THE HAND-BOOK OF HOUSEHOLD SCIENCE, A POPULAR ACCOUNT OP HEAT, LIGHT, AIR, ALIMENT, AND CLEANSING, nr THEJE SCIENTIFIC PRINCIPLES AND DOMESTIC APPLICATIONS. WITH inJMEBOUS ILLUSTRATIVE DIAGBAMS. ADAPTED FOR ACADEMIES, SEMINARIES, AMD SCHOOLS. BY EDWARD L. YOUMANS, 'TUB CLASS-BOOK OP CHEMISTET," "CHEMICAL ATLAS" AND " CHABT, "ALCOHOL AND THE CONSTITUTION OP MAN." NEW YORK : D. APPLETON & CO., 443 & 445 BKOADWAY. 1867. - ENTEEKD according to Act of Congress, In the year 186T, by D. APPLETON & CO In the Clerk's Office of the District Court of the United States for the Southern District of New York. Ag. Ref. GIFT rx/4? CONTENTS. PART I. HEAT. PAG PREFACE, 7 INTRODUCTION, 11 I. SOURCES AND DISTRIBUTION OF TERRESTRIAL HEAT, . . . , 17 II. INFLUENCE OP HEAT UPON THE LIVING WORLD, . . . . 19 III. MEASUREMENT OF HEAT THE THERMOMETER, 23 IV. RADIATION AND ITS EFFECTS, 27 V. CONDUCTION OF HEAT, AND ITS EFFECTS, 34 VI. HEAT CONVEYED BY MOVING MATTER, .... 86 VII. VARIOUS PROPERTIES AND EFFECTS OF HEAT, ... 37 VIII. PHYSIOLOGICAL EFFECTS OF HEAT, 48 IX. ARTIFICIAL HEAT PROPERTIES OF FUEL, 49 X. AIR-CURRENTS ACTION AND MANAGEMENT OF CHIMNEYS, . . 55 XI. APPARATUS OF WARMING, 60 1. Open fireplaces, 62 2. Stoves, 67 3. Hot-air arrangements, 70 PART H. LIGHT. I. .NATURE OF LIGHT LAW OF ITS DIFFUSION, 76 II. REFLECTION OF LIGHT, 79 ffl. TRANSMISSION AND REFRACTION OF LIGHT, 82 (V. THEORY OF LIGHT WAVE MOVEMENTS IN NATURE, .... 84 V. COMPOSITION AND MUTUAL RELATION OF COLORS, 88 fl. PRACTICAL SUGGESTIONS IN COMBINING COLORS, .... 102 772 iv CONTENTS. PAS* VII. PRODUCTION OP ARTIFICIAL LIGHT. 1. The Chemistry of Illumination, .... .105 2. Illumination by means of Solids, .... 108 3. Illumination by means of Liquids, 112 4. Illumination by means of Gases, US 5. Measurement of Light, 124 VIII. STRUCTURE AND OPTICAL POWERS OF THE EYE, 126 IX. OPTICAL DEFECTS OF VISION SPECTACLES, 131 X. INJURIOUS ACTION OF ARTIFICIAL LIGHT, 137 XI. MANAGEMENT OF ARTIFICIAL LIGHT, .... . 146 PART III. AIR. I. PROPERTIES AND COMPOSITION OF THE ATMOSPHERE, .... 150 II. EFFECTS OF THE CONSTITUENTS OF AIR. 1. Nitrogen, 154 2. Oxygen, 154 3. Moisture, 157 4. Carbonic acid, . 161 5. Ozone and electricity, 164 III. CONDITION OF AIR PROVIDED BY NATURE, ... . . 165 IV. SOURCES OF IMPURE AIR IN DWELLINGS, 168 V. MORBID AND FATAL EFFECTS OF IMPURE AIR, 174 VI. RATE OF CONTAMINATION WITHIN DOORS, 181 VII. AIR IN MOTION CURRENTS DRAUGHTS, . . . . . 185 VIII. ARRANGEMENTS FOR VENTILATION, 192 PART IV. ALIMENT. I. SOURCE OF ALIMENTS ORDER OF THE SUBJECT, 205 II. GENERAL PROPERTIES OF ALIMENTARY SUBSTANCES. 1. Principles containing no Nitrogen. A Water, ... 20Y B The Starches, 21* C The Sugars, 216 D The Gums, 223 E The Oils, ,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. V PAG* 8, Compound Aliments Vegetable Foods. A The Grains, 231 B Leguminous Seeds, . 241 C Fruits, 243 D Leaves, Leafstalks, etc., 244 E Roots, Tubers, Bulbs and Shoots, 245 4. Compound Aliments Animal Foods. A Constituents of Meat, 248 B Production and composition of Milk, .... 250 III. CULINARY CHANGES OF ALIMENTARY SUBSTANCES. 1. Combining the elements of Bread, 256 2. Bread raised by Fermentation, 259 3. Properties and action Of Yeast, 262 4. Raising 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 IV. COMMON BEVERAGES. 1. Properties and preparation of Tea, 289 2. Properties and preparation of Coffee, 293 3. Cocoa and Chocolate, 298 V. PRESERVATION OF ALIMENTARY SUBSTANCES. 1. Causes of their Changea'bleness, 300 2. 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. MATERIALS OF CULINARY AND TABLE UTENSILS, 318 VII. PHYSIOLOGICAL EFFECTS OF FOOD. 1. Basis of the demand for Aliment, 324 2. Digestion Changes of food in the Mouth, .... 330 3. Digestion Changes of food in the Stomach, . . . 335 4. Digestion Changes of food in the Intestines, ... 344 5. Final destination of Foods, 347 6. Production of Bodily Warmth, ...... 353 7. Production of Bodily Strength, 860 1 'fi CONTENTS. PAGE 8. Mind, Body, and Aliment, 364 9. Influence of Special Substances. A Saline Matters, 369 B Liquid Aliments, ... . . 374 C Solid Aliments. 383 10. Nutritive value of Foods, 392 11. The Vegetarian Question, 402 12. Considerations of Diet, 408 PART V. CLEANSING. L PRINCIPAL CLEANSING AGENTS, 422 II. CLEANSING OF TEXTILE ARTICLES, 428 III. CLEANSING OF THE PERSON, ........ 431 IV. CLEANSING OF THE AIB, 436 V. POISONS, 441 APPENDIX . k . 443 QUESTIONS .... ... . .445 INDEX . 466 PKEFACE. A DESIRE to prepare a better statement than has hitherto been offered, of the bearings of science upon the economy of the household, has led to the following work. The purpose has been, to condense within the limits of a convenient manual the largest possible amount of interesting and valuable scien- tific information of those agents, materials, and operations in which we have a concern, chiefly as dwellers in houses. The subjects are treated somewhat in an elementary way, but with constant reference to their domestic and practical relations. Principles are 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 in furnishing her house. Tht Agriculturist- is interested in the composition of food, as a producer ; the Householder equally, as a consumer. Tho VU1 PKEFACE. Doctor must know the constituents of air and its action upon the living system for professional purposes, and he studies these matters as parts of his medical education ; but for the same reasons of life and death, the inhabitants of houses are concerned to understand the same things. These examples illustrate the leading conception of the present work. Its preparation has been attended with grave difficulties. Of course, a volume of this compass can present only a compend of the subjects it considers. Heat, light, air, and aliment are topics of large extent, wide and complex in their principles, which are of boundless application. We do not profess to 'have treated them with any completeness, but only to have brought distinctly forward those aspects which have been formerly too much neglected. In deciding what to state, and what to omit, we have been guided by two rules ; first, to present such facts and principles as have the directest bearing upon household phenomena ; and, second, to bring into prominence many important things not found in common books nor included in the ordinary range of school study. As elementary principles may be found fully treated elsewhere, we have been brief in their statement, thus gaining opportunity for important hints and views not generally acces- sible. Our chemistries are deficient in information of the composition and properties of food, while the physiological class-books are equally meagre in statements of its efiects ; we have accordingly dwelt upon these points with something of the fulness which their importance demands. So ,with heat, light, and air. It is hoped that the following pages will vindicate the fidelity with which we have labored to enrich the volume with new and valuable facts and suggestions, not pro- curable in our family manuals or school class-books. Many of the subjects presented have recently undergone searching investigation. They are rapidly progressive ; facts are multi- plying, and views widening. 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 family and general reading, yet in the proper order of school PREFACE. 11. 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, from standard books upon the various topics, scientific magazines, original memoirs, personal correspondence, observation, house- hold experience and laboratory examinations. Constant refer- ence is made to authorities followed, and the language of others employed whenever it appeared to convey the most X PEEFACE. suitable 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. Yet the utmost care has been taken to make an accurate and reliable presenta- tion of the subjects considered. The Author desires to acknowledge his indebtedness to his sister, ELIZA A. 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. RICHAKD H. MANNING, who, though engaged in absorbing mercantile pursuits, has yet found time for thought in the di- rection of science and its applications, his thanks are due for valuable suggestions and important manuscript corrections. If the work shall serve, hi 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. YOEK, August, 1867. INTEODUCTION. WHEX a work is presented, claiming place in a systematic course of school study, two questions at once arise in the mind of the discrimi- nating educator : first, what is the nature, rank, and value of the knowledge it imparts? and, second, what will be its general influence upon the mind of the student? In this twofold connexion there are some thoughts to which we solicit the reader's earnest and considerate attention. The present volume has been prepared under a conviction that the knowledge it communicates is first in the order of importance among things to be considered by rational and civilized people. "Every man's proper mansion-house and home," says SIB HEXET WOTTON, " is the theatre of his hospitality, the seat of self-fruition, the com- fortablest part of his own life, the noblest of his son's inheritance, a kind of private princedom ; nay, to the possessors thereof an epitome of the whole world." Nothing needs to be added in eulogy of the household home, the place of life's purest pleasures and sweetest ex- periences, the perpetual rallying point of its hopes and joys. What- ever can render it more pleasant or attractive, or invest it with a new interest, or in any way improve or ennoble it, is at once commended to our sympathy and regard. To consider all the agencies which in- fluence the course and character of household life, is far from the ob- ject of the present work. Our concern is chiefly with its more mate- rial circumstances and conditions. That we should understand some- thing of the wonderful physical agencies which have control of our earthly being, and which are so incessantly illustrated in the dwelling, and be at least partially acquainted with those fixed natural ordi- nances upon which our daily welfare, comfort, health, and even life, immediately depend, must certainly be acknowledged by all. One of the most startling facts of man's history is, that placed in a world of Immutable order, and endowed with such exalted gifts of understand- Xll INTRODUCTION. ing and reason, he should yet have contrived to maintain so dense and perfect an ignorance of himself and the familiar objects by which he is surrounded. That exact knowledge of the ways of nature which puts her powers at human command, and bears the daily fruit of substan- tial improvement and universal beneficence, would seem to be the last and noblest achievement of mind; a fruition of long intellectual growth, the highest form in the latest time, after the 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. COPEENICIJS struck out the grand law of celestial circulation before HABVEY discovered that of the blood. The genius of NEWTON flashed an immortal light upon the mechanism of the universe, many years before KUMFOED 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 INTRODUCTION. Xlll the advantage of the many ; from utter ignorance and contempt of nature, to the revelation of all-embracing laws, and a beautiful and harmonious order in the commonest objects and operations of daily experience. To the truth of this general statement, the existence of the present book may be taken as a strong attestation. The mass of its facts and principles are the result of recent investigation. A hundred years ago such a work would have been, in all its essential features, a blank impossibility ; indeed, it had lacked its richest mate rials if prepared for the last generation. These facts should not be without their influence upon the schemt of popular education. It is its first duty to communicate that infor- mation which can be reduced to daily practice, and yield the largest measure of positive good. If recent inquiry has opened new treasures of available truth, it is bound to take charge of them for the general benefit. It must report the advance of knowledge, and eep pace with the progress of the human mind, or it is false to its trust. The subjects of study should be so modified and extended as to afford the largest advantage, intellectual and practical, of the labors of the great expounders of nature, especially in those departments where knowl- edge can be made most useful and improving. A rational and com- prehensive plan of education for all classes, which shall be based upon man's intrinsic and essential wants, and promptly avail itself of every new view and discovery in science, to enlighten him in his daily rela- tions and duties, is the urgent demand of the time. Nor can it be always evaded. We are not to trundle round for ever in the old ruts of thought, clinging with blind fatuity to crude schemes of instruction, which belong, where they originated, with the bygone ages. He who has surrendered his life to the inanities of an extinct and exploded mythology, but who remains a stranger to God's administration of the living universe ; who can skilfully rattle the skeletons of dead lan- guages, but to whom the page of nature is as a sealed book, and her voices as an unknown tongue, is not always to be plumed with the eupereminent designation of ' educated.' There are many things, unquestionably, which it would be most desirable to study : but opportunity is briefj and capacity limited ; and the acquisition of one thing involves the exclusion of another. We cannot learn every thing. The question of the relative rank of vari- ous kinds of knowledge what shall be held of primary importance and what subordinate, is urgent and serious. As life and health are the first of all blessings, to maintain them is the first of all duties, and to understand their conditions the first of mental requirements. XIV INTRODUCTION. Shall the thousand matters of mere distant and curious concernment be suffered to hold precedence of the solemn verities of being which are woven into the contexture of familiar life ? The physical agents which perpetually surround, and act upon, and within us, heat, light air, and aliment, are liable to perversion through ignorance, so as tt produce suffering, disease, and death; or they are capable through knowledge of promoting health, strength, and enjoyment. What higher warrant can be asked that their laws and effects shall become subjects of general and earnest study. It may seem strange that in regard to the vital interests of life and health, man should be left without the natural guidance of instinct, and be driven to the necessity of reflection and study ; that he for whom the earth seems mado should be apparently less cared for in these respects than the inferior animals. Nevertheless, such is the divine ordination. Neither our senses, instincts, nor uninstructed faculties are sufficient guides to good, or guards from evil, in even the ordinary conditions of the civilized state. Things which most deeply affect our welfare, the senses fail to appreciate. They can neither discern the properties nor the presence of the most deadly agents. The breathing medium may be laden with noxious gases to the peril of life, and the senses fail to detect the dan- ger. Hunger and thirst impel us instinctively to eat and drink, but they fail to inform us of the nutritive value of alimentary substances or their dietetical 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- dominating good, there is no other protection than intellect, instructed INTRODUCTION. XV in the material conditions which influence our health and life. For these, and kindred considerations of practical moment to all who oc- cupy dwellings and assume civilized relations, we urge the study of household science as an essential part of general education. It deserves to be better understood, that the highest value of science is derived from its power of advancing the public good. It is more and more to be consecrated to human improvement, as a sublime re- generative agency. Working jointly and harmoniously with the great moral forces of Christian Civilization, we believe it is destined to effect extensive social ameliorations. That it is not yet fully accepted in this relation is hardly surprising. The work of presenting scientific truth in those forms which may best engage the popular mind, is not to be fairly expected of those who give their lives to its original development. There is a deep satisfaction, an intrinsic compensating interest to the discoverer in the naked quest of truth, which is largely independent of any utility that may flow from the inquiry. In the exalted conscious- ness of achievement, the man of science finds an intellectual remunera- tion, so royal and satisfying that other considerations have compara- tively little weight. Hence the indifference, to a great degree inevi- table, with which original explorers contemplate the reduction of sci- entific principles to practical use. Moreover, this utter carelessness of results, where the mind is not biased, nor the vision blurred by ulterior considerations, is far the most favorable for successful investigation. Conscious that the effects of his labors are finally and always beneficial in society, the enthusiast of research may be excused his indifference to their immediate reception and uses. But the formal denial that the allegiance of mind is supremely due to the good of society is quite another affair. The sentiment too widely entertained in learned and edu- cational circles, that knowledge is to be firstly and chiefly prized for its own sake, and the mental gratification it produces, we cannot accept. The view seems narrow and illiberal, and is not inspired of human sym- pathy. It took origin in times when the improvement of man's con- dition, his general education and elevation, were not dreamed of. It came from the ancient philosophy, which was not a dispensation of pop- ular beneficence, an all-diffusive, ennobling agency in society, but con- fessed its highest aim to be a personal advantage, shut up in the indi- vidual soul. It was not radiant and outflowing like the sun, but drew all things inward, engulfing them in a malstrom of selfishness. The baneful ethics of this philosophy have given place to the higher and more generous inculcations of Christianity, which lays upon hu- man nature its broad and eternal requirement, ' to do good.' Fron) XVI INTRODUCTION. 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 uppn 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 l vapor,' but to the mass of mankind, life is a solid, unmistakable reality, that will not dissolve into mist and cannot be conjured out of its qualities. As such, we would deal with it in education, giving prominence to those forms of knowledge which will work the largest practical alleviations and most substantial improvement throughout the community. But it is wisely designed that those studies which may become in the highest degree useful are also first in intellectual interest. It is a grievous mis- take to suppose that the study of natural science martyrizes the more ethereal faculties of the soul, and dooms the rest to painful toil among 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 of God upon the rocks, revealing the history of our planet and its inhabitants through durations of which the mind had never before even presumed to dream ? In thus unsealing the mysteries of being in turning the commonest spot into a museum of wonders who can doubt that science has opened a new and splendid career for the play of the diviner faculties ; and that its pursuit affords the most exhilarating, as well as the healthiest and purest of intellectual enjoy- ments? Nor should we 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 INTRODUCTION. XV11 minds with the richest materials of thought, enlarging our capacities of heiiign exertion, and rising to a more intimate communion with the spirit of the Great Maker of all. But beyond these considerations, physical science has another claim upon the Instructor, in the kind and extent of the mental discipline it affords. The study of mathematics has a conceded value in this rela- tion, being eminently favorable to precision and persistence of the mental operations to steadfast concentration of thought upon ab- stract and difficult subjects. But we hope not to incur the charge of educational heresy,by expressing the opinion,that its training is some- what defective is neither sufficiently comprehensive, nor altogether of the right kind. Its influence is limited to certain faculties only, and the 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 Mcome 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 induc- tion. That the whole is greater than a part, or that two parallel lines will never intersect each other, are irresistible intuitions, taken for granted at once by all minds. But that matter attracts matter with a force proportional to the square of its distance ; or that chemical combination takes place in definite unalterable proportions, are truths of induction general laws, only arrived at after long and laborious in- vestigation of particular facts. These are essentially opposite methods of proceeding in different departments of inquiry, each correct in its own sphere, but false out of it. The human mind started with the mathematical method, and the greatest obstruction to the progress of physical science for many centuries arose from the attempt to apply it to outward phenomena ; that is, to assume certain principles as true of the external world, and to reason from them down to the facts ; in- XVU1 INTRODUCTION stead of beginning with the facts, and carefully evolving the general laws. The splendid achievements of modern science are the fruit of the inductive method. This should be largely joined with the mathe- matical to secure a full and harmonious mental discipline. It edu- cates the attention by establishing habits of accurate observation, strengthens the judgment, teaches the supremacy of facts, cultivates order in their classification, and develops the reason through the es- tablishment of general principles. It is claimed, as an advantage of mathematics, that it deals with certainties, and, raising the mind above the confusions and insecurities of imperfect knowledge, habituates it to the demand of absolute truth. That benefits re ay arise from this exalted state of intellectual requirement, we are far from doubting, and are conscious of the danger of resting satisfied with any thing short of perfect certitude, where that can be attained. But here again there is possibility of error. Mathematical standards and pro- cesses are totally inapplicable in the thousand-fold contingencies of common experience ; and the mind which is deeply imbued with its spirit, is little attracted to those departments of thought, where, after the utmost labor, there still remain doubt, dimness, 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 shall best prepare it for varied and serviceable intellec- tual duty in the practical affairs of life. There is still another thought in this connection which it is im- portant should be expressed. It has been too 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 all things are settled, and that wisdom has reached its last fulfilment. Instead of encouraging bold inquiry, and inciting to noble conquest, the effect has rather been to reduce the student to a mere tame, unquestioning recipient of established formulas and tune-honored dogmas. It is obvious on all sides that this state INTRODUCTION. XIX of things has been deeply disturbed. The introduction of Re- publicanism, with political freedom of speech and action; the advent of Protestantism, with religious liberty of thought; and the splendid march of science, which has enlarged the circle of knowledge, multiplied the elements of power, and scattered social and industrial re volution, right and left, for the last hundred years these new dispensations have invaded the old repose, and fired the minds of multitudes with a new consciousness of power. Yet we cannot forget that our education still retains much of its ancient spirit, is yet largely scholastic and arbitrarily authoritative. We believe that this evil may be, to a considerable degree, corrected by a frank admission of the incompleteness of much of our knowl- edge; by showing that it 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 the pupil's ambition, nevertheless it is imperatively demanded. We need to acquire more humility of mind and a sincerer reverence for truth ; to understand that much which passes for knowledge is unsettled, and that we should be constant learners through life. The active influences of society, as well as the school-room, teach far other lessons. We are com- mitted in early childhood to blind partisanships, political and religious, and drive on through life in the unquestioning and unscru- pulous advocacy of doctrines which are quite as likely to be false as true, and are perhaps utterly incapable of honest definitive adjustment. Science inculcates a different spirit, which is most forcibly illustrated in those branches where absolute certainty of conclusion is difficult of attainment. Mr. PAGET has urged the salutary influence of the study of physiology in this relation. He says, " It is a great hindrance to the progress of truth, that some men will hold with equal tenacity things that 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 INTRODUCTION. one who is early instructed in an uncertain science such as physiology.* In the present work, the chief statements comprised under heat, light, and air, may he 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 ihe same time apprised of the incompleteness of his knowledge. An important result of the more earnest and general pursuit of science, hy the young, will he, to find out and develop a larger number of minds having natural aptitudes for research and investigation. As there are born poets, and born musicians, so also there are born in- ventors and experimenters ; minds originally fitted to combine and mould the plastic materials of nature into numberless forms of useful- ness and value. It is a vulgar error that the work of discovery and improvement is already mainly accomplished. The thoughtful well understand that man has hardly yet entered upon that magnificent career of conquest, in the peaceful domain of nature, to which he is destined, and which will be hastened by nothing so much as a more general kindling of the minds of the young with enthusiasm for science. The harvest awaits the reapers how strange that man should have neglected it so long. Fuel, air, water, and the metals, as we see them acting together, now, in the living, laboring steam-engine, have been waiting from the foundation of the world for a chance to relieve man of the worst drudgeries of toil. Long and fruitlessly did the sunbeam court the opportunity of leaving upon the earth permanent impressions of the things he revealed ; while the lightning, though seemingly a lawless and rollicking spirit of the skies, was yet impatient to be pressed into the quiet and useful service of man. Can there be a doubt that other powers and forces, equally potent and marvellous, await the discipline of human genius ? Not in vain was man called upon, at the very morning of creation, to ' subdue the earth.' Already has he justified the bestowment of the viceroy al honor : who shall speak of the possibilities that are waiting for him in the future 1 THE HMD-BOOK OF HOUSEHOLD SCIENCE PART FIKST. HEAT. I. SOURCES AND DISTRIBUTION OF TERRESTRIAL HEAT. 1. Nature of onr Knowledge concerning Heat. When we place the hand upon a stove with a fire in it, a feeling of warmth is experienced, while if it 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 heat. Some have conjectured it to be a kind of material fluid, exceed- ingly subtle and ethereal, having no weight, existing diffused through- out all things, and capable of combining with every known species of matter ; and this supposed fluid has received the name of caloric. Others think heat is not a material thing, but merely motion : either waves, or undulations produced in a universal ether, or a very rapid vibration, or trembling of the particles of common matter, which is in some way contagious, and passes from object to object. Of the essen- tial nature of heat we understand nothing, and are acquainted only with its effects: our information is limited to its behavior. It resides in matter, mores through it, and is capable of variously changing its conditions. It is an agent producing the most wonderful results every 'where around and even within us ; a force of such tremendous energy, such far-reaching, all-pervading influence, that we may almost venture to say it has been appointed to take control of the material universe ; 18 SOURCES OF TEEEESTKIAL HEAT. while in tlie plan of the Creator, it is so disciplined to the eternal re straints of law, as to become the gentle minister of universal benefi- cence. 2. To what Extent the Earth is 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 & year would be sufficient to melt 5400 Ibs. weight of ice ; and as a cubic foot of ice weighs 54 Ibs., 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 sufficient to melt it in the course of a year. This quantity of heat would melt a shell of ice enveloping the surfs surface 38.6 feet thick in a minute, or 10.5 miles in thickness in a year. "We are, therefore, warmed by heat-rays shot through a hundred million miles of space, from a vast self-revolving grate having fifteen hundred thousand miles of fire-surface heated seven times hotter than our fiercest blast furnaces. 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 all directions from his surface, the earth receives but a small frac- tion. But it is neither lost nor wasted ; he not only warms the earth, but assists to warm the universe. Our globe catches a trifling portion of his rays ; but the rest fly onward to distant regions, where all are finally intercepted by the wandering host of orbs with which the heavens are filled. And what the sun does, all the other stars and planets are also doing. A mighty system of exchanges (32)* is estab- lished among the bodies of space, by which each radiates heat to all the rest, and receives it in turn from all the rest, according to the measure of its endowments. The whole stellar universe thus contrib- utes to our warmth. It is a startling fact, that if the earth were de- pendent alone upon the sun for heat, it would not get enough to make the existence of animal and vegetable life possible upon its surface, * These numbers refer to paragraphs. ITS UNEQUAL DISTRIBUTION. 10 It results from the researches of POTTILLET, that the starry spaces fur- nish heat enough in the course of a year to melt a crust of ice upon the earth 85 feet thick, almost as much as is supplied by the sun. This may appear strange, when we consider how immeasurably small must be the amount of heat received from any one of these distant bodies. But the surprise vanishes, when we remember that the whole firmament of heaven is so thickly sown with stars, that in some places thousands are crowded together within a space no greater than that occupied by the full moon. (Dr. LAEDXEE.) 4. Heat unequally Distributed upon the Earth. The quantity of heat which the earth receives from the sun is very unequal at different times and places. The earth turns around every day ; it is globular in form, and is constantly changing the position of its surface in rela- tion to the sun, as it travels about him in its annual circuit. The con- sequence is, that we receive more heat during the day than at night ; more at the equator than toward the poles ; more in summer than in win- ter. We are all aware that the temperature may fall from blood heat at mid-day, to the point of frost or freezing at night ; and while at the equator they have a temperature averaging, the year round, 81-5 degrees, at New 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- ing. NOT do places at the same distance from the equator receive equal amounts of solar heat. A great number of circumstances connected with the surface of the earth, disturb its regular and uniform distribution. Dublin for example, though between eight and nine hundred miles further from the equator than New York, has as high a yearly temperature. Some places also experience greater contrasts than others between the different seasons: thus while New York has the summer of Eome, it has also the winter of Copenhagen. H. INFLUENCE OF HEAT UPON THE LIVING WORLD. 5. It Controls the Distribution of Vegetable Life. It is this variable quantity of heat received at different places and seasons, which deter- mines the distribution of life upon the globe. Certain tribes of plants, for example, flourish in the hot regions of the tropics, and cannot live with a diminished intensity of heat. Accordingly, as we pass to the cooler latitudes, they disappear, and new varieties adapted to the new conditions take their place. As we pass into still colder regions, these again give way to others of a hardier nature, or which are capable of 20 INFLUENCE OF HEAT UPON THE LIVING WORLD. living where there is less heat. As we proceed from the hot equator to the frozen poles, or as we pass upward from the warm valley to the snowy summit of a lofty mountain, we cross successive helts of varying vegetation, which are, as it were, definitely marked off hy the different quantities of heat which they receive. "In the tropics wo see the palms, which give so striking a characteristic to the forests, the broad- leaved bananas, and the great climbing plants, which throw them- selves from stem to stem, like the rigging of a ship. Next follows a zone described as that of evergreen woods, in which the orange and the citron come to perfection. Beyond this, another of deciduous trees the oak, the chestnut, and the fruit trees with which, in this climate, we are so well acquainted ; and here the great climbers of the tropics are replaced by the hop and the ivy. Still further advanc- ing, we pass through a belt of conifers firs, larches, pines, and other needle-leaved trees and these, leading through a range of birches, which become more and more stunted, introduce us to a region of mosses and saxifrages, but which at length has neither tree nor shrub ; and finally, as the perpetual polar ices are reached, the red snow algae is the last trace of vegetable organization." 6. Heat Regulates the Distribution of Animals.- It is the same also with animal life. 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 to his torrid desert u' sand, the polar bear is imprisoned in the frigid desert of ice ; and, in both cases, the sunbeam is the chain by which they are bound. 7. Heat Influences Man's Physical 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 all- powerful influence of heat. " The intense cold, dwarfs and deforms the inhabitant of the polar regions. Stunted, squat, large-headed, fish- featured, short-limbed and stiff-jointed, he resembles in many points the wolves and bears in whoso skins he wraps himself. As he ap- proaches the sunny south, his stature expands, his limbs acquire shape IT AFFECTS MIND AND CHARACTER. 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 heauty consist." 8. Extremes of Dress in Different Localities. The remarkable contrasts of temperature which different races experience, is well illustrated by their circumstances of dress. While in the West Indian Islands a single fold of cotton is often found to be an incumbrance, the Green- lander wraps himself in layer after layer of woollens and furs, fox-skins, sheep-skins, wolf-skins, and bear-skins, until we might suppose him well guarded against the cold ; yet with a temperature often a hundred degrees below the freezing-point, he cannot always protect himself against frozen extremities. Dr. KANE observes, " rightly clad, he is a lump of deformity waddling over the ice: unpicturesque, uncouth, and seemingly helpless. It is only when yon meet him covered with frost, his face peering from an icy halo, his beard glued with frozen respiration, that you look with intelligent appreciation on his many- coated panoply against king Death." 9. Temperature and haraeter. 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, delighting in the gorgeous, the daz- zling, and the marvellous. In the medium heat of temperate climates, these marked excesses of character disappear; there is moderation without stupidity, and active enterprise without fierce impetuosity. Society has more freedom and justice, and the individual more con- stancy and principle : with loftiness of thought, there is also chastening of the imagination. By comparing the effects of climate in the tor- rid, temperate, and frigid zone, we observe the determining influence of external conditions, not only upon the physical nature of man, but over the mind itself. " We may appeal to individual experience for the enervating effects of hot climates, or to the common understanding of men as to the great control which atmospheric changes exercise, not only over the intellectual powers, tut even on our bodily well- 22 INFLUENCE OF HEAT UPON THE LIVING WORLD. being. It is within a narrow range of climate that great men have been born. In the earth's southern hemisphere, as yet, not one has appeared ; and in the northern, they come only within certain paral- lels of latitude. I am not speaking of that class of men, who in all ages and in every country, have risen to an ephemeral elevation, and have sunk again into their native insignificance so soon as the causes which have forced them from obscurity cease, but of that other class of whom God makes but one in a century, and gives him a power of enchantment over his fellows, so that by a word, or even by a look, he can electrify, and guide, and govern mankind." (Dr. DEAPEE.) 10. Influence 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 fuel is scarce, houses are small, and their occupants crowded together ; the external air is as much as possible excluded ; the body becomes dwarfed ; and the intellect dull. The diminutive Laplander spends his long and dreary winter in a hut heated by a smoky lamp of putrid oil ; an arrangement which afflicts the whole nation with blear eyes. Scarcity of fuel has not been without its effect in forming the manners of the polished Parisians, by transfer- ring to the theatre and the cafe those attractions, which, in countries where fuel is common and cheap, belong essentially to the domestic hearth. 11. Temperature and Language. ABBUTHNOT suggested not only that heat and air fashion both body and mind, but that they also have a great effect in forming language. He thought the serrated, close way of speaking among the northern nations, was owing to their reluctance to open their mouths wide in cold air, which made their speech abound in consonants. From a contrary cause, the inhabitants of warm climates formed a softer language, and one abounding in vowels. The Greeks, inhaling air of a happy medium, were celebrated for speaking with the wide-open mouth and a sweet-toned, sonorous elocution. 12. Man may Make his own Climate, So controlling is this agent, and yet man comes into the world defenceless from its invasions; provided with no natural means of protection from 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 INFLUENCES THE DIMENSIONS 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 hody, 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. in. MEASUREMENT OF HEAT. THE THERMOMETER. 13. Heat tends to Equal Diffusion. We have said that heat is a force, or energy, existing everywhere throughout nature. Every kind of matter which we know contains heat, but all objects do not contain equal quantities of it. If left to follow its own law, heat would dis- tribute itself through all the matter around, until each body received a certain share ; and it would then be in a condition of general rest, or equal balance, (equilibrium.} It is to this state that heat constantly tends. If a very hot body of any kind is brought into a room, we all know it will at once begin to lose its heat, and that the temperature continues to descend until it is the same as the surrounding air, walls, and furniture. 14. How do we get acquainted with Heat? But before heat can tend to equilibrium, it must first be thrown out of this state. There are forces which tend to disturb the equal lalance of heat, causing it to leave some bodies, and accumulate in others in unusual or excessive quantities. It is the passing of heat from body to body, from place to place, robbing one substance of it and storing it up in another ; in short, its motion, and the effects it produces, which enable us to become acquainted with it. How, then, may we know when one. sub- stance has been deprived of heat and another has received it ? or how can we ascertain the quantity of it which a body possesses ? 15. Heat accumulating in Bodies, enlarges them. It is an effect of heat, that when it enters into bodies it makes them larger ; it increases their bulk, or expands them, so that they occupy more space than they did before. A measure that will hold exactly a gallon in winter, will be expanded by the heat of summer so as to hold more than a gallon. The heat of summer lengthens the foot-rule and yard-stick. A pen- dulum is longer in summer than in winter, and therefore swings or vibrates slower, which causes the clock to lose time. Twenty-three 24 TtfEASUEEMENT OF HEAT. pints of water, taken at the freezing point, would expand into twenty four by being heated to boiling. The difference in the heat of the seasons affects sensibly the bulk of liquors. In the height of summer. FIG. 1. spirits will measure five per cent, more than in the depth of winter. (GKAHAM.) When 180 degrees of heat are added to iron, 1000 cubic inches become 1045 ; 1000 cubic inches of air become 1365. Some substances, however, in solidifying expand. This is the case with water, which attains its greatest density, or shrinks into its smallest space, at the temperature of 3 8 '8, as seen in fig. 1. From this point, either upward or downward, it enlarges ; and greatest at freezing, or 32, the expansion amounts to about lslty ' th of its bulk. Ice therefore floats upon the surface of water. The wisdom of this exception is seen, when we reflect, that if it sank as fast as it is formed, whole bodies of water would be changed to solid ice. 16. Relation 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 the same quantities of heat ; but when a certain measured amount is added to, or taken from the same kind of substance, it always swells or shrinks to exactly the same extent. The variation of size produced in solid sub- stances, such as wood, stone, or iron, is very small ; we should not be aware of it without careful measurement. The same proportion of heat causes liquids, such as water, alcohol, and mercury, to vary in bulk more than solids ; while heat added to gases, or airs, produces a much greater expansion than it does in liquids. Although heat thus causes bodies to occupy more space and become larger, yet it does not make them heavier. The same substance weighs exactly the same, no matter how cold or how hot it is ; hence heat is called imponderable. 17. Principle and Construction 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 filled with the liquid metal mercury. By suitable means, the air is removed from the empty part of the tube, and its open end sealed up. The bulb is then dipped into water containing ice, and a mark is made SCALES OF THERMOACETEBS. 25 2123 Centigrade Scale. 100 Zero. upon the tube at the top of the mercurial column. This point of melting ice is the same as that at which water freezes, and is hence called the frees ing point. The tube is then FIG. 2. removed, and dipped into boiling water. Fahrenheit's The heat passes from the water, through 6cale - | the glass, into the mercury, which rapidly expands and rises through the narrow bore. It passes up a considerable distance, and then stops ; that amount of heat will expand it no more. The height of the mercury is again marked upon the tube, and this is called the 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 boiling point with another pound at the freezing point, the result will be a medium ; and if the thermometer is plunged into it, the mercury will stand at the ninetieth space that is, it contains 90 degrees of heat according to this scale of meas- urement. And so, by dipping the thermometer into any vessel of water, we ascertain how much heat it contains. 18. How Thermometers are Graduated or Marked. But this is not the way that the scale of the common thermometer is actually marked. Its inventor, FAHRENHEIT, instead of beginning to count his degrees upward from the freezing point, thought it would be better to begin to count from a point of the extremest cold. Accordingly, he mixed salt and snow (55) together, and putting his thermometer in it, the mercury fell quite a distance lower than the freezing point of water. This he supposed to be the greatest cold it is possible to get, though an intensity of cold has since been obtained 150 lower. Marking off this new distance through which the mercury had fallen, in the Bame 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 counted up to the freezing point of water, which was 32, and 2 Zero. Thermometer. 26 MEASUREMENT OF HEAT. , adding this to the 180 above, lie 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 np to boiling water into 100 degrees. In Keaurnur'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 indicates* The word thermometer is derived from ihermo, heat, and metron, measure, and it therefore signifies heat-measurer. But what does it measure ? That which is measured we usually name quantity. But we must not suppose that the thermometer indicates quantities of heat in any absolute sense. For example, if we dip a 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 gill of water as in the gallon. The thermometer shows us simply the degree of in- \ tensity of the heat in its mercury ; and as this constantly tends to the same point as that of surrounding bodies, we take its degree to be their degree. If the thermometer suspended in a room stands at V0, we say the room is at 70, because heat tends to equalization. If by opening windows or doors the thermometer falls to 60, we say the room has lost 10 of heat, speaking of it as a measured quantity. The instrument indicates variable degrees of intensity, which are con- verted into expressions of quantity. We shall shortly see that there are certain conditions of heat which the thermometer totally fails to recognize. 20. Importance of the Domestic use of the Thermometer. As the ques tion of temperature is one of daily and hourly interest, not only of the utmost importance in conducting numerous household operations, but of the highest moment in relation to the maintenance of health, it will at once be seen that a thermometer is indispenscible. Every family should have one, and accustom themselves to rely upon it as a practical guide in relation to heat, and not to depend upon feeling or guessing. Thennorneters costing from fifty cents to a dollar and a half, svill answer all ordinary purposes. They are so mounted that the scale. THERMOMETERS AND THEIR INDICATIONS. 2V and tube may be drawn out of the frame, so that the bulb can be im- mersed in a liquid, if required. They must be gradually warmed before dipping in hot liquids to prevent fracture of the glass, and of course need to be handled with much care. Their scales extend no higher than the boiling point of water. There is usually some departure from the accurate standard in the indications of the cheaper class of instru- ments. Mr. TAGLIABTJE, a prominent maker of this city, states that these variations rarely exceed from 1 to 2 degrees. 21. Interesting Facts of Temperature. We group together a few points of temperature of familiar interest.* Best temperature for a room 65M58* Lowest temperature of human body (in Asiatic cholera) 67" Mean temperature at the equator 81" Heat of the blood 98 Beef s tallow melts 100 Mutton tallow melts ' 106 Highest temperature of human body (in tetanus or lockjaw) .... 110" Stearine melts Ill" Spermaceti melts 112* Temperature of hot bath . 110-180 Phosphorus inflames, Friction matches ignite 120" Tea and coflfee usually drank . 180-140 Butter melts ISO'-M) 8 Coagulation of albumen 145" Scalding heat , * 150 Wax melts 155" Milk boils 199 Sulphur melts 226 Cane sugar melts ... 320 Baking temperature of the oven 820 9 ^400 Sulphur ignites 660 Heat of the common fire ... 1000' IV. RADIATION OF HEAT AND ITS EFFECTS. 22. Heat passing through Bodies. Heat in motion around us is con- stantly passing through some substance, or from one material body to another. But all substances do not behave alike toward it. They do not all receive, retain, or part with it in the same way. Through cer- tain bodies it passes rapidly in straight lines, like rays of light, and is then termed radiant heat, and this kind of heat-motion is called radi- ation, and the substances which allow it to pass through them are said to transmit it. We receive radiant heat from the sun and from arti- ficial fires ; and the air is one of those substances which permit it to pass through. * For a further list of temperatures., sec Appendix, A. 28 BADIATION AND ITS EFFECTS. Radiation of heat. 23. Decrease in the Force of Heat-rays. When heat radiates from any source, as the sun, a stove, an open fire, or flame, it passes from each point in ah 1 directions Fig. 3 ; it spreads out or diverges as it FlG - 8 - passes away so as to become weaker and much / ^ less intense. It decreases in power at a regular //'s' numerical rate, as seen in Fig. 4. It is commonly /'Xx^x-''^- sa id 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 is, a surface, which is the way it is practically emitted, it does not decrease at so rapid a rate. 24. Different kinds of Heat. We all know that some substan- ces will let light pass through them, and others will stop it. It is just so with heat : but the same substances which transmit light, do not always transmit heat. Air allows both to pass Showing the rate at which radiant heat is without obstruction ; but water, diffused and weakened. , . , ,, , ,, which so freely allows the pas- sage of light, has very little power to transmit heat. Rays of light, passing through water, are strained of nearly all their heat. But there seems to be a difference in the source and nature of the heat itself, as to its power of getting through various bodies. Glass allows 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 Ueat ; but it may be used as a fire-screen. If we place a plate of jlass and of rock-salt before a hot stove, the dark heal, will pass 'Veely through the salt, but not through the glass. The glass is, oherefore, opaque to heat (if we may borrow the language of light), while salt is transparent to it, and is hence called the glass of heat. CraCUMSTANCES CONTEOLUNG 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 will be 92 ; flint glass, 67 ; crown glass, 49 ; alum, 12 ; water, 11. 25. Heat which does not go through 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 51 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. Conditions of Radiation. The power of a body to emit or radiate heat, depends first, upon the quantity which it contains. Other things being the same, the higher its temperature compared with the sur- rounding medium, the more rapidly will it throw off its heat. As it cools, the radiation becomes slower and slower. But all subtances at the same temperature, do not throw out their heat alike. The condi- tion of surfaces exerts a powerful control over radiation. Rough, 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 MELOXI, surfaces smoked or covered with lampblack, radi ate most heat. If the power of radiation of such a surface be repre- sented by 100, that of glass will be 90 (it is therefore an excellent radiator), polished cast-iron, 25 ; polished wrought iron, 23 ; polished tin, 14 ; brass, 7 ; silver, 3. By tarnishing, or rusting metallic surfaces, their radiating power is increased. LESLIE has shown that, compared with a smoke-blacked surface, as 100, clean bright leacl is 19, while if tarnished, it is 45. If the actual radiating surface is metallic, it matters little what substance is under it. Glass covered with gold-leaf, is re- duced in its radiating power to the condition of a polished metal. 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. KUMFOED 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 RADIATION AND ITS EFFECTS. heat which was thrown off by the covered cylinder in 36 minutes, required 55 minutes to radiate from the naked cylinder. 27. How Polishing affects Surfaces. Dr. LAEDNEB says " the diminu- tion of radiating power, which ordinarily accompanies increased polish of surface, is not a consequence of the polish in itself, but of the in- creased density of the outer surface, produced by the act of polishing ; and the effect of roughening is to be ascribed to the removal of the outer and denser coating." 28. Best Mode of Confining and Retaining Heat, These principles show us how best to enclose and retain heat when we wish to prevent waste from radiation. Glass, porcelain, and stone ware surfaces, radiate freely : vessels of these materials are not the best to preserve foods and fluids hot at table. They should either be of polished metal, or have bright metallic covers, which will confine the heat. Bright tea- urns and coffee-pots are best to retain their contents hot ; and a tea- kettle keeps hot water much more effectually if clean and bright, than if covered with soot, though it is much harder to boil. Pipes intended to convey heat should be bright and smooth, while those designed to radiate or expend it, should be rough. For the same reason, polished stoves and stove-pipes are less useful in warming rooms than those with rougher surfaces. 29. Color of Snrfaces 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 facility. 30. Heat thrown off from Bodies. Eadiant heat striking upon bodies, if it is not permitted to pass instantly through them in straight lines, is either absorbed or reflected. If reflected, it is instantaneously thrown back from the surface of the body, and therefore does not enter to warm it. If absorbed, it is gradually taken into the substance, and raises its temperature. A bright metallic surface will reflect the heat rays and itself remain quite cold. As heat cannot get out through a bright surface, BO 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 HEAT-EXCHANGES. 8l bad absorber. So a good radiating surface absorbs well and reflects badly, while a bad radiating surface absorbs badly but reflects well. The density, or polish of a surface controls the admission as well as the escape of radiant heat. Two kinds of heat may thus pass in straight lines from a body radiant 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. 81. Color of Surface influences 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. FBANEXIX spread differently colored pieces of cloth upon snow in the sunshine. That of the black color sunk farthest below the surface ; which showed that it melted the most snow, and consequently received most heat. The blue piece sunk to a less depth, the brown still less, and the white hardly at all, which showed that it absorbed least heat. Hence, by scattering soot over snow, its melting may be hastened : it will absorb more of the solar heat. A dark-colored soil warms easier in spring, is earlier, and has a higher temperature during summer, than one in other respects similar but of a lighter color. Darkening a soil in color, therefore, is equivalent to removing it farther south. Grapes, and other fruits, placed against a dark wall, will mature or ripen 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 all Substances. It has been stated that, down to 200 below the freezing point of water, substances contain heat and may part with it : and as we know of no means by which heat can be absolutely enclosed or confined within bodies, all are regarded as not only possessing the power of radiation, but as actu- ally exercising it. Rays of heat pass away in every direction, from all points of the surfaces of all bodies. When several objects of various temperatures, some cold and some hot, are placed near each other, their temperatures gradually approach the same degree, and after a time they will be found to have reached it. Now all these bodies are supposed to be constantly radiating heat to each other, and hence con- stantly exchanging it If we place a cannon-ball at a temperature of 1000 or a red heat, beside another at 100, it will part with its heat rapidly to the latter, as illustrated by the radiant lines in Fig. 5. But the ball at 100 also radiates its heat, although more svowly, and thus returns a portion to the hotter ball ; so that there is an exchange estab- lished. But if a ball of ice at 82 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 ii F I0 . 5. an ice-ball from the Arctic region at 100 below the freezing point, were placed be- side another at 32, ex- actly the same thing would occur. Thus all bodies are constantly Exchanges of heat ; it radiates from bodies at all temper- interchanging heat and tending to equalization. 33. Starlight Nights colder than cloudy Ones. The various objects upon the earth's surface, are not only continually radiating their heat to each other, but also upward through the air into space. If there be clouds above, they throw it back again to the earth's surface ; but if the sky is cloudless, the heat streams away into space, and there is none returned. At night, therefore, when there is no heat coming down from the sun, and no clouds to prevent its escape from the earth, the temperature of the earth's surface and the objects thereon, falls. Those which radiate best, cool fastest, and 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 Produced. 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 Oi the atmosphere. The alchemists regarded it as an exudation from the stars. They believed dew-water contained celestial principles, and tried to obtain gold from it. The problem was solved about forty years ago, by Dr. WELLS, who first considered it in connection with the radiation of heat. The air contains moisture in the state of invis- ible vapor ; if its temperature be high, it will hold more moisture, if low,less (286). "When, therefore, the air is sufficiently cooled, its moisture is condensed, and appears as drops of water. These are often seen in summer day^ upon the outside of the pitcher of cold water ; improp rly called the sweating of the pitcher. The moisture that is seen trickling down the window-pane in winter, is condensed from the vapor of the air in the room, by the outward escape of heat from the glass, and the consequent cooling of the air in contact with it inside. When, therefore, by nightly radiation, any objects upon the earth's surface have become so cold as to cool the air in contact with them, IT 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 Is formed upon them. Good radiators become covered with dew, while bad radiators remain dry. Grass, for example, is an excellent radiator, and it receives dew copiously, while under the same circumstances, stones, being bad radiators, are not moistened. Dew is deposited from a stratum of air only a few inches thick, which is condensed by contact with the cold body. If, however, that stratum of air is moved away before it gets sufficiently cooled, no dew will be formed. Hence, when the air is in motion, as on windy nights, there is no dew. Fall of temperature always precedes the formation of dew, and the greater the fall, the heavier the dews ; the quantity of moist- ure in the atmosphere, in both cases being the same. Farmers very well know that nights with heavy dews are very cold ; but the cold is the cause, not the effect, of the dew. The moister the air is, with the same descent of temperature, the more dew falls. Thus, arid deserts are dewless, notwithstanding the intense nightly radiation. 36. Exchanges of Heat may preyent Dew. We have noticed PBEVOST'S theory of the exchanges of heat, by which, all bodies are assumed to radiate heat to each other constantly (32). This explains why little or no dew is found under trees. While the grass radiates upward, the foliage radiates downward, and thus checks cooling. For this reason, no dew is precipitated on cloudy nights. As objects radiate upward, the clouds radiate back again, and prevent the falling of the tempera- ture. More dew falls upon the summits of mountains, where objects are most open to the sky, than in valleys^ where the angle of radiation or access to the open heavens is much less. Objects protected in 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 gram 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, preserves plants, as may also fires that fill the air with smoke. V. CONDUCTION OF HEAT AND ITS EFFECTS. 38. Heat creeps slowly through some Bodies. If we place one end f a bar of metal in a fire, that end becomes hotter than the other parts of the bar. But this effect is only temporary ; the heat will gradually pass through it, being communicated from particle to particle, until FIG. 6. the other extremity becomes heated. This is easily shown by taking several marbles, and sticking them to an iron or copper wire with wax Tig. 6. If now heat is applied 1 9 to one end of the wire, it The balls drop 7 the heat moves wax is melted, and the marbles drop off successively. The heat in this case is conducted by the metal. 39. Different Substances conduct at different Rates. Heat diffuses in this manner, at very unequal speed through different substances. If we hold one end of a nail in a candle flame, it soon gets so hot as to burn the fingers ; while we can fuse the end of a glass rod in a lamp, although holding it within an inch of the melting extremity. Iron thus conducts heat much better than glass. Those substances through which heat is diffused most rapidly, are called good conductors, while those through which it passes slowly, are 'bad conductors. In general, the denser a body is, that is, the closer are its particles, the better does it conduct heat ; while the more porous, soft, loose and spongy it is, the lower is its conducting power. The metals, therefore, are the best conductors, while bodies of a fibrous nature, "such as hair, wool, feathers, and down, are the worst conductors of heat. 40. Rumford's Scale of Conductors. KTTMFOKD arranged bodies in the following order, their conducting power progressively diminishing as the list proceeds. Gold, silver, copper, iron, zinc, tin, lead, glass, marble, porcelain, clay, woods, fat or oil, snow, air, silk, wood-ashes, charcoal, lint, cotton, lampblack, wool, raw silk, fur. 41. Conducting Power of Building Materials. Bad conductors, non- conductors, as they are called, afford the best barriers to heat, and they are employed when it is desired to confine it. In winter, nature protects tha earth and crops from excessive cold, by a layer of non- EFFECTS OF NON-CONDUCTING SUBSTANCES. 35 conducting snow. The birds, she protects by feathery and downy plu- mage ; quadrupeds, by hair, wool, fur ; and even the trees, by porous, non-conducting ^bark. In the management of heat, 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. HTTTCHINSON examined some building materials, and ascertained their conducting powers to be as follows, omitting fractions. (Slate being taken as 100.) Marble 75 to 58, fire brick 62, stock brick 60, oak wood 34, lath and plaster 25, plaster of Paris 20, plaster and sand 18. The hard woods conduct better than soft, and green woods better than dry. Dry straw, leaves, &c., are good non-conductors, and are used to cover tender plants in winter, but if wetted, they convey heat much better. 42. Son-conducting; properties of Air. Air is one of the most perfect non-conductors; RUMFOED thinks it is the best of all. The conduct- ing power of air, however, is greatly increased by moisture. If we represent the power of common dry air to conduct heat, by 80, its power, when loaded with moisture, rises to 230, it is nearly trebled. For this reason, damp air feels colder to the body it conducts away its heat faster. Those substances which enclose and contain air, as pow- dered charcoal, tan-bark, sawdust, chafi^ &c., 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. Jfon-eondueting Properties of Clothing. 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- Jeve the body of heat, but it cannot defend the system like flannel against the sudden changes of temperature in an inconstant climate. In local inflammation of the body, linen is the best for dressings and applications, as it is a better conductor, and therefore cooler than cot- 86 CONVEYANCE OF HEAT. ton.* The 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. Our Sensations of Heat depend upon Conduction, The sense of touch is an unreliable guide to the degree of heat, because substances are so diverse in conducting power. The badly conducting carpet feels warmer to the naked feet than the better conducting oilcloth, because the latter will carry away the heat faster from the skin, al- though both are at exactly the same temperature. This influence of conduction over sensation, as also the remarkable difference of con- ducting power among solids, liquids, and gases, may be shown in a forcible manner. If the hand be placed upon metal at 120 it will be burned, owing to the rapidity with which the heat enters the flesh. "Water will not scald, provided the hand be kept in it without motion, till it reaches the temperature of 150 ; while the contact of air at 250 or 300 may be endured. Sir JOSEPH BANKS went into a room, heated to 260, and remained there a considerable time without incon- venience. The particles of air are so far asunder, that the heat crosses their inter-spaces with difficulty ; and as but few of them can come in contact with the body at once, the amount of heat that they can impart is comparatively small. VI. HEAT CONVEYED BY MOVING MATTER. 45. It is carried by Particles in Motion. The freedom with which the particles of liquids and gases move among each other, is another source of the motion of heat. Water conducts heat but very imperfectly. If a glass tube filled with water, be inclined over a lamp, so that the Fia - 7t flame is applied at the upper end Fig. 7, the water will boil at the top of the column, but below the point where the flame is applied, the temperature of the water will be but lit- tle elevated in a long time. The conduction of heat is not influenced by the position of the body along which it passes. It moves through a conductor as swiftly downward as upward, The water d^Tot conduct or horizontally. Had the heat, in this case, the heat downwards. been conducted, it would 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 smooth, 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 TRANSPORTATION BY WATEK. 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-enmnts may be shown. The circulation thus pro- duced by ascending and descending currents, may be i)eautirally 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 Fig. 8. Two causes operate here to distribute the heat. The warm liquid constantly conveys it away, and at the same time, the colder particles are con- tinually brought back to the source of heat, at the bottom. Exactly the same thing takes place when air is heated ; it expands, becomes lighter, rises in currents, and carries with it the heat. We shall refer to this principle again, when speaking of the contrivances for warming rooms. FIG. 8. Currents produced in water by boiling. VII. VARIOUS PROPERTIES AND EFFECTS OF HEAT. 47. Heat added to Solids, liquefies them. Xot only is the size of bodies influenced by heat, but also their state, or form. As heat enters a solid body, its particles are forced asunder, until at length they lose their cohesive hold of each other, and fall down into the liquid state. The particles have become loosened and detached, and glide freely among each other hi all directions. Carbon and pure alumina are the only substances that have not been liquefied by any amount of heat yet applied. Some solids, at a given point of temperature, enter 38 VARIOUS EFFECTS OF 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 substance, is called its melting or fusing point. The com- mon temperature of the air is sufficient to melt some substances. From this point all along up to the highest heat, at which carbon re- fuses to liquefy, various substances melt at different temperatures, showing that each requires its particular dose of heat to throw it into the liquid state. Thus, mercury is a liquid at common temperatures, and is the only metal that exhibits this peculiarity. Phosphorus melts at 108, wax 142, sulphur 226, sugar cane 320, tin 442, lead 612, zinc 773, silver 1873, gold 2016, iron 2800. Liquidity seems thus to be produced by the combination of solids with heat. Take the heat from a liquid and it solidifies. Take away the heat from water until it falls to 32, and it becomes solid water, or ice. If kept per- fectly still, it may be lowered below 32 before the atoms lock to- gether into the crystalline or congealed state ; but if the water is jarred or agitated, crystalline ice results at that temperature. Heat taken from mercury until it falls to 39 below zero, causes it to harden into a solid, ringing metal -freezes it. - 180 of heat taken from alco- hol, do not freeze, but make it thick and oily. As heat combined with solids produces liquids, so heat combined with liquids produces vapors or gases. Heat added to ice generates water added to water generates steam. The heat which converts solids into liquids, is called caloric of fluidity, and as gases are known as elastic fluids, the heat which changes liquids to gases is called caloric of elasticity. 49. What is meant by Specific Heat. If we take equal weights of different substances, and expose them to the same sources of heat, they do not all receive it with equal readiness ; in the same length of time some will be much more warmed than others. If a lamp flame of a given size will raise the temperature of a pound of 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 will take the same flame twenty minutes, or twice as long. It is clear that the water in this case, in being raised through the same temperature, has received twice as much heat as the spirits of turpentine. If a flame of a certain size will heat a pound of mercury through a certain number of degrees in a certain time, it will take 30 flames of the same heating power, to raise a pound of water through the same range cf temperature in the same period ; to raise it through the same number of degrees, therefore, water requires thirty times WATER HOLDS LAEGE QUANTITIES OF IT. 39 the heat that mercury does. This would seem to show that different bodies have different capabilities of holding or containing heat, or, as it is usually said, they have different capacities for heat : and, as each substance seems to take a peculiar or particular quantity for itself; that quantity is said to be its * specific' 1 heat. The specific heat of water is greater than that of any other substance. In ascending from a given lower to a higher point, it takes into itself or swallows up more heat than any other body ; and in cooling down through that temperature, as it contains more to impart, so it gives out more heat khan any other body. If the specific heat of water is represented by 1000, that of an equal weight of charcoal is 241, sulphur 203, glass 198, iron 113.79, zinc 95.55, copper 95.15, mercury 33.32. 50. Why Water was made to hold a large amount of Heat. When we consider the extent to which water is distributed upon the earth, we see the wisdom of the arrangement by which it is made to hold a large amount of heat, and the necessity that it should slowly receive, and 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 Bummer 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 drunk. It is because water is capable of receiving so much heat, that it is better adapted than any other substance to quench thirst. A small quantity of it will go much further in absorbing the feverish heat of the mouth, and throat, than an equal amount of any other liquid. "When swallowed and taken into the stomach, or when poured over the inflamed skin, it is the most grateful and cooling of all substances, For the same reason, a bottle of hot water will keep the feet warm much longer than a hot etone or block. 52. Concealed or latent Heat. All changes in the densities of bodies by which their particles are forced into closer union, or to greater distances apart, are invariably accompanied by changes of heat. Caloric is supposed to be contained in bodies, something as water is Ueld in a sponge lodged in its cavities or pores. If a wet sponge is 40 VAKIOUS EFFECTS OF HEAT. compressed, water is squeezed out ; but, when it expands again, it will again imbibe the liquid. In like manner material substances, when condensed into less space, give out heat, and, when dilated, they take it in or absorb it. If a piece of cold iron is smartly ham- mered upon an anvil, its particles are forced closer together, and its heat is driven out of its concealment, the iron becomes hot. By suddenly condensing the air as in the instrument called the fire-syringe, FIG 9 * n wn * c h a c ^ ose fitting piston is driven down a tube (Fig. 9), the condensed air gives out so much heat as to set fire to tinder. Now, before condensing the iron, or the air, in these cases, they appeared cold, the thermometer de- tected in them no heat; yet they contained heat, and condensation brought it out. As we cannot find it by the ordinary test, we infer that it was concealed or latent in the iron and air. Heat is capable, therefore, of be- coming lost or hidden in bodies, and then of again re-appearing under proper circumstances. "We call this latent heat, because we must call it something, and the term is convenient ; but we are probably very far from a Air condenser. , . . , , -, , . . , true explanation of the facts in the case. 53. How much Concealed Heat Water holds. 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 32 degrees. It then becomes stationary, although the application of heat is continued. But another change now sets in the ice begins to melt. While this continues, the thermometer does not rise, and the water at the end of the melting is at exactly the same temperature that the ice was at its commence- ment. As soon, however, as the ice is all melted, the mercury begins again to ascend, and the water becomes warm. Now, all the heat which entered the ice to liquefy it while the mercury was standing still, went into retirement in the water which was produced became latent. It is very easy to. find out how much heat becomes thus hidden when ice changes to water. If we take an ounce of ice at 32, and an ounce of water at 174, and add them together, the ice will melt and we shall have two ounces of water at 32. The ounce of hot water, therefore, parted with 142 of its heat, which has disap- peared in melting the ice. 142 is thus the latent heat of fusion of ice, which is hidden in the resulting water. The quantity of latent heat absorbed by different solids in entering upon the liquid condition STABILITY OF FORMS PRESERVED. 41 Is variable, but a certain amount disappears in all cases. Thus, if a mass of lead be heated to 594, it will then become stationary, although the addition of heat is continued ; but the moment the temperature ceases to rise, it will begin to fuse, and the temperature will continue steadily at 594 until the last particle of lead has been melted, when it will again begin to rise. Those who have attempted to procure hot water from snow for culinary purposes, know by the delay of the result the great loss of heat which is involved. The heat necessary simply to melt 100 pounds of ice, without raising its temperature a single degree, would be sufficient to raise more than 80 pounds of ice- cold water up to boiling. 54. Beneficial Effects of this Law. This law of the latent heat of liquidity, operates admirably to preserve the 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, w r hen ice is at 32, the addition of one degree of heat would raise it to 33, and thus throw it into the liquid form, all the accumulated snows of winter might be turned almost in an hour into floods of water, by which whole countries would be inundated. But so large a quantity of heat is required to produce this change, that time must become an element of the process ; the snows are melted gradually in spring, and all evil consequences prevented. 55. Principle of Artificial Freezing. A solid may be changed to a liquid without the direct addition of heat. Attraction or affinity may produce the change. Yet the same amount of heat is required to go into the latent state. Salts have a strong attraction for water. If we put some common salt or saltpetre into water at the common temper- ature, it will become colder. The salt in dissolving, that is, in assum- ing the liquid state, must have heat ; it therefore takes it from the surroundiog water, which, of course, becomes colder. A mixture of five parts sal-ammoniac and five of saltpetre, finely powdered, and put in nineteen parts of water, will sink its temperature from 50 to 10 ; that is, 40 degrees. When snow is mixed with a third of its weight of salt, it is quickly melted. The powerful attraction of the salt forces the snow into a liquid state ; but it cannot take on this state without robbing surrounding bodies of the heat necessary to its fluidity. Ices for the table are made in summer by mixing together pounded ice and salt, anC immersing the cream or other liquid to be frozen (contained in a thin metallic vessel,) into the cold brine, produced by the melting of the ice and salt. A convenient method of freezing a little water 42 VARIOUS EFFECTS OF HEAT, without the use of ice, is to drench powdered sulphate of soda (glauberV salt) with muriatic acid. The salt dissolves to a greater extent in this acid than in water, and the temperature may sink from 50 to zero, ! The vessel in which the mixture is made, becomes covered with frost ; and water in a tube, immersed in it, becomes speedily frozen. 56. Freezing liberates Heat. If the change of a solid to a liquid 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 i thawing of snow and ice in spring, is delayed by the large amount of ; heat that must be stored away in the forming water, so the freezing processes of autumn are delayed, and the warm season prolonged, by the large quantities of heat that escape into the air by the changing of water to ice. The same principle is made available to prevent the freezing of vegetables, fruits, &c., in cellars during intense cold weather. Pails or tubs of water are introduced, which, in freezing, give out sufficient heat to raise the temperature of the room several degrees. Freezing is thus made a means of warming. 57. Evaporation of Water. Water, at the surface, is constantly changing into invisible vapor, and rising into the air, which is called evaporation. It goes on at all temperatures, no matter how cold the water is : indeed, evaporation constantly takes place from the surface of ice and snow. The ice upon the window often passes off as vapor, without taking on the 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 air, which is diffused through all natural waters, to the ex- tent of about four per cent., and which is partially expelled by heating. As the temperature increases, larger bubbles are formed at the bottom of the vessel, which rise a little way, and are then crushed in and dis- appear. These bubbles consist of vaporized water, or steam, which \ CONDITIONS WHICH INFLUENCE BOILING. 43 formed in the hottest part of the vessel ; but as they rise through the colder water above, are cooled and condensed. The simmering or singing sound of vessels upon the fire just before boiling, is supposed to be caused by vibratory movements produced in the liquid by the formation and collapse of these vapor -bubbles. As the heating continues, these steam globules rise higher and higher, until they reach the surface and escape into the air. This causes that agitation of the liquid which is called boiling or ebullition. 59. Influence of the vessel in Boiling. Different liquids boil at differ- ent temperatures : but the boiling point of each liquid varies with circumstances. The nature of the vessel has something to do with it, which depends upon its attraction for the water. To glass, and pol- ished metallic surfaces, it adheres with greater force than to vessels of rough surfaces. Before the water can be changed to vapor in boiling, this adhesion must first be overcome. Water upon the surface of oil, boils two degrees below water in a glass vessel, in conseauence of the oil having no attraction for the water. 60. Measuring the Pressure of the Air. Air has weight like visible ponderable matter, and presses down upon the surface of water the same as upon the ground. The pressure of the air is measured by a barometer, which is simply a glass tube about FIG. 10. 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 VARIOUS EFFECTS OF HEAT. certain quantity of air to press down upon, the earth, in go^ng 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 boiling. The reason is, that the boiling water is not hot enough ; and the reason of that is that the pressure of the air being partially taken off, the water finds less resistance to rising into vapor, and a lower degree of heat produces the 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 Principle in Refining Sngar. 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 ant 1 ', purified. It is then reproduced by evaporating away the water. But the heat of the common boiling point is too great. So the refiner pumps out the air from above the boiling pans, by means of a steam- engine. The pressure is taken off, and the water boils away at a low temperature, leaving the sugar crystals perfect. 63. Elevation of the Boiling Point. If the weight of air pressing upon a liquid affects its boiling point, for the same reason the weight of the liquid itself, must affect it. When salts are dissolved in water, they render it heavier, and its boiling point is always raised. Some salts, however, raise it more than others. "Water saturated with com- mon salt (100 water to 30 salt}, boils at 224 ; saturated with nitrate of potash ( 100 water to 74 salt}, it boils at 238 ; with chloride oi calcium, at 264. Ether boils at 96 (blood heat); alcohol, at 174; turpentine, at 316 ; mercury, at 662. The viscidity of a liquid, or the glutinous coherence of its particles is opposed to its free ebullition. 64. Spheroidal state of Water. Water in contact with highly heated metallic surfaces does not boil or vaporize. All may have noticed it dancing or darting about in globules upon a hot stove. The reason offered why a globule does not evaporate from a red-hot surface is, that a stratum of steam is formed under it, which props it up, so that it is not really in contact with the iron ; and steam being a noncon- ductor, cuts off also the heat. Water enters upon the spheroidal state between 288 and 340 of the hot surface : but when the temper- ature falls, the steam no longer sustains the drop ; it is brought into ITS RELATION 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 hy its effects upon a drop of saliva let fall upon it. If the drop adheres, wets the iron, and is rapidly vaporized, the temperature is considered low; tut if it run along the surface of the metal, it is regarded as suf- ficiently hot. 65. But little Heat required to maintain Boiling. If a liquid be con- fined in a sufficiently strong vessel, so that its vapor cannot escape, it may be heated to any desired point of temperature ; though at high heats, vapors acquire such an expansive and explosive energy as to ourst vessels of the greatest strength. But if the liquid be exposed to the air, it is impossible to raise its temperature above its natural boil- ing point. All the heat that is added after boiling commences, is car- ried away by the vapor. The rapidity with which water is raised to the boiling point, depends upon the amount of heat which is made to enter it. But when this point is reached, a comparatively small quan- tity of heat will maintain it there just as well as more. Water boiling violently, is not a particle hotter than that which boils moderately. When water is brought to the boiling point, the fire may be at once reduced. Attention to this fact would save fuel in many culinary operations. 66. Double Vessels to Regulate Heat. If we have a substance which, placed directly over the fire, would receive an indefinite quantity cf heat, but which we desire to raise only to a certain temperature, we place it hi a vessel surrounded by another vessel ; the outer one being filled with a liquid which boils at the desired temperature. HECKEE'S farina ket- tle, Fig. 11, is a culinary contrivance of this kind. The outer vessel is filled with water, while the inner one contains the material to be cooked, which, of course, can- not be heated higher than the boiling point, and is therefore protected from burning. By using any of the salt solutions mentioned (63), higher heats may be communicated to the internal vessel Section of a culinary bath : a opening to introduce water. 67. Wliy Puddings, Pies, &c., eool 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. FIG. 11. 46 VARIOUS EFFECTS OF HEAT. and so become diffused through it. We do not, therefore, heat it by conduction, but by currents produced within it (46), which distribute | and commingle the heat throughout its mass. It cools in the same way. As the particles at the surface or sides lose their heat, they fall to the bottom, and others succeed them. If the particles of water could remain stationary, it would be slow and difficult to heat, and i equally slow to cool. For this reason soups, puddings, pies, &c., which contain large amounts of hot water, so enclosed and detained in their - places that they are not free to circulate, and therefore, are not in at condition to lose their heat, keep hot longer, and cool slower than equal bulks of simple fluids. 68. Concealed Heat of Vapor. As the liquid state is the result oft heat combined with solids, the vaporous state is the further result of heat combined with liquids. Enormous amounts of heat are necessary to convert liquids into vapor, but the vapors are no hotter, according to the thermometer, than the liquids were ; they are, there- fore, reservoirs of insensible heat. All the heat which is necessary to boil off a liquid, becomes latent in its vapor. The heat that thus^ enters the boiling liquid without raising its temperature, must go somewhere. It is not sensible in the vapor which ascends from its , surface, for that is no hotter than the liquid from which it came. It ; is contained in the vapor, for it may all be again recovered from it. , The quantity of heat which becomes latent in the process of evapora- tion, is very large. With the same intensity of heat it takes 5| times as long to evaporate a pound of water, as it does to raise it from > freezing to boiling ; it therefore receives 5 times as. much heat. If, therefore, 180 were required to boil the pound of water, 1000 are required to change it into a pound of vapor ; but, as the pound of vapor is no hotter than the pound of water, 1000 of heat must of course be concealed in it. The latent heat of steam is then 1000 j , when condensed, it surrenders that 1000 of heat. The condensation of a pound of steam will raise 5^ pounds of water from the freezing to the boiling point. This fact makes steam a valuable agent for 1 transporting heat, as is done by means of steam pipes for warming buildings (129). Wherever condensed, it liberates large quantities of boat. 69. Cooling effect of Evaporation. Evaporation is therefore a cooling process it buries or temporarily destroys active heat. For this reason damp soils, although in all other respects like dry ones, are colder. Evaporation dissipates the heat which falls upon them. The heat poured down from the sun in torrid regions would be intolerable, ITS DELATION TO EVAPORATION. 47 were it not for the cooling effect of rapid evaporation. Apartments are cooled in hot countries by evaporation, which proceeds from wet curtains. The skin of the body contains millions of little microscopic pores, through which water (perspiration) is constantly pouring out to the surface. As it then evaporates into the air and absorbs heat, it becomes a powerful cooling agency and regulator of bodily temperature ; while the vapor, which escapes from the breath, exerts a cooling effect within the body. It is very interesting to observe how the great capacity of liquid water for heat, makes it so gratefully cooling as it enters the body ; and how its still greater capacity for heat, when passing from the liquid state to the condition of vapor, enables it so constantly to bear away from us the germs of ferer as it escapes from the system, in the form of insensible perspiration or vapor. The cooling effect of fanning the face, is partly due to the more rapid removal of the vapor of perspiration from the skin, and partly to the conduction of heat by the particles of moving air. Breezes cool us in the same way. Wet floors become a source of cold, in rooms, through vaporization. The pernicious effect of wearing wet clothing is caused by the rapid evaporation which proceeds from it, thus robbing the body of large quantities of heat. "When a person is obliged to remain in wet clothing, evaporation may be stopped by putting on an outer garment, which cuts off the external air. TO. Reason of " Wowing Hot and blowing Cold." It was stated that when air or gases are condensed, heat is set free ; on the contrary, when they are expanded, their capacity for latent heat is increased, it is absorbed, and cold is produced. This is a main cause of the danger when streams of air reach us through cracks and apertures, although a part of the mischief is caused by conduction-. This peril is expressed in the old distich "If cold air reach you through a hole, Go make your will and mind your souL" Ah*, spouting in upon us in this manner, not only cools by conduction and evaporation, but, having been condensed in its passage through the chink, it expands again, and thus absorbs heat. This is also familiarly illustrated by the process of cooling and warming by the breath. If we wish to cool any thing by breathing on it, the air is compressed by forcing it out through a narrow aperture between the lips ; as it then rarefies, it takes heat from any thing upon which it strikes. If we desire to warm any thing with the breath, as cold hands, for example, we open the mouth and impel upon it the warm air from the lungs without disturbance from compression. 48 INFLUENCE OF HEAT UPON THE BODY. VIII. PHYSIOLOGICAL EFFECTS OF HEAT. 71. Local influence of Heat npon the Body. It has been noticed tha*l the general effect of heat upon bodies is to expand them (15). It acts 1 in this way upon the living system, just as upon all other objects. The pleasant sensation of warmth is occasioned by an expansion of the vessels of the skin, and the liquids which they contain ; these are ren- dered less viscid and thick by heat, and made to flow more readily, which produces an agreeable feeling. If the application of heat to ai part be continued, the surface becomes red. The diameters of the minute capillary blood-vessels are so expanded, that the red blood-disks- are enabled to enter tubes which would not previously admit them. The temperature rises, and there is a slight swelling or increase of the volume of the part, owing partially to the dilatation of the solids and liquids, but chiefly to the presence of an increased quantity of blood. The living tissues at the same time become more relaxed, soft and flexible, and allow rapid perspiration. More heat still produces greater expansion. There is a sense of pain, the organic structure is decom- posed, the liquids begin rapidly to dissipate in vapor, and the surface becomes inflamed, blistered, and burned. Y2. General influence of Heat npon the System. The body is subject to the action of two kinds of stimulants. Vital stimulants are those external conditions, such as air, water, food and warmth, which are necessary to the maintenance of life. Medicinal or alterative stimulants < are those agents or forces which produce temporary excitement within the system, but ultimately depress and exhaust it. Now, in the pro- portion that is necessary simply to maintain the system at its natural temperature, heat is a healthful, vital stimulant; but beyond this it becomes a disturbing, exhaustive, health-impairing agent. The first effect in undue quantity is excitation ; the secondary effect, exhaustion. In the first instance, sensibility is agreeably promoted, voluntary muscular movement assisted, and the mind's action somewhat exalted ; but to these effects succeed languor, relaxation, listlessness, indispo- sition to physical and mental labor, and tendency to sleep. The body possesses a powerful means of self-defence against excessive heat, in the cooling influence of surface evaporation (69), but this power of the system cannot be taxed with impunity. The rush of the circulation to the surface, and the increased transpiration and secretion of the skin, are accompanied by a necessary diminution in the activity of some of the internal organs. As the exhalation from the skin rises, the secretion of the kidneys and mucous membranes falls. The pre- EFFECTS OF SUDDEN CHANGES FUEL. 49 vailing maladies of hot climates may be referred to, in illustration of the effect of continued heat on the body. Fevers, diarrhoea, dysen- tery, cholera, and liver diseases, may be regarded as the special mala- dies of the burning, equatorial regions. (PEREIBA.) 