- -■ • A. ■>-,. - - -. . AIR, WATER, AND FOOD FROM A SANITARY STANDPOINT. BY.» ELLEN H. RICHARDS and ALPHEUS G. WOODMAN, instructors in Sanitary Chemistry, Massachusetts Institute of Technology. "These cannot be taken as sufficient ... in these times when every word spoken finds at once a ready 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, knowing full well that nothing is certain. "—Henry A. Rowland. FIRST EDITION. FIRST THOUSAND. NEW YORK: JOHN WILEY & SONS. London : CHAPMAN & HALL, Limited. i goo 3? 36488 Library of Conareae i ' wu <>£$ Received AUG 20 1900 Copyright entry second copy. Delivered to ORDER DIVISION, AUG 22 1900 Copyright, igoo, BY ELLEN K. RICHARDS and ALPHEUS G. WOODMAN. ROBERT DRUMMOND, PRINTER, NEW YORK. 3 CONTENTS. CHAPTER PAGE I. Three Essentials of Human Existence i II. Air: Composition, Impurities, Relation to Human Ltfe 10 III. The Problem of Ventilation 19 IV. Methods of Examination 27 V. Water: Source, Properties, Solvent Power, as a Carrier. 43 VI. The Problem of Safe Water and Interpretation of Analy- ses 62 VII. Methods of Examination 82 VIII. Food in Relation to Human Life, Definition, Sources, Classes, Dietaries 121 IX. Adulteration and Sophistication of Food Materials 136 X. Methods of Food Analysis 146 Appendices, Tables, Reagents 195 Bibliography 213 <> s AIR, WATER, AND FOOD, CHAPTER I. THREE ESSENTIALS OF HUMAN EXISTENCE. Air, water, and food are three essentials for healthful human life. Sanitary Chemistry deals with these three com- modities 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 resulting from carelessness or cupidity. A large portion of the problems of public health come under these heads, and a discussion of them in the broadest sense includes a consideration of engineering 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 subject of Sanitary Chemistry as come directly under individual control, or which require the education of indi- viduals 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 2 AIR, WATER, AND FOOD. 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 living matter is seen to extend to mankind. Will power may guide human forces in most economi- cal ways, and may concentrate energy upon a focal point so as to seem to accomplish superhuman feats, but it cannot create force out of nothing. There is a law of conservation of human 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 school- houses, the cleanliness of the water in its reservoirs, and the reliability 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 respon- sible 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 interested public to the ventilation of college halls and dor- mitories, as well as to the exterior appearance and location. These results can be brought about only when the stu- dents themselves appreciate the possibilities of increased mental production under conditions of decreased friction, such as can be found only when the requirements of health are perfectly fulfilled. THREE ESSENTIALS OF HUMAN EXISTENCE. 3 Of the three essentials, air may well be considered first, although its office 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 important 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 abun- dance of this substance in securing great efficiency in the human being increases, we shall be led to attach more im- portance to the sufficiency of the supply. In northern climates air is not free to all in the sense of costing nothing, for the coming of fresh air into the house means an accompaniment of cold which must be counter- acted by the consumption of fuel. A mistaken idea of econ- omy leads householders, 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 wel- fare 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 inheri- tance. Primitive man could leave a given spot when the soil became offensive, and neighbors were then too few to require consideration; 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 pollution. Air is abundant and is kept in con- 4 AIR, WATER, AND FOOD. stant motion by forces of nature beyond human control, so that, save in the neighborhood 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. Without it man dies in a few days; without it the soil is bar- ren; without it air in motion parches all vegetation and carries clouds of dust-particles; without it there is no life. As population 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 office of carrier it not only brings nourishment in solution to the tissues of the 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 accumulation 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 THREE ESSENTIALS OF HUMAN EXISTENCE. 5 that it should not decompose too much soap. Manufactur- ing 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 high- lands may have the first use of the water, which then perco- lates 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. Al- though 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, withdrawing the carbon dioxide with which it would otherwise become loaded, so the water has also its plant life, 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 themselves water which is safe to drink, which will not impair the efficiency of the human machine. 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 substances eaten are not)* capable of com- bining with the oxygen of the air or of being dissolved in the water or the digestive juices; of less use still is it to par- take of substances which act as irritants 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 6 AIR, WATER, AND FOOD. are beginning 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 disregard 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 con- sideration 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 healthfulness and in quality? Third, if a food-substance is normal, what are its valuable ingredients and in what pro- portions 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 sub- stance so changed as to become a possible source of poison- ous products? Or has anything in the nature of a preserva- tive 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 foodstuffs, such as the cereals, especially in the nitrogen content. This is most important to the vege- tarian and to institutions where economy must be practised. The following variations in the composition of leading cereals will illustrate: THREE ESSENTIALS OF HUMAN EXISTENCE 7 •m *~~ Nitrogenous Crude Carbo- Flhr . Water - Substance. hat. hydrates. Flbre - Ash. Oats, maximum 20.80 18.84 10.65 64.63 20.08 8.64 " minimum 6.21 6.00 2. 11 48.69 4.45 1.34 " American hulled. 12. 11 13-57 7-68 63.37 1.30 2.03 Corn, maximum 22,20 14.31 8.87 52.08 7.71 3.93 " minimum 4-68 5-55 1-73 72-75 0.99 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 additional proteid 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 min- eral 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 de- serve to be carefully studied. Dried fruits and nuts are much undervalued as articles of food, as are rice and lentils. (See table, page 130.) The discussion of food values will be found in Chapter VIII. Probably the widest field for the sanitary chemist to-day is the study of the so-called predigested foods, infant foods, " hygienic " preparations, two-minute cereals, and the count- less proprietary packages, which, designed to meet the de- mand for quick results, prove traps for the unwary. Therefore the sanitary aspect of food demands a study 8 AIR, WATER, AND FOOD. of normal food and food value even more than of adulterants or of poisonous food, ptomaines and toxines. The cultiva- tion of intelligent public opinion is most important, and each student should go out from a sanitary laboratory a mission- ary 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 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 em- ployed 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 func- tions 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 pro- fessionally. 