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Air^ Water^ and Food

FROM A SANITARY STANDPOINT

BY

ALPHEUS G. WOODMAN and JOHN F. NORTON

Associate Professor of Assistant Professor of

Food A nalysis Chetnistry of Sanitation

MASSACHl,'SKTTS INSTITUTE OF TECHNOLOGY

" These cannot be taken as sufficient ... in these times when every word spoken finds at once a reidy doubter, if not an opponent. They are, however, specimens, and will serve to make comparisons in time to come." — Angus Smith.

" The ideal scientific mind, therefore, must always be held in a state of balance which the slightest new evidence may change in one direction or another. It is in a constant state of skepticism, know- ing full well that nothing is certain." — Henry A. RowIiANO.-i -•

FOURTH EDITION, RRVI5Eri''A^D>,J^>f:iVJiiT'tMN'

TOTAL ISSUE FIVE ^y'ltofu'sAigif. .' ;'.*,*>!

NEW YORK

JOHN WILEY & SONS, Inc.

London: CHAPMAN & HALL, Limited

1914

Copyright, 1900, 1904, 1909

BY

ELLEN H. RICHARDS and ALPHEUS G. WOODMAN Copyright, 19 14

BY

ALPHEUS G. WOODMAN and JOHN F. NORTON

Stanbopc jpress

F. H.GILSON COMPANY BOSTON, U.S.A.

^/3

PREFACE

Since the last edition (1909) of Air, Water, and Food was published there have been distinct advances in analytical meth- ods, and a changed point of view has brought about a somewhat different interpretation of results. This is particularly true with regard to the relation of air to health and comfort. At the present time the subject is still in a somewhat transitory state. In order that the book might remain useful it seemed necessary to make a careful revision of the whole.

The death of one of the authors, Mrs. Ellen H. Richards, made a change in authorship necessary. We are indebted to Prof. R. H. Richards for permission to use any material from the former edition. While realizing that the book was first written from a "missionary" standpoint (Mrs. Richards' strong point), it actually has been used mainly for college and technical school teaching; consequently the character of part of the general discussion has been considerably changed.

All of the discussion on air and water has been completely rewritten, as has the section on milk, the older methods revised, and numerous additions, to correspond with the latest practice, made. As in previous editions, these discussions are intended to be essentially elementary rather than exhaustive.

A. G. W. J. F. N.

Boston, July, 1914.

2061665

CONTENTS

Chapter Page

I. Three Essentials of Human Existence i

II. Air and Health q

HI. Air: Analytical Methods 21

IV. Water: Its Relation to Health, Its Source and Properties.. 43

V. Safe Water and the Interpretation of Analyses 56

VI. Water: Analytical Methods 69

VII. Food in Relation to Human Life, Definition, Sources, Classes,

Dietaries m

VIII. Adulteration and Sophistication of Food Materials 124

IX. Analytical Methods 135

Appendices 208

Bibliogr.'Vphy 228

AIR, WATER, AND FOOD

CHAPTER I

THREE ESSENTIALS OF HUMAN EXISTENCE

Air, water, and food are three essentials for healthful human life. Chemical Analysis deals with these three commodities in their relation to the needs of daily existence: first, as to their normal composition; second, as to natural variations from the normal; third, as to artificial variations — those produced directly by human agency with benevolent intention, or result- ing from carelessness or cupidity. A large portion of the prob- lems of public health come under these heads, and a discussion of them in the broadest sense includes a consideration of engi- neering questions and of municipal finances. This, however, is beyond the scope of the present work.

The following pages will deal chiefly with such portions of the Chemistry of Sanitation as come directly under indi\'idual control, or which require the education of individuals in order to make up the mass of public opinion which shall support the city or state in carrying out sanitary measures.

A notable interest in the subject of individual health as a means of securing the highest individual capacity both for work and for pleasure is being aroused as the application of the principles governing the evolutionary progress of other forms of Uving matter is seen to extend to mankind.

