FOOTNOTES:

1——1 +at

in whichtis the temperature of the calorimeter. The correction for pressure has also been worked out in a series of tables and the logarithmic factor here corresponds to the ratiop/760, in whichpis the observed barometer. The logarithm of the total volume is recorded as a result of the addition of these three logarithms enumerated, and from this logarithm is expressed the total volume of air in liters. Deducting the sum of the values (a) and (b) from the total volume leaves the volume of oxygen plus nitrogen.

The calculation of the residual volume of nitrogen and the record of the additions thereto was formerly carried out with a refinement that to-day seems wholly unwarranted when other factors influencing this value are taken into consideration. For the majority of experiments the residual volume of nitrogen may be considered as constant in spite of the fact that some nitrogen is regularly admitted with the oxygen. The significance of this assumption is best seen after a consideration of the method of calculating the amount of oxygen admitted to the chamber.

Calculation of residual amounts of nitrogen, oxygen, carbon dioxide and water-vapor remaining in chamber at 8.10 A. M., June 24, 1909.

Residual at end of Prelim. period. Exp.: Parturition. No.........

Subject: Mrs. Whelan. Calorimeter: Bed.

-------------------------------------------Barometer, 756.95 mm.Temp. cal., 20.08 °C----------------------------------------------Apparent Volume of Air

I containing H2O 715. litersI-II " CO2781. "I-III " O+N 755. "-------------------------------------------Log. wt. H2O to residual.0815 = 91116Log. I = 85431——76547 = 5.88 gms. H2OGms. to liters, 09462——(a) 86909 = 7.25 l. H2O

Log. wt. CO2in residual.0438 = 62634Log. I-II = 84392———49026 = 3.09 gms. CO2Gms. to liters, 70680———(b) 19706 = 1.57 l. CO2-------------------------------------------Miscellaneous Calculations875 48.65164.55 25.9——— 90.710.46 ———4.6 164.55———715.0 I14———781.0 I-II24———755.0 I-III-----------------------------(a) 7.26 l.(b) 1.57 l.———8.82 = l. CO2+ H2OLog. I-III = 87796" temp. = 96912" pressure = 99856———Total volume 84588 = 700.37 l.Volume CO2+ H2O = 8.82 l.———" O + N = 691.56 l." N = 552.96 l.———" O = 186.57 l.

Desiring to make the apparatus as practicable and the calculations as simple as possible, a scheme of calculation has been devised whereby the computations may be very much abbreviated and at the same time there is not too great a sacrifice in accuracy. The loss in weight of the oxygen cylinder has, in the more complicated method of computation, been considered as due to oxygen and about 3 per cent of nitrogen. The amount of nitrogen thus admitted has been carefully computed and its volume taken into consideration in calculating the residual oxygen. If it is considered for a moment that the admission of gas out of the steel cylinder is made at just such a rate as to compensate for the decrease in volume of the air in the system due to the absorption of oxygen by the subject, it can be seen that if the exact volume of the gas leaving the cylinder were known it would be immaterial whether this gas were pure oxygen, oxygen with some nitrogen, or oxygen with any other inert gas not dangerous to respiration or not absorbed by sulphuric acid or potash-lime. If 10 liters of oxygen had been absorbed by the man in the course of an hour, to bring the system back to constant apparent volume it would be necessary to admit 10 liters of such a gas or mixture of gases, assuming that during the hour there had been no change in the temperature, the barometric pressure, or the residual amounts of carbon dioxide or water-vapor.

Under these assumed conditions, then, it would only be necessary to measure the amount of gas admitted in order to have a true measure of the amount of oxygen absorbed. The measure of the volume of the gas admitted may be used for a measure of the oxygen absorbed, even when it is necessary to make allowances for the variations in the amount of carbon dioxide or water-vapor in the chamber, the temperature, and barometric pressure. From the loss in weight of the oxygen cylinder, if the cylinder contained pure oxygen, it would be known that 10 liters would be admitted for every 14.3 grams loss in weight.

From the difference in weight of 1 liter of oxygen and 1 liter of nitrogen, a loss in weight of a gas containing a mixture of oxygen with a small per cent of nitrogen would actually represent a somewhat larger volume of gas than if pure oxygen were admitted. The differences in weight of the two gases, however, and the amount of nitrogen present are so small that one might almost wholly neglect the error thus arising from this admixture of nitrogen and compute the volume of oxygen directly from the loss in weight of the cylinder.

As a matter of fact, it has been found that by increasing the loss in weight of the cylinder of oxygen containing 3 per cent nitrogen by 0.4 per cent and then converting this weight to volume by multiplying by 0.7, the volume of gas admitted is known with great accuracy. This method ofcalculation has been used with success in connection with the large chamber and particularly for experiments of short duration. It has also been introduced with great success in a portable type of apparatus described elsewhere.[27]Under these conditions, therefore, it is unnecessary to make any correction on the residual volume of nitrogen as calculated at the beginning of the experiment. When a direct comparison of the calculated residual amount of oxygen present is to be made upon determinations made with a gas-analysis apparatus the earlier and much more complicated method of calculation must be employed.

