be stated at about 1 per cent. Sugar in the natural state about 8-3, gum 0-55, or in the dry condition, sugar 13-47, gum 2-25. 465. Average Composition of Solid or Dry Batter of Potato.— This ia summed up by Professor Johnston in round numbers as follows : THE POTATO AOT) ONION, 247 Starch 64 Sngar and gam 15 Protein componnds k 9 Fat 1 Fibre 11 Total 100 The dry potato, therefore, is about equal ia 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-T5 Boda. 1-86 Magnesia 6-28 Lime 2-OT Phosphoric acid 12-67 Sulphorlc acid 13'64 Silica f-2S Peroxide of iron 0-52 Common salt '. T'Ol 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 powerftd odor to the garlic. The con- stituents of the onion are thus stated by Pebeiea : Volatile oil, Woodj fibre, ITncrystallizable sugar, Pcctio and phosphoric acid, Gmn, Phosphate and carbonate of lime, Vegetable albnmen, Iron. 467. Beeta. — The varieties of beets of course differ in composition, but they all contain much sugar. Their nutritive* qualities are not well determined. Beetroot is represented as containing 81 per cent 248 GENEEAL PEOPEETTES OF ALEkCBNTAET SCESIAKCES. of water, 10-20 of sugar, and 2-03 of nitrogenous matter. In the long blood-beet there is 89-09 per cent, of water, and 10-90 of dry matter. 468. Tnmips, Carrots, Parsnips.— Chemistry has hitherto cast but an uncertain light upon the composition of this class of substances. It appears from the best determinations, that the proportion of solid mat- ter in several roots is as follows : White Turnips jqi Yellow do Igi Mangel-wurzel 15 Carrot 14 The dry substance of these roots is much 'ower than that of the pota- to, which ranges at 26 per cent. Yet the flesh-forming constituents of dried turnips much exceed those of the potato, as the following com- parison shows. Protein CompouDdB. The dried potato 8 per cent. Yellow turnip 9j do. Mangel-wurzel 15j. do. The nitrogenous matter of dried mangel-wurzel being nearly twice as great as in the dried potato. In the carrot the proportion of waler is 85-78,- and dry matter 14-22. According to Ceome, the parsnip contains — Btarch 1-8 Albumen 21 Gum 6-1 Sugar 5-5 Kbre 5-1 "Water 79-4 Total 10000 4. OoMPomn) Aliments — ^Animal Food. A. — Constituents of meat, 469. — ^Various parts of animal bodies contribute materials for diet; the flesh and fat chiefly, but nearly all other portions, blood, intestines, membranes, bones, and skin, more or less. The staple constituents of animal food are fibrin, albumen, gelatin, fat, salts, and water, and in the case of mUk, casein and sugar. 470. Compositlott of Flesb-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. The muscles consist of fibrin ; they are separated into bundles by membranes, and into larger separate masses by cellular tissues, in which fat is deposited. The fleshy mass is pene- COKSTntTENTS OP MEA.T. 249 trated by a network of blood-vessels and nerves, and the whole is dis- tended by water, which composes about three-fourths of the weight of the meat. The composition of the muscular flesh of different ani- mals, according to Mr. Beakdb, is as follows: Water. Albumen nod Fibrin. Gelatin. Total BOltd matter. Beef 74 20 6 26 Veal 75 19 6 25 Mutton 71 22 j 29 Pork 76 19 5 24 Chicken 78 20 7 27 Cod 79 14 7 21 These results give an average of. very nearly 75 per cent, water. Ltebig assumes it at 74, with 26 per cent, of dry matter. The ratio of w.iter 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 trace 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 Kbtapp and LiEBiG to contain stiU about S 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. — (JoHHSTOif.) 471. Juice of Flesh. — The true color of the flbriii 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 jaice of flesh. It consists of the water of flesh, containing about 6 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 acid, from the presence of lactic and phoshporic acids, hence it is in the opposite state to that of the blood, which is invariably alkaline. The juice of flesh contains th^ savory principles which give taste to meat, and which cause it to differ in different animals. It also con- tains two remarkable substances, called hreatine and Tereatinine, nitro- genous compounds, which may be crystallized. The quantity yielded 11* 250 GENEEAi PEOPKETTES OF AUMEMTAET SUBSTANCES. is variable in different kinds of flesh, but in all is extremely smalL Kreatine is a neutral or indifferent substance, wMle kreatinine is a powerful organic base, of a similar nature with theine and cafeineof 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 substance 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 (ghie). It is sometimes partially extracted for this purpose by boiling. Marrow is a fatty substance, enclosed in very fine ceUular tissue ■within the bone. Skin, cartilage, and membrane, yield much gelatin. The tongue and lieart are muscular organs, agreeing in dietetioal proper- ties with lean flesh. BEACOomroT's analysis of the liver gives 68 per cent, of water, and 26 of nitrogenous matter; it also contains oU. The Irain is a nervous mass, containing 80 per cent, water, some al- bumen, and much of a peculiar phosphoric oily acid. The stomachs of ruminating animals which yield tii/pe, are principally composed of fibrin, albumen, and water. 473. Composition of £ggs. — ^The eggshell is a compound of lime, not the phosphate as exists in bones, but chiefly carbonate of lime. It is porous, so as to admit of air for the wants of the young animal in hatching, and usually weighs about one-tenth of the entire egg. The v?hite of egg consists of ■water containing 15 or 20 per cent, of albumen. The yolk is water and albumen, but contains, also, a large proportion (two-thirds of the dried yolk) of a bright yellow oil, containing sulphur and phosphoric compounds. A common-sized hen's-egg ■weighs about a thousand grains, of which the shell weighs 100, the white 600, and the yolk 300. The composition of its contents is : ■Water 74 Albamen r 14 Fat 10-5 Ash (salts) 1-5 Total 100 B.— Froduction and Composition of lllilk. 474. What it Contains. — This familiar liquid consists of oil or butter, sugar, casein or the cheesy principle, and salts, -with a large proportion of water. The sugar, casein, and salts are dissolved in the ■water, PEODUCnON AND COMPOSITION OF MILK. 251 While the butter is not, but exists diffused through the liquid in the form of numberless 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 nulk. 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 Henby and Ohevalibb : Cow. Woman. Casein , 4-48 1-52 Bntter 813 855 Milksngar 4-47 6-50 Salts -60 - 0-45 Water 8T02 8T-98 The following are Hadlbin's results : — The second column is the average of two analyses. Cow'i Mili. Woman's Milk.* Batter 3 2-853 Sngar of milk and salts solnWe In alcolol 46 8.75 Casein and insoluble salts 6-1 290 "Water 873 90-50 476. Ciicnmstances Influencing the Quality of Milk. — ^Both the quantity and quality of mUk arc influenced by various conditions apper-: taining to the animal. Its food exerts a powerful control in this respect. Green succulent food is more favorable to the production of milk than dry, and E. D. Tho^on's experiments go to show that of dry food, the richest in nitrogenous matter best promotes the milk secretion. Pla-hfaib 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 fi-om 15 to 20 years of age, contains more solid constitaents than of women between 80 and 40, "Women with dark hair also give a richer milk than wonlen with light hair. In acate diseases the sugar decreases one-fonrth, and the curd increases one-fourth; while in chronic afifectione the butter increases one-fourth, and the casein slightly diminishes. In both classes of diseases the proportion of saline mattef diminishes. — (JoBHSTOir.) 252 GENEBAl PEOPEETEES OT AUMENTAKT SUBSTANCES. milk rich in casein. It appeared from Thomson's observations, that tlie produce of milk of a cow, with uniform diet, gradually diminished, and increased again by a change of diet. It is well known that a cow fed upon one pasture wiU yield more cheese, while upon another it will give more butter. Hence the practice in dairy districts of al- lowing the animal to roam over a wide extent of pasture to seek out for itself the kind of herbage necessary to tlie 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 afiect, injuriously, the quality and taste of the milk. Butter is especially liable to be deteriorated in this way. An observ- ing dairy-manager remarks as follows : " If a cow be fed on ruta-baga, her butter and milk partake of that flavor. If she feeds on pastures where leeks, garlicks, and wild onions grow, there wUl be a still more offensive flavor. If she feeds in pastures where she ean get a bite oi brier leaves, beech or apple-tree leaves, or any thing of the kind, it injuriously affects the flavor of the butter though not to the same extent," and would scarcely be perceptible for immediate use. So with red clover. Batter made from cows fed on red clover is good when first made, but when laid down in packages, six months or a year, it seems to have lost all its flavor, and generally becomes more or less rancid as the clover on which the cow fed was of rank and rapid growth." — (A. B. Dickinson.) 477. Distance from the time of calving, — The colostrum, or flrst milk which the cow gives for several days after the birth of her young, differs from normal milk. Geegoey 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 : • ' Qaartfl pet day. QuarU. First50days 24 or in all 1200 Second " 20 " " 1000 Third " W " " ™ ronra " ' " " J!* Fiftli " ° „. ,,, „ 6 " " 800 Sixth " and at the end of ten months, they become nearly or altogether dry.^ 478. Time of year, age and condition of the animal.— In spring, milk is finest and most abundant. Moist and temperate climates and seasons are favorable to its production. In dry seasons the quantity is less, but the quality is richer. Spbengel states that cool weather favors the production of cheese and sugar in the milk, while hot weather PECDTTCnON AOT) COMPOSITION OP MHJK. 253 increases the product of butter. The poorer the apparent pondi- tion of the cow, good food being given, the richer, in general, is the mUk ; 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. Prodaetion and Composition of Cream. — We have stated that butter exists in mUk, as a fatty emulsion ; that is, not dissolved, but floating as exceedingly minute globules throughout the watery mass. These butter globules are lighter than water, and hence, when the milk is suffered to stand undisturbed, they slowly rise to the sur- face, forming cream. The oil-globules of cream do not coalesce or run together, they are always separated from each other, and sur- rounded by the soluble ingredients of mUk ; while at the same time, the body of the milk never becoTues 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 sr.pposed by some, that the butter particles are in some way invested or enclosed with casein ; at all events, a quantity of cheesy matter rises with the oU-globules. Its proportion in cream depends upon the richness of the milk, and upon the temperature at which it is kept during the rising of tiie cream. In cool weather, the fatty matter wiU 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 quahties of but- ter. The deeper the milk, the greater the diflBculty with which the 254 GENERAL PjBOPBETIBS OF ALIMBNTAET SUBSTANCES. oily matter ascends througliit ; hence, it is customary to set the milk aside in shallow pans, so that it may not he more than two or three inches in depth ; hence, if it is desired to prevent the formation of cream, the mills should be kept in deep vessels. Temperature 'po'weTfuUj 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 be perfectly creamed In 86 tours when tlie temperature of tlie air is 50' P. "24 " " " 55° "18 to 20 " " " 68' "10 to 12 " " " ir 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. — (Spbbngel.) 481. Milk Creams before It Is taken from the Cow. — ^This spontaneous tendency of mUk to separate itself mechanically into two sorts or qualities, explains the remarkable difference in the richness of mUk withdrawn at different stages of the milking process. The glands in the teats of the animals, which secrete the milk, are vessels interlaced with each other in such a way as to form hoUow spaces or reservoirs which distend as the milk is secreted. In these reservoirs the same thing takes place as occurs in an open vessel, and with still more facility as the temperature is up to blood heat (98°) — ^the rich creamy portion rises above, while the poorer milk falls below. Hence that which is first drawn is of an inferior quality, while that which is last drawn, the strippings or aftermgs, abounds in cream. Professor Aisr- DEESON states, that compared with the first mUk the same measure of the last will give at least eight, and often sixteen times as much cream. The later experiments of Reisex show, that where the milkings are 11 or 12 hours apart, the quantity of butter in the last drawn mUk is from three to twelve times greater than that obtained from the first drawn mSk. "Where the milkings were more often, the difference became less. As mUk before being taken from the cow is already partially separated— its richer from its poorer parts — ^the dairy man- ager should take advantage of this circumstance, and not commingle in the same vessel the already half-creamed mUk, if the object is the separation of butter. It has been shown that more cream is obtained PEODTJCnOlT AKD COMPOSITION OP MILK. 25£ 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 f,9. 96. quantity of cream that may be separated, but much delays the operation which, in hot weather, when milk soon sours, is objectionable. 482. Determining the valne of Milk. — ^Its valne is propor- tional to the amount of its sohd alimentary constituents, and is liable to variation, according to circumstances. If butter is to be manufactured irom it, that is most valuable which Contains most oily matter ; if cheese is desired, then that which contains most casein. Milk is heavier than water, and the richer it is the heaver it is ; hence it has been attempted to make the latter quality a guide to the former. Its weight compared with water, or spe- cific gravity, is determined by the hydrometer (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 ^ ""^ "'' in it ; the lighter the mUk, the deeper it sinks ; the heavier it i"!, the higher it floats. A scale is mai-ked upon the stem, which indicates at once how far the weight of the milk rises above pure water. Tet 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. Tet 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 fiUed with milk to the top space, is suffered to stand until the Laotonieter. » Made by Taguabue, of Hew Tork. Pia. 9T. 256 CUUNAEY CHANGES OF AUMENTAET 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 tuhe be marked . as shown in Kg. 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 8i per cent., although samples are liable to range much above and below this number.* If the mUk has been mixed, say with one-third water, the cream wiU faU to 6, if with one- half, it may fall to 5 per cent. 483. Mineral Matter in Milk, — The proportion of salts in mUk averages about half per cent. ; that is, 200 lbs. when dried and burned will yield 1 lb. of ash. The composition of this ash is shown, by the analysis of HAiDLBiif, who obtained from 1000 lbs. of milk 1 i Phosphate of lime 2-31 lbs. 8-44 1 K. Phosphate of magnesia. 0'42 " 0-64 " Phosphate of peroxide of iron 0-OT " O'OT " Chloride of potassium , 1-44 " 1-83 " Chloride of sodium 0-24 " 0-84 " Free soda 0-42 " 045 " Total 4-90 en ni.— CULINAEY CHANGES OP ALIMENTAET SUBSTANCES. 1. Combining the Elbmbnts ob Beead. 484. General Objects of Cnlinary 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, &o. &W. But few of these substances are best adapted for food in the condition in which they occur naturaEy. They are either too hard, too tough, insipid or injuri 0U3, and require to undergo various changes before they can be properly digested. Most foods, therefore, must be subjected to processes of manufacture or cookery before being eaten. In their culinary prep- aration, numerous mechanical and chemical alterations are effect- ed, in various ways; but the changes are chiefly wrought by means of water and heat. "Water softens some substances, dissolves others, some- times extracts injurious principles, and serves an important purpose in bringing materials into such a relation that they may act chemically upon each other. Heat, applied through the medium of water, or in va- rious ways and degrees, is the chief agent of culinary transformations. Another proper object of cooking is the preparation of palatable dishes, * The number given by the lactometer will, from the nature of the case,' be somewhat under the truth, as the butter globules do not all ascend through the long column of milk. COMBINING THB ELEMENTS OP BKEAD. 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 are capable of being preserved for a considerable time. Bread is made, as is well known, by first incor- porating water with the flour, and mating it iuto 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 flnaUy submitted to the action of heat in an oven, or baked. "We shall consider the suc- cessive steps of this important process, in the order of their occurrence ; and as the flour of wheat is the staple article in this country for the manufacture of bread, it will occupy our first and principal attention. 485. Water altsorbed In making Dongh. — The addition of much water to flour forms a thick liquid, caEed batter ; more fiour admixed stiffens it to a sticky paste, and still more worked through it produces a firm dough. The water thus added to flour does not remain loosely associ- ated with it, but enters into intimate combination with its constitu- ents, forming a compound, and is not all evaporated or expelled by the subsequent high heat of baking. In the dough, the liquid performs its usual office of bringing the ingredients into that closer contact which is favorable to chemical activity. As water is thus made to become a permanent part of solid bread, it is important to understand in what proportion, and under what conditions, its absorption takes place. Baked bread that has been removed from the oven from 2 to 40 hours, loses, by thorough drying at 220,° from 43 to 45 per cent, of its weight, or an average of 44 per cent. If we assume the flour to con- tain naturally 16 per cent, of water, lOJ lbs. of the 44 that was lost belonged to the flour itself, while 33i lbs. were artificially added in making the dough. Thus — Dryflour B6 ) Water in flour DstuMlly lOJ f ^ Water added in baking 88} 100 Ten pounds of fiour would thus absorb 6 lbs. of water, and yield 15 lbs. of bread. The best flours absorb more water than those of infe- rior quality. The amount with which they will combine is sup- posed to depend upon the proportion of gluten. In dry seasons flour 258 CULESTAET CHANGES OF AIIMEJSU'AET SUBSTANCES. Will bear more water than in wet, and a thorough process of kneading will also cause the dough to absorb a larger quantity without becoming the less stiff on that account. Certain substances added to flour aug- ment its property of combining with water (521). 486. Effects of the Kneading Process.— The purpose of water inter- mingled with flour is to combine with and hydrate the starch, to dis- solve the sugar and albumen, and to moisten the minute particles^of dry gluten, so as to cause them to cement together, and thus bind the whole into a coherent mass. But, as only a certain limited quantity of water can be employed to produce these results, it is obvious that it mnst be carefully and thoroughly worked throughout the flour — this is called hneading the dough, and is generally perforlned with the hands. The process is laborious, and attempts have been often made to accomplish it by machinery, but hitherto without success. Plours 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 yery adhesive, and clings to the fin- gers, but it becomes less so the longer the kneading is continued, and when the flst 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 Flour and Water. — ^When dough, made by simply workiiig 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 diffii- cult of digestion. -If baked a'; a stiU higher heat, and afterward sub- jected to prolonged drying, we have the common ahip-lread or sear liscuit, which is made in thin cakes and never in large loaves, and which is very dry, hard, and difficult to masticate, although it has an agreeable taste, derived from the roasting of the surface of the dough. Bread prepared ia this manner lacks two essential characters, — sufficient Boftness 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 KAISBD BY FBEMESSTTATION. 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, ^j the mechanical operation of kneading, the glutinous pSrts of the flour ai'e 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 niu:- pose, which will now be noticed ; and first of fermentation : 2. — ^Bbeab Kaiskd by Feementatioit. ■488. Substances capable of Putrescence. — ^It is a remarkable property of the nitrogenous alimentary principles, that wTien 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 air seizes upon the loosely held atoms, breaks up the chemical fabric, and produces from its ruins a new class of substances — the gaseous pro- ducts of putrefaction. Thus, it is well known that flesh, blood, milk, cheese, dough, bread, all of which are rich in nitrogenous substances, wiU preserve their properties in the air only a short time, but pass into a state of putrescence, becoming sour and nauseous, and sending forth offensive exhalations. This change is called putrefaction, and the compounds which are liable to it, pubrefidMe substances. 4:89. The Putrefactive change Contagious. — ^The other class of aliments, the non-nitrogenmcs, are in this respect of a very different nature. They contain fewer atoms, lack the fickle element nitrogen, and have a simpler and firmer composition. When pure starch, gum, sugar, or oil, are exposed to the air in a moistened state, they exhibit little ten- dency to change, and ^ve 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 pntrefiable substances are considered, with reference to the effects they prodiiee upon the other class, they take a new name, and are caliei ferments. The communication of that con- dition of change from one class to the other, is called fermentation, and the substances acted upon are named fermentable compounds. Thus, if some sugar be dissolved in water, and a portion of putrefying dough, meat, or white of egg be added to it, fermentation sets in; that is, the change is communicated to the sugar, the balance of its affini- ties is destroyed, and two new substances — one alcohol, containing aU 260 CULINABT CHAlfGES OP AUMBNTAET SUBSTAITCES. the hydrogen of the sugar, and the other carbonic acid, containing two-thirds of its oxygen — are produced. 490. Conditions of Fermentation. — ^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 T0° 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 oUs, sul- phurous acid, &c. 491. Different kinds of Fermentation. — When nitrogenous matters are just beginning to decompose, the action is too feeble to establish the true alcoholic fermentation in solutions of sugar. Yet even in this early stage they can change the sugar, not breaking it to pieces so com- pletely, but splitting each of its atoms into two equal atoms of lactia acid, the sour principle of milk. This process is called the lOfCtic acia fermentation, while that in which alcohol is produced is the vimnia oi alcoholic fermentation. If this be not checked, the process is liable to run on to another stage ; the ferment is capable of attacking' the alco- hol itself, and converting it to aeetie acid, the active principle of vine- gar. This is the acetous fermentation. There are several conditions of this acetous change. Mrat, 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, when moistened is capable of fermentation without adding any other substance. If simple flour and water be mixed and set aside in a warm place, after the lapse of several hours it will exhibit symptoms of internal chemical action, becoming sour from the formation of lactic acid, while minute bubbles appear, which are ow- ing to a gas set free within the dough. The changes are irregular and im- BREAD BAISED BY FEEMENTATION. 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 haked from such dough, is sour, heavy, and altogether bad. Yet the true vinous fer- mentation may be spontaneously established in the dough, by taking measures to qnicken 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 he placed in a jar or pitcher and set in a vessel of water, kept at a temperature from 100° to 110°, in the course of five or six hours decomposition wiU 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 mix^d and kneaded vnth 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 T — ^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 suflBciently 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 dongh. 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 CUUNAET CHAITGES OF AUMENTAET SUBSTANCES. to 494. Raising Dongli by Learen, — But the mode of raising dough bj Bpontaneous fermentation (492) is not snflScientlj 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 suffi- ciently long to ferment and turn sour, and then knead it up thoroughly with a large lump of fresh dough, the whole of the latter wUl 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 leamen. It may be made from any sort of flour, and is improved by the addition of pea and bean meal, which ferment easily. When properly made, leaven may be kept weeks or months fit for use, and by adding a portion of dough to the leaven, as large as that reserved for the bread-maker, the stock of leaven is always kept up. Although leaven when added to dough, awakens the true alcoholic fermentation, yet being in a sour state, it produces a portion of lactic acid, and often acetic acid ; the latter being mostly driven off in the process of baking, whUe the former remains in the bread. Hence, bread made with leaven always has a distinctly sour taste, partly caused by the acid of the leaven it- self, and partly by the sour fermentation which it induces in the dough. It is difficult to manage, and requires much skill to produce a good result. Leaven is but little used iq. this country, bread be- ing almost universally raised by means of yeast. 3. Peopeeties ijsm Action of Tbast. 495. Prodnctlon of Brewer's Teasti — ^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. Honce, seeds in germinating become sweet. Barley placed in these conditions, begins to germinate, swells, softens, and turns sweet ; it is then heated and dried, by which the process is stopped. The barley is then called malt. It is next crushed or ground and infused (mashed) in water at 160° so as to extract all the soluble matter it contains. The liquid {sweet-wort) is then boiled to coagulate the excess of vegetable albumen. Hops are added, to impart a bitter taste to the product (beer), and also to regulate the subsequent fermentation. The cooled wort is then run into the fer- menting vat, and yeast is added. "In three or four hours, bubbles of gas will be seen to rise from all parts of the liquid ; a ring of froth, PEOPEETTES AMD ACTION OP TEAST. 263 forming at first around its edge, gradually increases and spreads tDl it meets in the centre, and the whole surface becomes covered with a white creamy foam. The bubbles of gas (ca/rbonie CLciS) 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 intb httle pointed heaps, which become brownish on the surface and edges ; the yeast gradually thickening xcaiSi. 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 Teast— 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 ga8_escape from it. When dried it loses 70 per cent, of its weight, becomes solid, homy-looMng, 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 tliat it is a true plant belonging to the Fungus tribe. Under a powerful magni- fier, it is seen to consist of numberless minute rounded or oval bodies, which are true vegetable cells. Each little globule consists of an en- veloping skin or membrane, containing a liquid within. Such cells are the minute agencies by which all vegetable growth is affected. The leaves and pulpy parts of plants are built up of them, as a wall is built of bricks. All the numberless substances produced by plants, are generated within these little bodies. They grow or expand from the minutest microscopic points and seem to bud off from each other, as shown in Figs. 98 and 99. The little grains from which they spring or germinate are shown, and how they multiply by budding. They are of amazing minuteness, a single cubic inch of yeast, free . from adhering matter, containing as many as eleven hundred and fifty-two mUlions of them. In what manner yeast acts to decompose sugar is not known. The yeast is destroyed or expends itself in producing the effect, vet it furnishes none of its sub- Teast cells, showiDg how thoy ... .,•,,•, . J • multiply by budding, and by Stance to join with the sugar, m producmg CTanules or seeds escaping alcohol and carbonic acid. Libbi» supposes from their interior. the effect to be dynomio, that is, produced by an impulse of force ; the 264 CPLIVAET CHANGES OF AHIttENTAET SUBSTANCES. motions of the atoms of the decomposing ferment, being communi- cated to the atoms of sugar, set these also in motion, by which the sugar structm-e is, as it were, jarred and shaken to pieces, its atoms fallmg into new arrangements and forming new substances. 497. Domestic preparation of leas^-Fowne's method.— But, as many have no access to breweries, it is desu-able to know how to make yeast at home. If common wheaten flour be mixed with water to a thick paste, and 1% 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 time this smell disappears ; the gas evolved is greatly increased, and is accompanied with a dis- tinct agre'eable 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 crflsh-. 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 jvater, is added to it, and the temperature kept up by 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. Teast from Potatoes. — Boil half a dozen potatoes in three or four quarts of water, with a couple of handfula of hopi 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. A developed yeast plant, the numbers Indi- cating the successive stages of growth. PEOPEETIES AKD ACnOS OF TEAST. 265 499. Action of Hops in Teast-maklng. — Hop-flowers contain about 8 per cent, of a brownish yellow bitter volatile oil, upon whicb its pecu- liar odor depends. The hop has been long known for its soporific or sleep-prodncing 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 infiuence. 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 efliact 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^cale, 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 curious that meehmieal 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. LtEsia 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 until it becomes thin, and then spread with a brush over a piece of clean wood and dried. Successive coats may be thus applied, until it becomes an inch or two in thickness. When thoroughly dried, it can be preserved in bottles or canisters. Yeast is also commonly preserved by adding to it maize meal, and making it into a dough which is wrought into cakes and dried. They may be kept for months and are ready for use at any time, by crumbling down and soaking a few hours in warm water. We add minuter directions for making yeast-cakes. Eub three ounces of fresh hops until they are separated, boil half an hour in a gallon of water, and strain the liquid through a fine sieve into an earthen vessel. While hot, stir in briskly \i lbs. of rye flour. Next day, thoroughly mix in 7 lbs. of Indian meal, forming a stiff dough ; knead it well, roU 12 266 CniJNAET CHANGES OF ALIMENTAET SUBSTAlSrCES. 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 Teast— how corrected. — ^Yeast is often so bitter as to communicate a most disagreeable taste to bread. This may be de- rived from an excess of hops. To rectify this, mix with the yeast a considerable quantity of water, and set it by to rest for some hours, when the thickest part will fall to the bottom. Pour off the water which will have extracted a part of the bitter principle, and use only the stiff portion that has fallen to the bottom. But yeast sometimes acquires a bitter taste from keeping, which is quite independent of that derived from the hops. One method of remedying this, consists in throwing into the yeast a few clean coals freshly taken from the fire, but allowed to cool a little on the surface. The operation appears to depend in principle upon the power of freshly burnt charcoal to ab- sorb gases and remove offensive odors (811). 502. Acidity of Yeast— how corrected. — ^In country places, where it is customary to keep yeast for some time, and especially during the warmth of summer, it is very liable to sour. In such case, it may be restored to sweetness, by adding a little carbonate of soda or car- bonate of magnesia, only so much being used as may be necessary to neutralize the acidity. 503. Dough raised by Teast. — ^How fermentation lightens dough, has been shown (493). Teast produces these changes promptly and effec- tually. It is mixed with a suitable portion of water, flour, and salt, to form a stiff batter, which is placed near the fire for an hour or two, covered with a cloth. This is called setting the sponge. An active fer- mentation is commenced, and the carbonic acid formed in the viscid mass, causes it to swell up to twice its original size. If not then quickly used it /alls, that is, the accumulated gas within escapes, and the dough collapses. Tet after a time it may again rise, and even fall a second time and rise again. This, however, is not allowed. When it has fuUy risen, much more flour is thoroughly kneaded with the sponge, and the dough is left for perhaps an hour and a half, when it rises again. It is then again kneaded and divided into pieces of the proper size for loaves. The loaves should be moulded with care, as too much hand- ling is apt to cause the escape of the enclosed gas, and make the bread heavy. 504. Correction of Acidity in Dongh. — ^Dough is frequently sour from an acid condition of the flour. It may be in this condition from a sour state of the yeast, or the fermentation may be so feeble as to BAISrCTG BBEAJ) WITHOUT rEEMENTATION. 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 bout by running into the acetous fermentation. If the difl- oulty 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 ali-eady sour, it may be sweetened by alkaline substances. Carbonate of soda will answer this purpose. Carbonate of ammonia is perhaps better, as it is a volatile salt, and is raised in vapor and expelled by the heat of the oven (510). If too much be used, a portion of the excess is driven off by the heat, and in escaping assists in making the bread lighter. Caution should, however, be employed to use no more alkali than is really necessary to neutralize the acid. "When the acidity is but slight, it may be rectified by simply kneading the dough "with the fingers moistened with an alkaline solution. 505. Tbe Sngar of Flonr all decomposed in Bongb. — ^It is at the ex- pense of sugar destroyed that fermented bread is raised, but Tiow much sugar is thus decomposed is variously stated, and depends upon the activity and continuance of fermentation. Experiments would seem to show, that all the sugar present is rarely, if ever, destroyed. The raised dough and bread both contain sugar, often nearly as much as the flour before it was used. This is explained by remembering that one of the effects of fermentation is to change starch to sugar. 