A RESPIRATION CALORIMETER WITH APPLIANCES FOR [HE 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 3 ^- () L 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 Wesleyau University, was actively engaged in this investigation in its earlier stages and has subsequently from time to time given advice which has assisted greatl}r 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 n 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 (or 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 factors 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 analysis of 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 Vcluiue 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 8r 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 1 02 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 Heating circuits 117 Cooling circuits 118 Temperature regulations in the outer air-space 119 Gain or loss of heat through openings in the chamber 120 Gainorlossof heat through theaircurrent. 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 i?1 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 I77-J93 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 192 Conclusion 193 ILLUSTRATIONS. Page PlG. 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 OF 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.Ms 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. 1 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, z. 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 Zuntz1 and Jaquet.2 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 Chauveau5 and Laulanie4 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. 1 Traite' de Physique Biologique, I, p. 744. 4 ijl£ment8 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 Tigerstedt,4and by Atwater, Woods, and Benedict.5 It is interesting to note that Jaquet,6 by using a modification of the apparatus of Petterson 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 L,aulanie,10and 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 . de Chim. et Physique (1849), 3, Xxvi. 'Archiv. f. d. ges. Physiol. (1876), 12, p. 18. '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 Verhandluugen der naturforschenden Gesellschaft in Basel, 15 (1904), part 2, p. 252. 7Berl. klin. Wchnschr. (1887), p. 429. "Comptes 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. 12Journ. 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.:: 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). 8 Arch. d. Ver. f. wiss. Heilk. (1864), p. 422. 4 Comptes rendus (1899), 129, p. 249. 5 U. S. Dept. of Agr., Office of Experiment Stations Bull. 63. 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 EARUER 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,3 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 1902 by a report4 in which were given the results of twenty- four experiments with men and a general discussion of the same. A more extensive report 5 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.5 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. ZU. S. Dept. of Agr., Office of Experiment Stations Bull. 63. 3 U. S. Dept. of Agr., Office of Experiment Stations Bull. 69. 4 U. S. Dept. of Agr., Office of Experiment Stations Bull. 109. *U. S. Dept. of Agr., Office of Experiment Stations Bull. 136. *W. 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. 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. Asa 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 OF 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 1 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. .TABLE: ,. ^ --.,...--.....-..._. . EH 00 cm ALCOVt ALCOVt FIG. i.— General Plan of the Respiration Calorimeter Laboratory. 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. Fio. 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. Rearof Respiration Calorimeter Chamber showing Food Aperture. Absorbing System and Pans at right. 5- — Laboratory Room. View from Alcove near Water-Pressure Regulator. Details of Absorbing System, Elster 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 iu 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 CHAMBER 0 used HjO N , . cdj o deficient introduced FIG. 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. THK 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. pw> O.&.O. 3n n P x 0.0.0, p p i •3-8.3 o o p n n n BB 3 -•NO S«« III B p N P-B a . SS.f r- •a. n n n a I? 5 00 O 2. N o en n CS 50 n a wo S- ,55' B o. m p 3 s. p* <-»• n Q. •S O M. n> c 3 o B n p 3 (D 3 o- O P a. rt O o o p. " aq B- I O < 1 6 .A RESPIRATION CALORIMETER. one about 96 mm. above the other. Two brass pipes, 40 mm. internal diameter, 170 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 THE RESPIRATION APPARATUS. 17 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 wrax 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 oj 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 2B 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 Gl. 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 j_ 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 • j j the Drum B by Sliding Pistons G and G1, and is driven system a trap is provided, as outatd shown in figure 10. The tube / 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 raisiug 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 n, 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 o\ 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. 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 ' 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. COLLECTION 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 125. 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- densed 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. THE RESPIRATION APPARATUS. 25 Recourse was then had to earthenware absorbers, the parts of which, by means of heav}r 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 100° 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 uuabsorbed. 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. ii. — 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. THE RESPIRATION APPARATUS. 2J 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 curreat 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 OF 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 (cf, 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, d1, 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 ,. , •,-, -, ,, . j in Cylinder, when Absorber is filled with Soda Mme, of Wire- dlsic added, a tlllm gauze Disks rf, d, d. Thimbles T, T, and Square S, with layer of layer of Soda lime, cotton rf1, 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. 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, *. 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. 2, which is always opened a moment or two before the suction - pump. To prevent the entrance of air in the water current, a 4B Starting FIG> I9-— 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, w1} 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 wlt figure 19, the supply of water passing through the suction-pump may be regulated at will. PROCESS OF TAKING RESIDUAL 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 K1-1' ooooooooooodc IE 0 1 o 1 o o :• 3 O 0 o ° 1 0 1 > o c o 0 o o o o f o s 0 X 0 / o f o 0 / IK 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 too 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. Afterthe 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 role played by temperature fluctuations necessitates the use of a thermometer graduated in tenths of a degree centigrade, and read with a reading glass to 0.01°. 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 5j s2 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 18 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 Bj, 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 Br At the beginning of an analysis the burette B: is nearly filled with pure nitrogen, obtained either from a previous anatysis of air or from the gas above the reagent in the Hempel pipette. Having filled the burette B, 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 B, until the water level in the burette is the same as that in the reservoir R2. 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 B2 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 B2, and by lowering the reservoir R3 the reagent is drawn up through the rubber connection R and along the capillary 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 Rt is lowered until the level of the liquid in Rj and Bt are the same. The reading on Bj is then carefully noted. On raising Rj and carefully opening stopcock C pure nitrogen can be driven over into B2. 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 R, and Bj, the reading of the gas remaining in Bj 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 B2 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 B, added to this volume. The first reading on Bl 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 I3-53 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 -f- 0.34 = 80.70. The change in temperature amounted to 0.09°, the initial temperature being 18.64° and the final 18.73°. 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 16.05 mm- As there was no noticeable change in the barometric pressure, this tension is deducted from the original barometric pressure, i. e. , 753.29, and the resulting pressure is equal to 753.29 — 16.05 — 737-24 mni. Therefore 99.76 cc. of air at 18.64° an(i 737-33 mm. pressure yield 80.70 cc. of nitrogen at 18.73° and 737.24 mm. On reducing both these gas volumes to standard conditions of tem- perature and pressure we find that this particular sample of air contains 56 A RESPIRATION CALORIMETER. 80.856 per cent of nitrogen. A duplicate analysis gave 80.854 Per cent of nitrogen. It is only fair to state that such an agreement is excep- tional rather than the rule. In general, however, the agreement is within 0.03 to 0.05 per cent. During the process of each analysis a small quantity of water is un- avoidably forced into the pipette, and consequently, while 155 cc. of reagent will absorb nearly 500 cc. of oxygen in oxygen analyses, it will absorb only 150 cc. of oxygen in the air analyses. It seems reason- able to suppose that this diminished efficiency is due, in part at least, to the gradual dilution of the reagent by the introduction of water. Expe- rience has led to the renewing of the solution after eight analyses of air. It can be readily seen that this method of analysis, depending as it does on so many readings of burettes, thermometers, barometer, etc., is open to serious objections when used for the most accurate work.1 However, a series of analyses of samples of outdoor air taken on suc- cessive days indicated extremely close agreement, such as to lead us to believe that the method is as accurate as we can expect, in the absence of a constant-temperature room and the services of an expert gas ana- lyst, whose whole time can be devoted to this kind of work. ACCESSORY APPARATUS. Aside from the elaborate respiration apparatus proper, certain inci- dental apparatus is necessary, such as balances for obtaining the weights of gases absorbed by the residual U tubes, of the carbon dioxide and water in the absorbers, and of the oxygen, a barometer, and thermom- eters for determining the temperature of the air, both in the respiration chamber and in the exterior portions of the air-circuit. Other incidental apparatus, which has, however, more to do with the measurements of heat than of the respiratory products, will be described hereafter in connection with the discussion of heat measurements. BALANCES. Analytical. — For weighing the residual U tubes and all general ana- lytical work in the laboratory, in connection with experiments with the respiration calorimeter, short-beam analytical balances of standard types are used. Balance for weighing the carbon-dioxide and water absorbers and oxygen cylinders. — The quantitative determination of the total carbon dioxide, water, and oxygen in the air current necessitates the use of a balance at the moment of writing there is being installed in this laboratory the form of air-analysis apparatus used by Zuntz in his work on the respiratory exchange. ACCESSORY APPARATUS. 57 once sufficiently strong to stand the weight of the individual members of the absorbing system and of the oxygen cylinders and at the same time sufficiently sensitive to note a slight increase in weight with great accu- racy. The heaviest individual members of the absorbing system are the water-absorbers, which weigh, after the absorption of one-half kilogram of water, not far from 16 to 18 kg. The balance now in use for this purpose was obtained from the firm of Dr. Robert Muencke, of Berlin, through the Bausch & Lomb Optical Company, of Rochester, New York. It is shown in figure 21. The water and carbon-dioxide absorbers and oxygen cylinders are too large to be placed directly upon the balance-pan for weighing ; con- sequently the balance is so mounted that it is possible to suspend each separate member on a wire fastened to one arm of the balance. As is shown in figure 21, the balance is mounted on a heavy shelf fastened securely to the brick wall. The left-hand hanger of the balance has been removed and is replaced by a phosphor-bronze wire which extends through a hole in the bottom of the balance-case, and is provided with hooks or loops for suspending the objects to be weighed. Since changes in weight are here desired, rather than absolute weight, the larger part of the weight of these objects is balanced with lead coun- terpoises. The glass front of the balance-case can be raised and the counterpoises added or removed as desired. To prevent the effect of air currents along the floor, the lower part of the balance, i. e., the portion beneath the shelf, is inclosed as a closet. The framework, however, does not come in contact with the shelf, there being a small air gap between to eliminate the transmission of vibration from the floor to the shelf. The front of the closet consists of two doors, one of which is removed in figure 21. To provide illumination a glass window is placed in the left-hand side, and the whole interior is painted white. On dark days or during the night an electric light is inserted. A small piece of plate glass is set in the shelf immediately in front of the balance in such a way that the upper surface of the glass is just flush with the top of the shelf. After the doors of the closet have been closed it is possible for the assistant to look through this glass and see that the object to be weighed is freely suspended. The phosphor-bronze wire by which the objects are suspended is permanently fastened to the hanger on the left-hand balance-arm. The lower end is provided with a swivel, to which two wires with small hooks on the end are attached. These hooks can be conveniently attached to the handles of the water-absorbers. (See fig. n.) In weighing these heavy objects it was found much more convenient to place them first on a small platform which could be raised sufficiently 58 A RESPIRATION CALORIMETER. to allow the hooks from the suspension wire to be readily slipped under the handles of the absorber. By means of the wooden lever at the left- hand side of the weighing closet, the movable platform on which the absorber is placed can then be lowered slowly, thus gradually shifting the weight to the wires. When the wooden handle is in an upright position, the movable platform or elevator is at its lowest point, and the object to be weighed swings freely above it. A simple clutch holds the lever firmly when it is sustaining the weight of the absorber, and all that is necessary to release the clutch is to push the handle forward a short distance. The bracket- arm fastened to the lever has two chains attached to its outer end ; these travel through pulleys in the top of the closet and are so adjusted that both sides of the elevator are lowered to the same dis- tance and simultaneously, thus making an even up-and-down motion. The details of this apparatus are shown in figure 21. After weighing, the lever at the left of the balance is pushed for- ward, thus taking the weight off the wire. The hooks can then be unfastened and the absorber readily withdrawn. For weighing the carbon-dioxide absorbers, two copper loops act as extensions to the steel hooks. A similar device serves for suspending the oxygen cylinders. One of the most striking features of this balance is its great capacity and extreme sensitiveness. In weighing the water-absorbers, some of which weigh fully 18 kg., we have the greatest test on the sensitiveness of the balance, and it is found that these absorbers may be weighed so delicately that a difference of 20 mg. is readily detected — a degree of accuracy far beyond the ordinary requirements. A balance of the same type, but with one-half the capacity, z. T , N. _....- i,. (Start *-«-*« 43.99 H2O = 54.71 Hg . . = 0 I,. e @ Tm, = H3SO4 (End 3525 No. 6 (Start 3508 16 Less O = 46.07 Sum . = Diff = 52.63 3 = .05 L. Difference == CALCULATION OP RESULTS. 65 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 L, had increased in weight 18.8 grams and cylinder 1 2.5 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 carried 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. 1 1 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 ox3'gen 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. RESIDUAL 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 OF 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 OF 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 iu 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 OF 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 maybe 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, /. 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 OF 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 gasoinetric analysis. VOLUMES OF 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 a? 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. 1 6 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 OP 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. nian Contributio is to Knowledge (1895), 980, p. 109. "Smithsonian Misc. Coil. 11882), 27, p. 56. s Sinhhsonidii Contributions to Knowledge (1896), 1033, p. 14. CALCULATION OF RESULTS. 