Since the ventilating air-current has a confined volume, in which there are constantly changing percentages of carbon dioxide, oxygen, and water-vapor, it is important to note that the nitrogen present in the apparatus when the apparatus is sealed remains unchanged throughout the whole experiment, save for the small amounts added with the commercial oxygen—amounts well known and for which definite corrections can be made. Consequently, in order to find the amount of oxygen present in the residual air at any time it is only necessary to determine the amounts of carbon dioxide and water-vapor and, from these two factors and from the known volume of nitrogen present, it is possible to compute the total volume of oxygen after calculating the total absolute volume of air in the chamber at any given time.

While the apparent volume of the air remains constant throughout the whole experiment, by the conditions of the experiment itself the absolute amount may change considerably, owing primarily to the fluctuations in barometric pressure and secondarily to slight fluctuations in the temperature of the air inside of the chamber. Although the attempt is made on the part of the observers to arbitrarily control the temperature of this air to within a few hundredths of a degree, at times the subject may inadvertently move his body about in the chair just a few moments before the end of the period and thus temporarily cause an increased expansion of the air. The apparatus is, in a word, a large air-thermometer, inside the bulb of which the subject is sitting. If the whole system were inclosed in rigid walls there would be from time to time noticeable changes in pressure on the system due to variations in the absolute volume, but by means of the tension-equalizer these fluctuations in pressure are avoided.

The same difficulties pertain here which were experienced with the earlier type of apparatus in determining the average temperature of the volume of air inside of the chamber. We have on the one hand the warm surface of the man's body, averaging not far from 32° C. On the other hand we havethe cold water in the heat-absorbers at a temperature not far from 12° C. Obviously, the air in the immediate neighborhood of these two localities is considerably warmer or colder than the average temperature of the air. The disposition of the electric-resistance thermometers about the chamber has, after a great deal of experimenting, been made such as to permit the measurement as nearly as possible of the average temperature in the chamber. But this is at best a rough approximation, and we must rely upon the assumption that while the temperatures which are actually measured may not be the average temperature, the fluctuations of the average temperature are parallel to the fluctuations in the temperatures measured. Since every effort is made to keep these fluctuations at a minimum, it is seen that the error of this assumption is not as great as might appear at first sight. However, the calculation of the residual amount of oxygen in the chamber is dependent upon this assumption and hence any errors in the assumption will affect noticeably the calculation of the residual oxygen.

Attempts to compare the determination of the oxygen by the exceedingly accurate Sondén apparatus with that calculated after determining the water-vapor and carbon dioxide, temperature and pressure of the air in the chamber have thus far led to results which indicate one of three things: (1) that there is not a homogeneous mixture; (2) that during the time required for making residual analyses,i. e., some three or four minutes, there may be a variation in the oxygen content in the air of the chamber due to the oxygen continually added from the cylinder; (3) that the oxygen supplied from the cylinder is not thoroughly mixed with the air in the chamber until some time has elapsed. That is to say, with the method now in use it is necessary to fill the tension-equalizer to a definite pressure immediately at the end of each experimental period. This is done by admitting oxygen from the cylinder, and obviously this oxygen was not present in the air when analyzed. A series of experiments with a somewhat differently arranged system is being planned in which the oxygen will be admitted to the respiration chamber directly and not into the tension-equalizer, and at the end of the experiment the tension-equalizer will be kept at such a point that when the motor is stopped the amount of oxygen to be added to bring the tension to a definite point will be small.

Under these conditions it is hoped to secure a more satisfactory comparison of the analyses as made by means of the Sondén apparatus and as calculated from the composition of the residual air by the gravimetric analysis. It remains a fact, however, that no matter with what skill and care the gasometric analysis is made, either gravimetrically or volumetrically, the calculation of the residual amount of oxygen presents the same difficulties in both cases.

From the weights of the sulphuric-acid and potash-lime vessels, the amounts of water-vapor and carbon dioxide absorbed out of the air-current are readily obtained. The loss in weight of the oxygen cylinder increased by 0.4 per cent (see page 88) gives the weight of oxygen admitted to the chamber. It remains, therefore, to make proper allowance for the variations in composition of the air inside the chamber at the beginning and end of the different periods. From the residual sheets the amounts of water-vapor, carbonic acid, and oxygen present in the system at the beginning and end of each period are definitely known. If there is an increase, for example, in the amount of carbon dioxide in the chamber at the end of a period, this increase must be added to the amount absorbed out of the air-current in order to obtain the true value for the amount produced during the experimental period.

A similar calculation holds true with regard to the water-vapor and oxygen. For convenience in calculating, the amounts of water-vapor and carbon dioxide residual in the chamber are usually expressed in grams, while the oxygen is expressed in liters. Hence, before making the additions or subtractions from the amount of oxygen admitted, the variations in the amount of oxygen residual in the system should be converted from liters to grams. This is done by dividing by 0.7.