506. How much Alcohol is produced 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 60 cubic inches, 26 of which were solid bread, and 34, cell-cavi- ties ; consequently 34 cubic inches of carbonic acid of the heat of the oven were generated to raise it, which implied the production of about 15 grains of alcohol, or less than one-quarter of one per cent, of the weight of bread. It has been attempted to save this alcohol, which is vaporized and driven off into the air by the baking heat, but the product obtained was found to be so small as not to pay cost. It is also a current statement, that alcohol exists in the bread, contributing to its nutritive qualities. We have never found it there, and never saw a chemical analysis of bread that enumerated it as a constituent. 4. EAisDra Bebad without Feementation. 507. Objections to raising by Ferment. — ^Two or three objections have been nrged against raising bread by fermentation. First, the loss of 268 CUllNAET CHANGES OF ALIMBNTAET SUBSTAITCES. a portion of the sugar of the flour ■whicli is decomposed ; this loss, how- ever, is trifling, and the objection futile. It is said, seeondly, that as a destruction or incipient rotting process has been established in the dough, bread made from it cannot be healthful. This is otlIj fancy, experience is wanting to show that well-made fermented bread is in- jurious. TM/rdT/y, 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. 608. How it is done Trithont Ferment. — ^As the lightening and expan- sion of the dough are caused by-gas generated within it, it would seem that we may adopt any means to produce such a result. It is com- monly done in two ways; either by mixing chemical substances with the flour, which, when brought into contact and wet, act upon each other so as to set free a gas, or by introducing into the dough a volatile solid substance, which, by the heat of baking, 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. 509. Raising Bread Trlth Chemical Sniistances* — Bicarbonate of soda and hydrochloric acid are used for raising bread. The soda is mixed inti- mately with the flour, and the acid is added to the water requisite to form dough. Peeeiea. indicates the foUowing proportions : Flour 1 lb. Bicarbonate of Boda 40 grains. Cold water, or any liquid necessary \ pint. HydrocMoric 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 dhloride 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. K the acid be in excess, there win 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 — EAISING BEEAD WITHOXJT FEEMKNTATION. 269 Gabsokic acid; Water; (liqtdd,) and Common salt ; {solid.) Breaa is also raised with soda powders ; — tartaric acid, and bicar- bonate of soda, which are the active ingredients in effervescing draughts. The changes are these BiOAEBOuATB OP SODA; ) _„j„„„ ( Caebonio aoid; isoUd,) and i V^Xe' \ „ (?<">) """l Tabtahio Acm ; ( j"'"^ i Takteatk op soda; (soUd,) } """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 hke cream of tartar — ^gently aperient. Preparations which are known as egg-powder, tdHng-powder, and eusta/rd-powders, consist of bicarbonate of soda and tartaric acid, mixed with wheat flour or starch, and colored yellow with turmerie, or even poisonous chromate of lead. The diflSonlty with these powders, is to get them in perfect neutralizing proportions. This may be ascertained by dissolving them in water ; the mixture should be neutral to the taste, and produce no effervescence by adding either alkali or acid. Sour mUk, 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. Sesqnlcarlionate of Ammonia. — The perfect theoretic conditions of raising bread without ferment would be, to find a solid substance which could be introduced into the flour, but which would entirely es- cape as a gas during baking, raising the bread, and leaving no trace of its presence. Carbonate of ammonia complies with the first of these conditions ; it is a solid which, under the influence of heat, is decom- posed entirely into gases. Thus — '.solid,) j produces, Auhonia; {gas,) Bicarbonate op Auhonia; ■ Carbonic acid, {gas.) 270 CULINAET CHANGES OF ALIMBNTAET SUBSTANCES, Yet practically these gases do Bot all -escape in baking ; a portion of tliem 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 eflect. 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 Cantton in reference to tlie Cbemlcals nsed. — ^The class of substances thus introduced in the bread are not nut/ritwe but me- dicinal, and exert a disturbing action upon the healthy organism. And although their occasional and cautious employment may perhaps be tolerated, on the ground of convenience, yet we consider their ha- bitual use as highly injudicious and unwise. This is the best that can be said of the chemical substances used to raise bread, even when pure, but as commonly obtained they are apt to be contaminated with impurities more objectionable still. For example, the commercial mu- riatic acid which is commonly employed along with bicarbonate of soda, is always most impure — often containing chlorine, chloride of iron, sulpburous acid, and even arsenic, so that the chemist never uses it without a tedious process of purification for his purposes, which are of far less importance than its employment in diet. While common commercial hydrochloric acid seUs for 3 cents per pound wholesale, the purified article is sold for 36. Tartaric acid is apt to contain lime, and is frequently adulterated with cream of tartar, which is sold at half the price, and greatly reduces its efficacy ; while cream of tar- tar is variously mixed with alum, chalk, bisulphate of potash, tartrate of lime, and even sand. Sesquicarbonate of ammonia is liable by ex- posure to air to lose a portion of its ammonia. It is hence seen that the substances we employ are not only liable to injure by ingredients which they may conceal, but that their irregular composition must often more or less defeat the end for which they are intended. We may suggest that, in the absence of tests, the best practical defence is to purchase these materials of the druggist rather than the grocer. If soda is desired, call for the tica/rbonate 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). 612. Ridsing Dongb Tflth Oily Substances and Eggs.— If dough be mixed with butter or lard, rolled out into a thin sheet, and covered with a thin layer of the oily matter, then folded, rolled and recoated from 2 to 10 times, and the sheet thus produced be submitted to the oven, the AITBEATIONS PEODUCED IK BAKING BKBAD. 27J heat causes the disengagement of elastic vapor from the water and fatty matter, which, heing 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 with it air bubbles, which are expanded in baking. From its glairy, tenacious consistence when mixed with dough or pudding, it encloses globrJes of gas or steam, which are generated by fermentation or heat. In this way eggs contribute to the lightness of baked articles. 613. Baislng Gingcrliread« — 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. OoLQUHotm has found that carbonate of magnesia and tartaric acid may replace the saleratus (and alum also, which is sometimes used), affording a gingerbread more agreeable and wholesome than the common. His proportions are, 1 lb. of flour, I oz. carbonate of magnesia, \ oz. of tartaric acid, with the requisite molasses, butter, and aromatics. 5. AiTEEATioNS Peodttobd IN BAXQfa Bbead. 514. Temperatnie of the OTem — ^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 ita different parts, and remain constant for a considerable time. K the heat be insufficient, the bread will be soft, wet, and pasty ; if on thai 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. I^ 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 loa:^ immediately from the oven, and bury the bulb of a therr mometer in the crumb, it wiU rise to 212°. This heat is sufficient tp 272 CBUNAUT CHAJSTGES OP AUMENTABT SUBSTANCES. carry on the iimer chemical changes of baking, and it is obvious that the heat cannot rise above this point so long as the loaf continues moist (65.) Bread might be baked at a temperature of 212° (by steam), but then it would lack that indispensable part, the crust. The baking temperature of the oven ranges from 350° to 450° or 500°, and bakers have various means of jud^g about it. If fresh flour strewn upon the oven bottom turns brown, the heat is right, if it chars or turns black, the heat is too great. 615. Heat causes a loss of Weigbt. — The loaf loses a portion of its weight by evaporation. The quantity thus lost depends chiefly upon the size and form of the loaf. If it be small or thin, it will part with more water in proportion than if of cubical shape. Something de- pends upon the quality of the flour and the consistence of the dough. Various experiments would seem to show that bread parts with from one-sixth to one-tenth of its weight in baking. In those places where bread is required by law to be of a certain weight, this loss must be calculated upon and a proportionate amount of additionar 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 off, as is shown hj the spirituous odor yielded in the baking process. 51Y. Chemical Changes in prodadng the Cmst. — The heat of the oven falling upon the surface of the loaf causes first the rapid evaporatioD 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 formation of hard crusts on the loaf may be prevented by baking it in a covered tin, or, it is said, by rubbing a little melted lard over it after it is shaped and before it is set down to rise. 518. Chemical Changes in prodneing the Cmmb. — As the temperature within the loaf does not rise above 212°, no changes can go on there except such as are produced by the heit of the aqueous vapor. This is sxifficient to stop the fermentation, destroy the bitter principle of AITEEATIONS PRODUCED IN BAKHTQ BREIAJ). 273 the yeast, and kill the yeast plant. In baking about one-fourteenth of the starch is converted into gum, the rest is not chemically altered, as may be shown by moistening a little bread-crumb and touching it with solution of iodine, when the blue color will prove the presence of starch. The gluten, although not decomposed, is disunited, losing its tough, adhesive qualities. The gluten and starch-paste are intimately mixed, but they do not unite to form a chemical compound. 619. noistare 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 exposmg a stale loaf in a closely covered tin for half-an-hour to a boiling heat, when it will again have the appearance of new bread. The quantity of water which weU-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. Oile 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 hoUow cell in the bread, which coating does not readily allow the gas contained in the cell to escape, or the water to dry up and pass oflf 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. — (Johnbtoit.) 520. Qualities of Good Bread. — In baking bread, it is desirable to -avoid the evils of hardness on the one hand and pastiness on the other, nor should it be sour, dense, or heavy. It should be thoroughly and uniformly kneaded, so that the carbonic acid will not be liberated in excess in any one place, forming large hoUows and detaching the crumb from the crust. The vesicles should be numerous, small, and 12* 274 CTTUNAItT CHANGES OF AlIMENTAET StrBSTANCES. equally disseminated ; nor should the crust be bitter and black, but ol an aromatic agreeable flavor. " If the yeast be so diffused throughout the whole mass as that a suitable portion of it will act on each and every particle of the saccharine matter at the same time,' and if the dough be of such consistency and temperature as not to admit of too rapid a fermentation, then each minute portion of saccharine matter throughout the whole mass will, in the process of fermentation, pro- duce its little volume of air, which will form its little cell, about the size of a pin's head and smaller, and this will take place so nearly at the same time in every part of the dough, that the whole wiU be raised and made as light as a sponge before the acetous fermentation takes place in any part. And then, if it be properly moulded and baked, it will make the most beautiful and delicious bread, perfectly light and sweet, without the use of any alkali, and with all the gluten and nearly all the starch of the meal remaining unchanged by fermentation." — (Gbaham.) 6. Infltjenob of Fobeign Substances upon Bread. 521. Common Salt, Jlnm, &c — It has been found that certain mineral substances influence in a remarkable degree the aspect and properties of bread, causing that made of inferior flour to resemble, in appear- ance, bread made from the best quality. Common salt produces this effect in a decided degree. It whitens the bread and causes it to absorb and retain a larger amount of water than the flour would otherwise hold. In consequence of this influence and under cover of the fact, that salt is a generally admitted element of diet, it is often introduced into bread more freely than is consistent with health (697). Alum has exactly the same effect on bread as common salt, but in a much more marked degree. A small quantity of it will bring up a bad flour to the whiteness of the best sort, and wiU enable it to hold an extra dose of water. It is much used for this purpose, and the baker who employs it not only practises upon the consumer a double imposition, but drugs him with a highly injurious mineral into the bargain. Mitchell detected in ten four-pound loaves 819 grains of alum, the quantity in each loaf ranging from 34 to 116 grains. Sul- phate of copper (blue vitriol), in exceedingly minute proportions, exerts a striking influence upon bread in the same manner as alum. Oa/rbonate 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. Datt. xNPLUBNCB! OF FOREIGN SUBSTANCES UPON BItEAD. 275 recommended for correcting acidity in yeast, dough, &o., 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 aud deposits. 622. Lieblg recommends Lime-Trater In Bread. — However it is to be lamented, it is nevertheless a fact, that enormous quantities of flour, more or less deteriorated, are purchased in the markets of this country ; and if there be any method of improving its condition by means that are not essentially injurious, they are certainly most desirable. Indeed, it is well known that flour is injm-ed by time alciie, 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 toug|i 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 in 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 efiect 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, LiEBia 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; yeTj pure soft water, as clean rain water, may, however, be used. Mix a quarter of a pound of slacked lime in a gallon of such cold water in stoppered bottles or vessels kept tight from the air. The mass of the lime falls to the bottom, leaving the liquid above, which has dissolved l-600th its weight of lime, clear and transparent. This is to be poured ofl:' when required for use and replaced by pure water. Libbio 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, beautiftd, fine-grained elastic bread is obtained of exquisite taste, which is preferred by all who have 2'76 CDxnrAET changes op aiimentaet substances. eaten it for any length of time to any pther." — (Liebi&.) The use of lime-water removes all acidity from the dough, and also somewhat augments the proportion of water absorbed. 624. 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, with this artiflcially added the cereal grains stiU contain less of it than peas and beans. Indeed, Libbig has sug- gested that experience may yet prove the cereal grains to be incapable of perfect nutrition, on account of their small proportion of the bone forming element. , 625. 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. Bye makes a dark-colored bread, and is capable of being fermented and raised 'u 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. Indiam, 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 saleratns, and is generally eaten warm. Indian corn is ground into meal of various degrees of coarseness, but is never made so fine as wheaten flour. Bread or cakes from maize require a considerably longer time to be acted upon by heat in the baking process than wheat or rye. If ground wheat be unbolted, that is, if its bran be not separated, wheat meosZ or Qraham flowrtbsa\.\s, from which Graham or dyspepsia bread is produced. It is made in the same general way as other wheaten bread, hut requires a little peculiar man- agement. Upon this point Mr. Gkaham 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 as that made of superfine fiour ; and when it is raised, if it is found too soft to mould weU, 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 ■VBGETABU! POODS CHAlfGED BY BO^JITG. 211 In which flonr is an ingredient are changed by the baking process in the same way as bread. They are usually mixed with milk instead of water, and made thinner than dough. Yeast is not used to raise them, eggs being commonly employed for this purpose, and sometimes other substances. 526. WMte and Brown Bread— A new Freneli Plan. — M. MouErES, of Paris, has announced some new views of bread making, theoretic and practical, upon which a commiKion 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 drown color also of the bread, are due to cerealme. He says cerealine ferment will make a brown bread of the whitest flour, whereas, if it be neutralized, a white tread can te made from a da/rJo fiowr containing Iran. He grinds wheat so as to separate it into about Y4 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 faNua- ceous materials. 7. — ^Vegbtablb Foods ohanobd by BomirG. 527. Its CSeneral Effects. — ^BoUing differs from baking in several re- spects. First, the heat never rises above the boiling pointy ani the changes of course are such only as may be produced by that tempera- ture. Second, the food is surrounded by a powerful solvent, which more or less completely extracts certain constituents of the food. Veg- etable acids, sugar, gum existing in the organic matter, and gum formed from starch, with vegetable albumen, are all soluble in water, and by boiling are partially removed. The tougher parts are made tender, the hard parts softened, and the connections of the fibres and tissues loosened, so as to be more readily masticated, more easily pen- etrated by the saliVa and juices of the stomach, and hence more 278 CULINAET CHANGES OF AlIMBNTAET SUBSTANCES, promptly and perfectly digested. Perhaps we may here most con- veniently consider the specific effects of heat upon the chief constitu- ents of which vegetahle foods are composed. 628. Changes of Woody Fibre. — A constituent more or less abundant of all vegetable substances is woody fibre. "We find it in the husk or bran of grains, the membrane covering beans and peas, the vessels of leaves and leaf-stalks, the skin of potatoes, the peel and core of apples and pears, the kernels of nuts, and the peel of cucumbers, melons, &c., &c. We are hardly justified in ranking woody fibre, as Pereiea has done, among aliments. Indeed, he remarks, "althoagh 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. BoOing in water does not dissolve it ; but by dissolving various substances with which it is associated, it only renders it the more pure. Yet woody fibre seems capable, by the joint action of heat and chemical agencies, of being converted into nutritive matter. If old linen or cotton rags, paper, or fine sawdust, be hoiled in a strong solution of alkali, or moistened with pretty strong sulphu- ric acid, the. woody substance is changed, being converted first iato gum or dextrin, and then into grape sugar. By such modes of treat- ment old rags may be made to yield more than their weight of sugar. But weak solutions' of acid or alkali do not produce any such effect. Nor will strong vinegar. "We may therefore assume that woody fibre remains totally unchanged by exposure to culinary agencies and ope- rations. Professor Atjtbniueth, of Tubingen, announced some years sinfig, a method of preparing bread from wood-powder or wood-flour, which was changed into nutritive matter by successive heatings in an oven. We are not aware that his experiments have been confirmed, while it is suspected that whatever nutritive value his bread may have possessed, was due to starch associated with the wood. 529. Changes of Sugar. — Sugar, dissolved in cold water, or boiled to a sirup, has very different properties, as is well known to those who feed it to bees in winter. In the first case, the warmth of the hive will dry up the water and leave the sugar in hard crystals which the bees cannot take ; but by boiling, the water and sugar become so intimately united that the mixture does not become dry, but retains the consistence of sirup. If melted sugar be kept for some time at 350°, it loses the property of crystallizing when redissolved in water, its properties being in some way deeply altered. If dry sugar be heated to a little above 400°, it loses the sugar taste and becomes not VKGBTABLB FOODS CHAKGBD BY BOIllKG. 279 only very soluble in water, but also very absorbent of it (deliqueseenfy turns of a deep brown color, and is used to stain liquids of a dark red, or wine color, under the name of ca/rwmel. Sugar itself is slightly acid, and forms compounds with bases which are of a salt nature, and known as saceharatea. Caramel is more decidedly acid, and if the sugar be heated stiU higher it is converted into stiU 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 hihim. If „ ,„„ •' '^ Fig. 100. one of these grams be strongly compressed between two plates of glass it breaks apart into several pieces, as seen in Fig. 100, and all the planes of rupture generally pass through the hilum as if the substance were less resistent at that point. But under the joint action of heat and water, the grains break up difier- ently. Their membranes are torn apart, or exfoliated by internal swelling, as shown in Kg. 101. 681. GbangesofStareb. — Starch is but slightly acted throufTite Miom.' upon by cold water. When heated with water it does not dissolve j 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 approacMng the boiling point, and swell to such a degree as to occupy nearly the whole volume of the liquid, forming a gelatinous paste. If a pint of hot water be poured on a table- spoonful of arrow-root starch, it imme- diately loses its whitenes and opacity, be- Starch grain ruptured by boB- comes transparent, and the entire matter passes into the condition of a thick jeUy. If a little of this be diffused through cold water and examined with the microscope, it will be seen that the starch grains are greatly altered. They have increased to twenty or thirty times their original size ; the concentric lines are obliterated (384) ; the membrane of the grain is ruptured, and its inte- rior matter has escaped. A cold jelly of starch and water, left to stand, either closed or exposed to the air, gradually changes, first into gum (dextrin), and then into sugar. The process, however, is slow, and months must elapse before the whole of the starch is thus transformed. 280 CTTLINAET CHAITGES OF AUMHNTAET eUSSTASCEB. By being boiled in water for a considerable time, it undergoes the same change, and if the water be acidulous the change is quickened. When dry starch is gradually heated to a temperature not exceeding 300°, it slowly changes, acquires a yellow or brownish tint, and be- comes entirely soluble in cold water. It is changed to dextrin or gum (British gum). 532. How Potatoes are changed by Cookingt — ^By referring to the statement of the composition of potatoes (461), we shall notice that a pound contains about three-quarters of a pound of watery juice, to two ounces, or two and a half, of starch. When examined by the Fia. 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 fiU, 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- 1 cause the starch grains in the tubers are protected, partly by the coats of the cells in which they are I contained, and partly by the coagulated albumen. "Potatoes steamed or roasted — or if boiled, mash- ed so as to extract all hard lumps, are in the best condition for digestion. Frying them, toasting Btarch grains of potato them, baking them, or browning the surface, dries ^' up the starch into a hard, half-charcoally mass, which, except in most powerful stomachs, must act as a foreign body." 533. Qnallty of the Water for Culinary Fnrposes. — Soft water, or that which is free from dissolved mineral matter, makes its way into, or is imbibed by organized tissues, with much more readiness and facility than hard water. It also exerts a more powerful solvent or extractive action, and thus is a better vehicle for conveying alimentary sub- Fio. 108. HOW COOKHTG CHAITGES MEAT. 281 stances into the living system. In ouliQary 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 coflfee, 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 th6 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 boUed in soft water by afterwards salting them. It is well known that peas and beans do not boU 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 OooKuro changes Mkat. 534. Action of Heat upon the Constltnente of Flesb.. — Tf 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 albumen to the solid condition ; altering remarkably aU its physical properties. It neither dissolves in water, hot nor cold, and is impenetrable to it. If diffused through one or two hundred times its weight of water, it coagulates, forming fine fibrous meshes throughout the liquid snflBcient to entangle any mechanical substances that may be floatiag in it, and bring them to the surface or carry them to the bottom. In this way albumen is used as a /slarifying agent. If its proportion be much 282 CDXINAET CHANGES OF AUMENTAET SUBSTAIfCBS. larger, the entire water may combine with it and pass into the solid state. The egg, for example, contains 74 per cent, of water and 10 of oil, yet its contents are all solidified by boiling through the action of 14 per cent, of pure albumen. Fat is liquefied, of course, by the action of heat, and at a high temperature it is resolved into various acid and acrid bodies. The effect of heat upon flesh in the mass, has been in vestigated by LiEBia, with his usual acuteness and with highly inter- esting and practical results. 535. Properties of the Liquid and Solid parts of Flesh. — When mus- cular flesh or lean meat is chopped fine, and steeped or leached with cold water, there remains a solid residue consisting of the, muscular fibres, tissues, vessels, &c. If this be boiled, it is tasteless, or indeed slightly nauseating ; it cannot be masticated, and even dogs reject it. All the savory constituents of the flesh were contained in its juice ; and were entirely removed by cold water. The watery infusion thus obtained, is tinged red by some of the coloring matter of the blood. If it be boiled, this coloring matter separates, leaving the liquid clear and of a pale yellowish color. This liquid has the aromatic taste, and all the properties of soup made by boiling the flesh. 'When evaporated and dried, a soft brown mass amounting to 12 or 15 per cent, of the weight of the original PBOPEETEES OF CHEESE. 287 and a first-rate article there is a wide difference ; the former is com- mon, the latter is but rarelj seen. Cream and butter are both highly absorbent of impleasant 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, fl^, 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 wai not yield butter of the best quality. Almost every kind of butter, however, is good when newly made. The vital considerations of its manufacture are connected with its quality of keeping, which wiU be noticed when we reach the subject of preservation (S99). 10. Peepaeatiok and Pbopketies or Oheesb. 647. Spontaneous Curdling of Milki — ^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. ITow when fresh milk is exposed to the air, its ^ oxygen acting upon a portion of the nitrogenous casein, changes it to a ferment; and this takes effect upon the milk sugar, converting it into lactic acid, which causes the sourness of nulk. When sufficient of the lactic acid is thus formed, it seizes upon the soda, takes it away from the casein, and forms lactate of soda. The casein thus set free shrinks in bulk, and gathers into an insoluble, curdy mass, the opera- tion being aided by a gentle warmth. 648. Irtiflcial Cnrdling with Aeids. — ^In making cheese the milk is curdled artificially, and in different countries various substances are used for this purpose. But they all produce the effect in precisely the same way, that is, an acid substance is employed to neutralize the soda of the milk, by which the casein assumes the coagulated state. Almost any acid will have the effect of curdling milk. Muriatic acid, weakened with water, vinegar, tartaric acid, cream of tartar, lemon juice, and sour mUk, are each used for the purpose. 288 CTTLINAET CHANGES OP AUMENTAET SUBSTANCES. 649. Artificial CnrdUng with Rennet. — The salted and dried stomach of the unweaned caJf, lamb, or pig, is called rennet. If a smaR piece of this be soaked in water for a time, and the infusion be mixed with milk at a temperature of 90° or 95°, curdling shortly takes place. It was once supposed that it is the acid of the gastric juice of the stomach which produces the change ; but this cannot be, as the membrane acts with equal promptitude, though it has been thoroughly washed free from every thing of an acid nature. The change is due to the action of the animal matter itself. It is said that the rennet should never be used unless ten or twelve months old. During this period, by exposure to the air, a portion of the membrane has undergone decay and become soluble in water. This decomposing animal matter acts upon the sugar of milk, changing it to lactic acid, which produces curdling ex- actly as in spontaneous coagulation (547). There is much about the action of rennet that is not yet explained. Its condition seems to exert a decided influence on the quality of the cheese. The result 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 large 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 cheese are influenced by a great number of circumstances. Pure casein makes a cheese poor, hard, and homy. The admixture of the oU 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 aU its oil, whUe the richest cheeses are those made directly from cream (cream cheeses), and which hence contain an excess of oily matter. Between these extremities there are all grades of quality, which depend upon the proportion of the constituents. Thus if we use the new milk of the morning, mixed with the previous evening's mUk that has been deprived of its cream, we get a cheese of a certain quality ; if we use the whole 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 BtiU PEOPEETIES AND PBEPAEATION OP TEA. 289 richer. All the conditions which influence the properties of the mUk itself (334) affect also the quality of the cheese. The heat, in curd- ling, should not be too high, as it is apt to give excessive oilinesa 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, whUe too much rennet makes the curd tough, and otherwise affects disagreeably the subsequent changes and flavor of the cheese. The mode of separating the curd from the whey, its subsequent prepara- tion, and the degree and duration of the pressure applied, together with a great variety of other circumstances known to the 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). rV".— COMMON BEVERAGES. 1. Peopbetiks and Pebpaeation op Tea. 551. The Tea Shrub. — Tea consists of the prepared leaves of the tea-plant, a hardy shrub which grows from 3 to 6 feet high, chiefly in China. The plant is propagated from the seed, and matures in from two to three years, yielding usually three crops of leaves each season. When a year old, the young bushes are planted out in rows 3 or 4 feet apart, and being cropped down so as to grow thick and bushy, the tea-fleld resembles a garden of gooseberry bushes. The leaves are picked by hand in May and June, and the plant yields leaves from four to six seasons. 552. What causes different varieties of Tea. — ^Many varieties of tea of all grades of quality are known in market. These differences depend f/nt upon the soil, climate, culture, &c., of the locality where it is grown. SecoTid, upon the time of picking ; the young nnexpanded leaves that are gathered first being tender and delicate, while the sec- ond and third gatherings are more bitter, tough, and woody. Third, 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. v 553. Difference between Green and Black Teas. — All the different varieties of tea are classed as either green or llaek. What constitutes 13 290 COMMON BEVEBAasS. the real difference between these two sorts has long been a matter of doubt. It was at first supposed that they came from totally different species of plants ; but the latest accounts agree that they are both de- rived from the same plant, the difference being in conditions of growth and modes of dealing with the leaves. They may be thus contrasted : GBEBN TBA. BLACK TEA. 1. Gnltivated in manured soils. 1. Grown cliiefly on tlie slopes of hills 2. Leaves are steamed, withered and and ledges of monntaine. roasted almost immediately after gather- 2. Allowed to he spread ont in the air Ing. for some time after they are gathered. 8. They are dried qnickly after the 8. They are tossed ahont nntil they be- rolling process ; the whole operation being come soft and flaccid, brief and simple. 4. They are now roasted for a few min- ntes, and rolled. 5. They are exposed to the air for a few hours in a soil 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, bo as to impart to the entire leaf the dark hue it finally acquires. The precise nature of these changes has not been chemically investigated. — (Johnston.) The unchanging green color of green teas is produced, says Ejiapp, by employing steam to wither the fresh leaves, it being well known to collectors of plants, that many which inevitably turn black when simply dried, preserve their green color brilliant and permanent, when they are killed by steam, previously to drying. The same authority remarks, that green tea gives up much less of its juice in the drying process ; a circum- stance which fully explains its more energetic action upon the nervous system. 554. Varieties of Green and Black Tea. — ^The most important teas of commerce may be thus arranged, beginning with the lowest qualities. Annexed is an approximative scale of the prices per pound paid for them in Canton. Green TeM. Black Teai. Twangay 18 to 27 ots. Bohea 12 to 18 cts. HysonSkin 18 to SO " Congou 22 to 26 " ToungHyson 27 to 40 " Campoi , 22 to SO " Hyson 40 to 56 " Sonchong 20 to 85 " Imperial 45 to 58 " Caper 20 to 40 " Gtmpowder 45 to 60 " Pekoe 85 to 75 " PBOPEETIBS AMD PBTIPABATION OP TEA. 291 TSeangay is the coarsest and most inferior of the green teaB. The Hysons are of a hetter quality, and are more widely used. The word ' Hyson ' is derived from Hee-chun, the name of a celehrated Chinese tea-maker. Eyson-sTcin is composed of the light, inferior leaves, sepa- rated from Hyson by winnowing. Towng-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, Bohm is the poorest and cheapest of the black teas, and takes its name from being largely produced on the Bohea mountains ; Congou, from cong-fou, ' made with care,' and Souchong, from se-ou-chong, " a very Utile sort," are better varieties. Caper comes in little balls or grains, made up in the form of capers. PeTcoe is the best of all the black teas, and corresponds to gohpowder 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 Fhwery PeTcoe, which is erroneously supposed to refer to the blossom of the tea-plant ; but the tea flower itself has little fragrance, and although sometimes used in China, is not imported.' 