I 
 
LIBRARY OF CONGRESS. 
 
 ... Copyright N 
 ShelfJ&A£ 
 
 K r - 
 
 Chape. Copyright No. 
 
 UNITED STATES OF AMERICA. 
 
Handbook of Practical Hygiene 
 
HANDBOOK 
 
 OF 
 
 Practical Hygiene 
 
 BY 
 
 D. H. BERGEY, A.M., M.D., 
 
 First Assistant, Laboratory of Hygiene, 
 
 University of Pennsylvania, 
 
 Philadelphia, Pa. 
 
 EASTON, PA. I 
 
 Che Chemical publishing Company. 
 
 1899. 
 
. TWO COPIES RECEIVED, 
 
 48537 
 
 Library of C«ngr««% 
 Offlc. ,f t |, # 
 
 NOV 1 7 ?WM» 
 
 ft»fl*Ur of Copyrights 
 
 k W 3 7. 
 
 Copyright, 1899, by Eiward Hart, 
 
 SECOND COPY, 
 
 
PREFACE. 
 
 The lack of a convenient handbook for the guidance 
 of students in the sanitary analysis of air, water, soil, 
 and the principal food materials, and in testing the 
 ventilation of buildings, is my apology for the prepa- 
 ration of this little work. There are several excellent 
 handbooks in German that cover about the same field, 
 as well as a number of general treatises on hygiene in 
 English that contain some of the methods incorporated 
 in this work, but there is no short and concise* labora- 
 tory guide, in the English language, that satisfactorily 
 meets the wants of the student in practical hygiene. 
 
 I have felt this want as a student and as an instruc- 
 tor and I trust, therefore, that this work may be a 
 means of lightening the labor of others in this line of 
 study. 
 
 As a general rule only the more simple and ready 
 methods now in use have been here incorporated as it 
 is expected that when once a good foundation for re- 
 search has been laid the student will be stimulated to 
 make use of the more extensive treatises relating to 
 the subject. 
 
 The subject of food analysis has been gone into just 
 far enough to permit of the detection of the more com- 
 mon forms of adulteration that are likely to be en- 
 countered, while the subject of general food analysis 
 has been omitted entirely because, as a rule, medical 
 students are not prepared to take up such a difficult 
 subject in chemistry. For the same reason the sub- 
 ject of examination of clothing has been omitted. 
 
 Philadelphia, Pa., May 25, z8pp. 
 

 CONTENTS. 
 
 Page. 
 
 Introducti 
 
 on - 
 
 I 
 
 Part I. 
 
 Atmospheric air 
 
 6 
 
 Part II. 
 
 Water '- 
 
 63 
 
 Part III. 
 
 Soil 
 
 - 114 
 
 Part IV. 
 
 Sanitary Analysis of Foods 
 
 !25 
 
 Part V. 
 
 Ventilation and Heating 
 
 - I50 
 
INTRODUCTION 
 
 The practical hygiene of to-day is the logical out- 
 growth of observations in sanitary science as the re- 
 sult of the experiences of the peoples of different coun- 
 tries, cities, and towns. These observations were made 
 chiefly during the present century since sanitary science 
 had made very little progress from the empirical pro- 
 cedures of the ancients until these procedures had been 
 tested through the means and measures afforded by 
 modern chemistry and physics. 
 
 It will be of interest to trace briefly the more im- 
 portant steps in the development of sanitary science 
 which gave rise to what is known as practical hygiene 
 to-day, before taking up the various steps in the de- 
 velopment of practical hygiene. The earlier discov- 
 eries which have been of immense value to sanitary 
 science are those of Jenner with regard to vaccinia ; 
 those of Howard with regard to the relation of filth 
 and insufficient air-supply to the high death-rate in 
 prisons ; those of Bowditch, of Boston, and Middleton, 
 of England, with regard to the relation of dampness 
 of the soil of a locality to the prevalence of tubercu- 
 losis; those of Gerhard, of Philadelphia, with regard 
 to the differentiation between typhus and typhoid 
 fever; and those of von Pettenkofer, of Munich, with 
 regard to the relation of ground-water to the preva- 
 lence of typhoid and cholera. 
 
 The discovery of the etiological factors in infectious 
 diseases, the definite determination of the relation of 
 certain diseases to polluted water-supplies, and of the 
 
2 PRACTICAL HYGIENE 
 
 intimate relation of certain respiratory diseases with 
 the ventilation and general sanitary condition of build- 
 ings, mark the beginning of the practical application 
 of scientific methods to sanitary science. Practically 
 all of these discoveries have been made within the 
 last two or three decades. The influence of the sev- 
 eral sanitary commissions of England, as the Health 
 of Towns Commission, the Barracks Commission, and 
 the Rivers Pollution Commissions, in stimulating in- 
 vestigations and in the collection of valuable data, has 
 been very great. 
 
 The discoveries made during this period w T hich 
 stand out prominently and mark important steps in 
 the development of practical hygiene, are those of Pas- 
 teur, of Paris, and of Koch, of Berlin, upon the rela- 
 tion of micro-organisms to disease; those of Lister 
 upon the aseptic treatment of wounds ; the experi- 
 ments of Paul Bert on the influence upon life and 
 health of various atmospheric conditions ; those of von 
 Pettenkofer and Voit on expired air, and the latter's 
 accurate methods for the determination of carbon 
 dioxid in air. 
 
 Of the discoveries and adaptations of methods em- 
 ployed in chemistry and physics to sanitary science 
 which mark the rise of practical hygiene, it is impos- 
 sible to speak with any great definiteness, since the 
 advancement has been so gradual that it would be 
 difficult to trace out the various steps in order to make 
 special mention of them. Several of these methods, 
 however, stand out quite prominently, in addition to 
 those already mentioned, so that it is possible to 
 
INTRODUCTION 3 
 
 trace their birth and evolution. Among others the 
 following should receive special mention : The method 
 for the determination of organic matter in water by 
 means of potassium permanganate, published by Fore- 
 hammer, of Copenhagen, in 1849, and modified since 
 by Kubel and by Tiemann, and others; the method for 
 the determination of the hardness of water by means 
 of an alcoholic solution of soap, published by Mm. 
 Boutron and Felix Boudet in Comptes rendu s, March 
 26, 1855, and elaborated by Dr. Thomas Clark, of 
 Aberdeen ; the perfection of Levol's method of deter- 
 mining chlorin, by Mohr, in 1856, by the use of po- 
 tassium chromate solution as indicator and the appli- 
 cation of the method to the determination of chlorin in 
 water ; the discovery of a delicate reagent for the detec- 
 tion of ammonia, by Nessler, in 1 856; the method for the 
 determination of the nitrogenous organic matter in water 
 as free and albuminoid ammonia, published by YVank- 
 lyn, Chapman, and Smith before the Chemical Society, 
 of London, June 20, 1867; the discovery of a satisfac- 
 torv method for the determination of nitrogen as ni- 
 trites in water, by Griess, in 1881, and its improve- 
 ment by Warrington ; the discovery of a delicate test 
 for nitrates in water, by Grand val and Lajoux, in 1885. 
 The methods in use for the determination of organic 
 matter in air had their origin in the ingenuity of 
 Augus Smith, Chapman, Moss, and Remsen. 
 
 The evolution of practical hygiene has been very 
 rapid during the last two or three decades, so much 
 so that the student of to-day rarely realizes how re- 
 cently all of the different methods employed in the 
 
4 PRACTICAL HYGIENE 
 
 analysis of water have come into use. If we go back 
 to the year 1855 we find that the only chemical methods 
 known by means of which organic contamination of 
 water could be detected were : Loss on ignition ; Fore- 
 hammer's permanganate test ; the distillation of enor- 
 mous quantities of water, as much as 50 gallons, in 
 order to estimate the ammonia, which was done by 
 titration with standard acid. This procedure has long 
 since been very much simplified through the introduc- 
 tion of the Nessler process and the Wanklyn method 
 of distillation. The development of practical hygiene 
 has been of such recent date that so far it has failed 
 to receive the consideration in educational institutions 
 which it really merits from its immense practical 
 utility. 
 
 The opinion that the medicine of the future must 
 be largely preventive medicine is rapidly gaining 
 ground, consequently the study and application of all 
 the preventive measures known becomes of the great- 
 est importance in the training of medical men. 
 
 Since pure air, pure water and food, and sanitary 
 habitations and environment are of primary import- 
 ance in the maintenance and restoration of health, the 
 study of the character and sources of impurities in 
 these, of whatever nature, is highly essential in the 
 practical training of the physician of to-day. 
 
 The testimony of experts before recent sessions of 
 government and legislative investigation commissions, 
 has shown that food adulterations of a character which 
 is as yet practically unknown to the general public 
 are becoming quite frequent. Such disclosures as 
 
INTRODUCTION 5 
 
 those made by Dr. Wiley, chief chemist of the De- 
 partment of Agriculture, before the Senatorial Pure 
 Food Investigation Committee, in which he stated 
 that articles of food were imported from abroad, adul- 
 terated to such a degree that they would not be used 
 in the countries where they were produced, should 
 arouse us to more active supervision of the character 
 of the food materials exposed for sale in our markets. 
 While many of the adulterations specified in the testi- 
 mony before these investigation commissions are not 
 necessarily dangerous or even injurious to health, they 
 are nevertheless fraudulent and should not be tolerated 
 under any circumstances. On the other hand the use 
 of highly injurious food preservatives is far from un- 
 common and is rarely suspected. Some of these pre- 
 servatives act in such a manner as to render the food 
 practically indigestible aside from any injurious effect 
 which they may exert upon the digestive organs them- 
 selves. In order to properly control the healthfulness 
 of food supplies it is necessary to have more general 
 investigation into the nature and composition of the 
 different food materials offered for sale in the markets. 
 In order to make such a supervision feasible it is nec- 
 essary to have a considerable force of trained analysts 
 in all the larger cities and towns, in addition to a more 
 general supervision of the mode of preparation and 
 system of marketing of the different forms of prepared 
 foods. In this manner it would be possible to protect 
 the common people, at least more effectually than is 
 done at present, against gross fraud and against injury 
 to health from adulterated food. 
 
PART I 
 ATMOSPHERIC AIR 
 
 The air, when pure, is composed of 20.99 per cent, 
 by volume of oxygen, 0.03 to 0.04 per cent, of carbon 
 dioxid, about 78 per cent, of nitrogen, 1.0 per cent, of 
 argon, and varying proportions of watery vapor. 
 Traces of ammonia and organic vapors are also gener- 
 ally present. The relative proportion of the two prin- 
 cipal gases, oxygen and nitrogen, remains quite con- 
 stant in all portions of the globe, while the carbon 
 dioxid, aqueous and organic vapors, and the ammonia 
 vary quite perceptibly in different localities and under 
 various modifying influences. 
 
 For the hygienist, therefore, the constituents of the 
 atmosphere which vary in their relative proportions, 
 the carbon dioxid, aqueous and organic vapors, and 
 ammonia, are of primary interest. It is these con- 
 stituents, along with the temperature, barometric pres- 
 sure, and the force and direction of the wind, that will 
 engage our attention. 
 
 The nitrogen serves merely as a diluent for the 
 oxygen of the air, and, so far as known, has no other 
 influence upon man. The amount of aqueous vapor 
 in the air of dwellings is a most important factor in 
 relation to the comfort and health of the occupants. 
 
CHAPTER I. PHYSICAL EXAMINATION OF AIR-METEOROLOGY 
 
 A. OBSERVATION OF TEMPERATURE— THER- 
 MOMETERS 
 
 The observation of temperature in the laboratory is 
 commonly made by means of a mercurial thermometer. 
 
 a. Control of the zero-point. — The zero-point of a 
 mercurial thermometer should be verified from time 
 to time, and all new thermometers must be verified 
 before they are brought into use, to avoid any error 
 from variations which are liable to take place as the 
 result of contraction of the glass bulb. 
 
 Process. — The verification of the zero-point of a ther- 
 mometer is made by placing the bulb into a small glass 
 funnel filled with cracked ice, when, if the thermometer 
 is properly constructed, it will register o° C. in about five 
 minutes. 
 
 b. Testing the boiling-point of water as registered 
 by a thermometer. — The thermometer is placed in a 
 so-called hypsometer, in which it is quite surrounded 
 with streaming steam, so that only the upper part of 
 the scale is visible outside of the apparatus. 
 
 The water in the apparatus is boiled for ten min- 
 utes and then the reading of the thermometer is taken. 
 It is to be remembered that the boiling-point of water 
 is influenced by the barometric pressure — the greater 
 the pressure the higher the boiling-point of water, and 
 vice versa. For instance a correct centigrade ther- 
 mometer will indicate ioo° C. only when the baromet- 
 
8 PRACTICAL HYGIENE 
 
 ric pressure at o° C. is 760 mm. Consequently it is 
 necessary to observe, at the time of reading the ther- 
 mometer, the barometric pressure and the temperature 
 at the barometer. The observed barometric pressure 
 must then be corrected for o° C, according to the 
 
 formula, b = , l . where a = the coefficient of ex- 
 
 pansion for mercury for each degree of temperature, 
 or 0.00018. 
 
 The normal boiling-point for the corrected baromet- 
 ric pressure is then taken from Regnault's table (see 
 Table I) and if this coincides with the boiling-point 
 as indicated by the thermometer that is being tested, 
 then the latter is correct, otherwise the difference is 
 to be noted as the correction for the boiling-point. 
 
 Example. — A new thermometer registers the boiling- 
 point at 98. 2 C, with the barometric pressure at 713 
 mm., and the temperature at the barometer 15 C. The 
 barometric reading is' reduced to o° C. according to the 
 formula 
 
 bt 
 
 b = — ■ = 711.08 mm. 
 
 1 ^-a.t 
 
 According to the table the temperature of boiling water 
 at 711 mm. =98.-15° C, and at 712 mm. =98.19° C. 
 Difference = 0.04° for 1° of temperature, and for 0.01° 
 the difference is 0.0004°, aG d for 0.08° it is 0.0032°, 
 hence the temperature of boiling water at 711.08 mm. = 
 98.1532° C. Since our thermometer registered 98.2° C. 
 it registers 0.046 8° too high, and the correction for the 
 boiling-point is 0.0468°. 
 
 Testing the accuracy of the thermometer between 
 the two fundamental points : 
 
 The accuracy of the scale between the zero- and 
 
METEOROLOGY 9 
 
 boiling-point is determined by comparison with a nor- 
 mal thermometer. This is done by placing both in a 
 wooden vessel containing distilled water and gradually 
 raising the temperature of the water. The two ther- 
 mometers must be placed at equal distances from the 
 sides and bottom of the vessel. At intervals of several 
 degrees the reading is taken of each thermometer. In 
 case there is a difference between the readings of the 
 thermometers between two points another observation 
 should be made about half way between those points, 
 or one proceeds as follows: It has been found, for in- 
 stance, that the thermometer to be tested varies from 
 the normal thermometer -o.i° at io°, and at 20 it 
 varies — 0.4 . Undoubtedly the thermometer changes 
 between io° and 20 . We may assume that .the de- 
 gree of variation is evenly distributed between the two 
 points, and there are points at which the correction is 
 0.2 and 0.3 . These points may be determined by 
 calculation by dividing the space between io° and 20 
 into four parts of 2.5 each; after each 2.5 the cor- 
 rection changes by o.i°. 
 
 The correction 
 
 O. 
 
 1° 
 
 reaches from 
 
 10 
 
 ,o° 
 
 to 
 
 12 
 
 •5 
 
 a << 
 
 O. 
 
 ,2° 
 
 a a 
 
 12. 
 
 6° 
 
 i ( 
 
 15 
 
 ,o° 
 
 < < a 
 
 o. 
 
 3° 
 
 ct n 
 
 i5- 
 
 i° 
 
 ' ' 
 
 17 
 
 •5° 
 
 it < < 
 
 0. 
 
 4° 
 
 H I { 
 
 17- 
 
 6° 
 
 ' ' 
 
 20, 
 
 ,o° 
 
 For these corrections, however, such great differ- 
 ences in temperature, as io° to 20 , should not be 
 used, but a reading should be made at least once be- 
 tween the two points — preferably at 15 — or better 
 still at each degree of the scale. 
 
IO 
 
 PRACTICAL HYGIENE 
 
 Table I. 
 
 Regnault's Table Showing the Boiling-point of Water ac- 
 cording to the Degree of Barometric Pressure. 
 
 Barom- 
 
 Temper- 
 
 Barom- 
 
 Temper- 
 
 Barom- 
 
 Temper- 
 
 eter. 
 
 ature. 
 
 eter. 
 
 ature. 
 
 eter. 
 
 ature. 
 
 5 8o 
 
 92.6 
 
 650 
 
 95-7 
 
 715 
 
 98.3 
 
 585 
 
 92 
 
 8 
 
 655 
 
 95 
 
 9 
 
 720 
 
 98.5 
 
 590 
 
 93 
 
 1 
 
 660 
 
 96 
 
 1 
 
 725 
 
 98.7 
 
 595 
 
 93 
 
 3 
 
 665 
 
 96 
 
 3 
 
 730 
 
 98.9 
 
 600 
 
 93 
 
 5 
 
 670 
 
 96 
 
 5 
 
 735 
 
 99.I 
 
 605 
 
 93 
 
 7 
 
 675 
 
 96 
 
 7 
 
 740 
 
 99.3 
 
 610 
 
 94 
 
 
 
 680 
 
 96 
 
 9 
 
 745 
 
 99-4 
 
 615 
 
 94 
 
 2 
 
 685 
 
 97 
 
 1 
 
 750 
 
 99.6 
 
 620 
 
 94 
 
 4 
 
 690 
 
 97 
 
 3 
 
 755 
 
 99.8 
 
 625 
 
 94 
 
 6 
 
 695 
 
 97 
 
 5 
 
 760 
 
 1 00.0 
 
 630 
 
 94 
 
 8 
 
 700 
 
 97 
 
 7 
 
 765 
 
 100.2 
 
 635 
 
 95 
 
 1 
 
 705 
 
 97 
 
 9 
 
 770 
 
 100.4 
 
 640 
 
 95 
 
 3 
 
 710 
 
 98 
 
 1 
 
 775 
 
 100.5 
 
 645 
 
 95 
 
 5 
 
 
 
 
 
 
 B. SPECIAL THERMOMETERS 
 
 1. Spirit thermometer. — For temperatures below 
 o° C. — especially below — 20 C. — a spirit thermom- 
 eter is used. These are similar in construction to the 
 ordinary mercurial thermometer but contain alcohol 
 colored with some anilin dye, usually eosin, as the 
 thermometric fluid. 
 
 2. Thermometers for high temperatures. — For the 
 
 observation of temperatures over ioo° C. a long- 
 stemmed mercurial thermometer is used. In this 
 manner the scale may be lengthened so as to register 
 up to 300 ° C. For temperatures ranging from 300 ° 
 to 450 ° C. the capillary tube of the thermometer con- 
 tains nitrogen gas instead of a partial or complete 
 
METEOROLOGY I I 
 
 vacuum. In this manner the mercury is prevented 
 from boiling by the increased pressure within the cap- 
 illary tube. At still higher temperatures air ther- 
 mometers are used, air being the thermometric sub- 
 stance. 
 
 3. Pyrometer. — Pyrometers are constructed of a 
 bar of metal or graphite which is fastened to a support 
 at one extremity. Variations in temperature bring 
 about alterations in the length of this bar and these 
 changes are measured by means of a movable pointer 
 attached to the free end of the bar in such a manner 
 that the temperature is indicated on a fixed scale over 
 which the pointer moves. These instruments are 
 graduated by making comparative observations with 
 an air thermometer. The pyrometers are less accurate 
 than the air thermometers for the observation of high 
 temperatures. 
 
 4. Thermograph. — By means of mechanical or electri- 
 cal devices the variations in the temperature, curve, as 
 indicated by the pointer of the pyrometer, are recorded 
 on a revolving chart having appropriate rulings for 
 different degrees of temperature and also for definite 
 periods of time, as a day, a week, or a month. By 
 means of a pen or small piece of graphite attached to 
 the tip of the pointer, a permanent record of its to- 
 and-fro movements, under the influence of fluctuations 
 in the temperature, is produced. 
 
 5. Maximum-minimum thermometer.— These in- 
 struments record both the highest and the lowest 
 
12 PRACTICAL HYGIENE 
 
 points reached by the temperature during a definite 
 period of time, as twenty-four hours. The form of 
 instrument in common use is that of Six, consisting 
 of a U-shaped, capillary glass tube, the upper portions 
 of both arms being of somewhat larger caliber than 
 the body of the tube. A thermometer scale is attached 
 to each arm of the tube, the one arm forming the 
 maximum, the other the minimum, thermometer. The 
 upper portion of the arm corresponding to the maxi- 
 mum thermometer is expanded into a small, pointed 
 bulb and contains a little alcohol and vapor of alcohol. 
 The low r er portion or body of the tube contains mer- 
 cury. In addition to this each arm also contains an 
 index consisting of a small, barbed bar of steel, one 
 end of which rests on the surface of the column of 
 mercury forming the two thermometers. The ther- 
 mometric substance in this instrument is the alcohol 
 in the upper arm of the tube, while the mercury in 
 the body of the tube is the propeller of the indices. 
 Both indices are carried upward by the contraction on 
 the one hand, and the expansion on the other, of the 
 mercurial column as the result of a fall or rise in the 
 temperature, and each of them is arrested at the point 
 corresponding to the lowest temperature reached dur- 
 ing the period of time under observation in the one 
 case, and at the point corresponding to the highest 
 temperature reached during the same time on the 
 other hand, thus recording the two extremes in tem- 
 perature for that period of time. The indices are pre- 
 vented from falling w r ith the receding column of mer- 
 cury by the feathery projections along their sides. 
 
METEOROLOGY 1 3 
 
 After reading the thermometers the indices are again 
 brought in contact with the surface of the mercurial 
 column by drawing a small horseshoe magnet down- 
 ward along the side of each arm of the instrument. 
 
 6. Measurement of solar radiation. — The ordinary 
 mercurial thermometer indicates only the heat com- 
 municated to it by the surrounding media and is but 
 little influenced by the heat radiating from the sun 
 directly. To measure the amount of heat radiating 
 from the sun a maximum thermometer, with blackened 
 bulb, is commonly employed. This instrument is en- 
 closed in a larger glass tube exhausted of air, one 
 end of which is expanded into a bulb. The bulb of 
 this thermometer is influenced by the solar radiations 
 alone, reflecting the solar heat against the outer bulb 
 whose temperature is the same as that of the surrounding 
 atmosphere. The instrument is placed in a horizontal 
 position and registers higher than one that is exposed 
 to the air, the increase in temperature indicating the 
 amount of heat radiating from the sun. 
 
 7. Terrestrial radiation. — For the purpose of meas- 
 uring the radiation of heat from the earth at night a 
 minimum thermometer is placed in a horizontal posi- 
 tion, on wooden supports, in an exposed place. The 
 reading of this thermometer is compared with that of 
 another minimum thermometer at the same place, but 
 protected from such influence ; a higher reading of the 
 latter indicates the amount of heat radiating from the 
 earth. 
 
14 PRACTICAL HYGIENE 
 
 C. THERMOMETER SCALES 
 
 i. The centigrade scale. — The centigrade scale is 
 the one most commonly used in scientific investiga- 
 tions. It has for its zero-point the melting-point of 
 ice, while ioo° represents the boiling-point of water 
 with the barometer at 760 mm. 
 
 2. The Fahrenheit scale. — In this scale the zero- 
 point is 32 ° below the melting-point of ice, and the 
 boiling-point of water is at 21 2° with the barometer 
 at 29.905 inches in the latitude of London. This is 
 the standard scale in the United States, but, for ob- 
 vious reasons, the centigrade scale is preferable to it. 
 
 3. The Reaumur scale, — In this scale the melting- 
 point of ice also corresponds to the zero-point, while 
 the boiling-point of water is at 80 °. This scale has 
 never been used very extensively and is now falling 
 into disuse. 
 
 4. Relative values of the degrees on the three 
 scales. — 
 
 5 C.=9°F. 
 
 = 4°R- 
 
 i° C. =-5- °F. 
 
 5 
 
 = -± °R. 
 
 5 
 
 1° F. = -$- °C. 
 9 
 
 9 
 
 i°R.=^ °C. 
 
 =-£ °F. 
 
 4 4 
 
 To convert centigrade degrees into Fahrenheit degrees, 
 multiply by — and add 32. (C. X — ) + 32 = F. 
 
METEOROLOGY 1 5 
 
 To convert centigrade degrees into Reaumur degrees, 
 
 multiply by — . C. X — R. 
 5 5 
 
 To convert Fahrenheit degrees into centigrade degrees, 
 
 subtract 32, and multiply by — . (F. — 32) X — = C. 
 
 To convert Fahrenheit degrees into Reaumur degrees, 
 subtract 32, and multiply by — . (F. — 32) X — = R. 
 
 To convert Reaumur degrees into centigrade degrees, 
 
 multiply by ^-. R. X — = C. 
 4 4 
 
 To convert Reaumur degrees into Fahrenheit degrees, 
 
 multiply by — and add 32. (R. X — ) — 32 = F. 
 4 4 
 
 D. ATMOSPHERIC PRESSURE 
 
 The atmosphere having weight exerts, therefore, a 
 constant but variable amount of pressure upon the 
 earth's surface. The amount of pressure exerted by 
 the atmosphere is dependent upon the quantity of 
 moisture it is holding and upon its temperature. The 
 degree of pressure which it exerts is subject to con- 
 stant fluctuations through the incessant movements 
 occurring between its higher and lower strata, as well 
 as through its movements from one point to another 
 over the earth's surface, the latter movements giving 
 rise to what are known as winds. The movements 
 of the atmosphere are produced by an increase or a 
 decrease in the amount of moisture at one point of the 
 earth's surface as compared with other surrounding 
 points, such increase or decrease in the amount of 
 moisture being brought about through precipitation 
 
1 6 PRACTICAL HYGIENE 
 
 from the clouds, or through evaporation of moisture 
 from the earth's surface. On the other hand move- 
 ments of the atmosphere are also brought about by an 
 increase or decrease in its temperature as the result of 
 a greater amount of, heat radiation at one point than 
 at another, but more particularly through the influence 
 of the high temperature of the torrid zone and the 
 influence of the low temperature of the polar regions. 
 
 The barometer is high (a) when the air is cold, be- 
 cause it is then more dense than it is when warm ; (6) 
 when the air is dry, because it is then also more dense 
 than when it is moist ; (c) when an upward current 
 sets in towards a certain point, because in consequence 
 of this movement, the lower strata are compressed. 
 
 The barometer is low (a) when the lower strata are 
 heated there is an upward movement, as the density 
 of these strata decreases, and the upper or lighter 
 strata are displaced laterally ; (A) when the air is damp, 
 because the density of aqueous vapor, at 760 mm. and 
 o° C. is 0.622, air being 1, therefore the mixture be- 
 comes lighter the more moisture it contains; (V) when 
 the air • has a gradual upward movement without a 
 simultaneous lateral movement to replace the air that 
 is moving upward. 
 
 As the density of the atmosphere influences the 
 amount of pressure which it is capable of exerting it 
 is evident that the pressure must bear an inverse rela- 
 tion to the altitude ; the higher the altitude the greater 
 the rarification of the air and, consequently, the higher 
 the barometer. On the other hand the density of the 
 air increases as we descend to the level of the sea, or 
 
METEOROLOGY I 7 
 
 penetrate into the interior of the earth, and the ba- 
 rometric reading is lower, being at 760 mm. at the 
 sea-level, and gradually falling as we descend below 
 that level. 
 
 1. Mercurial Barometers 
 
 a. Cistern barometer. — Observations of barometric 
 pressure are commonly made with the cistern barom- 
 eter. It consists of a glass tube, 80 cm. in length, 
 sealed at one end. This is filled with mercury and 
 inverted in a small metal cistern containing mercury, 
 when a portion of the mercury in the tube escapes, 
 leaving a vacuum in the upper part of the tube. The 
 greater portion of the mercury in the tube is retained 
 through the pressure exerted on the surface of the 
 mercury in the cistern by the atmosphere. The top 
 of the cistern is partly closed in and has a small ivory 
 point projecting from the roof which serves as the 
 zero-point of the scale, and is called the " fiducial 
 point." The bottom of the cistern is composed of 
 leather and can be raised or lowered as required, so 
 that the surface of the mercury is always brought in 
 contact with the ivory point projecting from the roof. 
 In this manner the zero-point of the scale is regulated 
 at each reading. The barometer tube is enclosed in 
 a metal tube having a ring attached to its upper ex- 
 tremity from which it is suspended. It must hang 
 perpendicularly, but is prevented from swinging by 
 means of four small screws projecting from the inner 
 surface of the metal ring surrounding the cistern. 
 These screws are adjusted in such a manner that they 
 
1 8 PRACTICAL HYGIENE 
 
 prevent any marked swinging of the instrument, and 
 yet avoid communicating the influence of any jarring 
 from the supports to which it is attached. 
 
 The barometer scale. — For scientific observations 
 the metric scale is most commonly employed. In this 
 scale the standard pressure at sea-level is taken as 760 
 mm., with the temperature at o° C. In the standards 
 of the United States and Great Britain measurement 
 is made in inches, tenths, and hundredths, with the 
 temperature at 32 ° F. The standard pressure at sea- 
 level is 30 inches. 
 
 The vernier. — In order to facilitate the accurate 
 reading of the barometer, a small movable scale, called 
 a " vernier," is attached at the side of the fixed scale, 
 and is moved upward and downward by means of a 
 rack-and-pinion arrangement. This allows the read- 
 ing of the fractional parts of the millimeter. 1 
 
 To read the fractional parts of a millimeter of the 
 pressure recorded by the barometer, the zero-point of 
 the vernier is brought on a level with the top of the 
 meniscus of the column of mercury in the barometer 
 tube — to the point at which it cuts off the light pass- 
 ing between it and the top of the meniscus. The line 
 on the vernier scale that is on a level with, or nearest 
 to, one of the lines on the fixed scale indicates the 
 number of tenths of a millimeter to be added to the 
 
 1 The principle of the vernier is this, that a given length con- 
 taining n divisions of the fixed scale is divided into n -j- 1 divisions 
 on the vernier ; usually representing the length of one millimeter 
 on the fixed scale. 
 
METEOROLOGY I 9 
 
 reading of the fixed scale ; e. g., the reading of the 
 fixed scale is 764 mm., and the line on the vernier 
 scale that is on the same level with, or nearest to, one 
 of the lines on the fixed scale is the eighth, then the 
 correct reading of the barometer is 764.8 mm. 
 
 Temperature at the barometer. — Attached to the 
 metal case surrounding the barometer tube is a small 
 mercurial thermometer which records the temperature 
 at the barometer. The reading of this thermometer 
 should always be taken before reading the barometer 
 itself, otherwise the breath of the observer and the 
 heat given off from his body might change its read- 
 ing-, and thus affect the accuracv of his observations. 
 
 Manner and place of hanging a barometer. — Ba- 
 rometers should be hung in a room protected from di- 
 rect sunlight and removed from marked temperature 
 fluctuations. 
 
 Reading of the barometer. — The first point to be 
 observed in reading the barometer is to note and record 
 the temperature at the thermometer attached to it. 
 The next point to observe is whether the instrument 
 is properly suspended, after which the zero-point of 
 the scale is adjusted by bringing the surface of the 
 mercury in the cistern to the u fiducial point," by either 
 raising or lowering the bottom of the cistern, as may- 
 be required, by means of the screw attached beneath 
 it. The vernier is now raised above the top of the 
 column of mercury in the tube and then carefully 
 brought down on a level with the top of the meniscus. 
 In regulating the vernier it is very essential that the 
 eye of the observer is also on a level with the top of 
 
20 PRACTICAL HYGIENE 
 
 the meniscus. The number of millimeters' pressure is 
 shown on the fixed scale and the tenths of a millimeter 
 on the vernier scale. 
 
 Corrections of barometric readings. — To obtain ac- 
 curate results, as well as for purposes of comparison, 
 several corrections of the readings of the barometer 
 are necessary : (a) for variations in the meniscus ac- 
 cording to the diameter of the barometer tube. For 
 a tube of 12 mm. diameter the correction is so small 
 that it has but little influence on the results and may 
 be ignored. For the same reasons (b) variations in the 
 barometer scale, as well as (c) variations in the glass 
 tube under different conditions, may be ignored. The 
 only important influence on the barometric reading for 
 which correction must be made is that which is due 
 to the expansion and contraction of the mercury at 
 different degrees of temperature. With an increase of 
 i ° C. of temperature, mercury expands at the rate of 
 0.00018 times its volume, consequently the influence 
 of varying degrees of heat on the height of the column 
 of mercury in the barometer tube must be eliminated 
 from every observation. Correction of the barometric 
 reading for temperature is made according to the for- 
 mula : bjo = - — : -, reducing the reading to o° C. 
 
 temperature. 
 
 bjo = the barometer reduced to o° C, 
 
 b\t = " " as read, 
 
 a = " constant, 0.00018, the coefficient of expansion 
 of mercury for each degree of temperature. 
 
 t — " temperature at the barometer. 
 