73. Consequences" of sadden Changes. But the worst effect of exces- sive heat, is not always the immediate stimulation, and consequent ex- haustion which it induces ; it is the sudden exposure to various de- grees of cold which often follows, when the system is in a relaxed and depressed condition, that accomplishes the most serious mischief, lay- ing the train for so many cases of afflicting disease, and premature death. The effect of passing from an over-heated apartment out into a freezing air bath, is suddenly to check the cutaneous circulation, and drive the blood inward upon the vital organs, thus often engendering fatal internal disease. It is thought that a temperature from 60 to 65 is, perhaps, the safest medium at which an apartment should be kept, so that the individual may not suffer from transition to external cold. If this temperature seem uncomfortably low, it is better to in- crease the apparel than to run up the heat, and risk the consequences of subsequent exposure. IX. ARTIFICIAL HEAT PROPERTIES OF FUEL. 74. Artificial heat may be produced in various ways, but the com- mon method is by combustion, which is a chemical operation carried on in the air. AIT the heat which we generate for household purpo- ses, is caused by the chemical action of air upon fuel. But what part of the ah* takes effect ? The main bulk of the air is composed of two elementary gases, oxygen and nitrogen. In every five gallons of air, there are 4 of nitrogen and 1 of oxygen, mixed and diffused through each other (281). Nitrogen, when separated, proves to have no active qualities ; it cannot carry on combustion, it puts out fire. Oxygen, on the contrary, when separated, proves to be endowed with wonderful chemical energy. A fire kindled in it, burns with unnatu- ral violence ; its chemical powers constitute the active force of the air. The nitrogen dilutes and weakens it, thus restraining its ac- tivity. 75. Composition of Fnel, Office of Carbon. The fuel upon which oxygen of the air takes effect in the burning process, consists of vari- ous kinds of wood and coal. These are chiefly composed of three ele- ments oxygen, hydrogen, and carbon, in various proportions. The ygen they contain, contributes nothing to their value as fuel ; tTiat a 50 PROPERTIES OF FUEL. depends upon the other elements : hence, the more oxygen, the less there can be of these other substances, and, of course, the poorer the fuel. Carbon exists largely in all woods and coals. Oxygen and hy- drogen, when in their free state, that is, uncombined, are always gases ; they never appear as liquids or solids, and no one has yet been able to force them into these states. Carbon, on the other hand, is an unyielding solid. No chemist has ever yet been able to prepare either liquid carbon or gaseous carbon. At the intensest white heat, where nearly every other substance melts, or dissipates into vapor, carbon remains fixed. It is the solidifying element of fuel, and it is this property which makes our fires stationary. 76. Hydrogen, and its Office in Fnel. Hydrogen gas, the other ele- ment of fuel, when set free is the lightest substance known, being 14 times lighter than air. It is of so light and volatile a nature, that it will combine with solid carbon, and even iron, and carry them up with it into the gaseous state. When combined with fuel, it is condensed down into a solid state, but in the act of burning, it is released, and escapes into the gaseous form. It therefore lurns in motion, and it is this which produces flame. In all ordinary combustion, the flame is caused by the burning hydrogen, and the larger the quantity of this substance in fuel, the greater the flame it will yield when burnt. 77. Why it is necessary to kindle a Fire. Now, for these two sub- stances, oxygen has powerful attractions, and combines with them, producing combustion and heat. Yet atmospheric oxygen is every where in contact with all kinds of fuel without setting them on fire. Why is this ? Because the natural attractions of these substances are so graduated, that they do not come into active play at low tempera- tures. If carbon combined with oxygen at common temperatures, with the same readiness and force that phosphorus does, wood and coal would be ignited like a match, at the slightest friction, and com- bustive processes would be ungovernable. But as man, all over the world, civilized and savage, is designed to develope and manage fire through the agency of these substances, their energies have been wisely restrained within the limits of universal safety. This makes it necessary to resort to some means, as friction or percussion, to gener- ate heat necessary to start combustion, or kindle the fire. 78. Products of Combustion. When the combustive process has commenced, two things take place ; the fuel disappears, and the air is changed. The substance of fuel is not destroyed, it only changes its shape, takes on the invisible form, and mounts into the air. Oxygen sombines with carbon, both elements disappear, and a new product ITS CHEMICAL CONSTITUENTS. 51 results carbonic acid gas (293). As carbonic acid is thus given off every where by combustion, it is a constant and universal constituent of the atmosphere. It forms l-2000th of the air, and would increase in quantity, but it is constantly withdrawn by plants. When pure, it extinguishes fire, and when mingled with the air it rapidly diminishes its power of sustaining combustion. When oxygen combines with the hydrogen of fuel, it produces vapor of water, which rises with the carbonic acid and disperses through the air. 79. Fuel is changed before it is burned. In burning, oxygen does not combine directly with hydrogen and carbon, changing them at once to water and carbonic acid. The heat of combustion first decomposes the fuel and re- combines its atoms, forming various compounds under different circumstances, and it is with these that oxygen unites. They consist mainly of hydrogen and carbon, and are more abundant as the proportion of hydrogen in the fuel increases. It is rare that these products, thus distilled out of fuel in the burning process, are completely consumed by oxygen; a portion of them escapes, constituting smoke. 80. Heating powers of Hydrogen and Carbon. The proportion of carbon in fuel is always very much greater than that of hydrogen, but the amount of heat which they give out is not in proportion to their relative weights. A given weight of hydrogen, when burned, wiL produce three times as much heat as the same weight of carbon. A pound of charcoal, which is nearly pure carbon, in burning, produced sufficient heat to change 75 pounds of water from freezing to boiling ; while a pound of hydrogen yielded heat enough in burning, to change 236.4 pounds through the same number of degrees. The heat is in proportion to the oxygen consumed; the pound of hydrogen united with 8 pounds of oxygen ; while a pound of carbon took but 2| pounds of it. The heating power of fuel thus depends upon chemical com- position, but it is also influenced by other circum stances. 81. How Moisture affects the Value of Wood. When wood is newly cut, it contains a large quantity of water (sap), varying in different varieties, from 20 to 50 per cent. Trees contain more water in those seasons when the flow of sap is active, than when growth is suspend- ed ; and soft woods contain more than hard. Exposed to air a year, wood becomes air dried, and parts with about half its water ; 15 per cent, more may be expelled by artificial heat ; but before it loses the last of its moisture, it begins to decompose, or char. The presence of water in wood diminishes its value as fuel in two ways ; it hinders and delays the combustive process, and wastes heat by evaporation. 52 PROPERTIES OF FUEL. Suppose that 100 pounds of wood contain 30 of water, they havo then but 70 of true combustive material. When burned, 1 pound of the wood will be expended in raising the temperature of the water to the boiling point, and 6 more in converting it into vapor ; making a loss of 7 pounds of real wood, or ^ of the combustive force. Be- sides this dead loss of 10 per cent, of fuel, the water present is an an- noyance by hindering free and rapid combustion. 82. Heating Value of different kinds of Wood. Equal weights of differ- ent varieties of wood in similar conditions, produce equal quantities of heat ; but it will not do to purchase wood by weight, on account of the varying quantity of its moisture. It is sold by measure ; but equal measures or bulks of wood do not yield equal amounts of heat. According to the careful experiments of Mr. MARCUS BULL, the rela- tive heating values of equal bulks (cordx) of several American woods, are expressed as follows ; shell-bark hickory being taken as 100. Shell-bark Hickory . . .100 Pignut Hickory ... 95 White Oak . . . .81 White Ash .... 77 Dogwood 75 Scrub Oak . . . . 78 Witch Hazel .... 72 Apple tree 70 Red Oak 69 White Beech .... 65 Black Walnut .... 65 Black Birch ... 63 Yellow Oak 60 Hard Maple . .60 White Elm ... 58 Eed Cedar . .56 Wild Cherry .... 55 Yellow Pine .... 54 Soft Maple 54 Chestnut 52 Yellow Poplar .... 52 Butternut 51 White Birch .... 48 White Pine 42 83. Soft and Hard Woods. Some woods are softer and lighter than others, the harder and heavier having their fibres more densely packed together. But the same species of wood may vary in density, accord- ing to the conditions of its growth. Those woods which grow in for- ests, or in rich, wet grounds, are less consolidated than such as stand exposed in the open fields, or grow slowly upon dry, barren soils. 84. Why Soft and Hard Woods bnra differently. There are two stages in the burning of wood : in the first, heat comes chiefly from flame; in the second, from red-hot coals. Soft woods are much more active in the first stage than hard; and hard woods more active in the second stage than soft. The soft woods burn with a voluminous flame, and leave but little coal ; while the hard woods produce less fla?-e, and yield a larger mass of coal. The cause of this is partly, that the soft woods, being loose and spongy, admit the air more freely, but it is chiefly owing to differences in chemical composition. Pure BUBNING OF WOOD AND COAL. 53 woody fibre, or lignin, from all kinds of wood, has exactly the same composition ; a compound atom of it containing 12 atoms of carbon, 10 of hydrogen, and 10 of oxygen or there is just enough oxygen in it to combine with all its hydrogen and change it to water in burning. But in ordinary wood, the fibre is impure ; that is, associated with other substances which practically alter its composition. The hard woods are nearest in composition, to pure lignin, but the softer woods contain an excess of hydrogen. For this reason, they burn with more vehemence at first ; more carbon is taken up by the hydrogen, in pro- ducing flame and smoke, and the residue of coal is diminished. The common opinion, that soft wood yields less heat than hard (equal weights) is an error; it burns quicker, but it gives out an intenser heat in less time, and is consequently better adapted to those uses w r here a rapid and concentrated heating effect is required. 85. Charcoal as Fuel. Charcoal is the part that remains, when wood has been slowly burned in pits or close vessels, with but a limited sup- ply of air, so that all its volatile or gaseous elements are expelled. Wood yields from 15 to 25 per cent, of its weight of charcoal ; the more the process is hastened, the less the product. "When newly made, charcoal burns without flame, but it soon absorbs a considerable por- tion of moisture from the air, which it condenses within its pores. When this is burned, a portion of the water is decomposed, hydrogen is set free, and there is produced a small amount of flame. Being very light and porous, and its vacancies being filled with condensed oxygon, (81 1) it ignites readily, and consumes rapidly. Wood charcoal produces a larger amount of heat than equal weights of any other fuel. 86. Mineral Coal as Fuel Anthracite. The pit coal which is dug from j beds in the earth, is a kind of mineral charcoal. It gives evidence of j having been derived from an ancient vegetation, which was by some unknown means buried in the earth, and there slowly charred. Indeed, j the properties of the different varieties of coal, depend upon the degree to which this charring operation has been carried. In anthracite, 'i which is the densest and stoniest of all, it has reached its last stage ; ( the volatile substances are nearly all expelled, so that nothing remains [ but pure carbon with a trace of sulphur, and the incombustible ash. | From its great density, when we attempt to kindle it, instead of j promptly taking fire, the heat is rapidly conducted away, so that the f whole mass has to be raised together to the point of ignition. When j once thoroughly fired, this coal burns with an intense heat for a long ( time, though less freely in a grate than in a stove. It is difficult in the grate to keep the whole mass of coal in a state of vivid redness, as th* 54 PBOPEE1TES OF FUEL. air conveys away so much heat from the surface of the fire as to coo^ it down below the point of combustion (114). Anthracite burns without flame, sinoke, or soot, although with sulphurous vapors, which, when the draught is imperfect, or when burned in a stove, are liable to accumulate in the room, to the serious detriment of its inmates. The anthracite fire is objected to by many as causing headache, and other bad symptoms. Aside from its sulphurous emanations, the extreme in- tensity of its heat, undoubtedly, has a share in producing these effects. 87. Combustion of Bituminous Coal. When the great natural process of underground charring is less advanced, the coals are "bituminous that is, they contain bitumen or pitch, a substance rich in hydrogen. These ignite readily, and burn with much flame and smoke. Those which contain the largest proportion of pitchy material, are known as * fat' bituminous coal, and in burning, they soften or melt down into a cake, (caking coal) and stop the draught of air. Those with less hy- drogenous matter, are termed 'dry,' or 'semi-bituminous' coal; they burn freely without cementing or caking. Bituminous coals fur- nish illuminating gas by distillation in iron retorts ; a process of char- ring with entire exclusion of air. The residue left after charring bitu- minous coal, is called coke ; it is procured of the gas manufacturers and used as fuel, burning quietly like anthracite, though, owing to its sponginess, it is more easily kindled and yields less heat. Good bituminous coal burns freely and pleasantly in an open fire, with an agreeable, white flame, producing carbonic acid in large quantity, a small proportion of sulphurous vapor, and the common carbonaceous constituents of smoke (103). Its heat is much less violent than that of anthracite. 88. Lignite or Brown Coal is that variety which seems to have been least charred, and still retains the woody structure; its combu^tive value is low. 89. Heating Effects of the different Fuels. The heating value of these fuels, when burned under the same circumstances, have been deter- mined as follows : One pound of wood charcoal will raise from the freezing to the boiling point, 73 pounds of water. One pound of min- eral coal will heat 60 pounds of water through the same number of degrees ; and one pound of dry wood, 35 pounds of water in the same way. These are the highest results obtained by careful experiments. In practice, we do not get so great a heating effect ; and besides, the circumstances under which the fuel is burned, whether it be in a stove or fire-place, makes considerable difference in the result. 90. Amount of Air required to consume Fuel, As the weight of air ASCENT OF AIB THEOUGH CHIMNEYS. 55 necessary to burn fuel is vastly greater than the fuel itself, and as air is exceedingly light, it will be seen that immense bulks of it are con- sumed in combustion. It requires 11.46 pounds of air to burn one pound of charcoal; and as one pound of air occupies nearly 13 cubic feet of space, the pound of charcoal will require about 150 cubic feet of air. One pound of mineral coal is burned by 9.26 pounds of air, or 120 cubic feet ; and one pound of dry wood consumes 5.96 pounds, or 75 cubic feet of air. These are the smallest possible amounts that can be made to effect the combustion; as fuel is usually burned, much more is consumed. 91. Too much Air hinders Combustion. Yet if the object is simply to produce heat, the contrivances we employ should be adapted to admit the least possible quantity of air beyond what actively carries forward the combustion. Excess of air becomes detrimental to the burning pro- cess, by conveying away heat which it does not generate, cooling the fuel, and checking the rate of combustion. Indeed, so much air may be projected upon a fire, as to cool it down below the burning point, and thus put it out as effectually as water (114). X.-AIK CURRENTS ACTION AND MANAGEMENT OF CHIMNEYS. 92. Cause of the Chimney Draught. The candle flame tends upward; its hot gases and the surrounding heated air rising in a vertical stream, which illustrates the universal tendency of warmed air. No matter how it is heated, it expands, because rarer and lighter, and is pressed upward by that which surrounds it. Not that heated air has any mysterious tendency to ascend, but there being less of it in the same space, the earth does not attract it downward with the same force that it does the denser and colder surrounding air. As the atmospheric particles move among each other with the most perfect freedom, the colder and heavier air takes the lower position, to which gravitation entitles it, and thus drives the warmer air upward. This upward | tendency of rarified gases is the force made use of to supply our fires with the large amount of air which they demand. The fire is kindled at the bottom of a tube of iron or brick-work, called &flue or chimney. The atmospheric column within it is heated and rarified, and the outer I air drives in to displace it. This, in its turn, is also heated and ascends ; i a continuous current is established, and a stream of fresh air secured j to maintain the combustion. The chimney also serves to remove from I the apartment the noisome and poisonous products of combustion. 93. Conditions of the Force of Draught. The force of the chimney 56 ACTION AND MANAGEMENT OF CHIMNEYS. draught depends npon the velocity of the rising current, and that ag(u* upon the difference of weight between the column of air in the chim- ney, and one of equal size outside of it. Three circumstances influ- ence the force of draught : the temperature, length, and size of the air column within the chimney. The hotter it is, the higher it is, and the larger it is, within certain limits, the greater will be its ascensional force. All high chimney stacks, with large channels, containing highly rarified air, produce roaring draughts ; while if they be short and narrow, and their temperature low, the draught is proportionally enfeebled. ^Friction against the sides of the chimney, especially if it be small, operates powerfully to retard the draught. If the chimney be contracted at the bottom, the velocity of the entering air will bo increased. If it be narrowed at top, the smoke and hot air will be discharged above with more force, and hence be less likely to be driven down by slight changes in the direction of the wind ; yet con- tractions in the diameter of the chimney at any point, diminish the total amount of air passing through. In practice, chimney-draughts are influenced by several other circumstances, and are frequently so interrupted, that they refuse to carry off the products of combustion, and are then said to smoke. Yet these general statements require qualification. A chimney may be so high that the loss of heat through its walls shall cool the current down to a point of equilibrium with the outer air ; the draught of a high chimney shaft has been greatly augmented by enclosing it in an outer case to prevent radiation. Nor is the current of air that passes through a chimney, strictly in propor- tion to the degree of its heat. The draught, at first, increases very rapidly with the temperature, but gradually diminishing, it becomes constant between 480 and 5YO, beyond which it diminishes, and at 1800* it is less than at 212. The reason of this is found in the great expansion of air at a high temperature, by which its volume is so much increased, that, although the velocity may be very great, the quantity, when reduced to the temperature of the atmosphere, is less than at a lower temperature. WYMAN. 94. Winds eause Chimneys to Smoke. A high building, or a tree standing close to a chimney and overtopping it, often disturbs its draught. The wind passing over these objects, falls down like water over a dam, and stops the ascending current so that smoke is forced back into the room ; or the wind may strike against the higher object, and, rebounding, form eddies, and thus beat down the smoke. When chimneys are not thus commanded by eminences in the vicinity, gusts of air may still interfere with their draught. To prevent this, the.y DISTURBANCES OP THE DRAUGHT. 57 are often mounted with tumcaps, cowls, or ejectors (354) which are so constructed that the effect of the passing wind is to draw off the air from the chimney, forming a partial vacuum into which the gases and smoke rush from below, and so establish an upward current. 95. New and Damp Chimneys. When chimneys are new, the brick and mortar being damp, are good conductors of heat, and take it rapidly from the rising current of warm air. This condenses it, obstructs its ascent, and if the fire below be very hot, the chimney smokes. As it becomes dry, however, and is gradually covered with non-conducting soot, this source of difficulty is removed. 96. Cold Exposures Descending Draughts. Chimneys in the north end of a house, exposed to cold winds, often draw much less perfectly than those on other sides, or in the still more favorable warm interior of a building. The air in a chimney in the north or shaded side of a house is liable to cool in summer, so as to have a downward, draught when not used. If the temperature of the chimney be nearly the same as that of the outer air during the day, the external cooling at night may also create a descending current. When, therefore, the smoke from the neighboring chimneys passes over the tops of those that are drawing downwards, it is sucked in with the current and fills the room below. 97. Currents counteracting each other. We have seen that it is only when the atmosphere is of a perfectly uniform temperature that it is perfectly still ; the slightest inequality in its FIG. la degree of heat, throws it promptly into movement. We are apt to forget the exceeding delicacy with which the different portions of air are balanced against each other. This may be easily shown. If two tubes of unequal height be united by a third (Fig 13), the candle in the longer tube will over- come that in the shorter, and create a downward current in the latter; or if two tubes of equal length, united by a third, as in Fig. 14, have a candle in each, one is soon overcome by the other ; and this may happen, even when an opening is made in the thirfl tube, admitting a limited supply of air. It is sometimes attempted to make a current proceeding from a fire, traverse two flues, which join again before discharging their smoke into the air. But this is difficult, if not impossible ; for though currents may be commenced in both routes, one quickly neutralizes the other, and but a single flue \a used. 58 ACTION AND MANAGEMENT OF CHIMNEYS. FIG. 14. 98. One Chimney overpowering another. When there are two fire-places in a room, or in rooms communicating by open doors, a fire in the one may burn very well by itself; but, if we attempt to light fires in both, the rooms are filled with smoke. The stronger burning fire draws upon the shaft of the weaker for a supply of air, and of course brings the smoke down with it. This difficulty may be remedied by opening a door or window, so as to supply both fires with the necessary air. The same effect may take place, even though the two rooms be separated by a partition, when they communi- cate atmospherically by the joints and doors. Some- times, where the windows are tight, a ctrong kitchen fire may over- power all the other chimneys in the house and cause them to smoke. 99. Upper and lower Fines. A current entering a chimney through a flue horizontally, may interrupt its draught ; in all cases of flues entering chimneys, they should be so arranged that the smoke may assume an upward direction corresponding to the course of the main current. There is great danger of smoke when the flue of an upper room is turned into the chimney of a lower room. If a fire is kindled in an upper room when there is none below, the cold air in the main shaft rises, and, mixing with the warm air, dilutes it, and thus checks or obstructs the ascent j while if the lower fire only be kindled, the cold air from the upper flue will rush into the shaft, and cooling it down at that point, may cause the smoke to descend into both rooms. The remedy is, either to keep a fire in both fire-places or to close one with a fireboard. 100. Admission of too ranch Air. Too large openings in fire-places often occasion smoke by admitting so much air from the room as to cool the upward current, and thus impair its ascensional force. If the fire-place be too high or capacious, or its throat too large, the air is drawn from a large space, or it may pass round behind the fire by way of the jambs on both sides ; the current is thus impeded, and the flame, which should be drawn backward, rises directly against the mantel-bar and escapes into the room. The fire-place should be so constructed as to compel all the air which enters it, to pass through or close to the fire. 101. Admission of too little Air. It is well known that a smoky chimney is often relieved by opening a window or outer door ; where this is the case, the difficulty is a deficiency of air to supply the DEFICIENCY OF AIR-SUPPLY. 59 I! t! draught. Want of a copious and regular supply of air is by far the most common cause of smoky chimneys. However well constructed and arranged may be the flues and fire-places, if they are not supplied with a proper amount of air they will inevitably smoke. Of course if the room be nearly air-tight, there is no air to supply a current, and there will be no current, for as much air as escapes through the chimney must be constantly furnished from some other source. In such a case, the smoke not being carried off will diffuse through the room. There may even be a double current in the FIQ. 1&. chimney, one upwards from the fire and another from the top downwards, as shown in Fig. 15 ; these two currents meeting just above the fire, part of the smoke is driven into the room. To ascertain the quantity needed to be brought in under these circumstances, Dr. FEANKLIN'S plan was to set the door open until the fire burned properly, then gradually close it until again smoke began to appear. He then opened it a little wider, until the necessary supply was admitted. Suppose now the opening to be half an inch wide, and the door 8 feet high, the air-way will be 48 square inches, equal to an orifice 6 inches by 8. The intro- duction of this air is to be in some way effected, the question being where the opening shall be 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 j J^mne CU cauji- inmates, a thin shelf is to be placed below it, sloping ing smoke, upwards, which would direct the air toward the ceiling. The modes of introducing air will be noticed in another place (351). 102. Draughts through a Boom. Currents of air through a room, as from door to door, or window to window, when open, may coun- teract the chimney draught ; or a door in the same side of the room with the chimney may, when suddenly opened or shut, whisk a cur- rent across the fire-place, to be followed by a puff of smoke into the 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 APPARATUS OF WARMING. earth. Thus all that is visible of smoke is really heavier than air which may be shown by placing a lighted candle in the receiver of au 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. on tne pump-plate, as is seen in Fig. 16, because there is no air to support it. Often, in days when the wea- ther is said to be ' close' we notice that the smoke floats away from the chimney-top and falls instead of rising ; so that the air, even within the zone of breath- ing, becomes charged with the sooty particles. The atmosphere is so rare and light that it cannot sustain the heavy smoke. The common impression that the air on these occasions is heavy, which prevents smoke from rising, js quite erroneous. The visibility of smoke is not entirely due to sooty exhalations. Watery vapor is a large product of com- bustion, and, when the air is warm and dry, it remains dissolved and invisible ; but, when it is cold or saturated with moisture, it will absorb no more, and that which rises from the chimney appears as a vapor-cloud, and thus adds greatly to the apparent bulk of the smoke. 104. Other constituents of Smoke. Smoke contains many sub- stances beside the carbonaceous dust, which vary with the conditions of combustion and the kind of fuel used. Coal smoke is alkaline from the presence in it of ammoniacal compounds, while wood-smoke is acidulous from the ligneous acids it contains. The smarting sensation produced by wood-smoke in the eyes, is due to the highly irritating and poisonous vapor of creosote formed in the burning process. XI. APPARATUS OP WARMING. 105. The various devices for warming are to be considered in & twofold relation, as generating heat and affecting the breathing quali~ ties of the air. These topics are often treated together ; but, as we desire to present the subject of air and breathing with the utmost distinctness, a separate part will be assigned to it, and the heating contrivances will then be reconsidered in respect of their atmospheric influences. 106. How Rooms lose Heat. Apartments lose their heat at a rato proportional to the excess of their temperature above the external ah* ; the higher the heat, the more rapidly it passes away. Large quantities of heat escape through the thin glass windows. The win- dow panes both radiate the heat outward, and it is conducted away SOURCES OF THE LOSS OF HEAT. 61 by the external air. Glass is a bad conductor of heat, yet the plates used are so thin as to oppose but a very slight barrier to its escape ; on 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 enormous. Three-fourths or 76 per cent, of the heat which escapes through the glass, would be saved by double windows, whether of two sashes or of doable 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. Onr Bodies help to Warm the Rooms. In estimating the sources of heat in apartments, we must not overlook that generated in our own systems. 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. Aneient Method of Warming. The chimney is a modern device, coming into use only 500 or 600 years ago, with the mariner's compass, the printing press, mineral coal, and that array of capital inventions and discoveries which appeared with the daybreak of the new civili- 62 APPARATUS OF WAKMING. zation 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 Romans had advanced no further than this in the domestic manage- ment of heat. They kept fires in open pans called "braziers. Those of the Romans were elegant bronze tripods, supported by carved im- ages with a round dish above for the fire. A small vase below con- tained perfumes, odorous gums, and aromatic spices, which were used to mask the disagreeable odor of the combustive products. The por- tion of the 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 so^t might be easily cleared away. 1. OPEN FIRE-PLACES. 109. Structure and Improvements. "With the chimney came the fire-place, which is an opening on one side of its base. At first it was an immense recess with square side-walls (jambs) and large enough to contain several persons, who were provided with seats inside the jambs. These fire-places were enormously wasteful of fuel, and were in other respects very imperfect. They have been gradually improved in various ways. By reducing their dimensions and greatly contract- ing the throat, the force of draught is increased and the liability to smoke diminished. By lowering the mantle or breast, the flow of large masses of air which entered the chimney without taking part in the combustion, was stopped ; while, by bringing the back of the fire- place forward, th? fire was advanced to a more favorable position for heating the room. Rays of heat, like those of light, when they strike on an object, are reflected at the same angle as that at which they fall, that is, the " angle of incidence is equal to the angle of reflec- tion." Now, when the jambs were placed at right angles with the back, that is, facing each other, they threw their heat by reflection (and when hot by radiation) backward and forward to each other across the fire. By arranging the jambs at an angle, they disperse the heat through the room. COUNT RUMFOBD states that the proper angle for the positions of jambs is 135 degrees with the back of the fire-place. 110. How the open Fire-place warms the Room. The heat of com- bustion from the open fire is entirely radiant thrown off directly from the burning fuel, or reflected from the sides and back of the fire- OPEN FIRE-PLACES WASTE HEAT. 63 place. It strikes upon the 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 conduction, but they immediately rise into the chimney, and are, therefore, of no use in heating the room. As a fire- place is situated at the side of the apartment, and as radiant heat passing from its source decreases rapidly in intensity (23), it is obvious that the room will be very unequally heated. Near the fire it will be hot, while the remote places will be in the opposite condi- tion. There is a semicircular line around the fire-place, in which persons must sit to be comfortable, within which ."ine they are too hot, and beyond which they are too cold. Of course, in this method of warming, the body receives the excess of heat only upon one side at once. 111. The open Fire not Economical. Fuel gives out its heat in two ways, by radiation and by immediate contact. PEOLET has shown, by ingenious experiments, that the radiated heat from wood was i ; from charcoal and hard coal about ^, 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 fire-places T-8ths, and RUMFOED 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 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 register above. This is an excellent plan ; it is executed with various modifications, but, if well done, it answers admirably. Even a flue made of some thin FIG IT Air from with- out wanned by tho fire-place. 64 APPARATUS OF WAEMING. material, and contained in the chimney, the lower extremity com municating with the external air, and the upper with the room* (Fig. 17), answers a most useful purpose. Heat is saved; abundance of air is furnished to the room without unpleasant draughts, while a > common cause of smoke is avoided (101). 112. Franklin StoYe. Dr. FBANEXIN contrived a heating apparatus i of cast iron, which he called the Pennsylvania fire-place, but which i is generally known as the Franklin stove. It offers one of the best methods of managing an open fire. It is set up within the room, and the hot air and smoke from the fuel, instead of escaping from the fire directly up the chimney, is made to traverse a narrow and circuitous smoke flue, which gives out its heat like a stove-pipe; at the same time air is introduced from out of doors through air-passages which surround and intersect the smoke-flue, and, after being warmed, it is discharged into the room by means of proper openings. This appa- ratus warms, not only by radiation from the burning fuel like the common fire-place, but also by radiation from the hot iron ; besides, the air of the room is heated by contact with the metallic plates, and there is still another source of warmth in the hot air brought in from without. 113. Coal Grates. As coal contains more combustible matter in the same space than wood, and produces a more intense heat, a much smaller fire-place answers for it. A very narrow throat in the chim- ney is sufficient to carry off the smoke. The coal-grate is a more economical contrivance for warming than the larger wood fire-place, chiefly because it lessens the current of air which enters the flue. In the wood fire-place a copious stream of warm air passes up the chim- ney, which takes no part in combustion, but carries off with it much heat, the place of the escaping warm air being supplied by cold air from without. The coal-grate is closed, like the fire-place, on three sides, the front consisting of metallic bars or grates, which, while they confine the coal, suffer the heat to radiate between them into the room. The sides and back of the grate should be formed of fire-brick, soap-stone, or some slowly-conducting substance, and not of iron, which conducts away the heat so fast as to deaden the combustion for a fire may be effectually extinguished by contact of a good con- ducting solid body. For this reason, as EUMFOED first pointed out, there should be as little metal about a grate as possible, the bars being made as slender and as wide apart as practicable, so as to inter- cept the fewest radiations from the burning surface. 114. Conditions of Combnstion in the Grate. The form of the grate COMBUSTION IN GEATES. 65 should be such as to expose the largest surface of incandescent coal to the apartment. If it has a circular front, there will be not only more surface, but the heat may then be radiated in all directions ; yet, if too great a surface is exposed to air, hi extreme cold weather it carries off the heat faster than combustion renews it ; and the coal, if it be anthracite, grows black upon the exposed side and burns feebly. The art of burning fuel to the best advantage in open grates, is to main- tain the whole mass in a state of bright incandescence, by preventing all unnecessary obstruction of heat, either by contact of surrounding metal, or currents of cold air flowing over the fire. It is very difficult, however, to expose a large fire-surface to the atmosphere, and at the same tune properly regulate the quantity of air admitted. It is pos- sible for fuel to smoulder away and entirely disappear with the pro- duction of very little sensible heat. To be burned with economy, therefore, it must be burned rapidly under the most favorable condi- tions of vivid combustion. The heat absorbed by the fuel, the sur rounding solids, or the rising vapor, is of course not available, but only the excess which is emitted into the room. To cause this lively nd perfect combustion, all the air which comes in contact with tho fuel must be decomposed and part with the whole of its oxygen. Every particle of air passing up through the fire, which does not help the combustion, hinders it, first by carrying off a portion of the heat, and second by cooling the ignited surface so that it attracts the oxygen with less vehemence, and thus causes the fire to languish. The air should also be pure, that is, as little as possible mingled with tho gaseous products of combustion. Air entering below a fire, rapidly loses its oxygen and becomes contaminated with carbonic acid ; both changes unfitting it for carrying on the process actively in the upper regions of the fire. 1^ 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 will be found most economical. 115. Different kinds of Grate The modifications and variations ot the fire-place and coal-grate are innumerable : and the multiplied de- vices which are continually pressed upon public attention, are, many of them, but reproductions of old plans. The use of a simple iron plate for a fire-back has been employed to warm an adjoining room situated behind the fire-place. For the same purpose grates have been hung upon pivots, so as to revolve, and thus warm two rooms, as library 06 APPARATUS OF WAKMING. and bedroom alternately. In GOLSON'S stove-grate, the fire is contained in an urn or vase-shaped grating, and is surrounded by a circular re- flector which throws the rays, both of heat and light, into the room in parallel lines. Coal-grates are also constructed on the principle of the double fire-place, by which warmed air is introduced into the room from without. Dr. FEANBXIN devised an ingenious 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 smoke having to pass through the fire above them, was en- tirely consumed. 116. Arnott's new Orate* 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 beneath. When the first charge is consumed and the piston is raised to the bot- tom of the grate, a broad, flat shovel is pushed in upon the piston which supports the burning coals, and affords a temporary support for the fire. The piston is then let down to the bottom of the box, and a new charge of coal shot in. This arrangement is valuable for abating the smoke nuisance where bituminous coal is burned. Much inge- nuity has been spent upon contrivances to burn or consume smoke. The thing however is impracticable. When smoke is once produced by fire, we can no more advantageously convert it to heating purposes than we can the smoke of a badly burning candle to the purposes of lighting. When smoke escapes from the ill-adjusted flame of a lamp, we notice that the flame itself is 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 burns its smoTce, but that it burn* without smoTce. The aim should be, so to conduct the first combustion that smoke shall be prevented. 117. Grates should not be set too low. As the open fire warms by radiation, it should be so placed as to favor this mode of diffusing heat. The tendency of currents of heated air to rise, secures sufficiently the warmth of the upper portion of the room, so that the main object of EFFECT OF TOO LOW FIBES. 67 the grate should be to heat the floor. If the fire is situated very low, the radiation will he considerable upon the hearth, while hut few heat- rays will strike further hack 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 he raised, its downward radiations strike upon the floor and carpet at some dis- tance back, with sufficient force to warm them, just as the sun's rays are more powerful when he shines from a considerable distance above the horizon. If a in (fig. 18), represent a radiating point or fire in a room, and & c the floor, it will be seen that no heat-rays fall upon it ; while if the floor be at d e, it will receive rays from the fire. " In such arrange- ment it is seen by where the ray -lines intersect this floor, that much of the heat of the fire must spread over it, and chiefly between the middle of the room and the grate, where the feet of the persons forming the fireside cir- cle are placed. Striking proof of the facts here set forth, is obtained by laying thermometers on the floors of rooms with low fires, and with similar rooms with fires as usual of old, at a height of about 15 or 16 inches above the hearths. The temperature in the upper parts of all these being the same, the carpets in the rooms with low fires are colder by several degrees than in the others." 2. STOVES. 118. How Rooms are warmed by StOYes. The stove is an enclosure, with us, commonly of iron, so tightly constructed as to admit through an aperture or damper, only sufficient air to maintain the combustion of the fuel, which may be either wood or coal. The heat generated within is communicated, first to the metal, and then by that to the apartment. It is usually situated quite within the room, the products of burning being conveyed away by a flue or pipe. The stove imparts its heat by radiation in all directions ; it also heats the air in contact with it, which immediately rises to the upper part of the room, 'that which is cooler taking its place in the same manner as heat is dis- tributed through water in boiling (46). 119. Briek, Earthenware, and Porcelain Stores. Stoves made of these 68 APPARATUS OF WARMING. materials are most common in Germany and Kussia. They are gen- erally made to project into the room from one side, like a chest of drawers or a sideboard ; the door for the fire being sometimes in an adjoining apartment. These stoves heat more slowly, and conse- quently give out their warmth for a longer time than those made of iron, which are subject to rapid variations of temperature. 120. Self-regulating Stoves. These are stoves to which are appended contrivances for regulating the draught. The principle employed is the expansion of bodies by heat, and their contraction by cold. A bar of brass or copper is so attached to the stove, that when the heat within increases, it lengthens ; it then moves a lever and closes the aperture which admits the draught. This checks the fire, and causes the bar slowly to cool ; it now contracts, and again opens the aper- ture of draught. Dr. ABNOTT 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 ED ore readily than solids, a well constructed regulator of this kind woiJd be more sensitive and prompt in action than one of metal. 121. Air-tight Stoves. The so called air-tight stoves are very common. They are designed to admit the air in small and regulated quantities, so as to produce a slow and protracted combustion. This mode of generating heat is less economical than is generally supposed. To become most perfectly available, heat must be set free at certain rates of speed. The compounds formed by combustion at a low tem- perature, generate much less heat than those which result from quick burning. Indeed, in the low, smothered combustion, the fuel under- goes a kind of dry distillation, producing carburetted hydrogen gases which escape into the chimney as unburnt volatile fuel, and are of course lost. These gases are inflammable, and when mixed with air, often cause explosions in air-tight stoves. Dr. UEE found that while 3| pounds of coke evaporated 4| pounds of water, from a cop- per pan, when burned in a single hour, yet that when the same amount was burned in twelve hours, but little 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 sufficient length of pipe to have parted with nearly all their heat before entering the chimney, there remains noth- POINTS SECURED BY THE BEST STOVES. G9 Ing to be desired on the score of economy. It is evident that all the heat has been retained in the room, and in this case the stove becomes the most efficient heating apparatus. 122. Effect of Elbows in StOYepipes. The heating action of the sheet- iron flue or stovepipe, is derived from the hot current of air within it. In proportion therefore as it contributes to the warmth of the room, this current of escaping air is cooled. That this cooling of air within the pipe takes place rapidly, may be shown by the difference of tem- perature at its connection with the stove, and where it enters the chimney. The cooling takes place of course from without inwards ; the outer stratum of the hot air current which is in contact with the pipe cools faster than the interior portion, so that the centre of the current is the hottest. Now it is well known that the effect of elbow- joints in a pipe, is to make the same length of it much more efficacious in warming a room, than it would be if straight. The cause of this is, that the heated air, in making abrupt turns, strikes against the sides with sufficient force to break up and invert its previous arrangement, and so mingle it, that the hotter air from the interior of the current is brought more into contact with the sides of the pipe, and more heat is thus imparted. It also checks the rapidity of the current. As radi- ation proceeds much slower at lofr temperatures than at high ones, the pipe, as it recedes from the stove, becomes rapidly less and less useful as a means of diffusing heat into the apartment ; it gives out less heat, in proportion to what it contains, than the hotter parts of the pipe. There will, therefore, be little gained by greatly lengthening it. 123. Best qualities of a Stove. The desirable points to be secured in the construction and management of stoves, are, first, ready contriv- ances for regulating the draught; second, accurate fitting in the joinings, doors, dampers, and valves, to prevent the leakage of foul gases into the room ; third, enclosure of the fire-space, with slow conductors, as fire-brick or stone ; fourth, a high temperature, attained by the rapid and perfect combustion of the fuel ; and fifth, to bring all the heated products of the combustion in contact with the largest possible absorb- ing and radiating metallic surface, so that the iron in contact with the air may not be overheated, but give out its warmth at a low temperature. Large stoves, moderately heated, are therefore most desirable. The cooler the surface of the stove, or the nearer it is in temperature to the air of the room, the more agreeable and salubrious will be its influence. This desirable result is to be obtained only by exposing the greatest quantity of heating surface to the least quantity of fuel a condition almost reversed in our modern stoves. APPARATUS OF WARMING. FIG. 19. 3. HOT-AIR ARRANGEMENTS. 124. Hot-air Furnaces. Heating by hot air, as it is termed, has re cently come into very general use. In this case the heater is not situ- ated in the apartments to 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 fire-brick for burning anthracite, and has a flue connecting it with the chimney, to remove smoke. It is enclosed in a case of iron or brick-work, with an interval of space between, forming an air- chamber. Air is introduced into this chamber, either directly from the room, or by means of a conduit, from without the building. The furnace is situated in the cellar or base- ment, and the entering air heat- ed to the required temperature, by contact with the hot iron, escapes upward from the air- chamber through tin tubes, which distribute it to all parts of the dwelling. It enters the room through apertures called registers, which may be opened or closed at pleasure. This method is commended by its economy of space, the heating machine being excluded from the occupied apartments; fuel Manner of wanning by Hot-Air Furnaces. is also consumed more completely, and with better economy, in a single furnace, than if burned in several stoves or grates. A disad- vantage however, is, that the power of the furnace being gauged by the requirements of a certain sized building, or number of apartments, it is not easily accommodated to a fluctuating demand for heat. 125. Diffusion of Hot Air through the Apartment. There are serious DISTRIBUTION OP HEAT IN THE AIR OP ROOMS. 71 disadvantages attending the entrance of hot air in large streams through registers in the floor. If it be very hot, it will ascend directly to the ceiling, without imparting its heat to bodies around. In a church, heated by two large hot-air stoves, delivering the air through two large openings in the floor, we have found a difference, after the heating process has been going on three hours, of more than 20 be- tween the temperature near the ceiling and that of the floor. In some public buildings, a stratum of air has been observed at the height of 20 or 30 feet from the floor, with a temperature above that of boiling water, while below it has been disagreeably cool. In private houses, with the hot-air furnaces, now in general use, air is usually introduced at a high temperature. It rises directly to the ceiling, spreads out upon it, and on reaching the walls, descends by them and the windows, more rapidly by the latter (337), until it reaches the floor, along which it is diffused toward the register, when a part is again drawn into the ascending current. Hence wo see that those assembling just around the register, and not over it, are in the coldest part of the room. That this is the case, we have also proved by the thermometer ; while the air, midway between the floor and ceiling, in a moderate-sized sitting-room, was at 74, that near the register, was but 68. (WT- MAX.) 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' 42 " 70' 14. 7 86' 6. 3 " 72* 16. 8 90 8. 4 " 75* 19 94* 126. How we are warmed in Hot-air Booms. "We are to remember that after all, it is less the contact of heated air which warms us in hot- air apartments, than other agencies. "We may enter a room in which the atmosphere is at 70, or even higher, and yet be chilly. Great amounts of air contain but little heat. The quantity of heat that will raise 1 cubic foot of water 1 degree, would be so diffused as to raise 2,850 cubic feet of air one degree. (ABNOTT.) From the amount of air that comes in contact with our bodies, therefore, we cannot get sufficient heat to warm us rapidly. If the walls, floors, and furniture of the room are cold, though the air be warm, the individual radiates heat to them, and is compensated by none in return ; while if they are 72 APPARATUS OF WARMING. 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. 127. Heating by Hot Water. We have seen how water is put in motion by heat ; the accompanying figure shows the working of the FIG. 20. principle. As the lamp heats the water on one side of the tube, it expands and ascends, the colder water coming forward from below to take its place, which establishes a circulation. As the hot water passes round the circuit, it gradually parts with its heat through the tube to the surrounding air. The great specific heat of water (49) by which it holds a large quantity of caloric, adapts it 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 Circulation of water. w hi c h the water falls, it will raise through the same number of degrees 2,850 cubic feet of air. 128. Two forms of Hot Water apparatus. There are two methods of warming houses by hot water. In one the mechanism is placed in the cellar or basement, and heats air which is conveyed upward to warm the apartments above, as in the case of furnaces. In this form of the mechanism, the pipes do not ascend to any considerable height above the boiler ; but, in the other plan, a system of small tubes is distributed through the house, being laid along to fit any form and succession of rooms and passages, or they are coiled into heaps in various situations, and impart their heat by direct radiation. There is a difference in the 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 DANGER OP FIKE. 73 good hot-water arrangement, from its constancy and regularity of action, and when not heated above 200 or 212, affords one of the most agreeable modes of heating a dwelling, although it is at present so expensive as to place it beyond popular reach. 129. Steam Apparatus for Warming. As steam contains a large amount of heat (68), it becomes an available means of its transmission. If admitted into any vessel not so hot as itself it is rapidly condensed, and at the same time gives its heat to the vessel, which may then diffuse it in the space around. A system of tubes ascending from a boiler may be so arranged as to warm the air which is thrown into the room through a register, or they may be wound into coils as in the previous case (128), and dispense their heat by radiation. The pipes are so placed, that the water from the condensed steam flows back to the boiler, or the hot water may be drawn off into vessels which are made to contribute to the heating effect. This mode of heating requires a temperature always at 212 for the formation of steam, and often much higher to drive forward the condensed water and clear the pipes. A serious drawback to this mode of heating is that the apparatus often emits a disagreeable rattling or clacking sound, owing to the condensation within the pipes and the sudden movements of steam and water. There is also a fundamental objec- tion to the method of warming rooms by heat radiated from coils of pipes, whether they be heated by steam or hot water. In respect of the condition of the air, this is the worst of all methods of heating, for it makes no provision whatever for exchange of air. All the other heating arrangements involve more or less necessary ventilation, but radiating pipes afford none at all. 130. Risk of Fire by these methods of Warming. It has been supposed that the employment of hot water, hot air, and steam pipes, as a means of heating buildings, cuts off the common sources of danger from fires, and is entirely safe. This is a serious error. Iron pipes liable to be heated to 400, are often placed in close contact with floors skirting boards and wooden supports, which a much lower degree of heat may suffice to ignite. By the long-continued applica- tion of heat, not much above that of boiling water, wood becomes so baked and charred that it may take fire without the application of a light. A considerable time may be required to produce this change, EC that a fire may actually be " kindling upon 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 300, was found to have charred a circle at least a quarter of an inch '4 74 APPARATUS OF WARMING. deep in the wood beneath it in less than six months. There are nu- merous cases of buildings fired by these forms of heating apparatus. 131. Origin of Fires. The Secretary of a London Fire Insurance office stated that the introduction of lucifer matches caused them an annual loss of $50,000. Of 127" fires caused by matches, 80 were produced by their going off from heat ; children playing with them, 45 ; rat gnawing matches, 1 ; jackdaw playing with them, 1. Wax matches are run away with by rats and mice, taken into their holes and ignited by gnawing. These facts point to the indispensableness of match-safes. In London, during a period of nine years, the pro- portion of fires regularly increased from 1.96, at 9 o'clock, A. M, the time at which all households might be considered to be about, to 3.44 at 1 o'clock, P. M ; 3.55 at 5 P. M., and 8.15 at 10 P. M., which is just at the time that fires are left to themselves. 132. Benefits and Drawbacks of the yarious methods of Heating. Each plan of warming presents its special claims to attention, and vaunts its peculiar benefits. Modifications of every scheme are numerous, and still multiplying. As a result of this inventive activity, there is a gradual but certain improvement. The aim of inventors has hitherto been mainly to secure economical results ; a laudable purpose, if not pursued at the sacrifice, of health. As people generally become better informed respecting the principles and laws which influence the comfort and well-being of daily life, improvements will be demanded in this direction also. Meantime, each method is to be accepted with its imperfections, though we are not to forget that in their working results much must depend upon proper and judicious management. We recapitulate and contrast the chief advantages and disadvantages of the various methods of heating. Some of the points referred to, particularly those which relate to ventilation, have not been previ- ously noticed, and will be considered when speaking of air. ADVANTAGES OF OPEN FIRE-PLACES. DISADVANTAGES OF OPEN FIRE-PLACES. They promote ventilation afford a They are uncleanly require frequent heerful fireside influence warm objects, attention are not economical are apt to without disturbing the condition of the air strain the eyes heat apartments unequally and may furnish warm air from without. are liable to smoke. ADVANTAGES OF STOVES. DISADVANTAGES OF STOVES. They cost but little are portable are They afford no ventilation if not of quickly heated and consume fuel eco* heavy metal-plates, they quickly lose their ttomically heat yield fluctuating temperatures are liable to overheat the air are liable to leakage of gases and are not cleanly. HOT-WATER APPARATUS. ADVANTAGES OF HOT-AIR FURNACES. They are out of the way and save space are cleanly give but little trouble may afford abundant ventilation need waste out little heat and warm the whole house. DISADVANTAGES 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- ure is not supplied. ADVANTAGES OF HOT-WATER APPARATUS. They do not burn or scorch the air give excellent ventilation do not waste heat and they warm the whole house. These remarks do not apply to those which heat rooms by radiation from coils of pipe (128) DISADVANTAGES OF HOT-WATER APPARATUS. They are expensive in first cost if adapted for an average range of tempera- ture, they may fail in extreme cold weather (as may also furnaces) and may give a dry and parched air if moisture be not supplied. PART SECOND LIGHT. I. NATURE OF LIGHT LAW OF ITS DIFFUSION. 182. How the outward and inward Worlds Communicate. We sit at the window, and have report of the world without. That intelligent consciousness which has residence in the chambers of the brain, holds intimate communion with the external universe, by means of a com- pound system of telegraphing and daguerreotyping, as much superior in perfection to the devices of art, as the works of the Most High transcend the achievements of man. We lift the curtains of vision, and a thousand objects, at a thousand distances, of numberless forms and clad in all the colors of beauty, are instantaneously signalled to the conscious agent within. Each point of all visible surfaces darts tidings of its existence and place, so that millions upon millions of de- spatches which no man can number, enter the eye each moment. A landscape of many square leagues sends the mysterious emanation, which, entering the camera-box of the eye, daguerreotypes itself upon the retina with the fidelity of the Infinite. Fresh chemicals are brought every instant, by the little arteries, to preserve the sensitive- ness of the nerve-plate, while those that have been used and spent, are promptly conveyed away by the veins. As impressions are thus continuously formed, they are transmitted, perhaps by a true electric agency, along the line of the optic nerve, to be registered in the brain, and placed in charge of memory. By the magic play of these wonderful agents and mechanisms, the world without is translated within, and the thinking and knowing faculty is brought, as it were, into immediate contact with the boundless universe. Let us inquire farther then, into the nature and properties of this luminous principle, and how we are related to, and affected by it. 133. Exhilarating Agency of Light. Light is a stimulus to the ner- vous system, and through that, exerts an influence in awakening and OLDER NOTIONS OP ITS NATUBE. 77 quickening the mind. The nerves of sense, the brain and intel- lect, have their periods of repose and action. The withdrawal of light from the theatre of effort is the most favorable condition, as well as the general signal, for rest ; while its reappearance stirs ns again to activity. There is something in darkness soothing, depressing, quieting ; while light, on the contrary, excites and arouses. It is com- mon to see this illustrated socially ; a company assembled in an apart- ment dimly lighted, will be dull, somnolent and stupid ; but let the room be brightly illuminated, and the spirits rise, thought is enlivened, and conversation proceeds with increased animation. " Most delicate and mysterious is the relation which our bodies bear to the passing light! How our feelings, and even our appearance change with every change of the sky 1 When the sun shines, the blood flows freely, and the spirits are light and buoyant. When gloom overspreads the heav- ens, dulness and sober thoughts possess the mind. The energy is greater, the body is actually stronger, in the bright light of day, while the health is manifestly promoted, digestion hastened, and the color made to play on the cheek, when the rays of sunshine are allowed freely to sport around us." 134. Ancient Conceptions of Light. Light is that agent which reveals the external world to the sense of sight. The ancients believed it to be something born with us an attribute or appendage of the eye. They thought, that the rays of light were set into the organ of vision, and reached or extended away from it, so that we see in the same man- ner as a cat feels by the whiskers which grow upon its face, by a kind of touching or feeling process. 135. Newton's View of its Nature. Modern science regards light as an agent, or force, originating in luminous bodies, and flowing away from them constantly and with great rapidity, in all directions. But how ? The human mind is never satisfied with the mere appearances of things. It demands a deeper insight into their nature, an explana- tion of their causes. The first scientific attempt to explain the nature of light, and the cause of vision, likened the sense of sight to that of smell. We know that to excite the sensation of smell, material particles, emanating from the odorous body, pass through the air and are brought into contact with the olfactory nerve of the nose. It wag 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- HOW LIGHT IS DIFFUSED. ent thought that light is motion rather than matter, and that the eye is influenced by a mode of action resembling that of the ear rather than that of the nose. We omit further reference to this question here, as the analogy will be more fully traced when we come to speak of colors (150). 136. Light loses Intensity as it is Diffused. 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. 13V. How Bodies receive the Luminous Principle. When light falls upon various kinds of matter, they behave toward it very differently. Some throw it back (reflection) ; some let it pass through them (trans- mission) ; some swallow it up or extinguish it (absorption) ; and some, as it were, split it to pieces (decomposition). All bodies, according to their nature and properties, affect light in one or more of these modes, producing that infinite variety of appearances which the universe presents to the eye. FIG. 21. ITS EELATIOX TO SURFACES. II. REFLECTION OF LIGHT. 138. Those bodies which will not allow the light to pass through them, are called opaque. When the rays of light strike an opaque body, a portion of them, according to the 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 &, Fig. 22, be a ray of light falling perpendicularly upon a reflecting 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, THE ANGLE OF BEFLECTION is EQUAL TO THE ANGLE OF INCIDENCE, THE EEFLECTED EAT IS ON THE OPPOSITE SIDE OF THE PEBPENDICrXAB, AND THE PEBPENDICTJLAE, THE INCIDENT AND THE EEFLEOTED BAYS AEE ATT, 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 Light is scattered. Parallel rays falling upon a plane surface, are reflected parallel, as shown in Fig. 23 ; but sepa- rating rays falling upon such a surface are reflected divergently, or scattered. The beams of light from a candle Fig. 24 diverge before falling upon a mirror ; aid as each single ray makes the angle of incidence equal to that of reflection, it is clear that the rays must continue to diverge when they are reflected, as in the dotted lines in the figure. Thus when a burning candle is placed before a looking-glass, its diverging rays strike the mirror surface, and being reflected in divergent lines, are dispersed through the room. 141. The Image in the Looking-glass. A highly polished metallic surface, called a speculum, is the most perfect reflector. Mirrors, or looking-glasses, consist of glass plates coated with metal. It is 80 PEODUCTION OF IMAGES. FIG. 25. not the glass, in looking-glasses, that reflects the light, but the metallic coating behind it. If we place any illuminated object before Fw. 24. a P^ne mirror, rays of light pass from all points of its surface, and convey an image of it to the mirror. *X "X But ^ e polished surface does not retain the image ; ^^" v Ox^ it reflects or throws it back, so that the eye per- ceives it. The light which enters the eye conies 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 reflection comes to the eye. This will cause the image to appear as far behind the glass as the object is before it, as the accompanying diagram (Fig. 25) shows. A perfectly plane surface reflects ob- jects in their natural sizes and propor- tions ; but if the form of the reflecting surface be altered, made hollow (con- cave), or rounded (convex), they cause the image to appear larger or smaller than the objects ; or the image is dis- torted in various ways, according to the figure of the surface. "We see this constantly illustrated in the images of How the image appears behind the the faC6 > f rmed b ^ the bri ht metallic looking-glass. surfaces of domestic utensils. 142. A perfect Reflecting 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 would 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. If 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 illumi TWO KINDS OF REFLECTED LIGHT. 81 nation, and their multiplied images. Upon the earth's surface nothing would be visible but the reflected images of the sun and stars, and in a room, nothing except the spectres of the artificial lights, thrown back by one universal looking-glass. But perfect polish is impossible ; there are no surfaces which in this manner reflect all the light. 143. In what manner Light makes objects Visible. It is by reflected light that nearly every object is seen. No surfaces are perfectly flat ; they may appear so, but, when closely examined, they are found to consist of an infinite number of minute planes, inclined to each other at all possible angles, and therefore, receiving and reflecting the light in all possible directions. If a ray is let into a dark room, and falls upon a bright metallic surface, a brilliant spot of light will be seen from certain points, but the reflecting surface will be almost invisible in other directions, and the room will remain dark. If, now, a sheet of white paper be substituted for the mirror, it can be seen in all directions, and will slightly illuminate the apartment. The surface of the paper scatters the light every way, producing an irregular reflection. It is this scattered and diffused light which makes the surfaces of objects visible. Thus light irregularly reflected exhibits to us real objects, while light regularly reflected discloses only semblances and images. TTe see the image in a looking-glass, by light regularly reflected ; we see the surface of the glass itself, by the light scattered by the minute inequalities of its surface. This irregularly reflected light diverges from each point of every visible surface in all direc- tions, so that the object may be seen from whatever point of view we look at ,it, provided other light does not interfere (144). It follows the law of radiation, that is, it flows from each point as a focus, but it does not conform to the principle of regular reflection, which has just been noticed. The direction of the reflected rays is independent of each of the incident rays. In this manner light is radiated from surface to surface, 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 Pictnres.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 vrindow on one side of it, and we stand upon the other side, as at 5 (Tig. 4* 82 RELATION OF PICTTTKES TO LIGHT. 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 upon their height and the distance f * ne P om t a * 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 & (Fig. 27), its proper inclination would be to c ; but if it were elevated to d, it should fall forward to e. We will farther re- mark that pictures should be placed as nearly as possible in the same relation to light as when they were painted; that is, if the shadows fall to the right, the illumination should come from the left to produce harmonious effects. 145. Light scattered by the Atmosphere. By this kind of irregular reflection, the atmosphere diffuses and disperses the light, each particle of air acting as a luminous centre, radiates light in every direction. If it were not for this, the sun's light would only enter those spaces which are directly open to his rays, so that, shining through the window of an apartment, that portion only where the beams passed would be enlightened, and the rest of the room would remain totally dark. This secondary radiation occasions the mild and softened light which we experience when the heavens are screened with clouds, instead of the intense and often painful glare of a cloud- less summer day. In the same manner the atmospheric particles scatter the rays and diffuse a subdued illumination at morning and evening twilight, while the sun is below the horizon. III. TRANSMISSION AND REFRACTION OF 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 transparency. The metals are .east transparent, or most opaque, yet they are not entirelv so ; thin LIGHT REFRACTED OE BROKEN. 83 gold leaf, fbr 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 miles deep, the solar light would not pass through it, and the earth would be in dark- ness. The purest water of a depth of seven feet, absorbs one half the light which falls upon it, and of TOO feet depth, extinguishes it. 147. Fracture or Refraction of the Rays. When light passes from one substance to another of a different density, as from air to water, it is liable to be turned out of its straight course. If it pass from one medium to another in a line perpendicular to its surface, as a 5 (Fig. 28), it will not be diverted ; but if it fall at an angle, as at c d, it will not continue straight to d, but will be as it were broken or refracted and proceed to c. If the refracting medium have parallel surfaces, the ray on leaving it is again bent back to its original course, as is shown in the figure. For this reason common window panes, which consist of plates of glass with 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 from a per- pendicular, as shown in Fig. 28. 148. How Refraction may be shown. A stick, with half its length placed obliquely in water, appears bent at the surface ; this is because the rays are bent, so that those which come from that portion of the stick which is in the water, show it in a false place. Put a coin in any opaque dish upon a table, and step back, until the edge of the vessel just hides it from view. Now, if water be carefully poured in, without disturbing its position, the coin will become visible (Fig. 29) , the rays of light coming from it, which before ^_ passed above the eyes of the observer, are ^\ n <> w ) as they come into the air, bent down- >v wardyrom the perpendicular. Bodies possess N. different degrees of refractive power. "When we look through a mass of water, as in a pond X^X^ or stream, the rays are so altered that it appears only three-quarters as deep as it really is. Cases of drowning have happened through ignorance of this 84 WAVE THEOEY OP LIGHT. FIG. 30. FIG. 81. illusion. The degree to which any substance bends the light from its straight course is called its index of refraction. Each transparent body has its refracting index, which is one of the properties by which it may be known. 149. Effect of Lenses upon Light, This power which bodies have, of bending 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 leDses (248). FIG. 32. Double-convex Lens. FIG. Plane-concave Lens. Double-concave IV. THEORY OF LIGHT WAVE MOVEMENTS IN NATURE. 150. Light not Blatter but 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 Wayc 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, waves will be formed, which proceed along the string. The real motion, in this case, is at right angles to the di- rection of the string, the apparent motion is forward. The particles SOUND PEODUCED BY ALB-WAVES. 85 composing the cord make excursions right and left, or up and down, which gives rise to forward waverimpulses. 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 will be thrown into agitation, and waves will pass rapidly from the point where it struck, outward, in all directions. The water in this case does not move forward any more than the grain did. This is proved by the circumstance that any objects which may be seen floating upon the water are not carried along by the advancing waves, but only move up and down in their places. Thus, particles of water, moving verii cally, cause wave-motions to travel horizontally. 152. Sound the result of Wares in the Air. Air is the medium which conveys sound to the ear. If a bell be rung in a vacuum, we cannot hear it. The air in some way transmits or convoys the sound from point to point. How is it done ? There is no passage of air-particles, no current or breeze moving from the sounding body to the ear ; the atmospheric medium is thrown into vibratory motion, and it is air- waves only which move forward. We all know that sonorous bodies vibrate when struck, and that sound results. A harp-string, when struck by the fingers, swings rapidly backward and forward for a certain tune, producing a sound as long as the vibration lasts. A piece of steel wire, or a pin held between the teeth, utters a sound as often as the free end is inflected. By touching the teeth with the prongs of an excited tuning-fork, we can feel the vibrations. Sound is thus not only motion, but it is vibratory motion, and its transmission to the ear is due to the flight of air-waves, which, striking against the auditory drum, communicate sensations of sound to the brain througL the auditory nerve. 153. Upon 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 quali ty 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. EacJ 86 . WAVE-rHEOKY OP LIGHT. sound, therefore, that can be made, is the result of a certain number of air vibrations, and to that pitch of sound always belongs that num- ber. SAVAET 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. Harmonie Ratios of the Mnslcal Scale.- -It was found, experimen- tally, that the orchestra pitch note A, of the treble cleff, is produced by 853 vibrations per second. The number of pulsations in each note of the octave is as follows : EATIO OF HAEMOOTO SOUNDS. n C P E F Q A B i C> No. of Vibrations 512, 576, 640, 682, 768, 853, 960 1024, Intervals 64, 64, 42, 86, 85, 107, 64. It will be seen that in the highest note of this scale there are just twice as many vibrations as in the lowest ; the interval which they comprise is called an octave. The difference between the number of pulsations in any note, and the same note in the octave above, is as 1 to 2. Hence, by halving the numbers of any scale we obtain the numerical value of the octave below; while by doubling them we have the number of vibrations made by the notes in the scale above. The lowest note of a seven octave piano is made by 32 vibrations in a sec- ond, and the highest by 7,680. Two tones having exactly the same number of vibrations are said to be in unison. When their numbers are not the same, but are in some simple relation, a concord is pro- duced. If one has twice as many as the other an octave results, which is the most pleasing of all concords. The simpler the numerical ratio between the vibrations which generate a sound, or the air-waves which reach the ear, the more perfect and sweet the concord. When the difference is such that the proportion cannot readily be recognized by the ear, discord is the result. The whole phenomena of music thus resolve themselves into certain harmonious numerical ratios among air- waves, by which impressions are produced in a certain exact order, upon a mathematically constituted organ the brain. SCALE OF THE LUMINOUS VLBBATIONS. 87 155. Light and Colors result from Ware Motion. As all sound and music are thus due to measured wave movements in the air, it is thought also that light has a similar origin. This view assumes, that throughout the universe there exists a subtle, 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 meant the 4Js- tance from the top or crest of one wave to that of the next ; and it is inferred from certain interesting experiments made by NEWTON, that the length of waves, although exceedingly small, differs in the different colors, red being largest and violet smallest. In an inch length of a ray of red light there are 37,640 vibrations ; in an inch of yellow light, 44,000 ; and in an inch of the violet ray, 59,756. If the minute- ness of the wave excite surprise, it may be replied that this is by no means the strongest illustration of the smallness of the scale upon which nature's works are often constructed. Indeed, in this case it has been even outstripped by art. M. NOBEBT, of France, has ruled lines upon glass, for microscopical test-purposes, but the -3-5^$ of an inch apart.* 150. Vibrations per second of the luminous Ether. But the demon- strations of science carry us into far profounder regions of wonder. The speed of light has been measured ; the velocity with which it moves is in round numbers 200,000 miles per second. That is, when we look at any thing, an agent or force sent from the illuminated body streams into the eye at the rate of 200,000 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 thousand miles there are a thousand millions of feet, and, therefore, twelve thousand millions of inches. In each of these inches there are forty thousand waves of red light. In the whole length of the red ray, therefore, there are four hundred and eighty millions of millions of waves. Now as this ray enters the eye in one second, and the retina pulsates once for each of these waves, we arrive at the astonishing conclusion, that where we behold a red object the membrane of the eye trembles at the rate of four hundred and eighty millions of mil- lions of times between every two ticks of a common clock. Of yellow * See Appendix B. 88 COMPOSITION AND MUTUAL INFLUENCE OF COLORS. light five hundred and thirty-five millions of millions of waves entei 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.' 1 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 OF COLORS. 157. White Light taken to pieces. If a ray of common white light be admitted, through a small aperture, into a dark room, and be made j, IO 34 to strike upon a triangular piece of glass (prism\ the white ray disappears ; it is turned from its course, and there falls upon the iKOtv 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 as sllown in Fig. 34; but they prismatic colors. pass into each other gradually, so that it is difficult to tell where one ceases and another begins. NEW- TON assumed, as the result of this experiment, that white light is a compound principle, consisting of these seven colors, which he called primary, and taught that all other colors whatever are the result of various commixtures of these. For convenience of representing the relations of colors, we may represent white light by a circle, and the 3STJMBEE OP PEIMAEIES. 89 FHJ. 35. colors which compose it by divisions of the enclosed space. In that case the seven primaries of NEWTOX will be shown as in Fig. 35. 158. Newton's explanation of Colored Surfaces. "White light falls upon objects, and they ap- >ear colored : how is this ? NEWTON replied : oodies 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 "blade, it is absorbed and lost in the substance, and therefore does not return to make an impression upon the eye. But the blackest surfaces do not really absorb all the light, for then they would be invisible, and appear like dark cavities, presenting no surface. If the surface appears colored, it is because the white light is split up, or decomposed, one part being absorbed and lost, while the other is reflected to the eye, so that the object appears of the re- flected color. For example, grass absorbs all colors but green, which it reflects to the eye ; and in the same way the sky absorbs all but blue, and reflects that to the eye. Different surfaces reflect the pri- mary colors mixed in all manner of ways, and hence the endless modifications of color that meet the eye. 159. Bnt three Primary Colors. A more simplified vier/ of the com- position of colors has been propounded by Sir D. BEEWSTEE, and generally received. He considers that instead of seven, there are but three elementary colors, red, yellow, and blue, and that the others are compounds of these. "We cannot produce red, yellow, or blue, by the mixture of any other colors ; but we can pro- duce all others by the various com- binations of these three. BBEWS- TER maintains, that even the colors of the spectrum are not absolutely pure, but that each of the three exists throughout its whole extent, although greatly in excess at the different points where they are visible. Blue, yellow and red being primaries, violet, indigo, green and orange are secondaries derived FIG. 36. 90 .RELATION AND MUTUAL INFLUENCE OF COLORS. FIG. 37. from them. The separation of the impure or compound colors from the spectrum, leaving the three from which i 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 Tiff. 37. 160. What are Complementary Colors, The effect of a colored surface is to decompose the white light which falls upon it, reflecting one portion, and absorbing or extinguishing the rest. We "do not see any colored surface, except by the seperation of the light which falls upon it FIG. 88. Fro. 89. FIG. 40. FIG. 41. the one visible, the other absorbed. Now it is evi- dent that the rays ab- sorbed, added to those \ which are reflected ? make up the ordinary light. Hence, whatever be the color reflected, that which is not reflected, and which is, therefore, wanting to complete the full set of colors which form white, and make out the full complement, is called the comple- Re$ \ / \ \ mentary color. 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 iook, 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 took upon a yellow surface (Fig. 40), blue and red are deficient ; blue A NEW SYSTEM OF ARRANGING THEM. 91 and red produce violet, therefore violet is the complementary of yel- low, as seen in Fig. 41. Again, we look upon blue (Fig. 42) ; red and yellow are required to complete the circle into whiteness ; but red and JBlv. } j | Bine ^ Ocaryd yellow make orange, therefore orange is the complement of blue, as is shown in Fig, 43. 161. Tints and Shades, Tones and Scales. These terms have formerly been employed in the most loose and indefinite way ; they have, how- ever, now acquired a kind of scientific precision. The tones of a color are those aspects which it presents when altered from its maximum of brightness or highest intensity, by mixing with it either white or black : if we take the purest and brightest red as a standard, say car- mine, and mingle various proportions of black with it, we of course darken it and get deeper tones of red. If we mingle white with it, we lighten it and get lighter tones of red. By the addition of black the red is said to be shaded, by the addition of white it is tinted. Each color, in this case, is a tone of red, and the whole series of tones constitute a scale the red scale. It may consist of ten, twenty, or fifty tones, according to the quantities of black and white successively added. In the same manner we make tones of orange and get an orange scale, tones of blue and get a blue scale, and so each color has its scale, in which it moves in two directions, from its normal or standard point, towards black and towards white. 162. What are Hues I A hue is the result of the movement of a color, not in the direction of black or white, but of some other color out of its scale. If a little blue be mingled with red so as to change it slightly, the red still predominating, a hue of red is produced. So if blue be tinged in a similar manner by any color, hues of blue re- sult. In the same way are produced hues of orange, yellow, violet, green, &c. 163. Chevrenl's scheme for showing the relation of Colors. A plan has been suggested by M. CHEVEEHL, 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 BELATION AND MUTUAL ESHFLTJElSrCE OF COLOKS. 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 Ji 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 LLO.YI Omnge RED Plan of CHEVBETTL'S CHEOMATIO CIBCLES, illustrating the principle of com^lwnentary colors, tints, shades, tones, hues, and scales. with yellow ; its normal is at #, and that of blue at c. From these three primaries all the rest are derived. Midway between yellow and blue is the scale of green, which results from their combination in equal pro- portions, half blue and half yellow. Midway between green and blue is a scale that we might call a greenish blue. It is only one-quarter of the distance from blue to yellow, and therefore is three-quarters HOW THEY MAY BE EXHIBITED. 93 blue, and one-quarter yellow, a hue of blue. Space or distance represents proportions of color. It will be seen that colors may be altered in two ways, that is, may move in two directions along their scales, by admixture with white or black, producing tones, and out of their scales, in the direction of the circles, producing hues. The dia- gram represents twelve scales, with ten tones on each scale, giving an arrangement of 120 colors, each having a definite, known compo- sition. With 24 scales, and 24 tones on each scale, we should have a scheme of 576 colors. 164. Making a Chart with the real Colors. An instructive exercise is to produce such a chromatic chart with the actual colors. Make a circle upon paper a foot in diameter, designed for twelve scales of ten or twelve tones. From a box of paints select carmine for the normal red, gamboge for the normal yellow, and Prussian blue for the normal blue. By mixing the blue and red with a pencil brush in equal pro- portions, the violet is produced, and by varying the proportions all the hues between blue and red are obtained. By mixing blue and yellow, green, greenish-yellow and yellowish-green are made ; and by mingling red and yellow, orange, orange -yellow and yellow-orange are made. Thus all the hues are obtained. By mixing each with black and white, increasing the proportion of black regularly as you proceed outwards, and white as you go inwards, the scales will be formed. Familiar colors would at once locate themselves upon such a chart, so that we should understand their exact composition. For example, the crimson will be found near the red, but in the direction of blue, that is, it is red slightly blued, while scarlet is red, moved slightly in the opposite direction, toward yellow. So indigo is blue just started toward red. 165. How the Diagram shows Complementary Colors. We determine the complementary of any color in a moment, by a glance at the sys- tem of circles. For example, we want the complementary color of red ; this is formed by the union of blue and yellow, producing green. Green, therefore, which is the complement of red, is placed exactly opposite to it on the diagram. So, opposite blue we see its comple- ment orange, and opposite yellow, violet, which is its complement, and also the contrary ; the complement of green is red ; of orange, blue ; of violet, yellow. So of all the scales, no matter how many are formed, their complements are seen on exactly opposite lines of the circle. The complement of red-orange is observed to be blue- green ; of a reddish-violet, it is greenish-yellow, and so on round the whole circle. We may even say that the complement of black is 94 RELATION AND MUTUAL INFLUENCE OP COLORS. white, and of white, black, of a deep tone on one side, it will be a light tone on the other. Thus the complementary color of a deep tone of green will be a correspondingly light tone of red ; of a light tone of violet, it will be a deep tone of yellow. By means of the dia- gram, therefore, the complementary of any of the one hundred and twenty colors can be found by any one in an instant ; a fact of much practical importance, as we shall soon have occasion to see. 166. What is meant by Complementary Contrast. By a glance at the diagram it will be seen that the complementary of any color is its exact opposite. It is the color which differs from it the most possi- ble ; therefore it is in strongest contrast to it. Complementary colors are, hence, contrasted colors, and their relation is commonly indicated by the term complementary contrast. 167. Luminous and sombre Colors. It will be noticed that the three normals (Fig. 44) of red, yellow, and blue (represented by the larger dots), are not all located at equal distances from the circumference or centre. The reason of this is obvious. Yellow is a light, and blue a dark color. The natural position of yellow, therefore, at its height of intensity, is nearer to the white than to the black, and the natural position of bright blue is much nearer to the black than to the white, while red is intermediate. For this reason it requires more tones to shade yellow down to black than it does blue, and more also to tint blue up to white than it does yellow. Colors are thus divisible into luminous and 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 medium color. 