Will power may guide human forces in most economical ways, and may concentrate energy upon a focal point so as to seem to accomphsh superhuman feats, but it cannot create force out of nothing. There is a law of conservation of human

2 AIR, WATER, AND FOOD

energy. The human body, in order to carry on all its functions to the best advantage, especially those of the highest thought for the longest time, must be placed under the best conditions and must be supplied with clean air, safe water, and good food, and must be able to appropriate them to its use. The day is not far distant when a city will be held as responsible for the purity of the air in its schoolhouses, the cleanliness of the water in its reservoirs, and the rehability of the food sold in its markets as it now is for the condition of its streets and bridges. Nor will the years be many before educational institutions will be held as responsible for the condition of the bodies as of the minds of the pupils committed to their care; when a chair of Sanitary Science will be considered as important as a chair of Greek or Mathematics; when the competency of the food- purveyor will have as much weight with intelligent patrons as the scholarly reputation of any member of the Faculty. Within a still shorter time will catalogues call the attention of the inter- ested public to the ventilation of college halls and dormitories, as well as to the exterior appearance and location.

These results can be brought about only when the students themselves appreciate the possibilities of increased mental produc- tion under conditions of decreased friction, such as can be found only when the requirements of health are perfectly fulfilled.

Of the three essentials, air may well be considered first, al- though its ofiice is to convert food already taken into heat and energy. Its exclusion only for a few minutes causes death, and in quantity used it far exceeds the other two. Again, so im- portant is the action of air that the quality of food is of far less consequence when abundant oxygen is present, as in pure air, than when it is present in lessened quantity, as in air vitiated by foreign substances.

Individual habit has much to do with the appreciation of good air, and as our knowledge of the value of an abundance of this substance in securing great efficiency in the human being increases, we shall be led to attach more importance to the sufiSciency of the supply.

THREE ESSENTIALS OF HUMAN EXISTENCE 3

In northern climates air is not free to all in the sense of cost- ing nothing, for the coming of fresh air into the house means an accompaniment of cold which must be counteracted by the consumption of fuel. A mistaken idea of economy leads house- holders, school boards, and college trustees to limit the size of the air-ducts as well as of the rooms. It is therefore necessary to emphasize the facts which science has fully established, in order to secure the survival of the fittest of the race under the present pressure of economic conditions, which take so little account of the highest welfare of the human machine.

Air, water, and soil are the common possessions of man- kind. It is impossible for man to use either selfishly without injury to his neighbor and without squandering his inheritance. Primitive man could leave a given spot when the soil became offensive, and neighbors were then too few to require con- sideration; but neither man nor beast could with impunity foul the stream for his neighbor who had rights below him. The soil is permanent; one knows where to look for it and its pollu- tion. Air is abundant and is kept in constant motion by forces of nature beyond human control, so that, save in the neighbor- hood of an exceptionally offensive factory, man does not often foul the free air of heaven ; it is only when he confines it within unwonted bounds that it becomes a menace.

Water is the next precious commodity of the three. With- out it man dies in a few days; without it the soil is barren; without it air in motion parches all vegetation and carries clouds of dust particles; without it there is no Hfe. As popu- lation increases it becomes necessary to collect as much of the rainfall as possible, to store it until needed, and to use it with discretion. After use it is often loaded with impurities and sent to deal death and destruction to those who require it later, and yet, in nature's plan, it is the carrier of the world, and rightly treated and carefully husbanded there is enough for the needs of all. Its presence or absence has been the controlling force in determining the habitations of men. In its ofl&ce of carrier it not only brings nourishment in solution to the tissues of the

4 AIR, WATER, AND FOOD

human body, but also carries away the refuse material. It is a cardinal principle in all sanitary reforms to get rid of that which is useless as soon as possible. Too little water allows accumu- lation of waste material and a clogging of the bodily drainage system.

The average quantity needed daily by the human body is about three quarts. Of this a greater or less proportion is taken in food, so that at times only from a pint to a quart need be taken in the form of water as such.