METEOROLOGY 2 1 
 
 Example. — The barometer stands at 768.4 mm., with 
 the temperature at 18.3 C. Then 
 
 #/o= ^- 4 - 
 
 ' 1 + 0.00018 X 18.3 
 
 or b/o = 765.8 mm. 
 With the temperature below o° C. the formula is 
 
 b/o — -• 
 
 1 — a.t 
 
 b. Stationary barometer. — In the stationary barom- 
 eter the bottom of the cistern is fixed and the zero- 
 point of the scale cannot be adjusted at each reading 
 as in the cistern barometer. The scale is also fixed, 
 but it is arranged in such a manner, however, that its 
 zero-point indicates a barometric pressure of 760 mm. 
 
 c. Differential barometer. — This form of barometer 
 consists of a glass tube, of equal diameter throughout, 
 and which is bent in the form of the letter S. It is 
 sealed at its upper end, but the lower arm of the tube, 
 which is U-shaped, is open to the air. The tube is 
 somewhat constricted at the middle whereby the move- 
 ment of the mercury is impeded, to a slight degree. 
 The upper portion of the tube contains a vacuum, 
 hence the contraction and expansion of the mercury 
 lowers and raises the level of the column in both arms 
 of the tube. The scale is either fixed or movable, the 
 method of reading the barometer depending on this 
 point. The distance between the upper and lower 
 levels of the mercury is the height of the mercurial 
 column. This form of barometer is used principally 
 in determining degrees of altitude and the height of 
 mountains. 
 
22 PRACTICAL HYGIENE 
 
 2. Aneroid Barometer 
 
 The aneroid barometer consists of a thin-walled, 
 metallic chamber which has been nearly exhausted of 
 air, its sides being held apart by a strong spring. The 
 pressure of the atmosphere on the sides of the cham- 
 ber is indicated by means of a pointer which is at- 
 tached to the spring and moves over a dial. Aneroid 
 barometers are also so constructed as to be self-regis- 
 tering — like the thermograph. 
 
 Correction of the readings. — Three corrections of 
 the aneroid barometer are necessary : (a) for tempera- 
 ture, (b) for the divisions on the dial, and (c) for the 
 altitude of the place of observation. For each instru- 
 ment these factors must be ascertained, for the loca- 
 tion in which it is to be used, by comparison with a 
 mercurial barometer. 
 
 E. HUMIDITY OF THE ATMOSPHERE 
 
 At different temperatures air is capable of taking up 
 variable amounts of moisture, there being a saturation 
 point for each degree of temperature. The point of 
 saturation rises with the elevation of the temperature 
 of the air, so that when the air is saturated at a high 
 temperature and is then cooled, there is a precipitation 
 of moisture in the form of rain or dew, or in the form 
 of sleet, snow, or hail. 
 
 a. Dew-point. — The point of saturation at a certain 
 degree of temperature is known as the dew-point. 
 
 b. Absolute humidity. — The absolute humidity de- 
 notes the amount of moisture, in grains, which i cubic 
 
METEOROLOGY 23 
 
 meter of air, of a certain temperature, may be holding. 
 The absolute humidity varies with the temperature, 
 increasing in amount with increase of the temperature 
 of the air. 
 
 c. Maximum of saturation. — The maximum satu- 
 ration of air is the maximum amount of moisture, in 
 grams, which i cubic meter of air, at a certain tem- 
 perature, is capable of holding. 
 
 d. Deficiency of saturation. — Deficiency of satura- 
 tion denotes the amount of moisture, in grams, which 
 1 cubic meter of air, at a certain temperature, is capa- 
 ble of taking up, in addition to that which it already 
 contains, to become fully saturated. It is the differ- 
 ence between the maximum saturation for that degree 
 of temperature and the absolute humidity. 
 
 e. Relative humidity. — The relative humidity de- 
 notes the quantity of moisture contained in the air, at 
 a certain temperature, expressed in per cent, of the 
 quantity of moisture that can be taken up at that tem- 
 perature, or the absolute humidity expressed in per 
 cent, of the maximum of saturation. It is the great- 
 est near the surface of the earth during night when 
 the temperature approaches the dew-point, and it is 
 least during the middle of the day when the heat is 
 greatest. 
 
 F. ESTIMATION OF MOISTURE IN THE AIR 
 
 1. Direct hygrometers. — There are three forms of 
 direct hygrometer all depending on the same princi- 
 ple: (a) Daniell's, (b) Regnault's, an improved form of 
 
24 PRACTICAL HYGIENE 
 
 DanielPs instrument, and (c) Dines's. Dante/Ps hygrom- 
 eter consists of two glass bulbs connected by a glass 
 tube bent twice at right angles. The instrument is 
 attached to a samll wooden stand to which is fixed a 
 small mercurial thermometer. One of the bulbs is 
 made of black glass and contains a thermometer; the 
 other bulb is made of ordinary glass and is covered 
 with muslin. The bulbs contain some ether vapor. 
 By holding the covered bulb in the hand for a minute, 
 the ether contained in it evaporates and passes over 
 into the black bulb; some ether is then dropped on the 
 muslin, and, by its rapid evaporation, reduces the 
 temperature of this bulb, causing the ether vapor in 
 the black bulb to contract and distil over into the 
 other bulb. The temperature of the black bulb is now 
 reduced until the dew-point is reached and the mois- 
 ture! in the air surrounding it is deposited on the shi- 
 ning black bulb. The instant this occurs the tempera- 
 ture shown by the thermometer inside the bulb is noted 
 (the dew-point), as well as the temperature of the air 
 as shown by the thermometer on the stand. 
 
 Regnaulf s hygrometer is an improvement on Dan- 
 iell's, having a bright silver cup in place of a glass 
 bulb to contain the ether, and the ether is evaporated 
 by means of an aspirator or air-pump attached to the 
 cup. 
 
 Dines^s hygrometer consists of a vessel, containing 
 ice-cold water, and a black glass attached to a wooden 
 stand. The vessel containing the ice-cold water has 
 a tube attached that connects it with a small, closed 
 chamber underneath the glass plate, so that the water 
 
METEOROLOGY 25 
 
 passing into this chamber cools the bulb of a ther- 
 mometer within the chamber, just beneath the glass 
 plate. The flow of water is controlled by means of a 
 stop-cock. At the moment when dew begins to de- 
 posit on the glass plate the temperature at the ther- 
 mometer, attached to the instrument, is noted, the 
 air temperature being noted at the same time. 
 
 2. Indirect hygrometers. — There are two principal 
 kinds of indirect hygrometer : (a) the hair hygrometer, 
 and (b) the wet- and dry-bulb thermometer. 
 
 The hair hygrometer, of Wolpert, consists of a hu- 
 man or horse hair that has been freed from oily mat- 
 ter, one end of which is fixed, while a light weight is 
 suspended from the other end. A portion of the hair 
 passes over a pulley to which is attached a pointer 
 that moves over a scale and indicates the relative hu- 
 midity of the air in per cent, of saturation. The scale 
 of each instrument is graduated by wetting the hair 
 to complete saturation and marking the point ioo°, 
 then placing the instrument over sulphuric acid of 
 known strength and marking the point indicated 15 
 of saturation. The intervening space is divided into 
 eighty-five equal parts, each of which denotes a " de- 
 gree of relative humidity/' 
 
 The wet- and dry -bulb thermometer, or psychrometer. 
 — This consists of two ordinary mercurial thermometers, 
 as nearly alike as possible, and registering tenths of a 
 degree centigrade, which are attached to a small frame 
 or to a strip of wood. The bulb of one of the ther- 
 mometers is covered with a jacket of cotton threads 
 
26 PRACTICAL HYGIENE 
 
 which extend into a small cup of water attached to 
 the bottom of the frame of the instrument, thus keep- 
 ing the bulb continuously moist through capillary at- 
 traction. This is known as the u wet-bulb" and the 
 other as the u dry-bulb " thermometer. 
 
 As long as the atmosphere is not saturated, mois- 
 ture continues to evaporate from the wet-bulb and, in 
 consequence, the mercury cools and contracts and 
 shows a lower temperature than the dry-bulb ther- 
 mometer, which registers the temperature of the sur- 
 rounding atmosphere. The difference between the 
 temperature registered by the two thermometers is 
 greatest when the atmosphere contains the least mois- 
 ture, and when it is saturated they show the same 
 temperature, since there is no evaporation from the 
 wet bulb. When the temperature is below freezing 
 capillary action ceases and the readings of the wet- 
 bulb thermometer are unreliable. 
 
 A form of this instrument that is in common use is 
 the u sling" psychrometer. The two thermometers 
 are fastened on opposite sides of a small strip of wood, 
 having a handle attached to its upper end by means 
 of which the instrument can be made to revolve. The 
 wet-bulb thermometer projects three or four cm. be- 
 yond the lower end of the wooden support, and the 
 jacket surrounding it is thoroughly moistened with 
 distilled water whenever an observation is to be made. 
 
 Information derived from hygrometer observations. 
 — The important items of information to be derived 
 from hygrometer observations are : (a) the dew-point, 
 (f?) the tension of aqueous vapor, or the absolute hu- 
 
METEOROLOGY 27 
 
 midity, and (V) the relative humidity of the atmos- 
 phere. Each of these may be calculated from the dif- 
 ference between the temperature of the wet- and dry- 
 bulb thermometers, either by formulae, or from tables. 
 The dew-point of the atmosphere is determined 
 directly by means of one of the three forms of direct 
 hygrometers. 
 
 The absolute humidity can be calculated from the 
 readings of the wet- and dry-bulb thermometers accord- 
 ing to the formula: m = M — cd, where m = the ab- 
 solute humidity of the air at the temperature indicated 
 by the dry-bulb thermometer, t, and Tkf = the maximum 
 of saturation at the temperature of the wet-bulb ther- 
 mometer, f, which is found by reference to Fliigge's 
 table (see Table II). 
 
 c = a constant, usually 0.65, but in the winter, when 
 the bulb is covered with ice, 0.56, and 
 
 d = the difference between the wet- and dry-bulb 
 thermometer readings. 
 
 The product cd can also be taken directly from the 
 table. 
 
28 PRACTICAL HYGIENE 
 
 Table II. 
 
 Table of the Water Capacity of Air at Different Tempera- 
 tures. (From Emmerich and Trillich.) 
 Temp. 
 
 of o o.i 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 
 
 the Air. 
 
 — 20 
 
 1.06 
 
 
 
 
 
 
 
 
 
 
 — 15 
 
 1.57 
 
 
 
 
 
 
 ... 
 
 
 
 
 
 
 — 14 
 
 1.70 
 
 1.69 
 
 1.68 
 
 1.67 
 
 1.65 
 
 1.64 
 
 1.62 
 
 1.61 
 
 1.60 
 
 1.58 
 
 — 13 
 
 1.84 
 
 1.82 
 
 1. 81 
 
 1.80 
 
 1.78 
 
 1-77 
 
 1.76 
 
 i-74 
 
 i-73 
 
 1. 71 
 
 — 12 
 
 i-97 
 
 1.96 
 
 1-95 
 
 1.94 
 
 1-93 
 
 1. 91 
 
 1.90 
 
 1.89 
 
 1.87 
 
 1.85 
 
 — II 
 
 2.13 
 
 2.10 
 
 2.08 
 
 2.07 
 
 2.05 
 
 2.04 
 
 2.03 
 
 2.01 
 
 2.00 
 
 1.98 
 
 — IO 
 
 2.30 
 
 2.28 
 
 2.27 
 
 2.25 
 
 2.23 
 
 2.21 
 
 2.20 
 
 2.18 
 
 2.16 
 
 2.15 
 
 — 9 
 
 2.49 
 
 2.47 
 
 2.45 
 
 2.43 
 
 2.41 
 
 2.39 
 
 2.38 
 
 2.36 
 
 2-34 
 
 2.32 
 
 - 8 
 
 2.67 
 
 2.65 
 
 2.63 
 
 2.62 
 
 2.60 
 
 2.58 
 
 2.56 
 
 2.54 
 
 2.53 
 
 2.51 
 
 — 7 
 
 2.88 
 
 2.86 
 
 2.84 
 
 2.82 
 
 2.80 
 
 2.77 
 
 2.75 
 
 2-73 
 
 2.71 
 
 2.69 
 
 — 6 
 
 3-w 
 
 3.09 
 
 3.06 
 
 3.o4 
 
 3.02 
 
 2-99 
 
 2.97 
 
 2.95 
 
 2.93 
 
 2.90 
 
 — 5 
 
 3.36 
 
 3-33 
 
 3-31 
 
 3.28 
 
 3.26 
 
 3-23 
 
 3.21 
 
 3.18 
 
 3.i6 
 
 3.13 
 
 — 4 
 
 3.6i 
 
 3.58 
 
 3.56 
 
 3-53 
 
 3.5i 
 
 3-48 
 
 3.46 
 
 3-43 
 
 3.4i 
 
 3.38 
 
 — 3 
 
 3-90 
 
 3.87 
 
 3.84 
 
 3.81 
 
 3.78 
 
 3-75 
 
 3-73 
 
 3-70 
 
 3-67 
 
 3- 6 4 
 
 — 2 
 
 4.19 
 
 4.16 
 
 4.13 
 
 4.10 
 
 4.07 
 
 4.05 
 
 4.02 
 
 399 
 
 3-96 
 
 3.93 
 
 — 1 
 
 4.52 
 
 4-49 
 
 4-45 
 
 4.42 
 
 4.39 
 
 4-35 
 
 4.32 
 
 3.29 
 
 4.26 
 
 4.22 
 
 
 
 4.87 
 
 4.83 
 
 4.80 
 
 4.76 
 
 4-73 
 
 5.69 
 
 4.66 
 
 4.62 
 
 4-59 
 
 4.55 
 
 -j- 1 
 
 5-21 
 
 525 
 
 5.28 
 
 5-32 
 
 5-35 
 
 5-39 
 
 5-43 
 
 5.46 
 
 5.50 
 
 553 
 
 2 
 
 5-57 
 
 5.6i 
 
 5.65 
 
 5.69 
 
 5-73 
 
 5.76 
 
 5.8o 
 
 5.84 
 
 5.88 
 
 592 
 
 3 
 
 5.96 
 
 6.00 
 
 6.04 
 
 6.08 
 
 6.12 
 
 6.16. 
 
 6.21 
 
 6.25 
 
 6.29 
 
 6.33 
 
 4 
 
 6-37 
 
 6.41 
 
 9-45 
 
 6.50 
 
 6.54 
 
 6.58 
 
 6.62 
 
 6.66 
 
 6.71 
 
 6.75 
 
 5 
 
 6.79 
 
 6.84 
 
 6.88 
 
 6.93 
 
 6.98 
 
 7.02 
 
 7.07 
 
 7. 11 
 
 7.16 
 
 7.21 
 
 6 
 
 7.26 
 
 7-3i 
 
 7-35 
 
 7.40 
 
 7-45 
 
 7-49 
 
 7-54 
 
 7-59 
 
 7.64 
 
 7.68 
 
 7 
 
 7-73 
 
 7.78 
 
 7-83 
 
 7.89 
 
 7-94 
 
 7-99 
 
 8.04 
 
 8.09 
 
 8.15 
 
 8.20 
 
 8 
 
 8.25 
 
 8.30 
 
 8.36 
 
 8.41 
 
 8.47 
 
 8.52 
 
 8-57 
 
 8.63 
 
 8.68 
 
 8-73 
 
 9 
 
 8.79 
 
 8.85 
 
 8.91 
 
 8.96 
 
 9.02 
 
 9.07 
 
 9-13 
 
 9.19 
 
 9.24 
 
 9-3° 
 
 10 
 
 9-37 
 
 9-43 
 
 9-49 
 
 9-55 
 
 9.61 
 
 9.67 
 
 9-74 
 
 9.80 
 
 9.86 
 
 9.92 
 
 11 
 
 9.98 
 
 10.04 
 
 10. 11 
 
 10.17 
 
 10.24 
 
 10.30 
 
 10.36 
 
 10.43 
 
 10.49 
 
 10.56 
 
 12 
 
 10.62 
 
 10.69 
 
 10.75 
 
 10.82 
 
 10.88 
 
 10.95 
 
 11.02 
 
 11.08 
 
 11. 15 
 
 11. 21 
 
 13 
 
 11.28 
 
 11-35 
 
 11-43 
 
 11.50 
 
 11.58 
 
 11.65 
 
 11.72 
 
 11.80 
 
 11.87 
 
 if -95 
 
 14 
 
 12.02 
 
 12.09 
 
 12.17 
 
 12.24 
 
 12.32 
 
 12.39 
 
 12.46 
 
 12.54 
 
 12.61 
 
 12.69 
 
 15 
 
 12.76 
 
 12.84 
 
 12.92 
 
 13.00 
 
 13.08 
 
 13-15 
 
 13.23 
 
 13.31 
 
 13-39 
 
 13-47 
 
 16 13.54 13.63 13.72 13.80 13.89 13.97 14.05 14.14 14.22 14.31 
 
METEOROLOGY 29 
 
 Temp. 
 
 of o 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 
 
 the Air. 
 
 1; 14.39 M.48 I4-5 8 M.67 14-77 M-S6 14.95 15.05 15.14 15.24 
 
 iS 15.35 15.42 15.50 15.59 15.68 15.76 15.85 15.94 16.03 16.11 
 
 19 16.20 16.39 16.44 16.49 16.58 16.68 16.78 16.87 16.97 17.06 
 
 20 17.16 17.26 17.37 17.47 17-58 17.68 17.78 17.89 17.99 18.10 
 
 21 1S.20 18.31 18.41 18.52 18.63 J 8.73 18.84 18.95 19.06 19.17 
 
 22 19.29 19.41 19.52 19.64 19.75 19.87 19.99 20.10 20.22 20.33 
 
 23 20.45 20.56 20.68 20.79 20.91 21.02 21.14 2I - 2 5 21.37 21.48 
 
 24 21.60 21.73 21.85 21.98 22.11 22.23 22.36 22.49 22.62 22.74 
 
 25 22.87 23.00 23.13 23.27 23.40 23.53 23.66 23.79 23.93 24.06 
 
 26 24.19 24.33 2447 24.61 24.75 24.88 25.02 25.16 25.30 55.44 
 
 27 25.58 25.72 25.86 26.01 26.15 26.29 26.43 26.57 26.72 26.86 
 
 28 27.00 27. 15 27.31 27.46 27.61 27.76 27.92 28.07 28.22 28.38 
 
 29 28.53 28.69 28.85 29.01 29.17 29.33 29.50 29.66 29.82 29.98 
 
 30 30.14 30.31 30.47 30.64 30.81 30.97 31.14 3 I -3 I 3 I -48 31-64 
 
 31 31.81 31.98 32.16 32.33 32.51 32.67 32.86 33.03 33.21 33.38 
 
 32 33-56 33-74 33-92 34.10 34.28 34.45 34.63 34.81 34.99 35.17 
 
 33 35-35 35-54 35-73 35-93 36.12 36.31 36.50 36.69 36.87 37.08 
 
 34 37 27 
 
 The constant c varies indirectly according to the 
 barometric pressure and the air-movement, but, for 
 hygienic purposes, it is not necessary to make correc- 
 tions because the slight difference between the results 
 obtained with the above formula, and those obtained 
 by taking into consideration the influence of baro- 
 metric pressure, are of no vital importance. 
 
 Process. — Temperature at the drv-bulb thermometer 
 (0 = 32-5°C. 
 
 Temperature at the wet-bulb thermometer 
 (/) = 18. o° C. 
 d — the difference between the two thermometers = 
 
 14.5 c. 
 According to the table we find the maximum-satura- 
 tion of air at the temperature of the wet-bulb thermome- 
 ter (_/*) is 15.33 grams of water in 1 cubic meter. 
 
30 PRACTICAL HYGIENE 
 
 The formula m = M — cd is now as follows : 
 
 ™ = 15-33 — (°- 6 5 X 14-5), or 
 
 ™ = 15-33 — 9-425. or 
 
 m = 5.905, the absolute humidity of the air. 
 
 Calculation of the relative humidity. — According to 
 the table we find the maximum-saturation at the tem- 
 perature of the dry-bulb thermometer, 32. 5 C. = 34.45 
 grams, and the absolute humidity at 32. 5 C. = 5.905 
 grams. The difference betw r een the two, or deficiency 
 of saturation = 28.545 grams. Therefore, at 32. 5 C, 
 the air under observation is capable of taking up 
 28.545 grams per cubic meter, in addition to the 
 moisture it already holds. 
 
 The maximum-saturation is in proportion to the ab- 
 solute humidity as 34.45 : 5.905 :: 100 : x. 
 
 Theiefore ^=17.14 per cent. = the relative hu- 
 midity of the air. 
 
 3. Estimation of moisture in the air by chemical 
 methods. — A quantitative estimation of the moisture 
 in the air is made by aspirating a known volume of 
 air through some absorbent material, the weight of 
 which has been carefully determined, and thus any 
 increase in its weight will represent the amount of 
 moisture, in grams, absorbed from the measured vol- 
 ume of air aspirated through it. Pumice stone, sat- 
 urated with concentrated sulphuric acid, is used for 
 this purpose. It is placed in an absorption flask 
 through which the air is aspirated, the volume of air 
 aspirated being determined by means of a graduated 
 aspirator. 
 
METEOROLOGY 31 
 
 4. The hygroscope. — The hygroscope is employed 
 for the qualitative study of changes in the amount of 
 moisture in the air. The operation of these instru- 
 ments depends on the expansion and contraction of 
 certain substances, as straw, the bristles of chaff, etc., 
 or on changes in the color of certain salts, as cobalt, 
 nickel, or chromium salts, as the result of changes in 
 the humidity of the atmosphere. These instruments 
 are, however, not adapted for hygienic observations. 
 
 5. Evaporation of moisture from the earth's sur- 
 face. — 
 
 a. Evapo7Hmete7 r . — The evaporation of moisture 
 from the earth's surface can be estimated quantita- 
 tively by means of an instrument known as an evapo- 
 rimeter. It consists of a square tin chamber the sur- 
 face area of which is 100 sq. cm,, and is about 
 4 cm. in height. It is closed at the top by means 
 of a conical wire cover of w T ide mesh. The chamber 
 is filled with distilled water to two-thirds its height, 
 its weight accurately determined, and then placed 
 where the observation is to be made. After twenty- 
 four hours it is again weighed when the loss in 
 weight will represent the amount of water evaporated. 
 
 The loss in weight, in grams, divided by 100, the 
 surface area of the chamber, gives the amount of evap- 
 oration for 1 cm. in height, or multiplying this amount 
 by 10 the result is expressed in millimeters. 
 
 Example. — Grams. 
 
 Weight of chamber, Aug. 20, with water = 650 
 " 21, " " =578 
 " water evaporated in 24 hours = 72 
 
32 PRACTICAL HYGIENE 
 
 The air must have free access to the instrument from 
 all sides, but it must be protected from direct sunlight 
 and rain. The amount of moisture evaporated is de- 
 pendent upon the relative humidity of the atmosphere 
 and upon the relative, amount of moisture in the soil. 
 The rate at which evaporation takes place is depend- 
 ent upon the temperature, — the higher the temperature 
 the greater the rapidity, and the larger the amount of 
 evaporation. 
 
 b. Pische's atmometer. — This instrument consists of a 
 graduated glass tube, sealed at one end, which is filled 
 with water and suspended in the air. The lower end 
 of the tube is closed by means of a piece of paper of 
 definite size which has a small perforation to allow the 
 water to evaporate slowly. 
 
 The water in the tube of the apparatus passes 
 through the fine opening in the paper as fast as evap- 
 oration takes place, and air enters to take its place, 
 thus forming the index of the volume of water evap- 
 orated from the paper, the amount varying with the 
 size of the paper. The amount of evaporation is in- 
 dicated on the graduated scale of the glass tube. 
 
 G. PRECIPITATION OF MOISTURE 
 
 Moisture is precipitated either in the form of rain, 
 snow, hail, or sleet. 
 
 a. Rain. — The amount of precipitation in the form 
 of rain is estimated by means of the rain-gauge. This 
 instrument consists of a cylindrical tin chamber meas- 
 uring 500 sq. cm., or 1/20 sq. m. at the top, and has a 
 funnel-shaped bottom which terminates in a short tube 
 
METEOROLOGY 33 
 
 through which the rain-water collected by the cham- 
 ber is conducted into a vessel placed beneath it. The 
 rain is prevented from splashing over the sides of the 
 chamber by the vertical rim, about 15 mm. in height, 
 which projects from the upper edge of the funnel. 
 
 The water collected by the apparatus in an hour, or 
 during the observation period, is measured in the 
 graduated cylinder and the amount calculated for a 
 millimeter in depth, the result obtained indicating the 
 amount of rainfall in millimeters. 
 
 Example. — Quantity of water collected in 24 hours = 
 
 2 is cc, = 0.4^ mm. of rainfall. 
 
 D 500 ^ 
 
 b. Snow, hail, and sleet. — The amount of snowfall 
 is also estimated by means of the rain-gauge. The 
 snow that collects in the vessel beneath the cylinder, 
 during the observation period, is first melted and the 
 water formed from it is then measured and the amount 
 per millimeter calculated as in the case of rain. 
 
 The amount of precipitation as hail and sleet may 
 be estimated in the same manner as in the estimation 
 of snowfall. 
 
 Position of the rain-gauge, — The rain-gauge should 
 be at least 1.5 m. above ground and placed in such a 
 position as to escape the influence of eddying air-cur- 
 rents, and must, therefore, not be near any object. It 
 may be placed on the middle of the roof of a building, 
 high enough from its surface to escape the influence 
 of eddying currents. 
 3 
 
34 PRACTICAL HYGIENE 
 
 H. WIND : FORCE, RAPIDITY, AND DIRECTION OF 
 CURRENTS OF AIR 
 
 As the result of changes in temperature the den- 
 sity of the air is changed and sets in motion large 
 masses of air, that having the greatest density dis- 
 placing that which is less dense. The direction in 
 which the movement takes place is always along the 
 line of least resistance and toward the point of least 
 density. The rapidity of the movement is directly 
 proportional to the magnitude of the change in den- 
 sity ; i. e. to the rise in the temperature. These move- 
 ments of masses of air we call winds, and the most 
 important cause of winds is variations in the amount 
 of heat transmitted from the sun in different latitudes, 
 and at different altitudes on the earth's surface, and 
 the variations in temperature arising from the daily 
 revolutions of the earth on its axis. 
 
 a. Qualitative Estimation of Air Movements 
 
 i. In closed rooms candles, smoke, air-balloons or 
 dynamic manometers may be used to determine the 
 amount and direction of air movement, but a move- 
 ment of less than 0.2 meter per second cannot be esti- 
 mated by these means. 
 
 2. Wind vane. — In the open air the senses and wind 
 vanes are employed. The wind vane indicates the 
 direction in which the air is moving. It consists of a 
 wooden or metallic pointer the exact shape of which 
 is not of vital importance, an arrow, or a representa- 
 tion of some afiimal, being the most common form in 
 use. It is placed in a horizontal position on the end 
 
METEOROLOGY 35 
 
 of a vertical rod so that it can revolve with the great- 
 est facility. The point of suspension is not quite at 
 the center of gravity, one end being slightly heavier, 
 and this end is also expanded somewhat on its verti- 
 cal plane so as to afford a point of contact for the 
 wind, while the lighter end is generally more compact 
 in structure so as to offer as little impediment to its 
 movements as possible. The lighter end points in the 
 direction from which the wind is coming. The direc- 
 tion of the air movement, i. e., from which the wind 
 comes, is expressed in points of the compass. 
 
 b. Quantitative Estimation of Air Movements 
 
 The designations in common use to describe 
 the velocity of the wind denote movements rang- 
 ing from calm, when no movement is perceptible, 
 to the movement of greatest velocity which is known 
 as "hurricane." The designations denoting veloci- 
 ties between these two extremes, as the velocity in- 
 creases, are : weak, perceptible, fresh, strong, and 
 storm. The velocity of the air movements is usually 
 expressed so as to indicate the distance traveled in a 
 definite period of time, as meter per second. Instead 
 of expressing the air movement in terms representing 
 the distance traveled in a definite period of time, we 
 also express it in terms of the degree of force which 
 it exerts when coming in contact with an object, as 
 kilograms per square meter. The velocity of the air 
 movements may also be expressed so as to designate 
 the effect produced by it upon different objects, with 
 which it comes in contact, as, when there is a calm 
 smoke rising and the leaves are undisturbed, a slightly 
 
36 
 
 PRACTICAL HYGIENE 
 
 greater movement causes leaves to move, and as the 
 velocity of the current increases the effects are the 
 movement of small branches, of larger branches, whole 
 branches, until we have the effects of a hurricane in 
 the unroofing of houses and the uprooting of large 
 trees. All the different modes of expressing the amount 
 of air movement have been arranged into a scale of 
 thirteen degrees — from o to 12 — by Beaufort. (See 
 Beaufort's scale.) 
 
 Beaufort's Scale of Different Degrees of 
 Air Movement. 
 
 Beau- j^ • Velocity Pressure 
 
 fort's de- .. ** " in m. per in kg. 
 tion. ^-, & 
 
 grees. second, per sq. m. 
 
 Effect of the wind. 
 
 O 
 I 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 Calm 
 Weak 
 
 Breeze 
 Fresh 
 
 8 Strong 
 9 
 
 10 
 11 
 
 Storm 
 
 i-5 
 
 3-5 
 
 6.0 
 8.0 
 
 10. o 
 12.5 
 
 15.0 
 18.0 
 
 21.5 
 25.0 
 
 29.0 
 
 33-5 
 
 o.3 
 1-5 
 
 4.4 
 
 7.8 
 
 12.2 
 19.0 
 
 27.4 
 40.0 
 
 56.0 
 
 76.0 
 
 103.0 
 137.0 
 
 12 Hurricane 40.0 195.0 
 
 Smoke rises ; leaves 
 are undisturbed. 
 Perceptible to the 
 senses, moves leaves 
 and sails. 
 
 Moves leaves and the 
 smaller branches — 
 stretches sails. 
 Moves the smaller 
 branches of trees. 
 Moves whole branch- 
 es and weaker stems, 
 and hinders one in 
 walking. 
 
 Shakes whole trees, 
 breaks branches and 
 stems, and uproots 
 smaller trees. 
 
 Unroofs houses, 
 blows down chim- 
 neys, breaks and up- 
 roots trees. 
 
METEOROLOGY 37 
 
 Anemometer. — The determination of the rapidity 
 of the air movements is made by means of the anem- 
 ometer. One form of this instrument consists of 
 two bars crossing at right angles to each other, the 
 distal ends of which bear a small cup-shaped vessel, 
 arranged in such a manner that each in turn presents 
 its concave face toward the wind. These bars are 
 placed on the top of a vertical revolving shaft. The 
 revolutions of the shaft are communicated to a set of 
 pointers revolving over dials. The velocity of the 
 wind, expressed in meters per second, is registered on the 
 dials and mav be at once read off bv observing- the in- 
 strument for a minute. 
 
 The form of anemometer which is used in estima- 
 ting air movements in the ventilating shafts of build- 
 ings consists of a small wheel bearing a number of 
 flat blades radiating from its axis and placed at such 
 an angle that each, in turn, receives the impulse of 
 the air current and consequently causes the wheel to 
 revolve. The revolutions of the wheel are transmitted 
 to a set of indices, each revolving over the face of the 
 dial, and registering the velocity of the current in 
 meters or feet. 
 
 Direction of the wind — wind vane. — The direction 
 of the air movements are denoted by points of the 
 compass. The designations adopted by international 
 agreement are as follows : 
 
 N. 
 
 for north 
 
 S. 
 
 for south 
 
 NNE. 
 
 1 ' north-northeast 
 
 ssw. 
 
 1 ' south-southwest 
 
 NE. 
 
 1 ' northeast 
 
 sw. 
 
 1 ' southwest 
 
 ENE. 
 
 ' ' east-northeast 
 
 wsw. 
 
 ' ' west-southwest 
 
38 PRACTICAL HYGIENE 
 
 E. for east W. for west 
 
 ESE. " east-southeast WNW. " west-northwest 
 
 SE. " southeast NW. " northwest 
 
 SSE. " south-southeast NNW. " north-northwest 
 
 I. FOG AND CLOUDS 
 
 a. Fog. — Fog results from the cooling of moist air 
 below the dew-point and consists of fine droplets of 
 water. 
 
 b. Clouds. — When the condensed moisture of the 
 air collects as fog in the lower strata and rises into 
 the upper strata it takes the form and appearance 
 which we call clouds. According to the different forms 
 which clouds assume under different atmospheric 
 conditions they have been divided into four principal 
 types : (a) cirrus — light and feathery — which rise to a 
 great height, 4000 to 6000 meters or more ; (6) cumu- 
 lus — hemispherical or conical heaps like mountains 
 rising from a horizontal base— which rise to a height 
 of 500 to 2000 meters; (c) stratus — widely extended 
 continuous horizontal sheets, often forming at sunset ; 
 {d) nimbus or rain-cloud — is a horizontal sheet of 
 grayish color, and is a mixture of the first two types, 
 and rises to a height of less than 500 meters. 
 
 Between the three principal types we have compo- 
 sition forms, as cirro-cumulus, cirro-stratus, and cumu- 
 lostratus. 
 
 Estimation of the amount of cloud. — This is done 
 by a system of numbers : o, indicates a cloudless sky, 
 and 10, a fully clouded sky, and the intermediate num- 
 bers indicate the various intermediate degrees of cloudi- 
 
M KTKOROLOGY 39 
 
 ness. In making an observation the eye is directed 
 toward a point midway between the horizon and 
 zenith, then slowly turning round the eye is carried 
 along that plane and the relative amount of clear and 
 clouded sky noted. 
 