168. Grays and Browns ; Pure 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 pure, while -the addition of black produces a broken color. The browns are therefore all broken colors. A color may be broken, however, without directly adding black ; the three primaries mixed in certain proportions produce this effect. If a little blue, for example, be added to orange, it neutralizes a portion of the yellow and red, breaking the color and starting it towards black. 169. No Colors perfectly pure. "We must guard against the error of supposing that in practice we meet with any such thing as a pure or perfect color. Even those of the spectrum or rainbow are not per- fect ; BEEWSTEB has shown that the very brightest is contaminated by thers. But when we leave the spectrum, and begin to deal with the EFFECTS OF COMPLEMENTABIES. 95 commoner aspects of colors, paints, dyes, &c., their imperfections be- come much more obvions. We are to regard a red surface as reflect- ing to the eye, not a simple and perfect red, but along with the red a certain portion of the other colors of the spectrum, which have the effect of weakening and lowering the red. The true statement is, that the sensation of red is the result only of the predominance of that color. It is the same with all the colors we see ; others are more or less mixed with them, which impair their brightness. 170. How Colors mutually ImproYC each other. The action of colors upon each other is not a matter of hap-hazard, and although it was long inexplicable, and half suspected to be a field where nature ca- priciously refused to be curbed by rules, yet science has at length dis- covered the reign of law in the domain of colors. Some combinations of colors are pleasing to the eye, and others disagreeable ; some are harmonious, and others discordant. The harmonies of color are of several kinds, but the fundamental and most important one is the har- mony of complementary contrast. If a purchaser be shown succes- sively a dozen pieces of bright-red cloth by a shopkeeper, those last seen will be declared much inferior in intensity of color to the first, such being the actual appearance which they present to the purchaser's eye. If now the buyer's attention be directed by the merchant to green stuffs, they will appear extremely bright, unnaturally so ; and if the eye recur again to the reds, they will look much finer than before. Eed and green viewed in this way have the mutual effect of improving each other. It is the same if the two colors be placed side by side and observed together ; they will so heighten each other's in- tensity as to appear much brighter and purer than when they are viewed separately, that is, when the eye cannot be directed from one to the other. If now we take yellow and violet, or blue and orange, or violet-red and yellow-green, and observe them in the same manner, we shall get the same result ; their brilliancy and clearness will be mutually heightened. But these colors are complementaries of each other; complementaries then, when viewed together, improve each other. They are the most opposite or contrasted, and therefore the pleasing effect they produce upon the eye is denominated Harmony of Complementary Contrast. These effects are experimental facts which may be verified by any one. Take six circular pieces of paper, say an inch and a half in diameter, and color them respectively red, orange, yellow, blue, green, and violet. Place each one separately on a sheet of white paper, and then, with a thin wash of color, tint the white paper around each circle with its complementary color, gradually 96 EELATION AND MUTUAL INFLUENCE OP COLORS. weaker and weaker as the tint recedes from the colored circle. If now the red circle be placed upon the sheet that is colored green, it I 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- 1 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 upon 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- j 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, 1 and the eye producing changes in colors, more or less considerable, according to circumstances. The eye being a part of the bodily sys- ! tern, and governed by general physiological laws, is subject to the \ ' same vicissitudes of varying activity, acute and blunted susceptibility, i 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- 1 ence to its health (253). 172. Duration of Impressions upon the Retina. Impressions continue upon the nerve of the eye about one-sixth of a second after the object is removed. For this reason, a torch whirled swiftly round appears as a continuous streak or ribbon of fire. But the eye continues to be I affected for a much longer time ; although it is not, as we might at j first suppose, by a feeble, lingering impression left upon it, which j gradually fades out after the object is withdrawn from sight. If there ] were a continuance of the perception of an object after its removal, the effect of viewing another object would be the mixture of two colors. For example, if a bright blue object were seen, and then the THEY AFFECT EACH OTHER THBOUGH THE EYE. 97 eye suddenly directed to a red, the effect would be a perception of a mixture of the two, or violet, and this would remain until the first impression, or blue, faded away from the retina, after which the red object alone would be perceived. But such is not the case. 173. The Eye loses its 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 off^ we shall see a spectral image of the wafer upon the paper, ~but it will be green. The wafer so extinguished the sensibility to red upon a certain portion of the retina, that when it was removed, the eye saw the white, 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 tune of an eclipse, spectres of the solar disk are sometimes produced which continue for a time before the eye. The color of these is always complementary to the color of the glass through which the sun was viewed. 174. Simultaneous contrast of Colors, But colors placed side by side, 5 98 RELATION AND MUTUAL INFLUENCE OP COLORS. exert upon each 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 from it that are not green, but its opposite. Now if we could clear away or destroy these vitiating rays, we should improve both colors, and this is ac- tually done by placing them side by side. The reducing colors, which are active when the surfaces are viewed separately, seem to be, in some way, neutralized when they are brought together, and the com- plementary of each is thrown upon the other. 175. How associated Colors injure each other. If certain combina- tions of color alter each other for the better, it is easy to see how other combinations must act in other ways for the worse. If the mutual effect of colors most contrasted be to intensify and exalt each other, it follows that if those most nearly alike are associated to- gether, they will vitiate and injure each other. What the exact effect will be, may be seen at once by inspecting the chromatic diagram. The complement of violet is yellow. If violet be associated with yellow, therefore, the only effect it can produce is to make it yellower ; but suppose it be placed beside other colors, the result must be a ten- dency to yellow them all. Violet placed beside green drives it out of 4ts 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 ARE CHANGED BY CONTRAST. 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 vwill drive every tone of that scale one or two steps back, away from itself, by making them all still yellower, and you will notice that the effect of violet upon the other colors, by throwing yellow upon them, is to start every one of them away from itself in the direction of its antagonist, which is the yellow. If traced out it will be seen that the effect of any other color is precisely the same. The complementary of any color thrown upon another renders it more unlike, or increases the difference between them. 176. Contrast of 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 irn- perfect illustration of this effect. It consists of five bands, shaded successively deeper and deeper from left to right. As the eye glances at the scale, the bands appear darker at their left bor- ders and lighter at their right. But this appearance is an effect of contrast ; for if we take two slips of paper with straight edge* iu ^ ^ rf ^^ rf tone and cover all the diagram but any single band, its surface will be seen to be perfectly uniform. TVTien viewed together, however, there is a heightening of the real differences, the light tones seem lighter and the dark tones darker, almost as if the intention was to represent fluting. It is so with the different tones of any color which has been shaded with black or tinted with white. If we place two different tones of the same color together, they always alter each other's intensity ; dark tones making adjacent light ones appear still lighter, and light ones making dark tones seem still darker. This is, perhaps, because the absence of light in the dark color renders the eye more sensitive to the white light of the lighter color, and on the contrary the dark color appears darker, be- cause the white light of the lighter color destroys the effect of the small amount of white light reflected by the other. Thus if we place 100 RELATION AND MUTUAL INFLUENCE OF COLOES. a dark red beside a light rose-color, or a deep yellow in 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 CHEYEEUL holds good. " In the case where the eye sees at the same time two contiguous colors, they will appear as dissimilar as possible, loth in their optical composition and the height of their tone." 177. Harmonies of Analogy. The employment of glaring or intense colors in many cases, as often in dress, is not admissible by the rules of cultivated taste. It is chiefly among the rude and uncultured that we remark a passion for gaudy and flaunting colors. With the progress of a refined civilization there is a tendency to the employ- ment of more subdued colors in personal and household decoration. Not by any means that good taste requires the total rejection of bright colors, but only that they be used with skill and discretion be ameli- orated by combination, so as not to produce staring and stunning effects, or strong and deep contrasts which often offend the eye. Harmonies of complementary contrast are to be first and chiefly sought in chromatic arrangements ; but these are comparatively limited, and in the demand for variety, other concords are found, which, although less striking, often give beautiful results. In studying the best arrangement of colors to produce a harmonious grouping, regard must be had to the kind of effect required, whether lively, medium or sombre. In one case, bold striking contrasts will be sought, in another mild ones ; and again, rejecting contrasts altogther, we may get an agreeable effect by grouping together similar or analogous colors. Harmonies of analogy may be produced in three 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 DIFFERENT GROUPINGS. 101 its own peculiar hue over the whole, as when we view a carpet IE light that comes through a stained glass window. 178. Circumstances which disturb the influence of Colors. Yarious con ditions exert a modifying effect upon the mutual action of colors. The result may be greatly influenced by the shape of the object, and the manner of its exposure to light. The surface of a red curtain, for example, hung in folds, appears of different hues, the parts most exposed to the light being changed in the direction of scarlet, while those more protected from it are shaded so as to approach a crimson. The condition of surfaces is also important. "When they are glossy their colors affect each other much less, and a bad association may be concealed or overlooked where the elegance of symmetry of the object, or the light and shade are so related, or our ideas are in some way so associated with it as to draw the attention from the ill effects of the colors. It is often thus that flowers present bad associations, yet our feeling concerning them is such that we are not offended as when we see the same upon flat unglossed surfaces. The flower of the sweet pea, for instance, gives us the alliance of red and violet, which mutually injure each other, though the green leaves set off the red and help the result. 1V9. 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 so intense that in all its arrangements with color, except perhaps light tones of yellow, there will be contrast. It may often be interposed with advantage between colors which injure each other. All the pris- matic colors gain by grouping them with white, but not in an equal degree, for the height of tone of the color makes a decided difference in the result. The deep tones of blue, red, green, and violet, contrast too strongly with white, while the light tones of the same colors form with it the pleasantest contrasts we can obtain. Orange, the most brilliant of the colors, is almost too intense with white, while the deeper tones of yellow appear well with it. 180. Effect of associating Colors with Black and Gray. Black is agree- able if associated with almost any color. "With their light tones it contrasts well, making them appear lighter, and being itself darkened, while their sombre complementaries thrown upon the black scarcely affect it as its surface reflects so feebly. With the deep tones of the scales it forms harmonies of analogy, although their luminous com- 102 PEACTICAL SUGGESTIONS IN 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 COLORS. 181. Articles of Dress. A recollection of the foregoing principles may enable us to avoid gross errors in combining colors. Thus a ladj 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. We are not to overlook the effect of contrast of tone as well as color. A black coat that is much worn, will appear well in summer in contrast with white pantaloons ; but if put on over new black pants, it will appear older, rustier, and more threadbare than it really is. Stains upon garments are less apparent where there is considerable difference among the colors of the various articles of apparel, than where they are more uniform, the contrast among the colors rendering that be- tween the stain and the surrounding cloth less conspicuous. Colored articles of dress produce a deceptive effect in reference" to the size of the wearer. The influence of dark or black colors is to make the per- son wearing them seem smaller, while white or light dresses causes the figure to appear larger than the real size. Large figures or patterns upon dresses and horizontal stripes make the person look short, while narrow vertical stripes on a dress cause the wearer to seem taller. 182. Influence of Colors upon the Complexion. Any colored objects, as bonnet trimmings or draperies, in the vicinity of the countenance, change its color ; but clearly to trace that change we must know what the cast of complexion is. This varies infinitely, but we recognize two general sorts, light and dark, or Nonde and Irunette. In the blondes or fair-complexioned 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 AFFECT THE COMPLEXION. 103 its complement of red upon the face. If the complexion be pale and deficient in ruddy freshness, or admits of having its rose-tint a little heightened, the green will improve it, though it should be delicate in order to preserve harmony of tone. But green changes the orange hue of the brunette into a disagreeable brick-red. If any green at all be used, in such case it should be dark. For the orange complexion of brunette the best color is yellow. Its complementary, violet, neu- tralizes the yellow of the orange and leaves the red, thus increasing the freshness of the complexion. If the skin be more yellow than orange, the complementary violet falling upon 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 yellows the skin, and is inadmissible except where its tone is so deep as to whiten the complexion by contrast. Hose-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 light in such a way as to produce the same effect as gray. Black adjacent to the countenance makes it lighter. 183. Arrangement of Flowers in a Bouquet. In grouping flowers, com- plementary colors as far as possible should be placed side by side, blue with orange, yellow 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 PRACTICAL SUGGESTIONS IN COMBINING COLOES. fatiguing to the eye. Among the simple colors light blue, light greei (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 border we should seek for contrast, so that it may appear, as it were, detached from the hangings with which it is associated. If there is a double border, an interior one of flowers and an exterior one, the last must be deep in color and much smaller. Yellow hangings should be bordered with violet and blue mixed with white. Green will take any hue of red as a border. White hangings should have orange and yellow. Gray uniform hangings admit of borders of all colors, but no strong contrasts of tone ; gilt borders do well with them. If the gray be colored, the border should be com- plementary. The neutral tints of paper, drabs, stones, &c., are par- ticularly 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 will do with large oil-pictures, particularly if there is no gilding represented in the picture. Gilt frames also answer well for black engravings and lithographs, but a little margin of white should be left around the subject. Black frames, by their strong contrast of tone, tend to lighten the aspect of the picture, and often spoil a good engraving by taking the vigor from its dark colors. Gray frames are good, especially if the picture have a leading color, and the gray be slightly tinged with its complementary. As a rule, neither the frame nor the border within it should ever be suffered by their brightness, color, or ornaments, to injure the colors, shadows, or lights of the picture. The best ground for gilt ornaments is blue, because its complementary intensifies the color of the orna- ments ; hence shrewd shopkeepers who sell gilt articles line their show- cases with blue. A bright green ground reddens and improves gilt objects. Eed and orange pervert the gilt tint, and black lightens and weakens it (144). 186. Assortment of Colors for Furniture. In determining the colors COMBINATIONS IN HOUSE-FURNISHING. 105 to be used in furnishing a room, the amount of light is an important consideration ; dark colors, as dark blue, crimson, &c., require much light to be seen distinctly. Ked curtains redden the transmitted light of daj, 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. If the furniture exhibit various and vivid colors, the pattern of the carpet should be simple and sober, as green and black for example, while if the furniture is plain the carpet may be gay. VH. PRODUCTION OF ARTIFICIAL LIGHT. 1. THE CHEMISTRY OF ILLUMINATION. 187. Natural and Artificial Light. As respects its sources, light is of two kinds, natural light, or that which comes from the sun, moon and stars ; and artificial light, or that which man obtains at will by various means. Artificial light may be procured by electricity, gal- vanism, and phosphorescence ; but the ordinary method is by that kind of chemical action which is termed 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 OF ARTIFICIAL LIGHT. luminous, according to Dr. DEAPEK, who has lately investigated the subject, is 977 F. He enclosed a nnmber 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. DEAPEB showed that as the temperature rises, the colored rays appear in the order of their refrangibility, first red, then orange, yellow, green, blue, indigo and violet, are emitted in succes- sion. At 2130 all these colors are produced, and from their commix- ture the substance appears white-hot. The same Investigator also found, that as the temperature of an ignited solid rises, the intensity of the light increases very rapidly; platinum at 2600 emitting almost forty times as much light as at 1900. 189. All our illumination conies from burning 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 will quickly become red, showing that a degree of heat which makes the metal shine does not make the air luminous. And yet all ordinary illumination comes from the combustion of gases. We use those ma- terials for lighting, which in burning produce flame ; and flame is burning gas. All substances which can be used for light must be capable of conversion into the gaseous state. The process is essentially the same, whether we burn the illuminating gas which is brought to our dwellings in underground pipes, or the liquid oil, 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 burning. In all cases the light proceeds from a rising stream of gaseous mattei which is lighter than the air, and therefore tends to ascend. 190. What takes place in the Luminous Flame, The materials used for illumination contain hydrogen and carbon, and the gas they yield consists of these elements more or less pure. Hydrogen, as we have before stated, is the lightest and most ethereal of all substances (76). The gas which gives rise to flame in illumination is therefore com- pound a hydro-carbon. In burning, the oxygen of the air combines with these two elements, but it is not attracted to them equally. It CHEiHSTKY OF ILLUMINATION. 107 Fia. 46. FIG. 47. seizes upon the hydrogen first, burning it with an intense heat, and the production of water. As the hydrogen combines with oxygen, it abandons the carbon, which is thus set free in a pure state. Now pure carbon is always a solid. As the hydrogen leaves it, therefore, it is set free in the form of exceedingly mi- nute solid particles hi 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. Admirable simplicity of the LaW of lUnmination. There is a wonderful simplicity and beauty in this chemistry of illumination. The same active principle of the air which animates the living body and nourishes the fires which warm us, is also the awakener of light. All artificial illumination that we employ is due to the chemical energy of oxygen gas. The hydro-carbon compounds, upon which oxygen acts, are not only universal as life itself, being produced in all kinds * See the author's Atlas of Chemistry and Chemical Chart of Colored Diagram^ Illustrating combustion and illumination 108 PRODUCTION OF ARTIFICIAL LIGHT. of plants and animals, but the very crust of the globe is stored with endless accumulations of them. The hydrogen combines with and condenses a much larger amount of oxygen than any other element, and consequently produces a great heat. But the burning of these 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 all solids, which remains fixed without melting or vaporizing at the intensest heat which art can produce. These carbon atoms are set free, and shining brilliantly for an instant pass to the 'verge of the flame, and there unite with atmospheric oxygen, forming carbonic acid gas. The two products of combustion vapor of water and carbonic acid are both entirely transparent and invisible, so that although constantly formed within and around the flame, they do not eclipse or obscure it, but let the light pass freely in all directions. If oxygen were equally attracted to hydrogen and carbon, so as to burn them both at once, no solid particles would bo liberated in the flame, and consequently there could be no light. It is the successive combustion which takes place, first the hydrogen burning and then the carbon, which gives rise to the luminous effect. 193. Threefold form of Illuminating 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. ILLUMINATION 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 great a proportion of mutton tallow or suet, as this contains a peculiar orinciple called 7iircin, which causes it sometimes to give a disagree- able smell, especially in hot weather. "When of the best quality tallow ILLUMIXATIOX BY MEANS OF SOLIDS. 109 is white, firm and brittle. Alum is often pnt with it to harden it, The bad 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 dry, as dampness mildews and damages them. Light turns them yellow. 195. Candles made from Stearie Add. 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 hi all fats and oils is, when set free, a sweet liquid called glycerin. The substances combined with it are stearic acid, margaric acid, and oleic acid. Stearic acid, combined with glycerin, forms stearin. Margaric acid, with glycerin, yields mar- garin ; and oleic acid, with glycerin, produces olein. Oleic acid, or olein, is the more liquid portion of oleaginous bodies ; it predominates in the fluid oils. Stearic acid, on the contrary, abounds in the hard fats and tallows ; it is their chief solidifying element. Margaric acid is less solid, being intermediate between stearic and oleic acids. The intermixture of these, in various proportions, gives rise to all the various grades of softness and solidity which the endless oil and fat tribe exhibiff* Tallow contains seventy to seventy-five per cent, of stearic acid, and olive oil but twenty-five. Candles were at first made from stearin, and were much superior to tallow ; but they are now manufactured from stearic acid, which is more infusible. This sub- stance does not feel greasy to the touch, and is firm, dry, and brittle. It makes hard ami brilliant candles, which are considered nearly equal to wax. 196. Spermaceti and Wax. Spermaceti is a kind of stearine existing in the oil taken from cavities in the skulls of certain species of whales. It is manufactured into candles, which are of a beautiful silvery white aspect, translucent like alabaster, and having a high lustre. The wax of which bees construct their honeycomb is also used for candles. It is purified and bleached to a pure white. It burns with a clear and beautiful light, and is the most expensive material employed for illu- mination. Owing to its high price it is often adulterated. White lead, oxide of zinc, chalk, plaster, and other earthy bodies may be detected by boiling the wax in water, when these snbstances will separate and fall to the bottom. If starch or flour has been used, they 110 PEODUCTION OF ARTIFICIAL LIGHT. may be detected by boiling and adding a solution of iodine, "which will yield a beautiful blue color, the test for starch. Yellow bees'-wax is often adulterated with resin, pea and bean meal, and many other substances. The former may be detected by the smell, and the latter by the iodine solution. 197. Structure 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 burn solid tallow or wax in the lamp to produce light, it would be found very difficult to set it on fire, as it would melt away long before it could ignite. But if at length made to burn, a much larger amount of the combustible would be on fire than the air would perfectly consume ; there would therefore be a thick smoky flame instead of a clear white light. Some contrivance * s 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 wick. 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 (Tig. 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. In this case the spaces between the fibres act as tubes, of oil below. and attract llpward the liquid fat Qr wax> 198. The burning Candle a miniature Gas-Factory. We thus see that the ca*idle is a kind of lamp which constantly melts its own combus- tible. From the reservoir the wick draws up 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 The candle-flame hollow. wtat WG re ar(i as tne flam e IS really but a thin, hollow, luminous shell of fire surrounding the dark inner space. This space is filled with the hydro-carbon gas ILLUMINATION BY MEANS OP SOLIDS. Ill from the liquid tallow, stearine, spermaceti, or -wax, drawn up by the wick. This may be directly shown. If one end of a glass tube, having a bore of an inch, be introduced into a candle-flame, as seen in Fig. 60, the gas will be conveyed away through it, and may be lit at the other end, thus exhibiting a miniature gas manufactory, pipe and jet. When a candle is blown out, gaseous pro- ducts of distilled and burnt tallow continue to rise, emitting a disgusting odor, and the candle may be re-lit by applying a light to the smoky stream of combustible gas which will convey the flame back to the wick. It is the hydro- carbon gas that is really burnt and produces the light, the hydrogen and carbon being successively consumed, as we have seen, at the surface, or The interior of the candle- where the air comes in contact with the gas. 199. Interference of the Wick with Light. As the candle consumes downward, the wick of course rises into the flame. In a short time it becomes so much lengthened as to interrupt the combustion and interfere with the light. Particles of unconsurned carbon are gradu- ally deposited upon the wick, forming a large spongy snuff which nearly extinguishes the light. PECLET found that if the intensity of the light from a freshly snuffed candle be represented at 100, if left without being snuffed, its brightness is reduced in 4 minutes to 92, in 10 minutes to 41, in 20 minutes to 32, and in 40 minutes to 14, al- though the consumption of the candle remained the same. KUMFOBD fovjid that the brilliancy of an unsnuffed 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 PKODUCTION OF ARTIFICIAL LIGHT. combustible faster than it could consume it, tne liquid would overfih 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. ILLUMINATION BY MEANS OF LIQUIDS. 201. Argand'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. FEANKLIN showed that two small wicks placed in two candles and burnt side by side, will give more light than if they were combined and placed in one candle, as there is a greater burning surface ; hence the advantage of spreading the wick-fibres out, and using them in some other form than condensed in a solid mass. Very large wicks of this kind convert the oil into gas faster than the air can completely burn it, and the consequence is that the flame smokes. To remedy this evil, the most important improvement yet made in lamps was contrived in the year 1789 by AMI AEGAND of Geneva, and since called after him the " Argand Burner." He made the wick hollow, so as to burn in a ring or circle, and thus admitted a current of air to the inside of the flame, by which the central core of dark unburnt 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 effect of cooling the flame. M. LANGE, a Frenchman, improved the form of the chimney- ILLUMINATION BY MEANS OF LIQUIDS. 113 tube, by contracting its size and constructing it with a shoulder at such a point (Fig. 51 5), that the rising air striking against it was de- flected inward and thrown directly upon the flame. This had a power- ful effect in increasing the combustion and heightening the intensity of the light. Another improvement consisted in mounting a button just above the circular opening within the burner, so that the current of air that comes up from within, will be deflected outwards, as shown in fig. 54 a, and thus strike directly upon the inner surface of the flame. The main point to be considered in the structure FM gl 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, 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 successive combustion which is essential to illumination (192). 203. Points to be secured in the structure of Lamps. Lamps are made in a great variety of ways suited to burn different kinds of oily matter, and adapted to avoid, as far as possible, certain difficulties which are incident to this mode of lighting. The distance from the burning part of the wick to the surface of the reservoir from which the oil is derived should remain unchanged, so that an equal quantity of oil may be drawn up at all times, and the reservoir should be so shaped and placed that its shadow will occasion the least inconvenience. If the wick is supplied from a reservoir below, it is obvious that just in proportion as that is exhausted, the distance from its surface to the flame is increased ; the wick-fibres elevate less oil, and the light grows faint and dim. To remedy this, the reservoir in some cases is made to have a large surface of oil that will fall but little distance, although a considerable amount is 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 small shadow. The sinumbra lamps had this ring so shaped and mounted as to produce still less shade. Sometimes there is a fountain of oil placed on one side higher than 114 PEODUCTION OF ARTIFICIAL 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 OAEOEL lamp, or mechani- cal lamp, clockwork is applied to pump up the oil through tubes in a constant stream to the wick, thus keeping it thoroughly soaked, while the excess of the oil drops back into the cistern, which is situated so far below as to cast no shade. It is moved by a spring, and wound up like a clock. It runs 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 lies 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 introduced 2,000 water-grain measures of the liquid to be tested in a cup, and then drew it off with a glass syphon of j inch bore, having the inner leg 3, and the outer one 3] 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 28 ; so that the fluidity of oil of turpentine is 28 times greater than that of sperm oil. Sperm oil, when heated to 265, ran off in 800 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 still better by means of a cistern placed above the flame. PAEKEB'S Eng- lish Economic Lamp has its oil heated in this latter way, and is said to perform admirably. 205. Composition of Oils. The oils in general use in these lamps are those derived from fish, chiefly whales, and known as sperm-oil and train-oil. Lard-oil is also much employed. It is the more oily portion ILLUMINATION BY MEANS OF LIQUIDS. 115 of hogs'-fat separated by artificial means. The chemical composition of these oils is quite similar- to that of the harder substances which are wrought into candles. Sperm-oil consists in 100 parts of carbon 78, hydrogen 12, and oxygen 10 ; mutton tallow,' of carbon 78-10, hydrogen 11*70, and oxygen 2*30 ; wax, of carbon 80*4, hydrogen 11*3, and oxygen 8'3. 206. Properties of Spirits of Turpentine or Campliene. In addition to these substances a new class of compounds, the basis of which is de- rived from the turpentine of the pine tree, have latterly come into use. By distillation of the turpentine pitch, it is separated into a thin trans- parent liquid, spirits of turpentine or oil of turpentine, and a hard brittle residue knowr as common resin. The crude spirits of turpen- tine when rectified, that Is, separated as completely as possible from resinous matter by repeated distillation, is burnt in lamps under the name of camphene. It differs from the substances just mentioned in its extreme liquidity (being, as we have seen, 28 tunes more fluid than sperm oil) ; in its powerful pungent odor, and in chemical compo- sition, as it contains no oxygen, and consists of 88*46 parts in a hun- dred of carbon to 11*54 of hydrogen, and is therefore called hydro- carbon. Oil of turpentine is also much mope highly inflammable, and is volatile and explosive. 207. Conditions required for its Combustion. Oil of turpentine is a superior illuminating substance, but it contains so large a proportion of carbon, that if burned in the ordinary way, it smokes excessively. Lamps designed to burn it require to be so constructed as to supply to the flame a large and powerful draught of air, to effect the complete Combustion of its elements. Camphene burns with a flame very much whiter and brighter than any of the substances we have yet noticed, and which displays the natural colors of objects, as flowers or pictures in their true tints, much more perfectly than the light of candles and oil lamps. Although more luminous, the camphene flame is smaller than the oil flame. This is explained by the fact that camphene con- sists entirely of carbon and hydrogen, 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 PRODUCTIONS OF ARTIFICIAL 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 Canipucne soon spoils. Camphene, if exposed to the air, cannot he preserved pure. It belongs to a class of bodies known as essential oils, which by combination with oxygen are changed into substances of a resinous nature. Under the influence of oxygen, oil of turpentine undergoes this change, and becomes deteriorated by solid resinous impurities. When employed for illumination, therefore it should be procured in small quantities fresh from the manufacturer, 209. Nature and properties of Burning Fluids. There is another method by which oil of turpentine may be employed for illumination, which is generally much preferred, as it avoids the liability and trou- ble of smoke. It consists in mixing it with alcohol, so as to form what is known as "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 ve*ry little light, burning fluid is a very costly source of illu- mination (230). 210. In what way Burning Fluids are Explosive. Both alcohol and oil of turpentine are very volatile ; that is, when exposed to the air or not confined, they rapidly evaporate or rise into the gaseous state. In a lamp reservoir containing burning fluid, as it is gradually consumed, vapor rises from its surface and fills the upper space. In all vessels, whether lamps, cans, or jugs, if but partially filled with fluid, the re- maining space is occupied with its vapor, which may or may not be mixed with air. Or when exposed to the air in open vessels, vapor rises and charges the atmosphere immediately above. Now the liquid oil of turpentine and alcohol are both 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 fira. But the more volatile liquids, on the contrary, will take fire at any time when exposed, though cold, and burn with great violence. But the ILLUMINATION BY MEANS OP LIQUIDS. case is made much worse on account of the invisible vapor which exhale. This mixes with the air, and at the approach of the slightest spark or flame, ignites explosively. "When pure hydrogen is mixed with the air and ignited, it explodes with a sharp report like a pistol ; the cause is the sudden combination of the hydrogen with the oxygen of the air. Now when vapor of turpentine or alcohol, or any volatile hydro-carbon is mingled with air and fired, an explosion takes place in the same way. 211. Conditions under which Explosions oceur. The burning fluid itself, although excessively inflammable, is not explosive. It does not go off like gunpowder when set on fire, nor with a sudden noise or report, such as its vapor produces. But it is always accompanied by the invisible treacherous gas which catches fire at a distance, and this ignites the fluid. Most accidents that occur with these compounds result from attempts to fill or replenish lamps while they are lit, or where there is a light near by. The vapor of the opened lamp, jug or can, is fired ; it explodes with more or less violence and concussion, setting the liquid on fire, and perhaps scattering it upon the clothing of the person present, who is severely or fatally burned, while the house is very liable to be set on fire. If the lamp have a screw cap and be perfectly tight, heat may be conducted downwards from the flame through the metal, and increase the evaporation. There being no vent but through the interstices of the wick-threads, if these are close, the pressure will increase and force out the fluid and vapor so as to burn irregularly, and sometimes occasion little explosions in the flame. If the wick is loose, and the lamp be agitated so as to dash the liquid against the hot screw-cap, vapor is suddenly formed, and being pressed out the flame streams up, often producing alarm. If the pressure become too great, and there be no vent, the lamp may ex- plode. Dr. 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. 212. How Burning Fluids may be used with safety Newefl'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 PRODUCTION OF ARTIFICIAL LIGHT. FIG. 52. it eminently desirable that some safe way be devised to consume them. This has been done by Mr. JOHN NEWELL, by applying to them the principle of DAVY'S Safety Lamp. Hydro-carbon gases are often generated in coal mines, and when mixed with common air, are exploded by the lamp which the miners use. By surrounding these lamps with fine wire-gauze, they could be lit and carried into the dan- gerous mixtures without exploding them. The inside of the gauze would be filled with burning gas, but the fine wire texture has the 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 fluid escaping through them were lit, the flame could not enter the vessel. 213. Kerosene Oil as an Illuminator. 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, whict we have used with much satisfaction. It does not vaporize, and is therefore not explosive. The proprietors make large claims on the score of its economy (230), and are entitled to credit for hav- ing prepared a variety of elegant .lamps for burning- it. Fig. 52 represents one of their style of parlor lamps. The cistern is narrow, and so far below the wick as to cast but little shadow. When not burning, the oil emits a kind of empyreumatic gas- odor, to which many object ; but the smell is net perceived during combustion. 214. Light from Sylyic 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 Argand Lamp for Kero proper care in VAN BENSCHOTEN'S lamp. aene OIL ILLUMINATION BY MEANS OP GASES. 119 4. ILLUMINATION BY GASES. 215. Conditions of the Gas Manufacture. Tlie last source of illumi- nation to be noticed is gas, which gives the cheapest and brightest of all the generally employed artificial lights. It has come into use en- tirely within the present century, and has been very widely adopted in cities. It was first employed in London in 1802, and its use has extended until 408,000 tons of coal have been consumed in a single year by the establishments of that city alone ; producing four thou- sand millions of cubic feet of gas, and yielding an amount of light equal to that which would be produced by eight thousand millions of tallow candles, of six to the pound. How wonderful, that sunbeams absorbed by vegetation in the primordial ages of the earth's history, and buried in its depths as vegetable fossils through immeasurable eras of time, until system upon system of slowly-formed rocks have been piled above, should come forth at last at the disenchanting beck of science, and turn the night of civilized man into day. 216. Materials used for making it. Gas is chiefly produced from the bituminous varieties of coal (8V), those which are rich in the pitchy elements containing hydrogen. It is also made from tar, resin, oils, fats, and wood. 217. Prodnets of the distillation of Coal. If coal is used, it is placed in tight cast-iron vessels called retorts, which are fixed in furnaces and heated to redness by an external fire. The high heat decomposes the enclosed coal, producing numerous gaseous and liquid compounds. The principal products of this destructive distillation are colce, or the solid residue of the coal, a black oily liquid known as coal-tar; water or steam, various compounds of ammonia, among others that with sulphurous acid, sulphuretted hydrogen, carbonic acid and carbonic oxide, light carburetted hydrogen, heavy carburetted hydrogen or olefiant gas, and a small proportion of vapor of sulphur et of carbon. There are also variable traces of many other substances. 218. Purification of the Gas. This heterogeneous mixture is totally unfit for illuminating purposes until purified. The liquid and gaseous products, as they are set free, flow out from the retort through a tube into a "receiver called the hydraulic main, in which the liquid products of the distillation coal-tar and ammoniacal liquor are to a great extent separated from the gaseous products. But being hot they still retain various matters in a vaporous state, which would be deposited and clog the pipes ; these are still farther separated by passing through the condenser, which consists of iron tubes surrounded by cold water. 120 PRODUCTION OF ARTIFICIAL 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. Composition of Illuminating Gas. This is very variable, but it mainly consists of olefiant gas, light carburetted hydrogen, carbonic oxide, with free nitrogen and hydrogen, and sometimes other substan- ces in small amounts. It takes its value from the proportion of olefiant gas which it contains, as this is the chief light-producing compound. Olefiant gas consists of 86*21 per cent, carbon to 14-79 per cent, hy- drogen. Several other substances which burn with much light are liable to be associated with olefiant gas, as Butylene, Propylene, vapor of Benzole and Naphtha. Olefiant gas burns with a 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- .ow 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 hydrogen. The gas that comes off from a charge of good coals consists, when the retort is first raised to a vivid cherry-red heat, of 18 per cent, of ole- fiant gas, 82'5 carburetted hydrogen, 3 - 2 carbonic oxide, and 1-3 of nitrogen. After five hours the gas that continued to escape gave 7 per cent, of olefiant gas, 56 of carburetted hydrogen, 11 of carbonic oxide, 21 '3 of hydrogen, and 4*7 of nitrogen. Towards the end of the operation, or after about ten hours, it contained 20 parts of carburetted hydrogen, 10 parts of carbonic oxide, 60 of hydrogen, and 10 of nitro- gen. The best gas therefore is that which is produced first. 220. Gas deriyed from other sources. Crude and refuse oil, which is unfit for burning, is sometimes converted into gas. It is made to trickle into a retort, containing fragments of coke or bricks heated to redness. The oil, as it falls upon these fragments, is instantly decom- posed and changed to gas. It contains no sulphur products, and needs BO purification. It is very rich in olefiant gas, and has double the ILLUMINATION BY MEANS OF GAS. 121 illuminating 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 (mains) that run through the street, a pipe branches off leading to the dwelling to be illuminated. Before being distributed through the house the gas is made to pass through a self-acting instrument called a meter, which both measures and records the quantity consumed in a dwelling. The meter consists of an outer stationary cylindrical case, enclosing an inner and smaller cylinder which revolves upon its axis. Both cylin- ders are closed at the ends, water-tight and gas-tight. The inner one is divided into four compartments with crooked partitions, and the gaspipe passes into its centre or axis, and, turning up at the end, de- livers to them its contents successively. The meter is kept about two- thirds filled, with water, which the gas constantly displaces as the cylinder turns. The principle will be understood by the aid of the diagram (Fig. 53), which ex- hibits the meter as if seen endwise, with the ends of the drums removed. A A A A is the outer cylinder ; B B B B the four compartments of the inner one ; c is the gaspipe supplying one of the apartments. AJ it enters the partition E rises, and the water passes out at the slit Z>, into the space between the two cylinders. The in- ' I ternal one revolves from left to right, the Meter for me ^f g the flow of gas passing in the direction of the arrows, first displacing the water and filling the compartments, and then passing out into the space between the two drums, where it is con- veyed away by a tube not shown in the figure. The revolving drum is connected with clockwork, which shows by an index the number of revolutions made, and the capacity of the compartments being known, the quantity of gas which passes through is correctly deter- mined. The meter reports the amount of gas that actually passes through it ; but its indications are by no means to be taken as infalli- ole proofs of honesty on the part of the gas company. Their terapta- 6 122 PRODUCTIONS 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 corresponding increase of light (222). Nor do meters afford any indication whatever in reference to the quality of the gas ; the companies control this, and may do quite as they please, the customer being unprotected. We do not intimate, however, that the gas-companies ever yield to the evil temptations with which they are beset. 222. How Gas is burned. From the fountain of distribution the gasometer the gas flows away through the branching system of tubes under the influence of pressure. When little openings are made in the pipes, this pressure drives out the gas in jets or streams, and it is these which produce the light when ignited. The orifices are from J^th to the sV th of an inch in diameter. Eecent experiments by the "French tend to show that wider openings are more economical with the best kinds of gas. The openings are made in various ways. A circle of them round a large central orifice forms an Argand burner (201). Two holes drilled obliquely, so that the flames cross each other, produce what is called a swallow-tail jet. A slit gives a continuous sheet of flame, called a bat-wing jet. Other figures are also produced, as the "fan-jet," "fish-tail jet," &c. The quality of light depends much upon the mode of burning as well as the composition of the gas ; a good article may be spoiled by mismanagement. Its illuminating power is 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 air, as when we move a lighted candle rapidly through the atmosphere, the hydrogen and carbon are both burned at once, and we get only a feeble blue flame. This occurs when gas issues with considerable ve- locity from a minute orifice, and by expansion gets intimately mixed with a large proportion of air. When the current of gas does not ignite at a considerable distance (several lines) from the aperture, and then burns with a faint blue flame, the gas-stream is too rapid, it is improperly mingled with the air and consumes wastefully, that is, to the buyer. If chimneys are used, and the draught becomes too strong, for the same reason the light almost vanishes, yielding only a dull blue flame. On the other hand, too 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 OP GAS. 123 before seen how rapidly light is evolved by the addition of small quantities of heat at high temperatures (188). 223. Influence of the length of the Flame. The dimensions of the gas- flame may be controlled with perfect facility by simply turning a stop- cock, although its extent depends upon the width of the orifice &nd the amount of pressure. It was found that if the light from a flame 2 inches long were represented at 100, at 3 inches it became 109, at 4 inches 131, at 5 inches 150, at 6 inches 160, with an equal consump- tion of gas in each case. 224. How much, Gas-burning contaminates the Air. The active source of light in this kind of illumination, as has been stated, is olefiant gas and other compounds abounding in carbon. But these could not be burned alone even if it were possible to procure them. A diluting material is therefore necessary to give the flame sufficient bulk, and separate the particles of carbon so far asunder as to prevent the risk of imperfect combustion and smoke. Now the three substances found in gas light carburetted hydrogen, carbonic oxide, and free hydro- gen are all equally well adapted for this purpose. So far as light is concerned, it is of little consequence which of these is associated with the olefiant gas. But in other respects this becomes a matter of im- portance. The two objections most commonly urged against the use of gas in our apartments are, first, the heat which it communicates to the air ; and, second, the contamination of it by carbonic acid. Now, in these particulars, the three diluting substances have very different in- fluences. One cubic foot of 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 sufficient amount of heat, according to Dr FBANKLAND, 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 m 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- leg, by which the olefiant gas is diluted with hydrogen, and a mixture 124 PEODUCTIONS OF ARTIFICIAL LIGHT. produced of superior illuminating qualities and the least injurious effects. 225. Disadvantages of Gas-lighting. The chief obstacle to the use of gas-lights in private houses is, that the burners are stationary, and cannot be placed in positions available for all purposes. Candles and lamps 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-fixtures. 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 towards 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 ventilation of gas-burners will be de- scribed when treating of air (360). 5. MEASUEEMENT OF LIGHT. 227. Can Light be Measured ? It is sometimes of importance to de termine the cost of light produced in different ways and from different materials. There is no method known by which light can be directly measured ; that is, we have no mode of estimating the absolute quan- tity of light emitted by a flame, but we can ascertain how much more MODE OF ITS MEASUREMENT. 125 or less light one flame produces than another, and thus arrive at useful comparative results. AH flames are not equally bright, of two flames of equal size, one may be much more brilliant and emit more light than the other. "Wo do not judge of the intensities of 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 casts. 228. How Light is Measured. Before a piece of board, covered with unglazed white paper at a distance of two or three inches, let an iron rod be placed which has been previously blackened by holding it in the candle. Now if it is desired to compare two lights, they are to be placed opposite the Fjo board at the same height, and each will cast a shadow upon the paper as illustra- ted in Fig. 54. The lights should be so sit- uated that the shad- ows will fall close to each other, and the stronger flame should be so far removed, or ' 1 rl the weaker advanced, Pnotometer or contrivance for measuring the intensity 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 intense, or its illuminating power greater. The difference in the degrees of light is not proportional to the distances of the luminaries from their shadows, but to the squares of these dis- tances, in accordance with the law of radiation before explained (136). If one light at two feet, and another at six, give equal shadows, their difference is not as six to two, but as the square of 6, which is 36 to the square of 2, which is 4 ; that is, 36 to 4, or 9 to 1. The luminary at 6 feet gives nine times as much light as the one at 2 feet. 229. We haye no unit for measuring Light. This plan, modified in va- rious ways, affords a ready means of comparing the relative amount of light emitted by two flames. But we have not been able yet to reap the practical advantages which this success at first appears to promise. If we can measure light, why not establish the exact illumi- 126 STKTTCTUEE AND OPTICAL POWERS OF THE EYE. nating values of the various lighting materials, so that we may know precisely how far a dollar will go in buying light when the substances are at given prices. Something has been done in this way, but we have no results that command implicit trust. The composition of the materials is variable, and the same materials in different trials give different results. We are without an accepted unit to serve as a stand- ard for a scale of values. It has been proposed to make the sperma- ceti candle (6 to the lb.), burning 120 grains to the hour, the unit of measure. If this were satisfactory, we could compare other lighting materials with it. A burner consuming a certain amount of gas per hour would equal a given number of candles, and any variation in its quality would be easily detected. "We should speak of it as 10 candle- gas, 15 candle-gas, and 20 candle-gas, according to its grade, 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 Ure and Kent.. Dr. UKE gives the follow- ing as the cost of an equal amount of light per hour from several sources, according to his experiments. Pence. Carcel Lamp, with Sperm Oil 14- Wax Candles 6 Spermaceti Candles " 5i Stearic Acid Candles "4! Moulded Tallow Candles '. ..............'.'.'.'. '. ..'.'..'. 2 E. K KENT, of the U. S. Assay Office, experimented on various lighting materials with the following results : Retail price of Cost of an equal Materials. Lamp used. Oil per gallon. amount of light Kerosene Oil Kerosene $1 00 $4 10 Camphene Camphene 63 4 85 SylvicOil Eosin Oil 50 -6 05 Eape Seed Oil Mechanical 1 5ft 9 00 Whale Oil Solar ....100.. . . 1200 Lard Oil Solar 1 25 17 00 Sperm Oil Solar 2 25 26 00 Burning Fluid Large Wick 87 29 00 VIII. 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 all objects, whether immediately around us, or re- THE IBIS AND PUPIL, AND THELE USES. 127 motely distributed through the distant universe. In its adaptation to the agent which is designed to act upon it, the eye is a miracle ol 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 correct ideas upon the subject. 232. Selerotie Coat and Cornea, and their uses. When the eye is re- moved from its socket and dissected, it is found to consist of several coats. The outer one forms the 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, & may be 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 from the Latin cornu, which signi- fies horn. The general arrangement of the parts we are describing is shown in the accompanying view of the section of the eye (Fig. 55). 233. The Iris and Pnpil, and their uses. Behind the cornea there is a small space or chamber filled with a perfectly clear and col- orless liquid, which consists chiefly of pure water, and is called the aqueous humor. This chamber is divided by a thin partition known as the iris, in the centre of which there is a circular aperture called the pupil. The pupil is simply, therefore, a hole through the iris ; it is the round black spot which we see surrounded by a colored ring. That colored ring is the iris. It is black behind, and on the front or visible side, it is of different colors in different individuals. Tho color of the iris is observed to be, in some measure, connected with the color of the hair. The iris has the remarkable property of con- 128 STEUCTUKE AND OPTICAL POWEKS OF THE EYE. FIG. 55. Qystallinelcns Cornea, tracting and dilating under the influence of light, by which the pupil is enlarged and diminished. If the light be strong, the iris contracts and reduces the size of the pupil, so as to exclude a portion of the light ; if the light be weak, the iris expands so that more light is ad- mitted. This moderates and equal- izes the illumination of the organ, the delicate sensibility of which might otherwise be injured. The play of this mechanism may easily be seen by bringing a candle near to the eye while gazing upon its im- Keiation and names "of* "the several parts age in a looking-glass. These move- ments are involuntary, the eye reg- ulating the quantity of light it will receive, independent of the choice of the mind. 234. Crystalline Lens and Vitreons Humor. Behind the little chamber, of which we have spoken, and bounding it on the back side, is a sub- stance in the form of a double convex lens, called the crystalline lens. It is situated immediately behind the pupil, very near it, is a little larger than that opening, and is very convex, its thickness being al- most equal to its diameter. It is supported by a ring of muscles called the ciliary process. The crystalline has about the consistence of hard jelly, and is purer and more transparent than the finest rock-crystal. It is this part which becomes diseased in cataract. The space behind the crystalline lens constitutes the main body of the eyeball, and is filled with a clear gelatinous fluid, very much resembling the white of egg, and called, from its apparent similarity to melted glass, the vitreous humor. 235. The Choroid Coat, and how it is Colored, There is a second coat, lining the interior of the sclerotic, which consists of minute vessels, arteries, and veins, closely internetted, and is called the choroid. It extends around to the cornea, and supports the ciliary process. The inside of the choroid is covered with a slimy matter of an intensely black color, called the pigmentum nigrum (black pigment}. This gives to the interior of the eye a jet-black surface, which absorbs and stifles the light, so as effectually tp prevent reflection. 236. Optic Nerve and Retina. At the back part of the eye, the scle- rotic coat is formed into a tube which leads inwards to the brain. This tube contains the optic nerve. As it enters the globe, it spreads out over the inner surface of the choroid, in the form of a most deli- THE BETINA SUPPOSED TO FEEL THE PICTURE. 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 dissectioD it is easily separated from the choroid. It is absolutely transparent, so that light and colors penetrate and pass through it perfectly, and therefore fall upon the dark surface beneath. To prevent the delicate and transparent nerve tissues of the retina from being stained by the black pigment, a very thin film is interposed between them called JacoVs merrfbrane. 237. How Vision is Produced. From every object which we see, rays of light pass into the eye, penetrating the successive transparent media, the cornea, the aqueous humor, the crystalline lens, and the vitreous humor, and falling upon the retina, form there an image of the visible object, the impression of which is carried by the optic nerve to the brain. The diagram (Fig. 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 How the Images are formed in the perfect Eye. eye, of every thing 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 the same way that the hand of a blind person transmits to the or- gan of consciousness, the form of an object which it touches. This view seems to be confirmed by the fact, that at that portion of the retina where the optic nerve enters the eyeball, which therefore has not the black choroid behind, it is insensible, and produces no per- ception. It has been proved by experiment that images made to fall upon that spot, are instantaneously extinguished. 238. Wonderful Minuteness and Distinctness of the Images. Nothing is more calculated to awaken our astonishment than the perfect dis- 6* 130 STBUCTUKE AND OPTICAL POWERS OF THE EYE. 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 but the ^ part of an inch, and the entire surface of the picture is less than the 52 ^ 00 part of a 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 T V part of an inch. The face of such an image is included within a circle whose diameter is about ^ of the height, and therefore occupies on the retina a cir- cle whose diameter is about T \j- part of an inch ; nevertheless, within this circle, the eyes, nose, and lineaments are distinctly seen. The diameter of the eye is about ^ that of the face, and therefore, though perfectly visible, does not occupy upon the retina a space exceeding the 1-4,000, 000th of a square inch. If the retina be the canvas on which this exquisite miniature is delineated, how infinite^ 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 Light. The susceptibility of the eye under great variations of intensity in the light which en- ters it, is most wonderful. We can read a book either by the light of the sun or of the moon, yet sunlight is more than a quarter of a mil- lion times more brilliant than moonlight. "The direct light of the sun has been estimated to be equal to that of 5, 5 TO 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." Wollaston estimated the light from Sirius, one of the largest fixed stars, as twenty thousand million times less than that of the sun. 240. Conditions of the System affect the Eye. The eye is thus an opti- cal contrivance which challenges our wonder continually for the ex- quisite beauty and perfection of its parts. Yet we must not forget that it is a living organ of the body made up of vessels, membranes, muscles and nerves, and nourished by the vital blood-stream like any other organ. It is therefore liable to be influenced in numberless ways by conditions of the system. When in use, it acts, expends force, exhausts itself and becomes fatigued. Dr. WHAETON JONES remarks : STATES OF THE BODY AFFECTING THE EYES. 131 1 Much exertion of the eyes operates more prejudicially to the sight under some circumstances than under others. Exertion of the sight is especially prejudicial immediately after a fall meal; after the use of spirituous drinks ; while smoking ; when the body is in a recumbent or stooping posture, when dressed in tight clothing, especially a tight neckcloth ; tight corsets ; and even tight boots or shoes ; in close and ill- ventilated apartments lit with gas ; after bodily fatigue ; during men- tal distress ; late at night when sleepy ; after a sleepless night ; while the bowels are much confined ; during convalescence from debilitating illness. Though during recovery from severe disease the eyes cannot bear much exertion, yet, for want of other employment, it is not un- common for convalescents to read even more than when in health. Many persons have much injured 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 perspiratory 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 Writing. In this reading age, with such strong and insidious temptations to overuse and bad management of the eyes, it may be well to make some suggestions concerning this mode of exercising vision. The closer the eye is confined to the page, the more of course it is strained. Novel reading is worse than science, history, or any grave subjects, because in the first instance we read fast and uninterruptedly, while in the latter cases thinking alternates with the use of the eyes in reading. Reading 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, Reading when in motion, as in riding-'br 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 hi reading, comes from the bad quality of artificial light, which we shall notice particularly farther on. IX. OPTICAL DEFECTS 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 OPTICAL DEFECTS OF VISION SPECTACLES. FIG. 57. 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 outline and color, falls exactly upon the retina, as shown in Fig. 56. If the eye were a fixed or rigid mechanism, as if made of glass, only objects at certain precise distances would come to a point upon the retina, all others would produce their images either before or behind it, and thus give rise to imperfect vision. But the organ possesses a power of adjustment by which objects at different distances may be seen clearly. How this occurs 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-siglitedness.^-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 high 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- tend the body, and a consequent shrinking of the flesh and wrinkling of the skin. Th< Far-righted Eye with flattened 6 y e participates in this natural change of tissue, its contents seem to shrink, and the cornea becomes flattened or loses something of its convexity, appear- ing as shown in Fig. 5V. This produces far-sightedness, 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. Ii! FIG. 68. Far-sigited Eye the focal point thrown too far back. CORRECTION OF FAR-SIGHTED EYES. 133 Fig. 58 the object a has its focal point thrown back to 5, making a confused picture npon the retina at c. The further an object is from us, the less divergent or more parallel are the rays coming from it ; and the less divergent are the rays which enter the eye, the easier are they brought to a focus by it. This is the reason that to the far- sighted, distant objects are distinct, and near ones confused. The far- sighted see minute objects indistinctly at every distance, because when near they are out of focus, and when remote from the eye, they do not reflect sufficient light to make a strong impression. They hence strive to increase the light upon the object, as we often see when attempting to read by candlelight, they place the candle between the book and the eye, and both at arm's length. It is but rarely that eyes recover naturally from this defect, yet much may be done to preserve the sight by care, "When the eyes begin to 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- FlG- 59> ses gather the rays to a point at vari- ous distances de- pending upon their curvature. The greater the curve, the nearer the fo- cus and the higher the power ; while Far-sighted Eye corrected by double convex gl&sses. with less curvature, and a more distant focus, there is lower power. The refractive power of a glass is expressed by the distance of its focal point in inches. A 10-inch glass, or a No. 10, collects the rays to a point at a distance of 10 inches, a No. 5 at 5 inches, and a No. 20 at 20 inches. The higher numbers express the lower powers, and the lower numbers the higher powers. Fig. 59 shows the far-sighted eye, with its internal focus, properly adjusted by a convex glass. 245. Management of far-sighted Eyes. When the sight begins to fail, and glasses are sought, those of the lowest power, which 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 ia well to get two or three pairs from the optician, as nearly correct aa possible, and try them leisurely at home before deciding which to take. If the eyes only see clearly at a very 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, 70, 75, 80, 85, 90. Focal Length in Inches... ...36, 80, 24, 20 16, 14, 12, 10, 9, 8, 1. 246. Near-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- FlG 60 ' riving at a focus before reaching the ret- ina, cross, and are in a scattered state when they do fall upon it, as illustrated in Fig. 61, where a is the object, & 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 Protrud- inches they are usually accounted near- sighted. By bringing the object nearer it is distinctly seen, because the rays of light from it which enter the eyes, being more divergent than when it was distant, are not so soon brought to a focus. The near-sighted eye retains its power of adjust- ment to distances ; the nearest distance may be from 2 to 4 inches, while the greatest is from 6 to 12. Short-sighted people see minute objects more distinctly than other people, because from their nearness CORRECTION *> NEAK-SIGHTEDNESS. 135 they are viewed trader a larger angle and in stronger light. They can see better than others with a weak light, and hence can read small print with a feeble illumination. To persons who are occupied with minute objects, short-sightedness, unless extreme, is rather an advan- tage, as they can FlQ 61 observe all the details of their work very ac- curately, while for distant vis- ion they can get ready help from glasses. Yet if , , ,. Near-sighted Eye, the focus felling too fer forward. perfect, the constant employment of it upon small objects tends to produce near-sightedness, which is hence a common defect of vision among the educated classes, and those who do much minute work. On the contrary, the habitual exercise of the eyes upon distant objects improves their power in that direction. If young persons have a ten- dency to nearness of sight, and are designed for vocations in which lengthened vision is required, they should avoid much exertion of the eyes on small objects, and exercise them frequently in scenes in the open country. It is an error that the near-sighted acquire perfect vision as they advance in life. "We often see old people who are com- pelled to use near-sighted glasses ; indeed, this state of the eyes some- times occurs in old persons whose vision was previously at the usual distance. 247. Management of Near-sightedness. Concave glasses extend the vision of the near-sighted by separating or diverging the rays of light before they enter 62 the eye, so that they may be less quickly brought to a focus, and the image formed further back, as shown in Fig. 62. The powers of . . , , Near-sighted Eye, corrected by double concave 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 OPTICAL DEFECTS OF 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 short-sightedness, and although objects are seen better close by, yet they are not seen so distinctly as in true or optical short-sightedness. Such persons seek strong light, to get a more vivid impression, and use convex glasses to increase the light upon the retina. This use of glasses is perilous (266). Short-sightedness is sometimes a symptom of com- mencing cataract. This disease is not, as is commonly supposed, something growing over the sight on the outside of the ball. It is a change in the crystalline 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 fn 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 SUGGESTIONS CONCERNING SPECTACLES. 131 FIG. 63. mounting the glasses, and by the buyer in selecting the frames. It is essential that the lenses be so framed that their axes shall be 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 then* 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 then* 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 7iead. where those with- The a ?f s of the glasses, c left side, the veins, conveying carbonic acid. FIG. 70. Lesser or Pulmonary Circulation. Pulmonary Artery. Heart. Eight Auricle. Eight Ventricle, ?ena Cava. Pulmonary Vein. Left Auricle. Left Ventricle. Aorta. Greater or Systemic Circulation. 284. What Oxygen does in the body. The purpose of this incessant inflowing stream of oxygen, is to carry forward the great operations ojf the vital economy. Oxygen has a wide range of chemical attrac- tions, and combines with other elements with intense energy. It is the ever-laboring, tireless Hercules of the atmosphere. As it kin- dles and maintains the combustion of our fires, so it does our bodily vitality. The muscles are called into action through decomposition by oxygen, and as with the muscles in the manifestation of mechani- cal force, so with the brain in the exercise of intellectual power. This rNTLtTENCE OF OXYGEN MOISTURE. 167 organ is on an average only abont ^ the weight of the whole body, yet it receives from ^th to y^th of the entire oxygenated stream from the Inngs and heart. A torrent of oxygen is thus ponred incessantly into the material apparatus of thought to carry forward certain physio- logical changes upon which thinking depends. If the arterial stream be cut off from a muscle, it is paralyzed ; if it be stopped from the brain, unconsciousness occurs instantaneously. In proportion to the activity of muscle is its demand for the destructive agent ; in proportion also to the activity of the mind is the brainward flow of arterial blood. 285. Effects of Tarying the quantity of respired Oxygen. If an animal be deprived of this gas, it dies at once. If man undertake to breathe i less proportion than that naturally contained in the air, the effect is depression 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 preternatural speed. If pure oxygen is respired, the over action and fever become so great that life ceases in a short time. Mtrous 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. 8. MOISTUEE. 286. How much moisture the Air contains. The third constant ingre dient of the air is moisture, derived from evaporation upon the earth's surface. The quantity which the air 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 50, 4'24; at 60, 5-82; at V0, T94; at 80, 10-73 ; at 90, 14-38 ; at 100, 19-12 grams, and as the temperature goes higher still, the capacity for moisture also increases (308). After the air has imbibed its due quantity of vapor, at a given temperature, it is then said to be saturated, and will receive no more unless the heat be increased. To better appreciate how rapidly the capacity for moist- ure augments, as the temperature ascends, we will state the propor- tions in another form. A quantity of air absolutely saturated at 32, 158 EFFECTS OF THE CONSTITUENTS OF AIK. holds in solution an amount of vapor equal to the yl^ part of its weight; at 59, ^ ; at 86, ^; at 113, ^? and at 140, A- 287. Conditions of the drying power of the Air. If, when the air is saturated, its temperature falls, a portion of its moisture is precipitated, that is, it does not remain dissolved, but appears in drops of dew. Thus a cubic foot of air, saturated at 90, if cooled 10 would deposit 3-5 grains of water. Until it is saturated, air is constantly absorbing moisture from all sources whence it can procure it. A cubic foot of air at 90, and containing but 8 grains of moisture, is capable oi 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. Moisture in the Air of Rooms Dew-point. It has been explained that the temperature at which air is saturated, and begins to condenso its moisture in drops, is called the dew-point (34). When air contains so much moisture that its temperature needs to decline but little be- fore water appears, the dew-point is said to be high ; when it must lose much heat before drops are produced, its dew-point is low. Air, with a high dew-point, is therefore moist, while that with a low dew- point is always thirsty and drying. A simple means of finding out the dew-point, and ascertaining the drying power of the air, is as follows : Note the temperature of the air by a thermometer, taking care that the instrument is not influenced by the radiation of any heated body in its vicinity. Then introduce it into a glass of water and gradually add a little ice, carefully watching for the first ap- pearance of moisture on the outside of the tumbler. The tempera- ture at which the deposit commences is the dew-point ; and the difference between it and the temperature of the air, expresses its drying power. If the ah* 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 PRESERVATION IN THE BOOM. 159 by comparing the two scales ; cost, from 3 to 5 dollars. From obser- vations made at Washington through June, July, August, and Sep- tember, from 9 to 3 o'clock of the day, the dew-point was, on an average, 11 below the temperature of the air, and sometimes more than 20 below. The air is always dampest near the ground; a difference in height of 60 feet, in the same exposure, has been known to make a difference of 10| degrees in the dew-point. In our houses, we are to imitate as far as possible the external conditions of the air. As the temperature of freshly drawn well water is about 50, a vessel containing it should receive a deposit of moisture when brought into our rooms, if they have a temperature above 65. It is very rare that any such deposit is seen in apartments heated by a hot-air furnace even if a considerable quantity of water is evaporated. 289. How double Windows affect the moisture of Rooms. 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 will rapidly deposit its water, and then falling to the floor will -be succeeded by other air (337), so that the window acts as a perpetual drain upon the moisture of the apartment. It is often impossible to maintain the air properly humid on this account. Peo- ple are misled by this copious deposit of dew upon the glass, and it is hard to convince them that the air is deficient in moisture when they can see it condensed upon the windows. We have referred to double windows as a means of saving 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. Rate of Evaporation. When dry air is exposed to a source of moisture, a considerable time must elapse before it will become satu- * If doable windows 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 EFFECTS OF THE CONSTITUENTS OF AIB. rated. The diffusion of vapor into hot air is mnch more rapid than into that which is solder, but it is not at all instantaneous. Mr. DANIELL observed, that a few cubic inches of dry air, continued to expand by the absorption of humidity for an hour or two, when ex- posed to water at the temperature of the surrounding air. In cold regions there is much less moisture in the air than in hot, and less in winter than in summer. It is also subject to a regular diurnal variation. As the sun warms the air during the day, evaporation is increased, and the humid element rises into the atmosphere ; but as it declines toward evening, cooling begins, and at night the watery vapor again falls, and is deposited upon the earth. "We are not to infer that because there is an absence of rain, therefore the air is dry ; on the contrary, in long droughts the air is often heavily charged with mois- ture. 291. How moist lir 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 tb^ obstruc- tion of the insensible perspiration by an atmosphere surcharged with humidity. Not only are waste matters generated in the system thus unduly retained, but malarious poisons introduced through the lungs by respiration, are prevented from escaping ; which would lead us to anticipate a greater prevalence of epidemic diseases in damp than in dry districts. 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 amounted to an epidemic, the heat of the atmosphere was ac- companied by great humidity, the dew-point reaching the extraordi- nary height of 84. In Buffalo, in the summer of 1854, the progress of cholera to its height was accompanied by a steady increase in at- MOISTUBE CARBONIC ACID. 161 mospheric humidity. Air which 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 au exaggerated degree the influence of damp warm weather. "When it blows with any strength, the dew-point is seldom more than four or five degrees below the temperature of the air. The higher its tempera- ture, the more distressing its effects, owing to the little evaporation it produces. This, connected with its humidity, is the principal cause of all its 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. WTMAN. Damp air at the same temperature as dry air has a more powerful cooling effect, producing a peculiar penetrating chilling feel- ing, with paleness and shivering, painfully known to New England invalids as accompanying the east winds of spring. 292. Effects of dry Air. Dry air favors evaporation. By promoting rapid transpiration from the pores of the skin, it braces the bodily energies and induces exhilaration of the spirits. Cold dry air is invigorating and reddens the skin, with none of the distressing symp- toms of cold moist air. If very dry, it not only accelerates perspira- tion, but desiccates and parches the surface, and deprives the lining membrane of the throat and mouth of its moisture so rapidly as to pro- duce an uncomfortable dryness, or even inflammation. Dry climates which quicken evaporation, are best adapted for relaxed and languid constitutions with profuse secretion, as those afflicted with humid asthma, and chronic catarrh with copious expectoration. The Har- niattan, 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 small-pox infection be- comes incommunicable." 4. CAEBONIO AOID. 293. Physiological effects of Carbonic 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 iri vast quantities from 162 EFFECTS OF THE CONSTITUENTS OF AIB, 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, &c. and becomes dangerous. "When breathed pure, it causes suffocation by spasmodically closing up the glottis of the throat. When mixed with air in small quantities, it is admitted to the lungs, and then acts as a rapid narcotic poison. The symptoms of poisoning by carbonic acid gas are throbbing headache, 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, BERTHOLET, under the influence of mental de- pression, retired to a small room, locked the door, closed up every crevice which might admit fresh air, carried 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 5 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 difficulty. I have placed a funnel on each furnace to aid the action of the fire. 20 minutes past ten. The funnels fall : I replace them ; this does not go to my satisfaction. The pulse is calm, and beats as usual. 10 h. 30. A thick vapor spreads itself by degrees in the chamber. My candle seems ready to go out. My lamp does better. A violent headache commences. My eyes are filled with tears ; I have a general uneasiness. 10 h. 40. My candle is extinguished, the lamp still burns. The temples beat as if the veins would burst. I am sleepy. I suffer horribly at the stomach ; the pulse beats 40 per min. 10. 50. I am suffocated. Strange Ideas present themselves to my mind. I can hardly breathe. I shall not live long. I nave symptoms of madness. 10 h. 60. [Here, ho 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. [Here were some illegible characters]." THEIR HARMONIOUS AND BENEFICENT ACTION. 163 entheing. I think an individual may find a decided difference in his feelings when making part of a large company, from what he does when one of a small number of persons, and yet the thermometer give the same indication. When I am one of a large number of persons, I feel an oppressive sensation of closeness, notwithstanding the temperature may be about 60 or 65, which I do not feel in a small company at the same temperature, and which I cannot refer altogether to the absorption of oxygen, or the inhalation of carbonic acid, and probably depends upon the effluvia from the many present ; but with me it is much diminished by a lowering of the tem- perature, and the sensations become more like those occurring in a small company." 811. Air of Bedrooms. The escape of offensive matters from the liv- ing person becomes most obvious when from the pure air we enter an nnventilated bedroom in the morning, where one or two have slept 172 SOURCES OF IMPURE 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. Parity the Intention of Nature. Yet we are not to regard the human body as necessarily impure, or a focus of repulsive emanations. The infinite care of the Creator is seen nowhere more conspicuously than in the admirable provision made for the removal of waste matters from the system, the form in which they are expelled, and the prompt and certain means by which nature is ready to make them inoffensive and 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 le allowed. It is not by the natural and necessary working of the vital machinery that the air is poisoned, but by its artificial confinement antl the accumulation of deleterious substances. If evil results, man alone is responsible. 313. Other sources of Impurity. Gaseous exhalations of every sort escape from the kitchen, and are diffused through the house as their odors attest, and the darkening of walls and wood-work painted with white lead shows that poisonous sulphuretted hydrogen from some Bource has been thrown into the air, its sulphur combining with the lead and forming black sulphuret of lead.* From the imperfect com- bustion of oil and tallow for lighting, and the defective burning of gas jets there arise emanations often most injurious to health. The vapor of a smoky lamp, if disengaged in small quantities, and the fumes of the burning snuff of a candle, may fill the room with disgusting odora * White zinc paint does not thus turn black. INFLUENCE OF CELLABS AND 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 confound coolness with freshness, and disagreeable warmth with chemical impurity; whereas these properties have necessarily nothing to do with each other. Cold air may be irrespirable from contamination and warm air entirely pure. 314. Poisonous Colors on Paper Hangings. Attention has lately been called to the poisonous influence of green paper hangings upon the air. Cases are mentioned of children poisoned by chewing green colored hanging paper, and of persons sickened by breathing air in rooms in which certain green papers have been mounted. The basis of the bright green colors used for staining paper-hangings is the poisonous arsenite of copper ', a combination of arsenic and copper. This, however, is not volatile, and does not create poisonous fumes or vapors, unless perhaps by being dusted fine particles are loosened and set afloat in the air. Nevertheless, though it do not vaporize and get into our systems through the lungs, arsenite of copper is a deadly poison, and when spread over paper-hangings, utterly spoils theni/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 reeeiTe Contagion. Respiration of im- pure air, is a prolific source of disease, which appears in numerous forms and all degrees of malignity. The effect of breathing a con- fined and unrenewed atmosphere, is not only to taint the air, but by a double influence, to taint also the blood. It is an office of oxygen in the body, as we have seen, to throw the products of waste into a soluble state that they may be readily excreted, but if its quantity be diminished in the air, this work is imperfectly performed in the body ; and the vital current is encumbered with putrescent matter. The increase of carbonic acid in the air, by offering a barrier to exhalation from the lungs, conspires to the same result. Accumulation of these morbid products in the blood, greatly heightens its susceptibility of being acted upon by atmospheric malaria, the causes of epidemics. The blood is supposed, under these circumstances, to acquire a fer- mentable state, forming, as it were, a ready prepared soil for the seeds of infection. Atmospheric malaria seem not capable alone of producing epidemic disease. From those in real robust health, with perfect sanative surroundings, the arrows of contagion rebound harmless. The miasmatic poison must 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. Illustration in the ease of Cholera. Of the tendency of an at- mosphere charged with the emanations of the human body^ to favor 176 MOKBID AND FATAL EFFECTS OF IMPURE AIE. the spread of contagions disease, the illustrations that might be quoted are innumerable. Take an instance of cholera, for example. It is well known to those who have had the largest opportunities of study- ing the conditions which predispose to this malady, that 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 the inhabitants of the town, though there was considerable diarrhoea. The building was badly constructed, and the ventilation deficient ; but this was especially the case with the school-rooms, there "being only about 68 cubic feet of air for each girl, and even less for the boys. On Nov. 8d one of the inmates was attacked with the disease ; in ten minutes from the time of the seizure, the sufferer passed into a state of hope- less collapse. Within the space of 48 hours, from the first attack, 42 cases and 19 deaths took place; and in the course of one week, 60 of the inmates, or nearly 22 per cent, of the entire number were carried off; whilst almost every one of the survivors suffered more or less, from cholera or diarrhoea. Among the fatal cases were those of 25 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 and obedient in other respects, the boys could not be Tcept jrom breaking the windows" so that many of them probably owed their lives to the better ventilation thus established. In the jail of the same town, in which every prisoner was allowed from 800 to 900 cubic feet of air, and this continually renewed by an effcient system of ventilation, there was not the slightest indication of the epidemic influence. (Dr. CAKPENTEK.) 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. Feiers originate in impure Alt. 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 dwellings and in cities, and the exhalations of swamps, grave-yards, and sewers, called marsh miasm. This is supposed to give rise to yellow, remittent, lilious, IT PBODUCES FEVERS AND SCEOFULA. 177 and intermittent fevers, dysentery, and perhaps also cholera. And second, exhalations from the human body, confined and accumulated in ill-ventilated habitations, sometimes termed typhoid miasm, and which usually gives origin to common typhus and low nervous fevers It would thus appear, that the very type and character of febrile disease is determined by the Mnd of impurity which is breathed. Prof. SMITH, of New York, says, " Let us suppose the circumstances in which typhus originates, to occur in summer, such as the crowd- ing of individuals into small apartments badly ventilated, and ren- dered offensive by personal and domestic filth ; these causes would obviously produce typhus in its ordinary form. But, suppose there exist at the same time, those exhalations which occasion plague, and yellow fever, or remittent and intermittent fevers; 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 eonsequenee of Impure Air. There is a diseased condition of body known as scrofulous or strumous, which manifests itself in various forms, and in all parts of the system. It seems to be a result of deficient nutrition ; that is, not a want of material for nutricious purposes, but a failure of power to produce healthy and perfect tissue from the elements of food. Various causes have been assigned as tending to produce scrofulous habits of body, such as hereditary tendency, bad diet, depressing passions, too late, too early, or in-and-in marriages, sedentary occupations, want of ex- ercise, deficient clothing, bad water, &c., and these, under different cir- cumstances, may each contribute to the result ; but imperfect respira- tion is probably the most efficient and universal cause. An eminent French Physician, * who has made this subject a matter of extensive study, says, " Invariably it will be found on examination, that a truly scrofulous disease is caused by a vitiated air, and it is not always neces- sary that there should have been a prolonged stay in such an atmosphere. Often a few hours each day is sufficient, and it is thus that persons may live in the most healthy country, pass the greater part of the day in the open air, and yet become scrofulous, because of sleeping in a confined place, where the air has not been renewed." The same ob- server goes further, and affirms that the repeated respiration of the same atmosphere, is a primary and efficient cause of scrofula, and * M. 178 MORBID AND FATAL EFFECTS OF IMPURE AIR. that, " if there be entirely pure air, there may be bad food, bad cloth- ing, and want of personal cleanliness, but that scrofulous disease can not exist." In 1832, at Norwood School in England, where there were 600 pupils, scrofula broke out extensively among the children, and carried off great numbers. This was ascribed to bad and inef- ficient food. Dr. Arnott was employed to investigate the matter, and immediately decided that the food "was most abundant and good," assigning " defective ventilation, and consequent atmospheric im- purity " as the true cause. 