555. Composition of Tea. — ^The analysis of tea shows it to be com- posed of four principal constituents. First, an aromatic, volatile oil, which produces the peculiar odor and flavor. It is of a citron yellow color, floats on water, and when exposed to the air is quickly convert- ed into a solid resin by atmospheric oxygen. It has such a powerful taste, that when placed on the tongue it spreads over the entire throat, and exerts a 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 ponnd of the oil. Second, tea contains a peculiar principle called thein, a substance rich in nitro- gen, and classed among vegetable alkaUes. Stdnhousb states that or- dinary tea contains about two per cent, of theia ; but Pblisot 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 infiision of tea, therefore, contains dis- solved thein : and if the leaves be of good quality, an ounce wiU yield about 10 grains. TMrd, tommn or tannic acid, a substance so named because it is the ingredient in oak and hemlock bark, which combines with leather in the operation o;f 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 BETEEAGES. 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 constituents are com- municated to the water; they hence give its active properties to the ordinary beverage. But tea leaves contain, fourthl/y, another constit- uent, namely, gluten — which, not being dissolved by hot water, is usually lost with the dregs or grounds. The proportion of this sub- stance is stated to be as high as 25 per cent., so that the leaves, after exhaustion by steeping, are still highly nutritive. In some localities it is customary to eat them. 556. How Tea is best made. — ^The Chinese method is to throw some tea into a cup, and pour boiling water over it ; they cover the cup with a shallow saucer, and let it rest for some time. After it has stood suflBciently long, they pour the clear liquid into a saucer, and drink it hot. Various methods are pursued iu different countries, but a knowledge of the composition and properties of tea is the best guide in preparing its infusion. It is desirable to obtain from the leaves the largest possible amount of matter which water wiU extract, and retain them in the liquid. The thein of tea is in combination with tannic acid, forming a compound which requires boiling water to dissolve it. But, on the other hand, the aromatic oil of tea is volatile, so that the boil- ing tends to drive it off with the steam into the air. If lukewarm water is used, the most important element of tea, its thein, is not ob- tained ; while, by boiling, its fragrant aroma is wasted. The plan to be pursued, therefore, is to pour boiling water upon the tea, m close vessels, so that its active ingredients may be dissolved, and at the same time the volatile oil retained in the mixture. In cooling, a good de- coction of tea becomes slightly turbid, the tannate of thein being no longer held in solution, is precipitated and rises, forming a skin upon the surface. 657. Wlat 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 boUing will extract the thein, and tannic- acid, BO that, although it may be less fragrant, it wiU 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. Muldbb 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 PEOPERT/JSS AND PREPAEATION OP 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 ; while green teas give more of light-colored, and black of dark-colored ingre- dients. The gluten, in which tea leaves are rich, is not dissolved by 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, turmeric, 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 neDer 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 she and tJiorn are much mixed with tea. The Chinese also make a crude and worthless preparation of sweepings, dust, sand, leaves, and various impurities of the tea warehouses, cement- ed with gum or rice-water, which they honestly call lie-tea, and employ it extensively to mix with other teas. In England, exhausted leaves are bought up, their astringent property restored by the addition of catachu (a concentrated tanning extract), and colored with black lead, logwood, &c., are sold again as genuine tea. Another fraud of great prevalence consists in mixing inferior qualities of tea with the bettei 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 COMMOK BEVERAGES. varies from 10 to 80 feet ; but it is usually 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 ih& pwrchment. 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 smeU and taste. It is of a dark yellow color. The Java and East Indian coffees are larger and of a paler yellow, while Ceylon, West Indifln, and Bra&ilian 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 Patbn, is as follows : Water 12 Gum and Sugar. 15"50 Gluten 18 Cafein 00-75 Fat and Volatile Oil 13 Tannic Acid. 5 Woody Fibre 84 Ash 6-75 Dr. Stbnhotjsb states that it contains 8 per cent, of cane sugar. Oof 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 vegetable alkali, with the same composition and properties as thein of tea. A direct analysis of the two substances gave the following result : CarlKin. ITltrogeo. Hydrogens Qjjgea, Thein 60-1 29-0 6-2 15-T Cafein 49-8 28-8 6-1 162 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 PEOPEETIES AlfD PEEPAEATION OF COFFEE. 29£ FlO. 104. in the raw or natural state ; like tea, it is first altered by heat or roasted. 662. Effects of roasting Coffee. — The operation of roasting, produces a .^ several important changes in coffee. ^iS, In the first place, the raw coffee- berries .are so tough and homy, that it is very difScultto grind, and pulverize them sufficiently fine, that water may exert its full solvent effect upon them. Eoasting 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 and highly esteemed aroma which this beverage is distinguish- ed. Johnston states that the peculiar aromatic principle which gives flavor to coffee, exists in extremely minute quantity, (one part in fifty thousand,) and is generated in the roasting process. The heat also Appearance of nnroasted coffee-berries magnifted, showing the size and form of the cells, and the drops of oil contained in their cavities. Fio. 105. peculiar ^O,^^^^^ ■oma for Z-hT^ ^ Appearance of roasted coffee berries. 296 COMMOIT BEYDKAGES. sets a portion of the cafeln free from its comMnation with tannic acid, and evaporates it. The temperature is sufiBciently high -to de- compose the sugar, and change it to brown, burnt sugar, or ca/ramel. Ooffee 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. Ooffee roasted to a reddish brown, loses in weight, 15 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 darJi 'brown, it loses 25 per cent, of weight, and gains 50 in bulk. 563. Hints concerning tbe Soasting FroeesSi — The roasting of coffee is an operation of considerable nicety ; more, perhaps, depending upon it than upon the variety of the article itself. Coffee is roasted by the dealers, in hollow iron cylinders or globes, which are kept revolving over a fire. As the first effect is the evaporation of a consid- erable amount of water, if the vessel be close this is retained, and the coffee roasted in an atmosphere of its own steam. This is not thought to be the best plan, and if the operation be carried on at home, it is recommended that the coffee be first dried in an open pan over a gentle fire, until it becomes yellow. It should then be scorched in a covered vessel, to prevent the escape of the aroma ; taking care, by proper agitation, to prevent any portion from being burnt ; as a few charred grains communicate a bad odor to the rest. It is impor- tant that just the right temperature should be attained and kept. If the heat be too low, the aromatic flavor is not fully produced, and if it be too high, the rich oily matter is dissipated, leaving only the bitterness and astringeaoy of the chalrred 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 sufiBciently 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. Ooffee is very apt to be over-roasted, and even a slight excess of heat greatly injures its properties. 564. Effects of Time npott Coffee. — Ooffee berries undergo a change called ripening, by keeping ; that is, they improve in flavor. The Arabian coffee ripens in three years, and it is said that in ten or a dozen years the inferior American coffees become as good, and acquire as high a flavor as any brought from Turkey. — (Ellis.) But it is differ- ent after the coffee is roasted and ground. Its flavoring ingredients have a tendency to escape, and il should therefore be confined in ves- PBOPBETIES AND PEBPAEA.TION OP COFFEE. 297 sels dosed 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 cofifee have been spoiled from having been shipped with, or even put into vessels which had previously been freighted with sugar. A few bags of pepper are suffi- cient to spoil a whole ship-load of coffee. — (Nokmaudx.) 565. Diode 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 (Kuapp). If a cup of good coffee be placed upon a table, boiling hot, it will fiU the room with its fragrance. Its most valuable portion is thus liable to be exhaled and lost. Hence the same difBoulty 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 stewed rather than boiled, an infusion, and not a decoction being made. Some make.it a rule not to suffer the coffee to boil, but only to bring it just to the boiling point. Yet, a few minutes' boiling undoubtedly increases the quantity of the dis- solved, bitter, exhilarating principle. Dr. Donovan recommends that the whole of the water to be used be divided into two parts, one half to be put on the fire with the coffee, and, as soon as the liquor boils, 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 CoiTee-fflaking. — It is observed, that some natural waters give a stronger and better flavored coffee than others, and this has been traced as in Prague, to the presence of alkaline mat- ter in those which give the most agreeable infusion. Hence, to obtain a more uniformly strong and well-flavored coffee, it is recommended to add a little soda to the water with which the infusion is made. About forty grains of dry, or twice as much of crystallized carbonate of soda, are sufficient for a pound of coffee. — (Johnston.) 567. Adulterations of Coffee. — Ground coffee is very extensively adulterated. Various substances are employed for this purpose, as 13* 298 COMMON BEVBEAGES. roasted peas, beans, and com, and dried and roasted roots, such as tur- nips, carrots; potatoes, &o. But the most common adulterant is chiceory, a plant of the dandelion tribe, which has a large, white parsnip-like rdot, abounding in a bitter juice. The root is mashed, sliced, dried, and roasted with about two per cent, of lard, until it is of a chocolate color. A little roasted chiceory gives as dark a color and as bitter a taste to water, as a great deal of coffee ; and, costing only about one- third ae much, the temptation is strong to crowd it into ground coffee. So common has the use Of chiceory with coffee, become, that it has, in fact, created a taste for a solution of unmingled chiceory, as a bever- age, although it is destitute of any thing corresponding to the cafein, or exhilarating principle of coffee. As an illustration of the extent of adulteration, and how one fraud opens the door to another, it is found that pure chiceory 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. 668. How the Cbeats in Coffee may lie 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 chiceory 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 chiceory in a suspected sample of coffee by placing a little in cold water. If it be pure the water will remain uncolored; if chiceory be present it will be strongly discolored. It may be remarked, however, that if the coffee should be adulterated with burnt sugar, it will pro- duce a similar coloration of the water. It may be further noticed that particles of coffee float upon water, and, owing to their oiliness, are not melted, while chiceory absorbs water and sinks. The admixture of burnt and ground beans, peas, and grain, is not so readily shown. The most certain method of detecting these is by microscopic exami- nation. 3. OoooA Airt) Ohooolatb. 669. Sonce and Composltioii of Cacao Seeds. — ^These beverages are prepared from the cacao beans, which are derived from a fruit resem- bling a short, thick cucumber, grown upon the small cacao tree of the West Indies, Mexico, and South America. The beans are enclosed in COCOA AOT) CHOCOLATE. 299 rows, in a rose-colored, spongy substance, lite that of the watermelon. When shelled out of this fleshy part, they are snrronnded by a thin skin or husk, which forms about 11 per cent, of their weight. The cacao bean is brittle, of a dark brown color internally, cuts like a rich nut, and has a slightly astringent, but decidedly bitter taste. In pre- paring it for use, it is roasted, in the same way as coflfee, until the aroma is fully developed. The bean is now more brittle, lighter brown in color, and less astringent and bitter than before. The fol- lowing is its composition, according to Lampamus : Fatty matter, 53-16 Albammoiis brown matter, containing the aroma of th6 bean, 1670 Starch 1091 Gam, T-75 Iiignis, -90 Bed coloring matter, 2'01 Water, 5-20 Loss 8-4S The largest constituent is a fatty substance, called tutter of eaeao, of the consistence of tallow, white, of a imld, agreeable taste, and not apt to turn rancid by keeping. Cacao beans have also been found to contain a substance, in minute proportion, not included in this analysis, called theobromin, a nitrogenous body, similar in nature and properties to thein, of tea, and cafeine of coffee. 570. Forms of Preparation. — ^It is prepared in three ways. Mrsf. The whole bean, after roasting, is beat into a paste in a hot mortar, or ground between hot rollers. This paste, mixed with starch, sugar, &c., forms common cocoa,- sold under various names, as ' rich cocoa, ' ' flake cocoa,' ' soluble cocoa,' &c. These are often greatly injured from the admixture of earthy and other matters, which adhere to the husk of the beans. Second. The bean is deprived of its husk, and then crushed into fragments. These form commercial cocoa nibs, the purest state in which cocoa can be obtained from the retail dealer. Third. The bean, when shelled, is ground at once into a paste by means of hot rollers, mixed with sugar, «nd seasoned with vanilla, and some- times with cinnamon and cloves. This paste forma chocolate.^ — (JOHNSTOir.) 571. How these preparations are nsed. — First, the chocolate is made np into sweet cakes, sugar confectionery, &c., and is eaten in the solid state as a nutritious article of diet, containing in a smaU compass much strength-snstsdning capability. Second, the chocolate or cocoa is scraped into powder and mixed with boiling water, and boiling milk, when it makes a beverage somewhat thick, but agreeable to the pal- 300 PEESEEVATION OP AlIMENTAET SUBSTAITCES, ate, refreshing to tlie spirits, and highly nutritious. Tliird, the nihs are boiled in water, with which they form a dark brown decoction, which, like coffee, is poured off the insoluble part of the bean. With sugar and milk this forms an agreeable drink, better adapted for persons of weak digestion than the entire bean. The husk is usually ground up with the ordinary cocoas, but it is always separated in the manufac- ture of the purer chocolates. 572. AdulteTation of Cbocolate. — ^Pure or genuine chocolate should dissolve in the mouth without grittiness, and leave a peculiar sensation of freshness, and after boiling it with water, the emulsion should not form a jelly when cold ; if it does, etaroh or flour is present. Many of the preparations of the cocoa-nut, sold under the name of chocolate powder, consist of a most disgusting mixture of bad or musty cocoa- nuts, with their shells, coarse sugar of the very lowest quality, ground with potato starch, old sea-biscuits, coarse branny flour, animal fats (generally tallow). I have known cocoa-powder made of potato starch moistened with a decoction of cocoa-nut shells and sweetened with molasses ; chocolate, made of the same materials, with the ad- dition of tallow and ochre, a coarse paint. I have also met with chocolate in which brick-dust, or red ochre, had been introduced to the extent of 12 per cent. — (Nobmandt.) The temptation to fraud in these preparations seems to be as irresistible as in the case of ground coffee. There is no easy means of detection short of refined micro- scopic and chemical ezamination, so that the only practicable means of self-defence for the purchaser, is to de^l only with traders of unques- tionable integrity, where such can be found. v.— PRESERTATION OF ALIMENTARY SUBSTANCES. 1. Oattses of theie Ohangeableness. 573. Why is It Neeessary that Foods shonld be PerishaWe 1 — ^As in the plan of nature the production of force depends upon change of matter, and as the fundamental purpose of animal life is the evolution of pow- er, it is apparent that matter which is to act as food, must be capable of ready and rapid transformation. This inherent facility of change, by which alimentary substances are conformed to the deep require- ments of the animal economy, renders them extremely transient and perishable. If they are designed for change within the body, they must be subject to change without. In order that the gluten of flour, for example, may pass readily through the successive changes of the animal organism, being converted first into blood, then into muscular CAUSES 01" THEIE CHAUGBAHLBNESS. 301 fibre, and then decomposed for the development of contractile force, it is necessary that this substance should be so loosely built up, the attrac- tions amongst its atoms should be so feeble, that slight causes become capable of breaking down its chemical structure. 674. Change of Nntrient Hatter iritbin and witbont the Bodyi — It was formerly taught that the living body is the domain of a peculiar vi- tal power, which suspends the ordinary destriictive play of chemical aflSnities and physical forces, but that at death the vital energy ceases, and those forces resume their natural activity, causing the speedy dis- organization of the inanimate organism. But this is hardly correct. The vital force, or whatever we may name the presiding agency of the living system, does not suspend physical and chemical laws, but only regulates, and as it were uses them. We have already seen that strictly chemical changes go on constantly in the body, and shall shortly have occasion to notice their extent (634). They are of the same kind {oxidations), are carried on by the same agent (atmospheria air), and yield the same final products (carbonic acid, water and am- monia), in both conditions. In the living fabric the decompositions are measm-ed ; while in the lifeless body they are uncontrolled, and quickly spread through the entire organic mass. 575. Conditions of the PeriBhableness of Foods. — ^Alimentary substances are by no means alike changeable ; some keep longer than others un- der the same circumstances. There are certain specific causes of or- ganic decomposition, and accordingly as these act conjointly, or with variable intensity, is the rate of putrefactive change. In chemical composition, vegetable and animal substances are much more compli- cated than mineral compounds, and hence they are less permanent. Generally, mineral substances are combined in the simplest and most stable way, containing but few atoms, and consisting of pairs of elements, with nothing to disturb their direct attraction for each other. On the contrary, organized substances, in some cases, contain several hundred atoms, and consist of three, four or five difierent elements, joined by complex affinities into delicate and fragile combinations. We have seen, in speaking of fermentation, that albuminous substan- ces are, fi:om this cause, most changeable, and are universally present in substances designed for food. Water is a large constituent of all alimentary bodies, in their natural state, and is highly promotive of chemical changes ; indeed, it is indispensable to them. Tem- perature exerta an all-controlling influence-^warmth favoring, and cold retarding, or arresting, these transformations. The atmospheric medium, which is in contact with every thing, contains an element 302 PEESEETA.TION OF AUMENTAET SUESTANCHES. which is the ever-active and eternal enemy of organization. The in- satiable hunger of oxygen gas for the elements of organic substances, is a universal cause of decomposition — ^it is the omnipresent destroyer, consuming alike the living and the dead (662). Putrefactive decay may also be prevented by certain chemical substances which are used for the purpose. A knowledge of the laws and conditions of organic decom- position, has led to various practical methods of controlling it, which constitute the a/rt of presermng. 2. Pekseevation et Exolitsion of Ant. 576. Oxygen as an exciter of decay. — Other conditions being favor- able, that is, moisture being present and a proper temperature, access of air starts decomposition, — ^it is the prime mover of the destructive processes. • We have already noticed its mode of action, in speaking of fermentation (488). In the case of vegetables, as potatoes and apples, for example, if the air is excluded from their interior, they remain for a considerable time sound. But if we cut them, the oxygen quickly attacks the exposed surface and turns it brown, indicating the incipient stage of decay. When the surface of fruits and vegetables is injured, so that their juices come in direct contact with the air, the effect is at once seen. K an apple is bruised, the injured spot imme- diately turns dark, and decomposition gradually spreads from that point, until the whole apple becomes rotten. The juice of the ripe grape, while protected from air by an unbroken skin, remains sweet and scarcely changes ; it may be dried and converted into a raisin, its sweetness remaining. If it be crushed under mercury, and the juice be collected in a glass completely filled with mercury, so as to prevent all contact of air, it wDl remain unchanged for several days. But if air be once admitted, as by perforating the grape-skin with a needle's point, fermentation commences almost instantaneously, and the juice is soon entirely changed. The same is true of all animal fluids. Milk, while in the udder of the healthy cow undergoes no change, but in contact with air, its properties are soon totally altered — it is soured and coagulated (SiT). When life has been destroyed by bodily wounds, decomposition spreads from them ; or if the animal have not died by violence, the changes may begin internally in those parts, such as the lungs, which are in contact with the air. 67'r. Changes begun by Oxygen may proceed without it. — ^It is by no means necessary, in all cases, that air should be in constant contact with the changing substance; the decomposition once commenced, BT EXCLTJSIOK OF AIE. 303 may continne, though the oxygen be entirely excluded. Milk, if once exposed to the air, coagulates and sours, though sealed up in air-tight vessels. Grape juice, tliough oxygen be completely cut off, ferments, generates gases, and often explodes the bottles in -which it is confined. The impulse of disorganization being given, decomposition goes on without farther external aid. To explaia this, we must suppose that the atoms of the changing substance were at first in a kind of rest or equilibrium, without mutual activity, and that by the invasion of oxy- gen, this equilibrium has been disturbed, so that the elements of the substance begin to act and re-act upon each other, giving rise to new products. In-this way, a state of change commenced by merely jost- ling a few surface atoms through contact of oxygen, is propagated by intestinal action throughout the entire mass. 678. How changes begnn by Oxygen may be stopped. — " The property of organic substances to pass into a state of fermentation and decay in contact with atmospheric air, and in consequence to transmit these states of change to other organized substances, is annihilated in all cases without exception, ty heating to the toiling point." — Liebig. The substance most prone to be affected by air-contact, is liquid albu- men ; and this by boiling is solidified, and so altered in properties, as to lose its peculiar susceptibility of transmutation. The boiling cer- tainly obliterates the effect that oxygen has produced, and as the atoms of matter have no inherent power to put themselves in motion, and cannot change place unless influenced by some external cause, it is obvious that the nutritive substance will remain unaltered if the air is Jcept excluded. These facts indicate the most certain, manage- able, and perfect method of preserving alimentary substances. By simply heating to the boiling point, which produces no other change than that of partial oooHng, and afterward protecting from the air, alimentary substances, both animal and vegetable, may be presei-ved in their natural condition entirely unchanged va. both flavor and pro- perties, for an indefinite period. This plan was first brought into general notice by M. Appebt of France, in 1809. He preserved all kinds of fruits, vegetables, meats, soups, &c., in glass bottles. His prac- tical methods, however, were crude and unsatisfactory, and have been superseded by others. Captain Koss presented the society of arts with a box from the house of Gauble and Dabkcn (London), which con- tained cooked provisions sixteen years old, and that were in a state of perfect preservation. The details of the preparation on a large scale, as practised chiefly for marine consumption, we have no space here to describe. The vegetables, meats, poultry, &c., are cooked precisely 304 PEESEEVAHON OP ALIMENTAET, SUBSTAUCBS. in the same manner as for immediate consumption, and then sealed up in boxes and canisters which do not contain a particle of air. 579. Domestic preseryatioii in air-Uglit vessels. — The preservation of delicate fruit and vegetables in air-tight cans, has now become quite generally a household operation, and there can be no doubt that as people acquire experience in the process, they will employ it much more extensively. Of this process Prof. LiEBia remarks, "The pre- pared aliments are enclosed in canisters of tinned iron plate (609), the covers are soldered air-tight, and the canisters exposed to the temperature of boiling water. "When this degree of heat has pene- trated to the centre of the contents, which it requires about three or four hours to acomplish, the aliments have acquired a stability which one may almost say is eternal. When the canister is opened, after the lapse of several years, the contents appear just asif they were only recently enclosed. The color, taste, and smell of the meat, are com- pletely unaltered. This valuable method of preparing food, has been adopted by many persons in my neighborhood, and has enabled our housewives to adorn their tables with green vegetables in the midst of winter, and with dishes at all times which otherwise could be ob- tained only at particular seasons." 580. Canisters closed l»y soldering. — Perfectly tight tin canisters of almost any convenient shape are provided, and the article to be pre- served, sometimes raw, but generally cooked, is placed within it, and the lid soldered down. The lid, is however, perforated with a small aperture or pin-hole. The canister is then placed in boiling water, and the moisture within is converted into steam which drives out the air. The boiling is continued as long as may be required totally or partially to cook the contents of the can, which is then withdrawn, and the pin-hole closed with solder. This is an operation of considerable nicety. The heat drivea.out not only air contained in the canister, but also a jet of steam. The solderer, therefore, lets fail a few drops of cold water on the tin around the aperture, producing a momentary condensation of the steam, during which the pin-hole is dexterously closed. The delicacy and success of the operation, consists in carry- ing the condensation only so far as just to arrest the jet of steam, and in closing the opening at the instant. After the canister is closed, it is again exposed with its contents for a short period to a boUiog heat. 581. Spratt's self-sealing Cans. — In many cases a tinsmith may not be near, and the soldering operation for closing the canisters will be quite certain to fail in the hands of the inexperienced. To obviate BY BXCLTJSION OF AIE. 306 Fia. 108. this diflBculty, other arrangements have been contrived. Speatt's cans* are oblong tin cylinders (Fig. 106), holding from a quart to a gallon, which are closed with a screw acting npon a ring or ' com- press' of india-rubber, and then hermetically sealed with beeswax. The closure is simple and effectual, and can be managed'with a little care by any body. The articles being introduced into the can, the cap is screwed down tightly with the fingers, and the can submerged in a boiler of cold water, which is then raised to boiling. After boiling a sufiScient time they are withdrawn, the caps unscrewed^ and the cans left open for one minute. If i the previous boiling has been thorough, steam will escape freely. If it does not so escape, the boiling must be repeated. The cap is then screwed down, this time very tightly, viith a wrench provided, and the can introduced into the water and boiled a second time. On withdrawing it again melted beeswax is poured into a little channel or groove, which makes the sealing perfect, if the cap fits and is tightly screwed down. In all cases there are at least two boilings. The second might be thought unnecessary, but it is not. The vessel must be opened, that the steam may drive out the air, and there is always the possibility that a trace may be left. If so, during the second boiling the oxygen will be entirely converted into carbonic acid, which is innoxious. As the results of large experience the times required for the boiling are as follows : FirBt Iwiling. Second boiling. Berries of sll kinda 15 minutes. S minntes. Cherries or currants.. 15 " 5 Ehnbarb 15 " 5 Fescbes. 20 " 5 Flams 20 " 10 Qnincea, 'pears or apples '. 45 " 16 Tomatoes 80 " 15 Asparagns 60 " 80 Green peas, corn or beans 8 bonrs. Sbonrs. 683. Suggestions eoncernii^ the use of the Cans. — ^None but perfectly fresh sound fruit should be put up in the above manner. It is recom- Spratt's Belf-sealing Can. • Mannfaotnred by Wells & Feovost, New York. 3Q6 PBESEETATION OB" AUMENTAEY StJBSTAITOES. mended that peaches, qumoes, pears and apples he peeled, and tha seeds removed hefore preservmg, as seeds and peel emhitter and other- wise injm'e the flavor. Peach stones contain traces of Prussic acid, a powerful poison, which, if the fruit he preserved whole, is liable to be diffused through it. Fruits are preserved either with or without sugar ; if without, a quarter of a pint of water should be poured over every quart of fruit while in the can. If the fruit is to be sweetened, mate a sirup, and pour on it in the can, until it is nearly full. A sirup for summer fruits is made by adding a pound of crushed sugar to a pint of water, and boiling two minutes. Very acid fruits, such as quinces and plums, require a stronger sirop, say 1^ lb. sugar to a pint of water. If the cans are not perfectly tight when the steam condenses within, forming a vacuum, the external pressure of the air may drive the soft beeswax in through the crevice. Aliments well put up will keep in a room at any temperature ; if the cans bulge, it is a sign of development of gas by internal decomposition, and their contents will not keep. 3. Peesbevation at low Tbmpbeatuebs. 683. Influence of Temperatnre. — ^Degrees of temperature exert an absolute control over the duration of alimentary compounds. At 32° their juices are congealed, and they remain totally unchanged. At a few degrees above the freezing point changes are very slow. As we ascend the scale, the conditions of mutation become more favorable, except in the case of albumen, which is rendered more enduring by the heat of coagulation. In all other cases decomposition proceeds more rapidly as warmth increases, until the point of quick disorgani- zation, charring, and active combustion is reached. 584. Freezing as a means of Preservlng.^Oongelation, therefore, may be resorted to as a means of preservation, chemical action being im possible where the substance is reduced to a solid state. Eemarkable cases are on record in which the bodies of animals have been disen- tombed from masses of ice, in such a state of preservation that the flesh was fit to support nutrition, although they had been wrapped in ice for such a vast period that the race to which they belonged had become extinct. It is customary in many regions to preserve fresh meat by freezing it, and packing in snow. Some object that the flavor of meat is injured by freezing ; but the Russians, on the con- trary, insist that it is improved. Great care is necessary in thawing all frozen aliments, whether meat,. fish, or vegetables. It should be done slowly, and the best way is by immersion in very cold water. AT LOW TEMPERATUBKS. 307 Fta. 107. A shell of ice will be formed around them, as we have often seen in ' taking the frost out of apples ; ' — the water in contact with the sur- face being frozen into a scale, by parting with its heat to thaw the frozen apple within. If thawed too rapidly, as by placing them in a warm room or in hot water, the taste is impaired, and the composition of the substance so affected that pntrefaction is rapidly brought on. One of the effects of freezing and thawing potatoes and some fruits, is to increase the amount of sugar, as shown by their sweeter taste. 585. low TemperatiiTes above Freezing— KefrigeratorSi — ^We command -ow temperatures by cellars, and the use of ice. Excavations made below the surface of the ground have a temperature common to the surrounding strata of earth, which is cooler the deeper we go for nearly a hundred feet. The temperature is also very constant, the extremes of winter and summer being both excluded. The temper- ature of good cellars (40° to 60°), is below the range most favorable to putrefaction (60° to 100°). By the use of ice in the ice-house or refrigerator, the temperature may be kept down to within 5° or 10° of freezing. At these points changes proceed slowly, so that meat admits of being kept at this degree of coolness for a con- siderable time. It- is said that meat should never be suffered to touch ice, as it is toughened and otherwise injured. The refriger- ator is commonly a rude, shelved box. If openiag at top, it is troublesome of access and difficult to make its space available. If it have doors at the sides, the cold air flows out every time it is opened ; and . if the ice is placed at the bottom, there is no circu- lation of air or means of cooling Lyman's Bniesa Befrigeiator. the upper space. A. 8. Ljman, of IT. Y., has obviated these defects by a newly devised arrangement (Fig. 107). The ice is placed in an upper chamber over a grate opening to the flue a, through which, ice-cold air constantly falls. The body of the refrigerator is occupied by three drawers, I e d, e being represented as partially withdrawn. The cold sir fills these drawers, and as it becomes slightly warmer is pressed 808 PEESEEVATION OF AUMENTAET SDBSTAlfCES. upward in the direction of the arrows, and re-cooled by contact with the ice. It descends again through the flue, the temperature of the whole refrigerator being thus kept down nearly to freezing. The waste water is caught at g. The arrangement of drawers makes the whole space available, and is as convenient as a common bureau. When one is partially withdrawn, as at e, the air in, it being heavier than that of the room, does not escape, while the circulation of air con- tinues within. There is also a twofold means of purifying the air. At / there is a filter consisting of a wire-gauze box, through which the air passes ssA is disinfected. When it comes in contact with the ice, ,it is condensed and its moisture deposited, so that it has a real dry- ing effect upon the articles to be preserved. The water constantly form- ing by the melting ice is highly absorbent of the gases set free by de- composing food, so that these impurities are constantly washed out of the air in its progress. The charcoal filter, in effect, divides the space into two refrigerators ; thus preventing articles in one from smelling or tasting of those in the other. Cars are constructed upon this prin- ciple, in which meat is transported from the Western States to Ifew York in summer. 