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 referred to such works as those of Wiley, Allen, Blythe, etc., but for the student who needs to study, as a part of general education, only typical substances, and such methods as can THREE ESSENTIALS OF HUMAN EXISTENCE. 9 be carried out within the limits of laboratory exercises in a college 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. CHAPTER II. air: composition; impurities; relation to human LIFE. The average adult human being makes about eighteen involuntary respirations per minute. The tidal volume of air is from 300 to 500 cubic centimeters (30 cu. in.), about 2800 cubic centimeters (170 cu. in.) remaining in the lungs unless voluntarily expelled by deep breathing. The total volume expelled is often called the vital capacity, and is about 3400 cubic centimeters for men and 2500 for women. Even when at rest a volume of 7000 to 12,000 liters (250 to 420 cu. ft.) of air passes through the lungs of each individual in twenty-four hours. Under conditions of exercise more or less prolonged or violent this volume may be doubled. The composition of the normal inspired air by volume is approxi- mately: nitrogen and argon 79 per cent., oxygen 20.9 per cent., other constituents 0.1 per cent. The air as it leaves the lungs contains nitrogen 79.5 per cent., oxygen 16.0 per cent., carbon dioxide 4.4 per cent., and is saturated with water-vapor. There has therefore taken place an inter- change of gases (called the respiratory exchange), by which oxygen has passed into the fluids of the body, and carbon dioxide into the air contained within, the lung-cells.. Only about one-fifth of the total oxygen is abstracted during each tide. If the composition of the inspired air varies from the air: relation to human LIFE. II normal, this exchange is disturbed, owing to the difference in gaseous pressure and in rate of absorption which this variation causes. So delicate is the balance of the active forces that serious disturbance of the functions of the living organism occurs if the percentage of oxygen is lessened by one or two tenths, or if the pressure is raised or lowered by a fraction of an atmosphere. It is true that, like a tree bending before the wind, the organism soon adapts itself to changed circumstances, provided the change is not too great nor too suddenly made; but, like the exposed tree, the living being is never quite so vigorous and symmetrical as it would have been without the effort to overcome disadvantageous conditions. That a permanent or habitual lowering of the oxygen in inspired air must be harmful will be readily seen from a con- sideration of the office of this gas in the body. To Lavoisier and Laplace we owe the knowledge that animal heat is de- rived from a process of combustion. Lavoisier held, how- ever, that the seat of this combustion was in the lungs, and it is to Pfliiger and his pupils that we are indebted for the proofs that it is in the tissues themselves, while the lungs serve as a clearing-house or centre of exchange. By the union of the oxygen with the substances found in the tissues and brought to them by the circulating fluids of the body from the digested food, the heat necessary for the life and work of the body is produced. This heat is needed to keep the tissues at the temperature at which they can best accomplish their work, to give mechanical power for the in- voluntary action of heart and lungs, for the processes of assimilation, and to furnish the energy for all voluntary work and thought. Thus both water and food are intimately con- cerned in the processes in which air is an essential factor. The statement made in the first sentence of Chapter I is 12 AIR, WATER, AND FOOD. therefore justified, namely, that air, water, and food together are three essentials of human existence. A certain relation between the three means health, and any disturbance of this relation means unhealth, by which term may be designated a condition of less than perfect health not yet so serious as to be called sickness. Air being a mere mixture of the gases nitrogen and oxy- gen, in no definite atomic proportions, and carrying varying^ amounts of other substances, gaseous and suspended parti- cles, no definite composition can be given. The difference between the air over sea or forest plateau and that of city streets or of crowded tenements seems only slight if expressed in per cent. From 20.98 per cent, of oxygen in the first to 20.87 an d 20.60 in the last; from .022 per cent, of carbon dioxide in the purest air to .045 in cities and .33 in rooms, are the common variations; and yet the effect of these apparently sma 1 l differences on human beings subjected to them is very noticeable. It is customary to enhance these differences by expressing the results in parts per 10,000. That the carbon dioxide is of itself a disturbing factor is indicated by the observed fact that air which has had the per cent, of oxygen reduced by combustion to a point at which a candle will no longer burn may be made again a supporter of combustion by the removal of the carbon dioxide. A practical application of this principle is made in the devices used in diving and in entering mines filled with irre- spirable gases. There is a sensible effort in breathing, and a feeling of discomfort is usually experienced, if the carbon dioxide ac- cumulates to ten times the normal amount, or 40 parts per 10,000 instead of 4. This is probably due to its solubility and to its interference with the respiratory exchange, since the interchange of gases is influenced by their " partial pres- AIR: RELATION TO HUMAN LIFE. 1 3 sures." Each gas forming part of a mechanical mixture exerts a partial pressure proportional to its percentage of the mixture. For example, if atmospheric air, containing 20.81 per cent, of oxygen, is at 760 millimeters barometric pres- 20.81 sure, the partial pressure of the oxygen would be X 760=158.15 millimeters. The following partial pressures of oxygen and carbon dioxide in inspired air and in the lung- cells show the extent of variation in different parts of the respiratory tract: Inspired Air. Lung-cells. Oxygen 158.15 mm. 122 mm. Carbon dioxide 0.30 mm. 38 mm. Gas will always tend to diffuse from the region of high- est to that of lowest pressure. Hence the reason for the great influence of pressure in causing the diffusion of oxygen from the inspired air into the lung-cells and for the converse movement of carbon dioxide. That variation in pressure has much to do with the discomfort is shown in the so-called mountain-sickness, experienced at high altitudes in rarefied air, and in the so-called caisson-disease, developed in men working in compressed air. If the passage from the caissons to the open air is made gradually, there is little trouble, but a quick change is often dangerous. A sort of mountain- sickness is experienced by many on entering a close room from the outside air. Usually this passes away in a measure as the organism accommodates itself to the new conditions. Even if the symptoms are not severe, there is a dulness or an irritability which is not conducive to the best apprehen- sion of a difficult subject or to the fullest enjoyment of an entertainment. This lessening of mental capacity is especially to be de- 14 AIR, WATER, AND FOOD. plored in the case of school-children, who are at an age when, respiration is most frequent and the need of pure air the greatest, and also when economy of effort is most demanded. It has been said that from the study of the physiological effects of close air it seems to be indicated that the evil is due to the change in the respiratory quotient and to the con- sequent change in blood-pressure, which interferes with the circulation. The respiratory quotient is obtained by divid- ing the volume of carbon dioxide given off by that of the oxygen absorbed, and indicates how much of the oxygen has combined with carbon to form carbon dioxide, since one vol- ume of oxygen combines with cafbon to form one volume of carbon dioxide. The rate of exchange is influenced