Next in importance to quantity is the quality, dependent somewhat upon the uses to which it is to be put. As a rule, the moderately soft waters are the best for any purpose. For drinking purposes water must be free from dangers to health in the way of poisonous metals, decomposing matters, and disease- germs. For domestic use economy requires that it should not decompose too much soap. Manufacturing interests require that it should not give too much scale to boilers; for agriculture there should not be too much alkali.

From the nature of things, no one family or city can have sole control of a given body of water. Those on the highlands may have the first use of the water, which then percolates to a lower level and is used by the people on the slopes over and over before it reaches the sea to start again on its cycle of vapor, cloud and rain, brook and river. Although receiving impurities each time, there are many beneficent influences at work to overcome the evils resulting from this repeated use. That which is dissolved from one portion of earth may be deposited on another. As the plant is the scavenger of the air, withdraw- ing the carbon dioxide with which it would otherwise become loaded, so the water has also its plant hfe, purifying it and withdrawing that which would otherwise soon render it unfit for any use.

Pure water is found only in the chemical laboratory; the most that can be hoped for is that human beings may secure for them- selves water which is safe to drink, which will not impair the efficiency of the human machine.

THREE ESSENTIALS OF HUMAN EXISTENCE 5

The importance of the third essential for human life, food, and the close interdependence of all three, may be clearly shown. Of little use is it to provide pure air and clean water if the sub- stances eaten are not capable of combining with the oxygen of the air or of being dissolved in the water or the digestive juices; of less use still is it to partake of substances which act as irri- tants and poisons on the tissues which they should nourish, and thus prevent healthful metabolism and respiratory exchange.

And yet a large majority of those who have acquired some notion of the meaning and importance of pure air and are be- ginning to consider it worth while to strive for clean water pay not the least attention to the sanitary qualities of food; the palatable and aesthetic aspects only appeal to them.

Steam-power is produced by the combustion of coal or oil. Human force is derived by releasing the stored energy of the food in the body. The delicately balanced mechanism of the human body suffers even more from friction than the most sensitive machine, and the greatest loss of potential human energy occurs through ignorance, carelessness, and reckless dis- regard of nature's laws in regard to food.

It is necessary to know, first, what is the normal compo- sition of a given food-material. This is found by analyses of many typical samples. Second, is the sample under consider- ation normal? To answer this requires an analysis of it, and a comparison of the results with standards. If it is not normal, in what way does it depart from the standard both in health- fulness and in quality? Third, if a food-substance is normal, what are its valuable ingredients and in what proportions are they to be used in the daily diet?

In regard to meat, milk, and fish, the sanitary aspect for the chemist resolves itself into two questions: Is the substance so changed as to become a possible source of poisonous products? Or has anything in the nature of a preservative been added to it? If so, is it of a nature injurious to man?

There is, however, a great range of quality in some of the most abundant foodstuft's, such as the cereals, especially in the

AIR, WATER, AND FOOD

nitrogen content. This is most important to the vegetarian and to institutions where economy must be practiced. The fol- lowing variations in the composition of leading cereals will illustrate:

Water.

Nitro- genous substance.

Crude fat.

Carbo- hydrates.

Fibre.

Ash.

Oats, maximum

Oats, minimum

Oats, American hulled

Corn, maximum

Corn, minimum

20.80 6. 21

22. 20 4.68

18.84

6.00

13-57

14-31

5-55

10.65 2. II 7.68 8.87 1-73

.63	20.
.69	4-
•37	I .
.08	7-
■75	0.

.08

■45

■30

71

■99

8.64

1-34 2.03

3-93 0.82

One sample of wheat flour may contain 14 per cent of nitro- genous substance, another may yield only 9. A day's ration, 500 grams, will give 70 grams of gluten, etc., in the one case and only 45 in the other. This difference of 25 grams would be a serious factor in the dietary of an institution where little ad- ditional protein is given, and it alone might be the cause of dangerous under-nutrition.