586. Keeping Frnits at low Temperatnres. — The most important fact relating to the composition of fruits is the large proportion of water they all contain, and which constitutes the bulk of their peculiar juices. From three-fourths to nine-tenths of them being liquid, we are to regard them as consisting of a small amount of solid matter diffused through from four to l;en times their bulk of water. This con- dition is eminently favorable to the action of fruits upon the organs of taste in their n j,tural or uncooked state ; being in a kind of pulpy, half-dissolved condition, they are ready to take prompt effect upon the pappUse of the mouth. But the same property of fruits which adapts them so perfectly to our gustatory eiyoyment, 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 frtdts, as apples and pears, can be preserved for months in cellars where the necessary warmth for iaducing decay is not attained. Sometimes fruit, as many varieties of apples, are not really ripened at the time of gathering,, but imdergo a slow change during the winter months, their acid principle being converted into sugar. To be best preserved fruit should be picked when perfectly dry, at a time when the stalk separates easUy from the spur. Apples and pears should have their stalks or "stems" separated from BY DETINQ. 309 the tree, and not from themselves. The utmost care should be oh- 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 hear handling or wiping, as this rubs off the bloom which, when allowed to dry on some fruits, constitutes a natural varnish, closing up the pores and preventing the evaporation of the juices. Apples have been preserved a year in a fine fresh condition, by keeping them in an atmosphere within ten degrees of the fi^ezing point. Constancy of temperature is important, as alternations of heat and cold, by contracting and expanding the juices, seem to favor chemical changes. Grapes, cherries, currants, gooseberries, and other soft fruits have been preserved for use in win- ter by gathering them when not too ripe, and when very dry putting them unbruised into dry bottles, which are afterwards well corked, and then buried in the earth. The efficiency of this method of pre- serving is increased by immersing the bottles containing the fruit for a few minutes previously to corking, in hot water, which coagulates the vegetable albumen. The preservation is here due to the joint in- fluence of exclusion of air, and a low and uniform temperature. A preseroatory 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. Pkesbevation bt Deyin&. 587. Retention of Water in Fmits and Tegetaliles. — ^As nature places water in large quantities in organic bodies, in many cases she takes due precautions to keep it there. Unripe potatoes and unripe apples removed from the parent stock shrivel, shrink, and perish. These 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 corJe, through which water can scarcely pass, and by which, therefore, it is confine^d 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 fall 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 witltdrcmiing it. Both vegetable and animal substances are extensively preserved in this way. Drying is a 310 PEESBEVATION OF ALIMENTARY SUBSTANCES. kind of disorganization of the alimentary body, its largest constituent 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. Dryiag 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 kUn-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. 689. Preserving Sncenlent Vegetables. — These, if exposed to the air, evaporate their moisture, wUt, and lose their crispness and freshness. A damp cool place is best to prevent these changes for a time. Many are kept soundly during winter by burying in the earth. M. Masson, head gardener to the Horticultural Society of Paris, has described a mode of preserving succulent vegetables by drying and compression. He prepares cabbage, cauliflower, potatoes, spinach, endive, celery, parsley, &o., in such a manner that they keep for any length of time, and when soaked in water resume much of their original freshness and taste. They are chiefly prepared for marine consumption. The packages of dried vegetables are covered with tinfoil. Dr. Hassall speaks of a specimen of dried cabbage as follows : " On opening the package the contents, which formed a solid cake, were seen to consist of fragments of leaves of a yellowish color, interspersed here and there with some that were green. In this state it was difficult to de- termine what the nature of the vegetable was. Soaked in hot water for about half an hour, it gradually underwent a great expansion, so that it acquired several times its former bulk. When examined, it was evident at a moment's glance that the vegetable consisted of the sliced leaves of the whitfr-hearted garden cabbage, presenting the ap- pearance and color, and possessing the taste and smeE, to a remarkable extent, of the vegetable in its recent state." by autiseptic agents. 311 5. Pkeseetation by Aktiskpxios. 590. Bemarkable propertleg of common Salt. — Antiseptics aro op- posers of putrefaction. Certain- bodies when added to organized substances, possess the power of resisting or preventing their putre- factive decomposition; they are numerous, and act in various ways. Those used for preserving aliments are salt-petre, sugar, alcohol, creosote, vinegar, oil, and common salt. However ' common ' this last substance may be, we shall nevertheless be interested in giving it a moment's attention. Though mild and pleasant to the taste, it is composed of two elements, one a yellowish green, sufifocating,.poison- ous gas, chlorine, and the other a bright silvery-looking metal, sodium fhence 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 than the solid sodium alone did before the union. No known mechanical foroft 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 roeh 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 ofheat. 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- • .T Tj r J. 11- How crystals of common salt are pears m the sohd form, or crystallizes. ' 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 evaporation, they are naturally formed at the surface of the liquid, and present the appearance of little floating cubes, as shown in (Fig. 108), where the solid crystal is up- borne or floats in a little depression of the fluid surface. New crystals 312 PEESBETAHON OF ALIMENTABY SUBSTAITCES. soon form, which are joined to the first at its four upper edges, con Btituting a frame above the first little cube (Fig. 109). As the whole descends into the fluid, new crystals are grouped around the first frame constituting a second {Fig. 110). Another set added in the same way gives the appearance shown in Kg 111. The consequence of this arrangement is that the crystals are grouped into hoUow, four- sided pyi-amids, 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 Iwpper-shaped (Kg. 112). 591. Sources and Purification of Salt. — Salt is obtained from three sources ; first, it is dug from the earth in mines, in large masses, like transparent stones {roch salt) ; second, it is procured by ev&porating sea-water (]>ay salt) ; and, third, by boiling down the liquid of brine springs. It diflfers very much, in purity, from different sources, being in many cases contaminated by salts of calcium and magnesium, which render it bitter. Pure salt, in damp weather, attracts water from the atmosphere, and becomes moist, but parts with it again when the weather becomes dry. But the chlorides of calcium and magnesium are much more absorbent of water, and hence, if the salt is damp and moist when the air is dry, we may infer that a large proportion of these substances is present in it. Salt, for certain culinary pur- poses, as for salting butter, should be perfectly pure. Its bitter in- gredients are more readily soluble in water than is the salt itself; hence, by pouring two or three quarts of boiling water upon ten or twenty lbs. of salt, stirring the whole well now and then for a couple of hours, and afterwards straining it through a clean cloth, the ob- noxious substances may be carried away in solution. Among the purest, is that called Liverpool salt, which is an English rock-salt dug from the mines ; dissolved, reorystaUized and ground. 592. How salt preserves meat. — Salt is more widely used than any other agent in conserving provisions, especially meats. It is well known that when fresh meat is sprinkled with dry salt, it is found after a few days swimming in brine, although not a drop of water has been added. If meat be placed in brine it grows lighter, while the quantity of liquid is increased. The explanation of this is, that water has a stronger attraction for salt than it has for flesh. Fresh meat contains three-fourths of its weight of water, which is held in it as it is in a sponge. Dry salt will extract a large part of this water, dissolving in it and forming a saline liquid or brine. In this case, the water of the meat is divided into two parts ; one is taken up by the salt to form brine, while the other is kept back by the BT AUnSEPTIC AGEJSTS. 313 meat. The salt robs the meat of one-third or one-half the water of ita jtuce. Salting is therefore only an indirect mode of drying ; the chief canse, 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 tlesh 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. 693. How meat is Injured by saltingi — The separation of water from the fibre of meat shrinks, hardens, and consequently renders it less di- gestible. It is quite probable, also, that the salt, in some way not yet understood, combines with the fibre itself, thus altering injuriously its nutritive properties. -Peeeiea thinks that the separation of water is not sufficient alone to account for its preservative action, but that it must produce some further tmexplained efifect 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 of flesh with its albumen, kreatine, and valuable salts ; in fact, the brine is found to contain the chief soup-forming elements of meat. Salting, therefore, exhausts meat far more than simple boiling, and as the brine is not consumed, but thrown away, the loss is still greater In salting meat, however, there happens to be a slight advantage resulting from its impurities, lime and magnesia. These are decomposed by the phos- phoric acid of the juice of flesh, and precipitated upon the surface, forming a white crust, which may often be observed upon salt meat ; this constituent, therefore, is not^ separated in the brine. Saltpetre has a preserv^fctive effect, probably in the same way as common salt, but it is not so powerful, and unlike salt produces a reddening of the animal fibres. ' A little of it is often used along with salt for this purpose. 594. Sidting T^etaUes. — These may be preserved by salt, as weU as flesh, l)ut it is not so commonly done. In salting vegetables, however, a fermentation ensues, which gives rise to laatic acid. This is the' case in the preparation of scmerhrcmt from cabbages, and in salting cu- cumbers. The brine with which both vegetables are surrounded is found strongly impregnated with both lactic and butyric ^oids. 595. Preserratlon by Sngar. — This is chiefly employed to preserve 14 314 PEESEBVATION OF ALIMBNTAItT STDBSTAITCBS. fruits. Many employ both sugar and molasses for tlie preservation of meat ; sometimes alone, but more commonly xmited 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 sirnpy consist- ence. KuAPP states that the drops of water which condense from the state of vapor on the sides of the vessels in which the preserves are placed, are often sufficient to induce incipient decomposition, by diluting the upper layers of sugar. The effect of the acids of fruits is gradually to convert the cane sugar into uncrystaUizable and more fer- mentable grape sugar. 696. Preserving by Alcohol and other gnbetanees. — Strong alcoholic li- quors are used to prevent decomposition in both vegetable and animal bodies. They penetrate the substancej'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 preventer of putrefaction. Meat dipped for a short time in a solution of it mil not putrefy, even in the heat of summer. Or if exposed in a close box to the vapor of creosote, the effect is the sapae, though in both cases the amount producing the result is extremely small. The preservative effect of smoke-drying is partly due to creosote, which gives to the meat its peculiar smoky taste, and partly to desiccation. Oil is but little employed in saving, alimentary substances — two kinds of fish, amcTumies and sardines, are preserved in it. Oka/rcoal has always been ranked as an antiseptic or arrester of putrefaction ; but it has been lately shown that it is rather promoUve of decomposition. How this is, wiU be explained in another place (811). 6. Peesbbvation as Muk, Buttke, and Ohkbse. 697. Modes of preserving Milk. — The cause of the souring of milk we have seen to be the action of oxygen upon its casein, which altera the sugar to acid (647). I^ therefore, the milk be tightly bottled, and MILK, BUTTEB, 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 miming 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 smaU quantity of lactate of soda or magnesia which is formed, is but slightly objectionable. If milk be evaporated to dryness, at a gentle heat, with constant stirring, it forms a pasty mass, which may be long kept, and which reproduces milk when again dissolved in water. Aldenh 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. 698. Unpurified Batter quickly spoils. — ^Butter when taken from the chum contains more or less of all the ingredients of mUk, water, casein, sugar, lactic acid, which exist in the form of buttermilk, diffused through the oOy mass. Chevbetji, 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 DIecIiaiiical 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 mUk 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 Bnttor by WasUng.— Some join washing with 316 PEESEETATION OF AUMENTAEY SUBSTANCES. mechanical -working, to separate the buttermilk. It is objected to tliis, first, that water removes or impairs the fine aroma of the butter, and, second, that it exposes the particles of butter to the injurious action of air much more than mechanical working. On the other hand, it 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. Spbbngbl states that the butter absorbs the lime, and is unpleasantly affected by- it. A. B. DioKHTSoif 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 Bancidity in Batter. — Pure oil has little spontaneous tendency to change. If lard, for example, be obtained in a condition of purity, it may be kept sweet for a long time without salt, when protected from the air. That it does alter and 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 out off from the air, it may be long kept with- out adding any preservative substance. But a trifling amount of curd left in it is sufficient to infect the whole mass. It is decomposed, and acting in the way of ferment upon the sugar and oUy substance itself, develops a series of acids, the 'butyric, which is highly disagreeable and offensive, and the capric and caproio acids, which have a stron g sour odor of perspiration. The butter is then said to be rancid. In general, the more casein is left in butter, the greater is its tendency to rancidity. 602. Action of Air npon Batter. — The fat of butter is chiefly composed of ma/rga/rin, 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 various offensive substances. When, therefore, butter is much exposed to the UILK, BUTTEE, AlfTD CHEESE. 317 air it is certain to acquire a surface rancidity, wMch, without pene- trating into the interior, is yet snfiBcient to injure its flavor. It is in- dispensable to its- effectual preservation that tie air be entirely ex- cluded from it. Hence, in packing butter, the cask or flrkin 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 he 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 untU the butter has ceased shrinking, and the vacancies that have arisen between the but- ter and vessel's sides are carefully closed. 603. Substances nsed to preserve Butter. — Salt, added to butter, per- forms the twofold oflBce 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, whUe 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 mUk. Honey has been also nsed for the same purpose, at the rate of an ounce to the pound of butter. Some employ salt, saltpetre, and sugar all together. From an examination of upwards of forty samples of English butter, Hasball 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 aiid sink to the bottom. 604. Changes of Cheese liy 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 pla»e. The influence of temperature is shown by the fapt that in certain locali- ties, of France, especially at Roquefort, there are subterranean caverns which rent and are sold at enormous sums for the purpose of keeping 318 MATBBIALS OP CULINAET AITO TABLE CTENSIIS. and maturing cheese. These natural rook-oellars 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 Eggs, — 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 water escapes outward through the pores of the shell air passes inward and takes its place, and the amount of air that accumulates within de- pends, of course, upon the extent of the loss by perspiration. Eggs which we have preserved for upward of a year, packed in salt, small ends downwards, lost from 25 to 60 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 np the pores of the shell air-tight. This may be done by dipping them in melted suet, olive oil, milk of lime, solution of gum arable, or cover- ing them with any air-proof varnish. They are then packed in bran, meal, salt, ashes, or charcoal powder. Eeavmue is said to have coated eggs with spirit varnish, and produced chickens from ihem after two years, when the varnish was carefully removed. VI.— MATERIALS OF CULINABF 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. Utensils of Iron. — ^Iron is much employed for vessels iu kitchen operations. The chief objection to it springs from its powerful attrac- tion for oxygen, which it obtains from the atmosphere. It wUl even VESSELS OF IKON AND TUST. 319 decompose water to get it. In consequence of this strong tendency to oxidation, its surface becomes corroded and roughened by a coating of mst, which is simply oxide of iron. The rust combines with various substances contained in food, and forms compounds which discolor the (irtioles 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. There is one mode of managing cast iron vessels, by which the disagreeable effects of rust may be much diminished, if not quite prevented. If the inside of stew-pans, boilers, and kettles be simply washed and rinsed out with warm water, and wiped with a soft cloth instead of being scoured with sand or polishing materkds, 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 sort of ena/mel. 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 Tiui — ^As such protection, however, in- volves care and consideration, it is uncertain 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 tloeh 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. Adaptatton of Tin to Cnllnary Pnrposes. — Tin, in its metallic state, seems to have no injurious effect upon the animal system, for it is often given medicinally in considerable doses, in the form of powder and filings. It is frequently melted off from the sides of sauce-pans or other vessels in globules, and is thus liable to be swallowed, a circum- stance which need occasion no alarm. The attraction of tin for oxy- gen is feeble, and it therefore oxidizes or rusts very slowly. Strong ncids, as vinegar or lemon juice, boUed in tin-coated vessels, may dis- 320 MATERIALS OP CUUNAET AOTJ TABLE UTENSILS. solve a minute portion of the metal, forming salts of oxide of tin, but the quantity wiU be so extremely small that it need excite little apprehension. It is a question among toxicologists whether its oxide be poisonous. Peottst showed that a tin platter, which had been in use two years, lost only four grains of its original weight, and probably the greater part of this loss was caused by abrasion with whiting, sand, or other sharp substances during cleansing. If half of it had been taken into the system dissolved, it would have amounted only to yj ^ 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. Pbeeika 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 Objectionable. — ^Zinc is rarely employed as a mate- rial for culinary vessels. In many cases it would be unsafe, as a poi- sonous oxide slowly forms upon its surface. It has been recommended for milk pans on the ground that milk would remain longer sweet in them, and hence, more cream arise. But whatever power of keeping milk sweet zinc possesses, it can only be caused by neutralizing the acid of milk with oxide of zinc, thus forming in the liquid a poisonous lactate of zinc. 612. Behavlop of Copj)er In contact with F«od.-r-This metal suffers very little change in dry air, but in a moist atmosphere oxygen unites with it, forming oxide of copper ; and carbonic acid of the air, combin- ing with that substance, forms carbonate of copper, of a green color. Copper is easily acted on by the acid of vinegar, forming uerdigris, 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 generatftig poisonous combinations. Sugar also forms a compound with oxide of copper, — the sacharate of copper. 613. Test. — ^As the salts of copper are of a green color, vessels of this metal have a tendency to stain their contents green. They are sometimes employed purposely to deepen the green of pickles, &c., and cooks often throw a penny-piece into a pot of boiling greens to COPPER AND ENAMELLED VESSELS. 321 intensify their color. A simple test for copper in solution is, to plunge into the suspected liquid a plate of polished iron, (a knife blade, for example,) when in a short time, (from five minutes to as many hours,) it will become floated 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. Proteetion of Copper PtensUs. — Yet copper has several advan- tages as a material for culinary ntensUs. It is but slowly oxidized, and hence does not corrode deep, scale, become thin, and finally faU 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. Mttohbl 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. TIeb 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 CXTLTNAET AMD TABLE UTENSILS. 616. Earthettware Vessels— Glazing. — ^Vessels of earthenware are in universal liousehold use. Ttiey are made, as is well known, of clay and sand, of various degrees of purity, witli 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 theMesired artificial surface is given to earthenware, is by taking it from the fire when it has become suflBciently firm and stiff, immersing it in a pre-' pared liquid, and restoring it again to the furnace, where by the action of heat a vitreous or glassy coating is formed. 617. Earthenware Glaze containing Lead. — The preparations employed for glazing common earthenware, are chiefly combinations of lead with the alkalies, producing vitreous or glassy compounds. It is known that lead enters largely into many kinds of glass ; it imparts to them great brilliancy and beauty, but makes them soft, so that they are easily scratched, and liable to be attacked by strong chemical sub- stances. Lead glaze upon earthenware is also subject to the same objection. It is tender and can be scraped off with a knife, so that the plates soon become marred and roughened. They also soon black- en, or darken, when in contact with sulphurized substances. Gooking eggs or fish in these vessels gives them a brownish tinge. K less lead be used, the glaze becomes less fusible, the process of applying it more difBcult, and hence the ware more expensive. Lead glazing can be d(v, teoted by its remarkably smooth, lustrous surface, resembling varnish ; while the salt glaze, on the contrary, has less lustre, and the vessel has not so fine an appearance, all the asperities of the clay beneath being perfectly visible. Fatty matters, and the acids of fruits, exert a solvent action on oxide of lead combined in lead glaze, especially where the chenucal energy is increased by a boiling temperature. 618. Other defects of Eartbenware Glaze. — ^If a piece of earthenware be broken, we may observe upon the freshly fractured edge, the thin coating of glaze which has been fused on to the body of the ware. K the tongue be touched to the broken surface, it will adhere, showing the porous and absorbent nature of the material. Now it often hap- BABTHSN AJSD FOBCBLAIN WABS. 323 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 uneqttally when heated and cooled, the consequence be- ing, that the glaze breaks or starts,, and the surface of the plate, sau- cer, or vessel, becomes covered with a network of cracks. Ware in such a condition is said to be crazed. Through these cracks liquid or- ganic matters are liable to be absorbed, which make the articles un- cleanly and impure. Glaze that does not crack is often too soft. To determine this, drop a small quantity of ink upon it, and dry before the fire, and then waah it thoroughly ; if the glaze be too soft, an in- delible brown stain will remain. 619. How Forcelaln-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 stiU known as China-ware. But, after long and difficult 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 haolin, or Ohina-olay, and the other an infusible but not plastic substance, called the flux, 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 famace, 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 hom-s. The articles are then withdrawn and dipped into a glaze composed of felspar, of the same nature as the fiux, 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 imiform 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 PHTSIOLOSICAL EFFECTS OF FOOD. adopted, the heat is estimated to run np to 21,000 degrees of the Fahrenheit scale. The color of porcelaiu is milk-white, without any tinge of blue. The qualities which ^ve it pre-eminence among tha clay wares, are the entu'e absence of porosity, the intimate union of the glaze with the mass, and the indestructibleness of the glazed sur- face under the knife, or when exposed to changes of temperature, and various chemical agencies. The production of the naked porcelain- ware in its present perfection, is one of the most signal triumphs of inventive ingenuity and perseverance, which the history of domestic improvement affords. But when we observe the beautiful and deli- cate colors with which porcelain is now ornamented, we are aston- ished at the resources of art. The paints or pigments with which ex- quisite pictures are made upon it, consist of colored glass, stained of various hues by metallic oxides. The coloring materials require to be fire-proof, as they are painted upon the ware, and then melted iuto the flux or glaze by the heat of the furnace. 620. Repairing broken Poicelain, — ^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 boUing slices of skim-milk cheese with water into a paste, and then grinding it with newly slaked lime in a mortar. White of egg will cause a quite strong adhesion, where the objects are not exposed to moisture. It is however improved by mixture with slaked lime. Shellac dis- solved 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 then* anxiety to unite the fragments strongly, per- sons are apt to defeat their purpose by applying the cement too thick- ly, whereas the least possible quantity should be used, so as to bring the edges most closely together. This may be aided by heating the fragments to be joined. TIL— PHYSIOLOGICAL EFFECTS OF FOOD. 1. Basis qf the Demahd tob Alimbnt. 621. Creation a Continnons Work. — ^We are accustomed to conceive of the creation of man as a dim miraculous event of the most ancient time, half-forgetting that God's scheme of managing the living world is one oi perpetual creation. Had our earth been formed of an eternal adamant, subject to no vicissitudes of change through aH the cycles of duration, we might perhaps well refer to the act of bringing it into existence, as especially illustrative of creative power. But where .ill BASIS OF THE DEMAND FOB ALIMENT. 325 is changing, transitory, and incessantly dissolving away, so that noth- ing remains immntable, 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. The 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. Our Systems capable of being nnderstood. — That it was tesigned 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 v/nderstand & thing; that is, to bring it into agreement with reason. The mechanism of the eye was a mystery, until its optical adaptations and purposes were discovered; that is, the reason of its construction. The heart was an object of mere curious wonder and superstitious speculation, until the circula- tion was discovered, when the reasonable uses of its parts were at once understood. The whole scope and drift of past inquiry, and all the considerations which cluster around the subject, lead us to expect and demand a rational explanation of living processes. "Not many years ago, the most acute and distinguished physioans 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 PHTSIOLOGICAL EBTECTS OP FOOD. food." Chemistry has dispelled these crude fancies, and enabled us to underatwnd 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. Deapbk 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 aU. 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 tiU 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 IlTing System a theatre «f ehangei — The body of the grovra man presenta to us the same unaltered aspect of forni and size, for long periods of time. With the exception of furrows deepening in the countenance, an adult man may seem hardly to alter for half a hundred years. But this appearance is altogether illusory ; for with apparent bodily identity, there has really been an active and rapid change, daily and nightly, hourly and momently, an incessant waste and renewal of all the corporeal parts. A waterfall is permanent, and may present the same aspect of identity, and unchangeableness from generation to generation ; but who does not know that it is certainly made up of particles in a state of swift transition ; the cataract is only a form resulting from the definite course which the changing particles pursue. The flame of a lamp presents to us for a long time the same appearance ; but its constancy of aspect is caused by a cease- less change in the place and condition of the chemical atoms which carry on combustion. Just so with man ; he appears an unchanged being endowed with permanent attributes of power and activity, but he is really only an unvarying form, whose constituent particles are for ever changing. As the roar, spray, and mechanical power of the falling water are due to changes among the aqueous particles; and the heat and light of the flame are due to changes among com- bustible atoms ; so man's endowments of bodily activity, susceptibility, and force, originate in atomic transformations taking place in his BASIS OP THE DEMAND FOE AUMBNT. 327 system. As each part is brought into action, its particles perish and are replaced by others ; and thns destruction and reiiovation in the vital economy are indissolnbly 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 profonnder truth ; we begin to die as soon as we begin to live. 624. Bate at wMeh the vital changes proceedi — But very few persons have any correct conception of the rate at which change goes on in their bodies. The average amount cf 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 2j- lbs. avoirdupois of dry food per day are required for each individual ; of this about three-quarters are vegetable and the rest animal. Assuming a standard of 140 lbs. as the weight of the body, the amount of oxygen consumed daily is nearly 2 J lbs., which results from breathing about 25 or 80 hogsheads of air ; the quantity of water is nearly 4j\r lbs. for the same time. The weight of the entire blood of a full-grown man varies from 20 to 30 pounds; of this, the lungs, in a state of health, contain about half a pound. The heart beats, on an average, 60 or 70 times in a minute. Every beat sends forward two ounces of the fluid. It rushes on, at the rate of 150 ft. in a minute, the whole blood passing through the lungs every two minutes and a hal^ 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. — (Johnstow.) 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. Ohambbes.) At the same time there escapes from the Inngs nearly 2 lbs. of ca/rbonio acid and li of watery va/por. The skin 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 -bs. ; 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 328 PHTSIOLOGICAIi EFFECTS OF FOOD. 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 UlDStration of these changes. — ^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 Paee, of England, lived to the age of 152 years. If we take the twelve years of his childhood, and double them over upon the succeeding twelve years of his youth, we shall have 140 years of adult hfe, 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 ai-e fifteen lbs. weight of air resting u^on 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. Paee, therefore, consumed all the oxygen over a surface of 236 square feet of ground to the very summit of the earth's atmos- phere, and generated noxious gases enough to contaminate and render unfit for breathing ten times that space, or poison a column of air 45 miles high, having a base of nearly 2,400 square feet. If we may indulge in a somewhat violent supposition that the whole blood which was actually driven through his heart during that long period could have been accumulated and measured as one mass, by forming a pro- cession of vehicles, each takipg a ton and occupying two rods of space, such a procession would have 'attained the enormous length of 2,000 mUes. 626. Relation between Waste and Supply. — Such is the ground of our daily requirement for food. The annual supply of 3,000 lbs. of mattei to the body is demanded, because in the yearly exercise of its powers and functions 3,000 lbs. of matter have been used up or spent. It cannot be maintained for a moment that the bodily system possesses any power of producing or creating a single particle of the matter which it uses ; it must receive every thing from without, and maintain its uniform condition of weight by striking an exact balance between waste and supply, receipt and expenditure. There are two periods in the natural life of man when the balance between these antagonizing forces is overturned ; in infamA;y, oldMhood and youth, the reception BASIS OF THE DEMAND TOE 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 bodUy weight gradually declines. In the intervening period -of adult life these antagonizing forces are maintained with but little variation in a state of constant equilibrium. In all the deepest recesses of the body, in every springing muscle, and conducting nerve and connecting tissue, and even the thinking brain, myriads of atoms are continually passing into the condition of death, while by the profoundest law of physiological life an exactly equal number are constantly introduced to replace them, each of its proper kind and in its appropriate place. 