A RESPIRATION CALORIMETER WITH APPLIANCES FOR THE DIRECT DETERMINATION OF OXYGEN BY W. O. ATWATER and F. G. BENEDICT OF WESLEYAN UNIVERSITY WASHINGTON, D. C.: Published by the Carnegie Institution of Washington 1905 CARNEGIE INSTITUTION OF WASHINGTON PUBLICATION No. 42 WASHINGTON. D. C. PRESS OF JUDD & DETWEILER (INC.) 1905 PREFACE. The apparatus to be described in this report has been in process of development for twelve years. During this time the resources of Wes- leyan University have been supplemented by appropriations from the United States Department of Agriculture and the Connecticut (Storrs) Agricultural Experiment Station, and by contributions from private individuals. In aid of a series of experiments with the apparatus in its earlier stages, grants from the Elizabeth Thompson Science Fund and the Bache Fund were obtained. The addition of the apparatus for the determination of oxygen was made possible by liberal grants from the Carnegie Institution of Washington. In the development of apparatus necessarily so elaborate as this the active cooperation of a skillful instrument builder is absolutely essential. It has been our good fortune to have the service of Mr. S. C. Dinsmore, whose mechanical skill has insured the successful operation of many parts of the apparatus. Dr. Paul Murrill, formerly associated with this research, rendered invaluable assistance in devising the methods of computation. Mr. R. D. Milnerand Mr. H. L,. Knight have assisted materially in the preparation of this report. Dr. E. B. Rosa, physicist of the National Bureau of Standards, but previously professor of physics at Wesleyan University, was actively engaged in this investigation in its earlier stages and has subsequently from time to time given advice which has assisted greatly in the furtherance of the work. The first grant of the Carnegie Institution for the development of the apparatus for the direct determination of oxygen was made to my colleague, Prof. W. O. Atwater. It was then expected that the report containing the description of the apparatus would be issued under the joint authorship of Professor Atwater and the writer. It has been deemed fitting, therefore, to retain his name on the title page of this report. A serious illness has compelled his untimely retirement from the work, and the writer, who has had the personal supervision of the development of the apparatus since 1895, has continued the research. Inasmuch as this report has been written, some of the apparatus herein described has been developed, and the experiment with man has been carried out subsequent to Professor Atwater's retirement, the writer assumes full responsibility for this report as it stands, and against him alone should adverse criticism be directed. FRANCIS GANG BENEDICT. August, 1905. in CONTENTS. Page Introduction 1-4 The respiration calorimeter 4-11 Description of the apparatus in its earlier form 5 Description of laboratory and arrange- ment of apparatus 7 The respiration apparatus 11-56 General principle II The respiration chamber 12 Openings in the chamber 13 Window 13 Food aperture 14 Air-pipe openings 14 Opening for weighing apparatus 16 Opening for the water-pipes 16 Rod for adjusting position of shields.. 17 Electric-cable tube 17 Piping and valves to the blower 17 The rotary blower 18 Mercury valves 20 Apparatus for the determination of water.. 23-27 Collection of drip 23 Removal of water vapor from the air cur- rent 24 Description of the water-absorbers 24 Durability of the water-absorbers 26 Efficiency of the water-absorbers 26 Supply of sulphuric acid 27 Apparatus for the determination of carbon dioxide 27-31 Description of the carbon-dioxide ab- sorbers 27 Vise for tightening absorbers 28 Removal of spent soda lime from the absorbers 29 Preparation of soda lime 29 Efficiency of the carbon-dioxide ab- sorbers 30 Testing the water and carbon-dioxide ab- sorber system 32 Maintenance of the supply of oxygen 32 Analysis of oxygen 34 Preparation of the reagents 37 Converting percentage by volume to percentage by weight 38 Computation of percentage of nitro- gen by weight, using (actors 38 The tension equalizers 39 Calibration of the pans 41 Possibility of noxious gases in the system.. 42 Acid fumes carried over by air cur- rent 42 Mercury vapor in the air 42 Proportion of water vapor in the air.. 43 Page The respiration apparatus— Continued. Apparatus for the analysis of the residual air 44-56 Apparatus for absorption of water 45 Efficiency of absorption 45 Apparatus for carbon-dioxide absorption.. 46 Efficiency of absorption 46 The Elster meter 46 Calibration of Elster meter 47 Test for saturation of air passing through the Els-ter meter 47 Apparatus for drawing sample 48 Apparatus for constant water pressure 50 Process of taking residual samples.. 50 Sampling the air for the determination of oxygen 51 Method of sampling 52 The analysisof air 53 Accessory apparatus 56-62 Balances 56-58 Analytical 56 Balances for weighing the carbon- dioxide and water absorbers, oxy- gen cylinders, etc 56 Weights 58 The barometer 60 Observation of temperature 61 Calculation of results 63-95 Amount of water absorbed 63 Amount of carbon dioxide absorbed 65 Amount of oxygen admitted 65 Residual analytical data 66 Data for the rejection of air 67 Corrections for variations in volume and composition of residual air 67-83 Necessity for residual analyses 67 Possibility of leakage 68 Factors used in the calculation of the re- sidual analyses 69 Volume of air in air-circuit 69 Volume in chamber 69 Volume of air in air-pipe from cham- ber, mercury valves, and blower.. 70 Volume of air in water-absorbers 70 Volume of air in carbon-dioxide ab- sorbers 70 Volume of remainder of air system 71 Volume of objects in the chamber not permanent 71 Volume in an alcohol check experiment 71 Volume in experiments with man 72 Fluctuations in the air volume 72 Volume in the pans 72 Compression of air in absorbing system. 73 VI CONTENTS. Page Calculation of results— Continued. Correction for mercury valve 74 Increase in volume of the water-absorb- ers 74 Fluctuations in volume of the carbon- dioxide absorbers 74 Interchange of air through the food aperture 75 Addition of nitrogen with the oxygen.. 77 The rejection of air 77 The respiratory loss 79 Subdivision of air volumes 80 Composition gradient of air in the closed circuit 81 Data used in calculating relation of weights and volumes of gases 82 Calculation of residual analyses 83-95 Volume of the sample 83 Calculation of true volume of sample for determination of carbon diox- ide and water 85 Calculation of the true volume of air in the closed air-circuit 86 Total residual water vapor 87 Total residual carbon dioxide 87 Oxygen and nitrogen 88 The nitrogen in the system 88 Calculations for nitrogen 89 Calculations for total residual oxygen... 89 Accuracy of calculations of the residual amount of oxygen 91 Thermal gradient inside the chamber.. 91 Conclusions regarding the accuracy of the oxygen computation.. 92 Check on the computation method of determining oxygen 93 Computation -of the total carbon-dioxide and water output and oxygen in- take 93 Total carbon-dioxide output 93 Total output of water vapor 94 Computation for total intake of oxygen. 95 Alcohol check experiments 96-105 Kindof alcohol used 96 Determination of specific gravity 97 Alcoholometric tables 98 Factors for the actual amounts of carbon dioxide, water, and oxygen 98 Alcohol lamp 99 Frequency and duration of experiments.. 102 Calculation of the alcohol check experi- ments 102 Determination of carbon dioxide 103 Determination of water 104 The computations for oxygen 104 The calorimeter system and measurements of heat 106-169 General principle of the calorimeter 106 The calorimeter chamber 107 "Wooden walls surrounding the chamber 107 Air-spaces and heat insulation m Page The calorimeter system and measurements of heat— Continued. Facilities for removing metal chamber 112 Methods of preventing gain or loss of heat to the chamber 112-123 Prevention of gain or loss through the metal walls 112 The thermo-electric elements 113 Construction of the elements 113 Method of installing elements 113 Distribution of elements 115 Electrical connection of the elements. 116 Heating and cooling the air-space 117 Healing circuits 117 Cooling circuits 118 Temperature regulations in the outer air-space 119 Gain or loss of heat through openings in the chamber 120 Gain or lossof heat through theair current . 122 Measurement of heat 123-150 The heat-absorbing system 123 Regulation of rate of absorption of heat. 125 Supply of water for measuring heat 126 Water coolers 126 Water meter 126 Calibration of the meter 132 Accuracy of the meter 132 Check measurements of the accuracy of the meter 133 Thermometers for measuring tempera- ture of water 133 Correction for pressure of water on the mercury bulb 134 Measurement of temperature of the calo- rimeter 134 Observer's table 136 Electrical connections on the table 138 Mercury switch and bridge 139 Determination of the quantity of heat eliminated 150-169 Latent heat of water vapor 150 Sensible heat removed in water current... 151 Unit of heat 151 Calculation of the quantity measured... 151 Corrections to measurements of heat 152-167 The hydrothermal equivalent of the calorimeter 152 Corrections for temperature of food and dishes 153 Adiabatic cooling of gases 154 Correction for heat absorbed by bed and bedding 154 Correction for change of body tempera- ture and body weight 155 Measurement of body temperature... 156 Weighing objects inside the chamber.. 157 Description of weighing apparatus... 158 Weighing the absorbing system 161 Routine of the weighings 163 Checks on the accuracy 164 CONTENTS. VII Page The calorimeter system and measurements of heat — Continued. The ergometer 164 Correction for the magnetization of the fields of the ergometer. 166 Blanks used for heat records 166 Tests of the accuracy of the heat-measuring apparatus 169-176 Electrical check tests 169-174 Electrical unit used , 171 Length and duration of experiments 173 Results of electrical check experiments... 174 The combustion of ethyl alcohol as a check on the heat measurements 174-176 Heat of combustion of alcohol 175 Results of alcohol check experiment 176 Experiment with man 177-193 Measurement of intake and output of material 177 Measurement of intake and output of energy 178 Page Experiment with man — Continued. Analytical methods _ 178 Metabolism experiment No. 70 178-193 Subject.... 178 Food 179 Routine of experiment 179 Statistics of food, feces, and urine 180 Statistics of water eliminated 181 Statistics of carbon dioxide eliminated... 182 Statistics of oxygen consumed 183 Respiratory quotient.- 184 Summary of calorimetric measure- ments 185 Intake and output of material and en- ergy. 187 Gains and losses of body material.™ 187 Body weight 190 Intake and output of energy 190 Calculations of energy of body material gained and lost 193 Conclusion 193 ILLUSTRATIONS. Page FIG. i. General plan of the respiration calorimeter laboratory 8 2. The laboratory room. View from southeast corner 10 3. The laboratory room. View from east side 10 4. The laboratory room. View from near sink 10 5. The laboratory room. View from alcove 10 6. Diagram of the circulation of air through the respiration apparatus. n 7. Interior of the respiration chamber 12 8. Horizontal section of respiration calorimeter chamber 15 9. Rotary blower 16 10. Mercury valves 21 1 1 . Water-absorbers 26 12. A carbon-dioxide absorber 26 13. Cross-section of carbon-dioxide absorber 28 14. Vise for tightening carbon-dioxide absorbers 32 15. An oxygen cylinder with valve, rubber pressure bag, and purifying attachments 32 16. Apparatus for analysis of oxygen and air 32 17. Pans for equalizing pressure 44 18. Apparatus for analysis of residual air 44 19. Apparatus for drawing sample of air for residual analysis 49 20. Water-pressure system 51 21. Balance for weighing absorbers and oxygen cylinders 58 22. Alcohol lamp and connections loo 23. Vertical cross-section of calorimeter chamber through the end 109 24. Vertical (side) cross-section of calorimeter chamber no 25. Rear view of calorimeter chamber no 26. A thermo-electric element 114 27. Thermo-electric element mounted on wooden rod 114 28. Method of installing thermo-electric elements in metal walls 114 29. Side view of metal chamber rolled out on tracks 116 30. Front view of metal chamber removed from wooden casing 116 31. Details of interior of wooden casing 118 32. Sectional view of walls of chamber, showing method of installing air-pipes, water-pipes, and rod for raising and lowering shields. 124 33. Interior of respiration calorimeter chamber 124 34. The water-meter 126 35. The water-meter. Diagrammatic sections showing front and side views 128 36. Clutch to regulate tension on water-meter 130 37. Observer's table 136 38. Electrical connections on observer's table 138 39. A unit key of the mercury switch 140 40. The mercury switch, top removed 140 41. A general view of mercury switch 140 42. Under side of mercury switch showing electrical connections 140 43. Diagram of electrical connections of mercury switch 142 44. Diagram of simple form of Wheatstone bridge 144 45. The rectal thermometer 156 46. Weighing apparatus for objects inside the chamber 159 47- The bicycle ergometer 164 48. The electric counter 164 49. Connections for an electrical check experiment 170 IX A RESPIRATION CALORIMETER, WITH APPLIANCES FOR THE DIRECT DETERMINATION OE OXYGEN. BY W. O. ATWATER AND F. G. BENEDICT. INTRODUCTION. For a proper understanding of the metabolism or transformations of matter and energy in the body, a knowledge of both total income and total outgo is indispensable. Physiologists and physicians have long been accustomed to depend very largely upon data from the analysis of urine for information regarding the metabolism of matter, especially of proteid, in the body. In many cases, aside from gross or approxi- mate estimates of the quantities of food ingested, they made no attempt to determine the income, and the outgo of material in the feces was, as a rule, entirely neglected. In a study of the metabolism of proteid in the body the analyses of the urine have a very great significance, which in the light of recent researches, such as those of Folin1 and Burian,'is becoming even more intelligently comprehended. But it has been long understood that many other transformations of matter besides those in which the element nitrogen is involved occur in the body, for the proper study of which a knowledge of the income of carbon, hydrogen, oxygen, water, and mineral matters, in addition to that of nitrogen, is necessary ; and, since the disintegration of the proteids as well as of the fats and carbohydrates of the body is accompanied by an absorp- tion of oxygen from the air and an elimination of carbon dioxide and water, our knowledge of the outgo must include not only the quantity of nitrogen in the urine, but also the amounts of carbon dioxide and water excreted by the lungs and skin, and of the carbon, hydrogen, oxygen, and mineral matters of both urine and feces. Furthermore, for many purposes the measurement of intake and output of matter is not wholly sufficient, but must be supplemented by determinations of the transformations of energy, because one of the chief functions of food is to supply the body with energy. Moreover, the study of the transformations of matter is rendered more complete and intelligible by a knowledge of the transformations of energy. 1 Amer. Journ. Physiol. (1905), 13, pp. 45-115. 'Zeits. f. physiol. Chem. (1905), 43, p. 532. IB 2 A RESPIRATION CALORIMETER. Experiments in which the balance of income and outgo of nitrogen alone is determined are comparatively simple. The intake of nitrogen is that in the food and drink ; and since it is commonly accepted by physiol- ogists that none of the nitrogen from food or body material is eliminated in gaseous form, the only sources of output which are ordinarily con- sidered are the urine and feces. Doubtless because of the ease with which such experiments may be conducted, the number of nitrogen metabolism experiments that have been made is very large. For a study of the metabolism of fats and carbohydrates, however, an estimate of the gaseous output of the respiratory products, i. c. , carbon dioxide and water, and of the intake of oxygen, is, as has been stated, also necessary, in addition to the analyses of food, drink, and excreta. These determinations can not be even approximated without the use of apparatus specially constructed for the purpose, known as respiration apparatus, which is usually of necessity somewhat complicated. For the determinations of income and outgo of energy, which is measured in terms of heat, special forms of apparatus, designated cal- orimeters, are necessary, and these are likewise complicated. Since the more complete metabolism experiments are not so easily carried on, they are much less numerous than the simpler nitrogen metabolism experiments ; still the number in which more or less com- plete balances of income and outgo of matter, or energy, or even both, have been determined is relatively large, and several different forms of respiration apparatus and calorimeters have been used. It is not pos- sible to give here a detailed historical review of the development of such apparatus, and indeed it is hardly necessary, as extensive bibli- ographies and descriptions have been published elsewhere. It will be sufficient for the present purpose to mention these and to point out the different types of apparatus. Accounts of various types of respiration apparatus have been com- piled by Zuntz ' and Jaquet.* The various forms of apparatus which are of sufficient size to permit study of the respiratory changes in man or large animals may be divided into four classes. In the first class the subject is confined in a closed chamber for varying periods of time. The carbon-dioxide content of the air is de- termined at the beginning and again at the end, and the volume of the inclosed space being known, the amount of carbon dioxide eliminated during this period is thereby readily calculated. The apparatus of Chauveau* and Laulani^4 were constructed on this plan. 1 Hermann's Handbuch der Physiologic, 4, part 2, pp. 88-162. 1 Ergeb. der Physiol. (1903), 2, part i, pp. 458-469. ' Traite" de Physique Biologique, 1, p. 744. 4 ijle'ments de Physiologic, p. 355. INTRODUCTION. 3 The second type of apparatus is known as the "closed circuit." The subject is placed in a chamber through which a current of air is passed. The air leaving the chamber is purified by the removal of the carbon dioxide (and in some instances water) , replenished with oxygen, and returned to the chamber. This type of apparatus was that origi- nated by Regnault and Reiset. * It has been further developed by Hoppe- Seyler and Stroganow,2 and in principle is the basis of the apparatus to be described later in this report. This method permits of the deter- mination of carbon dioxide, water, and oxygen. A third form of respiration apparatus is that known as the "open circuit." The subject is placed in a closed chamber through which a current of air is drawn, the incoming and outgoing air being analyzed. This type of apparatus was first brought into successful use by Petten- kofer,3 and was afterward elaborated for use with man by Sonden and Tigers tedt,4 and by Atwater, Woods, and Benedict.5 It is interesting to note that Jaquet,6 by using a modification of the apparatus of Fetter son for exact gas analysis, has undertaken the deter- mination of oxygen consumed by man in an " open-circuit " apparatus. The fourth type of apparatus is used primarily for short experiments. By means of appliances attached to the mouth or nose the subject is supplied with normal air of known composition and the products of respiration are collected for analysis. With this apparatus it is possible to determine the oxygen absorbed and the carbon dioxide exhaled. This type has been perfected to a high degree by Zuntz7 and by Chauveau and Tissot.8 The development of calorimetric apparatus for use with animals and with man has been far less extensive than that of respiration apparatus. A summary of the methods and results of experiments on the income and outgo of heat of the animal body, which includes the work done up to about 1882, was published by Rosenthal.9 A description and discus- sion of more recent types of calorimeters is given by Laulanie,10 and also by Sigales.11 One of the earliest forms suitable for use with man and the larger animals was devised by Scharling12 in 1849. The subject 1 Ann. de Chim. et Physique (1849), 3, xxvi. 'Archiv. f. d. ges. Physiol. (1876), 12, p. 18. 3 Ann. der Chem. u. Pharm. (1862-3), Supp. 2, p. 17. 4Skand. Archiv. f. Physiol. (1895), 6, p. I. 5U. S. Dept. of Agr., Office of Experiment Stations Bull. 44. 6 Verhandlungen der naturforschenden Gesellschaft in Basel, 15 (1904), part 2, p. 252. 7Berl. klin. Wchnschr. (1887), p. 429. 8Comptes rendus (1899), 129, p. 249. 9 Hermann's Handbuch der Physiologic, 4, part 2, pp. 289-456. 10 Clements de Physiologic, pp. 556-565. "Traite" de Physique Biologique, 1, pp. 816-843. 12 Journ. f. prakt. Chem. (1849), 48, p. 435. 4 A RESPIRATION CALORIMETER. was placed in a closed chamber inside a larger room of constant tempera- ture. The rise in temperature of the inner chamber was noted and the heat emission thereby calculated. Similar types have been those of d'Arsonval,1 Him,2 and Vogel.s The newer forms are of two types : First, those in which the heat delivered from the body is lost through the walls by radiation and the calorimeter calibrated by determining the radiation constant ; and, second , those in which the heat developed is brought away by a cooling current of water flowing through the calorimeter chamber, the radiation constant being eliminated as far as possible. One of the most recent forms of the first type of apparatus is the ' ' emission ' ' calorimeter of Chauveau ; 4 the second type is that employed originally by Atwater and Rosa,5 and in its more developed form is to be described beyond. THE RESPIRATION CALORIMETER. As has been stated, the more satisfactory experiments are those in which the transformations of both matter and energy are studied. For such experiments it is essential that the apparatus used be so con- structed as to afford opportunity for" measuring at the same time both the respiratory products and the energy given off from the body. Among the various forms of apparatus referred to in the preceding paragraphs some were so constructed, and such is especially the case with the apparatus here to be described. To indicate its twofold func- tion as a respiration apparatus and as a calorimeter, it is designated a " respiration calorimeter." As will be explained in detail, the respi- ration apparatus is of the ' ' closed-circuit ' ' type of Regnault and Reiset ; the calorimeter is a constant-temperature, continuous-flow water calorimeter. In addition to the measurements of respiratory products and energy made directly by the apparatus, the experiments include, in determi- nations of matter, the analyses of the air in the apparatus and measure- ments of the amounts of oxygen introduced, and the weighing and analyzing of the food, drink, and solid and liquid excreta ; and in deter- minations of energy the measurement of the potential energy, i. e., heats of oxidation, of the solid ingredients of food, drink, and excreta. All these data constitute the factors of total income and outgo of both matter and energy. 1 Soc. de Biol. (1894), 27, i. *Recherches sur 1' Equivalent mecanique de la chaleur (1858). 3 Arch. d. Ver. f. wiss. Heilk. (1864), p. 422. 4Comptes reudus (1899), 129, p. 249. 5U. S. Dept. of Agr., Office of Experiment Stations Bull. 63. f DESCRIPTION. 5 Many of the forms of apparatus previously referred to were designed for experiments with lower animals, but some of them were for experi- ments with man. The particular apparatus here described was of this latter type (though it can be, and indeed in its earlier form has been, readily adapted for use with domestic animals) . Experimenting with man necessarily involves certain restrictions, such as the requirement of a varied and palatable diet, a rate of ventilation which shall insure proper purification of the air, an experimental period not unduly long, etc. ; but it is obvious that in investigations of the problems of nutri- tion of man it is a decided advantage to experiment directly with man. Otherwise, if domestic animals were used, it would be necessary to draw conclusions for omnivora (man) from results obtained with carnivora (dogs) or herbivora (sheep or cattle). Furthermore, in experimenting with apparatus as elaborate as this must necessarily be, it is of the greatest value to have the intelligent cooperation of the subject within the apparatus ; and the fact that there may be reasonable control of the muscular activity and sleep is also an advantage. As will be seen from the more detailed description beyond, the cham- ber of the apparatus is large enough to allow a man to stand or lie down at full length, and to move about to a limited extent, and it is provided with a chair, table, and bed, that may be folded up and put aside when not in use, so that the subject may sit, or lie down, or stand and move about at will, or as the conditions of the experiment prescribe. When the experiment involves muscular work, a suitable device on which work may be performed, and by means of which the amount of work done may be determined, is also provided. A window in one end of the chamber admits ample light for reading and writing, and as it faces a window in the laboratory, even allows something of a view out of doors. A telephone affords opportunity for communication with per- sons outside the apparatus. The air is kept constantly in circulation, the impurities removed from it, and oxygen restored to it. The temperature of the chamber is maintained very uniform, whatever the conditions of activity of the subject. Receptacles for food, drink, and excreta are introduced or removed through an aperture provided for the purpose. Every attempt is made to keep the subject comfortable and to have the conditions as nearly normal as possible. DESCRIPTION OF THE APPARATUS IN ITS EARLIER FORM. The respiration calorimeter at Wesleyan University has been in pro- cess of development about twelve years. Several publications describ- ing the earlier form of apparatus, with modifications and improvements, and reporting the experiments made with it, have been issued. 6 A RESPIRATION CALORIMETER. An account1 of the first form of the apparatus, published in 1897, consists of the description of a respiration chamber on the Pettenkofer principle, the arrangements for ventilating the same, and the accessory apparatus for analyzing the air of the chamber. With this description was included a report of four experiments in which the intake and output of nitrogen, carbon dioxide, and water were determined. Satis- factory determinations of the output of energy by means of the apparatus were not yet possible. In 1899 a description 2 of the apparatus in its next stage was published. This included a discussion of the measurement of heat eliminated from the body, together with a much more detailed description of the respi- ration chamber, accessory apparatus, and methods of manipulation and analysis. In this report was given a brief account of two experiments with man in which the balance of intake and output of both matter and energy was determined. A few months later another report,5 giving a detailed description of six metabolism experiments with men, including the methods of calcu- lating and interpreting the results, was published ; and this was fol- lowed in 1 902 by a report 4 in which were given the results of twenty- four experiments with men and a general discussion of the same. A more extensive report & of the results of twenty-six more experiments with men was published in 1903. This report gives also an account of many improvements and modifications of apparatus that had been developed in the course of the experiments ; and as the series of inves- tigations with the respiration calorimeter essentially as originally devised was completed, considerable discussion of general principles and deductions based upon results of the whole six years of experi- mentation was included. In addition to the research reported in the publications above referred to, the apparatus has been used for an investigation into the nutritive value of alcohol, the results of which are published in a separate report.' This report gives the detailed description and discussion of the results obtained in thirteen experiments with men in which alcohol formed a part of the diet. None of the experiments above referred to, however, were actually complete metabolism experiments, for the reason that determinations of 1 U. S. Dept. of Agr., Office of Experiment Stations Bull. 44. 