The next step would naturally be to determine how definitely these varying percentages mean varying nutrition. To this end a study of vegetable nitrogenous products in their combination or contact with cellulose, starch, and mineral matter is needed. Much work remains to be done before these questions can be even approximately answered.

At the low cost of one cent a pound, common vegetables yield only about one-fifth as much nutriment as one cent's worth of flour, yet they contain essential elements and deserve to be carefully studied.

The sanitary aspect of food demands a study of normal food and food value even more than of adulterants or of poisonous food, ptomaines and toxines. The cultivation of intelligent public opinion is most important, and each student should go out from a sanitary laboratory a missionary to his fellow men. That is, the office of a laboratory of sanitary chemistry should be so to diffuse knowledge as to make it impossible for educated

THREE ESSENTIALS OF HUMAN EXISTENCE ^

people to be deluded by the representations of unprincipled dealers. Freedom from superstition is just as important in this as in the domain of astronomy or physics. So long as chemists are employed by manufacturing concerns in making adulterated and fraudulent foodstuffs, so long must other chemists be employed in protecting the people until the public in general becomes wiser. A part of the common knowledge of the race should be the essentials of healthful living, in order that the full measure of human progress may be enjoyed.

There is needed a greater respect for food and its functions in the human body, a better knowledge of its effect on the daily output of energy, its absolute relations to health and life, and the enjoyment of the same. The familiarity with these facts which is given by a few hours' work in the laboratory will make a lasting impression and will enable the student to benefit his whole life, even if he never uses it professionally. It is purely scientific knowledge, just as much as that derived from a study of the phases of the moon or the formulas of integration.

The variety of operations in such work, calling for great diversity of apparatus and methods, is an educational factor not to be overlooked in laboratory training.

For all detailed discussions and methods the reader is re- ferred to such works as those of Wiley, Allen, Leach, etc., but for the student who needs to study, as a part of general educa- tion, only typical substances, and such methods as can be carried out within the limits of laboratory exercises in a col- lege curriculum, the following pages are written. Not enough is given to frighten or discourage the student, but enough, it is hoped, to arouse an interest which will impel him at every subsequent opportunity to seek for more and wider knowledge.

Food is too generally regarded as a private, individual matter rather than as a branch of social economy; it is, however, too fundamental to the welfare of the race to be neglected. Society, in order to protect itself, must take cognizance of the questions relative to food and nutrition.

Formerly each race adapted itself to its environment and

8 AIR, WATER, AND FOOD

trained its digestion in accordance with the available food supply. In America to-day the question is not how to get food enough, but how to choose from the bewildering variety offered that which shall best promote the health and develop the powers of the human being, and, what is of equal impor- tance, how to avoid over-indulgence, which weakens the moral fibre and lessens mental and physical efficiency. In spite of all preaching, few really beHeve that plain living goes with high thinking. Professor Patten says that the ideal of health is to obtain complete nutrition. Over-nutrition as well as under- nutrition weakens the body and subjects it to evils that make it incapable of survival.

No other form of social service will give so full a return for effort expended as the help given toward better diet for children and students. Fortunately help is coming fast. The United States Government is giving much study to food problems, and by publications is making available the work of other countries. The later bulletins Hsted in the bibliography at the end of this volume are especially valuable. What is now needed is a gen- eral recognition of the importance of the subject.

CHAPTER II

AIR AND HEALTH

The air we breathe is a mixture of various gaseous substances containing more or less finely divided solid particles. What may be called "pure" air contains 20.938 per cent * by volume of oxygen, 0.031 per cent of carbon dioxide, 78.09 per cent of nitrogen, 0.94 per cent of argon and other rare gases belonging to the argon group.

All the air with which we actually have to deal contains also varying amounts of moisture, expressed in terms of "relative humidity." Air at a low temperature can hold much less moisture than at a high temperature. For example, one cubic foot of air at 20° F. will hold 1.235 grains of water vapor, while at 70° 7.98 grains will be held. The relative humidity is the ratio of the amount of moisture which the air actually contains to the amount which it could hold at the same temperature if completely saturated. As water vapor is lighter than dry air, the higher the humidity the less will a given volume of air weigh. This effect is familiar in the action of a barometer which falls on the approach of a rain storm, — the reading on such an instrument being dependent on the weight of air above it.