by- questions of pressure, exposure, temperature, and water- vapor or moisture, muscular activity, and the like. Water-vapor is the most variable constituent, due to the changing capacity of air for moisture at different tempera- tures and to the character of the earth's surface. Whether over land or water, cultivated or forest region, air at o° C. contains only 4.87 grams of water per cubic meter, while air at 6o° F. (15 C.) can take up 12.76 grams, and at 90 F. holds 33.92 grams. Since the human body is constantly giving off moisture from skin and lungs, and since this exhalation is an important factor in the bodily economy, the presence of ex- cessive moisture in the air exercises a decided effect. On clear, invigorating days the moisture in the air may- be only 30 or 50 per cent, of that required for complete satu- ration at the given temperature, and although the ther- mometer reading may indicate 85 ° F. on a hot day, little discomfort follows; but let the humidity rise to 90 or 95 per cent, while the temperature remains the same, and oppres- sion, restlessness, or languor results. Much the same effects are seen in the case of close rooms and crowded halls. The. air: relation to human life. 15 watery vapor given off (about 20 grams per person per hour) soon saturates the air, and the consequent drowsiness and headache usually attributed to carbon dioxide will be felt; while if this moisture is removed, the same proportion of carbon dioxide would hardly inconvenience the occupants. A relative humidity of 60 per cent, is said to be the most comfortable for house temperature. In normal man, exposure to cold increases the respiratory exchange; but if he represses shivering and keeps still by force of will, it apparently does not. Politely sitting still in- creases the probability of taking cold. A high temperature lessens the production of carbon dioxide and therefore saves food. This may in part account for the oppressiveness felt by well-fed and warmly clothed persons in public places none too warm for those with a more restricted diet. Muscular activity increases respiratory exchange and causes a demand for food. A class of students passing across the campus, up several flights of stairs, into a lecture-room vitiate the air for the first ten minutes at a rate higher by one part of carbon dioxide per 10,000 than half an hour later. The exchange is also stimulated by a meal Not only the oxidation of the food itself, but the muscular activity of the alimentary canal and probably other accompanying activities call for an expenditure of energy which is supplied by in- creased heat production. Sodium sulphate is said to increase the various respira- tory activities, and some have held this fact to be one reason for the beneficial effects of certain mineral waters. The amount of carbon dioxide expired is estimated by Pettenkofer at .006 to .012 cubic foot per pound of body weight, according to the degree of exertion. Rubner con- siders that, in general, metabolic processes depend also upon the proportion of superficial area to the total volume of the l6 AIR, WATER, AND FOOD. body, hence the smaller the animal the greater the surface to the whole mass. Children give off in proportion to their body weight about twice as much carbon dioxide as adults. Another estimate gives the output of carbon dioxide as .0027 gram per hour per square centimeter of surface. Ammonia is also a constant component of the air of in- habited places and is washed out by rain and snow, as will be shown in Chapter VI. Of the occasional impurities, probably the most fatal is carbon monoxide arising from leaking gas-fixtures or de- fective furnaces. This gas has 250 times the affinity for haemoglobin and therefore forms with it a more stable compound than does oxygen, and hence its presence causes a deficiency of the latter gas in the blood, giving symp- toms like those observed in mountain-climbing or bal- loon ascensions. When the blood-corpuscles become about one-third saturated the effect becomes sensible; but if the quantity of gas is considerable, the symptoms are hardly noticeable before insensibility occurs. For this reason, glow- ing charcoal and open gas-jets are the favorite forms of cowardly self-destruction. In the neighborhood of factories, smelting-works, ore- heaps, and of cities burning soft coal there is a noticeable amount of sulphurous and sulphuric acids, sometimes so con- siderable as to destroy vegetation. In places where gas is burned, oxides of nitrogen are formed in small quantity, the effect of which is known to be harmful. Minute quantities of hydrogen sulphide and of com- pounds of carbon and hydrogen and of other gases may be present, especially in houses with defective plumbing or in the neighborhood of barns, cesspools, and filthy back yards. These may reach dangerous proportions, but, like carbon air: relation to human life. 17 monoxide, should not be permitted in or near any well-regu- lated household. Soot, being insoluble, accumulates in the lungs, as a post- mortem examination of persons who have lived for some time in a smoky city proves; nevertheless no definite ill effects have been as yet attributed to this cause. This again con- firms the inference that it is the gaseous constituents, and the varying temperature and pressure, which seriously affect the respiratory exchange The following results, obtained on the air of a large man- ufacturing city, will be of interest in this connection:* GRAMS PER 1,000,000 CUBIC METERS OF AIR.f Soot. H 3 S0 4 . FreeNH 3 . Alb. NH 3 . HNO,. HN0 2 . IOOO to 40000 7000 to 63000 1 IOO to 1000 97 to 557 45 to 1063 O to 155 1 Partly H a S0 3 . It is probable that much of the danger ascribed to sewer- air arises from other causes. Since the atmosphere in sewer- pipes is always moist, the only probable source of organisms is the splashing of the water. Only about one-half as many organisms have been found in the air a'bove flowing sewage as in out-door air. Professor Carnelley and Dr. Haldane found only one-half as much carbon dioxide and one-third as much organic matter in such air as in that of t'he streets above. Beyond individual control, and in a measure beyond gen- eral control, there exists suspended matter in the air: fine volcanic dust, pollen, spores of moulds and algae, dried bac- teria, diatoms, small seeds of plants, soot and the finely pulverized earth from roads and cultivated and barren lands. To this portion of the air we owe beautiful sunsets and dis- agreeable fogs. To it many affections of the throat and * Mabery: /. Am. Chem. Soc, 17 {1895) 105. f See also Bailey: " The Air of Large Towns," Science, Oct. 13, 1893. 1 8 AIR, WATER, AND FOOD. eyes are due, and by it disease may be transmitted. Some: kinds of dust lodge in the air-cells and by irritation render the individual liable to disease, as statistics of the mortality in dust-producing trades show. In the air of houses this. impurity increases a thousand-fold by means of the wear of furnishings and the accumulation on them of deposited par- ticles, by means of furnace-ashes and dried debris of all kinds. Only recently have the dangers of this part of the air we breathe been distinctly pointed out. Aitken * estimated that a cubic inch of air may carry 2000 dust-particles in the open country, 3,000,000 and more in cities, and 30,000,000 in inhabited rooms. Among these millions there may be found from ten to several hundred micro-organisms, moulds, and bacteria, and, under certain conditions, pathogenic germs. As methods of culture become more satisfactory and tests more universal, it may be demonstrated that many old or long-inhabited buildings furnish several varieties of patho- genic germs constantly to the air. According to some authorities, the most dangerous con- tamination of the air is the " crowd-poion," or organic matter given off with the carbon dioxide and moisture in the- breath. References will be found in the bibliography to dis- cussions of the subject. No evidence has ever been found in the