2 U. S. Dept. of Agr., Office of Experiment Stations Bull. 63. 3 U. S. Dept. of Agr. , Office of Experiment Stations Bull. 69. * U. S. Dept. of Agr., Office of Experiment Stations Bull. 109. 6U. S. Dept. of Agr., Office of Experiment Stations Bull. 136. 8W. O. Atwater and F. G. Benedict: Mem. Nat. Acad. Sci. (1902), 8; U. S. Senate, 57th Cong., first sess., Doc. 233, p. 231. An experimental inquiry on the nutritive value of alcohol. t DESCRIPTION. 7 the amounts of oxygen consumed could not be made. It was believed that with accurate determinations of the quantities of the other elements the quantity of oxygen consumed could be approximately estimated by difference, and in one of the reports above mentioned such estimates were made according to the method elaborated by Rosa.1 It is obvi- ously much more desirable, however, to be able to make the oxygen determinations directly, the same as those of the other elements. As a result of some eight years of experimenting with the apparatus above referred to, plans were gradually evolved for attempting the measure- ment of the amount of oxygen consumed by men, and thus obtaining data for the calculation of the respiratory quotient. To do this involved considerable modification of the form of apparatus and the addition of several new accessory devices. Concurrently with the devising of the above modifications, many appliances were developed to insure greater accuracy in the measure- ments of heat and to extend the range of the calorimeter sufficiently to afford means of measuring heat at the rate of 600 calories per hour. These fundamental changes extend to all parts of the respiration calo- rimeter, which is consequently so modified in form and principle from what has been previously described as to render it a new apparatus and to call for a new description. It is the purpose of the present publication, therefore, to describe in detail the respiration calorimeter as now used. In this description the two functions of the apparatus will be treated separately — first the respiration apparatus, and second the calorimeter. Preliminary to these sections is a description of the laboratory in which the respira- tion calorimeter is installed. DESCRIPTION OF LABORATORY AND ARRANGEMENT OP APPARATUS. The respiration calorimeter here described is located in a room in the northeast corner of the basement of a large stone building, known as Orange Judd Hall, of Wesleyan University, at Middletown, Connecti- cut. The north and east sides of the room are the masonry of the building, about 75 cm. thick. On the south side of the room is a brick partition, about 42 cm. thick, through which are three openings, one with a door opening into a small room, and the other two leading to an alcove. The west side of the room is a wooden partition with a door and a large glass window. The wooden floor is laid on cement. There are three windows on the north side, about 130 cm. wide and 150 cm. high, and two windows on the east side, about 130 cm. wide Physical Review (1900), 10, p. 129. 8 A RESPIRATION CALORIMETER. and 185 cm. high. The eastern exposure affords direct sunlight until about the middle of the morning. After that time the direct light does not enter, but the room is excellently lighted and the walls and ceiling are painted white to aid in the distribution of the light. OBSERVERS ,_..TAJ3LE AlCOVC. ALCOVt Fio. i. -General Plan of the Respiration Calorimeter Laboratory. t DESCRIPTION. 9 For protection against severe changes of external temperature during the winter months, double windows are provided. The room is heated by steam-pipes near the ceiling and by gas stoves. Two ventilating fans belted to the main shaft have their blades so adjusted that the warm air at the top of the room is continually forced down. It is pos- sible to keep the temperature of the room comfortable for work, but the regulation is far from that of a constant-temperature room. That accurate calorimetric work can be done in a room with such an uneven temperature is because of the peculiar construction of the calorimeter, as described beyond. The general plan of the laboratory room is shown in figure i. The room is entered by the door near the southwest corner. The door near the southeast corner leads into a small annex used for a kitchen, and containing ice-chests and tanks. The two other openings in the south wall lead to an alcove used as a tool and supply room. The respiration chamber is seen in about the middle of the north side of the laboratory, separated from the north wall by an air-space of about 75 cm. As may be seen in figure 2, the wooden walls sur- rounding the chamber extend from floor to ceiling. To the south of the respiration chamber, about in the center of the laboratory, is the long table on which are the rotary blower for maintaining a current of air through the apparatus, the absorbers for removing the water vapor and carbon dioxide from the air current, and the appliances for the introduction of oxygen. Suspended from the ceiling at the north side of the laboratory is the shafting by which power from the electric motors on the west side is transmitted to the water-pump and the rotary blower. The small table at the west of the chamber is convenient for the deposit of articles to be passed into or out of the chamber through the aperture just above it. At the east end of the chamber is the observer's table, and just beside this is the water-meter. Around the walls of the laboratory at convenient points are desks, tables, balances, sink, etc. Near the door entering the laboratory is a barometer, securely attached to stanchions and well isolated from sudden changes in temperature. The rack in one of the entrances to the alcove at the south is for storing extra carbon-dioxide absorbers. The disposition of the apparatus and accessories in the room was made with a view to facilitating manipulation and to conform to the previously existing shape and construction of the laboratory room, which was in no sense peculiarly adapted for calorimetric work. A general view of the laboratory room, taken from the southeast window, is shown in figure 2. 10 A RESPIRATION CALORIMETER. In figure 2, the table supporting the absorbing system, the rotary blower, and the apparatus for the introduction of oxygen appear in the center of the foreground. The respiration chamber in its wooden cas- ing, with the glass door in the east end, is immediately at the right, and adjacent thereto are the observer's table and water-meter. The air- pipes conducting air to and from the respiration chamber are suspended near the ceiling and extend across the front end of the chamber. At the left, securely attached to the brick wall, is the balance for weigh- ing the absorbing apparatus. In the rear and immediately at the right of the door is the barometer closet attached to two stanchions. Another general view of the laboratory, showing more of the detail of the respiration chamber, is given in figure 3. The door of the res- piration chamber is open, thus showing a little of the interior. The observer's table, water-meter, and galvanometer hood are at the right, and at the left the absorbing apparatus, rotary blower, and balance are shown. A view taken from near the sink, figure 4, shows the rear end of the chamber. In the center of this end of the chamber is the opening through which the food and excreta are passed, shown here with the outer door open. On the table immediately beneath it are character- istic vessels used to introduce or remove material from the chamber. The absorbing system is shown immediately at the right. On the end of the absorbing-system table are seen the two pans with rubber dia- phragms (one of which is distended) which are used to indicate apparent changes in volume of air in the whole system. Farther at the right is seen the water-pressure regulator standing in [the arch leading to the alcove room used for storing apparatus. The details of the absorbing system are better shown in figure 5, which was taken from a position in the alcove room near the water- pressure regulator shown in figure 4. The smaller of the two pipes near the ceiling at the right conducts the air from the respiration chamber to the rotary blower. The blower forces the air through the absorbers on the table. The air, freed from carbon dioxide and water vapor, then passes upward to the pipe lying on the top shelf of the table, to which the two pans are attached. To the right of the pans the oxygen is supplied to the air in this pipe from the cylinder with a large U tube attached to it, standing upright near the center of the top shelf of the table. After being supplied with oxygen the air proceeds along the horizontal pipe to the end of the table, where it passes through the vertical section, and thence along the ceiling around the corner of the chamber, entering it immediately at the left of the observer's table. The small tubes and the Elster meter at the right, on the top To face page 10-1. FIG. 2.— The Laboratory Room. View from southeast corner. Respiration Chamber at right; Water and Carbon-Dioxide Absorbing System in center ; Balance for Weighing Absorbers at left. FIG. 3. — Laboratory Room. View from east side. Observer's Table and Water-Meter in foreground ; Window of Respiration Chamber open ; Absorbing System and Balance at left. TO face page 10-2. FIG. 4. — Laboratory Room. View from near the sink. Rear of Respiration Calorimeter Chamber showing Food Aperture. Absorbing System and Pans at right. FIG. 5. — Laboratory Room. View from Alcove near Water-Pressure Regulator. Details of Absorbing System, Klster Meter Connections, Oxygen Cylinder, and Pans. THE RESPIRATION APPARATUS. II shelf of the table, are used for the analysis of the residual air in the chamber. These various features of the apparatus are described in more detail beyond. The above description is simply to afford a general idea of the laboratory and apparatus as a whole before the more specific explanation is undertaken. THE RESPIRATION APPARATUS. GENERAL PRINCIPLE. The respiration apparatus in its present modified form is constructed on the " closed-circuit " plan. It consists of a chamber large enough for the subject — a man — to live in comfortably, and ventilated'by a cur- rent of air which is kept in circulation by a rotary blower. Provision is made for purifying the ventilating current of air, which is, after puri- fication, returned to the chamber. The general scheme of the apparatus is shown diagrammatically in figure 6. RESPIRATION 0 used H30 CHAMBER ^-»,o i nt rpducsd FlG. 6. — Diagram of Circulation of Air through Respiration Apparatus. In the upper portion of the figure the respiration chamber is shown, and below it the blower and absorbing or purifying system. Air from the chamber, containing nitrogen, carbon dioxide, water vapor, and a somewhat diminished percentage of oxygen, passes through the blower and enters the absorbing system. Here it is forced through sulphuric acid to remove the water vapor, and through a specially prepared soda lime, which takes out the carbon dioxide. The soda lime, however, contains water, more or less of which is taken up by the air current. 12 A RESPIRATION CALORIMETER. The air is therefore again forced through sulphuric acid (not shown in the diagram) and then enters a pipe leading back to the chamber. It is now freed from carbon dioxide and water, but still deficient in oxy- gen. The oxygen is replenished by admitting the requisite amount from a steel cylinder of compressed oxygen through an opening in the ventilating air-pipe, as shown in the diagram, and the air when restored to a respirable condition reenters the respiration chamber. The metal walls of the chamber and the metal pipes confine the air in a definite volume, and to allow for expansion or contraction of the air volume as the result of barometric or thermometric fluctuations a compensating device, consisting of two pans with flexible rubber covers, is inserted in the ventilating air-pipe. The amounts of water and carbon dioxide absorbed by the sulphuric acid and soda lime and of oxygen admitted to the system are obtained by direct weighing on suitable balances. These weights give an approx- imate estimate as to the carbon dioxide, water, and oxygen involved in the transformations which have taken place in the body. There may be, however, considerable variations in the composition of the air in the system from time to time, especially as regards the oxygen content, which are not detected in this way. Since the volume of air in the closed circuit is comparatively large, even a slight variation produces a considerable error. It is therefore necessary to know the composition of the air at the beginning of an experiment, and also of the residual air at the end of each experimental period. Apparatus suitable for this purpose has been especially devised and is described in connection with the respiration apparatus. From these data as a whole, with suitable corrections to be explained in detail, it is possible to compute accurately the amounts of oxygen absorbed and carbon dioxide and water eliminated by the subject during an experiment. THE RESPIRATION CHAMBER. The respiration chamber is an airtight, constant-temperature room, 2.15 meters long, 1.22 meters wide, and 1.92 meters high, with a total volume of about 5,000 liters. It is lighted by a window on the east side, and has several other openings for the admission and removal of food, air, etc. It is furnished with a table and bed, both of which may be folded against the walls when not in use, a chair, a telephone, and, in certain classes of experiments, with a bicycle ergometer. A view of the interior taken from the window is shown in figure 7, and in figure 8 a cross-section of the chamber showing the location of some To face page 12. FIG. 7. — Interior of Respiration Chamber. Bicycle Ergometer in Foreground. Food Aperture with door open in rear. Heat-Absorbing System and Aluminum Troughs near Ceiling. Electrical- Resistance Thermometer-Coil just above Food Aperture. f THE RESPIRATION APPARATUS. 13 of the furniture and fixtures is given, while figure 33, on page 124, gives a clearer presentation of the interior appearance. The ceiling, floor, and walls of the chamber, with the exception of the window and the various other small openings to be described, are constructed of sheet copper. The use of metal is especially advanta- geous in securing an airtight chamber. A so-called " i4-ounce " sheet copper (Brown & Sharpe gage No. 24), cold-rolled, was selected, extra large sheets being specially obtained to reduce the number of seams to a minimum. For the floor of the chamber two of the sheets were soldered together in such a manner that one seam runs lengthwise of the chamber, and were then cut to the area and form of the chamber (the corners being rounded, as shown in several of the figures given). The ceiling is a duplicate of the floor. For the sides and ends of the chamber, five of the sheets were soldered together side to side, and bent to conform with the ceiling and floor, which were then soldered to the upper and lower edges. The copper chamber thus constructed is fastened to a wooden frame- work or skeleton by means of strips of copper soldered to the outside of the chamber. Beneath the copper floor the framework is made solid — practically a wooden floor — to prevent the denting and puncturing of the copper when stepped upon. The respiration chamber also serves as a calorimeter chamber and is fitted with many devices for the maintenance of constant temperature. For this purpose the chamber just described is surrounded by a similar chamber of zinc and an outer casing of wood. Detailed description of these features is deferred to that portion of the report dealing with the calorimetric apparatus. OPENINGS IN THE CHAMBER. While the copper wall of the chamber is carefully soldered at all joints, and therefore perfectly airtight, it contains, as has been indi- cated, a number of special openings. Certain precautions are neces- sary at these points to guard against leakage of air into or out of the system. Window. — The largest opening is that which serves both as door and window, shown at the front end of the chamber in figures 3 and 8. It is 49 cm. wide and 70 cm. high, being of sufficient size to allow a man to enter comfortably and to introduce and remove the various pieces of apparatus. A strip of metal which forms a small shoulder or beading on the inside of the window frame is securely soldered on all four sides. The opening itself is finally closed by a piece of plate glass which rests 14 A RESPIRATION CALORIMETER. against the metal shoulder and is held in place and made airtight by being thoroughly cemented with a wax prepared by melting together 9 parts of beeswax and 2 parts of Venice turpentine. The wax is first crowded around in the space between the edge of the glass and the metal, and then by means of a soldering iron it is melted and pressed into every crevice. A pin-hole through the wax is disastrous to accu- rate work. As the result of a number of tests, we have found that this method of closing the window is very satisfactory. Food aperture. — For passing smaller objects, e.g., food containers, etc. , into and out of the respiration chamber during the progress of an experiment, it is necessary to provide an opening which can be opened and closed without leakage of air. The arrangement adopted consists practically of a brass tube through the walls, with a hinged port at each end, such as is used on vessels. (Figs. 8 and 33.) The inner port is soldered directly to the copper wall and to a metal ring which in turn is soldered between the zinc and the copper wall. The door closes on a rubber gasket making an airtight joint. The outer port is tightly soldered to a brass tube 24.3 cm. long and 15.2 cm. in diameter, which extends into the food aperture to within 5 mm. of the door on the inside. This brass tube has a smaller diameter than that of the metal tube soldered between the metal walls, and there is accordingly an annular space between these metal tubes. Since the inside port is soldered to the ring forming the outer boundary of this annular space and the outside port is soldered to the tube forming the inner boundary, it is only necessary to fill this space completely to make an airtight joint. After considerable experimenting with solid-rubber rings, cement, wax, etc., a flat rubber tube with a smaller tube and valve attached to it in such a manner that it could be inflated like a bicycle tire was utilized. (See D, fig. 8.) The smaller tube and valve project through the outer wall of the calorimeter just below the opening for the food aperture. The large rubber tube is held in place between the two metal tubes by a thick coating of shellac, and when once put in place and well inflated a tight closure is maintained. Air-pipe openings. — The openings for the pipes conducting the air into and out of the chamber are placed on the right of the front end of the chamber (see V, figs. 8 and 30) a little above the center line. The two round openings in a rectangular box (see fig. 30) are the air- pipe connections. The construction of the box, the connection of the pipes, and the method of attaching and securing tight closure to the copper wall are shown in detail in figures 32 and 33. Two heavy brass flanges, threaded on the inside, are well soldered to the copper wall, the THE RESPIRATION APPARATUS. S. 3 O Oi O I O < 1 6 A RESPIRATION CALORIMETER. one about 96 mm. above the other. Two brass pipes, 40 mm. internal diameter, 1 70 mm. long, are screwed into these shoulders. To provide for slight differences in the exact position of the chamber when it is withdrawn and again put in place in the wooden house, it was found desirable to have the final coupling with the outside air-pipes more or less flexible, and consequently the coupling was attached to the brass pipes screwed into the wall by short lengths of thick- walled rubber tubing. A small wooden box with openings for the two pipes was attached by wax and small nails to the zinc wall of the chamber and wooden upright between the zinc and copper walls. The box was so adjusted that it held the flexible couplings in the proper position for satisfactory connection to the outer air-pipes. Plaster of Paris was poured into the top of the box and the whole mass allowed to set ; this serves as an excellent support for the pipes, and yet the flexibility of the rubber allows considerable twisting motion in making the connections. When the chamber is put in place in the house the rectangular box supporting the air-pipes fits perfectly into an opening through the two front panels, shown to the left of the window open- ing in figure 31. The box is sufficiently long to project clear through both wooden walls and thus allow the making of an easy connection with the air-pipes outside. With this arrangement there can be no leakage through the air-pipes or through the joint between the air-pipe and the inner copper wall. Opening for weighing apparatus. — In order to permit of accurate weighing of the subject inside the respiration chamber, the weighing apparatus shown in figure 46 is situated on the floor of the room above the chamber and a metal rod connects the scales with the chair upon which the subject sits ; consequently an opening through the top of the chamber is necessary to allow the passage of this rod. This opening is 35 mm. in diameter, and consists of a hard rubber tube tightly screwed into a metal flange soldered to the top of the copper wall. When the weighing apparatus is not in actual use the opening is closed by a tightly fitting rubber stopper. A number of tests have shown that this closure can be made uniformly without leak. Opening for the water-pipes. — As is described in detail beyond, a water current is used to bring away the heat generated by the subject. The passage of this current through the metal walls was secured by solder- ing to the opening in the walls a stiff metal ring, as in the case of the food aperture. A round wooden plug, previously well boiled with par- affin to render it non-porous and so prevent gain or loss of water, was then driven firmly into this ring and tightly sealed by means of wax. The plug is shown in position in figure 30 immediately at the right and t THE RESPIRATION APPARATUS. 1 7 a little below the window opening, and also in figure 32. The water- pipes were embedded in this plug, side by side, about 55 mm. apart, and the orifice sealed with wax at the point where the pipes leave the plug inside the chamber. By this means it is possible to have the water current enter and leave the chamber without leakage of water or air. Through the wooden plug also pass two wires used in the meas- urement of the temperature of the incoming air current (p. 122). The openings through which these wires pass are likewise sealed with wax. Rod for adjusting position of shields. — In order to raise and lower the aluminum shields of the heat-absorbing system described beyond, a rod passes through the metal walls and connects on the outside with a lever handle shown immediately beneath the window in figure 2, and with a metal quadrant (see fig. 32) to which the phosphor-bronze cables leading to the shields are attached on the inside of the chamber. In order to make the closure through which this rod passes airtight, we rely on a long close telescope-fit between the outside of the steel rod and the inner wall of the brass tube, which is soldered between the two metal walls. As an additional precaution, two or three layers of cotton wicking, well soaked with vaseline, are wound around the steel rod next the copper wall, the pressure of the lever handle on the outside holding the wicking tightly in place. Electric-cable tube. — The various electric circuits used in temperature measurements and for the telephone are brought together to form a large cable which passes through an opening in the two metal walls, shown in figure 29, a little above the center of the side of the chamber. In this opening, as in the food aperture and wooden plug, a copper tube was soldered to both the zinc and the copper walls. The cable was then inserted and the absolute closure made by coating the space be- tween the cable and both the inside and the outside ends of the copper tube between the two walls with wax. Furthermore, to prevent a leak- age of air through the cable itself (between the strands) , wax was melted into the end of the cable at the point where the wires separate. PIPING AND VALVES TO THE BLOWER. The air from the chamber passes through the opening A2 (fig. 33) to the air-pipe leading to the blower. This pipe is of galvanized iron 25 mm. in diameter, with ordinary steam fittings and connections. After the piping had been put in place it was subjected to a test of 50 pounds pressure to the square inch. The air leaves the chamber, rises through a short length of pipe, and then passes along the ceiling, makes a turn at the corner of the 1 8 A RESPIRATION CALORIMETER. chamber, and descends into the blower. The passage of 75 liters of air through this size and length of pipe results in a slightly diminished pressure (3 cm. of water). From time to time a sample of air is withdrawn from this pipe for analysis, it being assumed that the composition of the air in the pipe between the chamber and blower is essentially that of the air in the chamber. (See p. 81.) To obtain a valve that will close completely, an opening in the pipe in which there is a diminished pressure has been found a difficult thing, and recourse was had to a mercury valve which was attached to the vertical section of the pipe above the blower. This valve consists of a glass Y tube, one arm of which was attached to the air-pipe and the other connected to the residual-analysis apparatus. To the stem of the Y a glass bulb filled with mercury was attached by means of a piece of rubber tubing. By raising this bulb, mercury rises in the stem of the Y tube and closes the connection between the two arms of the Y. On lowering the valve a free passage is obtained for the air. An ordinary one-inch ' ' angle ' ' valve was placed in the pipe as it descends from the ceiling to aid in testing the air-circuit from time to time. This valve, as well as that in the return air-pipe, is shown in figure 5, near the ceiling. THE ROTARY BLOWER. Considerable difficulty has been experienced in obtaining a suitable apparatus for maintaining the ventilating current of air in the system. An attempt was made to use the Blakeslee mercury pump used in the earlier type of respiration apparatus,1 but the possible danger of mer- cury vapor in the air prevented its use in a closed circuit. Several other forms of mechanical pumps were devised, built, and tested, but were ultimately discarded in favor of a rotary blower. A blower was obtained in the market, and after undergoing modification was adapted to the specific purpose of maintaining a ventilating current of air for this apparatus. The advantages of a rotary blower over a pump are numerous. In the first place, the current of air is very much more constant, since with the pump there is more or less intermittent motion ; but more important than any other is the fact that it is possible to immerse the rotary blower in oil and thus minimize and detect leakage of air. The blower and the receptacle containing cylinder oil in which the blower is immersed, together with the air-pipes leading to and from the blower, are shown in figure 9. 