Besides moisture, the air in cities may contain a variety of substances such as ammonia, sulphur dioxide, sulphur trioxide, etc., and almost always dust, bacteria, yeasts, and molds. Samples of air f taken in the down town districts of New York and Boston showed at the street level numbers of dust particles per cubic foot of air varying from 170,000 to 500,000, the num-

* Benedict, Composition of the Atmosphere. Carnegie Institution, Publication No. 166.

t G. C. Whipple and M. C. Whipple, Am. J. Pub. Health, 1913, 3, p. 1140.

9

lO AIR, WATER, AND FOOD

ber gradually decreasing as the height above the street increased, until only about 27,000 were found in the air taken from the fifty-seventh floor of the Wool worth Building, 716 feet high. In a house, school room or public building the numbers of dust particles are equally variable, wuth a tendency to be somewhat higher, depending on the location of the building, and whether or not the air entering is purified. Thus in an investigation of the air of school rooms,* few cases were found where the num- bers were less than 200,000 per cubic foot, and they varied from this to over 1,500,000, the greater proportion being between 200,000 and 600,000, much higher than is generally found in outdoor air. The numbers of bacteria found in the air are small compared to the dust particles, there being about 200" ^^ many in outdoor air, and even less in indoor air, in 85 per cent of the samples taken in school rooms f the number of micro-organisms being less than 150 per cubic foot. In country districts the numbers of both dust particles and bacteria in the air are ex- tremely small.

Under ordinary conditions the presence of dust and bacteria has no particular significance. In fact it is the opinion of most sanitarians that the danger of the spread of disease by the carrying of bacteria through the air is small, the contact neces- sary for this to happen being much closer than generally exists in oflices and schoolrooms. There are certain special cases where dust particles may be harmful, — such as the dust con- sisting of small particles of metal found in certain factories, and the organic dust found in the air in certain rooms in textile mills. Some of these dusts, such as white lead, are themselves actually poisonous to the system, while others lodge in the lungs and lower the vitahty so that pneumonia and tuberculosis are more liable to gain a footing.

Poisonous gases are occasionally found in air, — the most important being carbon monoxide which comes from leaky gas jets or pipes, or from a defective furnace. As this gas has al-

* Winslow, Am. J. Pub. Heallh, 1913, 3, p. 1158. t Winslow, loc. cil.

AIR AND HEALTH II

most no odor, insensibility may occur without the victim realiz- ing what is taking place. For this reason it has been found necessary, where this gas is used for lighting, to require the in- troduction into it of some substances with strong odors. Car- bon monoxide acts as a poison by combining with the hsemo- globin of the blood, and preventing the absorption of oxygen.

In the air of mines, methane, — or fire damp as it is called, — is sometimes present. This forms an explosive mixture with oxygen, and is frequently the cause of mine explosions.

Respiration. — External respiration consists of alternately filling and emptying the lungs. In the lungs, oxygen, breathed in with the air, is exchanged for carbon dioxide brought to the lungs by the blood. The blood leaving the lungs contains oxy- gen which is carried to all parts of the body, and passes * from the blood in the capillaries into the tissues where oxidation takes place. The carbon dioxide formed passes back into the blood and hence into the lungs. Expired air, therefore, contains less oxygen and more carbon dioxide than inspired air. An average composition would be, — oxygen, 16.03 P^r cent; carbon di- oxide, 4.38 per cent; nitrogen, etc., 79 per cent.