 Designation of Amount of Cloud Formation. 
 
 ® cloudless = o 
 
 » half covered = 5 
 
 J three-quarters covered = 7 
 
 • entirely covered = 10, 
 
 Representations of results of observations. — The 
 
 results of meteorological observations can be presented 
 in a tabulated form or they can be presented graphic- 
 ally, though the latter method may unduly magnify 
 slight variations, or, on the other hand, it may imper- 
 fectly represent the variations that exist. 
 
 Weather prognostication. — From the observation of 
 meteorological conditions the following principles have 
 been established which give a definite insight into the 
 changes of the weather : 
 
 1. The condition of the weather is influenced di- 
 rectly by the direction of the wind. 
 
 2. The direction of the wind is influenced directly 
 by the barometric pressure, which again is directly 
 influenced by 
 
 a, the altitude of the location, 
 
 b, the specific gravity of the air, according 
 r, to the humidity of the atmosphere, and 
 d, the temperature. 
 
 3. The air flows from an area with high barometric 
 
40 PRACTICAL HYGIENE 
 
 pressure towards such areas that have a lower baro- 
 metric pressure, or from anticyclone toward cyclone, 
 or depression areas. 
 
 4. The rapidity of this movement of the atmosphere 
 is directly dependent upon the magnitude of the dif- 
 ference in the barometric pressure in adjacent areas. 
 
 5. In consequence of the earth's movements the 
 movement of the atmosphere is not in a vertical direc- 
 tion from the isobars, but in such a manner that the 
 observer (in north latitude), with his back toward the 
 wind, has the anticyclone area before and to the left 
 of him, and the cyclone area back of him and to the 
 right. 
 
 6. The weather in the anticyclone area is settled, 
 dry, and clear; in the cyclone area it is variable, cloudy, 
 and rainy. 
 
 7. The areas of anticyclone change their form and 
 position more slowly than those of cyclone, while the 
 latter nearly always pass to the right of the former in 
 their movements. 
 
 8. Low temperature is indicative of the approach 
 of the anticyclone area and high temperature of cyclone 
 areas. 
 
 The meteorological conditions of the country are 
 telegraphed twice daily — 8 a.m., and 8 p.m. — to the 
 seat of government where they are tabulated and rep- 
 resented graphically upon a map of the entire country. 
 Localities that have the same barometric pressure are 
 connected by means of lines — isobars — in like manner 
 the localities having the same temperatures ; these 
 lines are termed isotherms. 
 
ANALYSIS OF AIR 4 1 
 
 J. IMPURITIES IN THE AIR 
 
 The impurities in the air are both gaseous and solid. 
 
 a. Gaseous impurities. — The more important gase- 
 ous impurities in air that are of interest to the hygi- 
 enist are : carbon monoxid, carbon dioxid, hydrogen 
 sulphid, marsh-gas, and gaseous organic substances 
 and ammoniacal compounds. The air of manufactur- 
 ing establishments may contain other gaseous impuri- 
 ties. 
 
 b. Solid impurities. — The solid impurities in air 
 are : living organisms, such as bacteria, etc., and va- 
 rious forms of dust. The solid impurities in the air 
 which we recognize as dust particles consist of various 
 forms of debris arising from the disintegration of por- 
 tions of animal and vegetable life, and minute parti- 
 cles of mineral matter. 
 
 CHAPTER II. CHEMICAL ANALYSIS OF AIR 
 
 The normal and abnormal constituents of atmos- 
 pheric air which are of hygienic interest and for the 
 presence of which it is necessary to make air analyses 
 are : the relative proportion of oxygen, carbon dioxid, 
 aqueous vapor, and the determination of the presence 
 of hydrogen sulphid, marsh gas, carbon monoxid, and 
 organic matter. Under special conditions, as in the 
 air of manufacturing establishments, air analyses must 
 also be made to determine the presence of poisonous 
 metals and their compounds, as phosphorus, zinc, 
 arsenic, mercury, sulphur dioxid, nitrous, hydrochlo- 
 
42 PRACTICAL HYGIENE 
 
 ric, and sulphurous acids, chlorin, and of carbon di- 
 sulphid. 
 
 A. OXYGEN 
 
 Though the relative proportion of oxygen in the air 
 varies within very narrow limits under ordinary con- 
 ditions, it is, however, at times desirable to make 
 quantitative estimations of the amount of oxygen in 
 the air of confined spaces. 
 
 Process. — A ready method for the estimation of the 
 oxygen in the air is by means of the Bunte gas-burette. 
 This consists of a large graduated burette of over 160 cc. 
 capacity, closed at each end by means of a glass stop- 
 cock, the upper portion being expanded into a bulb. The 
 upper end of the burette is closed by means of a three- 
 w T ay stop-cock through which communication can be made 
 either with the small cup-shaped reservoir at the top 
 and the interior of the burette, or with the outside air. 
 In order to prevent rapid changes in the temperature of 
 the sample of air under analysis the body of the burette, 
 between the upper and lower stop-cocks, is surrounded 
 by a glass tube of larger calibre than the burette, the 
 ends of which are hermetically sealed to the outside 
 of the burette and the intervening space is filled with 
 water, forming a water-jacket for the body of the burette. 
 The capacity of the burette is shown on a scale engraved 
 on the stem of the tube, the zero-point being some dis- 
 tance above the lower stop-cock. From the zero-point 
 the scale extends downward for 10 cc. nearly to the lower 
 end of the tube, and upward for ioo cc, which is just 
 below the expanded portion. From the ioo cc. mark to 
 the upper stop-cock the capacity is 50 cc. The cup- 
 shaped reservoir at the top of the burette serves to hold 
 the solutions of the reagents used in the analysis and is 
 graduated at 20 cc. and at 25 cc. 
 
 Before collecting a sample of air for analysis the burette 
 is filled with distilled water, and the reservoir at the top 
 to the 20 cc. mark. The large three-way stop-cock at 
 
ANALYSIS OF AIR 43 
 
 the top is now turned so as to establish communication 
 with the interior of the burette and the outside air, when, 
 on opening the lower stop-cock, the water in the burette 
 flows out and the air enters through the stem' of the three- 
 way stop-cock. As soon as about 150 cc. of the water 
 have escaped the lower stop-cock is closed, and then the 
 upper stop-cock is turned so as to establish communica- 
 tion between the reservoir and the interior of the burette. 
 With 20 cc. of water in the reservoir the volume of air in 
 the burette will adapt itself to the pressure which it ex- 
 erts by either allowing some of the water to pass into the 
 burette if it is under less pressure, or by forcing some of 
 the air out of the burette if it is under greater pressure. 
 As soon as the sample of air in the burette has been 
 placed under the pressure of the 20 cc. of water in the 
 reservoir, the three-way stop-cock is turned so as to shut 
 off all communication with the outside and the burette is 
 set aside for several minutes to allow all the water to set- 
 tle to the bottom of the tube. The volume of the sample 
 of air taken is then read off on the scale. 
 
 A portion of the water remaining in the burette is now 
 withdrawn, by cautiously opening the lower stop-cock, 
 thus lessening the density of the air in the burette. A 
 larger portion of water can be removed by connecting the 
 lower end of the burette with a filter-pump. The w T ater 
 in the reservoir is poured out and about 10 cc. of a 25 
 per cent, solution of potassium hydroxid is poured into 
 the cup ; the three-way stop-cock is carefully turned so 
 as to allow the reagent to flow into the burette. To fa- 
 cilitate the action of the reagent the burette is turned up- 
 side down several times during five minutes. The potas- 
 sium hydroxid solution combines with the carbon di- 
 oxid in the air and it also renders the water in the burette 
 strongly alkaline. After the air has again been brought 
 under the pressure of 20 cc. of water in the reservoir, and 
 the burette has been set aside for two or three minutes, 
 another reading is made, the decrease in the volume of 
 the sample of air indicating the amount of carbon dioxid 
 contained in it. 
 
 The density of the air in the burette is now again de- 
 creased by removing some of the liquid through the lower 
 
44 PRACTICAL HYGIENK 
 
 stop-cock. The .water in the reservoir is poured out and 
 10 cc. of a 25 per cent, solution of pyrogallic acid, in 
 water, is poured into the cup and, turning the three-way 
 stop-cock, it is allowed to pass into the burette. In 
 strongly alkaline solutions this reagent combines with 
 the oxygen very readily. By turning the burette upside 
 down several times during five minutes the reagent is 
 brought in contact w r ith every portion of the air. The 
 pressure within the burette is now again brought to the 
 standard adopted for the other readings — that of 20 cc. 
 of water in the reservoir — and the volume of the sample 
 of air noted. The decrease in the volume as shown by 
 the second and third readings of the burette indicates the 
 amount of oxygen in the sample of air. The results in 
 air analyses are usually expressed in per cent. , less fre- 
 quently in parts per 1000 or 10,000 parts of air. The 
 portion of the sample of air remaining in the burette after 
 the absorption of the carbon dioxid and oxygen may 
 usually be considered as nitrogen. 
 
 Example. — 
 
 cc. 
 
 Volume of the sample of. air taken for analysis = 148.7 
 Second reading = 148.6 
 
 Difference — carbon dioxid = o. 1 
 
 148.7 : o. 1 : : 100 : x = 0.06 per cent, carbon dioxid. 
 
 cc. 
 Second reading = 148.6 
 
 Third " =119.2 
 
 Difference — oxygen = 29.5 
 
 148.7 : 29.5 :: 100 : x = 19.83 per cent, oxygen. 
 
 cc. 
 First reading =148.7 
 
 Volume of carbon dioxid and oxygen = 29.6 
 Difference — nitrogen = 1 19. 1 
 
 148.7 : 1 19. 1 :: 100 : x = 80.09 P er cent, nitrogen. 
 
 B. CARBON DIOXID 
 1. Qualitative Estimation 
 
 From the fact that carbon dioxid is always present 
 
ANALYSIS OF AIR 45 
 
 in the air, qualitative determinations have no scientific 
 
 value. 
 
 2. Quantitative Estimation 
 
 The most reliable methods for the quantitative es- 
 timation of carbon dioxid in air are the two introduced 
 by Prof, von Pettenkofer. 
 
 The Pettenkofer flask method. — This method is 
 based upon the reaction of carbon dioxid with a solu- 
 tion of barium, strontium, or calcium hydroxid in 
 water, producing an insoluble carbonate of the base. 
 The reduction in the alkalinity of the hydroxid solu- 
 tion indicates the amount of carbonate that has been 
 formed, and is determined through titration against 
 an acid solution, usually a solution of oxalic acid since 
 this reacts upon the hydroxid solution in a similar 
 manner as the carbon dioxid — the formation of an in- 
 soluble salt of the base. The barium hydroxid solu- 
 tion is now generally employed in the estimation of 
 carbon dioxid in air. The solution of oxalic acid em- 
 ployed is made of a definite strength : i cc. oxalic 
 acid = 0.25 cc. carbon dioxid. 
 
 Oxalic acid solution. — One molecule oxalic acid = 
 one molecule carbon dioxid, hence 
 
 1 molecule carbon dioxid = 44 parts by weight. 
 
 1 " oxalic acid = 126 parts by weight. 
 
 1 mg. carbon dioxid = 0.5084 cc. carbon dioxid (at 
 o° C. and 760 mm.). 
 
 44 mg. carbon dioxid = 22.3696 cc. carbon dioxid. 
 
 Therefore 126 mg. C.,H 4 4 2H 2 — 22.3696 cc. carbon 
 dioxid. 
 
 Since 1 cc. of the oxalic acid solution = 0.25 cc. of 
 
 carbon dioxid, the equation : 
 
46 PRACTICAL HYGIENE 
 
 22.3696 : 126 :: 0.25 : x = 1405 nig. oxalicacid, 
 shows that 1.405 grams oxalic acid must be dissolved 
 in a liter of distilled water. It is necessary to meas- 
 ure the water accurately and therefore the solution 
 must be made up in a graduated flask of a liter capac- 
 ity. This solution must be protected from light in 
 dark, glass-stoppered bottles. 
 
 Barium hydroxid solution. — This solution is pre- 
 pared of such strength that 25 cc. of it are about equal to 
 25 cc. of the oxalic acid solution. For this purpose 
 3.5 grams of pure, alkali-free barium hydroxid are dis- 
 solved in 1 liter of distilled water. In case the hy- 
 droxid should not be entirely alkali-free it is best to 
 add 0.2 gram barium chlorid to each liter of the solu- 
 tion. In order to protect the barium hydroxid solu- 
 tion from the carbon dioxid of the air, the solution is 
 preserved in a flask having two glass tubes passing 
 through the cork stopper. One of the glass tubes 
 reaches almost to the bottom of the flask and is bent 
 over above the stopper and passes down along the 
 outside of the flask nearly to the bottom when it 
 again bends upward. The mouth of this tube is closed 
 with a short piece of rubber tubing closed by means 
 of a pinch-cock. The second glass tube is cut off just 
 below the inner edge of the cork, and outside of the 
 flask it is twice bent at right angles and extends down 
 to the neck of the flask where it passes through the 
 cork stopper of a small wide-mouthed bottle contain- 
 ing pumice stone saturated with strong potassium or 
 sodium hydroxid solution. The cork stopper of the 
 small wide-mouthed bottle carries another glass tube 
 
ANALYSIS OF AIR 47 
 
 which reaches nearly to the bottom of the bottle, while 
 the portion outside the bottle is about 20 cm. in length, 
 and is bent at right angles above the cork. The mouth 
 of this tube is also closed with a short piece of rubber 
 tubing closed with a pinch-cock. This arrangement 
 allows the barium hydroxid solution to be withdrawn 
 from the " store bottle " by inserting the point of a 
 pipette into the end of the rubber tubing attached to 
 the glass tube that reaches nearly to the bottom of the 
 flask, while the air that enters to take its place, passes 
 through the wide-mouthed bottle containing the pum- 
 ice stone, and then through the second tube in the 
 cork stopper of the store bottle into the flask. In 
 passing through the small wide-mouthed bottle the 
 air is freed of carbon dioxid by the solution of caustic 
 with which the pumice stone is saturated, thus pre- 
 serving the alkalinity of the barium hydroxid solu- 
 tion. 
 
 Indicators. — For the purpose of sharply defining 
 the point of neutralization of the barium hydroxid so- 
 lution in titrating it with the oxalic acid solution we 
 employ a solution of some substance which undergoes 
 a change in color when its reaction is altered. 
 
 a. Rosalie acid solution. — A solution of rosolic acid 
 is commonly employed for this purpose. It gives a 
 delicate rose tint to the alkaline solution of barium 
 hydroxid which gradually fades as the point of neu- 
 tralization approaches and is completely decolorized 
 by a drop of the acid solution in excess. 
 
 The rosolic acid solution is made by dissolving 1 
 gram in 500 cc. of 80 per cent, alcohol. This solu- 
 
48 PRACTICAL HYGIENE 
 
 tion is slightly acid in reaction, yellow in color, and 
 is neutralized by the addition of barium hydroxid so- 
 lution until its color changes to red. 
 
 b. Phenolphthalein solution. — Another indicator 
 that is also frequently used is an alcoholic solution (i 
 to 30) of phenolphthalein. In acid solution this indi- 
 cator is colorless, but the least trace of alkali changes 
 it to a deep violet color. 
 
 Apparatus required. — 
 
 a. Four-liter flask. — The samples of air are col- 
 lected in a flask of about four liters' capacity that has 
 been accurately tared. This is done by thoroughly 
 cleansing it and, when dry, weighing it empty. It 
 is then filled with distilled water at 15 C. so that 
 the water stands level with the mouth of the flask 
 when it is again weighed, the increase in weight, in 
 grams, indicating its capacity in cubic centimeters. 
 
 Example. — 
 
 Grams. 
 
 Weight of flask with water =5250 
 
 " " empty = 1250 
 
 Capacity ' ' — 4000 
 
 or 4000 cc. = 4 liters. 
 
 The mouth of the flask is closed with a closely-fitting 
 rubber cap. 
 
 b. Hand bellows. — A hand bellows with a long rub- 
 ber tube attached to its nozzle is used to force the air 
 to be examined into the flask, thus replacing that con- 
 tained in the flask, for which about 100 strokes of the 
 bellows are necessary. 
 
 c. Thermometer. — A mercurial thermometer, regis- 
 tering tenths of a degree centigrade, is required to ob- 
 
ANALYSIS OF AIR 49 
 
 serve the temperature of the air at the place where the 
 sample is collected. 
 
 d. Barometer. — It is necessary to observe the baro- 
 metric pressure at the time the sample is collected. 
 The barometer may be at a convenient place in the 
 laboratory and need not be taken to the place where 
 the sample of air is collected. 
 
 e. Pipettes. — A ioo cc, and a 25 cc, pipette are re- 
 quired, the former to measure the barium hydroxid 
 solution used to precipitate the carbon dioxid in the 
 air, and the latter to measure the barium solution in 
 making the titrations. 
 
 f. Burette. — A Mohr's burette with glass stop-cock, 
 graduated in tenths of a cubic centimeter, is employed 
 to hold the oxalic acid solution. 
 
 g. Florence flasks. — Several Florence flasks of 100 
 cc. capacity are required to hold the barium hydroxid 
 solution for the titrations. 
 
 h. Glass-stoppered bottles. — Several small glass-stop- 
 pered bottles, of 125 cc. capacity, are needed in which 
 the barium solution is preserved, after it has been ex- 
 posed to the sample of air, to allow the precipitated 
 barium carbonate to subside. 
 
 Collection of the sample of air. — The four-liter flask 
 is carefully dried and taken to the place where the 
 sample of air is to be collected and allowed to remain 
 about fifteen minutes if the temperature differs con- 
 siderably from that of the laboratory. The thermom- 
 eter should be placed near the flask at the same time. 
 The rubber tube attached to the nozzle of the bellows 
 
 4 
 
50 PRACTICAL HYGIENE 
 
 is now placed into the mouth of the flask, extending 
 almost to the bottom. Care must be taken to prevent 
 the entrance of expired air, and, in collecting samples 
 out of doors, it is best to place the bottle to windward, 
 holding the bellows as far as convenient from the 
 body, and with the open side of the bellows turned 
 toward the wind. About ioo strokes of the bellows 
 are sufficient to completely change the air in the flask. 
 The mouth of the flask is then closed with a rubber 
 cap and the temperature of the air, as recorded by the 
 thermometer, is noted. 
 
 The flask containing the sample of air is now 
 brought into the laboratory and ioo cc. of the barium 
 hydroxid solution is at once placed in the flask by 
 carefully lifting the edge of the rubber cap sufficiently 
 to permit the introduction of the ioo cc. pipette into 
 the flask as far as the bulb, then carefully replacing 
 the rubber cap. When there is much difference be- 
 tween the temperature of the sample of air and that of 
 the laboratory, it is preferable to introduce the barium 
 solution into the flask before it is removed from the 
 place where the sample has been collected, in order to 
 avoid the loss of a part of the air, or the entrance of 
 laboratory air, while introducing the barium solution, 
 because some alteration takes place in the density of 
 the air in the flask as the result of the higher or lower 
 temperature in the laboratory. 
 
 The barometer should now be read and the temper- 
 ature indicated by the thermometer attached to the 
 barometer must also be noted. The barium solution 
 in the flask should be agitated from time to time by 
 
ANALYSIS OF AIR 5 1 
 
 rolling the flask on the table, or rotating it with the 
 hands, care being taken to avoid the splashing of the 
 solution against the rubber cap. After half an hour 
 the barium solution is transferred to a 125 cc. glass- 
 stoppered bottle and set aside for the precipitate to 
 subside. 
 
 Titrations of the solutions. — While the barium so- 
 lution is being agitated with the air in the flask, the 
 alkalinity of this reagent should be determined. By 
 means of a pipette 25 cc. of the barium solution are 
 taken from the " store bottle " and placed in a 100 cc. 
 Florence flask and several drops of the indicator solu- 
 tion added to it. The Mohr's burette having been 
 filled with the oxalic acid solution, the acid solution 
 is slowly added to the barium solution until the indi- 
 cator, by its changed color, shows that the point of 
 neutralization has been reached. The burette is then 
 read and denotes the number of cubic centimeters of 
 oxalic acid solution that are required to neutralize 25 
 cc. of the barium solution. 
 
 Reading the burette. — It is necessary to deduct 0.1 
 cc. from the reading of the burette because it required 
 the further addition of 0.1 cc. of oxalic acid solution 
 to change the color of the indicator, after all the ba- 
 rium had been neutralized, the greater affinity of the 
 barium for the acid preventing the reaction on the in- 
 dicator until all the barium had first been acted upon. 
 
 The alkalinity of the barium solution must be de- 
 termined each day when a sample of air is collected, 
 and the results obtained are then used subsequently 
 
52 PRACTICAL HYGIENE 
 
 for comparison with those obtained for the alkalinity 
 of the barium solution that has been exposed to the 
 sample of air collected at the same time. Unless the 
 alkalinity of the barium solution is determined for 
 each analysis the results may be unreliable on account 
 of its great liability to undergo change. 
 
 After standing for three or four hours the precipi- 
 tated barium carbonate has subsided leaving a clear 
 supernatant liquid. To determine the reduction in the 
 alkalinity of the barium solution through the action 
 of the carbon dioxid in the air, 25 cc. of the clear su- 
 pernatant liquid are carefully removed with a pipette 
 and transferred to a Florence flask of 100 cc. capacity 
 and several drops of the indicator added to it. It is 
 then titrated with the oxalic acid solution as before, 
 when the difference between the amount of oxalic acid 
 solution now required and that for the fresh barium 
 solution at the time the sample was collected, will 
 represent the reduction in the alkalinity, in one-fourth 
 of the barium solution employed in the analysis. From 
 this result can be calculated the proportion of carbon 
 dioxid in the air. It is best to make duplicate, or 
 triplicate titrations, and then take the mean of the 
 results obtained. 
 
 Example. — At the time the sample of air was collected 
 25 cc. barium hydroxid = 24.8 cc. oxalic acid solution: 
 now, 25 cc. barium hydroxid = 23.6 cc. oxalic acid solu- 
 tion ; therefore in each 25 cc. barium hydroxid solution 
 the equivalent of 1.2 cc. oxalic acid solution have been 
 precipitated by the carbon dioxid in the air, or the total 
 amount of carbon dioxid in the sample is equivalent to 
 4 X 1.2=4.8 cc. of oxalic acid solution. Since 1 cc. 
 oxalic acid solution =0.25 cc. carbon dioxid, we have 
 
ANALYSIS OF AIR 53 
 
 4.8 X 0.25 - 1.2 cc. of carbon dioxid in the sample of 
 air. 
 
 Calculation of the results. — 
 
 a. Correction for barometric pressure. — The baro- 
 metric reading is reduced to o° C. according to the 
 
 formula: b n = ; -• 
 
 1 + a. t 
 
 Example. — The barometer at the time the sample of 
 air was collected stood at 764.7 mm., the thermometer 
 attached registering 21.3 C. 
 
 Therefore b n = — ; / = 761.77 mm. 
 
 1 -h 0.00018 X 21.3 
 
 b. Reduction of the air volume to nor mal conditions. 
 — At o° C, and 760 mm., according to the formula 
 
 V = ^ 
 
 760 XU+a.t)' 
 
 Example. — The capacity of the flask employed, — the 
 air volume, — is 3814 cc, and the temperature of the air 
 at the place where the sample was collected was 14. 6° C. 
 The air volume is, therefore, 3814 — 100 Ba(OH) 2 = 
 
 37 14 cc - 
 Therefore 
 
 the air volume at o° C, and at 760 mm. 
 
 c. Calculation of- per cent, of carbon dioxid found. — 
 The amount of carbon dioxid found is 1.2 cc. 
 
 Therefore 3628.96 : 1.2 :: 100 : ^ = 0.03306 per 
 cent, or 3.306 parts of carbon dioxid in 10,000 parts 
 of air. 
 
 Pettenkofer's tube method. — Another method for 
 the estimation of carbon dioxid in the air is that known 
 
54 PRACTICAL HYGIENE 
 
 as Pettenkofer's tube method. In this method spe- 
 cially devised absorption tubes are employed. 
 
 Into each of these absorption tubes is placed ioo cc. 
 of barium solution and a measured quantity of air as- 
 pirated through them. The quantity of air flowing 
 from the aspirator represents the volume of air aspi- 
 rated. A thermometer is placed adjacent to the tubes 
 to register the temperature of the air. This ther- 
 mometer should be read at the beginning and at the 
 end of the aspiration of air, and the mean of the two 
 observations taken as the temperature of the air vol- 
 ume aspirated. The barometer must also be read dur- 
 ing the time that aspiration is going on. 
 
 C. AQUEOUS VAPOR 
 
 The method for the quantitative estimation of mois- 
 ture in air has already been considered. 
 
 D. HYDROGEN SULPHID 
 
 Hydrogen sulphid is detected by its characteristic 
 odor and by its action (blackening) on paper moistened 
 with solution of lead acetate, forming black sulphid 
 of lead. 
 
 For its quantitative estimation a known volume of 
 air is aspirated through a titrated solution of iodin, 
 the hydrogen sulphid being reduced as follows : 
 H 2 S + 2! = 2HI -f- S. The uncombined iodin re- 
 maining in solution is then estimated through titra- 
 tion with a standard (;//io) solution of sodium thio- 
 sulphate, using starch paper as an indicator, the iodin 
 
ANALYSIS OF AIR 55 
 
 coloring the starch papei a deep blue color. The re- 
 action which takes place is as follows : 
 
 2Na S © + 2l = 2NaI + NaS 6 . 
 
 2 2 3 ' ' 24O 
 
 /. Iodin solution. — A i/io normal iodin solution, con- 
 taining 12.685 grams of pure iodin, dissolved in i 
 liter of distilled water with the aid of 18 grams of pure 
 potassium iodide, i cc. of this solution = 1.7 mil- 
 ligrams hydrogen sulphid. 
 
 2. Sodium thiosulphate solution. — A 1/10 normal solu- 
 tion of sodium thiosulphate (Na 2 S 2 ) is made by dis- 
 solving 24.808 grams of pure, crystalline sodium thio- 
 sulphate in 1 liter of distilled water. 1 cc. of this 
 solution = 1-7 milligrams hydrogen sulphid. 
 
 Both of these solutions must be protected from the 
 air in glass-stoppered bottles. 
 
 j. Starch paste. — Freshly boiled starch paste is 
 made by boiling 1 gram of potato starch in 100 cc. of 
 water. 
 
 Process. — The air is aspirated through 100 cc. of the 
 normal iodin solution contained in an absorption flask, 
 or a Pettenkofer absorption tube. After several hundred 
 liters of air have been slowly aspirated through the iodin 
 solution it is transferred to a small glass-stoppered bottle, 
 then 25 cc. of it are placed in a 100 cc. Florence flask 
 with 1 cc. of the starch paste. The normal sodium thio- 
 sulphate solution is then added from a burette until the 
 iodin solution becomes colorless. The difference be- 
 tween the amount of sodium thiosulphate solution re- 
 quired to decolorize 25 cc. of the iodin solution, before 
 and after its exposure to the air, indicates the amount of 
 hydrogen sulphid in the air. The results are expressed 
 so as to show the number of milligrams of hydrogen sul- 
 phid in 1 cubic meter of air. 
 
56 PRACTICAL HYGIENE 
 
 E. CARBON MONOXID 
 
 a. Qualitative tests. — The spectroscope is usually 
 employed to determine the presence of carbon monoxid 
 in air. For this purpose 10 cc. of fresh blood are di- 
 luted with 40 cc. of distilled water and poured into a 
 flask of 6 to 10 liters' capacity. The flask is then 
 filled with the air under examination by means of a 
 hand bellows and closed with a rubber cap. The di- 
 luted blood is agitated with the air for fifteen to twenty 
 minutes so as to bring it in contact with all the carbon 
 monoxid in the air. The carbon monoxid displaces 
 the oxygen in the oxy-haemoglobin of the blood and 
 forms CO-haemoglobin. 
 
 Ten drops of this blood, as well as a like quantity 
 of normal blood, are each diluted to about 20 cc. and 
 compared by means of the spectroscope. Oxy-haemo- 
 globin, or normal blood, shows in the yellow and 
 green lines of the normal spectrum (Fraunhof s lines 
 D and E [b] ) two absorption bands with well-defined 
 margins. CO-haemoglobin also shows these bands, 
 but closer together, and with indistinct margins. 
 
 For absolute differentiation the action of some re- 
 ducing agent on both specimens of blood is to be noted; 
 for instance, the influence of ammonium sulphid. The 
 oxy-haemoglobin is reduced while the CO-haemoglobin 
 remains unchanged. This differentiation is readily 
 made with the spectroscope. One or two drops of 
 ammonium sulphid are added to the diluted blood ; 
 this is then gently agitated and again examined spec- 
 troscopically. The reduced oxy-haemoglobin now 
 shows an indistinct band lying about midway between 
 
ANALYSIS OF AIR 57 
 
 the two haemoglobin bands, while the CO-haemoglo- 
 bin shows very little change. 
 
 b. Chemical tests. — In order to detect carbon mon- 
 oxid in the air by chemical means, the CO-haemo- 
 globin that is formed when the diluted blood is agi- 
 tated with the air, is coagulated by heat, and the car- 
 bon monoxid that is given off is conducted into a i to 
 500 solution of palladium chlorid. The diluted blood 
 is passed into a flask closed with a doubly perforated 
 cork through which fresh air is aspirated. The air is 
 first conducted through an absorption flask containing 
 palladium chlorid in order to free it of carbon mon- 
 oxid or any other bodies capable of reducing palla- 
 dium chlorid. It is then conducted through the flask 
 containing the CO-haemoglobin which has been placed 
 on a boiling water-bath. The air takes up the carbon 
 monoxid, as it is liberated from the haemoglobin, and 
 then passes through the absorption flask containing 
 sulphuric acid where it is freed from moisture. It is 
 then conducted through another absorption flask con- 
 taining a solution of lead acetate where the ammonia 
 and hydrogen sulphid are taken up, as these would 
 vitiate the reaction. Finally the air passes into the 
 absorption flask containing the palladium chlorid so- 
 lution where the carbon monoxid is absorbed. The 
 warming of the blood on the water-bath, and the aspi- 
 ration of air must be continued for at least half an 
 hour. The carbon monoxid precipitates the palladium 
 chlorid as black metallic palladium. 
 
 While the spectroscopic method shows the presence 
 
58 PRACTICAL HYGIENE 
 
 of 2.5 per cent, of carbon monoxid in the air the chem- 
 ical method shows 0.2 per cent. 
 
 F. ORGANIC MATTER 
 
 a. Nitrogenous organic matter (Remsen's method 
 — Free and albuminoid ammonia). — The method for 
 the determination of organic matter in the air that is 
 open to least objection is that devised by Prof. Rem- 
 sen. It consists in aspirating a measured volume of 
 air through a small glass absorption tube containing 
 freshly-ignited, granular pumice stone which has been 
 moistened with pure distilled water. After several 
 hundred liters of air have been aspirated through the 
 tube the pumice stone is transferred to a clean, glass- 
 stoppered retort, 500 cc. of water that is practically 
 free from ammonia is added, and then the free and 
 albuminoid ammonia is determined by the Wanklyn 
 and Chapman method. 
 
 b. Oxidizable organic matter. — The organic matter 
 in air may also be estimated as oxidizable matter by 
 boiling the pumice stone, used in the Remsen absorp- 
 tion tube, with a weak, acid solution of potassium per- 
 manganate and titrating with solution of oxalic acid 
 as for oxidizable matter in water. 
 
 G. ESTIMATION OF DUST IN AIR 
 
 1. By weight. — The amount of organic matter in 
 air in the form of dust particles may be estimated by 
 aspirating a measured volume of air through an ab- 
 sorption tube containing freshly-ignited asbestos. The 
 increase in weight of the absorption tube will repre- 
 
ANALYSIS OF AIR 59 
 
 sent the weight of the dust particles collected from the 
 known volume of air aspirated. The relative propor- 
 tion of organic and inorganic matter in the dust may 
 be determined by carefully transferring the asbestos to 
 a weighed platinum crucible and incinerating the or- 
 ganic matter contained in the dust. The loss in weight 
 will represent the organic matter in the dust while the 
 difference between the first and second weighing will 
 represent the inorganic matter. 
 
 2. The number of dust particles (Aitken's dust 
 counter). — The number of dust particles in a definite 
 volume of air may be estimated by means of Aitken's 
 dust counter. This instrument consists of a small 
 metallic chamber with glass top and bottom. A small 
 lens is placed over the glass top of the chamber while 
 the glass forming the bottom of the chamber is divided 
 into squares of i/io millimeter each. The inner walls 
 of the chamber are lined with bibulous paper which 
 is moistened before making an analysis. To the side 
 of the chamber is attached a small vacuum pump by 
 means of which the air in the chamber can be rarefied, 
 when, on turning a small, three-way stop-cock at the 
 top of the pump, the outside air rushes into the cham- 
 ber. The stop-cock is then turned so as to close the 
 chamber and connect it with the pump. When the 
 piston of the pump is now rapidly lowered and raised 
 at short intervals, the tension of the air in the cham- 
 ber is alternately increased and diminished, thus 
 causing the moisture in the paper to vaporize and con- 
 dense on the dust particles in the air. On looking 
 through the small lens at the top of the chamber the 
 
60 PRACTICAL HYGIENE 
 
 dust particles are seen to fall within the chamber as 
 minute droplets of water and rest on the ruled glass 
 at the bottom. The total number of droplets falling 
 on one of the squares, after the air in the chamber has 
 been rarefied eight or nine times, with the proportion 
 of impure and pure air in the chamber, afford the data 
 from which the number of dust particles in the air 
 may be estimated. 
 