1U. S. Dept. of Agr., Office of Experiment Stations Bull. 63, p. 31. THE RESPIRATION APPARATUS. The blower consists of a cylinder A, perforated laterally by the open- ings a and b for the entrance and exit of the air current. Inside the cylinder and arranged eccentrically with it is a revolving drum B, bearing on its axis the rod F which carries at each end a piston, G and G1. The piston G has a tight connection with the rod, while G1 is cushioned on the springs H. As the drum B is revolved the rod slides so that the pistons press against the inner face of the cylinder and prevent a backward escape of air, and the current entering through a is forced out through b into the absorber system. The box in which the blower is placed is made of cast iron and provided with stuffing-boxes through which the shaft or axis of the revolving drum B and the pipes a and b pass. Any leakage of air in the blower is instantly detected by the bubbles of air in the thick cylinder oil. The shaft is oiled by unscrewing two long rods, which are tapped into oil-holes on each side of the blower. Leather washers on the rods insure tightness when screwed down. To avoid es- cape of air the blower is oiled only when at rest. In order that no oil may be drawn into the absorbing FIG. 9.— Rotary Blower. Air enters at a, is forced about System a trap is provided, as ^e Drum B by Sliding Pistons G and Oi, and is driven shown in figure 10. The tube .t is prolonged into the blind passage s s. The oil collects in the bottom of this tube, and by removing the plug h may be drawn off from time to time. It is impossible to eliminate the use of a small amount of lubricating oil from a blower of this type, but we have found that the amount of oil mechanically carried forward by the air current is ex- tremely small and is practically all collected in the trap. Furthermore, before reentering the chamber the air passes through strong sulphuric acid, by which any hydrocarbons would be absorbed. On the other hand, the partial reduction of sulphuric acid to sulphurous acid as a result of the absorption of hydrocarbons would do little harm, because of the absorption of this gas by the soda lime. The efficiency of the blower was tested by connecting it with a gas- meter for several weeks. It was found that the amount of air forced through the meter was almost directly proportional to the speed of 20 A RESPIRATION CALORIMETER. the blower ; consequently the meter was deemed unnecessary and was removed. For simplicity and efficiency, it is very much to be doubted if an apparatus could be devised which would materially improve the condi- tions now obtained with this simple form of blower. While the pressure of the air is, under the conditions here used, but 35 mm. of mercury, tests have shown that the blower would give still greater pressures in case they were necessary. By means of a small counter-shaft attached to the ceiling of the calo- rimeter laboratory, it is possible to start and stop the blower without disturbing the other machinery. MERCURY VALVES. Inasmuch as the experimental day is generally subdivided into twelve periods of two hours each, it is necessary to provide means for diverting the main air current at the end of each experimental period through a second series of absorbers, and thus provide for the weighing of the water and carbon dioxide absorbed by the first set. Accordingly, the main air-pipe conducting the air from the blower to the absorbers and that leading from the absorber system to the respiration chamber are divided, and a system of valves is employed to cut off the air-circuit at the beginning and end of each of the absorber systems. The two valves at the end nearest the blower are shown in figure 3, and figure 4 shows the two valves at the opposite end. A closer view of these valves is given in figure 18. By opening the valve at each end of one set of absorbers and closing both corresponding valves on the other set, air can be caused to traverse either system as desired. The requirements for these valves are such as to demand a special form of construction. At the point where the air enters the absorbing system it is under an increased pressure of 40 to 50 mm. of mercury. At the other end, i. e., where the air leaves the absorbing system, it is at atmospheric pressure. While the problem of a valve at the exit end of the system is simple, that of devising a suitable one for the other end presented certain difficulties which were overcome only after consid- erable time. It is necessary that this valve should be sufficiently tight to withstand without a leak an increased pressure of 40 to 50 mm. of mercury while the ventilating current of air is passing through it. On the other hand, for a period of at least two hours the valve must be capa- ble of being closed absolutely with atmospheric pressure on one side of the closure and an increased pressure of 40 mm. of mercury on the other. Furthermore, the valve must be of sufficient size to permit the passage of 75 liters of air per minute through it without a marked THE RESPIRATION APPARATUS. 21 resistance. No valve that we could find on the market would be guar- anteed by its manufacturers to meet these conditions. The form of valve finally used is shown in figure 10. The valve consists of a mechanical closure which is subsequently bathed in mercury, thereby giving a mercury seal. Air from the blower enters the tube /, passes around the annular space s to the valves, through the annular space a of the open valve, up through the vertical tube b, and then to the absorbers at d. Figure 10 shows the valves as in actual operation, one being open, the other closed. FIG. io.— Mercury Valves. By raising the mercury reservoir the mechanical closure made by the valve against end of tube b can be bathed in mercury. Direction of air current indicated by arrows. The valve at right is open, that at left closed. Tube G is inserted in mercury and is used for testing the system. To close the valve, the lower end of the tube b is shut off mechan- ically by pressing an iron disk, in which a fiber gasket g is inserted, firmly against its edges by means of the screw and spindle c. The closure is then made complete by immersion in mercury. The glass reservoir / is so raised that mercury can flow through the rubber tube m into the annular space a until the level desired is reached. To prevent leakage of air along the spindle, it is caused to traverse a length of pipe, the lower end of which is closed with a stuffing- box and gland nt and the annular space between the spindle and the 22 A RESPIRATION CALORIMETER. inner walls of the pipe is filled with mercury which flows down from above through the small holes o and ol. This column of mercury is approximately 100 mm. long, and its pressure, increased by the 50 mm. pressure of the air current, tends to force the mercury against the packing at the bottom and thus prevent the entrance of air. The valve is constructed of a 2-inch T, which is galvanized on the outside to fill possible blow-holes in the iron. Before galvanizing, the ends of the T were plugged to prevent the zinc entering the inner part and subsequently forming an amalgam. A reducer, r, is fitted in the top, and a short 2-inch nipple inserted in the lower part. The lower end of the nipple is covered with a cap, q. This cap was made from a special casting, and is provided with a small pipe to which the rubber tube m is attached. The ball and socket joint j minimizes lateral motion and consequent destruction of the fiber gasket g. The pipe b, which is screwed into the reducer r, has its lower end trued and the edges slightly rounded to prevent cutting the gasket. As is seen in figure 10, the connections from this pipe to both the blower and the absorbers are made with ordinary steam fittings. All the metal work of the valve is of iron or steel. When it is desired to open the valve, the reservoir / is lowered, and by reason of the pitch of the under side of the cap q every particle of mercury is drained out of the valve. The valve wheel is then turned and the mechanical closure opened. There is then a free passage for the air through the side tube, around the annular space, and up through the tube b. When the valve is opened the only chances for a leak are around the coupling d and through the stuffing-box n. The coupling d is the same as is used at all other junctions of the absorbing system, and when connected is always specially tested (see p. 32) to insure against leak at this point. The tendency of the mercury is to press out of the stuffing-box n ; consequently no leak has ever been found. When the valve is closed one of the chances for leak is shifted from the coupling d to the closure of the pipe b, for after removal of the water-absorber attached at d the air in the annular space a a is at a pressure of from 30 to 50 mm., while that in b is at atmospheric pres- sure. Because of the mechanical closure on gasket g and the mercury seal, no air can pass from a to b. It sometimes happens that the gasket g becomes worn or cut, or that a particle of dust gets in between g and the pipe b, thereby preventing a tight mechanical closure. Under these conditions, unless the column of mercury above the level of g is sufficiently high, there may be a slight leakage of gas down through the mercury into the inside of tube b. This condition is, however, seldom present, and suitable tests for such a leakage have been devised. t THE RESPIRATION APPARATUS. 23 The details of manipulation in changing from one absorber system to the other are somewhat important. The first step is to open the valve at the exit end of the new absorber system. This operation, of course, is not carried out until the absorber system has been tested and coupled up, as described on page 32. Inasmuch as there is no tension in the pipe leading from the absorber system to the chamber, this preliminary step does not affect the volume of air. At one-half minute before the end of the experimental period the reading of the pointer on pan No. i l is recorded, pan No. 2 being in general kept empty. At 10 seconds before the end of the experimental period the blower is stopped. The mercury reservoir on the valve connected with the new absorber system is then lowered, and at the exact end of the experi- mental period the reading of the pointer on pan No. i is again recorded. As soon as this is done the wheel on the valve connecting with the new absorber system is opened, and the wheel on the valve connected with the old absorber system is simultaneously closed. The mercury reservoir is then raised to seal the closed valve and the blower is started. The valve at the rear or exit end of the old absorber system is still open, but inasmuch as the air is under no pressure this valve may be closed at leisure. APPARATUS FOR THE DETERMINATION OF WATER. The water vapor eliminated by the subject through the lungs and skin is removed from the chamber in two ways — part of it is condensed within the chamber and collected as drip, but the major part is carried out in the air current as water vapor and removed from the air by dehydration by sulphuric acid. COI,I,ECTION OF DRIP. Condensation of water vapor within the chamber is due to the method of absorbing and removing the heat eliminated by the subject, as ex- plained on page 1 25. The apparatus for collecting the drip may be seen in figure 33, on page 124. The temperature of the water in the heat-absorbing system is some- times below the dew-point of the air of the chamber. It frequently happens, therefore, especially when the subject is working hard and there is a large quantity of water vapor in the air, that the surface of the heat absorber becomes covered with condensed moisture and the water drips from it. This water is collected in the aluminum shields (Sd in fig- 33) used to regulate the rate of heat absorption, which are pur- posely made water-tight. 1 For a description of the pans see page 39. 24 A RESPIRATION CALORIMETER. The cold air which settles in the bottom of the aluminum shields cools them so noticeably that frequently they, too, begin to condense water on the outside. To collect this water another trough, or, more properly speaking, gutter (Dt in fig. 33), is attached to the bottom of each shield to conduct the water dripping from the aluminum trough to a proper container (Dc in fig. 33). The shields do not encompass the heat-absorber pipes at the corners, as may be seen in figure 33. It was frequently found, however, that the copper pipe became coated with moisture and the water thus con- dens ed dropped to the floor of the chamber. To collect this moisture the drip-cans into which the water from the troughs is emptied are suspended from the copper pipe at the corners and are of such shape that they catch any water that drips from the pipe. The water may be drained from these cups into bottles and weighed. To determine the total quantity of water thus condensed it is neces- sary to know how much remains on the surface of the heat absorbers not collected as drip. For this purpose provision is made for weighing the whole heat-absorbing system, as explained elsewhere. REMOVAL OF WATER VAPOR FROM THE AIR CURRENT. The problem here is the removal of a large amount of water vapor from an air current flowing at the rate of 75 liters per minute. For this purpose the air is caused to pass through concentrated sulphuric acid in a specially devised container. From numerous preliminary experiments it was learned that none of the common solid absorbents for water, such as calcium chloride and phosphorus pentoxide, could be relied upon to remove water from a large air current as completely as does the acid. DESCRIPTION OF THE WATER-ABSORBERS. The difficulty with using sulphuric acid as the absorbent is that it is next to impossible to obtain a satisfactory container for it other than glass, and it was feared that the large size of the absorber would make a glass vessel so unwieldy that it would be readily broken. A large number of experiments were made testing the resistant powers of copper, aluminum, hard rubber, gold-plated copper, and various enameled wares. As the result of these tests it was found that enameled iron resisted the action of the strong sulphuric acid admirably, and a set of absorbers made from this material was in use for over a year. It was, however, impracticable to construct a form of absorber from this material of fewer than two parts, and equally impossible to join the two parts so as to prevent permanently leakage of air. Consequently the use of enameled ware was abandoned. t THE RESPIRATION APPARATUS. 25 Recourse was then had to earthenware absorbers, the parts of which, by means of heavy glazing, could be tightly joined together. This type of absorber, while by no means all that could be desired, has given fair results and is still in use.1 The external appearance of the water absorber is shown at the right in figure 1 1 . The absorber is 300 mm. high, 285 mm. in diameter, and contains about 14.5 liters. There are three openings in the top — two 40 mm. in diameter for the entrance and exit of the air current, and a smaller one of 15 mm., which is used for emptying and recharging the absorber with acid. When the absorber is in use this opening is closed by a well-vaselined rubber stopper, and the larger openings are connected by couplings to the remainder of the absorber system. For convenience handles are put on each side of the absorber, each being perforated in the center to admit of the attachment of hooks for supporting the absorber during weighing. Each can is numbered with enamel paint. The interior construction of the absorber is shown at the left in figure 1 1 . The tube through which the air enters extends nearly to the bottom of the can and has four openings or slots in its lower edge. A circular disk not seen in the figure, 160 mm. in diameter, having a rim 30 mm. deep, with a large number of holes in its edge, is fastened 30 mm. above the lower end of the extension tube. A larger disk 240 mm. in diameter, having a still deeper rim also provided with holes in its periphery, is attached to the central tube 35 mm. above the first disk. Acid is poured into the can until the whole flaring end of the extension tube is immersed in acid, about 5.5 kg. being sufficient for this purpose. Air descending through the entrance tube first passes through the four openings in the end of the tube and, bubbling through the acid, collects under the first disk ; it then passes out through the small holes in the periphery and, bubbling through sulphuric acid the second time, enters the second chamber, where it collects under the second or larger disk. It then passes through the openings in the edge of the larger disk and bubbles a third time through the acid to the sur- face, whence it escapes through the second large opening in the top of the can. To prevent spattering and escape of acid fumes through this opening it is protected by a perforated earthenware cup filled with a layer of pumice stone and a layer of asbestos. A thimble of wire gauze is then fitted into the opening to prevent any of this material from sifting out when the can is turned over, as in emptying. It is thus seen that the air bubbles through acid three times, and as the bubbles are subdivided by the holes in the periphery of the disks, the 1 We are indebted to the Charles Graham Chemical Pottery Works of Brooklyn, New York, for much assistance in obtaining these absorbers. 26 A RESPIRATION CALORIMETER. dehydration is very complete, even though the depth of acid through which the air passes is not great. The absorbers are constructed to withstand increased pressure, and consequently in testing for tightness a water manometer is attached and air forced in. If a leak is indicated by the manometer it can be located by either coating the joints with soap solution or immersing the whole absorber in a vessel of water and noting any escape of air in the form of bubbles. For connecting the absorbers to each other and to the valve, metal couplings are used, but the desired flexibility of the parts is secured by means of a specially made elbow of rubber.1 The simple form of coupling shown in figure n, when used with a soft rubber gasket 2 mm. thick, has invariably resulted in a perfectly tight closure. Durability of the water-absorbers. — When the absorbers were first obtained they gave excellent satisfaction in every way. After about three months' use, however, it was noted that the acid had penetrated the earthenware and was collecting in drops on the outside of the absorber. As a result of a number of tests it was found that after thoroughly washing the absorbers to free them from acid and then drying at 1 00° in a water-oven until thoroughly dry, boiling- hot paraffin could be forced into the porous material and thus prevent leaking. The hot dry absorber was removed from the water-oven, a pint of boiling paraffin poured into it and well shaken about so as to insure contact with all portions of the interior, and then the excess of paraffin poured out. The openings in the top of the absorber were then carefully corked and a pressure of 10 or 15 pounds applied by forcing air into the absorber with a bicycle pump. As the absorber cooled, the paraffin solidified, filling the porous portions of the absorber. This treatment has thus far given excellent satisfaction. Efficiency of the water-absorbers. — The greater the efficiency of the water-absorbers the fewer required in series and the longer they can be used. It was found that with a current of air passing at the rate of 75 liters per minute an absorber freshly charged with sulphuric acid would remove 500 grams of water vapor from the air current before allowing any water vapor to pass through unabsorbed. As the system is now arranged, one absorber is used to remove the water from the air cur- rent and another to collect the water taken up by the air current in its passage through the carbon-dioxide absorbers. In practice, a record is kept of the weight of each absorber, and when a gain of 400 grams 1 These elbows were furnished upon specifications by the Davol Rubber Co., Providence, Rhode Island. To face page 26. FIG. it.— Water-Absorbers. At the right is a complete Absorber with rubber elbows and connections. At the left is represented the interior of an Absorber, showing the method for breaking up air-bubbles as the air passes through the acid, the device for preventing the escape of acid through outgoing air-pipe, and the opening by means of/which the Absorber is filled and emptied. FIG. 12.— A Carbon-Dioxide Absorber showing Cylinder Cap, Collars, Wire-gauze Disks, and Cakes of spent Soda Lime. t THE RESPIRATION APPARATUS. 27 is noted, /. e. , 100 grams less than tests have shown to be absolutely safe, the spent acid is removed and replaced by a fresh supply. Supply of sulphuric acid. — With this form of absorber for the removal of water vapor from the air the use of considerable quantities of sul- phuric acid is necessary. It has been found that the ordinary grades of concentrated sulphuric acid, specific gravity 1.84, are admirably adapted for this work. The acid is purchased in carboys and conse- quently the expense for this reagent is small. APPARATUS FOR THE DETERMINATION OF CARBON DIOXIDE. As the air leaves the first water-absorber it is perfectly dry, but still contains carbon dioxide and is somewhat deficient in oxygen. The next step in the process of purification is the removal of the carbon dioxide. For a number of years prior to the introduction of the closed-circuit system soda lime of special preparation was used in this laboratory for removing carbon dioxide from the air samples taken for analysis. The success attending its use for this purpose was such as to suggest it as a means for removing the total quantity of carbon dioxide from the main ventilating air current. From the area of the ordinary U tube, described on page 45, the rate and length of time of flow through it, and the length and weight of the layer of soda lime, it was calculated that a soda-lime container with a diameter of approximately 150 mm. and a length of approximately 380 mm. would be as efficient in removing carbon dioxide from an air current with a rate of 75 liters per minute (the usual rate of ventilation) as was the U tube in removing carbon dioxide from the air current with a rate of 2 liters per minute. After a number of experiments an absorber was devised which in its present form is shown in figure 1 2 and in cross-section in figure 13. DESCRIPTION OP THE CARBON-DIOXIDE ABSORBERS. The absorbers are constructed of seamless drawn brass tubing 150 mm. internal diameter, 380 mm. long, and with walls 1.5 mm. thick. One end consists of a brass disk to which a 64 mm. length of brass tube is permanently soldered and the joints stiffened by being well banked with solder. The other end is detachable and consists of a similar brass disk somewhat larger in diameter (157 mm.), which can be drawn up against a rubber gasket fitting against the face of a shoulder on the end of the main tube, so that by means of the large collar C (fig. 13) the opening can be tightly closed. All parts are heavily plated internally and externally with silver, which has been found to stand the action of the soda lime indefinitely. For convenience each can is lettered with blue enamel. 28 A RESPIRATION CALORIMETER. In order to facilitate the passage of the air current through the soda lime and prevent channeling, a number of wire-gauze disks about 148 mm. in diameter and 8 mm. in thickness (d, d, d, in fig. 13) are in- serted in each cylinder so as to divide it into compartments. In filling the cylinder the detachable cover is removed and a square of wire gauze is inserted in the opposite end. A layer of cotton, dl, about 10 mm. thick is then inserted and a cover of wire gauze is placed above it, these precautions being taken to prevent any of the soda lime from sifting out. For the same reason a small thimble of wire gauze, T (also shown in the extreme left of figure 13), is inserted in each end of the cylinder. The cylinder is then filled with soda lime for about one-fourth of its depth, one of the wire-gauze disks inserted, a second layer of soda lime of equal thickness in- troduced, another FIG. 13.— Cross-section of Carbon-Dioxide Absorber. Arrangement ,. . ,, , , . , in Cylinder, when Absorber is filled with Soda Ume, of Wire- dlsk added, a tnird gauze Disks d, d, rf. Thimbles T, T, and Square S, with layer of layer of Soda lime, cotton d1. are here shown. and then a disk, and finally a fourth layer of soda lime. A square of wire gauze, S, is then put in, the rubber gasket and cover set in place, and the collar screwed down tightly. Vise for tightening absorbers . — It is absolutely essential that this joint be tight, and as it is not safe to rely on the hands alone for this closure, we resort to the use of a clamp and vise devised by our mechanician, Mr. S. C. Dinsmore, and shown in figure 14. This device consists of two blocks of wood which offer a good sur- face to grip the smooth cylinder. By means of two metal screws on the top of the vise the two jaws are brought together and the cylinder firmly held without distorting it. A wooden clamp which is readily adjustable is then placed about the large collar C (see fig. 13), and by means of this the end and the cap can be screwed down tightly against the rubber gasket. Before removing the cylinder from the vise the tightness of closure is tested by means of a water manometer and air-pump. With proper precautions no difficulty is experienced in securing a tight joint. The cylinders are weighed on the large balance shown in figure 21, being suspended from one end of the balance beam by two loops of wire fitting over the small tubes in both ends of the can. When charged with soda lime they weigh approximately from 9.3 to 9.5 kg. t THE RESPIRATION APPARATUS. 29 Six of these soda-lime cans are always on the absorber-system table, three of them connected ready for use. The same form of coupling, i. e., that shown at right of figure 13, is used throughout the whole absorber system, i. e., on the water-absorber cans and on the valves at both ends of the absorber system. The cans not in use are closed at both ends with rubber stoppers and all extra cans are placed on a rack fastened to the wall. (See fig. i.) Removal of spent soda lime from the can. — After an absorber has be- come exhausted, i. e., when no further increase in weight is observed, the can is placed in the vise and the collar started one or two turns of the thread by means of the clamp. The can is then carried to some convenient place, the collar unscrewed with the hand, and the top removed. When the can is inverted the soda lime generally slips out of the can without any difficulty. The spent soda lime is of much lighter color than the fresh, and is usually found to have agglomerated into the form of cakes such as are shown at the right of figure 12. To insure the free removal of the spent soda lime the cans are occasionally given a thorough washing. Preparation of soda lime. — The use of a partially moist soda lime for the absorption of carbon dioxide seems to have been first adopted by Haldane1; but as our method of preparing soda lime is markedly dif- ferent from that used by Haldane, and tests that we have made indi- cate that its efficiency as an absorbing agent is considerably greater than that of the earlier preparation, a description of the method of its prepa- ration is given herewith. One kilogram of commercial caustic soda, preferably in the form of fine powder, is dissolved in 750 cc. of water in an iron dish. We have found a round-bottomed iron kettle admirably adapted to this pur- pose. When the caustic soda has all dissolved, or by stirring with an iron poker can be held in suspension, and while the liquid is still hot from the action of the soda and water, one kilogram of pulverized fresh quicklime is poured into the solution with constant and rapid stirring. The lime should all be added before the expiration of 10 seconds. The stirring should be continuous and the lime held in sus- pension as much as possible. In a few seconds the lime begins to slack in the soda solution and the mass in the iron dish becomes very hot, large quantities of steam escaping. Care should be taken to avoid the spattering of drops of hot alkali. Rubber gloves should be worn, and the operation conducted in a well-ventilated room or in the open air. . Physiol. (1892), 13, p. 422. 