83 ing to Hirti, this is not strictly true. The coefficient of thermal expan- sion of perfect gases is taken as 0.00367, whereas Hirn1 states that the coefficient of thermal expansion of water vapor is 0.00419 between o° and 119°, the value seeming to diminish as the temperature rises and increasing numerically for lower temperatures. Perman,2 however, concludes that the density of saturated aqueous vapor is probably only very slightly (if at all) above normal at temperatures up to 90°, and from the data at hand it seems reasonable to assume that water vapor at 20° behaves as a perfect gas, and that the weights of a liter of hydrogen and water vapor are directly proportional to their molecular weight. CALCULATIONS OF RESIDUAL ANALYSIS. In calculating the total amounts of carbon dioxide, water, oxygen, and nitrogen in the residual air of the system at the end of any given period, the volumes of the sample and the apparent volume of the whole air system are reduced to the same basis, i. e. , the standard con- ditions at o° and 760 mm. pressure, thus simplifying the calculations greatly. Reference has already been made to the process by which the residual samples are taken, and specimen data for such samples are shown in the upper left-hand corner of the record sheet previously explained (p. 64). There remain for consideration, first, the calculation of the true volume of gas in the sample and in the system, and second, from these corrected data the calculation of the amount of the various gases in the system. These calculations are simplified as much as possible, and for con- venience are recorded on a blank shown on page 84. VOLUME OF THE SAMPLE. The calculation for the samples for the residual analyses involves a reduction of the gas volume as measured by the meter to standard con- ditions of temperature and pressure, making a due allowance for the volume of water vapor and carbon dioxide absorbed by the reagents, thus giving the corrected volume of air withdrawn in the samples reduced to standard conditions. The calculations for the reduction of these volumes to standard conditions is made on the residual sheet (p. 84). Under the head " Air sample for analysis " is first entered the apparent volume of air which is passed through the meter. To the logarithm of this volume must be added the logarithm of the calibration correction 1 Hirn : Recherches sur 1'equivalent mechanique de la chaleur (1858). 2 Proc. Roy. Soc. (1904), 72, pp. 72-83. 84 A RESPIRATION CALORIMETER. RESIDUAI, SHEET. No. 16. Calculation oj the Residual Amounts of Nitrogen, Oxygen, Carbon Dioxide, and Water Vapor Remaining in Chamber at 7 a. m., April o, Residual at end of i2th period. Metabolism experiment Ko. 77. Volume of nitrogen in chamber at 5.00 a. m. Nitrogen in air sample rejected, liters,.. 3574- M liters. Nitrogen rejected with absorbers, — .10 Nitrogen admitted with oxygen, + .54 No interchange through food aperture, in (+), or out(-). Nitrogen present at end of period, - ... 3574-58 OXYGEN CORRECTIONS. .7) — .OS liters. — .04 grams. AIR SAMPLE FOR ANALYSIS. Log. 10.016 Correction, T , Pressure Wt. H2O. •0554 Cms. to liters, Wt. CO2 .0441 Cms. to liters, 1. .00069 .98895 .96858 .97992 .93814 = 8.672 I. 74351 63 83813= .069 1. 64444 7068O Log. — 94265 351 24= .022 1. »o = 8.763 1. Colog. f0 =05735 Manometer = 12.28 mm. e @ Tm, = 17.84 mm. Sum = 30.12 mm. Barometer =755.78 mm. Difference =725.66 mm. Barometer •= 755.78 mm. Tm = 20.44° C. Tc = 2o.79°C. TI = 20.0 °C. I. II. III. IV. = APPARENT VOLUME OF AIR. 4909.88 + .05 5, 14.60 — .04 (41.08) 1 13.7 ) 4909.93 1. @ To 6.55 I- ® TI 14.56 1. @ T! 54.78 1. @ Tj Log. I. To Pressure Log. II. TI Pressure Log. III. - T, - - Pressure - Log. IV. - TI - - Pressure - Total volume of air Volume CO2 + H2O 0-fN " N - - O =69107 =96806 = 99758 65671 = 4536.4° 1- = 81624 = 96924 =99758 78306 . 6.07 1. 4542.47 I- =16316 = 96924 = 99758 12998= 13.49 I- 4555-96 1. = 73862 =96924 =99758 70544= 50-75 1. = 4606.71 1. - - 47.38 1. = 4559-33 1- 357458 1. 984.75 v2 V3 Log. wt. H2O in residual -0554 - - = 74351 Log Vt - - = 65729 Colog. v0 - = 05735 45815= 09463 = 28.72 gms. HSO Cms. to liters (a) 55277 = 35.71 1- H20 Log. wt. CO2 in residual .0441 Log. V2 Colog. z< Cms. to liters 64444 = 65858 •= 05735 36037= 22.93 gms. COS 70680 (b) 0671 7=11.67 1. COS (a) (b) 35-71 11.67 1. 1. Log. 984.75 " 4559-33 By calculation By analysis 47.38 = 1. C02 + H20 = 99333 = 65890 33443 21.60 £ 21.62$ CALCULATION OF RESULTS. 85 for the Elster meter (see p. 47), the cologarithm of the correction corresponding to the temperature of the meter Tm, i. e.,(i +.00367 Tm) , and the logarithm corresponding to the corrected pressure. The pressure of the air in the meter during the process of taking the resid- ual sample is affected by three factors — first, the atmospheric pressure ; second, the tension of aqueous vapor at the temperature of the meter, and third, the tension of the air on the meter as measured by the water manometer. By referring to the data given for the water manometer on the blank (p. 64), it is found that in this instance the manometer when reduced to millimeters of mercury indicates 12.28 mm. The temperature of the meter was 20.44°, afld the tension of aqueous vapor at this temperature indicated in the calculations by e equals 17.84 mm. The sum of these two pressures equals 30.12 mm., which must be de- ducted from the barometric pressure to give the corrected pressure on the air in the meter, namely, 725.66 mm. The logarithmic correction for this pressure, i. e., p-t-j6o, is .97992. The true volume of air then drawn through the meter is 8.672 liters. This does not, however, represent the total volume of air withdrawn from the chamber in the sample, since there were 0.0554 gram of water and 0.0441 gram of car- bon dioxide absorbed in the U tubes before the air entered the meter. By converting these weights to volume by means of the standard log- arithmic factors, .09462 and .70680, we find there was withdrawn from the air system in the sample 0.069 liter of water vapor and 0.022 liter of carbon dioxide, thus showing that the total volume of air withdrawn in the process of taking a sample, vn) was 8.672 -f 0.069 + 0.022 = 8.763 liters. The logarithm of this amount is .94265 and the cologarithm •°5735- This is more clearly expressed algebraically as follows : CALCULATION OF TRUE VOLUME OP SAMPLE FOR DETERMINATION OF CARBON DIOXIDE AND WATER. v0 = volume of air sample containing carbon dioxide and water vapor at o° and 760 mm. v = apparent volume of sample (i. e., meter reading). f = factor for correcting meter readings. w = weight of water in sample. wl = weight of carbon dioxide in sample. 1.2434^ = theoretical volume of water vapor at o° and 760 mm. 0.5091 w1 — volume of carbon dioxide at o° and 760 mm. Tm— temperature of water (air) in meter. e = tension of aqueous vapor at Tm (millimeters of mercury). m — manometer reading, expressed in millimeters of mercury. 86 A RESPIRATION CALORIMETER. h = height of barometer (in millimeters), corrected to o°. p = h — e — m, X-+ I- 24334 " + 0.5091*'. CALCULATION OF THE TRUE VOLUME OF AIR IN THE CLOSED AIR-CIRCUIT. The apparent volumes of air in the different portions of the air- circuit are, as has been stated before, subject to fluctuations, the most noticeable of which is the variation in the quantity of air inclosed in the pans. Volume I, that portion of the air in the air-chamber and the air- pipe and blower and the first water- absorber (see p. 80), is subject to fluctuations which may normally occur inside the respiration chamber, such as interchange of air through the food aperture, respiratory loss, etc., in addition to the normal changes as affected by temperature and pressure. The record of the apparent volume of air is given at the right-hand side of the residual sheet (p. 84) . In this particular instance the initial apparent volume of air in section I is 4,909.88 liters, to which a correction of + 0.05 is added for the respiratory loss,1 thus making a total volume of 4,909.93 liters. This volume of gas is at a temperature (Tc) of 20.79° and at a barometric pressure of 755.78 mm. To reduce this volume to that under standard conditions of temperature and pressure the logarithm of the volume is added to the cologarithm of the correction for temperature and the logarithm for pressure, which are taken from tables prepared for convenience. The cologarithm of the correction for the temperature (Tc) 20.79° is .96806 and the logarithm for reducing the barometric pressure is .99758. On adding these three factors together it is found that the corrected volume under standard conditions is 4,536.40 liters. This calculation is carried out on the left-hand lower side of the sheet. The apparent volume of air in section II, the air-pipe leading from the chamber, the blower, and entrance pipe to the first water-absorber is equal to 6.55 liters measured at a temperature (T,) of 20.0° and under the same barometric pressure as I. To reduce this volume to standard conditions a similar process is carried out, the calculation being placed immediately beneath the first on the sheet, and we find that the volume 6.55, when reduced to standard conditions, becomes 6.07 liters. Since both these volumes contain water vapor, they are added together, their sum giving V1} the volume of the air containing water vapor. 1 For calculation of respiratory loss for this particular period, see the record sheet on page 64. CALCULATION OF RESULTS. 87 The air in section III is subject to a fluctuation as a result of the increase in volume in the first water-absorber, and consequently the initial volume in this particular case, 14.60, must be decreased by the volume of the water absorbed, 0.04, ' yielding a volume of 14.56 liters. This volume is likewise reduced to standard conditions, and, since it contains carbon dioxide, the reduced volume, i. e., 13.49, is added to the volume of Vn giving 4,555.96 liters as the volume of air containing carbon dioxide, i. e., V2. The air in section IV consists of the constant volume of 41. 08 liters, which represents the volume of the air-pipes and the fluctuating vol- ume inclosed in the pans. The amount so inclosed during this particular period is 13.7 liters,2 making a sum total of 54.78 liters. The apparent volume of air in section IV is also reduced to standard conditions, and when so reduced it amounts to 50.75 liters, which, when added to V2, equals 4,606.71 liters, or V3, the total volume of air in the system. TOTAL RESIDUAL WATER VAPOR. Since the amount of water vapor in the sample and the corrected volumes of both sample and residual air are known, the calculation of the total residual amount of water vapor is a simple matter. The computations are made on the right of the residual sheet. To the log- arithm of the weight of water found in the air sample are added the cologarithm of the corrected volume of air withdrawn in the sample v0 and the logarithm of the corrected volume Vt of residual air contain- ing water vapor. In the instance here cited there were 28.72 grams of water vapor in the air-circuit. It is convenient to know not only the weight of water vapor in the air, but also the volume, and consequently the computation is carried a step farther by adding the logarithmic factor .09462 to the logarithm of the weight of w.iter, thus indicating that 35.71 liters of water vapor were in the system. TOTAL RESIDUAL CARBON DIOXIDE. The residual amount of carbon dioxide in the whole closed circuit is determined in a similar manner, i. e., by adding together the logarithm of the weight of carbon dioxide found in the sample, the cologarithm of the corrected volume of air taken for a sample, z'0, and the logarithm of the total volume of air containing the carbon dioxide (V.2), i, e., the 1The calculation for the amount of air displaced by the water absorbed is made on the sheet, page 64. 2 For the calculation of this volume of air, see the record sheet, page 64. 88 A RESPIRATION CALORIMETER. corrected volume of air in the chamber and air-pipes up to the second soda-lime cylinder. The weight of carbon dioxide in the system at the end of the period cited was 22.93 grams. By the use of the logarithmic conversion factor .70680 this weight of carbon dioxide is found to correspond to 11.67 liters. OXYGEN AND NITROGEN. The residual volume of oxygen and nitrogen together is readily de- termined by deducting the volumes of water vapor and carbon dioxide from the total corrected volume of air in the system, V3. By reference to page 84 it will be seen that the carbon dioxide and water occupied a volume of 47.38 liters. On deducting this volume from V3, i. e., 4,606.71 liters, the volume of the remaining gas, oxygen, and nitrogen is equal to 4,559.33 liters. What portion of this volume is nitrogen can be found by direct calculation. THE NITROGEN IN THE SYSTEM. The amount of nitrogen present in the system at the beginning of an experiment is determined directly by an analysis of the air, from which the oxygen is removed by means of potassium pyrogallate. From this analysis the composition of the air free from carbon dioxide is obtained, i. e. , the percentages of nitrogen and oxygen. From the apparent vol- ume, the true volume of the gases in the system is calculated, and, with due allowance for the volume of carbon dioxide and water vapor, the initial volume of nitrogen present may be computed. This volume is commonly referred to as the base line. Nitrogen may enter the system in either one or both of the following ways : ( i ) With the oxygen in the steel cylinders ; from 2.5 to 8 per cent of the contents of the cylin- der is nitrogen. Inasmuch as each cylinder varies in composition and the amount of oxygen and nitrogen must be known for each cylinder, it is necessary to make an analysis before the cylinder is used. (See p. 34. ) (2) In air admitted through the food aperture. Nitrogen may leave the system either in small quantities through the food aperture by the interchange of material, through loss in changing absorbers, or in the sample removed for the determinations of oxygen, but more especially, however, in the large sample of air rejected from time to time. In addition to these regular channels for the escape of nitrogen, any leakage of air out of the system through defects in the couplings or connections obviously carries with it a large amount of nitrogen. The discussion of this point will be deferred until later. CALCULATION OF RESULTS. 89 CALCULATIONS FOR NITROGEN. It will be noted that at the top of the sheet (p. 84), the first space below the heading is arranged for the calculation of the amount of nitrogen. The amount of nitrogen in liters found, either by analysis or calculation, in the chamber at the beginning of the experimental period is first recorded. In case air has been rejected during the period, as explained on page 67, the number of liters of air, the percentage of nitrogen, and the number of liters of nitrogen thus lost are then deducted. The negative correction for the amount of the nitrogen removed with the absorbers and the positive correction for the amount admitted with the oxygen are then added, together with a correction for the interchange through the food aperture, if any, which may be either positive or negative, according to whether nitrogen was admitted or removed. On applying these corrections, the nitrogen present at the end of the period is found. This value may then be transferred to the next residual sheet under the heading "Volume of nitrogen in chamber at m liters," and serves as the basis of new nitrogen calculations until a new analysis has been completed. This method of calculation assumes that there is no free nitrogen eliminated from the body other than that entering and leaving the lungs in the free state ; in other words, that there is no production of free nitrogen from food or body protein. That this is probably the case, all experimental evidence thus far seems to show, although the desirability of an absolute demonstration is obvious. Furthermore, it is assumed that there is no unaccounted-for leakage of nitrogen into or out of the system. Indeed, as will be explained beyond, this calculation is used ultimately to detect a leak. CALCULATION FOR TOTAL RESIDUAL OXYGEN. From the total volume of oxygen and nitrogen determined by de- ducting the volumes of carbon dioxide and water from the total air volume, Vs, is deducted the volume of the nitrogen as computed at the head of each residual sheet. In this instance, the volume of oxygen plus nitrogen being 4,559.33, on deducting the computed residual nitrogen, 3,574.58, the volume of oxygen was computed to be 984.75 liters. It is thus seen that if the corrected volume of air is known as well as the volume of nitrogen, carbon dioxide, and water vapor, the differ- ence is obviously the volume of oxygen. Since no other gases are present in any considerable amounts, this method seems to suffice for 90 A RESPIRATION CALORIMETER. all practical purposes. It is seen that this method determines oxygen by difference, while usually the factor in air analyses that is determined by difference is the nitrogen. The calculation may be expressed algebraically in the following way : v0 = volume of air sample. Vj = volume of air containing water =(!-)- II). V2 = volume of air containing CO.2 = (I -j- 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. WJ= total weight of CO2 in system ; zvl = weight in air sample. w V V 7/;1 V V W— - A ! \V' = i . 2434 w X V! . 509 1 w1 X V, a 0 = — It was formerly assumed that at the beginning of the experiment ^=.2091 (V3 — 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. B C 03 * rt s u 33 N e To face page 116-2. FIG. 30. — Front View of the Metal Chamber removed from the wooden casing. Through the •window opening are seen a shield for the heat-absorber, the food aperture door, and the chair. The piping and wiring ou the inner wooden panels as well as the movable partitions subdivid- ing the inner air-space are also shown. THE CALORIMETER SYSTEM AND MEASUREMENT OF HEAT. 1 17 are very small, and by constantly heating or cooling the air-space next the zinc, as indicated by the positive and negative deflections on the galvanometer, the temperature of the zinc itself is increased or dimin- ished, as the case may be, so that the temperature of the two metal walls shall always be very nearly alike. The arrangements for heating and cooling the air-space next the zinc wall are next to be considered. HEATING AND COOLING THE AIR-SPACK. The air-space surrounding the zinc wall and between this and the inner wooden casing has been described (p. 1 1 1 ) , and it has been shown that this space is divided by narrow strips into four sections, corre- sponding with the top and bottom of the chamber and the upper and lower halves of the walls. (See fig. 23.) Comparing this with the ex- planation in the paragraphs just above, it will be seen that these divisions of the air-spaces correspond with the areas covered by the different groups of elements into which the whole system of thermo-electric elements is subdivided. The devices here described for heating and cooling the air-spaces are arranged so that the different sections of the space may be heated or cooled independently. In other words, pro- vision is made for determining temperature differences in different sec- tions of the surface area of the calorimeter, and also for heating or cooling the corresponding areas in the zinc wall as may be indicated. Thus, it is possible to heat one space and cool the adjoining space at the same time. Heating circuits. — For heating the air-spaces a current of electricity is passed through a circuit of German-silver wire, each separate space having its individual heating circuit. The wire is threaded through porcelain rings at the ends of each wooden panel and wound once around porcelain knobs at three different points in the length of the panel. By this arrangement the wire is firmly held in place, and even during the slight sagging due to expansion when heated, is prevented from coming in contact with the metal wall of the chamber. The white porcelain knobs or insulators on which the heating wires are strung are readily seen in figures 25, 29, 30, and especially in figure 31. The wire itself is so fine that it is hardly discernible in some of the figures, being quite plainly seen, however, in figure 30. In the upper and lower side spaces the current flows around all four sides at the same time. The wires are attached to the wooden walls, however, in such manner that they may be disconnected