course of investigations in this laboratory, covering a period of fifteen years, that the healthy human lung gives off any toxic substance. * Nature, 31 {1870), 265; 4 1 (iSSo), 394. CHAPTER III. THE PROBLEM OF VENTILATION. From the preceding chapter it will be seen how impor- tant is the purity of the air to human well-being, and how essential is the diffusion of the knowledge of the methods by which it can be secured. It is often said that artificial ventilation is a modern necessity. Remains of aqueducts and sewers have testified to the sanitary intelligence of his- toric peoples, but the ventilating fan does not seem to have been included, although natural ventilation by shafts and flues has been practised since man came out of cave-dwellings. It is true that customs have changed as to many items of daily life. In cities more people live on an acre of ground, thus fouling the air above and the ground beneath ; more factories are belching smoke; more coal is burned; houses are built with smaller rooms and less pervious walls; schools and lecture-halls are more crowded; people are better fed, con- sequently there is more garbage; streets are macadamized, allowing finely ground particles to fill the air with every puff of wind; gas-pipes traverse the walls of every house and pass under every street; carpets, draperies, and much passing in and out cause an accumulation of dust unknown fifty years ago. Kerosene lamps require more oxygen than many candles. Besides, people are becoming less hardy and more sensitive physically, so that well-ventilated living-spaces are a modern necessity if human efficiency is to be maintained. 19 20 AIR, WATER, AND FOOD. As we have seen, the air of open spaces presents only very slight variation at the same level or for several thousand feet above it. The movement of the air caused by the wind is usually so rapid, and the reservoir of air for many miles above the earth is so immense in comparison with the thin vitiated layer, that there are only to be considered enclosed spaces in which human beings remain for a period of time. To supply the 7000 to 12,000 liters (250 to 430 cubic feet) of tidal air per person in maximum purity, there must be. brought to the person at rest some 1800 cubic feet of air per hour. If he were in an air-tight chamber 12 feet square and 8 feet high, a man would reach the limit of purity in 38 minutes; but no ordinary room is air-tight, and when the difference between inside and outside temperature is consid- erable, a rapid exchange is taking place even with doors and windows shut. To secure the passage of this large volume of air through a small space without causing a draft that will be objected to by the abnormally sensitive victim of modern luxurious habits is the problem of ventilation — one not yet satisfactorily solved. The sanitary engineer is expected to design the appara- tus and to aid the architect in so placing and proportioning flues, inlets, and outlets as to accomplish the desired results. Unfortunately it is too common, especially in the case of school and college buildings, to economize in the first cost by dispensing with the services of the expert and to leave to the builder and " practical " architect all such details. In any case, it often becomes necessary to call in the chemist to prove the need of reform, or to show by the composition of the air whether or not the ventilating plant is doing its work efficiently. The sanitary inspector, whose business it is to decide air: the problem of VENTILATION. 21 upon the legal questions connected with tenements and fac- tories, must often rely upon chemical examinations of the air. The validity of these depends not only upon the per- fection and delicacy of apparatus and methods used, but also upon the judgment and intelligence with which the samples are taken. Many errors in the construction of buildings have been perpetrated because of an ignorance of the physical proper- ties of air and, consequently, a mistaken notion of the be- havior of a vitiated atmosphere. The lecturer on popular science who some forty years ago enlightened (?) the com- munity on the chemistry of daily life was accustomed to use, as a striking illustration, a glass jar in which a small lighted candle was instantly extinguished on pouring into the jar a tumblerful of carbon dioxide which had been collected for the purpose. The inference was plain: carbon dioxide was heavier than air, therefore it falls to the floor and must be allowed to flow out as if it were a stream of water. Further confirmation of this inference was found in the frequently observed fact that a candle lowered into a well often went out just before the water was reached. Hence for many years the habits of thoughtful persons were formed on a belief in the heaviness of carbon dioxide or " bad air," and in its tendency to go to the bottom of the room and into any holes it could find. This is only another instance of danger in half a truth. When do we find cold carbon dioxide generated in living-rooms? And how warm must the gas be in order to be lighter than the ordinary air? How quickly does diffusion take place? Until within a very few years the almost unanimous belief among the so-called educated classes was that the bad air could be let out by opening a window at the bottom, and, in spite of the lessons which might have been learned by any observant person in 22 AIR, WATER, AND FOOD. hanging pictures or Christmas greens, the common practice in private houses, churches, and schools is to open the win- dows at the bottom. All ordinary vitiation of the air proceeds from a heated source. Human breath and warm air are lighter than cold air and rise even with their burden of carbon dioxide. It is only when they impinge on a very much colder surface, as on the window-pane on a very cold day, that they become suffi- ciently chilled to fall without mixing with the neighboring air. The freedom with which the gases of the air mix, as well as the rapidity of the action, may be illustrated in a variety of ways. Open a bottle of any volatile and pungent substance, as ammonia or hydrogen sulphide, in one corner of a room, and almost instantly it may be perceived in the most distant part. In natural ventilation we have only to avail ourselves of these characteristic properties of gases; and whether we wish to get rid of the light gases escaping from furnace, stove, or gas-pipe, or of the specifically heavier carbon dioxide, or of the most dangerous dust, we must furnish an outlet at the place to which the fleeing enemy first arrives, lest it turn and rend us for our ignorance. It is usually sufficient to furnish this opportunity, the current caused by this willing escape drawing in sufficient fresh air to take its place except in very crowded rooms, and even these might be so ventilated provided the whole roof were one large ventilating flue. If, however, the air is to be drawn from the bottom of the room, its unwilling current must be pulled by a superior force, as by an open fire on the hearth, which heats the air above it so that, in rushing into the free air above, it draws after it all things movable within reach. Then, indeed, even the top of the room becomes quickly cleared and no corner can escape; but if the fire be air: the problem of ventilation. 