626. Practical Inference from these facts. — As thus the living being is the result and representative of change on a prodigious scale, the question of the course, rate, and regulation of those changes must be controlling and fundamental. Matter is introduced into the system in one condition and escapes from it in another ; the change (jneta/mor- phosia) that it has undergone is oxidation, or a true burning. The solid aliment is all combustible, oxygen is the agent which bums 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 temporaiily from the outward world to be quickly restored to it again. And as the supply of nutritive matter is effected through our own voluntary agency ; as we select, mingle and prepare the nutritive mate- rials, and control the times, frequency, quantity and condition in which they shall be taken, and influence their physiological results in num- berless ways, it is clear that our practice, whatever it may be, must exert a direct and powerful influence upon the whole being ; its states of feeling, conditions of action, health, and disease. It is desirable therefore to gain the fullest possible understanding of the subject. 627. Beneficent use of Hanger and Thirst. — ^It wiU be seen from the nature of the case, that the necessities of the system for matter from without, are pressing and momentous! If the inflowing tide of gases be arrested but for a few moments, suffocation and death 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, whUe the cost of nutritive matter is laborious struggle and exertion, both of body and mind. Now it is plain, that if in the plan of our being the bodily requirement for food were left to the determination of reason, the purposes of nature would 330 PHYSIOLOGICAL EFFECTS OF FOOD. be liable to continual defeat from indolence, carelessness or urgency of occupations. The Divine Architeet has therefore wisely intrenched in the system two monitors, hanger and thirsty which are independent of reason or wiD, cannot be dislodged while life lasts, and whose duty it is to proclaim that further nom-ishment is required for bodUy sup- port. And beside the sensations of hunger and thirst, imperative as they are, there is attached to their proper indulgence a degree of pleasure which never fails to insure attention to their demands. In what hunger and thirst consist, what state of the stomach or vessels produces them, or how the general nutritive wants of the sys- tem get expressed in feeling or sensation, we do not know ; several explanations have been offered upon this point, but they are all un- 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. Fie ST Stage of DiassTioN — Ohaitgbs of Food m the Moitth. 629. The great olyect of Digestion. — The prepared food upon our tables is in the form of crude, unmixed, and chiefly solid masses. Various vegetables, breads, meats, butter, each with its peculiar constituents and properties, are ready for use. Their physiological purpose is to make blood, the source upon which the whole system draws for what- ever it requires. The blood contains every thing necessary to form 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, while each part is endowed with the special power of withdrawing from the current as it passes along, just those particular constituents that it may require ; compounds of lime for bones and teeth, sulphurized compounds for the muscles, and phosphorized for the nerves, 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 with facility through the minutest vessels. Now, it is obvious that the food before us must be profoundly changed before it can be- come blood. No one element of diet contains all the necessary ma- DIGESTION — 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. Bedacing llccliaitism of the Month. — The food, liquefied or soft ened, or with its texture relaxed, loosened, or made spongy by culi- nary methods, is reduced to small pieces by table instruments,, and thus transferred to the mouth. An ingenious cutting and grinding mechanism here awaits it, to complete the mechanical operation of crushing and reducing. It consists of a double system of teeth, planted firmly in the jaws, and made to work against each other by a set of powerful muscles. The teeth are so shaped and placed '°' as to combine cutting, crushing and grinding, through vertical and side movements of the low- er jaw. The teeth are 82 in number, and their differences are illustrated by Fig. 118, which represents half the lower jaw. A shows two of the front or ... . . T. 11 J ■ . UlTistration of the different kinds of Teeth, cutting teeth, called tnoisors ; 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 licuspids or double-heaved, from their resemblance to a double-headed canine tooth ; and D the mola/rs, double-rooted, with broad, irregular, grinding surfaces.* 681. Conditions of the flow of Saliva. — Bat 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 ofSce of the saliva or spittle to commence this work. The saliva is separated from the blood and poured into the mouth by three pairs of glands (Fig. 114). The rate at which it is secreted varies at different times and under different circumstances. The sight, or even the thought of dinner may fill the mouth with it, while continued mental attention to other subjects, or a state of anxi- *" In Latin, cuspis signifles the point of a spear ; eania, dog ; mola, a mill ; ineUor anything which cats." 332 PHTSIOLOGIC'Al EFFECTS OF FOOD, Fia. 114. ety, will dry it np. The movements of the . mouth, as in speaking, reading, or singing, excite its flow, but it is most copiously furnished at times of eating, by the contact and pressure of food during masti- ■ cation. Hence, the glands on that side of the mouth which is most used in mastication, secrete more than the others. The nature of the food causes the quantity furnished at meals to vary exceedingly ; hard, dry ali- ments provoking a much greater dis- charge than those which are moist and soft. It streams out abundantly 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 larotid, » eubmaxil- contains also an organic principle lary, esu-biingaai. jj^med ptyalin, an albuminous sub- stance which acts as a strong ferment. The tartar which coUeots 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 be readily incorporated with the food by the teeth ; it also contains much lime. Submaxillary saliva is so thick and glutinous that it may be readily drawn out Into threads. It is supposed to facilitate swallowing by affording a sort of anti-friction coating to the masticated food. The sublingual saliva is more limpid, resembling the parotid. 633. Uses of Saliva^ — Saliva serves not only to moisten and lubri- cate the mouth, and wet the aliment, so that it may assume a pasty or pulpy condition, but it is an indispensable medium for the sense of taste, as every thing is tasteless which the saliva cannot dissolve. By its frothy quality it embroils globules of air, and thus serves to convey oxygen into the stomach, where it probably plays a part in promoting the transformations. . But beyond these important effects, the saliva actually begins the operation of digestion in the mouth. If a little Salivary glands; a pa lubl DIGESTION — CHANGES IN THE MOUTH. 333 pure starch be chewed for a, short time, it will become sweet ; a por- tion of it has midergone a chemical transformation, and been con- verted into sugar. By its joint alkaline and fermentative powers, saliva produces an almost instantaneous effect upon starch, changing it first into sugar, and in a Uttle 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 win 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 aQ in our food (382). We furthermore draw a practical inference opposed to the current opinion which assumes that animal food, from its tough, fibroas nature, needs more mastication than vegetable. Meat and albuminous substances require to 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 soUd 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 crade and iU-prepared, and the whole digestive function is just so far imperfect and enfeebled. It is of much consequence that meals should not be precipitated, but that proper time should be allowed to perform that portion of the digestive opera- tion, which falls so directly under voluntary control. Besides thought- lessness, and business pressure which pleads want of time, there is an- other cause of inattention to this matter which deserves notice. Many persons have placed themselves in such a false relation to nature, aa 334 PHTSIOLOGICAl EFFECTS OF FOOD. to imagine tiat they exalt the spiritual attributes of their being by casting contempt upon the physical. Such are inclined to regard the act of eating as a very animal and materializing operation, and any considerations of the way it should be conducted, ai-e apt to weigh but lightly upon their minds. This view is false, and leads to conse- quences practically mischievous. Dr. Oombb 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 refiect that even in eating, nature makes it our interest to give attention to the process in whic_i 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 suflicient admixture with the saliva — ^now deficient in quantity — and consequently lie on the stomach for hours unchanged. A certain degree of attention to taste and the pleasures of appetite is, therefore, both reasonable and bene- ficial ; and it is only when these are abused that we oppose the inten- tion of nature." 635. Effect of profuse Spitting. — ^The salivary juices are parts of a great water circulation of secretion and absorption. They are poured into the mouth, not to ie 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 effect which takes place in the reduced quantity of the urinal excretion, and an in- stinctive desire for water, a kind of perpetual thirst. It is probable that, under these disgusting circumstances, the percentage amount of saline substances in the saliva is increased, and that, so far as that WGESTION — CHANGES IN THE STOMACH. 335 class of bodies is concerned, the salivary glands act vicariouslj lor the kidneys, and the mouth is thns partially converted into t urinary aqueduct." — (Dr. Dbapee.) 3. Seooot) Stage or Digestion — Change of Food ht the Jtomaoh. 636. Flgnre and Dimensions of the Oigani — ^Having undere >ne more or less perfectly the changes which appertain to the mouth, the food Lsswallowed, and pass- Fio. lis. ing down the esophar gus, or gullet, enters the stomach. This or- gan is a pouch-shaped enlargement of the di- gestive tube, having the form shown in Kg. 115. The larger ex- tremity is situated at . the right side of the body, and its lesser end 4■4■'Un^aft■ TTiof TirtT Section of tliehmaanstomacli: a esopbagas ;& c cardiac at tne leiD. inatpor- orifice; (fe greater curvature ;/fl' lesser curvature; A tion where the esoph- »?'»"" '"^'=* ' *^ duodennm ; * bUe duct agus enters it, is termed the cardiac region (because it is in the vicin- ity of the Jeem- 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 will hold when moderately distended about three pints. As a general rule, it is larger among those who live upon coarse, bulky diet. In different animals the size of the stomach varies exceedingly, according to the concen- tration of the food upon which tley liv^. 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 intG an enormous cavity, or rather into several, as in the rimiinamitx, 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 musculap fibres or binds, one of which runs lengthways, and the other crossways. 336 PHTSIOLOGICAl EFFECTS OF FOOD. or around the organ. By means of these muscles the stomach may contract its dimensions in all directions, so as to adapt its capacity to the amount of its contents. They also give to the organ its constant motion during digestion. The third layer of the stomach (mucoits mem- hrane) lines its iaternal surface. It is a soft, velvet-like membrane, of a pale pink color, in health, aod of much gi'eater 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 tUe Stomacli' — 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. Maetbt, 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 ] eft to right. The bolus (swallowed mouthful), as it enters the cardiac, turns to the left, descends into the splenic extremity (large extremity near tlie spleeK), and foUows 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, li the food remains in the stomach three hours it travels round and round through this circuit two or three hundred times : — to what purpose ? 639. Mlnnte arrangements for Stomach Digestioii. — ^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- ^, onsly and admirably constructed, though it requires ^.y^S^^^^^ *^® microscope to see it. Magnified about 70 I^B^B^A diameters the mucous membrane exhibits the honey- ^B.^k^„A^^ combed appearance seen in Fig. 116. Into these ^B) reticulated spaces, there open little cup-shaped sHI cavities called stomach follicles, which are about '' 1-2Q0 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 Fio. IIT. like palisading, or like little flasks or test-tubes close packed and up- right ; many thousands of these upright cylindrical cavities being eet 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 ; a, from the middle re- gion of the stoniach ; J, from near the pylorus ; e d, the mouths opening upon the surface, e f, the closed tubes imbedded in the membrane below. The walls of these cavities are webbed over with a tissue of most dehoate 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 poeket-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 tubular roots, the seeds or germs of cells arise in immense numbers. Eeourring 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 until they are driven up in crowds into the hand or larger cavity, and hav- ing reached their ftill maturity, are pushed out at the surface, burst, and deliver their contents into the stomach. 641. The periodle 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 fiuid. During fasting, no ftdl-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 15 333 PHYSIOLOGICAL EFFECTS OP FOOD. that 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 Jnlcei — 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 excWded 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 Stomacli Digestion. — ^Recent physiological investigations have exploded the opinion long entertained, that the stomach is the exclusive or principal seat of digestive changes. In tracing the. properties of foods, we had occasion to divide them into two great classes based upon fundamental diflferences in chemical composition — the nitrogenous and the non-nitrogenous aliments. We find this dis- tinction recognized by nature in arranging her plan of digestion. So different are these two kinds of aliments that they require totally different agents to dissolve them, — nay, solvent fluids of entirely opposite characters. We have seen that digestion began in the mouth with an alkaline liquid, and took effect only upon the non-nitrogenoua principles. Upon proceeding to the stomach we flnd new conditions — an acid liquid replaces the alkaline — the changes that commenced in the mouth are partially or totally suspended, the non-nitrogenous com- DIGESTION — CHAifGES IN THE STOMACH. 33 S pounds remain unaltered, the gastric flnid taking effect only upon nitrogenous substances. 645. letlon 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 oxmce of water mixed with twelve drops of hydrochloric acid and one grain of pepsin, will completely dissolve the white of an egg in two hours at the temperature of the stomach (100°). It acts in the same manner on cheese, flesh, vegetable gluten, and the whole nitrogenous group, changing them to the Uquid form. These are the results of an arti- ficial gastric juice, but they are exactly the same m Mnd as those which take place in the stomach. Drs. Bidder and Sojeuidt, 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, th^ action proceeds about five times faster vyithin the body than without, but the nature of the results is iden- tical. 646. Wiiat is the Digestive Ferment Snlstance 7 — ^There has been much controversy about pepsin ; what is it ? A substance in the gastric fluid discovered by Schwas a few years ago, and supposed to be. a peculiar principle specially prepared for digestive purposes. It may be obtained from gastric juice, or by soaking the membrane of a calf's stomach (rennet). When proper means are taken to separate and dry it, it appears as a yellow gummy mass. Its potency for digestive pur- poses was proved by WASMANif, 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 due 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 celts ; and physiologists have discovered, that during digestion it separates oornpletely from the other layers of the 340 PHTSIOLOGICAI, EFFECTS OP FOOD. membrane. This epithelium, acted on by the oxygen swallowed in the frothy saliva, excites the digestive fermentation attributed to pepsin. It may be remarked that this stomach fermentation cannot change the starch of food into alcohol and carbonic acid, nor give i-ise to gases, although in morbid conditions of the organ other fermenta- tions may arise in the alimentary mass. 647. Gastrie Digestion something more than Solution. — ^It was formerly thought that digestion was simply solution, or change of alimentary matter to the liquid state ; but late investigations inform us that nu- tritive substances are more than dissolved, they are reaUy altered in properties. The nitrogenous matters are not only dissolved, but are so modified as to remain AissolveA. 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 gastrie digestion ; the digestive fluid dissolves albumen, fibrin, casein ; but as it cannot accompany them to maintain them in this state, it impresses upon them a stiU further change, by which they continue soluble. Casein in mOk, and liquid albumen are already dissolved when swaUowed ; 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 purpose in passing through it. The nitrogenous matters are not chemically altered, except perhaps by combining with water. 648. Action of Saliva in tbe Stomacli, — The alkaline saliva attacks the sugar and starch in the mouth, and has the power of rapidly changing the starch into sugar, and that into lactic acid. But the food tarries only a few moments in the mouth ; charged with its alka- line solvent, it descends into the acid region of the stomach. But acids and alkalies cannot get on together. , They either kill each other, or if one is the strongest or most abundant, it destroys the other though not without injury to itself. Hence, 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. Tet this does not occur instantaneously, as the food is swallowed. The effect of the gastric juice is superficial, acting at first upon the food where it comes in contact with the bedewed coats of the stomach, while the saliva, iuj 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, wiU generate the required substitute. 649. Quantity of Gastrle Jnlee 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- fitmction 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, Biddee 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. Getjhe- wAiDT has however quite recently had an opportunity of determining the quantity yielded by the hnman 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 v?ith 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. Bigestibiilty of FoodSi — ^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 ahmentary tract. Digestion is therefore an affair of many conditions, and itsVe- Bults 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 stomach, although of great importance, aflforda hut a partial view of the whole operation. Dr. Beaumont made an admirable series of observations upon this organ, and did much to advance the inquiry. Yet the value of his observations was diminished by the imperfect knowledge of his time, for we see him constantly misled by the conviction that there is but one digestive agent, the gastric juice, and but one digestion, that in the stomach. "We speak of his time, as if he might have lived long ago. Measuring the time by the course of investigation, he did live long ago. The history of science has a chronology of deeds, and marks off time by what has been accomplished. Dtifat, announcing the first laws of electricity, in 1737, stood much nearer Thales, of ancient Greece, rubbing his piece of amber, than to Prof Moese, patenting the electro- magnetic telegraph, in 1837. Within a quarter of a century, organic and animal chemistry have risen to the position of separate and in- dependent branches of science ; and it is hardly an exaggeration to say that more has been done to elucidate the subject of digestion in the 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. Eegarding digestion comprehensively, as the blood-forming function, we are to take into account not only the solubility of ali- ments, but their oonformability to the blood. If two substances are dissolved with equal ease, that wUl be the more digestible which has (the greatest similarity to some constituent of the blood. Gum, for example, is much more easUy 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" tibilify of foods is not the mere matter of the time of solution in the stomach that has been generally supposed, but involves much more. Meanwhile, Dr. Beattmont's statements of the periods which various alimentary substances require to break down into chyme in the stomach, may be serviceable, if received with due restrictions. We Bubjoin an abstract. i DIGESTION — CHANGES IN THE STOMACH. 343 MEAN TIMES OF CHTMIFICATION 'OF FOOD. Eice , Pi^'s feet, soused .... Tnpe, soused... Trout, salmon, fresh., Apples, sweet, mellow VeniBon, steak Amies, sour mellow. Cabbage wiui Tinegar Codfish, cured, dry Eggs,fresh Liver, beefs, fresh Milk ■ Tapioca Milk Turkey, wild " domesticated Potatoes, Irish Parsnips Pig, sucking Meat hashed with i 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 Com cake Dumpling, apple.. E^s, fresh Mutton, fresh Frflparatlon. Boiled. Boiled Boiled. . . . . Boiled Pried Eaw Broiled . . . Boiled Eaw Eaw Boiled. . . . . Eaw Broiled Boiled . . . . Boiled . . . . Eaw Boasted. .. Boiled Eoasted . . . Baked Boiled . . . . Eoasted . . .' "Warmed. . . Broiled. , . . Eoasted... Baked. Eaw Boiled .... Baked. Fricasseed. Eaw ' Eaw Broiled Eoasted... Broiled Baked Boiled..... Boiled soft. Broiled Boiled .... h. m, 1 — 1 — 1 — 1 80 1 80 1 80 185 1 45 2 — 2 — 2 — 2 — 2 — 2 15 2 18 2 80 2 SO 2 80 2 80 2 SO 2 80 2 80 2 45 2 45 2 60 2 55 3- 8 — 8 — Pork, recently salted. . Sonp, chicken Oysters, fresh Pork, recently salted . Pork steak Corn bread Mutton, fresh , Carrot, orange Sausage, fresh Beef, Iresh, lean, dry. . Bread, "wheat, fresh; . . Butter Cheese, old, strong Dggs, fresh Flounder, fresh Oysters, fresh Potatoes, Irish Soup, mutton " oyster Turnip, flat Beets Corn, ^een, & beans. . Beef, fresh, lean Fowls, domestic Teal, fresh Soup, beef, vegeta- ( bles, and bread t Salmon, salted Heart, animal Beef, old, hard, salted Pork, recently salted. Cabbage, with vinegar Ducks, wild .'. .. Pork, recently salted. Suet, mutton Teal, fresh Fork, fat and lean Suet, beef fresh. Tendon PrepRTation. Timo. h. m. Eaw 8 — Boiled.... 8 — Eoasted... 8 15 Broiled.... 8 15 BroUed.... 8 15 Baked..... S16 Eoasted... 8 15 Boiled .... 3 15 Broiled.... 8 20 Eoasted . . . S M) Baked 8 80 Melted.... 8 80 Eaw 8 80 Hardboil'd 8 80 Fried 8 80 Fried 8 30 Stewed... S 30 Boiled.... 3 30 Boiled.... 8 80 Boiled.... 3 80 Boiled.... 8 30 Boiled.... 8 45 Boiled .... 8 45 Fried 4 — Boiled.... 4 — Eoasted... 4 — Broiled... 4 — BoUed.... 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... 6 15 Boiled.... 5 80 Boiled.... 6 80 651. Absorption from tbe Stomaeb. — ^The power possessed by liquids and gases of penetrating and passing throngii 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 apertnre. 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. Tljis 844 PHTSIOLOGICAl EFFECTS OF FOOD. is proved by tlie fact that when the ontlet 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 circutnstances. In the same way portions of sugar, lactic acid and digested nitro- genous substances, which are dissolved in water, pass into the blood by absorption through the stomach veins. The contents of the stomach thus leave it in two directions, — a portion is absorbed through the coats of the organ, whUe the xmabsorbed matters gradually ooze through the valvular opening that leads into the intestine. 4. Thied stagb of Digestion — Changes of Food in thb Intestestes. 652. Digestive Jnlces of the Intestinal Tnlie. — The partially digested food dismissed from the stomach enters the duodemim, the first por- Fia. 118. Large mtestines CoBCnm AppeQdra of ,'■ CCBCUIB Spleen Cdloo SniBll inteatinei Digestive tract in man. Small istestiQeft DIGESTION — CHANQIS IN THE INTESHNKS, 345 tion of the intestinal tract (small mtestim). This is a tube about 20 feet in length, with a surface of some 3,500 square inches, and is the organ designed for finishing the digestive process. The general scheme of the digestive tract in man is exhibited in Fig. 118. Into the duodenum, and but a few inches from the valve of entrance, two small tubes (ducU) open, one leading from the liver and pouring in bile, and the other from the pancreas, yi&ldiag 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. 658. Changes in the Intestinal Passage. — We find that the alkaline digestion of the mouth is now resumed. The starch is attacked ener- getically and rapidly changed into sugar, and that to lactic acid. The oily substances hitherto untouched by the digestive agents are now acted upon, not perfectly dissolved like the other alimentary matter but reduced to the condition of an emulsion, its particles being verj 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 effect in some way not yet understood. As undigested albuminous matter is constantiy liable to escape through the pyloric gateway into the in- testines, it seems required that they should be capable, upon emer- gency, of completing the unfinished work, and such really appears to be the case. Although the secretions poured into the intestine are aU distinctiy alkaline, yet they convert sugar so actively into lactic acid, that the intestinal mass quickly becomes acidulous, — strongly so, as ii 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, whUe 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 tabes arising in the 15* 346 pirrsiOLOGioAL ebtects of food. intestinal coata. They were formerly supposed to be open at their ex- tremities, but they are now seen to present fine, blunt ends to the in- testinal cavity. How oily substances get entrance into these tubes is an old physiological puzzle. The membrane is moist, and water repels oil ; how then can it be imbibed ? Yet it constantly flows through. The thing is accomplished by the agency of cells, which are produced in vast numbers during lacteal absorption. These contain the oil, and bursting, deliver it to the absorbent vessels. The liquid which enters the laeteals is wbite, milk-like, and rich in oil. These veseels are gathered into knots (glands), so as to be greatly prolonged without consuming space. They finally gather into a tube {thoracic duct), and pour their contents into a large vein near the left shoulder. In its route, there is a disappearance of the large proportion of oil ; and albumen, which either entered from the intestine, or has afterwards transuded from the bloodvessels into the laeteals, is gradually changed to fibrin, the liquid acquiring the power of clotting or coag- ulating. 655. Constipating and Lasatire Foods. — The walls of the alimentary canal having absorbed from its contents such parts as are adapted for nourishment, there remains an undigested residue which passes at in- tervals from the bowels. The conditions of the intestines in reference to the retention or ready passage of excrementitious matters, is liable to variation from many causes. Amongst these, the nature of the food itself is influential. Some aliments have a relaxing effect, and others are of a binding nature, or tend to constipation, and they differ much in the degree in which these effects are produced. These re- sults are not, however, always due to specific active effects produced upon the bowels ; for some foods, as meats, eggs, 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 OP A LAXATIVE TENDENCY. Bread and cakes, from flue wheaten Wheaten bread and cakes from un» flour; rice, beans, peas, meate, eggs, tea, bolted flonr, rye bread, corn bread, raw Rlcobolic drinks. sngar, (from the molasses it contains,) frnits, raw and cooked, and generally substances abounding in ligneous matter,as skins, cores, husks, bran, &c. ITS FINAL DESTINATION. 347 5. Final Destination of Foods. 656. Digested alimentary matter enters the circulation and becomes bLOOD. This fluid is contained ia a system of vessels, which extends to aU 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 age, sex, constitution, and state of health ; it is also liable to acci- dental variations, as the supplies to it are periodic and fluctuating, while the di'aught upon it, though constant, is unsteady. It consists of about 78 per cent, water and 22 per cent, solid food dissolved in it. "When evaporated to dryness, the solid matter is found to consist of: Fibrin Albumen Gelatin 93 per cent. Fat, a little sugar, and a trace of starcli 2 " Saline matter, orasb 5T " 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, watery fluid, containing vast numbers of little floating cells or discs, which are the grand instruments of change in the sanguinary fluid. Their minuteness is amazing; fifty thousand would be required to cover the head of a small pin, while in a single drop of blood which would remain suspended upon the point of a fine needle, there must be as many as three millions. And yet each of these little bodies, which dwells down so low in the regions of tenuity that the unas- sisted eye cannot discover it, seems to be an ., ,„ •* ' Fi&. 119. independent individual, which runs a deflhite career, is born, grows, performs its oflSces, and dies like the most perfect being, though the phy- '**' ^^ ^^ffSi S Biologist tells us that twenty millions of them /a ^**^ Q perish at every beat of the pulse. Figs. 119 anc" "^ 120, from a work of Dr. Hassaxl, represent ^*' ^1^ difierent aspects of the blood discs, as seen under ©,# the microscope. The physiology of the blood v-J in its details is curious and most interesting, but „... we have no space to consider it here, and it is ^^^^ ^^ ^^^'^^ ^^^^^.^^ not necessary to the general view we propose showing their natural form . . j.ii_^i.i3 J.J.J J.X. an* appearance when to give of the final influence of food upon the brought faiiy into focus, system. 348 PHYSIOLOGICAL EFFECTS OF FOOD. 659. found purpose of the Hainan Body. — The living man is pre- Bented to our consideration as an engine of power — a being capable of producing effects. The bony framework within is broken into numer- ous pieces to admit of free motion. A complicated and extensive ap- paratus of contractile muscles is provided for me- chanical movement. The nervous system binds the whole into a co-operating unity, presided over by the brain, which not only regulates and' gov- erns the animal nature, but is the material seatoi intellectual power. Altogether, "the body dis- closes its supreme purpose to be the reception of impressions by the senses, and the development and expenditure of physical and mental force. But force cannot be produced out of nothing. The body cannot and does not create it. As there Blood discs, seen united is no evidence that in the course of events upon into rollfe, like adherent pieces of money. the earth, 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 different forms, but its total amount is thought to correspond with the total quantity and fixed properties of matter. Power is thus not literally generated in the body, but is developed or made active there by cer- tain definite causes. It is desirable to understand, as far as we may be able, the conditions of its production. 660. Food produced by tbe action 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 inclined to depart. These three substances constitute the chief nourishment of the ■vegetable kingdom. Through the roots, or by direct absorption from the air, they get admission into the vegetable leaf, the crucible of nature, where organized compounds originate. They are there decomposed and thrown into new arrange- ments, forming new compounds. Simple substances, those having few atoms, are destroyed, and the atoms built together into more complex substances, with greater numbers of atoms. The changes are from the lower to the higher, ascending, constructive. Now carbonic acid, water, and ammonia cannot separate and re-arrange themselves, nor can they be separated and re-arranged without an enormous expenditure of ITS FINAL DESTINATION. 349 power. Man witli his utmost skill cannot imitate the first step in tha 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 vpon. Carbonic acid is only decomposed in the leaf during the daytime by the power of light ; the effect is produced by solar radiations. A]] 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 aU 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 constitaents of blood are generated in plants, stored up in their seeds, which are the crowning results of vegetable life, and with the maturity of which, most plants employed by man, as food, perish. Aliments are thus composed of atoms that have been forced from a lower into a higher combination in plants, and in their new state they represent the 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 Foree. — ^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 EFFECTS OE FOOD, sisted in forcing carbon and liydrogen out of its grasp ; but in the ani- mal fabric it is destined to take possession of them again. The food, as we have seen, is not destroyed in digestion, it is only dissolved ; but in the blood and tissues it is destined to undergo a series of 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 deccmposition of ali- ment, under the influence of inspired oxygen, bodily force originates. We see 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 power are the oxidation of food and its products in the system. It is not from the mere introduction of aliment into the system that we obtain strength and nourishment, but from its destmetion. A portion of food, of course, serves to buUd up the bodily fabric, but it only continues in that state 'transiently; it is aU finally decomposed and dissevered into the simplest inorganic forms. 662. DestrnctiTe agency of Oxygen. — The body is buUt 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, be arrested, those parts instantaneously lose their power of action. The body of every animal is kept charged with this gas every instant of its active existence. If a man is aban- doned to the action of air, that is, if no other matter is taken into his sjatem, we 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 emacia,ted, yet the waste must proceed if life is to last. The brain is attacked, its oflBces disturbed, delirium supervenes, and there is an end of life. "We call this sta/rvatior?; it is a conditio m in which '• atmos- Dheric oxygen acts like a sword, which gradually but irresistibly pen- ITS FINAIi DESTIKATION. 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 fatal inroading effects of oxygen. 663. Combnstton witlilii the Body. — ^The term comlustion is com- monly applied to that rapid combination of oxygen with other ele- ments, by which a high heat is produced, accompanied with light. But the essence of the process is, not its rate, but the nature and di- rection of the changes. . It may go forwarc at 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 tliose in the stove. There is loss of oxygen, destruction of combustible matter, oxidized products (car- bonic acid and water), and the development of heat, in one case rapidly, in the other slowly ; in both cases, in proportion to the amount of matter changed. The destruction of aliment 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 allsaline 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 fi:om 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 852 PHYSIOLOGICAL EFFECTS OF 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. 