The process of exchange of oxygen and carbon dioxide in the lungs is partly a physical one, — that is, the vapor pressure of oxygen is greater in the lungs than in the blood, and, therefore, oxygen passes from the former to the latter. With carbon dioxide the reverse is true. Therefore, if air high in carbon dioxide is breathed into the lungs this will increase the vapor- pressure of this substance, and hinder the elimination of it from the blood. But it appears to be impossible to account for the interchange of gases on a purely physical basis, and, therefore, it is thought that enzymes, which aid in the interchange, are at work.

Comfort. — The first two theories that were advanced to

account for effects of discomfort when a room becomes "close"

were based on the supposition that the products of respiration

were poisonous when taken back into the lungs. In one theory

* See Haramarsten-Mandel. "A Text-book of Physiological Cheinistr>-."

12 AIR, WATER, AND FOOD

this poisonous substance was supposed to be carbon dioxide. That animals cannot live in an atmosphere composed of nitro- gen and carbon dioxide, and that oxygen is necessary has long been known, but it was thought that carbon dioxide had a specific poisonous action and, therefore, should be present in any air used for human beings, in only very small amounts. This theory has been entirely disproved and carbon dioxide can no longer be regarded as in itself poisonous. If too much of the oxygen in the air becomes displaced by carbon dioxide it is im- possible for animals to utilize the oxygen left, but this only happens when the oxygen content decreases to about 12 per cent. Practically such a low per cent is never found, as inter- change of the air between a room and the outside is continually going on around windows and through walls. If, however, the •oxygen is allowed to remain at about 21 per cent, very large quantities of carbon dioxide may be present without any ill effects. Experiments have shown conclusively * that carbon dioxide cannot be blamed for discomfort in a crowded hall or theatre.

The other theory, — known as the "crowd poison" theory was based on some experiments which seemed to show that organic poisons were given off during respiration, and that these substances were the cause of the headaches and nausea some- times experienced by sensitive persons in "close" rooms. At the present time there are some adherents to this theory, but there has been little real evidence produced in its support. The first proofs of the non-poisonous character of exhalations were obtained by Formanek in a long series of experiments f and more recently Winslow J using the principles of anaphylaxis failed to obtain any results which showed the presence of the poisons (or toxins) in expired air.

At the present time it is quite generally believed that sen-

* See Crowder. "Ventilation of Sleeping Cars." Arch. Intern. Med., 1911, 7,

PP- 85-133-

t Archiv fiir Hygiene, 1900, 38, p. i. I Loc. cit.

AIR AND HEALTH

13

sations of comfort and discomfort are dependent upon the rate of loss of heat from the body. If this is normal, then comfort results, if either too high or too low, then discomfort, headaches and nausea may follow. Just what this heat loss should be, measured in any system of units, is not known, but certain of the methods by which the loss takes place, and the factors which influence the rate may be discussed.

There are three ways by which heat can be transferred from the body to the surrounding atmosphere, (i) Evaporation. — The change from the liquid to the gaseous state is accompanied by an absorption of heat. Thus when water evaporates from the surface of the body, heat is removed with it. (2) Trans- mission (by conduction and convection). Heat passes from a warm to a cold body when the two are in contact. For the greater part of the year the animal body is warmer than the atmosphere, and, therefore, the latter is continually receiving heat from the body. Since warm air rises, convection currents may be set up carrying away the heat already given up to the air. (3) Radiation. — The first two methods depend directly on the presence of matter. In radiation heat is transferred in all directions by means of ether waves, and the medium through which the radiation takes place does not necessarily become heated. There is no data available on the loss of heat from the body in this way, and we do not know what part it actually plays in comfort.

These three methods by which heat may be given off from the body may be acting simultaneously, — in fact they generally are doing so, — and one or more may be negative in its action, — that is may be supplying heat to the body. Further, while they act entirely independently of each other, they are each in- fluenced by the same conditions of the atmosphere, and it is these physical conditions which are the ones capable of regu- lation, and which determine good or bad ventilation. These are, — temperature, humidit}' and motion.