321. Consumption induced by Impure Air. When scrofula localizes itself in the lungs, there ispulmonary or tubercular consumption. The essence of the nutritive process consists in the vital transformation of albumen (678) into fibrin and organized tissue. Now the tubercles which in this disease make their appearance in the pulmonary organs, consist of crude, coagulated, half organized masses of albumen the abortive products of incomplete nutrition. In this manner, bad air, by producing the strumous condition, becomes a cause of con- sumption. It seems natural to expect that the organs with which the foreign gaseous ingredients of the atmosphere come more im- mediately into contact, and whose blood-vessels they must enter on their passage into the system, should feel, in a distinctive manner, their noxious influence ; and this expectation" is strengthened by observation, and experiment upon both men and animals. It has been observed that when individuals habitually breathe impure air, and are exposed to the other debilitating causes which must always influence, more or less, the inhabitants of dark ill- ventilated dwellings, scrofula, and consumption, as one of its forms, are very apt to be engendered. 322. State of the Air influences Infant Mortality. The same malign in- fluence of the air of unventilated rooms is seen in the mortality of infants. That the new-born and tender child should be infinitely sus- ceptible to the influence of contaminated air is what we might well expect. We are, therefore, not surprised, that in the foul and stifling air of Iceland habitations, two out of three of all the children should die before twelve days old. Opportunities have been 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 *nth the introduction of efficient ventilation. " On the imagination of mothers, educated as well as ignorant, the feeling still seems to be Btereotyped, that the free, pure, unadulterated air of heaven falls upon JT BREAKS DOWN CONSTITUTIONAL VIGOE. 179 the brow of infancy as the poppies of eternal sleep, and enters the lungs and circulates as a deadly poison; and still the 'shawls and blankets,' sleeping and awake, are pretty generally employed to de- prive the objects of the most rapturous paternal solicitude, of what was originally breathed into the nostrils of the great archetype of the human race as the ' breath of life.' " 323. Bad Air undermines the Vital Powers. And yet the fatal effects of mephitic air are by no means confined to those terrible maladies, Cholera, Fevers, Consumption, and Infantine disease, by which the earth is ravaged ; by undermining the health it paves the way for 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 [xerhaps a more correct measure of the real vigor of the body than its outward appearance of health. Individuals may often continue for years to breathe a most unwholesome atmosphere without apparent ill-effects ; and when at last they yield, and are prostrated, or carried off by some sudden disease, the result is attributed to the more ob- vious cause, the long course of preparation for it by subtle and insidi- ous poisoning being entirely overlooked. The mass of mankind refuse to recognize the action of silent, unseen causes. Our youth in the uiorning 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 foul air are not confined to those cases in which the immediate results of its poison are seen. Because it requires a given quan- tity of carbonic acid in the air to exhibit decided effects, it does not follow that a much lower proportion does not seriously impair the vital energies, and especially the power of resisting disease. "We are firmly convinced that many a case of scarlet fever or of measles proves fatal on account of an unperceived depression of the little sufferer's strength by previous continued exposure to an atmosphere tainted with carbonic acid and other exhalations from his own lungs. We know that all diseases of low grade, such as typhoid and typhus fever, prevail to a very great extent in ill ventilated houses ; we know that an epidemic inflammation of the eyes has been frightfully prevalent in the Irish work-houses, and that it has been traced to imperfect ventilation, the eye-disease being merely the index of the general depression of the vital powers ; we know, too, that in one of the Trans-Atlantic Hospitals, the mortality went down from forty in a thousand to nine, upon the adoption of a proper system of ventilation, and that it rosa again to 24 on the subsequent abandonment of that system. These are only illustra- tions ; hosts of similar facts could be cited from the records of medical science." 180 MORBID AND FATAL EFFECTS OF IMPURE AIR. would immediately suffer, did not some vital conservative principle accommodate our functions to circumstances and situation. But this seems to get weaker from exertion. The more we draw on it, the less balance it leaves in our favor. The vital power, which in a more natural state would carry the body to seventy or eighty years, is pre- maturely exhausted, and like the gnomon shadow, whose motion no eye can perceive, but whose arrival at a certain point in a definite time is inevitable, the latent malaria, which year after year seems to inflict no perceptible injury, is yet hurrying the bulk of mankind, with un- deviating, silent, accelerating rapidity, to an unripe grave. It should never be overlooked, that by breathing pent-up effete air, all the ad- vantages of an abundance of fuel, and every blessing of a genial sky are utterly thrown away, and though the habitation were on the hill- top, fanned by the sweetest 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-posts V , ^ Conditions in which openings in rooms produce exchange of air. there be but a single opening to a room, although all other condi- tions are favorable for a change, yet the counter currents meeting in the passage conflict, and to a certain extent obstruct each other. There should, therefore, be separate openings for currents of ingress and egress. 341. Friction of eonnter-eurrents of lir. The importance of having two independent openings to an apartment, if we desire to secure a change of air, is shown by the following simple experiment : Take a bot- tle with the bottom removed, or a lamp chimney (Fig 79), place under it a short piece of burning candle in a shallow dish of water, so that no air can get in from below ; now, although the stopper be removed so that the inside of the bottle has direct communication with the outer air, the candle will go out. Although there is a tendency of the burnt air to escape and of the fresh air to rush in, yet they cannot pass each other at the open mouth ; the currents conflict and the 190 AIR IN MOTION CURRENTS DRAUGHTS. FIG. 80. exchange does not take place. Yet, if a slip of paper be inserted in the mouth of the bottle or lamp-glass, as seen in Fig. T9, thus dividing it into two distinct apertures, the lit candle will con- tinue to burn. The foul air will pass out on one side of the pasteboard and the pure air enter on the other, as may be shown by the smoke from the snuff of a candle held near ; it will be drawn in on one side and carried up on the other. The purity of the air within is thus secured. When the opening, how- ever, is sufficiently large, the currents pass without difficulty, as is easily illustrated. If the door of a warm apartment be opened, and a candle placed near it on the floor, the flame will be blown in- wards ; if it be raised nearly to the top of the door it will be blown outward, as illustrated in Fig. 80. The warm air flows out at the higher openings. If the air of the room be warmer than that without, it enters by all the crevices near the bottom, and escapes by those near the top, and the reverse if it be colder. 342. Currents through Windows. Draughts through windows and doors are often not effectual in removing all the air of rooms. In the case just .instanced (Fig. 80), of the open door, the cold air below enters and expels 'an equal portion of the warmer air, but only that will flow out which lies Counter-currents in the doorway. t>do W the level of the door-top. The mass of air above this level will not be displaced. If, however, the temperature of the room were at 60, and that of the outer air at 70, an open door would evacuate the room entirely of its airy contents ; the colder air in the room tending to fall would pour out at the bottom, and the warm air enter at the top to take its place. If a window be situated in the upper part ot the room and opened, its action is different, and in a manner opposite to that of the door. When the air is cold without and warm within, and the window opened above and below, the apartment is emptied and refilled as in Fig. 81. If the external air is warm and that within cool, all above the window sill is removed (Fig. 82), but the cold ah below that level continues undisturbed. By thus understanding the INTERCHANGES THBOUGH WINDOWS AND DOORS. 191 Fia. 81. conditions of inflow and outflow, we are enabled to regulate windows having both sashes movable, and which are often valuable for venti- lating private rooms. Although the interference of other causes is liable to modify, and perhaps often confuse and divert these movements, yet they are quite sufficient to show that the motion and rest of air are controlled by laws as definite and reg- ular as those which govern the mo- tion and rest of water. Though infi- nitely more light, mobile, and easily agitated, yet it is never thrown into commotion except by adequate and ap- preciable causes. 343. How currents of Air affect the Sys- The sensations produced upon te Condition in which the air escapes above. FIG. 82. the body by gently-moving currents of air in proper conditions of temperature and moisture are extremely agreeable, but in many cases streams of air directed against the per- son become most injurious. Air at low temperatures of course has a cooling effect. "We lose no more heat by radiation in moving air than in still air, but by conduction we lose heat in proportion to the velocity of the cur- rent or the number of particles which come in contact with the body. The cur- rent also drives the cold air through the clothing, displacing the warm air which was entangled in its pores. Increased evaporation, proportional to the dryness and speed of the air, is also a further source of cold. If the whole surface of the body is exposed to the current, the effect will be simply a general cooling without any necessarily injurious effects. But if the draught fall only upon some one part of the body, it is liable to produce serious mischief, disturb- ing the circulation and producing febrile movements, which may be directed to the part exposed to the draught or even to remote organs, in either case often laying the foundation for serious and fatal disease. This point should be particularly considered in introducing air in sum- mer which has been artificially cooled (352) ; its diffusion should be Conditions in which the air escapes below. 192 ARRANGEMENTS FOR VENTILATION. very extensive and its velocity hardly perceptible. Of course we can- not have ventilation without movement of air, but the motion should be so moderated that we are not aware of it, and is always to be con- sidered in connection with the two important conditions of tempera- ture and moisture. We have made several trials to determine the ve- locity which, as a general rule, with a proper regard to other condi- tions, will not be found unpleasant, and give as the result about two feet per second. It is evidently no greater than that with which we should pass through still air when walking with the same velocity. (WYMAN.) Yet it is important that we be exposed to currents. Few things are more favorable to taking cold than the confined and stag- nant air of unventilated apartments. Just in proportion as we habit- uate ourselves to such still, stagnant air, do we become sensitive to at- mospheric changes, against which it is impossible perfectly to protect ourselves on going out. The effect of a free internal circulation of air in our rooms is therefore most salutary; the more we are accustomed to it, the safer we are in the vicissitudes of changing weather. VIII. ARRANGEMENTS FOR VENTILATION. 344. The open Fireplace. The mechanical expedients for securing exchange of air in dwellings are numerous, but they are chiefly con- nected with arrangements for heating. Wherever there is active com bustion in stove or fireplace, there must be a stream of air passing out of the room through the chimney. If the room be absolutely tight, so that no air can enter it, none will ascend, and if the fire be kindled the chimney will smoke. A draught through a chimney im- plies openings somewhere for air to enter the room, and thus there is some ventilation as a matter of necessity. In noticing the heating ef- fect of the fireplace, we saw that the open space above the fire con- veys away a large amount of warmed air from the room, which took no part in the combustion and wasted much heat. But this fault was an advantage in respect of ventilation. The magnitude of the open space above the fire represents the ventilating capacity of the chim- ney. But it is from the air below the level of the mantel the purest in the apartment that the fireplace is supplied. Only so much of the foul imprisoned air above as gradually cools and descends, be- ing swept into the chimney. When the weather is quite cold, the briskness of the fire that is demanded, occasions a powerful draught and produces annoying currents. So powerful were these draughts in old times, that they were compelled to use a settle, a long bench with ACTION OF FIREPLACES AND STOVES. 193 a high wooden back, to protect the body from currents and retain the radiant heat in order to keep warm. " It would be well for those who question the importance of ventilation, because our forefathers lived to a good old age without even understanding the meaning of the word, to remember their fireplaces, the kind of dwellings they occu- pied, and the quantity of air which must have passed through their houses." It cannot be doubted that the changes which have of late years been effected in the structure of the fireplace to secure the greater economy of fuel the contraction of its dimensions and the lowering of the chimney-piece, by diminishing the amount of air that was forced through the room to fill the capacious chimney, and by bringing the foul-air space down more completely within the zone of respiration have been altogether unfavorable ; although, even in their newer construction, open fires may be considered as affording a toler- able amount of ventilation. Fresh air is well secured by the double fireplace, which warms and introduces into the room a steady stream of air from without. (111.) 345. Ventilation by Stoves. As respects the condition of the air, the exchange of even the low and contracted fireplace for the close and stifling stove, has been eminently promotive of discomfort and disease. Stoves afford the least ventilation of all our means of heating. They take little more air than just sufficient to consume the fuel, and that is withdrawn from the purer portion near the floor. In most cases of the use of stoves, no provision whatever is made for the removal of bad air. They may be made subservient to ventilation in several ways ; first, by allowing air to pass through tubes in the body of the stove; second, by admitting it between the stove and an external casing ; and third, by simply allowing it to strike upon the external surface of the stove. In either case the entering air will be warmed, rise toward the ceiling, and afterward gradually descend as the air below is drawn off, producing a downward ventilation through the whole apartment. Mr. BUTTAN, of Coburg, C. W., has devised a plan of heating and ventilating, strongly recommended by those who have used it, although we have had no opportunity of seeing its operation. He locates his 'air-warmer' in the hall, or where required, brings in the air from below, heats and transmits it through the building. For the best working of his arrangement it is important that the house be built with reference to it ; indeed, he insists that the general failure to ventilate is because the architects fail to provide the necessary lungs in the original construction of dwellings (362). 346. Ventilation by Hot-Air Arrangements. Sources of warmth be- 9 194 ARRANGEMENTS FOR VENTILATION. come the most effective means of ventilation when air itself is made the vehicle for conveying heat into the room, as in the use of hot- water apparatus, furnaces, &c. The hot current enters through a register, or guarded opening, and streams up at once to the ceiling ; and by diffusion through the apartment, displaces the air already present, which must find escape somewhere, and thus the renewal of the breathing medium is constantly secured. Apartments warmed in this manner require a chimney or other place by which air may escape. The fireplace answers perfectly ; but under the impression that rooms heated by air-currents require no channel of escape, houses have been constructed with no flues at all. The air ought to be projected into the room horizontally or at different points, so as to be well diffused (125). It should always be derived from perfectly pure sources, and never used a second time. But the chief difficulty and danger, as before noticed, is to be found in that condition of the air itself, which results from its -being 1 Suddenly heated (305). 347. The supply of Moisture. The provision for supplying moisture by evaporation is rarely any thing like adequate, a supply of 35 cubic feet of air per minute introduced at the temperature of freezing and heated to 90 D , is capable of taking up an ounce of water per minute, or four pounds in an hour. Dr. REID states, that in ventilating the English House of Commons, when it was crowded, he often exposed the air furnished to 5,000 feet of evaporating surface, to impart the necessary moisture, and subsequently made the air flow through jets of water. The artificial supply of moisture to air in the exact quan- tity required, involves grave difficulties. The common method of supplying humidity by simmering water in an open vessel, is glaringly insufficient. A pan of water is placed in a furnace,* but of the torrent of air that rushes through, how little is brought into contact with the water. We place a vessel upon a stove with a few square inches of water-surface, and fancy all is right, but the air may still be parching dry. Where air in cold weather is introduced, suddenly rarefied by heat, and actively changing, we have little conception of the amount of moisture which must be artificially added to give to it soft and balmy qualities. The best thing to be done of course is, to obtain the largest possible evaporating surface. To accomplish this, a piece of linen or cotton cloth dipped in a vessel of water, may be hung in folds from any convenient framework or support. The cloth, by sponging * "Walker's furnace, manufactured by S. B. JAMES, No. 77 White streev, New York, nas large provision for evaporation, which the proprietors offer to increase to any extent that individuals may demand. HEATING CONTKTVANCES THAT BEST EFFECT IT. 195 np the water is always wet, and gives out its moisture to the air. If previously dipped into a solution of potash, which is very absorbent of water, it continues more perfectly wet. If it be unsightly, the sus- pended cloth may be concealed from view by any graceful screen, as by a tower-shaped cover of porcelain, open above and below to admit the passage of air. Where hot-air is used, it may even become neces- sary to mingle with it the vapor of boiling water. 348. Best method of Warming and Ventilation. If we would have the pleasantest mode of warming and ventilating a dwelling-house, with- out regard to trouble or expense, we should certainly combine the open fireplace with air-heating apparatus, which should never exceed in temperature 212. The first is desirable for its pleasant light and radiant heat, while the second gives to the entries and chambers a mild atmosphere, which prevents cold draughts from open doors, and at the same time, through an opening in each apartment, moderately warms it, and likewise supplies air for the ventilation going on by the fireplace. The fireplace also has its influence upon the introduction of the warmed air. The heat of the chimney establishes a current which draws from the air-heating apparatus a large supply of air at a lower temperature than would otherwise enter the apartment. We know of no single apparatus which warms and ventilates a dwelling- house in so healthy and comfortable a manner as is accomplished by this combination. WYMAN. Yet it can only be had by very few ; for the mass of the people it is entirely out of the question from expen- giveness. 349. Supply of Air by loose Joinings, CreYiees, &e, Hot-air con- trivances of any kind, although coming more into use, especially in cities, are by no means general. Grates and stoves are the nearly universal sources of heat, and the latter of these cannot be said to ventilate at all. No provision is made for the entrance and exit of air. The use of doors to rooms is for the admission of their occu- pants, windows are for the entrance' of light, and it would certainly seem, both from its importance and peculiar properties, that air also is entitled to an entrance of its own. Yet in most cases we treat the air as if it had no business in our dwellings. It has to avail itself of the mechanics' botch- work or the chance shrinkages of time, and creep through any crevices and wind-chinks that there may happen to be, or dodge in and out at the casual opening of windows and doors. These cracks and loose joinings afford a kind of imperfect accidental ventilation, which, by effecting the purpose in a partial 196 ARRANGEMENTS FOE VENTILATION. degree, has prevented mankind from discovering the want of any thing better. 350. Four points to be secured in Ventilation. That ventilation may be complete, and do for us its best service, four things must be at- tended to. First. Pure air must be introduced. Second. The foul air must be removed. Third. The supply must be sufficiently copious. Fourth. There must be no offensive currents. Now as things usually are, none of these points are certainly se- cured. There is no constant and regulated supply of air, this being left entirely to chance. There is no provision for the exit of the vitiated gases. All the air that is drawn off from the apartment is taken from its lower and purer portion by the draughts of the stove and fireplace, while that which should escape stagnates above. The quantity furnished is therefore variable and usually stinted, while in- jurious draughts are notoriously common. Independent and effective methods of changing the air, by which these enumerated benefits may be gained, are on every account desirable. 351. Modes of introducing pure Air from without, In summer the free opening of doors and windows ensures a supply of air. It is a good plan to have light door-frames fitted to the outer entrances, and covered with wirecloth or some loose fabric, as millinet, through which the air will pass readily, but in a diffused manner. In winter the air should always, if possible, be warmed before being thrown into the apartment. For introducing more fresh air than accidental fissures will admit, the readiest way is to lower the top window sash, although the stream of cold air which presses in and is both unpleas- ant and unsafe, falb to the floor and glides to the stove or fireplace without being sufficiently commingled with the general atmosphere to serve the purpose of ventilation, It becomes a mere feeder of the fire. To disperse cold currents of air from above, a plate of zinc perforated with numerous holes is made to replace the pane of glass furthest from the fireplace and in the upper row of the window. Louvres made either of tin, zinc or glass, with horizontal openings and slats like Venetian blinds, are also substituted for window panes. A small tin wheel or whirligig, which revolves and scatters the inflowing current, is sometimes mounted in the window ; it is often noisy and rattling. In arranging openings for the entrance of air, several circumstances are to be borne in mind. The air should always be fresh from with- out and not, as is too often done where hot-air furnaces are used, INTRODUCTION OF AIK INTO DWELLINGS. 197 taken from cellars or basements, or what is still worse, nsed over and over again. If there be local sources of impnrity in the vicinity, apertures should not be placed favorably to its admission. Where dnst is an annoyance, or from any cause there is contamination of air near the ground, the supply may be brought from the top of the house. Openings are made under the caves, or in some eligible place near the summit, leading to channels left in the walls, called fresh-air venti- ducts, which pass down and open into the room in any convenient manner. The prevailing direction of the wind should also be noticed, as it is desirable to command its aid as far as possible in forcing air into the building. EMEESON'S injector (Fig. 83) causes a downward current from whatever quarter the wind may Fio blow upon it. All outer apertures should be guarded with valves. Air entering them and led along proper passages, either in tin tubes or air-tight wooden boxes, is admitted into the room at various points. There may be an air passage made along behind the base or mop-board, communicating with the room by innumerable minute openings, through which the air passes. Or the inflowing currents , ,, , . , , . Emerson's Injector. may be received through registers or made to rise through small apertures in the floor. 352. The downward Current Air once breathed must not be again brought within the sphere of respiration, but should it be removed downward or upward? The air thrown from the lungs escapes hori- zontally from the mouth and downward from the nostrils ; it may then be swept without difficulty by the ventilating current in either direction. In cases where hot air is thrown into the room, it first rises to the ceiling, and then, as it is gradually cooled, falls, and is mainly drawn off by the fireplace below the plane of respiration. This is in effect a downward current, but it is hardly strong enough to carry the breath down with it. It ascends, is diluted by the upper air, and fall- ing again is liable to be reinhaled. A descending current of air arti- ficially cooled has been employed for ventilation ; in fact, rooms can be as effectually ventilated in summer by the aid of coolers placed above them, as they are in winter by the heater J)elow them. LYMAX ? S ventilator (Fig. 84), consists of a reservoir of ice A, the bottom of which is an open grate; B is a gutter to catch the water from the melting ice ; G is a pipe or flue, through which a stream of cold condensed air falls constantly, as shown by the course of 198 ARRANGEMENTS FOR VENTILATION. the arrows ; Z>, a wire gauze "box filled with char coal, which prevents the waste of ice by radiation, and disinfects and purifies the descending air. The force of the current depends on the length of the cold air flue and its temperature, compared with the outer air. In hot weather the breeze continues quite brisk. This arrangement, on a small scale, has been mounted on secretaries, to secure a cool and refreshing air while writing; over beds, to cool the air while sleeping; and over cradles, to furnish pure air for sick children Lyman's cold air 353. The ascending Current most Natural. We have noticed that by a beautiful provision of nature, venti- flue. lation of the person is constantly taking place. The exquisite mechanism of the human system would have been created to little purpose if it had been left to smother in its own poison. A gentle and insensible current constantly rises from the body, which carries all that might be injurious into the higher spaces. Vitiated air would thus constantly escape from us if it could. But in our houses we de- feat the benign intentions of nature by enclosing the spaces above us, so that the detrimental gases accumulate in the upper half of the room, surrounding the head and corrupting the uespiratory fountain. It is thus evident that if we desire to aid nature in her plans, we must remove or puncture the air-tight covers of our apartments, so that the ascent and complete escape of foul air shall not be obstructed. 354. Ventiducts and Ejectors. Openings for the escape of these bad gases above are indispensable. Each room fifteen feet square, for the accommodation of six or eight individuals, should have a flue for the escape of foul air, either in the chimney or elsewhere, of at least 100 inches area. A bedroom should have an outlet of nearly the same dimensions. But in practice a serious difficulty is encountered here. If we make an opening out from the top of the room, either by low- ering the top sash of a window or by carrying up a duct through the roof, instead of the foul air escaping through them, a flood of cold air rushes in from without. Tubes or ventiducts, connecting the room with the top of the house, may be made to act exhaustively, and drain the apartment of its polluted air, when the wind Hows, by surmount- ing it with EMERSON'S Ejector (Fig. 85), and as the air is almost con- stantly in more or less rapid motion, this arrangement becomes very serviceable. 355. Opening into the Chimney Arnott's Valve. But the force of ABNOTT'S SELF-ACTING VALVE. 190 FIG. 85. draught in the chimney is after all to be the main reliance in convey- ing away foul air. Its necessary action is that of a drawing or suck- ing pump, which exhausts the room of large quantities of air. As the velocity of smoke in a chimney with a good fire is estimated to be from 3 to 4 feet per second, its exhaustive power is amply sufficient to make it serve the secondary purpose of a ventilating flue. Hence, if we make a hole into the chimney, by knock- ing out two or three bricks near the ceiling, the foul gases will rush in, and mingling with the ascending current will escape. Yet these ven- tilating chimney openings are liable to the se- rious and even fatal objection, that when from any cause the current hi the chimney is inter- rupted, smoke is driven into the room. An ordinary register, requiring personal attendance to open and close it, would be of no service. To Emerson's Ejector, remedy this inconvenience, Dr. AENOTT has contrived a self-acting sus- pension valve. It is so placed in the aperture, and so mounted, that a cur rent of air passing into the chimney opens it, while a current in the con- trary direction closes it. It is so delicately suspended that the slight- est breath of air presses it back, while any regurgitation of the chimney current p== shuts it, and thus prevents the backward flow of smoke into the room. It is shown in Fig. 86. Owing to the unsteadiness of the currents, the valve is constantly vibrat- ing or trembling, and would be noisy but that it is made to strike against soft| leather. A modification of this valve Amott's Valve, consists of a square piece of wire gauze set in the opening, with a cur- tain of oiled silk sus| -ended behind it. The current into the chimney pushes back the pendant flap, while a reversed current drives it against the gauze, and thus closes the aperture against the admission of fire- fumes and smoke. These are easily placed in fire-boards used to close the fronts of chimneys. 356. Importance of Arnott's Valve. The value of this valve to the public can hardly be exaggerated. Mr. TEEDGOLD expressed what many have felt, when he said that all the plans he had seen or read ol for drawing off the air from the top of a room are objectionable, either from being wholly inefficient or from causing the chimney to smoke. This valve first meets the difficulty. It is cheap, easily inserted, may FIG. 86. 200 AEEANGEMENTS FOB VENTILATION. be managed with trifling care, and drains the room effectively of its gaseous pollutions. In the thousands of stifling, stove-heated rooms, where palor of countenance, headache, and nervousness, bear painful witness to the perverted and poisoned state of the air, this simple me- chanical contrivance might bring happy relief. It is much used in England, but has not been made sufficiently known in this country. "We have inquired for it in vain at many establishments. It is manu- factured by S. B. JAMES & Co., TV White street price, $2 50 to $5, according to size. If the orifice in the chimney be deemed unsightly, it may be screened from view by placing a picture before it. 357. Chimney Currents in Summer. The air in the chimney is usually somewhat warmer than the external air, even when there is no fire, and this will occasion a slight draught, so that if there be an aperture in the upper part of the room into the flue, and the fireplace be closed, the vitiated air above will be removed. This exhaustive ac- tion of the chimney without fire, is aided by winds blowing across its top, which exert a slight suction influence, or tendency to form a vacuum within it. This effect of the wind will be much increased if the chimney be mounted with an ejector (354). A slight fire in afire- place, even when not wanted for warmth, is often desirable for ven- tilation. Lamps have been sometimes introduced into flues for the purpose of exciting currents. 358. An additional Ventilating Flue. If an extra flue be constructed adjoining the chimney, warmed by it and opening into the top of the room, there will be a draught through it, and it may be devoted ex- clusively to ventilation. It would seem that such a secondary flue would not be liable to refluent smoke, and might have connected tubes extending to remote rooms, thus effectually ventilating the whole building. But practically such shafts do not well succeed. Double outlets in the same apartment rarely work satisfactorily. The chimney is liable to convert the extra flue into a feeder of the fire, and thus, if it be of the same height as the chimney, to suck back the smoke into the room: " Such cases have occurred, and the ventilating flue has been closed in consequence. This evil can be remedied by providing a free supply of air for both air and smoke flues. But the air which enters must be warmed, or it will not be tolerated, and if it is too much warmed, as compared with the air of the room, it will rise immediately to the ceiling and escape. through the ventilator, and, not mingling with the air of the room, it will greatly diminish or en- tirely prevent any change of air where most wanted." 359. Ventilation of Bedrooms. The bedroom, the place where we SPECIAL DEMANDS OF THE BEDROOM. 201 spend nearly half of our lives, in its general condition and manage- ment is the opprobrium of civilization. No place in the house should be more copiously supplied with air to guard us against the injurious agencies to which we are nightly exposed. The materials of which bedding is composed have a strong tendency to attract moisture from the air and become damp. Not only are the textile fibres highly hy- groscopic, or absorbent of atmospheric moisture, but the coldness of rooms in which beds are usually placed, favors the deposit of moisture when the air is charged with it. They are also saturated with bodily perspiration. Beds should, therefore, be often and thoroughly aired. Their injurious effects when damp are much more dangerous than those of wet clothes. As the body is at rest while we sleep, there is no exercise to warm the surface and throw off the ill effect, as can be done with damp clothes. Moreover, as the vital activity is depressed during the state of slumber, the system is more open to the malign in- fluence of cold or other causes. Many and fatal diseases, inflamma- tions, rheumatisms, catarrhs, asthmas, paralysis and consumption, are induced by a want of precaution in this particular. Yet with all these demands for capacious drying air-space, bedrooms are apt to be scan- dalously small and low, damp and unwholesome. They do not usually contain fireplaces to drain off the bad air, and the lack of all ventila- tion is made worse by the popular dread of draughts, which prevents the opening of windows. There is urgent necessity for the adoption of some means of relieving them. Opening the window Fi gT above and below is very serviceable; lowering the upper sash, with an opening over the door, and currents in halls? also gives relief. But if the bedroom have no fireplace, it should be connected by tubes with the chimney flue, the aperture being guarded by an Arnott's valve. 360. Ventilating Gas-burners. As we before remarked, the common mismanagement of gas is a forcible illustration of the effect of ignorance or thoughtlessness, in often turning the best things to the worst account. Gaslight is cheap, brilliant and convenient, the very qualities we want ; and so we turn it on and enjoy the flood of light. But bad air and headache supervene, and then gas-lighting is condemned, though the real fault is lack of ventilation. The use of gas- light greatly heightens the necessity for effective change of air ; it generates poison exactly in proportion to its brilliancy. Dr. FARA- DAY adopted the following successful plan to ventilate gas-burners 202 ARRANGEMENTS FOR VENTILATION. He placed a metallic tube about an inch in diameter over the lamp- glass, dipping down into it (Fig. 87) one or two inches, and connect- ing by its other extremity with a flue. But this was thought to be ar ungraceful appendage to the chandelier, and has not come into use. He devised another, by which the tube carrying off the products Oi combustion, returned parallel with the supply pipe, but we have not seen it. There is report also of a still more elegant and successful English contrivance, but it cannot yet be found in this country. 361. Ventilation of Cellars. I was seen that cellars are fountains of offensive air, which ascends through crevices in the floor, doors, windows, and stairways, often infecting the upper apartments with the noxious cellar atmosphere. If cellars are to be tolerated under our houses, they should be thoroughly ventilated. Perhaps the best plan is to extend a flue from the chimney down into the cellar, by which the fire-draught above shall constantly drain it. A tube or passage from the cellar to tbe top of the building, mounted with an ejecting cowl, answers a good purpose. Some go for abolishing cellars altogether.* 362. Ventilation should be provided for In Building. There can be little question that the whole policy of warming and ventilating dwellings is yet in an unsettled and transition state, although this affords no apology for neglecting the subject. Much is known, and a great deal may be done about it to promote health and preserve life. * " "While I would condemn cellars and basements entirely, the common plan of build- ing, in their absence, must be condemned also. The house being built above the surface of the earth, a space is left between the lower floor and the ground, which is even closer and darker than a cellar, and which becomes, on a smaller scale, the source of noxious emanations. Under-floor space should be abolished as well as cellars and basements. The plan that I have adopted with the most satisfactory success, to avoid all these evils, is the following : Let the house be built entirely above the ground ; let the lower floor be built upon the surface of the earth, at least as high as the surrounding soil. If filled up with any clean material a few inches above the surrounding earth, it would be better. A proper foundation being prepared, make your first floor by a pavement of brick, laid in hydraulic cement, upon the surface of the ground. Let the same be extended into your walls, so as to cut off the walls of your house with water-proof cement, from all communication with the moisture of the surrounding earth. Upon this foundation build according to your fancy. Tour lower floor will be perfectly dry impenetrable to moist- ure and to vermin; not a single animal can get a lodgment in your lower story. By adopting this plan, your house will be dry and cleanly ; the atmosphere of your ground floor will be fresh and pure ; you will be entirely relieved from that steady drain upon life, which is produced by basements and cellars, and if you appropriate the ground- floor to purposes of storerooms, kitchen, &c., you will find that the dry apartments thus constructed are infinitely superior to the old basements and cellars. And if you placi your sitting and sleeping rooms on the second and third floors, you will be as thoroughly exempt from local miasma as Architecture can make you." Dr. BUCHANAN. WHY THEY ABE NOT UNIVERSAL. 203 Provision should be made for ventilation in the first construction of dwellings, as it may then be effectually and cheaply accomplished. The introduction of adequate arrangements, after the building i? finished, is costly and difficult. The necessity is absolute for including ventilating provisions in houses as well as those for heat. Architects and Builders should make them a primary and essential element of then* structural arrangements, and design in accordance with the prin- ciples of ventilation as an established art. It is to be regretted that too many in those professions to which a careless public commits its interests in this particular, are profoundly unconscious of the just claims of the subject, and totally unqualified to deal with it properly. This is hardly a matter of surprise when we recollect how recent it is that science has thrown its light upon the physiological relations of air. It is almost within the memory of men still living that oxygen gas was first discovered, and it is within twenty years that LIEBEG an- nounced the last constant ingredient of the atmosphere (280). Archi- tecture on the contrary rose to the dignity of a regular art thousands of years ago, when men had little more intelligent understanding of the real import of the breathing process than the inferior animals. TTe have therefore little cause for amazement when a book appears upon the subject of Architecture, of more than a thousand pages, and dispatches the whole matter of ventilation in ten lines and that, too, with a sneer. Our buildings are hence commonly erected with less reference to healthful comfort than outside show, and ventilation is too much looked upon as a mere matter of tin tubes and knocking out bricks, that may be attended to at any tune when it may be thought necessary. 363. Ventilation invokes necessary loss of Heat. The real practical difficulty in ventilation is its cost. Although the atmosphere is every one's property, and is the cheapest of all things, yet a supply of pure air in dwellings is by no means free of expense. To ensure ventilation we must have motion of air, and to produce motion demands force, which is a marketable commodity. "Whatever will produce available force has value in it. "Whether it be fans and pumps driven by steam- engines, or upward currents set in motion by naked fire, in both cases there is expenditure of fuel. It is true we may use the fire that must be kindled to produce warmth, and thus secure the additional result of ventilation, apparently without additional cost. But in most cases foul air is also warm air, and in escaping conveys away its heat, which ia thus lost. Contrivances have been proposed, by which the outflow- ing warm air may be made to impart its heat to the incoming cold 204 ARRANGEMENTS FOR VENTILATION. air, but they are not yet reduced to practice. Until that is done, heat must continue to be lost by ventilation, just in proportion to its extent. Hence, as was before remarked, ventilation may be classed with food and apparel, and it becomes a question of how much can be afforded. But there is this important difference, that while economy in the latter a plain table and coarse clothing are at least equally favorable to health with more expensive styles of eating and dressing, economy of ventilation on the contrary, that is, any cheapening or deterioration of the vital medium of breathing, is injurious to health. One of the worst evils of scarce and expensive fuel is, that the poorer classes feel compelled to keep their rooms as tight as possible to prevent the escape of warm air and the consequent waste of heat. PART FOURTH. ALIMENT. I. SOURCE OF ALIMENTS ORDER OF THE SUBJECT. 364. View of the origin of Foods. The ground thus far traversed baa furnished abundant illustration of the close alliance between man and the material universe, and of his subjection to physical influences ; but we are now to see that he is composed of exactly the same materials as the solid globe upon which he dwells. Kocks, corroded by the agencies of time and crumbled into soils, join with the ethereal ele- ments of the atmosphere, to furnish the substances of which the living body is composed. But rocks, soils, and air are not food. They are unorganized, lifeless matter ; and can neither nourish the body, nor have they the power of uniting themselves together into nutritive compounds. The forces which play upon terrestrial atoms, throwing them into movement, arranging them into vital groups, and endowing them with the capability of becoming parts of animal systems, are shot down from the heavens. The impulses of organization and growth are not inherent powers of our earth, residing in air and soil. In the plan of the universe the SUN, a star among the stellar systems, is the architect of living forms, the builder of terrestrial organization, the grand fountain of vitality. His rays are streams of force, which, after travelling a hundred millions of miles through the amplitudes of space, take effect upon the chemical atoms of the earth's surface- its gases, waters, minerals, and combine them into nutritive, life-sus- taining compounds. The vegetable world is the laboratory where this subtle chemistry is carried forward, and matter takes on the properties of organization. Such is the ultimate source of all our food. The solid materials which we perpetually incorporate into the oodily fabric, originated in plants, under the direct agency of the sun 206 SOURCE OF ALIMENTS ORDER OF THE SUBJECT. beam. The vegetable leaf is the crucible of vitality, the consecrated mechanism appointed to receive the life-forces which God is per- petually pouring through his universe. In partaking of the bounties of the table, are we not, then, consummating a purpose to which planetary systems are subservient ? We repair the failing textures of animal life, but it is with tissues woven in a loom of invisible airs by the flying shuttles of light. That a single grain of wheat may br ripened that its constituent starch, gluten and sugar may be per fected, this ponderous orb must shoot along the ecliptic at the rate of 68,000 miles per hour, from Taurus to Libra, whirling perpetually upon its axis as it flies, that all parts may receive alike the vitalizing radiations. When therefore we contemplate the grandeur of the operations by which the Creator accomplishes the problem of life in this state of being, the subject of foods rises to a transcendent interest. The consideration of these questions, however, the forces that control vegetable growth and give rise to organic compounds, pertains to chemistry and vegetable physiology ; neither our plan nor our space will allow us to consider them here. We direct attention first to the general properties of foods, as we find them already produced and presented for preparation and use. 365. How Foods may be considered. A systematic presentation of the subject of aliments, that shall be quite free from scientific objec- tion, appears in the present state of knowledge to be impossible. We shall adopt an arrangement which aims only to be simple and popular. All articles of diet are composed of certain substances, which are known as alimentary principles, simple aliments, and. proximate prin- ciples. These are not the ultimate elements, carbon, oxygen, hydro- den, nitrogen, sulphur, &c., but are formed by combinations of these. They differ from each other in properties, exist in very different proportions in various kinds of food, and are capable of being sepa- rated from each other and examined independently. These require to be first considered. Next in order we shall speak of the products which these simple principles form when united together. Thus starch, sugar, gluten, &c., are simple aliments; while grain, roots, meats, &c., are made up of them, and are therefore called compound aliments. We shall give the composition of these, and as much of their history and preparation as may be necessary to understand their properties, and then trace the changes which they undergo in culinary management. The principles involved in various modes of preserving alimentary substances will next be described, and the subject closed by an examination of their physiological effects and nutritive power* WATEE ITS SOLVENT PBOPEKTIES. 207 366. Division of Alimentary Principles. The simple alimentary prin- ciples are separated into two important divisions, based on their com- position ; first, the non-nitrogenous aliments, or those containing no nitrogen in their composition ; and second, the nitrogenous aliments, or those which do contain this element. The first group consists of starch, sugar, gum, oil, and vegetable acids ; while the second com- prise albumen, fibrin, gluten, casein. Of these two classes the first is simpler in composition and much more abundant in nature than the other class ; we shall hence consider them first. There is, however, another alimentary substance of peculiar properties, and of the first importance water, which cannot be ranked strictly with either group. It is not a product of vegetable growth, but is rather a kind of univer- sal medium or instrument of all sorts of organic changes. As the most abundant and indispensable of all the principles of diet, it claims our first attention. II. GENERAL PROPERTIES OF ALIMENTARY SUBSTANCES. 1. PRINCIPLES CONTAINING NO NITBOGEN. A. Water. 367. Solvent Powers of Water. One of the most important proper- ties of water is its wonderful power of dissolving many solids ; that is, when placed within it they lose their solid form, disappear, and be- come diffused through the liquid. Such a combination is called solu- tion. It is the result of a mutual attraction between the liquid and the solid, and it becomes weaker between the two substances as this attraction is satisfied. The action of water upon soluble substances is very powerful at first, but as solution proceeds the action gradually de- creases, until the water will dissolve no more; it is then said to be saturated. TVater saturated with one substance, may lose a portion oi its power to dissolve others, or its solvent energy may sometimes be increased ; this depends upon the compound which it contains in solu- tion. With some substances it combines in all proportions, and never gets saturated. "Water does not dissolve a II substances ; if a fragment of glass and a piece of salt be put into it, the glass will be unchanged, while the salt will vanish and become liquid. Nor does it dissolve ilike all that it acts upon ; a pound of cold water will dissolve two pounds of sugar, while it will take up not over six ounces of common salt, two and a half of alum, and not more than eight grains of lime. Heat influences the solvent powers of water, most generally increasing it ; thus, boiling water will dissolve 17 times as much saltpetre as ice 208 GENERAL PROPERTIES OF ALIMENTARY SUBSTANCES. water. This it seems to do by repelling the particles of the solid body from each other, thus assisting the water to insinuate itself among them, by which its action is helped. But there are exceptions to the rule, of which lime is an example ; sixty-six gallons of water at 32 dissolves one Ib. of lime, but it takes 75 gallons at 60, or 128 at 212 to produce the same effect, so that ice-cold water dissolves twice as much lime as boiling water. 368. How best to hasten Solution. Solids should be crushed or pulverized, to expose the largest surface to the action of the solvent liquid. Substances which in the lump would remain for days undis- solved, when reduced to powder are liquefied in a short time. When a solid, as common salt or alum, is placed in a vessel of water to dis- solve, it rests at the bottom. The water surrounding it becomes sat- urated, and being heavier, remains also at the bottom, so that the solu- tion proceeds very slowly. By stirring, the action is hastened, but this takes up much time. The best plan is to suspend the salt in a colan- der, basket, or coarse bag, at the surface of the liquid. As the parti- cles of water take up the particles of salt, they become heavier and sink; other particles take their places, dissolve more of the salt, and sink in turn, so that the action of a constant current of liquid is kept up on the suspended crystals, and always at that portion most capable of dissolving them. 369. Solution of Gases Soda-water. Water also dissolves or absorbs various gases, some more and some less. It may take 780 times its bulk of ammonia, an equal bulk of carbonic acid, or -g its bulk of oxygen. The quantity is, however, controlled by heat and pressure ; heat acts to expel the gases, so that as the temperature rises, the water will hold less and less, while with increased pressure, on the contrary, it will receive an increased amount. Soda-water is thus by pressure overcharged with carbonic acid gas, which escapes with violent effer- vescence when the pressure is withdrawn. The effect is the same, whether the gas is forced into the water from without, or generated in a tight bottle or other vessel, as is the case with fermented liquors. The gas gradually produced is dissolved by the water, which, escaping when the cork is withdrawn or the vessel unclosed, produces the foam- ing and briskness of the liquor. 370. Different Tarieties of Water. In nature water comes in contact with a great number of substances which it dissolves, so that there is consequently no perfectly pure, natural water. The substances which t takes up are numerous, and differ under various circumstances and eonditions, and as these foreign substances or impurities which the THE GASES DISSOLVED IN WATER. 209 water acquires, communicate their properties to the liquid, it results that there are many varieties of natural water, as for example, spring- water, river-water, sea-water, rain-water, &c. 371. Rain-water and Snow-water. Rain-water is the least contami- nated of all natural waters, yet it is by no means perfectly pure. As it falls through the air, it absorbs oxygen, nitrogen, carbonic acid and ammonia, with which it comes in contact, and it also washes out of the atmosphere whatever impurities, it may happen to contain. Thus, in the vicinity of the ocean, the air contains a trace of common salt ; in the neighborhood of cities, various saline, organic, and gaseous impurities, while dust is raised from the ground and scattered through it by winds, and these are all rinsed out of the air by rains. The water which falls first after a period of drought, when contaminations have accumulated in the air for some time, is most impure. Rain fall- ing in the country, away from houses, and at the close of protracted storms, is the purest water that nature provides. It differs from dis- tilled water only in being aerated, that is, charged with the natural gases of the air. Falling near houses, it collects the smoky exhala- tions, and flowing over the roofs it carries down the deposited soot, dust, &c. "Water from melted snow is purer than rain-water, as it de- scends through the air in a solid form, incapable of absorbing atmos- pheric gases. When melted, the water which it produces is insipid from their absence, and should be exposed for a day or two to the at- mosphere, that it may absorb them. 372. The Gases contained in Water. There is an atmosphere diffused through all natural waters. It is richer in oxygen than is 'the upper atmosphere ; in the latter there is but 23 per cent., while in the air of water there is 33 per cent. The animals which dwell in water absorb this oxygen by breathing, just as land animals do from the air, while water-plants in the same manner live on the carbonic acid it contains. These absorbed gases also influence its taste, giving it a brisk and agreeable flavor. If it is boiled they are driven ofi^ and the liquid be- comes flat and mawkish. The presence of as much oxygen as water will hold, improves it as a beverage, as this gas is necessary to the ac- tive performance of several of the most important vital functions. Water that is quite cold contains more oxygen than that which has been made warm hi any way, as by exposure to the sun or the warmth of a close room, which causes a portion of it to escape. 373. Organic Contaminations of Water. From the dust and insects of the air, the wash of the ground and the drainage of residences, from mud and decayed leaves, the decomposing bodies of dead ani- 210 GENERAL PROPERTIES OF ALIMENTARY SUBSTANCES. mals, and a variety of other causes, waters are liable to conta /A ganic impurities, or those vestiges of living structures whici are capable of decomposition and putrefactive change. The effect of this organic matter may be shown by taking a little of the sediment that has accumulated at the bottom of a cistern, and placing it in a bottle of perfectly pure distilled water, when in a short time, if the weathei be warm, it will begin to smell offensively. This kind of contaminla- tion may be either suspended mechanically in water as solid particles, or it may be dissolved in it so that the water shall still have an appear- ance of purity. 374. The living Inhabitants of Water, Under certain favorable con- ditions of warmth, access of air, light, &c., countless numbers of living beings, both plants and animals, make their appearance in water. They are nourished upon the dead organic matter which the water may happen to contain, and belong either to the animal kingdom as animalcula or infusoria, or are of a vegetable nature, as fungi. There are other conditions which influence the Mnd of life which ap- pears in water. If the liquid be slightly alkaline, animalcula will be produced, while if it be a little acid, fungi or microscopic plants will appear. This may be shown by diffusing a little white of egg through water in a wine glass, and keeping it in a warm place. If it be made in a small degree alkaline, it will swarm with animalcula in a few days ; if, on the contrary, it be slightly acid, vegetable forms will be princi- pally originated. It is important to notice also that the alkaline solution will run rapidly into putrefaction, and yield a putrescent smell, while the acid fluid will scarcely alter at all, and emit no unpleasant odor. It is hence obvious that these two kinds of water have different rela- tions to human health, the slightly acid beirfg more favorable to it than alkaline waters. These living inhabitants are never found in freshly fallen rain- water, caught at a distance from houses, nor in spring or well-water, but they more or less abound in cistern water, reservoir water, and marsh, pond, and river waters. 375. Use of living beings in impure Water. The presence of living tribes in impure water, fulfils a wise and beneficent purpose. If the large amount of organic matter present in many waters could be re- moved only by the common process of putrefaction, and the forma- tion of injurious compounds and offensive gases, immense mischief would be the consequence. To obviate this, nature has ordained that some of the organic matter of impure water, in place of undergoing decomposition, shall be imbibed by living beings, and these dying that others shall take their place and fulfil the same important office. The MINERAL MATTER DISSOLVED BY WATER, 211 living races thus exert a preservative influence upon water, although this is more especially true of aquatic vegetation. 376. Water dissolves variable quantities of Mineral Matter. Rain which falls upon high ground filters through the porous soil and strata of the earth until stopped hy impenetrahle clay or rock ; it then passes along the surface of the hed until it finds an opening or crevice, through which it is forced up to the surface of the ground, producing a spring. Water which has thus leached through the mineral mate- rials of the earth, dissolves such portions of its soluble materials as it meets with, and carries them down to the lower levels, so that they ultimately collect in the sea. The amount of mineral matter thus dis- solved is extremely various. The water of the river Loka, in North- ern Sweden, which flows over impervious, insoluble granite, contains only 2V of a grain of mineral matter in a gallon weighing TO, 000 grains. Common well-waters, spring- water and river-water, contain from 5 to 60 grains in a gallon, but generally, in waters of average purit} T , which are employed for domestic purposes, there are not pres- ent more than 20 or 30 grains of mineral matter to the gallon. "When the dissolved substances accumulate until they can be tasted, a mineral water results. The celebrated Congress water, at Saratoga, contains 611 grains to the gallon. Ocean water has as much as 2,500 grains of saline substances, and the water of the Dead Sea the enormous quan- tity of 20,000 grains in the gallon. Of the two natural waters those of the river Loka and the Dead Sea the latter contains 400,000 tunes more saline matter than the former. 377. Rinds of Mineral Matter dissolved by Water. The mineral sub- stances dissolved in spring and well waters, are chiefly iron, soda, magnesia and lime, combined with carbonic and sulphuric acids, and forming salts, which are compounds of acids with alkalies or bases ; sulphates and carbonates, together with chloride of sodium or common salt. Iron, mixed with carbonic and sulphuric acids, is present in most waters which percolate through the ground; soda and magnesia also often exist in these waters, but their most universal and important ingredient is lime. This exists in almost all soils in combination with carbonic acid as carbonate of lime, or powdered limestone, and it is also very common in the shape of sulphate of lime, or plaster. Most of these substances are soluble in pure water, but this is not the case with the widely diffused carbonate of lime. The power of dissolving this substance depends upon the presence of free carbonic acid con- tained within in the water. If charged with this gas, water becomes a solvent of limestone. 212 GENERAL PROPERTIES OF ALIMENTARY SUBSTANCES. 378. Hard and Soft Water. The presence in water of these dis- solved mineral substances, though in extremely small proportion, pro- duces important changes in its properties. Compounds of lime and magnesia give it hardness, while rain and snow-water, and that from some springs which are free from these mineral matters, are called soft. This distinction of waters into hard and soft is usually connected with its cleansing qualities and its behavior towards soap, which wo shall consider in another place. It is also important dietetically (533). 379. Water in contact with Lead. There has been much contradic- don among scientific men in regard to the effects of storing water in leaden vessels, or transmitting it through leaden pipes. It was known that some kinds of water would corrode or dissolve the lead and be- come poisonous ; but wJiat waters ? Dr. OHEISTISON said those which were soft, while hard waters would form a crust in the interior surface of the lead, and thus protect it from corrosion. But later experi- menters declare hard waters to be even worse than soft in their action upon lead. It may be remarked that water can act upon lead, cor- roding it without becoming itself actively poisonous, if the compound formed be insoluble ; it is only when the lead is dissolved that the water containing it becomes dangerous. When ordinary water is placed in contact with lead, the free oxygen it contains combines with the metal, forming oxide of lead ; water immediately unites with that producing hydrated oxide of lead, which is nearly insoluble in water. There is also more or less carbonic acid existing in all natural waters; this combines with the oxide of lead, forming carbonate of lead, which is also highly insoluble. But if there be in the water much carbonic acid, a "bicarbonate of lead is formed, which is very soluble, and therefore remains dissolved in the water. Hence waters which abound in free carbonic acid, as aiso those which contain bi carbonates of lime, magnesia, and potash, are most liable to become poisoned by lead. Water containing common salt acts upon this metal, forming & soluble, poisonous chloride of lead. On the other hand, water con- taining sulphates and phosphates is but little injured, these salts exert- ing a protective influence on the lead. "From a review therefore of the whole of the arguments and experiments now advanced, respect- ing the action of different waters on lead, we deduce the following general conclusions : That while very soft water cannot be stored for a lengthened period, with impunity, in leaden vessels, the danger of the storage of hard water under the same circumstances is in most cases much greater. This danger, however, is to be estimated neither by the qualities of hardness or softness, but altogether depends upon SOFT WATER STARCH. 213 the chemical constitution of each different kind of water ; thus, if this be ever so soft, and contain free carbonic acid, its action on lead will be great ; whereas if it be hard from the presence of sulphates and phosphates principally, and contain but few bicarbonates, &c., little or no solution of the lead will result." Dr. HASSALL. Water is powerfully corrosive of iron when conveyed through this metal in pipes, but the compounds formed are not injurious. Galvanized iron pipes, which have received a coating of tin (610), are coming much into use instead of lead for the conveyance of water. 380. Snpply of Soft Water. Wells and springs are often inacessible, or the water furnished is bad. In such cases the heavens furnish an unfailing resource, which, with well-constructed cisterns, filters, and ice, leave little to be desired in the way of aqueous luxury. Taking the annual rainfall at 36 inches, we have 3 cubic feet of water falling upon a square foot of surface in a year. A cubic foot contains 6 gallons, so that we get 18f gallons upon each surface foot annually. A house 25 by 40 has a thousand feet of surface, and collects nearly 19,000 gallons of water annually, which if stored in cisterns of suf- ficient capacity, will furnish more than 50 gallons per day throughout the year. B. The Starches. 381. Whence obtained, and how separated. Starch, when pure, is seen to be a fine snow-white glistening powder. It is found univer sally distributed in the vege- table kingdom in much greater quantity than any other substance formed by plants for food. It exists in grain, peas and beans ; in all kinds of seeds ; in roots, as potatoes and carrots, and in the stem, pith, bark, and fruit ef many plants. When wheat flour is mixed up into a dough, and washed (Fig. 88), on a linen cloth with clean water, a milky liquid passes through containing wheat starch, which grad- FIG. 88. Separating Starch from flour by \vashing. ually settles to the bottom of the vessel. If raw potatoes are 214 GENERAL PROPERTIES OF ALIMENTARY SUBSTANCES. grated, and the pulp treated in a similar manner, potato starch is separated. 382. Proportions in various substances. The variable proportion of starch in different articles of food is as follows, in decreasing order : Starch per cent. Kice flour 84 to 85 Indian corn 77 to 80 Oatmeal. 70 to 80 "Wheat flour 39 to 77 Barley flour . 67 to 70 Rye flour 50 to 61 Buckwheat 52 Pea and bean meal 42 to 43 Potatoes, containing 73 to 78 water, 13 to 15 383. Starch Grains their size. Starch consists of exceedingly small rounded grains. They cannot be distinctly seen with the naked eye, and are so extremely minute that the finest wheat flour, which has been ground to an impalpable dust, contains its starch grains mostly unbroken and perfect. The granules of potato starch arc largest, while those of wheat and rice are much smaller (Fig. 89), e.nd those of turnips and parsnips still smaller, varying all the way from FIG. 89. Starch-grains of potatoes. Starch-grains of plantain. Starch-grains of rico. the l-300th to 1-10, 000th of an inch in diameter. Assuming the grains of wheat starch to be l-1000fch of an inch in diameter, a thou- sand million of them would be contained in a cubic inch of space. 384. Their Appearance and Structure. Viewed under a high mag- nifier, starch grains from various sources exhibit marked peculiarities in form as well as in size. Several kinds havo a ringed or grooved aspect, as seen in Fig. 89, which appearance is explained by the fact that they consist of concentric layers or membranes, like the coats DIFFERED VARIETIES OF STARCH. 215 of an onion. The grains of potato starch are ovoid or egg-shaped. Many of the grains of pea starch are hollowed or concave in the direc- tion of their length, while wheat starch consists of dull, flattened, lens-shaped grains, sticking together when not perfectly dry, on which account the wheat starch of commerce always comes in loose lumps. Thus each variety of starch-grain has some peculiar appear- ance of its own, by which the practical microscopist is enabled to identify it. He can hence detect adulterations of the more valuable with the cheaper varieties, as wheaten flour or maranta arrow-root with potato starch. 385. Sago Starch is procured from the pith of several varieties of the palm tree. It comes in various forms. Sago meal or flour is a whitish powder. Pearl-sago, the kind in general use for domestic purposes, consists of small pinkish or yellowish grains, about the size of a pin's head. Common or brown sago consists of much larger grains, which are of a brownish white color, each grain being brownish on one side and whitish on the other. As all the kinds of sago contain coloring matters, they are considered inferior to those varieties of starch, as arrow-root and tapioca, which are perfectly white. 386. Tapioca is a variety of starch which comes from South Ameri- ca, and is obtained from the root of a plant containing a poisonous milky juice. When it appears as a white powder, it is called Brazil- ian arrow-root. The term tapioca is commonly applied to that form of it which appears in small irregular lumps, caused by its having been dried on hot plates, and then broken np into fragments. 387. Arrow-root. A root growing in the West Indies (the Maranta arundinacea), contained a juice supposed to be capable of counter- acting the effects of wounds inflicted by poisonous arrows. This root yielded a starch which took the name of maranta arrow-root. But afterward starches from other plants which had a resemblance to maranta starch, took also the name of arrow-roots. Thus there is Tahiti arrow-root, Manihot arrow-root, from the plant which yields tapioca, and potato arrow-root, or British arrow -root, as it is some- times called. Maranta arrow-root, which is a very pure white starchy powder, is the most prized of all the varieties, but it is often adulter- ated with other and cheaper kinds. 388. Corn Starch. This is a preparation of the starch of Indian corn, which has been separated as perfectly as possible from the other constituents of the grain. Chemical means are used to effect the separation. The starch is freed from the glutinous, oily and ligneous elements of the seed, by the aid of alkaline solutions, and by grinding 216 GENERAL PROPERTIES OF ALIMENTARY SUBSTANCES. and bolting the corn in a wet condition. The grain is reported to yield from 30 to 35 per cent, of pure starch, which bears a general price, about one-third greater than wheaten flour. The culinary changes of starch and its effects upon the system will be considered under these topics (516). 389. Chemical Composition. Starch consists of three elements, carbon or charcoal, oxygen, and hydrogen. The two latter are found in starch in exactly the same proportions that they exist hi water, so that the composition of this substance may be given as simply char- coal and water. A compound atom of starch consists of twelve atoms of carbon, combined with ten of oxygen and ten of hydrogen, or twelve atoms of carbon to ten of water. C. The Sugars. 390. Proportion in various Substances, This is the sweet principle of food, and is produced by both plants and animals. It exists in milk, and it has lately been shown that it is generated in the animal liver. But our supplies come entirely from the vegetable world, where it is produced in great abundance, both in the sap and juices of plants, and stored up in their fruits and seeds. The following is the proportion of sugar obtainable from various sources : Per cent, of Sugar. Juice of Sugar cane 12 to 18 Beet root 5 to 9 "Wheat flour 4 to 8 Barley meal 5*2 Oat ineaL. 4-8 Cow's milk 8-3 Eye meal 8-2 Peas 2 Indian corn 1*5 Rice -2 There are several varieties of sugar, but we are practically concerned with but two, cane sugar and grape sugar. 391. Grape Sugar or Fruit Sugar. The white sweet grains of raisins or dried grapes take the name of grape sugar. Most other fruits, however, as apples, pears, plums, figs, cherries, peaches, gooseberries, currants, &c., grow sweet in ripening, which is owing to the same kind of sugar which exists in the grape. It may be readily extracted from fruits, but this is rarely done. 392. Sugar Artificially Produced. If starch be boiled for some time in water which has been .soured by adding to it one or two per cent, of sulphuric acid, the solution gradually acquires a sweet taste. If, PRODUCTION AND COMPOSITION OP now, by suitable means, tbe acid be neutralized and removed, and the solution boiled down, it yields a rich sirup or a solid sugar. This comes from the transformation of starch ; the acid taking no direct part in the change, but only inducing it by its presence. Potatoes treated in this way, it is said, will produce ten per cent, of then* weight of sugar. But what is still more singular, the fibre of wood may also be converted into sugar. Paper, raw cotton, flax, linen and cotton rags, and even sawdust, may be changed to sugar by the same agency. The boiling with acid must, however, in this case, be continued longer, as the woody matter has first to be changed to starcli before it be- comes sugar. This product, known as starch sugar, has the same nature and properties as grape sugar. 393. Honey. This is obtained by bees from the juices found in the nectaries, or honey-cups of flowers. They collect it in the crop, or honey-bag, which is an enlargement of the gullet, and when filled is about the size of a pea. Laden with its sweet treasure, the insect returns to the hive and disgorges it into a previously prepared cell of the honeycomb, which it then caps over by a thin covering of wax. To procure it in the purest liquid form, and of the best flavor, the plan is to unseal the cells by removing a slice from the surface of the comb, after which it is laid upon a cullender to drain. It is some- times warmed, to facilitate the flowing, but this is said to injure the delicacy of its flavor. It is more commonly pressed. This increases the quantity, and saves time ; but it is then contaminated by traces of wax, and fouled by the juices of crushed bee-maggots, which may happen to be in the comb. 394. Properties and Composition. Honey, in different localities, differ- ent seasons, and from different flowers, varies very much in color, flavor, and fragrance. That from clover, or from highly fragrant flowers, is far superior to that from buckwheat ; spring-made honey is better than that produced hi autumn. Virgin honey, or that made from bees that never swarmed, is finer than that yielded by older swarms ; and while some regions are renowned for the exquisite and unrivalled flavor of their honeys, that made in some other places is actually poisonous. We can hardly suppose honey to be a simple vegetable liquid. It probably undergoes some change in the body of the insect by the action of the juices of the mouth and crop, as when bees are fed upon common sugar alone they produce honey. Honey is an in- tensely sweet sirup, varying in color from nearly white to a yellowish brown. It consists of two sorts of sugar. One of these remains always in a liquid or sirupy condition, and the other is liable to crystallize or 10 218 GENERAL PROPERTIES OP ALIMENTARY SUBSTANCES. change to solid grains (granulate), this is grape sugar. The lighte colored and most valuable honeys contain the most of it, and hence, are most liable to granulate and grow thick. Honey contains an acid, and aromatic principles, which together with its uncrystallizable sweet part, are not very well understood. 395. Cane Sugar its Sources. Our common sugar is obtained, as is well known, from the sugar-cane. Eleven-twelfths of all the sugar of commerce has this origin. That which is procured from the ai cending sap of the maple, the descending sap of the birch, and als| from the walnut and other trees ; from the juice of beets, carrota turnips and melons, from green corn-stalks, and the unripe seeds of grain, is identical in essential properties with that of the sugar-cane, and they are all distinguished as cane sugar. 396. Cane and Grape Sugars, different conditions of origin. It is neces- sary to understand clearly the difference between can% sugar and grape sugar. We have seen that the agency of acids is employed to convert starch into grape sugar, and they have the same effect upon cane sugar. This change takes place even in the interior of growing plants. Those plants and fruits which possess sour or acid juices, yield grape sugar, while those which contain little or no acid in their saps, contain generally cane sugar. Grape sugar may be produced by art, while cane sugar cannot. 397. Cane and Grape Sugars, chemical differences. Sugar, like starch, consists only of carbon and water ; but these two sugars differ in the proportion of these elements. While cane sugar contains twelve atoms of carbon to eleven of water, grape sugar contains twelve atoms of carbon to fourteen of water. Grape sugar Is therefore less rich in carbon than cane sugar, and cane sugar may :>e transformed into grape sugar by the addition of chemically combined water. It is an essential property of sugar, that under the action of ferments, they are decomposed ; converted into carbonic acid and alcohol. Grape sugar is most prone to this change ; and cane sugar, before it can undergo fermentation, must be first changed into grape sugar. Cane sugar passes into the solid state much more readily than grape sugar, taking on the form of clear, well defined crystals of a constant figure ; grape sugar, on the contrary, crystallizes reluctantly and imperfectly, with- out constancy or form. Crystals of cane sugar are regular six-sided figures, while those of grape sugar are ill-defined, needle-shaped tufts. 898. Difference of solubility and sweetening powers. Pure cane sugar remain* perfectly dry and unchanged in the air, while grape sugar PEODUCTION OF COABSE SUGAB. 2 It attracts atmospheric moisture, becoming mealy and damp. Yet can* sugar dissolves in water much more readily than grape sugar. While a pound of cold water will dissolve three pounds of the former, it will take up but two-thirds of a pound of the latter. Cane sugar will, therefore, make a much thicker and stronger sirup than grape sugar, dissolving also more freely in the juices of the mouth, (a property upon which taste depends). Cane sugar possesses a higher sweetening power than the other variety. Powdered grape sugar has a floury taste when placed upon the tongue, and very gradually becomes sweet and gummy or mucilaginous as it dissolves. Two parts by weight of cane sugar are considered to go as far in sweetening as five of grape sugar. To make them economically equal, therefore, five pounds of grape sugar should cost only as much as two of cane sugar ; and hence the mingling of grape with cane sugar is a serioua deterioration of it. 399. How Raw, or Brown Sugar is produced. The sugar of commerce appears in various forms, and is sold at various prices. It is impor- tant to inquire into the source of these differences which involves a reference to the manufacture. Cane-juice contains vegetable albu- men, a substance which has a strong tendency to fermentation (488), hence, when left to itself in warm climates, it is rapidly changed ; the acid of vinegar being generated ; twenty minutes is, in many cases, sufficient to produce this effect. To neutralize any acid that may ba thus formed, and partially to clarify the crude juice, lime, which has a powerful attraction for organic matter, is added. The juice is then boiled, the water being evaporated away until a sirup is produced. The liquid is then drawn off into shallow vessels and stirred. As it cools the sugar granulates, or appears in the form of small irregular grains or crystals, which are kept from uniting together by some of the sirup (which has been so altered by the heat that it refuses to crystallize), and is known as molasses. The product is then placed in suitable circumstances to drain, when a large portion of the molasse< flows away, and is collected in separate vessels. The sugar, packed ii hogsheads, is then sent to the market as raw or muscovado, or as it is more commonly known, as "bream, sugar. 400. Of what Brown Sugar consists. The article when packed by the sugar-boiler, consists of sugar more or less browned and dampened by molasses, according to the completeness of the draining and dry- ing process. It contains more or less vegetable albumen, lime from the added lime-water, minute fragments of crushed cane-stalks, often in considerable quantity, with grit or sand from the unwashed canea, 220 GEIOIRAL PROPERTIES OF ALIMENTARY SUBSTANCES. Fia. 90. or which may have been introduced into the granulating vessels by careless management. 401. Brown Sugar undergoes a slow fermentation* We have stated that albumen is a very changeable substance, and by its own decompo- sition, when in contact with sugar, tends to alter that also. Cane sugar, it transforms into grape sugar. Hence, in nearly all raw sugars, there is an incipient, slow fermentation going forward, by which a portion of cane sugar is converted into grape sugar. Dr. HASSALL, perhaps the highest authority in matters pertaining to alimentary im- purities, states that nearly all samples of brown sugar contain also grape sugar, and that its proportion is greater where there is most vegetable albumen. This change, of course, just according to its ex- tent, lowers the value of brown sugar. 402. Living contaminations of Brown Sugar. We had occasion, when speaking of water, to correct that common impression of the ill-in- formed, that swarms of animalcule are present in every thing we eat and drink. On the contrary, they exist only in certain circumstan ces, and when they do occur, of course impair the value of food for dietetical use. As all animal structures, from the largest to the smallest contain nitrogen, one of the conditions of the exist- ence of animalculsB is the pres- ence of . nitrogeneous matter upon which to feed. Now pure sugar contains no nitrogen, and therefore cannot sustain animal life. But in brown, coarse sugars the existence of vegeta- ble albumen offers nourishment to these beings, and accordingly they are commonly found in- fested with minute insects called sugar-mites. In general, the more the sugar is contaminated with albumen, the more numer- Sngar-mite, as ^ np^n~ a fragment of cane, OUS are these disgusting insects, magnified 130 diameters. ^^ may be detected in tho less pure sugars by dissolving two or three tea-spoonfuls in a large wine-glass of tepid water. After standing at rest an hour or two, the animalculse will be found, some on the surface of the liquid, some ad- hering to the sides of the glass, and some in the dark sediment at 221 the bottom, mixed with cane-fragments, grit, and dirt. The mite ia visible to the naked eye, as a mere speck ; the microscope, however, exhibits its appearance, and history, from the egg state to the per- fectly developed animal, which is represented in Fig. 90. 403. Properties and Composition of Molasses. Common molasses is a dense brown liquid, the drainage of the brown sugar manufacture. It contains a portion of sugar that has been burnt and darkened in boil- ing ; another part that has been so changed to the mucilaginous state, by boiling, that it does not crystallize, together with a quantity of crystallizable sugar. It is strongly absorbent of water ; indeed, many kinds of raw sugar melt into sirup when exposed to the air. Chemi- cally considered sugar is an acid substance, and combines with bases, as potash, soda, magnesia, to fbrm salts called saccharates. Molasses contains a portion of saccharine matter, combined with the lime used in the sugar manufacture (399) ; als with small quantities of the alka- lies. Molasses itself is also acidulous. It has a peculiar strong taste, which CADET states may be removed by boiling for half an hour with pulverized charcoal. Sugar-house molasses and sirups are the residue which remains uncrystallized in purifying and refining brown sugar. 404. Refined Sngar. To cleanse it of impurities and improve it in color and taste, crude sugar is refined. It is melted and has mingled with it a small portion of albumen (ox-blood), which clears it of me- chanical contaminations. The sirup is then filtered through a bed ol animal charcoal (burnt bones crushed), by which it is decolorized, and lastly, it is crystallized, by boiling at a low temperature in vacuum- pans, in which the atmospheric pressure is removed (62). The discol- oring and darkening principle in the various grades of sugar is the molasses which has not been removed, but which remains in the crys- tallized mass. 405. Sugar-candy and how it is Colored. When the pure sugar is melted or dissolved, it forms a clear liquid, and when allowed to cool or dry without disturbance, it crystallines into a transparent solid, like glass. When threads are suspended in the sngar solution, crystals of extreme hardness collect upon them, which are known as rock-candy. The cause of whiteness in refined sugar is that the crystals are small, con- fused, and irregular. To make candy white, the sugar, while cooling, is agitated and worked (pulled), which breaks up the crystals and ren- ders the mass opaque. Candy is commonly adulterated with flour, and frequently with chalk. Various colors are given to sugar-confec- tionery by adding paints and dies expressly for the purpose. Some of these are harmless and others poisonous, Tho^e which are least inju- 222 GENERAL PROPERTIES OF ALIMENTARY SUBSTANCES. rious are the vegetable and animal coloring matters, but these neithef form so brilliant colors nor are they so lasting as the mineral com- pounds, which are far the most deadly. The following are the chief coloring substances used by confectioners to beautify their sugar preparations : / Oxide of lead (red lead). REDS ) Bisulphuret of mercury (vermilion). ( Bisulphuret of arsenic (red orpim&nt). I Gamboge. YELLOWS. . . -< Chromate of lead (chrome, yellow). I Sulpmiret of arsenic (yellow orpirnctif). {Ferrocyanide of iron (Prussian Uue). Cobalt. Smalt (glass of cobalt). Carbonate of copper (verditer). t Ultramarine. {Diacetate of copper (verdigris). Arsenite of copper (emerald green . Carbonate of copper (mineral green). WHITES Carbonate of lead (white lead). PURPLES 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 cJiromate of lead and 11 with gamboge. That of the reds 61 were colored with cochineal, 12 with red lead, and 6 with vermilion. Of the blues, one sample was colored by indigo, 22 by Prussian Hue, and 15 by ultra- marine. Of the greens 10 were colored by a mixture of chr ornate of lead and Prussian ~blue, 1 with carbonate of copper, and 9 with arsen ite of copper. These colors were variously combined in the different cases, as many as from three to seven colors occurring in the same parcel, including three or four poisons. 406. Their dangerons and fatal Effects. The Dr. remarks: "It may be alleged by some that these substances are employed in quantities too inconsiderable to prove injurious, but this is certainly not so, for the quantity used, as is amply indicated in many cases by the eye alone, is often very large, and sufficient, as is proved by numberless re- corded and continually recurring instances, to occasion disease and death. It should be remembered, too, that these preparations of lead, mercury, copper, and arsenic, are what are termed cumulative, that is, they are liable to accumulate in the system, little by little, until at length the fall effect of the poisons become manifested. Injurious con- sequences have been known to result from merely moistening wafers with the tongue ; now the ingredients used for coloring these include GUMS AND OILS. 223 many that are employed in sugar confectionery. How much more in- jurious, then, must the consumption of sugar thus painted prove when these pigments are actually received into the stomach." !>. Tlie Gums. 407. Properties of the Gums. The juices of many plants contain substances 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. Cherry-tree gum is insoluble in cold water, but dissolves readily in boiling water, while gum-arabic dissolves in cold water, and gum-tragacanth dissolves in neither, but only swells up into a kind of mucilage. The solutions of gums are clear and tasteless, and have a glutinous and sticky nature, which adapts them for paste. 408. Artificial Gum. When common starch is heated to 300 degrees in an oven, or boiled in water made sour by a little sulphuric acid, it is so altered as to dissolve in cold water, forming a clear, viscid solu- tion. The substance thus produced from the starch has the properties of gum, and is known as dextrine. 409. How Gum is Composed. In chemical composition, gum and dextrine do not differ from starch; they consist of 12 atoms of carbon combined with 10 of water. Gum exists in grains, and many vegetables, and hence is a widely-diffused element of food, although it does not occur in large quantities. Its dietetical value, as shown by its composition, is the same as starch and sugar, and hence it is grouped with the saccharine alimentary principle. E. Tlie Oils. 410. Distinction between Volatile and Fixed Oils. Oils are of two classes : 1st, those which, when smeared upon paper, produce a stain or grease spot, which does not disappear by time or warmth, and hence called fixed oils; and, 2d, such as will vanish from paper, under such circumstances leaving no permanent stain, and there- fore called volatile oils. The former is a universal and important element of diet, the latter presents itself chiefly among condiments, and will be there considered. 411. Sonrces and Forms of Oily Bodies. Oil is largely procured both from plants and animals, and from both sources it is chemically the game thing. It exists in many parts of vegetables, but is chiefly stored up ir their seeds, from many of which it is obtained by pressure 224 GENERAL PBOPERTTES OF ALIMENTAKY SUBSTANCES. in large quantities. In animal bodies it is deposited in the sacks or cavities of cellular tissue, and becomes accumulated in large quanti- ties in different parts of the body. Oils and fats are chemically iden- tical, differing only in consistence, and this quality depends upon tem- perature. Lowering the temperature of a liquid oil sufficiently, changes it to a solid, while raising that of a solid tallow converts it into a flowing oil. That which, in the hot climate of Africa, is liquid palm oil, is with us solid palm butter. Those oils, however, which at ordinary temperatures are not perfectly fluid, but have what is called an oily consistence, become much thinner ai?d completely liquid when heated. 