at the corners when the panels are to be removed. The heating circuits for the top and bot- tom sections are attached in one unbroken wire stretched continuously back and forth across each of the respective panels. Il8 A RESPIRATION CALORIMETER. Each heating circuit is connected with a variable resistance and a rheostat on the observer's table. It is possible to cut out any or all of the resistance and cause varying amounts of electricity to pass through the circuit of wire in the air-space, thus controlling its heating effect. The electrical method of heating a large air-space is ideal, in- asmuch as the heat is evenly distributed all through the air-space and liberated simultaneously at all points. Furthermore, the amount of heat which can thus be liberated is instantly controlled with the greatest accuracy by varying the external resistances. The variable resistance here used consists of a series of seven coils of German-silver wire wound on a corrugated sheet-iron pipe (galvanized conductor pipe) which has been covered with asbestos paper. There are in all nine heating circuits used for temperature control about the calorimeter, four for the inner air-space, four for the outer air-space, and one to heat the ventilating current of air as it enters the chamber, each of which is connected with the rheostat and has its variable resist- ance. The nine variable resistances are laid side by side under the calorimeter in the space between the laboratory floor and the outer bottom panel. As the floor of the laboratory is always cold, the extra heat developed in these resistance coils in a measure counteracts the cold floor and aids in warming the outer bottom dead-air space. Cooling circuits. — Means for cooling the air-spaces are as essential as those for heating them. Unfortunately, there is no such ideal method for cooling as for heating an air-space. The best method available is that depending upon the passage of cold water through a small pipe which is suspended in the air-space parallel to the wires of the elec- trical heating circuit. (See figs. 25, 30, and 31.) Water from the city main, which has a temperature varying from 6° in winter to 16° or 17° in summer, is caused to flow through small pipes (one-eighth inch) in the air-space. The cold water absorbs the heat and thus cools the air rapidly, and as a result the zinc wall is cooled. Heretofore iron pipe has been used for the cooling circuits, but as it rusts easily and so is liable to clog, brass pipe is being substituted. The cooling system in the top space and that in the bottom space are individual units, in which the water enters at one end, circulates around the numerous bends in the pipe, and goes out at a point close to where it enters. With the cooling circuits for the upper and lower zones, on the other hand, it is necessary to make arrangements for dis- connecting the piping when the calorimeter is to be withdrawn. The position of the pipes across the rear end of the calorimeter is shown in figure 25. These pipes are attached to elbows connecting with the pipes on the side panels by means of a brass union at each end. By dis- TO face pagfe 118. FIG. 31.— Details of Interior of Wooden Casing, showing cooling pipes, electrical heating wires, partitions for subdividing inner air-space and openings in the case to correspond to the windows, air-pipes, and water-pipes. The tracks on which the metal chamber stands are seen on the floor. THE CALORIMETER SYSTEM AND MEASUREMENT OF HEAT. 1 19 connecting the unions, each pipe can be sprung a little and thus readily removed. The heat-absorbing capacity of the mass of water in the pipe is very great, much more so than that of the metal of the pipe itself, since the specific heat of water is about ten times that of the pipe. Consequently, in order to secure a quick and easily controlled heat absorption, it is necessary to provide for the rapid draining out of the water in the cool- ing system. As the water leaves the valve connected with the water main it traverses the section of the pipe with which the valve is con- nected. When the valve is shut off a check-valve attached to an upright section of pipe (see fig. 37) opens, allowing air to enter. As each section is purposely piped in such a manner as to allow a free outflow of the water, the water in the pipes quickly drains out, and thus the cooling effect is much more rapidly arrested. TEMPERATURE REGULATIONS IN THE OUTER AIR-SPACE. The temperature regulation of the air-space next the zinc wall is affected by the fluctuations in temperature inside the metal chamber, and also, in spite of the insulating of the wooden walls papered with asbestos, by the temperature of the calorimeter laboratory. The outer air-space, i. e., that between the inner and outer wooden casings, dampens the effect of sudden changes in temperature of the calorimeter laboratory, but to aid in regulation provision is made to heat and cool the outer air-spaces at will. The heating and cooling circuits in these spaces are of exactly the same nature as those described above for the inner spaces, except that, since the delicate control of the temperature in the outer air-space is much less important, no provision is made for draining the water out of the water-pipes installed in this air-space. The necessitjf for heating or cooling the outer spaces is likewise determined by deflections on a galvanometer connected with a series of thermo-electric elements. These are inserted in the inner wooden walls, one end of the junctions being in the inner and the other end in the outer space. There are fifty-four such elements (containing each four pairs of thermal junctions) distributed throughout the six inner panels at equal distances from each other, so as to assume more nearly the average temperature of the air-space. The black irregular line (not to be con- fused with the series of parallel black iron pipes) on the right-hand inner wall in figure 31 shows the method of connecting these elements. Along the upper portion of the panel, running parallel to the iron pipes, is one straight row of four elements. A somewhat different view is given in figure 30, and the distribution on the inner rear panel may be seen in figure 25, in which the panel is removed and standing at the right. 120 A RESPIRATION CALORIMETER. As with those on the metal chamber itself, the thermo-electric ele- ments in this system are also subdivided into four sections — the top, upper zone, lower zone, and bottom. On the chamber itself the different members of each group of ele- ments are permanently connected in series, but with the system here considered it is necessary to break connections in the upper and lower zones when removing the end panels and withdrawing the chamber. The connections between the elements in the top panel and in the bottom panel are in no wise disturbed by withdrawing the metal chamber ; only the wires joining the elements of the upper and lower zones on the side panels with the elements of the upper and lower zones on the end panel must be disconnected. These connections are made by nuts or binding posts. GAIN OR Loss OF HEAT THROUGH OPENINGS IN THE CHAMBER. The various openings through the metal walls of the chamber have been described in detail (p. 13). The nature of some of these, or at least of the objects for which they are provided, precludes the passage of any appreciable quantity of heat in either direction. In the case of two of them, however, namely, the window in the front and the food aperture in the rear, there is a possibility of gain or loss of heat, de- pending upon differences between the temperature of the air within the chamber and that of the calorimeter laboratory. In fact, that there may be under certain circumstances appreciable interchange of heat through these two openings has been proved by a number of experi- ments in which the temperature of the calorimeter laboratory was markedly different from that of the chamber. To prevent such inter- change of heat it has been found necessary, therefore, to keep the temperature of the laboratory as nearly as possible the same as that within the chamber. To this end a mercury thermometer is hung inside the calorimeter chamber with its bulb opposite the center of the window, and a similar thermometer, with exactly the same corrections, is hung outside the window with its bulb at the same level as that of the thermometer inside. It has been found by experiment that when the thermometer on the outside registers exactly the temperature of that on the inside the interchange of heat through the glass is negligible. One of the duties of the observer at the table is to record the temper- ature of these thermometers frequently and make such alteration in the heating or cooling of the laboratory as to control the temperature within the necessary limits. Unfortunately the arrangement of the heat- ing system in the building in which the calorimeter is located is such THE CALORIMETER SYSTEM AND MEASUREMENT OP HEAT. 121 as to necessitate the placing of the steam-pipes near the ceiling of the calorimeter laboratory, and consequently the upper layer of air is very much warmer than that near the bottom. In fact, a temperature dif- ference of from 6° to 10° is not at all uncommon. By means of two rotating ceiling fans, however, it is possible to distribute the warm air and thus equalize the temperature in the laboratory to a considerable degree, the blades of the fan being so adjusted as to force the warm air downward. Cooling the air is effected by opening windows at different parts of the laboratory. By these means it has been found possible to regulate the temperature opposite the window of the calorimeter with considerable accuracy. Another mercury thermometer is hung on the outside of the rear of the calorimeter, near the food aperture. This likewise serves as a guide whereby the temperature of the air in which it is hung may be kept not far from 20°, i. e., that of the calorimeter chamber. Any great inter- change of heat through the food aperture is thus prevented. Further- more, the tube of the food aperture is surrounded for part of its length by the air in the inner air-space and through another part of its length by the air in the outer air-space, and the temperature of these portions of the tube is of course that of the air in the spaces, which is controlled, as explained above, in accordance with that of the chamber. Interchange of heat between the metal of the tube and the orifice in the metal walls through which it passes is prevented by the rubber tube filled with compressed air (D, in fig. 8) by which they are separated. The window opening in front of the calorimeter, and through it the food aperture in the rear end, may be plainly seen in figure 30. Adja- cent to the window in the front end are three other openings, at the places where the dark objects are seen projecting from the metal wall. These are shown in detail in the perspective view in figure 33. The smallest of these openings, near the lower corner of the window, is for the passage of an iron rod, which is the axis of the device for raising and lowering the shields to the heat-absorbers, described beyond. The rod is fitted very closely into a sleeve in the copper wall through which it passes. The metal of the rod is of course a good conductor of heat, but, as it passes through the two outer air-spaces, its temper- ature is controlled by that of the air surrounding it, and thus little opportunity is afforded for the passage of heat through it. The larger circular opening to the right of the rod (fig. 32) is very tightly closed by a wooden plug through which pass the two pipes for conducting the water used to bring away heat from the interior of the chamber, as explained later. The wood itself is a very poor heat-con- ductor, and furthermore it is surrounded by the two air-spaces in which 122 A RESPIRATION CALORIMETER. the temperature is controlled ; hence heat is not conducted from the chamber by the plug. To prevent the conduction of heat through the metal pipes, each pipe is broken about half way through the plug and the ends are connected by rubber tubing (N, fig. 32). The other opening, which is rectangular in shape, is very tightly filled by a wooden box packed with plaster of Paris, through which pass the pipes for the ingoing and the outcoming air. Gain or loss of heat through the box is prevented by the poor conductivity of the box and packing and by the regulation of the temperature of the air sur- rounding the box. To prevent loss by conduction through the metal pipes, each pipe is broken within the box and the ends connected with rubber tubing. (See H, fig. 32.) The nature of the opening in the side for the electric cable tube and that in the top for the weighing apparatus is such that no opportunity for loss of heat is afforded. GAIN OR Loss OF HEAT THROUGH THK AIR CURRENT. As explained elsewhere, part of the heat generated within the cham- ber is carried out as latent heat of water vapor in the outgoing air. So far as the air itself is concerned, however, gain or loss of heat to the chamber due to cooling or heating of the air is prevented by regulating the temperature of the air entering the chamber so that it is exactly the same as that leaving it. The difference between the temperature of the incoming and that of the outgoing air is detected by means of iron and German-silver thermal junctions, of much simpler construction than those described above. These are made of double cotton-covered insulated wire, and are bound tightly together in the center like a sheaf of wheat, the bared ends of the junctions being spread out and separated, thus relying on air insulation. These junctions are installed in such a manner that one end is in the incoming and the other in the outgoing air. The apparatus in which they are inserted, designated the vestibule, is shown at T. in figure 33. It consists of a 7.5 cm. copper pipe, with a copper partition. The ends of the thermal junctions are on opposite sides of this partition. The air entering the chamber passes along the under side, and that leaving is in contact with the upper side of the par- tition. The ends of the junctions are connected with a galvanometer, the deflections of which indicate differences in temperature of the air on either side of the partition. The incoming air is heated or cooled as necessary, in order that the deflection may be zero. The arrangements for heating or cooling the air are shown in figure 32. THE CALORIMETER SYSTEM AND MEASUREMENT OF HEAT. 123 The ingoing air is caused to pass over a 32-candlepower 2 20- volt lamp, which is placed in an enlargement of the air-pipe made of a gal- vanized-iron T and a short section of pipe, with a cap. The position of the lamp is shown in figure 32. The connections between this lamp and the electrical circuits are shown in figure 37, in which it is seen that the lamp-cord is connected with two binding posts on the wall of the calorimeter. These binding posts are connected in turn by two wires leading to the rheostat on the observer's table. As with the heating circuits for the air-spaces about the calorimeter, here also the amount of heat developed in the electric lamp, and consequently the degree of warming the air current, can be regulated with great exact- ness by means of the variable resistance (see p. 1 18) connected with the rheostat. When, as is occasionally the case, the temperature of the air in the calorimeter laboratory is greater than that of the interior of the cham- ber, it is necessary to cool the air current. This is accomplished by causing a current of cold water to flow through a lead pipe which is closely coiled about the ingoing air-pipe. The lead pipe is connected at one end with the water supply and at the other end with the drain. By opening a small wheel valve at the extreme left of the lower row of valves at the observer's table (see fig. 37) water can be caused to pass through this pipe and effect the cooling of the air. To prevent sudden changes caused by variations in the room temperature, the lead pipe is covered with cotton felt and canvas, as is seen in figures 3 and 37. MEASUREMENT OF HEAT. It has been stated that most of the heat generated within the chamber is carried away by a current of cold water. The quantity thus brought out is determined from the amount of water, its rise in temperature, and the specific heat of water at different temperatures. The devices for absorbing the heat and the method of determining the quantity generated are here described. For illustration of this description refer- ence is continually made to the view of the interior of the chamber shown in figure 33. THE HEAT-ABSORBING SYSTEM. The device for absorbing heat is shown at H, H, H, in figure 33. Copper pipe, of about 10 mm. outside diameter, bent to conform to the shape of the chamber, is suspended from the ceiling at about 13 cm. from each wall. A large number of sheet copper disks, about 5 cm. in diameter, are soldered along the pipe at intervals of about i cm., their purpose being to increase the area of surface exposed to 124 A RESPIRATION CALORIMETER. the heat. Two coils of such pipe, one above the other, comprise the heat-absorber. The water for taking away the heat enters the calo- rimeter chamber through a brass tube in the wooden plug in the front end of the chamber, flows through the rubber tube Wl into the lower FIG. 32.