Temperature. — Temperature affects evaporation, because the higher the temperature of the air the more moisture is it cajxible

14 AIR, WATER, AND FOOD

of taking up. It affects conduction, because the greater the difiference of temperature between two bodies the greater the amount of heat passing from that at the higher to that at the lower temperature. It affects convection, because convection currents are started by warm air rising and cooler air taking its place.

Humidity. — Heat loss by evaporation is more dependent on humidity than on any other factor. Relative humidity is a measure of the per cent saturation of the air by water vapor, and it is obvious that the higher the humidity the less will be the opportunity for the air to take up more moisture, and, therefore, the less rapid the evaporation from the body. Trans- mission of heat from the body is affected by the humidity, be- cause moist air is a better conductor than dry air, and, therefore, the higher the humidity the greater the rate of heat conduction. (Relative humidity, as can be seen from a foregoing discussion, is itself affected by the temperature.)

Motion. — The motion of the air influences evaporation by carrying away from the body more or less rapidly the air which has become completely saturated with moisture, and thus al- lowing access to unsaturated air. If the air and the body are perfectly quiet evaporation will be gradually retarded until it is nearly zero. Convection currents are movements in the air started by differences in temperature. These movements will be greatly increased by any motion in the air, and, therefore, the greater the motion the more rapid will be the transference of heat in this way.

It is important to remember that these three factors, tem- perature, humidity and motion, — are always acting simul- taneously, and that there may be an increase in the rate of heat loss above the normal by one or more of them at the same time that the rest tend to decrease this rate. Furthermore, the same factor, humidity for example, may tend to increase the heat loss above the normal by one method, — perhaps by evaporation, — while at the same time, the same degree of humidity may tend to decrease below the normal the heat loss by another method,

AIR AND HEALTH 1 5

perhaps by transmission. The degree of comfort felt under any specified conditions is, therefore, the resultant of all effects, some tending to increase and others to decrease the rate of heat loss from the normal.

This can be readily illustrated. Suppose that the temper- ature is 95° F., the humidity 90 per cent and there is but very little motion in the air. The result is well known, — a feeling of heaviness and considerable discomfort. Why?

(i) The high temperature allows the air to take up a con- siderable amount of moisture, thus tending to increase the heat loss by evaporation, with the consequent cooling effect on the body. On the other hand, the heat loss by conduction, con- vection and radiation arc only very small as they depend on the difference of temperature of the body and the air.

(2) The high humidity prevents the rapid evaporation of moisture, and, therefore, tends to decrease the heat loss from the body. This more than counteracts the increased capacity of the air for moisture, due to the high temperature. On the other hand, the high humidity makes the air a better conductor of heat, and, therefore, tends to increase the heat loss by con- duction. This, again, is counteracted by the high temperature, temperature being the more important factor in this method of loss.

(3) The very slight motion of the air tends to decrease the heat loss by evaporation and convection.

The net result is that heat does not leave the body as rapidly as it should, and we feel hot and uncomfortable.

Application of this theory of regulation of loss of heat is not wholly adequate to explain all conditions. Another factor seems to be involved, that of loss of moisture, apart from any loss of heat which accompanies this. "Probably much of the harm attributed to damp and to cold is due to diminished water cir- culation, etc."* With this added factor it is possible to ex- plain most of the uncomfortable conditions. The uncertainty of the theory lies in the fact that we have been unable to test it

* Macfie, Air and Health.

i6

AIR, WATER, AND FOOD

THE CURVE OF COMFORT

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AIR AND HEALTH 17

experimentally and to determine the exact heat loss due to each factor.

Hill * has plotted a series of curves which are intended to represent the various conditions of comfort in terms of tem- perature and humidity. Thus it is seen that a temperature of 55° F. and a humidity of 70 per cent gives comfort, and as the temperature increases the humidity must be decreased. At 68° F., the temperature generally desired in the house, the humidity must be around 50 per cent.