23 long gone out and the chimney cold, the reverse takes place and cold, heavy air sinks to the floor, helping to confine the had air at the top of the room. What the cold chimney cannot accomplish the mechani- cally driven fan can do, namely, by a slight compression force a draught even up a cold chimney. In this case the very unwillingness of the air to take the prescribed path helps in the result as water forced through a mill-wheel de- velops mechanical work. The warmed fresh air forced in near the top of the room loses its velocity as it mingles with that already present, and finds its way along the line of least resistance to the opening provided at the bottom of the room, into the flue, but only in case there is no easier way. Open doors or windows interfere with the prescribed course, and blindness to this fact on the part of the occupants of mechanically ventilated buildings has caused unjust com- plaints of the system. The necessity of regulating the con- sumption of fuel and admission of fresh air in accordance with variations of temperature, as well as the great care and trouble this involves, renders the " natural " system of ventila- tion practicable only in less crowded dwelling-houses where intelligence can control the varying factors. For schools, lecture-halls, or any enclosed spaces occupied by numbers of persons at one time, some form of mechanical ventilation offers the only hope of good air in cold climates. What form that shall take is for the engineer to decide. The chem- ist's part is to devise means of readily determining whether the persons in charge of the apparatus are using it to gain the results designed by the expert. As a test of how nearly practice approaches the theoreti- cal value, carbon dioxide is taken as the indicator, since it is present in a thousand times larger quantitv than any other impurity and since it is easily determined. If the air has 24 AIR, WATER, AND FOOD. only the normal amount of carbon dioxide, it is but rarely that it contains enough of anything else to be harmful. The presence of hydrogen sulphide or of coal-gas is betrayed by the odor. Where the gas-supply is " water-gas," contain- ing 30 to 40 per cent, of carbon monoxide, there is greater danger; but if legal restrictions are complied with, the pres- ence of this can be detected in the same way, viz., by the odor. Danger may also arise from the presence of so-called " sewer-gas," which, however, is not a single gas, but a most complex and variable mixture of the more volatile products of decomposition. For the detection of " sewer-air " chemi- cal tests are of little value, since it contains no constituent in sufficient quantity and with sufficient regularity to serve as an index of its presence. Ill-smelling gases are given off only when sewage is about eighteen hours old, hence dirty house-pipes are the chief cause of foul air. The delicate sense of smell is of value here. Indeed, an edu- cated nose is most essential in all examinations of house- air. " Crowd-poison," if it exists, keeps company with the increase of the products of respiration, and if the incoming air is strained or taken from a place free from dust, the par- ticles added to the air which is in the rooms will also be re- moved with the carbon dioxide. From nearly all points of view, carbon dioxide is an indi- cator of the efficiency of ventilation, especially if combined with observations of temperature and moisture. It is an in- dicator also readily understood and accepted by the public. The principles of ventilation may be readily illustrated to a class by means of simple apparatus. Such an apparatus, using candles and designed to illustrate the section of an ordinary room, is shown in Fig. 1. In testing the efficiency of ventilation of any room or AIR: THE PROBLEM OF VENTILATION. 25 building, it is necessary to determine first the direction of the air-currents, for there can be no ventilation without currents. If the architect who designed the building, or the engineer who advised the architect, is responsible, then the chemist has only to follow directions in taking the samples; but fre- quently the chemist, as well as the sanitary engineer, is called Fig. 1. — Apparatus to Illustrate the Principles of Ventilation. upon to make tests of rooms and buildings of which no plans are available. In the examination of such rooms, then, the position of flues or conduits, both inlets and outlets, which were intended to convey air or which serve without such intention, should first be located. Possible avenues of ingress and egress by means of loose windows, cracks around doors, etc., are to be considered. When there is great difference of temperature between outer and inner air, these allow of quite rapid change of air. Some means of rendering visible these currents is de- sirable, such as smouldering paper, magnesium powder, or fumes of ammonium chloride. 26 AIR, WATER, AND FOOD. When the direction and intensity of these air-currents have been determined, the places from which the air-samples are to be taken may be chosen. It will be evident in what part of the room stagnation occurs and where eddies are formed, also where the air escapes. In a room or building without artificial ventilation the air-currents are seen to be ascending until they become chilled, when they fall. An empty room will not show so decidedly the rise of air-currents as will an occupied one in which the vitiated air, being much warmer, rises more rap- idly and cools less quickly. In taking the samples all acci- dental means of contamination must be avoided and the occupants must be quiet, for the moving of persons causes disturbance in the air-current. There is room for great in- genuity in this part of the examination, as circumstances greatly modify the method of procedure. A fa'r sample, or a sufficient number of samples to give a fair average, must be taken. Having secured and analyzed the samples of air, the de- cision as to the efficiency of ventilation must be rendered. If the room examined is a study- or recitation-room, the stratum of air at the level of the students' heads should not contain over 8 or 9 parts per 10,000 of carbon dioxide, should not show a temperature of over 70 ° F., nor a humidity of over 35 or 50 per cent., and these conditions should be main- tained for hours at a time. For lecture-halls and spaces occupied for on 1 y one hour at a time, with ample time between occupation, it is admis- sible to allow 9 to 11 parts. If fan ventilation is used, the outlet should give the average degree of contamination. If no system is used, the air at the top of the room is first vitiated; only at the end of twenty minutes to half an hour do the lower layers begin to show it, CHAPTER IV. ANALYTICAL METHODS. DETERMINATION OF CARBON DIOXIDE. General Statements. — The methods of determination all rest upon the property which the " caustic alkalies," the hydroxides of potassium, calcium, and barium, possess of uniting with carbon dioxide and forming stable compounds. Where it is necessary to absorb large quantities of the gas in a slight volume of solution, potassium or sodium hy- droxide is used. For nearly all of the " popular tests " cal- cium hydroxide, lime-water, is used because of its harmless nature and the ease with which it can be obtained from the corner drug-store, or from the quicklime procured fro:u the mason's barrel. For vol- umetric methods barium hy- droxide is generally preferred, because of the less solubi.ity of the barium carbonate, it being only about two-thirds as soluble as the calcium salt. The very avidity with which these substances take up car- bon dioxide is a hindrance to the preparation of standard solutions in an atmosphere Fig. 2. 2$ AIR, WATER, AND FOOD. already rich in it. When once prepared the solution must be preserved with especial care, since contact with the hands or a whiff of the breath will reduce its strength and vitiate the results. All such solutions are best kept in bottles well protected from the air by tubes filled with soda-lime and de- livered from a burette, as in Fig. 2. For some of the methods it will be found advantageous to have the solution measured for each test by means of an automatic pipette, as shown in Fig. 3. This can be attached directly to a liter bottle containing the stock solution, and, if placed in a suitable case to prevent in- jury, may be easily carried from one place to another. This is especially con- venient for several of the " popular tests." Pettenkofer Method. — The method for the determination of carbon dioxide which has been found most satisfactory in accurate work is a modification of the Pettenkofer method.