— Sectional View of Walls of the Chamber, showing method of installing air-pipes, water- pipes, and rod for raising and lowering shields. The copper wall A, zinc wall B, and two wooden walls C and D are penetrated by the box E for the air-pipes F and G and by the wooden plugK. The electrical lamp I shows method of heating, and the water coil J that of cooling, the ingoing air. THE CALORIMETER SYSTEM 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. e. , the contents of the pipe of the absorber, about 400 grams. REGULATION OF RATE OF ABSORPTION OP HEAT. In order that the temperature of the chamber may be kept constant, it is necessary to provide that the rate at which heat is absorbed may be varied in accordance with that at which it is produced. This is accom- plished in different ways. The coarser regulations are easily made either by increasing the flow of water through the system or by lowering the temperature of the ingoing water. The finer regulations that are essen- tial for maintaining a constant balance between heat production and heat absorption are made by increasing or diminishing the amount of heat-absorbing surface exposed, by lowering or raising shields (Sd, in fig. 33) provided for the purpose. When the shields are raised the air in them is cooled, and, serving as heat insulation, retards the absorp- tion. When the shields are lowered the absorbing surface is exposed directly to the heat. The shields are constructed of sheet aluminum. The shorter ones, which protect the absorbers on the ends of the chamber, are raised or lowered when necessary by the subject inside the chamber. Those on the sides are operated by the observer outside. A flexible cord attached to each of these side shields travels over pulleys and connects with an iron quadrant on the rod which extends through the wall of the appa- ratus and transmits the motion of the hand lever, shown in figure 32. It is thus possible, by raising or lowering this lever, to raise or lower the long shields inside the chamber, and the distance through which these shields are raised or lowered determines the area of the absorbing system, either exposed or covered up. A graduated arc over which the hand lever travels permits of very slight motions in the movement of the lever, and consequently of the most delicate adjustment of the position of the shields. In ordinary experiments the two end shields are always up, and all the finer regulation is done by means of the two long shields. During the night, and when the subject is sound asleep, it is necessary to raise these shields to the highest point, cut down the rate of flow of water to a minimum, and raise the temperature of the incoming water until it is nearly at the top of the scale on the incoming water thermometer. During work experiments all the shields are lowered as far as they 126 A RESPIRATION CALORIMETER. will go, the incoming water is cooled to as near zero as possible, and the rate of flow through the absorbing system is at the maximum. Indeed, in one series of experiments with a professional athlete a third pipe with disks was suspended above the absorber system, thus increas- ing the heat-absorbing area by 50 per cent. It is thus seen that the heat-absorbing capacity of this form of ab- sorber can be varied within very wide limits. It is possible to vary the rate of heat absorption with this apparatus so as to bring away as low as 40 calories per hour and as high as 600 calories per hour. Both of these measurements being irrespective of the amount of heat required to vaporize the water vapor issuing in the air current, they indicate the heat- absorbing capacity of this form of absorber rather than the heat- measuring capacity of the calorimeter. Besides serving to increase and diminish the effective surface of the absorbing system, these troughs and the gutters attached to them serve also the important purpose of collecting the large quantity of water which condenses on the surface of the absorbers and the shields, as explained on page 23. SUPPLY OF WATER FOR MEASURING HEAT. A regular pressure of water in the absorber pipe is quite essential. Owing to the marked fluctuations in the city water pressure, the water flowing through the heat-absorber system is taken from a tank in the second story of the building 10 meters above the point at which it enters the calorimeter. A constant-level attachment on the tank gives a steady pressure and flow of water. WATER COOLERS. The temperature of the water entering the calorimeter is regulated according to the amount of heat to be brought away, and may vary from i° to 12°. In order to secure such variation, provision is made for directing a portion of the water through two coils of iron pipe in tanks that can be filled with crushed ice. These tanks are placed in a small unheated room adjoining the calorimeter laboratory. Two valves near the calorimeter provide a means for mixing the cooled water and the water direct from the supply tank in whatever proportions are de- sired. A system of pipes and valves makes it possible to use either one or both cooling tanks at will. WATER METER. To determine the quantity of heat brought out of the chamber it is necessary to measure accurately the quantity of water that flows through the absorber. Formerly the measurement of water was made TO face page 126. FIG. 34. — The Water Meter. The large cans in which the water collects are here shown, together with method of attachment to balance-arm and lead counterpoises just behind them. Above the cans may be seen the dials on which the weight is indicated, and below them the device for shifting from one can to the other. The various electrical connections are also shown. THE CALORIMETER SYSTEM AND MEASUREMENT OF HEAT. 127 by volume, by alternately filling and emptying two copper cans grad- uated in liters. This method involved a not inconsiderable error, i. e., neglect of the variation in density of water at different temperatures. For a more accurate determination of the quantity of heat, therefore, it is essential to measure the quantity of water by weight. For this pur- pose the water-meter or balance shown in figure 34 was devised. A copper can holding about 10,000 grams of water is suspended on one arm of an equal beam, and a lead counterpoise, equal in weight to the weight of the can and about 9,800 grams of water, is suspended from the other end. In addition, the remaining weight of water is taken by a spring balance, which indicates about 400 grams for a com- plete revolution of the pointer. When the can is nearly filled with water and the weight of the counterpoise has been overcome, the beam begins to settle. As it settles, a flexible cord attached to one arm of the beam throws the weight upon the spring balance, and the pointer on the dial indicates the exact amount of weight taken care of by the spring. The dial is graduated into 100 divisions, and the differences between divisions can be read easily by halves. To make the meter as nearly automatic as possible and not to inter- rupt the flow of water through the calorimeter, two cans are provided, as is shown in figures 34 and 35. The cans and balances are mounted side by side on a stout wooden frame. In the front view, figure 35, the two cans with their respect- ive balances are shown. In the side view one can, the equal beam, and the lead counterpoise are shown. The equal beams were specially made by the E. & T. Fairbanks Company, of Saint Johusbury, Vermont. It was found by preliminary tests that with a load of nearly 20 kg. on each arm, differences of one gram could be detected. The spring balances were made by the John Chatillon Company, of New York. These are also quite sensitive. In experiments with man the amount of water passing through the heat-absorber varies greatly at different times in the same experiment, and especially with experiments of different nature. When the sub- ject is asleep in the middle of the night, 10 kg. of water passing through the absorber system above described will suffice to bring away the heat as fast as it is generated for over an hour, and at times the rate of flow may even be cut down to 10 kg. in 2 or 2)4 hours. This is the slowest rate. During periods when the subject is hard at work, on the other hand, the rate is much faster, a flow of 10 kg. in 7 minutes being some- times necessary. In devising the water-meter, therefore, the problem was to provide for the accurate weighing of as much as 80 kg. of water in an hour. Furthermore, in order that the observer may be relieved 128 A RESPIRATION CALORIMETER. as much as possible from the necessity of manipulating and readjusting the apparatus every few minutes, it should be as nearly automatic as practicable. The means of providing for alternate filling and emptying of the cans automatically is illustrated in figure 35. "IT FIG. 35.— The Water-Meter. Diagrammatic sections showing front and side views. The two upper cans A and B deliver the water into the lower cans C and D by the movement of valves between these two cans. The bulk of the weight is taken up by the lead counterpoise at right of beam E. Just below the spring dials a small cup-shaped attachment (water- receiving chamber), with curved tubes from the bottom on each side and a partition in the middle, is attached to the framework. The current of water to be measured enters through a piece of brass pipe, THE CALORIMETER SYSTEM AND MEASUREMENT OF HEAT. 129 the lower end of which is in this cup-shaped vessel. By swinging this pipe through a small arc the current of water is deflected to either side of the partition in the receiving cup and directed through the bent tubes into either can. This pipe is moved to one side or the other by means of wire projections, W, extending below the arms of the balance-beams. When one can is full of water and sinks, the falling end of the beam pushes against the wire and moves the outlet pipe so that the water current is deflected to the opposite side of the receiving cup, from which it flows into the empty can. As the full can sinks, a valve in the outlet pipe is opened and the water drains into a smaller can, D, below. While this is filling there is no loss in weight, but as soon as it is full the water begins to flow away through a siphon, and also through an overflow pipe. As is seen from the construction in the drawing, the small can is provided with two openings, one of which, the overflow C, is made by soldering a piece of pipe into the bottom of the small can in such a manner that the upper end of the pipe nearly touches the top of the can. A small siphon attached to a nut, F, screwed into the bottom of the can is the second opening. As soon as the small can is filled the siphon is started. As the diameter of the siphon tube is very much less than that of the opening through the valve, the lower chamber fills up to the level of the overflow C, and water soon begins to flow out of this opening. As soon as all the water has passed out of the upper can, the overflow through the large tube ceases and the lower can is completely emptied by means of the siphon. The end of the short arm of the siphon nearly touches the bottom of the small depression in the cap F, into which all the water from the can drains. It is thus seen that the lower cham- ber is constructed on the principle of the Tantalus cup. It has been found by repeated experiment that the quantity of water adhering to the walls of both the upper and the lower cans is remarkably constant. The valves in the outlets to the large cans are opened or closed au- tomatically, as the balance-arm assumes a level position. The valve on each can has a long lever, the end of which is between the upper and lower compartments of the other can, and is moved upward or downward with the motion of the can. This construction is seen in figure 35. Thus, as one of the cans sinks, the effect is to open the valve at the bottom of the moving can and to close the valve at the bottom of the stationary can. In figure 35 the water is shown as entering the right-hand can. The valve between the upper and lower can is represented as being closed. If, now, this can settles, the water will be deflected to the other side of the receiving chamber, the handle of the valve, which 9B r3o A RESPIRATION CALORIMETER. almost touches the projection on the upper side of the lower compart- ment on the other can, will be moved upward, and at the same time a projection attached to the bottom of the can will accomplish the closing of the valve on the other can. In order that the force required to open and close the valves may not interrupt the descent of the can and interfere with the proper weighing of the water, an arrangement for increasing the momentum of the full can is provided. This device is illustrated in figure 36. The rod on which the counterpoise is suspended from the beam is tipped on the lower end with a small bulb which opens the jaws of a spring clutch, a. By means of a small nut with a right and left hand thread the tension of the spring may be varied at will, and is so adjusted that a pull of about 200 grams is necessary to release the bulb. lil. FIG. 36.— Clutch to regulate tension on Water-Meter. Two curved steel springs hold a bulb on the end of a steel rod at bottom of lead counterpoise of the water meter. When the tension of the clutch has been overcome the bulb is released rather suddenly, and as it passes through the jaws of the clutch, these snap together, and their converging ends, rubbing on the bulb, give a distinct impetus to the upward movement of the counterpoise, thereby imparting momentum to the whole system. By this means sufficient force is obtained to operate the valves ; indeed, the end of the beam that bears the cans is invariably forced to a position below the level, and the pointer on the spring balance travels much farther than the true weight would warrant. The spring in the balance, however, soon im- parts a movement in the opposite direction. This reverse movement of the spring aids materially in the use of the balance, for by its means the balance-beam is drawn a little distance away from the wire projection used to deflect the water current, and the ends of the levers on the valves are slightly removed from the projections on the cans, and thus the whole system is freely suspended. Inasmuch as about 20 seconds elapse in the passage of the water from the upper chamber to the lower THE CALORIMETER SYSTEM AND MEASUREMENT OF HEAT. 131 chamber before the water actually runs out of the system, ample time is given to record the exact position of the pointer on the dial. After this position is recorded, the apparatus requires no more attention until the next can is filled. As soon as about 400 grams of water have run out of the system, the equipoise settles back to the position shown in the diagram, the bulb projection on the bottom of the counterpoise resuming its position between the jaws of the spring. As a result of the impetus given the system by the spring clutch, and that in the opposite direction by the balance-spring, the momentum of the large mass of metal and water has a tendency to cause the sys- tem to oscillate for several seconds before finally assuming a position of equilibrium. Preliminary experiments showed that this motion per- sisted a considerable time — longer, indeed, than the 20 seconds required for the water to flow into the lower can and begin to run out of the system. Consequently some method was necessary to check this oscil- lation and have the system attain equilibrium as rapidly as possible. To accomplish this end, an iron armature (£ in fig. 35) was fastened to one of the connections between the upper and lower cans. An electro- magnet was fastened to the upright wooden frame supporting the whole system in such a position that when the can was released and was vibrating back and forth the iron armature would rub over the end of the electro-magnet. By having a feeble current passing around the magnet, the movement of the can could be very readily checked. It was found, however, practically impossible to regulate the strength of the current so as to retard the vibration and yet not hold the armature against the end of the magnet, and thereby prevent the system from swinging freely and being weighed accurately. A circuit-breaker was devised and attached to the shaft supplying power to the calorimeter room. (See fig. i.) By this simple device the current is made and broken every few seconds — indeed, at approximately such times as would rep- resent the end of the vibration. The effect, therefore, is to have the armature attracted by the magnet and held firmly for an instant ; the current is then broken and the system begins another oscillation, at the end of which the current again holds the system for an instant, the effect being to diminish the momentum each time the armature is in contact with the magnet. Finally, by the observer's raising a switch and thus completely breaking the current around the magnet, the can swings freely and may be weighed accurately. By means of the two nuts on the central rod of the magnet the distance of the ends of the magnet from the armature when the system is in equilibrium can be altered at will. 132 A RESPIRATION CALORIMETER. The end of the soft iron core of the magnet is surrounded by a brass cap, which gives a rounded surface at the end of the coil, so that when the armature settles into position it will easily slide along the end of the magnet and not catch at any point. The current used to magnet- ize these fields is taken from the observer's table (see p. 136), and has in series with it two i6-candlepower no-volt lamps, one of them being the galvanometer lamp. The strength of current through the two magnets is varied by means of the resistance coil R shown in figure 35. The equipoise beam in its descent touches the wire W, used to deflect the water current, thereby closing an electric circuit and causing an electric signal-bell to ring continuously until the operator lifts a switch on the observer's table. In operating the meter, then, the only care required on the part of the observer is to see that the readings of the pointer on the dial are accurately recorded each time the bell rings. Calibration of the meter, — The meter was calibrated by weighing the total amount of water delivered from each can, noting carefully the position of the pointers. For this purpose a large enameled-ware pot with a hard-rubber cover was accurately weighed on the large balance (p. 56). A specially constructed funnel was placed under the overflow and siphon of one of the cans and the neck of the funnel inserted in a hole in the cover of the previously weighed pot. When the can was released the water was delivered into the weighed pot instead of into the drain. After all the water had drained out of the can and funnel, the pot, plus the water, was weighed. These weights were usually made to the tenth of a gram. A curve was plotted which showed the weights of water delivered by the meter with the pointer at different positions, and consequently it is now only necessary for the observer to record the position of the pointer. Accuracy of the meter. — The extreme accuracy of this water-meter has been surprising, for while the amounts as indicated by the readings on the dial may be from i to 2 grams either side of the true amount delivered, these differences tend to counterbalance each other, and it is safe to state that in a series of observations 10 cans full, or 100 kg. of water, will be weighed to within a very few grams. To facilitate in ascertaining the weights of water remaining in the can at the end of a short period in which less than 10 kg. of water were flowing, a water-gage graduated in liters is attached to the front of each can. It is thus possible for the observer at the end of a period to note the quantity of water in the can to within a tenth of a liter. A more exact estimate of this amount can be made by noting the time between the emptying of the last can and the end of the period. THE CALORIMETER SYSTEM AND MEASUREMENT OF HEAT. 133 Check measurements of (he accuracy of the meter. — From time to time the accuracy of the meter is checked by direct weighing. By means of the pot and funnel mentioned above, this check is very readily and rapidly carried out. Usually, one weighing of the water delivered from each can is all that is required. With the weighing, the reading of the pointer is taken and the weight actually observed, then directly com- pared with the weight as indicated by the curve. The meter has been in use for two years and has given excellent satisfaction. "} -/THERMOMETERS FOR MEASURING TEMPERATURE OF WATER. |The temperature of the water for absorbing heat is measured as it enters and as it leaves the chamber. The thermometers used for these measurements are seen in the small closet on the front wall of the cal- orimeter, at the left of the observer's table, in figure 37. The method of installing them in the water-pipes may be seen in figure 32. These thermometers are of special form. They are L-shaped, with one arm 52 cm. long and the other 36 cm. long. The arm with the mercury bulb is inserted in the water-pipe, extending through the wooden plug (N", N, in fig. 32), the length of the arm being such that the bulb comes directly under the upright pipe that conducts the water to or from the heat-absorber. By this provision the temperature that affects the mercury in the bulb is that of the water just as it enters or just as it leaves the chamber. The graduations on the other arm of the thermometer begin just above the b;ad and extend to near the end of the arm. The thermometer used to determine the temperature of the ingoing water is graduated from zero to 12° in fiftieths of a degree. The 12 degrees of the grad- uation cover a section of the stem 420 mm. long, thus allowing o. 70 mm. for each one-fiftieth degree, or 0.35 mm. for each one-hundredth degree. Readings can be taken accurately without the use of a lens to one- hundredth of a degree. The thermometer for the temperature of the outgoing water is graduated from 8° to 21°. As the temperature of the calorimeter chamber, especially in the summer time, frequently goes above 21°, an enlargement of the capillary is made at the top of the thermometer to permit of the expansion of the mercury without danger of breaking the instrument. The thermometers have been very carefully calibrated twice each year, and although the zero points changed slightly at first, they have appar- ently now become fixed. The readings of the two thermometers were compared with those on a metastatic thermometer of the Beckmann type, manufactured by Fuess and calibrated by the Physikalisch-technische Reichsanstalt, of Charlottenburg, Germany. 