 H. SULPHUROUS ACID 
 
 a. Qualitative test. — The presence of sulphurous 
 acid in air may be detected by its peculiar penetrating 
 odor. 
 
 b. Quantitative estimation.— For the quantitative 
 estimation of this gas the air is aspirated through i/io 
 normal iodin solution whereby it is oxidized to sul- 
 phuric acid : 
 
 2l + SO + 2H O = 2HI + H SO . 
 
 1 2 i 2 '24 
 
 The i/io normal iodin solution is titrated with 1/10 
 normal sodium thiosulphate solution as in the estima- 
 tion of hydrogen sulphid. 1 cc. 1/10 normal sodium 
 thiosulphate solution = 3.2 milligrams of sulphurous 
 acid. 
 
 I. HYDROCHLORIC ACID 
 
 a. Qualitative test. — The fumes or vapor of hydro- 
 chloric acid in air are detected by their reaction upon 
 silver nitrate in solution, producing a white precipi- 
 tate of silver chlorid. 
 
 b. Quantitative estimation. — In the quantitative 
 estimation of hydrochloric acid the air is drawn through 
 
ANALYSIS OF AIR 6 1 
 
 a i/io normal solution of sodium hydroxid which is 
 then titrated with i/io normal sulphuric acid. The 
 decrease in the alkalinity of the soda solution repre- 
 sents the quantity of hydrochloric acid in the known 
 volume of air aspirated. 
 
 J. CHLORIN 
 
 In the quantitative estimation of chlorin, known 
 volumes of air are conducted through a solution of 
 potassium iodid (i gram in 20 cc. of water) whereby 
 the iodin is liberated : KI + CI ■= I + KC1. The 
 amount of iodin that has been liberated is then deter- 
 mined by titration with 1/10 normal solution of sodium 
 thiosulphate : 1 cc. = 3.55 milligrams chlorin. 
 
 K. AMMONIA 
 
 a. Qualitative test. — Ammonia, when present in 
 the air, in considerable quantities, can be detected by 
 its characteristic odor. When present in smaller quan- 
 tities it may be detected by means of a strip of litmus, 
 haemotoxylon, or curcuma paper placed between two 
 glass plates, in such a manner that one-half of it pro- 
 jects from the margin of the plates and is the only 
 portion acted upon by the ammonia in the air. The 
 presence of ammonia is showm by the changed color 
 of the portion of the paper exposed to the air, the ex- 
 tent to which the color is changed indicating the rela- 
 tive amount of ammonia present. 
 
 b. Quantitative estimation. — 
 
 /. Gravimetric method. — For the quantitative esti- 
 mation of ammonia large volumes of air are aspirated 
 
62 PRACTICAL HYGIENE 
 
 through dilute hydrochloric acid with which it unites 
 to form ammonium chlorid. This salt is then pre- 
 cipitated with platinic chlorid and the resulting dou- 
 ble chlorid of ammonium and platinum is collected on 
 a filter, dried, and weighed. 
 
 2, Volumetric method. — By this method large quan- 
 tities of air are aspirated through pure water acidu- 
 lated with sulphuric acid which retains all the ammo- 
 nia. The quantity of ammonia retained is then de- 
 termined by means of Nessler's reagent. 
 
PART II 
 WATER 
 
 CHAPTER I. THE NATURE AND COMPOSITION OF WATER 
 
 a. Physical properties. — Pure water is a colorless, 
 tasteless, and odorless liquid of neutral reaction. At 
 760 mm. barometric pressure, and at the temperature 
 of its greatest density (4 C), its specific gravity is 
 taken as 1000, one liter weighing one kilogram. At 
 o° C. it changes into ice, and at ioo° C. it is converted 
 into steam. Its density decreases as the temperature 
 rises above 4 C, and also as the temperature falls 
 below that point. At o° C, in the form of ice, it has 
 a specific gravity of 0.91674. 
 
 b. Chemical composition. — Pure water (H 2 0) con- 
 sists of 2 parts by weight of hydrogen and 16 parts by 
 weight of oxygen, having a molecular weight of 18. 
 Two volumes of hydrogen are combined with one vol- 
 ume of oxygen and form two volumes of water-gas, 
 
 1 8 
 having a density of — =9- The percentage compo- 
 sition of water, by weight, is p e r cent. 
 Hydrogen, . . . n.il 
 Oxygen, . . . 88.89 
 
 100.00 
 Water, as it is found in nature, is not chemically 
 
64 PRACTICAL HYGIENE 
 
 pure, but contains various substances in solution and 
 suspension which it derives from the air and soil. 
 Many of these substances are present in variable quan- 
 tities in nearly all waters and are therefore not looked 
 upon as impurities, from a hygienic point of view. 
 The substances which fall under this class are : the 
 gases of the atmosphere — oxygen, nitrogen, and car- 
 bon dioxid — which all waters hold in solution ; the 
 salts of different metals and the alkaline earths, vary 
 in their nature with the character and composition of 
 the soil of the locality — principally chlorid, sulphate, 
 nitrate, carbonate, and silicate of sodium, potassium, 
 calcium, and magnesium. 
 
 On the other hand, those substances in water which 
 are called impurities from their detrimental influence 
 on health, do not originate from the natural constitu- 
 ents of the soil but arise from the refuse matter around 
 human habitations, lying within, or on the surface of 
 the soil traversed by the water. The most important 
 of the impurities in water is organic matter, in the 
 form of living and dead vegetable and animal organ- 
 isms, and their products. As the result of the chem- 
 ical and vital processes of nature's laboratory, the or- 
 ganic matter in water is constantly being destroyed, 
 the resulting products being ammonia, nitrous and 
 nitric acids, chlorids, carbonates, etc. 
 
 CHAPTER II. SANITARY ANALYSIS OF WATER 
 
 i. Collection of the Sample 
 
 A bottle of about four liters' capacity is cleansed 
 with hot water, then repeatedly rinsed with distilled 
 
NATURE AND COMPOSITION OF WATER 65 
 
 water, and, finally, it is rinsed several times with the 
 water to be examined. It is then filled with the water 
 and closed with a clean, new cork that has also first 
 been rinsed in the water, The cork should be held 
 in place with a heavy cord. 
 
 In collecting a sample from a pond, lake, or stream 
 the bottle should be immersed for 20 or 30 cm. below 
 the surface of the water in order to avoid the entrance 
 of refuse matter that may be floating on the surface. 
 The sample should be collected at a sufficient distance 
 from the shore to avoid impurities lodged along the 
 banks of the stream or pond. A sample of well water 
 or hydrant water should be collected only after it has 
 been flowing for several minutes. In collecting a 
 sample from a town supply, the end of the supply-pipe 
 should be avoided in order to secure a sample that is 
 fairly representative of the condition of the water. 
 
 2. Data on the Label 
 
 After the sample of water has been procured, a label 
 should be attached to the bottle giving the following 
 data : (a) the source of the sample, and date of collec- 
 tion ; (b) the presence of any contaminating influences, 
 as the general character of the drainage — the presence 
 or absence of sewers, density of the population, the 
 presence or absence of epidemic diseases. 
 
 3. The Physical Examination of the Water 
 
 a. Clearness. — Note whether the water is clear, 
 opalescent, or cloudy ; whether it contains any sus- 
 pended particles, and their nature. 
 5 
 
66 PRACTICAL HYGIENE 
 
 b. Color. — This is determined by comparison with 
 distilled water by filling a glass cylinder, 50 cm. in 
 height, with the water, and holding it over a white 
 surface. The color may also be estimated by placing 
 50 cc. of water in a long Nessler tube and comparing 
 it with the standards used in determining the free and 
 albuminoid ammonia. The result is expressed as 0.1 
 or 0.2 according to the particular standard to which 
 the color corresponds. 
 
 c. Odor. — A marked odor can be detected at once 
 on opening the bottle containing the sample of water. 
 When there is only a slight odor a liter flask may be 
 half filled with the water and strongly agitated for 
 several minutes when the odor may be detected on 
 removing the stopper. If this procedure fails a por- 
 tion of the water should be warmed to 40 C. when, 
 if any odoriferous substances are present, their pres- 
 ence will be manifested by a faint or distinct odor ac- 
 cording to their nature. The addition of some potas- 
 sium hydroxid, before warming, at times hastens the 
 liberation of the odors. 
 
 d. Taste. — Aside from organic matter the taste of 
 water is influenced by its temperature and by the 
 quantity of carbon dioxid which it contains. 
 
 e. Reaction. — Most waters are of neutral reaction 
 or very slightly acid, an alkaline reaction being com- 
 paratively rare. The reaction may be determined 
 with litmus paper, but for accuracy and delicacy the 
 phenolphthalein test is preferable. 
 
ANALYSIS OF WATER 67 
 
 Process. — Take 100 cc. of the water and add 1 cc. of 
 the phenolphthalein solution; then add from a burette a 
 dilute (w/10) solution of either sodium or potassium hy- 
 droxid. The violet tint of the water, showing the neu- 
 tralization of the acid, is readily noticeable. 
 
 4. Chemical Analysis for Impurities 
 
 The chemical analysis of water for hygienic pur- 
 poses consists, ordinarily, in the quantitative estima- 
 tion of the total solids, of chlorin, free and albuminoid 
 ammonia, nitrates and nitrites, oxidizable organic 
 matter, and the hardness of the water. 
 
 The chemical analysis of water may be either quali- 
 tative or quantitative in character. 
 
 I. QUALITATIVE CHEMICAL ANALYSIS OF WATER 
 
 a. Gases 
 
 1, Free carbonic acid (Pettenkofer's Method). — To 
 100 cc. of the water add 10 drops of rosolic acid solu- 
 tion. Note the color, as compared with sample of dis- 
 tilled water. Free carbon dioxid turns color to yellow. 
 
 2. Hydrogen sulphid. — Warm ioo cc, of water in a 
 flask in the neck of which is a strip of filter-paper 
 moistened with solution of lead acetate, and held in 
 place by a loosely fitting cork. Black color indicates 
 hydrogen sulphid. 
 
 b. Salts in Solution 
 
 1. Silicic acid. — 250 cc. of water are evaporated to 
 dryness. The residue is dissolved in a few drops of 
 hydrochloric acid, again evaporated to dryness, and 
 
68 PRACTICAL HYGIENE 
 
 again dissolved in dilute hydrochloric acid. The sil- 
 icic acid remains undissolved in the form of white 
 flakes, and can be washed, dried, and weighed. 
 
 2. Sulphurous acid, — To 50 cc. of water add a few 
 drops of hydrochloric acid and 1 cc. barium chlorid 
 solution. Sulphurous acid is precipitated as heavy 
 white barium sulphate. 
 
 Na 2 S0 4 + BaCl 2 = BaS0 4 + 2NaCl. 
 
 3. Chlorin. — To 50 cc. of water add 5 drops of di- 
 lute nitric acid and a few drops of silver nitrate solu- 
 tion. An insoluble, white, flaky precipitate of silver 
 chlorid is formed, dissolving in excess of ammonia. 
 
 NaCl + AgNO s = AgCl + NaN0 3 . 
 
 4. Nitric acid. — Dissolve a few crystals of diphenyl- 
 amin in 2 cc. sulphuric acid. Float 10 drops of the 
 water on the acid. A blue color indicates the pres- 
 ence of nitric acid. 
 
 5. Nitrous acid. — Place 50 cc. of water in a tall 
 glass cylinder, add 5 drops concentrated sulphuric acid, 
 and 1 cc. of zinc-iodin-starch solution. Shake. A 
 blue color indicates the presence of nitrous acid. 
 
 Znl 2 + 2KN0 2 + 2H,S0 4 = 
 
 2NO + K 2 S0 4 + ZnS0 4 + 2H 2 - I 2 . 
 
 6. Phosphoric acid. — Evaporate 250 cc. of water 
 down to 50 cc. in a platinum crucible. Acidify with 
 nitric acid. Add ammonium molybdate solution. A 
 yellow precipitate forms within twenty-four hours. 
 
ANALYSIS OF WATER 69 
 
 c. Bases 
 
 1. Potassium and sodium. — (See page 101). 
 
 2. Calcium. — Acidify ioo cc. water with hydro- 
 chloric acid, boil, render alkaline with ammonia, and 
 add 1 cc. ammonium oxalate solution. A white pre- 
 cipitate rapidly forms = calcium oxalate. 
 
 CaCl 2 + (NH 4 ),CA = 2(NH 4 )C1 + CaC 2 4 . 
 It is necessary to first remove iron and the earthy 
 bases. 
 
 3. Magnesium. — The precipitate of the oxalate of 
 lime is filtered off, the filtrate again treated with 10 
 drops ammonium oxalate solution to remove all the 
 lime. Then add ten drops sodium phosphate solution. 
 Stir. White crystalline precipitate of magnesium am- 
 monium phosphate forms. 
 
 MgCl 2 + Na 2 HP0 4 + NH 4 HO = 
 
 Mg(NH 4 )P0 4 + 2NaCl + H 2 0. 
 
 4. Iron. — The residue of 250 cc. of water is dis- 
 solved in hot dilute nitric acid, and 5 drops of potas- 
 sium ferrocyanid solution added. A green to blue 
 color is produced. 
 
 2Fe 2 Cl 6 + 3 K 4 Fe(CN) 6 = Fe 7 (CN) 18 + 12KCI. 
 
 5. Heavy metals. — Five liters of water are treated 
 with a few drops of nitric acid, and ammonium nitrate 
 solution. This is evaporated to 50 cc, then treated 
 with hydrogen sulphid. 
 
 A black precipitate may be lead or copper. 
 Filter and wash with hydrogen sulphid solution. 
 Dissolve in hot dilute nitric acid, filter, and add a few 
 
70 PRACTICAL HYGIENE 
 
 drops of sulphuric acid. If lead is present there is a 
 white precipitate of lead sulphate. 
 
 a. PbN 2 6 + H 2 S = PbS + 2HN0 3 
 
 b. PbS + 2HNO3 = PbN 2 6 + H 2 S. 
 
 c. PbN.O, + H 2 S0 4 = PbS0 4 + 2HNO a . 
 
 Copper, — The filtrate is then treated with potas- 
 sium ferrocyanid solution. Reddish brown, flaky- 
 precipitate is copper in form of ferrocyanid. 
 
 Zinc. — The filtrate of the copper serves to show the 
 presence of zinc. Boil to drive off hydrogen sulphid. 
 Add excess of sodium hydroxid. Zinc hydroxid is 
 formed. Filter and treat with hydrogen sulphid gas. 
 White precipitate is zinc sulphid. 
 
 a. ZnN 2 O e + 2NaOH = Zn0 2 H 2 + 2NaN0 3 . 
 
 b. Zn0 2 H 2 + H 2 S = ZnS + 2H 2 0. 
 
 6. Ammonia* — Nessler's reagent, 1 cc, added to 50 
 cc. of the water. 
 
 NH 4 C1 + 2HgKI 3 + 4KHO = 
 
 Hg 2 NH 2 OI + 5KI + KC1 + 3 H 2 0. 
 A yellowish color indicates the presence of ammonia. 
 
 II. QUANTITATIVE CHEMICAL ANALYSIS OF WATER 
 1. Total Solids 
 
 A definite quantity of the water (100 to 1000 cc.) 
 is placed in a weighed porcelain capsule and evapo- 
 rated to dryness on a water-bath. The capsule is then 
 dried for an hour, at ioo° C, allowed to cool in a des- 
 iccator, and again weighed. For very accurate re- 
 
ANALYSIS OF WATER 7 1 
 
 suits the residue must be dried to a constant weight. 
 The increase in the weight of the capsule represents 
 the weight of the solids in the amount of water evap- 
 orated. 
 
 Incineration of the residue, — In order to determine 
 the proportion of organic and inorganic matter in the 
 solids obtained from the w 7 ater evaporation, the residue 
 is carefully incinerated, and, after cooling in a desicca- 
 tor, the capsule is again weighed. The loss in weight 
 represents approximately the organic matter and the 
 remainder the inorganic matter. From the color of 
 the residue, and the odors given off during incinera- 
 tion, we derive some information as to the nature of 
 the organic matter — whether of vegetable or of animal 
 origin; an odor resembling burning hair indicates 
 animal matter. A dark and greasy residue usually 
 indicates the presence of sewage. 
 
 2. Chlorin 
 
 From the fact that chlorin is found in practically 
 all waters, in variable quantities, quantitative estima- 
 tions are always necessary. Chlorin in water is esti- 
 mated by means of a solution of silver nitrate, using a 
 few drops of a solution of potassium chromate as an 
 indicator. 
 
 a. Solution of silver nitrate. — The solution of silver 
 nitrate used in the estimation of chlorin in water is 
 made of such strength that i cc. = i milligram chlorin. 
 
 The molecular weight of silver nitrate = 170, 
 li chlorin = 35.5, 
 
72 PRACTICAL HYGIENE 
 
 Therefore 35.5 : 170 :: 1 : x = 4.788 milligrams silver 
 nitrate are equal to 1 milligram of chlorin, and 4.788 
 grams silver nitrate must be dissolved in a liter of 
 water in order that 1 cc. of solution = 1 milligram 
 chlorin. 
 
 b. Solution of sodium chlorid. — The solution of sil- 
 ver nitrate is standardized by titrating against a solu- 
 tion of sodium chlorid of such strength that each cubic 
 centimeter represents 1 milligram chlorin. 
 
 35-5 : 5 8 -5 :: 1 : ■*. = 1.647 m g- Na Cl. = 1 mg. CI. 
 
 Therefore 1.647 g rams sodium chlorid must be dis- 
 solved in a liter of water. The reaction which takes 
 place between these two solutions is as follows : 
 
 NaCl + AgN0 3 = AgCl + NaN0 3 , 
 and, as soon as all the chlorin in the solution has been 
 precipitated by the silver the further addition of a 
 slight excess of the silver solution produces a reaction 
 between it and the indicator, potassium chromate, and 
 is manifested by a change in the color of the solution 
 from the precipitate of red chromate of silver which 
 is now produced, the reaction being 
 
 K s Cr0 4 + 2 AgNO, = Ag,Cr0 4 -f 2KN0 3 . 
 
 c. The indicator. — This consists of a 10 per cent, 
 solution of potassium chromate which has been freed 
 from chlorin, three or four drops being used for each 
 titration. 
 
 Process. — Before each determination of chlorin in 
 water the solution of silver nitrate must be standardized 
 by titrating it against a standard solution of sodium 
 chlorid. Then 100 cc. of the water are placed in a half- 
 liter Florence flask with three or four drops of the indi- 
 cator, and the silver solution added from a burette, con- 
 
ANALYSIS OF WATER 73 
 
 stantly agitating the water in the flask, until the reddish 
 tint produced by the silver chromate remains permanent. 
 In order to avoid adding an excess of the silver solution 
 the flask should be placed in a porcelain capsule, com- 
 paring the color of the solution from time to time with 
 that of a duplicate sample in another flask placed under 
 similar conditions, and in which the end-reaction was 
 accurately determined. The number of cubic centimeters 
 of silver solution required to precipitate the chlorin in 
 the water will represent the number of milligrams of 
 chlorin in ioo cc. of the water. From the fact that the 
 end-reaction requires the addition of an excess of silver 
 solution it is necessary to deduct o. i cc. from the reading 
 of the burette. 
 
 Example. — ioo cc. of water required 1.3 cc. silver ni- 
 trate solution ; therefore, deducting 0.1 cc. for the end- 
 reaction, we have 1.2 cc. silver nitrate = 1.2 milligrams 
 chlorin in 100 cc. of water. If, however, the silver ni- 
 trate solution varies from the normal strength, as shown 
 by its titration against the sodium chlorid solution, it is 
 necessary to make a corresponding correction of the 
 results obtained. For example : 
 
 10 cc. NaCl = 10. 1 cc. AgN0 3 . 
 Hence 10. 1 : 10. o :: 1.2 : x = 1.188 mg. CI. ; 
 
 or if 10 cc. NaCl = 9.8 cc. AgN0 3 , 
 
 then 9.8 : 10 :: 1.2 : x= 1.224 m g- CI. 
 
 In waters containing much organic matter the color 
 of the water may interfere with the satisfactory detec- 
 tion of the end-reaction when potassium chromate is 
 used as an indicator. In such instances Salkowski's 
 modification of Volhard's method of using ammonium 
 thiocyanate as an indicator should be employed. 
 
 Solutions required : 
 
 1. Pure nitric acid, of 1.20 specific gravity. 
 
 2. Concentrated solution of ammonioferric alum. 
 
74 PRACTICAL HYGIENE 
 
 3. A standard sodiiim chlorid solution, 1 cc. = 1 
 milligram chlorin. 
 
 4. A standard silver nitrate solution, 1 cc. = 1 mil- 
 ligram chlorin. 
 
 5. A titrated solution of ammonium thiocyanate. 
 This is made by dissolving 2 grams of pure ammonium 
 thiocyanate in water and diluting it to 1100 cc. A 
 burette is filled with this solution, and 10 cc. of the 
 silver nitrate solution are placed in a flask, diluted to 
 100 cc, and 5 cc. of nitric acid and 5 cc. of the alum so- 
 lution are added. The mixture is agitated and the 
 thiocyanate solution added in small portions until 
 the red color remains permanent, but still weak. This 
 titration is repeated and then a liter of the thio- 
 cyanate solution is diluted until 10 cc. of it are equiv- 
 alent to 10 cc. of the silver nitrate solution. 
 
 Process. — 1000 cc. of the water are acidulated with nitric 
 acid, and a known amount of the standard silver nitrate 
 solution is added, enough to leave a small excess. This 
 is well shaken and then filtered through a dry filter. To 
 a measured portion of the clear filtrate (100 cc. ) a little 
 alum solution is added, and finally the standard ammo- 
 nium thiocyanate solution is dropped from a burette 
 until the red color of ferric thiocyanate makes its ap- 
 pearance. The quantity of ammonium thiocyanate 
 solution used (calculated for the entire quantity of water 
 taken) gives the amount of excess of silver solution in 
 the liquid, and this by subtraction from the whole amount 
 of silver solution used, gives the amount corresponding 
 to the chlorin present in the water. 
 
 3. Free and Albuminoid Ammonia 
 
 The nitrogenous organic impurities in water are 
 generally estimated by the Wanklyn and Chapman 
 process as free and albuminoid ammonia. 
 
ANALYSIS OF WATER 75 
 
 a. Nessler's reagent. — Nessler's reagent is prepared 
 by dissolving 62.5 grains of potassium iodid in 250 
 cc. of water, and to this a hot saturated solution of 
 mercuric chlorid is added until a slight permanent 
 precipitate of red mercuric iodid is formed. Solid 
 caustic potash, 150 grams, dissolved in 150 cc. of 
 water, is then added to the mixture and the solution 
 rendered sensitive to ammonia by the addition of a 
 small amount of the saturated mercuric chlorid solu- 
 tion. It is then filtered through asbestos and pre- 
 served in a glass-stoppered bottle. 
 
 b. Alkaline potassium permanganate solution. — 
 
 This solution is prepared by dissolving 8 grams of po- 
 tassium permanganate in 600 cc. of distilled water, 
 and 200 grams of caustic potash in 500 cc. of water. 
 As soon as each of these has become entirely dissolved 
 the two solutions are mixed and the mixture evapo- 
 rated to a liter, thereby freeing it of ammonia. 
 
 c. Standard ammonium chlorid solution. — A strong 
 solution of ammonium chlorid is prepared by dissolv- 
 ing 3. 141 grams of ammonium chlorid in a liter of dis- 
 tilled water. The standard solution is prepared from 
 this strong solution by diluting it 1 : 100 with dis- 
 tilled water when each cubic centimeter will contain 
 0.01 milligram of ammonia, or 0.0082 milligram of 
 nitrogen. 
 
 d. Ammonia-free water. — In making up the stand- 
 ards containing definite amounts of the ammonium 
 chlorid solution, it is necessary to employ distilled 
 water that is practically free from ammonia. This 
 
76 PRACTICAL HYGIENE 
 
 water must be specially prepared as it is not on the 
 market. The best way to secure such a water is by 
 redistillation of pure distilled water or spring water. 
 At times it has been found almost impossible to ob- 
 tain a satisfactory water from the city water supply 
 because of the large amounts of sewage contained in 
 it. In preparing ammonia-free water from pure dis- 
 tilled water the first portion of the distillate is always 
 discarded, usually about a third of the distillate. The 
 water distilling over, after the first third has been dis- 
 carded, is tested with Nessler's reagent, and if found 
 ammonia-free, is collected in a clean glass-stoppered 
 flask. Where this method fails to yield satisfactory 
 amounts it may be advisable to add a few drops of 
 pure, concentrated sulphuric acid to the water before 
 distilling, so as to convert the ammonia into the sul- 
 phate, when the distillate will come over fairly free 
 from ammonia. 
 
 Process. — A glass-stoppered retort of 1250 cc. capac- 
 ity, and a Iyiebig's condenser, with constant water-sup- 
 ply, are required to carry out this process. The retort 
 is thoroughly cleansed and partly filled with pure dis- 
 tilled water. The water is then distilled over until it 
 comes off free from ammonia, as shown by testing 50 cc. 
 of the distillate with 1 cc. of the Nessler reagent. As 
 soon as the distillate is found to be free of ammonia the 
 distillation is stopped, the retort disconnected from the 
 condenser, and the remainder of the distilled water poured 
 out leaving the last drops to drain away. Then, without 
 rinsing, it is again connected with the condenser and 500 
 cc. of the water to be examined placed in it. The dis- 
 tillation of the water is now begun and each 50 cc. of the 
 distillate collected separately in short glass cylinders and 
 transferred to long Nessler tubes of 50 cc. capacity, which 
 
ANALYSIS OF WATER 77 
 
 have been thoroughly cleansed by rinsing repeatedly with 
 pure water, and allowed to drain in a suitable rack or 
 frame. When four portions of 50 ee. each, or 200 ce. 
 altogether, have been distilled over the free ammonia has 
 usually all been removed, and the distillation is arrested. 
 50 ee. of the alkaline potassium permanganate solution 
 are now added to the remainder of the water in the retort 
 and the distillation resumed. Five portions of 50 ce. 
 each of the distillate are collected as before, these repre- 
 senting the so-called albuminoid ammonia. 
 
 A set of standards is now prepared by placing o. 1, 0.2, 
 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 cc. of the stand- 
 ard ammonium chlorid solution into Nessler tubes of 50 
 cc. capacity and diluting with water that is practically 
 free of ammonia. These are then placed in a suitable 
 rack in regular order according to the strength of the 
 standards they represent. The standards and distillates 
 are now ' ' nesslerized " by adding 1 cc. of Nessler' s rea- 
 gent to the contents of each tube. After standing for 
 ten minutes the comparisons may be made. The total 
 amount of ammonia found in the first four distillates rep- 
 resents the amount of free ammonia in 500 cc. of the 
 water. The total quantity of ammonia found in the last 
 five distillates represents the amount of albuminoid am- 
 monia in the same amount of the water. By multiplying 
 each of these amounts by two we learn the number of 
 milligrams of free and of albuminoid ammonia in a liter 
 of the water. 
 
 Example. — The first 50 cc. of distillate =0.3 cc. of 
 the standard ammonium chlorid solution, or 0.003 m g- or " 
 ammonia; the second 50 cc. =0.15 cc. of the standard 
 solution, or 0.0015 mg. of ammonia ; the third 50 cc. = 
 0.005 cc -> or 0.0005 m £- OI ammonia ; and the fourth 50 
 cc. — - 0.000 cc. of the standard solution. The total 
 amount of free ammonia found in the 500 cc. of water is 
 0.005 m g-> or °- 01 m g- °f ammonia in a liter of the water. 
 
 The distillates containing the albuminoid ammonia 
 are as follows : 
 
78 PRACTICAL HYGIENE 
 
 First = 0.4 cc, or 0.004 m &- °f ammonia ; 
 Second =0.3 cc, or 0.003 m g- °f ammonia ; 
 Third =0.2 cc, or 0.002 mg. of ammonia ; 
 Fourth =0.1 cc, or 0.001 mg. of ammonia ; 
 Fifth = 0.05 cc, or 0.0005 m g- °f ammonia. 
 
 The total quantity of albuminoid ammonia found in the 
 500 cc. of water is 0.0105 mg., or 0.021 mg. of ammonia 
 in a liter of the water. 
 
 4. Oxidizable Organic Matter 
 
 a. Oxalic acid solution. — This solution is made of 
 such strength that each cubic centimeter of it will 
 represent o. 1 milligram of oxygen. 
 
 Therefore 16 : 126 :: 0.1 : .r = 0.7875 milligram 
 oxalic acid in each cubic centimeter, or 0.7875 gram 
 of oxalic acid are dissolved in a liter of distilled water, 
 so that 1 cc of the solution = 1 milligram of oxygen. 
 
 b. Potassium permanganate solution. — This is like- 
 wise made of such strength that 1 cc. of it will equal 
 about 0.1 milligram of oxygen, and therefore, 0.4 gram 
 of potassium permanganate are dissolved in a liter of 
 water. 
 
 c. Sulphuric acid of 25 per cent, strength.— 
 
 Cleansing the casserole. — A porcelain casserole of 
 about 200 cc. capacity is freed from organic matter by 
 introducing 100 cc. of distilled water, 5 cc. of the 25 
 per cent, sulphuric acid, and several cubic centimeters 
 ,of the potassium permanganate solution and boiling 
 for five minutes. This water is then poured out leav- 
 ing the last few drops to drain away. 
 
 Into the clean casserole is now introduced 100 cc. of 
 the water to be examined, 5 cc. of the 25 per cent, sul- 
 
ANALYSIS OF WATER 79 
 
 phtiric acid, and 6 to 8 cc. of the potassium perman- 
 ganate solution and boiled for five minutes. Into the 
 hot liquid is now introduced 10 cc. of the oxalic acid 
 solution by means of a pipette, and then the potas- 
 sium permanganate solution is carefully added, drop 
 by drop, from a Gay-Lussac burette, until the liquid 
 assumes a faint rose tint. The total quantity of the 
 potassium permanganate solution added represents the 
 amount necessary to oxidize the 10 cc. of oxalic acid 
 solution and the organic matter in the ioo cc. of water. 
 Standardizing the solutions. — In order to ascertain 
 the amount of potassium permanganate solution re- 
 quired to oxidize the 10 cc. of oxalic acid solution, it 
 is necessary to again introduce 6 or 8 cc. of the potas- 
 sium permanganate solution into the liquid in the 
 casserole, which is now free of organic matter, and heat 
 it to boiling, again adding io cc. of the oxalic acid 
 solution, and finally the potassium permanganate so- 
 lution, drop by drop, until the faint rose tint is repro- 
 duced. The amount of potassium permanganate so- 
 lution required now for the io cc. of oxalic acid solu- 
 tion alone will indicate the amount of potassium per- 
 manganate solution required to yield i milligram of 
 oxygen. 
 
 Example. — The ioo cc. of water examined and the io 
 cc. of oxalic acid solution required 13.4 cc. of the potas- 
 sium permanganate solution to bring about the rose tint 
 of the liquid in the first instance. In the second instance 
 the 10 cc. of oxalic acid solution alone required only 10.4 
 cc. of the potassium permanganate solution to bring about 
 the same result. It is necessary to deduct o. 1 cc. from 
 each of these results as that amount of potassium per- 
 
80 PRACTICAL HYGIKNE 
 
 manganate solution is necessary to bring about the end- 
 reaction. Therefore 10.3 cc. of the potassium permanga- 
 nate solution represent 1 milligram of oxygen, and the 
 organic matter in the 100 cc. of water under examination 
 required 3.0 cc. of the potassium permanganate solution 
 for its oxidation. From these data we can calculate the 
 amount of oxygen required to oxidize the organic matter 
 in a liter of the water under examination. 
 
 10.3 : 1 : : 30 : x = 2.912 milligrams O. 
 
 The role of the sulphuric acid.- — The necessity for 
 the addition of the sulphuric acid in this process is 
 twofold. The reaction of the potassium permanga- 
 nate is more energetic in acid solutions, and in the sec- 
 ond place, the potassium permanganate in breaking 
 up will unite with the sulphuric acid to form mangan- 
 ous sulphate, a colorless salt : 2KMnO + 3H 2 SO = 
 2MnS0 4 + K S0 4 + 3HO + 5O. 
 
 Boiling for five minutes. — In carrying out this pro- 
 cess it is highly important to boil the water for a defi- 
 nite period of time. Some authors recommend boil- 
 ing for ten minutes and there may be instances where 
 it would be necessary to do so in order to oxidize cer- 
 tain organic substances present in the water, but for 
 most substances boiling for five minutes is considered 
 sufficient. In making comparative estimations it is 
 essential to boil for the same length of time in each 
 determination — always counting from the beginning 
 of ebullition. 
 
 5. The Hardness of Water 
 
 The hardness of water is due to the presence of lime 
 and magnesia in the form of carbonates, chlorids, sul- 
 
ANALYSIS OF WATER 8 1 
 
 phates, or nitrates. In exceptional instances the hard- 
 ness of water is also in part due to the presence of 
 salts of iron. 
 