412. Proportion of Oil in Articles of Diet. The proportion of oily matter from many sources is variable, as in the case of meat, which may more or less abound in fat. Nor has its amount in many vege- tables been determined with sufficient certainty. The following are the quantities given by the later authorities : Yolk of Egg 28*75 per cent. Ordinary Meat (LiEBie) 14-03 " Indian Corn , 9- " Oatmeal (husk excluded) 6' " Cow'sMilk 3-18 " Eye Flour 3*5 " "Wheat Flour 1 to 2 " Barley Meal 2' " Potatoes (dried) ! " Eice -8 " Buckwheat -4 " *13. Its Composition, Oleaginous bodies are distinguished from all the other alimentary principles, by their chemical composition, and the resulting properties. They resemble the preceding substances which we have been considering in containing three elements, carbon, hydrogen and oxygen ; but they differ from all of them in this im- portant respect, that they are composed almost entirely of hydrogen and carbon, with but a small proportion of oxygen. The composition of hogs-lard, as given by CHEVEEUL, may be taken as an example of the' general structure of this alimentary group. It consists of carbon 79, hydrogen 11, oxygen 10 parts in a hundred. We have seen that hydrogen and carbon are the active fire-producing elements of fuel (80). As the oils are so rich in these, they rank high as combus- tibles, burning with great intensity, and yielding much heat. It has been also noticed that oils may be decomposed into several acid and basic principles (195). THE ACIDS FOUND IN FEUITS. 225 F. The Vegetable Acids. 414. Combination and Composition. The sourness of fruits and suc- culent vegetables is due to various acids produced in the plant, and which they contain usually in quite small proportions. They exist in two states : 1st, as pure acids, or free, when they are strongest ; and, 2d, combined with bases, as potash, lime, &c., by which they are partially neutralized, and thus rendered less pungent to the taste. In this case they exist as acid salts (691). The vegetable acid group con- sists of but three elements, carbon, oxygen, and hydrogen, 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 Malic-Acid. This is the peculiar acid of apples, and it is also found in numerous other fruits. Thus, it exists free in pears, quinces, plums, peaches, cherries, gooseberries, currants, straw- berries, raspberries, blackberries, elderberries, pineapples, grapes, tomatoes, and several other fruits. It exists very abundantly in green apples, causing their extreme acidity, and diminishes as they ripen. The wild crab-apple is much richer in malic-acid than the cultivated fruit, and generally speaking, in proportion as we obtain sweetness by culture, we deprive the apple of its malic-acid. No use is made of this acid in the separate state. 416. Acid of Lemons Citric-Acid Gives their sourness to the lemon, orange, citron, and cranberry. Mixed with malic-acid, it exists also in the gooseberry, red-currant, strawberry, raspberry, and cherry. Citric-acid is separated from lemon juice, and sold in the form of crys- tals, which may be at any time redissolved in water, and by flavoring with a little essence of lemon, an artificial lemon juice is produced, which is used like the natural juice in the preparation of refreshing and cooling beverages. 417. Acid of Grapes Tartarie-Arid. 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 efler- 10* 226 GENERAL PROPERTIES OF ALIMENTARY SUBSTANCES. vescing, or soda powders, consist of 30 grains of bicarbonate of soda, contained in a blue paper, and 25 grains of tartaric acid, in a white paper, to be dissolved in half a pint of water. 418. Oxalic-Acid Exists in sorrel, and also in the garden rhubarb or pie-plant, combined with and partially neutralized by potash or lime. It is a prompt and mortal poison when pure, and fatal results frequently occur from mistaking its crystals for those of Epsom salts, which they much resemble. 419. Vegetable Jelly, Pectine or Pectic-Acid. 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, ft is commonly prepared by mixing sugar with the juice, and suffering it to stand for some time in the sun, by which a portion of the water is evaporated ; or it may be boiled a short time. But when long boiled, it loses the property of gelatinizing by cooling, and becomes of a mucilaginous or gummy nature. This is the reason that in making currant or any other vegetable jelly, when the quantity of sugar is not sufficient to absorb all the water, and consequently it bscomes neces- sary to concentrate the liquor by long boiling, the mixture often loses its peculiar gelatinous properties, and the jelly is of course spoked. 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. Jains consist of vegetable pulps preserved with sugar. They are very simi- lar in their uses and effects to the fruit-jellies, from which they prin- cipally differ in containing a quantity of insoluble, and therefore indi- gestible ligneous matter (or vegetable membranes, cellular-tissue and sometimes seeds), which in the healthy state of the system contribute by their mechanical stimulus to promote the action of the bowels, but in irritable conditions of the alimentary canal, sometimes prove injuri- ous. (PEREIE A .) 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 THE ALBUMINOUS PRINCIPLES. 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 most fruits contain all the elements necessary for fermentation and souring. Apple and grape juice, at first, undergo the vinous change producing cider and wine, and the process continued converts them both into vinegar (cider-vinegar and wine-vinegar), which are prized, on account of the fruity aroma which accompanies them. 2. PEINCIPLES CONTAINING NITEOGEN. A. Vegetable and Animal Albumen. 421. It exists In both organized Kingdoms. 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 KEGNATTLT, about 19 per cent, of healthy human blood, and is therefore found in large quantities in all parts of the system. It exists in the peculiar animal juices, in the glands, nerves, brain, and around the muscular fibres of flesh. 422. Composition of Albnmen. 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 GENERAL PROPERTIES OF ALIMENTARY SUBSTANCES. of sulphur. Vegetable and animal albumen are essentially the same thing in properties and composition, differing no more upon analysis than two samples from the same source. 423. General Properties of Albumen. 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 insoluble at 145, and separates in flakes at 167. "When excessively diluted, no turbidity can be produced by a less heat than 194, and it will only separate in solid masses after it has been 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. Vegetable and Animal Casein. 424. Source and Composition. The water in which flour has been 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 anu animal casein is well illustrated by the fact that the Chinese make a real cheese from peas. They are boiled to a thin paste, passed through a sieve, and coagulated by a solution of gypsum. The curd is treated like that formed in milk by rennet. The solid part is pressed out, salted, and wrought into cheese in moulds. This cheese gradually acquires the smell and taste of milk cheese ; and when fresh, is a favorite article of food with the people. The composition of vegeta- ble and animal casein is nearly if not quite identical with that oi albumen (422). C. Vegetable and Animal Fibrin. 425. The Blood and Vegetable Juices. When blood is drawn from FIBRIN AND GLUTEX. 229 FIG. 91. Fibres of lean meat magnified. the living body, in a short time it clots ; that is, a net- work of fibres is formed within it. These fibres consist of animal fibrin, which was dissolved in the blood, and then took on the solid form (spontaneous coagulation). Vegetable juices, as those expressed from turnips, car- rots, beets, &c., also contain the same kind of matter which they deposit on standing, that is, it spontaneously coagulates, and this is known as vegetable fibrin. If a piece of lean beef be long washed in clean water, its red color, which is due to blood, gradually disappears, and a mass of white fibrous tissue re- mains, which is known as animal 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 strise are made to approach each other, become less distinct, and the fibre increases considerably in breadth and thickness. 426. Gluten. If wheat flour be made into a dough, and then kneaded on a sieve or piece of muslin under a stream of water (Fig. 92), its starch is washed away, and there remains a gray, elastic, tough substance, almost resembling a piece of ani- mal skin in appearance. When dried it has a glue- like aspect, and hence its name, gluten. When thus produced, it consists chiefly of vegetable fibrin ; but it contains also a little oil, with albumen and casein. That from other grains is different in the proportion of these constituents ; rye gluten, for example, con- sists largely of casein, and has less of the tenacious fibrinous princi- ple. By acting upon crude gluten with different solvent agents, it Is separated into four principles as follows : FIG. 92. 230 GENERAL PROPERTIES OF ALIMENTARY SUBSTANCES. Vegetable fibrin 72 percent* Gluten 20 Casein (mucine) 4 Oil 3-7 " Starch (accidental), small quantity Total 99-7 " 427. Animal Fibrin. The muscles or lean meat of animals are prin- cipally composed of this substance, its proportionate quantity being greatest in flesh that is dark-colored, and belongs to animals that have attained their full growth. Its characters vary somewhat in different animals, and in the same animal at different ages. Its color is vari able ; in beef and mutton it is red ; in pigeons and many kinds of game it is brownish ; pink in veal, salmon color in pork ; in fish, white or semi-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 exhale a pungent odor like that of burnt feathers. They may be long preserved when dried, or even hi 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- malculas. We shall consider these substances again (678). D. Gelatin. 429. ItsSonrces, Properties and Uses. There exists in the bone, carti- lages and various membranes of animal bodies, a principle rich in ni- trogen, called gelatin. It is not identical in composition with the ni- trogenous class which we have been considering, nor is it like them produced in the vegetable kingdom ; but it is supposed to be derived from them in the animal system. It dissolves in hot water, and when cooled, forms a white jelly. It is the universal principle of animal jellies. Common glue consists of gelatin, but in this form it is not DIFFERENT NAMES OF THE NITROGENOUS PRINCIPLES. 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 calves foot jelly, and calves' heads are also employed to furnish jelly in mak ing mock turtle soup. Gelatin is used not only to produce jellies, but to thicken and enrich gravies and sauces, and also as a clarifying or ' fining ' agent to clear coffee or other mixtures. 430. Different Names applied to these Substances. The recent rapid progress of organic chemistry, has brought this class of substances for- ward into new and highly interesting dietetical relations, and there has been a confusion in the terms applied to them, which, though perhaps inevitable, is at firat very embarrassing to unscientific readers. As they all contain nitrogen, they are called nitrogenous alimentary principles ; and as one of the names of nitrogen is azote, they are call- ed azotized compounds. As they have all (except gelatin) the same composition as albumen, and are convertible into it, they are often called albuminous substances. As they form the material from which the body is nourished and built up, LIEBIG named them plastic ele- ments of nutrition ; they are also called nutritive principles, iliejlesh- forming and blood-maTcing substances. MULDEB 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 protein, and hence the group has-been called protein or pro- tcinaceous compounds. MULDER'S peculiar views are abandoned, but his terms are still in current use. 3. COMPOUXD ALIMENTS. VEGETABLE FOODS. 431. Our common articles of diet consist of the alimentary princi- ples which have just been noticed, combined together and forming what are known as compound aliments. They are naturally divided into vegetable foods and animal foods; of the former first. A. The Grains. 432. Composition of Wheat. We begin with wheat, the prince of 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 hi wheat is liable to considerable variation 232 GENERAL PROPERTIES OF ALIMENTARY SUBSTANCES. from many causes, as variety of seed, climate, soil, kind of fertilizers, seed, time of harvest, &c. We give five analyses. YAUQTTELIN. DUMAS. BHCK. Flinty Wheat. 12-00 14-60 56-50 8-50 4-90 2-30 Soft Wheat. Flinty Wheat. Soft Wheat. Genesee Wheat. 10-00 12-00 62-00 7-40 5-80 1-20 12-00 14-55 56-50 8-48 4-90 2-30 10-00 12-00 62-00 7-36 5-81 1-29 98-46 12-40 11-46 70-20 j-5'20 Bran Total 98-80 98-40 98-73 99-26 433. Proportion of Gluten in Wheat. It will be shown when we come to speak of the physiological influence of foods, that the most valuable portion, the strictly nutritious part, is that containing nitrogen, and that therefore 'gluten,' the properties of which have bewer than that of the pota- to, which ranges at 25 per cent. Yet the flesh-forming constituent? of dried turnips much exceed those of the potato, as the following com- parison shows. ^ Protein Compounds. The dried potato 8 per cent. Yellow turnip 9* do. Mangel-wurzel 15$ do. The nitrogenous matter of dried mangel-wurzel being nearly twice as great as in the dried potato. In the carrot the proportion of water is 85 -78, and dry matter 14'22. According to OEOME, the parsnip contains Starch 1-8 Albumen 2*1 Gum . 6-1 Sugar 5'5 Fibre 51 Water... .. 79-4 Total 100-00 4. COMPOUND 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 milk, casein and sugar. 470. Composition of Flesh-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- CONSTITUENTS OF MEAT. 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. BBANDE, is as follows: Water. Albumen and Fibrin. Gelatin. Total solid matter. Beef 74 20 6 26 Veal 75 19 6 25 Mutton 71 22 7 29 Pork 76 19 5 24 Chicken 73 20 7 27 Cod 79 14 7 21 These results give an average of very nearly 75 per cent, water. LIEBIG assumes it at 74, with 26 per cent, of dry matter. The ratio of water in meat, fowl, and fish, is quite uniform, ranging from 70 to 80 per cent., but the proportion of the other constituents, muscular fibre, fat, and bone, exhibits the widest possible diversity. In some animals, more especially wild ones, as deer, &c., there may be hardly a 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 KNAPP and LIEBIG to contain still about 8 per cent, of fat. In beef and mutton, such as is met with in our markets, from a third to a fourth of the whole dead weight generally consists of fat. (JOHNSTOX.) 471. Juice of Flesh. The true color of the fibrin of meat is white, yet flesh is most commonly of a reddish color (flesh-color). This is due to a certain portion of the coloring matter of the blood, by which it is stained. Yet the liquid of meat is not blood ; when that has been withdrawn from the animal, and the blood-vessels are empty, there remains diffused through the muscular mass a peculiar liquid, known as the juice of flesh. It consists of the water of flesh, containing about 5 per cent, of dissolved substances, one-half of which is albumen, and 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 the savory principles which give taste to meat, and which cause it to differ in different annuals. It also con- tains two remarkable substances, called Tcreatine and Icreatinine, nitro- genous compounds, which may be crystallized. The quantity yielded 11* 250 GENERAL PROPERTIES OF ALIMENTAEY SUBSTANCES. is variable in different kinds of flesh, but in all is extremely small* Kreatine is a neutral or indifferent substance, while kreatinine is a powerful organic base, of a similar nature with theine and cafeine of tea and coffee. 472. Blood, Bones, and Internal Organs. The leading constituents of blood are the same as flesh ; it contains only some three per cent, more of water. Its nitrogenous matter, however, is chiefly liquid albu- men. Blood has been called liquid flesh, and flesh solidified blood. About half the weight of bones is mineral matter, lime combined with phosphoric acid, forming phosphate of lime the 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 (glue). It is sometimes partially extracted for this purpose by boiling. Marrow is a fatty substance, enclosed in very fine cellular tissue within the bone. Skin, cartilage, and membrane, yield much gelatin. The tongue and heart are muscular organs, agreeing in dietetical proper- ties with lean flesh. BKACCONETOT'S analysis of the liver gives 68 per cent, of water, and 26 of nitrogenous matter; it also contains oil. The ~brain is a nervous mass, containing 80 per cent, water, some al- bumen, and much of a peculiar phosphoric oily acid. The stomachs of ruminating annuals which yield tripe, are principally composed of fibrin, albumen, and water. 473. Composition of Eggs, The eggshell is a compound of lime, not the phosphate as exists in bones, but chiefly carbonate of lime. It is porous, so as to admit of air for the wants of the young animal in hatching, and usually weighs about one-tenth of the entire egg. The white of egg consists of water containing 15 or 20 per cent, of albumen. The yolk is water and albumen, but contains, also, a large proportion (two-thirds of the dried yolk) of a bright yellow oil, containing sulphur and phosphoric compounds. A common-sized hen's-egg weighs about a thousand grains, of which the shell weighs 100, the white 600, and the yolk 300. The composition of its contents is : Water 74 Albumen 14 Fat 10-5 Ash (salts) 1-5 Total 100 B. Production and Composition of Milk. 474. What it Contains. This familiar liquid consists of oil or butter, ugar, casein or the cheesy principle, and salts, with a large proportion of water. The sugar, casein, and salts are dissolved in the water, PRODUCTION AND COMPOSITION OF MILK. 251 wlrile 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 milk. 475. Proportion of its Elements. This is variable. It generally con- tains about 86 per cent, water, 4 to 7 of casein, 3 -5 to 5-5 of butter, and 3 to 5-5 of sugar of milk and salts. The following are analyses by HEXEY and CHEVALIER : Cow. Woman. Casein 4-48 1-52 Butter 8-13 8'55 Milk sugar 4-47 6'50 Salts -60 0-45 Water 87D2 87'98 The following are HADLEra's results : The second column is the average of two analyses. Cow'. MUk. Woman'a Milk.* Butter 3 2-35J Sugar of milk and salts soluble in alcohol 4-6 8.75 Casein and insoluble salts 5-1 2-90 Water 87-3 90-50 4Y6. Circumstances Influencing the Quality of Milk. Both the quantity and quality of milk are influenced by various conditions apper- taining to the animal. Its food exerts a powerful control in this respect. Green succulent food is more favorable to the production of milk than dry, and E. D. THOMSON'S experiments go to show that of dry food, the richest in nitrogenous matter best promotes the milk secretion. PLAYFAIB was led, by his brief experiments, to conclude that food low in nitrogenous matters (as potatoes) yielded a large quantity of milk which was rich in butter, and that quiet (stall feed- ing) had the same effect, whilst cows grazing in the open air upon poor pasture, and consequently obliged to take much exercise, yielded * The milk of women from 15 to 20 years of age, contains more solid constituents than of women between 80 and 40. Women with dark hair also give a richer milk than women with light hair. In acute diseases the sugar decreases one-fourth, and the curd increases one-fourth; while in chronic affections the butter increases one-fourth, and the casein slightly diminishes. In both classes of diseases the proportion of saline matte* iiminishes. (JOHNSTON.) 252 GENERAL PROPERTIES OF ALIMENTARY SUBSTANCES. milk rich in casein. It appeared from THOMSON'S observations, that the produce of milk of a cow, with uniform diet, gradually diminished, and increased again by a change of diet. It is well known that a cow fed upon one pasture will yield more cheese, while upon another it will give more butter. Hence the practice in dairy districts of al- lowing the animal to roam over a wide extent of pasture to seek out for itself the kind of herbage necessary to the production of the richest milk ; hence, also, the propriety of adding artificial food to that de- rived from grazing. Plants and weeds found scattered in many pastures are apt to affect, injuriously, the quality and taste of the 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 will be a still more offensive flavor. If she feeds in pastures where she can get a bite of brier leaves, beech or apple-tree leaves, or any thing of the kind, it injuriously affects the flavor of the butter though not to the same extent, and would scarcely be perceptible for immediate use. So with red clover. Butter made from cows fed on red clover is good when first made, but when laid down in packages, six months or a year, it seems to have lost all its flavor, and generally becomes more or less rancid as the clover on which the cow fed was of rank and rapid growth." (A. B. DICKINSON.) 477. Distance from the time of calving. The colostrum, or first milk which the cow 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 ATTON : Quarts per day. Quarts. First50days 24 or in all 1200 Second " 20 " 1000 Third " 14 " " 700 Fourth " 8 " " 400 Fifth " 8 " " 400 Sixth " 6 " " 300 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. SPEENGEL states that cool weather favors the production of cheese and sugar in the milk, while hot weathef PRODUCTION AND COMPOSITION OF MILK. 253 increases the product of butter. The poorer the apparent condi tion of the cow, good food being given, the richer, in general, is the milk ; but it becomes sensibly poorer when she shows a tendency to fatten. A state of comparative repose is favorable to all the impor- tant functions of a healthy animal. Any thing which frets, disturbs, torments, or renders her uneasy, affects these functions, and among other results, lessens the quantity, or changes the quality of the milk. Such is observed to be the case when the cow has been newly de- prived of her calf when she is taken from her companions in the pasture-field when her usual place in the cow-house is changed when she is kept long in the stall after spring has arrived when she is hunted in the field, or tormented by insects, or when any other circumstance occurs by which irritation or restlessness is caused, either of a temporary or of a permanent character. (JOHNSTON.) 479. Production and Composition of Cream. We have stated that butter exists in milk, as a fatty emulsion ; that is, not dissolved, but floating as exceedingly minute globules throughout the watery mass. These butter globules are lighter than water, and hence, when the milk is suffered to stand undisturbed, they slowly rise to the sur- face, forming cream. The oil-globules of cream do not coalesce or run together, they are always separated from each other, and sur- rounded by the soluble ingredients of milk ; while at the same time, the body of the milk never becomes perfectly clear by the complete separation of these globules. Hence, cream may be viewed as milk rich in butter, and skimmed milk as containing little butter. It is supposed by some, that the butter particles are in some way invested or enclosed with casein ; at all events, a quantity of cheesy matter rises with the oil-globules. Its proportion in cream depends upon the richness of the milk, and upon the temperature at which it is kept during the rising of the cream. In cool weather, the fatty matter will bring up with it a larger quantity of the curd, and form a thicker cream. 480. Conditions of the Formation of Cream. The globules of butter being extremely minute, and but slightly lighter than the surround- ing liquid, which is at the same time somewhat viscid or thick, they of course ascend but slowly to the surface. The larger globules of butter, which rise with greater ease, mount first to the surface. If the first layer of cream, consisting of these largest particles, be taken off after 6 or 12 hours, it affords a richer, fresher, and more palatable butter than if collected after 24 or 30 hours standing. Milk is, there- fore, sometimes skimmed twice, and made to yield two qualities of but- ter. The deeper the milk ? the greater the difficulty with which the 254 GENERAL PROPERTIES OP ALIMENTARY SUBSTANCES. oily matter ascends through it ; hence, it is customary to set the milk aside in shallow pans, so that it may not be more than two or three inches in depth ; hence, if it is desired to prevent the formation of cream, the milk should be kept in deep vessels. Temperature powerfully in- fluences the formation of cream, or the rapidity with which it rises. Heat, by increasing the thinness and limpidity of the liquid, and the lightness of the oil-globules, favors their ready ascent ; while cold, by thickening the liquid, and solidifying the 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 hours when the temperature of the air Is 50 F. "24 " " " 55 " 18 to 20 " " " 68* "10 to 12 " " 77* 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. (SPBENGEL.) 481. Milk Creams before it is taken from the Cow. This spontaneous tendency of milk to separate itself mechanically into two sorts or qualities, explains the remarkable difference in the richness of milk withdrawn at different stages of the milking process. The glands in the teats of the animals, which secrete the milk, are vessels interlaced with each other in such a way as to form hollow 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 offerings, abounds in cream. Professor AN- DEESON" states, that compared with the first milk the same measure of the last will give at least eight, and often sixteen times as much cream. The later experiments of KEISET show, that where the milkings are 11 or 12 hours apart, the quantity of butter in the last drawn milk is from three to twelve times greater than that obtained from the first drawn milk. "Where the milkings were more often, the difference became less. As milk before being taken from the cow is already partially separated its richer from its poorer parts the dairy man- ager should take advantage of this circumstance, and not commingle in the same vessel the already half-creamed milk, if the object is the separation of butter. It has been shown that more cream is obtained PKODUCTION AND COMPOSITION OF MILK. 255 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 FIG. 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 value is propor- tional to the amount of its solid alimentary constituents, and is liable to variation, according to circumstances. If butter is to be manufactured from it, that is most valuable which contains most oily matter ; if cheese is desired, then that which contains most casein. Milk is heavier than water, and the richer it is the heaver it is ; hence it has been attempted to make the latter quality a guide to the former. Its weight compared with water, or spe- cific gravity, is determined by the hydrometer (Fig. 96). A tin or glass cylinder is filled with milk to be tested, and the hydrometer, a glass bulb with a stem above, is placed I in it ; the lighter the milk, the deeper it sinks ; the heavier it is, the higher it floats. A scale is marked upon the stem, which indicates at once how far the weight of the milk rises above pure water. Yet the results of the instru- ment are to be received with caution. Milks, though pure, differ naturally in specific gravity ; while it is easy to add adulterating substances that shall in- crease their weight, thus causing the hydrometer to report them rich. Yet as giving an important indication it has value, and with experience and judgment, may be made useful.* An instrument called the lactometer (milk measurer) has been used to determine the propor- tion of cream. It consists of a glass tnbe ten or twelve inches long, marked off and numbered into a hundred spaces. The tube being filled with milk to the top space, is suffered to stand until the Lactometer. * Made by TAGUABUE, of New York. FIG. 97. 256 CULINARY CHANGES OP ALIMENTARY SUBSTANCES. cream rises to the surface, when its per cent, proportion is at once seen. It will answer if only the upper portion of the tube be marked as shown in Fig. 97. The percentage of cream, that is, the thickness? of its stratum at the top of the tube, varies considerably. We have found the average to be 8 per cent., although samples are liable to range much above and below this number.* If the milk has been mixed, say with one-third water, the cream will fall to 6, if with one- half, it may fall to 5 per cent. 483. Mineral Matter in Milk, The proportion of salts in milk averages about half per cent. ; that is, 200 Ibs. when dried and burned will yield 1 Ib. of ash. The compositios of this ash is shown by the analysis of HAIDLEIN, who obtained from 1000 Ibs. of milk l s Phosphate of lime 2-31 Ibs. 3-44 i e. Phosphate of magnesia 0'42 " 0-64 " Phosphate of peroxide of iron 0'07 " 0'07 " Chloride of potassium 1'44 " 1-88 " Chloride of sodium 0'24 " 0'34 " Free soda 0'42 " 0-45 " Total 4-90 6-77 III. CULINARY CHANGES OF ALIMENTARY SUBSTANCES. 1. COMBINING THE ELEMENTS or BEEAD. 484. General Objects of Culinary Art. We have seen that the ma- terials employed as human food consist of various organized substances derived from the vegetable and animal kingdoms, grains, roots, stalks, leaves, flowers and fruit, with flesh, fat, milk, eggs, &c. &o. But few of these substances are best adapted for food hi the condition in which they occur naturally. They are either too hard, too tough, insipid or injuri ous, and require to undergo various changes before they can be properly digested. Most foods, therefore, must be subjected to processes of manufacture or cookery before being eaten. In their culinary prep- aration, numerous mechanical and chemical alterations are effect- ed, in various ways ; but the changes are chiefly wrought by means of water and heat. Water softens some substances, dissolves others, some- times extracts injurious principles, and serves an important purpose in bringing materials into such a relation that they may act chemically upon each other. Heat, applied through the medium of water, or in va- rious ways and degrees, is the chief agent of culinary transformations. Another proper object of cooking is the preparation of palatable dishes, * The number given by the lactometer will, from the nature of the case, be somewhat under the truth, as the butter globuloa do not all ascend through the long column of milk. COMBINING THE ELEMENTS OF BREAD. 25 ? 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 making it into dough, and then by various means causing it to rise, that is, to expand into a light, spongy mass, when, after being moulded into loaves, it is finally submitted to the action of heat in an oven, or baked. We shall consider the suc- cessive steps of this important process, in the order of their occurrence ; and as the flour of wheat is the staple article in this country for the manufacture of bread, it will occupy our first and principal attention. 485. Water absorbed in making Dongh. The addition of much water to flour forms a thick liquid, called batter ; more flour admixed stiffens it to a sticky paste, and still more worked through it produces a firm dough. The water thus added to flour does not remain loosely associ- ated with it, but enters into intimate combination with its constitu- ents, forming a compound, and is not all evaporated or expelled by the subsequent high heat of baking. In the dough, the liquid performs its usual office of bringing the ingredients into that closer contact which is favorable to chemical activity. As water is thus made to become a permanent part of solid bread, it is important to understand in what proportion, and under what conditions, its absorption takes place. Baked bread that has been removed from the oven from 2 to 40 hours, loses, by thorough drying at 220, from 43 to 45 per cent, of its weight, or an average of 44 per cent. If we assume the flour to con- tain naturally 16 per cent, of water, 10^ Ibs. of the 44 that was lost belonged to the flour itself, while 33| Ibs. were artificially added in making the dough. Thus Dry flour 56 ) Water in flour naturally 10* j " Water add^d in baking 83* 100 Ten pounds of flour would thus absorb 5 Ibs. of water, and yield 15 Ibs. 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 CULINARY CHANGES OF ALIMENTARY 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 must be carefully and thoroughly worked throughout the flour this is called Tcneading the dough, and is generally performed with the hands. The process is laborious, and attempts have been often made to accomplish it by machinery, but hitherto without success. Flours differ so much in their dough-making properties, that judgment is re- quired in managing them. As the eye cannot penetrate into the inte- rior of the doughy mass to ascertain its condition, we have no guide equal to the sense of touch. Differences of consistence, foreign sub- stances, dry lumps of flour, are readily distinguished by the hand of the kneader, who is also by feeling able to control the gradual and perfect admixture of water, yeast, and flour, better than any machine yet devised. Much of the excellence of bread depends upon the thoroughness of the kneading, the reasons of which will soon be apparent. At first the dough is very adhesive, and clings to the fin- gers, but it becomes less so the longer the kneading is continued, and when the fist upon being withdrawn leaves its perfect impression in the dough, none of it adhering to the hand, the operation may be dis- continued. 487. Bread from plain Flour and Water. When dough, made by simply working up flour and water, is dried at common temperatures, a cako is produced, not very hard, but which is raw, insipid, and indi- gestible. If baked at 212 (ordinary steam heat), a portion of the starch becomes soluble, but the cake is dense, compact, and very diffi- cult of digestion. If baked a* a still higher heat, and afterward sub- jected to prolonged drying, we have the common sTiip-tiread or sea- 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 in this manner lacks two essential characters, sufficient softness to be readily crushed in the mouth or chewed, and a looseness of texture or sponginess by which a large surface 18 exposed to the BREAD KAISED BY FEKMENTATTON. 259 action of the digestive juices in the stomach. To impart these quali- ties to bread, the dough is subjected to certain operations before bak- ing, which are technically called raising. The capability of being raised is due to the gluten. By the mechanical operation of kneading, the glutinous parts of the flour are rendered so elastic that the mass of dough is capable of expanding to twice or thrice its bulk without cracking or breaking. Various methods are employed for this t>ur- pose, which will now be noticed ; and first of fermentation : 2. BKEAD KAISED BY FEKMEXTATION, 488. Substances capable of Putrescence. It is a remarkable property of the nitrogenous alimentary principles, that when in a moist state, and exposed to atmospheric oxygen, they speedily enter upon a state of change or rapid decay. They are of very complex composition (422), the attractions of their atoms being so delicately adjusted that 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, will preserve their properties in the air only a short time, but pass into a state of putrescence, becoming sour and nauseous, and sending forth offensive exhalations. This change is called putrefaction, and the compounds which are liable to it, putrefidble substances. 489. The Putrefactive change Contagious. The other class of aliments, the non-nitrogenous, are in this respect of a very different nature. They contain fewer atoms, lack the fickle element nitrogen, and have a simpler and firmer composition. "When pure starch, gum, sugar, 01 oil, are exposed to the air in a moistened state, they exhibit little ten- dency to change, and give rise to none of the effects of putrefaction. Yet if placed in contact with putrefying substances, the change proves contagious; they catch it, and are themselves decomposed and de- stroyed. Hence, when the putrefiable substances are considered, with reference to the effects they produce upon the other class, they take a new name, and are called 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 all 26 C CULINARY CHANGES OF ALIMENTARY SUBSTANCES. 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 upon, and when the limited quantity of ferment made use of is ex- hausted, or spent, the effect ceases, no matter what the amount of fermentable matter present. Two parts by weight of ferment decom- pose no more than one hundred of sugar. Temperature controls the rate or activity of fermentation. At 32 no action takes place; at 45 it proceeds slowly ; at 70 to 86, which is the proper range of warmth, it goes on rapidly. The operation may be stopped by the exhaustion of either the ferment or the sugar, by drying, by exposure of it to a boiling heat, and by various chemical substances, as volatile oils, sul- phurous acid, &c. 491. Different kinds of Fermentation. When nitrogenous matters are just beginning to decompose, the action is too feeble to establish the true alcoholic fermentation in solutions of sugar. Yet even in this early stage they can change the sugar, not breaking it to pieces so com- pletely, but splitting each of its atoms into two equal atoms of lactic acid, the sour principle of milk. This process is called the lactic acia fermentation, while that in which alcohol is produced is the vinous or alcoholic fermentation. If this be not checked, the process is liable to run on to another stage ; the ferment is capable of attacking the alco- hol itself, and converting it to acetic acid, the active principle of vine- gar. This is the acetous fermentation. There are several conditions of this acetous change. First, a spirituous or alcoholic solution ; second, a temperature from 80 to 90 ; third, a ferment to give impulse to the change ; and, fourth, access of air, as oxygen is rapidly absorbed in the process, combining with and oxidizing the alcohol. 492. Dough 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 hi 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 un- BREAD RAISED BY FERMENTATION. 261 certain, according to the proportion and condition of the constituents of the flour. They also proceed with greater or less rapidity at the surface or in the interior, accordingly as the parts are exposed to the cooling and oxidating influence of the air. Bread baked from such dough, is sour, heavy, and altogether had. Yet the true vinous fer- mentation may he spontaneously established in the dough, by taking measures to quicken the action. If a small portion of flour and water be mixed to the consistency of batter (its half-fluid state being favor- able to rapid chemical change), and the mixture be placed in a jar or pitcher and set in a vessel of water, kept at a temperature from 100 to 110, in the course of five or six hours decomposition will have set in, with a copious production of gas bubbles, which may be seen by the appearance of the batter when stirred. If this be now mixed and kneaded with a large mass of dough, moulded into loaves and set aside for an hour or two in a warm place, the dough will swell, or ' rise ' to a much larger bulk ; and when baked, will yield a light spongy bread. A little salt is usually added at first, which promotes the fermenta- tion, and hence, bread raised in this manner is called 'salt raised bread.' Milk is often used for mixing the flour, instead of water ; the product is then called * milk-emptyings bread.' 493. What makes the Dongh rise 1 The cause of the rising is the vinous fermentation produced by the spontaneous change of the gluten or albumen which acts upon the sugar, breaking it up into alcohol and carbonic acid gas. If the fermentation is regular and equal, the knead- ing and intermixture thorough, and the dough kept sufficiently and uniformly warm, the production of gas will take place evenly through- out the dough, so that the bread when cut will exhibit numberless minute cavities or pores, equally distributed throughout. For its capa- bility of being raised, dough depends upon the elastic and extensible properties of its gluten, which is developed by the admixture of water with flour. Hence the proper quantity of water is that which im- parts to the gluten the greatest tenacity; an excess of it lowering the adhesiveness of the glutinous particles. The toughness of the gluten prevents the small bubbles of gas from uniting into larger ones, or from rising to the surface. Being caught the instant they are pro- duced, and expanding in the exact spot where they are generated, they swell or raise the dough. All rising of bread depends upon this prin- ciple the liberation of a gas evenly throughout the glutinous dough. No matter what the mode of fermentation, or what the substances or agents employed instead of it, they all bring about the result in the same way. 262 CULINARY CHANGES OF ALIMENTARY SUBSTANCES. 494. Raising Dongh by Leaven. But the mode of raising dough bj spontaneous fermentation (492) is not sufficiently prompt and conve- nient ; we require some readier means of establishing immediate de- composition. If we take a piece of dough which has been kept suffi- ciently long to ferment and turn sour, and then knead it up thoroughly with a large lump of fresh dough, the whole of the latter will shortly enter into a uniform state of fermentation ; and if a little of this be re- served for the next baking, it may be worked into a fresh mass of dough, and in this way, active fermentation may be induced at any time. Fermenting dough thus used is called leaven. It may be made from any sort of flour, and is improved by the addition of pea and bean meal, which ferment easily. When properly made, leaven may be kept weeks or 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, while the former remains in the bread. Hence, bread made with leaven always has a distinctly sour taste, partly caused by the acid of the leaven it- self, and partly by the sour fermentation which it induces in the dough. It is difficult to manage, and requires much skill to produce a good result. Leaven is but little used in this country, bread be- ing almost universally raised by means of yeast. 3. PKOPEKTIES AND ACTION OF YEAST. 495. Production of Brewer's Yeast. When grains are placed in the proper conditions of germination, that is, moistened and exposed to atmospheric oxygen at the proper temperature, a portion of their glu- ten is changed to the state of ferment, and acquires the property of transforming starch into sugar. Hence, seeds in germinating become sweet. Barley placed in these conditions, begins to germinate, swells, softens, and turns sweet ; it is then heated and dried, by which the process is stopped. The barley is then called malt. It is next crushed or ground and infused (mashed) in water at 160 so as to extract all the soluble matter it contains. The liquid (sweet-wort) is then boiled to coagulate the excess of vegetable albumen. Hops are added, to impart a bitter taste to the product (beer), and also to regulate the subsequent fermentation. The cooled wort is then run into the fer- menting vat, and yeast is added. " In three or four hours, bubbles of gas will be seen to rise from all parts of the liquid ; a ring of froth, PBOPEBTEES AND ACTION OP YEAST. 263 forming at first around its edge, gradually increases and spreads till it meets in the centre, and the whole surface becomes covered with a white creamy foam. The bubbles of gas (carbonic acid) then rise and break in such numbers, that they emit a low hissing sound, and the white foam of yeast continues to increase in thickness, breaking into little pointed heaps, which become brownish on the surface and edges ; the yeast gradually thickening until it forms a tough, viscid crust." Although a portion of the yeast was spent in the operation, yet a much larger quantity has been produced from the nitrogenous matter of the grain in the solution. 496. Appearance of Yeast It is a Plant. Yeast, as usually procured from the brewer, is a yellowish gray or fawn-colored frothy liquid, of a bitter taste, and which shrinks in a few hours into one-fourth the space it occupied at first. When fresh, it is in constant move- ment, and bubbles of gas escape from it. When dried it loses TO per cent, of its weight, becomes solid, horny-looking, half-transparent, and breaks readily into gray or reddish fragments. The nature of yeast was for a long time matter of doubt and speculation, but the micro- scope has at length cleared up the question, and showed tkat 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 millions of them. In what manner yeast acts to decompose sugar is not known. The yeast is destroyed or expends itself in producing the effect, yet it furnishes none of its sub- Yeast cells, showing how they .L-L it j multiply by budding, and by Stance to join With the SUgar, in producing granules or seeds escaping alcohol and carbonic acid. LIEBIG supposes from their interior. the effect to be dynamic, that is, produced by an impulse of force ; the FIG 98. 264 CULINARY CHANGES OF ALIMENTARY SUBSTANCES. Fia. 99. 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 structure is, as it were, jarred and shaken to pieces, its atoms falling into new arrangements and forming new substances. 497. Domestic preparation of Yeast Fowne's method. But, as many have no access to breweries, it is desirable to know how to make yeast at home. If common wheaten flour be mixed with water to a thick paste, and exposed slightly covered, and left to spontaneous change in a moderately warm place, it 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 agreeable vinous odor ; this will happen about the sixth or seventh day, and the substance is then in a state to excite fer- mentation. An infusion of crush- ed malt (wort) is then boiled with hops, and when cooled to 90 or 100, the altered dough, above described, after being thoroughly mixed with a little lukewarm water, is added to it, anrl tliA fpmnprntnrp Irpnt rn Tw A developed yeast plant, the number 6 Kept Up Dy cat i ng the successive stages of growth. placing the vessel in a warm situ- ation. After a few hours fermentation commences, and when that is complete, and the liquid clear, a large quantity of excellent yeast is formed at the bottom. 498. Yeast from Potatoes. Boil half a dozen potatoes in three or four quarts of water, with a couple of handfuls of hops placed in a bag. Mash the potatoes and mix with the water, adding and stirring in a little salt, molasses and flour, until it is of a battery consistence. Then mix in a couple of spoonfuls of active yeast. Place before the fire, when it will soon begin to ferment. In a cool place it may be kept for weeks. A developed yeast plant, the numbers indi- PROPERTIES AND ACTION OP YEAST. 265 499. Action of Hops in Yeast-making. Hop-flowers contain about 8 per cent, of a brownish yellow bitter volatile oil, upon which its pecu- liar odor depends. The hop has been long known for its soporific or sleep-producing properties, which are supposed to be duo to this volatile narcotic oil. When dry hop-flowers are beat, rubbed and sifted, they yield about 8 per cent, of fine yellow dust an aromatic resin, which has an agreeable odor, and a bitter taste. When taken internally it has a soothing, tranquillizing, sleep-provoking influence. It is called lupulin. Hops also contain a considerable proportion of another strong bitter principle, which is said not to be narcotic. In brewing, the chief use of hops is to impart an agreeable bitterness to the beer, but it also has the effect of arresting or checking fermenta- tion before all the sugar is converted into alcohol, and then prevent- ing the production of acid. It is also well-known that in the domestic preparation of yeast, hops serve to prevent the mixture from souring, though how this is affected we cannot tell. 500. Yeast preserved by drying. The liquid, or active yeast, is liable to turn sour and spoil in warm weather, losing its properties and im- parting to bread a most disagreeable flavor. Drying has therefore been resorted to, as a means of preserving it. On a large scale, it is pressed in bags and dried at a gentle heat, until it loses two-thirds of its weight of water, leaving a granular or powdery substance, which, if packed and kept from the air and quite dry, may be preserved a long time. It is curious that mechanical injury kills or destroys yeast. Falls, bruises, a rough handling spoils it, so that great care is required to remove it from place to place. LIEBIG remarks that simple pressure diminishes the power of yeast to excite the vinous fermentation. Yeast is also preserved by dipping twigs in it and drying them in the air. Or it may be worked round with a whisk 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. Kub 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 3 Ibs. of rye flour. Next day, thoroughly mix in V Ibs. of Indian meal, forming a stiff dough ; knead it well, roll 12 266 CULINARY CHANGES OF ALIMENTARY SUBSTANCES. it out a third or half an inch thick, cut into cakes and dry in the sun turning every day and protecting from wet. If preserved perfectly from damp they will keep long. 501. Bitterness of Yeast how corrected, Yeast is often so bitter as to communicate a most disagreeable 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 Yeast. How fermentation lightens dough, has been shown (493). Yeast produces these changes promptly and effec- tually. It is mixed with a suitable portion of water, flour, and salt, to form a stiff batter; which is placed near the fire for an hour or two, covered with a cloth. This is called setting the sponge. An active fer- mentation is commenced, and the carbonic acid formed in the viscid mass, causes it to swell up to twice its original size. If not then quickly used it falls, that is, the accumulated gas within escapes, and the dough collapses. Yet after a time it may again rise, and even fall a second time and rise again; This, however, is not allowed. When it has fully risen, much more flour is thoroughly kneaded with the sponge, and the dough is left for perhaps an hour and a half, when it rises again. It is then again kneaded and divided into pieces of the proper size foi loaves. The loaves should be moulded with care, as too much hand- ling is apt to cause the escape of the enclosed gas, and make the bread heavy. 504. Correction of Acidity in Dough. Dough is frequently sour from an acid condition of the flour. It may be in this condition from & sour state of the yeast, or the fermentation may be so feeble as to BAISESTG BREAD WITHOUT FERMENTATION. 267 produce acid (476), or it may be too active and rapid, if too much or too strong yeast has been used ; or in hot weather when the dougli is liable to sour by running into the acetous fermentation. If the diffi- culty is too sluggish a change, it should be hastened by securing the most favorable warmth. If, on the contrary, it is too violent, it may be checked by uncovering the dough, and exposing it to the air in a cool place. If the dough be already sour, it may be sweetened by alkaline substances. Carbonate of soda will answer this purpose. Carbonate of ammonia is perhaps better, as it is a volatile salt, and is raised in vapor and expelled by the heat of the oven (510). If too much be used, a portion of the excess is driven off by the heat, and in escaping assists in making the bread lighter. Caution should, however, be employed to use no more alkali than is really necessary to neutralize the acid. When the acidity is but slight, it may be rectified by simply kneading the dough with the fingers moistened with an alkaline solution. 505. The Sngar of Flow all decomposed in Dough. It is at the ex- pense of sugar destroyed that fermented bread is raised, but how much, sugar is thus decomposed is variously stated, and depends upon the activity and continuance of fermentation. Experiments would seem to show, that all the sugar present is rarely, if ever, destroyed. The raised dough and bread both contain sugar, often nearly as much as the flour before it was used. This is explained by remembering that one of the effects of fermentation is to change starch to sugar. 506. How mnch Alcohol is produced in Bread. Of course the quantity of alcohol and carbonic acid generated in bread is in exact proportion to the amount of sugar destroyed, which, as we have said, is by no means constant. In an experiment, a pound of bread occupied a space of 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. RAISING BKEAD WITHOUT FERMENTATION. 507. Objections to raising by Ferment. Two or three objections have been urged against raising bread by fermentation. First, the loss of 268 CULINARY CHANGES OF ALIMENTARY SUBSTANCES. a portion of the sugar of the flour which is decomposed ; this loss, how- ever, is trifling, and the objection futile. It is said, secondly, that as a destruction or incipient rotting process has been established in the dough, bread made from it cannot be healthful. This is only fancy, experience is wanting to show that well-made fermented bread is in- jurious. Thirdly, it is said that the fermenting process is not only uncertain, but slow, and requires more time than it is often convenient to allow. There is such force in this latter objection, that means have been sought to replace fermentation by some quicker and readier method of raising the dough. 508. How it is done without Ferment. As the lightening and expan- sion of the dough are caused by gas generated within it, it would seem that 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 with Chemical Substances. Bicarbonate of soda and hydrochloric acid are used for raising bread. The soda is mixed inti- mately with the flour, and the acid is added to the water requisite to form dough. PEEEIEA indicates the following proportions : Flour 1 Ib. Bicarbonate of soda 40 grains. Cold water, or any liquid necessary } pint. Hydrochloric acid 50 drops. The soda and flour being mixed, the acidulated water is added gradu- ally, with rapid stirring, so as to mix speedily. Divide into two loaves, and put into a hot oven immediately. The acid combining with the soda, sets free its carbonic acid, which distends the dough. Both the acid and the alkali disappear, are destroyed, and the new sub- stance formed by their union is chloride of sodium, or common salt ; so that this means of raising bread answers also to salt it. If the in- gredients be pure, the proportions proper, and the mixture perfect, no other substance will remain in the bread. If the acid be in excess, there will be sourness; and if there be too much alkali, or if it be not en- tirely neutralized, unsightly yellow stains in the bread crumb will be apparent, accompanied by the peculiar, hot, bitter, alkaline taste, and rarious injurious effects. The changes that take place are thus shown. We begin with RAISING BREAD WITHOUT FERMENTATION, 269 CARBONIC ACID; BICARBONATE OP SODA; ) A f~*j,'j \ ~~A i and HYDROCHLORIC ACID DA ' ) and get, > in the ) dough, (,W,)and ' (? n %f e ' TT ^nm . ^ T ^ . C i" IU " WATER ; (liquid,} 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 BICARBONATE OF SODA ; ) , , ( CARBONIC ACID ; (solid,) and ( P[ d t c e e > ) (gas,) and TARTARIC ACID ; ) TARTRATE OF SODA ; (solid,} ) dou g h ' ( (solid.} Cream of tartar, consisting of tartaric acid combined with and partly neutralized by potash, is also used with soda, one being mixed with flour, and the other dissolved in water. Double the quantity of cream of tartar to soda is commonly used, but of tartaric acid only an equal, or slightly less quantity. In these cases tartrate of soda is formed in the bread, which, in its action upon the system, is like cream of tartar gently aperient. Preparations which are known as egg-powder, ^baking -powder, and custard-powders, consist of bicarbonate of soda and tartaric acid, mixed with wheat flour or starch, and colored yellow with turmeric, or even poisonous chromate of lead. The difficulty with these powders, is to get them in perfect neutralizing proportions. This may be ascertained by dissolving them in water ; the mixture should be neutral to the taste, and produce no effervescence by adding either alkali or acid. Sour milk, or buttermilk, are often used with soda or saleratus. In these cases the lactic acid they contain combines with the alkali, forming lactate of soda, or potash, and set- ting carbonic acid free, which lightens the dough, just as in all the other instances. 510. Sesqnicarbonate 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 AMMONIA ; SESQUICARBONATE OF AMMONIA ; f ,80lid t } (in baking produces, BICARBONATE OP AMMONIA; CARBONIC ACID, ' (gas.} 270 CULINARY CHANGES OF ALIMENTARY SUBSTANCES. Yet practically these gases do not all escape in baking ; a portion of them is apt to remain, communicating a disagreeable hartshorn flavor. All these methods have one common and serious disadvantage tha gas is set free too suddenly to produce the best effect. Alum and car- bonate of ammonia are sometimes used ; they act more slowly, but leave an unwholesome residue of alumina and sulphate of ammonia in the bread. 511. Important Caution in reference to the Chemicals used. The class of substances thus introduced in the bread are not nutritive but me- dicinal, and exert a disturbing action upon the healthy organism. And although their occasional and cautious employment may perhaps be tolerated, on the ground of convenience, yet we consider their ha- bitual use as highly injudicious and unwise. This is the best that can be said of the chemical substances used to raise bread, even when pure, but as commonly obtained they are apt to be contaminated with impurities more objectionable still. For example, the commercial mu- riatic acid which is commonly employed along with bicarbonate of soda, is always most impure often containing chlorine, chloride of iron, sulphurous acid, and even arsenic, so that the chemist never uses It without a tedious process of purification for his purposes, which are of far less importance than its employment in diet. While common commercial hydrochloric acid sells for 3 cents per pound wholesale, the purified article is sold for 35. Tartaric acid is apt to contain lime, and is frequently adulterated with cream of tartar, which is sold at half the price, and greatly reduces its efficacy ; while cream of tar- tar is variously mixed with alum, chalk, bisulphate of potash, tartrate of lime, and even sand. Sesquicarbonate of ammonia is liable by ex- posure to air to lose a portion of its ammonia. It is hence seen that the substances we employ are not only liable to injure by ingredients which they may conceal, but that their irregular composition must often more or less defeat the end for which they are intended. We may suggest that, in the absence of tests, the best practical defence is to purchase these materials of the druggist rather than the grocer. If soda is desired, call for the licarlonate of soda ; it contains a double charge of carbonic acid, and is purest. Soda-saleratus is only the crude, impure carbonate soda-ash. The cream of tartar should appear white and pure, and not of a yellowish tinge (698). 512. Raising Dongh with Oily Substances and 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 ALTERATIONS PRODUCED IN BAKING BREAD. 271 heat causes the disengagement of elastic vapor from the water and fatty matter, which, being diffused between the numerous layers of dough, causes them to swell up, producing the flaky or puffy appearance which is seen in pastry. This kind of lightness must not be confound- ed with that produced by the other methods described ; for, although the layers are partially separated, yet the substance of each stratum is dense and hard of digestion. The albumen of eggs, when smartly beaten, becomes frothy and swells, by entangling much air in its meshes. If then mixed with dough, it conveys with it air bubbles, which are expanded in baking. From its glairy, tenacious consistence when mixed with dough or pudding, it encloses globules of gas or steam, which are generated by fermentation or heat. In this way eggs contribute to the lightness of baked articles. 513. Raising Gingerbread* Gingerbread usually contains so much molasses that it cannot be fermented by yeast. But the molasses is of itself always acidulous, and takes effect upon the saleratus, setting free carbonic acid gas. Sour milk, buttermilk, and cream, are also used, which act in the same way upon the carbonate of soda or potash, and thus inflate the dough. Dr. COLQTJHOUN 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 Ib. of flour, \ oz. carbonate of magnesia, \ oz. of tartaric acid, with the requisite molasses, butter, and aromatics. 5. ALTERATIONS PRODUCED DT BAKIXG BEEAD. 514. Temperature of the Oven. Bread is usually baked by heat radi- ated or conducted from the brick walls or iron plates of which ovens are made. The oven should be so constructed that the heat may be equal in its different parts, and remain constant for a considerable time. If the heat be insufficient, the bread will be soft, wet, and pasty ; if on the other hand the heat be too great at first, a thick, burnt crust is produced, forming a non-conducting carbonaceous cov- ering to the loaf, which prevents the heat from penetrating to the interior. Hence a burnt outside is often accompanied by half-raw dcugh within. If, however, the temperature be proper, the heat passes to the interior of the loaf and produces the necessary changes before the outside becomes thickly crusted. If we cut open a well baked loaf, immediately from the oven, and bury the bulb of a ther- mome f -er in the crumb, it will rise to 212. This heat is sufficient to 272 CULINARY CHANGES OF ALIMENTARY SUBSTANCES. carry on the inner chemical changes of baking, and it is obvious that the heat cannot rise above this point so long as the loaf continues moist (65.) Bread might 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 judging about it. If fresh flour strewn upon the oven bottom turns brown, the heat is right, if it chars or turns black, the heat is too great. 515. Heat causes a loss of Weight. The loaf loses a portion of its weight by evaporation. The quantity thus lost depends chiefly upon the size and form of the loaf. If it be small or thin, it will part with more water in proportion than if of cubical shape. Something de- pends upon the quality of the flour and the consistence of the dough. Various experiments would seem to show that bread parts with from one- sixth to one-tenth of its weight in baking. In those places where bread is required by law to be of a certain weight, this loss must be calculated upon and a proportionate amount of additional flour used. PEECHTL states from experiment that loaves which, after baking and drying, weigh one pound, require that an extra weight be taken, in dough, of six ounces ; if the loaves are to weigh three pounds, twelve ounces additional must be taken, and if 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 by the spirituous odor yielded in the baking process. 517. Chemical Changes in producing the Crust. The heat of the oveo falling upon the surface of the loaf causes first the rapid evaporation of its water, and then begins to produce a disorganization of the dough. The starch-grains are 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 producing the Crumh. As the temperature within the loaf does not rise above 212, no changes can go on there except such as are produced by the heat of the aqueous vapor. This Is sufficient to stop the fermentation, destroy the bitter principle of ALTERATIONS PRODUCED IN BAKING BREAD. 273 the yeast, and kill the yeast plant. In baking about one-fonrteenth of the starch is converted into gum, the rest is not chemically altered, as may be shown by moistening a little bread-crumb and touching it with solution of iodine, when the blue color will prove the presence of starch. The gluten, although not decomposed, is disunited, losing its tough, adhesive qualities. The gluten and starch-paste are intimately mixed, but they do not unite to form a chemical compound. 519. Moisture contained In Bread. In newly-baked bread the crust is dry and crisp, while the crumb is soft and moist, but after a short time this condition of things is quite reversed. The brown products of the roasting process attract moisture and the crust gets daily softer, while the crumb becomes dry. Bread, two or three days old, loses its softness, becoming hard and crumbly. But this apparent dry- ness is not caused by evaporation or loss of water, for it may be shown by careful weighing that stale bread contains almost exactly the same proportion of water as new bread that has become com- pletely cold. The change to dryness seems to be one of combination going on among the atoms of water and bread. That the moisture has only passed into a state of concealment may be shown by exposing a stale loaf in a closely covered tin for half-an-hour to a boiling heat, when it will again have the appearance of new bread. The quantity of water which well-baked wheaten bread contains amounts, on an average, to about 45 per cent. The bread we eat is, therefore, nearly one-half water. It is, in fact, both meat and drink together. One of the reasons why bread retains so much water is, that during the baking a portion of the starch is converted into gum, which holds water more strongly than starch does. A second is, that the gluten of flour when once thoroughly wet is very difficult to dry again, and that it forms a tenacious coating round every little hollow cell in the bread, which coating does not readily allow the gas contained in the cell to escape, or the water to dry up and pass off in vapor ; and a third reason is, that the dry crust which forms round the bread in baking is nearly impervious to water, and, like the skin of the potato we bake in the oven or in the hot cinders, prevents the moisture from escaping. (JonxsTox.) 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 hollows and detaching the srumb from the cnst. The vesicles should be numerous, small, and 12* 274 CULINARY CHANGES OF ALIMENTARY SUBSTANCES. equally disseminated ; nor should the crust be bitter and black, but 01 an aromatic agreeable flavor. " If the yeast be so diffused throughout the whole mass as that a suitable portion of it will act on each and every particle of the saccharine matter at the same time, and if the dough be of such consistency and temperature as not to admit of too rapid a fermentation, then each minute portion of saccharine matter throughout the whole mass will, in the process of fermentation, pro- duce its little volume of air, which will form its little cell,- about the size of a pin's head and smaller, and this will take place so nearly at the same time in every part of the dough, that the whole will be raised and made as light as a sponge before the acetous fermentation takes place in any part. And then, if it be properly moulded and baked, it will make the most beautiful and delicious bread, perfectly light and sweet, without the use of any alkali, and with all the gluten and nearly all the starch of the meal remaining unchanged by fermentation." (GrEAHAM.) 6. INFLUENCE OF FOEEIGN SUBSTANCES UPON BEEAD. 521. Common Salt, Alum, &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 will enable it to hold an extra dose of water. It is much used for this purpose, and the baker who employs it not only practises upon the consumer a double imposition, but drugs him with a highly injurious mineral into the bagain. 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. Carbonate of magnesia has a similar effect, and its use in so large quantities as from 20 to 40 grains to the pound of flour has been re- commended on scientific authority.* This substance has been also * Dr. C. DAVY. INFLUENCE OF FOREIGN SUBSTANCES UPON BREAD. 275 recommended for correcting acidity in yeast, dough, &c., instead of soda, and because it is less powerfully alkaline. But from its diffi- cultly soluble earthy nature, it tends to accumulate in the system in the highly objectionable shape of concretions and deposits. 522. Liebig recommends Lime-water in Bread. However it is to be lamented, it is nevertheless a fact, that enormous quantities of flour, more or less deteriorated, are purchased in the markets of this country ; and if there be any method of improving its condition by means that are not essentially injurious, they are certainly most desirable. Indeed, it is well known that flour is injured by time alone, so that freshly ground flower is always more prized than that which is several months old. The scientific reason is apparent. Vegetable gluten in contact with water becomes chemically changed, and loses its peculiar tough elastic properties. As these are essential to bread-making, flour that has been altered in this way necessarily makes a bad dough. Now, flour is 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 effect of the substances noticed in the previous paragraph is to combine with the gluten thus partially changed, and in a measure to restore its lost properties. Upon inves- tigating this subject, LIEBIO found that lime-water is capable of pro- ducing this effect, and thus of greatly improving old, or low grade flour. 523. How Lime-water Bread is prepared. To make lime-water chemists usually employ water that has been distilled; very pure soft water, as clean rain water, may, however, be used. Mix a quarter of a pound of slacked lime in a gallon of such cold water in stoppered bottles or vessels kept tight from the air. The mass of the lime falls to the bottom, leaving the liquid above, which has dissolved 1 -600th its weight of lime, clear and transparent. This is to be poured oft when required for use and replaced by pure water. LIEBIG recom- mends 5 Ibs. or pints of lime-water to every 19 Ibs. of flour, although this quantity of lime-water does not suffice for mixing the bread, and of course common water must be added, as much as is requisite. *' If the lime- water be mixed with flour intended for the dough, and then the yeast added, fermentation progresses in the same manner as in the absence of lime-water. If at the proper time more flour be added to the risen or fermented dough, and the whole formed into loaves and baked as usual, a sweet, beautiful, fine-grained elastic bread is obtained of exquisite taste, which is preferred by all who have 276 CULINARY CHANGES OF ALIMENTARY SUBSTANCES. eaten it for any length of time to any other." (LIEBIG.) The use of lime-water removes all acidity from the dough, and also somewhat augments the proportion of water absorbed. 524. Its Physiological claims. The quantity of lime introduced into the system by the use of this bread, is by no means large. A pound of lime-water suffices for 4 Ibs. of flour, which with the common water added, yields 6 Ibs. of bread ; and as the pound of lime-water contains but l-600th of lime, with this artificially added the cereal graina still contain less of it than peas and beans. Indeed, LIEBIG 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'. 525. Different kinds of Bread. Eice flour added to wheaten flour enables it to take up an increased quantity of water. Boiled and mashed potatoes mixed with the dough cause the bread to retain moisture, and prevent it from drying and crumbling. Eye makes a dark-colored bread, and is capable of being fermented and raised in the same manner as wheat. It retains its freshness and moisture longer than wheat. An admixture of rye flour, with that of wheat, decidedly improves the latter in this respect. Indian corn bread is much used in this country. Mixed with wheat and rye, a dough is produced capable of fermentation, but pure maize meal cannot be fer- mented so as to form a light bread. Its gluten lacks the tenacious quality necessary to produce the regular cell-structure. It is most commonly used in the form of cakes, made to a certain degree light by eggs or sour milk and saleratus, and is generally eaten warm. Indian corn is ground into meal of various degrees of coarseness, but is never made so fine as wheaten flour. Bread or cakes from maize require a considerably longer time to be acted upon by heat in the baking process than wheat or rye. If ground wheat be unbolted, that is, if its bran be not separated, wheat meal or Graham flour results, from which Graham or dyspepsia bread is produced. It is made in the same general way as other wheaten bread, but requires a little peculiar man- agement. Upon this point Mr. GEAHAM 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 flour; and when it is raised, if it ia found too soft to mould well, a little more meal may be added." It should be remarked that dough made of wheat meal will take on the acetous fermentation, or become sour sooner than that made of fine flour. It requires a hotter oven, and to be baked longer. Puddings VEGETABLE FOODS CHANGED BY BOILING. 27? Iii which flour is an ingredient are changed by the baking process in the same way as bread. They are usually mixed with milk instead of water, and made thinner than dough. Yeast is not, used to raise" them, eggs being commonly employed for this purpose ; and sometimes other substances. 526. White and Brown Bread A new French Plan. M. MOUEIES, of Paris, has announced some new views of bread making, theoretic and practical, upon which a commission of the French Academy has just reported favorably. He claims the discovery of a nitrogenous sub- stance called cerealine, which is a very active feiment, rendering starch soluble, altering gluten to a brown substance, and actively pro- ducing lactic acid instead of carbonic acid and alcohol. It resides near the surface of the wheat-grain, so that in grinding, it is nearly all separated in the bran, leaving but little in the white flour. M. Mou- EIES states that in bread made from unbolted flour, the tendency to sourness, the softness, crumbliness, and want of firmness of the crumb, and the brown color also of the bread, are due to cerealine. He says cerealine ferment will make a brown bread of the whitest flour, whereas, if it be neutralized, a white bread can be made from a dark flour containing bran. 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 farina- ceous materials. Y. VEGETABLE FOODS CHANGED BY BOILING. 527. Its General Effects. Boiling differs from baking in several re- spects. First, the heat never rises above the boiling point, and the changes of course are such only as may be produced by that tempera- ture. Second, the food is surrounded by a powerful solvent, which more or less completely extracts certain constituents of the food. Veg- etable acids, sugar, gum existing in the organic matter, and gum formed from starch, with vegetable albumen, are all soluble in water, and by boiling are partially removed. The tougher parts are made tender, the hard parts softened, and the connections of the fibres and tissues loosened, so as to be more readily masticated, more easily pen- etrated by the saliva and juices of the stomach, and hence more 278 CULINABY CHANGES OF AIJMENTARY 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 vegetable 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 PEEEIEA has done, among aliments. Indeed, he remarks, " although I have placed ligneous matter among the alimentary principles, yet I confess I am by no means satisfied that it is capable of yielding nutriment to man." Yet it is important to understand how it may be affected by the heat of culinary operations. Boiling in water does not dissolve it ; but by dissolving various substances with which it is associated, it only renders it the more pure. Yet woody fibre seems capable, by the joint action of heat and chemical agencies, of being converted into nutritive matter. If old linen or cotton rags, paper, or fine sawdust, be boiled in a strong solution of alkali, or moistened with pretty strong sulphu- ric acid, the woody substance is changed, being converted first into gum or dextrin, and then into grape sugar. By such modes of treat- ment old rags may be made to yield more than their weight of sugar. But weak solutions of acid or alkali do not produce any such effect. Nor will strong vinegar. We may therefore assume that woody fibre remains totally unchanged by exposure to culinary agencies and ope- rations. Professor ATJTENEEETH, of Tubingen, announced some years since, a method of preparing bread from wood-powder or wood-flour, which was changed into' nutritive matter by successive heatings in an oven. We are not aware that his experiments have been confirmed, while it is suspected that whatever nutritive value his bread may have possessed, was due to starch associated with the wood. 529. Changes of Sngar. 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 VEGETABLE FOODS CHANGED BY BOILING. 279 only very soluble in water, but also very absorbent of it (deliquescent)) turns of a deep brown color, and is used to stain liquids of a dark red, or wine color, under the name of caramel. Sugar itself is slightly acid, and forms compounds with bases which are of a salt nature, and known as saccharates. Caramel is more decidedly acid, and if the sugar be heated still higher it is converted into still stronger acid pro- ducts with inflammable gases. 530. Breaking 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 Jiilum. If 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 differ- ently. Then* membranes are torn apart, or exfoliated by internal swelling, as shown in Fig. 101. 531. Changes of Starch. Starch is but slightly acted S< fhite wiJ** upon by cold water. When heated with water it does not dissolve ; but the grains swell, forming a viscid mucilaginous mass, a kind of stiff, half opaque jelly. When starch is diluted with twelve or fifteen times its weight of water, the tempefature of which is slowly raised, all the grains burst on approaching the boiling point, and swell to such a degree as to occupy nearly the whole volume of the liquid, forming a gelatinous paste. If a pint of hot water be poured on a table- spoonful of arrow-root starch, it imme- diately loses its whitenes and opacity, be- starch grain ptared by boil- comes transparent, and the entire matter passes into the condition of a thick jelly. If a little of this be diffused through cold water and examined with the microscope, it TV ill 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 raptured, 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 CULINARY CHANGES OF ALIMENTARY SUBSTANCES. By being boiled in water for a considerable time, it undergoes the same change, and if the water be acidulous the change is quickened. "When dry starch is gradually heated to a temperature not exceeding 300, it slowly changes, acquires a yellow or brownish tint, and be- comes entirely soluble in cold water. It is changed to dextrin or gum (British gum). 532. How Potatoes are changed by Cooking. By referring to the statement of the composition of potatoes (461), we shall notice that a pound contains about three-quarters of a pound of watery juice, to two ounces, or two and a half, of starch. When examined by the FIG. 102. microscope, the tissue c.f the potato is found to consist of a mass of cells, containing starch grains. Each cell contains some 10 or 12 grains, loosely situated, as shown in Fig. 102, and surrounded by the potato juice, which contains albumen. If potatoes be of good quality, they boil dry, or mealy, as it is term- ed. But their water or juice does not sepa- rate, or boil out. It is absorbed by the starch Starch grains of potato before grains, which form a compound with it, and swell up so as completely to fill, and even burst the cells, as seen in Fig. 103. The albumen at the same time coagulates, so as to form irregular fibres, which are seen among the starch grains. When the juice of the' potato is only partially absorbed by the starch, it is said to be watery, waxy, or doughy. Potatoes by boiling in water do not form a jelly, like common starch, be- cause the starch grains in the tubers are protected, partly by the coats of the cells in which they are contained, and partly by the coagulated albumen. "Potatoes steamed or roasted or if boiled, mash- ed so as to extract all hard lumps, are in the best condition for digestion. Frying them, toasting starch grains of potato them, baking them, or browning the surface, dries up the starch into a hard, half-charcoally mass, which, except in most powerful stomachs, must act as a foreign body." 533. to increase the crop of fruit. All are familiar with the structure of coffee seeds ; they are of an oblong figure, convex on one side, and flat, with a little straight furrow, on the other. They are en- closed in a pulpy berry of a red color, which resembles a cherry, and are situated within it with their flat sides together, and invested by a tough membrane called the parchment. The seeds are separated by fermenting the berries, crushing them under heavy rollers, drying, grinding, and winnowing. 560. Varieties of Coffee. The best coffee is the Arabian; that grown in the province of Mocha (Mocha coffee) is of the finest quality. It may be known by having a smaller and rounder berry than any other, and likewise, a more agreeable smell and taste. It is of a dark yellow color. The Java and East Indian coffees are larger and of a paler yellow, while Ceylon, West Indian, and Brazilian coffees are of a bluish or greenish gray tint. 561. Composition of Coffee. The raw coffee, as it comes to market, is but slightly aromatic ; its odor is faint, while its taste is moderately bitter and astringent. In this state its composition, according to PAYEX, is as follows : Water 12 Gum and Sugar 15'50 Gluten 13 Cafein 00'75 Fat and Volatile Oil 13 Tannic Acid 5 Woody Fibre 34 Ash 6-75 Dr. STENHOUSE states that it contains 8 per cent, of cane sugar. Cof fee, it will be seen, contains tannin, the same astringent principle as tea, but in much smaller proportion ; and the substance itself is of a somewhat different chemical nature. They both contain much gluten ; but the most remarkable point of similarity between tea and coffee, is found in the fact, that the cafein of coffee is a vegetable alkali, with the same composition and properties as thein of tea. A direct analysis of the two substances gave the following result : Carbon. Nitrogen. Hydrogen. Oxygen. Thein 501 29'0 5'2 15T Cafein 49'8 28'8 5'1 16'2 The proportion of cafein in coffee is probably somewhat higher than the preceding analysis indicates. It is of course variable ; but is about half that of thein in tea (555). Coffee, however, is not used PBOPEETTES A3TD PREPARATION OP COFFEE. 295 in the raw or natural state ; like tea, it is first altered by heat or roasted. Fw> 1ML 562. Effects of roasting Coffee. The operation of roasting, produces several important changes in coffee. In the first place, the raw coffee- berries are so tongh and horny, that it is very difficult to grind, and pulverize them sufficiently fine, that water may exert its full solvent effect upon them. Roasting ren- ders them yielding and brittle, so that they may be" more readily ground ; while, at the same time, it increases the amount of matter so- luble in hot water. If we examine the raw coffee seed with the micro- scope, it will be found to consist of an assemblage of cells, in the cavi- ties of which are seen small drops of the aromatic volatile oil of cof- fee. This appearance is shown in (Fig. 104). If now we place a fragment or section of roasted cof- fee under a magnifier, it will be observed that these drops of oil in the cells are no longer visible (Fig. 105). They have, in part, been dissipated by the heat, and in part, become more generally dif- fused throughout the mass of the seed ; a portion being driven to the surface. It is obvious, that roasting produces certain chemical changes in coffee, which alter its flavor and taste, and bring out the peculiar and highly esteemed aroma for which this beverage is distinguish- ed. JOHNSTON states that the peculiar aromatic principle which gives flavor to coffee, exists in extremely minute quantity, (one part in fifty thousand,) and is generated hi the roasting process. The heat also Appearance of unroasted coffee-berries magnified, showing the size and form of the cells, and the drops of oil contained in their cavities. FIG. 105. Appearance of roasted coffee berries. 296 COMMON BEVERAGES. sets a portion of the cafein free from its combination with tannic acid, and evaporates it. The temperature is sufficiently high to de- compose the sugar, and change it to brown, burnt sugar, or caramel. Coffee darkens in color during roasting, swells much in bulk, and loses a considerable portion of its weight, by evaporation of its water and loss of other constituents. Coffee roasted to a reddish brown, loses in weight, 15 per cent., and gains in bulk, 30 per cent. To a chestnut brown, it loses 20 per cent, in weight, and gains 50 in bulk. To a darlc brown, it loses 25 per cent, of weight, and gains 50 in bulk. 563. Hints concerning the Roasting Process. The roasting of coffee is an operation of considerable nicety; more, perhaps, depending upon it than upon the variety of the article itself. Coffee is roasted by the dealers, in hollow iron cylinders or globes, which are kept revolving over a fire. As the first effect is the evaporation of a consid- erable amount of water, if the vessel be close this is retained, and the coffee roasted in an atmosphere of its own steam. This is not thought to be the best plan, and if the operation be carried on at home, it is recommended that the coffee be first dried in an open pan over a gentle fire, until it becomes yellow. It should then be scorched iu a covered vessel, to prevent the escape of the aroma ; taking care, by proper agitation, to .prevent any portion from being burnt ; as a few charred grains communicate a bad odor to the rest. It 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 astringocy of the charred seeds. The operation should be continued until the coffee acquires a deep cinnamon or chestnut color, and an oily appearance, and the peculiar fragrance of the roasted coffee is sufficiently strong. It may then be taken from the fire, and allowed to cool without exposure to the air, that the aromatic vapor may condense and be retained by the roasted grains. Coffee is very apt to be o^er-roasted, and even a slight excess of heat greatly injures its properties. 564. Effects of Time upon Coffee. Coffee berries undergo a change called ripening, by keeping ; that is, they improve in flavor. The Arabian coffee ripens in three years, and it is said that in ten or a dozen years the inferior American coffees become as good, and acquire as high a flavor as any brought from Turkey. (ELLIS.) But it is differ- ent after the coffee is roasted and ground. Its flavoring ingredients have a tendency to escape, and il should therefore be confined in ves PROPERTIES AND PREPARATION OF COFFEE. 297 eels closed from the air. It should not be exposed to foreign or dis- agreeable odors, as it has a power of imbibing bad exhalations, by which it is often injured. Many cargoes of coffee have been spoiled from having been shipped with, or even put into vessels which had previously been freighted with sugar. A few bags of pepper are suffi- cient to spoil a whole ship-load of coffee. (NOKMAXDY.) 565. Mode of Preparing the Beyerage. To prepare the coffee, it should be roasted and ground just before using, no more being ground at a time than is wanted immediately. Of course the finer it is re- duced the stronger will be the extract from a given weight of coffee, one-fourth more soluble matter being obtained from coffee ground to the fineness of flour than from the ordinary coarse powder (KSAPP). If a cup of good coffee be placed upon a table, boiling hot, it will fill the room with its fragrance. Its most valuable portion is thus liable to be exhaled and lost. Hence the same difficulty is encountered as in tea making ; boiling dissipates the much-prized aroma ; but a high heat is necessary to extract the other important ingredients of the coffee. It should therefore be steeped rather than boiled, an infusion, and not a decoction being made. Some make it a rule not to suffer the coffee to boil, but only to bring it just to the boiling point. Yet, a few minutes' boiling undoubtedly increases the quantity of the dis- solved, bitter, exhilarating principle. Dr. DOXOVAN 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 Coffee-making. It is observed, that some natural waters give a stronger and better flavored coffee than others, and this has been traced as in Prague, to the presence of alkaline mat- ter in those which give the most agreeable infusion. Hence, to obtain a more uniformly strong and well-flavored coffee, it is recommended to add a little soda to the water with which the infusion is made. About forty grains of dry, or twice as much of crystallized carbonate of soda, are sufficient for a pound of coffee. (Jonxsxox.) 667. Adulterations of Coffee. Ground coffee is very extensively adulterated. Various substances are employed for this purpose, as 13* 298 COMMON BEVERAGES. roasted peas, beans, and corn, and dried and roasted roots, such -as tur- nips, carrots-, potatoes, &c. But the most common adulterant is chiccory, a plant of the dandelion tribe, which has a large, white parsnip4ike root, abounding in a bitter juice. The root is mashed, sliced, dried, and roasted with about two per cent, of lard, until it is of a chocolate color. A little roasted chiccory gives as dark a color and as bitter a taste to water, as a great deal of coffee ; and, costing only about one- third 06 much, the temptation is strong to crowd it into ground coffee. So common has the use of chiccory with coffee, become, that it has, in fact, created a taste for a solution of unmingled chiccory, as a bever- age, although it is destitute of any thing corresponding to the cafein, or exhilarating principle of coffee. As an illustration of the extent of adulteration, and how one fraud opens the door to another, it is found that pure chiccory is almost as difficult to be met with in market as unadulterated coffee. Venetian red is employed to impart to it a true coffee color, while brick dust is used by the painter to cheapen and modify the shade of his Venetian red. 568. How the Cheats in Coffee may be Detected. When cold water is poured upon coffee the liquid acquires color only very slowly, and it does not become very deep after prolonged soaking; even when boiling water is employed, the infusion, although somewhat deeper, still remains clear and transparent. When, however, cold water is poured upon roasted and ground chiccory root, it quickly becomes of a deep brown, and in a short time is quite opaque ; with boiling water the result is still more prompt and marked. We may therefore detect chiccory in a suspected sample of coffee by placing a little in cold water. If it be pure the water will remain uncolored ; if chiccory be present it will be strongly discolored. It may be remarked, however, that if the coffee should be adulterated with burnt sugar, it will pro- duce a similar coloration of the water. It may be further noticed that particles of coffee float upon water, and, owing to their oiliness, are not melted, while chiccory absorbs water and sinks. The admixture of burnt and ground beans, peas, and grain, is not so readily shown. The most certain method of detecting these is by microscopic exami- nation. 3. COCOA AND CHOCOLATE. 569. Source and Composition of Cacao Seeds. These beverages are prepared from the cacao beans, which are derived from a fruit resem- bling a short, thick cucumber, grown upon the small cacao tree of the West Indies, Mexico, and South America. The beans are enclosed in COCOA AND CHOCOLATE. 299 rows, in a rose-colored, spongy substance, like that of the watermelon. "When shelled out of this fleshy part, they are surrounded by a thin skin or husk, which forms about 11 per cent, of their weight. The cacao bean is brittle, of a dark brown color internally, cuts like a rich nut, and has a slightly astringent, but decidedly bitter taste. In pre- paring it for use, it is roasted, in the same way as coffee, until the- aroma is fully developed. The bean is now more brittle, lighter brown in color, and less astringent and bitter than before. The fol- lowing is its composition, according to LAMPADITJS : Fatty matter, 58-16 Albuminous brown matter, containing the aroma of the bean, 16-70 Starch, 10*91 Gum, 7-75 Lignin, "90 Eed coloring matter, 2-01 Water, 5'20 Loss, 3-48 The largest constituent is a fatty substance, called butter of cacao, of the consistence of tallow, white, of a mild, agreeable taste, and not apt to turn rancid by keeping. Cacao beans have also been found to contain a substance, in minute proportion, not included in this analysis, called iheobromin, a nitrogenous body, similar in nature and properties to them, of tea, and cafeine of coffee. 