134 A RESPIRATION CALORIMETER. It was found with both thermometers that the maximum corrections occurred near the beginning of the graduation, and that along toward the top of the scale the correction became smaller. This would be expected from the increase in length of the column of mercury pressing on the thermometer bulb. The thermometer readings are corrected accordingly, and only the corrected readings used in determining the differences in temperatures. CORRECTION FOR PRESSURE OF WATER ON THE MERCURY BULB. As pointed out by Armsby,1 the pressure of the water current on the bulb of the thermometer may introduce an appreciable error in measure- ment. Since differences in temperature are what is desired, this error would of course be negligible were the pressure the same on both thermometers. This, however, is not the case. The pressure on the thermometer bulb in the water entering the chamber is greater than that on the bulb of the second thermometer, as the latter is much nearer the water exit. It was found by actual trial that when the water was pass- ing through the system at the rate of 10 kg. in 7 minutes, which is the maximum rate in experiments, suddenly shutting off the current caused a fall of 0.07° in the column of mercury in the thermometer in the ingoing water, and of 0.015° in that of the thermometer in the outgoing water. For this rate of flow, therefore, the mercury in the ingoing water thermometer reads 0.07° too high, and that of the outgoing water ther- mometer 0.015° too high. Unless these corrections are applied, the difference in temperature is obviously 0.055° too low; consequently this amount is added to the difference as observed. The necessary correc- tions for all rates of flow occurring in actual experiments have been determined and are always applied to the readings, though in many of the experiments the rate of flow is so slow that the effect of pressure on the bulb is inappreciable. MEASUREMENT OF TEMPERATURE OF THE CALORIMETER. It has been stated that the rate at which heat is absorbed and carried out of the chamber is regulated in accordance with that at which it is generated within it, so that the temperature of the chamber may be kept constant. To this end it is necessary to be able to determine fluctuations in the temperature of the chamber. While mercury thermometers have been used to indicate the temper- ature of the water current in the heat-absorbing system, their use in measuring the temperature of the air in the calorimeter, or of the metal walls of the chamber, has not been successful, and we rely on the measurement of changes in resistance of coils of pure copper wire which are distributed at several points on the walls of the chamber. 1U. S. Dept. of Agr., Bureau of Animal Industry Bull. 51, p. 34. THE CALORIMETER SYSTEM AND MEASUREMENT OF HEAT. 135 The resistance of pure copper wire to the passage of an electric cur- rent increases proportionally with the temperature. By means of a Wheatstone bridge and a delicate galvanometer it is possible to meas- ure with great accuracy the changes in resistance of a coil due to tem- perature fluctuations. Where, as in this case, temperature differences rather than absolute temperatures are involved, the problem becomes a comparatively simple one. Inasmuch as the average temperature of the whole mass of air inside the chamber is desired, it is necessary to distribute the coils in such manner that the variations in resistance will represent as closely as possible the actual temperature fluctuations of the air. For this pur- pose the amount of wire the resistance of which is to be measured is wound on five separate coils connected in series and suspended from hooks at different points on the walls of the chamber. Whatever local temperature fluctuations there may be in the different parts of the chamber, each coil will rapidly acquire the temperature of the air im- mediately surrounding it, and consequently the average variations of the five coils taken as a whole will closely approximate the average temperature fluctuations of the air inside the chamber. The coils consist of No. 32 pure copper wire, double-silk covered. They are wound on wooden frames and are well protected by metal guards. The total resistance of the coils is not far from 20 ohms. Variations in resistance which indicate temperature changes of 0.01° are easily detected by the Wheatstone bridge and galvanometer used in connection with these coils. These coils (Ta, fig. 33), suspended as they are about 2.5 cm. from the copper wall, acquire the temperature of the air rather than that of the copper wall itself. In determining accurately the temperature changes of the whole mass of material, it is frequently desirable to know the temperature changes, not only of the air, but of the copper wall. For this purpose four copper coils (Tw, fig. 33) , having an aggre- gate resistance of about 20 ohms, are wound on wooden frames and slipped into copper pockets made by soldering a copper box to the copper wall. These coils, therefore, are likely to assume the temperature of the copper wall rather than that of the air. The temperature changes can be detected by means of the switch, galvanometer, and bridge as closely as suggested above for differences in temperature of the air. Variations in resistance of the copper coils are detected by means of a Wheatstone bridge and a galvanometer. For many years we have used a D'Arsonval galvanometer constructed by O. S. Blakeslee in the mechanical laboratory of Wesleyan University. This instrument is very sensitive and dead beat, allowing 10 readings each minute. The 136 A RESPIRATION CALORIMETER. phosphor-bronze suspension wire of the instrument is still intact after eight years' use. The galvanometer is placed in a black-cloth hood, shown in figure 37, and a straight filament, i6-candlepower lamp (a so-called bung-hole lamp) used as a source of illumination, the image of the filament being reflected on a millimeter scale immediately before the observer. The variations in resistance of the copper coils can be measured in two distinct ways. In the one case it is possible to adjust a very deli- cate variable resistance so that by comparing the resistances of the copper coils with a Wheatstone bridge the slight variations in resist- ance due to temperature fluctuations can be expressed in fractions of an ohm. The second method depends upon the fact that the deflec- tions on the galvanometer are very nearly proportional to the amount of current passing through it, and consequently slight variations in the current caused by slight alterations in resistance will produce corre- sponding alterations in the deflection of the galvanometer. The amount of current passing through the galvanometer is a function of two vari- ables— electro motive force and resistance. If the electro-motive force is maintained constant, any alterations in resistance of the copper ther- mometer coils, through which the current must flow when passing through the galvanometer, will result in variations in the amplitude of the galvanometer deflection. The first method of temperature measurements, i. c. , the use of the slide- wire Wheatstone bridge, was followed entirely in the earlier form of respiration calorimeter,1 but the long-continued use of the slide-wire bridge is open to serious objections. Temperature measurements in experiments with the respiration calorimeter are made at intervals of not more than 4 minutes, and frequently the experiments continue from 10 to 13 days. The constant wear and tear of the sliding contact on a bridge of this type is a factor that must be taken into account in the most accurate work, and accordingly we have devised an apparatus for indicating temperature changes on the second of the two plans outlined above. This apparatus is described in detail on pages 139-150. OBSERVER'S TAB^E. The various devices concerned in the regulation of the temperature of the calorimeter and the measurement of heat are controlled from the observer's table at the front of the apparatus. Figure 37 gives a gen- eral view of the table and the adjacent apparatus. The wires from the systems of thermal junctions in the metal walls and the surrounding air-spaces, and those from the resistance thermometers 'U. S. Dept. of Agr., Office of Experiment Stations Bull. 63, pp. 25-27. TO face page"i36. FIG. 37.— Observer's Table. At left, the window, lever for raising shields, and water ther- mometers; on table at left is the rheostat, above it the valves for controlling cooling water, and in the center of table the mercury switch. Incidental electrical connec- tions and instruments are shown on right of table. The galvanometer scale is imme- diately above table. THE CALORIMETER SYSTEM AND MEASUREMENT OF HEAT. 137 within the chamber, pass out through a groove in the under side of the circular wooden plug projecting from the wooden walls at the left of the table and terminate in the mercury switch at the rear of the center of the table. This switch is described in detail beyond. The electrical connections for the heating systems in the different sections of the air-spaces are made through the rheostat at the rear of the left end of the observer's table. Inasmuch as there are eight sections of the air-spaces, and one resistance lamp is used to vary the temperature of the incoming air, the rheostat has nine sections, each of which is connected, by means of a cable passing through the floor of the platform (seen under the table in fig. 37), with its resistance coil lying between the respiration chamber and the floor, as explained on page 1 18. The flow of water through the pipes for cooling the different sections of the air-spaces, and through the pipe for cooling the ingoing air, is regulated by the ten valves immediately above the rheostat. The upper four valves control the four sections of the inner air-space, the four immediately beneath them those of the outer air-space, and the fifth valve on the lower line, the circuit for coolingthe ingoing air. The valve at the extreme left is used to maintain a constant flow of water into the supply tank in another part of the building. (See p. 1 26. ) At the right of the table* are several resistance coils, and upon the table a portable voltmeter, used in electrical check experiments. (See p. 169.) The millimeter scale on which the deflections of the galvanometer are read is immediately in front of a small clock on the black-cloth hood in which the galvanometer is placed. The two upright thermometers inserted in the wooden plug at the left of the observer's table indicate the temperatures of the ingoing and outcoming water for the heat- absorbing system. A little below and at one side is seen the lever for raising or lowering the shields to the heat-absorbers inside the chamber. This moves over a graduated arc into which a peg on the handle fits, thus allowing for fine adjustments. Of the three small switches under the edge of the table, at the left, one completes the telephone circuit to the chamber and the others are for connections with the bicycle ergometer (see p. 164) and with electrical devices used within the cham- ber in electrical check experiments. The water-meter, which is not shown in figure 37, stands on the floor immediately at the right of the observer, as it appears in figure 3. Thus it is seen that from the position of his chair the observer can note through the glass door the movements of the subject inside the chamber, read the mercurial thermometers in the water-cooling circuit, heat or cool various sections of the chamber, raise or lower the shields, note temperature differences on the galvanometer, and note the quantity of water passing through the water-meter. 133 A RESPIRATION CALORIMETER. ELECTRICAL CONNECTIONS ON THE TABI.E. The scheme of the various electrical connections on the observer's table is given in figure 38. OOOOO o oooo OOOO c OOOOO o m O O FIG. 38.— Electrical Connections on the Observer's Table. All electrical connections are, for con- venience, brought to the observer's table. The rheostat controlling the heating circuits, the mercury switch, the thermal junctions and thermometer circuits, and, at right, connections for storage battery for use in electrical check experiments and for magnetizing the fields of the bicycle ergometer are shown. THE CALORIMETER SYSTEM AND MEASUREMENT OF HEAT. 139 The thermal junctions are indicated in the upper left-hand corner by the numbers i, 2, and 3. In No. i there are four subdivisions corre- sponding to the four sections — top, upper zone, lower zone, and bottom— of the metal walls of the chamber. No. 2, which is here indicated as in series with No. i, represents the thermal junctions in the air cur- rent. No. 3 represents the four subdivisions of the system of thermal junctions in the inner and outer air-spaces. The resistance thermometers for indicating temperature changes in the air of the chamber and the copper wall are represented by the coils 5,7, and R. These are here shown to be connected so as to have one common return. The coil W represents a resistance thermometer for measuring differences in temperature of ingoing and outgoing water for heat absorption. (See p. 149.) All the above connections terminate in the mercury switch at the rear of the center of the table. Extending backward from this are two wires leading to the galvanometer. In the upper right-hand corner of the table is the rheostat controlling the heating circuits. No. i represents the four circuits in the different sections of the inner air-space and No. 3 the circuits for the corre- sponding sections of the outer air-space. The 32-candlepower lamp is that used in heating the ingoing air. The switch in the upper right- hand corner of the diagram connects the rheostat with the city electric main. On the lower right-hand corner are wires leading to a storage bat- tery. The binding posts numbered 3, 4, 5, and 6 are for connections for electric check tests and for magnetization of the fields of the bicy- cle ergometer. MERCURY SWITCH AND BRIDGE. In order to keep the two metal walls of the chamber adiabatic, each thermal junction system — i. e., those corresponding to the top, upper zone, lower zone, and bottom — is connected so that the differences in electro-motive forces of the junctions in thermal contact with the zinc and the copper walls can be measured on the galvanometer and thus furnish an indication as to whether the zinc wall should be warmed or cooled. Similarly, the four outer thermal junction systems in the inner wooden wall are so connected that they may be put in series with the galvanometer. Not only are the individual sections of these two ther- mal junction systems thus connected, but the wiring is such that the algebraic sum of the electro-motive forces of the junctions in all four sections may be noted for each system ; consequently there are five connections necessary for each system, /. e. , the four parts and the 140 A RESPIRATION CALORIMETER. whole. The thermal junction system in the air current is likewise capable of being placed in series with the galvanometer. There are, then, eleven different thermal junction connections to be made with the galvanometer. Any system of switches for such a number of connections must obvi- ously be somewhat complex, and, furthermore, the wear and tear on them would be such as to render their use extremely unsatisfactory. The sliding contacts would frequently become covered with dirt or grit, . 39.— Unit Key of Mercury Switch. By depressing the key the two eiids of a copper link are caused to dip into mercury in holes in a wooden block. The mercury insures connection of the screw and nut with the proper electrical devices. and the working parts would soon give way. An ingenious method of using mercury contacts for the thermal junction systems, thereby avoid- ing poor contacts and excessive wear and tear, was devised by our mechanician, Mr. S. C. Diusmore. L,ater, this mercury contact device was incorporated in an instrument which combined a mercury switch and a bridge system. The connection between each thermal junction circuit and the galva- nometer is made by dipping two copper links into four mercury cups, two of which are connected with the wires leading from the thermal TO face page 140. Flo. 40.— Meicury Switch, top removed. At leit, the switch with its mercury cups and comparison coils ; at right, the top with the keys and copper links. In the foreground are shown the com- parison coils and nuts for holding top in place. iG. 41. — General View of iMercury Switch. Fio. 42. — Under side of Mercury Switch, showing electrical connections. THE CALORIMETER SYSTEM AND MEASUREMENT OF HEAT. 141 junction system and two with wires extending to the galvanometer. The special feature of this switch is the device for closing the circuit. The two copper links, each of which is in fact composed of several strands of No. 16 copper wire, are fastened to a square of hard rubber on the end of a steel rod. A cross-section of a unit connection on this switch is shown in figure 39. A hole drilled in a block of oak serves as the mercury cup. At the bottom of each cup there is an iron or steel screw which extends through the oaken block to a brass nut on the under side. The wires leading to the galvanometer and thermal junction circuit, respectively, are sol- dered to the brass nuts. The holes in the oaken block used for mercury cups are shown at the left in figure 40. The wood was boiled for sev- eral hours in paraffin and a thick coating of paraffin covers all of it. The crater-like appearance of each hole is due to the deposit of par- affin about the rim. The cover of the switch, which is not so thick as the base, is made of mahogany. The steel rod to which the square of hard rubber with the copper links is attached passes through a metal bushing set in the cover, and the two copper links are held suspended over the mercury cups by a spring coiled around the steel shaft. On the upper end of the steel shaft a hard-rubber button is attached. A steel guide wire driven into the cover and passing through a hole in the square of hard rubber insures the copper links entering the mercury cups in the proper position when the key is pressed. The manipulation is not unlike that of depressing the key of a typewriter, save that the key is held down for several seconds. The details of the under side of the cover are shown in the right-hand portion of figure 40. The whole switch, with the cover in place, is shown in figure 41. In figure 37 the switch may be seen in position on the observer's table. Some idea of the intricacy of the wiring is obtained from the view given in figure 42, which shows the under side of the switch. The details of the electrical connections between the switch and the different parts of the calorimeter with which it is concerned are illus- trated in figure 43. Here it is seen that a number of connections other than those having to do with the thermal junction system are included in this switch. To distinguish the different thermal junction systems, we have designated those belonging to the system between the two metal walls of the cham- ber as No. i ; those in the air current as No. 2, and those in the inner wooden walls as No. 3. The different sections of circuits Nos. i and 3 are further subdivided into top (T), upper zone (U), lower zone (L,), and bottom (B). Consequently the circle on figure 43, in which the 142 A RESPIRATION CALORIMETER. designation T No. 3 is placed, represents the outline of the key, which, when pressed, will connect the two wires leading from the upper section of the thermal junction system in the inner wooden wall with the two wires leading to the galvanometer. 