* Principle. — In principle this consists in absorbing the car- bon dioxide from a known volume of air in barium hydroxide solution and titrating the excess with standard sulphuric acid. It is essential for the complete absorption of the carbon dioxide that the barium dioxide be largely in excess so that not more than one-fifth of it is neutralized; furthermore, the absorbing solution must be shaken up with the air for a considerable time. Collecting the Samples. — The samples are collected in four- or eight-liter bottles, the volume of which is accurately * Pettenkofer: Annalen, 2, Supp. Band {1862), p. 1. Gill: Analyst, 17 (1892), 184. Fig. 3. air: analytical methods. 29 known, the bottles having been calibrated by weighing them filled with water. These bottles are provided with a rubber stopper carrying a glass tube over which a rubber nipple is slipped. They are filled with the air to be tested by means of a pair of nine-inch blacksmith's bellows, fitted with valves so arranged as to draw the air out of the bottle. The bel- lows is connected with a three-quarter-inch brass tube reach- ing nearly to the bottom of the bottle; fifteen or twenty strokes should be sufficient to replace the air in a four-liter bottle. At the time of collecting the samples the following observations should be recorded: Room, date, time, weather, place in room, number of people present, number of gas-jets or lamps burning, condition of the doors, windows, and transoms; in short, everything which would tend to affect the amount of carbon dioxide in the air, or to cause currents or eddies. The bottles should be distinctly labelled and their volumes re- corded. If the temperature at the point where the samples are collected should be essentially different from that of the laboratory, the bottles should be allowed to stand in the laboratory for half an hour or until they have attained its temperature. Directions for Laboratory Work. — The solutions of barium hydroxide and sulphuric acid which are used are approxi- mately of equal strength; but since it is impracticable to pre- pare exact solutions of barium hydroxide and to keep them without change, the exact value of the barium hydroxide so- lution must be found by titration against the standard sulphuric acid, which is made of such a strength that 1 cubic centimeter is equivalent to exactly 1 milligram of C0 2 . This standardization, as well as the subsequent titration, is best made in a small flask to lessen the error from absorption of carbon dioxide from the air. It will be found most gen- erally satisfactory to measure into the flask about 25 c.c. of 30 AIR, WATER, AND FOOD. the barium hydroxide, add a drop of phenolphthalein solu- tion, and titrate with the sulphuric acid to the disappearance of the pink color. In all cases the first end-point should be taken as the correct one, because the pink color will some- times return on standing. This is due to the presence of minute quantities of potassium or sodium hydroxide in the solution. The alkali sulphates will react with any barium carbonate which may be suspended in the liquid with the formation of alkali carbonates which give a pink color with phenolphthalein. The standardization should be repeated until consecutive results are obtained which check within 0.2 per cent, of each other. Determination. — Remove the cap from the tube in the stop- per of the 'bottle, insert the tube-tip of the burette so that it projects into the bottle, and run in rapidly 50 c.c. of barium hydroxide from the burette. Replace the cap and spread the solution completely over the sides of the bottle while waiting three minutes for the burette to drain. In doing this take care that none of the solution gets into the cap. Note carefully the temperature and barometric pressure. Place the bottle on its side and roll or shake it at frequent intervals for forty- five minutes, taking care that the whole surface of the bottle is moistened with the solution each time. At the end of this time thoroughly shake the bottle to mix the solution, re- move the cap, and pour the solution into a stoppered bottle of hard glass of 40 c.c. capacity, taking care that the solution shall come in contact with the air as little as possible. Under these conditions a full, well-stoppered bottle may safely stand for days before titration. For the titration, measure out with a pipette 25 c.c. of the clear liquid into a 75-c.c. flask and titrate it with the sulphuric acid as in the standardization. The difference between the number of cubic centimeters of standard acid required to neutralize the total barium hy- air: analytical methods. 31 droxide before and after absorption gives the number of milligrams of dry carbon dioxide in the sample tested. The results may be expressed in parts per 10,000, by volume, under standard conditions (o° and 760 mm.), saturated with moisture (Method 1) or dry (Method 2). Tables for this purpose will be found in Appendix A.* Example. — Data: Standardization, 1 c.c. Ba (0H) 2 = 1.020 c.c. H 2 S0 4 ; volume of bottle = 8490 c.c; Ba(OH) 2 used = 49-9 c.c. ; H 2 S0 4 used = 21.1 c.c. ; temperature and pressure = 21 and 766 mm. Before absorption 49.9 c.c. Ba(OH) 2 = 49.9 X 1.020 = 50.90 c.c. H 2 S0 4 . After absorption 49.9 c.c. Ba(OH) 2 = 4^2. x 21. 1 =42.12 c.c. H 2 S0 4 . .". 8440.1(8490 — 49.9) c.c. air contain 50.90 — 42.12 = 8.78 mg. C0 2 . Method 1. — 1 c.c. C0 2 saturated with moisture at 21° and 766 mm. weighs 1.79624 mg. (Table II, Appendix A). 8 78 .-. 8.78 mg. = — -^ — =4.887 c.c. C0 2 saturated with moisture. xx r • 1 4.887 Hence in 10,000 c.c. of air there are -^ — X 10,000 = 8440. 1 5.79 parts C0 2 . Method 2. — In this method the volume of air is reduced to standard conditions of temperature and pressure, under which conditions the weight of a cubic centimeter of dry C0 2 is a constant quantity. * Dietrich's Table, the one in general use, is not absolutely correct, the weight of a cubic centimeter of carbon dioxide at o° C. and 760 mm. being somewhat different from that given at present by the best authorities, but it is sufficiently close for any but the most exacting work. 32 AIR, WATER, AND FOOD. Thus v' = v\i + o.oo366(/'— /°)]. v' = 8440.1, t'=2i° r t° =zQ°\ hence v = 7&Z7.7 c.c. Also, v : v"=H":H, or 7837.7 :*= 760: (766— 18.5)* (18.5 = tension aqueous vapor at 21 .) Then v" = 7709 c.c. = volume of air at o° and 760 mm. I c.c. C0 2 at o° and 760 mm. weighs 1.9643 mg. 8.78 „ ^^ 4.469 4.469 c.c. CO2. X 10,000= 5.79 parts 1.9643 " * 7709 C0 2 per 10,000. Two samples are to be taken, closely following the notes, and the results calculated by both methods before collecting more samples. Then some one room may be taken and the quality of the air determined for the different hours of the day, or a comparison of different rooms may be made, or a building may be tested as a whole. All data and results ob- tained should be arranged in tabular form on a separate page of the note-book. Notes. — This method of collecting the air in a large bottle possesses a decided advantage over the method of slowly drawing the air through barium hydroxide contained in a long tube, in that a sample represents the condition of the air at a given time and not its average condition for a period of an hour or so. In collecting samples, care must be taken to avoid cur- rents of air or the close proximity of people. Duplicate samples can be obtained only in empty or nearly empty rooms. Even two sides of the same room will probably show differences, but two samples taken carefully side by side ought to agree within 0.05 part per 10,000. The chief source of error lies in the contamination of the samples or of the solutions by air from the lungs, the exhaled breath containing on an average from 50 to 100 times as much carbon dioxide as the air under examination. It is air: analytical methods. 