665. NUrogcn Lowers the Com1>nsti1iility of Food. — Of all the elements of the animal body, nitrogen has the feeblest attraction for oxygen ; and what is still more remarkable, it deprives all combustible ele- ments with -which it combines, to a greater or less extent, of the power of combining with oxygen, or of undergoing combustion. Every one knows the extreme combustibility of phosphorus, and of hydrogen ; but by combining with nitrogen, they produce compounds entirely destitute of combustibility and inflammability under the usual ciroum- Btances. Phosphorus takes Are at the heat of the body ; while the phosphuret of nitrogen only ignites at a red heat, and in oxygen gas, but does not continue to burn. Ammonia, a compound of nitrogen, with hydrogen, contains 75 percent., 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 nil 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, ol ne- cessity, put an end to life." — (Liebig.) 666. Heat-prodaclng and Tissnc-maMng Foods. — In considering the final uses of foods, we are to preserve the distinction with which we began. The non-nitrogenous aliments, by their ready attraction for exygen, seem devoted to simple combustion in the system, with only uhe evolution of heat ; while the albuminous compounds are devoted PEODUCTION OF BODILY WAEMTH. 363 to the prodnotion of tissue. Tlie first class is hence called the Tieat- produeing, caloriftent, or respiratory aliments, while the second ia designated as the tissue-forming, plastic, or nutritime aliments (430). This distinction is to be received with dne limitation, for on the ona 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 LiBBia. 6. Peodttction of Bodht "Waemth. 667. Constant TemperatnTe 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, daUy with the appearance and disappearance of the sun, and annually with the course of the seasons. JV^e 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 ns to a variation of more than a hundred degrees, whOe 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 9^*. 668. How tie Body loses Heat. — ^In view of these facts, it has been maintained that the living body possesses some vital, myfete^ous, in- ternal defence against the influence of external agents; indeed, &at it is actually emancipated from their eflfects. 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 which is considerable when the air is in motion. This rapid carrying away of heat by air-currents, explains why it is that our sensations often indicate a more intense cold than the thermometer. But, lastly, the body loses heat faster by evapora- tion than in any other way. This takes place from the surface of the skin, and from the lungs. About 8i 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 prodnces Heat. — To keep the system up to the standard point, notwithstanding this rapid and constant loss, there must be an active and unremitting source within. Heat-force cannot be created out of nothing; it must have a definite and adequate cause. PRODUCTION OF BODILY WAEMTH. 355 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 distiuctive 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 bum 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 iu the air, this change is accompanied by a disengagement of heat and light, 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 wotdd 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 stiU. 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 lireatbtiig ratified Air. — ^The doctrine, that animal heat is due to oxidation in the system, is strikingly Ulnstrated by what migh 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 bum on such mountain tops ; the air is 356 tHTSIOLOSICAIi EPPBCTS OF FOOD. too thia and rare to support them ; and so these oombustione which go on at a measured rate in the interior of the body, are greatly re- duced in intensity, and leave a sense of penetrating cold. Such jour- neys, moreover, illustrate how completely the action of the muscular system, and also of the brain, is dependent on the introduction of air and under the opposite condition of things, where men descend in diving-bells, though surrounded by the chilly inflneiices of the water, they experience no corresponding sensation of cold, because they are breathing a compressed and condensed atmosphere. — (Dr. Deapbe.) 671. How the nneqnal demands for Heat are 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. Liebi& states their relative values, or power of keeping the body at the same temperature during equal times, as follows : To produce the same effect as 100 parts of fat, 240 of starch will be required, 249 of cane sugar, 263 of 3ry grape sugar and milt sugar, and 770 of fresh lean flesh. We shall illustrate this point mora clearly, when we come to speak of the nutritive value of foods (743). A pound of fat thus goes as far in heating as 2f lbs. of starch, or 7^ lbs. of muscular flesh. In regions of severe cold, men instinctively resort to food rich in fatty matters, as the blubber and train oil, which are the staples of polar diet. Bread, which consists of starch and gluten, and which, therefore, as shown by the above Ulustration, falls far be- low oleaginous matter in calorifying power, is found to be very insuflS- eient in the arctic regions for the maintenance of animal heat PEODUCTION OF BODILT WAEMTH. Sii'l All breads are, however, not alike in this respect, for the Hudson's Bay Traders have found, according to Sir John Biohabdsok, 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 net relish a slice of ra* blubber, or a chunk of frozen walrus beef. The hver 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 ahrost inevitable, from the modes of living of the people, walrus holds the first rank. Cei"tainly, its finely condensed tissue, and delicately permeating fat — oh ! 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 abimdance, 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. 673. Begalatton of Bodily TempeTatiiTe> — ^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 Ihnit 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. During the heat of 358 PHYSIOLOGICAL EFFECTS OF FOOD. Bummer, much water evaporates from the 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 stoves 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. 673. Honses 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 b^temperate in warm climates, or to bear hunger for a long time under the equator ; but cold and hunger united very soon produce exhaustion. A starving man is soon frozen to death." 674. Times of Life when Cold is most fatal. — The potent influence of temperature upon life must, of course, be most strikingly manifested where there is least capability of resistance — ^in infancy and old age. During the first months of infant life the external temperature has a very marked influence. It was found in Brussels that the average infant mortality of the three summer months being 80, that of January is nearly 140, and the average of February and March 125. As the constitution attains vigor of development, the influence of seasons upon mortality becomes less apparent, so that at the age of from 25 to 30 years, the diflference between the summer and winter mortality IS very slight. Yet this difference reappears at a later period in a marked degree. As age advances, the power of producing heat de- fines, old people draw near the fire and complain that ' theii- blood is PKODUCnON OF BODILY WAEMTH. 359 i^iiU.' The Brussels statistics show iiiat the mortality uetween 50 and 65 is nearly as great as in early infancy ; and it gradually becomes more striking until at the age of 90 and upwards the deaths in Jan- 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 daily changes of Temperatiire. — 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 more prompt and decided as the heat-producing function is more and more depressed. As the system is unequally acted upon by the daily assaults of cold, it becomes necessary to make provision against the periods of severest pressure. In the ever admirable arrangements of Providence, the diurnal time of lowest temperature is made to coincide with the time of darkness, when animals resort to their various shelters to rest and recruit, and are there most perfectly protected from cold. Dr. Deapbs 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 hind, but also the time. It seems to be against our instinct to commence the morning with a heavy meal. We Ireak fait, 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 faH 360 PHTSIOLOGICAIi EFFECTS OF FOOD. of temperature attending on the maxima and minima of daily heat. The light breakfast has a preparatory reference to noonday, the solid dinner to m.idnight." Y. Peoduotion OF Bodily SiEENaTH. 676. Amonnt of meebanical 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. SuflBoient 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 effects which present themselves to us in a twofold aspect ; those which are involuntary, constant, and connected with the maintenance of life, and the volun- tary movements which we execute under the direction of the will, for multiplied purposes and in numberless forms. That which produces movement is force, and there can be no movement without an adequate force to impel it. If a load of produce or merchandise is to be trans- ported from one place to another, we all understand that force must be applied to do it. And so with the human body ; not a particle of any of its flowing streams can change place, nor a muscle contract to lift the hand or utter a sound, except by the application of force. We may form an idea of the amount generated to maintain the invol- untary motions essential to life, by recalling for a moment their num- ber and extent. We make about nine millions of separate motions of breathing, introducing and expelling seven hxmdred thousand gallons of air in the course of a year. At the same time the heart contracts and dilates forty millions of times — each time with an estimated force of 13 lbs., 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 forms 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 Ms body through 10,000 feet in a day. Smbaton states, that working with his arms he can produce an effect equal to PEODUanON OB" BODILY STEBN6TH. 361 raising 370 lbs. ten feet high, or 3,700 lbs. one foot high in a minute for eight hours in the day. 677. Tlssnes destroyed In prodadng Forte. — ^The expenditure of force in labor, if not accompanied by a sufficiency of food, rapidly wears down the system, — there is a loss of matter proportioned to the amount of exertion, and which can only be renewed by a correspond- ing quantity of nourishment. The parts brought into action during exercise are of course those possessing tenacity, firmness, and strength ; that is, the tissues and organized structures. The unorganized parts, such as water and fat, which are without texture, have no vital pro- perties, and cannot change their place or relative position by any in- herent capability. It is the bodily tissues that are called into action, and these undergo decomposition or metamorphosis in the exact ratio of their active exercise. We have stated that the motions within the system are numerous and constant. If we look on a man externally, he is never wholly at rest ; even in sleep there is scarcely an organ which is not in movement or the seat of 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. Ohossat ascertained the waste in various animals to be an average of l-24th part of their total weight daily ; and Schmidt deter- mined it to be, in the case of the human being, l-23d of the weight. Professor JoEtrsTON 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 da/ys. 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. Albumen is the universal starting point of animal nutri- tion j it is the liquid 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 PHTSIOLOGICAl EFFECTS OF FOOD. the porous shell, under the influence therefore^ of the same oonditiona ■which accompany respiration, all the tissues, membranes and hones, (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 eombustibility, 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 tie Tissnes. — Oxygen plays the same im- portant part in tissue destruction as in the simple development of heat by combustion of respiratory food. It is the agent by which the moving parts are decomposed and disintegrated. The muscles are paralyzed if the supply of arterial blood containing the oxygen which is to change them, and the nutritive matter which is to renew them, be cut ofi". 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 I'ise to mechanical force. But oxidation is invariably a cause of heat ; decomposition of the tissues, therefore, must develop heat at the same time with me- chanical effect. Indeed, violent muscular exercise is often resorted to in winter as a source of bodily warmth, by increasing the respirations and muscular waste. In this subordinate way, the nitrogenous ali- ments become heat-producers. It is not to be supposed that oxygen seizes upon aU the atoms of tissue indiscriminately, or upon those which it iinds next before it. There is a wonderful selective power, some particles are taken and others left. Those only are seized upon which in some unknown way, perhaps under the regulating influence of the nervous system, are made ready for change. 680. Relation between Waste and Snpply. — ^If an organ or part be the PEODUCnOK OF BODBLT STEENGTH. 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 nutrition. That portion of the mechanism which is independent of voluntary control, is thus self-sustaining. StUl, in the case of these parts, the equipoise between waste and supply may be lost, as in bodily growth when nutrition exceeds decomposition, or in deficiency of nutriment, when destruction proceeds at the expense of the tissue, which loses weight faster than the food renews it. As re- gards the waste and renovation attending voluntary movement, there is the same periodicity. Destruction gains upon nutrition during the exercise of the day, and what was lost is regained by nutrition during rest at night. In sleep, nutrition is at its height while waste falls to its minimum. As bodily exertion costs tissue destruction, which can only be made good again by albuminous substances, it follows that these will be demanded for food, in proportion to the amount of eflFort 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 faU, for human effoil; is cwmiBorovs, 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 tissue cbangesi — ^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 check it. Common salt, for example, and an excess of water, act as hctsteners of tissue change, while alcohol and tea act' as (wreatera 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 PHTSIOLOGICAIi EFFECTS OF FOOD. clines in weight with more rapidity than otherwise. If we employ the arresters of metamorphosis, we a,re supposed to have tissue, and can maintain our usual strength and weight on a more slender diet. That certain substances produce these effects, may he regarded as establish- ed, but it cannot be admitted that they are proper aliments. We re- cognize transformation of the living parts,. as the highest and final physiological fact, the necessary condition of human activity. Dr. Ohambees remarks — " Metamorphosis is life, or an inseparable part of life." Undoubtedly the rates of bodily change are liable to certain variations, within limits of health ; but the whole import •of the vital economy, leads us to connect accelerated and retarded changes with variations in the exercise of force, by a fixed organic ordinance. With high activity, a rapid change, and with rest, a minimum of loss is evi- dently nature's purpose, and her law. Substances introduced into the system, which act upon the tissues, as it were from without, and in- terfere with this fundamental relation between rate of exertion and rate of change, can be regarded in no other light than as disturbers of physiological harmony. Still, we are to be cautions about theoretically prejudging any substance ; whether it be beneficial or injm'ious is as- certainable only by careful observation and experience of its effects. 8. Mind, Body, and Aximent. 682. lITiad brongM into relation mth 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 lie 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- controlKng activity of the universe, so the mind of man, created in his Maker's image, is perpetually demonstrating an over-mastering con- trol of tiie 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. 688. STental Exereise destroys Nenons Matter. — Of the nature of this men), BODY, AlifD AUMENT, 365 union, Jimo 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 ther« 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 untU the dis- organization of other parts is far advanced. The mind's throne is the last part invaded, and the last to be overturned. We are struck with the wisdom of this arrangement, but we cannot explain it. 684. Can we measnie Brain and Iferve waste 1 — ^The appropriation of certain specific parts to certain purposes, is the basal fact of physiolo- gy. A part may indeed perform several offices, but they are determi- nate and limited, and the different portions cannot change duties ; the stomach cannot respire, nor the lungs digest, the mind cannot act di- rectly upon the muscular system (only through the intermedium of the nerves), nor can the nerves exert mechanical force. Each part, therefore, does its appropriate work ; and as it has a special composi- tion, its metamorphosis gives rise to peculiar products. Muscular de- 366 PHYSIOLOGICAL EFFECTS OF FOOD. composition must hence yield one set of substances, and nerve-waste another. It has been attempted to identify these products, and thus get indications of the amount of change in each part, as a measure of the degree of ita 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 *he same way, salts of phosphoric acid have been regarded as the peotdiar products of brain and nerve waste, and their amount in the kidney evacuations, as a measure of the exercise of brain and nerves. From the researches of Dr. Bbnse Jones, it appeared that where there is a periodical demand iipon 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. Tet here, too, there is uncertainty, for we are not sure that these phosphatio salts may not have other sources also. 685. The Mind's action wears and exhausts tbe 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 the sensation of hunger, that is, prevent its being felt, but after a time the appetite returns with augmented force. In sleep, the mechanism of sense, consciousness, volition, and passion, is at rest, and unhindered nutrition makes up for the losses of the waking hours. If the brain be overworked, either by long and harassing anxiety, or by severe and continued study, it may give way ; that is, its nutrition takes place 80 imperfectly as to produce morbid and unsound tissue, which can only be restored to the healthy state by long mental tranquillity and cessation of effort. 686. The Phosphatlc eonstitnents of Brain. — We have spoken of the phosphates as special products of brain and nerve waste. That phos- MIND, BODY, AND ALIMENT. 36') pliorns, 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 tliose 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, *nd 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 the active to the passive form. It has been main- tained that in the leaf and by the sun, elementary phosphorus is sepa- rated from its 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'Hbeitiee's analysis of nervous mat- ter (quoted by standard physiological authorities), it is stated that the proportion of phosphoi-us in infants is 0'80 parts per 1,000, in youths' 1-65 (more than double), in adults 1'80, in aged persons 1-00, and in idiots 0'85, thus apparently connecting the quantity of this substance in the brain with maturity and vigor of mental exercise. From this point of view Dr. Moleshott leaps at once to the conclusion, ' no phosphorus, no thought;' Liebi&, however, denies point-blanc that elementary phosphorus has ever been found in nervous matter. He says, " no evidence is known to science tending to prove that the food of man contains phosphorus, as such, in a form analogous to that in which sulphur occurs in it. N"o one has ever yet detected phosphorus in any part of the body, of the brain, or of the food, in any other form than that of phosphoric acid." As phosphorus and phosphoric acid, in their properties, are as wide asunder as the poles of the earth, it is highly incorrect to use the terms interchangeably, or (according to the statement of Liebig) to apply the term phosphorus in this con- nection. It may be remarked that the phosphoric compound is a con- stituent of the oily matters of nerve tissue, which are hence called 'phosphorized fats.' 687. ire there speelai Brain Ifnlrlments. — 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 PHTSIOLOaiCAIi EPE^ECTS OF FOOD. Bpecially or pectdiarly constructed to protnote brain nutrition and pro- tract mental exercise. But while it would seem as if care had been taken to secure these high results in the universal constitution of food, still it is certainly in accordance with analogy, that specific aliments should be adapted, or at all events iest adapted, to produce certain kinds of effect in the system. Special means for special ends make up the unitary scheme of the living economy. The waste prodnced by mental exertion is repaired only by food, but to say by all food alike transcends the warrant of science. Professor Liebi& remarks, " It is certain that three men, one of whom has had a fuU meal of beef and bread, the second cheese or salt fish, and the thii-d potatoes, regard a difficulty which presents itself frora entirely different points of view. The effect of the different articles of food on the brain and nervous system is different, ac6ording 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 cami- 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 unimportant, and should be carefully conformed to their peculiar cir- cumstances. They should avoid the mistake of supposing that, as they do not work physically, it is no matter how slight their diet, and the perhaps still more frequent en'or, 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. rtTFLTIENCE OF SPECIAL SXTBSTAITCES. 369 689. Hen seek for Brain ExcitantBi — ^Although specific brain nutri- ents and though t-sustainers are not determined among foods, yet sub- stances exerting a powerful influence through the brain upon the mind, are but too well known. By a kind of ubiquitous instinct, men have ransacked nature in quest of agents which are capable of influencing their mental and emotive states, and they have found them every where. It is estimated that the peculiar narcotic resin of Indian hemp (haachish), 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 otnarcotism; 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 efiects of tea and coflee will be noticed when speaking of drinks (704). 9. iNTLIIBIfOE OF SPBOIAL SUBSTANOES. A, — Saline matters. 690. The Ash elements of Food essential to Life. — ^When vegetable sub- stances are burned, there remains a small portipn of incombustible mineral matter. It was formerly thought that this consisted merely of contaminations from the soil, which happened to be dissolved by water that entered the roots, and was therefore present in the vegeta- ble by accident. We now understand that such is far from being the fact. The ash-principles of food are indispensable to animal life. In- deed, without them neither group of the alimentary substances which we have been considering could do its work. It has been found, in numerous experiments, made upon the lower animals, that neither gluten, casein, albumen, sugar, oil, nor even a mixture of these, when "deprived as far as possible of their mineral ingredients, are capable of sustaining life ; the animal thus fed actually perishes of starvation. 691. Acids, Alkalies, Salts.— We remember that aeids are bodies hav- ing the power of tummg blue test paper red, and that alkalies change the red to blue. They also combine together, each losing its peculiar properties, ajid produce salU. If the properties of the acid and alkali both disappear, the salt produced is neutral, that is, neither acid nor 16* 370 PHYSIOLOGICAL EFFECTS OF FOOD. alkaline. If the acid be stronger, or there be a donble or treble dos« of it combining with the alkali, the compound is still acid, an acid salt; or if the alkali be strongest or in excess, it overpowers the acid and an 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 aU the effects of acidity ; if an alkaline salt, the liquid will be alkaline, producing alkar line effects. The ash of foods consists of potash, soda, lime, magnesia, oxide of iron, sulphuric, carbonic and phosphoric acids, silica and com- mon salt. Fruits abound in acid salts, that is, powerful organic acids, as oxalic, tartaric, and malic acids, with potash and lime ; the acids be- ing in excess. When fruits are burned, the organic acids are consumed or converted into carbonic acid, and the salts become carbonates — neu- tral carbonates of lime or alkaline carbonates of potash. The quanti- ties of salts, alkalies, and alkaline earths contained 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 constarttly withdrawn from the circulation, some at one point and same at others, to contribute to special local nutrition. Thus phosphate of lime is selected to promote the growth of bones, while the muscles withdraw the phosphates of magnesia and potash ; the cartilages appropriate soda in preference to potash ; silica is se- lected by the hair, skin, and nails ; while iron is attracted to the red coloring matter of the blood, and the black colormg matter within the eye. 693. The Blood Alkaline, and why 1 — But there remains constantly dissolved in the blood and animal juices, a proportion of acids, al- kalies, and salts, which impart to these liquids either acid or alkaline properties. The result, however, is not left to accident. Whether a liquid be acid or alkaline is of essential importance in refer- ence to the offices it has to perform. We have seen that it is the determining fact of the digestive juices ; one is always acid, and the other alkaline, and their peculiar powers depend .upon these properties. So with the blood. It contains potash, soda, lime, mag- nnPLUENCE OF SPECIAL SUBSTANCES. 371 nesia, oxide of iron, phosphoric acid, and common salt ; yet these are BO proportioned that soda is in excess, and hence the Wood of aU animals is invariahly alkaline. An alkaline condition is indispensahle to the action of this fluid. Liebig remarks, " The free alkali gives to the hlood a numher of Tery remarkahje 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." AlkaU 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. — (Chevbettl.) The alkalies of the blood exert a precisely similar action, increasing the combustibility of the respiratory foods. 694. Flesh and its Jniees, Add. — ^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 the System. — The properties of commercial or common salt, have been noticed when speaking of its preservative powers (§90). We may now consider its action in the system. It is 3'?2 PHYSIOLOGICAL EFFECTS OP FOOD. a larg^ 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 the solid tissues, except the cartilages. Its offices in the system are of the first importance. It increases the so- lubility of albuminous matters. Dissolved in the liquids of the ali- mentary canal, it carries with it their important principles, preserves them fluid through the chyle and blood, then parting from them 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 ©ifected 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 eoonony 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 different, that while chloride of sodium exists largely in the Wood, 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 he 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 we obtain it both in the solid food we consume and in the water we drink, though not always in quantity sufficient for the demands of the system. Yet the proportion we obtain in food is variable, animal diet containing more than vegetable ; though the parts which most abound in this ingredient, — ^the blood and carti- lages — are not commonly used for food. Of vegetable foods, seeds ^iontain the least amount of common salt, roots vary in their quantity, INBTiTmNCE OF SPECIAI, SUBStANCES, 373 tnmips 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 suflBcient is furnished naturally in the food and drink, or that animals suffer for the want of it. The quantity annually consumed by each individual in France, has been estimated at 19^ lbs ; in England at 22 lbs. 697. Effects of too little and too much Salt. — ^From what has been said, we see that a due supply of salt is of the first necessity ; its de- ficiency in diet can only prove injurious. The most distressing symp- toms, ending in death, are stated as the consequence of the protracted use of saltless food. The ancient laws of Holland " ordained men to be kept on bread alone, unmixed with salt, as the severest punish- ment that could be inflicted upon them in their moist climate ; the effect was horrible ; — these wretched criminals are said to have been devoured by worms engendered in their own stomachs." Taken into the system in large quantity (a table spoonful), it excites vomiting ; when thrown into the large intestines, it purges. A too free use of salt engenders thirst ; in moderate quantities, it increases the appetite and aids digestion. - A long course of diet on provisions exclusively salt-preserved, produces the disease called scurvy. This condition of body is ielieved 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 anUseorhutics — correctives of scurvy. Fresh flesh yieldr potash to the system unequally ; for in that of the ox, there is three times, in that of the fowl, four times, and in that of the pike, five times as much potash as soda. Experiments relating to the influence of com- mon salt upon animals, have given somewhat discordant results. In some cases, it improved their appearance and condition decidedly ; while in others, no such result followed. Yet the amount supplied naturally in the food, in the several instances, was not determined. Salt is supposed to be in some way closely allied to the nutritive changes, and some think it increases the metamoi-phosis of the body ; so that a free use of it would only be consistent with a liberal diet. 374 PHYSIOLOGICAL EFFECTS OF FOOD. 698. Cartonates of Soda and Potash. — The exclusive employment of these substances in extemporising light bread (509), makes a reference to their physiological action necessary. Carbonate of potash in its crude shape, appears aspewrlash; in its more purified form it is saleratus. Crude soda is known as sal-soda or soda-saleratus ; refined and cleared of its chief impurities, it forms carbonate and bicarbonate of soda. All these compounds have the common alkaline or burning property, which belongs to free potash and soda; lut it is lowered or weakened Dy the carbonic acid united with them. The potash compounds are the strongest, those of soda being of the same nature but weaker. Yet the system, as we have just seen, recognizes essential difierenoes be- tween them ; one pertains to the blood and the other to the fiesh. According to the theory of their general use for raising bread, they ought to be neutralized by an acid, muriatic, tartaric, acetic, or lactic, thus losing their peculiar properties and becoming salts. These changes do take place to a certain extent, and the saline compounds formed, are much less powerful and noxious than the unneutraUzed alkalies ; their efiects are moderately laxative. Yet, in the 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 powerful corrosive poisOn ; disorganizing the stomach, and dissolving its way through its coats, quicker, perhaps, than any other poisonous agent. When the alkalies are taken in small quantities, as where there is an excess in bread, they disturb healthy digestion in the stomach, by neutralizing its necessary acids (643). They are sometimes found agreeable as palliatives, where there is undue acidity of the stomach ; and, on the other hand, they may be of service in the digestion and absorption of fatty substances. It is alleged that their continued use tends to reduce the proportion of tho fibrin in the blood. Cases are stated, where families have been poisoned by the excessive employment of saleratus. B.— I.lq.uld AUmentSa 699. Physiological importance of Water. — ^Wateris the most abundant compound in the body, constituting 80 per cent, of the blood, and 75 per cent, of the whole system, — in importance to life it ranks next to oxygen of respiration. An adult 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 aliments (366). It is the simple and Tmiversal beverage furnished by nature, for bU living beings, and exists in greater or less proportion, as we have nnFLUENCB OF SPECIAL SDBSTASCES. 375 Been, in all solid food. VegetaTjlea 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 consmnption 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 '.s 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 sUky 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 small de- gree, in the animal kingdom. Plants decompose it, and use its ele- ments to form their peculiar compounds. The animal possesses this ■ power in but a limited way, if at all ; on the contrary, it is one of its leading offices to combine the elements which the plant separated, and thoa 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. Inflnenee of Water upon Digestion. — We have referred to the remarkable solvent powers of water (367). If we could look into the living organism, we should see that its whole scheme is but an illus- tration of it. Blood, juice of flesh, bile, gastric and pancreatic fluid, saliva, mucus, tears, perspiration, and all other peculiar 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 effect of taking liquids is of course to dilute the bodily fluids, just in proportion to the amount 376 PHYSIOLOGICAL KFFECTS OF FOOD. taken. The first effect will be a dUntion of the gastric juice of the stomach, but the water is rapidly absorbed into the Wood, which ia thus made thinner. It has been taught that the effect of swallowing much liquid during meals is to lower the digestive power by diluting and weakening the gastric juice. This is, however, denied by high authority. We know that excessive eating is usually accompanied by a copious 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. Ohambees, of London, asserts that, " A moderate meal is certainly easier digested when diluents are taken with it." Again he remarks, " Aqueous fluids in large quan- tities during meals, burden the stomach with an extra bulk of matter, and, therefore, often cause pain and discomfort, but that they retard digestion I do not believe. Indeed, among . the sufferers from gastric derangements of all kinds, cases frequently occur of those who cannot digest at aU without a much more fluid diet than is usual among heal- thy persons.'' 703. Water inflnences change of Tissne. — ^Beyond digestion is meta- morphosis of structure, and this is influenced by the amount of watei drank. Eecent careful experiments by Dr. Bookee, 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 longei restore it — the balance inclined on the destructive side. Neither tht pulse nor respiration were affected, but there was more languor aftei exercise, while the sensation of hunger kept pace with the increased metamorphosis of matter. 704. Tea and Coffee. — These are t^en 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 peculiar action are thein and cafein, taimlc acid and volatile or erapyreumatic oil. INS'LUBJSrCE OF SPBCLAI, SUBSTANCES. 