 The hardness of water is usually determined by 
 means of a standard soap solution. The fatty acids in 
 the soap solution form insoluble stearates, palmitates, 
 etc., of lime and magnesia. As long as any of the 
 lime and magnesia is unprecipitated the soap solution 
 fails to produce a permanent lather with the water. 
 As soon as a distinct lather is formed, and remains 
 permanent for five minutes, all the lime and magnesia 
 present in the water have been precipitated, and the 
 lather, therefore, forms the indicator of the end-reac- 
 tion. 
 
 a. Standard soap solution. — The standard soap so- 
 lution is made by softening 150 grams of lead plaster 
 (U. S. P.) on a water-bath and thoroughly mixing it 
 with 40 grams of pure potassium carbonate until a 
 homogeneous mixture is obtained. This mixture is 
 then diluted with dilute alcohol and transferred to a 
 glass-stoppered bottle and agitated at intervals for sev- 
 eral days. The solution is then filtered and standard- 
 ized by means of a solution of barium nitrate — 0.559 
 gram dissolved in a liter of distilled water — of which 
 100 cc. contain an amount of barium equivalent to 12 
 milligrams of lime. The standard soap solution is 
 made of such strength that 45 cc. of it are required to 
 form a lather with 100 cc. of the barium solution ; 
 therefore 45 cc. are equal to 12 milligrams of lime. 
 The filtered alcoholic soap solution is diluted with 
 dilute alcohol until the required strength is attained. 
 
82 PRACTICAL HYGIENE 
 
 b. Degrees of hardness. — The hardness of water is 
 expressed in degrees. In England a degree of hard- 
 ness — Clark's scale — represents i grain calcium car- 
 bonate in a gallon of water. In Germany i degree of 
 hardness represents i part by weight of calcium oxide 
 in 100,000 parts by weight of water, or 1 milligram 
 calcium oxide in 100 cc. of water. In France 1 de- 
 gree of hardness represents 1 part of calcium carbon- 
 ate in 100,000 parts of w 7 ater, or 1 milligram calcium 
 carbonate in 100 cc. of water. This is also known as 
 the metric scale. In America the metric scale is com- 
 ing into more general use as being preferable to 
 Clark's scale. One degree of hardness in the metric 
 scale represents 0.7 degree of Clark's scale, and from 
 these data results expressed in either of these systems 
 may readily be converted into the other. 
 
 The hardness of water is expressed as total hardness 
 (the hardness resulting from the action of all the lime 
 and magnesium salts present in the water) and as per- 
 manent and removable hardness. The removable 
 hardness represents the proportion of the salts of lime 
 and magnesium in the form of carbonates and bicar- 
 bonates. The carbon dioxid combined with the lime 
 and magnesium in this manner is liberated by boiling 
 the water for half an hour. The permanent hardness 
 represents salts of lime and magnesium present in the 
 water as sulphates, chlorids, or nitrates and is deter- 
 mined by applying the soap test to a part of the water 
 that has been subjected to boiling, while the remova- 
 ble hardness is determined by taking the difference 
 between the total and permanent hardness. 
 
ANALYSIS OF WATER 83 
 
 Process. — To determine the total hardness of water 
 50 ec. of the sample are placed into a glass-stoppered 
 bottle of 125 ec. capacity and the standard solution of 
 soap is added from a burette graduated in tenths of a 
 cubic centimeter. The soap solution is added, at first, 
 in amounts of about 0.5 cc, and the water agitated thor- 
 oughly after the addition of each portion of the soap so- 
 lution. As soon as a slight lather begins to form the soap 
 solution is added drop by drop, until the lather is 1 cm. 
 in thickness and remains unchanged for five minutes. It 
 is customary to deduct 0.2 cc. from the quantity of soap 
 solution used in the determination as that amount is 
 necessary to produce a permanent lather in distilled 
 water. 
 
 Very hard waters that require more than 45 cc. of the 
 standard soap solution, must be diluted with distilled 
 water, because of the formation of double salts of lime 
 and magnesium with the fatty acids in the presence of 
 excessive amounts of these bases, and, in consequence of 
 which, the reaction is irregular and the results unsatis- 
 factory. 
 
 To determine the permanent hardness of water, 100 cc. 
 of the sample are placed into a suitable vessel and boiled 
 for half an hour, but without evaporating to dryness. 
 After cooling the concentrated water is diluted to 100 cc. 
 with distilled water and the hardness determined in the 
 same manner as for the total hardness, or, if the evapo- 
 ration has removed half of the water, then the whole of 
 this may be used, if the degree of hardness is low, in 
 making the determination of the permanent hardness. 
 
 The removable hardness of water is determined by de- 
 ducting the amount of soap solution required for the per- 
 manent hardness from the amount required for the total 
 hardness, the remainder representing the removable 
 hardness. 
 
 Calculation of the results. — As each o.i cc, or 
 measure, of the standard soap solution represents 0.25 
 milligrams calcium carbonate, and all the results are 
 
84 PRACTICAL HYGIENE 
 
 expressed in terms of calcium carbonate because it is 
 the principal agent producing the hardness of water, 
 the calculation is very easily made. Two measures of 
 soap solution are deducted from each reading for the 
 end-reaction. The number of measures required X 
 0.25 milligram calcium carbonate = the number of 
 milligrams of calcium carbonate in 50 cc. of the water 
 tested. This result is multiplied by 2, converting it 
 into milligrams calcium carbonate per 100 cc. of water, 
 or parts per 100,000, or degrees of hardness according 
 to the metric scale. This result multiplied by 0.7 
 converts it into grains per gallon, or degrees of hard- 
 ness of Clark's scale. 
 
 Example. — 50 cc. of water required 32 — 2 = 30 meas- 
 ures of soap solution. Then 30 X 2 X 0.25 = 15.0 de- 
 grees of hardness according to the metric scale or 15 X 0.7 
 = 10.5 degrees of hardness of Clark's scale. This repre- 
 sents the total hardness of the water. 100 cc. of the 
 same water, after being boiled down to 50 cc. , required 
 20 — 2 = 18 measures of soap solution. Then 18 X 0.25 
 = 4.5 degrees of permanent hardness according to the 
 metric scale, or 4.5 X 0.7 = 3. 15 degrees of Clark's scale. 
 The removable hardness is determined by finding the 
 difference in the two amounts of soap solution required 
 for the total and permanent hardness — 60 — 18 = 42 
 measures, then 42 X 0.25= 10.5 degrees in the metric 
 scale, or 7.35 degrees of Clark's scale. 
 
 Hehner's method of determining the hardness of 
 water. — The solutions required in this method are a 
 n/50 sodium carbonate solution and n/50 sulphuric 
 acid. Each cubic centimeter of the standard acid ex- 
 actly neutralizes 1 milligram of calcium carbonate, 
 and each cubic centimeter of the sodium carbonate so- 
 
ANALYSIS OF WATER 85 
 
 lution represents alike amount of calcium carbonate, 
 or its equivalent of magnesia, when present in a sam- 
 ple of water. 
 
 The sodium carbonate solution is prepared by dis- 
 solving 1.06 grams of recently ignited pure sodium 
 carbonate in a liter of water, i cc. = 1.06 milligrams 
 sodium carbonate = 1.0 milligram calcium carbonate. 
 
 The standard sulphuric acid is prepared by adding 
 1 cc. of pure concentrated sulphuric acid to about a 
 liter of water. 50 cc. of the standard sodium carbon- 
 ate solution is placed in a porcelain dish, heated to 
 boiling, a few drops of indicator added (phenacetolin 
 or lacmoid), and the sulphuric acid cautiously run in 
 from a burette until a change of color is produced. From 
 the result obtained the degree of dilution required for 
 the sulphuric acid may be calculated so that 1 cc. of 
 the sulphuric acid = 1 cc. of the sodium carbonate 
 solution. 
 
 Process — Temporary hardness. — 100 cc. of the water 
 is tinted with 1 cc. of the indicator and heated to boiling, 
 and the sulphuric acid cautiously added until a change of 
 color is produced. Each cubic centimeter of acid required 
 represents one part of calcium carbonate, or its equiva- 
 lent in 100,000 parts of water, or the number of degrees 
 of hardness according to the metric scale. 
 
 Permanent hardness. — To 100 cc. of the water is added 
 an amount of sodium carbonate solution in excess of that 
 required to decompose the calcium and magnesium sul- 
 phates, chlorids, and nitrates present : usually 50 cc. of 
 the solution will be all that is required. The mixture is 
 evaporated to dryness in a platinum dish and the residue 
 ■dissolved in distilled water. The solution is filtered 
 through a very small filter, washed, and the filtrate and 
 washings titrated while hot with sulphuric acid. The 
 
86 PRACTICAL HYGIENE 
 
 difference between the amount of sodium carbonate added 
 and the sulphuric acid required for the residue, will give 
 the permanent hardness. 
 
 If the water contains sodium or potassium carbonate 
 there will be no permanent hardness, and there will be 
 more acid required for the filtrate than the equivalent of 
 the sodium carbonate added. From this excess the quan- 
 tity of sodium carbonate in the water may be determined. 
 The amount of sodium carbonate found in the water must 
 be deducted from the result obtained for the temporary 
 hardness. 
 
 The indicator. — The lacmoid solution is made by 
 dissolving 2 grams of lacmoid in a liter of 50 per cent, 
 alcohol. When the test is carried out in the cold 
 methyl orange may be used as the indicator. It is 
 well to use a second flask containing water colored to 
 the same depth with the indicator for comparison, in 
 order to determine the first change of color which 
 marks the end-reaction. 
 
 Hehner's method is far more satisfactory than Clark's 
 method by means of standard soap solution in testing 
 hard waters. It is also preferable to Clark's method 
 because it gives more definite information as to the 
 nature of the constituents causing the hardness of 
 water. It is customary to speak of the temporary 
 hardness of water as determined by this method as 
 the u alkalinity" of the water, and the permanent 
 hardness as the " incrusting constituents " of the water, 
 expressed in terms of calcium carbonate. 
 
 Gravimetric determination of the hardness of wa- 
 ter. — For the more exact determination of the hard- 
 ness of water the quantities of lime and magnesia 
 present are determined gravimetrically. 
 
ANALYSIS OF WATER " 87 
 
 Estimation of lime. — The amount of lime is deter- 
 mined by concentrating 50 cc. of the water through 
 evaporation and treating the residue with ammonium 
 chlorid, an excess of ammonium oxalate, and a 
 small amount of ammonia. The lime is precipitated 
 in the form of calcium oxalate while the magnesia re- 
 mains in solution as magnesium oxalate. The pre- 
 cipitated calcium oxalate is collected on a filter, 
 washed, dried and heated strongly, whereby it is con- 
 verted into caustic lime and then weighed as such. 
 
 Estimation of magnesia. — The magnesia, which is 
 now 7 in the filtrate in the form of oxalate, is treated 
 with ammonium chlorid, ammonia, and w T ith sodium 
 phosphate, when it is precipitated as ammonium-mag- 
 nesium phosphate. The precipitate is collected on a 
 filter, dried and fused, and is then weighed as mag- 
 nesium pyrophosphate. 
 
 6. Determination of Nitrogen as Nitrates 
 
 I, Marx-Tromsdorf method, — In this method the 
 water is titrated with indigo solution in hot acid solu- 
 tion. The water is mixed with an equal volume of 
 concentrated sulphuric acid free of nitrogen, when a 
 heat of i20°-i25° C. is generated, which. favors the 
 conversion of the nitrates into nitric acid and sulphates, 
 causing the indigo solution to be decolorized. As 
 soon as all the nitrates have been so changed the 
 further addition of indigo solution will change the 
 liquid to a yellowish-green color. 
 
 a. The indigo solution. — About 3 grams commercial 
 indigotin are pulverized in a mortar and digested with 
 
88 PRACTICAL HYGIENE 
 
 about 60 cc. concentrated sulphuric acid. Indigodi- 
 sulpho acids are formed, besides some indigomonosul- 
 pho acids. After standing twenty-four hours the reac- 
 tion is completed and the solution is poured into four 
 times the quantity of distilled water, when, on stand- 
 ing, the insoluble indigomonosulpho acids are precipi- 
 tated. The solution is now filtered and preserved in 
 a glass-stoppered bottle. This solution is diluted with 
 distilled water, before using, so that 6 to 8 cc. will be 
 decolorized by 1 milligram of nitrogen pentoxid. 
 
 b. Standard potassium nitrate solution. — To stand- 
 ardize the indigo solution a solution of potassium ni- 
 trate is prepared of which 25 cc. = 1 milligram of 
 nitrogen pentoxid (1 liter = 40 milligrams nitrogen 
 pentoxid), but since such a small quantity cannot be 
 weighed accurately we dissolve 7.5037 gram of potas- 
 sium nitrate in a liter of water, and dilute this solution 
 1 : 100 before using it. 25 cc. of the dilute solution 
 = 1 milligram of nitrogen pentoxid, and it should re- 
 quire from 6 to 8 cc. of the indigo solution to neutral- 
 ize 25 cc. of the standard potassium nitrate solution. 
 
 Process. — It is important that the operation be car- 
 ried out under the same conditions each time, especially 
 as to the temperature of the solutions. 25 cc. of the di- 
 lute potassium nitrate solution are placed in a 100 cc. 
 Florence flask with 25 cc. (nitrogen-free) concentrated 
 sulphuric acid, quickly mixing them, when the tempera- 
 ture will rise to 120 to 125 C, and the nitrates are 
 changed into nitric acid and sulphuric acid salts. Into 
 this boiling solution the indigo solution is added drop by 
 drop, at first, from a burette measuring tenths of a cubic 
 centimeter, then in quantities of about a cubic centimeter, 
 shaking the flask after each addition of indigo solu- 
 
ANALYSIS OF WATER 89 
 
 tiou. Not more than 8 cc. of the indigo solution should 
 be required. If more is required the solution is too weak. 
 The examination of a sample of water is conducted in the 
 same manner only that 25 cc. of the water are used in- 
 stead of 25 cc. of the potassium nitrate solution. If more 
 than 8 cc. of the indigo solution are required the water 
 must be diluted. 
 
 Example. — For 25 cc. of potassium nitrate solution 7.5 
 cc. of indigo solution are required, therefore 7.5 cc. of 
 indigo solution = 1 milligram of nitrogen pentoxid. For 
 25 cc. of the water 6.4 cc. of indigo solution were re- 
 quired, and for 1000 cc. of water 40 X 6.4= 256 cc. of 
 
 indigo solution, or — ^— = 34.13 milligrams of nitrogen 
 
 pentoxid in a liter of water. 
 
 2. Method of Grandval and Lajoux. — Five cc. of 
 the water are placed in a porcelain dish of about 35 cc. 
 capacity, two or three drops of a 1 per cent, solution 
 of sodium carbonate added, and then evaporated to 
 dryness on the water-bath. The steam should not be 
 allowed to come in contact with the dish itself. The 
 evaporation residue is treated with about 0.5 cc. of 
 phenolsulphuric acid (made by digesting 23 grains of 
 pure crystallized phenol in 200 cc. of pure sulphuric 
 acid for some hours). By appropriate manipulation 
 the acid is worked well over the bottom and sides of 
 the dish. After some time a few cc. of distilled water 
 are added and then a solution of caustic potash until 
 the yellow color is well brought out. The strength 
 of the caustic potash solution should be 10 per cent, 
 or more. It is important that too great an excess of 
 this reagent be not added, for if this occurs crystals of 
 potassium sulphate are thrown down, a result which 
 is not desirable. 
 
90 PRACTICAL HYGIENE 
 
 A set of standards is made up for each analysis from 
 i, 2, 3, 4, 5, and 6 cc. of a solution of potassium ni- 
 trate, of which i cc. contains o.ooi milligram of nitro- 
 gen as nitrate. These portions of the potassium ni- 
 trate solution are placed in small porcelain dishes of 
 35 cc. capacity and treated in the same manner as de- 
 scribed for the sample of water. (In making up the 
 standard solution of potassium nitrate 0.7215 gram is 
 dissolved in a liter of water, and this solution is then 
 diluted 1 : 100 before using.) 
 
 After treating the sample of water and the stand- 
 ards as already described, the contents of the dishes 
 are transferred to the long Nessler tubes of 50 cc. ca- 
 pacity. More distilled water is added until they are 
 filled to within 2 or 3 cm. of the top, and the readings 
 are then made. 
 
 3. The Schultze-Tiemann method. — By boiling with 
 ferrous chlorid the nitrogen pentoxid is reduced to ni- 
 tric oxid gas, which is measured and calculated to 
 N 2 5 . The reduction is as follows: 6FeCl 2 + 8HC1 
 +V 2 ON 2 5 = 3Fe 2 Cl 6 + 2NO + JhTo + 2KCI. From 
 108 parts nitrogen pentoxid result 60 parts nitric oxid, 
 or from 9.67689 (108 X 0.0896) nitrogen pentoxid re- 
 sult 4 liters nitric oxid; L e., 1 liter nitric oxid = 
 2.419 grams nitrogen pentoxid. 
 
 Apparatus required : 
 
 100 cc. flask. 
 
 Glass tubing. 
 
 Pinch-cocks. 
 
 Beaker, 30 cc. capacity. 
 
 Glass dish, 10 cm. diameter, and 5 to 6 cm. in height. 
 
ANALYSIS OF WATER 91 
 
 Measuring tube of 30 to 50 ec. capacity, scale divided 
 into 1/10 cc. 
 
 A vessel somewhat higher than the measuring tube. 
 
 20 per cent, sodium hydroxid solution, boiled. Satu- 
 rated solution of ferric chlorid. 
 
 Concentrated hydrochloric acid. 
 
 Sufficient water must be taken to yield 10 to 20 cc. of 
 nitric oxid gas. This will depend on the richness of the 
 water in nitrates, 
 o — 50 milligrams nitrogen pentoxid use 250 cc. water. 
 50 — 250 " " " " 100 cc. " 
 
 The water is concentrated to about 5 cc. on a water- 
 bath, and then transferred to the 100 cc. flask and 
 the dish washed with about 15 cc. distilled water, and 
 this added to the water. It is not necessary to add 
 the precipitated alkaline earths. The stopper is now 
 put in position, and boiling commenced with both 
 pinch-cocks open, until the quantity of water is re- 
 duced to about 10 cc, whereby all the air is removed 
 from the apparatus. The glass tube is now inserted 
 under the mouth of the measuring tube, which has 
 been filled with sodium hydroxid and inverted over 
 the dish containing the sodium hydroxid. 15 cc. fer- 
 rous chlorid solution, and 10 cc. hydrochloric acid, are 
 now placed in the beaker. The flame is now removed 
 and the pinch-cocks closed, so that on cooling there is 
 negative pressure in the flask. When cooled the pinch- 
 cock is carefully opened when the ferrous chlorid 
 and hydrochloric acid is drawn over into the flask. 
 Care must be taken that no air gains entrance at the 
 same time, closing the pinch-cock before all the liquid 
 has passed over. The flame is now again applied, 
 heating with the pinch-cocks closed at first, until the 
 
92 PRACTICAL HYGIENE 
 
 negative pressure in the flask is entirely removed, 
 then the pinch-cock is carefully opened to allow 
 the nitric oxid gas to escape into the measuring tube. 
 Any carbon dioxid formed is absorbed by the sodium 
 hydroxid. When no more bubbles of gas are given 
 off the pinch-cock is closed and the flame removed, 
 when negative pressure again develops and the re- 
 mainder of the nitric oxid gas is liberated. The flame 
 is now again applied and the pinch-cock opened 
 to allow the gas to escape into the measuring tube. 
 The nitric oxid gas is measured at o° C. and 760 mm. 
 The sodium hydroxid is allowed to cool, the cyl- 
 inder is filled with boiled water, and the measuring 
 tube is carefully transferred to the cylinder, where 
 it is allowed to remain for several hours at room tem- 
 perature. The measuring tube is raised, by means of 
 a pair of tongs, so that the level of the water within 
 and without the tube are the same. The temperature 
 of the water is taken, as well as the barometric pres- 
 sure and the temperature at the barometer. It must 
 be remembered that the gas is moist and correction 
 must be made for the increased volume due to the 
 tension of the aqueous vapor, and deducted from the 
 observed barometric pressure. 
 
 The reduction is made according to the following 
 formula : 
 
 V VX(*-T) 
 
 760 x (1 + 0.00366 x 
 
 T = the tension of the aqueous vapor in millimeters 
 at the observed temperature. This must be taken 
 from tables of tension of aqueous vapor. 
 
ANALYSIS OF WATER 93 
 
 4. The aluminum method. — A 50 cc. tube is filled 
 with the water, and an excess (about 2 grams) of alu- 
 minum wire is added, with 2 cc. of a strong solution 
 of sodium hydroxid free from nitrogen. It is then 
 allowed to stand over night in a warm place, and a 
 measured portion, usually from 2 to 10 cc, removed 
 and made up with distilled water (free from nitrates), 
 of the same temperature as the ammonia standards, to 
 50 cc, and nesslerized. 
 
 The ammonia carried off by the evolved hydrogen 
 has frequently been caught in a trap and determined, 
 but with 2 cc of the caustic soda and at temperatures 
 below 30 C, the loss will not exceed 2 per cent, in 
 any case. Using too little caustic soda, or keeping 
 the tubes at too low a temperature, the nitrate is not 
 all reduced, while with the opposite conditions an ap- 
 preciable amount of ammonia is carried away by the 
 hydrogen. Taking due care as to these conditions 
 very satisfactory results may be obtained. 
 
 In calculating the nitrate, reduction is made for the 
 free ammonia and nitrites, but when the ammonia 
 amounts to a considerable fraction of the total nitro- 
 gen, it is first removed by boiling with the caustic 
 soda and thoroughly cooled before adding- the alumi- 
 num. When waters do not give good colors by direct 
 nesslerization it is necessary to distil. This can be 
 most conveniently done indirectly by a current of 
 steam. 
 
 Preparation of nitrate-free water. — Eight liters of 
 ordinary distilled water are treated with 100 cc of a 
 50 per cent, solution of sodium hydroxid and 5 grams 
 
94 PRACTICAL HYGIENE 
 
 of pure aluminum foil. After some hours the water 
 is placed in a still with 3 grams of potassium perman- 
 ganate and distilled ; the middle portion of the dis- 
 tillate is free from nitrates. 
 
 Sodium hydroxid solution. — One liter of nitrate-free 
 water and 50 grams of the purest sodium hydroxid 
 obtainable are brought together in a porcelain dish 
 with about 2 grams of pure aluminum foil. When 
 the foil is all dissolved, the solution is boiled down to 
 a volume of 500 cc, and after being allowed to settle, 
 filtered through asbestos. Two cc. of this solution 
 with 50 cc. of water and 0.35 gram of aluminum foil, 
 should indicate the presence of only a very slight 
 amount of ammonia when treated in the same manner 
 as samples for analysis. 
 
 7. Determination of Nitrogen as Nitrites 
 
 1. Warrington's modification of the Griess method. 
 
 — The process consists in adding to 45 cc. of the water 
 to be tested two or three drops of hydrochloric acid 
 (50 cc. strong acid in 50 cc. water), then 2 cc. of a sat- 
 urated solution of sulphanilic acid, and finally 2 cc. 
 of a saturated solution of naphthylamin hydrochlorid 
 (8 grams naphthylamin, 8 cc. strong hydrochloric acid 
 and 992 cc. of water). The presence of nitrites is in- 
 dicated by the production of a most intense and beau- 
 tiful rose-red color due to the formation of azobenzol- 
 naphthylaminsulphuric acid. The rose color produced 
 when nitrites are present is compared with the depth 
 of color obtained from known amounts of a standard 
 sodium nitrite solution under the same conditions. The 
 
ANALYSIS OF WATER 95 
 
 standards are made up from a dilute solution of sodium 
 nitrite. 1.815 grams of sodium nitrite are dissolved 
 in a liter of distilled water. 10 cc. of this solution 
 are diluted to a liter with distilled water before using : 
 1 cc. = 0.01 milligram of nitrogen tetroxid. With 
 this dilute solution ten standards are made up con- 
 taining from 0.1 cc. to 1.0 cc. each. These standards 
 are treated in the same manner as the sample of water, 
 and the readings are made in the long Nessler tubes 
 after allowing them to stand for one-quarter of an hour 
 to permit the color to fully develop. 
 
 Water containing more than 0.002 part of nitrogen 
 as nitrogen tetroxid per 100,000, must be diluted with 
 a known amount of distilled water free from nitrites. 
 Surface waters having a color above 0.1 must be de- 
 colorized by shaking with aluminum hydroxid and 
 rapidly filtering before testing for nitrites. 
 
 2. Schuy ten's method, — When 5 cc. of a 1 per 
 cent, solution of antipyrin in acetic acid (1/10) is added 
 to a solution containing nitrites, a green color is pro- 
 duced. 
 
 Antipyrin solntioit. — Dissolve 10 grams of antipyrin 
 in dilute acetic acid (1 : to), and add water sufficient 
 to make a liter. 
 
 Process. — To 45 cc. of the sample of water in one 
 of the long Nessler tubes, 5 cc. of the antipyrin solution 
 are added. After standing for about half an hour the 
 reading is made. The same standards of sodium nitrite 
 solution may be used for comparison as in the former 
 method. This method will show the presence of 1 part 
 of nitrogen as N0 2 in 20,000 parts. It is therefore not 
 as delicate as the former method but it is not hindered 
 
96 PRACTICAL HYGIENE 
 
 by the presence of any of the ordinary contaminations in 
 water. 
 
 8. Detection of Lead in Water 
 
 a. Method. — The presence of lead in water may be 
 determined by taking 200 cc. of the water and precipi- 
 tating the lead with acetic acid and then passing hy- 
 drogen sulphid gas through the mixture and convert- 
 ing it into the sulphid, the presence of lead being in- 
 dicated by the black precipitate which forms. To dis- 
 tinguish the precipitate thus formed from the sulphid 
 of some of the other metals, it is necessary to collect 
 the precipitate on a filter, dissolve it in warm nitric 
 acid, dilute with water, and then precipitate with sul- 
 phuric acid. A white precipitate forming on the ad- 
 dition of sulphuric acid shows the presence of lead in 
 the water, and is now in the form of lead sulphate. 
 
 b. Colorimetric method. — The estimation of lead 
 can be made colorimetrically if it is shown that the 
 water contains no copper. 
 
 A solution of lead of known strength is prepared, 
 by dissolving o. 1 gram of pure lead in excess of acetic 
 acid and diluting with distilled water to a liter. 
 1 cc. = 0.000 1 gram lead. 
 Five narrow cylinders of colorless glass are rilled 
 with 
 
 99 > 97) 95) an( i 93 cc - water, 
 to which are added 
 
 i, 3, 5, and 7 cc. lead solution, 
 representing 
 
 1, 3, 5, and 7 milligrams lead, 
 in a liter of the mixture. 
 
ANALYSIS OF WATER 97 
 
 In a fifth cylinder is placed ioo cc. of the water 
 acidified with a few 7 drops of acetic acid. 
 
 To each cylinder is now added 20 cc. of freshly pre- 
 pared hydrogen snlphid w T ater, shaking well, and com- 
 paring the intensity of the brown color formed in the 
 water with that of the cylinders of lead solution. If 
 it compares with the cylinder containing 5 cc. of the 
 lead solution, then 100 cc. of water contain 0.5 milli- 
 gram of lead, or a liter contains 5 milligrams. 
 
 9. Detection of Zinc in Water 
 
 The presence of zinc in water may be determined 
 by treating some of the water with ammonium sul- 
 phid, when any zinc that may be present will be pre- 
 cipitated as zinc sulphid. When lead and iron are 
 also present they are likewise precipitated as sulphids, 
 and these must be removed by boiling with sodium 
 acetate in weak acid solution and filtering. The zinc 
 is then recovered from the filtrate. 
 
 10. Estimation of Carbon Dioxid 
 
 1. Free carbon dioxid. — 100 cc. of water are placed 
 
 in an Erlenmeyer flask and 10 drops of phenolphthal- 
 
 ein solution are added and titrated with 1/10 normal 
 
 sodium hydroxid solution until the liquid is distinctly 
 
 red. The titration should be repeated and nearly the 
 
 entire amount of sodium hydroxid added at once, the 
 
 titration being completed under constant agitation of 
 
 the liquid. 
 
 1 cc. 1/10 normal sodium hydroxid = 4.4 milligrams 
 carbon dioxid. 
 
 NaOH + C0 2 = NaHC0 3 . 
 
 7 
 
98 PRACTICAL HYGIENE 
 
 2. Partially combined and free carbon dioxid 
 
 (Trillick's modification of Pettenkofer's method). — The 
 free and partially combined carbon dioxid are com- 
 bined by the addition of barium hydroxid, thereby 
 precipitating the whole of the carbon dioxid, the ex- 
 cess of the barium hydroxid being determined by 
 titration. 
 
 The solutions required are : 
 
 i. Barium hydroxid of the same strength as that 
 used in carbon dioxid determination in air. 
 
 2. Barium chlorid solution i : io; neutral. 
 
 3. Hydrochloric acid, of which 1 cc. = 1 milligram 
 carbon dioxid. About 7 cc. of hydrochloric acid of 
 1. 1 24 specific gravity are diluted to 1 liter with water, 
 so that 22 cc. of the acid will neutralize 10 cc. 1/10 
 normal sodium hydroxid. 
 
 4. The indicator solution of phenolphthalein, or 
 cochineal. 
 
 In a determination flask of 200 cc. capacity, closed 
 with a rubber stopper, is placed, by means of a pipette, 
 100 cc. water, 45 cc. barium hydroxid, and 5 cc. barium 
 chlorid ; this is then well shaken and allowed to stand 
 for twelve hours. Through the addition of the barium 
 hydroxid (1) the free and half-combined carbon dioxid 
 in the water is changed into insoluble barium carbon- 
 ate ; (2) the calcium carbonate in the water, being now 
 robbed of its solving material through the operation 
 in (1), also becomes insoluble; (3) the alkaline car- 
 bonate in the water is changed into alkaline chlorid 
 through the action of the barium chlorid and is con- 
 
ANALYSIS OF WATER 99 
 
 verted into insoluble barium carbonate; (4) all the 
 magnesium in the water is precipitated as magnesium 
 hydroxid, and the magnesium carbonate, which is con- 
 verted into insoluble barium carbonate and magnesium 
 chlorid by the action of the barium chlorid, is precipi- 
 tated finally as magnesium hydroxid; and (5) all the 
 sulphur trioxid is combined with barium, and in place 
 of the same the equivalent quantities of sulphur tri- 
 oxid combined with bases. 
 
 The resulting precipitate contains all the carbon 
 dioxid contained in the water in the form of barium 
 and calcium hydroxid, and all the magnesium as hy- 
 droxid, and all the sulphur trioxid as barium sulphate. 
 
 During the sedimentation the strength of the barium 
 hydroxid is determined by taking 100 cc. of distilled, 
 carbon dioxid free (boiled) water, 45 cc. barium hy- 
 droxid, and 5 cc. barium chlorid solulion, mixing well, 
 and taking by means of a pipette 50 cc. (= 1/3 the 
 total amount), placing it in a flask with several drops 
 of phenolphthalein solution, then adding the hydro- 
 chloric acid from a burette until the red color has dis- 
 appeared. 
 
 After twelve hours the precipitate in the flask has 
 become crystalline ; 50 cc. are then taken of the clear 
 supernatant solution by means of a pipette and titrated 
 as above. The difference in the amount of hydro- 
 chloric acid required, expresses the quantity of barium 
 required (1) to precipitate the free and half-combined 
 carbon dioxid, and (2) to precipitate the magnesium. 
 
 The magnesium in the water must then be deter- 
 
JOO PRACTICAL HYGIENE 
 
 mined gravimetrically and by multiplication with 
 
 — = i.i, calculated to carbon dioxid. 
 40 
 
 If for example for 50 cc. of the mixed solution a 
 cc. hydrochloric acid have been required, and for the 
 water b cc, and the amount of magnesium in the wa- 
 ter is m milligram in 100 cc, then 1 liter of water 
 contains [3 X (a — b) — 1.1 X nt\ X 10 milligrams 
 free and half-combined carbon dioxid. 
 
 Example. — A water contains in 100 cc 3.3 milligrams 
 MgO — m. 
 
 50 cc of the mixed solution = 12.7 cc. hydrochloric acid. 
 50 cc " " water = 7.0 cc 
 
 Then 1 liter of the water contains [3 X (12.7 — 7.0) — 
 i.i X 3.3] X 10 milligrams free + combined carbon 
 dioxid = [3 X 5.7 — 3.63] X 10 = 134.7 milligrams free 
 and half-combined carbon dioxid. 
 
 3. Total carbon dioxid. — After the removal of the 
 50 cc. the sedimentation flask still contains 100 cc. 
 and the precipitate. This remainder is now titrated 
 with hydrochloric acid, from the amount of hydro- 
 chloric acid required is subtracted the amount re- 
 quired for the 100 cc which is known form the deter- 
 mination of the free and half-combined carbon dioxid. 
 The remainder is the amount of hydrochloric acid re- 
 quired for the precipitate which contains all the car- 
 bon dioxid and all the magnesium. 
 
 An excess of the hydrochloric acid is added (e. g., 
 100 cc), and the flask is placed in warm water, then 
 in hot water, when all the carbon dioxid is driven off. 
 Cochineal solution is now added and the solution ti- 
 trated with 1/10 normal sodium hydroxid until it be- 
 
ANALYSIS OF WATER IOI 
 
 comes red, i. e., alkaline. If for the ioo cc. of solu- 
 tion + precipitate, d cc. hydrochloric acid were used, 
 then d — 2b cc. of hydrochloric acid were required for 
 the precipitate alone, and 1 liter of water contains 
 then \_(d — 2b) — 1.1 X m\ X 10 milligrams total car- 
 bon dioxid. 
 