After having brought to as high a degree of perfection as possible the apparatus for determining carbon dioxide, water, and oxygen, it becomes necessary to submit the apparatus to a severe test and thus demonstrate its ability to give satisfactory results under conditions that can be accurately controlled. The liberation of a definite amount of carbon dioxide from a carbonate by means of acid has frequently been employed for controlling an apparatus used for researches in gaseous exchange, but this only furnishes a definite amount of carbon dioxide and throws no light whatever upon the ability of the apparatus to determine the other two factors, water-vapor and oxygen. Some of the earlier experimenters have used burning candles, but these we have found to be extremely unsatisfactory. The necessity for an accurate elementary analysis, the high carbon content of the stearin and paraffin, and the possibility of a change in the chemical composition of the material all render this method unfit for the most accurate testing. As a result of a large number of experiments with different materials, we still rely upon the use of ethyl alcohol of known water-content. The experiments with absolute alcohol and with alcohol containing varying amounts of water showed no differences in the results, andhence it is now our custom to obtain the highest grade commercial alcohol, determine the specific gravity accurately, and burn this material. We use the Squibb pyknometer[28]and thereby can determine the specific gravity of the alcohol to the fifth or sixth decimal place with a high degree of accuracy. Using the alcoholometric tables of Squibb[29]or Morley,[30]the percentage of alcohol by weight is readily found, and from the chemical composition of the alcohol can be computed not only the amount of carbon dioxide and water-vapor formed and oxygen absorbed by the combustion of 1 gram of ethyl hydroxide containing a definite known amount of water, but also the heat developed during its combustion.

With the construction of this apparatus it was found impracticable to employ the type of alcohol lamp formerly used with success in the Wesleyan University respiration chamber. Inability to illuminate the gage on the side of the lamp and the small windows on the side of the calorimeter precluded its use. It was necessary to resort to the use of an ordinary kerosene lamp with a large glass font and an Argand burner. Of the many check-tests made we quote one of December 31, 1908, made with the bed calorimeter:

Several preliminary weights of the rates of burning were made before the lamp was introduced into the chamber. The lamp was then put in place and the ventilation started without sealing the cover. The lamp burned for about one hour and a quarter and was then weighed again. Then the window was sealed in and the experiment started as soon as possible. At the end of the experiment the window was taken out immediately and the lamp blown out and then weighed. The amount burned between the time of weighing the alcohol and the beginning of the experiment was calculated from the rate of burning before the experiment and this amount subtracted from the total burned from the time that the lamp was weighed before being sealed in until the end, when it was weighed the second time. For the minute which elapsed between the end of the experiment and the last weighing, the rate for the length of the experiment itself was used.During the experiment there were burned 142.7 grams of 92.20 per cent alcohol of a specific gravity of 0.8163.

During the experiment there were burned 142.7 grams of 92.20 per cent alcohol of a specific gravity of 0.8163.

A tabular summary of results is given below:

Found.Required.Carbon dioxide gms.259.9251.4Oxygen "278.5274.8Water-vapor "165.8165.6Heat cals.829.0834.5

Thus does the apparatus prove accurate for the determination of all four factors.

The loss or gain in body-weight has always been taken as indicating the nature of body condition, a loss usually indicating that there is a loss of body substance and a gain the reverse. In experiments in which a delicate balance between the income and outgo is maintained, as in these experiments, it is of special interest to compare the losses in weight as determined by the balance with the calculated metabolism of material and thus obtain a check on the computation of the whole process of metabolism. Since the days of Sanctorius the loss of weight of the body from period to period has been of special interest. The most recent contribution to these investigations is that of the balance described by Lombard,[31]in which the body-weight is recorded graphically from moment to moment with an extraordinarily sensitive balance.

In connection with the experiments here described, however, the weighing with the balance has a special significance, in that it is possible to have an indirect determination of the oxygen consumption. As pointed out by Pettenkofer and Voit, if the weight of the excretions and the loss in body-weight are taken into consideration, the difference between the weight of the excretions and the loss in body-weight should be the weight of the oxygen absorbed. With this apparatus we are able to determine the water-vapor, the carbon-dioxide excretion, and the weight of the urine and feces when passed. If there is an accurate determination of the body-weight from hour to hour, this should give the data for computing exactly the oxygen consumption. Moreover, we have the direct determination of oxygen with which the indirect method can be compared.

In the earlier apparatus this comparison was by no means as satisfactory as was desired. The balance there used was sensitive only to 2 grams, the experiments were long (24 hours or more), and it seemed to be absolutely impossible, even by exerting the utmost precaution, to secure the body-weight of the subject each day with exactly the same clothing and accessories. Furthermore, where there is a constant change in body-weight amounting to 0.5 gram or more per minute, it is obvious that the weighing should be done at exactly the same moment from day to day. It is seen, therefore, that the comparison with the direct oxygen determination is in reality an investigation by itself, involving the most accurate measurements and the most painstaking development of routine.

With the hope of contributing materially to our knowledge regarding the indirect determination of oxygen, the special form of balance shown in fig. 9 was installed above the chair calorimeter. This balance is extremelysensitive. With a dead load of 100 kilograms in each pan it has shown a sensitiveness of 0.1 gram, but in order to have the apparatus absolutely air-tight for the oxygen and carbon-dioxide determination, the rod on which the weighing-chair is suspended must pass through an air-tight closure. For this closure we have used a thin rubber membrane, weighing about 1.34 grams, one end of which is tied to a hard-rubber tube ascending from the chair to the top of the calorimeter, the other end being tied to the suspension rod. In playing up and down this rod takes up a varying weight of the rubber diaphragm, depending upon the position which it assumes, and therefore the sensitiveness noted by the balance with a dead load and swinging freely is greater than that under conditions of actual use. Preliminary tests with the balance lead us to believe that with a slight improvement in the technique a man can be weighed to within 0.3 gram by means of this balance. A series of check-experiments to test the indirect with the direct determination of oxygen are in progress at the moment of writing, and it is hoped that this problem can be satisfactorily solved ere long.