570. Forms of Preparation. It is prepared in three ways. First. The whole bean, after roasting, is beat into a paste in a hot mortar, or ground between hot rollers. This paste, mixed with starch, sugar, &c., forms common cocoa, sold under various names, as 'rich cocoa,' ' flake cocoa,' * soluble cocoa,' &c. These are often greatly injured from the admixture of earthy and other matters, which adhere to the husk of the beans. Second. The bean is deprived of its husk, and then crushed into fragments. These form commercial cocoa nibs, the purest state 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, and seasoned with vanilla, and some- times with cinnamon and cloves. This paste forms chocolate. (JOHNSTON.) 571. How these preparations are used. 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 small compass much strength-sustaining capability. Second, the chocolate or cocoa is scraped into powder and mixed with boiling water, and boiling milk, when it makes a beverage somewhat thick, but agreeable to the pal- 300 PRESERVATION OP ALIMENTARY SUBSTANCES. ate, refreshing to tlie spirits, and highly nutritious. Third, the nibs 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 sugai 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. Adulteration of Chocolate. Pure or genuine chocolate should dissolve in the mouth without grittiness, and leave a peculiar sensation of freshness, and after boiling it with water, the emulsion should not form a jelly when cold ; if it does, starch or flour is present. Many of the preparations of the cocoa-nut, sold under the name of chocolate powder, consist of a most disgusting mixture of bad or musty cocoa- nuts, with their shells, coarse sugar of the very lowest quality, ground with potato starch, old sea-biscuits, coarse branny flour, animal fats (generally tallow). I have known cocoa-powder made of potato starch moistened with a decoction of cocoa-nut shells and sweetened with molasses ; chocolate, made of the same materials, with the ad- dition of tallow and ochre, a coarse paint. I have also met with chocolate in which brick-dust, or red ochre, had been introduced to the extent of 12 per cent. (NOEMANDY.) The temptation to fraud in these preparations seems to be as irresistible as in the case of ground coffee. There is no easy means of detection short of refined micro- scopic and chemical examination, so that the only practicable means of self-defence for the purchaser, is to deal only with traders of unques- tionable integrity, where such can be found. V. PRESERVATION OF ALIMENTARY SUBSTANCES. 1. CAUSES OF THEIR CHANGEABLENESS. 573. Why Is it Neeessary that Foods should be Perishable ? As in the plan of nature the production of force depends upon change of matter, and as the fundamental purpose of animal life is the evolution of pow- er, it is apparent that matter which is to act as food, must be capable of ready and rapid transformation. This inherent facility of change, by which alimentary substances are conformed to the deep require- ments of the animal economy, renders them extremely transient and perishable. If they are designed for change 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 OF TTTRTR CHANGEABLJLNESS. 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. 574. Change of Nutrient Matter within and without the Body. It was formerly taught that the living body is the domain of a peculiar vi- tal power, which suspends the ordinary destructive play of chemical affinities and physical forces, but that at death the vital energy ceases, and those forces resume their natural activity, causing the speedy dis- organization of the inanimate organism. But this is hardly correct. The vital force, or whatever we may name the presiding agency of the living system, does not suspend physical and chemical laws, but only regulates, and as it were uses them. We have already seen that strictly chemical changes go on constantly in the body, and shall shortly have occasion to notice their extent (624). They are of the same kind (oxidations), are carried on by the same agent (atmospheric air), and yield the same final products (carbonic acid, water and am- monia), in both conditions. In the living fabric the decompositions are measured ; while in the lifeless body they are uncontrolled, and quickly spread through the entire organic mass. 575. Conditions of the Perishableness of Foods* Alimentary substances are by no means alike changeable ; some keep longer than others un- der the same circumstances. There are certain specific causes of or- ganic decomposition, and accordingly as these act conjointly, or with variable intensity, is the rate of putrefactive change. In chemical composition, vegetable and animal substances are much more compli- cated than mineral compounds, and hence they are less permanent. Generally, mineral substances are combined in the simplest and most stable way, containing but few atoms, and consisting of pairs of elements, with nothing to disturb their direct attraction for each other. On the contrary, organized substances, in some cases, contain several hundred atoms, and consist of three, four or five different elements, joined by complex afiinities into delicate and fragile combinations. We have seen, in speaking of fermentation, that albuminous substan- ces are, from this cause, most changeable, and are universally present in substances designed for food. "Water is a large constituent of all alimentary bodies, in their natural state, and is highly promotive of chemical changes; indeed, it is indispensable to them. Tem- perature exerts an all-controlling influence warmth favoring, and cold retarding, or arresting, these transformations. The atmospheric medium, which is in contact with every thing, contains an element S02 PRESERVATION OF ALIMENTARY SUBSTANCES. 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 li ving and the dead (662). Putrefactive decay may also be prevented by certain chemical substances which are used for the purpose. A knowledge of the laws and conditions of organic decom- position, has led to various practical methods of controlling it, which constitute the art of preserving. 2. PEESEEVATION BY EXCLUSION" OF AIR. 576. Oxygen as an exciter of decay. Other conditions being favor- able, that is, moisture being present and a proper temperature, access of air starts decomposition, it is the prime mover of the destructive processes. "We have already noticed its mode of action, in speaking of fermentation (488). In the case of vegetables, as potatoes and apples, for example, if the air is excluded from their interior, they remain for a considerable time sound. But if we cut them, the oxygen quickly attacks the exposed surface and turns it brown, indicating the incipient stage of decay. "When the surface of fruits and vegetables is injured, so that their juices come in direct contact with the air, the effect is at once seen. If an apple is bruised, the injured spot imme- diately turns dark, and decomposition gradually spreads from that point, until the whole apple becomes rotten. The juice of the ripe grape, while protected from air by an unbroken skin, remains sweet and scarcely changes ; it may be dried and converted into a raisin, its sweetness remaining. If it be crushed under mercury, and the juice be collected in a glass completely filled with mercury, so as to prevent all contact of air, it will remain unchanged for several days. But if air be once admitted, as by perforating the grape-skin with a needlo's point, fermentation commences almost instantaneously, and the juice is soon entirely changed. The same is true of all animal fluids. Milk, while in the udder of the healthy cow undergoes no change, but in contact with air, its properties are soon totally altered it ia soured and coagulated (547). "When life has been destroyed by bodily wounds, decomposition spreads from them ; or if the animal have not died by violence, the changes may begin internally in those parts, Buch as the lungs, which are in contact with the air. 577. Changes began 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, BY EXCLUSION OF ATE. 303 may continue, though the oxygen be entirely excluded. Milk, if ones exposed to the air, coagulates and sours, though sealed up in air-tight vessels. Grape juice, though oxygen be completely cut off, ferments, generates gases, and often explodes the bottles in which it is confined. The impulse of disorganization being given, decomposition goes on without further external aid. To explain this, we must suppose that the atoms of the changing substance were at first in a kind of rest or equilibrium, without mutual activity, and that by the invasion of oxy- gen, this equilibrium has been disturbed, so that the elements of the substance begin to act and re-act upon each other, giving rise to new products. In this "way, a state of change commenced by merely jost- ling a few surface atoms through contact of oxygen, is propagated by intestinal action throughout the entire mass. 578. How changes begun by Oxygen may be stopped. " The property of organic substances to pass into a state of fermentation and decay in contact with atmospheric air, and in consequence to transmit these states of change to other organized substances, is annihilated in all cases without exception, ~by heating to the 'boiling 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 Tcept excluded. These facts indicate the most certain, manage- able, and perfect method of preserving alimentary substances. By simply heating to the boiling pointy which produces no other change than that af partial cooking, and afterward protecting from the air, alimentary substances, both animal and vegetable, may be preserved in their natural condition entirely unchanged in both flavor and pro- perties, for an indefinite period. This plan was first brought into general notice by M. APPEET of France, in 1809. He preserved all kinds of fruits, vegetables, meats, soups, &c., in glass bottles. His prac- tical methods, however, were crude and unsatisfactory, and have been superseded by others. Captain Ross presented the society of arts with a box from the house of GAMBLE and DAEKIN (London), which con- tained cooked provisions sixteen years old, and that were in a state of perfect preservation. The details of the preparation on a large scale, as practised chiefly for marine consumption, we have no space here f 10 *' suits from the agency of chemical af- finity (FABBADAY). If a lump of com- mon salt, (it occurs in large masses in the shape of rock salt,} be cut into the form of a thin plate, and held before a fire, it does not stop the heat-rays, but has the singular property of permitting them to dart through it, as light does through glass it is the glass of heat. A hundred Ibs. 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- pears in the solid form, or crystallizes. How crystals^conunon salt are Its crystals are cube shaped ; if the evaporation taked place slowly they are large, but if it be rapid, they are small, and formed in a curious manner. Resulting 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 PRESERVATION OF ALIMENTABY SUBSTANCES. soon form, which are joined to the first at its four upper edges, con stituting a frame above the first little cube (Fig. 109). As the whole descends into the fluid, new crystals are grouped around the first frame constituting a second (Fig. 110). Another set added in the same way gives the appearance shown in Fig 111. The consequence of this arrangement is that the crystals are grouped into hollow, four- sided pyramids, the walls of which have the appearance of steps, be- cause the rows of small crystals retreat from each other. This mode of grouping is called hopper-shaped (Fig. 112). 591. Sources and Pnrification of Salt. Salt is obtained from three sources ; first, it is dug from the earth in mines, in large masses, like transparent stones (rock salt} ; second, it is procured by evaporating sea-water (bay salt) ; and, third, by boiling down the liquid of brine springs. It differs 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 snbstances 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 Ibs. of salt, stirring the whole well now and then for a couple of hours, and afterwards straining it through a clean cloth, the ob- noxious substances may be carried away in solution. Among the purest, is that called Liverpool salt, which is an English rock-salt dug from the mines ; dissolved, recrystallized and ground. 592. How salt preserves meat. Salt is more widely used than any other agent in conserving provisions, especially meats. It is well known that when fresh meat is sprinkled with dry salt, it is found after a few days swimming in brine, although not a drop of water has been added. If meat be placed in brine it grows lighter, while the quantity of liquid is increased. The explanation of this is, that water has a stronger attraction for salt than it has for flesh. Fresh meat contains three-fourths of its weight of water, which is held in it as it is in a sponge. Dry salt will extract a large part of this water, dissolving in it and forming a saline liquid or brine. In this case, the water of the meat is divided into two parts ; one is taken up by the salt to form brine, while the other is kept back by the BY ANTISEPTIC AGENTS. 813 meat. The salt robs the meat of one-third or one-half the water of its juice. Salting is therefore only an indirect mode of drying ; the chief cause, perhaps, of the preservation of the meat, being, that there is not sufficient water left in it to allow putrefaction. The surrounding brine does not answer this purpose, as it does not act upon the meat ; its relation to flesh being totally different to that of fresh water. If fresh water be applied to a piece of dry meat, it is seen to have a strong attraction for it, but if we use even a weak solution of salt, it flows over it wetting it but very imperfectly. 593. How meat is injured by salting. The separation of water from the 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 unexplained effect upon the muscular tissue. The main and well-established injury of salting, however, is caused by the loss from the meat of valuable constituents, which escape along with the water which the salt withdraws. It has been shown that the most influential constituents of meat are dissolved in its juice (471). The salt, therefore, 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 preservative effect, probably in the same way as common salt, but it is not so powerful, and unlike salt produces a reddening of the animal fibres. A little of it is often used along with salt for this purpose. 594. Salting Vegetables. These may be preserved by salt, as well as flesh, but it is not so commonly done. In salting vegetables, however, a fermentation ensues, which gives rise to lactic acid. This is the case in the preparation of sauerkraut from cabbages, and in salting cu- cumbers, The brine with which both vegetables are surrounded is found strongly impregnated with both lactic and butyric acids. 595. Preserration by Sugar. This is chiefly employed to preserve 14 314 PRESERVATION OP ALIMENTARY SUBSTANCES. fruits. Many employ both sugar and molasses for the preservation oi meat ; sometimes alone, but more commonly united with salt. Th principle of preserving by means of sugar is probably similar to that of salting. In the case of fruits, the sugar penetrates within, changing the juices to a sirup, and diminishing their tendency to fermentation or decomposition. "Weak or dilute solutions of sugar are, however, very prone to change ; they require to be of a thick or sirupy consist- ence. KNAPP states that the drops of water which condense from the state of vapor on the sides of the vessels in which the preserves are placed, are often sufficient to induce incipient decomposition, by diluting the upper layers of sugar. The effect of the acids of fruits is gradually to convert the cane sugar into nncrystallizable and more fer mentable grape sugar. 596. Preserving by Alcohol and other substances. Strong alcoholic li- quors are used to prevent decomposition in both vegetable and animal bodies. They penetrate the substance, combine with its juices, and as the organic tissues have less attraction for the spirituous mixture, it escapes ; and the tissues themselves shrink and harden in the same way as when salted. Alcohol also obstructs change by seizing upon atmospheric oxygen, in virtue of its superior attraction for that gas, and thus preventing it from acting upon the substance to be preserved. Vinegar is much used for preserving, but how it acts has not been ex- plained. Spices exert the same influence. Creosote, a pungent com- pound existing in common smoke, and which starts the tears when the smoke enters the eyes, is a powerful antiseptic, or preventer of putrefaction. Meat dipped for a short time in a solution of it will not putrefy, even in the heat of summer. Or if exposed in a close box to the vapor of creosote, the effect is the same, though in both cases the amount producing the result is extremely small. The preservative effect of smoke-drying is partly due to creosote, which gives to the meat its peculiar smoky taste, and partly to desiccation. Oil is but little employed in saving alimentary substances two kinds of fish, anchovies and sardines, are preserved in it. Charcoal has always been ranked as an antiseptic or arrester of putrefaction ; but it has been lately shown that it is rather promotive of decomposition. How this is, will be explained in another place (811). 6. PEESEBVATION OF MILK, BUTTEE, ASTD CHEESE. 597. Modes of preserving Milk, The cause of the souring of milk we have seen to be the action of oxygen upon its casein, which alters the sugar to acid (547). If, therefore, the milk be tightly bottled, and MILK, BUTTEK, AND CHEESE. 315 then boiled, the fermentative power of the curdy matter is destroyed, and it may be kept sweet for several months. When, however, the milk is again exposed to the air, the curd resumes its power of acting upon sugar, and acid is again formed. When milk is kept at a low temperature, the cold retards its changes. If the vessels contain- ing it are placed in a running stream of cool water, or in a place cooled by ice, it will remain cool for several days. Milk may also be pre- vented from souring, even in warm weather, by adding to it a little soda or magnesia." The alkali destroyes the acid as fast as it is pro- duced, and the liquid remains sweet. The small quantity of lactate of soda or magnesia which is formed, is but slightly objectionable. If 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. Alden's concentrated milk is a solidified pasty preparation, made by evaporating milk, with sugar, and affords an excellent substitute for fresh milk, in many cases, when dissolved in water. 598. Unpurificd Batter quickly spoils. Butter when taken from the churn contains more or less of all the ingredients of milk, water, casein, sugar, lactic acid, which exist in the form of buttermilk, diffused through the oily mass. CHEVEEUL 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. The casein passes into incipent putrescence, generat- ing offensive compounds, from both the sugar and oily matter. 599. Butter Purified by Mechanical Working. It is obvious, therefore, that in order to preserve butter, it must first be freed from its butter- milk, which is done by working it, over and over, and pressing or squeezing it, which causes the liquid slowly to ooze out and flow away. The working or kneading is done with a wooden ladle, or a simple machine adapted to the purpose, or else by the naked hand. It is ob- jected that the employment of the hand is apt to taint the butter by its perspiration ; but while it is admitted that moist hands should never do the work, many urge that those which are naturally cool and dry, and made clean by washing in warm water and oatmeal (not soap), and then rinsed in cold water, will remove the sour milk from the butter more effectually than any instrument whatever, without in the least degree injuring it. Overworking softens butter, renders it oily, and obliterates the grain. 600. Preparation of Butter by Washing. Some join washing with 816 PRESERVATION OF ALIMENTARY SUBSTANCES. mechanical working, to separate the buttermilk. It is objected to thia, 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 ia spring water. These the butter is sure, to extract, and their only effect can be to injure it. The calcareous waters of lime- stone districts are declared to be unfit for washing butter. SPEENGEL states that the butter absorbs the lime, and is unpleasantly affected by it. A. B. DICKINSON is of opinion that the best butter cannot be made where hard water is used to wash it ; he employs only the soft- est and purest for this purpose. 601. Cause of Rancidity in 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 cut off from the air, it may be long kept with- out adding any preservative substance. But a trifling amount of curd left in it is sufficient to infect the whole mass. It is decomposed, and acting in the way of ferment upon the sugar and oily substance itself, develops a series of acids, the butyric, which is highly disagreeable and offensive, and the capric and caproic acids, which have a strong 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 upon Butter. The fat of butter is chiefly composed of margarin, which is its main solidifying constituent, and abounds also in human fat. It is associated with a more oily part, olein. Now, air acts not only upon the curdy principle, causing its putres- cence ; but its oxygen is also rapidly absorbed by the oleic acid. One of the effects of this absorption may be to harden it, or convert it into 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 MILK, BUTTER, AND CHEESE. 317 air it is certain to acquire a surface rancidity, which, without pene- trating into the interior, is yet sufficient to injure its flavor. It is in dispensable to its effectual preservation that the air he entirely ex- cluded from it. Hence, in packing butter, the cask or firkin should be perfectly air tight. Care should be taken that no cavities or spaces are left. If portions of butter are successively added, the surface should be either removed or raised up in furrows, that the new portion may be thoroughly mixed with it, or it should be kept covered with brine, and the vessel ought not to be finally closed until the butter has ceased shrinking, and the vacancies that have arisen between the but- ter and vessel's sides are carefully closed. 603. Substances used to preserve Butter. Salt, added to butter, per- forms the twofold office of flavoring and preserving it. The salt be- comes dissolved in the water contained in it, and forms a brine, a portion of which flows away, while the butter shrinks and becomes more solid. Salt preserves butter by preventing its casern from chang- ing ; hence the more of this substance is left in it the more need of salt. The quantity used is variable, from one to six drachms to the pound of butter. It is objected to salt that it masks the true flavor of butter, especially if it be not of the purest quality (591). Salt- petre will preserve butter ; but it is less active than common salt, and some think its flavor agreeable. Sugar is sometimes added to aid in preservation, and to compensate for the loss of the sugar of milk. Honey has been also used for the same purpose, at the rate of an ounce to the pound of butter. Some employ salt, saltpetre, and sugar all together. From an examination of upwards of forty samples of English butter, HASSALL found the proportion of water in them to vary from 10 to 20, and even 30 per cent., and the proportion of salt from one to six or seven per cent. A simple method of ascertaining the quantity of water in butter is, to melt it and put it in a small bottle near the fire for an hour. The water and salt will separate and sink to the bottom. 604. Changes of Cheese by Time. Cheese requires time to dei^lop its peculiar flavor, or ripen. A slow fermentation takes place within, which differs much according to the variety of circumstances con- nected with its preparation, and the degree and steadiness of the tempe- rature at which it is kept. The fermentation, which is gentle and pro- longed at a low temperature, becomes too rapid in a warm, moist place. The influence of temperature is shown by the fact that hi certain locali- ties of France, especially at Roquefort, there are subterranean cavern g rent and are sold at enormous sums for the purpose of keeping SI 8 MATERIALS OF CULINARY AND TABLE UTENSILS. and maturing cheese. These natural rock-cellars are maintained, bj gentle circulation of air, at 41 to 42. The nature of the changes that cheese undergoes has not been clearly traced. .It is known that the casein becomes so altered as to dissolve in water. The salt intro- duced to preserve it is said to be decomposed ; the oily matter gets rancid, as may be shown by extracting it with ether ; and peculiar volatile acids and aromatic compounds are produced. Cheese of poor or inferior flavor, it is said, may be inoculated with the peculiar fer- mentation of a better cheese, by inserting a plug or cylinder of the latter into a hole made to the heart of the former. To prevent the attacks of insects the cheese should be brushed, rubbed with brine or salt, and smeared over with sweet oil, the shelves on which they rest being often washed with boiling water. 605. Preseryation of Eggs. When r ewly laid, eggs are almost per- fectly full. But the shell is porous, and the watery portion 6f its contents begins to evaporate through its pores the moment it is ex- posed to the air, so that the eggs become lighter every day. As the water escapes outward through the pores of the shell air passes inward and takes its place, and the amount of air that accumulates within de- pends, of course, upon the extent of the loss by perspiration. Eggs which we have preserved for upward of a year, packed in salt, small ends downwards, lost from 25 to 50 per cent, of their weight, and did not putrefy. As the moisture evaporated the white became thick and adhesive, and the upper part was filled with air. To preserve the interior of the egg in its natural state, it is necessary to seal up the pores of the shell air-tight. This may be done by dipping them in melted suet, olive oil, milk of lime, solution of gum arabic, or cover- ing them with any air-proof varnish. They are then packed in bran, meal, salt, ashes, or charcoal powder. KEAUMTTE is said to have coated eggs with spirit varnish, and produced chickens from them after two years, when the varnish was carefully removed. Y I. MATERIALS OF CULINARF 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 in kitchen operations. The chief objection to it springs from its powerful attrac- tion for oxygen, which it obtains from the atmosphere. It will even VESSELS Otf IKON AND TIN. 319 decompose water to get it. In consequence of this strong tendency to oxidation, its surface becomes corroded and roughened by a coating of rust, which is simply oxide of iron. The rust combines with various substances contained in food, and forms compounds which discolor the articles cooked in iron vessels, and often impart an irony or 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 lesa liable to rust than malleable, or wrought iron. There is one mode of managing cast iron vessels, by which the disagreeable effects of rust may be much diminished, if not quite prevented. .If the inside of stew-pans, boilers, and kettles be simply washed and rinsed out with warm water, and wiped with a soft cloth instead of being scoured with sand or polishing materials, the vessel will not expose a clean metallic surface, but become evenly coated with a hard, thin trust of a dar} brown color, forming a sort of enamel. If this coating be allowed to remain, it will gradually consolidate and at last become so hard as to take a tolerable polish. The thin film of rust thus prevents deeper rusting and at the same time remains undissolved by culinary liquids. 609. Protection of Iron by Tin. As such protection, however, in- volves care and consideration, it is uncertain and unsatisfactory, and besides it is 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 llock tin is generally supposed to consist of the pure metal. This is an error. It is only tinned iron plate, better planished, stouter, and heavier than ordinary. All tin ware, therefore, is only iron plate coated or protected by tin : yet, practically, it is the metallic tin only that we are concerned with, as that alone comes in contact with our food. 610. Adaptation of Tin to Cnlinary Purposes. Tin, in its metallic 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 as vinegar or lemon juice, boiled in tin-coated vessels, may dis- 820 MATERIALS OF CULINARY AND TABLE UTENSILS. solve a minute portion of the metal, forming salts of oxide of tin, but the quantity will be so extremely small that it need excite little apprehension. It is a question among toxicologists whether its oxide be poisonous. PKOTJST showed that a tin platter, which had been in use two years, lost only four grains of its original weight, and probably the greater part of this loss was caused by abrasion with whiting, sand, or other sharp substances during cleansing. If half of it had been taken into the system dissolved, it would have amounted only to ^j of a grain per day, a quantity too trifling to do much harm, even if it were a strong poison. Common tin, however, is contaminated with traces of arsenic, copper, and lead, which are more liable to be acted upon by organic acids and vegetables containing sulphur, as onions, greens, &c. PEEEIEA remarks that acid, fatty, saline, and even albuminous substances may occasion colic and vomiting by having remained for some time in tin vessels. Still, tin is unquestionably the safest and most wholesome metal that it is found practicable to employ ii domes- tic economy. 611. Zinc Vessels Objectionable. Zinc is rarely employed as a mate- rial for culinary vessels. In many cases it would be unsafe, as a poi- sonous oxide slowly forms upon its surface. It has been recommended for milk pans on the ground that milk would remain longer sweet in them, and hence, more cream arise. But whatever power of keeping milk sweet zinc possesses, it can only be caused by neutralizing the acid of milk with oxide of zinc, thus forming in the liquid a poisonous lactate of zinc. 612. Behavior of Copper in contact with Food, This metal suffers very little change in dry air, but in a moist atmosphere oxygen unites with it, forming oxide of copper ; and carbonic acid of the air, combin- ing with that substance, forms carbonate of copper, of a green color. Copper is easily acted on by the acid of vinegar, forming verdigris, or the acetate of copper, which is an energetic poison. Other vegeta- ble acids form poisonous salts with it in the same way. Common salt is decomposed by contact with metallic copper during oxidation, the poisonous chloride of copper being formed. All kinds of fatty and oily matter have the property of acting upon copper and generating poisonous combinations. Sugar also forms a compound with oxide of copper, the sacharate of copper. 613. Test. As the salts of copper are of a green color, vessels of this metal have a tendency to stain their contents green. They are sometimes employed purposely to deepen the green of pickles, &c., and cooks often throw a penny-piece into a pot of boiling greens to 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 coated with metallic copper. The solution ought to be only very slightly acid. Now, as acid, oil, or salt, is found in almost every article of diet, it is clear that this metal, unprotected, is quite unfit for vessels designed to hold food. 614. Protection of Copper Utensils. Yet copper has several advan- tages as a material for culinary utensils. It is but slowly oxidized, and hence does not corrode deep, scale, become thin, and finally fall into holes as iron vessels are liable to do. Besides, copper is a better con- ductor of heat than iron or tin plate, and consequently heats more promptly and with less fuel, and as it wears long, and the metal when old bears a comparatively high price, its employment, in the long run, is unquestionably economical. Copper vessels ought never to be used, however, without being thoroughly protected by a coating of tin and when this begins to wear off they should be at once recoated, which the copper or tin-smith can do at any time. It has been stated that a small patch of tin upon the surface of a copper vessel would entirely prevent the oxidation of the latter by galvanic influence ; but Mr. MITCHEL has shown by experiment that such is not the fact, and that the only safeguard is in covering completely the entire copper surface. Brass is an alloy of zinc and copper, and although less liable to oxidize, is nevertheless unsafe. Kettles of brass are often employed in preparing sauces, sweetmeats, &c., but this ought never to be done unless they are scrupulously clean and polished, and hot mixtures should not be allowed to cool or remain in them. 615. Enamelled Ironware Vessels. It would seem that no one mate- rial possesses all the qualities desirable to form cooking vessels. Some of the metals are strong and resist heat ; but, as we have seen, various kinds of food corrode them. Earthenware, on the contrary, if well made, resists chemical action, but is fractured by slight blows and the careless application of heat. An attempt has been made to combine the advantages of both by enamelling the interior of iron ves- sels with a kind of vitreous or earthenware glaze. Various cooking vessels, as saucepans, boilers, and the like, have been prepared in this manner, and answer an admirable purpose. Dr. UEE remarks, I con- sider such a manufacture to be one of the greatest improvements recently introduced into domestic economy, such vessels being remark- ably clean, salubrious, and adapted to the delicate ciilinary opera- tions of boiling, stewing, making of jellies, preserves, &c. 14* 322 MATERIALS OF CULINARY AND TABLE UTENSILS. 616. Earthenware Vessels Glazing. Vessels of earthenware are in universal household use. They are made, as is well known, of clay and sand, of various degrees of purity, with, other ingredients, forming a plastic mass, which is moulded into all required shapes, and hardened by baking in a hot furnace. The ware, as it thus comes from the baking process, is porous, and absorbs water. To give it a smooth, glossy, water-resisting surface, it is subjected to the operation of glaz- ing. This is effected in two ways; first, when the stoneware has at- tained a very high temperature, a few handfuls of damp sea-salt are thrown into the furnace. The salt volatilizes, the vapor is decomposed, the hydrochloric acid escaping ; while the soda, diffused over the sur- face of the ware, combines with its silica, and glosses over the pieces with a smooth, hard varnish. Another mode by which the desired artificial surface is given to earthenware, is by taking it from the fire when it has become sufiiciently firm and stiff, immersing it in a pre- pared liquid, and restoring it again to the furnace, where by the action of heat a vitreous or glassy coating is formed. 617. Earthenware Glaze 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 ara easily scratched, and liable to be attacked by strong chemical sub- stances. Lead glaze upon earthenware is also subject to the same objection. It is tender and can be scraped off with a knife, so that the plates soon become marred and roughened. They also soon black- en, or darken, when in contact with sulphurized substances. Cooking eggs or fish in these vessels gives them a brownish tinge. If less lead be used, the glaze becomes less fusible, the process of applying it more difficult, and hence the ware more expensive. Lead glazing can be do- tected by its remarkably smooth, lustrous surface, resembling varnish ; while the salt glaze, on the contrary, has less lustre, and the vessel has not so fine an appearance, all the asperities of the clay beneath being perfectly visible. Fatty matters, and the acids of fruits, exert a solvent action on oxide of lead combined in lead glaze, especially where the chemical energy is increased by a boiling temperature. 618. Other defects of Earthenware Glaze. If a piece of earthenware be broken, we may observe upon the freshly fractured edge, the thin coating of glaze which has been fused on to the body of the ware. If the tongue be touched to the broken surface, it will adhere, showing the porous and absorbent nature of the material. Now it often hap- EARTHEN AND POBCELAIN WAKE. 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 unequally when heated and cooled, the consequence be- ing, that the glaze breaks or starts, and the surface of the plate, sau- cer, or vessel, becomes covered with a network of cracks. Ware in uch a condition is said to be crazed. Through these cracks liquid or- ganic matters are liable to be absorbed, which make the articles un- cleanly and impure. Glaze that does not crack is often too soft. To determine this, drop a small quantity of ink upon it, and dry before the fire, and then wash it thoroughly ; if the glaze be too soft, an in- delible brown stain will remain. 619. How Poralain-ware is made* This is the purest and most per- fect product of the plastic art. We are indebted for several suggestions concerning its processes to Messrs. HAVILAND, of this city, whose ex- tensive establishment in France has afforded them a large experience in the porcelain manufacture. This ware was first made in China, and is still known as China-ware. But, after long and difficult experience, the manufacture has at length become so perfected in Europe as greatly io 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 kaolin, or China-clay, 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 furnace, and penetrates as a vitreous or glassy matter the whole body of the clay, completely filling up the pores, and covering all the surface ; it binds the whole together into a dense impenetrable mass. Porcelain-ware is translucent, or permits the partial passage of light, which is due to the clay body being satu- rated as it were with glass, as transparent paper is permeated with oil. The material is moulded with great care and nicety into the de- sired forms, and then, placed in cases of clay made expressly to hold and protect them, are put into the kiln or furnace, and subjected to an intense heat for 15 or 20 hours. The articles are then withdrawn and dipped into a glaze composed of felspar, of the same nature as the flux, and which never contains either lead or tin. The ware is then returned to the furnace and subjected to the most intense white heat that art can produce, for 10 or 20 hours longer. The glaze is thus melted into the flux, so that the porcelain has a uniform body, aa we see when it is broken. There is no accurate mode of measuring the very high temperatures produced in these kilns, but by the method 824 PHYSIOLOGICAL EFFECTS OF FOOD. adopted, the heat is estimated to run up to 21,000 degrees of the Fahrenheit scale. The color of porcelain is milk-white, without any tinge of blue. The qualities which give it pre-eminence among thnto blood and flesh ; but when angry, despises, or spoils the best 326 PHYSIOLOGICAL EFFECTS OF FOOD. food." Chemistry has dispelled these crude fancies, and enabled us to understand how such marvellous transformations occur. We are getting daily clews to the profounder secrets of the organism ; know- ledge is here as rapidly progressive as in any other department of science. In this connection Dr. DRAPER remarks, " Since it is given us to know our own existence, and be conscious of our own individu- ality, we may rest assured that we have what is in reality a far more wonderful power, the capacity of comprehending all the conditions of our life. God has formed our understanding to grasp all these things. For my own part, I have no sympathy with those who say of this or that physiological problem, it is above our reason. My faith in the power of the intellect of man, is profound. Far from suppos- ing that there are many things in the structure and functions of the body which we can never comprehend, I believe there is nothing in it that we shall not at last explain. Then, and not till then, will man be a perfect monument of the wisdom and power of his Maker, a created being knowing his own existence, and capable of explain- ing it." 623. The liying System a theatre of change. The body of the grown man presents to us the same unaltered aspect of form and size, for long periods of time. With the exception of furrows deepening in the countenance, an adult man may seem hardly to alter for half a hundred years. But this appearance is altogether illusory ; for with apparent bodily identity, there has really been an active and rapid change, daily and nightly, hourly and momently, an incessant waste and renewal of all the corporeal parts. A waterfall is permanent, and may present the same aspect of identity, and unchangeableness from generation to generation ; but who does not know that it is certainly made up of particles in a state of swift transition ; the cataract is only a form resulting from the definite course which the changing particles pursue. The flame of a lamp presents to us for a long time the same appearance ; but its constancy of aspect is caused by a cease- less change in the place and condition of the chemical atoms which carry on combustion. Just so with man ; he appears an unchanged being endowed with permanent attributes of power and activity, but he is really only an unvarying form, whose constituent particles are for ever changing. As the roar, spray, and mechanical power of the falling water are due to changes among the aqueous particles; and the heat and light of the flame are due to changes among com- bustible atoms ; so man's endowments of bodily activity, susceptibility, and force, originate in atomic transformations taking place in his BASIS OF THE DEMAXD FOE ALIMENT. 327 s>-iem. As each part is brought into action, its particles perish and ar replaced by others ; and thus destruction and renovation in the vital economy are indissolubly connected, and proceed together. It is said, with reference to the casualties to which man is every where exposed, that "in the midst of life we are in death,'' but physiologi- cally, this is a still profounder truth ; we begin to die as soon as we begin to live. 624. Bate at which the vital changes proceed. But very few persons have any correct conception of the rate at which change goes on in their bodies. The average amount c-f matter taken into the system daily, under given circumstances, has been determined with a con- siderable degree of precision. From the army and navy diet-scales of France and England, which of course are based upon the recognized necessities of large numbers of men in active life, it is found that about 2 j Ibs. 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 Ibs. as the weight of the body, the amount of oxygen consumed daily is nearly 2} Ibs., which results from breathing about 25 or 80 hogsheads of air; the quantity of water is nearly 4^ Ibs. for the same time. The weight of the entire blood of a full-grown man varies from 20 to 30 pounds; of this, the lungs, in a state of health, contain about half a pound. The heart beats, on an average, 60 or 70 times in a minute. Every beat sends forward two ounces of the fluid. It rushes on, at the rate of 150 ft. in a minute, the whole blood passing through the lungs every two minutes and a half, or twenty tunes in an hour. In periods of great exertion the rapidity with which the blood flows is much increased, so that the whole of it sometimes circulates in less than a single minute. (JOHNSTON.) According to these data, all the blood in the body, travels through the circulatory route 600 or TOO times in a day, or a total movement through the heart of 10,000 or 12,000 Ibs. 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 Ibs. ; bile, 3 to 4 Ibs. ; pan- creatic juice, Ib. ; intestinal juice, Ib. (Dr. CHAMBEBS.) At the same time there escapes from the lungs nearly 2 Ibs. of carbonic acid and 13 of watery Taper. The skin loses by perspiration 21 Ibs. of water, and there escape in other directions about 2 Ibs. 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 Carious forms, is estimated at 1,500 Ibs., or all together a ton and a 328 PHYSIOLOGICAL 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 heing more than a thousand times. 625. A striking illustration 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 PAKE, 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 life, or twice the common allotment of man. Applying to his case then the established physiological constants, we get the following startling results of the amount of possible change in matter produced in the lifetime of a single man. He drank upwards of a hundred tons of water, ate nearly sixty tons of solid food, and absorbed from the air one hundred and twelve thousand Ibs. of oxygen gas to act upon that food. There are fifteen Ibs. weight of air resting upon every square inch of the earth's surface ; of this one-fifth is oxygen, there being therefore 3 Ibs. of oxygen over every square inch of the earth, extending to the top of the atmosphere. The daily consumption by respiration is 2 Ibs. PAEK, therefore, consumed all the oxygen over a surface of 236 square feet of ground to the very summit of the earth's atmos- phere, and generated noxious gases enough to contaminate and render unfit for breathing ten times that space, or poison a column of air 45 miles high, having a base of nearly 2,400 square feet. If we may indulge in a somewhat violent supposition that the whole blood which was actually driven through his heart during that long period could have been accumulated and measured as one mass, by forming a pro- cession of vehicles, each taking a ton and occupying two rods of space, such a procession would have attained the enormous length of 2,000 miles. 626. Relation between Waste and Supply. Such is the ground of our daily requirement for food. The annual supply of 3,000 Ibs. of mattei to the body is demanded, because in the yearly exercise of its powers and functions 3,000 Ibs. of matter have been used up or spent. It cannot be maintained for a moment that the bodily system possesses any power of producing or creating a single particle of the matter which it uses ; it must receive every thing from without, and maintain its uniform condition of weight by striking an exact balance between waste and supply, receipt and expenditure. There are two periods in the natural life of man when the balance between these antagonizing forces is overturned ; in infancy, childhood and youth, the reception BASIS OF THE DEMAND FOE ALIMENT. 329 of matter prevails over its loss, and the body steadily augments io weight ; in old age reparation does not keep pace with decay, and the bodily weight gradually declines. In the intervening period of adult lite these antagonizing forces are maintained with but little variation in a state of constant equilibrium. In all the deepest recesses of the body, in every springing muscle, and conducting nerve and connecting tissue, and even the thinking brain, myriads of atoms are continually passing into the condition of death, while by the profoundest law of physiological life an exactly equal number are constantly introduced to replace them, each of its proper kind and in its appropriate place. 626. Practical inference from these facts. As thus the living being is the result and representative of change on a prodigious scale, the question of the course, rate, and regulation of those changes must be controlling and fundamental. Matter is introduced into the system in one condition and escapes from it in another ; the change (metamor- phosis) that it has undergone is oxidation, or a true burning. The solid aliment is all combustible, oxygen is the agent which burns or destroys the food by uniting with it, and water the medium which brings them into proper relation to act on one another. Hence the life, activity, and multiform endowments of the organism, originate in the chemical action and reaction of prepared matter, borrowed temporarily from the outward world to be quickly restored to it again. And as the supply of nutritive matter is effected through our own voluntary agency ; as we select, mingle and prepare the nutritive mate- rials, and control the times, frequency, quantity and condition 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 Hunger and Thirst. It will be seen from the nature of the case, that the necessities of the system for matter from without, are pressing and momentous. If the inflowing tide of gases be arrested but for a few moments, suffocation and death follow. If the liquid and solid aliments be withheld, indescribable agonies shortly ensue, and in a few days the extinction of life. There is, therefore, an irresistible life-demand for the supply of nutriment which cannot be put off upon peril of existence, while the cost of nutritive matter is laborious struggle and exertion, both of body and mind. Now it is plain, that if 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 Architect has therefore wisely intrenched in the system two monitors, hunger and thirst, which are independent of reason or will, cannot be dislodged while life lasts, and whose duty it is to proclaim that further nourishment is required for bodily sup- port. And beside the sensations of hunger and thirst, imperative as they are, there is attached to their proper indulgence a degree of. pleasure which never fails to insure attention to their demands. In what hunger and thirst consist, what state of the stomach or vessels produces them, or how the general nutritive wants of the sys- tem get expressed in feeling or sensation, we do not know ; several explanations have been offered upon this point, but they are all un- satisfactory. 628. Impelled by the demands of the constitution food is procured, and in several ways, which have been described, prepared for use. When taken into the system it is subject to various changes in a cer tain natural and successive order, which will next be noticed. 2. FIRST STAGE OF DIGESTION CHANGES OF FOOD IN THE MOUTH. 629. The great oty'ect of Digestion. The prepared food upon our tables is in the form of crude, unmixed, and chiefly solid masses. Various vegetables, breads, meats, butter, each with its peculiar constituents and properties, are ready for use. Their physiological purpose is to make blood, the source upon which the whole system draws for what- ever it requires. The blood contains every thing necessary to form 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 separat 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 coat* 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 torials 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. Reducing Mechanism 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 mLmm f and side movements of the low- er jaw. The teeth are 32 in number, and their differences are illustrated by Fig. 113, which represents half the lower jaw. A shows two of the front or ... ,, ,, , . . Illustration of the different kinds of Teeth. cutting teeth, called incisors; B the cuspid, canine, or dog tooth, so called from being large in the dog and carnivorous animals, and used by them to seize and tear their food ; C the bicuspids or double-speared, from their resemblance to a double-headed canine tooth ; and D the molars, double-rooted, with broad, irregular, grinding surfaces.* 631. Conditions of the flow of Saliva. But no amount of mechani- cal action alone will convert solid aliment into the fluid state. If the food is to be dissolved, there must be a solvent or liquid to bring about the solution. It is the office of the saliva or spittle to commence this work. The saliva is separated from the blood and poured into the mouth by three pairs of glands (Fig. 114). The rate at which it is secreted varies at different times and under different circumstances. The sight, or even the thought of dinner may fill the mouth with it, while continued mental attention to other subjects, or a state of anxi *" In Latin, cuspis signifies the point of a spear ; cants, dog ; mola, a mill ; incisor anything which cuts " 332 PHYSIOLOGIC 1 AX EFFECTS OF FOOD, FIG. 114. ety, will dry it up. The movements of the mouth, as in speaking, reading, or singing, excite its flow, but it is most copiously furnished at times of eating, by the contact and pressure of food during masti- cation. Hence, the glands on that side of the mouth which is most used in mastication, secrete more than the others. The nature of the food causes the quantity furnished at meals to vary exceedingly ; hard, dry ali- ments provoking a much greater dis- charge than those which are moist and soft. It streams out abundantly under the stimulation of spices, and continues to flow after the meal is concluded ; the secretion also goes on 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 contains also an organic principle named ptyalin, an albuminous sub- stance which acts as a strong ferment. The tartar which collects on the teeth is the residue left by evaporation of the water of the sa- liva, and consists of earthy salts, cemented together by animal matter. The salivary juice of the mouth is, however, a mixture of three differ- ent salivas poured out by three pairs of glands. Parotid saliva is thin and watery, so as to 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 parotid, & submaxil lary, c sublingual. DIGESTION CHANGES IN THE MOUTH. 333 pure starch be chewed for a short time, it will become sweet ; a por- tion of it has undergone a chemical transformation, and been con- verted into sugar. By its joint alkaline and fermentative powers, saliva produces an almost instantaneous effect upon starch, changing it first into sugar, and in a little longer time converting the sugar into lactic acid. This important change seems to be effected, not by any one of the salivary secretions,, but is due to their combined action. Saliva exerts no solvent influence upon the nitrogenous aliments. It will thus be noticed that the first chemical attack, at the very thresh- old of the digestive passage, is made upon that alimentary principle which abounds most of all in our food (382). We furthermore draw a practical inference opposed to the current opinion which assumes that animal food, from its tough, fibrous nature, needs more mastication than vegetable. Meat and albuminous substances require to Le thor- oughly disunited and subdivided in order that each particle may be brought into contact with the secreting membrane of the stomach, while bread, and substances which abound in starch, have not only to be reduced fine, but to be well imbued with the salivary liquid. In animal food, it is possible to supply the place of mastication by the use of implements in the kitchen and at the table ; but culinary science cannot compound an artificial saliva to be mixed with starchy food, so as to save the trouble of chewing it. The changing of this substance from a solid to a liquid form, as in gruel and sago slops, so that they are swallowed without being delayed in the mouth and mingled with its secretions, is unfavorable to digestion, especially if the stomach be not vigorous. The best condition in which starch can be taken is where the outer membrane has been ruptured by heat, and the mass made light, as in well-baked bread and mealy potatoes (532). 634. Importance of thorough Mastication. The mechanism of insali- vation has been inserted in the mouth for a definite and important purpose, and as the act of mastication is under the control of the will, it is very easy to defeat that purpose. If the food be imperfectly chewed, and hastily swallowed, or as the phrase goes, ' bolted,' the aliment passes into the stomach crude and ill-prepared, and the whole digestive function is just so far imperfect and enfeebled. It is of much consequence that meals should not be precipitated, but that proper time should be allowed to perform that portion of the digestive opera- tion, which falls so directly under voluntary control. Besides thought- lessness, and business pressure which pleads want of time, there is an- other cause of inattention to this matter which deserves notice. Many persons have placed themselves in such a fake relation to nature, as 334 PHYSIOLOGICAL EFFECTS OF FOOD. to imagine that they exalt the spiritual attributes of their being by casting contempt upon the physical. Such are inclined to regard the act of eating as a very animal and materializing operation, and any considerations of the way it should be conducted, are apt to weigh but lightly upon their minds. This view is false, and leads to conse- quences practically mischievous. Dr. COMBE remarks, " Due mastica- tion being thus essential to healthy digestion, the Creator, as if to insure its being adequately performed, has kindly so arranged that the very act of mastication should lead to the gratification of taste the mouth being the seat of that sensation. That this gratification of taste was intended, becomes obvious when we reflect that even in eating, nature makes it our interest to give attention to the process in whicj. we are for the tune 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 sufficient admixture with the saliva now deficient in quantity and consequently lie on the stomach for hours unchanged. A certain degree of attention to taste and the pleasures of appetite is, therefore, both reasonable and bene- ficial; and it is only when these are abused that we oppose the inten- tion of nature." 635. Effect of profuse Spitting. The salivary juices are parts of a great water circulation of secretion and absorption. They are poured into the mouth, not to l)e 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 DIGESTION CHANGES IN THE STOMACH. 335 class of bodies is concerned, the salivary glands act vicariously lor the kidneys, and the mouth is thus partially converted into t urinary aqueduct." (Dr. DEAPEB.) 8. SECOND STAGE OF DIGESTION CHANGE OF FOOD ES* THE JM-OMACH. 636. Figure and Dimensions of the Organ. Having underfc >ne more or less perfectly the changes which appertain to the mouth, the food is swallowed, and pass- F IG . 115. ing down the esopha- gus, or gullet, enters the stomach. This or- gan is a pouch-shaped enlargement of the di- gestive tube, having the form shown in Fig. 115. The larger ex- tremity is situated at the right side of the body, and its lesser end L .tv i A on, * Section of the human stomach : a esophagus ; 5 c cardiac at the left. Inat por- orifice ; d e greater curvature ; / 9 lesser curvature ; A tion where the esoph- l orifice ; '* Duodenum ; * bile duct, agus enters it, is termed the cardiac region (because it is in the vicin- ity of the J:ear 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 they live. Thus in the flesh-eating animals it is very small, only a slight enlargement of the esophagal tube ; while in those which feed upon herbage, it is distended intG an enormous cavity, or rather into several, as in the ruminants, cows, sheep, &c. 637. Layers of the Stomach. The walls of the stomach consist of three membranous coats. The outer layer is a smooth, glistening, whitish membrane (serous membrane), lining the abdomen, and cover ing all the internal organs, which it strengthens, and by its smoothness and constant moi sture, permits them to move upon each other with- out irritation. The middle coat consists of two layers of muscular fibres or bands, one of which runs lengthways, and the other crossways. 336 PHYSIOLOGICAL 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 (mucous mem- brane) lines its internal surface. It is a soft, velvet-like membrane, of a pale pink color, in health, and of much greater extent than the outer coats, hy which it is thrown into folds or wrinkles. It is con- stantly covered with a thin, transparent, viscid mucus. 638. Motions of the Stomach The food upon which operations have been commenced in the mouth, is passed into the stomach, but it is not permitted to rest. By the successive contraction and relaxation of its muscular bands, the stomach imparts to its contents a constant churning, or revolving motion. In the celebrated case of ST. MARTIN, a Canadian soldier, whose stomach was opened by a gunshot wound in the side, and healed up leaving a permanent orifice (gastric fistula), Dr. BEAUMONT made numerous observations of digestive phenomena. He thus describes the movements of food within the or- gan. " After passing the esophagal ring it moves from right to left along the small arch ; then through the large curvature from left to right. The bolus (swallowed mouthful), as it enters the cardiac, turns to the left, descends into the splenic extremity (large extremity near the spleen), and follows the great curvature towards the pyloric end. It then re- turns in the course of the smaller curvature, performing similar revolu- tions. These revolutions are completed in from one to three minutes. They are slower at first, than after digestion is considerably ad- vanced." The motion is not absolutely constant, but continues for a few minutes at a time. If the food remains in the stomach three hours it travels round and round through this circuit two or three hundred times: to what purpose? 639. Minute arrangements for Stomach Digestion. Before considering what takes place hi the stomach, we must have a closer view of its _, mechanism. The lining layer of this organ is curi- ously and admirably constructed, though it requires the microscope to see it. Magnified about 70 diameters the mucous membrane exhibits the honey- combed appearance seen in Fig. 116. Into these reticulated spaces, there open little cup-shaped cavities called stomach follicles, which are about T2QO 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 FIG. 117. like palisading, or like little flasks or test-tubes close packed and up- right ; many thousands of these upright cylindrical cavities "being set in a square inch of surface. They are of different depths in different parts of the stomach, and they terminate at the bottom in minute closed tubes. The arrangement has been likened to a little glove, the hand of which opens into the stomach, while the fingers are buried in the tissue beneath. Fig. 117, represents the se- creting follicles in the stomach of a dog after twelve hours' abstinence ; a, from the middle re- gion of the stomach ; &, from near the pylorus ; c d, the mouths opening upon the surface, e f, the closed tubes imbedded in the membrane below. The walls of these cavities are webbed over with a tissue of most delicate bloodvessels, carrying streams of blood a network of veins surrounds their outlets upon the surface of the membrane, while nerves innu- e\ merable pervade the whole arrangement. 640. Use of these little pocket-shaped vessels. What, now, is the purpose served by these interesting little contrivances ? It is to separate from the blood the digestive fluid of the stomach. But they do not effect this directly ; another agency, that of cells (496) , is called into play. The gastric juice does not simply ooze or distil from the blood into the stomach. It is manufactured by a determi- nate process. " For each minutest microscopic drop of it, a cell of complex structure must be developed, grow, burst and be dissolved." At the bottom of the cavities, in the little tubular roots, the seeds or germs of cells arise in immense numbers. Recurring to the simile of the glove, within each finger, at the tip and upon its sides, the cells take origin, and, nourished by the blood, multiply and swell until they are driven up in crowds into the hand or larger cavity, and hav- ing reached their full maturity, are pushed out at the surface, burst, and deliver their contents into the stomach. 641. The periodic supply of Food. The digestive principles are thus a product of cell-action, and into their preparation there enters the element of time. Though short-lived, a certain period must elapse for their production. During digestion the cells are perfected in in- credible numbers, and yield large amounts of fluid. During fasting, no full-grown cells escape ; the tubes collapse, and an opportunity is allowed for the production of a new stock of germs or cell-grains. If this be so, it must follow that we cannot with impunity interfere with 15 338 PHYSIOLOGICAL EFFECTS OF 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 Gastrie Juice. The digestive juice of the stomach is a colorless, inodorous, slightly viscid fluid, which when removed from the organ, retains its active properties for a long time, if kept excluded from the air. A boiling heat destroys its activity, but freez- ing does not. In a healthy state, it is always distinctly sour, which is caused by an uncombined acid, usually the hydrochloric, but some- times lactic acid. "With its acid principle, the gastric juice also con- tains a peculiar albuminous body called * pepsin ' or ' ferment sub- stance.' If the juice be evaporated to dryness, this pepsin constitutes three-fourths of the solid residue. As the food is rolled round in the stomach, it is incorporated with this juice, and changes gradually to a pulpy semi-fluid mass. Digestion is fully under way in an hour after the meal is taken, and is usually finished in about four. 644. Limit of Stomach Digestion. Recent physiological investigations have exploded the opinion long entertained, that the stomach is the exclusive or principal seat of digestive changes. In tracing the properties of foods, we had occasion to divide them into two great classes based upon fundamental differences in chemical composition the nitrogenous and the non-nitrogenous aliments. We find this dis- tinction recognized by nature in arranging her plan of digestion. So different are these two kinds of aliments that they require totally different agents to dissolve them, nay, solvent fluids of entirely opposite characters. We have seen that digestion began in the mouth with an alkaline liquid, and took effect only upon the non-nitrogenous principles. Upon proceeding to the stomach we find new conditions an acid liquid replaces the alkaline the changes that commenced in the mouth are partially or totally suspended, the non-nitrogenous com- DIGESTION CHANGES IN THE STOMACH. 339 pounds remain unaltered, the gastric fluid taking effect only upon nitrogenous substances. 645. Action of the Add and Ferment If coagulated white of egg be placed in water acidulated with hydrochloric acid, no solvent action takes place at common temperatures for a long time. If the temperature be raised to 150, a slow dissolving effect begins, which is much increased at the boiling heat. But if a little * pepsin ' be added to the liquid the solution goes on actively, so that the pepsin, as it were, replaces the effect of a high temperature. An ounce of water mixed with twelve drops of hydrochloric acid and one grain of pepsin, will completely dissolve the white of an egg in two hours at the temperature of the stomach (100). It acts in the same manner on cheese, flesh, vegetable gluten, and the whole nitrogenous group, changing them to the liquid form. These are the results of an arti- ficial gastric juice, but they are exactly the same in kind as those which take place in the stomach. Drs. BIDDER and SCHMIDT, whose researches upon digestion are the most recent and extensive, have shown that gastric juice withdrawn from the stomach and placed in -vials, produces upon food precisely the* same alterations as occur in the stomach, only much more slowly. In consequence of the motions of the stomach turning the aliment round and round, and the flow of the secretions which constantly washes away the dissolved parts and exposes fresh surfaces, the fiction proceeds about five times faster within the body than without, but the nature of the results is iden- tical. 646. TTliat is the Digestive Ferment Snbstanee ? There has been much controversy about pepsin ; what is it ? A substance in the gastric fluid discovered by SCHWAN a few years ago, and supposed to be a peculiar principle specially prepared for digestive purposes. It may be obtained from gastric juice, or by soaking the membrane of a calfs stomach (rennet). "WTien 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 WASMANX, who showed that a solution containing only 1-60, 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 cells ; and physiologists have discovered, that during digestion it separates completely from the other layers of the 340 PHYSIOLOGICAL EFFECTS OF 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 rise to gases, although in morbid conditions of the organ other fermenta- tions may arise in the alimentary mass. 647. Gastric 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 really altered in properties. The nitrogenous matters are not only dissolved, but are so modified as to remain dissolved. In ordinary solution a solid body is changed to a liquid by the action of another liquid or solvent ; but when the solvent is removed the dissolved substance again resumes its solid condition. Not so, however, in gastric digestion ; the digestive fluid dissolves albumen, fibrin, casein ; but as it cannot accompany them to maintain them in this state, it impresses upon them a still further change, by which they continue soluble. Casein in milk, and liquid albumen are already dissolved when swallowed ; but they are not digested, and the first act of the stomach is to coagulate or solidify- both. They are then dissolved again, and so altered as to retain the new condition under circumstances which would have been before impos- sible ; while their 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 the Stomach. The alkaline saliva attacks the sugar and starch in the mouth, and has the power of rapidly changing the starch into sugar, and that into lactic acid. But the food tarries only a few moments in the mouth ; charged with its alka- line solvent, it descends into the acid region of the stomach. But acids and alkalies cannot get on together. They either kill each other, or if one is the 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. Yet this does not occur instantaneously, as the food is swallowed. The effect of the gastric juice is superficial, acting at nrst upon the food where it comes in contact with the bedewed coats of the stomach, while the saliva, in- corporated within, is allowed a little time for- action. - In this limited sense there may be two digestions going on in the stomach, although gastric digestion speedily overpowers and suspends the salivary. It is interesting to remark that lactic acid may replace hydrochloric in stomach digestion, and that if from any cause the latter is not supplied in due quantity, the saliva, acting upon the contents of the stomach, will generate the required substitute. 649. Quantity of Gastrie Juice seereted. There has been, and indeed there still is, much doubt upon this point ; but it is now generally con- ceded that former estimates ranged much too low. The hourly de- struction of fibrin throughout the system, in average muscular action, has been assumed at 62 grains, and it has been found that 20 parts of gastric juice are needed to dissolve one part of dry nitro- genous matter. To digest this quantity only, some 60 or 70 ounces of the fluid would be required. It is obvious that the natural quanti- ty must much exceed this, as a considerable portion will be neutralized by the saliva, and much inevitably escapes into the intestines. But observation indicates quantities greatly higher than any calculated re- sults. In the case of dogs, BIDDER and SCHMIDT found from experi- ment the proportion to be one-tenth of their weight. This proportion applied to man would give a daily secretion of 14 Ibs. Dr. GRiraE- WALDT has however quite recently had an opportunity of determining the quantity yielded by the human body, in the case of a stout, healthy peasant girl, weighing 120 Ibs., who had a fistulous opening in her stomach, from childhood, that did not in the least degree interfere with her general health. His experiments gave the astonishing result of 31 Ibs. of the gastric secretion in 24 hours, or one-fourth the weight of the body. Making every possible allowance for error in these in- vestigations, we must conclude that the quantity of digestive fluid poured out each day must, at any rate, be very large. 650. Digestibility of Foods. By this we understand their capability of yielding to the action of the digestive forces, the joint result of seve- ral distinct chemical agents fitted to act upon special constituents of the food, and brought into play throughout the whole alimentary tract. Digestion is therefore an affair of many conditions, and its re- sults are by no means capable of being so simply stated as has been 342 PHYSIOLOGICAL EFFECTS OF FOOD. formerly believed. What goes forward in the stomach, although of great importance, affords but a partial view of the whole operation. Dr. BEAUMONT made an admirable series of observations upon thia 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. DUFAY, announcing the first laws of electricity, in 1737, stood much nearer THALES, of ancient Greece, rubbing his piece of amber, than to Prof. MORSE, patenting the electro- magnetic telegraph, in 1837. Within a quarter of a century, organic and animal chemistry have risen to the position of separate and in- dependent branches of science ; and it is hardly an exaggeration to say that more has been done to elucidate the subject of digestion in the 30 years that have elapsed since Dr. BEAUMONT began his experiments, than was accomplished by all the physiologists who preceded him, though we are far enough yet from any thing like a clearing up of the subject. Kegarding digestion comprehensively, as the blood-forming function, we are to take into account not only the solubility of ali- ments, but their conformability to the blood. If two substances are dissolved with equal ease, that will be the more digestible which has the greatest similarity to some constituent of the blood. Gum, for example, is much more easily dissolved than fat, yet the latter is a constant constituent of blood, while the former is never found there. Gum, to be made available, must pass through a series of transforma- tions, sugar, lactic acid, butyric acid, while fat passes into the circu- lation without decomposition. " If the conformity of two alimentary principles with the constituents of the blood is equal, the more soluble is the more digestible. Soluble albumen and fibrin stand equally near to th-3 blood, both being contained in it ; as the soluble albumen is however more readily dissolved in the digestive juices than fibrin, the digestion of the latter is more difficult." We thus see that the diges* tibility of foods is not the mere matter of the time of solution in the stomach that has been generally supposed, but involves much more. Meanwhile, Dr. BEAUMONT'S statements of the periods which various alimentary substances require to break down into chyme in the stomach, may be serviceable, if received with due restrictions. We subjoin an abstract. DIGESTION CHANGES IN THE STOMACH. 843 MEAN TIMES OF CHYMIFICATION OF FOOD. Articles. Preparation. Time. Articles. Preparation. Tkne. Eice . . Boiled. . . Boiled Boiled..... Boiled.... Fried Eaw h.m. 1 1 1 1 80 1 80 1 80 1 85 1 45 2 2 2 2 2 2 2 2 15 2 18 2 25 230 2 30 2 30 2 30 2 30 2 80 280 2 30 2 30 2 30 2 45 2 45 2 50 2 55 3 8 3 8 3 3 _ 3 3 Pork, recently salted.. Soup chicken Baw h.m 3 3 3 15 3 15 3 15 3 15 8 15 3 15 320 S iO 3 30 3 30 3 30 3 30 8 80 3 30 3 30 8 30 3 30 3 30 3 30 3 45 3 45 4 4 4 4 4 4 4 4 15 415 4 30 4 30 430 4 30 4 30 5 15 5 30 5 30 Pig's feet, soused Tripe, soused Trout, salmon, fresh. . Apples, sweet, mellow Venison, steak. Boiled .... Boasted... Broiled.... Broiled.... Baked. .... Boasted.. . Boiled .... Broiled.... Boasted . . . Baked Melted... Eaw Hard boil'd Fried Oysters, fresh Pork, recently salted . Pork steak Corn bread Broiled . . . Boiled Eaw Kaw Mutton, fresh Sago Carrot, orange.. Apples, sour, mellow. Cabbage with vinegar Codfish, cured, dry. . . Eggs, fresh Liver, beefs, fresh Milk. . Sausage, fresh Beef, I'resh, lean, dry. . Bread, wheat, fresh. . . Butter Boiled..... Eaw Broiled.... Boiled .... Boiled.... Eaw Boasted... Boiled..... Boasted... Baked..... Boiled .... Boasted... Warmed... Broiled. . . . Boasted... Baked Cheese, old, strong Eggs, fresh Tapioca Milk Turkey wild Flounder, fresh. F-ied Stewed... Boiled .... Boiled.... Boiled.... Boiled.... Boiled .... Boiled .... Fried Boiled Boasted... Broiled . . . Boiled .... Boiled . . , Fried " domesticated Potatoes, Irish Potatoes, Irish Soup, mutton " oyster Parsnips Turnip flat Beets Meat hashed with j vegetables j Corn, green, & beans. . Beef, fresh, lean Fowls, domestic. Lamb fresh Goose Cake, sponge Yeal, fresh Cabbage-head . . Eaw Soup, beef, vegeta- } bles, and bread f Salmon salted Beans, pod Boiled .... Baked..... Fricasseed. Eaw Baw . . . Custard Chicken, full-grown . . Apples, sour, hard Oysters, fresh Heart, animal Beef, old, hard, salted Pork, recently salted. Cabbage, with vinegar Ducks, wild Pork, recently salted. Suet, mutton Boiled .... Fried Boiled Boasted... Boiled Boiled .... Fried Boasted . . . Boiled .... Boiled .... Bass, striped, fresh . . . Beef, fresh, lean, rare " steak Broiled.... Boasted... Broiled.... Baked Boiled Boiled soft Broiled.... Boiled .... Corn cake. Dumpling, apple Veal, fresh Pork, fat and lean Suet, beef fresh Tendon Mutton, fresh 651. Absorption from the Stomach. The power possessed by liquids and gases of penetrating and passing through membranes, is of the highest physiological importance ; indeed it is one of the primary conditions of life. The little cell, the starting-point of organization, is a closed bag without an aperture. All its nourishment must therefore pass through its membranous wall. So also with the perfect animal body. Currents and tides of juices are constantly setting this way and that, through the membranous sides of vessels. The liquefied food is destined to pass into the blood, but there is no open door or passage by which it can get there, and so it enters the circu- lating vessels by striking at once through their sides. In this way, water drank is absorbed by the minute veins distributed over the sur- face of the stomach, and enters the circulatory current directly. This 344 PHYSIOLOGICAL EFFECTS OF FOOD. is proved by the fact that when the outlet to the stomach is closed by tying the pyloric extremity, water which has been swallowed rapidly disappears from the organ, and medicines taken produce their effects upon the system almost as promptly as under natural circumstances. In the same way portions of sugar, lactic acid and digested nitro- genous substances, which are dissolved in water, pass into the blood by absorption through the stomach veins. The contents of the stomach thus leave it in two directions, a portion is absorbed through the coats of the organ, while the unabsorbed matters gradually ooze through the valvular opening that leads into the intestine. 4. THIED STAGE OF DIGESTION CHANGES OF FOOD IN THE INTESTINES. 652. Digestive Juices of tlic Intestinal Tnbe. The partially digested food dismissed from the stomach enters the duodenum, the first por- FIG. 118. Gall bladder Large intestines - Small intestines Coecnm Append ra of ^^~~ rxBcum Small intestines Digestive tract in man. DIGESTION CHANGES IN THE INTESTINES. 345 tion of the intestinal tract (small intestine). This is a tube about 20 feet in length, with a surface of some 3,500 square inches, and is the organ designed for finishing the digestive process. The general scheme of the digestive tract in man is exhibited in Fig. 118. Into the duodenum, and but a few inches from the valve of entrance, two small tubes (ducts) open, one leading from the liver and pouring in Vile, and the other from the pancreas, yielding pancreatic juice, the quantity of the former being much greater than of the latter. Both of these liquids are strongly alkaline from the presence of soda. The pancreatic juice much resembles saliva in properties; indeed the pancreas itself is so like the salivary glands as to be grouped with them. From the walls of the intestine there is also poured out a fluid called the intestinal juice. It is secreted in small but variable quantities, and is alkaline like the other secretions. 653. Changes in the Intestinal Passage. We find that the alkaline digestion of the mouth is now resumed. The starch is attacked ener- getically and rapidly changed into sugar, and that to lactic acid. The oily substances hitherto untouched by the digestive agents are now acted upon, not perfectly dissolved like the other alimentary matter but reduced to the condition of an emulsion, its particles being 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 constantly liable to escape through the pyloric gateway into the in- testines, it seems required that they should be capable, upon emer- gency, of completing the unfinished work, and such really appears to be the case. Although the secretions poured into the intestine are all distinctly alkaline, yet they convert sugar so actively into lactic acid, that the intestinal mass quickly becomes acidulous, strongly so, as it advances to the lower portion. The conditions are thus afibrded for the digestion of nitrogenous matters in the intestines, which is known often to take place, although their ordinary function is admitted to be digestion of non-nitrogenous substances, starch, sugar, and fat. 654. Absorption from the Intestine. The nutriment being finely dis- solved, is absorbed through the coats of the intestine, but not all in the same manner. Those substances which are completely dissolved in water, are taken up by the veins,, which are profusely distributed over the intestinal surface, while the oily and fatty matters, which are not so perfectly dissolved, are taken up by a special arrangement of vessels, called the lacteals, which are extremely fine tubes arising in the 15* 346 PHYSIOLOGICAL EFFECTS OF FOOD. intestinal coats. 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 lacteals is white, milk-like, and rich in oil. These veseels are gathered into knots (glands), so as to be greatly prolonged without consuming space. They finally gather into a tube (thoracic duct), and pour their contents into a large vein near the left shoulder. In its route, there is a disappearance of the large proportion of oil ; and albumen, which either entered from the intestine, or has afterwards transuded from the bloodvessels into the lacteals, is gradually changed to fibrin, the liquid acquiring the power of clotting or coag- ulating. 655. Constipating and Laxative Foods. The walls of the alimentary canal having absorbed from its contents such parts as are adapted for nourishment, there remains an undigested residue which passes at in- tervals from the bowels. The conditions of the intestines in reference to the retention or ready passage of excrementitious matters, is liable to variation from many causes. Amongst these, the nature of 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 OF A LAXATIVE TENDENCY. Bread and cakes, from fine wheaten "Wheaten bread and cakes from un- flour; rice, beans, peae, meats, eggs, tea, bolted flour, rye bread, corn bread, raw alcoholic drinks. sugar, (from the molasses it contains,) fruits, raw and cooked, and generally substances abounding in ligneous matter,as skins, cores, husks, bran, &c. ITS FINAL DESTINATION. 347 5. FINAL DESTINATION OF FOODS. 656. Digested alimentary matter enters the circulation and becomes BLOOD. This fluid is contained in a system of vessels, which extends to all parts of the body. It has been aptly called the floating capital of the system, lying between absorption and nutrition. Its quantity in an average-sized man is estimated at from 20 to 241bs. It is whirled as a rapid stream incessantly through the body, circulating round and round, so as to be brought into relation with all parts (624). 657. Composition of Blood. The composition of blood varies slightly with age, sex, constitution, and state of health ; it is also liable to acci- dental variations, as the supplies to it are periodic and fluctuating, while the draught upon it, though constant, is unsteady. It consists of about V8 per cent, water and 22 per cent, solid food dissolved in it. When evaporated to dry ness, the solid matter is found to consist of: Fibrin Albumen Gelatin 93 per cent. Fat, a little sugar, and a trace of starch 2 a Saline matter, crash 57 w Blood TlOO " 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 independent individual, which runs a definite career, is born, grows, performs its offices, and dies like the most perfect being, though the phy- siologist tells us that twenty millions of them perish at every beat of the pulse. Figs. 119 anvater, 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 with Ms utmost skill cannot imitate the first step in the chemistry of the plant. Every green leaf npon 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 upon. Carbonic acid is only decomposed in the leaf during the daytime by the power of light ; the effect is produced by solar radiations. All true aliments originate under these circumstances in vegetation. Though we consume flesh, we only go by the route of another animal back to the plant ; our food is all fabricated there. Animal life begins and is sustained by compounds which are the last and highest product of the creative energy of plants. The animal is nourished from its blood, but it does not in any sense produce it, it only gives it form ; the constituents of blood are generated hi 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 Force. Food represents force, but it is force in a state of equilibrium or rest, just like a pond of water enclosed on all sides. But if we make an outlet to the pond, its force at once becomes active and available. So the quiescent force of food is to become active animal power ; but how ? There enters the vital current incessantly from the outward world another stream of matter, not solid but gaseous, oxygen from the air, which came by the route of the lungs. It is the office of this agent to unlock the organic springs throughout the vital domain. We have stated before that oxygen is an agent of destruction (284) ; it is the foe of the organized state. The first step of growth, and the production of food in the leaf, con 350 PHYSIOLOGICAL EFFECTS OF FOOD. sisted in forcing carbon and hydrogen out of its grasp ; but in the ani- mal fabric it is destined to take possession of them again. The food, as we have seen, is not destroyed in digestion, it is only dissolved ; bul 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 decomposition of ali- ment, under the influence of inspired oxygen, bodily force originates. We see every day that steam power results from the destruction of 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 destruction. A portion of food, of course, serves to build up the bodily fabric, but it only continues in that state transiently ; it is all finally decomposed and dissevered into the simplest inorganic forms. 662. Destructive agency of Oxygen. The body is built of aliment, which gives rise by its destruction to force, but the immediate active agent which destroys the body, and thus develops force, is oxygen withdrawn from the air. From the moment of birth to the moment of death, every living animal is incessantly occupied in introducing this element into the body to maintain the conditions of force by its constant destructive action. If the current of oxygen flowing toward a 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 system, 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 emaciated, yet the waste must proceed if life is to last. The brain is attacked, its offices disturbed, delirium supervenes, and there is an end of life. We call this starvation; it is a conditim in which " atmos- pheric oxygen acts like a sword, which gradually but irresistibly pen- ITS FINAL DESTINATION. 351 ttratcs to the central point of life, and puts an end to its activity." (LIEBIG.) Had food been regularly introduced, it would have opposed a constant resistance to that agent, that is, it would have offered itself for destruction and for repair, and thus have protected the system from the fatal inroading effects of oxygen. 663. Combustion within the Body. The term combustion 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