 Example. — 100 cc. solution + precipitate, required 43.3 
 cc. hydrochloric acid. 1 liter of water contains then 
 [(43-3 — 2 X 7.0) — 1.1 X 3.3] X 10 milligrams total 
 carbon dioxid = [29.3 — 3.63] X 10 = 256.7 milligrams 
 total carbon dioxid. 
 
 4. Combined carbon dioxid. — 100 cc. of the water 
 are placed in an Erlenmeyer flask and 5 drops of phe- 
 nolphthalein solution are added, the water is heated 
 to boiling and titrated with hydrochloric acid (1 cc. = 
 1 milligram carbon dioxid) until after boiling for five 
 minutes the decolorized liquid does not again redden. 
 
 11. Alkalies — Potassium and Sodium 
 
 The estimation of potassium and sodium is necessary 
 only in rare instances. Usually the indirect method 
 will suffice, wherein the potassium and sodium is es- 
 timated as sodium sulphate. 
 
 250 cc. of water are evaporated to dryness after ad- 
 dition of excess of sulphuric acid, the residue is incin- 
 erated to drive off the excess of sulphuric acid, then 
 adding some ammonium carbonate and again incin- 
 erating. 
 
 The residue now contains only sulphates and silicic 
 acid. The calcium and magnesium is calculated to 
 sulphate, the silicic acid is added to it, and the whole 
 
102 PRACTICAL HYGIENE 
 
 subtracted from the total weight. The remainder is 
 sulphate of potassium and sodium, the former being 
 expressed as sodium sulphate. 
 
 i gram sodium sulphate = 0.437 g ram sodium oxid. 
 
 12. Iron 
 
 Iron is estimated according to the following method: 1 
 The following are the solutions required : 
 
 i. An oxid of iron solution of known strength, — 
 
 0.4306 gram pure crystalline ammonio-ferrous sulphate 
 is diluted to a liter, and some hydrochloric acid 
 added. 1 cc. = 0.00005 g ram iron, or 0.00035 gram 
 ferrous oxid. 
 
 2. Ammonium thiocyanate solution. — 7.5 grams 
 ammonium thiocyanate dissolved in 1 liter of water. 
 
 3, Hydrochloric acid (1 : 3). — The method is based 
 on the comparison of the intensity of the red color of 
 a water treated with acid ammonium thiocyanate 
 solution with the red color of a ferrous oxid solution 
 of known strength. It is a colorimetric method. 
 
 Method, — 500 cc. of water are placed in a porcelain 
 dish, nitric acid added, and then evaporated to about 
 50 cc, transferred to a measuring cylinder, and diluted 
 to 100 cc. 
 
 The liquid is now brought into a narrow cylinder 
 of colorless glass, set on white paper, and 5 cc. of the 
 ammonium thiocyanate solution and 1 cc. of diluted 
 hydrochloric acid are added to it. 
 
 Besides the cylinder are placed four other cylinders 
 
 A. Jolles : Arch. f. Hygiene, 8,' 402. 
 
ANALYSIS OF WATER 103 
 
 of the same kind ; into the first is placed i, into the 
 second 3, into the third 5, and into the fourth 7, 
 cc. of the ferrous oxid solution. These cylinders are 
 now filled with distilled water to 100 cc. and the color 
 compared after several minutes with that containing 
 the sample of water. 
 
 If its color compares with that of the fourth cylin- 
 der, there are in the 100 cc. concentrated water 7 X 
 0.00005 gram of iron, or 7 X 0.00035 g ram ferrous 
 oxid. This quantity of iron is contained in the 500 
 cc. of the water, or in a liter of the water there are 
 0.0007 gram or 0.7 milligram of iron, or 0.0049 g ram 
 ferrous oxid. 
 
 Quantitative estimation of iron in water, 1 — A stand- 
 ard solution of iron is made by dissolving 0.7 gram of 
 pure ammonia-ferrous sulphate in half a liter of water, 
 acidulating with sulphuric acid, adding sufficient per- 
 manganate solution to convert the iron exactly into 
 ferric salt, then diluting to a liter. Hydrogen peroxid 
 may also be used in place of permanganate, taking 
 care to dissipate the excess by boiling. 1 cc. of this 
 solution contains 1/10 milligram of iron. 
 
 Process. — Evaporate 100 cc. of the water to dryness 
 on a water-bath. Pour 1 cc. 50 per cent, nitric acid 
 over the residue and evaporate to dryness. Dissolve the 
 residue in 1 cc. 10 per cent, hydrochloric acid and add 
 about 10 cc. distilled water, filter and wash through a 
 small filter. Make up the filtrate to 50 cc. in a Nessler 
 tube. 1 cc. nitric acid is added and then tested with 1 
 
 1 According to Sutton's Volumetric Analysis, sixth edition, p. 
 194. 
 
104 PRACTICAL HYGIENE 
 
 cc. potassium ferrocyanid solution. The presence of free 
 acid facilitates the process. 
 
 A second Nessler tube is prepared containing i cc. 
 standard iron solution, i cc. nitric acid, enough distilled 
 water to fill up to the 50 cc. mark, and treated with 1 cc. 
 potassium ferrocyanid solution. If the color in the two 
 tubes is not the same other tubes are prepared, with more 
 or less of the iron solution, until one is found to compare 
 in color with that containing the sample of water. 
 
 Example. — The sample of water compared in color with 
 a tube containing 2.5 cc. of the standard iron solution, 
 hence it contained 2.5 X 1/10 milligram or 1/4 milli- 
 gram of iron in 100 cc. of the water, or 2.5 milligrams of 
 iron per liter of the water. 
 
 13. Oxygen 
 
 The estimation of oxygen in water is made accord- 
 ing to the method of L. M. Winkler. 1 It is based on 
 the fact that manganous chlorid in alkaline solution 
 is oxidized to manganic chlorid through the action of 
 oxygen, and with the manganic chlorid an equivalent 
 quantity of iodin is set free from an alkaline solution 
 of potassium iodid, the iodin liberated being deter- 
 mined by means of a titrated solution of sodium thio- 
 sulphate (Na 2 S 2 3 ). 
 
 The processes of the operation are as follows : 
 
 1. MnCl + 2NaOH = MnO H + 2NaCl 
 
 2Mnd H + O + H O = Mn CXH,. 
 
 22 1 ■ ■ 2 266 
 
 2. Mn 6 H 6 + 6HC1 = Mn Cl 6 + 6H O 
 Mn'CL + 2KI = 2MnCl 2 + I + 2KCI. 
 
 2 o ' 2 ' 2 ' 
 
 3. I + 2Na SO = Na S CX 4- 2NaI. 
 
 *J 2 ' 223 246 
 
 The following solutions are required : 
 
 1. Manganous chlorid solution of 40 per cent, 
 strength. 
 
 1 Ber. d. chem. Ges., (1888), 2843. 
 
ANALYSIS OF WATER IO5 
 
 2. Alkaline potassium iodid solution. 32 grains 
 nitrogen-free potassium hydroxid dissolved in 100 cc. 
 distilled water, to which are added 10 grams potassium 
 iodid. 
 
 3. Concentrated hydrochloric acid. 
 
 4. 1/100 normal sodium thiosulphate solution. 2.48 
 grams sodium thiosulphate dissolved in a liter of dis- 
 tilled water. 
 
 1 cc. = 0.055825 cc. O, at o° C. and 760 mm. 
 
 5. Starch solution as indicator. 
 
 The capacity of a glass-stoppered flask of about 500 cc. 
 is carefully determined when filled with distilled water 
 at 1 5 C. up to the stopper. This flask is then filled 
 with the water to be examined in such a manner as to 
 avoid bringing it too much in contact with air. 
 
 With a long pipette 4 cc. of the manganous chlorid 
 solution and 4 cc. of the alkaline potassium iodid 
 solution are introduced into the bottom of the flask, 
 the stopper put in place and then the flask shaken. 
 
 The yellowish-brown precipitate is allowed to sub- 
 side, and then 5 cc. of concentrated hydrochloric acid 
 are added, the stopper replaced and the flask shaken, 
 when the precipitate is again dissolved, but the liquid 
 becomes brown from the iodin. 
 
 The solution of sodium thiosulphate is now placed 
 into a burette graduated to 1/10 cc. 100 cc. of the 
 brown liquid are taken from the flask and placed 
 in an Erlenmeyer flask, and 2 cc. of starch solu- 
 tion are added when the liquid becomes bluish green. 
 The sodium thiosulphate solution is now added from 
 
106 PRACTICAL HYGIENE 
 
 the burette until the liquid becomes colorless. The 
 titration is controlled by a second titration. 
 
 If the volume of the flask is a cc, then the oxygen 
 in {a — 8) cc. of water has been determined. 
 
 If ioo cc. of the liquid required £cc. of sodium thio- 
 
 sulphate solution, then a cc. require cc. of sodi- 
 
 , 1 a — SXd 
 um thiosulphate, or X 0.0558 cc. oxygen. 
 
 This quantity was contained in a — 8 cc. ; then a 
 
 ,.-, r - 1000 X a X b X 0.0558 . 
 
 liter 01 water contains — — ? rr cc. otox- 
 
 100 X (a — 8) 
 
 ygen at o° C. and 760 mm. 
 
 14. Phosphoric Acid 
 
 A colorimetric method for the estimation of phos- 
 phoric acid in water, 1 — Since we know that the pro- 
 toplasm of the cells does not consist of albumin, in 
 the usual sense of the word, but of nucleo-proteids rich 
 in phosphorus, and that consequently, in the decom- 
 position of animal and vegetable excreta, we have not 
 only nitrogenous substances but also phosphorous com- 
 pounds gaining access to water. 
 
 In the method usually given for the determination 
 of phosphoric acid in water, the water (three liters) is 
 concentrated to a small volume, treated with nitric 
 acid, treated with ammonium phosphomolybdate 
 and the phosphoric acid precipitated from the water 
 is then estimated as magnesium pyrophosphate. In 
 this process the presence of organic matter causes the 
 
 Dr. Adolf Jolles : Arch. f. Hygiene, 34, 22. 
 
ANALYSIS OF WATER 107 
 
 result to express only from 65 to 80 per cent, of the 
 phosphoric acid present. By evaporating the water 
 to dryness and treating the residue with nitric acid, 
 and again evaporating to dryness, then dissolving the 
 residue in 10 cc. of dilute nitric acid, a much higher 
 result is obtained than in the former process. 
 
 Jolles' method is based on the fact that small amounts 
 of phosphoric acid salts produce a yellow color with 
 potassium molybdate, which color is increased in in- 
 tensity with increased temperature up to about 8o° C, 
 where the maximum intensity is obtained. The method 
 is extremely sensitive and allows the detection of 
 0.000025 g* ram phosphorus pentoxid, in the cold in 
 20 cc. of liquid, and in warm solutions 0.0000025 
 gram can be detected. 
 
 Reageitt. — Dissolve 8 grams chemically pure potas- 
 sium molybdate in 50 cc. of water and add 50 cc. 
 chemically pure nitric acid of 1.20 specific gravity and 
 filter. 
 
 Solution of sodium phosphate for comparisons, 
 
 NaHPO + 12HO. 
 
 2 4 ' 2 
 
 Solution A. — Fresh uncrystallized sodium phosphate, 
 53.23 grams, dissolved in a liter of water. This is a 1 
 per cent, solution. From this a series of dilute solutions 
 are prepared. 
 
 Solution B.— 10 cc. Sol. A -f 90 cc. H,0 = 0.1 % P,0 5 
 C— 10 cc. Sol. B 4- 90 cc. H,0 = 0.01 % P. 2 5 
 D.— 10 cc. Sol. C — 90 cc. H 2 == 0.001 % P 2 5 
 E — to cc. Sol. D — 90 cc. H 2 = 0.0001 % P,0 5 
 
io8 
 
 PRACTICAL HYGIENE 
 
 IO.O cc. 
 
 Sol. 
 
 C — 0.00 1 
 
 7-5 " 
 
 ' ' 
 
 C = 0.00075 
 
 5.0 " 
 
 i i 
 
 C = 0.0005 
 
 2-5 " 
 
 i i 
 
 C = 0.00025" 
 
 10.0 " 
 
 i i 
 
 D = 0.0001 
 
 7,5 " 
 
 ' ' 
 
 D = 0.000075 
 
 5-o " 
 
 i i 
 
 D = 0.00005 
 
 2-5 "' 
 
 i 1 
 
 D = 0.000025 
 
 10.0 " 
 
 i i 
 
 E = 0.0000 1 
 
 7-5 " 
 
 i i 
 
 E = 0.0000075 
 
 5.o " 
 
 1 1 
 
 E -— 0.000005 
 
 2-5 " 
 
 i i 
 
 E = 0.0000025 
 
 per cent. P 2 5 
 
 It is necessary to thoroughly remove all silicic acid 
 from the water as it is capable of yielding a yellow 
 color with the potassium molybdate. To accomplish 
 this a liter of the water to be examined is evaporated 
 to dryness in a platinum dish, the residue treated with 
 nitric acid, and again evaporated to dryness, at 130 
 C, then dissolved in dilute nitric acid and again evap- 
 orated to dryness, dissolved in nitric acid and filtered. 
 The filtrate is diluted to 20 cc, and then tested for 
 phosphoric acid ; the resulting color is compared with 
 the sodium phosphate solution. 
 
 15. Recording the Results in Water Analyses 
 
 The results obtained in the analysis of water for 
 sanitary purposes are recorded either according to the 
 English system (in grains per gallon of water) or ac- 
 cording to the metric system (in parts per 100,000 or 
 per 1,000,000 parts of water). 
 
 The metric system is the preferable one for our pur- 
 poses inasmuch as the metric system of weights and 
 measures has been employed exclusively in the de- 
 
ANALYSIS OF WATER 109 
 
 scription of the various methods of analysis and in the 
 preparation of the standard solutions. 
 
 In the different examples given under the various 
 methods the results have always been calculated to 
 milligrams per liter of water. With such a basis it 
 will be easy to express the results either in parts per 
 100,000 or in parts per 1,000,000, since the number of 
 milligrams per liter at once represent the parts in 
 1,000,000 parts of water, and, in consequence, this 
 method of recording the results is given the prefer- 
 ence. 
 
 If it is desired to express the results in grains per 
 gallon this is readily done by multiplying the results 
 in parts per 100,000 by 0.7 and the result obtained is 
 the number of grains per gallon. 
 
 16. Interpretation of the Results in Water Analyses 
 
 The form of the most serious pollution of water is 
 organic matter. This may be present as living orga- 
 nisms and the product of organic life, or the matter may 
 be present in various stages of decomposition. It is 
 customary to classify the condition of the organic mat- 
 ter by means of the condition of the nitrogenous or- 
 ganic matter. In this way the albuminoid ammonia 
 is taken as an indication of the amount of undecom- 
 posed organic matter. When decomposition has be- 
 gun its extent is indicated by the presence of so-called 
 free ammonia. Further changes result in converting 
 the free ammonia into nitrites, and finally into nitrates, 
 the last stage in the process of alteration by which 
 
IIO PRACTICAL HYGIENE 
 
 organic matter is converted again into a form suited 
 for assimilation by organic life. 
 
 It. is imprudent to state that because a water con- 
 tains unusually large amounts of any of these com- 
 pounds of nitrogen that it is necessarily polluted. The 
 signification of each compound may be stated briefly 
 as follows, it being understood that only surface wa- 
 ters are now under consideration : Albuminoid ammo- 
 nia was formerly considered as an indication of the 
 presence of an equivalent amount of organic matter 
 liable to decay, but within recent years it has been 
 found that this is not necessarily so. The lesson to 
 be learned from this compound is indicated most clearly 
 by successive analyses of a water, for if the albuminoid 
 ammonia remains unchanged for months without de- 
 velopment of free ammonia, a comparatively large 
 amount may be harmless. This is especially the case 
 with brown coloring-matter which water dissolves 
 from grasses, leaves, and roots, according to Dr. T. M. 
 Drown, who instances the very dark water of Acushuel 
 River, the source of New Bedford's supply, as a water 
 containing enough albuminoid ammonia to be classi- 
 fied as a polluted water according to most European 
 standards. 
 
 Free ammonia is a characteristic ingredient of sew- 
 age, but the conditions which influence its develop- 
 ment and accumulation in natural waters are so vari- 
 ous that one must be extremely cautious in deciding 
 what is the signification of its presence in individual 
 cases. It may be safely said that if an analysis shows a 
 large amount of free ammonia in a water from a catch- 
 ment area having dwellings upon it, further investiga- 
 
ANALYSIS OF WATER I I I 
 
 tion should be made into the causes of its presence. 
 
 Nitrites are compounds of much interest, as their 
 amount is generally found to vary less with the sea- 
 sons than the other organic derivatives, and they are 
 therefore a better index of sewage pollution. High 
 free ammonia and high nitrites together are character- 
 istic of recent pollution, and when they are uniformly 
 high in a surface water they point to continuous pol- 
 lution. 
 
 Nitrates indicate the complete change of organic to 
 inorganic matter, and their importance can only be 
 settled satisfactorily when the surface from which they 
 were derived is known. The organic matter that is 
 discharged into a w r ater is rarely dangerous if it is 
 given time to change to nitrates, but the disease germs 
 that may have been discharged at the same time may 
 still be a source of danger when the chemical changes 
 are over. Chemical analysis, by indicating the amount 
 of albuminoid and free ammonia, nitrites, and nitrates, 
 points to the possibility of such germs being in the 
 water and the time that has elapsed since they were 
 discharged into it. The time is probably least when 
 the albuminoid ammonia is high, and greatest when 
 the nitrates are high in the analysis. 
 
 Chlorin is also a valuable indication of sewage pol- 
 lution. The amount of chlorin found in natural wa- 
 ters varies greatly according to the proximity of the 
 ocean, deposits of salt, or the proximity of natural gas 
 and oil regions. In Massachusetts the chlorin content 
 of surface waters decreases as the distance from the 
 seashore increases. It is therefore necessary to know 
 
112 PRACTICAL HYGIENE 
 
 always the normal chlorin content of surface waters of 
 the locality from which the sample is derived before 
 deciding upon the signification of the amount found 
 in the sample analyzed. The chlorin in the reservoirs 
 of the Boston water system has been found to vary di- 
 rectly with the population upon the respective water- 
 sheds. High free ammonia, high nitrites, and high 
 chlorin are considered to afford complete proof of sew- 
 age pollution. Dr. Drown has pointed out, however, 
 that when the chlorin is not much above the normal 
 in waters containing high free ammonia and nitrites, 
 the inference is that the pollution comes from farm- 
 yards or manured fields, a distinction that is often im- 
 portant to make. 
 
 Wanklyn gives the following rules for the interpre- 
 tation of the results obtained in a water analysis: "If 
 a water yield o.oo part per 1,000,000 of albuminoid 
 ammonia it may be passed as organically pure, despite 
 much free ammonia and chlorin, and if, indeed, the 
 albuminoid ammonia amount to 0.02, or to less than 
 0.05 part per 1,000,000, the w^ater belongs to the 
 class of pure waters. When the albuminoid ammonia 
 amounts to 0.05 parts, then the proportion of free am- 
 monia becomes an element in the calculation ; and I 
 should be inclined to regard with some suspicion a 
 water yielding a considerable quantity of free ammo- 
 nia, along with 0.050 part of albuminoid ammonia. 
 Free ammonia, however, being absent or small, a wa- 
 ter should not be condemned unless the albuminoid 
 ammonia reaches something like 0.10 part per 1,000,- 
 000. Albuminoid ammonia above 0.10 per 1,000,000 
 
ANALYSIS OF WATER 
 
 113 
 
 begins to be a very suspicious sign; and over 0.15 
 part ought to condemn a water absolutely." 
 
 17. Limits of Impurity in Water 
 
 According to the amounts of impurity in water we 
 may form four classes into which we classify the wa- 
 ters according to the degree of pollution. These classes 
 are pure, usable, suspicious, and impure. In the fol- 
 lowing table these classes of water are given with the 
 degrees of impurities in each. 
 
 Table III. 
 Approximate Composition of Drinking-water. 
 
 (Stated in parts per million. ) 
 
 Chemical Con- 
 stituents. 
 
 Pure. 
 
 Usable. 
 
 Suspicious. 
 
 Impure. 
 
 Total Solids 
 
 70.000 
 
 430.000 
 
 430.000 to 
 
 710.000 
 
 710.000 
 
 Chlorin 
 
 14.000 
 
 40.000 
 
 40.000 to 
 
 70.000 
 
 70.000 
 
 X. as Nitrates 
 
 0.140 
 
 1. 120 
 
 1 . 200 to 
 
 2.400 
 
 2.400 
 
 N. as Nitrites 
 
 nil 
 
 nil 
 
 0.500 
 
 
 0.500 
 
 N. as free NH 3 
 
 0.020 
 
 0.050 
 
 0.050 to 
 
 O.IOO 
 
 O.IOO 
 
 N. as alb. NH 3 
 
 0.050 
 
 O.IOO 
 
 0. 100 to 
 
 0.125 
 
 0.125 
 
 Organic matter 
 
 0.250 
 
 1. 000 
 
 1. 000 to 
 
 1.500 
 
 1.500 
 
PART III 
 SOIL 
 
 i. MECHANICAL ANALYSIS 
 
 a. Collection of the Sample 
 
 In collecting a sample of soil for analysis it is im- 
 portant to exercise care in order that the portion col- 
 lected represent, as far as possible, the average com- 
 position of the soil of the locality. The surface cov- 
 ering is carefully removed and then, by means of a 
 spade, portions of equal thickness and extending to 
 the same depth are taken up and thoroughly mixed. 
 From the mixture obtained in this manner samples 
 may be taken for the analysis. In instances where it 
 is desired to ascertain the porosity and filtering capac- 
 ity of the soil in situ a sample may be taken by 
 means of a metal cylinder. 
 
 b. Separation of the Different Sized Grains 
 
 For hygienic purposes it is usually considered nec- 
 essary to separate the soil particles into a number of 
 groups corresponding to their size, because of the great 
 importance of the relative proportions of the number 
 of particles belonging to these different groups in a 
 particular soil from the influence it would exert upon 
 the health of the locality. The porosity and drainage 
 capacity of a soil are almost wholly dependent upon 
 
MECHANICAL ANALYSIS 115 
 
 the relative proportions which the size of the different 
 groups of soil particles bear to each other. A rela- 
 tively large quantity of soil particles falling within 
 the groups representing the smaller sized grains will 
 lessen, to a considerable degree, the adaptability of such 
 soil for a building site. Soil is damp or dry accord 
 ing to the preponderance of the smaller or larger sized 
 grains making up its structure. 
 
 Sieving the soil, — The separation of the soil parti- 
 cles into groups according to their sizes is accom-" 
 plished most readily by means of a set of sieves hav- 
 ing meshes of different sizes. Knopp has devised a 
 scale in which the soil particles are separated into six 
 groups according to their size, as follows: 
 
 1st group = particles coarser than 7 mm. 
 
 = coarse gravel. 
 
 2nd " = " ranging from 4 to 7 mm. 
 
 == medium gravel. 
 
 3rd " =. " " " 2 " 4 mm. 
 
 = fine gravel. 
 
 4th l ' — " " ". 1 " 2 mm. 
 
 = coarse sand. 
 
 5th " = " " " 0.3 " 1 mm. 
 
 = medium sand. 
 
 6th " = " finer than 0.3 mm. 
 
 = fine sand. 
 
 Process. — An average sample of the soil is taken, iooo 
 grams are carefully weighed, dried at ioo° C, and then 
 sieved. The quantity remaining in each of the sieves is 
 then weighed, as follows : 
 
 Coarse gravel = 544 grams. Coarse sand = 55 grams. 
 Medium " =156 grams. Medium " --=64 grams. 
 Fine " = 90 grams. Fine " = 90 grams. 
 
 Total = 999 grams, loss = 1 gram. 
 
 Elutriation. — The separation of the different sized 
 grains of soil into groups may also be accomplished 
 by the process known as elutriation. This is a very 
 delicate and tedious operation and is rarely employed 
 in the analysis of soil for hygienic purposes. This 
 
Il6 PRACTICAL HYGIENE 
 
 process is more generally employed in the analysis of 
 soil for agricultural purposes. 
 
 Knopp has devised a small apparatus for the further 
 separation of the soil particles comprising the sixth 
 group of his scale, those finer than 0.3 mm. in diame- 
 ter. This apparatus consists of a glass cylinder 55 
 cm. in height which is fitted with four glass tubes 
 with stop-cocks coming off from the side, the first at 
 10 cm. from the bottom, and the others 10 cm. above 
 each other. 
 
 Process. — The soil particles forming the sixth group 
 in the mechanical analysis described above, are placed 
 into the apparatus. Distilled water is then added until 
 it rises to a point 10 cm. above the highest glass tube. 
 The contents of the cylinder are now agitated thoroughly 
 for five minutes, then, after standing undisturbed for five 
 minutes, the stop-cock of the upper glass tube is opened 
 and the dirty water collected in a porcelain capsule. After 
 again agitating the contents of the cylinder for five min- 
 utes, and allowing another five minutes for the subsidence 
 of the coarser particles, the second stop-cock is opened 
 and this portion of dirty water is also collected in a por- 
 celain capsule. In like manner a third and fourth por- 
 tion are collected from the third and fourth tubes. The 
 cylinder is then again filled with distilled water, and, in 
 like manner, the dirty water from each of the tubes col- 
 lected in the capsules containing that portion previously 
 collected from each of the tubes. The dirty water col- 
 lected in each of the four porcelain capsules, as well as 
 the portion remaining in the bottom of the apparatus, is 
 then carefully evaporated to dryness and weighed. 
 
 2. PHYSICAL ANALYSIS OF SOIL 
 
 a. The Porosity of Soil 
 
 The porosity of a soil is dependent upon several dif- 
 ferent factors, as the looseness or compactness with 
 
MECHANICAL ANALYSIS 117 
 
 which the soil particles are packed together, the pre- 
 ponderance of the larger or smaller sized soil particles, 
 and also what is known as the " separate grain struc- 
 ture" of the different soil particles; t. e., whether they 
 are distinctly angular or distinctly spherical in form, 
 and the amount of gradation between these two ex- 
 tremes. All these factors have a direct bearing upon 
 the amount of air and water that the soil is capable of 
 taking up and also on the movement of the air and 
 water within the soil. It is evident that the volume 
 of the pores varies within wide limits in different soils. 
 
 Estimation of the porosity. — For the estimation of 
 the porosity of soil as it occurs in nature a metallic 
 cylinder — 20 cm. in height and 5 cm. in diameter — is 
 pressed into the soil and a corresponding portion of 
 the soil thus removed. The bottom of the cylinder is 
 closed with wire gauze or with a perforated metal 
 plate. According to the formula r 2 X 3.14 X// = the 
 volume of soil taken is 2.5 X 2.5 X 3.14 X 20 — 392.5 
 cc. This same cylinder may also be used to estimate 
 the porosity of a sample of soil taken from a mixture. 
 It is carefully filled with the soil and well packed by 
 tapping the cylinder on the work table. After the 
 sample of soil has been thus carefully collected it is 
 transferred from the cylinder to a 1000 cc. measuring 
 cylinder containing 500 cc. of distilled water. The 
 volume of the mixture of soil and water is then read 
 off, and this amount deducted from the sum of the 
 volume of soil and water employed — 500 -j- 392.5 cc. 
 = 892.5 cc. For instance, if the volume of the mix- 
 ture of soil and water is 840 cc, then the volume of 
 
Il8 PRACTICAL HYGIENK 
 
 the pores is 52.5 cc, or 392.5 : 52.5 :: 100 : x = 
 13.37 per cent., the porosity of the soil. 
 
 Pettenkofer's method, — Another method for esti- 
 mating the porosity of the soil, devised by v. Petten- 
 kofer, consists in placing the dried soil into a glass 
 tube 30 cm. in length, a portion 18 cm. in length 
 having a diameter of 25 mm., and the remaining 12 
 cm. only 5 mm. in diameter, which is graduated at 50 
 cc. The narrow portion of the tube is connected be- 
 low T with a burette by means of rubber tubing on 
 which is fastened a screw-clamp, the burette and rub- 
 ber tubing containing distilled water. The tube is 
 filled with the soil to be examined, up to the 50 cc. 
 mark ; then on opening the screw-clamp the water 
 passes into the tube, and when it appears just above 
 the column of the 50 cc. of soil in the tube the clamp 
 is closed and the quantity of water so used is noted by 
 reading the burette. 
 
 Calculation of the results. — 50 cc. of the dry soil ab- 
 sorbed 9.5 cc. of water; then 50 : 9.5 : : 100 : x = 19 per 
 cent., the porosity of the soil. 
 
 b. Water Capacity of Soil 
 
 According to the relative size of the soil particles, 
 and consequently the porosity of the soil, different 
 soils take up and retain varying quantities of water. 
 When the porosity is great the amount of w 7 ater re- 
 tained is small as compared with soil composed of 
 smaller particles. The water capacity of soil is ex- 
 pressed in per cent, of the volume of the pores. 
 
MECHANICAL ANALYSIS 119 
 
 i. Estimation with the metal cylinder. — The wa- 
 ter capacity of soil may be estimated by means of the 
 metal cylinder used in estimating the porosity. The 
 cylinder is weighed, and then filled with the sample 
 of soil and again weighed. The soil is now saturated 
 with water by holding the cylinder in a beaker of dis- 
 tilled water, whereby the water passes through the 
 perforated bottom of the cylinder and gradually dis- 
 places all the air and fills the pores of the soil. As 
 soon as the surface of the soil is covered by the water 
 within the cylinder, and every portion of the soil has 
 been thoroughly saturated, the cylinder is removed 
 from the beaker and the excess of the water allowed 
 to drain away. When the water has ceased dropping 
 the exterior of the cylinder is carefully dried. The 
 weight of the cylinder and moistened soil are now as- 
 certained, when the increase in the weight of the 
 cylinder will represent the weight of the water re- 
 tained in the soil. 
 
 Example. — The porosity of the soil has been found to 
 be 13.37 P er cent. 
 
 Weight of cylinder and soil 1050 grams, 
 
 empty 250 grams. 
 
 ' ' the soil 800 grams. 
 
 Volume of the soil 39 2 -5 cc. 
 
 After saturation with water — 
 
 Weight of cylinder and moistened soil 1095 grams. 
 
 dry " 1050 grams. 
 
 Increase in weight of the soil 45 grams. 
 
 Therefore 800 grams, or 392.5 cc. of soil have retained 
 45 grams, or 45 cc. of water. The 392.5 cc. of soil, have 
 pores equal to 52.5 cc, or 13.37 P er cent. Of the 52.5 
 cc. of pores 45 cc. remained filled with water, or 
 52.5 : 45 : : 100 : ^=85.81 cc, or 85.81 per cent. = 
 the water capacity. 
 
120 PRACTICAL HYGIENE 
 
 The soil may also be moistened by slowly pouring 
 the water into the top of the cylinder until it pene- 
 trates through the soil and flows out at the bottom. 
 The results obtained by these two methods are not 
 exactly the same ; the former method gives somewhat 
 higher results and seems most likely to afford results 
 that are satisfactory. 
 
 2. The Pettenkofer apparatus. — The water capac- 
 ity of the soil may also be estimated by means of the 
 Pettenkofer apparatus. After the soil has been mois- 
 tened with water, as in the determination of the po- 
 rosity, the reading of the burette is taken. The rubber 
 tubing is now removed and the excess of water allowed 
 to drain away and collected in a graduated measur- 
 ing cylinder. The difference between the reading of 
 the burette and the water drained away will represent 
 the water capacity, or the amount of water retained 
 in the soil. 
 
 c. The Drainage Capacity of Soil 
 
 The drainage capacity of a soil is of great hygienic 
 importance, and, like the porosity and water capacity, 
 is dependent upon the " separate grain structure " of 
 the soil. It is directly dependent upon the water ca- 
 pacity since it represents the quantity of water that is 
 capable of penetrating through it. The unit of meas- 
 urement of the drainage capacity of soil is the amount 
 of water that is capable of penetrating through a defi- 
 nite volume of clean, coarse sea gravel. If, for in- 
 stance, 50 cc. of coarse sea gravel absorb 40 cc. of wa- 
 ter, as estimated by the Pettenkofer method, of which 
 
MECHANICAL ANALYSIS 121 
 
 35 cc. drain away, — equal to 70 cc. of water for 100 
 cc. of gravel. The 70 cc. of water draining away 
 from 100 cc. of gravel are represented as 1 in the com- 
 parison of the drainage capacity of any soil with coarse 
 sea gravel, the result being expressed in decimal frac- 
 tions of 1, the unit of comparison. 
 