33 hardly possible to exercise too much caution in collecting- the samples and in carrying out the analytical procedure. All rubber stoppers which are used should first be boiled in dilute caustic soda, then in a dilute solution of potassium bichromate and sulphuric acid and thoroughly washed. Popular Tests. — In addition to the standard method for determining carbon dioxide just described, there are also cer- tain so-called " popular methods " which can often be used with advantage. These methods do not give so accurate re- sults as those obtained by the standard method, but on the other hand the apparatus required is much simpler and more compact, can be more easily carried from one place to an- other, and if used carefully and intelligently will give fairly good results. Several of these simple tests will be described in detail. (1) Method of Cohen and Appleyard.* — Principle. — This method is based upon the fact that if a dilute solution of lime-water, slightly colored with phenolphthalein, is brought in contact with a sample of air containing more than enough carbon dioxide to combine with all the lime present, the solution will be gradually decolorized, the length of time required depending upon the amount of carbon dioxide present. That is, the quantity of lime-water and the volume of air remaining the same in each case, the rate of decoloriza- tion will vary inversely with the amount of carbon dioxide. The method is scientific in principle because it recognizes the fact that the absorption of carbon dioxide by dilute alkali solutions is a time-reaction. Directions. — Collect several samples of air in white, glass- stoppered bottles of one liter capacity, either by exhausting the air from the bottle with a pair of bellows or by com- pletely filling the bottle with water and then emptying it at * Chem. News, JO (7S94), in. 34 AIR, WATER, AND FOOD. the point where the sample is to be taken. Run in quickly from the burette 10 c.c. of the standard lime-water (see Re- agents, p. 204), replace the stopper and note the time. Shake the bottle vigorously with both hands until the pink color disappears. Note the time required, and ascertain the cor- responding amount of carbon dioxide from the following table. TABLE. Time in Minutes to nrs ._,., Time in Minutes to rn . _,„ . Decolorize the Solution. C0 * P er I0 ' 000 - Decolorize the Solution. CO a per IO '° 00 - Ii 16.0 3£ 7.0 i£ 13-8 4 5-3 l| 12.8 4i 5.1 2 12.0 5 4.6 2i 11. 5 5i 4-4 2| 8.6 6i 4.2 3i 7.7 7| 3.5 Modified Cohen Method. — If all the tests of air by this method are to be made in the laboratory, it will be found best to keep the standard solution in a bottle carefully protected from the air, and to draw it off from a burette as wanted for each test. In order to make the apparatus more portable and convenient for a number of tests at a distance from the laboratory, the following modification of the method is used, and has been found to give excellent resu 1 ts. The 10 c.c. portions of the standard lime-water are measured into thin glass vials which are tightly closed with rubber stop- pers. A number of these vials can be filled at once, since the solution will keep its strength for a long time if the vials are clean and the stoppers have been boiled with potash and bichromate as previously directed. In order to avoid get- ting traces of acid on the outside of the filled vials through handling, it is best to rinse them off thoroughly and keep them in a beaker under water until wanted for use. The samples are collected in the bottles as before, the glass stop- air: analytical methods. 35 per removed for a second, and the vial of lime-water quickly dropped in, stopper downward. The bottle is shaken once violently to break the vial, and is then shaken with a rotary motion until the solution is decolorized. If desired, a bottle of half the size, and smaller vials holding only five cubic centimeters of solution, may be used. Note. — Much of the difficulty experienced in the use of these simpler methods arises from the lack of defmiteness in the composition of "a saturated solution of lime-water" which is generally recommended for use in making up the test solu- tion. The amount of lime that water will take up varies considerably with the way in which the solution is made; for example, whether the water is simply shaken up with a cer- tain quantity of lime, or whether the solution, once saturated, is kept standing over an excess of lime. For this reason it is much better to have the strength of the lime solution definitely fixed by some method of titration. (2) Method of Dr. G. W. Fitz — Principle.— In this method the volume of air that must be brought in contact with a definite quantity of lime-water, in order to neutralize all of the lime, is taken as a measure of the amount of carbon dioxide in the air. The quantity of lime-water and the time of reaction remaining constant, the amount of carbon diox- ide will vary inversely as the volume of air required. In this laboratory the same solution is used for this method that is used in the Cohen method. The apparatus consists of a graduated tube or " shaker," of about thirty cubic centimeters capacity, and a number of homoeopathic vials, each containing ten cubic centimeters of standard " lime-water." Directions.— Be sure that the inner tube of the shaker slides easily within the outer one, then remove the inner tube and pour into the large tube the contents of one of the vials. Introduce the inner tube and press it to the bottom 36 AIR, WATER, AND FOOD. of the larger, then withdraw it to the " T " mark, the bottom of the inner tube serving as the index. Close the mouth of the small tube with the finger and shake the instrument vig- orously for thirty seconds. The volume of air thus brought in contact with the solution is 30 cubic centimeters, as there are 25 cubic centimeters of air above the solution when the inner tube is forced to the bottom of the larger. Then re- move the finger closing the small end, press the inner tube to the bottom of the larger and draw it up again to the 20-c.c. mark, thus admitting 20 cubic centimeters of fresh air. Shake the apparatus again for thirty seconds. The total volume of air now used is 30 + 20 c.c. = 50 c.c. Repeat the operation until the color of the solution is discharged. The first trial made will probably give the approximate amount of carbon dioxide, and subsequent tests with the other vials will aid in giving the correct result. After determining the volume of air which is required to decolorize the solution reference is made to the table given below. TABLE. Air in c.c. used. co a per 10,000. Air in c.c. used. C0 a per 10,000. 30 28 91 9 Bad 36 22 103 8 46 18 Very bad 117 7 58 14 138 6 69 12 165 5 Good 82 10 207 4 Notes. — The stoppers and vials should be washed and dried after use and kept separate, and the parts of the shaker should be kept separate. In using the shaker see that the fingers are clean, or close the mouth of the shaker with a rubber stopper instead of the finger; also take care to avoid loss of liquid upon the addition of fresh air. The same objection applies to this method as to the tube method of Pettenkofer, namely, that the air taken air: analytical methods. 