6ATTERY f ADJ. RES. — Mi -^www — — WATER WATER LEAVING N0.7 ENTERING rJVWWWW— i ^yyywyyy^ R NO.E — A/WWWl 1 NO I T U L B GALVANOMETER T y°'^. Kio. 43. — Diagram of Electrical Connections of Mercury Switch. The upper portion of diagram represents the thermometers and junctions and the galvanometer with which the bridge is connected. The four sections of this thermal junction system are connected with the four upper keys of the switch. The four sections of the inner thermal junction system, z. e. , No. i, are connected with the four keys immediately beneath those for system No. 3. In order that the alge- braic sum of the electro-motive forces for the four parts of system THE CALORIMETER SYSTEM AND MEASUREMENT OF HEAT. 143 No. i may be read at once, the outer connecting wires which take in all the junctions in system No. i are carried to the mercury cups beneath the key designated A L, L, No. i . As is seen on page 1 16, this deflection corresponds to the average temperature difference between the zinc and copper wall. In the same way the algebraic sum of the deflections of the four parts of No. 3 system can be read directly by depressing the key designated as A L, L, No. 3. The key designated as No. 2 controls the connecting wires from the ventilating air-circuit, and by depressing this key the temperature dif- ferences between the ingoing and outcoming air are noted directly, not as absolute temperature measurements, but rather as an indication of the necessity for warming or cooling the entering air to adjust its tem- perature to that of the air leaving the calorimeter chamber. It is thus seen that eight keys control the temperature indications of the sections of the thermal junction circuits, and that three keys indi- cate temperature conditions respectively in the whole of system No. i , the whole of system No. 3, and the air current. For the indication of these temperature conditions, therefore, eleven keys are employed. The connections shown by the wires in figure 42 can be followed more exactly by the plan of wiring given in figure 43. This diagram can be compared advantageously with the view of the switch given at the left in figure 40, as the diagrammatic features of the plan of wiring are made to correspond very closely with the exact location of the dif- ferent parts of the switch proper. For example, the two coils wound on hard-rubber spools and fastened to the switch by screws through the center of the spool, which are shown in figure 40 at the top, correspond to the two coils marked 2o-ohm res. on the diagram. The two iron cups which are filled with mercury when the switch is in use, and in which the galvanometer terminals are immersed, are between these two coils, while the iron post from which wires pass to each of the 2o-ohm coils is between the galvanometer connections, exactly in the middle of the upper portion of the switch. The two wires leading from the gal- vanometer can readily be traced on figure 43 to these two iron cups. It can be seen further that one of the wires from the battery connects directly with the iron post between the galvanometer cups, which corre- sponds to point B' in figure 44 beyond. On each side of the circle designating the galvanometer is placed a diagram of a thermal junction system, that corresponding to the inner metal-wall system, i. e., No. i, on the left, and that corresponding to the outer system, i. e., No. 3, on the right. Furthermore, the connec- tions of the separate sections, T, U, L,, B, are shown for each system. Immediately above system No. i is the representation of system No. 2, i44 A RESPIRATION CALORIMETER. — BATTEFV. or that in the ventilating air current. It will be noticed that systems No. i and No. 2 unite at the left of T in system No. i , and thus one wire serves for the return from both systems. The connections between the several thermal junction systems and the galvanometer are relatively simple ; it is with the bridge system for temperature measurements that the electrical connections are the most complicated. For these measurements a type of Wheatstone bridge, illustrated by the diagram in figure 44, is used. In the simple form of Wheatstone bridge shown in figure 44 there are in fact four parts — two 2o-ohm resistance coils, a standard resist- ance, and the coil of copper wire whose temperature fluctuations (varia- tions in resistance) are to be measured. The battery is connected at the two points B' and B". The galvanometer connections are made at G' and G". The two 2o-ohm resistance coils A and B are made of a form of wire that has no temperature coefficient, /. e. , there are no changes in electrical con- ductivity due to changes in temper- ature. These two coils are calibrated with the greatest accuracy, so that the resistance of the coils and connections between B' and G' is exactly equal to those between B' and G"; thus A and B correspond to the proportional arms of a Wheatstone bridge. These two coils are shown in the diagram, figure 43, being marked 2o-ohm res. Their position on figure 40 is likewise clearly seen. The iron post between these two coils corresponds to the point B' of figure 44. The points B" and G' and G" are not so readily discerned on the drawing in figure 43, owing to the complex nature of the elec- trical connections. The other two arms of the Wheatstone bridge (fig. 44) are com- posed of a standard coil, D, made of wire similar to that used in coils A and B and having approximately 20 ohms resistance. This coil is used for comparison with the unknown resistance of the copper ther- mometer coil and connections, which correspond to coil C in figure 44. As this coil (for example, the copper thermometer used for measuring the temperature fluctuations of the air in the calorimeter chamber changes in resistance, and obviously may rarely be exactly equal in resistance to coil D, there is a disturbance of the equilibrium of resist- FiG. 44. — Diagram of simple form of Wheatstone Bridge. A current from a battery passes through an adjustable resistance and connects with the bridge at points B' and B". When all arms of the bridge are proportional, no current flows through the galvanometer G. If C is greater or less in resistance than D, the current passes through G. THE CALORIMETER SYSTEM AND MEASUREMENT OF HEAT. 145 ances in the two arms of the bridge, C and D, and consequently a small current of electricity passes through the galvanometer. The current may pass from G' to G" if the coil C has a greater resistance than D, or it may pass from G" to G' if the coil C has less resistance than coil D. It is important to bear in mind that the resistances of the coils, plus the resistance of connecting wires, must be taken into consideration rather than the resistance of the coils alone. Unless the resistance of the coil C and all its connections with the points G' and B" (fig. 44) is exactly equal to the resistance of the coil D and its connections with the points G" and B", a current of electricity will pass through the galvanometer. In the ordinary form of Wheatstone bridge, provision is made for alteringthe resistance of coil D until the equilibrium is again established, the degree of alteration in coil D being an index of the resistance change (temperature change) in coil C. The so-called " slide-wire " form of Wheatstone bridge alters the position of the point B", thus varying the total resistances between B" and G', and B" and G", until the equilib- rium is established and no current flows through the galvanometer. With either of these two methods of resistance adjustment, elaborate and delicate apparatus is required and the continuous use of such instru- ments is accompanied by a constantly increasing inaccuracy in their use, due to the wearing of parts. In the mercury contact switch and bridge described here, the use of a Wheatstone bridge and resistance box, or a slide-wire bridge, is obviated. If in the system shown in figure 44 the resistance of coil C varies and is not identical with coil D, a current will pass through the gal- vanometer and produce a deflection. This deflection will, in general, be nearly proportional to the amount of current flowing through the galvanometer, and, as the current is equal to the electro-motive force divided by the resistance, it follows that with a constant electro-motive force the current varies inversely as the resistance. Assuming that the resistance, coil C (fig. 44), at a given temperature is such as to cause a current of electricity to pass through the galvanometer and produce a deflection of 100 mm. on the scale, if the resistance of the coil C is nowr decreased a larger current will pass through the galvanometer and the deflection will become larger. Conversely, if the resistance of C increases, a smaller current of electricity will flow through the galva- nometer and the deflections will grow smaller. If, now, the resistance of C is increased further, there will be a point at which the resistance of C is equal to D and no current will pass through the galvanometer, and if the resistance is still more increased, the current will tend to flow through the galvanometer in the opposite direction, and con- stantly increasing deflections, though in the opposite direction from I OB 146 A RESPIRATION CALORIMETER. those at the beginning, will be obtained. Obviously, the direction of the current through the galvanometer and the direction of the deflection for increasing or diminishing resistances in C depend upon the direction of the current from the battery and also upon the connections through the galvanometer terminals, for by interchanging the wires leading from the galvanometer to G' and G" the current through the galvanometer may be made to pass in the opposite direction. Of the four resistances in the bridge system, but one is affected by temperature changes, i. e. , that composed of the copper coils ; hence any differences in the deflection of the galvanometer may be ascribed directly to variations in resistance of the copper coil, provided the electro-motive force of the battery remains constant. To insure a constant electro- motive force, we have relied upon the establishment of an arbitrarily adjusted bridge system, in which the coils C and D are slightly out of pro- portion, i. e. , coil C has a somewhat lower resistance than coil D. Both coils (C and D) in this system are made of wire with zero temperature coefficient. These coils are mounted on the mercury contact switch (fig. 40), one on each side of the rows of mercury cups in the oak base and about midway of the sides. The coils are similar in form to the two 20- ohm coils mentioned before, and while one has a resistance of exactly 20 ohms, the other is a small fraction of an ohm lower in resistance. Inas- much as these coils belong to a bridge system that is used to standardize the electro-motive force from the battery, they are called standard coils, or standard resistances, and on figure 43 they are marked St'd res. With the bridge system thus arranged, the closing of the battery and galvanometer circuits should result in a deflection of the galvanometer, owing to the inequality of arms C and D of the bridge. The deflection of the galvanometer is then approximately proportionate to the electro- motive force, and by adjusting the number of cells of the battery and varying the resistance in the battery circuit it is possible to produce a deflection of any definite magnitude. Since all coils are of wire with zero temperature coefficient, no changes in temperature will affect the bridge system, and the amount of current necessary to produce a deflec- tion of 100 mm., for example, will be constant, provided there are no variations in the galvanometer constant. This latter factor can be tested readily, and in fact varies but slightly, so that we have by this bridge system an excellent method of compensating for variations in the electro- motive force of the battery. As a source of current, we use ordinary dry cells, with a small variable resistance in series with them. With this arrangement and with the connections as now made, the amount of current required to produce a deflection of 120 mm. is used as the standard for all our work. Inasmuch as the temperature of the cal- THE CALORIMETER SYSTEM AND MEASUREMENT OF HEAT. 147 orimeter room is always of such uniformity as to cause only slight vari- ations in the electro-motive force of the batteries, small alterations in the variable resistance serve to keep the standard current well in hand. Variations from hour to hour rarely amount to more than 2 or 3 mm. on a deflection of 1 20 mm . This method of obtaining a constant current is, for the purpose of this research, sufficiently accurate and on the whole distinctly preferable to the use of a standard cell. The adaptation of the mercury contact to this form of bridge is shown in figure 43. By depressing the key marked S the copper links enter the mercury in the cups in such a manner that the bridge and battery circuits are made before the galvanometer circuit. In this key it is necessary to have five mercury cups instead of four, as in the keys connecting the thermal junction systems. The fifth mercury cup is made outside of the square inclosing the regular cups, and is seen at the right, immediately in line with the standard resistance coil in fig- ure 40. The fact that these bridge systems were added to the mercury contact switch after it was first built explains the irregularity of the position of the extra mercury cups, not only in this standard circuit, but also in the four bridge circuits controlled by the four keys on the bottom row. The flow of the current through the different connections, when the key is depressed, may be followed very readily if it is borne in mind that all the copper links connect cups with those that are immediately above. On the whole switch there is but one exception to this rule, and that is the connection for the battery circuit for the standard system. Here the copper link connects the extra mercury cup with the nearest cup. In figure 40 the top of the switch at the right is removed and shown in such a position that were it brought over like the cover of a book the copper keys would fall over the proper mercury cups. Hence it can be seen that the two upper rows are for the cups connecting with the two thermal junction systems, while the first key on the next to the lower row corresponds to the standard bridge system. Indeed, the copper link extending on one side is clearly seen. This link dips into the extra mercury cup. The four lower keys, each with one or more extension links, belong to the four other bridge systems. Of these four systems, one controls the measurement of temperature changes in the copper thermometer suspended in the air in the calo- rimeter chamber. This is designated as system No. 5, and is controlled by the lower left-hand key (fig. 43). The standard coil of zero tem- perature coefficient wire used for comparison with the copper ther- mometer No. 5, i. e., the coil corresponding to D in the bridge system (fig. 44), is wound on a small hard-rubber spool, and is provided with 148 A RESPIRATION CALORIMETER. two heavy copper terminals, which can be dipped in the iron mercury- cups. Four of these coils, corresponding to the four bridge systems, are shown immediately in front of the switch in figure 40. They are shown in position in figure 41. The terminals of the coil for system No. 5 are slipped through two hard-rubber bushings in the cover, and extend beneath the cover far enough to have their lower ends well immersed in mercury in two iron cups similar to those used for the galvanometer terminals. Those for system No. 5 are at the left and near the top of the switch, as shown in figure 40. A line terminating in arrow-heads and broken by the designation No. 5 shows in figure 43 the position of these cups and the connections with their lower ends. The iron mercury-cups, as well as the iron posts for the battery and bridge connection previously mentioned (see p. 143), are provided on the under side with hexagonal nuts, which are used to insure the best elec- trical contact for the various parts of the bridge system. These nuts and the wiring from several of the iron cups and posts are shown in figure 42. As can be seen by a comparison with the direction of the bundle of wires extending outward from one side, the switch has been tipped forward through 180° from the position in figure 40 to give the view in figure 42 ; consequently the three nuts at the bottom of figure 42 correspond in figure 40 to the two galvanometer terminal mercury cups and the iron post connecting with the batter}'. Although the hexagonal nuts aid in making a good contact, the con- nections for all the bridge systems, especially the connections which, if defective, would disturb the equilibrium of either arm of the bridge, are further insured by having soldered joints. All connections between the iron mercury-cups and the calorimeter chamber are made of very heavy (No. 10) copper wire to eliminate the effect of temperature fluctuations other than those in the thermometer coils. The key controlling the temperature measurements of the copper thermometers which indicate the temperature of the copper wall, No. 7, is in the bottom row (fig. 43), at the extreme right. The compari- son coil dips in two iron cups filled with mercury. These cups are at the right of the switch, in a position corresponding to that occupied by the comparison coil No. 5. The line terminating in arrow-heads is broken by the designation No. 7. The key marked R controls the temperature measurement of a cop- per coil used for obtaining the rectal temperature of the subject of the experiment. This thermometer is described in detail elsewhere. (See p. 156.) The comparison coil for R is immediately at the left of the keys ALL, No. i and No. 5. THE CALORIMETER SYSTEM AND MEASUREMENT OP HEAT. 149 The key marked W is not as yet in practical use. Experiments are in progress to utilize this method of temperature measurement to obtain the differences in