30 A RESPIRATION CALORIMETER. While the mixture is cooling the stirring is continued and the larger lumps broken into smaller bits as much as possible. It is then trans- ferred to a shallow pan and broken into small particles with a large iron pestle. Before being used the material is sifted through wire gauze with a mesh 4 mm. square, the larger particles being reduced by means of a pestle to a size that will pass through the sieve. When properly made the soda lime is sufficiently moist to appear distinctly damp, no dust being visible, and yet not so damp that it will ' ' cake ' ' when being crushed with the pestle. In color it is white with a slight yellowish tinge. The finished product is stored in galvanized - iron ash-barrels with the top hermetically sealed by a tin cover waxed at the edges. The caustic soda is purchased in cans varying in weight from 5 to 25 pounds, and as fast as a can is opened it is emptied into a large glass jar, which can be tightly closed. The requisite quantity for each batch is weighed out into a porcelain evaporating dish on scales weighing to within one or two grams. As a matter of fact, the observance of the exact proportions is not strictly necessary, and probably the weights taken vary from 10 to 20 grams from those given above. The pulverized quicklime is best obtained by taking a barrel of the best quality of fresh lime, pulverizing it with a pestle, and storing it in an iron ash-barrel, which can be carefully closed at the top. The lime in this condition is ready to be weighed and added directly to the strong lye. It is important that the lime used be very fresh, and each barrel should be tested to make sure that the material slacks freely. If the lime is not of standard strength, or if the proportions of the soda and lime are not carefully maintained, the mixture is likely to be too moist and form pasty lumps. In some instances it is possible to utilize such a product by mixing with it some especially dry soda lime, though as a rule the product would better be rejected and another lot of lime used. With due precautions and care, however, the manufact- ure proceeds smoothly and with minimum waste of material. A ton or more of this soda lime has been made in this laboratory in the past three years, and the method and finished product have been all that could be desired. Efficiency of the carbon-dioxide absorbers. — In the absorption of carbon dioxide by soda lime the reaction may be considered as resulting in the formation of calcium carbonate and sodium carbonate from calcium oxide and sodium hydroxide. Assuming that the soda lime is a mix- ture of equal parts by weight of sodium hydroxide and calcium oxide, a soda-lime can containing 6 kilos of soda lime should, theoretically, absorb not far from 4,000 grams of carbon dioxide. In practice, how- t THE RESPIRATION APPARATUS. 31 ever, the actual efficiency falls far short of these figures, and under the most favorable conditions only about 400 grams can be absorbed. While this efficiency is very far from the theoretical, it is none the less remarkably good, considering the conditions under which the absorp- tion takes place, /. e., a solid absorbent limited to surface absorption only, and indicates that the apparatus is well adapted for the absorp- tion of a relatively large amount of carbon dioxide from a rapidly moving current of air. The efficiency of the absorber has been found to depend very largely upon the rate of evolution of carbon dioxide. In the alcohol check experiments and in rest experiments with men, where the rate of evo- lution of carbon dioxide is fairly constant and does not exceed 50 to 60 grams per hour, the soda lime is more completely exhausted than in work experiments with men, where the amount of carbon dioxide may rise to 200 grams per hour. With this large quantity of carbon dioxide passing through the absorber system, the reaction between the soda lime and the carbon dioxide is so intense that the cans become very much heated. The soda lime seems to fuse or cake on the edges, and the in- terior of each section of soda lime is thereby partially protected from the action of the carbon dioxide. Under such conditions it is found that each can will not, as a rule, take up much more than from 100 to 125 grams of carbon dioxide before it is necessary to change. Further- more, all three cans in the system, shown in figure 5, during a two- hour period when the man is at hard work, take up approximately the same amount and all become heated. While it is possible to use these partially exhausted cans during the night period, when the subject is at rest and the rate of evolution of carbon dioxide at a minimum, it is not found safe to use such a partially exhausted can during a second work period ; consequently the can is opened and the soda lime re- moved. It is found on removing the different sections of the soda lime that instead of adhering in a solid white cake, as is the case when the soda lime is completely exhausted (see fig. 12), it crumbles and falls apart, except where the partial fusion or caking has taken place. By picking out the larger lumps of the partially fused material ' the major portion of the unused material can be saved and used to refill the cans. In this way the efficiency of the soda lime is not impaired, and the total amount of carbon dioxide absorbed by a given weight of soda lime need not, under such manipulation, fall much below the maximum amount under the most favorable conditions. *By "partially fused" it must not be understood that the temperature of the soda lime rises to anything like the fusing point of soda lime, but that there is an appearance not unlike fusion. 32. A RESPIRATION CALORIMETER. TESTING THE WATER AND CARBON-DIOXIDE ABSORBER SYSTEM. In a closed-circuit apparatus every precaution must be taken to guard against leakage of air ; hence the absorber system is frequently subjected to the most rigid tests for tightness. Each water-absorber is tested, immediately after being weighed, in the following manner : A one-holed rubber stopper fitted with a Y tube is inserted in the coupling of the water-absorber at the end through which the air leaves the can. One arm of the Y is connected with a water manometer capable of indicating pressures up to 4 feet of water, and the other arm is connected by means of a length of rubber tubing to a bicycle pump for obtaining an increased air-pressure. A solid-rubber stopper is used to insure a tight closure of the other coupling on the absorber. By means of the bicycle pump the desired pressure is put on the absorber, and the screw pinchcock on the rubber tube between the pump and the manometer is then tightly closed. After a prelim- inary fluctuation in pressure, which lasts for a moment or two, a piece of paper is slipped between the glass arm of the manometer and the wooden support at such a point that its lower edge just coincides with the bottom of the meniscus. A leakage of air from the absorber is accompanied by a fall of water in the manometer. No leakage should be apparent at the end of from three to five minutes. At the conclusion of the test the manometer is disconnected and the pressure released. An extended experience shows that after the removable ends of the carbon-dioxide absorbers are well screwed on a leak rarely occurs at this point ; consequently it is not necessary to test each individual absorber after weighing. The water- absorbers are then coupled with the three carbon-dioxide absorbers as in use and the system as a whole is tested to prove not only the tightness of the individual absorbers themselves, but also of all the couplings. In this test a solid-rubber stopper is used to close the coup- lings on the exit end of the last water-absorber, and the Y tube of the manometer is connected with the side tube G, figure 10, attached just beyond the mercury valve. Pressure is then put on the system by means of the bicycle pump and the tightness of closure tested, as for the separate cans. By the use of this method of testing, leaks in this por- tion of the apparatus have been practically eliminated. MAINTENANCE OP THE SUPPLY OF OXYGEN. To replace the oxygen consumed by the subject, as well as to main- tain a constant volume inside the system, supplies of oxygen are ad- mitted from time to time. The oxygen used for the purpose is a com- mercial product, the so-called "commercial oxygen" manufactured by FIG. 14.— Vise for tightening Carbon-Dioxide Absorbers. Top of Absorber is held in a wooden vise clamp by two handles ; Collar held in special clamp. FIG. 15.— An Oxygen Cylinder with Valve, Rubber FiG.i6.— Apparatus for Analysis of Oxygen and Air. Pressure Bag, and Purifying Attachments. On opening valve oxygen escapes through the metal tube through the purifying attachments. If the pressure is excessive, excess of gas enters bag. Two water-jacketed burrettes, Bt and B», each with water reservoirs, RI and Rj, are connected by the 3-way stopcock C. Pipette H is connected through a capillary (T) with the apparatus. t THE RESPIRATION APPARATUS. 33 the S. S. White Dental Manufacturing Company, of Philadelphia. This oxygen has been in use for some years in this laboratory in con- nection with the bomb calorimeter1 and the carbon and hydrogen determinations.2 It contains, besides oxygen, from 2.5 to 8 per cent of nitrogen and small quantities of carbon dioxide and water vapor, but no appreciable quantities of hydrogen or gaseous hydrocarbons. In preparing it for use it is necessary only to remove the carbon dioxide and water and determine quantitatively the percentage of nitrogen. The oxygen is contained in steel bottles or cylinders (fig. 15) 6 1 cm. high, ii cm. in diameter, weighing (exclusive of purifying apparatus), when charged with 283 liters of oxygen at a pressure of 2,000 pounds to the square inch, about 7 kg. A metal yoke is securely fastened to the valve with a screw clamp and leather washer, and a brass T tube conducts the oxygen into a rubber gas-bag * and through the side outlet to the purifying device. The use of the bag is imperative, for the pressure in the cylinder is so high that however carefully the valve is opened the gas escapes so sud- denly that the connections are liable to be disturbed unless an overflow for the surplus gas is provided. The gas then enters a large U tube fastened to the side of the cylin- der by means of two rubber bands. The U tube is filled with soda lime, such as is used in the carbon-dioxide absorbers in the main system. To prevent any particles of soda lime from being carried mechanically out of the U tube, a tuft of cotton batting is placed at the exit end. In its passage through the soda lime the gas is completely freed from carbon dioxide. It still retains the moisture it originally contained, and some that it has taken from the moist soda lime. To remove the moisture, the gas is next passed through a drying tube of special con- struction, filled with pumice stone drenched with sulphuric acid. A bulb at the lower end allows for the accumulation of spent acid. By an actual test it has been found that such a tube will remove all the water vapor from the oxygen in at least ten cylinders before it needs refilling. As a matter of fact, when the bulb at the lower end becomes filled with spent acid, the tube is removed, inclined so as to drain out the ^our. Am. Chem. Soc. (1903), 25, p. 569. 2 Benedict, Elementary Organic Analysis, p. 4. 3 The bags are made for us by the Davol Rubber Company, of Providence, Rhode Island. They are extra heavy wall, of pure rubber, and will withstand considerable tension without noticeable leak. It is estimated that a bag 21 cm. long (measured, when folded) will, as a rule, readily take care of 2 or 3 liters of oxygen without loss. It is seldom, however, that an excessive amount of gas enters the bag, as the adjustment can usually be readily made by means of the valve. 3B 34 A RESPIRATION CALORIMETER. acid, and several portions of concentrated acid poured in at the top, each successive portion being allowed to drain out before the next is added. Obviously such replenishment of acid is made only when the purifying system is to be changed from an empty cylinder to a new one, and, as pointed out above, at least ten cylinders can be used with each charge of acid. The replenishment of the soda lime in the U tube is made only when the reagent becomes exhausted, as is readily noted by the whitening effect on the reagent. (See p. 29.) By attaching the purifying device to the cylinder itself and noting the loss in weight in the system as a whole, the weight of gas used can be obtained, since it corresponds to the amount of oxygen and nitrogen leaving the cylinder. The quantity of oxygen consumed in the course of 24 hours by a subject, varying as it does from 350 to 1,500 liters, can be best determined in this way. By means of the balance described on page 57 it is possible to note the loss in weight of an oxygen cylinder to within 10 mg. As 10 cc. of oxygen weigh but 14 mg., it is thus seen that 283 liters (the contents of one cylinder) can be measured with an accuracy far beyond that of any gas-meter with which we are familiar. In all of the work with the respiration calorimeter this method of measuring oxygen is constantly used. In weighing, the cylinder is suspended on a wire from the balance- arm by two loops of wire, one around the valve end of the cylinder and the other, a much larger loop, around the bottom of the cylinder. The manipulation of the cylinder and its adjustment on the balance require a little care on the part of the assistant, but in spite of the use of glass tubes for absorbers there has been as yet no loss by breakage during weighing. ANALYSIS OF OXYGEN. Since the gas in the cylinder contains nitrogen as well as oxygen, and the amount of oxygen admitted to the system is estimated from the loss in weight of the cylinders, it is obviously necessary to analyze the gas and determine the percentage of nitrogen. As has been stated, the amount of nitrogen generally present is not far from 2.5 to 8 per cent. There is also a small amount of carbon dioxide, but this is removed by the soda-lime U tube attached to the cylinder. Of the three standard methods for absorbing oxygen, i. 3 and w^ are used to admit water to the suction-pump. The valve w^ is permanently adjusted so that the supply of water pass- ing through the pump will be that best fitted for drawing the sample 1 Smithsonian Meteorological Tables (1897), p. 133. THE RESPIRATION APPARATUS. 49 of air through the U tubes and meter at a proper rate of flow, while the water is ordinarily turned on and off by the valve w,,. At t a glass T tube is inserted for the rejection of air (see p. 77), to the stem of which a rubber tube dipping into a small vial contain- ing water is attached. The rubber tube is ordi- narily closed with a screw pinchcock, the tightness of the closure being proved by the absence of bubbling of water in the small vial. The water used for act- uating the suction-pump enters at m and passes into the large chamber F, which serves as a trap. This chamber consists of 2-inch gas-pipe with a cap at each end. To prevent sediment from clogging the fine jet of the water- pump, the supply of water for the pump itself is drawn from a point somewhat above the bot-v torn of the trap. The sediment in the water col- lects below this point, and can be drawn off through the valve ze>2, which is always opened a moment or two before starting the suction - pump. To prevent the entrance of air in the water current, a 43 FIG. 19.— Apparatus for Drawing Sample of Air for Residual Analysis. A glass suction-pump A draws air from the Elster meter and delivers it, together with the water used for aspiration, into separating chamber B. The water flows off through overflow through pipe d and the air passes through exit tube t into drying chamber D. 50 A RESPIRATION CALORIMETER. valve, wlt is provided. Any air that may have been brought along by the water current will accumulate in the upper part of the chamber F, and when this valve is opened will pass out into the drain, the chamber becoming completely filled with water. Apparatus for constant water pressure. — In using a water suction-pump for drawing the sample of air, it is of great importance that the water pressure be constant, as otherwise the air will be drawn through the U tubes and meter with a varying degree of rapidity, and consequently under varying tension as measured by the water manometer. The measurement of the absolute volume of air passing through the meter is of great importance, since its relation to the larger volume of residual air (10 : 5,000) necessitates the use of a very large factor when comput- ing the residual amounts of carbon dioxide and water in the system ; consequently every precaution must be taken to secure the most uni- form sampling. The city water pressure was found to be entirely inadequate for the degree of accuracy required for this work, and a special water system, shown in figure 20, was installed. A force-pump, which is belted to the line shaft in the calorimeter laboratory, draws water from a galvanized-iron pail, which is supplied from the city main, and forces it into an upright boiler, which serves as an air-chamber. The boiler is filled about half full of water, the level of which is noted by the glass water-gage at the side, and then com- pressed air from a cylinder is admitted to the boiler until the manometer at the top indicates a pressure of about 100 pounds. The water with- drawn from this chamber for use in the suction-pump is taken from a pipe extending several inches above the bottom of the boiler, so as to eliminate sediment as much as possible. By means of the valve w±, figure 19, the supply of water passing through the suction-pump may be regulated at will. PROCESS OF TAKING RESIDUAI, SAMPLES. The residual analysis is started at about 10 minutes before the end of each experimental period. Ten liters of air (apparent volume as measured by the meter) are used for each determination. A dupli- cate analysis follows, beginning at about three minutes before the end of the experimental period. The rate of flow of air through the meter is such that the second sample is about one-half taken at the end of the experimental period, the remaining 5 liters of air being taken during the beginning of the next period. It is assumed that the average com- position of the sample will be that of the air at the moment of changing from one period to another. The differences in results by the two samples are usually insignificant, in which case the second series of THE RESPIRATION APPARATUS. results is invariably used in the calculations. Occasionally, though rarely, wide discrepancies in the two analyses will appear. Under these conditions a third analysis is made and the figures agreeing most closely are used. In such cases the error is almost always directly traceable. SAMPLING THE AIR FOR THE DETERMINATION OF OXYGEN. Of the four constituents of the ventilating current of air, carbon dioxide, water vapor, nitrogen, and oxygen, the amounts of the first two in the residual air are determined by the apparatus described above. In order to know accurately the amount of oxygen in the air, a determina- tion of this element is necessary. The actual determination of oxygen in the air current, by absorption by potassium pyrogallate, is usually made once each 24 hours, the sample being generally drawn at the close of the experimental period ending at 7 a. m. It is of great im- portance to obtain a sample of air in which the percent- age of oxygen shall represent accurately that in the respira-. tion chamber. For- merly the air was sampled after it had passed through the blower and absorb- ing system, and it was assumed to be Bide ooooooooooodc E l i_ r lo 1° P |E to \ o o o 1 o o o 0 1 0 j o o i o o o o o o 0 o o 0 o j 0 o o o / O y^ 0 / O f o / n |K •=$} Wc= FIG. 20.— Water-Pressure System. Water from reservoir at left is forced by pump into the large air-tank at right. The release valve immediately to right of pump returns the water to reservoir in case pressure in tank exceeds 100 pounds. Water is drawn from tank for suction-pump used for drawing residual samples. 52 A RESPIRATION CALORIMETER. free from carbon dioxide when taken under these conditions. It was found, however, that at the time when the air sample is usually taken, i. e., immediately after the end of the experimental period, the air in the main ventilating pipe leaving the absorbers is a mixture of purified air from the respiration chamber and normal air from the laboratory contained in the carbon-dioxide and water absorbers that had just been put into use, and, since the percentage of oxygen in the normal air is somewhat larger than that in the air from the chamber, the pro- portion of oxygen in the sample would of course be too large. If the taking of the sample was delayed for several minutes, i. c, , until the air in the absorbing system had been thoroughly swept out, this diffi- culty was no longer experienced, but, as any delay in taking the sample of air was accompanied by a gradually varying percentage of oxygen, it was evident that this method of taking the sample was erroneous. To avoid these difficulties, the air that has been through the residual U tubes and meter is now utilized as the sample. Inasmuch as this sample is always taken during the second residual, i. e. , after the air in the meter has been thoroughly swept out by air of the same composition as the sample, the air thus collected probably represents better than any other the true composition of the carbon-dioxide free air inside the chamber. METHOD OF SAMPLING. It has been found that if the analyses are made immediately after drawing the sample the air may be collected in an ordinary rubber foot-ball bladder. In taking the sample it is customary to slip the rubber neck of the bag over the glass tube connecting with the T tube (/, fig. 19). The rubber neck of the bag is provided with a screw pinchcock. On opening this pinchcock and the one above, air rushes into the bladder rather than through the sulphuric acid in the drying bottle until the tension on the rubber bag is sufficiently great to force the air again through the sulphuric acid in the drying bottle. By squeezing the bag together with the hands the air can be discharged again into the drying bottle and thence into the main air-pipe. In so doing there is no gain or loss of air to the system. Care must be taken, however, to see that the pressure on the rubber bag is not enough to force the level of the water in the separating chamber B (fig. 19) down to such a point that air can escape along with water through the overflow. It has been found by repeated tests that the amount of air contained by an ordinary foot-ball bladder under the tension here used is about 0.80 liter, and this quantity of air is removed from the main air-circuit. A correction for this amount is made in the data for the experimental period from 7 a. m. to 9 a. m., in making which it is customary to assume that this volume of air consists of one-fifth of oxygen and four- THE RESPIRATION APPARATUS. 53 fifths nitrogen, since the actual composition rarely varies sufficiently to make any material difference in the calculation. After the sample is taken , both pinchcocks are closed , the rubber bag re- moved, and the glass tube again dipped in water to insure tight closure. In the alkaline pyrogallate method of determining oxygen it is abso- lutely essential that the air sample be free from carbon dioxide. In the procedure outlined above the sample is taken after the air has passed through the three U tubes for the residual analysis, and consequently should be free from carbon dioxide. We have frequently tested the efficiency of these U tubes for removing completely the carbon dioxide from an air current and have found them to be remarkably satisfactory. Furthermore, it is to be remembered that the amount of residual carbon dioxide is usually low, and absorption is presumably correspondingly complete. It is therefore reasonable to assume that the air sample is absolutely free from carbon dioxide. THE ANALYSIS OF AIR. The desirability of exact analysis of air during the progress of an experiment with the respiration apparatus has been emphasized on page 12. The methods and apparatus used thus far in this work are essentially those outlined previously for analyzing oxygen, and reference is made in the following description to the illustration previously given (fig. 16). But in the analysis of air certain refinements of the method described are necessary. The chief of these is an accurate observation of changes in temperature of the gas between the time of the first and final readings- While a variation in temperature of several tenths of a degree could not have any appreciable effect on the small volume of residual nitrogen obtained in the analyses of oxygen, in air analyses, where the residual nitrogen amounts to about 80 cc., fluctuations in temperature will be accompanied by marked fluctuations in the residual volume. Further- more, fluctuations in barometric pressure, although seldom occurring during the actual process of analysis, might affect perceptibly the percentage of nitrogen. The important r61e played by temperature fluctuations necessitates the use of a thermometer graduated in tenths of a degree centigrade, and read with a reading glass to o.oi °. This thermometer is placed in the water-jacket surrounding burette B2. To insure a more equable temperature of the gas in the burettes, provision is made for stirring the water in the water-jackets. A slow stream of air is forced through two fine jets at the bottom of the water-jackets, openings in the corks in the top allowing for the free escape of air. As the air bubbles through the long column of water, the water is very completely stirred . 54 A RESPIRATION CALORIMETER. By means of the screw pinchcocks sl sz the amount of air bubbling through the water can be regulated at will. Some difficulty was expe- rienced in getting an air pressure sufficient to force air through such a long column of water, but compressed air from a cylinder was eventu- ally found satisfactory. The air is first saturated with water vapor by bubbling through water in a gas-washing bottle, thus diminishing the cooling effect in the water-jackets due to the evaporation of water. In case there is clogging of the tubes and consequent increased pressure, a mercury trap provides a safety escape. Inasmuch as the percentage of oxygen in the carbon-dioxide free air from the respiration chamber is seldom less than 17 to 1 8 per cent, the graduations on burette B2, which extend only from 90 to 100 cc. , do not permit of reading directly the volume of unabsorbed gas when drawn from the pipette back into B2. This volume may be as great as 83 cc. or as small as 78 cc. To overcome this difficulty, we have adopted the plan of driving a definite volume of nitrogen from the burette Bw through the 3-way stopcock C, into burette B2, in order to depress the level of the water in B2 to such a point that it can be read on the graduations from 90 to 100 cc. In general, about 10 to 14 cc. of nitro- gen are thus expelled from the burette Bj. At the beginning of an analysis the burette Bx is nearly filled with pure nitrogen, obtained either from a previous analysis of air or from the gas above the reagent in the Hempel pipette. Having filled the burette El with nitrogen, the neck of the rubber bag used to collect the sample of air to be analyzed is slipped over the end of the capillary tube T. On opening the stopcock C the air is drawn into the burette B2 until the water level in the burette is the same as that in the reservoir R,. The stopcock C is then closed, the screw pinchcock on the neck of the rubber bag closed, and the bag removed. Theoreti- cally, it is better to leave the bag on until just before reading the volume, but the difference in composition of the room air and the small sample in the open portion of the tube is so slight that practically no difference in results is to be expected. After allowing the water in burette B, to drain down the customary time, readings are taken of the volume in the burette, of the thermometer, and of the barometer. The gas is then driven over through the stopcock C into the Hempel pipette described for oxygen analysis (p. 37), all the gas in the capillary tubes being forced out by the pressure of the water in the elevated reservoir R2. After closing the stop- cock C and the pinchcock P on the pipette, the air is shaken vigorously with the reagent for five minutes. The residual unabsorbed gas is then returned to the burette Ba, and by lowering the reservoir R2 the reagent is drawn up through the rubber connection R and along the capillary t THE RESPIRATION APPARATUS. 