371 705. Effects of Tea. — Though tea is so imiversally 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 oU of tea are its most active ingredients, producing, perhaps jointly, its characteristic effects upon the nervous system. It is acknowledged that tea is a brain excitant, that it influences the mind, and produces exhilaration and wakefulness. How it effects the men- tal faculties, observers have been unable to decide, judging by their discrepant statements. If the quantity af 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. Bockeb 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 inveistigations lead to the conclusion,^**, 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 insufficient, tea limits the loss of weight thereby entailed ; third, when the diet is sufficient, the body is more likely to gain weight when tea is taken than when not ; fourth, tea diminishes the loss of substance in the shape of urea, lessens the solid excretions, and limits the loss by perspiration. It is thus claimed that this beverage is an enlivener of the mind, a soother of the body, and a lessener of the waste of the system. 706. Influence of Coffee in Digestion. — The active ingredients of cof- fee are cafein, which is identical in properties with thein of tea, and the peculiar empyreumatic or burnt oil produced in roasting. " By the presence of empyreumatic substances, roasted coffee acquires the property of checking those processes of solution and decomposition which are begun and kept up by ferments. We know that all em- pyreumatic bodies oppose fermentation and putrefaction, and that, for example, smoked fleSh is less digestible than that which is merely salted. Persons of weak or sensitive organs wUl 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- 3?8 PHYSIOLOGICAL EFFECTS OF FOOD. fioiently delicate reagents to detect such effects, coffee after eating serves from the same cause to moderate the activity of the stomach, exalted beyond a certain limit by wine and spices. Tea has not the same power of checking digestion ; on the contrary, it increases the peristaltic motions of the intestines, and this is sometimes shown in producing nausea, especially when strong tea is taken by a fasting person" — (Libbio.) TOY. Lebman on the inflnenee of Coffee.— We are indebted also to Pro- fessor Lehman for valuable experiments to ascertain the effects of cof- fee. He states that coffee produces two leading effects upon the gen- eral system, which it seems difficult to associate together, viz : height- ening vascular and nervous activity, and at the 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, congestipns, 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." Y08. Chocolate is allied to tea and coffee by its nitrogenous princi- ple (theobromin), but the effect of this substance seems to be 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. ilcobolic Liquors. — The common and active principle of spirit- ous liquors is aUoTiol, obtained from sugar by fermentation. -It varies in proportion in the different sorts from 1 to 60 or 60 per cent. Liquors contain various accompanying substances, traces of albumen, sugar, acids, volatile oUs, 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 alcohohc liquors 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 the sys- tem. Yet it is the alcoholic principle found in all these mixtures that INFLUENCB OF SPECIA.L SUBSTANCBS. 379 gives them life, and a common character, and groups them all together under the common title of mtmcaim^. liquors. 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 with favor upon its general use. 710. They eannot replace Water In the Sjstenii — ^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 th« reverse. Alcohol mbced 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 tannot nourish 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 giyes rise to heat in the system, but so do other agents, whose claim to the charac- ter of foods would be on their fece 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 Liebig's scale of respirants (743), it win be seen that the strongest spirits drank are inferior, pound for pound, to starch and sugar, and not nearly half so valuable aa oily substances for a heat generator. Tet 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. 718. Dr. Boeker'8 Observations. — This gentleman tested the effects of alcohol in small quantities upon his own person, in a course of skilfully 380 PHTSIOLOGICAl EFFECTS OF FOOD, conducted experiments. He 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 the 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 nse 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. Chambees justly remarks, " This is going rather too far. When alcohol limits 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 insufficient food), at the ettpense of his iody, 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 be always re- newed, because, for want of means, he cannot take it up; he con- sumes his capital instead of his interest, and the result is the ineeita- lie hanhruptcy of his body." 715. Stimulating effect of the Beverages. — They produce general stim- ulation; the heart's action is increased, the 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 »ided to pour out a more copious solvent, which promotes digestion, or If it INFLUENCE 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 conferring 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 0L: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 suffeiing and soitow, — ^for nature always vindicates herself at last.* 716. 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 mUk, or asses' milk, and for this reason often disagrees with delicate stomachs. By aMm- ming, however, cow's mUk is made to approach human milk in quality. It still,'however, contains nearly all the cheese, the sugar of mUk, the salts, and some butter. It is therefore scarcely less nutriUoits than new mUk, 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 stimnlus or excitement. It is also recommended as a good diet for children, especially in scrofulous complaints. 717. Properties and effects of Sonps. — The soluble extract of various animal and vegetable substances, obtained by boiling or steeping, forms * " When, by habit, the Btimnlant has become a necessity, an enervating relaxation in- fallibly fellows, as sometimes mournfully illnstrated 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, untli 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 PHTSIOLOGICAIi EFFECTS OP FOOD. soups. They are made from a great number of materials, and thoif effects, of course, 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 Boups, 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, &o. It is an exclusive animal pro- duct, and 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, far while the true respirants 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 Magendik 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 insufficiency as an article of diet, but causes also diarrhoea, wliether 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, so as to render it capable of being absorbed ; then again perhaps they line the irritable membranes with a slimy coat, and it is not impossi- ble that ia some cases they are beneficial because not nutritious, con- stituting, in fact, an agreeable mode of abstaining from food." mPLUENCB OF SPECIAL SUBSTANCES 383 C— Solid AlimentSa 718. 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 c-taroh, 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. Pbrbiea declares the opinion totally unfounded, saying that no peo- ple 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 EFFECTS OF FOOD, 720. Gnm, in composition, resembles sngar and starch, and, there- fore, wonld seem to be devoted in 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 Snlistances. — These are furnished to the system mingled by nature with, nearly all the food we take. Milt 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, &o., contain the smallest proportion of it. The system is thus largely furnished with fat, ready prepared ; and moreover, when its snpply 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 ; fint^ when laid up in the body, in a passive state ; and, second, as par- ticipating in the active changes of the system. 722. The accmniilated Fat of the Body. — The necessity of some sub- stance adapted to fiU 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 aU 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 we consider that the oUy 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 oi 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 the 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 the mechanical violence to which the body is constantly liable. Besides, 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 corners mPLTJENCE OF SPECIAL SUBSTANCES. 385 and angles, and the narrow muscles of the face, is the cosmetic em- ployed \>j nature to stamp the human countenance with the incom- parahle impress which exalts it far ahove all the lower animals." Fat in a fluid state is also a very 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 we should be able to swim, and this is only made possible by the 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. Bebavior of Fats in the Stomacli. — ^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 digestioUj in very nnmerous cases, is well miderstood. 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 examjde, 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 17 386 PHYSIOLOGICAL EFFECTS OP POOD. being permeated by the gastric secretion, and so renders beef indiges- tible to all but robust persons. The 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 suflSciently plentiful to wash away the oily envelope and pene- trate the muscular fibre, it is wholesome. — (Chambeks.) Even the healthy stomach often recoils at certain oombiuations of fat, starch and gluten, as in the instance of the oily meats of nuts, filberts, almonds, walnuts, &c. 724. Cooking Influences the Digestibility of FatSi — 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 frying, the temperature runs high, tending to decomposition and the jrfoduotion of various acrid and irritant fatty acids. Fatty matters thus changed, or even predisposed to change, are liable to become rancid by the fermenting aoti«n of the stomach, producing heartburn and nausea. This explains why cakes are less healthy and digestible than hread. The large proportion of butter, cream, and «ggs, (the yolks 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. Pbebiea. 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, marrow, butter, and oU,) 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. Chambees says : " Fatty food can be taken without pain by gastric invalids, very closely in proportion as it is fresh, and without rancidity. If ew made butter often agrees, when the empyreumatio 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 rNPLUENCE OP SPECIAL SUBSTAlfCES. 387 cannot be foond capable of supplying nutriment to the failing adipose tissue." 725. Belatioa of the Fats to Nnttltion. — The 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 thoy 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 ibrmation 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. Oleaglnons Diet and Consumption. — ^Masses of crude unorganized matter containing coagulated albumen and half-formed cells, and called tiiberdes, are sometimes found in the lungs, producing tuberculwr consumption. The immediate cause of the disease is an abortive or perverted nutrition, 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 nutrition, 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 Zwer 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. Slmpson 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 neoes- 888 PHYSIOLOGICAL EFFECTS OF FOOD. Bary, rendered imperative. Dr. Oarpbntke 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 the 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 asually 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. HooKBE, in a report on the diet of the sick, says : 1st. Of all persons between the ages of 16 and 22 years, more than one- fifth eat no fat meat ; 2d. That of persons at the age of 45, aU 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 16 and 45, nine-tenths at least have never used fat meat. 727. Effects of Undue Proportions of illmentary 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 wrongly-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 lungs, the burden of disposing of it falls upon the liver, the blood becomes charged with the elements of bUe, and a iilioiia condition of the sys- tem results. The rheumatic state of the body, like the gouty, is sup- posed to be connected with mal-assimUation ; 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 we have just seen, to produce the scrofulous state, and a lack of fruits and fresh vegetables engenders the scorbutic condition of body, or sDur'oy. 728. Flesh Heats. — Having considered the action of the constitu- ents of flesh, little needs to be added here concerning their combined effect. The less the fibre of meat has been dried or altered by cook- rNPLUENCE OB" 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, but more soluble al- bumen and gelatin, and is hence more teader. This preponderance of gelatin explains why the broth of veal and lamb coagulates sooner in cooling 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 boUed, not too hard, are therefore quite as digestible as if taken raw. 729. Piepaiations 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, " AH 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 ; iatter 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 will 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 ai-e far preferable to those of wheat." 730. Coarse and Fine Bread. — ^As respects the final or nutritive effects of groimd grains, it makes every diflTerence 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-building 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 PHYSIOLOOICAL EFEECTS OF FOOD. tides act as a kmd of mechanical divisor, separating and diluting the highly-concentrated food, renderine the mass looser and more pene- trable to the solvent liquids, and suomitting it more gradually to the membranous absorbing surface. The ground grain, or -woody fibre, mingled with the flour, tog^her vrith the adhering oil, are further ser- viceable by promoting the action of the intestiuea. Bread from fins 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 regulated action of the bo-weis, and Mr. Graham insists strongly, as the result of large ob- servation, that coarse bread is corrective, not only 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 we miss the fuU 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 sacrifloed several most important qualities, and gained. oviljwMteness. We trifle with the flrst 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 iu soft water, the nutritive principle softens, partially dissolves, and becomes more digestible if the hu&s 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 antiseor- huties, — preventives, and remedies of scurvy. They of course vary in digestibility, according to the proportion of their constituents, and the thorough softening and decomposing effect of culinary heat. Most esculent vegetables abound in indigestible ligneous tissues, which pro- voke intestinal movement, and thus incline to produce aperient effects. Leaves and young shoots contain organic acids; thus, asparagus and the whole cabbage tribe contain acid of apples, or malic acid ; rheu- barb, malic and oxalic acid ; white cabbage converted into sour krout ferments and yields large quantities of lactic acid. These acids may mPLUKNCE OF SPKCIAIi STrBSTANOES. 391 oontribnte to stomach-digestion, promoting tte solution of the more nutritive aliments. In the case of fruits, which are still richer in acids, this effect is more marked. 733. Edible Roots, 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 aspwragin, 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. 734. Fntlt. — 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 LiEBie concerning the value of apples, afford ns 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, exti active 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 CondimentSi — Substances taken iu 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. Bugar, oil, a«ids, and common salt, have been described as aliments, but they are also employed as condiments. 736. Cleese. — ^We may regard cheese as an aliment when consider- 392 PHTSIOLOGIOAL EFFECTS OF FOOD. ing it as composed simply of caseia 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 way, 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 the action of the 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 excitiug 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. Vinegar, 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 prevailed that the free use of vinegar promotes leanness. However the fact may be, the experiment of reducing corpulence in this way is fraught with the danger of establishing deeply-rooted disease (775), 738. Spices, &c. — A class of substances rich in pungejit 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 viuegar are exceptions, and are not obnoxious to this charge, when used in moderation." — (Dr. Beatimont.) 10. NuTEiirvK Valtte op Foods. 739. Limitation of the Nntritive Powers. — It is to be expected that substances differing so widely as those which constitute food — sub- stances of such various composition — some containing nitrogen, while others are free from it, some containing sulphur, others none, some an excess of carborl, others the reverse — must serve very different pur- poses in tl e economy. Each has its special work to do, while their duties are not interchangeable. A certain degree of variety is thus ITS NUTErrrvB vaiub. 393 the fandamental requirement of the system ; and accordingly we find that where nature herself has prepared the food, as in the case of the mother's miilk for her young, it is always of a mixed nature, emhracing alimentary principles of very different composition. We have no shadow of evidence that the living hody possesses the power of converting one element into another ; it cannot transmute hydrogen into nitrogen, or carhon into phosphbrus ; 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 du'ection ; it can effect some changes, as we have seen ; it cannot effect others. It can destroy compounds hy a progressive series of changes, each descending step heing a new suh- stance, hut it cannot work upward in a formative direction, — that is the office of plants. The materials necessary to form a compound may be present in the hody 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 respu-atory 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 glaten. " That none of the non-nitrogenous substances can be made capable, hy 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 condasion, 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. Oaepbntek.) As the system has no mysterious energy to change wliat it will and as it win, 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, 894 PHTSIOLOGICAIi EFFECTS OF FOOD. and experience of their effects. We shall have occasion to note botli agreement and discordance, in many particulars, between general habits and the indications of science. 741. Proportions of Solid JUatter and Wateri — The following scheme. Fig. 121, illustrates the proportion 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- Fia. 121. PKOPOETIOir OF SOLID MATTEE AND WATER IN TOODS, Wleat, Peas. Bico, Bye, Beans, Corn. Wheat Bread. Mutton. Chicken. Lean Beef. Eggs. Teal.' Potatoes. Pork. Cod. Blood. Trout. Apples. Carrots. Beets. Milk. Muskmelon. Cabbage. |iP' Turnips. Watermelon. Cucumbers. ae proportion of solid mat- The length of the bars represents upon the scale, the percentage p . ter in the various articles of diet, opposite to which they are placed. lence of the aqueous eleirlent 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, wo must throw this constituent out of the ao- rrS NUTKITIVE VALUE. 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 nutritive power. 742. How far we can measure Nntritive Values. — A fall view of the nutritive value of foods, requires us to take into account aU 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 tbat 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 caloriflent 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, while the albuminous may prodnoe heat (666). 743. Different Takes of tie Respiratory Principles. — The albuminous substances are identical in composition, and have equal nutritive ' powers ; whether in the form of gluten, fibrin, casein or albumen, EBLATIVK P0WBE8 OP THE HEAT-PEODTTOING PEDTOIM-ES OF TOOD. FlO. 122. Fat I Starch. Cane Sngsr. Grape Sagar. eplrlts, 50 per ct. AlcohoL Lean Flesh, The relative lengths of fhe^bars illostrate the comparative amount of heat produced in the system hj equal weights of the substances mentioned. they are replaoable in nutritive effect. Not so, however, with the caloriflent principles; their heat-giving powers are very unequal. The preceiUng diagram (Fig. 122), exhibits the relative proportions of heat produced by equal weights of the substances mentioned. It wiH be thus seen that 10 parts of fat go as far as 24 of starch in generating heat. This is Liebio-'b estimate. He calculates the oil as i,arch, by multiplying it by 2'4. Thus the 9 per cent, of oil in Indian 396 PHTSIOLOGICAIi EFFECTS OF FOOD. corn, would be equal to adding 22 per cent, to its real amount of Etarch. In this way, the nutritive and calorifient powers of foods are readily brought into comparison. It appears from this estimate of LiEBiG, that the strongest spirits are not only incomparably inferioi to the oils, in heat-producing power, but also rank decidedly below starch and sugar (712). When we remember 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 exclnsive Meat Diet. — It is seen by the fore- going scale, that lean meat is the 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 alimentarj 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, that since fifteen lbs. of flesh contain no more carbon than four lbs. of 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 to produce the carbon necessary for respiration. 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 ' staff of life.' 745. Equilibrium of Valaes Distnrbed. — When the due proportion demanded by our physiological welfare, 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 diflBcult 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, are 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 sources of respiratory food, in the shape of starch, sugar, ITS SXTTEITIVJJ! YAIAIE. 397 and oil, are cut off. We fall back upon the animal world, but this is chiefly a grand s^ore of nitrogenous matter, without its due proportion of other constituents. The balance being thus lost, respiratory food rises in demand and value. 746. ProporUon of NntritlYe to Caloriflent Prinelples.— The following scheme represents approximately the values, nutritive and caloriflent — 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. Fis. 128. \ oompabativjs scale of the nttteittve ajtd eespibatoet values of vabiotjs aeti0le8 of food. Natritive or tissne- CaloriSent or heat-pro- forming principles. dacinff principlea. *Teal. Hare. Dried Beef. Eggs. Beef. Beans. Peas. Fat Matton. Pork. Cow's Milk. Haman Milk, Wheat Flomr. Eye Flour. White Potatoes. Indian Com. Turnips* Blue Potatoes. Kice. BncEwheat Flour. Airow-Toot, sa- ( go, tapioca,-! com-starch ( This scheme represents, by the relatire length of the harSj the proportion of nitrogenous to the non-nitrogenons principles In each article given, the latter being all reduced to the value of starch. The upper part of the scale represents those foods which are highest in proper nutri- tive power, and lowest in heat-prodacing 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 ,op downward : 1, 2, 5, 6, T, 8, 9, 10, 11, 12, 13, 14, IT, 18, 19 (Ubbig) ; 8, 4, 16 (Pro£ Johk ton); 20 (Prof. B.D.Thokpsoh); 15 (Aothoe). 398 PHYSIOLOGICAL EFFECTS OF FOOD. The poiat to whioli we called attention in the previous paragraplj must not be forgotten, or the scheme Trill certainly mislead us. The caloriflent 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 shaJl get a result different from that in the table, 10 of nutritive, to 18 or 20 of respiratory food. LiBBiG says in substance, in connection with this statement, that the relative proportions of the nutritive constituents fn mUk, 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. Y4T. Sntrifive 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 flU the fall 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 varying conditions. It is the appointed diet of th^ 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 young INFLUENCE OF SPECIAI SUBSTANCES. 399 of the animal world, none lead so qniescent a life, or advance so slow- ly to maturity, as does the human infant. The young of other ani- mals more quickly develop, and are called upon to put forth exertion much earlier. Hence the mUk of these animals, as for exattiple the cow, is richer ui the curdy, or bnUding and strength-giving principle than human milk. 748. Wheat resembles 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 mUk and blood, is shown in the following analytical statement : FUywr. Mood. Fibrin, Albumen, Casein, Fibrin, Albumen, Casein, Gluten, Oil and staich, Sngar, Chloride of potassimn. Chloride of sodium, Coloring matter, Fats and oils, Sngar, Phosphate of soda, " lime, Ditto. " " magnesia, " iron. 1 MUk. Albumen, Casein, Butter, Milk-sngar. Ditto. 749. How Wheaten preparations meet the losses of the System. — The attempt has been made to determine the daily consuinption in the sys- tem of nutritive and respiratory matter. The problem is most diffi- cult, and the resnlts 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. Poggailb states that the researches of the last 20 years have shown that an adult Zas- loring mem consumes each day between 11 and 12 ounces of heat-pro- ducing principles, and about 4^ ounces (d/ry) of nitrogenous matters, charged with the regeneration of the tissues ; that his nourishment ia not complete unless it is formed of one part nitrogenous matter and four parts respiratory. Bbnbke, 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 PHTSIOLOfilCAL ETFECTS 01" FOOD. genous as one to five. Febeiohs calculates that the daily consnmp tion should be 2'17 ounces avoirdupois of nitrogenous, and 15*54: ounce* of non-nitrogenous food, that is, about as one to seven. Wheat aver- ages, perhaps, one to five. But starch is a bulky form of respirator> 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. Butter, 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. Y50. Variations in Nntritive Talne of Wbeat. — ^Th«> proportion of nu- tritive to respiratory principles in wheat, fluctuates ranch, which 01 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 will produce the blood constituents most copiously, and yield most strength. Yet, ac we have 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 pricf which win be paid for wheat, it is quite the reverse. "We prize anc" estimate flour directly in proportion to its whiteness, which is gener- ally in inverse ratio to the proportion of its gluten. We give most for the wheat that will nourish least. As the chief object of the farmej^ is to produce an article which will command the highest mar^ef 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. High Jfntritive Power of coatse Bread. — In the seventeenth century, Vattean 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 are now gained to the population immense masses of nutritious matter, of. the annual value of many millions, which were formerly used for animals ; the brg,n 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, 1 fine bran, 3 bran flour) ; and the ordinary mills produce as much as 25 per cent, of bran, containing 60 or 70 per cent, of the most nutritious rrs mjTEiTivi!! vALtrE. 401 constituents of the flour. By baking bread with unbolted flour, the mass of it may be increased from one-sixth to one-fifth, and th$ price of it lowered iy the difference hetween the price of the Iran as fodder for cattle, and that of the flour gained ty not iolting 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 lie corrected by InteTmixtniei — ^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 respiratory 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 sufficient 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 different 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 all 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, ia 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 eggi). 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 of diet, and there is a deficiency of meat, they attempt a compensation by mingling with the potatoes boiled cabbage, which is rich in nitro- 402 PHTSIOLOGICAl EFFECTS OF FOOD. genous matter, witli perhaps a little meat, making a dish known as tiol- ccmnon. Rice 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 unsubstantial diet, cannot be substituted for meat and dry vegetables in soldiers' rations — and must always be combined with nitrogenous principles. Hence, whenever they can be 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 spu'it and power to defective diet. 753. Diet required by Childreft. — We are reminded agam, by refer- ence to the preceding scale of equivalents, of the ill-adaptation of rice, sago, arrow-root, corn-starch, &o., 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 aU 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. — (Geegoet.) 11. The Vegktaeiait 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 the one hand, and the partisans of an exclusive vegetable diet, on the other ; the point of contention being the dietetical fitness ja_ jjT. and nature of its defile- ments. The outer layer of the skin (cuticle) is formed of albuminous cells, which, losing their liquid contents by evapo- ration at the surface, are flattened into exceeding- ly minute thin scales, of a horny, resisting quality, which serves as a pro- tection to the sensitive or true skin underneath. The surface of the cuticle is constantly loosening, Suxfece of the ^^«cle^|r»«r^^agnmea, showing and wearing off in fine, powdery scales, -which are replaced by new growths from below. Figs. 127, 128, exhibit the structure of the skin. It is an organ of 432 CLEAHSING OP THE rEESON. I-ia. 128. drainage, with a double, function; co-operating, with the kidneys, on the one hand, to relieve the system of water, and with the lungs on the other, to extrude its gases. The perspiratory tubes, which open through the cuticle upon the surface, forming pores, are spi- ral-shaped, as shown in the fig- ure, and terminate in glands be- low. Prof. ■Wilson says, "I counted the perspiratory pores on the palm of the hand, and found 3528 in a square inch. Each of these pores being the aperture of a little tube, about a quarter of an inch long, it fol- lows, that in a square inch of skin on the palm of the hand, there exists a length of tube equal to 882 inches. I think that 2800 might be taken as a fair average of the number of pores on the square inch, and dfled: 700 the number of inches in a the cuticle, outer, or scan skin : & d tne true , _,-, j; .i_ ■, -, ^ i* 8km;coil-tubeandgland;«BweatglandBand iengtu lor the whole Suriace 01 their dncta, the outlets at the surfkce being +T,„ hnrlv Wnw thn nnmlioT- r>f the pores; / hairs; g ceUular substances. ^^^ °°-°-^- -""^ '"^^ numoer 01 square inches of surface, in a man of ordinary height and bulk, is 2500 ; the whole number of pores, there- fore, is 7,000,000f and the amount of perspiratory tube 48,600 yards, or nearly 28 miles." Twenty or thirty ounces of perspiration escape through these channels daily, and upon evaporating into the air, leave a residue upon the sm-face, of animal and saline matter, consisting of acids, alkahes, calcareous earth, &c. 798. Impurities of the Skin. — We have noticed the enormous ex- haling and absorbing surface of the lungs (283), and the consequent danger to which we are exposed by the inhalatidn of foreign, poison- ous substances, from the air. Evidently, if the skin were in the same condition, if its millions of little mouths were constantly and freely open to the air, the danger from absorption of infections matter would be greatly heightened. But this consequence is wisely guarded against by a set of glands, whose special oflBce it is to secrete oily matter to bedew the surface of the body. We notice that where this oily coat- ing is in excess, it often gives an unseemly polish to the features ; Vertical section of the skin, greatly m MAXAGBMENT OF THE SKIN. 433 ■while if it be deficient or absent, the skin is dry, harsh, and rough. Now this oleaginous pellicle, while offering no hindrance to exhala- turn, or the outward escape of waste matter, protects the system against too free absorption from without. It is this oily distUment, perpetually covering the cutaneous surface, that seizes upon aU forms of dirt and impuri^, cementing them into an adherent layer of dirt, comprising also the dregs of perspiratory evaporation, and the scales of scarf-skin just noticed; This crust of dirt may at length accumulate and oonsohdate, until it obstructs the poresjjiarrests free drainage, and thus seriously interferes with the functions of the skin, and the health of the body. As a consequence of the neglected state of this organ, the sedentary and irregular habits of refined society, the unctuous sys- tem of the skin becomes sluggish, and its actions torpid Fio. 129. and irregular, and instead of the constant flow through ih^ oil-tubes, their contents become dry, dense, impacted, and do not freely escape. They accumulate in the ob- structed passages and forni pimples. When those are squeezed between the finger nails, there issues a little cylindrical mass of white unctuous matter, which, when examined with the microscope, reveals a little animalcula, represented by Fig. 129. It is called by Dr. "WiLsoisr, who has studied its history and habitudes for six months at a time, steatosoonfolliculorwm; that is, the 'animal of the oUy product of the skin.' These little personages are caterpillar-like, with head, feelers, four pair of legs, and a long taU. They are about the l-45th of an, inch in length, and always occupy the. same position in the oil- tube, the head being directed inwards. ' The little mass shot out from the pimple may contain from two to twenty of them. 799. Cleansing »f flie Skin— lUntlon. — ^As oil is the basis of the coat- ing of dirt which daUy concretes upon the skin, it is obvious that water alone is incapable of removing it. Soap is the proper skin- detergent. It partially saponifies the oil, rendering it miscible and soluble in water. The alkaline efement of soap also softens and dis- solves a part of the cuticle which, when rubbed off, carries v?ith it the dirt. Thus any washing with soap removes the face of the old scarf- skin and leaves a new one. If the 'hands are too long exposed to the action of an alkaline soap, they become tender, that is, the cuticle dissolves away, and gets so thin as not to protect the inner or sensitive skin. Wash powders are inferior to soap, and injure the whiteness 19 434 CLEANSING OF THE PERSON. and purity of tlie skin. If soap produce irritation, it is because th« skin is in some way morbid. It should then be used in smaR quantity at first, increasing it gradually. 800. FUIosopliT of washing tlie Faee.