During the process of weighing, the ventilating air-current is stopped so as to prevent any slight tension on the rubber diaphragm and furnish the best conditions for sensitive equilibrium. After the weighing has been made and the time exactly recorded, the load is thrown off the knife-edges of the balance, and then provision has been made to raise the rod supporting the chair and simultaneously force a rubber stopper tightly into the hard rubber tube at the top of the calorimeter, thus making the closure absolutely tight. It is somewhat hazardous to rely during the entire period of an experiment upon the thin rubber membrane for the closure when the blower is moving the air-current.

To raise the chair and the man suspended on it in such a way as to draw the cork into the hard-rubber tube, we formerly used a large hand-lever, which was not particularly satisfactory. Thanks to the suggestion of Mr. E. H. Metcalf, we have been able to attach a pneumatic lift (fig. 9) in that the cross-bar above the calorimeter chamber, to which the suspension rod is attached, rests on two oak uprights and can be raised by admitting air into an air-cushion, through the central opening of which passes the chair-suspending rod. As the air enters the air-cushion it expands and lifts a large wooden disk which, in turn, lifts the iron cross-bar, raising the chair and weight suspended upon it. At the proper height and when the stopper has been thoroughly forced into place, two movable blocks are slipped beneath the ends of the iron cross-bar and thus the stopper is held firmly in place. The tension is then released from the air-cushion. This apparatus functionates very satisfactorily, raising the man or lowering him upon the knife-edges of the balance with the greatest regularity and ease.

The striking relationship existing between pulse rate and general metabolism, noted in the fasting experiments made with the earlier apparatus, has impressed upon us the desirability of obtaining records of the pulse rate as frequently as possible during an experiment. Records of the respiration rate also have an interest, though not of as great importance. In order to obtain the pulse rate, we attach a Bowles stethoscope over the apex beat of the heart and hold it in place with a light canvas harness. Through a long transmission-tube passing through an air-tight closure in the walls of the calorimeter it is possible to count the beats of the heart without difficulty. The respiration rate is determined by attaching a Fitz pneumograph about the trunk, midway between the nipples and the umbilicus. The excursions of the tambour pointer as recorded on the smoked paper of the kymograph give a true picture of the respiration rate.

Of still more importance, however, is the fact that the expansion and contraction of the pneumograph afford an excellent means for noting the minor muscular activity of a subject, otherwise considered at complete rest. The slightest movement of the arm or the contraction or relaxation of any of the muscles of the body-trunk results in a movement of the tambour quite distinct from the respiratory movements of the thorax or abdomen. These movements form a very true picture of the muscular movements of the subject, and these graphic records have been of very great value in interpreting the results of many of the experiments.

In the numerous previously published reports which describe the construction of and experiments with the respiration calorimeter, but little attention has been devoted to a statement of the routine. Since, with the increasing interest in this form of apparatus and the possible construction of others of similar form, a detailed description of the routine would be of advantage, it is here included.

Prior to an experiment, the subject is usually given either a stipulated diet for a period of time varying with the nature of the experiment or, as in the case of some experiments, he is required to go without food for at least 12 hours preceding. Occasionally it has been deemed advisable to administer a cup of black coffee without sugar or cream, and by this means we have succeeded in studying the early stages of starvation without making it too uncomfortable for the subject. The stimulating effect of the small amount of black coffee on metabolism is hardly noticeable and for most experiments it does not introduce any error.

The urine is collected usually for 24 hours before, in either 6 or 12 hour periods. During the experiment proper urine is voided if possible at the end of each period. This offers an opportunity for studying the periodic elimination of nitrogen and helps frequently to throw light upon any peculiarities of metabolism.

Even with the use of a long-continued preceding diet of constant composition, it is impossible to rely upon any regular time for defecation or for any definite separation of feces. For many experiments it is impracticable and highly undesirable to have the subject attempt to defecate inside the chamber, and for experiments of short duration the desire to defecate is avoided by emptying the lower bowel with a warm-water enema just before the subject enters the chamber. Emphasis should be laid upon the fact that a moderate amount of water only should be used and only the lower bowel emptied, so as not to increase the desire for defecation.

The clothing is usually that of a normal subject, although occasionally experiments have been made to study the influence of various amounts of clothing upon the person. There should be opportunity for a comfortable adjustment of the stethoscope and pneumograph, etc., and the clothing should be warm enough to enable the subject to remain comfortable and quiet during his sojourn inside the chamber.

The rectal thermometer, which has previously been carefully calibrated, is removed from a vessel of lukewarm water, smeared with vaseline, and inserted while warm in the rectum to the depth of 10 to 12 centimeters. The lead wires are brought out through the clothing in a convenient position.

The stethoscope is attached as nearly as possible over the apex beat of the heart by means of a light harness of canvas. In the use of the Bowles stethoscope, it has been found that the heart-beats can easily be counted if there is but one layer of clothing between the stethoscope and the skin. Usually it is placed directly upon the undershirt of the subject.

The pneumograph is placed about the body midway between the nipple and the umbilicus and sufficient traction is put upon the chain or strap which holds it in place to secure a good and clear movement of the tambour for each respiration.