55 to the mark G. The volume of gas thus returned to the burette must be supplemented by a volume to be delivered from the burette B, before the gas can be read on B2. The reservoir Rj is lowered until the level of the liquid in R: and B: are the same. The reading on B, is then carefully noted. On raising R! and carefully opening stopcock C pure nitrogen can be driven over into B.2. It is necessary, however, that in this case the reservoir R2 should be at or about the level shown in figure 1 6. As soon as sufficient nitrogen has been forced into B2 to bring the water level well on the graduated portion of the burette the stopcock C is closed. After again adjusting the water levels in Rj and BI, the reading of the gas remaining in B, is made and the difference in volume subtracted from the final reading on B2. The final readings of volume and temperature are, of course, not taken until the water has settled and drained down the sides of the burette. A specimen analysis of a sample of the air taken from the respiration chamber is given below as illustrating the methods of analysis. The sample of air was drawn at 7 a. m. on April 29, 1904. The reading on B, was 99.25 cc. -(- 0.51 = 99.76 cc. The initial temperature was 18.64; the corrected barometer reading was 753.29 mm. After absorbing the oxygen the gas was run back into B2 and nitrogen from Bj added to this volume. The first reading on E1 was 19.00, the second 5.47, in- dicating that 13.53 cc. of nitrogen had been added to the volume of the gas in B2. The final reading on B, was 93.89. On deducting the J-S-SS cc- °f nitrogen that were added from B1} the corrected volume of gas measured in B2 was 80.36. There still remained, however, the constant volume 0.34, which should be added for the gas remaining in the stopcock and connection to graduation point G. The final result, then, is 80.36 + 0.34 = 80.70. The change in temperature amounted to 0.09°, the initial temperature being 18.64° an(i the final I8.73°. In increasing its temperature the gas has expanded and the tension of aqueous vapor has increased slightly ; consequently it is necessary to take into consideration its effect on the tension of the gas in the burette. The tension of aqueous vapor at 18.64° is equal to 15.96 mm. of mer- cury. This, subtracted from the barometric reading, 753.29, gives the reduced pressure as 737.33 mm. The tension of aqueous vapor at 18.73° is J6.o5 mm. As there was no noticeable change in the barometric pressure, this tension is deducted from the original barometric pressure, i. AMOUNT OF CARBON DIOXIDE ABSORBED. The weight of carbon dioxide absorbed was determined by noting the increase in weight of each of the three soda-lime cylinders S, L, and I and the water-absorber No. 6, through which the air passed after leaving the soda-lime cylinders. Soda-lime cylinder S weighed at the start 2,416.2 grams more than the counterpoise. At the end of two hours it was ob- served that the weight had increased by 6. 5 grams. Similarly , cylinder I, had increased in weight 1 8 . 8 grams and cylinder 12.5 grams, while water- absorber No. 6 had increased in weight 16.3 grams. To find the total weight of carbon dioxide during this period, therefore, the increases in weight of these four parts of the carbon-dioxide absorbing system were added together, the amount of carbon dioxide absorbed in the two re- sidual analyses, i. e., 0.09 gram, added, and the usual correction of 0.20 gram for the increase in weight of absorber No. 6 subtracted. It is thus seen that the total weight of carbon dioxide absorbed during this period was 43.99 grams. It will be noted on the blank that space is left for a fourth soda-lime cylinder. Frequently, in experiments in which there is an excessive amount of carbon dioxide absorbed, it becomes necessary to stop the air current for a moment or two and replace an exhausted soda-lime cylinder with a fresh one. AMOUNT OF OXYGEN ADMITTED. The calculation of the weight of oxygen admitted to the chamber is c arried out on the upper right-hand side of the blank. To avoid errors and to aid in referring to the cylinder, the cylinder number is first re- corded. The weight of the cylinder over and above the counterpoise at the beginning of the period and the weight under the same conditions at the end are recorded immediately beneath this. The difference, which represents the loss in weight of the cylinder, is the weight of the oxygen plus the nitrogen, for, owing to the purifying attachments on the cylinder itself , the gas issuing from the rubber tube consists only of oxygen and nitrogen. It becomes necessary, therefore, to calculate the amount of nitrogen admitted with this oxygen, and this is done by adding the logarithm of the percentage of nitrogen of this particular cylinder, as determined by the analysis (see p. 34), to the logarithm of the weight of oxygen and nitrogen admitted. The sum of these loga- rithms is the logarithm of the weight of nitrogen, which, in this in- stance, amounted to 0.67 gram, and, since the weight of the oxygen plus the nitrogen was 46.78 grams, the true weight of oxygen admitted during this period was 46.11 grams. For purposes of calculation, to be explained beyond (p. 88), it is desirable to know the volume of nitrogen admitted to the chamber, 66 A RESPIRATION CALORIMETER. and consequently at this point the calculation converting the weight in grams of nitrogen to liters is made. This calculation is based on the relations between the weights and volumes of gases as discussed on page 82, and is here simplified by adding the logarithmic factor .90078 to the logarithm of the weight of nitrogen in grams. It is thus seen that the volume of nitrogen admitted with the oxygen in this case was o. 54 liter. On the blank a space is left for several calculations of this nature, as it frequently happens that more than one cylinder of oxygen is used during an experimental period. The oxygen is always admitted as long as it will flow from the cylinder, and even in ordinary rest exper- iments it is rare that the last of a cylinder of oxygen is coincident with the end of an experimental period. During excessively hard-work experiments, several cylinders may be used. In case more than one cylinder is used, the weights of oxygen and liters of nitrogen are footed up at the bottom. Furthermore, a slight constant correction, amount- ing to — 0.04 gram of oxygen (see p. 74), is made for certain alterations in volume, due either to interchange of air through the food aperture or opening and closing of mercury valves, which correction, for the sake of convenience, is made on this sheet. During this period we find that the total amount of oxygen admitted is 46.07 grams. It is thus seen that, when no reference is made to the variations in composition of the residual air, the amount of carbon dioxide and water eliminated per given period and the amount of oxygen absorbed may be determined from the weights of water and carbon dioxide taken up by the absorbing system and the weight of oxygen admitted from the steel cylinder, with due allowance for the accompanying weight of nitrogen. RESIDUA!, ANALYTICAL DATA. The data for the two residual analyses are likewise recorded side by side on this sheet. They include the amount of air passing through the meter, the temperature of the meter, correction for the thermometer used in the meter, pressure on the meter expressed in millimeters of water as read on the manometer, its conversion to millimeters of mer- cury, and the gains in weight of the U tubes used for analysis. Beneath the record of these data are placed the temperature records and the position of the pans. When the thermometer has a correction, the corrected temperature is placed at the right of that observed. In this instance the thermometer had a zero correction. Pan No. 2 was empty, and in this position it is assumed that 2.5 liters of air are inclosed by this pan, diaphragm, and pipes. (Seep. 41.) The pointer on the wheel of pan No. i stood at the graduation 575, and from a previously prepared table it is found that at this position the rubber diaphragm, pan, and CALCULATION OP RESULTS. 67 pipe inclosed 11.2 liters of air, thus making a sum total of 13.7 in the tension equalizing system . DATA FOR THE REJECTION OP AIR. As the amount of nitrogen in the system gradually accumulates dur- ing an experiment, by reason of the fact that the admission of oxygen is unavoidably accompanied by an admission of nitrogen, it becomes necessary from time to time to reject a considerable volume of air, vary- ing from 30 to 70 liters, by drawing it through the Elster meter, and to replace it with oxygen. The calculations by which the exact amount of air thus rejected is determined are made in the lower right-hand corner of this sheet. Here are recorded the time at which the air is rejected, the number of liters passing through the meter, the thermom- eter reading and correction for the thermometer in the meter, the water manometer, with its equivalent in mercury, the tension of aqueous vapor at the temperature of the meter, and the barometer reading. It is thus possible to calculate the corrected volume of oxygen and nitro- gen rejected. The proportions of oxygen and nitrogen in this corrected volume are obtained from the analysis of air taken immediately before the air is rejected. (See p. 77.) CORRECTIONS FOR VARIATIONS IN VOLUME AND COMPOSITION OP RESIDUAL AIR. NECESSITY FOR RESIDUAL ANALYSES. The amounts of carbon dioxide and water eliminated and oxygen absorbed as determined by the gains in weight of the absorbing system and the loss in weight of the oxygen cylinder, with due corrections for nitrogen, give, on the whole, a general approximation of the amounts of carbon dioxide and water eliminated and oxygen absorbed by the sub- ject ; but in this calculation, as has been pointed out, no notice is taken of the alterations in composition of the residual volume of air. The chief factors influencing such variations are muscular activity of the subject with its consequent fluctuations in carbon-dioxide and water production and oxygen absorption, rapidity of ventilation, and baro- metric pressure. The fluctuations in the amounts of carbon dioxide and water are in the main of a temporary nature. There may be variations of over 100 grams of carbon dioxide and 20 grams of water vapor in the amounts of these gases in the air in different periods of the day, as, for example, at the beginning and cessation of hard muscular work ; but with ap- proximately uniform muscular activity for the whole period the residual amounts of these gases are almost invariably the same from day to day 68 A RESPIRATION CALORIMETER. at the end of each experimental day, i. c., 7. a. m., after an eight- hour sleep. On the other hand, in the case of oxygen there is present in the sys- tem from the very beginning not far from 1,000 liters of oxygen, which store can be drawn upon by the subject, and, indeed, is drawn upon to a very considerable extent. It is of course immaterial to the subject whether he uses oxygen from the steel cylinder in which the oxygen is duly weighed, or oxygen from the large store in the residual air. Obviously, when taken from this second source, provision must be made for noting the amount thus used. If, furthermore, we are to ob- tain data regarding the exact quantities of carbon dioxide and water vapor used in short periods, the fluctuations in the amounts of these materials in the air current must likewise be determined, and our analy- ses of residual air should include determinations of water and carbon dioxide as well as oxygen. POSSIBILITY OF LEAKAGE. From a consideration of the construction of the whole apparatus, it is seen that it is practically impossible for carbon dioxide to leak into or out of the air-circuit ; for if there were a leak into the system, a very large number of liters of room air would have to enter to affect materially the weight of carbon dioxide, inasmuch as there are only 4 parts of carbon dioxide per 10,000 of air. Similarly, a very con- siderable leakage of air out of the system would be necessary before any noticeable amount of carbon dioxide would have escaped. With reference to the water vapor, much the same can be said, although the percentage of water vapor in the air of the calorimeter laboratory is much greater than the percentage of carbon dioxide. There is, more- over, a possibility (although in all of our experience it has never yet occurred) that water from the cooling current of water used to bring away the heat may leak into the system through the connections with the heat-absorbers (see p. 123); but, for all practical purposes, we may consider that the construction of the apparatus is such as to make it impossible for any appreciable amounts of carbon dioxide or water vapor to leak into or out of the system. In the case of oxygen and nitrogen, however, it is of fundamental importance that there be no leakage of these gases into or out of the system. The precautions taken to secure thorough closure of the sys- tem have already been discussed in considerable detail. The residual analyses give, as is shown on page 88, data for determining any gain or loss of nitrogen to the residual air, and consequently, as a leakage of air in either direction would result in a marked disturbance of the amount of nitrogen remaining in the chamber, the residual analysis is CALCULATION OP RESULTS. 69 frequently of great assistance in indicating such leakage. Furthermore, the residual analysis is used to measure the amount of leak. This point, as well as the general significance of leaks of either oxygen or nitrogen, will be taken up more in detail beyond. FACTORS USED IN THE CALCULATION OF THE RESIDUAL ANALYSES. The chief factors necessary in the calculations of the residual amounts of carbon dioxide, water vapor, oxygen, and nitrogen in the ventilating air current are the volumes of the gases in the various parts of the sys- tem, the composition of the different portions of air, the volume of the sample taken for analysis, the weights of carbon dioxide and water in the sample drawn through the meter, and the volume percentage of oxygen and nitrogen found by the gasometric analysis. VOLUMES OP AIR IN AIR-CIRCUIT. The volume of the residual air in the different parts of the chamber, pipes, absorbing apparatus, and pans is calculated with considerable accuracy from measurements of dimension, especially for those parts of the system in which the air volumes are not liable to fluctuate. VOLUME IN CHAMBER. The respiration chamber is 19.27 decimeters high, 12.17 decimeters wide, and 21.38 decimeters long. The corners of the floor and ceiling are rounded, the radius of curvature being 1.27 decimeters. From these data the volume of the chamber proper is computed to be 4,987.0 liters. A recess in the wall provides for the window, and as this does not set flush with the inner wall, its volume must be added to that of the rest of the chamber. The recess is 7.24 decimeters high, 5.20 deci- meters wide, and 0.57 decimeter deep. Its volume consequently equals 21.4 liters, which, added to the volume of the chamber, 4,987.0 liters, equals 5,008.4 liters. A certain amount of material in the apparatus can be considered permanent fixtures, such as the absorbing system, the air-pipe and metal work (other than the metal of the walls) , the telephone and bat- teries, and various smaller pieces of apparatus that are in regular use. The volume occupied by these permanent fixtures is determined by measurement of their dimensions or by calculating the volume by means of the specific gravity when the weight is known. The volumes thus obtained are as follows, in liters: Heat-absorbing system, 5.94; air- pipes and metal work, i.o; switch, 0.3 ; telephone and battery, 2.0 ; making a total of 9.24 liters to be deducted from the apparent volume, 5,008.4 liters, in all calculations. 70 A RESPIRATION CALORIMETER. VOLUME OF AIR IN THE AIR-PIPE FROM THE CHAMBER, MERCURY VALVES, AND BLOWER. The ventilating air-pipes consist of ordinary iron gas-pipe galvanized inside and out, and vary considerably in length as well as diameter. From measurements of the length and internal diameter their volume was computed, as were also the volumes of the accessory members of the air system, such as the blower, mercury valves, and rubber con- nections. From these data it is calculated that the air between the chamber and the level of the acid in the first water- absorber occupies a volume of 6.55 liters. VOLUME OF AIR IN WATER-ABSORBERS. The content of the water-absorbers was estimated by filling them to the top of the exit tube with water and noting the amount required. For one absorber this was found to be 14.38 liters, for the other 14.69 liters, or an average of 14.54 liters. The rubber tubes which serve to connect the absorbers increase the volume to 15.16 liters each. Of this, 0.93 liter is contained in the entrance tube reaching to the bottom of the absorber, or 14.23 liters for the remainder of the absorber. From this figure must be deducted the volume occupied by the sul- phuric acid. This is originally 3 liters, leaving as the air volume 1 1.23 liters. VOLUME OF AIR IN CARBON-DIOXIDE ABSORBERS. The volume of air in the soda-lime cylinders was calculated by obser- vations upon the contraction in the volume of air under a known press- ure. Three soda-lime cylinders were connected in series in the usual way. In one end of the system a water manometer was placed and the other end connected with a bottle, the volume of which was determined by weighing it when empty and when full of water. When a known amount of water was poured into the bottle through a long funnel-tube, the air in the bottle and in the three absorbers became compressed, the pressure being measured by the manometer. From the volume of water poured into the bottle, the reading on the manometer, and the barometric pressure, the volume of air in the system could be calculated. Inasmuch as the experiments were all made in a very few minutes, no difference in temperature was taken into consideration in the calcu- lations. From three determinations, in which varying quantities of water were used, the total volume of air in the three absorbers varied from 10.128 to 10.486 liters, averaging 10.28 liters as the volume of air in the three soda-lime cylinders. Since the apparatus for the absorption CALCULATION OF RESULTS. JI of carbon dioxide includes a water-absorber in addition to the three soda- lime cylinders, the volume of air in this absorber and connections, i. 0 = volume of air sample. Vj = volume of air containing water = (I + II). V2 = volume of air containing CO2 = (I + II + III) . V3 — volume of air containing O + N = (I + II + III + IV). a = total volume of water vapor. b = total volume of carbon dioxide. c = total volume of nitrogen. d — total volume of oxygen. W= total weight of water vapor in system; w— weight in air sample. W'= total weight of CO2 in system ; wl = weight in air sample. W = «'XV1 Tpi^XV. ^0 »« i. 2434 a> XV! , .5091 w1 XV, - It was formerly assumed that at the beginning of the experiment ^=.2091 (Vg— a — £); ^=.7909 (V3— a — £). These values for the amounts of oxygen and nitrogen were deter- mined by assuming the composition of the air free from carbon dioxide and water vapor as 20.91 per cent oxygen and 79.09 per cent nitrogen. We now secure greater accuracy, however, by using the actual analysis of the carbon-dioxide and water free air as made at the beginning of an experiment, i. e., at 7 a. m. This consequently changes the factors used in the last two equations from o. 209 1 and o. 7909 to those found by analysis. In calculating the composition of the air at the end of the first experimental period, c is determined from the record of the amount of nitrogen entering with the oxygen, lost or gained through interchange through the food aper- ture, rejected with the absorbers, and lost if a sample of air has been rejected. All of these corrections are applied to the original initial volume of nitrogen found by analysis. Under these conditions, then, we have . M Required by theory. (/) Ratio of amount found to amount required. d-=re. April 6 Do. . Preliminary. . . First Grams. 22.72 20. 4S Grams. — 2.27 Grams. 88.78 Grams. 8651 Grams. 84.08 Per cent. IOI.8 Do Second 21. IO -j- 0.65 123.68 124. •*•* 125.15 QQ.'t April 7.. Third 20. 1 7 — o.()i, 264.08 26^.15 260.83 IOO.Q Total 47VQQ 47O.Q6 100.6 THE COMPUTATIONS FOR OXYGEN. Inasmuch as carbon dioxide and water have been determined by other methods with apparatus as large as this with great accuracy,1 especial interest in this particular form of apparatus lies in its power for deter- 1U. S. Dept. of Agr., Office of Experiment Stations Bull. 136, pp. 37, 38. ALCOHOI, CIT:CK EXPERIMENTS. 105 mining accurately the amount of oxygen consumed, either by men or by an alcohol lamp. In Table 3 beyond are recorded, first the date of the experiment, then in succession the number of the period, the amount of oxygen residual in the chamber expressed in liters, and the differences in the amounts of oxygen residual in the chamber at the beginning and end of the different periods, expressed first in liters and then in grams. The weight of oxygen admitted from the steel cylin- der is next recorded, followed by the corrected amount of oxygen used in the combustion, the theoretical amount of oxygen required to burn the weighed amount of alcohol, and, finally, the ratio of the amount found to the amount required, expressed in per cent. The same considerations which affect the accuracy of computations of this nature for short periods, i. e., the possible effect of errors in residual analyses, which were discussed when considering the compu- tation of carbon dioxide, also influence, perhaps in a more marked degree, the computation of the amount of oxygen ; but here, as in the previous case, the errors are more or less compensating, and, generally speaking, the longer the period the less the effect of the residual analy- ses. It would seem that in this experiment the determinations for the oxygen were, even in the short periods, extremely satisfactory. . — Record of Oxygen in Ventilating Air Current. Alcohol check experiment, April 6-7, 1905. Date. Period. (a) Total amount in cham- ber at end of period. Gain (+) or loss(— ) during period. M Amount admitted to cham- ber from cylinder. <«) Corrected amount used in combus- tion. d-c. 00 Required by theory. Or) Ratio of amount found to amount required. <-=-/. <*) Volume. (g Weight. b -i- 0.7. April 6 Do. Do. April 7 Preliminary Liters. 911.26 927.02 951-95 956.24 Liters. + 15.76 + 24-93 + 4-29 Grams. + 22.51 + 35-61 + 6.13 Grams. 161.86 242.70 437.22 Grams. 139-35 207.09 431.09 Grams. 138.9° 204.56 426.33 769.79 Per cent. 100.3 IOI.2 101. 1 First Second Third Total 777-53 IOI.O In the discussion of the tests of accuracy of the complete apparatus, i. «?., the respiration calorimeter taken as a whole, the heat-measuring ability of the apparatus must also be shown, and in Table 4, on page 176, we have a complete statement of the accuracy of the ' ' respiration calo- rimeter ' ' in measuring not only the chemical factors — carbon dioxide, water vapor, and oxygen — but also the heat. The table referred to gives a summary of all the results of this particular experiment. 