 Example. — 50 cc. of a sample of soil are placed in the 
 glass tube of the Pettenkofer apparatus and the water 
 allowed to pass slowly from the burette until it covers 
 the column of soil to the extent of several centimeters, 
 w r hen the excess of water is allowed to flow 7 back until it 
 is just on a level with the surface of the column of soil. 
 The quantity of water absorbed by the soil is then noted, 
 indicating the porosity of the soil. The water is now al- 
 lowed to drain away from the soil and is collected in a 
 100 cc. measuring cylinder, representing the drainage 
 capacity of the soil, while the amount of water retained 
 represents the water capacity. If the 50 cc. of soil used 
 absorbed 25 cc. of water, its porosity is equal to 50 per 
 cent. Of the 25 cc. of water absorbed 15 cc. drained 
 away, or 30 cc. with 100 cc. of the soil. Therefore the 
 drainage capacity is 70 : 30 : : 1 : .r = 0.428, coarse sea 
 gravel being taken as unity. 
 
 d. Estimation of Moisture in Soil 
 
 Soil moisture is estimated by taking a known quan- 
 tity of the soil, 10 or 100 grams, drying it at ioo° 
 C, and again weighing it. The loss in weight repre- 
 sents the amount of moisture driven off. The result 
 is expressed in per cent, of the volume of soil taken. 
 
 e. Estimation of the Level of the Ground-water 
 
 At varying depths below the surface of the soil all 
 the interstices are filled with water, the level of which 
 is subject to fluctuation from various causes, as the 
 
122 PRACTICAL HYGIENE 
 
 amount and frequency of rainfall, the proximity to 
 streams and bodies of water either above or below the 
 surface, the amount of evaporation that takes place 
 from the surface, the nature of the surface covering, 
 etc. The movement of the ground-water takes place 
 both vertically and horizontally. Since it has been 
 supposed that the height of the level of the ground- 
 water influences to some extent the propagation and 
 spreading of certain diseases, as typhoid fever and 
 cholera, it is considered necessary for the hygienist to 
 study the movements and fluctuations in the level of 
 the ground-water. 
 
 The height of the level of the ground-water may be 
 determined by ascertaining the depth at which water 
 stands in a well, or in special borings made for the 
 purpose. The measurement is made either by means 
 of a long rod or a weighed tape-measure. A special 
 apparatus devised by Pettenkof er for this purpose con- 
 sists of a number of small cups fixed to a rod which 
 is lowered into the water when the uppermost cup that 
 contains water indicates the level of the water. Sev- 
 eral other mechanical devices have been constructed 
 for this purpose. The measurement must be made 
 from a fixed point at the top of the well and the ele- 
 vation of this point above the sea-level accurately de- 
 termined. For purposes of comparison it is also nec- 
 essary to make a number of observations on other 
 wells or on borings in the vicinity. It is also neces- 
 sary to determine the effect, upon the level of the wa- 
 ter, of pumping water from the well for some hours. 
 
MECHANICAL ANALYSIS 1 23 
 
 Course of the ground-water. — The direction in 
 which the ground-water moves is influenced by the 
 direction in which surface streams are flowing, since, 
 like these, it usually tends toward the sea. The direc- 
 tion and degree of movement which it undergoes may 
 be determined by placing some substance in one of a 
 series of borings and noting the direction and rapidity 
 of the movement by computing the time required to 
 convey the substance used to the surrounding borings 
 in succession whereby the direction of the movement 
 will also be indicated. 
 
 f. Estimation of the Amount of Carbon Dioxid in 
 Soil Air 
 
 The amount of carbon dioxid in soil air is obtained 
 by means of the Pettenkofer tube method. The ab- 
 sorption tube containing barium hydroxid solution of 
 double strength is attached to the top of a driven well, 
 by means of glass and rubber tube connections: The 
 air is aspirated through the absorption tube by means 
 of an aspirator. The driven wells used for this pur- 
 pose consist of an iron cylinder, closed at the lower 
 end, about 2 meters in length, which are driven into 
 the soil. The lower end of the tube is closed with a 
 pointed metal cap, above which are the perforations 
 for the entrance of the soil air. The top of the tube 
 is closed by means of a metal screw-cap. In order to 
 procure the sample of air from the bottom of the well 
 a glass tube is lowered into the well and held in place 
 by a closely fitting perforated cork, so that the top of 
 the tube is on a level with the top of the well and may 
 be connected with the Pettenkofer absorption tube. 
 
124 PRACTICAL HYGIENE 
 
 g. Estimation of the Soil Temperature 
 
 The soil temperature is estimated by constructing a 
 well 3 meters in depth, lined with wood, into which 
 a block of wood of the same size will slide easily. At- 
 tached to this sliding block of wood are several ther- 
 mometers, one above the other, penetrating to definite 
 depths of the soil. The block of wood carrying the 
 thermometers may be so constructed as to allow its 
 being raised and lowered by means of a weight and 
 pulley. 
 
PART IV 
 SANITARY ANALYSIS OF FOODS 
 
 CHAPTER 1. MILK 
 
 Nature and composition of milk, — Milk, the secre- 
 tion of the mammary glands of mammels, is an aque- 
 ous solution of casein, lactose, and small quantities 
 of mineral matter, and holds in suspension a quantity 
 of fat in the form of minute globules. Normal milk 
 is an opaque, white or yellowish-white liquid, of some- 
 what sweetish taste, and possesses an odor resembling 
 that of the animal from which it has been derived. 
 The reaction of fresh milk is amphioteric ; i. e., it turns 
 red litmus blue and blue litmus red. Its specific grav- 
 ity ranges from 1028 to 1035. 
 
 Composition of Milk (Hirt). 
 
 
 Water 
 
 Casein 
 
 A1UU- 
 
 min 
 
 JLUlcU p , 
 
 Albumin 
 
 Lactose 
 
 Salts 
 
 Human 
 
 87.09 
 
 0.63 
 
 2-35 
 
 2.48 3.90 
 
 6.04 
 
 0.49 
 
 Cow 
 
 87.41 
 
 3.01 
 
 0.75 
 
 3.41 3.66 
 
 4.82 
 
 0.70 
 
 Ewe 
 
 81.63 
 
 4.09 
 
 1.42 
 
 6.95 5-83 
 
 4.86 
 
 0.73 
 
 Ass 
 
 90.04 
 
 O.60 
 
 i-55 
 
 2.00 I.39 
 
 6.25 
 
 0.31 
 
 Mare 
 
 90.71 
 
 1.24 
 
 0.75 
 
 2.05 1. 17 
 
 5-70 
 
 0.37 
 
 Goat 
 
 89.91 
 
 2.87 
 
 1. 19 
 
 3.69 4.09 
 
 4-45 
 
 O.86 
 
 EXAMINATION OF MILK 
 a. Physical Examination 
 
 The physical examination of milk embraces the de- 
 tection, through the senses, of such variations in its 
 
126 PRACTICAL HYGIENE 
 
 character as are denoted by its appearance, taste, and 
 odor when compared with a sample of fresh milk. 
 
 i. Specific gravity. — The specific gravity of milk 
 varies with the temperature, the average at 15 C. 
 being 1030; at 37.5 C, the specific gravity of the 
 same milk is 1024. The specific gravity of milk is 
 lowered by the addition of w r ater, while the removal 
 of fat raises its specific gravity, and, consequently, the 
 normal specific gravity of good milk may be main- 
 tained by the simultaneous addition of water and the 
 removal of fat. This is a common form of adultera- 
 tion of market milk. 
 
 Determination of the specific gravity. — The specific 
 gravity of milk may be determined by means of the 
 lactodensimeter of Quevenne. The scale of this in- 
 strument shows the specific gravity in degrees Que- 
 venne by using only the second and third decimal, as 
 32 ° Quevenne indicates a specific gravity of 1032. 
 
 The sample of milk is well mixed by pouring it 
 several times from one vessel into another, or by gen- 
 tly agitating it for several minutes, w T hen it is trans- 
 ferred to the cylinder of the instrument, filling it up to 
 the mark near the top. The temperature of the milk 
 is now noted with a small mercurial thermometer. 
 The lactodensimeter is then dried and floated in the 
 milk. When it has become quiet the eye is brought 
 on a level with the surface of the milk and the de- 
 grees Quevenne read off on the scale, using the kwer 
 meniscus. A second, or control, observation should 
 always be made. 
 
ANALYSIS OF FOODS 1 27 
 
 The reading of the specific gravity is, however, only 
 correct when the temperature of the milk is at 15 C. 
 If this is not the case a correction of the reading is 
 necessary. For each degree above 15 C, 0.2 degree 
 Quevenne must be added to the observed reading, 
 while a corresponding amount must be subtracted from 
 the reading for each degree below 15 C. 
 
 The specific gravity of milk increases during the 
 first twenty-four hours from 1 to 1.5 degrees Que- 
 venne, and it is preferable, therefore, to place the sam- 
 ple of milk on ice for several hours before making the 
 observation. The specific gravity of milk is also 
 readily determined by means of a Westphal balance. 
 In this determination the temperature of the milk 
 should be, as nearly as possible, at 15 C. 
 
 2. Estimation of fat in milk. — In the examination 
 of market milk by inspectors the fat is usually deter- 
 mined by means of optical methods. 
 
 a, Lactoscope. — The lactoscope of Feser is com- 
 monly employed for this purpose in Germany. The 
 principle on which this instrument operates rests upon 
 the fact that the degree of opacity of milk is depend- 
 ent upon the percentage of fat that it contains, the 
 higher the percentage of fat the larger the amount of 
 water that has to be added to the milk to render it 
 transparent. 
 
 The lactoscope consists of a glass tube 3 cm. in di- 
 ameter and 17 cm. long, the lower 5 cm. of the tube 
 being only 2.3 cm. in diameter. Within this lower 
 portion is a cylinder of white, opaque glass on which 
 
128 PRACTICAL HYGIENE 
 
 is a scale of six black lines. The expanded portion 
 of the tube also bears a scale which denotes the per- 
 centage of fat in the milk. Each instrument is ac- 
 companied with a small pipette graduated at 4 cc. 
 With this pipette 4 cc. of milk, well mixed, are trans- 
 ferred to the lactoscope, when the dark lines on the 
 cylinder of opaque glass in the bottom of the tube 
 cannot be seen. Water is now added, in small quan- 
 tities, after repeated agitation, until the dark lines are 
 just visible and can be counted when the instrument 
 is held between the eye of the observer and a white 
 wall. The amount of diluted milk in the tube is then 
 read off on the larger scale, denoting the per cent, of 
 fat in the milk. 
 
 b. Cremometer. — This instrument consists of a glass 
 cylinder into which 150 cc. of milk are placed and 
 allowed to stand in a warm room for twenty-four hours. 
 The cylinder bears a scale at the top on which the 
 amount of cream is denoted. The reading of the 
 amount of cream is made on the scale of the instru- 
 ment, each division of the scale representing one per 
 cent, of cream when the instrument is filled to the 
 highest mark of the scale. 
 
 These instruments are even less accurate than the 
 lactoscope, though they afford definite knowledge, 
 within fairly narrow limits, of the fat content of a 
 sample of milk. 
 
 b. Chemical Analysis of Milk 
 
 1. Total solids. — 10 cc. of milk are placed in a 
 weighed porcelain crucible and carefully weighed. 
 The milk is then evaporated to dryness in the drying 
 
ANALYSIS OF FOODS 1 29 
 
 oven at ioo° C. When cool the residue is weighed. 
 
 Example. — Grams. 
 
 Weight of empty crucible I2 -73 
 
 " milk and " 22.84 
 
 " " alone io.ii 
 
 ft " residue 1.32 
 
 Per cent, of solids in the milk = 13.056 
 
 2. Ash. — The evaporation residue is carefully in- 
 cinerated at a low temperature until it is fully white 
 when the crucible is again cooled and weighed. 
 
 Example. — Grams. 
 
 Weight of crucible and residue 1 4-°5 
 
 " " ash 12.781 
 
 " " ash 0.051 
 
 Per cent, of ash in the milk = 0.504 
 
 3- Fat.— 
 
 a. The Extraction Method, — About 10 grams of 
 milk are carefully weighed in a glass or porcelain cap- 
 sule and mixed with about 10 grams of freshly ignited 
 sand, pumice stone, or asbestos, and evaporated to dry- 
 ness on a water-bath. 
 
 The dish, with its contents, is then finely pulver- 
 ized and transferred to a Soxhlet extraction apparatus, 
 and the fat extracted with ether for at least five hours. 
 The ether extract of the flask is then evaporated to 
 dryness on a water-bath and the residue dried to con- 
 stant weight (at ioo° C.) and weighed. The increased 
 weight of the flask will represent the fat in the 10 
 grams of milk. 
 
 b. Estimation of fat by means of the lactobutyrom- 
 eter. — The method depends on the solution of the 
 fat in ether through the action of alcohol. From the 
 
 9 
 
13° 
 
 PRACTICAL HYGIENE 
 
 volume of the ethereal fat solution is calculated the 
 per cent, of fat in the milk. 
 
 Process. — The lactobutyrometer consists of a glass 
 tube of 40 cc. capacity, closed at its lower end. 10 cc. 
 of milk are first placed into the tube, then 10 cc. of ether 
 (sp. gr. 0.725-0.730, at 1 5 C.) are added thereto. The 
 mouth of the tube is closed with the thumb or a soft cork 
 and the solutions gently mixed until a homogeneous mix- 
 ture is obtained, carefully lifting the stopper from time 
 to time. Now 10 cc. of 91 per cent, alcohol (sp. gr. 
 0.8203) are added and again agitated for several minutes, 
 until the small clumps of casein are evenly distributed, 
 when the tube is placed in a cylinder containing water at 
 40 ° C. After fifteen or twenty minutes, when the clear, 
 yellowish ethereal fat solution has risen to the top of the 
 tube, the tube is placed in a cylinder filled with w r ater at 
 20 C, when further portions of fat will rise to the sur- 
 face. The amount of ethereal fat solution is now noted 
 by reading the scale of the instrument, when the per 
 cent, of fat can be determined by reference to Table IV. 
 
 Table IV 
 
 Lactobutyrometer Table of Tollens and Schmidt 
 
 (From Lehmann's Handbuch.) 
 
 A 
 
 B 
 
 A 
 
 B 
 
 A 
 
 
 B 
 
 1/10 cc. 
 
 % Fat 
 
 1 10 cc. 
 
 % Fat 
 
 1 10 cc. 
 
 % Fat 
 
 1.0 
 
 1-339 
 
 8.0 
 
 2.767 
 
 14.5 
 
 4-093 
 
 1.5 
 
 1. 441 
 
 8.5 
 
 2.869 
 
 15.0 
 
 4 
 
 195 
 
 2.0 
 
 1.543 
 
 9.0 
 
 2.971 
 
 15-5 
 
 4 
 
 297 
 
 2.5 
 
 1.645 
 
 9-5 
 
 3.073 
 
 16.0 
 
 4 
 
 399 
 
 3-0 
 
 1.747 
 
 IO. O 
 
 3.175 
 
 16.5 
 
 4 
 
 501 
 
 3-5 
 
 I.849 
 
 10.5 
 
 3.277 
 
 17.0 
 
 4 
 
 628 
 
 4.0 
 
 I-95I 
 
 II. O 
 
 3-379 
 
 17-5 
 
 4 
 
 792 
 
 4-5 
 
 2.053 
 
 11. 5 
 
 3.481 
 
 18.0 
 
 4 
 
 956 
 
 5-o 
 
 2.155 
 
 12.0 
 
 3o83 
 
 18.5 
 
 5 
 
 129 
 
 5-5 
 
 2.257 
 
 12.5 
 
 3.685 
 
 19.0 
 
 5 
 
 306 
 
 6.0 
 
 2-359 
 
 13.0 
 
 3.787 
 
 19-5 
 
 5 
 
 483 
 
 6.5 
 
 2.461 
 
 13.5 
 
 3.889 
 
 20.0 
 
 5 
 
 660 
 
 7.0 
 
 2.563 
 
 14.0 
 
 3.991 
 
 20.5 
 
 5 
 
 837 
 
 7.5 
 
 2.665 
 
 
 
 
 
 
ANALYSIS OF FOODS 131 
 
 c. The Babcock method. — A method of determining 
 fat in milk which is in very general use by dairymen 
 and creameries, and which is giving very general sat- 
 isfaction, is known as the Babcock method. In this 
 method a centrifugal machine is used which is capa- 
 ble of making from 700 to 1200 revolutions per min- 
 ute. In this method the casein is dissolved by sul- 
 phuric acid and the separation of the fat is then aided 
 by the centrifugal apparatus. The test-bottles con- 
 taining the samples of milk are revolved in a tank 
 filled w T ith hot water (about 95 ° C). The acid and 
 dissolved casein in the milk being heavier than the 
 fat are thrown outward (to the bottom of the test-bot- 
 tle) by the rapid motion of the machine, while the fat 
 rises to the top and collects in the graduated neck of 
 the test-bottle. The separation of the fat is rapid and 
 very complete. If the whirling is carried out as soon 
 as the acid is mixed with the milk it will not be nec- 
 essary to fill the tank with hot water, as the addition 
 of the strong acid to the milk generates enough heat 
 to cause the fat to rise to the top. 
 
 Process. — With the graduated pipette measure off 
 17.6 cc. of milk and place it into the test-bottle. Great 
 care must be exercised to have the milk and cream uni- 
 formly mixed before taking the sample. Add to the milk 
 in the test-bottle 17.5 cc. of commercial sulphuric acid, 
 specific gravity 1.82. If too little acid is added the casein 
 is not all dissolved or is not all held in solution through- 
 out the test and an imperfect separation of fat results. 
 If too much acid is added the fat itself is attacked. After 
 adding the acid to the milk they should be thoroughly 
 mixed together by gently shaking with a rotary motion. 
 There is a large amount of heat evolved on mixing the 
 acid and milk, and the solution, at first nearly colorless, 
 
132 PRACTICAL HYGIENE 
 
 soon changes to a very dark brown, owing to the char- 
 ring of the milk-sugar and perhaps some other constitu- 
 ents of the milk. 
 
 As soon as the bottles have been whirled for five min- 
 utes they are filled up to the neck with hot distilled water 
 and whirled for one minute, then filled up to the seven 
 per cent, mark with hot water and again whirled for two 
 minutes, after wdiich the amount of fat is read off on the 
 graduated neck of the test-bottle. The fat, when meas- 
 ured, should be warm enough to flow readily, so that the 
 line between the acid liquid and the column of fat will 
 quickly assume a horizontal position when the bottle is 
 removed from the machine. Any temperature between 
 45 C. and 65 C. will answer, but the higher temperature 
 is to be preferred. The slight difference in the length of 
 the column of fat due to the difference in temperature is 
 not sufficient to materially affect the results. 
 
 To measure the fat, take the bottle from its socket in 
 the machine, and, holding it in a perpendicular position, 
 with the scale on a level with the eye, observe the divi- 
 sions which mark the highest and lowest limits of the 
 fat. The difference between these gives the per cent, of 
 fat directly. Five of the divisions on the scale on the 
 neck of the test-bottle are equal to 1 per cent, of fat when 
 17.6 cc. of milk are used in the test, it being assumed 
 that the specific gravity of the butter-fat, at the temper- 
 ature at which the reading is made (about 48 C), is 0.9. 
 The reading can easily be taken to the half division, or 
 to one-tenth per cent. In reading the position of the 
 upper level of the column of fat it is important to select 
 the point where the upper surface of the fat meets the 
 side of the tube. 
 
 The Babcock method can also be employed to deter- 
 mine the fat in cream, in skim-milk, buttermilk, and in 
 whey. In testing the fat in cream 18 cc. should be taken 
 instead of 17.6 cc. The reason for this is that cream is 
 lighter than milk and more of the former always adheres 
 to the pipette. A special cream te^t-bottle is to be used 
 for the purpose of making the determination. For skim- 
 milk a test- bottle of twice the ordinary size is usually 
 employed. 
 
ANALYSIS OF FOODS 1 33 
 
 The test -bottles should always be cleaned out as soon 
 as the reading has been recorded. If the bottles are al- 
 lowed to cool before cleaning it will prove far more diffi- 
 cult. It is best to rinse them thoroughly with hot water, 
 or hot water containing caustic soda solution. 
 
 d. The Leff man-Beam method. — This method is 
 somewhat similar to the Babcock method inasmuch 
 as the fat is separated with the aid of a centrifugal 
 machine. In this method the casein is dissolved with 
 3 cc. of a mixture of equal parts of amyl alcohol and 
 strong hydrochloric acid, and sufficient concentrated 
 sulphuric acid to fill the bottle up to the neck. 
 
 Process. — 15 cc. of a well-mixed sample of milk are 
 placed into the test-bottle, and then 3 cc. of amyl alcohol 
 and hydrochloric acid added and mixed ; then the con- 
 centrated sulphuric acid is added and the liquids thor- 
 oughly mixed. The neck of the bottle is now filled to 
 about the zero-point with a freshly prepared mixture of 
 sulphuric acid and water. The bottle is placed in the 
 centrifugal machine and whirled for one to two minutes 
 when the amount of fat is read off on the graduated neck 
 of the bottle. 
 
 CHAPTER II. BUTTER 
 
 Composition of Butter. — 
 
 Per cent. 
 Fat .... 87.0 
 
 Water. . . . 11. 7 
 
 Casein . . . . 0.5 
 
 Lactose + lactic acid . 0.5 
 
 Mineral matter . . . 0.3 
 
 Adulteration of Butter. — 
 
 a. By the addition of water and salt in excess. 
 
 b. By the addition of other fats, as beef, swine or 
 
134 PRACTICAL HYGIENE 
 
 vegetable fats, as cocoanut butter, cottonseed oil, etc. 
 For the adulteration of butter these fats must first be 
 mixed with water so that they may resemble butter. 
 Margarine and butterine are examples of artificial butter. 
 Well-cleaned, melted beef-fat is allowed to solidify 
 at 35 C. and then pressed to remove the heavy melted 
 stearin; the oleomargarine is then treated with sour 
 milk, coloring-matter, and oil to convert it into arti- 
 ficial butter. 
 
 The examination of butter includes the estimation 
 of water, mineral matter, and testing for foreign fats. 
 
 a. Water 
 
 Into a platinum crucible are placed 5 grams of incin- 
 erated asbestos in threads, and a glass rod. This is 
 dried at ioo° C. and weighed. 10 grams of butter 
 are now weighed accurately and placed in the cruci- 
 ble, melted on the water-bath ; the fat is well mixed 
 with the asbestos, and dried at ioo° C. to constant 
 weight. 
 
 b. Mineral Matter 
 
 10 grams butter are placed in a porcelain crucible, 
 weighed and melted, and the larger part of the fat is 
 removed by filtration by passing through a filter with- 
 out ash, washing with ether. The filter is then again 
 placed in the crucible and the residue incinerated un- 
 til it is white and then weighed again. 
 
 c. Fat, Casein, and Ash 
 
 The dried residue from the water determination is 
 treated with 76 ° benzine and stirred until the lumps 
 
ANALYSIS OF FOODS 1 35 
 
 disappear. The contents of the dish are then trans- 
 ferred to a weighed crucible with the aid of a wash- 
 bottle containing benzine, and weighed until free from 
 fat. The contents of the crucible are now dried at 
 ioo° C. for two hours and weighed. This weight, 
 less the weight of the crucible, represents the weight 
 of the casein and ash. The w T eight of the fat is calcu- 
 lated from the data obtained. 
 
 The contents of the crucible are then ignited, below 
 a red heat, and then weighed again. The loss in 
 weight represents the casein, the remainder the min- 
 eral matter, chiefly salt. 
 
 d. Foreign Fats 
 
 The pure fat is prepared by melting butter, heat- 
 ing to 60 ° C, and filtering off the clear fat from the 
 residue. 
 
 Milk-fat consists of a variable quantity of triglyc- 
 erides of different fatty acids, of which the principal 
 amount is the glyceride of stearic, palmitic, and oleic 
 acids (83 to 90 per cent.); the remainder consists of 
 glycerides of the so-called volatile fatty acids (butteric, 
 capronic, caprylic, and caprinic). 
 
 In all other animal or vegetable fats the glycerides 
 of the volatile fatty acids are present in quantities of 
 5 per cent., the milk-fat being characterized by the 
 high proportion of combined volatile acids. 
 
 Consequently the estimation of the volatile fatty 
 acids is the safest method to discover adulteration of 
 the milk-fat. The Reichert-Meissl method is best 
 adapted for this purpose. 
 
136 PRACTICAL HYGIENE 
 
 5 grams of clear, filtered fat are placed in a round- 
 bottomed flask of about 300 cc. capacity and carefully 
 weighed, and 2 cc. of the sodium hydroxid solution 
 and about 10 cc. of alcohol (96 per cent.) are added. 
 The mixture is shaken and placed on a boiling watei- 
 bath for fifteen minutes, then the alcohol is distilled 
 off. 100 cc. distilled water are now placed in the 
 flask and it is again placed on the water-bath for fifteen 
 minutes so that the soap is fully dissolved. It is 
 essential to have the flask closed with a well-fitting 
 cork at all times so as to exclude the carbon 
 dioxid of the air. To the contents of the flask 
 are now added several granules of pumice stone 
 and 40 cc. dilute sulphuric acid of which 30 to 
 32 cc. = 2 cc. of the sodium hydroxid solution, and 
 the flask connected with a condenser. The flask 
 is heated with a small flame until the insoluble 
 fatty acids are melted to a transparent mass, during 
 which time (about half an hour) exactly no cc. have 
 been distilled over. The distillate is now well mixed 
 and 100 cc. filtered through a dry. filter into a beaker 
 holding 200 to 250 cc, 0.5 cc. phenolphthalein solu- 
 tion added, and titrated with 1/10 normal sodium hy- 
 droxid solution until a red color is produced. The 
 number of cubic centimeters of sodium solution used 
 should be increased by one-tenth. The Meissl degree 
 expresses the number of cubic centimeters of 1/10 
 normal solution of sodium hydroxid that are required 
 to neutralize no cc. of the distillate derived from 5 cc. 
 of fat. At its lowest this is 26. The Meissl degree 
 for animal and vegetable fat is 0.6-1.0; of cocoa-fat, 
 7.0 
 
ANALYSIS OF FOODS 1 37 
 
 If the Meissl degree is below 26, and the fat ap- 
 pears otherwise normal, there is no doubt that it has 
 been adulterated with cheaper fats. 
 
 If a = the Meissl degree then the mixture of fat 
 contains 3.J (a — 0.6) per cent, milk-fat. 
 
 Example. — 5 grams of fat were taken, and for 100 cc. 
 of distillate 15.2 cc. of tenth normal sodium hydroxid so- 
 lution were required, and the Meissl degree is 15.2 + 
 1.52 = 16.72. 
 
 The fat was therefore not pure, but contained only 
 3.7 (16.72 — 0.6) or 59.6 per cent, of milk-fat, and 
 40.4 per cent, of foreign fat. 
 
 e. Melting-point 
 
 The melting-point of fat can also be employed to 
 detect adulteration. 
 
 The melted fat is drawn into a capillary glass tube 
 which is then sealed at the lower end, the other end 
 being attached to the bulb of a mercurial thermometer 
 by means of a piece of rubber tubing, and then pla- 
 cing it into a wider cylinder containing glycerin. The 
 latter is then warmed with a small gas flame, observ- 
 ing when all the fat is entirely melted, and observing 
 the thermometer. This indicates the melting-point 
 of the fat. 
 
 Melting-point of Fats 
 
 Milk-fat . . . 33-37° C. 
 
 Beef-fat . . 4i~47° C. 
 
 But since the addition of various oils may influence 
 the melting-point of the mixture this is not a reliable 
 method. 
 
138 PRACTICAL HYGIENE 
 
 f . Solubility in Hot Alcohol 
 
 A more reliable method is the determination of the 
 solubility of the fat in hot alcohol. 
 
 The fat is melted on a boiling water-bath and 
 filtered. 5 cc. are taken and placed in a round flask 
 of 60 cc. capacity, 20 cc. of absolute alcohol are added, 
 and the flask set in the water-bath and boiled for two 
 minutes. Pure butter-fat is wholly soluble in alcohol 
 and remains clear at the room temperature longer than 
 120 seconds, while other fats (as suet and lard) are not 
 easily dissolved to clear solution and become cloudy 
 when removed from the water-bath within 60 seconds. 
 
 g. Detection of Preservatives 
 
 1. Boric acid. — 10 grams butter are saponified in a 
 platinum crucible w T ith alcoholic caustic potash solu- 
 tion, evaporated to dryness, and incinerated. The ash 
 is treated with hydrochloric acid and tested with cur- 
 cuma paper which in the presence of boric acid, after 
 drying at ioo° C, turns red, and when treated with a 
 solution of sodium carbonate is turned blue. 
 
 2. Salicylic acid. — 4 cc. of 20 per cent, alcohol are 
 placed in a test-tube and two or three drops of dilute 
 ferric chlorid are added. To this 2 cc. of butter-fat 
 are added and shaken. When salicylic acid is pres- 
 ent the lower portion of the solution is colored violet. 
 
 3. Formaldehyde. — 50 grams of butter are placed 
 into a 250 cc. flask with 50 cc. water and melted, and 
 then placed on a steam-bath, and 25 cc. distilled off. 
 10 cc. of the distillate are treated with two drops of 
 
ANALYSIS OF FOODS 1 39 
 
 ammoniacal silver solution (i gram silver nitrate dis- 
 solved in 30 cc. water and treated with ammonia until 
 the precipitate is again dissolved, and then made up to 
 50 cc. with w T ater). If formaldehyde is present it 
 causes a black clouding to appear after standing for 
 several hours in the dark. 
 
 CHAPTER III. MEAT AND MEAT PRODUCTS 
 
 Meat consists of the muscle fibers of the animal 
 body which are held together by connective tissues 
 and surrounded or interposed by fat, sinews, and bone. 
 
 The meat is of a quite variable composition, accord- 
 ing to the portion of the body from which it is derived 
 and the mode of fattening, the age of the animal, and 
 other conditions. The pure muscle fiber is of less 
 variable composition, but this does not reach the mar- 
 ket as such. 
 
 The chemical constituents of muscle meat are, on 
 an average, 
 
 75.0 per cent, water, 
 
 21.7 per cent, nitrogenous substances, 
 
 2.0 per cent, fat, 
 
 1.3 per cent, mineral matter. 
 
 The nitrogenous substances are muscle fiber, con- 
 nective tissue, albumin, inosin, uric acid, and meat 
 bases (kreatin, kreatinin, karnin, xanthin). 
 
 The chemical analysis of meat is made according 
 to the general methods. 
 
 Sausage is generally preserved by the addition of 
 saltpeter, boric acid, sodium borate, salicylic acid, or 
 so-called preserving salt (usually a mixture of sodium 
 
140 PRACTICAL HYGIENE 
 
 chlorid, saltpeter, and boric acid), or they are colored 
 with anilin-red. 
 
 The examination of sausage for these preserving 
 salts is made by taking 10 grams and boiling with 100 
 cc. of water and filtering. 
 
 Several drops of the filtrate are added to 5 cc. sul- 
 phuric acid containing a few crystals of diphenylamin 
 in solution. If on shaking a blue color appears there 
 is saltpeter present (KNO ). 
 
 A portion of the filtrate is evaporated to dryness 
 after adding a solution of sodium carbonate, the resi- 
 due is incinerated, dissolved in hydrochloric acid, and 
 this acid solution tested with strips of curcuma paper. 
 If on drying the latter is colored red, boric acid is 
 present. 
 
 The remainder of the filtrate is shaken with ether, 
 the latter is pipetted off, and the remainder is then 
 evaporated in a porcelain dish. The residue is dis- 
 solved in a few drops of water and tested with ferric 
 chlorid. A violet color indicates the presence of 
 salicylic acid. 
 
 Animal Fats 
 
 Beef-fat is pretty hard, melting only above 45 ° C, 
 and has a specific gravity of 0.859 at ioo° C. 
 
 Lard is of a consistence of a salve, melting between 
 42°-45° C, and has a specific gravity of 0.860 at 
 ioo° C. 
 
 In the examination of fats they are melted to re- 
 move foreign bodies (water, salts, etc.) and then filtered 
 and the melting-point determined. 
 
ANALYSIS OF FOODS 141 
 
 The estimation of the specific gravity is made at 
 ioo° C. by means of a Westphal specific gravity bal- 
 ance, or by means of an areometer of Koenig. 
 
 Of great value in determining the purity of fats is 
 the estimation of the iodide degree. 
 
 Lard is frequently adulterated with the stearates of 
 cottonseed oil. To determine this mode of adultera- 
 tion 10 cc. of the clear, melted fat are placed in a flask 
 and 20 cc. of absolute alcohol added. This is then 
 placed on a boiling water-bath and 2 cc. of an alco- 
 holic-ether solution of silver nitrate added. (Beche's 
 reagent : 1 gram silver nitrate dissolved in 200 cc. al- 
 cohol, and 40 grams ether added.) 
 
 If cottonseed oil is present a reduction of the silver 
 nitrate takes place causing a brown color, or a precipi- 
 tation of the metal, while with pure fat it remains 
 unchanged. 
 
 CHAPTER IV. FLOUR 
 
 Examination for the Presence of Foreign Seeds 
 
 About 2 grams of the flour are placed into a test- 
 tube and 10 cc. of acid-alcohol added (70 cc. absolute 
 alcohol, 30 cc. water, and 5 cc. hydrochloric acid); 
 this is slightly warmed, shaken, and the resulting 
 color observed. 
 
 Presence of secale cornutum (ergot) = reddish to violet. 
 " lolium . temulentum (garlic) = ( orange-red 
 " agrostemma githago (cockle) = ( to yellow. 
 " rianthus, etc. = greenish. 
 
 Flour is sometimes adulterated with white mineral 
 substances, gypsum, calcium carbonate, this form of 
 
142 PRACTICAL HYGIENE 
 
 adulteration being detected by estimating the amount 
 of ash in 10 grams of flour. 
 