The subject is then ready to enter the chamber and, after climbing the stepladder, he descends into the opening of the chair calorimeter, sits in the chair, and is then ready to take care of the material to be handed in to him and adjust himself and his apparatus for the experiment. Usually several bottles of drinking-water are deposited in the calorimeter in a convenient position, as well as some urine bottles, reading matter, clinical thermometer, note-book, etc. Before the cover is finally put in place, the pneumograph is tested, stethoscope connections are tested to see if the pulse can be heard, the rectal thermometer connections are tested, and the telephone, call-bell, and electric light are all put in good working order. When the subject has been weighed in the chair, the balance is tested to see that it swings freely and has the maximum sensibility. All the adjustments are so made that only the minimum exertion will be necessary on the part of the subject after the experiment has once began.

The cover is put in place and wax is well crowded in between it and the rim of the opening. The wax is preferably prepared in long rolls about the size of a lead-pencil and 25 to 30 centimeters long. This is crowded into place, a flat knife being used if necessary. An ordinary soldering-iron, which has previously been moderately heated in a gas flame, is then used to melt the wax into place. This process must be carried out with the utmost care and caution, as the slightest pinhole through the wax will vitiate the results. The sealing is examined carefully with an electric light and preferably by two persons independently. After the sealing is assured, the plugs connecting the thermal junctions and heating wires of the cover with those of the remainder of the chamber are connected, the water-pipe is put in place, and the unions well screwed together. After seeing that the electrical connections can not in any way become short-circuited on either the metal chamber or metal pipes, the asbestos cover is put in place.

Some time before the man enters the chamber, an electric lamp of from 16 to 24 candle-power (depending upon the size of the subject) is placed inside of the chamber as a substitute for the man, and the cooling water-currentis started and the whole apparatus is adjusted to bring away the heat prior to the entrance of the man. The rate of flow with the chair calorimeter is not far from 350 cubic centimeters per minute with a resting man. The proper mixture of cold and warm water is made, so that the electric reheater can be controlled readily by the resistance in series with it. Care is taken not to allow the water to enter the chamber below the dew-point and thus avoid the condensation of moisture on the absorbers. The thermal junctions indicate the temperature differences in the walls and the different sections are heated or cooled as is necessary until the whole system is brought as near thermal equilibrium as possible.

After the man enters, the lamp is removed and the water-current is so varied, if necessary, and the heating and cooling of the various parts so adjusted as to again secure temperature equilibrium of all parts. When the amount of heat brought away by the water-current exactly compensates that generated by the subject, when the thermal-junction elements in the walls indicate a 0 or very small deflection, when the resistance thermometers indicate a constant temperature of the air inside the chamber and the walls of the chamber, the experiment proper is ready to begin.

The physical observer keeps the chemical assistant thoroughly informed as to the probable time for the beginning of the experiment, so that there will be ample time for making the residual analyses of the air. After these analyses have been made and the experiment is about to begin, the observer at the table calls the time on the exact minute, at which time the blower is stopped and the purifying system changed. The physical observer takes the temperatures of the wall and air by the electric-resistance thermometers, reads the mercury thermometers, records the rectal thermometer, and at the exact moment of beginning the experiment the current of water which has previously been running into the drain is deflected into the water-meter. At the end of the period this routine is varied only in that the water-current is deflected from the water-meter into a small can holding about 4 liters, into which the water flows while the meter is being weighed.

The rate of flow of water through the apparatus is determined before the experiment begins. This is done by deflecting the water for a certain number of seconds into a graduate or by deflecting it into the small can and weighing the water thus collected. The water is then directed into the drain during the preliminary period. Meanwhile the main valve at the bottom of the water-meter is opened, such water as has accumulated from tests in preceding experiments is allowed to run out, and the valve is closed after the can is empty. The meter is then carefully balanced on the scales and the weight is recorded. At the beginning of the experiment the water is deflected from the drain into the meter. At the end of the period,while the water is running into the small can, the water-meter is again carefully weighed and the weight recorded. Having recorded the weight, the water is again deflected into the large meter and what has accumulated in the small can is carefully poured into the large meter through a funnel. If the meter is nearly full, so that during the next period water will accumulate and overflow the meter, it is emptied immediately after weighing and while the small can is filling up. About 4 minutes is required to empty the can completely.

After it is emptied, it is again weighed, the water-current deflected from the small can to the meter, and the water which has accumulated in the small can carefully poured into the meter. All weights on the water-meter, both of the empty can and the can at the end of each period, are checked by two observers.

Shortly after the subject has entered the chamber and in many instances before the sealing-in process has begun, the ventilating air-current is started by starting the blower. The air passes through one set of purifiers during this preliminary period, and as no measurements are made for this period it is not necessary that the weights of the absorbers be previously known.