106 A RESPIRATION CALORIMETER. THE CALORIMETER SYSTEM AND MEASUREMENT OF HEAT. This section deals with that portion of the respiration calorimeter which is involved in the calorimetric measurements. It has been ex- plained (p. 4) that the arrangements for measuring respiratory products aud those for measuring heat are intimately combined in the same apparatus. In this description, however, the calorimeter will be con- sidered for the most part as if it were independent of the respiration apparatus, though in a few instances it will be convenient to refer, for more detail, to what has already been described. GENERAL PRINCIPLE OF THE CALORIMETER. As a device for measuring heat, the apparatus here described may be designated a constant temperature, continuous-flow water calorimeter. It is so devised and manipulated that gain or loss of heat through the walls of the chamber is prevented, and the heat generated within the chamber can not escape in any other way than that provided for carry- ing it away and measuring it. A small part of the total quantity leaves the chamber as latent heat of water vapor in the air current of the respiration apparatus, but the larger part is sensible heat absorbed by a current of cold water passing through a coil of pipe within the chamber. By regulating the temperature and rate of flow of this current of water, the rate at which the heat is absorbed may be controlled in accordance with that at which it is generated within the chamber, and thus the temperature of the chamber may be kept constant. The quantity of heat carried out of the chamber as latent heat of water vapor is determined from the quantity of water vapor removed from the air current and the latent heat of vaporization of water. The quantity of heat absorbed and removed by the water current is determined from the quantity of water passing through the coil, its increase in tempera- ture, and the specific heat of water at different temperatures. Theo- retically the sum of these two quantities of heat thus determined should equal the total generated within the chamber, but in actual experiments with man various corrections, such as heat gained or lost by articles sent into or brought out of the chambers, etc., must also be taken into account. The things to be especially considered in this discussion, then, are the arrangements for preventing gain or loss of heat through the walls of the chamber and the arrangements for bringing heat away from the chamber and measuring it. In the description of these many subordinate related topics must also be discussed. THE CALORIMETER SYSTEM AND MEASUREMENT OP HEAT. 107 THE CALORIMETER CHAMBER. The dimensions of the chamber and its construction of metal have been given in the discussion of the respiration apparatus (p. 12). The walls, ceiling, and floor of the chamber are of sheet copper, polished on the inner surface. Copper offers many advantages as a metal surface for the interior of the calorimeter chamber, because it will take a high polish, thus aiding in the distribution of heat by reflection, and it con- ducts heat rapidly, tbereby tending to equalize local differences in temperature. As a further aid in the reflection and distribution of heat and equalization of temperature, the four upright corners of the chamber are rounded. These features are of particular importance in the matter of determining changes in temperature of the walls, which is funda- mental to the prevention of the gain or loss of heat through the walls, as explained beyond. Outside the copper walls of the chamber and concentric with them, but separated by an air-space of 7.6 cm., corresponding to the width of the wooden framework by which the copper walls are supported, is another metal covering, the purpose of which will be described later. For this covering the cheaper metal, zinc, is very satisfactory. Sheets of zinc (Brown & Sharpe gage 25), each 3 by 7 feet and weighing 14 pounds, were used in this construction. Since this covering need not be airtight, the joints were soldered only at convenient places, and the zinc is nailed to the wooden framework between the two layers of metal. There are, however, no apertures large enough to disturb the ' ' dead air ' ' in the space between the zinc and the copper. WOODEN WALLS SURROUNDING THE CHAMBER. To protect the calorimeter chamber against fluctuations in the tem- perature of the calorimeter laboratory, and especially to provide op- portunity for controlling the temperature of the metal walls in the manner described beyond, there are two concentric coverings of wood completely surrounding it, with an air-space of 7 cm. between the zinc wall and the inner wooden partition and a corresponding space between this and the outer wooden covering. This construction is equivalent to a double-walled wooden house, into which the calorimeter chamber is inserted. The details of the construction follow, reference being made to the horizontal cross-section in figure 8 and the end and side vertical cross-sections in figures 23 and 24. At each corner of the house, between the two wooden walls, an up- right (b, b, and c, c, in fig. 8) extends from floor to ceiling of the labo- ratory, thus providing rigid supports. As seen in figure 8, the two 108 A RESPIRATION CALORIMETER. uprights at one end (6, b} are grooved to fit the inner walls ; those at the other end (c, c) are rectangular in cross-section. All four up- rights are well painted to prevent absorption of moisture and conse- quent warping, such precaution being especially necessary because of the location of the laboratory in the basement of a stone building. Extending between these uprights in both directions, at the top and bottom of the structure, are joists ; those extending across the shorter dimension are shown in cross-section in figure 24 (a, a and b, £), and those running lengthwise in figure 23 {a, a and b, £) . These eight joists and the four uprights form a rigid support for the wooden walls. Like the two uprights b, b, shown in figure 8, the two joists a, a, shown in figure 24, are grooved to receive the inner wooden partition. The floor of the outer wooden structure rests upon two pieces of cedar 15 by 15 cm. , shown in cross-section (c, c, in fig. 24), which are laid directly upon the laboratory floor. These hold the ends of the floor of the outer casing firmly against the lower edges of the joists a and b. In addition to these there are nine large blocks (Q-* 2,s E;^3 ^ W *-»• 3 cr i s- 5='S2 ll " lla 1^3 °5£. S'2 e B ' n Resp the s ;; a «: ~ » H S- 2 g. n.o 3 £. ft n 1| cro 3" to 2 ^'.TT rt » ^o" »2 £3- ^— O — P O p '< 0-2 r.3 ,H> pho Vr. THE CALORIMETER SYSTElt AND MEASUREMENT OF HEAT. 125 pipe of the heat- absorber, passes once around the chamber, then enters the upper pipe and makes another circuit of the chamber, and finally passes out of the chamber by way of the wooden plug through another brass pipe connected by the rubber tube W2. With this arrangement the water absorbs heat very rapidly, although the actual mass of water inside the calorimeter at any one time is kept at a minimum, i. i.ooio. The difference between CM and C0 is one of nearly i per cent. 152 A RESPIRATION CALORIMETER. experiments, and leaves the chamber, after having passed through the absorbing pipes, at 12°, the result will be in terms of C(z-i2) or in terms of the mean calorie from 2° to 12°. From the table above referred to it is found that the specific heat at 2° is 1.0076 and at 12°, 1.0020. The average of these two is 1.0047. This variation is approximately 0.5 per cent. Since the accuracy of the calorimetric measurements is considerably within i per cent, it is evident that the correction above suggested must be applied. In making the correction, the quantity of heat measured in terms of Ct is multiplied by the specific heat of water at Ct referred to that at CM as a standard. CORRECTIONS TO MEASUREMENTS OF HEAT. As explained above, to obtain the true final measurement of heat, allowance must be made for certain quantities of heat introduced or removed in various ways. The different corrections to be made are dis- cussed in the following sections. THE HYDROTHERMAL EQUIVALENT OF THE CALORIMRTER. With the heat- regulating devices previously described, it is in gen- eral not at all difficult to control the temperature of the calorimeter within very narrow limits ; but there are times when the calorimeter system, as a whole, may have a different temperature at the end of a period than at the beginning, and there may be accordingly either a storage or a loss of heat in the system. Obviously, in accurate experi- menting, especially in short periods, it is necessary to know the actual amount of heat thus stored or lost. This involves a knowledge of the hydrothermal equivalent of the calorimeter, since the mass of material thus raised or lowered in temperature must be known and expressed in its equivalent weight of water. With a calorimeter of this type of construction it is not an easy matter to determine the hydrothermal equivalent with great accuracy. The inner copper wall is heated by the heat radiating from the subject. The outer zinc wall is heated by the electrical current in the air-space surrounding it. If the chamber undergoes a certain rise in tempera- ture, it is difficult to state exactly what proportion of the heat given off by the subject is utilized in raising the temperature of the copper wall and what proportion is utilized in raising the temperature of the zinc wall, for while there is obviously a distinct period during which the copper wall is warmer than the zinc wall, it is by no means absolutely certain that when the temperature is rising all the heat from the man's body escapes to the zinc wall before the electrical heating circuit begins THE CALORIMETER SYSTEM. AND MEASUREMENT OF HEAT. 153 to warm up this wall. Conversely, if there be a fall in temperature, it is possible that the reverse may result. Inasmuch as with experienced observers the variations in tempera- ture are very slight, and as the press of experimental work has pre- vented our making further determinations of the hydrothermal equiva- lent, we have used in all the investigations so far the results of an experiment published 1 in 1899. In this test the calorimeter was held at a constant temperature for several hours ; a small electrical current was then passed through a resistance coil in it for two hours. During this period of time especial pains were taken to keep the thermal junc- tion circuits in the metal walls at equal temperatures, and as a result, since no heat was allowed to pass through the walls, the temperature of the calorimeter slowly rose. At the end of two hours the current was stopped and the calorimeter allowed to assume a constant tempera- ture. From the rise in temperature and the amount of heat generated by the electric current, it was calculated that the apparatus required about 60 large calories to raise its temperature i ° ; hence its hydro- thermal equivalent is not far from 60. The true significance of this factor is becoming less and less each year as the experimental skill of the manipulators increases. It is our pur- pose, however, to repeat these tests, and consider a fall in temperature as well as a rise in determining exactly the hydrothermal equivalent of the apparatus. Suffice it to say that for the fluctuations ordinarily occur- ring in experimental apparatus, it is known with sufficient accuracy. An attempt has been made to calculate the hydrothermal equivalent from the weight of the different parts of the apparatus ; but, as these weights were not taken at the time the apparatus was constructed and the quantity 'of wood, solder, etc., involved in the framework is not definitely known, these results are not at present available for use. CORRECTIONS FOR TEMPERATURE OF FOOD AND DISHES. In order to compute the total income and outgo of heat from the cal- orimeter system, it is necessary to know the temperature of all articles passed into or taken out of the calorimeter chamber. If the food, drink, and dishes going into the chamber are below the calorimeter temper- ature, there will be a certain amount of heat absorbed in warming the material to the temperature of the chamber; and, conversely, if any of the materials are warmer than the interior temperature, they will grad- ually radiate heat until they assume the temperature of the calorimeter. Similarly, if material is passed out of the chamber at a higher or lower temperature, there is a loss or gain of heat. 1 U. S. Dept. of Agr. , Office of Experiment Stations Bull. 63, p. 44. 154 A RESPIRATION CALORIMETER. Theoretically, all material should enter or leave the calorimeter cham- ber at the inside temperature, but in practice it has been found impos- sible to do this ; hence a correction is necessary. From the weights of all materials entering the chamber and their specific heats, their hydrothermal equivalent can be readily calculated, which, multiplied by the difference in temperature, gives the amount of heat added to or lost from the chamber. These corrections are made for each experimental period, the data being determined directly from a record sheet posted near the food aperture. ADIABATIC COOLING OP GASES. With fluctuations in barometric pressure, the air inside the calorim- eter expands or contracts, and consequently liberates or absorbs heat according to the well-known laws of adiabatic cooling. In considera- tion of the large volume of air in the calorimeter, the probable effect of fluctuations in barometric pressure on the amount of heat liberated during a given period has to be considered. From data furnished by the chief of the Weather Bureau,1 it has been computed that a maximum fall of 10 mm. in the barometer is accompanied by a cooling of 1.1°, which is equivalent to 1.624 large calories, or 0.1624 calorie per millimeter. This amount of heat is absorbed (rendered latent) as the barometer falls, and liberated as the barometer rises. Save in very exceptional fluctuations in the barometer, this correc- tion does not have to be taken into consideration, and thus far has not been necessary. It is possible, however, that in rest or fasting experi- ments, in which the amounts of heat liberated are small, this correction may amount to a percentage of the whole so large that it should be allowed for. CORRECTION FOR HEAT ABSORBED BY BED AND BEDDING. When the subject retires (at 1 1 p. m. ) , the heat radiated from the body is absorbed by the bed and bedclothes till the temperature of the por- tions nearest his body are warmed from chamber temperature (20°) to approximately that of the body (35°). As a result, the heat measured from ii p. m. to i a. m. is too low. On the other hand, when the sub- ject leaves his bed (at 7 a. m.), the bed and bedding again cool down to the temperature of the chamber, and the heat measured from 7 a. m. to 9 a. m. is too high. In determining the heat output by periods, correc- tion should be therefore made for heat stored in this way. The data available for estimating the exact amount of this heat are by no means 1 U. S. Weather Bureau, Report (1899), u, p. 492. THE CALORIMETER SYSTEM AND MEASUREMENT OF HEAT. 155 so complete as could be desired. A tentative figure, which is, however, little more than a rough estimate, is 30 calories. In practice it has been our custom to add 30 calories to the heat measured during the period from 1 1 p. m. to i a. m. , and to deduct 30 calories from the heat measured during the period from 7 a. m. to 9 a. m. following. If the subject be restless or uneasy during the night, so that bedding is removed, the correction is of course affected, and such condition must be considered in applying the correction. This correction applies only to the measurements of heat for different periods of the day. For the whole day the two corrections are com- pensating and are therefore negligible. CORRECTION FOR CHANGE OF BODY TEMPERATURE AND BODY WEIGHT. In the calculations thus far outlined it has been assumed that the temperature of the body of the subject has been constant throughout an entire period, and that there has been no gain or loss of body weight. It is obvious, however, that in an actual experiment either or both of these assumptions may be incorrect. Accurate temperature measure- ments show a considerable variation even under apparently uniform conditions, and the body weight undergoes a continual loss through the elimination of body carbon and hydrogen as carbon dioxide and water vapor by the lungs and skin, besides the marked gains and losses fol- lowing the intake of food and the excretion of feces and urine. The effect of such fluctuations may be that of either increasing or decreasing the amount of heat measured during the period. Thus, if the body weight has remained constant, but the body temperature has increased, there has been an absorption of heat by the body which has escaped measurement. An amount equivalent to the gain in temper- ature multiplied by the body weight and the specific heat of the body is therefore to be added. On the other hand, a fall in temperature would give a correction to be subtracted. Similarly, if the temperature remains constant, a gain in weight denotes a correction to be added to the heat measured, since with this gain of weight a certain amount of heat, depending upon the specific heat of the substance gained and the difference in temperature of the body and the chamber, has been required to raise the substance from the temperature of the chamber to that of the body. In case both body temperature and body weight have varied, the correction may be either positive or negative. In practice, readings of body temperature are taken, when practi- cable every four minutes, and arrangements are such as to permit of weighing the subject at the end of each period if desired. The neces- sary corrections may then be applied. 156 A RESPIRATION CALORIMETER. Measurements of body temperature. — In experiments in which the heat production is determined, it has been commonly supposed that the body temperature at any given hour of the day is practically the same from day to day. Inasmuch as the body temperature undergoes a daily fluctuation, with a minimum in the morning, usually between 2 and 4 o'clock, and a maximum in the afternoon about 5, a true measure of the heat production by short periods (two or three hours) can only be determined by making corrections for changes in body temperature at the beginning and end of any given period. To ascertain these fluctua- tions of temperature, a special form of thermometer, based on variations in electrical resistance, was devised. The thermometer, its calibration and method of use, and a large number of observations made with it are described in detail elsewhere.1 An illustration of the apparatus and a brief description of it are here given. FIG. 45.— Rectal Thermometer. A coil of fine platinum or copper wire inclosed in a pure silver tube is connected by an incandescent lamp cord to two metal plugs which fit in a switch. About 20 cm. of the other end is covered with rubber. A coil of fine double-silk covered wire (either copper or platinum), having a resistance of about 20 ohms, is inclosed in a small silver tube 30 mm. long and 5 mm. in diameter. The two ends of a flex- ible cable pass through a hard-rubber plug in the end of the silver tube and connect with the coil. A piece of soft- rubber tubing is slipped over the flexible cable and the ends well fastened with silk and shellac. The thermometer may then be inserted some 10 to 12 cm. in the rectum and worn with little inconvenience to the subject. The cable is connected with the plug switch and the variations in resistance of the rectal ther- mometer are measured by one of the bridge systems in the special form of mercury switch previously described. (Seep. 148.) Fluctuations of one-hundredth of a degree Centigrade can be readily determined, is thus possible to have observations of the body temperature of the subject within the respiration chamber recorded independently by the observer outside of the chamber. Observations are usually made every 4 minutes. 1 Archiv. f. d. g. Physiol. (Pfluger), 1901, 88, pp. 492-500, and 1902, 90, pp. 33-72. THE CALORIMETER SYSTEM .AND MEASUREMENT OF HEAT. 157 Weighing objects inside the chamber. — Aside from the variable weight of the body of the subject of the respiration calorimeter experiments, there is a continually fluctuating weight of the absorber system, the bed- ding, furniture, and clothing, due to variations in water content. A number of preliminary experiments, made several years ago in this laboratory, to attempt to determine the variations in weight of sheet copper exposed to different hygrometric conditions, gave negative re- sults, and hence it has been assumed that any changes in the amount of water condensed on the surface of the metal chamber must be very slight and may be neglected ; but we have found repeatedly that wood and textile fabrics absorb an appreciable amount of water which must be considered in accurate work. There is not, however, much wood in the chamber. A wooden chair is used, in which the man is weighed, and there is some woodwork on the bicycle ergometer and telephone, but these are well shellacked and polished, and we have no reason to believe that they alter in weight, although the construction of the apparatus is such as to render actual weighings somewhat difficult. With the clothing and bedding of the subject, we have conditions under which there may readily be wide fluctuations in weight. If, however, provision can be made for weighing such articles accurately, the fluctuations in weight can be determined and a correction applied accordingly. The large differences in the amount of water condensed on the ab- sorbing system have been referred to on pages 23 and 126. In order to know the exact amount of water in the chamber at any given time, it is necessary to know the variations in weight of the absorbing system. The variations in weight of the subject are of special significance in their use as a check on the oxygen determinations, for if we have the weight of the income of food and drink, the weight of the outgo, and the variations in weight of the body of the subject, it is possible to cal- culate arithmetically the amount of oxygen taken out of the air by the man. In considering the fluctuations in the weight of the subject, however, it is impossible to distinguish between the water in the body of the subject and that on the surfaces of metal, or absorbed by the woodwork, clothing, etc. , all of which are liable to changes in weight ; and since the water on the coat of the subject can not be differentiated from the same weight of water in the body of the subject, it is there- fore necessary to know not only the changes in weight of the body of the subject, but also the changes in weight of the bedding, absorber system, etc. Only by knowing these variations in weight can the 158 A RESPIRATION CALORIMETER. changes taking place in the water content of the body be stated accu- rately. It is evident further that inasmuch as it is impossible to dis- tinguish between water in the body of the subject and the water on the bedclothes, it is useless to weigh the bedclothes any more accurately than the weight of the man's body can be obtained, and also useless to provide for the weighing of the bedclothes if the man's body can not be weighed. In the earlier experiments we endeavored to weigh the subject by means of a platform balance ; but though the balance was extremely sensitive when standing on the laboratory floor, it was found that when placed inside of the calorimeter chamber the inequalities of the floor surface were such as to make accurate weighing practically impos- sible, though probably the error was not greater than 100 to 200 grams under the most favorable circumstances. Description of weighing apparatus. — In considering any method for weighing the subject inside the chamber, it was seen that, to be of any value, the weights should be accurate to at least within 5 grams, since 5 grams would correspond to the weight of about 3 liters of oxygen. Furthermore, the weighings must be carried out fairly rapidly, and what- ever apparatus was used must be capable of sustaining a weight equal to that of the body of the subject. It was, moreover, deemed highly important to devise a method by which all of the weighings could, if possible, be made outside of the respiration chamber, where the weights could be properly checked by a second observer. The space between the ceiling of the laboratory and the top of the calorimeter is small, but it was possible, by going to the floor above and cutting through the ceiling, to arrange a platform balance imme- diately over the center of the top of the chamber. A hole was then cut straight down through both top panels of the calorimeter and through the double wall of the metal chamber, and through this an apparatus was arranged for suspending objects within the chamber from the plat- form scale. The arrangement of the apparatus is shown in figure 46. A copper shoulder, threaded on the inside, was securely soldered to the copper wall of the chamber. A long fiber tube was screwed into this wall and thus gave an opening in the wall through which could pass vertically a cord or rod on which the object to be weighed could be suspended. To make the opening continuous to the upper side of the ceiling of the calorimeter laboratory, the fiber tube was lengthened out by screwing a brass tube to its end. This gave a straight opening, 30 mm. in diameter, from the floor above down into the calorimeter chamber. It was well adjusted in a vertical position and thus permitted the suspen- sion of a weight by a rod without having the rod touch the sides of the tube. THE CALORIMETER SYSTEM AND MEASUREMENT OF HEAT. 159 In weighing any suspended object, some up-and-down motion is of course necessary. If an equipoise were used, this motion would extend through several inches, but if a platform balance is used, it may be cut down to a small fraction of an inch. Moreover, a series of tests showed that if all lateral motion could be eliminated it was pos- sible to remove the hooks fastened to the under side of the platform and designed to prevent lateral motion and thus ma- terially increase the sensitiveness of the balance. The balance in use is of the Fairbanks platform type, designated by the manu- facturers as a silk platform scale. It is graduated to 10 grams and has a capacity of 150 kg. It was put in place exactly over the opening through the floor down into the calorimeter, carefully leveled by placing thin strips of copper under each of the corners, and was rigidly fixed in this position. A hanger was constructed of half-inch pipe, and a quarter-inch rod attached to the lower part of the hanger extended through the opening into the calorimeter. On the lower end of this rod was attached a rubber stopper for closing the opening when the weighing is com- pleted, and a stout iron ring into which various supports for weighing the man and other objects could be hooked. The adjustment of the balance and this tube were such that the rod swung freely, and even with considerable vibration on the lower end would not touch the sides of the tube. The same conditions affecting the open- FIG. 46-— Weighing Apparatus for Ob- mg through the food aperture as regards jects inside the chamber, necessity for preventing leakage of heat or air obtained in making this opening through the calorimeter chamber. The leakage of heat was prevented by using A chair is suspended on a rod extending from top of calorimeter chamber. A metal yoke is hung over the platform of bal- ance, so that chair and subject can be weighed directly. A rubber dia- phragm prevents escape of air. 160 A RESPIRATION CALORIMETER. the fiber tube, which is an excellent non-conductor of heat. To pre- vent the leakage of air, we at first used a thin rubber balloon with a small opening in one end so that the rod could pass through it, the balloon being tightly tied to the rod and attached to the tube. It was thus possible to provide for not only the necessary up-and-down motion, but also a slight lateral motion which would accompany the weighing and at the same time prevent any loss of air from the system. Later, thin- walled rubber tubing of large diameter was substituted. This thin rubber diaphragm prevents the escape of air ; but it is necessary to rely on this closure only during the actual period in which the weighings are being made, since the flexibility of the diaphragm is such as to allow the rubber stopper on the lower end of the suspension rod to be raised about 1.5 cm., which is sufficient to crowd it well into the open end of the fiber tube, thus completely shutting off the tube from the calorimeter chamber proper. The rubber diaphragm is so light that the slight vertical motion pro- duces no variation in weight. The extreme sensitiveness of the platform balance under these conditions makes it possible to read not only the graduations on the scale-beam, which are made in ic-gram divisions, but also the differences in height at the end of the scale-beam itself. A small metal pointer is attached to the end of the scale-arm and a milli- meter scale is placed immediately behind it in such a manner that, during the progress of weighing, the pointer moves over the millimeter scale. A certain arbitrary point is taken on this scale as the zero point. The finer weighings are made by means of a second hanger, which is very much smaller, consisting practically of a stout piece of copper wire, which is of such a weight that moving it through a section of the grad- uated beam corresponding to 200 grams is equivalent to an alteration in weight of 5 grams ; and it was found that by its use, even with a weight of 90 kg. suspended from the platform balance, weighings to within 2 grams or even i gram could be accurately made. In using this balance it is necessary only to obtain actual differences in weight, and hence no correction is made for the added weight of the pointer on the scale-arm, the removal of the hooks from the platform balance itself, the weight of the hanger and suspension rod, or of the stopper and ring at the lower end. The actual weight of the man can be obtained, however, since two series of weighings are made, one in which the man, bedding, clothing, etc., are weighed with the man sitting in the chair, and one in which only the chair plus bedding and clothes are weighed. The difference between these two weights obviously gives the weight of the man himself. THE CALORIMETER SYSTEM AND MEASUREMENT OF HEAT. l6l To support the man in a comfortable position while being weighed, we have provided a chair which can be suspended from the rod of the weighing apparatus. A hard-wood folding-chair, which has been in use regularly inside the chamber for a number of years, was utilized for this purpose. This is shown in figure 46. A chain (or at present a phosphor-bronze tiller rope) is fastened to the back of the chair and to the legs in such a manner that it can be suspended. To spread the rope at the front end of the chair seat, two oak blocks through which the rope passes were hinged under the seat. . A piece of gas-pipe with a hook serves to suspend the chair and act as a spreader at the top. By using this spreader arm more space is given between the chains for the arms and shoulders of the subject. The chair is hooked into the spreader arm in such a position that during the weighing the subject faces the window. The upper end of the suspension rod for the weighing system passes through a hole in the hanger on the platform balance. Two nuts are screwed on the end of the rod, the upper one of which serves as a lock- nut. It is thus possible to raise or lower the rod by adjusting these two nuts. The rod is so adjusted that when the rubber stopper is removed from the fiber tube it swings perfectly free, and there is no danger of touching the side of the fiber tube. When the stopper is put in place, the suspension rod slips freely up through the hole in the hanger, and the friction of the rubber stopper in the fiber tube holds the rod up in place. It has been found by experience that the taper on the stopper is such