temperature of the ingoing and outcoming water cur- rents, temperature differences now measured by mercurial thermom- eters. (See p. 133.) The coil W is immediately at the right of the keys marked S and No. 7. With the large area of wire exposed in the copper thermometer coils No. 5 and No. 7, and the consequent rapid radiation, we have found that the slight amount of current, 0.03 ampere, produces no appre- ciable local heating effect in the coils ; hence the reading of the gal- vanometer may be taken with the circuit closed and after the deflec- tion has become constant. The method of reading the deflection ob- tained when the R coil is used is that of observing the amplitude of the first swing. As the coil for the R thermometer is compactly wound, and therefore does not radiate heat readily, the passage of the current through it heats the coil, giving rise to erroneous readings. The amplitude of the first swing has been found to be sufficiently accurate for these readings, and the rectal thermometers are calibrated to be read under these conditions. At the upper left-hand side of figure 43 the various coils and their connections with the switch are shown. It is thus seen that coils No. 5, No. 7, and R all have a common return wire from the calorimeter chamber. The connections for the coils for the bridge system inside the calo- rimeter— i. e., copper thermometer for the air (No. 5), thermometer for the copper walls (No. 7), and the rectal thermometer — are con- ducted from the mercury switch through a cable having a number of strands of heavy flexible wires to a plug switch fastened to the copper wall of the calorimeter. This cable is seen in figures 29 and 30, while the location of the plug switch is seen at M, figure 33. The connections for the bridge systems corresponding to No. 5, No. 7, and R are made by inserting tapered plugs into the different sections of this switch. Other sections (there are ten in all) can be used for other electric cir- cuits, such as the telephone, wires for electrical check experiments, and connections for the bicycle ergo meter (see p. 164), but they are connected with much smaller (No. 18) wires with a set of switches under the edge of the observer's table. (See fig. 37.) In the connections between the thermal junction system and the gal- vanometer, relatively large changes in resistance in the contacts are without effect on the deflection of the galvanometer ; but it is readily seen that with the bridge systems the matter is very different. Here the mercury contacts become a part of the connection between G' and 150 A RESPIRATION CALORIMETER. B", and G" and B", of figure 44 ; hence the necessity for the reliability of these connections. With clean mercury and good copper links, the connections are all that could be desired. This switch has been in constant use three years and has given excellent satisfaction. Inasmuch as all temperature measurements are relative, not absolute, and the variations in temperature are slight, it can readily be seen that this form of bridge is especially well suited for experimental work of this nature. The sensitiveness is all that could be desired, since with the present adjustment 60 deflections (millimeters) correspond to i° C. ; hence readings of 0.01° are readily obtained, an accuracy sufficient at present for experiments with the respiration calo- rimeter. That some form of potentiometer could be used for this work with good results is, of course, not to be doubted, but the compact form of this switch and bridge leaves little to be desired for the purposes for which it was devised. DETERMINATION OF THE QUANTITY OF HEAT ELIMINATED. It has been shown that heat is regularly carried out of the calorim- eter chamber in two ways — partly as latent heat of water vapor in the air current, but chiefly as sensible heat taken up by a current of water circulating in the heat-absorbers. Theoretically, the sum of the two quantities of heat thus removed should equal the total amount elim- inated within the chamber, but in actual practice various corrections must be made to determine the actual quantity of heat. The method of computing the quantity of heat removed in these two ways and the necessary corrections to be applied remain to be described. LATENT HEAT OF WATER VAPOR. The quantity of heat removed from the chamber in water vapor is found by multiplying the quantity of water collected in the water-ab- sorbers by the factor for latent heat of vaporization of water. In these experiments the factor used is 0.592 calorie per gram, which was de- duced from Regnault's formula, as discussed in detail elsewhere.1 It is greatly to be desired that this factor be verified by investigations in which water is vaporized under the conditions that obtain during an experiment with man ; but although considerable preliminary investi- gation of this nature has been made, we have no results that warrant our taking other than the commonly accepted figures of Regnault for this calculation. Presumably the error involved, if any, is not very large. Certainly it is not larger than the probable physiological error in experiments of this type. 1U. S. Dept. of Agr., Office of Experiment Stations Bull. 63, p. 57. THE CALORIMETER SYSTEM AND MEASUREMENT OF HEAT. 151 The number of grams of water removed by the absorbers multiplied by the above factor gives the number of calories of heat escaping from the chamber in water vapor. To obtain the total quantity of heat involved in the vaporization of water, however, it is necessary to make allowance for the latent heat of water vapor still remaining in the chamber, the correction being added or subtracted according to whether the amount of residual vapor at the end is larger or smaller than that present at the beginning of the experimental period. SENSIBLE HEAT REMOVED IN THE WATER CURRENT. UNIT OF HEAT. The ordinary definition of the large calorie is the quantity of heat required to raise the temperature of i kg. of water i° C. This, how- ever, is only approximately correct, because the specific heat of water varies with the temperature.1 It is therefore necessary to define the unit of heat somewhat more exactly. In experiments the temperature of the calorimeter chamber is main- tained very constant at 20° ; hence the specific heat of water at 20° is taken as the standard ; and the calorie here used is the quantity of heat necessary to raise a kilogram of water from 19.5° to 20.5°. CALCULATION OF THE QUANTITY OF HEAT MEASURED. The weight of the water determined by the water-meter, multiplied b}1 the difference between the temperature of the water as it enters and that as it leaves the chamber, gives the quantity of heat as measured at the mean between the temperatures of the ingoing and outgoing water. According to the explanation given above, however, this must be cor- rected for the difference between the specific heat of the water at this mean temperature and that at 20° . The latter value is designated as heat measured in terms of C20 ; the former value is designated as heat measured in terms of Ct, in which / is any temperature other than that of 20°. In finding the true value of Ct, it is necessary to know the mean specific heat of water for the range of temperature employed in any given period. The temperature of the ingoing wTater is sometimes as low as i° ; that of the outgoing water is rarely above 15°, and more frequently not far from 10°. If, for example, the water enters the cal- orimeter at 2°, a condition that is very common during the hard- work 1 The results of a large number of experiments on the specific heat of water at different temperatures have been discussed in considerable detail in another publi- cation (U. S. Dept. of Agr., Office of Experiment Stations Bull. 63, p. 55). From a table there given showing the specific heat of water at different temperatures and referring to that at 20° as a unit, it is seen that the specific heat of water at o° is 1.0090; at .5°, 1.0056; at 10°, 1.0029; at J5°. i.ooio. The difference between C.i9 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(2_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 Cao 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 HYDROTHKRMAI, EQUIVALENT OF THE CAI,ORIMKTER. 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 l 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 h3Tdrothermal 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 OF 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), 11, 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. A RESPIRATION CALORIMETER. Measurements of body temperatiire. — 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. It 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- ing through the food aperture as regards 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 FIG. 46. — Weighing Apparatus for Ob- jects Inside the Chamber. 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 IIB 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 theTwere 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 lowened 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. in. He immediately rose, and, having slept in underclothing and socks, no change in clothing was made. He then rolled up the bedding, fasteued 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 Krgometer. The rear wheel of a bicycle is replaced by a copper disk which can be rotated in 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 AND MEASUREMENT OP 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.1 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. 'U. 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 ergoraeter 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 ALL 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 ALL No. 3. The readings obtained from these three keys are recorded, 1 The calculation is made according to the formula C X E X t 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. + Moving air. No. 2. l T 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 S=I20. 8% % 14.24 14.18 10.00 2 % i io6J4 10.39 10.38 3.80 60 20.3 20.84 31« 02 14.26 14.20 04 5 *% % 1 08 10.29 10.28 3-92 61 31% Sitsupand drinks. 06 68.4 at 10:08:42 14.29 14-23 O8 8% % 5 H3 10.24 10.23 4.OO 63 45.25 at 4.114 31 yi I^iesdown; reads. 1O 10.050 K.. 14-32 14.26 12 2% % 13 116 10.16 10.15 4.11 66 3i/4 41-35 calo- ries. 14 14-51 M-45 16 4 i iJ4 H5 10.16 10.15 4.30 66% 3iJ* 18 14.58 I4-52 2O 3J4 ij* i% 114 IO.I2 1O.II 4.41 66 3<>% 22 I4.6O 14-54 24 iM iji iJ4 "2% JO.O4 10.03 4.51 65 31 26 14.58 I4-52 28 ij* ij* sy2 Hlji IO.23 IO.22 •4.30 64^ 3lM 30 Telephones. 14-59 14-53 32 H M 6M IIOJ4 10.20 IO.I9 4-34 63^ 31 y2 Sits up and opens lood 34 19.8 20.87 aperture. 14.68 14.62 36 6 3J* i% "7^ 10.14 10.13 4-49 67 3^/2 38 Lies down 14.87 I4.8l and reads. 4O 2 }* 13 "7M 10.14 10.13 4.68 68 33^ 42 14-99 14-93 44 6 3 7 "35* IO.2I 1O.2O 4-73 67% 33^ 46 I5.OI M-95 48 2% 2 554 in IO.26 10.25 4-7° 65 335* 50 79.8 at 10:52:38 14.76 14.70 52 Ij* I SK 110% IO.26 10.25 4-45 64% 49.02 at 4.456 33^ 54 IO.IO2 K.. 45.01 calo- 14-57 14.51 ries. 56 Ij* 2% Ij* no 10.32 10.31 4.20 63 34% 58 27% 29% 12% 10% REMARKS : 1 68 A RESPIRATION CALORIMETER. if positive, on the right-hand side of their respective columns, under the sign -f , 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 HE AT- 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. 170 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. PIG. 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 120. ELECTRICAL UNIT USED. In the fall of 1904, in a discussion of the accuracy of the bomb calo- rimeter1 used in connection with these experiments, it was pointed out by Dr. L,. 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* 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. '* Sitzungsber. K. Akad. Wiss. (1904), pp. 687-715. 3 Verhandlungen ber. deut. phys. Gesell. (1903), 5, 2, pp. 50-59. 172 A RESPIRATION CALORIMETER. The energy of an electric current is CE/ X io7 ergs. , and this expressed in calories at 10° is CE/? x io7 ~~, _ , . . -j = CE/ x o. 23846 calories. 4. 1935 x io7 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 0.2 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 OT? . , , -j = LE/ x 0.2380, as before. 4.2016 x 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 earlier1 (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 = 0.0017. H340 Thus 0.23845 x 1.0017 = °- 23885, which is the proper value at 15° to use in Germany ; that is, with German electrical units. A value as large as 0.2394 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 1 U. S. Dept. of Agr., Office of Experiment Stations Bull. 63, p. 43. 2 Winkelinann'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 0.2394, 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 aud 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. (1903), 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 t X 0.2385 — 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 ELECTRICAL 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 OF 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 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 CnHpNrOq, 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 Hrs. Mins. 3 54 5 44/4 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 burned. Oxygen. Energy. Found. Required. Ratio. Found. Required. Ratio. First Hrs. Mins. 3 54 5 44/£ it 52 Grams. 73-4 1 08. 1 225.3 Gra ms. 139-35 207.09 431-09 Grams. 138.90 204.56 4^6.33 Percent. 100.3 IOI.2 IOI.I Calories. 417.86 619.03 1,292.97 Calories. 421.40 620.61 1,293-45 Per cent. 99-2 99-7 IOO.O Second Third 21 30% 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. I2B 178 A RESPIRATION CALORIMETER. MEASUREMENT OP INTAKE AND OUTPUT OF ENERGY. The intake is derived from the potential energy, i. e., heats of com- bustion of the food. The output consists of sensible heat given off from the body, the latent heat of the water vaporized, and the potential energy, i. e., heat of combustion of the unoxidized portions of the dry matter of urine and feces. In certain cases, e. g. , work experiments, a not inconsiderable portion of the output is in the heat equivalent of external muscular work. As has been stated elsewhere, the heats of oxidation are determined by burning the substances in the bomb calorimeter ; the heat given off from the body is measured by the respiration calorimeter ; the external work is measured by a specially devised ergometer. Allowance is made for heat introduced and removed by the ventilating air current, food, feces, and urine, and for that involved in changes of body temperature, which is also measured. ANALYTICAL, METHODS. The nitrogen is determined by the Kjeldahl method, the carbon and the hydrogen by the modified L,iebig method,1 and the heats of com- bustion by the bomb calorimeter.2 The observers work in relays and all the work is systematized. An elaborate system of checking weights and observations serves to mini- mize errors or faulty manipulation. METABOLISM EXPERIMENT NO. 70. The particular experiment here used as an illustration was not pre- ceded by the customary preliminary period, as it was designed to study metabolism after a period of fasting. The experiment shows the met- abolism on the first day after a 5-day fast. Since it is not the purpose of this report to discuss metabolism in general, but rather to describe the apparatus and methods of calcula- tion, the results for the experimental day are here given mainly in the form of tables. SUBJECT. The subject was a young medical student, B. A. S., who had accus- tomed himself to periods of fasting varying from 3 to 10 days. He was in excellent health, and previous to beginning his fast had lived his usual routine of life. 1 Benedict : Elementary Organic Analysis. 2 Jour. Am. Chem. Soc. (1903), 25, p. 659. EXPERIMENT WITH MAN. 179 FOOD. On the experimental day here reported, the diet consisted of 1,652.90 grams milk modified by a large proportion of butter fat, and 5 grams of the desiccated milk proteid sold under the trade name Plasmon. In addition to the milk and Plasmon, 139 grams of water were used. These quantities of food furnished 53.31 grams of protein, 21 1.87 grams of fat, 75.41 grams of carbohydrates, and 2,569 calories of energy. ROUTINE OF EXPERIMENT. The experiment was carried out according to the customary routine established in this laboratory for experiments with the respiration calorimeter. Detailed accounts of this routine have been published elsewhere.1 Minor, though important, changes in the preparation, sam- pling, and analysis of the milk and cream have since been introduced to facilitate in accuracy and manipulation. The feces were separated in the usual way by means of lamp-black capsules, though in experiments either during fasting or immediately following fasting we have experienced great difficulty in securing satis- factory separations. For the want of more satisfactory technique, therefore, we are now in the custom of collecting the total feces for the food period (in this case 3 days), including that passed after the subject has left the respiration chamber, and ascribing an aliquot portion of the feces to each food-day. The daily routine followed by the subject in the respiration chamber consisted mainly in rising from bed, dressing, eating, care of food and excreta, sitting at a table, reading or writing, and occasionally stand- ing or taking a few short steps. In general, the subject followed pretty closely a definite program previously prepared. Ordinarily the subject enters the respiration chamber at 1 1 p. m. on the day before the actual experiment begins. This enables him to become accustomed to the environment, and affords opportunity to secure constant-temperature conditions inside the chamber after a long night's sleep. In this particular case, the subject had already remained in the chamber for 5 days of fasting, so that there was no preliminary period for the food experiment, which began at 7 a. m. From this time to the close of the experiment a careful record was kept of all data for computing the total income and outgo of matter and energy. So far as the measurements of heat, carbon dioxide, water, and oxygen are concerned, the day was, as usual, divided into 12 periods of 2 hours each. It has not been found feasible to make such short separations 1U. S. Dept. of Agr., Office of Experiment Stations Bulls. 44, 63, 69, 109, and 136. i8o A RESPIRATION CALORIMETER. of the urine, and consequently the analyses are not made on periods shorter than 24 hours, save in the case of determinations of total nitrogen, which are at times made on 6-hour periods. STATISTICS OF FOOD, FECES, AND URINE. In Table 5 the percentage composition of the food materials, feces, and urine are given. TABLE 5. — Percentage Composition of Food Materials, Feces, and Urine, Metabolism Experiment No. 70. Lab. No. Material. (a) Water. (*) Protein. w Fat. (d) Carbo- hydiates. w Ash. (/) Nitro- gen. to) Carbon. (*) Hydro- gen. (0 Energy per gram. ^806 Milk... Per ct. 79.14 Per ct. 3.00 Per ct. 12.63 Per ct. 4-SQ. Per ct. o 64 Per ct. o 48 Per ct. 12 86 Per ct. 2 OO Calories. I S2<\ 7807 do 78.46 3.00 13.56 4-^5 0.63 O.48 17 SO 2 IO I so8 077-2 0.80 74.. SO 0.15 6.88 867 1 1 Q2 A A 21 A 82O •?8lQ Feces 66 •JQ ^.71 2.78 20. is 6.Q7 O SO IQ 7S 7 I 1 2 4/17 3815 Urine 96.11 0.44 0.86 0.23 O.IOO These values are determined directly in the case of water, fat, ash, nitrogen, carbon, and hydrogen. The protein is obtained from the nitrogen by multiplying by the factor 6.25. The carbohydrates are determined by difference. The heat of combustion per gram is deter- mined by combustion in the bomb calorimeter. In all cases except that of the feces the materials are analyzed on the fresh basis, i. c., original weights are on the fresh material. The feces of necessity are analyzed after drying. The total amounts of food, with the quantities of nutrients and energy supplied, are shown in Table 6. TABLE 6. — Weight, Composition, and Heat of Combustion of Food, Metabolism Experiment No. jo. Lab. No. Food material. (a) Total weight. (*) Water. Water-free substance. w Pro- tein. (d) Fat. (<•) Car- bohy- drates. (/) Ash. (9) Nitro- gen. (A) Car- bon. (0 Hy- dro- gen. (/) Oxy- gen. (*) Energy. 