All precautions are taken, however, so far as securing tightness in coupling and installing them on the absorber system are concerned. During this period the other set of absorbers is carefully weighed and made ready to be put in place and tested and about 10 minutes before the experiment proper begins the residual analyses are begun. The series ofU-tubes, which have previously been carefully weighed, are placed on small inclined racks and are connected with the meter and also with the tube leading to the mercury valve. The pet-cock which connects the return air-pipe with the drying-tower and the gas-meter is then opened and the mercury reservoir is lowered. The rate of flow of air through theU-tubes is regulated by a screw pinch-cock on the rubber tube leading to the firstU-tube. This rate is so adjusted by means of the pinch-cock that about 3 liters of air per minute will flow through theU-tubes, and as the pointer on the gas-meter approaches 10 liters the mercury reservoir is raised at just such a point, gained by experience, as will shut off the air-current when the total volume registers 10 liters on the meter. The pet-cock in the pipe behind the meter is then closed, theU-tubes disconnected, and a new set put in place. A duplicate and sometimes a triplicate analysis is made.

When the physical observer calls the time for the end of the period, the switch which controls the motor is opened and the chemical assistant then opens the rear valve of the new set of absorbers and closes the rear valve of the old set, and likewise opens the front valve of the new set and closes the front valve of the old set. As soon as the signal is given that the oxygenconnections have been properly made and that the oxygen has been admitted to the chamber in proper amount, the blower is again started. It is then necessary to weigh theU-tubes and disconnect the old set of absorbers and weigh them. If the sulphuric-acid absorbers have not exceeded the limit of gain in weight they are used again; if they have, new ones are put in their place.

The first sulphuric-acid absorber is connected to the front valve, then the potash-lime can, and then the last sulphuric-acid absorber; but before connecting the last sulphuric-acid absorber with the sodium-bicarbonate can, a test is made of the whole system from the front valve to the end of the second sulphuric-acid absorber. This is made by putting a solid-rubber stopper in the exit end of the second sulphuric-acid absorber and, by means of a bicycle pump, forcing compressed air in through a pipe tapped into the pipe from the valve at the front end until a pressure of about 2 feet of water is developed in this part of the system. This scheme for testing and the method of connecting the extra pipe have been discussed in detail in an earlier publication.[32]Repeated tests have shown that this method of testing the apparatus for tightness is very successful, as the minutest leak is quickly shown.

After the system has been thoroughly tested, the rubber stopper in the exit end of the second sulphuric-acid absorber is first removed, then the tube connected with the pump and manometer is disconnected and its end placed in the reservoir of mercury. Occasionally, through oversight, the pressure is released at the testing-tube with the result that the air compressed in the system expands, forcing sulphuric acid into the valves and down into the blower, thus spoiling completely the experiment. After the testing, the last sulphuric-acid absorber is coupled to the sodium-bicarbonate can. It is seen that this last connection is the only one not tested, and it has been found that care must be taken to use only the best gaskets at this point, as frequently leaks occur; in fact, it is our custom to moisten this connection with soapsuds. If new rubber gaskets are used a leak is never found.

To maintain the apparent volume of air through the whole system constant, oxygen is admitted into the tension-equalizer until the same tension is exerted on this part of the system at the end as at the beginning. This is done by closing the valve connecting the tension-equalizer with the system and admitting oxygen to the tension-equalizer until the petroleum manometer shows a definite tension. After the motor is stopped, at the end of the experimental period, there is a small amount of air compressed in the blower which almost instantly leaks back through the blower and the whole system comes under atmospheric pressure, save that portion whichis sealed off between the two levels of the sulphuric acid in the two absorbing vessels. A few seconds after the motor is stopped the valve cutting off the tension-equalizer from the rest of the system is closed, the pet-cock connecting this with the petroleum manometer is opened, and oxygen is admitted by short-circuiting the electrical connections at the two mercury cups. This is done by the hands of the observer and must be performed very gently and carefully, as otherwise oxygen will rush in so rapidly as to cause excessive tension. As the bag fills with gas, the index on the petroleum manometer moves along the arc of a circle and gradually reaches the desired point. At this point, the supply of oxygen is cut off, the valve connecting the tension-equalizer with the main system is opened, and simultaneously the needle-valve on the reduction-valve of the oxygen cylinder is tightly closed, preliminary to weighing the cylinder. At this point the motor can be started and the experiment continued.

It is necessary, then, that the oxygen cylinder be weighed. This is done after first closing the pet-cock on the end of the pipe conducting the gas beneath the floor of the calorimeter room, slipping the glass joint in the rubber pipe leading from the reduction valve to the pet-cock, and breaking the connections between the two rubber pipes, the one from the pet-cock and the other to the reduction valve, also breaking the electrical connection leading to the magnet on the cylinder. The cylinder is then ready to swing freely without any connections to either oxygen pipe or electrical wires. It is then weighed, the loss in weight being noted by removing the brass weights on the shelf attached to the counterpoise. It is important to see that there is a sufficient number of brass weights always on the shelf to allow for a maximum loss of weight of oxygen from the cylinder during a given period. Since the cylinders contain not far from 4 to 5 kilograms of oxygen, in balancing the cylinders at the start it is customary to place at least 4 kilograms of brass weights on the shelf and then adjust the counterpoise so as to allow for the gradual removal of these weights as the oxygen is withdrawn.

As soon after the beginning of the period as possible, theU-tubes are weighed on the analytical balance, and if they have not gained too much they are connected ready for the next analysis. If they have already absorbed too much water or carbon dioxide, they are replaced by freshly filled tubes.