that it can be inserted in the fiber tube and support the rod above it without any danger of slipping out. When not in actual use for weighing, the stopper is always crowded well into place. On the end of the suspension rod there is simply a large iron ring, and it was found inconvenient to suspend everything from this ring without any intervening adjustment ; consequently a hanger consisting of a regular gas-fitter's cross was attached. Into opposite sides of two of the openings in the cross two half -inch pipes (16 mm. internal diam- eter) are screwed. These pipes are 14 cm. long, are open at the end, and have a 7 mm. hole drilled on the under side 8 mm. from the open end. A stout iron hook is screwed into a hole drilled in the side of the cross, and can be inserted in the ring on the end of the suspension rod. When suspended in this way, the cross lies parallel to the top of the chamber. In the other two arms of the cross, reducers and smaller pipes 1 8 cm. long and 10 mm. internal diameter are screwed and are used for suspending the absorbing system. Weighing the absorbing system. — In weighing the absorbing system as was formerly done by the use of spring balances, the accuracy was not I IB 1 62 A RESPIRATION CALORIMETER. at all comparable with the precision obtainable in weighing with the system just described. Arrangements were accordingly devised so that the absorbers could be weighed by this system. The bulk of the weight of the absorbing system is borne by three equipoises, one of which is shown in figure 33. These three points of support prevent any great lateral motion of the system. The system is suspended by attaching eighth-inch iron pipe (3 mm. internal diam- ter) to the pipes in the hanger and thence to the absorbing system. A piece of stout copper wire was wound about the upper coil of pipe in the absorbing system at the rear of the chamber so as to form a loop. The 3 mm. pipe was slipped through one end of this loop and the other end into the pipe of the hanger. Two similar loops of stout copper wire were attached to the absorbing system near the front on both sides about 42 cm. from the corner. A long T was then made of three pieces of the 3 mm. pipe, the two arms of theT were slipped through these copper loops, and the stem of the T inserted in the pipe in one arm of the cross or hanger. When the shields were lowered to such a point that their weight rested on the copper disks, the lead counterpoises were raised from their position and the whole system became suspended on the central suspension rod of the weighing system. Owing to varia- tions in the amount of water condensed on the surface of the different portions of the absorbing system, it became necessary to balance the system in such a manner that the three lead counterpoises and equal beams should be in an approximately level position and clear of the absorbing system. This balancing was done by shifting two lead weights provided with hooks in the top, which could be hung on the 3 mm. pipe used to support the absorbing system. After a little practice the subject could slide the weights along these pipes and bring the whole system into equilibrium very rapidly. When in equilibrium an observer out- side signaled the assistants stationed at the balance overhead and the weighing was made. Owing to the multiplicity of bearings of the three equipoises, the degree of accuracy obtained when weighing the man was not to be ex- pected. It was found, however, that when the adjustments were prop- erly made, differences in weight of the absorbing system of i or 2 grams could be accurately determined. Thus we have a method for noting changes in weight of the absorbing system that is as accurate as could be desired, for it is more than probable that the amount of moisture condensed on the surface of the calorimeter, the bicycle ergometer, the telephone, connecting wires, etc., sometimes amounts to i or 2 grams, and hence weighings closer than this would have no significance. THE CALORIMETER SYSTEM AND MEASUREMENT OP HEAT. 163 Before weighing the absorbing system, it is necessary that the subject draw off all drip water that can be removed from the cans at the corners of the absorbing system. It is absolutely essential that no considerable amount of water remains in the aluminum shield. It occasionally happens that the outlet pipe from the shield becomes clogged with dirt or dust, and the drip water, instead of running directly into the cans, accumulates in the shield itself. Under these conditions, when the subject attempts to adjust the absorbing system for weighing, the water will flow back and forth from one end of the absorber to the other end and thus produce a constantly changing weight that can not be properly estimated. After the weighing is completed, the observer outside raises the lever- arm until the flexible cable begins to raise the shields, thus removing a portion of the weight of the absorbing system. The lead counterpoises then settle into position and the subject can remove the pipes used to suspend the absorbing system. After removing the cross, the rubber stopper can be re-inserted in the fiber tube. Routine of the weighings. — Since the experimental day begins at 7 o'clock in the morning, it is desirable to have the weight of the sub- ject, bedding, and furniture at this hour every day ; consequently the following routine was utilized in the later experiments of 1904 : The subject was called at 7 a. m. He immediately rose, and, having slept in underclothing and socks, no change in clothing was made. He then rolled up the bedding, fastened the bed to the side of the wall, sus- pended the chair in which he was to be weighed from the iron hook in the end of the suspension rod, and, taking all the bedding and clothing in his lap, sat in the chair. By means of a speaking tube and an electric bell connected with the closet upstairs in which the balance is placed, a signal was given, whereupon two observers upstairs brought the balance to equilibrium and the actual weight was recorded by both. The subject was then signaled to get up from the chair, and he immediately placed all the clothing (save that which he was actually wearing) and the bedding in the chair. This weighing was made, followed by the adjust- ment and weighing of the absorbing system. It is thus seen that the most rapidly fluctuating weight, i. e., the weight of the man, was made first, almost immediately after 7 o'clock. The weight next most liable to fluctuate, i. e., that of the bedding and of the clothing, was made a few moments later, and the absorbing system, which it is supposed would fluctuate in weight the least, especially at this hour of the day, was not weighed until the last. The necessity for weighing the man as soon as possible after 7 o'clock is seen when it is considered that there is a loss in respiration and per- 164 A RESPIRATION CALORIMETER. spiration amounting to not far from i to 2 grams per minute, and hence it was our effort to have the weight of the man recorded at exactly the same moment after 7 o'clock. Theoretically, inasmuch as the quantities of carbon dioxide and water vapor in the air are determined precisely at 7 o'clock, the three weighings should be made at exactly this hour ; but, as a matter of fact, this was distinctly impracticable, and we believe that the routine here employed gives results that are not far from correct. With a subject who had never been inside the chamber before, this routine of weighing man, then chair plus bedding, then absorbing system, took not far from 10 to 12 minutes each morning. Checks on the accuracy. — This method of weighing was very carefully checked by weighing the subject in the chair and then placing several brass weights in his lap. It was found that, allowing for the slight loss from perspiration and respiration, the gain noted by the observers on the platform balance above corresponded exactly to the weights added. The accuracy of the weighing of the absorbing system was determined in a similar way. A small wire basket was constructed so as to hang directly from the hanger itself or in any position on the trough, and thus correspond to varying quantities of moisture. By placing weights in the basket in different positions, the accuracy and sensitiveness of the whole system could thus be easily tested. Frequently weights were placed on the lead counterpoises, and the apparent loss of weight of the system, as detected on the platform balance, always agreed very satisfactorily with the weights thus added. It seems fair to assert, therefore, that it is possible to weigh a man,, his bedding and clothing, and the absorbing system to within 5 grams, if not less, and thus the weighing of these objects is now sufficiently accurate to serve as a check on the oxygen determinations. Indeed, it is not impossible that the indirect determination of oxygen by this means may ultimately take the place of the direct method now employed. THE ERGOMETER. Many problems in metabolism require for proper study a knowledge of the external muscular work performed by the body. The utilization of the various nutrients as sources of muscular energy, the isodynamic replacement of the nutrients in diets for muscular work, and the efficiency of the body as a machine may be mentioned as among the problems of this nature. Considerable attention has therefore been devoted by investigators to securing an accurate measurement of external muscular work. The first method used in connection with the experiments with the respiration calorimeter consisted of raising and lowering a weight by To face page 164. FIG. 47. — The Bicycle Ergometer. The rear wheel of a bicycle is replaced by a copper disk which can be rotated iu the field of a magnet. The strength of the magnet can be varied by the quan- tity of electricity passing through the field coils. The principle is that of the electric brake. Kio. 48. — The Electric Counter. An armature which is attracted by two magnets is caused to actuate the ratchet on a revolution counter. The instrument is connected electrically with the bicycle ergometer. THE CALORIMETER SYSTEM ? ND MEASUREMENT OF HEAT. 165 means of a cord over a pulley, though the still cruder means of filing a given weight of iron filings from a piece of cast iron was used in one of the preliminary experiments. In both of these methods obviously but very crude estimates as to the actual amount of external muscular work performed could be made. As measures of relative rather than absolute amounts, they were less objectionable, but at best they were far from the accuracy that has been striven for in the development of the respiration calorimeter and its accessory apparatus. It was observed that the greatest amount of work, with the minimum fatigue, could be performed on a bicycle, and accordingly an ergometer was constructed in which a pulley attached to the armature shaft of a small dynamo was braced against the rear tire of a bicycle wheel. ' This instrument could be calibrated but roughly, to be sure, but did, how- ever, serve its purpose in the transitional period during which the bicycle ergometer described beyond was in process of development. Retaining the bicycle form so that the bulk of the work is done by the powerful leg muscles, the present ergometer consists of an arrange- ment for rotating a heavy copper disk, corresponding to the rear wheel of a bicycle, in the field of an electro-magnet, which thus gives the effect of an electric brake. The apparatus is shown connected ready for use in figure 47. The principle is the well-known one of magnetic induction. A current of electricity is passed through the field coils of the magnet, and when power is applied to the pedals of the wheel and transmitted to the revolv- ing disk, it is transformed into heat. To calibrate the apparatus, it is put inside the respiration chamber in such a way that the axle of the wheel is connected to a shaft which passes through the food aperture and is revolved by power applied outside. The rate of revolution is shown by a cyclometer. The strength of the magnet is determined by the electric current through the coils, which is measured. With a given strength of magnetization the power applied to the pedals and conse- quent heat generated will vary directly as the speed of revolution ; the heat is therefore measured for different rates of speed. The data thus obtained show the amounts of energy transformed per revolution with the given magnetization. The mechanical friction in the ergometer per revolution is constant and included in the calibration. Accordingly, when the man is working on the ergometer, the number of revolutions as recorded by a cyclometer multiplied by the energy per revolution gives the muscular work done at the pedals. We believe the measure- ments are accurate within a fraction of I per cent. The apparatus has proved very satisfactory. aU. S. Dept. of Agr., Office of Experiment Stations Bull. 136, p. 31. 166 A RESPIRATION CALORIMETER. The number of revolutions of the pedal of the ergometer is recorded on the observer's table by the cyclometer shown in figure 48, which is designated as the Dinsmore electric counter, since it was devised by our mechanician, Mr. Dinsmore. This instrument consists of an electro-magnet and armature, the latter having a projection which extends to the ratchet wheel of the cyclometer. A device on the crank wheel of the ergometer closes a circuit to the magnet at each revolution, and thus actuates the armature. Correction for the magnetization of the fields of the ergometer. — In work experiments with the ergometer a correction of the heat measured by the calorimeter is necessary because of the heat added to the chamber in magnetizing the fields of the ergometer. The amount of heat thus added varies with the strength of current.1 For the strength generally employed, namely, 1.25 amperes, it amounts to 10.94 large calories per hour, which is accordingly deducted from the heat measured. BLANKS USED FOR HEAT RECORDS. A specimen page from the calorimetric records, showing the printed blank in use in the heat calculations, with observations for a portion of an actual experiment recorded therein, is given on page 167. For a clear understanding of this sheet, reference to figure 43 is also necessary. It will be noted that at the top of the sheet are recorded the date, the number of the experiment, and the name of the observer. Then follow ten vertical columns, in which are inserted the various readings for one hour. A space at the bottom of the sheet allows for further observa- tions if necessary. In the first vertical column is inserted the time of each reading. It is so arranged that these may be recorded every two minutes, though as a matter of fact it has been found that in ordinary rest experiments four-minute readings are sufficient, except at periods of increased bodily activity, as at 7 a. m., when the subject is dressing and carrying out the somewhat extensive routine elsewhere outlined. At such times certain readings are recorded every two minutes as long as vigorous activity continues. The second column is headed " Inner walls, No. i." In this are recorded the deflections produced by pressing down the key marked A Iy I, No. i, in figure 43. The third column gives similar readings for the incoming air current, as shown by key No. 2, and the fourth the deflections for the outer walls, as indicated by the key marked A Iy L No. 3. The readings obtained from these three keys are recorded, 1 The calculation is made according to the formula C X E X I X 0.2385 = calories. See page 172. THE CALORIMETER SYSTEM AND MEASUREMENT OF HEAT. 167 Metabolism Experiment No. 70. H. C. Martin, Observer. Date, December 20, 1904. Time, (a.m.) Inner walls. No. i. 1 Moving air. No. 2. - + Outer wall. No. 3. — + Inside temp. No. 5. Temp, water therm. Cor- rected temp. Dif- fer- ence. Heat calculations. No. 7. T B Sundries. R 8=120. &% % 14-24 14.18 10.00 2 ^ i 106^ 10.39 10.38 3-8o 60 20.3 20.84 3>J4 02 14.26 14.20 04 5 i^ % 108 10.29 10.28 3-92 61 31% Sits up and drinks. 06 68.4 at 10:08:42 14.29 14-23 OS &% % 5 H3 10.24 10.23 4.00 63 45.25 at 4.114 31^ Liesdown; reads. 10 10.050 K. 14-32 14.26 12 1% X 13 116 10.16 10.15 4.11 66 3i/4 41-35 calo- ries. 11 I4-5I 14-45 16 4 I i% H5 10.16 10.15 4-30 66% yM 18 14.58 14-52 30 3% 1^ i% 114 10.12 10. II 4.41 66 3oH 22 14.60 14-54 24 1% IM i% «aM IO.O4 10.03 4-5i 65 3i 26 14.58 14-52 28 i* 1% 3% in% 10.23 10.22 4-30 64% 31* 30 Telephones. 14-59 14-53 32 % % 6% 1 10^ 10.20 10.19 4-34 63% 31 y2 Sits up and 31 19.8 20.87 opens food aperture. 14.68 14.62 36 6 3% i% "7M IO.I4 10.13 4-49 67 32j* 38 Lies down 14.87 I4.8I and reads. 40 2 % 13 »7M 10.14 10.13 4.68 68 335* 42 14-99 14-93 44 6 3 7 »3J* IO.2I 10. 2O 4-73 67* 33% 46 15-01 M.95 48 1% 2 5^ in IO.26 10.25 4.70 65 33% 60 79.8 at 10:52:38 14.76 14.70 52 i* I 5% noM 10.26 10.25 4-45 64^ 49.02 at 4.456 33% 54 10.102 K. 45.01 calo- 14-57 14.51 ries. 56 iM 2* *% no 10.32 10.31 4.20 63 34 J* 58 27^ 29^ I2}6 lOji REMARKS : 1 68 A RESPIRATION CALORIMETER. if positive, on the right-hand side of their respective columns, under the sign +, and if negative, on the left-hand side, under the sign — . As has been explained, the deflections should with each key be as near zero as possible. This is especially necessary with Nos. i and 2. At the end of each hour the sum of the readings in each of these columns is taken, and the difference between the sums carried over to the following sheet, to be compensated for if possible during the next hour. The fifth column is headed "Inside temp., No. 5." In this are recorded the deflections with key No. 5, which represent the temper- ature just inside the copper walls as measured by the electrical ther- mometer described on page 135. This temperature is held as nearly uniform as practicable. The three columns following are used for recording the temperature of the incoming and outgoing water current. That headed ' ' Temp, water therm. ' ' gives the readings of the mercurial thermometers, that in the outgoing water current being recorded above with the correspond- ing reading of the incoming water current immediately below. In the next column are the readings as corrected for the calibrations of the thermometers (see p. 133). The column headed ' ' Difference ' ' contains the differences between the corrected readings for the incoming and outgoing water current, or, in other words, the rise in temperature of the water current. In the column headed " Heat calculations " are recorded various mis- cellaneous data. The left-hand margin contains the readings with key No. 7, the electrical thermometer connected with the copper walls and showing their temperature. Readings of T, the mercurial ther- mometer just outside the window, and of B, the mercurial thermometer inside (see p. 120), are also taken from time to time and recorded in this column. Whenever one of the cans on the water-meter is full, the reading of the dial, together with the time, expressed in hours, minutes, and seconds, is recorded ; for example, 79.8 at 10 o'clock 52 minutes 38 seconds. Just below this is written the sum of all temperature dif- ferences while the can was filling. This sum divided by the number of readings gives the average rise in temperature of the water in the can. For example, the sum of n readings was 49.02, the average of which was 4.456. This value, multiplied by the weight of the water as determined from a plotted curve for the point corresponding to the figure registered by the dial (see p. 132), gives the heat in calories brought out from the calorimeter system for the period of time. This value is recorded in the last column (45.01 calories). The final column, marked "Sundries," also serves for miscel- laneous data. When the rectal thermometer is in use, its readings TESTS OF ACCURACY OF HEAT-MEASURING APPARATUS. 169 are here recorded under the designation R. Occasional readings of S, giving normal or standard deflections of the galvanometer, are here given, and any additional observations of the assistant, particularly as to the movements of the subject, are here briefly stated. The heat sheet therefore serves as a source of original data regarding the gain or loss of heat through the walls, the maintenance of constant temperature, the estimation of the heat brought away by the water cur- rent, the body temperature, and the more important movements of the subject. TESTS OF THE ACCURACY OF THE HEAT-MEASURING APPARATUS. For testing the accuracy of the calorimetric features of the apparatus two special forms of test have been devised. In one a definite amount of heat is generated inside the chamber by means of the passage of an electric current through a known resistance. Knowing the strength of current and the fall of potential, it is possible to calculate accurately the quantity of heat thus developed and compare it with that brought away by the water current. These tests are called electrical check experiments. A second test is obtained by burning known weights of ethyl alcohol inside the calorimeter and measuring the energy thus produced. From the weight of the alcohol and the heat of combustion as determined by the bomb calorimeter it is possible to compute the amount of heat which theoretically should be developed and compare it with that brought away by the water current. These are called alcohol check tests. ELECTRICAL CHECK TESTS. The development of a known amount of heat by means of the electric current necessitates an accurate knowledge of four factors : First, the strength of current; second, the fall of potential; third, the time in seconds, and fourth, the factor for the conversion of electric units to that of heat. Of these four factors we have to consider only those of the strength of electric current, fall of potential, and the conversion factor. The strength of the current in these experiments was deter- mined by passing it through a milli-ammeter, which was especially calibrated for us by the Weston Electrical Instrument Company, of Newark, New Jersey, and guaranteed by them to give readings within o. i per cent. In this instrument the maximum current that could be measured was 1.5 amperes. The instrument has been compared from time to time with a Kelvin balance with no noticeable variations in accuracy. A RESPIRATION CALORIMETER. The fall in potential is measured by an accurate voltmeter, constructed by the same company, with an accuracy guaranteed to be within o. i per cent. The maximum voltage that can be read on this instrument is 150. The accuracy of this instrument has been frequently tested by comparison with a standard Weston voltmeter. The electrical connections are shown diagrammatically in figure 49. The present arrangement consists of a loo-ohm resistance coil of German-silver wire wound on a wooden frame and suspended within the chamber. This coil is capable of carrying a current of i . 5 amperes. FIG. 49. — Connections for Electrical Check Experiment. An electric current from a storage bat- tery is passed through the ammeter and then through a coil hung in calorimeter chamber. By means of a variable resistance the strength of current can be kept constant. A voltmeter gives the fall of potential. Connections are made with the milli-ammeter on one side and with a switch connected with the storage battery on the other side. The milli- ammeter is also connected with a switch. Two wires connect the volt- meter with the coil inside the chamber, and thus the fall of potential as the current passes through the coil is accurately measured. The current from the storage battery therefore passes in series through the milli- ammeter, the coil inside the chamber, and then through a variable resist- ance back to the switch. By varying this resistance, the strength of current passing through the coil can be adjusted with great accuracy. Both electrical instruments can be read with a magnifying glass to i TESTS OF ACCURACY OF, HEAT-MEASURING APPARATUS. 171 part in 1,000. A sufficient number of cells of storage battery are employed to give a strength of current through the coil of about i ampere with a voltage of about 1 20. ELECTRICAL UNIT USED. In the fall of 1904, in a discussion of the accuracy of the bomb calo- rimeter l used in connection with these experiments, it was pointed out by Dr. I,. J. Henderson, of Harvard University, that the heat of combus- tion of standard materials such as naphthalene, benzoic acid, and cane sugar were noticeably different when determined by the bomb calorimeter used at Wesleyan University and when determined by the bomb calo- rimeter used by Fischer and Wrede." The calorimeter used by these writers was standardized by Jaeger and von Steinwehr 3 by an electrical method in which the factor 0.2394 was used to convert watt-seconds to calories. This matter was referred to Dr. E. B. Rosa, formerly professor of physics in Wesleyan University and at present physicist of the National Bureau of Standards. The following statements are essentially those furnished us by Dr. Rosa. The values found for the mechanical equivalent of heat by the elec- trical method differ appreciably from those obtained by the mechanical method. There is reason for believing, however, that the values of the international volt and ampere are about o. i per cent too large. This is a subject the Bureau of Standards and others are now investigating, but absolute measurements for determining independently the volt and ampere are difficult to make and the question is not yet settled. Assuming this error in the electrical units, the values of J deter- mined electrically agree very well with Rowland's value determined mechanically, and this is the best value yet obtained by the mechanical method. The most probable value for J (assuming the correction of o. i per cent in the electrical units) is J= 4.181 x io7 ergs, at 20°. Allowing for the variation in the specific heat of water, the heat required to raise the temperature of a gram of water i° at 10° would require 4.181 x io7 x 1.0030 = 4.1935 X io7 ergs. 1 For a description of the form of bomb calorimeter here used see Jour. Am. Chem. Soc. (1903), 25, p. 659. '-1 Sitzungsber. K. Akad. Wiss. (1904), pp. 687-715. 3 Verhandlungen ber. deut. phys. Gesell. (1903), 5, 2, pp. 50-59. IJ2 A RESPIRATION CALORIMETER. The energy of an electric current is CE/ X IOT ergs. , and this expressed in calories at 10° is IE/ x IQT_= cE/x 0.23846 calories. 4. 1935 X 10' But this is on the assumption that our electric units are o. i per cent too small. Since we are using these same small units in our work, it is evident that the numerical values of C and E are both too large by this amount, and therefore the product too large by o. 2 per cent. This gives 0.23846 — 0.00048 = 0.2380 as the true conversion factor. We can reach the same result by taking the mean of the results for the mechanical equivalent of heat obtained by Griffiths (4. 192), Schuster and Gannon (4.189), and Callendar and Barnes (4.186) without correc- tion for the supposed error in the electrical units. The mean of these three values is J = 4. 189 X io7 at 20°. Correcting this to 10°, we have, multiplying by 1.003 as before, J = 4.2016 x io7 at 10°. Then CE/ X io7 s before> 4-2OI6X IO7 Thus no account need be taken of the supposed error in the electrical units, inasmuch as the three English investigators above quoted all used substantially the same electrical units that are now used in Middletown. This value (0.2380) is slightly different from that used earlier l (0.2378), because the latter is based on Griffith's value, which is somewhat larger than the mean of the three used in this calculation. To compare this with the value given by Fischer and Wrede, it is necessary to reduce to 15° and to correct for the difference between our electrical units and those used in Germany. The first correction amounts to 0.0019, giving 0.2380 x 1.0019= 0.23845. The second amounts to 9/1 = 0.0017. H340 Thus 0.23845 x 1.0017 = 0.23885, which is the proper value at 15° to use in Germany ; that is, with German electrical units. A value as large as o. 2394 can not, in the light of the most recent work, be justified. As used by Jaeger and von Steinwehr it was apparently taken from the values given by Graetz.2 1U. S. Dept. of Agr., Office of Experiment Stations Bull. 63, p. 43. s Winkelmann's Handbuch der Physik, 2, 2, p. 415. TESTS OF ACCURACY OF HEAT-MEASURING APPARATUS. 