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 all compounds of nitrogen are, compared with other bodies, difficultly combustible, and are never regarded as fuel, because when they do burn, they develop a low degree of heat, not sufficient to raise the adjacent parts to the kindling point. So with albuminous principles in the blood and tissues ; they are placed so low in the scale of com- bustibility, that the other group of aliments is attacked and destroyed first. " Without the powerful resistance which the nitrogenous con- stituents of the body, in consequence of their peculiar nature as com- pounds of nitrogen, oppose, beyond all other parts, to the action of the air, animal life could not subsist. Were the albuminous compounds as destructible or liable to alteration by the inhaled oxygen, as the non-nitrogenous substances, the relatively small quantity of it daily supplied to the blood by the digestive organs, would quickly disappear, and the slightest disturbance of the digestive functions would, ol ne- cessity, put an end to life." (LIEBIG.) 666. Heat-producing and Tissue-making Foods. In considering the final uses of foods, we are to preserve the distinction with which we began. The non-nitrogenous aliments, by their ready attraction for axygen, seem devoted to simple combustion in the system, with only die evolution of heat ; while the albuminous compounds are devoted rEODucnoN OF BODILY WABMTH. 353 to the production of tissue. The first class is hence called the heat- producing^ calorifient, or respiratory aliments, while the second is designated as the tissue-forming, plastic, or nutritive aliments (430). This distinction is to be received with due limitation, for on the one hand, fat, which stands at the head of the heat-producers, is deposited and retained in the cells of the tissues, without being immediately con- suined ? and probably serves other important purposes beside produc- ing heat (722) ; on the other hand, some nitrogenous substances (a 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 LIEBIG. 6. PEODUOTION OF BODILY WABMTH. 667. Constant Temperature of the Body. The influence of tempera- ture over chemical transformations is all-controlling ; they are modified, hastened, checked, or stopped, by variations in the degrees of heat. The living body is characterized by the multiplicity and rapidity of its chemical transmutations. Indeed, the whole circle of life-functions is dependent upon the absolute precision of rate with which these vi- tal changes take place. A standard and unalterable temperature is therefore required for the healthy animal organism, as a fundamental, controlling condition of vital movements a certain fixed degree of heat to which all the vital operations are adjusted. This standard temperature of health in man, or blood heat, varies but slightly from 98, the world over. Yet the external temperature is constantly changing, daily with the appearance and disappearance of the sun, and annually with the course of the seasons. We are accustomed to fre- quent and rapid transitions of temperature, from 30 to 60 degrees, by the alternations of day and night, sudden changes of weather, and by passing from warmed apartments into the cold air of winter. The circle of the seasons may expose us to a variation of more than a hundred degrees, while the extreme limits of temperature to which man is nat- urally sometimes subjected in equatorial midsummer, and arctic mid- 354 PHYSIOLOGICAL EFFECTS OF FOOD. winter, embrace a stretch of more than 200 of the thermometric scale Yet through all these thermal vicissitudes, the body of man in health varies but little from the constant normal of 98. 668. How the Body loses Heat. In view of these facts, it has been maintained that the living body possesses some vital, mysterious, in- ternal defence against the influence of external agents; indeed, that it is actually emancipated from their effects. But this is wholly errone- ous ; the body possesses no such exemption from 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 8^ Ibs. 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 (T97). "We shall appre- ciate the extent of this cooling agency, by recalling what was said of the amount of heat swallowed up by vaporization (68). The water of the body at 98 receives 114 of sensible heat, and then 1000 of latent heat, before it is vaporized; hence it carries away 1114 of heat from the body. 669. How the Body produces Heat. To keep the system up to the standard point, notwithstanding this rapid and constant loss, there must be an active and unremitting source within. Heat-force cannot be created out of nothing ; it must have a definite and adequate cause. PRODUCTION OF BODILY WAEMTU. 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 distinctive character of breathing, with the equally distinctive character of greater warmth ; to suppose that the incessant breathing so necessary to life, is the source of the equally incessant supply of heat from within, so necessary also to the continuance of life ; and this connection is placed, beyond all doubt, when we attend to the physical circumstances by which the change of starch and fat into carbonic acid and water is accompanied in the external air. If we burn either of these substances in the air or in pure oxygen gas, they disappear and are entirely transformed into carbonic acid and water. This is what takes place also within the body. But in the air, this change is accompanied by a disengagement of heat and 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 would soon become cold and stiff. The formation of carbonic acid and water, therefore, continually goes on ; and when the food ceases to supply the materials, the body of the animal itself is burned away, so to speak, that the heat may still be kept up. (JOHNSTOX.) There are certain periods in the history of the plant, as germination and flowering, when oxy- gen is absorbed, combines with sugar and starch, and produces car- bonic acid and water. In these cases, the temperature of the seed and the flower at once rises, and becomes independent of the sur- rounding medium. 670. Effect of breathing ratified Air. The doctrine, that animal heat is due to oxidation in the system, is strikingly illustrated 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, th effect upon the system has been graphically expressed as * a cold to the marrow of the bones,' a difficulty of making muscular exertion is ex- perienced ; the strongest man can scarcely take a few steps without resting ; the operations of the brain are interfered with ; there is a pro- pensity to sleep. The explanation of all this is very clear. In the accustomed volume of air received at each inspiration, there is a less quantity of oxygen in proportion as the altitude gained is higher. Fires can scarce be made to burn on such mountain tops ; the air is 356 PHYSIOLOGICAL EFFECTS OF FOOD. too thin and rare to support them ; and so these combustions which go on at a measured rate in the interior of the body, are greatly re- duced in intensity, and leave a sense of penetrating cold. Such jour- neys, moreover, illustrate how completely the action of the muscular system, and also of the brain, is dependent on the introduction of air and under the opposite condition of things, where men descend in diving-bells, though surrounded by the chilly influences of the water, they experience no corresponding sensation of cold, because they are breathing a compressed and condensed atmosphere. (Dr. DEAPEE.) 671. How the unequal demands for Heat are met. The steady main- tenance of bodily heat being a matter of prime physiological necessity, we find it distinctly and largely provided for by a class of foods pre- pared in plants and devoted to this purpose. Much the largest por- tion of food consumed by herbivorous animals, and generally by man, is burned at once in the blood for the production of heat. But there are varying demands upon the system at different places and seasons, and the provision for these is wise and admirable. First, as the cold increases, the atmosphere becomes more dense, the watery vapor is reduced to its smallest proportion, and pure air occupies its place, so that breathing furnishes to the body a considerably higher per- centage of oxygen in winter than in summer, in the colder regions of the north, than in the warmer vicinity of the equator. On the other hand, there is an important difference among the heat-producing principles of food. They vary widely in calorific power. The fats and oils head the list ; they consist almost entirely of the two highly combustible elements, carbon and hydrogen, containing from 77 to 80 per cent, of the former, to 11 or 12 of the latter. Starch occurs next in the series, then the sugars, and lastly the vegetable acids and lean meat. LIEBIG states their relative values, or power of keeping the body at the same temperature during equal times, as follows : To produce the same effect as 100 parts of fat, 240 of starch will be required, 249 of cane sugar, 263 of dry grape sugar and milk sugar, and 770 of fresh lean flesh. "We shall illustrate this point more clearly, when we come to speak of the nutritive value of foods (743). A pound of fat thus goes as far in heating as 2f Ibs. of starch, or 7 T 7 F Ibs. of muscular flesh. In regions of severe cold, men instinctively resort to food rich in fatty matters, as the blubber and train oil, which are the staples of polar diet. Bread, which consists of starch and gluten, and which, therefore, as shown by the above illustration, falls far be- low oleaginous matter in calorifying power, is found to be very insuffi- cient in the arctic regions for the maintenance of animal heat PRODUCTION OF BODILY WAEMTH. 367 All breads are, however, not alike in this respect, for the Hudson's Bay Traders have found, according to Sir JOHN RICHABDSON, that Indian corn bread, which contains about nine per cent, of oil, is de- cidedly more supporting than wheaten bread. Dr. KANE, in the nar- rative of his last arctic expedition, remarks : " Our journeys have taught us the wisdom of the Esquimaux appetite, and there are few among us who do not relish a slice of raw blubber, or a chunk of frozen walrus beef. The liver of a walrus, eaten with little slices of his fat, of a verity it is a delicious morsel. The natives of South Greenland prepare themselves for a long journey in the cold by a course of frozen seal. At Upernavick they do the same with the norwhal, which is thought more heat-making than the seal. In Smith's Sound, where the use of raw meats seemed akt ost inevitable, from the modes of living of the people, walrus holds the first rank. Certainly, 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 abundance, and in which the carbonaceous matter, according to LIEBIG, falls as low as 12 per cent. The demands of ap- petite seem to correspond closely with the necessities of the system ; for while oranges and bread-fruit would be but poor dietetical stuff for an Icelander, the "West Indian would hardly accept a dozen tallow candles as a breakfast luxury ; but reverse these conditions and both are satisfied. A knowledge of the calorifying powers of the various elements of food, and of the proportions in which they are found, enables us to modify our diet according to the varying temperature of the seasons. 672. Regulation of Bodily Temperature. The question naturally arises, why is it that when the external temperature is 100 and even higher for a considerable time, and the system is constantly generating ad- ditional heat, that it does not accumulate, and elevate unduly the bodily temperature? How is it constantly kept down in health to the limit of 98 ? This is effected by the powerful influence of evapo- ration from the lungs and skin, already referred to in speaking of the way the body loses heat (668). The large amount of water daily drank and taken hi 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. summer, much water evaporates from tlie skin, and a corresponding]} 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. Houses and Clothing replace Food. We have seen that the neces- sity for the active generation of heat within the body is in proportion to the rapidity of its loss. If the conditions favor its escape, more must be produced ; if on the other hand the surrounding temperature be high, the loss is diminished, and there is less demand for its evo- lution in the body. We have also described the various expedients by which heat is produced in our dwellings in winter, thus forming an artificial summer climate. Clothing also acts to protect the body from loss, and enable it to preserve and economize the heat it gen- erates. Hence in winter we infold ourselves in thick non-conducting apparel. Clothing and household shelter thus replace aliment ; they are the equivalents for a certain amount of food. The shelterless and thinly clad require large quantities of food during the cold of winter to compensate for the rapid loss of heat. They perish with the same supply that would be quite sufficient for such as are adequately clothed and well-housed. " It is comparatively easy to be temperate in warm climates, or to bear hunger for a long time under the equator ; but cold and hunger 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 npon mortality becomes less apparent, so that at the age of from 25 to 30 years, the difference 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- elines, old people draw near the fire and complain that ' their blood is PRODUCTION OF BODILY WAKMTH. 359 chill. 1 The Brussels statistics show that the mortality oetween 50 and 65 is nearly as great as in early infancy ; and .'t 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 Temperature. The heat of inani- mate objects, as stones, trees, &c., rises and falls with the daily varia- tions of temperature. The living body would do the same thing if it did not produce its own heat independently. If we disturb the calo- rifying process, the body becomes immediately subjected to the muta- tions of external heat. In starving animals, this temperature rises and falls with the daily rise and nightly fall of the thermometer, and this response of the living system to external fluctuations of heat is more and 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. DRAPER 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 Jcind, but also the time. It seems to be against our instinct to commence the morning with a heavy meal. We "break fast, as it is significantly termed, but we do no more ; postponing the taking of the chief supply until dinner, at the middle or after part of the day. I think there are many reasons for supposing, when we recall the time that must- elapse between the taking of food and the completion of respiratory digestion, that this distribution of meals is not so much a matter of custom, as an instinctive preparation for the systematic rise and fal? 860 PHYSIOLOGICAL 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 midnight." 7. PKODTTCTION OF BODILY STRENGTH. 676. Amount of mechanical force exerted by the Body. We have seen how the double stream of alimentary and gaseous matter which enters the body incessantly gives rise to heat, an agent which we every day convert into mechanical power through the medium of the steam engine. Sufficient heat is produced in this way annually by an adult man, if it were liberated under a boiler, to raise from 25,000 to 30,000 Ibs. 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 hundred thousand gallons of air in the course of a year. At the same time the heart contracts and dilates forty millions of times each time with an estimated force of 13 Ibs., 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 his body through 10,000 feet in a day. SMEATON states, that working with his arms he can produce an effect equal to PRODUCTION OF BODILY STRENGTH. 361 raising 370 Ibs. ten feet high, or 3,700 Ibs. one foot high in a minute for eight hours in the day. 677. Tissues destroyed in producing Force. The expenditure of force in labor, if not accompanied by a sufficiency of food, rapidly wears down the system, there is a loss of matter proportioned to the amount of exertion, and which can only be renewed by a correspond- ing quantity of nourishment. The parts brought into action during exercise are of course those possessing tenacity, firmness, and strength ; that is, the tissues and organized structures. The unorganized parts, such as 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. CHOSSAT ascertained the waste in various animals to be an average of l-24th part of their total weight daily ; and SCHMIDT deter- mined it to be, in the case of the human being, l-23d of the weight. Professor JOHNSTON says : " An animal when fasting will lose from a fourteenth to a twelfth of its whole weight in twenty-four hours. The waste proceeds so rapidly that the whole body is now believed to be renewed in an average period of not more than thirty days. 678. Destination of the Nitrogenons 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 ^ 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 PHYSIOLOGICAL EFFECTS OF FOOD. the porous shell, under the influence therefore of the same conditions which accompany respiration, all the tissues, membranes and bones, (by the aid of lime from the shell,) are developed. The foundation material from which they are all derived is albumen, and it is the same with the growth and constant reproduction of our own bodies during life. The course of transformation by which albumen is con- verted into the various bodily tissues, has not yet been certainly traced. But it is now universally agreed that it is the nitrogenous principles of food, those of low combustibility, which are employed for the nutrition of animal structures the reparation of tissue- waste. Those substances furnish the instruments of movement, and minister directly to the production of mechanical force. Their design is two- fold, to form and maintain the bodily parts in strength and integrity, and to be finally destroyed for the development of power. 679. Action of Oxygen upon the Tissues. Oxygen plays the same im- portant part in tissue destruction as in the simple development of heat by combustion of respiratory food. It is the agent by which the moving parts are decomposed and disintegrated. The muscles are paralyzed if the supply of arterial blood containing the oxygen which is to change them, and the nutritive matter which is to renew them, be cut off. On the other hand, if there is rapid muscular exercise and consequent waste, the circulation is increased and the breathing quickened, by which the supply of oxygen is augmented. The changes of the tissues in action are, moreover, retrogressive, and downwards to simpler and simpler conditions. The products of metamorphosis are oxidized, and then made soluble in the blood by which they are promptly conveyed away, and thrown out of the body by the liquid excretion. It is thus that oxygen, by slow corrosion and burning of the constituents of the muscles, gives rise to mechanical force. But oxidation is invariably a cause of heat ; decomposition of the tissues, therefore, must develop heat at the same time with me- chanical 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 all the atoms of tissue indiscriminately, or upon those which it finds next before it. There is a wonderful selective power, some particles are taken and others left. Those only are seized upon which in some unknown way, perhaps under the regulating influence of the nervous system, are made ready for change. 680. Relation between Waste and Snpply. If an organ or part be the PRODUCTION OF BODILY STRENGTH. 36li 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. Still, in the case of these parts, the equipoise between waste and supply may be lost, as in bodily growth when nutrition exceeds decomposition, or in deficiency of nutriment, when destruction proceeds at the expense of the tissue, which loses weight faster than the food renews it. As re- gards the waste and renovation attending voluntary movement, there is the same periodicity. Destruction gains upon nutrition during the exercise of the day, and what was lost is regained by nutrition during rest at night. In sleep, nutrition is at its height while waste falls to its minimum. As bodily exertion costs tissue destruction, which can only be made good again by albuminous substances, it follows that these will be demanded for food, in proportion to the amount of effort expended. If such food be not adequately supplied, or if from any cause the body be incapable of digesting or assimilating it, the apparatus of force begins at once to give way, the acting tissues shrink and fail, for human effort is carnivorous, flesh-consuming. If, on the other hand, the system is main- tained at rest, that is, if force is not exerted, the nutriment is not used or expended, but is laid up in the body, and serves to increase the mass. 681. Hastening and retarding tissue changes. Ingested substances have a twofold relation to waste or metamorphosis of the tissues. Some, as we have seen, become portions of the animal solids, and then un- dergo transformation. Others have the power of modifying or con- trolling these changes, without in the same way participating in them. Some of these increase metamorphosis, and others check it. Common salt, for example, and an excess of water, act as hasteners of tissue change, while alcohol and tea act as arresters of metamorphosis. li we consume those substances which augment the waste, it is said we require a fuller diet to compensate for the extra loss, or the body de 364 PHYSIOLOGICAL EFFECTS OF FOOD. clines in weight with more rapidity than otherwise. If we employ the arresters of metamorphosis, we are supposed to have tissue, and can maintain our usual strength and weight on a more slender diet. That certain substances produce these effects, may be regarded as establish- ed, but it cannot be admitted that they are proper aliments. "We re- cognize transformation of the living parts, as the highest and final physiological fact, the necessary condition of human activity. Dr. 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 cautious about theoretically prejudging any substance ; whether it be beneficial or injurious is as- oertainable only by careful observation and experience of its effects. 8. MIND, BODY, AND ALIMENT. 682. Blind brought into relation with Matter. In his ultimate destiny, we contemplate man as an immortal spirit, but in the Divine arrange- ment, that .spirit is to be educated and prepared in nature and time for its onward career. Spirit or mind partakes in nothing of the attri- butes of matter, but it corresponds closely to our conception of force. The passions are regarded as the mind's motors, or motive powers. The directive or governing element we call will, or will-power. We speak constantly of intellectual force, and mental energy, and regard Lhe 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- con trolling activity of the universe, so the mind of man, created in his Maker's Image, is perpetually demonstrating an over-mastering con- ' trol of tlie 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. 668. Mental Exercise destroys Nervous Matter. Of the nature of this MLND, BODY, AND ALIMENT. 365 union, Twio it is accomplished, we know nothing, but some of its con- ditions are understood. "We are certain that the brain and nerves wear and waste by exercise, and require renewal, just like all the other tissues. Nervous matter in this respect is no exception to the general law of the organism. The external universe pours in its im- pulses through all the avenues of sense, along the nerve routes to the cen- tral seat of consciousness, the brain ; while the mind, exerting itself through that organ, and another system of nerves, calls the muscles into action, and produces its thousand-fold effects upon external objects. In both cases there is decomposition and loss of nerve-substance, and there must, therefore, be a nutrition of brain and nerves, as truly as of any other part ; nay, more truly, for destruction and renovation are perhaps more active in these parts than in any others. Arterial blood, with its agent of disorganization (oxygen), and its materials of repair, are sent to the brain in a far more copious flood than to any other equal portion of the body. Blood-vessels are also distributed most abundantly around the nerves, so as to effect their nutrition in a perfect manner ; while if the vital stream be checked or arrested, the nerve loses its power of conducting impressions, and the brain its capacity of being acted upon by the mind ; the interruption of the blood-stream through this organ producing instantaneous unconscious- ness. Besides, the nerve-tissue consists of the most changeable mate- rials, 70. to 80 per cent, water, 10 of albumen, and 5 to 8 of a peculiar oily or fatty substance, with various salts. It is interesting to re- mark, that in starvation the parts are disorganized and consumed in the inverse order of their physiological values. First, that which is of lowest service, and can be best spared ; the fatty deposits are wasted away, then the muscular and cellular tissues, and lastly the nervous system, which remains undisturbed and intact until the dis- organization of other parts is far advanced. The mind's throne is the last part invaded, and the last to be overturned. "We are struck with the wisdom of this arrangement, but we cannot explain it. 684. Can we measure Brain and Nerve waste ? The appropriation of certain specific parts to certain purposes, is the basal fact of physiolo- gy. A part may indeed perform several 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- 866 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 its exercise. But the results yet obtained are probably only approaches to the truth. Thus, urea is undoubtedly a result of muscular change, and some have regarded its amount in the renal ex- cretion as an index to the degree of muscular exercise. But others affirm that it may also come from unassimilated food, as well as active muscle, which casts a doubt over conclusions thus formed. In +he same way, salts of phosphoric acid have been regarded as the peculiar products of brain and nerve waste, and their amount in the kidney evacuations, as a measure of the exercise of brain and nerves. From the researches of Dr. BENSE JONES, it appeared that where there is a periodical demand upon the mental powers (as among clergymen, for example, in preparation for their Sunday exercises), there is a corre- sponding rise in the quantity of alkaline phosphates voided by the renal organs. Yet here, too, there is uncertainty, for we are not sure that these phosphatic salts may not have other sources also. 685. The Mind's action wears and exhausts the 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 BO imperfectly as to produce morbid and unsound tissue, which can only be restored to the healthy state by long mental tranquillity and cessation of effort. 686. The Phosphatic constituents of Brain. We have spoken of the phosphates as special products of brain and nerve waste. That phos- MIND, BODY, AND ALIMENT. 36 1 phorus, in some state, or combination, is a leading ingredient of nervona and cerebral matter, is unquestionable ; and that it stands related in some way to the fundamental exercise of those parts, will hardly be doubted. "We remember that it is a very remarkable element, shining in the dark (from which it takes its name), and having a most powerful attraction for oxygen, combining with a large amount of it, and generating phosphoric acid with intense heat *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'HEEITIEE'S analysis of nervous mat- ter (quoted by standard physiological authorities), it is stated that the proportion of phosphorus in infants is O80 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, 4 no phosphorus, no thought;' LIEBIG, 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. No one has ever yet detected phosphorus in any part of the body, of the brain, or of the food, in any other form than that of phosphoric acid." As phosphorus and phosphoric acid, in their properties, are as wide asunder as the poles of the earth, it is highly incorrect to use the terms interchangeably, or (according to the statement of LIEBIG) to apply the term phosphorus in this con- nection. It may be remarked that the phosphoric compound is a con- stituent of the oily matters of nerve tissue, which are hence called ' phosphorized fats.' 687. Arc there special Brain Nutriments. 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* terinined facts. "We are not authorized by science to prescribe a diet 368 PHYSIOLOGICAL EFFECTS OF FOOD. specially or peculiarly constructed to promote brain nutrition and pro tract mental exercise. But while it would seem as if care had been taken to secure these high results in the universal constitution of food, still it is certainly in accordance with analogy, that specific aliments should be adapted, or at all events lest adapted, to produce certain kinds of effect in the system. Special means for special ends make up the unitary scheme of the living economy. The waste produced by mental exertion is repaired only by food, but to say by all food alike transcends the warrant of science. Professor LIEBIO remarks, " It is certain that three men, one of whom has had a full meal of beef and bread, the second cheese or salt fish, and the third potatoes, regard a difficulty which presents itself from entirely different points of view. The effect of the- different articles of food on the brain and nervous system is different, according to certain constituents peculiar to each of these forms of food. A bear kept in the anatomical department of this university, exhibited a very gentle character as long as he was fed exclusively on bread. A few days' feeding with flesh rendered him savage, prone to bite, and even dangerous to his keeper. The carni- vora are, in general, stronger, bolder, and more pugnacious than the herbivorous animals on which they prey ; in like manner those nations which live on vegetable food differ in disposition from those which live chiefly on flesh. The unequal effects of different kinds of food, with regard to the bodily and mental functions of man, and the de- pendence of these on physiological causes, are indisputable ; but as yet the attempt has hardly been made to explain these differences accord- ing to the rules of scientific research." 688. Diet of Brain-workers. Yet the diet of the literary, of artists, and those who devote themselves to intellectual labor, is by no means 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 error, on the other hand, of excessive eat- ing, the fruitful cause of dyspepsia, and numerous ailments of the sed- entary. The best condition of mind corresponds with the most healthy and vigorous state of body. The blood prepared by the di- gestive and pulmonary organs, and taking as it were its quality an<3 temper from the general state of the system, nourishes the brain and influences the mind. That diet and regimen are therefore best for thinkers, which maintain the body in the most perfect order. They should select nutritious and easily digestible food, avoiding the more refractory aliments, leguminous seeds, heavy bread, rich pastry, &c. INFLUENCE OF SPECIAL SUBSTANCES. 369 689. Men seek for Brain Excitants. Although specific brain nutri- ents and thouglit-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 (JiascfiisTi), is chewed and smoked among from two to three hun- dred millions of men. The betel 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'? inhabitants. These substances act powerfully, although somewhat differently, upon the nervous system, and thus directly affect the state of the mind and feelings. We here touch upon the myste- rious world problem of narcotism; but its discussion, though of abscib- ing interest, would be too extensive for our limits, besides being for- eign to the present inquiry, which is restricted to the general subject of foods. The effects of tea and coffee will be noticed when speaking of drinks (704). 9. INFLUENCE OF SPECIAL SUBSTANCES. A. Saline Matters. 690. The Ash elements of Food essential to Life. When vegetable sub stances are burned, there remains a small portion of incombustible mineral matter. It was formerly thought that this consisted merely of contaminations from the soil, which happened to be dissolved by water that entered the roots, and was therefore present in the vegeta- ble by accident. We now understand that such is far from being the fact. The ash-principles of food are indispensable to animal life. In- deed, without them neither group of the alimentary substances which we have been considering could do its work. It has been found, in numerous experiments, made upon the lower animals, that neither gluten, casein, albumen, sugar, oil, nor even a mixture of these, when deprived as far as possible of their mineral ingredients, are capable of sustaining life ; the animal thus fed actually perishes of starvation. 691. Acids, Alkalies, Salts. We remember that acids are bodies hav- ing the power of turning blue test paper red, and that alkalies change the red to blue. They also combine together, each losing its peculiar properties, and produce salts. If the properties of the acid and alkali both disappear, the salt produced is neutral, that is, neither acid nor 16* 370 PHYSIOLOGICAL EFFECTS OF FOOD. alkaline. If the acid be stronger, or there be a double 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 all the effects of acidity ; if an alkaline salt, the liquid will be alkaline, producing alka- line effects. The ash of foods consists of potash, soda, lime, magnesia, oxide of iron, sulphuric, carbonic and phosphoric acids, silica and com- mon salt. Fruits abound in acid salts, that is, powerful organic acids, as oxalic, tartaric, and malic acids, with potash and lime ; the acids be- ing in excess. When fruits are burned, the organic acids are consumed or converted into carbonic acid, and the salts become carbonates neu- tral carbonates of lime or alkaline carbonates of potash. The quanti- ties of salts, alkalies, and alkaline earths contained 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 per cent. 692. The Ashes of the Food are Assimilated. When the organic mat- ter of food is burned away in the system, a residue of ashes is left, just as in open combustion in the air. But they are not cast at once from the body as useless, foreign, or waste matters. They have im- portant duties to perform as mineral substances, after being set free from organized compounds ; and they hence remain dissolved in the blood and various juices of the system. Portions of these mineral matters are constantly withdrawn from the circulation, some at one point and some at 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 coloring matter within the eye. 693. The Blood Alkaline, and why ? But there remains constantly dissolved in the blood and animal juices, a proportion of acids, al- kalies, and salts, which impart to these liquids either acid or alkaline properties. The result, however, is not left to accident. Whether a liquid be acid or alkaline is of essential importance in refer- ence to the offices it has to perform. We have seen that it is the determining fact of the digestive juices ; one is always acid, and the other alkaline, and their peculiar powers depend upon these properties. So with the blood. It contains potash, soda, lime, mag INFLUENCE 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 blood of all animals is invariably alkaline. An alkaline condition is indispensable to the action of this fluid. LIEBIG remarks, u The free alkali gives to the blood a number of very remarkable properties. By its means the chief constituents of the blood are kept in their fluid state, the ex- treme facility with which the blood moves through the minutest ves- sels, is due to the small degree of permeability of the walls of these vessels for the alkaline fluid. The free alkali acts as a resistance to many causes, which, in the absence of the alkali, would coagulate the albu- men. The more alkali the blood contains, the higher is the tempera- ture at which its albumen coagulates ; and with a certain amount of alkali, the blood is no longer coagulated by heat at all. On the al- kali depends a remarkable property of the blood, that of dissolving the oxides of iron, which are ingredients of its coloring matter, as well as other metallic oxides so as to form perfectly transparent solu- tions." Alkali in the blood also promotes the oxidation of its consti- tuents. A number of organic compounds acquire by contact with, or in presence of, a free alkali, the power of combining with oxygen (burning), which alone they do not at all possess at. the ordinary temperature of the air, or at that of the body. (CHEVEEUL.) The alkalies of the blood exert a precisely similar action, increasing the combustibility of the respiratory foods. 694. Flesh and its Juices, 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 (590). "We may now consider its action in the system. It la 372 PHYSIOLOGICAL EFFECTS OF FOOD. a large and constant ingredient of the blood, forming nearly sixty pe/ 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. It 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 effected in the system, indeed there is no other source for the hy- drochloric acid of stomach digestion. The considerable quantity of soda in the bile and pancreatic juice, which serve for intestinal diges- tion, as well as the soda of the alkaline blood, are chiefly derived from common salt. A portion comes directly from the food, but by no means sufficient for the wants of the body. Yet it is highly probable, that in the econony of the system, the same materials are used over and over, the acid of the stomach, as it flows into the intestine, com- bining with the soda it finds there, and reproducing common salt, which is absorbed into the blood, decomposed, and yielded again to the digestive organs. "We recollect that common salt consists of chlorine and sodium ; it is a chloride of sodium. Chloride of potassium is another salt of apparently quite similar properties. Yet in their physiological effects, they are so different, that while chloride of sodium exists largely in the blood, it is not present in muscles or juice of flesh, chloride of potassium being found there. They seem to have distinct and different offices, and are not replaceable. But the chlo- rine of the chloride of potassium comes from common salt. It may be remarked, that as phosphate of soda exists in the blood, phosphate of potash belongs to flesh-juice and muscles. 696. 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 contain the least amount of common salt, roots vary in their quantity, INFLUENCE OF SPECIAL SUBSTANCES. 372 turnips having hardly a trace. Yet much depends upon its abundance in the soil, and even in the atmosphere ; the air near the sea being saline from salt vapor. Plants near the sea are richer in soda than those grown inland, the latter abounding in potash. When we reflect upon the importance of the duties of salt in the organism, and that its necessary proportion in the blood is so much larger than in the food, often tenfold greater and besides, that its quantity is extremely vari- able in our aliments, its almost universal use as a condiment, will not surprise us. The craving for it is very general probably instinctive but where it does not exist, we conclude, either that sufficient is furnished naturally in the food and drink, or that animals suffer for the want of it. The quantity annually consumed by each individual in France, has been estimated at 19| Ibs; in England at 22 Ibs. 697. Effects of too little and too much Salt. From what has been said, we see that a due supply of salt is of the first necessity ; its de- ficiency in diet can only prove injurious. The most distressing symp- toms, ending in death, are stated as the consequence of the protracted use of saltless food. The ancient laws of Holland " ordained men to be kept on bread alone, unmixed with salt, as the severest punish- ment that could be inflicted upon them in their moist climate ; the effect was horrible ; these wretched criminals are said to have been devoured by worms engendered in their own stomachs." Taken into the system in large quantity (a table spoonful), it excites vomiting ; when thrown into the large intestines, it purges. A too free use of salt engenders thirst ; in moderate quantities, it increases the appetite and aids digestion. A long course of diet on provisions exclusively salt-preserved, produces the disease called scurvy. This condition of body is believed by some to be due to a deficiency of potash com pounds in the system, as in the act of salting, various valuable ali ments are abstracted (593). Potatoes, and vegetables rich in potash are excellent antiscorbutics correctives of scurvy. Fresh flesh yieldr potash to the system unequally ; for in that of the ox, there is three times, in that of the fowl, four times, and in that of the pike, five times as much potash as soda. Experiments relating to the influence of com- mon salt upon animals, have given somewhat discordant results. In some cases, it improved their appearance and condition decidedly ; 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 metamorphosis of the body ; so that a free use of it would only be consistent with a liberal diet. 374 PHYSIOLOGICAL EFFECTS OF FOOD. 698. Carbonates of Soda and Potash. The exclusive employment of these substances in extemporising light bread (509), makes a reference to their physiological action necessary. Carbonate of potash in itf crude shape, appears aspearlash; in its more purified form it issaleratus. 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 oy the carbonic acid united with them. The potash compounds are the strongest, those of soda being of the same nature but weaker. Yet the system, as we have just seen, recognizes essential differences be- tween them ; one pertains to the blood and the other to the flesh. According to the theory of their general use for raising bread, they ought to be neutralized by an acid, muriatic, tartaric, acetic, or lactic, thus losing their peculiar properties and becoming salts. These changes do take place to a certain extent, and the saline compounds formed, are much less powerful and noxious than the unneutralized alkalies ; their effects are moderately laxative. Yet, in the common use of these substances, as we have stated, the alkali is not 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. Liquid Aliments. 699. Physiological importance of Water. Water is the most abundant compound in the body, constituting 80 per cent, of the blood, and 75 per cent, of the whole system, in importance to life it ranks next to oxygen of respiration. An adult 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 universal beverage furnished by nature, for all living beings, and exists in greater or less proportion, as we have INFLUENCE OF SPECIAL SUBSTANCES. 375 seen, in all solid food. Vegetables and meats are, at least, three- fourths water ; while bread is about 45 per cent, or nearly one half. Athough there is a little water even in the dryest food, yet the demand for it is so great, and its consumption so rapid, that our mixed ali- ments do not furnish sufficient, while the most nutritious, are the most provocative of thirst. Hence, we daily drink large quantities of it in the free or liquid condition. TOO. 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 -a in the world of commerce, it is an agent of transportation. Its par- ticles glide so freely among each other, as easily to be put in motion, which makes it a perfect medium of circulation, and transportation of atoms. It is the largest constituent of the fleshy parts, serving to give them fulness, softness, and pliancy. Water is a vital and essen- tial portion of the animal structure, but hardly an organized constitu- ent. It is intimately absorbed and held in a peculiar mechanical combination, which permits of separation by pressure. " The milk- white color of cartilage, the transparency of the cornea, the flexibility and elasticity of muscular fibre, and the silky lustre of tendons, all depend on a fixed proportion of water in each case." 701. Water generated in the Animal System. Water in large quantities is as necessary to plants as to animals ; but it serves an important pur- pose in the vegetable world, which it does not, or but to a 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 thus produce water. Hydrogen and oxygen combine continually in the combustion of food, so that in reality, a considerably larger quantity of water is excreted from the system, than was introduced into it hi that form. 702. Influence of Water npon Digestion. We have referred to the remarkable solvent powers of water (367). If we could look into the living organism, we should see that its whole scheme is but an illus- tration of it. Blood, juice of flesh, bile, gastric and pancreatic fluid, saliva, mucus, tears, perspiration, and all other 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 EFFECTS OF FOOD. taken. The first effect will be a dilution of the gastric juice of the stomach, but the water is rapidly absorbed into the blood, which 18 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. CHAMBEES, 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 all without a much more fluid diet than is usual among heal- thy persons." 703. Water influences change of Tissue. Beyond digestion is meta- morphosis of structure, and this is influenced by the amount of watei drank. Kecent careful experiments by Dr. BOCKEE, performed upon himself, show that the use of any quantity of water above the actual demand of thirst, and the essential wants of the system, increase the transformations of the solid parts of the body. He first ascertained what quantity of food and drink was just sufficient to satisfy his appe- tite and cover the losses of the system. He then found that by con- tinuing the same quantity of food, and increasing the proportion of water, the weight of the body constantly diminished. The excess of water increased the waste, so that the same food would no longei restore it the balance inclined on the destructive side. Neither thi 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 taken in the form of infusions, th* composition and preparation of which have been described (551). They are allied to foods by whatever nutritive constituents they hap- pen to have, which are inconsiderable, and they are distinctly separa- ted from them by possessing certain additional qualities which do not pertain to nutriment. The ingredients to which tea and coffee owe their peculiar action are thein and cafein, tannic acid and volatile or empyreumatic oiL INFLUENCE OP SPECIAL SUBSTANCES. 371 705. Effects of Tea. Though tea is so universally employed in diet, yet its effects upon the constitution are by no means precisely ascer- tained. Its tannic acid gives an astringent taste, and a constipating in- fluence in the intestines. It also acts as a diuretic. Thein and vola- tile oil of tea are its most active 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 theii discrepant statements. If the quantity of thein contained in an ounce of good tea (8 or 10 grains), be taken, unpleasant effects come on, the pulse becomes more frequent, the heart beats stronger, and there ia trembling of the body. At the same time the imagination is excited, the thoughts wander, visions begin to be seen, and a peculiar state oi intoxication supervenes; all these symptoms are followed by, and pass off in, a deep sleep. Dr. BOCKEE has made several careful sets of ex- periments upon his own person to determine the physiological effecta of tea. He took exact account of the quantity of aliment ingested, oi the substances excreted, of his own weight, and the general bodily sensations. His investigations lead to the conclusion, first, that tea in ordinary doses has no effect on the amount of carbonic acid expired, the frequency of the respirations, or of the pulse ; second, when the diet is insufficient, tea limits the loss of weight thereby entailed ; third, when the diet is sufficient, the body is more likely to gain weight when tea is taken than when not ; fourth, tea diminishes the loss of substance in the shape of urea, lessens the solid excretions, and limits the loss by perspiration. It is thus claimed that this beverage is an enlivener of the mind, a soother of the body, and a lessener of the waste of the system. 706. Influence of Coffee in Digestion. The active ingredients of cof- fee are cafein, which is identical in properties with thein of tea, and the peculiar empyreumatic or burnt oil produced in roasting. " By the presence of empyreumatic substances, roasted coffee acquires the property of checking those processes of solution and decomposition which are begun and kept up by ferments. We know that all em- pyreumatic bodies oppose fermentation and putrefaction, and that, for example, smoked flesh is less digestible than that which is merely salted. Persons of weak or sensitive organs will perceive, if they at- tend to it, that a cup of strong coffee after dinner, instantly checks digestion ; it is only when the absorption and removal of it has been effected, that relief is felt. For strong digestions, which are not suf- 378 PHYSIOLOGICAL EFFECTS OF FOOD. ficiently delicate reagents to detect sucli 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" (LiEBia.) 707. Lehman on the influence of Coffee. "We are indebted also to Pro- fessor LEHMAN for valuable experiments to ascertain the effects of cof- fee. He states that coffee produces two leading 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, congestions, restlessness, and incapacity for sleep ; and that excess of cafein pro- duces increased action of the heart, rigors, derangement of the renal organs, headache, a peculiar inebriation, and delirium." 708. Chocolate is allied to tea and coffee by its nitrogenous princi- ple (theobromin), but the effect of this substance seems to 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. Alcoholic Liqnors. The common and active principle of spirit- ous liquors is alcohol^ obtained from sugar by fermentation. It varies in proportion in the different sorts from 1 to 50 or 60 per cent. Liquors contain various accompanying substances, traces of albumen, sugar, acids, volatile oils, ethers, bitter principles produced in the pro- cess of fermentation or distillation, or purposely added to suit the de- mands of taste. The scale of commercial valuation of alcoholic liquora 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- f em. Yet it is the alcoholic principle found in all these mixtures that INFLUENCE OF SPECIAL SUBSTANCES. 379 gives them life, and a common character, and groups them all together under the common title of intoxicating liquors. It has been insisted by some that alcoholic beverages are entitled to rank as food or nutri- njent, 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 cannot replace Water In the System. Water is the ap- pointed solvent within the living body. Aided by acids, alkalies, salts, it brings the various solids into the required condition of solution. But alcohol cannot rl^lace water in this duty. Its solvent powers are not the same as those of water. What alcohol dissolves, water may not, and the reverse. Alcohol mixed with water may deprive it of its solvent powers in particular cases. This is precisely what is done when alcoholic liquids are taken into the stomach. They coagulate, and precipitate the pepsin dissolved in the watery gastric juice, and if not quickly absorbed by the stomach into the blood, they would in this way effectually stop digestion. Their action while within the stomach is to disturb and arrest the digestive process. 711. They cannot nourish Tissne. Alcohol contains no nitrogen ; it cannot, therefore, be transformed into tissue, nor take part in meta- inorphic changes. Its composition forbids the possibility of any such effect, and nobody acquainted with the rudiments of physiology claims it. 712. Their relation to Animal Heat The assumption that alcohol is a respiratory aliment is plausible at the first blush, but conceding the utmost demand that it undergoes combustion in the body it is en- tirely impossible to sustain the doctrine. True, alcohol gives rise to heat in the system, but so do other agents, whose claim to the charac- ter of foods would be on their face preposterous. The question is, do these liquors produce heat in the manner of foods, or in some unnatu- ral and injurious way. By reference to LIEBIG'S scale of respirants (743), it will be seen that the strongest spirits drank are inferior, pound for pound, to starch and sugar, and not nearly half so valuable as oily substances for a heat generator. Yet they act in such a rapid, flashy way, as to produce preternatural excitement and irritation in the system. In sustained calorific effect, they are not to be compared with the aliments provided by nature, as is emphatically attested by the concurrent experience of Arctic voyagers exposed to the utmost se- verities of cold. 713. Dr. Bocker's ObserYations. This gentleman tested the effects of alcohol in small quantities upon his own person, in a course of skilfully 380 PHYSIOLOGICAL 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. Tlfc apologists for the general and moderate use of alcoholic beverages, cannot agree among themselves upon any philosophy to suit the case. Dr. MOLESHOTT says, "Alcohol may be considered a savings-box of the tissues. He who eats little and drinks a moderate quantity of spirits, retains as much in the blood and tissues as a person who eats proportionally more, without drinking any beer, wine, or spirits. Clearly, then, it is hard to rob the laborer, who in the sweat of his brow eats but a slen- der meal, of a means by which his deficient food is made to last him a longer time." Upon which Dr. CHAMBERS justly remarks, " This is going rather too far. When alcohol 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 expense of his lody, to consume to-day that quantity which ought naturally to have been employed a day later. He draws, so to speak, a bill on his health which must 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 inevita- lle ~bankruptcy 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 ?uled 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 ns 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 o^ nature designed should be distributed more equally through the pass- ing time. We cannot doubt that God has graduated the flow of these life-currents, in accordance with the profoundest harmonies of being, and the highest results of beneficence. By habitually resorting to this potent stimulant, man violates the Providential Order of his con- stitution, loses the voluntary regulation and control of his conduct, in- augurates the reign of appetite and passion, and reaps the penal con- sequences in multiform suffering and sorrow, for nature always vindicates herself at last.* 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 milk, or asses' milk, and for this reason often disagrees with delicate stomachs. By skim- ming, however, cow's milk is made to approach human milk in quality. It still, however, contains nearly all the cheese, the sugar of milk, the salts, and some butter. It is therefore scarcely less nutritious than new milk, but from its loss of butter is less fattening, and has a lower power of sustaining, through respiration, the temperature of the body. Physicians order milk when they are desirous of affording stimulus or excitement. It is also recommended as a good diet for children, especially in scrofulous complaints. 717. Properties and effects of Soups. The soluble extract of various animal and vegetable substances, obtained by boiling or steeping, forms * " When, by habit, the stimulant has become a necessity, an enervating relaxation in- fallibly follows, as sometimes mournfully illustrated by less prudent literary men. The stimulant ceases to excite the debilitated organs have already been indebted to it for all the activity it can give. In this case the victim continues to seek his refuge, until dangerous diseases of the stomach cripple the digestive powers ; with the decay of the digestive organs, the formation of blood and nutrition are disturbed ; and with the di- gestion vanish clearness of thought, acuteness of the senses, and the elasticity of the m uscles." (MOLESHOTT.) 882 PHYSIOLOGICAL EFFECTS OF FOOD. soups. They are made from a great number of materials, an for many purposes. Genuine castile soap consists of olive oil, saponified with soda, and colored ; that which is commonly sold under this name, however, is an imitation, made with common fatty materials. Windsor soap consists of tallow, a small proportion of olive o'l and soda. Ordinary white soap or curd soap consists of tallow pr.d soda. Cocoa-nut oil forms a soap that gives a strong lather. Toilet soaps are made with lard, almond oil, palm oil, olive oil, or "net, combined either with soda or potash, accordingly as they are doeired to be hard or soft, and with as little excess of alkali as possible. They are colored and perfumed to taste. Fancy soaps are essentially common soaps, mixed with different aromatic oils and coloring substances, and diversified in form so as to suit the fashion of the day. Soaps are mottled, streaked or stained, by metallic oxides, chiefly oxides of iron ; which can only be worked through the body of the soap, to give it the desired marbled appearance, when it is -)f a certain consistence; such soaps, therefore, cannot be charged with an excess of water. Transparent soap, is white soap that has been dissolved in alcohol ; in addition to the detergent properties of the soap itself, it joins the alcohol, which is sometimes useful for cleansing purposes, and always harmless. But it wastes rapidly, and its advantages hardly compensate for its extra cost. Besides water and soap, the universal and most important agent, other substances are also employed for special purposes, which we shall notice in con- nection with their applications and uses. 428 CLEANSING OP TEXTILE AETICLES. II. CLEANSING OF TEXTILE ARTICLES. 793. Composition of the Dirt. The general principle of cleansing away all dirt, spots, and stains, consists in applying to them a sub- stance which shall have a stronger attraction for the matter composing them, than this has for the cloth or surface to which it adheres. The dirt is to be dissolved, and hence for each special form of impurity we require, if possible, to find special solvents. It is a matter of chemical affinities. In cleansing textile articles, for example, we desire to remove the dirt without injuring the fibre of the cloth ; and if it be possible, without disturbing the color. Alkalies are able to dissolve almost every thing that presents itself in the form of dirt, but they are too powerful, discharging colors and corroding the tissue. In soap, their activity is so restrained that they become generally avail- able for cleansing purposes. The leading cementing constituent of dirt upon our garments, is some form of oily substance communicated oy perspiration or contact of the skin, which is constantly covered by an oleaginous film. The oily, greasy basis of dirt, may be de- rived from many sources. But water has no affinity for oily matter? in any form, and cannot dissolve them or alone remove them from any surface to which they may adhere. This is readily effected by soap, which being always alkaline, takes direct effect upon the grease, partially saponifies it and forms with it a compound which dissolves in water. The oily nature of the soap also increases the pliancy of the articles with which it is washed. 794. Reactions of Soap and Water. Water is the common liquid vehicle of cleansing, and soap the agent resorted to, to render dirt soluble in water. The soap is either applied directly to the article it is desired to cleanse, or it may be first dissolved in water. As soap and water thus act jointly, it is proper to inquire as to their behavior toward each other. If the water be pure or soft, soap dissolves in it entirely ; if it be hard, that is, if it contains sulphate of lime or mag- nesia, the soap, whes added, instead of dissolving, curdles or is de- composed, and a new soap is formed, which contains lime instead of potash or soda. This new lime soap will not dissolve, and may be seen upon the surface of the water as a kind of greasy scum. It adheres to whatever is washed in it, and gives that unpleasant sensa- tion called harshness when we wash our hands. Hence, with hard water, an excessive quantity of soap is required, while the operation is much less agreeable and satisfactory than with soft water. To test its quality of harshness, dissolve a little soap in alcohol and put a few STRUCTURE OF THEIR ULTIMATE FIBRES. 429 FIG. 135. drops in the water it is wished to examine. If it remains clear, the water is perfectly soft ; if it becomes cloudy or opaque, the water ia ranked as hard, and according to the degree or density of the cloudi- ness, is the hardness of the water. 795. Cotton, Linen, and Woollen articles. All textile articles are, however, not to be treated alike in cleansing. There is a radical dif- ference in the structure of the fibre between woollen fabrics on the one hand, and cotton and linen on the other, which makes it necessary that they should be differently man- aged. Fig. 125 represents the straight smooth form of linen and cotton fila- ments, while Fig. 126 exhibits the toothed and jagged structure of woollen fibres. It is evident that these, by compression and friction, will mat and lock together, while the cotton and linen fibres, having no such asperities of surface, are in- capable of any thing like close me- chanical adherence. Hence, the pe- culiar capabilities of woollen fabrics, of felting, fulling, and shrinking, caused by the binding together of the ultimate filaments. "We see therefore, the impolicy of excessive rubbing in washing woollen fabrics, and of changing them from hot to cold water, as the contraction that it causes is essentially a fulling pro- cess. The best experience seems to indicate, that woollen cloths should never be put into cold water, but al- ways into warm; and if changed from water to water, they should go from hot to hotter. In the most skilful modes of cleansing, and pre- paring delaines for printing, the plan is, to place them first in water at 100 or 120, and then treat them 8 or 10 times with water 10 hotter in Woollen fibres. each case. Some soak articles in warm water, to which a little wheat- bran has been added over night. The dirt is loosened, perhaps by a kind of fermentation. Soaking in weak soda-water is useful, but too free a use of alkalies shrinks the fibres of cloth and impairs the Cotton fibres. Linen fibres. FIG. 126. 430 CLEANSING OF TEXTILE AETICLES. strength of the tissue. Resin-soap should not be employed to wasK woollen, as the resin has the effect of hardening the fibres. Delicate textures, and especially white linen, should never be boiled in hard water. The carbonate of lime precipitated by boiling (786) is not only itself deposited upon the fabric, but carries down with it whatever coloring matter happens to exist in the water, and fixes it upon the fabric, imparting to it a disagreeable, unremovable dirty hue. 796. RemoYal of Stains, Spots, &e. To do this without injury to the color or the fabric, is sometimes easy, frequently most difficult, and often impossible. Much may depend upon skilful and persevering ma- nipulation ; and although various agents, which we are now to men- tion, are oftentimes valuable, yet good soap, after all, is the chief re- liance. Grease-spots may generally be removed by the patient appli- cation of soap and soft water, but other means are also employed. Alumina, or the pure principle of clay, has a strong attraction for fatty substances, and is much used in the form of fullers' earth, a fine- grained clay, which is prepared by baking and elutriation. It is used by diffusing a little through water, so as to form a thin paste, spread- ing upon the stain, and leaving to dry ; the spot then only remains to be brushed. French chalk, a very resinous mineral, is also highly ab- sorbent of grease. Ox-gall is an excellent and delicate cleansing agent. It is a liquid soda soap. It removes grease, and is said to fix and brighten colors, though it has a greenish tinge, which is bad for the purity of white articles. The application of a red-hot iron closely above a grease-spot often volatilizes the oily matter out of it. Brown- paper pressed upon a stain with a warm iron, will often imbibe the grease. Stains by wax, resin, turpentine, pitch, and substances of a resinous nature, may be removed by pure alcohol. The fats, resins, and unctuous oils, are dissolved by essential oils, as oil of turpentine. Common spirits of turpentine, however, requires to be purified by re- distillation, or it will leave a resinous stain upon the spot where it ia used. When pitch, varnish, or oil-paint stains have become dry, they should be softened with a little butter or lard, before using turpentine and soap. Burning -fluid combines the solvent powers of both alco- hol and turpentine. Fruit-stains, wine-stains, and those made by col- ored vegetable juices, are often nearly indelible, and require various treatment. Thorough rubbing with soap and soft water ; repeated dipping in sour butter-milk, and drying in the sun; rubbing on a thick mixture of starch and cold water, and exposing long to sun and air, are among the expedients resorted to. Sulphurous acid is often employed to bleach out colors. It may be generated at the moment REMOVAL OP STAINS. 431 of using, by burning a small piece of sulphur in the air, under the wide end of a small paper funnel, whose upper orifice is applied near the cloth. Coffee and chocolate stains require careful soaping and washing with water at 120, followed by sulphuration. If discolora- tion has been produced by acids, water of ammonia should be applied ; if spots have been made by alkaline substances, moderately strong vinegar may be applied ; if upon a delicate article, the vinegar should be decolorized by filtering through powdered charcoal. For iron mould, or ink stains, lemon-juice or salt of sorrel (oxalate of potash) may be used. If the stains are of long standing, it may be necessary to use oxalic acid, which is much more powerful. It may be applied in powder upon the spot, previously moistened with water, well rubbed on, and then washed off with pure water. It should be effectually washed oufr, for it is highly corrosive to textile fibres. The staining principle of common indelible ink is nitrate of silver. It may be re- moved by first soaking in a solution of common salt, which produces chloride of silver, and afterwards washing with ammonia, which dis- solves the chloride. III. CLEANSING OF THE PERSON. 797. Strnctnre and Offices of the Skin, A glance at the curious and beautiful structure of the skin, and its important offices, will assist us to understand the causes Fie 12 i 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- ^J9HBJ ^\^ ly minute thin scales, of a horny, resisting quality, <2p| which serves as a pro- ^"J tection to the sensitive or true skin underneath. ^ ^ / ^T > ' The surface of the cuticle is constantly loosening, Surface 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 CLEANSING OF THE PERSON. FlG 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 Vertical section of the skin, greatly magnified : 700 the number of inches in a the cuticle, outer, or scarf skin ; & d the true -, , , , , , , ,, skin; o oil-tube and gland; e sweat glands and length lor the whole Surface of their ducts, the outlets at the surface being ^^ hndv "NTmv th mirror nf the pores; / hairs; g cellular substances. ^ V ' * ow tne num er ol square inches of surface, in a man of ordinary height and bulk, is 2500 ; the whole number of pores, there- fore, is 7,000,000, 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 surface, of animal and saline matter, consisting of acids, alkalies, 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 inhalation 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 infectious matter would be greatly heightened. But this consequence is wisely guarded against by a set of glands, whose special office 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 ; MANAGEMENT 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- tion, or the outward escape of waste matter, protects the system against too free absorption from without. It is this oily distilment, perpetually covering the cutaneous surface, that seizes upon all forms of dirt and impurity, 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 consolidate, until it obstructs the pores, arrests 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 FIG. 129. and irregular, and instead of the constant flow through the oil-tubes, their contents become dry, dense, impacted, and do not freely escape. They accumulate in the ob- structed passages and form 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. WILSON, who has studied its history and habitudes for six months at a time, steatozoon folliculorum ; that is, the 'animal of the oily product of the skin.' These little personages are caterpillar-like, with head, feelers, four pair of legs, and a long tail. 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 of the Skin Ablution. As oil is the basis of the coat- ing of dirt which daily 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 element of soap also softens and dis- solves a part of the cuticle which, when rubbed off, carries with 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 OP THE PERSON. and purity of the skin. If soap produce irritation, it is because the skin is in some way morbid. It should then be used in small quantity at first, increasing it gradually. 800. Philosophy of washing the Face. Dr. WILSON thus pleasantly discourses on the art and mystery of cleansing the face. " And now, dear reader, having determined to wash your face, how will you set 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. Fill your basin about two-thirds full with fresh water ; dip your face in the water, and then your hands. Soap the hands well, and pass the soaped hands with gentle friction over the whole face. Having per- formed this part of the operation thoroughly, dip the face in the water a second time, and rinse it completely : you may add very much to 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 say, ' What are the wrong ways of washing the face ? ' Why, the 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 will see at once that the hands are the softest and the most perfect means of carrying the soap, and employing that amount of frictiQn 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 combine efficient 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- sur3 may be enough to excoriate the skin ; and a very soft towel is equally open to objection from its inadequacy to fulfil the obligation of friction during the process of drying. In washing the face you SUBSTANCES ACTESa UPON THE TEETH. 435 have tLree objects to fulfil to remove the dirt, to give freshness, and to impart tone and vigor to the skin." 801. Geansing the Teeth. The effect of talking, singing and breath- ing through the mouth, is to evaporate the water of the saliva, leaving its solid constituents, animal matter and salts, as a residue which accu- mulates upon the teeth as tartar. This, together with the fragments of the food which get lodged in the 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 chemically to dissolve the tar- tarous incrustation, as dilute muriatic acid, which also removes dis- colorations and whitens the teeth. But it also corrodes their enamel, and rapidly destroys them. Its habitual or frequent use is, therefore, most pernicious. It may be rarely and cautiously employed to efface dark spots or black specks upon the teeth, but it should be quickly neutralized with chalk, and washed away 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. Yet 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 ~bol& armeniac. Myrrh, cin- namon, &c., are added as perfume. ETiatany, cinchona, and catechu, are added to exert an astringent and hardening effect upon the gums. If substances are required which shall dissolve in using, sulphate of potash, pliosphate 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 efficiency to chloride of lime (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. (PEEEIEA.) 436 CLEANSING THE AIR. IV CLEANSING THE AIR. 802. It was noticed (303) that the atmosphere constantly tends to self-purification ; its oxygen is a universal 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 effect in various ways. 803. Palliatives and Disguisers. - 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 smell. 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 effects of uncleanliness. " They are thFonly resources in rude and dirty times against the offensive emanations from decay- ing animal and vegetable substances, from undrained and untidy dwell- ings, from unclean 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 ventillation, the attar of roses seems to render the scavenger unnecessary, and a sprinkling 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 OP LIME AND CHLORINE. 4 3 7 804. Action of Disinfectants. A large number of substances have been discovered which destroy evil odors and injurious gases. These are termed disinfectants, and act chemically either to decompose the noxious substances or to combine with them, producing new and harm- less compounds. 805. Freshly Bnrned Lime Quicklime. Lime newly burned, caustic and hydrated (slaked), is used to purify the air. It has a powerful at- traction for carbonic acid, half a cubic foot of it absorbing nearly 40 cubic feet of the gas. A few Ibs. of it placed upon a board or tray in the bed-room, or oftentimes in the sick-room, rapidly absorbs this de- leterious substance, while the condensed gas is immediately replaced by an equal volume of fresh air from without. The OLly inconve- nience is, that as the lime combines with the acid, the water used in slaking is set free, which charges the air with aqueous vapor. The in- habitants of newly built houses, and even after a considerable time, often experience a similar annoyance. It is not from the ordinary wetness of new walls that the moisture proceeds, but from the dry hydrate of lime in the mortar. The carbonic acid of the room, from the lungs of its inmates, gradually penetrates the plaster and displaces this water. When quicklime is strewed over fresh animal and vegeta- ble substances, it retards their decay, and so influences the changes that ammonia and other volatile and strong-smelling compounds are less freely produced. If spread upon putrefying refuse, it acts differ- ently, seizing upon the acids and setting free the pungent gaseous alka- lies. It at first liberates a large amount of offensive gaseous matter, and then checks the decomposition. 806. Chlorine as a Disinfectant. But the most powerful disinfecting agent is chlorine gas, one of the elements of common salt (590). It is an energetic chemical agent, used for the destruction of coloring mat- ters, as in bleaching cotton, linen, fatty substances, &c. The remark- able lightness and tenuity of hydrogen have been referred to (76). It combines with many heavier elements, forming compounds of extreme volatility, lighter than the air, and which constantly ascend into it. It is this highly rarefied gas which seems to stand closest upon the bor- ders of nothing, but becomes potent through its very nothingness, that gives wing to the deadly exhalations, lifting them away from the ground into the breathing region. The gaseous poisons of the air, so far as known, are compounds of hydrogen. For this substance chlo- rine has a strong attraction, decomposing and destroying its com- pounds, and being a gas, it may also diffuse through the air, and thus eleanse and disinfect it. 438 CLEANSING THE AIB. 807. Forms of its use Chloride of Lime. Chlorine gas may be set fire in two ways : first, by pouring hydrochloric acid upon finely powdered black oxide of manganese ; and second, by 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 be removed as far as possi- ble from apartments in which it is to be used. (Other disinfecting gases are liable to the same objection.) If it be desired to generate large quantities of chlorine, the methods just mentioned may be re- sorted to, but 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 lime combines with all acid bodies as carbonic acid, sulphuretted hydrogen, while chlorine diffuses 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 diluted 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 lime. 808. Disinfection by Sulphurous Add. "When sulphur is burned in the open air, oxygen combines with it, producing sulphurous acid gas. It has a noxious odor, and if largely mingled with the air, is injurious to health. It is an active chemical agent, much used for bleaching, as may be illustrated by holding over a burning sulphur match, a red rose, which is immediately whitened. Woollen, silk, and other garments are bleached by it. It is of a strongly acid nature and combines with alkaline vapors of the air, while it decomposes and de- stroys other substances, as sulphuretted and phosphuretted hydrogen. When an apartment is fumigated by burning sulphur, it is necessary to leave it ; it corrodes metals. 809. Other Substances used for Disinfection. Chloride of iron is a CHAKCOAL HASTENS CHANGE OF MATTEE. 43& cheap and efficient disinfectant, though it imparts a bro\\n or bluish stain wherever its solution falls. Chloride of zinc is equally efficient, but more expensive. Sulphate of iron (copperas or green vitriol) has strong disinfecting power. Either of these substances dissolved in water, (one, two, or three Ibs. to the pailful,) thrown into vaults, cess- pools, or gutters, or over any foul masses of fermenting matter, exert not only a disinfecting and deodorizing action, but partially arrest putrefactive change. Acetate and nitrate of lead are strong disin- fectants. These substances are all solids. They do not assume the gaseous form, but act, dissolved in water, by fixation of n; xious sub- stances 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 inchea of gaseous ammonia ; 50 or 60 of sulphuretted hydrogen, and nearly 10 of oxygen. The charcoals are not all 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 s changed to nitric acid, and sulphuretted hydrogen to sulphuric acid. 440 CLEANSING THE AIE. In this way, charcoal promotes oxidation, so that instead of being an antiseptic or preventer of change, it is really an accelerator of decom- position.* This active property of hastening decomposition has been made medically available in the form of poultice, to corrode away sloughing and gangrenous flesh in malignant wounds and sores. Dr. 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 six hours the dead portion was reduced in size fully one-quarter. At the same time, the poultice thus made, effectually prevents any odor or putrefying exhalations proceeding from the slough and pervading the apartment." Dr. STENHOUSE, who, in 1855, first drew distinct atten- tion to the fact, that charcoal is rather a hastener of decomposition than an antiseptic, has contrived ventilating arrangements in which the air of dwellings is filtered through charcoal. He has also a 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 strongly commended as a disinfectant. It has many advantages over the preparations of chlorine, as it neither injures the texture of substances, nor corrodes metals, nor discharges the color of fabrics by contact, nor gives off dis- agreeable fumes. It is never in anj application or use, poisonous or danger- ous, but is entirely innocent, and in only one solitary instance can it become pernicious, and that is vhen it ceases to become charcoal, and is burnt in a perfectly closed room. * " I took the body of an English terrier, weight about ten Ibs., 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 could be detected. By some accident the charcoal \v*s disturbed, and a large portion of the mass was left uncovered ; in spite of this the cucumjacent charcoal was sufficient to prevent any offensive stench. Upon seeing this, I left the body completely uncovered, merely surrounding it with the deodorizing agent ; this again prevented any disagreeable smell. Having determined this fact, I again cov- ered the carcass. In less than a fortnight not a particle of flesh remained upon the bones, which were picked perfectly clean, ani were of a snowy whiteness." (BiBD o CHA.BCOAL.) POISONS, AND TEEIB ASTTTDOTES. 441 V. POISONS. 812. Poisons tnd Poisoning. Poisons are divided into three classes according to the way they act upon the system. Acrid or irritant poisons directly corrode or destroy the tissues with which they come in contact, and cause intense pain, but do not suspend consciousness. Strong acids, and alkalies, and indeed all poisonous metallic substances, belong to this class. Narcotic poisons are such as produce stupor, aa opium, carbonic acid. Narcoto-acrids, as tobacco, alcohol, position and in burning? 86. What is the origin of mineral coal ? Why must other fuel be used to kindle it ? What is said of the burning of anthracite ? 87. What is bitumin ous coal ? How does it burn? Fat coal? Coke ? What are its qualities? Why is it preferred to anthracite ? 88. What is lignite ? 89. How do these fuels compare in heat- ing power? 90. How much air is required to burn a pound of charcoal ? Of mineral coal ? 91. What is said of excess of air in combustion ? PAGE 55. X. AIR CURRENTS-ACTION AND MANAGEMENT OF CHIMNEYS. 92. Why does the can die flame tend upward? Explain the draught in chimneys. 93. Why has a tall chimney a stronger draught than a short one ? What conditions insure a violent draught? Within what limits must these conditions be restricted? Why? 94. When and how does wind cause chimneys to smoke? How may it be prevented? 95. Why do new chimneys sometimes smoke? 96. What trouble often occurs from chimneys on the cold side of a house ? 97. How may it be shown that air currents are tery easily established ? Why cannot the current from a fire traverse two flues at a time ? 448 QUESTIONS. 98. How may one chimney overpower another? Is there any remedy for such a stat of things ? 99. How shorfld flues entering chimneys be arranged ? What is the effect of kindling a fire in an upper room, when there is none below ? In the lower room, when there is none above? How is this difficulty obviated ? 100. What results are apt to flow from large openings in fireplaces? How should the throat be constructed? 101. What is the most common cause of smoky chimneys ? How are double currents in chimneys caused ? What was Dr. Franklin's plan for remedying this difficulty ? 102. What is said of currents in a room affecting the chimney draught ? 103. What is smoke ? How is its weight shown ? What is said of the falling of smoke in bad weather ? What of watery vapor in smoke ? 104. How does smoke vary in composition ? PAGE 60. XL APPAEATUS OF WAEMINGK 105. Why are the effects of heating on the air of rooms not mentioned here ? 106. How do rooms lose their heat ? How may much of the loss by windows be prevented ? 107. How do our bodies warm a room ? Describe the experiment. How does a crowd affect the air ? 108. Before the time of chimneys, how were rooms warmed ? 109. De- scribe the first fireplace. How have they been improved ? What is said of the jambs ? 110. How does the open fireplace warm the room? What becomes of the heated air? How are the different parts of the room heated ? 111. In what two ways does fuel give out heat ? Why is the open fireplace so wasteful of heat ? How much heat is lost in those best constructed ? By what means may it be improved in economy? 112. De- icribe the Franklin stove. What are its advantages ? 113. Why will a smaller fireplaco do for coal ? Why is the coal-grate more economical than the fireplace ? How should it be made ? 114. What considerations determine the form of the front ? In what does the art of burning fuel in grates consist ? What is said of the depth of fuel in the grate ? 115. What is said of the different kinds of grate ? Describe Golson's. Franklin's. 116. Describe Dr. Arnott's grate, and the mode of using it. What is said of the idea of burn- ing smoke? What should be the aim? 11T. What is the objection to placing grates very low? Explain Fig. 18. 118. How do stoves communicate their heat? 119. What is said of different materials used for making stoves ? 120. What is the principle of tho self-regulating stove ? Describe it. 121. Why is the air-tight stove not economical ? What was the result of Dr. lire's experiments ? What is the most economical mode of getting heat from fuel ? 122. How Is the heated current from the stove affected in pass- ing through the pipe? How do elbow joints act? Why is little gained by extending the pipes greatly ? 123. What are the most desirable qualities in a stove ? 124. What is the plan of the hot-air furnace ? What is said for and against these furnaces ? 125. What are the disadvantages of sending streams of hot air into a room through a register ? Where will the coldest part of the room be found? How has the air been found to ar- range itself in heated rooms ? 126. Why are we not readily warmed by hot air ? How is it shown that hot air may be made a source of cold ? 127. How is the principle of the hot water apparatus illustrated ? How is water adapted for heating ? 128. What are the two methods of heating by hot water ? How do the results obtained from them dif- fer ? 129. Describe the construction of the steam apparatus. What is said of its action ? 130. How are these methods of warming in respect of danger from fire ? 131. What is eaid of the origin of fires in London ? 132. Give the chief advantages and disadvantages of heating by the fireplace. The stove. The hot-air furnace. The hot water ap- paratus. PAET II. LIGHT. PAGE 76. I. NATUEE OF LIGHT. 132. What is said of the means by which we gain a knowledge of the outward world 1 133. How do light and darkness affect the mind ? How is this illustrated? 134. What was the ancient idea of light ? 135. What was the first scientific explanation of light ? QUESTIONS. 449 What view of light is now generally accepted? 186. At what rate does the intensity of light diminish, from the point of emission? What circumstance modifies the result! 137. In what different ways do bodies receive the light that falls upon them ? PAGE T9.-II. EEFLECTION OF LIGHT. 133. What is reflection of light? 139. How is a perpendicular ray reflected? An oblique ray ? How may this be shown ? 140. Explain Fig. 23. Fig. 24. 141. What is it that reflects the light in looking-glasses? How is the image formed ? Why does it appear behind the glass ? How does the form of the reflecting surface affect the image ? 14-2. What would be the effect of perfect polish in a surface ? 143. What is irregular re- flection ? Why can a sheet of white paper be seen where a mirror cannot ? How do objects become visible, in the absence of an original fountain of light? 144. How should pictures be managed in respect to reflection? Why are they inclined forward when hung high ? How should the light fall upon a picture ? 145. What is said of tho effect of the atmosphere on light ? PAGE 82. IIL TEANSMISSION OF LIGHT. 146. What is said of perfect opacity? Of perfect transparency? What depth of ail would absorb all the sun's light? Of water? 147. Explain refraction of light. Why do window panes produce no distortion ? When light passes from one medium to an- other, how is it affected? 148. Explain Fig. 29. What is meant by index of refraction ? 149. What are lenses ? How do the different lenses change the direction of light ? PAGE 84. IV. THEOET OF LIGHT WAVE-MOVEMENTS. 150. What is light ? 151. What examples are given of visible wave-motions in nature ? 152. How is sound communicated? How is it shown to be vibratory motion? 153. What causes difference of pitch in sounds? Describe Savart's machine. 154. What re- sults were obtained in reference to the musical scale? How is a unison produced? A concord? A discord? 155. What is assumed in the wave-theory of light ? What is meant by wave-length ? How do the wave-lengths differ in the different colors ? 156 How is the number of pulsations of the retina in a second determined? What is said o-. the credibility of these statements? PAGE 88. V. COMPOSITION AND INFLUENCE OF COLOE. 157. How is the solar spectrum produced ? What is it composed of? Explain Fig. 85. 158. How does Newton explain colored surfaces ? 159. What is Brewster's view of the composition of colors? Explain Fig. 36. Fig. 37. 160. What are complementary colors? How are they shown by the figures? 161. What are tones of color? Shades? Tints ? What is a scale of colors ? 162. What are hues ? 163. Explain the chromatic circle. In what two ways are colors seen to be modified ? 164. How may any one easily make such a chart with the real colors? 165. How are complementaries found upon the chart? 166. What is meant by complementary contrast ? 167. What are luminous col- ors? Sombre? Medium? 168. What are grays? Browns? Pure colors? Broken colors ? 169. What is said of finding pure colors in practice ? 170. What is said of a purchaser looking at colored cloths ? How may this be verified ? What are the two kinds of result seen ? 171. What are colors ? What do we mean by the expressions, ' snow is white,' 'blood is red ' ? From this view, what might we expect ? 172. What is said of the duration of impressions upon the retina ? 173. What is the effect of gazing at a color for some time? How is this easily shown? 174. What is said of the simultane- ous influence of colors upon each other ? How is it explained ? 175. What is the effect of placing violet beside green ? Beside orange ? Beside blue ? What is the law of the mutual influence of colors ? What is the effect of placing violet by the yellow scale ? 176. Explain Fig. 45. How is this result accounted for ? 177. What does good taste dictate in combining colors ? What are the finest combinations ? How are harmonies of analogy 450 QUESTIONS. produced ? 178. "What circumstances may disturb the mutual action of colors ? 1T9 How are colors affected by associating them with white ? Is the white changed ? 18tt What is said of associating colors with black ? With gray ? PAGE 102. VI. PEACTICAL SUGGESTIONS IN COMBINING COLORS. VI. 181. How are these principles applied to dress ? 182. Describe the complexion of the blonde ? Of the brunette ? What colors suit the blonde, and why ? What the bruneii;o ? 183. What is said of the arrangement of flowers in a bouquet ? 184. Why are dark paperhangings bad ? What is the objection to red and violet? To orange and yel- low ? What colors are recommended ? What is said of the border ? 185. What sugges- tions are given concerning picture frames? Why are black frames objected to ? What should be the ground for gilding ? 186. What is eaid of dark colored furniture ? Of red ? Of selecting chairs and hangings ? Of trimming chairs and sofas ? Of the carpet ? PAGE 105. VII. PRODUCTION OF ARTIFICIAL LIGHT. VII. 1ST. What are the sources of natural light ? Of artificial light ? 188. Describe Dr. Draper's experiment showing the relation between light and temperature? 189. How is all our illumination produced ? What processes must all substances used in light- ing undergo ? 190. What elements are employed in illumination ? Which burns first ? What happens to the carbon ? 191. How may these facts be shown ? 192. What is said of the laws of illumination ? What is the office of oxygen in this process ? Why is a solid necessary ? Why must these elements be burned successively ? 193. In what three forms are illuminating substances used ? 194. From what are candles made ? What kinds of tallow are best? How should they be kept? 195. What is the composition of the fats and oils? What are the properties of stearin candles ? 196. What is said of sper- maceti candles ? Of wax ? 197. What is the use of the candlewick ? How is the burn- ing carried on? 198. How is the flame shown to be hollow? What is contained in the dark space ? What causes the odor of a candle just blown out ? 199. How is the neces- sity for snuffing shown ? What of plaited wicks ? 200. Why cannot the wick of a tal low candle be slender ? 201. How are liquids burned ? Why are large wicks in lamps apt to smoke? Describe the Argand burner? What are its advantages ? 202. What is Lange's improvement upon this lamp ? Describe Fig. 51. What is the point to be considered in managing such lamps ? 203. How should the reservoir be constructed ? How is it, in the Astral and Sinumbra lamps ? In the Carcel lamp ? 204 What is one great difficulty in using lamps? What was Dr. Ure's experiments ? How has this difficulty been met ? 205. What oils are chiefly used in lamps ? 206. What is camphene ? What are its prop- erties ? 207. Why must peculiar lamps be used to burn oil of turpentine ? What is said of the light from camphene ? Why is its flame more luminous than that of oil ? 203. Why must it be used fresh? 209. What is burning fluid? What is said of this sub- stance ? 210. What properties of this substance lead to explosions ? 211. How are most accidents with it occasioned ? What causes the irregularity of the flame ? How are tho lamps made safe ? 212. Describe NewelFs lamp. 213. What is Kerosene oil ? What are its advantages ? 214. What is said of Sylvic oil ? 215. What Is said of the consump- tion of gas ? 216. What is it chiefly made from ? 217. What are the products of the dis- tillation of coal? 218. How is the gas purified? 219. What is its composition ? Why cannot these gases be burned separately ? How does the gas differ as the process of dis- tillation goes forward ? 220. How is gas made from oil ? From resin ? How does it compare with coal gas in expense ? 221. Explain the gas meter. What does it indicate ? 222. Describe the process of burning the gas. What if there is too little or too much air? 223. Does the length of the flame make a difference in the light ? 224. What ob- iections are urged against the use of gas? How do the constituents of gas differ in this respect? 225. When gas is so cheap, why is there no saving in its use? 226. How do the tubes become obstructed ? What causes the jumping of the flame? 227. In what aray can light be measured ? 228. Describe the photometer, Fig. 54. 229. Why have QUESTIONS. 451 we reached no practical advantages from this? What has been proposed? 280. Give the results of the experiments of Ure. Of Kent PAGE 126. VIII. STEUCTUBE AND OPTICAL POWEES OF THE EYE. 231. "What is said of the eye ? "Why is it treated of here ? 232. Describe the coats of the eye. 233. "What is the pupil ? Describe the iris and its action. 234. "What is the crystalline lens ? The vitreous humor ? 235. "What is the choroid coat ? Thepigment- vm nigrumf 236. How is the optic nerve surrounded? "What is the retina? Jacob's membrane ? 237. How is vision produced ? "Where is the image formed? "What is said of the touch of the retina ? 233. "What is the size of the image of the full moon upon the retina ? Of a man 70 inches high at 40 feet distance ? 239. "What is the difference in in- tensity between sunlight and moonlight ? Between sunlight and that of Sirius ? 240. When should we avoid using the eyes ? 241. Why is novel reading worse for the eye than grave subjects ? What other suggestions are made concerning reading habits ? PAGE 131. IX. OPTICAL DEFECTS OF VISION. SPECTACLES. 242. In perfect vision where is the image ? What would follow if the eye were rigid ? What is the limit of perfect vision ? 243. What causes far-sightedness ? Where is the Image formed? Why? Why do the far-sighted never see minute objects well? How do they often manage to see them ? 244. What is the remedy ? How do they act ? 245. What directions are given for managing far-sighted eyes? 246. Describe the near-sight- ed eye. Why can short-sighted people see with a weak light ? How may near-sighted- ness be produced? How should the young, if near-sighted, manage their eyes to correct the difficulty ? 247. How do concave glasses act ? What directions are given for their selection? What is nervous near-sightedness? What is cataract? 243. How should spectacle glasses always be mounted ? Why do persons wearing spectacles turn the head instead of the eye ? Where is the clearest vision through glasses ? Hence what follows ? What are pebble glasses ? PAGE 137. X. INJURIOUS ACTION OF ARTIFICIAL LIGHT. 249. How does artificial differ from daylight in composition ? 250. How may this be shown ? 251. Give a list of the substances used in illumination in the order of the purity of light yielded by them. 252. How are colors affected by artificial light ? 253. What was Dr. Hooker's experiment? 254 How are these effects explained? 255. What inju- rious result may follow such use of the eyes ? 256. How have the colors of the spectrum been characterized ? How may this be explained ? 257. What is said of the distribution of heat through the spectrum ? Why is artificial light more heating to the eyes than sun- light ? 258. Why do we use more of impure light than any other ? 259. What is said of the carbonic acid produced by artificial light ? 