Immediately at the end of the experimental period the barometer is carefully set and read, and the reading is verified by another assistant. Throughout the whole experiment an assistant counts the pulse of the subject frequently, by means of the stethoscope, and records the respiration rate by noting the lesser fluctuations of the tambour pointer on the smoked paper. These observations are recorded every few minutes in a book kept especially for this purpose.

A most excellent preservation of the record of the minor muscular movements is obtained by dipping the smoked paper on the kymograph drum in a solution of resin and alcohol. The lesser movements on the paper indicate the respiration rate, but every minor muscular movement, such as moving the arm or shifting the body in any way, is shown by a large deflection of the pointer out of the regular zone of vibration. These records of the minor muscular activity are of great importance in interpreting the results of the chemical and physical determinations.

FOOTNOTES:[5]W. O. Atwater and F. G. Benedict: A respiration calorimeter with appliances for the direct determination of oxygen. Carnegie Institution of Washington Publication No. 42, p. 91. (1905.)Francis G. Benedict: The influence of inanition on metabolism. Carnegie Institution of Washington Publication No. 77, p. 451. (1907.)[6]W. O. Atwater and F. G. Benedict: A respiration calorimeter with appliances for the direct determination of oxygen. Carnegie Institution of Washington Publication No. 42, p. 114. (1905.)[7]W. O. Atwater and F. G. Benedict: A respiration calorimeter with appliances for the direct determination of oxygen. Carnegie Institution of Washington Publication No. 42, p. 158. (1905.)[8]Armsby: U. S. Dept. of Agr., Bureau of Animal Industry Bull. 51, p. 34. (1903.)[9]Benedict and Snell: Eine neue Methode um Körpertemperaturen zu messen. Archiv f. d. ges. Physiologie, Bd. 88, pp. 492-500. (1901.)W. O. Atwater and F. G. Benedict: A respiration calorimeter with appliances for the direct determination of oxygen. Carnegie Institution of Washington Publication No. 42, p. 156. (1905.)[10]Rosa: U. S. Dept. of Agric., Office of Experiment Stations Bul. 63, p. 25.[11]Smith: Heat of evaporation of water. Physical Review, vol. 25, p. 145. (1907.)[12]Philosophical Transactions, vol. 199, A, p. 149. (1902.)[13]This is in agreement with the value 579.6 calories found by F. Henning, Ann. d. Physik, vol. 21, p. 849. (1906.)[14]Pembrey: Schäfer's Text-book of Physiology, vol. 1, p. 838. (1898.)[15]Benedict and Snell: Körpertemperatur Schwankungen mit besonderer Rücksicht auf den Einfluss, welchen die Umkehrung der täglichen Lebensgewöhnheit beim Menschen ausübt. Archiv f. d. ges. Physiologie, Bd. 90. p. 33. (1902.)Benedict: Studies in body-temperature: I. The influence of the inversion of the daily routine: the temperature of night-workers. American Journal of Physiology, vol. 11, p. 145. (1904.)[16]W. O. Atwater and E. B. Rosa: Description of a new respiration calorimeter and experiments on the conservation of energy in the human body. U. S. Dept. of Agr., Office of Experiment Stations Bul. 63. (1899.)[17]Specific heat of water at average temperature of the water in the heat-absorbing system referred to the specific heat of water at 20° C.[18]W. O. Atwater and F. G. Benedict: A respiration calorimeter with appliances for the direct determination of oxygen. Carnegie Institution of Washington Publication No. 42, p. 18. (1905.)[19]For a description of the apparatus and the method of filling see W. O. Atwater and F. G. Benedict: A respiration calorimeter with appliances for the direct determination of oxygen. Carnegie Institution of Washington Publication No. 43, p. 27. (1905.)[20]W. O. Atwater and F. G. Benedict: A respiration calorimeter with appliances for the direct determination of oxygen. Carnegie Institution of Washington Publication No. 42, p. 56. (1905.)[21]W. O. Atwater and F. G. Benedict: A respiration calorimeter with appliances for the direct determination of oxygen. Carnegie Institution of Washington Publication No. 42, p. 20. (1905.)[22]Thorne M. Carpenter and Francis G. Benedict: Mercurial poisoning of men in a respiration chamber. American Journal of Physiology, vol. 24, p. 187. (1909.)[23]Francis G. Benedict: A method of calibrating gas-meters. Physical Review, vol. 22, p. 294. (1906.)[24]Atwater and Benedict:Loc. cit., p. 38.[25]Atwater and Benedict: Carnegie Institution of Washington Publication No. 42, p. 77.[26]In the use of logarithms space is saved by not employing characteristics.[27]Francis G. Benedict: An apparatus for studying the respiratory exchange. American Journal of Physiology, vol. 24, p. 368. (1909.)[28]Squibb: Journal of American Chemical Society, vol. 19, p. 111. (1897.)[29]Squibb: Ephemeris, 1884 to 1885, part 2, pp. 562-577.[30]Morley: Journal of American Chemical Society, vol. 26, p. 1185. (1904.)[31]W. P. Lombard: A method of recording changes in body-weight which occur within short intervals of time. The Journal of the American Medical Association, vol. 47, p. 1790. (1906.)[32]Atwater and Benedict:Loc. cit., p. 21.