173 Graetz quotes the results obtained by Joule, Rowland, and Miculescu. The more recent investigations of Griffiths, Schuster and Gannon, and Callendar and Barnes are not given. Joule's value for J is a little smaller than Rowland's and the recent values found by the electrical method. Graetz takes the mean of the three values quoted, and the lower value of Joule's result makes the mean a little lower, namely, 4.177 x io7 at 15°. The reciprocal of this is o. 2394, the value used by Jaeger and von Steinwehr and Fischer and Wrede. According to Dr. Rosa, the best principle would be to use the number 0.2385 at 15° and then correct the number of gram-degrees measured to calories at 15° by multiplying by the ratio of the specific heat at the given temperature to that at 15°. The importance of the electrical unit and conversion factor in connec- tion with the experiments with the respiration calorimeter is seen when it is considered that, given accurate electrical units and factors, it is possible to verify the bomb calorimeter by the respiration calorimeter. By burning alcohol in the bomb calorimeter a certain heat of combustion is obtained, and if the alcohol is then burned in the respiration chamber, which has been calibrated and standardized by the electrical method, obviously the same heat of combustion determined by both forms of calorimeter is a verification of the bomb.1 It is furthermore significant that the difference between the heat of combustion of cane sugar, naphthalene, benzoic acid, and other standard materials, when determined by the bomb calorimeter used in Middle- town and when determined by Fischer and Wrede, is exactly propor- tional to the difference between the two conversion factors used. Pend- ing a revision of the electrical units by the National Bureau of Standards, we use here the factor 0.2385 for converting watt-seconds to calories at 15°. LENGTH AND DURATION OF EXPERIMENTS. After the coil and connections are properly installed inside the chamber the switch is closed, and the water current passing through the heat-absorbers is regulated so that the heat is brought away at the same rate at which it is generated. After an hour or two, during which period the apparatus comes into equilibrium, the experiment proper is begun. The experiment lasts usually from eight to twelve hours, during which time the current is measured by the milli-ammeter and is kept 1 For a discussion of the verification of the bomb calorimeter by the respiration calorimeter see Atwater and Snell, Jour. Am. Chem. Soc. (i9°3). 25> P- 698- 174 A RESPIRATION CALORIMETER. constant by means of the variable resistance. Readings on both elec- trical instruments are taken frequently to insure complete accuracy. At the end of the period the time in seconds is noted and the average reading of the instrument taken. The formula for computing the amount of energy developed during the experiment is therefore C X E X / X o. 2385 — calories, in which C is the strength of the cur- rent in amperes, E the fall of potential in volts, and / the time in seconds. RESULTS OF EI.ECTRICAI, CHECK EXPERIMENTS. The last electrical check experiment made with the apparatus was on November 22, 1904. The actual period of measurement extended from i. 06 p. m. to 10.04 p. m., or 8 hours and 58 minutes. During this period there was a current of 0.950 ampere passed through the coil and a fall of potential of 99 volts. By using the formula given above, the heat generated during this period was computed to be 723.7 calories. The heat measured during this period by the respiration calorimeter was 721.73 calories, or 99.72 per cent of that generated. A test con- ducted a month before gave the ratio of heat measured to that generated corresponding to 99.59 per cent. It thus appears that the apparatus measures heat developed within it electrically with great accuracy. THE COMBUSTION OP ETHYL ALCOHOL AS A CHECK ON THE HEAT MEASUREMENTS. Although the electrical check experiments are carried out with great accuracy, they still do not permit of the testing of the apparatus under conditions approximating those in which it is used in actual experi- menting, and obviously the question of the heat of vaporization of water plays no r61e in the electrical check experiment. As early as 1779, Crawford l endeavored to study the accuracy of the heat measurements of his calorimeter by burning known weights of charcoal, lamp oil, wax, and tallow inside the chamber. Subsequent experimenters have used hydrogen, stearin candles, ether, and other substances. As a result of a large number of experiments in which a number of different combustibles were tried, we have relied upon the combustion of ethyl alcohol of known water content for this purpose. Inasmuch, however, as the combustion of ethyl alcohol inside the chamber results not only in an evolution of heat, but also of carbon dioxide and water, and in the absorption of 1 Experiments and Observations on Animal Heat ; see also Zeits. f. Biol. (1894), 30, p. 76. TESTS OF ACCURACY OF HEAT-MEASURING APPARATUS. 175 oxygen, the combustion of alcohol is also used to check the accuracy of the respiration apparatus. Such experiments, as well as the kind of alcohol used and determination of its specific gravity, have already been considered in detail (see pp. 96-105). For the purpose of checking the apparatus as a calorimeter, a knowl- edge of the heat of combustion of the alcohol used is essential. HEAT OF COMBUSTION OF ALCOHOL. For the determination of the heat of combustion we resort to direct combustions in the bomb calorimeter. A large number of such com- bustions have been made in this laboratory. Since absolute alcohol absorbs water rapidly from the air, we have prepared aqueous solutions of varying degrees of strength for use in these tests. A known weight of alcohol is placed in small gelatin capsules, such as are used frequently for the administration of medicine. When gela- tin capsules are used there is no loss by volatilization, and as the heat of combustion of the gelatin is quite constant (about 4.452 calories per gram) the absolute amount of heat introduced with the alcohol can be determined with considerable accuracy. The capsules weigh not far from 0.3 gram, thus introducing about 1.3 calories. Inasmuch as in the combustion of alcohol a certain portion of the oxygen combines with the hydrogen of the alcohol to form water, which is condensed inside the bomb, the gas in the bomb is at a somewhat less pressure at the end than at the beginning of the combustion. The slight expansion of the residual gas, as a result of a diminished press- ure, produces a cooling effect, and the heat of combustion of the alcohol must be corrected for constant pressure. It is necessary, therefore, to add to the heat of combustion of the alcohol a certain factor which is obtained in the following manner : To reduce the molecular heat of combustion of a solid or liquid, the formula of which is CnHpNrO(l, from that at constant volume to that at constant pressure, a correction would be added of (% p — q — r)T calories, where T equals the absolute tem- perature of the calorimeter.1 To reduce the specific heat of combustion at constant volume to that at constant pressure, the amount to be added is, therefore, (% p — q — r) T -=- M, where M equals the molecular weight of the substance. For alcohol this correction amounts to 13 calories per gram. The corrected heat of combustion of anhydrous ethyl alcohol is taken in this discussion as 7.080 calories per gram. 1 For discussion of this point see Atwater and Snell, Jour. Am. Chem. Soc., 25, I9°3, PP- 690, 691. 176 A RESPIRATION CALORIMETER. RESULTS OF ALCOHOL CHECK EXPERIMENT. As has been stated, the combustion of known amounts of ethyl alcohol inside the respiration chamber furnishes the means for verifying the accuracy not only of these portions of the apparatus which have to do with the measurement of the respiratory products, but also of the heat- measuring features. Consequently, instead of discussing the check on the heat determinations as a separate section, a summary of the alcohol check experiment in its relation to the determination of water, carbon dioxide, and oxygen as given on pages 102-105 is included in Table 4, with the data on the determination of energy. TABLE 4. — Summary of Determinations of Water, Carbon Dioxide, Oxygen, and Energy. Alcohol check experiment, April 6-7, 1905. Period. Duration. Alcohol burned. Water. Carbon dioxide. Found. Required. Ratio. Found. Required. Ratio. First Mrs. Mins. 3 54 5 441A ii 52 Grams. 73-4 108.1 225.3 Grams. 86.51 124-33 263.15 Grams. 84.98 125.15 260.83 Percent. 101.8 99-3 100.9 Grams. 126.70 187.39 392.10 Grams. 127.32 18751 390-81 Per cent. 99-5 99-9 100.3 Second Third 21 30% 406.8 473-99 470.96 100.6 706.19 705.64 IOO.I Period. Duration. Alcohol burued. Oxygen. Energy. Found. Required. Ratio. Found. Required. Ratio. First firs. Mins. 3 54 5 44^ ii 52 Grams. 73-4 108.1 225.3 Grams. 139-35 207.09 431-09 Grams. 138.90 204.56 426.33 Percent. 1003 IOI.2 IOI.I Calories. 417-86 619.03 1,292.97 Caloriet. 421.40 620.61 1,293-45 Per cent. 99-2 99-7 IOO.O Second Third 21 3<>M 406.8 777-53 769.79 IOI.O 2,329.86 2,335-46 99.8 This experiment, a fair sample of a large number of the sort, gives a true test of the apparatus in all its phases. The determinations of energy are as satisfactory as could be expected, averaging 99.8 per cent of the required amount. The summarized results for the determina- tion of water, carbon dioxide, and oxygen show that the apparatus is sufficiently accurate to determine these three factors as well as the energy with an accuracy approaching that of the most approved methods of chemical analysis. EXPERIMENT WITH MAN. 177 EXPERIMENT WITH MAN. Obviously with an apparatus constructed on this plan, the final test of its practicability lies in an experiment with man. Since the comple- tion of the new apparatus, 22 experiments with 5 different subjects, covering a total of 60 days, have been conducted. These experiments lasted from i to 13 days, during which time the subject remained inclosed in the calorimeter chamber. Ordinarily the experiment lasts 3 or 4 days. In general, each experiment is preceded by a preliminary period outside the chamber, during which the subject is given the special diet to be tested, and his habits of life so modified as to conform with those to be followed in the chamber. When the subject is to be engaged in muscular work, he devotes considerable time in the preliminary days to riding a bicycle in the open air, the amount of work performed being as nearly as can be judged equivalent to that to be done later on the bicycle ergometer inside the chamber. The food for the whole experi- mental period, including the preliminary days, is carefully weighed, sampled, and daily portions placed in proper containers ready for con- sumption. The more easily decomposed materials, such as milk and cream, are sampled, weighed, and analyzed each day. The bread and meat when used are carefully sterilized in glass jars. The diet may be so planned as to maintain a uniform quantity of nitrogen and a constant calorific value from day to day. MEASUREMENT OF INTAKE AND OUTPUT OF MATERIAL. In experiments with man as carried out with this apparatus and accessories, the following determinations of intake and output of ma- terial are made : The intake consists of food, drink, and oxygen from respired air. The amounts are determined by weighing. The analyses include de- terminations of water, ash, nitrogen, carbon, hydrogen (organic), and at times sulphur and phosphorus. The output of material consists of products of respiration and perspiration, urine, and feces. The dry matter of feces and urine is subjected to a series of analyses similar to those for food, and the water and carbon dioxide of perspiration and respiration are determined according to the methods discussed in this report. The determinations of nitrogen in perspiration are made, when necessary, according to methods given elsewhere.1 1 U. S. Dept. of Agr., Office of Experiment Stations, Bull. 136, pp. 52-53. 12B 178 A RESPIRATION CALORIMETER. MEASUREMENT OF INTAKE AND OUTPUT OP ENERGY. The intake is derived from the potential energy, i. . 64.42 16.07 0.96 Calories. 2,013 532 24 do Plasmon Total... 1,657.90 -,306.33 53-31 211.87 75-41 10.98 8-54 2l6.0X> 33-70 81.45 2,569 For purposes of further computation the amount of oxygen in the water- free substance of the food is here given, though obviously this is a result of indirect determination. EXPERIMENT WITH MAN. Similar data for the feces and urine are given in Table 7. 181 TABLE 7. — Weight, Composition , and Heat of Combustion of Urine and Feces Metabolism Experiment No. 70. («) Total weight. (*) Water. Water-free substance. to Ash. w Nitrogen. to Carbon. (/) Hydrogen. Or) Oxygen. (A) Energy. Urine Grants. 1,031.50 60.97 Grams. 991-37 40.48 Grams. 4.54 4-25 Grams. 13.04 0.36 Grams. 8.87 12.04 Grams. 2-37 1.91 Grams. 11.31 1-93 Calories. 103 149 Feces The amount of oxygen in the water-free material is also included in the table for subsequent use. Summaries of the data for the determination of water, carbon dioxide, and oxygen are given in Tables 8 to 10. STATISTICS OF WATER ELIMINATED. The quantities of water exhaled by the subject during each experi- mental period are calculated from the determinations of the amount of water removed from the ventilating air current and the difference between the quantity remaining in the air inside the apparatus at the beginning and end of the period. These computations are summarized in Table 8. TABLB 8. — Record of Water in Ventilating Air Current, Metabolism Experiment, No. 70. («) (*) (c) (d) (') (/) Or) Change Total Total Date. Period. amount of vapor in cham- ber at end of period. Gain (+) or loss ( - ) over pre- ceding period. weight of heat- absorb- ing sys- tem — gain (+), loss ( — ). Change in weight of chair, bedding, etc. amount gained (+)or lost(-) during period. (6+c+d) Total amount in out- going air. water of respi- ration and per- spira- tion. <*+/)* 1904. Grams. Grams. Grams. Grams. Grams. Grams. Grams. Dec. 20 5 a. m to 73. m.. 36.07 Dec. 20-21 7 a. m to 9 a. m.. 38 74 + 2 67 71 87 9 a. m to ii a. m.. 39.91 + 1. 17 66 7Q ii a. m to i p. m.. 38.91 — 1. 00 67^5 66.55 i p. m to 3 p. m.. 41.73 + 2.82 61.85 6467 3 p. m to 5 p. in.. 36.93 — 4.80 6895 64.15 5 p. m to 7 p. m.. 37.76 + 083 7 p. m to 9 p. m.. 37-28 — 0.48 65.96 65.48 9 p. m to ii p. m.. 37.23 — O.O5 66.26 66 21 ii p. m to la. m.. 39-97 i a. m to 3 a. m.. 46.06 + 6.OQ 84.41 3 a. m to 53. m.. 39-71 -6-35 76.55 70.20 5 a. m to 73. m.. 33-18 -6-53 70.31 63.78 Total — 2 80 •4- * 26 *8j8 30 *The total for this column is the sum of (e) + (/). 1 82 A RESPIRATION CALORIMETER. The quantity of water removed from the air current during each period is determined by weighing the water- absorbers at the beginning and end of the period. The values thus found are expressed in column (/"). The quantity of water in the air remaining in the chamber at the end of each period is learned by analysis of a sample of the air. These determinations are given in column (a). The increase or decrease in the quantity of vapor residual in the air for each period, which is simply the difference between the quantity at the end of one period and that at the end of the next, is given in column (£) , an increase being indi- cated by + and a decrease by — . The quantity of water exhaled by the subject during each period, shown in column (g}, is the algebraic sum of the quantities in columns (£) and (/). If the value is indicated by + in column (£) it is added, because it represents an excess that has been added by the subject during the period ; it is subtracted when the sign is — , because that means that the absorbing apparatus has removed from the air so much more than was exhaled by the subject. As a result of the variation in hygrometric conditions inside the respi- ration chamber, there may be a noticeable change in the amount of moisture deposited upon the bedding, clothing, etc., of the man and also upon the heat-absorbing system. In general, this latter is negli- gible in the case of the rest experiments, such as experiment No. 70 reported here. On the particular day here given there was a loss of weight in the heat-absorbing system amounting to 2 grams, and an increase in weight of the chair, bedding, etc. , of 5. 26 grams. These are recorded in columns (c) and (aT), Table 8. In column (e) the algebraic sum of (£), (c)t and (d} is given. Obviously, for the entire day the total water of respiration and perspiration is the algebraic sum of (tf) and (/) and not of (6) and (/). STATISTICS OF CARBON DIOXIDE ELIMINATED. The determinations of the quantity of carbon dioxide exhaled by the subject during each period depend, like those for water, upon the quan- tity removed from the ventilating air by the absorbers and that remain- ing in the air within the apparatus. These data for carbon dioxide are summarized in Table 9. The determinations of the total quantity of carbon dioxide removed from the air current during an experimental period, ascertained by weighing the absorbing apparatus at the beginning and end of each period, are shown in column (V). The quantities of carbon dioxide remaining in the air of the chamber at the end of each period, as determined by analysis of a sample of the air, are shown in column (a). The difference between the quantity residual in the air at the end of one period and that at the end of the next period is shown EXPERIMENT WITH MAN. 183 in column (£) , with a plus sign to indicate a gain and a minus sign a loss in the residua! amount in the air during the given period. The total amount of carbon doxide given off by the subject, as shown in column (d), is the sum of the quantities in columns (£) and (V). 9. — Record of Carbon Dioxide and Carbon in Ventilating Air Current, Metabolism Experiment No. 70. Date. Period. Carbon dioxide. (/) Carbon in carbon dioxide exhaled. (rfX3/"> («) Amount in cham- ber at end of period. (*) Gain(-f) or loss (— ) over preced- ing period. (c) Amount absorbed from out- coming air. (d) Corrected weight exhaled by subject. l*+«J w Volume exhaled by subject. (dX 0.5091) 1904. Dec. 20 Dec. 20-21 Grams. Grams. Grams. Grams. Liters. Grams. 33-47 5I-I9 37-97 55-.S9 39 '3 33-°3 37-32 30.80 28.76 2683 28.03 21.96 5.63 69.24 42.35 68.71 42.10 73.67 66.17 55-68 60.02 53-45 51.04 40.41 47.16 63.61 60.07 55-49 59-72 57-21 60.07 59-97 53-50 5'.4i 49.11 41.61 41.09 32.38 30.58 28.25 30.40 29.13 30-58 30.53 27.24 26.17 25.00 21. 18 20.92 17-35 16.38 15-13 16.29 15.60 16.38 16.36 14-59 14.02 13.39 ".35 II. 21 9 a. in to ii a. m + 17-72 — 13.22 + 17.62 — 16.46 — 6.10 + 4-29 6 12 ii a. in to i p. m i p. in to 3 p. ro 3 p. m to 5 p. m 5 p. m to 7 p. m 7 p. m to 9 p. m ii p. m to i a. in — 2.04 — 1-93 -f- 1. 20 — 6.07 i a. m to 3 a. m 3 a. in to 5 a. m 5 a. m to 73. 111 Total — I7-H 670.00 652.86 332-36 178.05 In computing the respiratory quotients given in Table 10, it is neces- sary that the quantities of carbon dioxide exhaled by the subject be expressed in volume rather than in weight. These values are shown in column (c) in Table 9, which are obtained from those in column (d) by the factor expressing the relation of volume to weight of carbon dioxide. The quantities of carbon in the carbon dioxide exhaled by the subject during each period, which are likewise used in computations of later tables, are shown in column (/). These values are calculated directly from those in column (a?) . STATISTICS OF OXYGEN CONSUMED. The quantity of oxygen consumed by the subject during each period is learned from the determinations of the quantity admitted from the cylinders to the chamber and that remaining in the air at the end of the period. These data are summarized in Table 10. The amount of oxygen supplied during each period is determined by the loss in weight of the cylinder between the beginning and end of the period and the purity of the oxygen in the cylinder, and is recorded in column () by use of the factor o. 592 as the latent heat of vapor- ization of water per gram. These values are given in column (./). In addition to the above, a certain amount of heat is concerned in the changes in temperature of the walls of the respiration chamber and other parts of the apparatus. Each degree of change of temperature for the whole calorimeter is assumed to represent 60 calories of heat. The difference between the initial and final temperatures of each period gives the total change of temperature to be taken into account. These data are shown in column (3). Multiplying these values by 60 gives the total quantity of heat involved in the changes of temperature, as shown in column (c). Food materials, dishes, etc., when sent into the chamber through the food aperture, of course deliver heat when they are warmer than the air of the chamber, and remove heat by absorption when they are cooler. The amount of heat thus introduced or removed during the different periods of the experiment, as calculated from the weight and specific heat of each material and the difference between its temperature and that of the chamber, is shown in column (d~). The total amount of heat determined in an experimental period, column (£-), is therefore the algebraic sum of the quantities of heat brought away by the circulating water current, as shown in column (a), with the correction due to changes in temperature of the calorimeter, column (V), the correction for heat removed or introduced by food, dishes, etc., column (cT)t and the heat latent in the water vaporized, column (/"). It should be added that the temperature of the ventilating air current is so regulated as to be the same in entering as in leaving, so that it carries out the same amount of heat as it brings in, and need not be taken into account in the tables. No corrections have been made for variations in heat measurement due to changes in body temperature, changes in body weight, or to the absorption and radiation of heat by the bed and bedding, as previously EXPERIMENT WITH MAN. 187 explained. These corrections are chiefly of importance from their bear- ing upon the question of heat production versus heat elimination, and they are accordingly omitted from the present brief summary. INTAKE AND OUTPUT OF MATERIAL, AND ENERGY. From the data derived from the preceding tables the balance between the intake and output of material and energy in the body may be cal- culated. The methods and results of these calculations may be explained as follows : GAINS AND LOSSES OF BODY MATERIAL. In order to compute the gains and losses of body material as expressed in terms of protein, fat, and carbohydrates it is necessary first to deter- mine the gains and losses of the elements which make up these com- pounds. This is done by comparing the amounts of the elements in the intake of the body with those of the output, as shown in Table 12. 12. — Gain or Loss of Body Material, Metabolism Experiment No. 70. (a) Total weight. <*) Nitrogen. w Carbon. (rf) Hydro- gen. GO Oxygen. (/) Ash. Intake. Grams. 622.40 Grams. Grams. Grams. Grams. 622.40 Grams. 139.00 15.55 123.45 Water in food 1,306.33 351.57 854 216 90 146.18 33.70 1,160.15 81.45 10. qS Total 2,419.30 8.54 216.90 195.43 1,987.45 10.98 Output. 40.48 4-53 35-95 20.49 0.36 12.04 1.91 1.93 4.25 991.37 110.94 880.43 40.13 13.04 8.87 2.37 11.31 4-54 838.30 93.81 744 49 COa of respiration 652.86 178.05 474.81 Total 2,583.63 13.40 198.96 213.56 2,148.92 8.79 4 86 — 18.13 + 2.19 — 0.45 — 164 78 + 1-74 Gain or Loss of Body Material. — 4 86 — 2.04 — 6.41 — 0.45 Fat ... Glycogen Water . ... + 33-54 + 17-53 18888 + 25-52 + 7-78 + 3-96 + i.°9 — 21.14 + 4.06 + 8.66 — 167 74 Ash + 2-J9 Total — 164.78 — 4.86 + 17.90 — 18.13 — 161.43 + 1-74 The intake of the body is made up of the following: (i) Oxygen from the air, which is found for this experiment in column ( Heat meas- ured by. respi- Heat measured greater or less than esti- mated. gained oxi- ration («) Food. (*) Feces. (f) Urine. a-(b+c) w Pro- tein. (/) Fat. (f) Gly- co- gen. or lost. (e+S+e) dized in the body. (d-h) calo- rim- eter. (*) Amount. (I) Pro- por- tion. 1904- Cals. Cals. Cals. Cals. Cals. Cals. Cals. Cals. Cals. Cals. Cals. Perct. Dec. 20 2,569 149 103 2,317 -165 +321 + 73 + 229 2,088 2,113 + 25 + 1.2 In this discussion the intake of energy is the energy from the mate- rial actually katabolized, z. e., broken down and oxidized in the body, including, therefore, not only the energy of katabolized food but also that of the body material lost. The output of energy is that given off by the body as heat, measured either as sensible heat by the respi- ration calorimeter or as heat of vaporization of water. The intake of energy may be measured in a number of ways. First, we may con- sider the intake as the potential energy of the food ingested and consider the potential energy of the unoxidized material in the urine and feces as a part of the output. Second, we may correct the potential energy of the food for that of the feces and urine by deducting the amount of energy in these latter, thus obtaining the so-called ' ' available ' ' energy. Without entering into any discussion here as regards the merits of the two methods of computation, we may proceed to the discussion of Table 15. The available energy of the food is calculated from the heat of combustion of the food, column (a), the heats of combustion of the unoxidized material in the feces, column (£), and urine, column (c). These quantities are taken from Tables 6 and 7, respectively. As previously explained, they are the results of actual determinations. When the available energy of the food is more than sufficient for the needs of the body, more or less of the surplus food may be stored as body material, and the quantity of energy in the material so stored must be subtracted from the available energy of the food to obtain the energy of the material actually metabolized, which is the energy of intake here considered. On the other hand, if the available energy of the food is not sufficient, the body will draw upon its own previously stored material, and the amount of energy thus derived must be added to that available from the food to give the total energy of material oxidized in the body. 1 92 A RESPIRATION CALORIMETER. It may happen that the body will increase its store of one material while drawing upon that of another. Thus the figures for the experi- ment under discussion (Table 12) show a gain of glycogen and fat at the same time with a loss of protein in the body. Under these circum- stances, the quantity of energy from body material that is to be added to the available energy of food is the difference between the energy of material lost and that of material gained. CALCULATIONS OP ENERGY OF BODY MATERIAL GAINED AND LOST. Returning now to the summary of intake and output of energy in Table 15, the total energy of body material gained or lost, as given in column (^), is the algebraic sum of the quantities in columns (^), (/), and (£•) . These latter quantities are calculated from the amounts of body material gained or lost, as shown in Table 12, by use of factors for the heats of combustion per gram of body materials. The factor for protein, 5.65 calories per gram, is that for fat-free muscular tissue from which the non-proteid nitrogenous compounds have not been removed. The factor for fat, 9.54 calories per gram, is the average of the results of several determinations of the heat of combustion of fat from the human body; and the factor for glycogen, 4.19 calories per gram, is likewise the result determined by actual combustion of that material. Applying these factors to the amounts of body material gained or lost, and adding (algebraically) the results, gives the total amount of energy from body material, as illustrated by the following computations for December 20 : Protein, — 29.16 grams X 5.65 = — 165 calories. Fat, + 33.65 grams X 9.54 = -f 320 calories. Glycogen, + 17-34 grams X 4.19 = + 73 calories. Total energy from body material = + 229 calories. The minus sign in column (