 The total ash of flour does not exceed 2 per cent. 
 (wheat flour 0.5 to 1 per cent.; rye flour 2 per cent.), 
 in all of which 0.2 per cent, of sand is included. 
 
 The amount of sand is estimated by treating the 
 ash of 10 grams of flour with 25 cc. of 10 per cent, 
 hydrochloric acid, and after standing one quarter of 
 an hour the insoluble part is filtered off, washed, dried, 
 and weighed. 
 
 To test for coarser mineral adulteration a teaspoonf ul 
 of flour is placed in a test-tube and shaken with 20 cc. 
 of chloroform, and allowed to stand. Pure flour collects 
 in the upper portion of the liquid ; the mineral parti- 
 cles sink to the bottom. 
 
 CHAPTER V. VINEGAR 
 
 Vinegar should not contain less than 4 per cent, 
 acetic acid, as experience has shown that when less is 
 present it does not keep well. Besides acetic acid the 
 vinegar contains alcohol and extractives, according to 
 the raw material from which it is made, besides other 
 constituents. 
 
 The estimation of acetic acid is made by titrating 
 10 cc. of vinegar with normal sodium hydroxid solu- 
 tion and phenolphthalein. 
 
 1 cc. normal sodium hydroxid = 0.06 gram acetic 
 acid. 
 
 Adulteration of vinegar with free mineral acids is 
 detected as follows : 10 cc. of vinegar are placed in a 
 
ANALYSIS OF FOODS 1 43 
 
 test-tube with 3 drops of an aqueous solution of methyl 
 violet ( 1 : 1000). If mineral acids are present the 
 color changes to light blue or green. 
 
 The nature of the acid is determined as follows : 
 
 10 cc. of vinegar are treated with — 
 
 1 Barium chlorid and hydrochloric acid. A heavy 
 white precipitate indicates the presence of sulphuric 
 acid. 
 
 2. Silver nitrate and nitric acid. If this turns dark 
 it indicates the presence of hydrochloric acid. 
 
 3. Calcium chloride. A white precipitate indicates 
 the presence of oxalic acid. 
 
 It is to be remembered that a faint reaction is no 
 indication of the presence of free acids as this may be 
 brought about by salts in solution. 
 
 4. Nearly fill a test-tube with vineger and sulphuric 
 acid, one and one, being careful to pour the sulphuric 
 acid on the vinegar, and not the vinegar on the acid ; 
 cool the mixture and add, cautiously, along the side of 
 the test-tube, a few drops of ferrous sulphate solution, so 
 that the liquids will come in contact, but not mix ; if 
 nitric acid is present, the stratum of contact will show 
 a purple or reddish color, which changes to brown. If 
 the liquids are then mixed, a clear brownish purple 
 liquid will be obtained. 
 
 The Brucine Test, — To a few cubic centimeters of 
 vinegar in a test-tube add four or five drops of brucine 
 and then a few drops of concentrated sulphuric acid, 
 and if nitric acid is present, a red color will be de- 
 veloped. 
 
144 PRACTICAL HYGIENE 
 
 To distinguish cider vinegar from spirit vinegar. 
 
 — Place a weighed quantity of the sample to be tested 
 in a porcelain dish, and evaporate it at a temperature 
 of ioo° C.j until constant; the residuum should be, 
 for cider vinegar, not less than 2 per cent., and should 
 be from a clear, light brown to a dark brown color, 
 soft, viscid, and hygroscopic; and, when burned, 
 should give off the odor of burned apples. A lead 
 acetate solution will cause an immediate light yellow- 
 ish brown precipitate in cider vinegar, the precipitate 
 settling, usually in flakes, in less than five minutes. 
 
 CHAPTER VI. FOOD MATERIALS CONTAINING ALKALOIDS 
 
 a. Coffee 
 
 By the term coffee we understand bean-like seeds 
 of the fruit of the coffee-tree. The quality varies with 
 the country in which it grows. 
 
 The unroasted beans have a yellowish green color. 
 These are often imitated by artificial preparations, but 
 the latter are commonly colored with ochre which is 
 harmless. 
 
 Before using the beans are roasted, whereby their 
 constituents are changed and the beans take on a 
 brownish color. In the preparation of coffee as a 
 beverage the beans are ground and an infusion made 
 with hot water, when about 26 per cent, is dissolved. 
 
 The constituents of coffee are the alkaloid caffein, 
 (C 8 H io N 2 ) acid, an ethereal oil, and the product of 
 roasting, besides which it contains fat, albumen, min- 
 eral matter, and cellulose. 
 
ANALYSIS OF FOODS 1 45 
 
 Coffee is not unfrequently adulterated by the addi- 
 tion of sugar-beats, chicory, yellow beets, figs, pears, 
 cereals, malt, acorns, leguminosae, and coffee berries. 
 
 Estimation of caffein content. — 5 grams coffee are 
 finely pulverized and extracted with hot water, the 
 infusion precipitated with neutral lead acetate solu- 
 tion, filtered, and the filtrate treated with hydrogen 
 sulphid, mixed with magnesia and sand, and evapo- 
 rated to dryness, the residue thoroughly extracted with 
 chloroform. This is then evaporated to dryness, 
 boiled with water, filtered, the filtrate evaporated in 
 vacuo and in the drying oven. The resulting caffein 
 is then also examined microscopically to determine 
 whether it is pure or not. 
 
 Estimation of extractives. — 10 grams of dry coffee 
 are placed in a beaker with 25 cc. water. This is 
 weighed to 0.1 gram and then warmed, boiling for 
 fifteen minutes, preventing the loss of foam at the be- 
 ginning of the boiling. After cooling, water is again 
 added to the original weight, mixed, filtered, and the 
 specific gravity of the filtrate determined at 15 C. by 
 means of a Westphal balance, or a pycnometer. 
 
 By consulting Schultze's extract table, the extractive 
 content of the solution is read off in per cent, by w r eight, 
 #£ = .r, and calculate (a) the extract content, and its wa- 
 ter content (c) according- to the formula a = x : — 
 
 v 7 & 100 — x 
 
 Per cent. 
 Trillich found the average for chicorv to be 70.7 
 
 " fig coffee 73.5 
 
 " barley coffee 65.0 
 
 " " coffee husks only 20.0 
 
 and for true coffee about 25.0 
 
146 PRACTICAL HYGIKNK 
 
 b. Tea 
 
 The thein content of tea varies from one to three 
 per cent. 
 
 1. Estimation of Thein. — Five grams of finely pow- 
 dered tea are extracted three times, for one hour, each 
 time with 300 cc. of water, the three extracts are mixed 
 and concentrated to one-fourth the volume, and while 
 hot freshly precipitated lead hydroxid is added and 
 coarse, washed sand mixed with it. The mixture is 
 evaporated to dryness on a water-bath and the residue 
 is extracted with chloroform for three hours in a 
 Soxhlet extraction apparatus. The residue which re- 
 mains is dissolved in water, the filtrate placed in a 
 porcelain dish, and evaporated on a water-bath, the 
 residue dried at ioo° C. and weighed. 
 
 2. Determination of ash. — The ash determination 
 is of greater importance than the estimation of the 
 thein content in determining adulteration. It should 
 not be less than 3 per cent, nor more than 7 per cent. 
 Of the ash only 2.5 to 4 per cent, should be soluble 
 in water, and not more than 1 per cent, soluble in 
 acid. 
 
 EXAMINATION OF FOOD MATERIALS FOR CHEM- 
 ICAL PRESERVATIVES 
 
 The chemical preservatives most frequently em- 
 ployed to preserve food materials are boric, sulphur- 
 ous, benzoic, and salicylic acids, and formaldehyde, 
 either alone or in various combinations. 
 
ANALYSIS OF FOODS 1 47 
 
 Boric acid and borates 
 
 Qualitative test. — The substance to be tested is ren- 
 dered alkaline with milk of lime, evaporated to dry- 
 ness, and incinerated. The ash is dissolved in the 
 smallest possible quantity of concentrated hydrochloric 
 acid, filtered, and the filtrate evaporated to dryness on 
 the water-bath. No great loss of boric acid need be 
 feared in this operation. The residue is moistened 
 with a little dilute hydrochloric acid, and curcuma 
 tincture added, and again evaporated to dryness. The 
 presence of the least trace of boric acid is shown by 
 the cinnabar or cherry-red color of the residue. This 
 reaction is extremely delicate, 0.5 to 1.0 milligram of 
 boric acid in the residue, or, for instance, 0.001 to 
 0.002 per cent, in milk is shown with the greatest cer- 
 tainty in this manner. 
 
 Concentrated hydrochloric acid also gives with cur- 
 cuma tincture a red color which, however, disappears 
 upon the addition of water, and on drying changes to 
 brown, while the boric acid color appears only on dry- 
 ing and disappears only on the addition of much wa- 
 ter, or boiling water. The red color adheres very te- 
 naciously to the vessels but is easily removed with 
 alcohol. 
 
 The ash, after treatment w T ith curcuma tincture, can 
 be used for the flame reaction by moistening it with 
 hvdrochloric acid and transferring it to the gas flame. 
 The flame shows a green border. 
 
 Quantitative estimation. — The quantitative estima- 
 tion of boric acid is quite difficult, and in the presence 
 of sodium salts can only be carried out by expert 
 
148 PRACTICAL HYGIENE 
 
 chemists. Traces of boric acid are widely distributed 
 in nature, and are also contained in glass vessels and 
 great care must be exercised in giving an opinion on 
 this account. 
 
 Sulphurous Acids and Sulphides 
 
 Qualitative test. — The intense and characteristic 
 odor of sulphurous acid is noticeable only on the very 
 copious application of this agent for purposes of the 
 preservation of food materials. If only small quanti- 
 ties are present the following preliminary tests are 
 made : The material to be tested is treated with hy- 
 drochloric acid and zinc and a strip of filter-paper 
 moistened with lead acetate is laid over the mouth of 
 the flask containing the mixture. If a brown or black 
 color is produced on the strip of paper one must de- 
 termine whether sulphur dioxid w T as really present. 
 If the paper is not colored no sulphurous acid was 
 present. From recent observations we know that sul- 
 phurous acid results from the fermentation of differ- 
 ent substances, from the reduction of sulphates or 
 from albuminous substances, and the simple qualita- 
 tive determination of the presence of sulphurous acid 
 or its salts does not show that it was added as a pre- 
 servative. 
 
 Quantitative estimation. — For this purpose 200 cc. 
 of beer or wine, for instance, are treated with 5 cc. of 
 phosphoric acid, placed in a retort or distillation flask 
 attached to a Liebig's condenser, and 100 cc. are dis- 
 tilled off. The condensation tube must be conducted 
 into 20 cc. of tenth normal iodin solution. It is rec- 
 
ANALYSIS OF FOODS 1 49 
 
 ominended to carry out the procedure by conducting 
 a continuous stream of carbon dioxid gas washed in 
 water, through the distillation flask ; one prevents in 
 this manner the return of the distillate on cooling off 
 the distillation flask. The iodin solution should not 
 be entirely decolorized. The iodin converts the sul- 
 phurous acid into sulphuric acid (S0 2 + 2H 2 + 2l = 
 H 2 S0 + 2 HI), which, after acidulation with hydro- 
 chloric acid, can be precipitated with barium chlorid 
 and weighed as barium sulphate. 1 milligram barium 
 -sulphate represents 0.2748 milligram sulphur dioxid. 
 
 Salicylic Acid and Salicylates 
 
 Qualitative test. — If salicylic acid is plentifully 
 present it is easily detected ; 50 cc. of the liquid, beer . 
 or wine for instance, are acidulated with sulphuric 
 acid, shaken with 50 cc. of equal parts of ether and 
 petroleum ether and the clear ether extract filtered. 
 The ether and petroleum ether in the filtrate are fully 
 removed and to the remaining liquid a few drops of 
 highly diluted neutral ferric chlorid solution are added. 
 A violet color indicates the presence of salicylic acid ; 
 the intensity of the color is indicative of the quantity 
 present. 
 
 Detection of salicylic acid in milk and butter. — 100 
 
 cc. of milk are diluted with 100 cc. of distilled water 
 of 6o° C, and precipitated with 8 drops of acetic acid 
 and 8 drops of a solution of mercuric oxid in nitric 
 acid, shaken and filtered. The filtrate is shaken with 
 50 cc. of ether which takes up the salicylic acid. But- 
 ter is first treated with sodium carbonate by making a 
 
150 PRACTICAL HYGIENE 
 
 homogeneous mixture, and then proceeding as in 
 testing wine or beer. 
 
 Benzoic Acid and Benzoates 
 
 Quantitative test of Meissl. — The substance to be 
 examined is mixed with barium hydroxid and evap- 
 orated to dryness on a water-bath (milk is first mixed 
 with clean sand). The residue is then acidulated with 
 sulphuric acid and shaken three to four times with 
 cold 50 per cent, alcohol. For the removal of milk- 
 sugar and salts it is necessary to treat with barium 
 hydroxid, evaporate to dryness, acidulate with sul- 
 phuric acid, and then extract the benzoic acid with 
 ether. The ether is evaporated under 6o° C, when 
 the benzoic acid crystallizes out. Dissolved in water, 
 benzoic acid gives a beautiful reddish yellow color 
 with dilute, neutral ferric chlorid solution. 
 
PART V 
 VENTILATION AND HEATING 
 
 CHAPTER I. VENTILATION 
 
 a. Natural ventilation. — The study of the inter- 
 change between the inside and outside air in the ven- 
 tilation of rooms and buildings may be made in sev- 
 eral different ways. The most common method is 
 that devised by Pettenkofer. This method consists in 
 generating carbon dioxid in a closed room, by burning 
 candles, or by the action of acids on carbonates, mix- 
 ing it thoroughly with the room air, and then deter- 
 mining the rate at which the carbon dioxid in the air 
 diminishes through the interchange between the in- 
 side and outside air. The proportion of carbon dioxid 
 in the room air and in the outside air is first deter- 
 mined, then, after generating the carbon dioxid, ex- 
 aminations of the air are made, at intervals of fifteen 
 minutes, during one or several hours. The quantity 
 of the incoming air, or the amount of ventilation, is 
 then calculated by means of Seidell formula : 
 
 p. — a 
 
 x = 2.303 X m X log -± cubic meters ; 
 
 Pi a 
 where m = the cubic content of the room in cubic 
 
 meters, 
 
 p x = carbon dioxid in room air at beginning of 
 observation, 
 
 fl 2 = carbon dioxid in room air at end of ob- 
 servation, 
 
152 PRACTICAL HYGIENE 
 
 a = carbon dioxid in outside air, 
 x = quantity of incoming air. 
 
 b. Artificial ventilation. — To determine the inter- 
 change brought about between the room air and the 
 outside air through artificial ventilation we measure 
 the velocity of the current of the incoming air as it 
 issues from the ventilator openings, or as it passes out 
 through the exit openings. This is done by means 
 of an anemometer. 
 
 Anemometers are of two kinds: (1) dynamic ane- 
 mometers, in which the air current sets in motion a 
 small wheel whose motion is communicated by means 
 of clock-work to a set of dials on which the velocity 
 of the air current is recorded in meters; and (2) static 
 anemometers, in which the air current is measured by 
 the pressure which it exerts on a thin sheet of metal 
 which is connected with a scale on which the degree 
 of deflection from the zero-point denotes the rate of 
 movement. 
 
 Each anemometer should be tested first as to the 
 degree of its efficiency. It requires a definite velocity 
 of current to start the wheel of a dynamic anemome- 
 ter, and this factor is different for each instrument. 
 Usually the necessary calculations for the correction 
 of these instruments have been determined by the 
 maker — therefore it is not necessary to go into the 
 details of the operation. 
 
 Process. — A reading of the dials of the anemometer 
 is made when it is placed in the ventilator opening for 
 one minute and another reading taken. The difference 
 between the two readings will indicate the velocity of the 
 
VENTILATION AND HEATING 1 53 
 
 air current in sixty seconds, or divided by sixty, will in- 
 dicate the velocity of the current per second. The 
 result is expressed in meters per second. 
 
 It is not sufficient to make a single observation at 
 the center of the ventilator opening as the velocity of 
 the air current there is greater than at any other point. 
 Usually an observation is made at the center and at 
 each of the four corners of a rectangular opening, or at 
 least two of the opposite corners besides the center, 
 and then taking the mean of all the observations. 
 Similar observations must be made at all the ventila- 
 tor openings in a room if more than one exists, to as- 
 certain the total amount of the incoming air. The 
 amount of ventilation may also be determined by ma- 
 king similar observations on the exit openings of the 
 ventilators as to the amount of air leaving the room. 
 
 In order to determine the amount of natural venti- 
 lation we find the cubic content of the room — the 
 cubic space — by multiplying the length, width, and 
 height of the room in meters, together. We also de- 
 termine the area of the ventilator openings. 
 
 Example. — A room measuring 5 meters long, 3 meters 
 wide, and 4 meters high = 60 cubic meters = the cubic 
 content. (Ordinarily it is not necessary to make any de- 
 duction from the cubic content of a room on account of 
 the furniture nor any additions for the recesses of win- 
 dows and doors, since the corrections would make very 
 little change in the result.) The ventilator opening is 
 circular in shape and 48 cm. in diameter, or 24 cm. ra- 
 dius— then it is 24 X 24 X 3.14 = 1808.64 sq. cm. = 
 0.180864 sq. m. in area. 
 
154 PRACTICAL HYGIENE 
 
 The velocity of the incoming air current is as follows : 
 In one minute — Meter. 
 
 At the center of the circle = 0.7386 
 " lower margin = 0.6700 
 
 " upper " = 0.7200 
 
 " right " =0.7480 
 
 " left = 0.7500 
 
 or 3.6266 -r- 5 = 0.7253 meter per second. The volume 
 of air entering each second is found by multiplying the 
 area of the opening by the velocity of the current — 
 0.1808 X 0.7253 = o. 131 134 cubic meter per second, or 
 472.08 cubic meters per hour. The dimensions of the 
 room are 5X4X3 meters = 60 cubic meters, the cubic 
 content, and it requires, therefore, 60 -r- 7.868 (the veloc- 
 ity per minute) =7.62 minutes to change the air of the 
 room, or the air is changed nearly eight times each hour. 
 
 CHAPTER II. HEATING 
 
 The investigation of the warming of a building 
 should include the following : 
 
 a. The extent of the combustion. 
 
 b. The heating effect produced in different parts 
 of the building. 
 
 c. The possibility of any detrimental effect on 
 health. 
 
 1. The study of the extent of the combustion com- 
 prises : 
 
 a. The chemical analysis of the combustion ma- 
 terials in order to estimate the theoretical 
 amount of heat it can yield. 
 
 b. The estimation by means of a calorimeter of 
 the amount of heat passing off as water, ex- 
 pressed in calories. 
 
VENTILATION AND HEATING 1 55 
 
 By calorie is meant the amount of heat necessary 
 to raise the temperature of a liter of water i ° C. 
 
 c. The estimation by means of a pyrometer, of 
 the temperature of the air entering and leav- 
 ing the heater. 
 
 d. The estimation of the volume, the tempera- 
 ture, and the chemical composition of the 
 smoke. The volume of smoke is estimated by 
 measuring the size of the chimney and the ra_ 
 pidity of current of smoke passing out of it. 
 The temperature is measured by means of a 
 pyrometer or air-thermometer. 
 
 The determination of the chemical composition of 
 the smoke is made through gas analysis — though it 
 usually consists of carbon dioxid, nitrogen, and oxygen, 
 with the addition of carbon, watery vapor, though 
 carbon monoxid is also frequently present, and is de- 
 tected by means of palladium chlorid solution. In 
 the absence of carbon monoxid the estimation of the 
 carbon dioxid and oxygen usually suffices. 
 
 2. The estimation of the heating effect on the dif- 
 ferent rooms requires the determination of 
 
 a. The temperature. 
 
 b. The humidity, especially the deficiency of sat- 
 uration. 
 
 c. The cubic contents of the rooms. 
 
 d. The amount of natural ventilation. 
 
 3. The determination of the possibility of any det- 
 rimental effect upon the health of the occupants is 
 
156 PRACTICAL HYGIENE 
 
 not very readily determined. We may determine the 
 presence or absence of carbon monoxid, the tempera- 
 ture of the room, the humidity of the atmosphere, and 
 in this manner derive some information as to the 
 healthfulness of the room. 
 
INDEX. 
 
 Acid, boric, in butter 137 
 
 hydrochloric 60 
 
 nitric 68 
 
 nitrous 68 
 
 phosphoric 68, 106 
 
 salicylic, in butter 138 
 
 silicic 67 
 
 sulphurous 60, 68 
 
 Air, atmospheric 6 
 
 chemical analysis of 41 
 
 Pettenkof er flask method 45 
 
 tube method 53 
 
 collection of samples of 49 
 
 impurities in 41 
 
 gaseous . > 41 
 
 solid 41 
 
 moisture in 23 
 
 movements, qualitative estimation of 34 
 
 quantitative estimation of 35 
 
 physical examination of 7 
 
 soil 123 
 
 volume, reduction of 53 
 
 water capacity of 28 
 
 Aitken's dust counter 59 
 
 Alkalies in water 101 
 
 Alkaloids, food material containing 143 
 
 Aluminum method for nitrates 93 
 
 Ammonia in air 61 
 
 qualitative test 61 
 
 quantitative test 61 
 
 gravimetric method 61 
 
 volumetric method 62 
 
 Ammonia in water 70 
 
 free and albuminoid 74 
 
 Ammonia-free water, collection of 75 
 
 Analysis of air, chemical 41 
 
 foods, sanitary 125 
 
 milk, chemical 128 
 
 physical • . 125 
 
 soil, mechanical 114 
 
 water, sanitary 64 
 
 Anemometer 37, 151 
 
 Animal fats, examination of 140 
 
 Aqueous vapor, estimation of, in air 23, 30, 54 
 
 tension of 22, 26 
 
158 INDEX 
 
 Ash in butter 134 
 
 milk 129 
 
 tea 145 
 
 Atmometer, Pische's 32 
 
 Atmospheric air 6 
 
 pressure 15 
 
 Babcock's method 131 
 
 Barometer - 17, 49 
 
 aneroid 22 
 
 manner and place # of hanging 19 
 
 mercurial 17 
 
 cistern 17 
 
 differential 21 
 
 stationary 21 
 
 scale 18 
 
 Barometric pressure, correction for 8, 20, 28 
 
 Bellows, hand r 42 
 
 Benzoic acid and benzoates in food 146 
 
 Beaufort's scale of air movements . . 36 
 
 Boiling-point of water 7 
 
 Regnault's table 10 
 
 Boric acid in butter 137 
 
 and borates in food 146 
 
 Bottles, glass-stoppered 49 
 
 Brucine test in vinegar - 143 
 
 Burette, Bunte gas 42 
 
 Mohr's 49 
 
 reading of ' 51 
 
 Butter, adulteration of 133 
 
 casein in 134 
 
 composition of 133 
 
 detection of preservatives in 137 
 
 melting-point of 136 
 
 mineral matter in 134 
 
 solubility of, in hot alcohol 137 
 
 Caffein, estimation of, in coffee 144 
 
 Calcium 69 
 
 Carbon dioxid 44, 67, 97, 98, 100, 101 
 
 qualitative estimation of, in air 44 
 
 quantitative estimation of , in air 45 
 
 monoxid, qualitative tests 56 
 
 chemical tests 57 
 
 spectroscopic method 56 
 
 Casein in butter 134 
 
 Casserole, cleansing of 78 
 
 Centigrade scale 14 
 
 Chemical analysis of air 41 
 
 milk 128 
 
 preservatives in food 146 
 
 water 67 
 
INDEX 159 
 
 Chlorin : 66, 68, 71 
 
 Cleansing the casserole 78 
 
 Clearness of water 65 
 
 Clouds, designation of amount of 39 
 
 estimation of amount of 38 
 
 Coffee ; 143 
 
 Collection of sample of air . 49 
 
 soil 114 
 
 water 64 
 
 Color of water 66 
 
 Copper in water ' 70 
 
 Corrections of barometric readings 8, 20, 53 
 
 Cremometer 128 
 
 Data on the label 65 
 
 Deficiency of saturation 23 
 
 Degrees of hardness, Clark's scale 82 
 
 Metric scale 82 
 
 Dew-point 22 
 
 Drinking-water, approximate composition of 1 13 
 
 Dust counter, Aitken's 59 
 
 Dust in air, estimation of, by weight . 58 
 
 Dust particles 59 
 
 Elutriation of soil 115 
 
 Estimation of moisture in air 23, 30 
 
 thein in tea 145 
 
 Evaporimeter 31 
 
 Extractives, estimation of, in coffee 144 
 
 Fahrenheit scale 14 
 
 Fat in butter 134 
 
 milk, estimation of 127, 129 
 
 Babcock method 131 
 
 by means of lactobutyrometer 129 
 
 extraction method 129 
 
 Leff man-Beam method 133 
 
 Fats, animal 140 
 
 foreign, in butter 135 
 
 Florence flask 49 
 
 Flour 140 
 
 Fog 38 
 
 Food materials containing alkaloids 143 
 
 Foods, sanitary analysis of 125 
 
 Foreign fats in butter 135 
 
 Formaldehyde in butter 138 
 
 Gaseous impurities in air 41 
 
 Hail 33 
 
 Hand bellows 48 
 
 Hardness of water 80 
 
 permanent 85 
 
 temporary 85 
 
160 INDEX 
 
 Heating, testing efficiency of 153 
 
 Hehner's method for hardness of water 84 
 
 Humidity of the atmosphere 23 
 
 absolute 22 
 
 relative 22 
 
 calculation of 30 
 
 Hydrochloric acid, qualitative test 60 
 
 quantitative test 60 
 
 Hydrogen sulphid 54, 67 
 
 Hygrometers 24 
 
 direct 24 
 
 Daniell's 24 
 
 Dines's 24 
 
 Regnault's 24 
 
 indirect 25 
 
 hair 25 
 
 wet- and dry-bulb thermometer 25 
 
 Hygroscope 31 
 
 Hypsometer 7 
 
 Impurities in air, gaseous 41 
 
 solid 41 
 
 ammonium thiocyanate * 73, 75 
 
 water, limits of 1 r3 
 
 Indicators, lacmoid 86 
 
 phenolphthalein 48 
 
 potassium chromate 72 
 
 rosolic acid 47 
 
 Indigo solution 77 
 
 Interpretation of results in water analyses 109 
 
 Iron in water * . . 69 
 
 quantitative estimation of 102, 103 
 
 Knopp's elutriator 116 
 
 Lactobutyrometer 129 
 
 table 130 
 
 Lactoscope 127 
 
 Lead, in water, detection of 69, 96 
 
 colorimetric method 96 
 
 LefTman-Beam method 133 
 
 Lime, estimation of 69, 87 
 
 Limits of impurity in water 113 
 
 Magnesia, estimation of 69, 87 
 
 Manometer, dynamic 34 
 
 Marx-Tromsdorf method for nitrates 87 
 
 Materials, food, containing alkaloids 143 
 
 Maximum of saturation - 23 
 
 Meat and meat products 138 
 
 Mechanical analysis of soil 114 
 
 Melting-point of butter 136 
 
 Metals, heavy, in water 69 
 
INDEX l6l 
 
 Meteorology 7 
 
 Milk, chemical analysis of 128 
 
 ash 129 
 
 fat 129 
 
 total solids 128 
 
 estimation of fat in 127 
 
 lactoscope 127 
 
 cremometer 128 
 
 examination of 125 
 
 nature and composition of 125 
 
 physical examination of 125 
 
 specific gravity of 126 
 
 Mineral matter in butter 134 
 
 Moisture, in air, estimation of 23 
 
 by chemical methods 30 
 
 evaporation of, from the earth's surface 31 
 
 precipitation of . 32 
 
 in soil, estimation of 121 
 
 Nitric acid . 68 
 
 Nitrogen as nitrates, determination of 87 
 
 aluminum method 93 
 
 Marx-Tromsdorf method 87 
 
 method of Grandval and Lajoux 89 
 
 Schultze-Tiemann method 90 
 
 nitrites, determination for 94 
 
 Schuyten's method 1 95 
 
 Warrington's modification of Griess' method 94 
 
 Nitrous acid 68 
 
 Observation of temperature 7 
 
 Odor of water 66 
 
 Organic matter 58 
 
 determination of, Remsen's method 58 
 
 nitrogenous 58 
 
 oxidizable 58, 78 
 
 Oxygen 42, 104 
 
 Phosphoric acid 68, 106 
 
 Pipettes 49 
 
 Potassium 69, 101 
 
 Precipitation of moisture 32 
 
 Preservatives, detection of, in butter 138 
 
 Pressure, atmospheric 15 
 
 Psychrometer 25 
 
 sling - 26 
 
 Pyrometer 11 
 
 Radiation, solar, measurement of 13 
 
 terrestrial 13 
 
 Rain 32 
 
 Rain-gauge 32 
 
1 62 INDEX 
 
 Rain-gauge, position of 33 
 
 Reaction of water 66 
 
 Reading of barometer 17 
 
 Reaumur scale 14 
 
 Recording results in water analyses 108 
 
 Residue, incineration of 71 
 
 Results, calculation of 53, 83 
 
 interpretation of 109 
 
 representation of 39 
 
 Salicylic acid in butter 138 
 
 food 149 
 
 Salts in solution in water 67 
 
 Sanitary analysis of food 125 
 
 water 64 
 
 Saturation, deficiency of 23 
 
 maximum of 23 
 
 Scales, thermometer 14 
 
 Schultze-Tiemann method, for nitrates 90 
 
 Silicic acid 67 
 
 Sleet 33 
 
 Snow 33 
 
 Soap solution, standard 81 
 
 Sodium 69, 101 
 
 Soil air, estimation of carbon dioxid in 123 
 
 mechanical analysis of 114 
 
 elutriation of 115 
 
 sieving of 115 
 
 physical analysis of 116 
 
 drainage capacity of 1 20 
 
 estimation of level of ground-water in 121 
 
 moisture in 121 
 
 porosity of 116, 117 
 
 Pettenkof er's method 118 
 
 water capacity of 118, 119 
 
 Pettenkof er's apparatus 120 
 
 Solar radiation 13 
 
 Solid impurities in air 41 
 
 Solids, total, in water 70 
 
 Solubility, in hot alcohol, of butter 138 
 
 Solutions, standard : 
 
 alkaline potassium iodid 105 
 
 permanganate 75 
 
 ammonium chlorid 75 
 
 ammoniof erric alum 73 
 
 ammonium thiocyanate 102 
 
 antipyrin 95 
 
 barium hydroxid 46 
 
 hydrochloric acid 102, 105 
 
 iodin 55 
 
 manganous chlorid 104 
 
INDEX 163 
 
 Solutions, standard : 
 
 Nessler's reagent 75 
 
 nitric acid 72 
 
 oxalic acid 45, 73 
 
 oxid of iron 108 
 
 potassium nitrate 88 
 
 permanganate 78 
 
 silver nitrate 71, 74 
 
 soap 81 
 
 sodium chlorid 72, 74 
 
 hydroxid 94 
 
 phosphate 107 
 
 thiosulphate 55, 105 
 
 starch...... 55, 105 
 
 sulphuric acid 78 
 
 standardizing of 79 
 
 titration of 51 
 
 Sulphurous acid, qualitative test 60, 68, 148 
 
 quantitative test 60, 148 
 
 Taste of water 66 
 
 Tea 146 
 
 Temperature, observation of 7 
 
 at barometer 19 
 
 of soil 124 
 
 Thein in tea, estimation of 146 
 
 Thermograph 1 r 
 
 Thermometers 7, 48 
 
 for high temperatures 10 
 
 maximum-minimum 11 
 
 mercurial 7 
 
 scale 14 
 
 special 10 
 
 spirit 10 
 
 Vapor, aqueous 23 , 30, 54 
 
 tension of 22, 26 
 
 Ventilation, testing efficiency of 151 
 
 artificial 152 
 
 natural 151 
 
 Vernier 18 
 
 Vinegar, cider 144 
 
 spirit 144 
 
 Water, 63 
 
 ammonia-free 75 
 
 chemical analysis of 67 
 
 qualitative 67 
 
 quantitative 70 
 
 composition of 65 
 
 clearness of 63 
 
164 INDEX 
 
 , « 
 
 Water, collection of sample of 64 
 
 color of 66 
 
 drinking-, approximate composition of 113 
 
 ground-, course of 1 23 
 
 height of 121 
 
 hardness of 80 
 
 Clark's method 82 
 
 Hehner's method 84 
 
 gravimetric determination of 86 
 
 nature and composition of 63 
 
 nitrate-free 93 
 
 odor of 66 
 
 physical examination of 65 
 
 properties of 63 
 
 reaction of 66 
 
 sanitary analysis of 64 
 
 taste of 66 
 
 Weather prognostication 39 
 
 Wind, force, rapidity, and direction of 34 
 
 Wind vane 34, 37 
 
 Zero-point, control of 7 
 
 Zinc in water, detection of 70, 97 
 
 ERRATA. 
 On pape 16, 3d line from bottom, for " higher " read " lower.' 
 On page 17, 2nd line from top, for " lower" read " higher." 
 On page 17, 3d line from top, for " falling" read " rising." 
 
Partial List of 
 
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 BILTZ. 
 
 Practical Methods for Determining Molecular Weights.— By 
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 #* # Specimen pages of any of the above books free upon application. 
 
 The Chemical Publishing Company, 
 
 EASTON, PENNA. 
 
NOV 17 1899