37 is an average sample extending over some time and does not show its condition at any one time. New stoppers should be boiled in dilute caustic soda and then in bichromate solu- tion before being used. (3) Wolpert's Method. — Principle. — When air contain- ing carbon dioxide is passed through lime-water the solution gradually becomes turbid from the formation of calcium car- bonate, and the richer the air is in carbon dioxide the less will be the volume of air required to produce a definite degree of turbidity. This is the principle on which this simple method is based. Directions. — A small test-tube provided with a black ref- erence-mark on the bottom is filled to a definite height with " saturated " lime-water. The air is collected in a small rub- ber bulb and slowly forced through the solution, the operation being repeated until the reference-mark can no longer be seen through the turbid solution. The instrument is first calibrated by observing the volume of air required to produce turbidity out of doors or in some room where the percentage of carbon dioxide is known, after which it affords a ready means for comparative tests in cases where the air contains 20 parts or more. For testing modern systems of ventilation, where the amount is usually less than 8 parts, it does not give reliable results. The difficulties in the use of this method are the same as those noted under the Fitz meth- od, with the increased error due to the solubility of calcium carbonate in solutions of carbon dioxide. (4) Wolpert's "Luftpriifer" (Air-tester). — This is an- other simple instrument for testing the purity of the air. Its action is based upon the well-known fact that the alkali carbonates give a pink color with phenolphthalein, while the bicarbonates do not. By means of a capillary siphon a one per cent, solution of sodium carbonate colored with phe- 38 AIR, WATER, AND FOOD. nolphthalein is allowed to drop at regular intervals upon a cord suspended vertically. As the solution flows down the string it absorbs carbon dioxide from the air, converting the sodium carbonate into the bicarbonate, so that the lower part of the cord will be white, while the upper part is pink. The height of the dividing line indicates on a scale the amount of carbon dioxide in the air. The chief value of this instru- ment lies in the fact that it acts continuously, one filling being enough to last for ten days, and can be consulted at any time to learn the condition of the air, just as a ther- mometer is used to indicate the temperature. In practice the usefulness of the apparatus has not been fully realized on account of the dryness of the air in ordinary rooms, which, interferes with the continuous flow of liquid down the cord. Carbon Monoxide. — The detection and estimation of carbon monoxide in the very minute quantities in which it is found in the air of ordinary rooms is a problem of consider- able difficulty. Detection. — Probably the most convenient test for detect- ing small quantities is the blood test. Dilute a large drop of human blood, freshly drawn by pricking the finger, to 10 c.c. with water. Divide the solution into two equal portions, and shake one portion gently for ten minutes in a bottle con- taining about ioo c.c. of the air to be tested. Compare the tints of the two portions by holding them against a well- lighted white surface. The presence of carbon monoxide is indicated by the appearance of a pink tint in the blood which has been shaken with air. One part in 10,000 can be de- tected in this way.* The delicacy of the test can be increased by examining the blood, after shaking with the air, with a spectroscope. By collecting the sample in an 8-liter bottle * Clowes: " Detection and Estimation of Inflammable Gas and Vapor in the Air," p. 138. air: analytical methods. 39 and examining it in this way o.oi part in 10,000 may be de- tected. Determination.* — Principle. — Oxidation of the carbon monoxide to carbon dioxide by iodine pentoxide, iodine being liberated according to the following equation: I 2 5 +5CO= I 2 + 5C0 2 . N The iodine is titrated with sodium thiosulphate. 1000 r Directions. — Place 25 grams of iodine pentoxide, free from iodine, in a small U tube which is suspended in an oil-bath and connected with a small absorption-bulb containing 0.5 gram of potassium iodide dissolved in 5 c.c. of water. Heat the oil-bath to 150 C, and pass the air, previously drawn through U tubes, — one containing sulphuric acid and the other solid potassium hydroxide, — through the apparatus at the rate of a liter in two hours. Titrate the liberated iodine N bv sodium thiosulphate and starch. J 1000 r Notes. — The temperature and barometric pressure should be noted and all volumes reduced to o° C. and 760 mm. pres- sure. Using 1000 c.c. of air, it is possible to determine in this way 0.25 part per 10,000, by volume, of carbon monoxide. The use of tubes containing sulphuric acid and potassium hydroxide is to free the air from unsaturated hydrocarbons, hydrogen sulphide, sulphur dioxide, and similar reducing gases. Nitrites. — The determination of the amount of nitrites or nitrous acid in the air can be readily made as follows: Collect a sample of the air in a calibrated eight-liter bottle, as in the determination of carbon dioxide. Add 100 c.c. of * Kinnicutt and Sanford: Jour. Am. Chem. Soc, 22 (igoo), 14, 40 AIR, WATER, AND FOOD. N approximately — sodium hydroxide solution. (This should be free from nitrites and is best made by dissolving metallic sodium in redistilled water.) Shake the bottle occasionally and let it stand for about twenty-four hours. Take out 50 c.c. of the solution and determine the amount of nitrites as directed on page 94. Micro-organisms. — For the quantitative determination of the number and distribution of the micro-organisms in air, the method employed by Tucker * in the examination of the air of the Boston City Hospital answers very well. The apparatus used consists essentially of three parts: (1) a special glass tube called the aerobioscopc, in which is placed the filtering material; (2) a stout copper cylinder of about sixteen liters capacity, fitted with a vacuum-gauge; (3) an air-pump. The filtering medium which is used to retain the micro-organisms is a narrow column of sterilized granulated sugar about four inches long. In using the apparatus, the required amount of air is first drawn from the cylinder by means of the air-pump. A sterilized aerobioscope is then attached to the cylinder and the air is slowly drawn through it, leaving its germs in the sugar- filter. After the air has been drawn through, the aerobioscope is taken to the culture-room and the sugar dissolved in melted sterilized nutrient gelatine. The gelatine is con- gealed in an even film on the inside of the tube, where, after four or five days, the colonies will develop, and can be counted by the aid of squares engraved upon the glass. This method possesses several peculiar advantages. The use of a vacuous cylinder allows a known volume of air to be readily aspirated, and the rate of flow through the filter is easily controlled. Another great advantage is the use of a * Report State Board of Health, Mass., 1889, 161. air: analytical methods. 41 soluble filter (sterilized granulated sugar), since insoluble substances seriously interfere with the counting. Further- more, the removal or transference of the filter and its germs is avoided. The apparatus is portable, and the method, as compared with others, is exceedingly rapid of execution. Organic Matter. — In regard to the presence of organic matter in the air there is at present considerable variance of opinion. While some investigators have obtained results which indicate the presence of such organic matter, it has been found also that the amount which is obtained is very much less when the dust of the air is first removed by filtra- tion. The quantity of organic matter is therefore closely re- lated to the amount of dust, and there is strong evidence that this dust in the air is the source of the greater part, if not all, of the organic matter, unless there are present persons with decayed teeth, diseased lungs, etc. The methods of determination that are in general use may be divided into two groups. In the first group are those methods in which the organic matter is converted into ammonia and determined by Nessler's reagent. In the sec- ond group the organic matter is oxidized by boiling with dilute potassium permanganate, the excess being titrated with oxalic acid. No one method gives results which are wholly satisfactory, the chief difficulties being to secure an absorbing material which shall itself be free from organic matter, and to avoid the introduction of minute particles of organic matter or dust during the analytical process. Remsen * and Bergey f recommend the use of freshly ignited granular pumice-stone contained in a narrow glass absorption-tube. After aspirating a known volume of air, the pumice-stone is transferred to a flask, the ammonia dis- * National Bd. Health Bulletin, I, 233; II, 517. f Mis. Coll of Smithsonian Institution, No. 1037 (iS