[5]W. O. Atwater and F. G. Benedict: A respiration calorimeter with appliances for the direct determination of oxygen. Carnegie Institution of Washington Publication No. 42, p. 91. (1905.)Francis G. Benedict: The influence of inanition on metabolism. Carnegie Institution of Washington Publication No. 77, p. 451. (1907.)

[5]W. O. Atwater and F. G. Benedict: A respiration calorimeter with appliances for the direct determination of oxygen. Carnegie Institution of Washington Publication No. 42, p. 91. (1905.)

Francis G. Benedict: The influence of inanition on metabolism. Carnegie Institution of Washington Publication No. 77, p. 451. (1907.)

[6]W. O. Atwater and F. G. Benedict: A respiration calorimeter with appliances for the direct determination of oxygen. Carnegie Institution of Washington Publication No. 42, p. 114. (1905.)

[7]W. O. Atwater and F. G. Benedict: A respiration calorimeter with appliances for the direct determination of oxygen. Carnegie Institution of Washington Publication No. 42, p. 158. (1905.)

[8]Armsby: U. S. Dept. of Agr., Bureau of Animal Industry Bull. 51, p. 34. (1903.)

[9]Benedict and Snell: Eine neue Methode um Körpertemperaturen zu messen. Archiv f. d. ges. Physiologie, Bd. 88, pp. 492-500. (1901.)W. O. Atwater and F. G. Benedict: A respiration calorimeter with appliances for the direct determination of oxygen. Carnegie Institution of Washington Publication No. 42, p. 156. (1905.)

[9]Benedict and Snell: Eine neue Methode um Körpertemperaturen zu messen. Archiv f. d. ges. Physiologie, Bd. 88, pp. 492-500. (1901.)

W. O. Atwater and F. G. Benedict: A respiration calorimeter with appliances for the direct determination of oxygen. Carnegie Institution of Washington Publication No. 42, p. 156. (1905.)

[10]Rosa: U. S. Dept. of Agric., Office of Experiment Stations Bul. 63, p. 25.

[11]Smith: Heat of evaporation of water. Physical Review, vol. 25, p. 145. (1907.)

[12]Philosophical Transactions, vol. 199, A, p. 149. (1902.)

[13]This is in agreement with the value 579.6 calories found by F. Henning, Ann. d. Physik, vol. 21, p. 849. (1906.)

[14]Pembrey: Schäfer's Text-book of Physiology, vol. 1, p. 838. (1898.)

[15]Benedict and Snell: Körpertemperatur Schwankungen mit besonderer Rücksicht auf den Einfluss, welchen die Umkehrung der täglichen Lebensgewöhnheit beim Menschen ausübt. Archiv f. d. ges. Physiologie, Bd. 90. p. 33. (1902.)Benedict: Studies in body-temperature: I. The influence of the inversion of the daily routine: the temperature of night-workers. American Journal of Physiology, vol. 11, p. 145. (1904.)

Benedict: Studies in body-temperature: I. The influence of the inversion of the daily routine: the temperature of night-workers. American Journal of Physiology, vol. 11, p. 145. (1904.)

[16]W. O. Atwater and E. B. Rosa: Description of a new respiration calorimeter and experiments on the conservation of energy in the human body. U. S. Dept. of Agr., Office of Experiment Stations Bul. 63. (1899.)

[17]Specific heat of water at average temperature of the water in the heat-absorbing system referred to the specific heat of water at 20° C.

[18]W. O. Atwater and F. G. Benedict: A respiration calorimeter with appliances for the direct determination of oxygen. Carnegie Institution of Washington Publication No. 42, p. 18. (1905.)

[19]For a description of the apparatus and the method of filling see W. O. Atwater and F. G. Benedict: A respiration calorimeter with appliances for the direct determination of oxygen. Carnegie Institution of Washington Publication No. 43, p. 27. (1905.)

[20]W. O. Atwater and F. G. Benedict: A respiration calorimeter with appliances for the direct determination of oxygen. Carnegie Institution of Washington Publication No. 42, p. 56. (1905.)

[21]W. O. Atwater and F. G. Benedict: A respiration calorimeter with appliances for the direct determination of oxygen. Carnegie Institution of Washington Publication No. 42, p. 20. (1905.)

[22]Thorne M. Carpenter and Francis G. Benedict: Mercurial poisoning of men in a respiration chamber. American Journal of Physiology, vol. 24, p. 187. (1909.)

[23]Francis G. Benedict: A method of calibrating gas-meters. Physical Review, vol. 22, p. 294. (1906.)

[24]Atwater and Benedict:Loc. cit., p. 38.

[25]Atwater and Benedict: Carnegie Institution of Washington Publication No. 42, p. 77.

[26]In the use of logarithms space is saved by not employing characteristics.

[27]Francis G. Benedict: An apparatus for studying the respiratory exchange. American Journal of Physiology, vol. 24, p. 368. (1909.)

[28]Squibb: Journal of American Chemical Society, vol. 19, p. 111. (1897.)

[29]Squibb: Ephemeris, 1884 to 1885, part 2, pp. 562-577.

[30]Morley: Journal of American Chemical Society, vol. 26, p. 1185. (1904.)

[31]W. P. Lombard: A method of recording changes in body-weight which occur within short intervals of time. The Journal of the American Medical Association, vol. 47, p. 1790. (1906.)

[32]Atwater and Benedict:Loc. cit., p. 21.

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