— Dr. WrLsoN thus pleasantly discourses on the art and.mystery of deansing Uie face. " And.nov, dear reader, having determined to wash your face, how will you se| about it ? there are many, wrong ways of effecting so simple a pur- pose ; there is but one right way, I will tell it to you. Eill youir basin about two-thirds full with fresh water ; dip your face in the water, and then your hands. Soap the hands, weU, and pass th^ soaped hands with gentle friction over the whole face. Having pejci formed this part of the operation thoroughly, dip the face in the ■^ater a second time, and rinse it completely : you may add very much tQ the luxury of the latter part of the process by having a second basin ready with fresh water to perform a final rinsing. And now you will Bay, 'What are the wrong ways of washing the face?' "Why, th«! wrong ways are — using the towel, the sponge or flannel as a means of conveying and applying the soap to the face, and omitting the rinsing at the conclusion. If you reflect, you wiU see at once that the hands are the softest and the most perfect means of oarryiag the soap^ and employing that amount of friction to the surface with the soap which is necessary to remove the old and dirty scarf, and bring out the new and clean one from below. Moreover, the hand is a sentient rubber, or rubber endowed with mind ; it knows when and where to rub hard, where softly, where to bend here or there into the little hollows and crevices where dust is apt to congregate ; or where to find little ugly clusters of black-nosed grubs, the which are rubbed out and off, and dissolved by soap and friction. In a word, the hand enables you to oombiae eflScient friction of the skin with complete ablution ; whereas in every other way ablution must be imperfect. Then, as regards drying the face, a moderately soft and thick towel should be used ; a very rough towel is not desirable, nor one of thin texture. This is a point that may be safely left to your own taste and feelings. The question of friction during the drying is of more con- sequence, and this is a reason why the towel should be moderately soft, that you may employ friction and regulate the amount. With a very rough towel it is impossible to use friction, for its tenderest pres- sure may be enough to excoriate the skin ; and a very soft towel is equally open to objection from its inadequacy to fuMl the obligation of friction during the process of drying. In washing the face you SUBSTAJTCBS ACTTNO UPOU THE TEETH. 43£ haye tihree objects to fulfil — to remove the dirt, to give freshneas, and to impart tone and vigor to the skin." 801. Cleansing the Teeth. — The effect of talking, singing and breath- ing through the month, is to evaporate the water of the saliva, leaving its solid constituents, animal matter and salts, as a residue which accn- mulates upon the teeth as tartar. This,; together with, the fragments of the food which get lodged in th{B cavities, between the teeth, is a constant cause.of impurity, in the mouth, which should, therefore,. be often cleansed. Dentifrices are preparations of liquid, paste and pow^ der for. cleansing the teeth. Some act ohejnicajly to dissolve the tar^ tarous jnoru^t&tion, as dilute muriatic acid, which also removes dis- oolorations and whitens thete^th. iBut it also corrodes their enamel, and rapidly destroys them. Its habitual or frequent use is, therefore, most pernicious. ,It may be rarely and cautioosly employed to efface dark spots or black specks npon the t^eth, but it should be quickly neutralized with chalk, and washed aw;ay with water. Tooth pow- ders, which act mechanically, are better. They require to have a cer- tain degree of hardness or grittiness to enable them to remove the foreign substances adherent to the teeth ; but if too hard, they injure the enamel. The powder of ground pumice stone is employed, but it is too sharp for any thing more than exceptional use — say once in two or three months. Chalk is soft and excellent ; not common chalk pulverized, for that contains flinty particles, but prepared chalk of the druggist. Charcoal and powdered cuttle fishbone are good tooth de- tergents. Tet all insoluble powders are liable to the objection, that they accumulate in the space formed by the fold of the gum and the neck of the tooth, presenting a colored circle. The powder is there- fore often colored red with carmine or iote armmiae. Myrrh, cin- namon, &e., are added as perfume. Shatany, cmohona, and catechu, are added to exert an astringent and hardening effect upon the gums. If substances are required which shall dissolve in using, wulphate of potash, plwtphaU of soda, cream of tartar, and com- mon salt may be used. Disinfecting and deodorizing tooth-powders and washes which destroy the unpleasant odor of the breath, and tend to whiten stained teeth, owe their efBciency to chloride of limo (807). Such a preparation may be made by mixing one part chloride of lime with twenty or thirty of chalk. A disinfecting mouth-wash is made by digesting three drachms of chloride of lime in two ounces of distilled water, and to the filtered solution adding two ounces of spirit, and scenting, as with attar of roses. — (Pbbbiea.) 436 CLKAHSmG THE AIE. IV— CLEANSING THE AIR. 802. It was noticed (303) that the atmosphere constancy tends to 8e]f-pnrifioation ; its oxygen is a Tiniveraal cleanser ; it gradually but certainly consumes the noxious gases that are poured into it, from whatever source. Yet its action is slow, and it often happens that in- jurious exhalations are set free in such quantities, or in such confined spaces, as to require other and active means for their removal. Besides ventilation, other methods are also to some extent available for getting rid of atmospheric impurities, some of which will now be noticed. The subject of malaria, air-poisons, atmospheric infection — what they are, how they act, and in what manner and to what extent they are capable of counteraction — ^is yet involved in much obscurity. The substances which relieve us of disagreeable odors and noxious emana- tions are numerous, and take efiect in various ways. 803. PalliatlTes and Bisgnlsers.— When atmospheric impurities report themselves to the olfactory sense, they are pretty sure to receive at- tention, though we too often seek only relief from the disagreeable smeU. This is done, not by removing it, but by smothering or over- powering it with sweet scents. With musk, attar of roses, lavender, odoriferous gums, fragrant spices, aromatic vinegars, &c., a cloud of perfume is raised which masks the unwholesome odor. This may be often an excusable resort, but it is too frequently a slovenly expedient to conceal the eflfects of uncleanliness. " They are the only resources in rude and dirty times against the offensive emanations from decay- ing animal and vegetable substances, from tmdrained and untidy dwell- ings, from nnolean clothes, from ill- washed skins and ill-used stom- achs. The scented handkerchief in these cases takes the place of the sponge and the shower-bath, the pastile hides the want of ventiUation, the attar of roses seems to render the scavenger unnecessary, and a eprinkling of musk sets all other stenches and smells at defiance. The fiercest demand for the luxury of civilized perfumes may exist where the disregard of healthy cleanliness is the greatest." In this connexion we may mention those agencies which exert a palliative effect, remov- ing rather than concealing or destroying the offensive bodies. Thus, sulphuretted hydrogen, the gas of rotten eggs, and which is copiously set free from putrefying animal bodies, may be absorbed by water, but the water does not decompose or neutralize it ; if heated, it all escapes back again into the air. The moist soil also acts as an absorbent of bad gases, fixing and retaining them during cold and wet weather, and setting them free during drought or heat. ACTION OF LIME A2 pouring sul- phuric acid upon a mixture of common salt with the same oxide. Chlorine stands first as a disinfectant. It is cheap, easily prepared, acts efficiently though diluted with much air, and in this state of dilu- tion is breathable without injury even by the sick. It corrodes me- tallic substances, which should therefore he removed as far as possi- ble from apartments in which it is to he used. (Other disinfecting gases are liable to the same objection.) If it be desired to generate large quantities of chlorine, the m'ethods just mentioned may be re- sorted to, hut apartments cannot then be occupied, as chlorine in any considerable amount is to a high degree irritating and inflammatory to the throat and air passages. In all common cases chloride of lime may be employed. This is lime charged with chlorine gas, which combines with it so easily that it is slowly set free when exposed to the air. It has a double action : the Ume combines with all acid bodies as carbonic acid, sulphuretted hydrogen, while chlorine diflfiises through the air, decomposing all the noxious compounds of hydrogen. It may be spread upon any putrefying substance, when it destroys noxious bodies as they are formed. It may be placed in a room, when carbonic acid slowly combines with the lime, and the chlorine is gradually set free. It may be dissolved in water and sprinkled through bad smelling apartments, or cloths dipped in a dilute.d solution of it can be hung up in the room. After infectious diseases, a weak solution of chloride of lime should be sprinkled over sheets and family linen before washing, and the "walls of the room washed down with it. Chloride of soda is used in the same manner as chloride of hme. , . 808. Disinfection liy SnlpbnTons icld. — ^When sulphur is bnmed in the open air, oxygen combines with it,, producing sulphurous acid gas. It has a noxious odor, and if largely mingled- with the aif{ is injurious to health. It is an active chemical agent, much used for bleaching, as may be iUustrated: by holding over a burning sulphur match, a red rose, which isimmediately whitened. Woollen, silk, and other garments are bleafehed by it. It is of a strongly acid nature and combines with alkaline vapors of the air, while ifdecomposes and de- stroys other substances;' as sulphuretted arid phosphuretted hydrogen. When an apartment is fumigated by burning sulphur, it is necessary to leave it ; it corrodes metals. 809. Otber Substances used for Dlslnfeetioii. — Ghhride of iron ia a CHAECOAl HASTENS CHAUGB OF MATTEB. 439 cheap and effiofent disinfectant, though it imparts a brown or bluish stain wherever its solution falls. Chloride of sine is equally efladent, 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. Aeetate onA nitrate of lead are -strong disin- fectants. These substances are all solids. They do not assume the gaseous form, but act, dissolved in water, by fixation, of c- xious snb- Btances as they are 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 offensive, 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 effects in a particular manner, unlike 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 aoid, and sulphm-etted hydrogen to sulphuric acid. 440 CXEAKSmG THE 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.* This active property of hastening decomposition has been made medically availahle in the form of ponltice, to corrode away sloughing and gangrenous flesh in malignant wounds and sores. Dr. BiED,in his work on the medical uses of charcoal, quotes several cases: we give one. " A man was admitted to St. Mary's hospital with a slough- ing sore upon his leg. A poultice of this kind was put on, and in sis hours the dead portion was reduced in size fuUy one-quarter. At the same time, the poultice thus made, effectually prevents any odor or putrefying exhalations proceediQg from the slough and pervading the apartment." Dr, Stbnhouse, 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 breath-filter or respirator, consisting of a hollow case of fine flexible wire-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 strcngly 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 hy contact; . nor ^ves 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. * "I took the body of an English terrier, weight about ten lbs., placed It on a stone •loor in a small apartment, and lightly covered it with charcoal; although the weather was very warm, not the slightest odor coold be detected. By some accident the charcoal was disturbed, and a large portion of the mass was left uncovered ; in spite of this the circumjacent charcoal was sufficient to prevent any offensive stench. Upon seeing this, I left the body completely uncovered, merely snrrounding it with the deodorizing agent; this again prevented any disagreeable smell. Having determined this fact, I again cov- ered the carcass. In less than a fortnight not a particle of flesh remained upon the bones, which were picked perfectly dean, and were of a snowy whiteness." — (Bird os CnABOOAL.) I POISONS, A2n} THBIE AimDOTES. 441 'v.— POISONS. 812. Poisons and Poisoidng.— Poisons are divided into three classes according to the way liiey 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 dp not suspend consciousness. Strong acids, and alkalies,- and indeed all poisonous metallic substances, belong to this class. Narcotic poisons are such as produce stupor, as opium, carbonic acid. ITa/rcoto-acridg, 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 froni 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. Kesonrees In ease of Poisoning. — ^If the vial or vessel from ■which the poison was 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, epsom 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 teaspoonfal of mustard stirred 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. But while this circumstance is fitted to tempt the mur- 19* 442 AKSENIC POISONING. derer, there follows another which is' fraught with sure retrihution Ifo poison is so ready and certain of detection as arsenic. And not only this, but " 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 combines 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. ADDITIONAL LIST OF TEMPEEATUEES. Lowest artificial cold 187° below zero, or 219° below freezing water Carbonic acid freezes 148° beloWzero, or 180° below freezing water. Lowest natural temperature at Yakutsk, in Siberia, 84° below zero. Estimated mean temperature of tbe North Pole, 13° below zero. Salt water of specific gravity 1*104, and oil of turpentine freezes, "Wine freezes, .... JBlood freezes, ..... Milk freezes, .... Water freezes, ..... Alcobol boils in a yacunm. Mean winter temperatare of England, Temperatore of hybernating animals, . Mean winter temperatare at Eome, Mean annual temperature at Toronto, . Putrefaction begins, .... Cultivation of the vine begins at a mean annual temperature of^ Mean annual temperature of New York, . Mean annual temperature at Eome, CultiTation of the yine ends, "Water boils in a vacuum. Temperature of glow-worm and cricket, Silk-worm hatches— temperature of germination, Tepid bath begins, .... Acetous fermentation, Putreikction rapid, .... Tepid bsth ends, — ^warm bath begins, . Temperature in man — ^blood heat, . Warm bath ends,— vapor bath begins, . Cold-blooded animals die, Yapor bath ends, .... Temperature in a boat in Upper Egypt, . Steamboat's engine-room ("West Indies), Starch converted to sugar, . Einland vapor bath, Alcohol (spedflc gravity •T94) 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, ..... l*" 28° 80° 87.8° 88° 41° 48° B0» B0° 54° 69° 65° 72° 74° 77° 95° 106° 180° 138° 155° U0° 170° 174* 182°' 202° 212° 444 APPENDIX. Syrup, 52 per cent. 6ugar, boUs, ...... 216" Water of the Dead Sea boils, ...... 223° Syinp, 80 per cent, sugar, boils, ...... 264° Gypsum converted to plaster, . . . , . . 291° B. We append an illustration of tlie aatdnishing scale of minuteness upon which eren 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. Feoment, by an exquisite mechanical contrivance, exediited an elaborate piece of writing and engraving. Of course no result was visible to the naked eye ; but when the 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 mfinMesima^ moyements performed. rio. isi. INDEX. Ablation of the face, 434 Acidfi, vegetable, 225 ; composition o^ 225 ; of apples, 225; of lemons, 225; of grapes, 225 ; nature of, 869. Acetic acid, 226. Air, non-conduction oi^ 35 ; pressure of, 43, 151 ; composition of, 49, 153 ; contami- nation of 07 gas burning, 123 ; general offices of; 150 ; weight o^ 151 ; effect of vaTylng pressure of; 152 ; intermixture oi; 153 : constituents of; 154 ; oxygen of, 154 ; moisture, in, 157; conditions of drying power ot, 158; system affected by moist, 160 ; by dry, 161, 170 ; . effects of its ingre- dient^ 163 ; impurities of external, 165 ; conditions of salubrity, 166 ; self-purify- ing, 167 ; causes of impurity of in dwell- ings, 168; bad influence of beating appa- ratus upon, 168 ; affected by hot-iron sur- faces, 169 ; composition of; altered by heating, 169 ; impurities o:^ from the body, 170 ; Dr. Farraday on, 171 ; of bedrooms, 171 ; purity of the design of nature, 172 ; danger of foul, 174* contamination of, in- doors, 181 ; -vitiated by illumination, 183 ; vitiated by the person, 184 ; influence of plants upon, 185; in motion, 185; cur- rents in close rooms, 186, 187 ; stratificar tion o^ in rooms, 187 ; currents through doors and windows, 189, 190; currents affecting the system, 191 ; supply of, by crevices, Ac, 195 ; modes of introducing, 196 ; effect of breathing rarifled, 855. Albumen, vegetable, 227; composition of, 227 ; properties o^ 228. Alcohol, as an illuminator, 11&; as a pre- server, 314 ; the principle of spirituous liquors, 878. Aliments, source of, 205; classification of, 206, 207; undue proportions oi; 388; cor- rection of; 4oi. Alkalies, 369. Amaurosis, 145; subjects of, 146. Apartments, size of for breathing, 184. Appetite, regulation ot 410, Apples, composition of, 244. Argand burners, 112. Amott's valve, 193; importance of, 199, Arrow-roof. 215. Arsenic, 441. Artificial light, 105; from ignition, 105; measurement oi; 124 ; color of, 137 ; inju- rious action o^ 137 ; how it affects the eyes, 189 ; effects upon the retina, 140, 144; heat accompanying, 141; unsteadi- ness of, 142 ; extraneous rays, 143 ; may produce inflammation, 144 ; management o^ 146 ; whitening by absorption, 143. B Barley, 240. Barometer, 43. Beans, composition, 242 ; mineral matter in, 243 ; digestibility of, 390. Beaumont, Dr's. table, 348. Bedrooms, air of, 171 ; ventilation of, 201. Beets, 247. Beverages, 289. Blood, constituents of, 250, 347; globules, 847; alkaline, 870. Boiling, culinary changes by, 277. Boiling point, elevation of, 44. Bran, composition of, 235. Brain, measure of its change, 365; phos- phatic constituents of, 866 ; has its spetf*sl nutriments, 367 ; excitants, 369. Braziers, 61, 62. Bread, from plain flour and water, 258 ; fer- mented, 259 ; objections to fermented, 267; unfermented, 268 ; raised by chemi- cals, 269, 270; heat of baking, 271; loss of weight in baking, 272; changes in the cmst, 272 ; In the crumb, 272 ; moisture in, 273: good, 273 ; influence of salt on, 274; alum, 274; effects of lime water, 275; different kinds o^ 276; white and brown, 277 ; coarse and fine, effects of, 889. Broth for theisick, 284. Buckwheat, composition of, 241. Burning fluids, composition of, 116 ; bow explosive, 116 ; conditions of accident from, 117 ; how used with safety, 117. Butter, separation, o^ 285 ; composition and properties of, 286; cause of its change' ableness, 315 ; cause of rancidit/, !II4 : ac- tion of air upon, 316 ; aubstuioM juai to preserve, 817, 446 c Cabbage, nutritire properties of, 244. Campliene,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; snuffing of. 111; shade for, 148. 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, 162; necessity for, in air, 168; exhaled by respiration, 182. Carrots, 248. Casein, composition of, 228. Cataract, 186. Cellars, foul air in, 178. Changes in the living system, 826 ; rate of, 827 ; equalization of bodily, 862 ; hasten- ing and retarding, 868. Charcoal, as fuel, 53 ; as a disinfectant, 439 ; mode of its action, 439 ; respirator, 440. Cheese, preparation of, 288; changes by time, 817 ; influence in digestion, 891. Ohevreul, 91. Chimneys, draught o^ 55 ; causes of smoky, 56, 57, 58, 59 ; currents in summer, 200. Chocolate, 298 ; adulterations, 800 ; effects, 878. yholera and foul air, 175. Ohurning, 285. Citric acid, 225. Cleansing, principles involved in, 422; by alkaline substances, 435 ; of textile arti- cles, 428 ; cottons, linens, and woollens, 429 ; of spots and stains, 480 ; agents for, 430 : of the person, 431 ; of the skin, 433 ; of the face, 434; of the teeth, 485; of the air, 486. Climate, artificial, 22. Coal, mineral, ^, 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 on the effects of, 878. Cold, when most fatal, 858. Color, influence upon radiation, 80; npon absorption, 81 ; Newton's theory o^ 89 ; Brewster's theory, 89; complementary, 90 ; tints and tones of, 91 ; chromatic cir- cles, 92 ; contrast of; 97; mutually inju- rious, 98; contrast of tone, 99; harmonies of, 100; circumstances influencing, 101; associated with white, black, gray, 101 ; combining, 102 ; influence o^ upon com- plexion, 102 ; arrangement of flowers, 103 ; f)aper-hanging8, 108 ;.furniture, 106 ; popu- ar recognition of the effects o^ 140 ; asso- ciated heat of, 141. . . Combustion, products of, 50; air hinders, 55 ; within the body, 851. Common salt transparent to heat, 28; effect npon bread, 274; uses of, in the system, 871; containedin food, 872; modeofcrys- tallization, 311 ; purification Of, 812; how It preserves meat, 812; how it injures meat, 818 ; too little and too much, 877. Comi>lexion, 102. Condimenta, 891. Contagion and foul air, 175. Com starch, 215. Cream, production of, 253. Culinary art, objects of, 256. Culinary utensils, 818 ; of iron, 813 ; of tin, 819; zinc, 320; copper, 820, 821; enam- elled ironware, 821 ; earthenware, 322 ; Porcelain ware, 823. Dentifrices, 485. Dew, cause of, 82 ; dew-point, 168. Diet, for brain-workers, 868 ; mixed indis- ,'pensiable, 898; exclusive meat, bad econ- omy, 396; required by children^ 402 ; oj flesh, influence of, 405; mineral matters replacable in, 406 ; economy of vegetable and animal, 407 ; diversities of, 408, 409 ; scale of U. B. 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; ol middle life, 420; of advanced life, 420. Dif^sion of gases, 158. Digestion, object of, 830; ia stomach, 838; extent of gastric, 840 ; influence of coffee ;on, 877. ■ ■ ' Dirt, composition o^ 428. Disguising bad smells, 436. Disinfectants, 437; quicklime, 487 ; chlorine, 437; chloride of lime, 438; sulphurous acid, 438 : charcoal, 439. Double windows, 159. Dough, water absorbed by, 257 ; effecte of kneading, 258 ; what makes it rise, 261 ; raising by leaven, 262 ; raised by yeast, 2G6 ; acidity in, 266 ; sugar in, 267 ; alco- hol in, 267 ; raised with eggs, 270. Dress, 21, 85 ; 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 o^ 87. Evaporation, 42 ; cooling effects of; 46 ; rate of, 159. Eye, sensibility to colors, 97 ; parts of, 127, 128 ; minuteness of images in, 129 ; adap- tation to light, 180 ; affected by conditions of the system, 180 ; influence of reading and writing upon, 181 ;. cause of far-sight- ed, 182 ; remedy of far-sightedness, 188 : cause of near-sighted, 184; remedy ox near-sighted, 185 ; cataract in, 136 ; influ- ence of carbonic acid upon, 142 ; bad light inflames, 144. . Faraday, Dr., 171. Eats, see Oils. ' Farina, 337. Farina kettle, 45. Fermentation, 260; conditions of, 260; dif fereat kinds of, 260 ; spontaneous, 260. Fibriri,;228. INDEX. 447 Fire, ktndUng of; 60 ; risk oi; 78 ; orlrin oi;T4. Fireplace, form oi; 62; action of, 62; econ- omy of, 63; Tentilation by, 192. Flame, cause of; 50 ; illuoLinatioil from, 106 ; hollowness of, 110 ; length o£ in sas barn- ing, 123. Flesh, composition o^ 248 ; juice o^ 249 ; action of heat upon, "BSl; changes by cooking, 282 ; loss of weight In, 2S2 ; beat plan of cooking, 283 ; common method objectionable, 283; its juices acid, 871; digestion oi; 388. Flour, -white and dark, 236; evaporation from, 236; changes in, 236; efiects of its preparations, 389. Foods, why perishable, 300; conditions of perishableness, 301 ; eflfectsof, maybe un- derstood, 325; periodic supply ot, 837; digestibility o( 341, 342, 348; changes in mouth, 330; in stomach, 835; in mtes- tines, Bii ; constipating and laxative, 846 ; final destination o^ 347 ; produced by forces, 348; produces animal force, 849; unequal combustibility of; 351 ; heat-pro- ducing and tissue-making, 352 ; replaced by houses and clothing, 358 ; ash elements of, 369; dem&nd for variable, 408 } daily reqiurement of; 409. Force, production oi; destroys tissue, 861. Freezing, artificial, 41 ; heat produced by, 42. Frost, cause o^ 83. Fruits, composition o^ 243; dietetic effects of; 891. Fuel, influence o^ 22 ; composition o^ 49 ; heating effects ol^ 54 Furniture, colors o^ 104. G Gas fixtures, 124. Gas, illumination by, 119; sources o^ 119; composition oi; 120; purification of; 119; various sources of, 120 ; measurement of; 121; how burned, 122; contaminations of air, by burning of, 123 ; disadvantages of lighting by, 124; fixtures of; 124; isJight- ing by, injurious, 149.. Gas meter, 121. Gastric juice, 338; its acid and ferni,ent, 839; quantity 0(341. Gelatin, 230. Gingerbread, 271. Glass, opaque to heat, 28. ' Gluten, 229 ; quality of; 232. Glycerine, 109. Grain, grinding ot, 284; strnctnre oi; 234; sifting oi; 235. Grates, 64; combustion in, 64; Circular, 66; Amott's, 66; heightoi;67., Uum,. artificial, 223; composition of, 223 ; ' physiological effects of, 364. Heat, from the sun, 18; fW>m the stars, 18; distribution o( 19 ; influence on vegeta- tKin, 19; distribution of animal, 20; in- '.ftnences man^a development, 20; relation to character, 21 ; diffnaion o( 28 j iajui- librinm ot 23; ezvansion of, 28 ; -siieight «<; 24; radiation of, 27, 29, 80; transmis- sion of, 28; absorption oi; 29; exchanges of, 81; conduction of, 84; convection of; 86; circulation of, 87; capacity for, 88; latent, 89, 40, 41, 46; influence on the body, 48 ; loss of, in rooms, 60 ; source of in rooms, 61 ; amount of bodily, produced, 360. Heating arrangements compared, 74. Honey, 217. Hot-air furnace, 70 ; ventilation by, 193. Hot-water apparatus, 72. Human boc^, purpose of, 848 ; constant temperature o^ 853; how it loses heat, 854 ; how it produces heat, 354 ; resources against cold, 356; force exerted by, 360 ;• limited action over fbod, 392 ; its restricted transforming power, 404. Hunger, use of, 329. Hydrogen, its office in fuel, 50; heating powers of; 51. Hydrometer, 255. I • Illumination, artificial, 105 ; Dy Ignition, 106 ; from burning gas, 106 ; simpuo'f; 82 ; refraction o£ 82; yave thoory of, 87; arti- ficial, 105 ;- from Ignition, 105 ; measure- ment of, 124 ; results of Ure,and Kent, 126 ; color of artificial, 187; injurious action of artificial, 187. Liquefaction, $7. Liquors, alcoholic, 878 ; cannot replace wa> ter in the svstem, 379, and- anunal heat, 379; Booker's observations, 879; nOt eco- nomical, 38; stimulating effect, 380. . Looking-glass, 79. Lyman^ cold-air fine, 198 ; reCrigentor tOT Macaroni, 233. Malaria, 166. US INDEX. Malic add, 225. Margaric acid, 109. Margarine, 109. Mastication, importance of, 883. Meals, frequency in times of, 410 ; rest be- foi-e, 411 ; state of mind during, 412 ; ex- ercise after, 412 ; eflFects of excess at, 414. Melting points, 88, 111. Milk, composition of, 250 ; qualities of, 251, 252; cream of, 253; value of, 255; mineral matter in, 256 ; spontaneous curdling of, 287; curdling with acids, 287; with ren- net, 288; preserving, 814; eifects of, S81. Mind, relation o^ to matter, 864; its action destroys the nerves, 865 ; wears the body, 866. Moisture, in air, 15T ; in the air of rooms, 158 ; amount required in air, 183 ; the supply of, 194 M. Mouries, 277. Musical sounds, 85 ; scale, 86. N Night-air, 167. Nitrogen, 154 ; lowers the combustibility of foo^ 852. Nitrogenous principles, properties of, 230 ; names of, 281 ; destination of, 361. Non-nitrogenouB principles, different values of, 895. Nutrition, effects of, insufficient, 414. Nutritive'values, 395; scale of, 897; equi- librium of, 396; milk, 898; wheat, 399; adaptations of wheat, 399 ; coarse bread, 400. O Oats, 289. Oils, proximate composition of, 109, 114; flui(fity of, 114; kerosene, 118; sylvic, lis ; volatile and fixed, 228 ; sources of, 223 ; proportion of in articles of di et, 224 ; ultimate composition of, 224; supply oJ^ in diet, 884; accumulation o^ 384; in stomach, 885 ; digestibility of, 886 ; rela- tion of to nutrition, 887; to consumption, 887. Oleaic acid, 109. Oleaine, 109. Onions, 247. Oxygen, 49, 154 ; how it enters the syfitem, 155 ; what it does in thp body, 156 ; effect of varying the quantity of, respired, 157 : consumed by respiration, 181 ; consumed by combustion, 182 ; an exciter of decay, 802; destructive ^ency oi^ 850; action of, upon tissues, 862. Oxalic acid, 226. Ozone, 164. P Paper-hangings, colors of, 103; poisonous colors on, 178. Parr, Thomas, 828. 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 m, 245 starch in, 246 ; nutritive part of, 246 ; dry matter of, 246 ; ash of, 247 ; changed by cooking, 280. Potash, 874. Preservation, by exclusion of air, 802; Ap- pert's method, 803; in canisters, 804; in Spratt's cans, 805 ; at low temiieratures, 806; by freezing, 806; in refrigerators, 807 ; fruits, 308 ; by drying, 809 ; by anti- septics, 811 ; by sugar, 813 ; by alcohol, 814L Putrefaction, 259. E Eeflectors, 146; blue, 147. Eetina, image formed upon, 129; loss of sen- sibility of, 144; paralysis of, 145. Bice, composition of, 241. Roots edible, dietetic effects of, 891. Eye, anatomy o^ 285 ; composition of, 288. B Sago, 215. Saliva, flow of, 331; properties of, 382; uses o:^ ^2 ; action in stomach, 840. Salta, 369. Shades, ground glass, 146 ; blue, 147 ; struc- ture and mounting of, 147. Simultaneous contrast of colors, 97. Skin, structure of, 481 ; impurities oi^ 432 ; cleansing of^ 438. Smoke, 59, 60. Soap, how made, 425 ; hard and soft, 426 ; -water in, 426 ; varieties oi^ 427 ; its re- action with water, 428. Soda, 874. Solution, 208. Sound, transmission of, 85. Soup, preparation and properties of, 284; effects of, 381. Spectacles, 131; for the far-sighted, 188; for the near-sighted, 135 ; suggestions In selecting, 136 ; management, 187 ; pebble- glass, 187 ; colored glasses for, 148. Spectrum, 88. Specific heat, 88. Spermaceti, 109. Spitting, effects of, 384. Starch, separation of, 213 ; proportion of, 214; grains, 214; sago, 215; tapioca, 215: arrow-root, 215; corn-starch, 215; com- position, 216; culinary changes of, 279: physiological effects of, 333. Steam, warming by, 78. Stearine, 109. Stearic acid, 109, Stomach, figure tff, 835; layers of, 835; mo- tions of, 386 ; folUcles of, 836 ; absorption from, 846. Stovepipe, 69. Stove, Franklin, 64; self-regalating, 68; air- tight, 68 ; best, 69 ; ventilation by, 193. Sugar, proportion from various sources, 216 ; 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, 231 ; candy, 221 ; culinary changes oi^ 278 ; as a preserver, 818 ; phy Biological effects of, i883; refining of, 44. rNDEX. 449 'f sploca, 21S. Tartaric acid, 225. Tea, 289; the shmb, 289; varieties, 289; freen and black, 290 ; composition at, 291 ; owbest made, 292; grounds, 292; adul- teration, 298 ; physiological effects ot ST7. Teeth, 821 ; cleansing ot, 485. Temperature, feotso£2T; of body ednstant, 858 ; regulation of bodily, S5T ; diet and dally changes of, 859. Thermometer, 23, 24, 25, 2$. Turpentine, spirits oi; 115. Turnips, 24a V Vegetables, influence o^ In diet, 890. Vegetarian question, 402; statements ot contrasted, 403, 404. Ventiducts, 198. Vermicelli, 2SS. Vinegar, effects o^ 392. Vision, conditions of, 76; value of the sense of, 126; how produced, 129; mechanism of, 128 ; optical defects of. 131 ; limits of perfect, 131 ; paralysis of the nerve o^ 145. Ventilation, of the person, 186; arrange- ments for, 192 ; by the fireplace, 192 ; by stoves, 193; by hot-air arrangements, 193; points to be secured in, 196 ; downward current in, 197 ; ascending current in, 198 ; by an additional flue, 200 ; of gas-burners, 201; of cellars, 202; should be provided for in building, 202 ; involves loss of heat, SOS. W "Warming by steam, 78 ; by hpt water, 72 ; and ventilation best method oi^ 195. "VTarming of rooms by air, 71. ■Waste and supply, 228. Water, its relations to heat, 89 ; evaporation of, 42 ; boiling oi; 42, 48 ; spheroidal state oia ; solvent powers ot 207 ; to hasten solution, 208 ; its dissolved gases, 203, 209 ; varieties of, 208 ; rain and snow, 209 ; or- fanic contaminations of, 209 ; living in- abitants of, 210 ; their use, 210 ; its min- eral matter, 211 ; hard and soft, 212 ; in contact with lead, 212; supply of rain, 218 : for culinary uses, 280 ; physiological effects oi^ 874, 875; influences digestion, 875 ; change of tissue, 376 ; proportions of In foods, 394; as a cleansing agent, 422; filtration of, 428 ; its dissolved impurities, 424 .Wave movements, 84. Wax, 109. Wheat, composition of, 232 ; gluten in, 232 water in, 238; mineral matter in, 237 nutritive value o^ 899. Wood, water in, 51 ; heating value of, 52 soft and hard, 52. Woody fibre, 278. Yeast, brewer^B, 262 ; a plant, 263 ; aomestio .preparation of, 264; hops in, 265; drying oi; 265; bitterness ot, 266; acidity at, TESTIMONIALS. OF THE CLASS-BOOK OF CHEMISTRT. Fnm, tktlt.Y. Commercial AiieerHser, Either for sdiools or for geneTal reading we know of no elementaiy work VI Chemistry wliich in every respect pleasea ns so much as tliis. i'rem the Albion. A remarkably interesting and tlioronghly popular work on Chemistry, re- eommended to the general reader by the clearness of its style, and its fk'ecdom from technicaUtles. S^om the Soston CoTnmon School, Jonmalt We consider this Chart a great simplification of a somewhat confiised f ob- ject : slid wo welcome it as another snocesslhl attempt, not only to simplify tmth, but to fix it in the mind by the assistance of the eye. If we were called to teach the elements of chemistry in a school-room, we ^ould be very nnwilUng to lose the Talnable assistance of this ingentons chart. From the JfationaZ ImteCUgencer. Besides the folness with which this work treats of the chemistiy of agri- enltnre and the arts, we regard it as chiefly Talnable for the clear account it gives of the action of chemical agents upon the greatly varied fhnctions of life. It is ver^ elementary and practical ; and whether for the use of schools or of private libraries, it is an appropriate because an instructive and entertaining book. JFrom the BdeitMJio Americcm. Such a book In the present state of chemical science was demanded, but to present the subject in such a clear, comprehensive manner, in a work of the size before us, is more than we expected. The author has happily succeeded in clothing his ideas in plain language — true eloquence— ^o as to render the subject both interesting and easily comprehended. The number of men who can write on science, and write clearly, is small ; but our author is among that number. From the Farmer a/tvA Mecham^, A Class-Book of Chemistry for the use of beginners and young students, which should he divested as much as possible of its tedious technicalities and , dry repulsiveness, so often attending their first efforts in this important study, has long been a desideratum. To supply this need, the present volume is fhlly adequate. It is designed as a popmar introduction to the study of this beautifal science, and presents it in such a manner as to win the attention and engage the interest. - OF THE CHEIOICAIi CHART. From TLas^as "SLkmi, Preeident (^Aidioch CoUege. 1 have been highly delighted by inspecting a Chart, shown to mo by Mr. E. L. Youmans, of New York, the object of which is to represent the ratios in which chemioal atoms are combined to form compound bodies. The different atoms are represented by square diagrams of different colors; and then the compounds exhibit the exact number or numbers of the respective atoms that unite to form them, each atom retaining its original color. Thus the eye of the learner aids his memory; and as the eye, in regard to all objects hav TOUIkltANS' CnENHOAJL CHART. Ptthlisked by D. Appleton & Co., 443