260. What is the objection to an unsteady light? Why are the variations of a strong light less injurious? How does reading in railroad cars affect the eyes ? 261. Why do we not see the moon in the day time ? How does this apply to our use of artificial light ? How can we prove that protecting the eye makes objects more distinct ? 262. What does Dr. Hooker remark on this point ? 263. Describe the symptoms that bad light produces in the eyes. 264. When the disease is on the nerve, what are the symptoms ? 265. If these continue, what others are liable to follow? 266. What is amaurosis ? What is said of it ? 267. Who are most subject to it* PAGE 146. XL MANAGEMENT OF AETIFICIAL LIGHT. 269. How do ground glass shades affect the light ? 269. When should reflectors be used ? 270. What is said of blue shades ? 271. How may these be made ? 272. How should they be colored ? 273. What is said of a blue glass chimney ? Of the use of tho water globe ? 274. Why are colored glasses in spectacles objectionable ? 275. Is gas-light necessarily Injurious ? In what way is it doing much mischief? 452 QUESTIONS. PART III. AIR. PAGE 150. I PEOPEETIES AND COMPOSITION OF THE ATMOSPHEEE. 276. "What considerations lead us to regard the air with amazement ? "What view gi res it a still deeper interest ? 277. Why do we not think of the air as a reality ? What is said of its weight? How does its pressure vary ? 278. What is the weight of a cubic foot of air ? How many feet are in a pound ? How large a room contains a ton ? 279. How do the variations in atmospheric density affect our bodies ? How our minds ? Why are inhabitants of low, marshy places much affected by a light atmosphere ? 280. Why must we study the chemical properties of air ? What is its composition ? Explain Fig. 68. 281. How do these gases arrange themselves ? What is said of this provision ? PAGE 154. II. EFFECTS OF THE CONSTITUENTS OF AIK. 282. What are the properties of Nitrogen in the air? 283. What is the office of oxy- gen ? How does it get access to all parts of our bodies ? 284. What is its purpose in our bodies? What does it accomplish in the brain ? 285. If the proportions of this gas are increased or diminished what follows ? 286. How much moisture does the air contain at different temperatures? How is the increased capacity for moisture as the temperature ascends, shown ? 287. What is the effect of cooling saturated air? How is its drying power determined ? Where should the openings be in laundries ? Why ? 288. When is the dew-point said to be high ? When low ? How is it found ? What is Mason's hy- grometer ? What results of observations in different places are given ? 289. What is said of moisture on windows ? Of double windows ? 290. How does humidity vary with seasons, climate, hour of the day, &c. 291. What provision is made for the removal of moisture from the body ? How much is given off in a day ? How is this process affected by damp air? What bad consequences follow ? Describe the sirocco. 292. How does dry air affect the system ? If very dry, how ? What is the Harmattan ? 293. What are the sources of carbonic acid in the air ? What are its effects when breathed pure ? When mixed with air in small quantities? 294. What per cent, of carbonic acid renders the air dangerous to breathe? What is the effect of retaining it in the body ? What etate of the air does this ? 295. Why is it found in the air at all ? 296. What follows if we breathe any of the elements of the air separately ? What is said of their combined action? 297. What is Alotropism? What is Ozone ? What are its effects ? 298. What is the common idea about electricity ? How is electricity developed in the air ? When does the air contain most of it? What do we know on the subject? PAGE 165. IIL CONDITIONS OF AIE PEOVIDED BY NATURE. 299. What becomes of the carbonic acid thrown into the air by respiration ? What other impurities does the air contain ? What is said of their minuteness ? 300. Why should not the dwelling be situated low ? What is the effect of dense foliage ? What ia the best soil around a dwelling? 801. Why is night air unwholesome? 302. How may the air differ in the different stories of the house ? 803. How does the atmosphere main- tain its purity ? 304 Do these remarks apply to air within doors ? PAGE 168. IV. SOUECES OF IMPUEE AIE IN DWELLINGS. 305. What is the effect of breathing and combustion upon the air of rooms ? 806. What is said of the leakage of air-tight stoves ? How is it with all stoves and furnaces ? 807. How do very hot stoves affect tho air ? How is this explained ? 308. What advan- tage have grates and fireplaces over stoves ? What is the consequence of heating the air? Upon what does the dryness of the air depend? Explain Fig. 71. How does parched air affect the body ? How can this difficulty with stoves and furnaces be obvi- ated ? 809. What common error is mentioned ? What is the true statement ? What is ,he state of the air from the ventilator of a crowded room ? 810. What is Dr. Faraday's QUESTIONS, 453 testimony on this point ? 811. What is the condition of the air in an unventilated bed room \vhere two have slept in it ? "Why are its occupants unaware of it ? "When the air of inhabited rooms is not changed, what do we see ? 312. "What is said of man alone being responsible for breathing foul air ? 813. "What other sources of impurity in houses are mentioned? 314 "What colors on paper hangings are poisonous? 315. "When are cellars sources of bad air ? Why should they be ventilated ? PAGE 174. V. MOEBID AND FATAL EFFECTS OF IMPURE ALE. 816. Why are we more exposed to injury from bad air than bad food ? Why is thought required to guard us from its effects ? 317. How does breathing bad air load the blood with impurities? What consequences does this prepare for? 318. What were the circumstances of the cholera outbreak in Taunton workhouse, and what do they in- dicate ? 319. What relation has been thought to exist between the kind of impurity breathed, and the disease induced ? What may occur to modify the symptoms ? 320. What is said of the causes that produce scrofula ? 321. How may impure air bring on consumption? 322. What is said of ventilation in regard to infant mortality ? What feeling seems to prevail among mothers ? 323. What is said of the undermining action of bad air upon the health ? 324. Why must the mind suffer at once from bad air ? How is it affected? PAGE 181. YI. KATE OF CONTAMINATION WITHIN DOOES. 325. How is the amount of oxygen consumed by one person in an hour estimated ? Why do the estimates of different persons vary ? 326. How does the carbonic acid ex- haled correspond in volume with the oxygen inhaled? To what extent does one person vitiate the air in an hour? 327. Why is it difficult to estimate the amount of oxygen withdrawn by combustion ? How does the combustion of fuel differ from breathing in its effects upon the air? 328. How rapidly do candles contaminate the air? Oil lamps ? Coal gas? 829. What relation exists between the dew-point of the air and our bodily comfort ? What estimates are given ? 330. How much air is vitiated by one person in a minute ? What is said of the economical aspect of this subject ? 831. What estimates are given of the effects produced upon the air by a certain number of persons in a room of given size ? How is it in actual practice ? What is said of size of apartments in this relation ? 832. How do plants affect the air of rooms ? PAGE 185. VIL AIE IN MOTION CUEEENT3 DEAUGHTS. 863. By what two methods may the air be purified ? 334. How is ventilation effected on a large scale ? What force is employed in private residences ? 335. Explain Fig. 72. Fig. 73. If several lights are in the room, what follows ? 336. What is said of the ac- tion of the body in producing currents ? 337. Explain how it is that tight windows pro- duce currents. What caution is given ? How is it in summer ? 338. What causes the air to arrange itself in layers ? How are the impurities distributed ? Will the action of windows and fireplace prevent this ? What is said of sleeping on the floor ? 339. Explain Figs. 75 and 76, showing that simple openings do not produce currents. 340. When the conditions are changed, as in Figs. 77 and 78, what happens ? Why should there be two openings ? 341. Explain Fig. 79. Fig. 80. S42. When will an open door or window empty the room of its air, and when not ? What is said of the laws which govern the motion of air ? 343. How does exposure to air-currents affect the system ? What is said of the velocity of currents ? Why is it important to be exposed to them ? PAGE 192. VIIL AEEANGEMENTS FOE VENTILATION. 344. Why cannot a fire be kindled in a tight room ? Why were the early fireplaces better than the modern ones for ventilation ? Why was the settle used ? How are the upper portions of the room affected ? How does the double fireplace act ? 345. How do stoves rank as a means of ventilation ? How can they be made to a'd in ventilation ? 4,54 QUESTIONS. 846. "What is said of ventilation by hot- air arrangements ? Why is a flue necessary What is the great danger in this mode of ventilation ? 347. How much moisture wil air heated from freezing to 90 require ? How is moisture supplied to the air of th* House of Commons ? "What is said of the usual supply ? What is recommended ? 348 How do the fireplace and air-heating apparatus act in combination ? Why cannot thia method become common ? 849. How does bad carpentry influence the progress of the art of ventilation ? 350. What four points should ventilation secure ? What is the real state of things in these respects ? 351. For what are milinet and wirecloth doors recom- mended ? What is said of lowering the top sash in winter ? of louvres and other contri- vances ? Where should the air brought into rooms come from ? What is Emerson's Ejector ? What methods of admitting air are mentioned ? 852. Describe Lyman's Ven- tilator. 853. What considerations naturally lead us to make openings in the upper por- tions of our apartments ? 854. What is the practical difficulty with these openings ? How may this be avoided ? 855. What, after all, must be the main reliance ? What difficulty is Arnott's valve designed to obviate ? How does it do it ? 356. What is said of its value ? 857. What use are chimneys in summer ? 358. What is said of the action of additional flues for ventilation ? 359. Why do the bedrooms require special care ? How do we generally find them ? What can be done ? 860. How may gas-light be ventilated ? 361. How may cellars be ventilated ? 362. What is the present state of the art of ven- tilation? Why is it little surprising that it should be so? 863. What is the main ob- stacle to ventilation ? Why is it bad economy to neglect it ? PART IV. ALIMENT. PAGE 205. I. SOUECE OF ALIMENTS-OEDEE OF THE SUBJECT. 864. From whence are the materials of the human body derived ? By what agencies are they wrought into food ? 865. How is the subject of foods to be considered ? What are simple aliments ? compound aliments ? 866. How are alimentary principles divided ? Which will be treated first ? PAGE 207. II. GENEEAL PEOPEETIES OF ALIMENTAEY SUBSTANCES. 1. PRINCIPLES CONTAINING NO NITROGEN. 367. What is a solution ? When does water dissolve substances most rapidly ? When saturated with one, will it dissolve others? Give some examples of the extent of its solvent power. How does heat affect solution ? What exception is mentioned ? 368. Why should solids be crushed before solution ? Why placed at the top of the liquid ? 369. How much ammonia does water dissolve ? How is soda water prepared ? 370. What causes the difference in natural waters ? 371. What are the contaminations of rain-water ? When is it most impure ? What is said of snow-water ? 372. Why are boiled waters flat to the taste ? 373. When does water pu- trefy ? 374. What living beings are found in water ? Do they exist in all water ? What is said of acid and alkaline water ? 375. Of what use are these beings in water ? 876. Describe how rain-water becomes charged with mineral matter. Give instances of its varying quantity. 877. What are the minerals in spring and well water ? When will water dissolve limestone ? 878. What is hard water ? soft water ? 379. How may water act upon lead and not be injured ? Give an example. What is the effect if much car- bonic acid be present ? What kinds of water should not pass through lead pipes ? What is said of iron pipes ? 380. In the absence of wells and springs, how may we supply our selves with soft water ? STARCH. 331. What is starch ? Where is it found ? How may it be separated ? 382. What substances contain most of it ? 883. What is said of the size of the starch grains in flour ? How much do they vary in size from different sources ? 384. Describe their appearance. How do they aid in detecting adulterations? 885. What is sago? 886. What is tapioca ? 887. What is arrow-root? 888. How is corn-starch obtained? 889. What to the composition of starch? QUESTIONS. 455 SUGAR. 390. Where is sugar found? How much do the different vegetables jield? 891. What is grape sugar ? 392. How may sugar be produced artificially ? 893. How is honey obtained ? 394 What is the best honey ? What is its composition ? 395. From whence do we get cane sugar ? 896. State clearly the difference in origin of cane and grape sugar. 897. How do they differ in composition ? in their properties ? 398. What is the difference in their solubility? in their sweetening power ? 399. How is brown sugar obtained from the cane juice ? 400. What does brown sugar consist of ? 401. What is said of the presence of grape sugar in cane sugar ? 402. How may we find animalcules in brown sugar ? What contains most ? 403. What is molasses ? What are its properties ? What are sirups and sugarhouse molasses ? 404. How is sugar refined ? 405. How is candy made ? What are its common adulterations ? What substances are used in coloring it ? What is said of them ? 406. What does Dr. Hassal say of the danger of using them ? GUMS. 407. What are the properties of the gums ? 408. How may gum be made arti- ficially ? What is dextrine ? 409. What is the composition of gum ? What is its dietctical value ? OILS. 410. How are the oils divided ? What are the properties of the fixed oils ? Of the volatile oils ? 411. How are they obtained ? What is said of their consistency ? 412. Give the proportion of oily matter in some of the leading articles of diet 413. "\V hat is there remarkable in their chemical composition ? For what do they seem spe- cially adapted ? VEGETABLE ACIDS. i!4 In what state do acids exist in plants ? What is their com- position, their nutritive value ? 415. What is malic acid ? What is the effect of culture upon it? 416. What is citric acid? 417. Where is tartaric acid found? For what is it used? 418. What are the properties of oxalic acid? 419. What is pectic acid? What are its properties ? How does boiling affect it? What is said of jellies and jams ? 420. What are the properties of acetic acid ? How is it easily obtained ? What kinds are most prized ? 2. PRINCIPLES CONTAINING NITROGEN. 421. In what form are we all familiar with albumen ? How may it be separated from the juice of plants ? Where else is it found ? 422. What is its composition ? 423. At what temperature does it coagulate ? What is the effect of diluting it ? By what other means may it be coagulated ? 424. How may vegetable casein be obtained ? how animal ? Do they differ ? What is their composition ? 425. What is animal fibrin ? How is it obtained pure ? What is its appearance ? How may it be obtained from vegetables ? 426. How is crude gluten obtained ? What are its properties ? What may be separated from it ? 427. What flesh contains most fibrin ? How does its character vary ? 428. In what are all these substances alike ? How do they differ? 429. What is gelatin? What is said of it ? What is glue? Isinglass? What are the uses of gelatin ? 430. What is said of the names given to these substances ? Explain them. 3. COMPOUND ALIMENTS VEGETABLE FOODS. 431. How are the compound alimenta naturally divided ? GRAINS. 432. What is the composition of wheat? What causes it to vary? 433. What is the most valuable portion of food ? What is said of the amount of gluten ob- tained by different chemists ? What is thought to be about an average ? 434 How does gluten differ in quality? How is the quality of flower determined by dealers? -De- scribe Boland's invention ? By its use, how are flours found to differ ? 435. What are macaroni and vermicelli pastes made from ? What wheats are best for this use ? What are the qualities of good macaroni ? 436. How is the difference in plumpness of grain la different wheats produced ? How does the proportion of water in wheat differ ? 437. lK-scribe the process of grinding. 438. What is the structure of the wheat grain ? Describe the husk. How are the other elements of the seed distributed ? 439. Explain Fig. 93. 440. How are these different substances affected by the millstone? 441. From these statements, what follows in regard to quantity of bran ? What is the compo- sition of bran ? What is the use it excess of oil in the husk ? 442. How do white and 456 QUESTIONS. flark-colored flowers differ in composition ? Describe the marks of good flour. 448. What Is said of evaporation from wheat ? 444. How does age affect flour ? How does grinding affect its composition? "Why should it be quickly cooled and dried? Why is freshly ground flour recommended ? 445. What is farina ? What are its properties ? Compo- sition ? 446. What are the mineral constituents of wheat ? Which is the most abundant and characteristic ? How are they diffused ? What is said of their importance ? 44T. How does rye differ from wheat? What is said of its husk? Of its gluten? Of its analysis ? 448. For what is Indian corn distinguished ? What is its composition ? Whjjt is samp ? Hominy ? Why does it not keep well when ground ? 449. What is said of oats ? For what is it distinguished ? What is its composition ? What is avena T Why has the meal a rough taste ? What are grits? How are they used? 450. What is the composition of barley ? What is pot-barley? pearl-barley? 451. For what is rice re- markable ? What is said of it ? 452. What is said of buckwheat ? LEGUMINOUS SEEDS. 453. What is said of the nutritive power of peas and beans f What is the composition of peas ? Why cannot their meal be made into bread ? 454. What is the composition of beans ? 455. What is said of the ash ? FEUITS. 456. For what are fruits prized? What is their general composition ? How does ripe differ from unripe fruit in composition ? Why do they decay so easy ? Why do we know so little of them? 457. What is said of apples ? What blacks the knife in cutting apples ? What is the proportion of water to dry matter in apples ? In melons 9 What is the dry matter of melons composed of? LEAVES, LEAFSTALKS, ETC. 458. What is said of leaves as the food of animals? What of their nutritive qualities ? 459. How much gluten does dry cabbage contain ? How much water does it lose in drying ? What is said of its decay ? 460. What are the properties of lettuce leaves? Water-cress? Horseradish? What is said of greens? What is the composition of rhubarb stalks ? EOOTS, TUBEKS, BULBS AND SHOOTS. 461. What is said of water in the potato ? What is the average amount they contain ? 462. How much starch do they contain ? How does the time of year affect the quantity ? 463. What is the form of the nitro- genous matter in potatoes ? How much do they contain ? 464. What are the remaining constituents of the potato ? 465. What is said of its analogy to the grains ? What is asparagin ? What are the results of the analysis of its ash ? 466. What is the propor- tion of nutritive matter in the onion ? To what is its odor due ? 467. What is the com- position of beets? 468. What do we know of turnips, carrots, and parsnips ? COMPOUND ALIMENTS ANIMAL FOOD. 469. What are the chief constituents of ani- mal diet ? 470. What is flesh-meat ? Describe its structure. What is its composition ? How much does the quantity of water vary in flesh ? Of oil ? 471. What gives flesh Its red color ? What is the juice of flesh ? What does it consist of ? What are its pro- perties? What is kreatine ? Kreatinine? 472. How does blood differ from flesh? What is the composition of bones ? marrow ? Skin, cartilage, and membrane ? Tongue and heart? Liver? Brain? Stomach? 473. Describe the eggshell. What does the egg consist of ? What does it weigh ? MILK. 474 What is milk ? In what respect is it a solution ? In what an emulsion ? What is its specific gravity ? Its taste when first drawn ? 475. What is said of the pro- portion of its elements ? 476. How does the kind of food consumed by the animal affect her milk? Why should there be change of diet? What is said of the effect of different foods upon butter? 477. How does the first milk after calving differ from that yielded afterward? 478. What time of year is most favorable for milk ? What climate ? What weather ? What other causes are mentioned as affecting the milk ? 479. How is cream formed? What does it consist of ? 480. What advantage is there in skimming milk in five or six hours after setting it, and again afterwards ? Why should it be set in shallow pans ? What is said of temperature ? 481. How is it that the milk last drawn from the cow is the richest ? How much will the first and last drawn milk differ ? 482. For what is the hydrometer used ? What is said of the value of its indication ? Describe QUESTIONS. 457 the lactometer. What is the average proportion of cream in milk ? 483. "What is tho composition of the ash of milk ? PAGB 256. III. CULINAEY CHANGES OF ALIMENTAEY SUBSTANCES. 1. COMBINING THE ELEMENTS OP BREAD. 484. "Why is the art of cooking necessary ? "What are the chief agents employed in changing our food ? "What are the advantages of changing the cereal grains into bread ? How is bread made ? How is the process to be considered ? 4S5. What is batter ? Paste ? Dough ? What is said of the combination of water with the flour ? What proportion of water will bread lose in thorough drying? How much of this belongs naturally to flour? How much is absorbed in mixing? What kinds of flour absorb most water? What is the amount supposed to depend upon ? What circumstances increase the quantity ? 486. What purposes does the water serve? What is the object of kneading? What is said of kneading by machinery? How may we know when the bread is sufficiently kneaded? 437. What is said of bread from simple flour and water? What is sea-biscuit? What two important characters does such bread lack ? How may these be imparted ? What element of flour makes this possible ? 2. BREAD RAISED BY FERMENTATION. iS3. What is the effect of moisture and oxygen upon the nitrogenized alimentary principles ? What are putrefiable substances ? 489. How are the non-nitrogenous aliments in this respect ? How are they affected by con- tact with putrefying substances ? What are ferments ? Give an example of this action. 490. What is said of the amount of ferment as influencing the process ? Of temper- ature? 491. What is lactic acid fermentation ? Yinous? Acetous? What are the con- ditions of acetous fermentation ? 492. What ensues if flour and water be mixed and set aside for a time in a warm place ? How may a true vinous fermentation be established ? What is such bread called ? 493. What causes the rising ? How does it take place ? Is this true of all kinds of raised bread ? 494. Why is leaven used ? What is said of it ? 3. PROPERTIES AND ACTION OP YEABT. 495. What is malt ? How is yeast produced ? 496. What is the appearance of yeast ? What is the effect of drying ? What has tho microscope revealed concerning it ? How does it act to decompose sugar ? 49T. How may yeast be made at home ? 493. How is yeast made from potatoes ? 499. What are the properties of hop flowers ? What use are they in brewing ? 500. Why is yeast often dried? What is said of mechanical injury to yeast? How is dried yeast prepared? 501. How may the bitterness of yeast be removed ? 502. How may we correct its acid- ity ? 503. Describe the process of raising dough by yeast 504. What causes sourness in dough ? How may it be removed ? 505. What becomes of the sugar in flour when bread is made ? Then, how is it that sugar is found in bread ? 506. How much alcohol is produced in bread ? What is said of the attempts to save it ? 4. RAISING BREAD WITHOUT FERMENTATION. 507. What objections have been urged against fermented bread ? What is said of them ? 508. By what two methods is unfer- mented bread made ? 509. Explain the changes that take place in raising bread with bicarbonate of soda and hydrochloric acid? What are soda powders? What other preparations are used ? What is the difficulty with them all ? What is said of sour milk and soda? 510. What is said of sesqui-carbonate of soda in raising bread ? 511. Why should these substances be used only occasionally ? How are they adulterated ? What advice is given in their purchase ? 512. How is puff paste made ? How do eggs give lightness ? 513. How is gingerbread made ? 5. ALTERATIONS PRODUCED IN BAKING. 514. How is bread commonly baked ? How should the oven be made ? If the heat be too great or too little, what follows ? What is the proper temperature of the oven ? How may it be tested ? 515. What weight does bread lose in baking? 516. What causes the swelling of the loaf? 517. What changes occur in the crust ? How may a hard crust be prevented ? 518. What changes occur in the crumb ? 519. What are the qualities of newly -baked bread ? What causes 20 458 QUESTIONS. staieness in bread ? How is this proved ? What further is said of the water in bread f 520. What are the qualities of good bread ? What conditions will secure it? 6. INFLUENCE ov FOBEIGN SUBSTANCES IN BEEAD. 521. How does common salt affoct bread ? What is said of the use of alum? Of sulphate of copper ? Carbonate of mag- nesia ? 522. How is so much bad flour produced ? How do these mineral substances act upon altered gluten ? Is there any harmless substance that will do the same thing. 523. How is lime water made ? How is it used ? With what result ? 524. What are ita effects upon the consumer ? 525. What is the effect of rice added to wheaten flour ? Of rye ? How is Indian corn chiefly used ? What is said of Graham bread ? Of pud dings ? 526. What is M. Mourie's new theory of bread-making ? 7. VEGETABLE FOODS CHANGED BY BOILING. 527. How does boiling differ from bak- ing ? 528. In what parts of edible vegetables is woody fibre found ? How does boiling affect it? How may it be changed to nutritive matter? What is said of Autenrieth's experiments ? 529. How does sirup differ from dissolved sugar ? What is the effect of heating melted sugar to 350 ? Of heating dry sugar to 400 ? What are saccharates ? 530. Explain Fig. 100, showing the breaking up of starch grains. How do heat and water together affect them ? 531. How does the appearance of a mixture of starch and water change by heating it ? When allowed to stand for some time, what does it be- come ? How may the process be hastened ? How is dry starch changed to dextrine ? 532. How does starch occur in the potato ? What makes potatoes mealy after boiling ? When are they waxy? What is said of the different methods of cooking them? 538. Why is soft water recommended in cooking ? When is hard water best ? How" may soft water be made hard? What vegetables cannot be boiled soft in hard water? What s said of boiling onions ? 8. How COOKING CHANGES MEAT. 534. What is the effect of moderate heat upon pure fibrin ? Of still higher heat ? How does boiling affect it ? How does heat alter albumen ? How may albumen be used as a clarifying agent ? What proportion of albu- men suffices to make its solution solid ? How is fat affected by heat ? 535. How is ex- tract of flesh obtained ? What are its properties ? How may we change the taste of beef to that of fowl ? 536. What is the first effect of heat upon fresh meat ? In what three ways is heat applied in cooking meat? How are the losses in each mode stated? Why are they greater in baking and roasting ? 537. Describe the best method of cook- ing meat. When is it underdone ? When quite dono ? Why should the fire be hot at first in baking and roasting ? 539. Why is the fibrin more tender in this method ? Why- Is the flesh of young animals more tender than that of old ones ? What is said of th size of the piece of meat as modifying its quality ? 540. What is the object in making soaps, broths, &c. ? What is the best method ? What is said of gelatin in soup? 541. What are Liebig's directions for the preparation of meat broth for the sick ? 9. PEEPAEATION AND PEOPEETIES OF BUTTEE. 542. What is the effect of heat upon milk ? Upon cream ? What is said of this butter ? 543. What changes occur to the milk and cream in churning ? 544. How should the motion in churning be regulated ? 645. What is the length of time required for churning milk and cream ? How does thia circumstance affect the quality of the butter ? What should be the temperature of the cream at the beginning of the process ? Does it change during the churning ? What is said of the use of the thermometer ? 546. To what is the flavor of butter due ? What is its texture ? Why is it different in this respect from lard ? What is said of first-rate butter ? Of the absorbent qualifies of butter and cream ? Of the kind of food best for the cattle ? 10. PEEPARATION AND PEOPEETIES OF CHEESE. 547. What is the curdling of milk ? What causes it ? 548. How is milk curdled artificially ? 549. What is rennet ? How is [t used ? To what is its action due ? 550. What does the separated curd of milk consist of? What the whey? What sort of cheese does pure casein make? How does the cream of milk change it? What 10 said of the heat employed in curdling? Of the amount of rennet used ? QUESTIONS. 459 PAGB 289.-IV. COMMON BEVERAGES. 1. PBOPEBTTES AND PBEPAEATION OF TEA. 551. What is tea? How is the plant grown? 552. How are the different varieties produced ? 553. What two classes include all kinds of tea? What is the real cause of difference between these classes? What is said of the effect of steam in withering fresh leaves ? 554 Give the list of green teas oi commerce. Of black teas. Explain the name, and give the origin of each of them 555. What is the composition of tea ? Which of these are soluble ? What proportion remains insoluble ? 556. What is tho Chinese method of making tea ? What does its composition seem to indicate as the best method? What is the appearance of a good decoction of tea on cooling ? 557. If the water of tea be not boiling when poured upon the leaves, what do we get ? How is it commonly ? What were the experiments oj Mulder and Peligot ? What is said of variation in the composition of teas bearing the same name in market ? How may the gluten be dissolved ? 558. How are the green teas much adulterated in China? How do the English adulterate tea? How may these frauds be detected ? 2. PEOPEETIES AND PEEPAEATION OF COFFEE. 559. Describe the coffee tree and its seeds. How are they separated ? 560. What is the best coffee ? How does it differ in appearance from other varieties ? 561. What is the composition of coffee as it comes to market ? 562. What is the effect of roasting upon coffee ? How are its bulk and weight affected? 563. What is said of the importance of careful roasting? Of covering the vessel ? Of the temperature ? 564. How does ago affect coffee ? How is it often spoiled ? 565. How should it be ground ? What is said of the fragrance of coffee ? OJ steeping and boiling ? What is Dr. Donovan's method ? 566. What is the effect of put- ting soda in the water of which coffee is made ? 567. With what is coffee adulterated? What is chiccory ? How is it adulterated ? 568. How may the cheats in coffee be de- tected ? 3. COCOA AND CHOCOLATE. 565. What are cocoa beans ? How are they prepared for use? What is their composition? 570. What is "flake cocoa"? Cocoa nibs? Chocolate? 571. How are these preparations used? 572. What are the qualities of good chocolate ? What cheats are practised by dealers in chocolate ? PAGE 300. Y. PEESEEVATIOX OF ALIMEXTAEY SUBSTANCES. 1. CAUSES OF THEIR CHAXGEABLENESS. 573. Why must food be easily changeable ? What is said of gluten as an example ? 574 What has been the idea of vital forces in the body ? What is at present known ? How do the changes going on in the 'living and lifeless body differ ? 575. Upon what does the rate of change in aliments depend ? What substances are most changeable ? What is said of water as promoting change ? Of tem- perature ? Of the atmosphere ? 2. PBESEBVING BY EXCLUSION OF AIE. 576. How is it shown that air excites decay ? 577. Does all decay require the presence of oxygen ? How is this explained ? 573. How does boiling arrest these changes ? What is Appert's plan of preserving ? 579. What does Prof. Liebig say of preserving aliments in air-tight vessels ? 580. How is this done when the cans are soldered ? 581. How, by Spratt's cans ? 582. What suggestions ar given to aid in their use ? 3. PBESEEVATION AT Low TEMPEEATUBES. 583. What is the effect of a temperature Of 32' upon the changes of aliments ? Of a boiling temperature ? Of still greater teat ? 5S4. What is said of freezing as a means of preserving ? What cautions are given ? 585. What is said of cellars ? Of refrigerators ? Describe Lyman's refrigerator, Fig. 107. 586. Why are fruits so perishable? How do cellars preserve them? What precautions are necessary in gathering fruit for winter? What other modes of preserv- ing fruits are mentioned? 4 PBESEBVATION BY DEYINO. 587. How has nature provided for the retention of water in some of her products ? 588. What is said of drying ? How may it be effected? 460 QUESTIONS. What is said of drying by artificial heat ? 589. How are succulent vegetables best pr* served ? 5. PKESEBVATION BY ANTISEPTICS. 590. "What are antiseptics? Mention those in domestic use. What is the composition of common salt ? What remarkable things are stated of it ? 591. What are the sources of common salt ? How may pure salt be known ? How may it be purified ? 592. How does salt act in preserving meat ? What is the effect of brine upon flesh ? 593. What beside water does salt extract from meat? Why is saltpetre used with salt ? 594. What is said of salting vegetables? 595. How does sugar act as an antiseptic ? What is said of weak solutions ? 596. What is said of alcohol ? Of vinegar ? Of creosote ? Of oil ? Of charcoal ? 6. PBESERVATION OP BUTTEB AND CHEESE. 597. How may milk be preserved sweet ? What is concentrated milk? 598. What is the composition of butter just from the churn ? 599. Why is it worked mechanically ? How may it be done ? 600. What is said of the practice of washing butter ? 601. What is rancid butter ? How is it pro- duced ? 602. Why must butter be made air-tight in packing ? 603. Why is salt added to butter ? How does it preserve it ? What other substances are used ? What is said of them ? 604. Why is old cheese best ? What are the best conditions for the perfec- tion of cheese ? What changes take place in it ? 605. How do eggs change by time ? How may they be preserved ? PAGE 318. VI. MATEKIALS OF CULINAKY AND TABLE UTENSILS. 606. What is the purpose of this chapter ? 607. What is the chief objection to iron for kitchen vessels ? What is said of these compounds ? How should iron kettles be managed ? What is this enamel ? 609. How is all tin ware made ? 610. Is metallic tin injurious to the system ? What substances affect it ? Is it much acted upon ? How is common tin contaminated ? 611. Why cannot zinc be much used ? 612. What is verdi- gris ? What other substances may be formed when copper is used in cooking ? 613. What is said of the salts of copper? 614. What qualities commend this metal for kitchen vessels ? How may it be protected ? What is said of brass kettles ? 615. What attempt has been made to form more perfect cooking vessels ? What is remarked of them ? 616. Of what is earthenware made ? Why must it be glazed ? How is this done ? 617. What materials are used in glazing common earthenware ? What are the qualities of this glaze ? How can it be detected ? What substances act on it ? 618. Why does glazing sometimes crack ? How may soft glaze be detected ? 619. What is said of por- celain. Of what is it made ? What are its qualities ? Describe its manufacture. What is said of its permanence among clay wares? Of its beauty? How is it colored? 620. What precaution is given in the use of cements ? PAGE 324. VII. PHYSIOLOGICAL EFFECTS OF FOOD. 1. BASIS OF THE DEMAND FOE ALIMENT. 621. What is a common thought of men re- specting creation ? What is the true idea about it ? 622. What is said of our ability to understand our own organization ? 623. How do we maintain our identity through con- stant changes ? 624 By what calculations is the extent of change going on in the body shown? 625. State the case of Thomas Parr. 626. Why must such an amount of mat- ter be taken into the system yearly ? How is it in the growing period of life ? What is the relation between waste and supply in old age ? In adult life, what changes are per- petually carried on in the system ? 626. What important questions occur in relation to these changes ? What is said of the materials introduced into the body, and of the agent that acts upon them ? How do we influence the nutritive processes that take place in our bodies ? 627. What is said of the beneficent use of hunger and thirst ? In what do they consist? 628. How will the subject be considered ? 2. FIRST STAGE OF DIGESTION CHANGES OF FOOD IN THE MOUTH. 629. For what purpose is all food destined? Of what does the blood consist? What then must occur to the food before it can become blood? What is digestion ? 630. In what state is the QUESTIONS. 461 food introduced into the mouth ? Describe the mechanism for reducing it still finer, 631. Why is mechanical action insufficient ? What is the saliva ? What conditions pro- duce a flow of saliva ? 632. What are the properties of saliva ? What is the " tartar " of teeth ? Describe the different salivas. 633. What aro the offices of saliva ? What part of our food does it act upon ? What practical inference follows from this ? 634 What is said of careless, hasty eating ? How does the state of mind affect the digestion of food f 635. What is the effect of profuse spitting ? 3. SECOND STAGE OF DIGESTION CHANGES OP FOOD IN THE STOMACH. 636. What be- comes of the food as it passes from the mouth ? Describe the stomach ? How does it vary in different animals? 637. How many coats has the stomach? How do they differ ? 638. What movements of the food occur in the stomach ? How are they pro- duced ? 639. What are the stomach follicles ? Explain Fig. 117. 640. What is the pur- pose of this arrangement ? 641. What is said of the necessity of regular times of eating ? 643. What are the properties of gastric juice ? Ho-.v soon after eating does digestion get fully under way ? 644. How does the digestion of the stomach differ from that of the mouth ? 645. How may artificial gastric juice be prepared ? How does the digestion 01 the stomach differ from artificial digestion ? 646. What is pepsin ? What can it not do ? 647. How does gastric solution differ from common solution ? What is meant by the term peptone f 648. What follows when the alkaline saliva enters the stomach ? 649. How have people erred in estimating the quantity of gastric fluid secreted ? What is now believed about it ? 650. What is meant by digestibility of foods ? What is said ol Dr. Beaumont's investigations ? In regarding the times of digestion, what consideration beside the solubility of aliment must be taken into account ? What are some of the re- sults of Dr. Beaumont's observations ? 651. How do the liquids of the stomach get inte the blood ? How is this proved ? 4. THIRD STAGE OF DIGESTION CHANGES OF FOOD IN THE INTESTINES. 652. What is the duodenum ? What fluids enter it ? How do they differ from gastric fluids ? 653. What portions of food are affected by these juices ? What changes occur ? What pro- vision is made for undigested albuminous matter that has escaped from the stomach ? 654. In what ways are substances absorbed from the intestines ? How do the lacteals perform their office ? What is the course of these lacteal fluids ? 655. What foods are most laxative ? 5. FINAL DESTINATION OF FOODS. 656. How much blood has an average-sized man ? 657. What causes the composition of the blood to vary? What is it stated to be. 658. How does the blood appear when viewed by the microscope ? What is said of these globules? 659. How is the development of power shown to be the leading purpose ol the body? What is said of the creation of force ? 660. What are the chief elements 01 our food ? Through what agency do they become food ? What force acts upon the vege- table kingdom ? Is the case different when we eat flesh ? In this view, what is said ot the blood ? 661. In what state does force reside in food ? How is it made active ? What is the nature of these changes ? 662. How is the necessity of the constant introduction of food shown ? What is starvation ? 663. What is combustion ? How is the action of oxygen in the body shown to be combustive ? 664 How do we find foods divided in reference to their destination ? What is said of the difference in combustibility of dif- ferent aliments? 665. What is said of the combustibility of nitrogen? 666. What names are given to non-nitrogenous food ? To the nitrogenous ? How must these dis- tinctions be regarded? 6. PRODUCTION OF BODILY WARMTH. 667. Why must the body possess a fixed tem- perature ? What is the temperature of health ? What is said of the power of the body to maintain it ? 668. In how many ways does the body lose heat ? How much is lost by evaporation ? 669. How is the supply of heat kept up ? What is the physiological difference between warm and cold-blooded animals ? When no food is taken, how is warmth sustained ? What occurs in plants when they exhale carbonic acid ? 670. How iocs the experience of those who ascend high mountains accord with this view ? How 462 QUESTIONS. is it with those who go down in diving "bells? 671. What is the final destination of most of our food ? "When do we require most heat-producing food ? Among foods, which haa the highest calorific power? How do other foods rank? How are they compared? What is said of the use of bread in the arctic regions ? What was Dr. Kane's expe- rience ? How is it in warmer regions ? 672. In very hot weather, how is the temper- ature kept down ? 673. What is said of houses and clothing as replacing food ? 674. At what times of life does cold affect the body most ? What has been observed in hospitals for the aged ? 675. What relation is there betwsen periods of rest and eating, and the daily changes of temperature ? 7. PRODUCTION OF BODILY STRENGTH. 676. What is the annual amount of heat pro- duced by an adult man estimated to be ? What is said of the force required to execute the involuntary motions of the body ? 677. What is said of the waste that accompanies this expenditure? How much does the body lose daily ? 678. From what part of food is flesh formed ? What is said of albumen ? How is it in the bird's egg ? What is the double purpose of albuminous food ? 679. Explain how oxygen acts upon the tissues. In what sense are nitrogenous matters heat-producers ? 680. When waste and supply are equal, what takes place in the body? When waste exceeds supply ? When supply exceeds waste ? 681. What is the relation of common salt, tea, &c., to nutrition. Why are they not true foods ? 8. MIND, BODY, AND ALIMENT. 682. What is the relation of mind to matter ? What Is said of the brain ? 683. What material changes occur accompanying the manifestation of mind? What provision is made for its nutrition? If this is interrupted, what fol- lows ? How does starvation affect nervous tissue ? 684. What measure has been found of the amount of exercise a part has experienced ? Can these results be fully depended upon ? 685. What is said of the exhausting effect of mental exercise ? 686. What re- markable properties has phosphorus ? How does the proportion of phosphorus in the brain vary in different classes of persons ? In what form is it found ? 687. What is said of special brain nutriments ? What does Liebig say in this connection ? 688. What im- portant considerations of diet should govern brain-workers ? 689. What is said of brain excitants ? 9. INFLUENCES OF SPECIAL SUBSTANCES SALINE MATTERS. 690. How were the min- eral elements of plants once regarded ? What is now known ? 691. What is a salt ? A neutral salt? An alkaline salt ? An acid salt? What does the ash of foods consist of ? How are the acids changed in burning ? What proportion of salts is found in celery ? Sallad ? Cabbage ? 692. What becomes of the mineral parts of food when taken into the system ? 693. What is said to be the state of all the animal juices ? How is it with the blood in this respect ? What properties of the blood depend upon its free alkali ? 694. What is the character of flesh and its juices ? Do acids or alkalies predominate in the system ? What are the chief flesh acids ? What do these conditions of blood and flesh juice seem to indicate ? 695. Where and to what extent does common salt exist in the system ? What are its offices ? What does it yield by its decomposition ? What is said of the salts of sodium and potassium in blood and flesh ? 696. How does salt escape from the system ? How is the supply kept up ? What is said of its presence in vege- tables? Of the natural demand for its use? 697. What are the effects of eating too little salt? What is scurvy? What are anti-scorbutics? How does flesh differ in the proportion of salt it contains ? 698. What compounds of soda and potash are used in making bread, and how do they differ ? What are their relations to the system ? When are they usefal, and when harmful ? LIQUID ALIMENTS. 699. How much of the body is water ? In what forms and to what extent is it taken ? 700. In what conditions is it found in the body ? 701. How do plants and animals differ in their relations to water ? 702. How does water affect the digestive process ? 703. In Dr. Booker's experiments upon the use of an excess of water, what conclusions did he reach ? 704. What is said of the relation of tea and coffee to foods ? 705. How do the different elemeats of tea affect the system ? What are the con QUESTIONS. 463 fusions from Dr. Becker's experiments ? 706. What is the effect of enipyreumatic sub- tances upon digestion ? What will people whose stomachs are sensitive, observe to bo the effect of strong coffee ? How is tea different ? 707. What are Lehma^s statements on the influence of coffee ? 708. What is said of chocolate ? 709. What substances are found in the various liquors ? Upon what does their commercial value depend ? What is the main element of them ? 710. How does the action of alcohol compare wTth that of water in the system ? 711. What is said of its power to nourish tissue ? 712. Why is It not a respiratory aliment? 713. What were the results of Dr. Booker's experiments with this substance ? 714. How do the statements of Moleshott, Chambers, and Liebig, upon the use of this substance, compare with each other ? 715. How are the stimulating effects of these beverages described ? 716. What is said of milk ? How does milk from different species of animals differ ? How does skimming alter the dietetical qualities of milk? 717. What kinds of soup are strength-giving? What is said of gelatin ? Why may it be good for invalids ? SOLID ALIMENTS. 713. Why must starch be cocked ? In what form is starch best digested, and why ? 719. What changes does sugar undergo in the system ? What ia said of its injuring the teeth ? 720. What purposes does gum serve in the body ? 721 What proportion of oil do we obtain from different foods ? How may the uses of fats be considered ? 722. What is the relation of fat to bodily movement? To beauty of form ? To swimming ? 723. What is said of the action of fat in the stomach ? How does the distribution of fat in meat affect its digestibility ? Why are fish and poultry easily diges- tible ? How is it when they a/e dressed with fat ? 724. What changes are produced in the fats by heat? Why are cakes less digestible than bread? What does Dr. Pereira say upon the use of the oils ? Dr. Chambers ? 725. How does fat aid in the nutrition of the body? 726. What is tubercular consumption? What is the cause of it? Why have oily matters been prescribed for this disease ? What is said of its prevention ? 727. How are bilious conditions produced ? Rheumatic ? Scrofulous ? Scorbutic ? 728. In what state is meat most digestible ? How does veal and lamb broth differ from that of beef and mutton ? 729. What is said of pastry and puddings ? Of boiled dough ? 730. How do coarse and fine bread differ in composition, and in their effects upon the system ? 731. How should beans and peas be cooked ? 732. What is said of the healthfulness of vegetables ? 733. What is the dietetical value of the potato ? The turnip ? The onion ? 734. What is said of fruits? Of the apple? 735. What are condiments? 736. When regarded as an aliment, what are the qualities of cheese ? What are they as a condi- ment ? 737. What is the influence of vinegar upon digestion ? Upon corpulence ? 738. How do condiments act upon the system? x 10. NTITEITIVB VALTTE OF FOODS. 739. What would we infer of the purposes of foods from their composition ? What is said of the power of the system to transmute food ? 740. What must our diet contain ? How must it be varied ? 741. What does Fig. 112 represent ? Explain it Has the quantity of solid matter any relation to nutritive power ? 742. What is the best that can be done in estimating the comparative value of foods ? With what restrictions must this be taken? 743. Explain "Fig. 122, giving the relative powers of the caloriflent elements of food. Why is there no such table for the nutritivo group? What is said of alcohol? 744. Why is an exclusive meat diet bad economy ? What estimate has been made showing the advantage of starchy food in the case of a savage ? What is said of bread in this relation ? 745. What makes the nutritive elements of diet most expensive P When do the calorifient rise in value ? 746. What does Fig. 128 represent ? Explain it What idea must be borne in mind in studying this diagram ? 447. What makes the composition of milk an interesting study? How does the human infant differ from the young of all other animals ? Why is the milk prepared for them richer in curd ? 748. What are the advantages and deficiencies of wheat ? How doea wheat flour compare with milk and blood ? 749. How much is the daily waste of tissue ? How much food does an adult laborer require to restore this loss ? What is the propel proportion of nitrogenous to non-nitrogenous matter? Why is bread a bad respiratory 464 QUESTIONS. aliment ? How does instinct provide against this need ? 750. How does wheat flom vary in composition? What is said of the relation of commercial and nutritive values 1 751. What is said of the amount of bran separated in grinding now and formerly ? 01 the effect of bolting? 752. What must be eaten with lean flesh, and why ? What com binations of food have the instinctive cravings of men prepared, and what do they illus- trate ? 753. Why are sago, &c., unfit for children's food ? What do they require ? What is said of the use of lime ? 11. TUB VEGETARIAN QUESTION. 754. What controversy exists upon the subject of diet ? What does the vegetarian diet consist of ? What do the advocates of vegetable diet insist on ? What is replied by the friends of mixed diet ? What course will here be pursued in reference to the subject? 755. What has formerly been believed of the power of the system to transform food ? What is now known ? 756. What is said of the iden- tity of vegetable and animal principles ? What does this seem to indicate ? 757. What difference exists between vegetable and animal food ? Why is flesh the most perfect of all aliments ? How does it increase the activity of the system ? What is said of its stimu- lating effects? Are vegetarians tempted to excessive eating? 758. What remarkable fact concerning the mineral constitutions of these two forms of food is mentioned ? 759. What are the characteristics of human saliva ? What does it indicate ? 760. What is said of the relative economy of the two kinds of diet? 761. What is said of the diversity of diet that exists among men ? 12. CONSIDERATIONS OF DIET. 763. What circumstances influence the quantity of food needed ? What is told of the Manchester manufacturer ? 764. Why is it difficult to classify diet as low, high, &c. ? 765. How should rules of diet affect us ? What is said of diet scales ? 766. What reason is given for eating slowly ? 767. What considerations should fix our times of eating ? Why should breakfast be early ? Why is luncheon com- mended ? Why are late suppers condemned ? 768. Why should we not eat when tired ? Why should little exercise be taken before breakfast ? 769. What is said of the sympa- thy between brain and stomach ? What is hence recommended ? 770. Why should we rest after a full meal ? 771. What bad results flow from excessive eating ? 772. What is said of the necessity for prompt supplies of food ? How does hunger affect the mind ? 773. What relation is there between great exertion and hearty eating ? What is said of the habits of students ? Of Americans ? 774. Why is a stiff regularity in the recurrence of dishes condemned ? 775. What causes promote corpulence ? What is a good diet for corpulent people ? 776. What directions are given to nursing mothers ? What is said of procuring and managing wet nurses? How may cow's milk be corrected for children? What directions are given in reference to their solid food ? 777. What changes are going on in the system during childhood and youth ? What food does this period require ? 778. What should be the diet of middle life ? 779. What changes are going on in the system as ago advances? What do they indicate in regard to the food ? What conse- quences may flow from neglecting these cautions ? PAKT V. CLEANSING. PAGE 422. I. PEINCIPAL CLEANSING AGENTS. 780. What is dirt ? How is it removed ? 781. How does water act in cleansing ? 782. W hat impurities are sometimes found in water ? 783. How is water purified by sub* Bidence ? 784. How by filtering ? 785. Describe the filter Fig. 124. What is said of char- coal as a filtering agent ? 786. How may dissolved impurities be separated from water ? How has the hardness of water been expressed ? What causes the fur on the tea-kettle ? Does the length of time of boiling affect the result ? 787. What are the alkalies used in cleansing? What is said of the alkaline carbonates ? Of aqua ammonia? 788. What is eoap? 789. How is soap mado? 790. What conditions produce hard, and what soft eoap ? 791. What is said of th<* water in soap ? How does the solubility of soap vary ? 792. What is Castile soap ? Cui I soap ? How are fancy soaps made ? Transparent soap 1 QUESTIONS. 465 PAGE 428, IL CLEANSING TEXTILE FABBICS. 793. What is stated to be the general principle of cleansing ? Why must the power of the alkalies be restrained ? By what means is the dirt held to the garment ? How ia soap adapted to this state of things? 794. How may we test the hardness of water with soap ? 795. Explain the difference in texture between woollen, cotton, and linen fibres. Why do the woollens shrink? How should they be washed? 796. What is said of the removal of spots ? How is alumina used ? What is French chalk ? Ox gall ? How does a portion act in removing stains ? How may wax, resin, and pitchy spots be taken out ? How, oil-paint stains ? Coffee and chocolate ? Fruit stains ? Ink spots ? Indel- ible ink? PAGE 431. HI. CLEANSING THE PERSON. 797. Describe the structure and offices of the skin? 798. What are the oil glands? How do they protect the system ? When the skin is neglected, how are these altered ? What is Fig. 129 f 799. Why must soap be used in washing the skin ? What is said of its use ? 800. What directions are given for washing the face ? 891. What causes tartar to accumulate on the teeth ? How may it be removed ? What are the best tooth- powders ? PAGE 436. IV. CLEANSING THE AIE. 802. What is said of this subject ? 803. When we can smell the impurities of the air, how are we apt to relieve ourselves ? What is said of this method ? What plan should be adopted? 804. What are disinfectants? How do they act? 805. What are the pro- perties of newly burned lime? How does it act in purifying the air? How does it supply moisture to the air ? What are its effects when spread upon fresh animal and vegetable substances ? How does it act upon putrefying matter ? 806. What is chlorine ? What is said of hydrogen ? How does chlorine destroy the impurities of the air ? 807. How may it be obtained ? What cautions are necessary in its use ? What is chloride of lime ? How may it be used ? 808. What is said of sulphurous acid gas ? What are its properties ? 809. What is said of chloride of iron ? Chloride of zinc ? Sulphate of iron ? Acetate and nitrate of lead ? 810. What are the deodorizing effects of charcoal ? How is it used? 811. Explain the structure of charcoal? How does it act? How does it hasten destructive changes ? How has this quality been applied in hospitals ? Explain the breath filter. What advantages has it over many disinfectants ? PAGE 441. V. POISONS. 812. How are poisons divided ? What is said of prompt action when poison has been swallowed ? What symptoms indicate poisoning ? 813. When poisoning is suspected, what should first be observed? If it be acid, what are antidotes ? If there is no clue to the kind of poison, what may te done ? What la arsenic ? What is said of its employ- ment? INDEX. Ablution of the face, 434. Acids, vegetable, 225; composition of, 225; of apples, 225; of lemons, 225; of grapes, 225 ; nature of, 369. Acetic acid, 226. Air, non-conduction of, 35 ; pressure of, 43, 151 ; composition of, 49, 153 ; contami- nation of by gas burning, 123; general offices of, 150 ; weight of, 151 ; effect of varying pressure of, 152 ; intermixture of, 153 ; constituents of, 154 ; oxygen of, 154; moisture in, 157; conditions of drying power of, 158 ; system affected by moist, 1GO ; by dry, 161, 170 ; effects of its ingre- dients, 163; impurities of external, 165; conditions of salubrity, 166 ; self-purify- ing, 167; causes of impurity of in dwell- ings, 168 ; bad influence of heating appa- ratus upon, 1 68 ; affected by hot-iron sur- faces, 169 ; composition of, altered by heating, 169 ; impurities of, 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 ; stratifica- tion of, in rooms, 187 ; currents through doors and windows, 189, 190; currents affecting the system, 191 ; supply of, by crevices, &c., 195 ; modes of introducing, 190; effect of breathing rarifled, 355. Albumen, vegetable, 227; composition of, 227 ; properties of, 228. Alcohol, as an illuminator, 116; as a pre- server, 314 ; the principle of spirituous liquors, 378. Aliments, source of, 205; classification of, 206, 207; undaio proportions of, 388; cci- rection of, 401. Alkalies, 369. Amaurosis, 145; subjects of, 146. Apartments, size of for breathing, 184. Appetite, regulation of, 410. Apples, composition of, 244 Argand burners, 112. Arnott's valve, 193; importance of, 199. Arrow-root, 215, Arsenic, 441. Artificial light, 105; from ignition, 105 measurement of, 124 ; color of, 137 ; inju rious action of; 137; how it affects the eyes, 139; effects upon the retina, 140, 144; heat accompanying, 141 ; unsteadi- ness of, 142 ; extraneous rays, 143 ; may produce inflammation, 144 ; management of, 146 ; whitening by absorption, 148. Barley, 240. Barometer, 43. Beans, composition, 242; mineral mattei in, 243 ; digestibility of, 390. Beaumont, Dr's. table, 343. Bedrooms, air of, 171 ; ventilation of, 201. Beets, 247. Beverages, 2S9. Blood, constituents of, 250, 347; globules, 347; alkaline, 370. Boiling, culinary changes by, 277. Boiling point, elevation of, 44. Bran, composition of, 235. Brain, measure of its change, 865; phos- phatic constituents of, 366 ; has its special nutriments, 867 ; 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 crust, 272 ; in the crumb, 272 ; moisture in, 273; good, 273; influence of salt on, 274; alum, 274; effects of lime water, 275; different kinds of, 276; white and brown, 277 ; coarse and fine, effects of, 389. Broth for the sick, 284. Buckwheat, composition of, 241. Burning fluids, composition of, 116; how explosive, 116 ; conditions of accident from, 117 ; how used with safety, 117. Butter, separation, of, 285 ; composition and properties of, 286; cause of its change- ableness, 315 ; cause of rancidity, 316; ac- tion of air upon, 816; substances used tn preserve, 317. INDEX. 467 Cabbage, nutritive properties of, 244. Camphene, 115 ; combustion of, 115 ; why it spoils, 115. Candles, 108 ; stearic acid, 109 ; tallow, 109 ; spermaceti and wax, 109 ; structure of, 110; office of wick, 110; how it burns, 110; 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, 163; exhaled by respiration, 182. Carrots, 248. Casein, composition of, 228. Cataract, 136. Cellars, foul air in, 173. 327 ; equalization of bodily, 362 ; hasten- ing and retarding, 363. 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, 391. Chevreul, 91. Chimneys, draught of, 55 ; causes of smoky, 56, 57, 58, 59 ; currents in summer, 200. Chocolate, 293; adulterations, 300; effects, 878. Cholera and foul air, 175. Churning, 285. Citric acid, 225. Cleansing, principles involved in, 422 ; by alkaline substances, 425; of textile arti- cles, 428; cottons, linens, and woollens, 429 ; of spots and stains, 430 ; agents for, 430 ; of the person, 431 ; of the skin, 433 ; of the face, 434; of the teeth, 435; of the air, 436. Climate, artificial, 22. Coal, mineral, 53, 54. Cocoa, composition, 298 ; preparation, 299 ; how used, 299. Coffee, varieties, 294 ; composition, 294; effects of roasting, 295 ; effects of time upon, 296 ; mode of preparation, 297 ; adul- teration, 297; how detected, 298; Lehman on the effects of, 378. Cold, when most fatal, 358. Color, influence upon radiation, 30; upon absorption, 31; Newton's theory of, S9; Brewster's theory, 89; complementary, 90 ; tints and tones of, 91 ; chromatic cir- cles, 92 ; contrast of, 97 ; mutually inju- rious, 93 ; contrast of tone, 99 ; harmonies of, 100 ; circumstances influencing, 101 ; associated with white, black, gray, 101 ; combining, 102 ; influence of, upon com- plexion, 102 ; arrangement of flowers, 103 ; paper-hangings, 103 ; furniture, 105 ; popu- lar recognition of the effects of, 140 ; asso- ciated heat of, 141. Combustion, products of, 50; air hinders, 55 ; within the body, 351. Common salt transparent to heat, 23; effect upon bread, 274; uses of, tn the system, 871 ; contained in food, 372 ; mode of crys- tallization, 311 ; purification of, 312 ; how it preserves meat, 312; how it injures meat, 313; too little and too much, 377. Complexion, 102. Condiments, 391. Contagion and foul air, 175. Corn starch, 215. Cream, production of, 253. Culinary art, objects of, 256. Culinary utensils, 318 ; of iron, 813 ; of tin, 819; zinc, 820; copper, 320, 321; ei elled ironware, 321 ; earthenware, Porcelain ware, 323. Dentifrices, 435. Dew, cause of, 32 ; dew-point, 153. Diet, for brain-workers, 368 ; mixed indis- pensable, 393 ; exclusive meat, bad econ- omy, 896 ; required by children, 402 ; of flesh, influence of, 405 ; mineral matters replacable in, 406 ; economy of vegetable and animal, 407 ; diversities of, 408, 409 ; scale of U. S. Navy, 410, and the capacity of exertion, 415 ; order and variety in, 416, and corpulence, 417; of infancy, 417, 418; of childhood and youth, 419; of middle life, 420 ; of advanced life, 420. Diffusion of gases, 153. Digestion, object of, 830; in stomach, 833; extent of gastric, 340; influence of coffee on, 377. Dirt, composition of, 428. Disguising bad smells, 436. Disinfectants, 437 ; quicklime, 437 ; chlorine, 437; chloride of lime, 438; sulphurous acid, 438 : charcoal, 439. Double windows, 159. Dough, water absorbed by, 257 ; effects of kneading, 258 ; what makes it rise, 261 ; raising by leaven, 262; raised by yeast, 266 ; acidity in, 266 ; sugar in, 267 ; alco- hol in, 267 ; raised with esgs, 270. Dress, 21, 35 ; colors of, 102. Ebullition, 42 ; effects of pressure upon, 44. Eggs, composition of, 250; preservation of, 318. Electricity, atmospheric, 164. Emerson's injector, 197; ejector, 198. Ether, luminous, vibrations of, 87. Evaporation, 42 ; cooling 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, 130 ; influence of reading and writing upon, 131 ; cause of far-sight- ed, 132; remedy of far-sightedness, 183; cause of near-sighted, 134; remedy oi near-sighted, 135; cataract in, 136 ; influ- ence of carbonic acid upon, 142 ; bad light inflames, 144. Faraday, Dr., 171. Fats, see Oils. Farina, 237. Farina kettle, 45. Fermentation, 260 ; conditions of, 260 ; dif ferent kinds of, 260 ; spontaneous, 260. Fibrin, 228. 468 INDEX. Fire, kindling of, 50; risk of, 73; origin of, 74. Fireplace, form of, 62; action of, 62; econ- omy of, 63; ventilation by, 192. Flame, cause of, 50 ; illumination from, 106 ; hollowness of, 110 ; length of, in gas burn- ing, 123. Flesh, composition of, 248 ; juice of, 249 ; action of heat upon, 281; changes by cooking, 282; loss of weight in, 282; best plan of cooking, 283 ; common method objectionable, 283 ; its juices acid, 371 ; digestion of, 388. Flour, white and dark, 236; evaporation from, 236; changes in, 236; effects of its preparations, 889. Foods, why perishable, 800; conditions of perishableness, 301 ; effects of, may be un- derstood, 325; periodic supply of, 337; digestibility of, 341, 342, 843 ; changes in mouth, 830; in stomach, 335; in intes- tines, 344 ; constipating and laxative, 846 ; final destination of, 847 ; 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 ; demand for variable, 408 ; daily requirement of, 409. Force, production of, destroys tissue, 361. Freezing, artificial, 41 ; heat produced by, 42. Frost, cause of, 33. Fruits, composition of, 243 ; dietetic effects of, 391. Fuel, influence of, 22 ; composition of, 49 ; heating effects of, 54. Furniture, colors of, 104. G Gas fixtures, 124. Gas, illumination by, 119; sources of, 119; composition of, 120; purification of, 119; various sources of, 120 ; measurement of, 121 ; how burned, 122 ; contaminations of air, by burning of, 123 ; disadvantages of lighting by, 124; fixtures of, 124 ; islight- ing by, injurious, 149. Gas meter, 121. Gastric juice, 838; its acid and ferment, 839 ; quantity of, 841. Gelatin, 230. Gingerbread, 271. Glass, opaque to heat, 28. Gluten, 229 ; quality of, 232. Glycerine, 109. Grain, grinding of, 234; structure of, 234; sifting of, 235. Grates, 64; combustion in, 64; Circular, 66 ; Arnotfs, 66 ; height of, 67. Gum, artificial, 223; composition of, 223; physiological effects of,SS4. Hett, from the sun, 18 ; from the stars, 18 ; distribution of, 19; influence on vegeta- tion, 19; distribution of animal, 20; in- fluences man's development, 20 ; relation to character, 21; diffusion of, 23; equi- librium of, 23 ; expansion of, 23 ; weight of, 24; radiation of, 27, 29, 30; transmis- sion of, 28 ; absorption of, 29 ; exchanges of, 31 ; 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, 860. Heating arrangements compared, 74. Honey, 217. Hot-air furnace, 70 ; ventilation by, 193. Hot-water apparatus, 72. Human body, purpose of, 848 ; constant temperature of, 853; how it loses heat, 854; how it produces heat, 354; resources against cold, 856 ; force exerted by, 360 ; limited action over food, 392 ; its restricted transforming power, 404. Hunger, use of, 329. Hydrogen, its office in fvel, 50; heating powers of, 51. Hydrometer, 255. I Illumination, artificial, 105 ; by ignition, 106 ; from burning gas, 106 ; simplicity of the laws of, 107; by means of solids, 108; by liquids, 112 ; by gases, 119. Impure air, and contagion, 175 ; cholera and, 175; fevers and, 176; scrofula and, 177; consumption and, 178; infant mortality and, 178; undermines the health, 179; morbid mental effects of, 180. Indian corn, 239. Intestines, juices of, 344; changes in, 345; absorption from, 345. Jelly, vegetable, 226, Kneading, effects of, 258. Lactometer, 255. Lamps, 112 ; structure of, 113 ; astral, 113 ; Carcel, 114 ; sinumbra, 113 ; hot oil, 114 : Newell's 117 ; study, 148. Language, 22. Lead, vessels for water, 212. Leaves, nutritive properties of, 244. Lenses, 84. Lettuce, 245. Light, exhilarating effects of, 76 ; theory of. 77; diffusion of, 78; reflection of, 79. 80 ; scattered by air, 82; transmission of, 82 ; refraction of, 82; wave theory of, 87 ; arti- ficial, 105 ; from ignition, 105 ; measure- ment of, 124 ; results of Ure and Kent, 126 ; color of artificial, 137; injurious action of artificial, 187. Liquefaction, 87. Liquors, alcoholic, 378 ; cannot replace wa- ter in the system, 879, and animal heat, 879; Booker's observations, 379; not eco nomical, 88 ; stimulating effect, 880. Looking-glass, 79. Lyman's cold-air flue, 198 ; refrigerator 807 Macaroni, 233. Malaria, 166. INDEX. 469 Malic acid, 2-25. Margaric acid, 109. M:i:-_-arine, 109. Mastication, importance of, 383. Meals, frequency in times of, 410 ; rest be- fore, 411 ; state of mind during, 412 ; ex- ercise after, 412; effects of excess at, 414 Melting points, 88, 111. Milk, composition of, 250; qualities of, 251, ream of, 253; value of, 255; mineral matter in, 256 ; spontaneous curdling of, 287 ; curdling with acids, 287 ; with ren- net, 2S8; preserving, 814; effects of, 381. Mind, relation of, to matter, 864; its action destroys the nerves, 365 ; wears the body, 366. Moisture, in air, 157; in the air of rooms, 15S ; amount required in air, 183 ; the supply of. 194 Molasses, 221. M. Mouries, 277. Musical sounds, 85 ; scale, 86. N Nisht-air, 167. Nitrogen, 154; lowers the combustibility of food, 352. Nitrogenous principles, properties of, 230 ; names of, 231 ; destination of, 361. Non-nitrogenous principles, different values of, 395. Nutrition, effects of, insufficient, 414. Nutritive values, 395; scale of, 397; equi- librium of, 396; milk, 898; wheat, 399; adaptations of wheat, 399 ; coarse bread, 400. O Oats, 239. Oils, proximate composition of, 109, 114; fluidity of, 114; kerosene, 118; sylvic, 118; volatile and fixed, 223; sources of, 223 ; proportion of in articles of diet, 224 ; ultimate composition of, 224; supply of, in diet, 384; accumulation ot, 384; in stomach, 335; digestibility of, 386; rela- tion of to nutrition, 837 ; to consumption, 337. Oleaic acid, 109. Oleaine, 109. Onions, 247. Oxygen, 49, 154 ; how it enters the system, 155 ; what it does in the body, 156 ; effect of varying the quantity of, respired, 157; consumed by respiration, 181 ; consumed by combustion, 182; an exciter of decay, 3ir2; destructive agency of, 350; action of, upon tissues, 862. Oxalic acid, 226. Ozone, 164 P Paper-hangings, colors of, 103; poisonous colors on, 173. Parr, Thomas, 328. Parsnips, 243. Pectic acid, 226. Peas, composition, 241 ; digestibility of, 390 Photometer, 125. Pictures, hanging of, 81 ; frames oi; 104 Poisons, used to color candy, 222 ; how di- vided, 441 ' how managed, 441. Potatoes, composition of, 245 ; water in, 245 starch in, 246 ; nutritive part of, 246; dry matter of, 246; ash of, 247; changed by cooking, 2SO. Potash, 374 Preservation, by exclusion of air, 302 ; Ap pert's method, 303; in canisters, 304; in Spratt's cans, 305; at low temperatures, 306; by freezing, 306; in refrigerators. 307.; fruits, 308; by drying, 309; by anti- septics, 311 ; by sugar, 313 ; by alcohol, 814 Putrefaction, 259. Eeflectors, 146; blue, 147. Eetina, image formed upon, 129 ; loss of sen sibility of, 144; paralysis of, 145. Eice, composition of, 241. Boots edible, dietetic effects of, 391. Eye, anatomy of, 235 ; composition of, 288. S Sago, 215. Saliva, flow of, 331 ; properties of, 332 ; uses of, S32 ; action in stomach, 840. Salts, 369. Shades, ground glass, 146; blue, 147; struc- ture and mounting of, 147. Simultaneous contrast of colors, 97. Skin, structure of, 431 ; impurities of, 432 ; cleansing of, 433. Smoke, 59, 60. Soap, how made, 425 ; hard and soft, 426 ; water in, 426 ; varieties of, 427 ; its re action with water, 428. Soda, 374 Solution, 208. Sound, transmission of, 85. Soup, preparation and properties of, 284; effects of, 381. Spectacles, 131; for the far-sighted, 133; for the near-sighted, 135 ; suggestions in selectins, 136 ; management, 137 ; pebble- glass, 137 ; colored glasses for, 148. Spectrum, 88. Specific heat, 38. Spermaceti, 109. Spitting, effects of, 334 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, 383. Steam, warming by, 73. Stearine, 109. Stearic acid, 109. Stomach, figure of, 835 ; layers of, 335 ; mo- tions of, 336 ; follicles of, 336 ; absorption from, 846. Stovepipe, 69. Stove, Franklin, 64; self-regulating, 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, 221; candy, 221; culinary changes of, 278 ; as a preserver, 313 ; phy Biological effects of, 383; refining of, 44 470 INDEX. f ftp?oca, 215. Tartaric acid, 225. Tea, 289; the shrub, 289; varieties, 289; green and black, 290 ; composition of, 291 ; how best made, 292 ; grounds, 292 ; adul- teration, 293 ; physiological effects of, 377. Teeth, 321 ; cleansing of, 435. Temperature, facts of, 27 ; of body constant, 853 ; regulation of bodily, 357 ; diet aud daily changes of, 859. Thermometer, 23, 24, 25, 26. Turpentine, spirits of, 115. Turnips, 248. V Vegetables, influence of, in diet, 390. Vegetarian question, 402; statements of, contrasted, 403, 404. Ventiducts, 198. Vermicelli, 233. Vinegar, effects of, 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 of, 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, UoL w steam, 73 ; by hot water, T2 and ventilation best method of, 195. Warming of rooms by air, 71. Waste and supply, 228. Water, its relations to heat, 39 ; evaporation of, 42 ; boiling of, 42, 43 ; spheroidal state of, 44 ; solvent powers of, 207 ; to hasten solution, 208; its dissolved gases, 208, 209 ; varieties of, 208 ; rain and snow, 209 ; or- ganic contaminations of, 209 ; living in- habitants of, 210 ; their use, 210 ; its min- eral matter, 211; hard and soft, 212; in contact with lead, 212; supply of rain, 213 : for culinary uses, 280 ; physiological effects of, 374, 375; influences digestion, 375 ; change of tissue, 376 ; proportions of in foods, 394; as a cleansing agent, 422; filtration of, 423 ; its dissolved impurities, 424. Wave movements, 84. Wax, 109. Wheat, composition of, 232 ; gluten in, 232 water in, 233; mineral matter in, 237 nutritive value of, 399. Wood, water in, 51 ; heating value of, 52 soft and hard, 52. Woody fibre, 278. Teast, brewer's. 262 ; a plant, 263 ; domestic preparation of, 264; hops in, 265; drying of, 265; bitterness of, 266; acidity of, Works published by D. Appleton & Co. A NEW CLASS-BOOK OF CHEMISTRY. BY EDWAED L. YOUMANS, M. D. 460 Pag-es. 910 Engravings. Price $1 75. Tne Class-Book of Chemistry, published some ten years ago, has been rewritten, re illustrated, and much enlarged, and now appears as an essentially new work. Its aim Js to present the most important facto and principles of the science in their latest as- pects, and in sucL a manner as shall be suitable for purposes of general education. This volume brings up the science to the present date, incorporating the new discoveries, the corrected views, and more comprehensive principles which have resulted from recent inquiry. Among these may be mentioned the newly -received doctrines of the nature of Heat, the interesting views of the Correlation and Conservation of Forces, the dis- coveries in Spectrum Analysis, and the new and remarkable researches on the artificial production of organic substances, and on the crystalloid and colloid conditions of mat ter, with many other results of recent investigations not found in contemporary text- books. For philosophical accuracy of arrangement, clearness of statement, and felicity of il- lustration, the Class-Book is unsurpassed. N. Y. Teacher. Prof. Youmans possesses a rare faculty for bringing the intricacies of science right within the comprehension of the masses of readers, and his book presents all the in- terest of a novel. Boston Post. The most recondite topics are placed in a transparent light before the common mind, the language is eminently choice and attractive, not an unwieldy paragraph, scarcely a superfluous word can be found from the beginning to the end of the work, and, in spite of the extreme economy of expression, there is no apparent constraint or formality, out every page flows smoothly and gracefully along, presenting a rare model of lucid and agreeable didactic statement. N. T. Tribune. The chapters on the Mutual Kelations of the Forces, and on the Dynamics of Vege- table Growth, are alone worth the price of the volume. B. F. Leggett, Prof. Nat. Science, Whitewater College, Ind. The present volume exhibits plentiful traits of what we believe we have before called Prof. Youmans' educational genius. Methodist Quarterly Review. Unrivalled as a practical treatise. Its introduction on the " Origin and Nature of Scientific Knowledge " should be read by every teacher. Mass. Teacher. One of its peculiar merits is that it can all be taught. Prof. Phelps, N. J. Nor- mal School. Clear, accurate, recent, and imbued with the enthusiasm of its author. .K. M. Man- ley, Pres. N. H. Fern. College. It is eminently terse and compact, is amply and lucidly illustrated, and few cf our many class-books that have crossed the ocean and been welcomed in Europe, are calcu- lated to do us more credit than this admirable work, N. Y. Independent. A thorough perusal of the bok enables us to pronounce it the best elementary chemistry that has been written in our language. It is penetfcated by a fearless yet dis- ciplined scientific spirit, and is completely up to the level of the latest discoveries in the science of which it treats. We have read it with all the interest usually given to romance. New Nation. This manual is distinguished from most other Class-books in setting almost wholly aside what is merely technical and experimental, for the sake of the completest possible exhibition of the principles of the subject For the thorough student, and even for the general reader, a careful, lucid, and connected exposition of the new views was needed, such as we are glad to acknowledge in the present volume. The author has given an intellectual value to his treatise very much abov the standard aimed at in similar works. Christian Examiner. D. APPLET ON & CO. 8 PUBLICATIONS. Chemical Atlas : Or, the Chemistry of Familiar Objects. Exhibiting the General Princi- ples of the Science in a Series of Beautifully Colored Diagrams, and accompanied by Explanatory Essays, embracing the latest views of the subject illustrated. Designed for the use of Studenta in all Schools where Chemistry is taught. By EDWARD L. YOUMANS. Large Quarto, 105 pages. The Atlas is a reproduction (hi book form), and a continuation of the mode of exhibiting chemical facts and phenomena adopted in the author's '*' Chemical Chart." The application of the diagrams is here much extended, occupying thirteen plates, printed in sixteen colors, and accompanied by 100 quarto pages of beautifully printed explanatory letter-press. It is a Chart in a portable and convenient form, containing many of the latest views of the science which are not found in the text-books. It is designed as an additional aid to teachers and pupils, to be used in connection with the author's " Class-Book," or as a review, and for individuals who are studying alone. It is intended to accompany the author's Class-Book of Chemistry, but it may be employed with convenience and advantage in connection with any of the school text-books on the subject. From the Home Journal. "Here we have science in pictures Chemistry in diagrams eye- dissections of all the common forms of matter around us ; the chemical composition and properties of all familiar objects illustrated to the most impressible of our senses by the aid of colors. This is a beautiful book, and as useful as it is beautiful. Mr. Toumans has hit upon a happy method of simplifying and bringing out the profonndest abstractions of science, so that they fall within the clear comprehension of children." From the TTUca Morning Herald. "An excellent idea, well carried out. The style is lucid and happy, the definitions concise and clear, and the illustrations felicitous and appropriate." From the Lawrence Sentinel. " We have devoted some little time in looking over this Atlas, and comparing its relative merits with similar treatises heretofore published, and feel bound to accord to it the highest degree of approbation and favor." From Life Illustrated. " This method of using the eye in education, though not the royal road to knowledge, Is really the peopled railroad a means of saving both time and labor. This work is worth for actual instruction in common schools far more than a set of apparatus, which the teacher might not be able to use, while every one can teach from the Atlas. We pronounce it, without exception, the best popular work on Chemistry in the English language." from the New York Tribune. "Mr. Toumans is not a mere routine teacher of his favorite science; he has hit upon novel and effective methods for the illustration of its princit les. In his writings, as well as his lectures, he is distinguished for the comprehensive order of his state- ments, his symmetrical arrangement of scientific facts, and the happy manner in which he addresses the intellect through the medium of ocular demonstration. In this last wepect, his method is both origiual and singularly ingenious." D. APPLETON & CO:S PUBLICATIONS. Chemical Chart. By EDWARD L. YOUMANS, M. D. On rollers, 6 feet by 6 in size New Edition. This popular work accomplishes for the first time, for Chemistry, what maps and charts have for geography, geology, and astronomy, by presenting a new and valuable mode of illustration. Its plan is to represent chemical composition to the eye by colored diagrams, so that numerous facts of pro- portion, structure, and relation, which are the most difficult hi the science, are presented i,o the mind through the medium of the eye, and may thus be easily acquired and long retained. The want of such a chart has long been felt by the thoughtful teacher, and no other scientific publication that has ever emanated from the American press has met with the universal favor that has been accorded to this Chart. In the language of a distin- guished chemist, "Its appearance marks an era hi the progress of the popularization of Chemistry." It illustrates the nature of elements, compounds, affinity, definite and multiple proportions, acids, bases, salts, the salt-radical theory, double de- composition, deoxidation, combustion and illumination, isomerism, com- pound radicals, and the composition of the proximate principles of food. It covers the whole field of Agricultural Chemistry, and is invaluable as an aid to public lecturers, to teachers in class-room recitation, and for reference hi the family. The mode of using it is explained in the class-book. From the late HORACE MANN, President of Antioch College. * 1 think Mr. Youmans is entitled to great credit for the preparation of his Chart, because its use will not only facilitate acquisition, but, what is of far greater import- ance, will increase the exactness and precision of the student's elementary ideas." From DR. JOHN "W. DRAPER, Professor of Chemistry in the University of N. Y. " Mr. Youmans' Chart seems to me well adapted to communicate to beginners a knowledge of the definite combinations of chemical substances, and as a preliminary to the use of symbols, to aid them very much in the recollection of the examples it contains. It deserves to be introduced into the schools." ""We cordially subscribe to the opinion of Professor Draper concerning the vaiao to beginners of Mr. Youmans' Chemical Chart. JOHW TOREET, Prof, of Chemistry in the College of Physicians &Surg. N. T. WM. H. ELLET, late Professor of Chemistry in Columbia College, S. C. JAMES B. ROGERS, Professor of Chemistry in the University of Pennsylvania." From BENJAMIN SILLDIAN. LL.D. Professor of Chemistry in Yale College. I have hastily examined Mr. Youmans' new Chemical Diagrams or Chart of caemical combinations by the union of the elements in atomic proportions. The deslgB appears to be an excellent one." D. APPLETON & CO:S PUBLICATIONS. The Hand-Book of Household Science. A Popular Account of Heat, Light, Air, Aliment, and Cleansing, in their Scientific Principles and Domestic Applications. By E. L. YOUMANS, M.D. 12mo, Illustrated, 470 pages. Various books have been prepared which cross the field of domestic science at different points, but this is the first work that traverses and occupies the whole ground. Hardly a page can be opened to that does not convey information interesting and valuable to every person who dwells in a house. The work will be found not only of high practical utility, but capti- vating to the student, and unequalled in the interest of its recitations. From the Superintendent of Public Instruction in the State of Pennsylvania. " The daily and hourly importance of the topics embraced in the work, their im- perious claims upon public attention, and their intimate connection with individual and social welfare, together with the compendious arrangement and copious fulness of information presented, and the cautious accuracy and precision of statement, make it a publication of the highest practical value for both the household and the school. " Very respectfully yours, "Prof. EDWARD L. YOTTMANS. HENRY C. HICKOK." From the Superintendent of Schools of the State of New York. care, and so clearly stated that even the ordinary mind can scarcely fail to grasp and retain the truths it unfolds and illustrates. It would prove a most valuable class-book in pur high schools, and I am satisfied that an examination into its merits would result in its general introduction into such institutions. Very respectfully yours, "H. H. VAN DYCK, Superintendent Public Instruction." From the Springfield EepubUam. " It is the work of a man thoroughly scientific and thorougly practical. It is no extravagance to say that a mastery of its contents will secure a better knowledge of the applications of Chemistry, Physiology, and Natural Philosophy, to life and life's concerns, than the combined treatises upon these subjects which are usually found in our school-rooms." From the Detroit Advertiser. "This is one of the most valuable and important books that has of late been issued from the press. It will do more to elevate and connect the ordinary duties of house- hold life with the domain of science than any other work yet published. It is so ar- ranged that the general reader and the man of science may refer to it with satisfaction ; but it is also a book which ought by all means to be introduced in our schools, and which every young woman who expects to be any thing more than a doll or parlor automaton, should study and become as familiar with as she is with her prayer-book. 11 From the Philadelphia Saturday Courier. " Few persons realize few persons begin to realize the importance of thoroughly understanding the nature and effects of light, heat, air, and food ; yet the value of such knowledge can hardly be overstated. Mr. Youmans' work is the clearest and fullest exposition of science in those relations that has yet appeared. School committees and persons directly interested in education, who have long been searching for a work of this kind, will rejoice to find the fruit of their quest in this manual. It is a valuable book, written for a valuable purpose : the desire to lift our ordinary domestic life int* Ihfe dignity of intelligence pervades it throughout, and tinctures it in the grain." D. APPLETON & CO: 8 PUBLICATIONS. THE Correlation and Conservation of Forces. WITH AN INTBODTTCTION AND BRIEF BIOGRAPHICAL NOTICES. By EDWARD L. YOUMANS, M.D. 12mo, 490 pages. CONTENTS. I. By W. R. GROVE. The Correlation of Physical Forces. IE. By Prof. HELMHOLTZ. The Interaction of Natural Forces. HI. By J. R. MAYER. 1. Remarks on the Forces of Inorganic Nature. 2. On Celestial Dynamics. 3. On the Mechanical Equivalent of Heat. IV. By Dr. FARADAY. Some Thoughts on the Conservation of Forces. V. By Prof. LIEBIG. The Connection and Equivalence of Forces. VL By Dr. CARPENTER. The Correlation of the Physical and Vital Forces. " This work is a very welcome addition to our scientific literature, and will be particularly acceptable to those who wish to obtain a popular, but at the same time precise and clear view of what Faraday justly calls the highest law in physical science, the principle of the conservation of force. Sufficient attention has not been paid to the publication of collected monographs or memoirs upon special subjects. Dr. Youmans' work exhibits the value of such collections in a very striking manner, and we earnestly hope his excellent example may be followed in other branches of science.'" American Journal of Science. " It was a happy thought which suggested the publication of this volume. The question is often asked, and not so easily answered, What are the new doctrines of the Correlation and Conservation of Forces? In this volume we have the answer, and with the reasons of its chief expounders ; those who are ignorant on that theme, can thus question the original authorities." New Englander. " We here have the original expositions of the new Philosophy of Forces, accompa- nied by an excellent exposition of both the expositions and the expositors; the whole will be a rare treat to the lovers of advancing scientific thought." Methodist Quarterly Review. " This is, perhaps, the most remarkable book of the age. We have here the latest discoveries, and the highest results of thought concerning the nature, laws, and con- nections of the forces of the universe. No higher or more sublime problem can engage the intellect of man than is discussed by these doctors of science intent alone on arriv lag at the truth." Detroit free Press. " T'Tiis work presents a praiseworthy specimen of complete and faithful authorship, and itfe publication at this time will form an epoch in th experience of many thinking minds." ibune. D. APPLET ON & CO: 8 PUBLICATIONS. Class-Book of Physiology. By B. N. COMINGS, M. D., Professor of Physiology, Chemistry, and Natural History, in Connecticut State Normal School. 12mo. 324 pages. Revised Edition, with an Appendix. Professor Comings' thorough acquaintance with every department of Physiology, and his long experience as a teacher of that science, qualify Mm in an eminent degree for preparing an accurate and useful text-book on the subject. He has lost no opportunity of introducing practical instructions in the principles of hygiene, thus not only making tne pupil acquainted with the wonderous workmanship of his own frame, but showing him how to preserve it in a sound and healthy state. Avoiding technical terms, as far as possible, he has brought the subject fully within the comprehension of the young, and has clothed it with unusual interest, by judicious references to the comparative physiology of the inferior animals. Pictorial illustrations have been freely introduced, wherever it was thought they could aid or interest the student. Physiology cannot but be considered, by every intelligent and reflecting mind, an exceedingly interesting and necessary study. It makes us ac- quainted with the structure and uses of the organs of life, and the laws by which we may keep them active and vigorous for the longest period. The publishers would respectfully urge its importance on such teachers as have not heretofore made it a regular branch in their institutions ; and would solicit, at the hands of all, an impartial examination of what is pronounced by good judges, " the best elementary text-book " on the science. From M. Y. BROWN, Principal of Webster School, New Haven. " I have used Comings' Class-Book of Physiology for nearly two school terms in the First Department of my school. I am happy to say that I regard it the best text-book on this important branch with which I have any acquaintance. The subjects are system- atically arranged ; the principles, facts, and illustrations, are clearly represented to the pupil. I find that his introduction of Comparativs Anatomy and Physics tends greatly to increase the interest of the pupil in this most important and necessary study. 1 therefore can cheerfully recommend this admirable work to my fellow-teachers as one of rare excellence, and hope it may take the rank it deserves as a text-book upon this subject." From ABRAHAM POWELSON, JK., TeacJier, Brooklyn, New York. " After a very careful examination of the Class-Book of Physiology by Comings, I ein freely say that I consider it a performance of superior excellence. It embodies a fund of information surpassing in importance and variety that of any other work of th kind which has come under my notice." RETURN MARIAN KOSHLAND BIOSCIENCE AND TO > NATURAL RESOURCE LIBRARY 2101 Valley Life Sciences Bldg. 642-2531 LOAN PERIOD 7 DAYS ALL BOOKS MAY BE RECALLED AFTER 7 DAYS. DUE AS STAMPED BELOW. ; ?0fl7 ""TTORFC^ FORM NO DD 8 UNIVERSITY OF CALIFORNIA, BERKELEY 24M 4-00 Berkeley, California 94720-650C