3806 3807 3773 Milk Cms. 1,320.10 332.80 5-00 Cms. 1,044.73 261 . i i 0.49 Cms. 3960 9-98 3-73 Cms. 166.73 45-13 O.OI Cms. 60.59 14.48 o.34 Cms. 8.45 2.IO 0.43 Cms. 6-34 i. 60 0.60 Cms. 169.76 44-93 2.21 Cms 26.40 6.99 0.31 <7>«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 8-54 216.90 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. (a) Total weight. (*) Water. Water-free substance. (c) Ash. (rf) Nitrogen. (e) Carbon. (/) Hydrogen. (g) Oxygen. w Energy. Urine Grams. 1,031-5° 60.97 Grams. 991-37 40.48 Grams. 4.54 4-25 Gra ms. I3-04 0.36 Grams. 887 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. TABLE 8. — Record of Water in Ventilating Air Current, Metabolism Experiment^ No. jo. Date. Period. (a) Total amount of vapor in cham- ber at end of period. (*) Gain(+) or loss ( - ) over pre- ceding period. (c) Change in weight of heat- absorb- ing sys- tem — gain (+), loss ( - ). (d) Change in weight of chair, bedding, etc. M Total amount gained (+)or lost ( — ) during period. (6+c+d) (/) Total amount in out- going air. Or) Total water of respi- ration and per- spira- tion. (*+/)* 1904. Grams. Grants. Grams. Grams. Grams. Grams. Grams. Dec 20-21 •*8 7 A -4- 2 67 71.87 74. "\4. 9 a m to 1 1 a m 7Q QT + I 17 /»•"/ OS 22 66 T.Q •*S or 67. SS 66 s* i p ni to 3 p m At 7? + 2 82 6i.8s 6d. 6? 3 p m to 5 p in 76 Q-I — 4 80 68 os \jt^.\jf 64.1^ 5 p in to 7 p in •37 76 -f- o 83 y yo 60.70 7O.S1* 7 p. in to 9 p. m 77 28 — 0.48 ,-v '/. 65. 06 65.48 9 p ni to 1 1 p m 77 21 — o 05 66 26 66 21 1 1 p m to i a. in •JQ Q7 4- 2 74. 60 30 72. OA i a. m. to 3 a. m. 46 O6 + 6 OQ 84.41 90.50 3 a. m. to 5 a. m. V3.7I — 6. is 76.55 70.20 5 a. m. to 7 a. m. IT. 18 — 6 s^ 70. 3 1 63.78 Total — 2 So + Volume of carbon dioxide exhaled. (n) Respira- tory quotient. (g+f) (*) Volume. (c) Weight. (*H-0.7) Dec. 20, 1904. Liters. Liters. Grams. Grants. Grams. Liters. Liters. 5 a ni to 7 a in QO7 23 Dec. 20-21, 1904. 7 a. m. to 9 a. m.. 9I3.54 + 6.26 + 8.94 72-34 6^.40 44-38 32-38 0.7296 9 a. m. to ii a. m.. 899.46 — 14.08 — 20. IF 36.78 56.89 39-82 30.58 0.7680 ii a. m. to i p. m.. 898.36 — 1. 10 — 1-57 52.49 54.06 37-84 28.25 0.7466 i p. m. to 3 p. in.. 881.96 — 16 40 - 23.43 33-74 57-17 40 02 30.40 0.7596 3 p. m. to 5 p. m.. 8-9.44 -r 7.48 + 10.69 62.36 51-67 36.17 29.13 0.8054 5 p. m. to 7 p. m.. 888.34 — 1. 10 — 1-57 57-97 59-54 41.68 30.5« 0.7337 7 p. m. to 9 p. m.. 8HI.65 — 6.69 — 9.56 46.66 56.22 39-3S 30-53 0-7759 9 p. m. to ii p. m.. 878.59 — 3.06 — 4-37 48.47 52.84 36.99 27-24 0.7364 ii p. m. to i a. m.. 871.47 — 7.12 — 10.17 39-09 49.26 34-48 26.17 0.7590 i a. m. to 3 a. m.. 871.10 — 0.37 - °53 48.38 48.91 34-24 25.00 0.7301 3 a. m. to 5 a. m.. 879.10 + 8.00 + H-43 48.42 36.99 35.89 21. 18 08181 5 a. m. to 7 a. in.. 907.04 + 27-94 + 39-91 75.36 35-45 24.82 20 92 0.8429 Total — 0.24 - 0.34 622.06 622.40 435-68 332.36 0.7629 RESPIRATORY QUOTIENT. The ratio between the volume of carbon dioxide exhaled and the volume of the oxygen inspired, and indicating in marked degree the nature of the materials burned inside the body, is commonly called the respiratory quotient. In the experiments with men, it is computed on the sheets upon which are recorded the data for the determinations of the amount of oxygen consumed, Table 10, and is recorded in column (^). In determining the respiratory quotient, the weight of carbon dioxide found is converted to liters by multiplying by the factor 0.5091 , column (tf) , Table 9, while the weight of oxygen absorbed by the body is converted to liters by multiplying by 0.7, column (/) of Table 10. The ratio between the volumes of carbon dioxide eliminated and oxygen absorbed, CO2-f-O2, represents the so-called " respiratory quotient." EXPERIMENT WITH MAN. 185 When carbohydrates are burned in the body, the volume of oxygen consumed is equal to the volume of carbon dioxide given off, since the hydrogen and oxygen in the carbohydrate molecule are in the same proportions as in water, and in the conversion of carbon to carbon dioxide the volume of carbon dioxide is invariably the same as the volume of oxygen required. In the case of the proteids, where not only carbon is oxidized, but also some hydrogen, it is found that the respiratory quotient is generally not far from 0.809, while in the case of fats, where the amount of hydrogen oxidized is quite consider- able, the respiratory quotient may fall as low as 0.711. It has been found as a result of experimenting with other types of respiration apparatus, especially those of Zuntz and Chauveau (see p. 3), that the respiratory quotient on an ordinary mixed diet is not far from 0.9. From an inspection of column (/;) of Table 10 of experiment 70 given "herewith, it will be seen that the large proportion of fat in the diet re- sulted in a marked lowering of the respiratory quotient. SUMMARY OF CALORIMETRIC MEASUREMENTS. The records of the heat measurements by means of the respiration calorimeter are summarized in Table 1 1 . TABLE n.— Summary of Calorimelrlc Measurements, Metabolism Experiment No. 70. (a) (*) M (d) M (/) (g) Water Period. Heat meas- ured in terms Cao- Change in tempera- ture of calo- rimeter. Capacity correc- tion of calo- rimeter. Correc- tion due to tem- perature of food and dishes. vapor- ized equals total in outgoing air plus excess residual Heat used in vapori- zation of •water. (e X 0.592) Total heat de- termined. (a+c + d+f) vapor. Dec. 20-21, 1904. Calories. Degrees. Calories. Calories. Grams. Calories. Calories. 7 a. m. to 9 a. m. 172.35 + 0.03 + i. 80 + 9-22 74-54 44-13 227.50 9 a. m. to ii a. m. 132.56 — 0.05 — 3-00 + 2.87 66.39 39-30 171 73 ii a. m. to i p. m. 122.23 + 0.03 + i. 80 + I2.O2 66.55 3940 175-45 18 28 175.69 i p. m. to 3 p. m. 3 p. m. to 5 p. m. 149.84 + O.02 + 1.20 + 4-37 64.15 37.98 193-39 5 p. m. to 7 p. m. -t- o oi + 0.60 + 8.23 70-53 4L75 201 .89 •ft 4-j-» «-v m _ 0 . _ 18 76 l82 98 4 '4 + 1 2O 66 21 172.83 -f- o 05 4- 7 OO 72.04 4^-65 l6l.29 C7 =8 162.23 118 10 -f- o 13 70.20 41.56 167.46 08 8^ — 18 60 61.78 IlS.OI 9 • J o/ Total I 5QS SQ — O.22 — 13.20 +36.71 835.04 494-35 2,11345 The major part of the heat generated within the apparatus is absorbed and carried away by a current of cold water through the heat-absorbers. The quantity of heat thus brought out is determined from measurement 1 86 A RESPIRATION CALORIMETER. of the amount of water which flows through the absorbers and the difference between the temperature of the water as it enters and as it leaves the chamber. These determinations are given in column (a). Part of the heat generated within the respiration chamber is brought away as latent heat of the water vapor carried out in the ventilating air current. The amount of heat brought out in this way, being simply the amount necessary to vaporize the water, is calculated from the amount of water vaporized. The amount of water vapor for each experimental period, shown in column (e), is taken from column (£•) of Table 8, and the amount of heat necessary to vaporize it is calculated from the quan- tities in column (e) by use of the factor 0.592 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 (£). 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 (rf). The total amount of heat determined in an experimental period, column O) , 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 (rf), 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. 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. TABLE 12. — Gain or Loss of Body Material, Metabolism Experiment No. 70. Total weight. (b) Nitrogen. (<0 Carbon. (d) Hydro- gen. (e) Oxygen. (/) Ash. Intake. Oxygen from air Grants. 622.40 Grams. Grams. Grams. Grams. 622 40 Grants. Drinking water 139.00 IS.SS 123. 4S Water in food T. 306.33 146.18 i 160 15 Solids in food 351.57 8.S4 216.90 "^.70 8I.4S 10.08 Total 2..1IQ.3O 8 S4 216 90 IQS.4"* I QS7 4^ TO OS Output. Water in feces do. 48 4.C-5 •1C QC Solids in feces 20. 4Q o 36 I2.OJ I.QI I Q^ i 2S Water in urine QQI.37 IIO.Q4 88O AT, Solids in urine 40.13 i^.oa. 8.87 2.37 II V 4.C4 "Water of respiration 838. 30 Q-3 Si COg of respiration 652 86 I?8 O^ Total 2 ^83.63 T -2 AQ 108 06 21^ ^6 i IA& Q2 8 -Q l6A ^^ — 4 86 + I7.Q4 — 18.13 — l6l 47 + 2 IQ Ash of protein — O.4S — O.4S — 164 78 -r- I 74 Gain or Loss of Body Material. Protein 4 86 Fat + 2-; ZA -4- 2s; ^2 -U -2 06 Glycogeu -i- 17 C7 + 7 ?8 4- i OQ -f- 8 66 Water — 188 88 Ash 4- 2 IQ + 2 IQ Total — 164 78 4 86 l8 11 + 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 (e} of Table 10 ; (2) water in drink, which is taken from the record of the amount 1 88 A RESPIRATION CALORIMETER. of water consumed during the experiment ; (3) water of food, which is taken from column (£) of Table 6 ; (4) solids of food, the quantity of which is determined as the difference between the total weight of food material and the weight of water which it contains, as shown by columns (a) and (£) of Table 6. In such computations milk is con- sidered as food rather than as drink. The output consists of (i) water and (2) solids of feces and (3) water and (4) solids of urine, which are all obtained by simple computation from columns («) and (£) of Table 7 ; (5) water of respiration and per- spiration, which is obtained from column (£-) of Table 8, and (6) car- bon dioxide obtained from column (af) of Table 9. The quantity of oxygen consumed by the subject from the air is directly determined. The quantities of hydrogen and oxygen in the water of drink, food, feces, urine, and respiration are calculated from the composition of water, and the quantities of carbon and oxygen in the carbon dioxide exhaled by the subject are calculated from the composition of carbon dioxide. The quantities of nitrogen, carbon, hydrogen, oxygen, and ash of solids of food, feces, and urine are taken from Tables 6 and 7, respectively. The differences between the amounts of the elements of intake and those of output show how much of each was gained or lost. Compu- tation of the gains or losses of protein, fat, carbohydrates, and water from those of the elements depends upon the elementary composition of the compounds. The values for percentage composition employed in these investiga- tions are as follows : Body material. N. C. H. o- Mineral matters (includ- ing S). Proteids Per cent. 16 67 Per cent. S2 80 Per cent. 7 OO Per cent. 22 OO Per cent. I ^i Fat 76.IO 1 1. So 12 IO *•• oo Carbohydrates /\A,AC> 6 20 AQ AO Water II. IQ 88 81 Disregarding the mineral matters, the following equations may be derived from the above data, letting p = protein, /= fat, r= carbohy- drates, and w — water : 0.4440 r + 0.7610 / 4- 0.5280/1 =• C 0.1119 w ~f- 0.0620 r -\- 0.1180 t + 0.0700 p = H 0.8881 7t> + 0.4940 r -+- o.i 2 10 t + 0.2200^ = O EXPERIMENT WITH MAN. Solving these equations in terms of N, C, H, and O, the following formulae are obtained : Protein = 6.0 N Fat = 0.005 C + 9.693 H — i. 221 0—2.476 N Carbohydrates = + 2.243 C — 16.613 H -f 2.093 O — 2.892 N Water = -1.248 C + 7.920 H + 0.128 O +0.460 N Substituting for the elements in these formulae the quantity of each gained or lost as expressed in grams in Table 1 2 , and performing the calculations, gives the weights of the compounds gained or lost. In the following illustration the figures are taken from the data for the first day of the experiment (Table 12). Thus : Protein = 6 N = 6 (—4.86) = — 29.16 indicating that 29.16 grams of protein were lost on that day. Again : Fat = + 0.005 C r+ 0.005 (-17-94) = + 0.090 = + 33-65 + 9.693 H — 1. 221 O — 2.476 N + 9-693 ( l8.I2) 1. 221 ( 161.48) — 2.476 (—4.86) — 175-637 +197.167 +12.033 indicating that 33.65 grams of fat were lost on that day. The results for carbohydrates and water are derived in the same way from the other two formulae. The results as thus computed are given in the bottom division of column (a) of Table 12. The correctness of the computations is tested mathematically as follows : From the total weight of each compound gained or lost and its percentages of the elements assumed in the tabular statement above, the quantities of the elements gained or lost are com- puted. The total for each element thus derived should be the same as the difference between the income and outgo of the same element. The gains or losses of material expressed in terms of chemical ele- ments and protein, fat, carbohydrates, and water are summarized in Table 13. TABLE 13. — Gain or Loss of Elements and Protein, Fat, Carbohydrates, and Water, Metabolism Experiment No. 70. Nitrogen. Carbon. Hydrogen. Oxygen. Protein. Fat. Carbo- hydrates. Water. December 20 ... Grams. -4.86 Grants. + 17-94 Grams. - 18.12 G> a ms. - 161.48 Grams. — 29.16 Grams. + 33.65 Grams. + 17-34 Grams. — 188.80 1 90 A RESPIRATION CALORIMETER. BODY WKIGHT. The figures of Table 12 imply that the body lost 164.78 grams of material during the experiment. If there were no experimental errors the body should have weighed 164.78 grams less at the end than at the beginning of the experiment. This calculated balance was checked by actual weighings of the body. TABL,E 14. — Balance of Gains and Losses of Body Material and Gain and Loss o/ Body Weight, Metabolism Experiment No. 70. Intake. Output. Balance. Gain Gain Food. Water. Oxy- gen. Total. Urine. Feces. CO8. Water. Total. or loss (-)of body or loss (-)of body Dif- fer- ence. terial. weight. Gms. Gms. Gms. Gms. Gms. Gms. Gms. Gms. Gms. Gms. Gms. Gms. Dec. 20 1,657-9° 139.00 622.40 2,419.3° 1,045.80 652.86 838.30 2,536-96 — 117.66 — III.OO 6.66 The platform balance, with weighing arrangements, shown in figure 46, was used in this experiment for checking the body weights, and in the next to the last column of Table 14 we have the exact loss in weight as recorded on this particular day by this balance. As a matter of fact, it is seen that the loss in weight as recorded by the balance was in grams, which differs somewhat from the amount computed from the figures in Table 12, i. e., 164.78 grams. In this connection it may be stated that the experimental routine, especially with reference to the weighing, was not in a satisfactory condition on the date on which this experiment was made, and consequently the corrections for the differ- ences in amount of urine passed each day at 7 a. m. before the actual weighing account in large measure for the discrepancy noted above. In Table 14 the balance of intake and output of material in grams is given, and from these figures the loss of body material is calcu- lated to be 117.66 grams, making, therefore, an actual discrepancy between that computed and that found by the platform balance equal to 6.66 grams. Subsequent experience with the platform balance has shown that with a perfected technique the agreement between the computed gain or loss of body material and that actually found is very close. INTAKE AND OUTPUT OF ENERGY. Table 15 summarizes the data regarding the intake and output of energy in the body during this experiment. EXPERIMENT WITH MAN. TABLE 15. — Intake and Output of Energy, Metabolism Experiment No. jo. Date. Heat of combustion of food and excreta as determined by use of the bomb calorimeter. (rf) Avail- able energy Heat of combus- tion of body ma- terial gained or lost as calcu- lated by use of factors. Total energy from body material Esti- mated energy from mate- rial Heat meas- ured by respi- Heat measured greater or less than esti- mated. from gained oxi- ration Food. Feces. (c) Urine. a-(d+c) Pro- tein. Fat. Or) Gly- co- geu. or lost. (e+f+g) dized in the body. (d-h) calo- rim- eter. I*) Amount. w Pro- por- tion. 1904. Cals. Cals. Cals. Cals. Cals. Cals. Cals. Cals. Cals. Cals. Cals. Per ct. 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, i. 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 OF 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 (g}. 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 =- + 32° calories. Glycogen, + 17.34 grams X 4.19 = + 73 calories. Total energy from body material— + 229 calories. The minus sign in column (^) indicates that the body has lost the energy from the amount potential in its previously stored material, while the plus sign in columns (/) and (g~) indicates that the energy was potential in body material stored. The total amount of energy derived from the body material that was utilized, shown in column (/z), is therefore the difference between the amount lost and the amount stored, or, in other words, the algebraic sum of the quantities in col- umns (*), (/), and (£•). The figures in column (z) represent the estimated amounts of energy of the material oxidized in the body. They are the difference between the quantities in column (d), the available energy of the food, and those in column (A), the energy from the body material stored. Since the CONCLUSION. 193 energy of this stored material was obtained from that of the food in excess of that required to supply the needs of the body, the figures of column (//) are subtracted from those of column (d) to make the total energy of material oxidized. The output of energy consists of the heat given off from the body either as sensible heat or heat of vaporization of water. Both quanti- ties are measured directly by the respiration calorimeter. The figures in column (/) show the amounts of heat thus measured. These are taken from column (g} in Table n. Theoretically, the quantity for intake should be the same as that of the output. It would hardly be expected, however, that results agreeing exactly would be obtained. Column (£) shows the difference between the heat measured by the respiration calorimeter and the energy of material oxidized in the body as estimated from the heat of combustion of food, feces and urine, and that of body material gained or lost. This difference is expressed in column (/) in percentages of the amounts in (/). CONCLUSION. Throughout this report the attempt has been made to indicate the experimental limitations as well as the relative accuracy of this appa- ratus. Believing that improvement in experimental technique is an essential in increasing our knowledge of those processes of physiolog- ical chemistry that have special reference to the nutrition of man, we have aimed in the development of this apparatus to secure in so far as possible the accuracy of those forms of physical apparatus ordinarily designated as instruments of precision. The incidental errors of manipulation and computation are by no means wholly eliminated. Indeed, as is to be expected with an apparatus involving so many mechanical details, the number of possible errors is not inconsiderable. We believe, however, that in fundamental principles and practical use it has proved as exact as could well be expected of an apparatus for physiological experimenting. M,?.L. W. LIBRARY WH IflEA 'i •, Y; ' •,:«.'.•: : ...:• ' m •':•:. ; . : a '>-•.•;•••;+• • '.'.'\