Ventilation. — In ventilating a public building or a house, it is necessary to supply a sufficient quantity of air in the proper condition. In most cases this condition is, that the air in the room shall be at a temperature of 68° to 70° F., and with a humidity of 50 to 70 per cent. As long as the humidity does not go too high, it seems to be a secondary factor so far as health is concerned. More discomfort is felt from overheating than from any other cause. This is also true in many factories, but there are some where high humidity must be considered, such as is necessary to maintain in connection with certain textile operations. It should be remembered that the higher the tem- perature the more sensitive does one become to high himiidity.

Another condition which must be met in ventilation practice is that governed by the carbon dioxide content of the air. As pointed out above, this substance is not itself poisonous, but it is useful in serving as an index of the amount of unused air be- ing supplied. The normal individual gives off from 0.6 to 0.8 cubic feet of carbon dioxide per hour, and this will gradually accumulate in a room unless the air is continually being replaced. The amount of carbon dioxide present in a room can, therefore, be used to determine whether or not there is sufficient replace- ment of used air by fresh air. The allowable amount of carbon dioxide is about 10 parts per 10,000 of air. Arnounts above this may be allowed in certain special cases where the carbon dioxide does not come from man or animals. If only 6 or 7 parts are present, the ventilation may be considered excellent. In order

* Hill, Recent Advances in Physiology and Biochemistrj'.

l8 AIR, WATER, AND FOOD

to accomplish this about 2000 cubic feet of fresh air per person per hour must be supplied. The amounts actually recommended depend somewhat on the use to which the room or building is to be put, these amounts varying between 1000 cu. ft. for a waiting room and 2500 for a hospital. Where it is difficult to determine how many people will be present the calculations may be based on the number of complete changes of air per hoar, these being from one to five in a residence, and from one to two in an auditorium.*

It is also possible to calculate from analytical data the inter- change of air going on under given conditions, and thus test the efficiency of a ventilating system. If, after a room has been occupied and the occupants removed, the air is analyzed for carbon dioxide, the room allowed to remain a definite length of time, and another analysis made, the interchange may be cal- culated from a formula given by Barker: f

^=f'°^(l^:)

where C is the contents of the room in cubic feet, T the time in hours between the original amount of carbon dioxide ki in one cubic foot of air, and the final amount ^2 in one cubic foot of air, a the proportion of carbon dioxide in one cubic foot of pure atmospheric air, and V the interchange in cubic feet per hour.

Ventilation depends on the movement of air currents in such a way as to continually supply fresh air and to remove used air. This must be done so that no drafts will be felt at any part of the room. The system actually used will depend on the kind of building and room, — as well as on the kind of heat- ing used. In the ordinary dwelling house ventilation is almost ahvays left to look after itself. Even in the best built houses there is going on constantly an interchange of air around the windows and doors. This is not sufficient on winter evenings

* Greene, "Elements of Heating and Ventilation," p. 23.

t Baker, "The Theory and Practice of Heating and Ventilation," p. 164. A number of other useful ventilating formula; are also given.

AIR AND HEALTH 19

when kerosene or gas lamps are burning, and most rooms soon become stuffy. To aid this natural ventilation, windows, open fire places and hot air furnaces are used. Excellent results may be obtained from the careful use of the open window, but it re- quires considerable time as well as care to operate them so that no drafts will result. Where a hot air system of heating is used a house may be well ventilated, — the air which is forced in through registers going out after proper circulation, through ven- tilators or around windows. Care should be taken to place registers to get this circulation.

In a large building, — office, educational, or auditorium, — the problem is somewhat different. Here it is useless to depend on natural ventilation and some artificial means must be employed. There are two general methods of air circulation in use, upward and downward. Both have their advantages and disadvantages. Upward ventilation would seem theoretically the best, as ex- pired air, being warm, rises and creates an upward current, which can be easily drawn into an outlet. This system can be used, but it presents certain difficulties. The first is that un- less air comes into the room through a very large number of small holes in the floor, drafts of cold air around the feet are certain to be felt. This would only be practical in an audi- torium with stationary seats. Besides, objection is sometimes made that odors from the clothing are made more noticeable by being carried past the nose. The reverse system, downward ven- tilation, seems