50 A RESPIRATION CALORIMETER. 



valve, w lt is provided. Any air that may have been brought along by 

 the water current will accumulate in the upper part of the chamber F, 

 and when this valve is opened will pass out into the drain, the chamber 

 becoming completely filled with water. 



Apparatus for constant water pressure. In using a water suction-pump 

 for drawing the sample of air, it is of great importance that the water 

 pressure be constant, as otherwise the air will be drawn through the 

 U tubes and meter with a varying degree of rapidity, and consequently 

 under varying tension as measured by the water manometer. The 

 measurement of the absolute volume of air passing through the meter 

 is of great importance, since its relation to the larger volume of residual 

 air (10 : 5,000) necessitates the use of a very large factor when comput- 

 ing the residual amounts of carbon dioxide and water in the system ; 

 consequently every precaution must be taken to secure the most uni- 

 form sampling. The city water pressure was found to be entirely 

 inadequate for the degree of accuracy required for this work, and a 

 special water system, shown in figure 20, was installed. 



A force-pump, which is belted to the line shaft in the calorimeter 

 laboratory, draws water from a galvanized-iron pail, which is supplied 

 from the city main, and forces it into an upright boiler, which serves 

 as an air-chamber. The boiler is filled about half full of water, the level 

 of which is noted by the glass water-gage at the side, and then com- 

 pressed air from a cylinder is admitted to the boiler until the manometer 

 at the top indicates a pressure of about 100 pounds. The water with- 

 drawn from this chamber for use in the suction-pump is taken from a 

 pipe extending several inches above the bottom of the boiler, so as to 

 eliminate sediment as much as possible. By means of the valve w, 

 figure 19, the supply of water passing through the suction-pump may 

 be regulated at will. 



PROCESS OF TAKING RESIDUAI, SAMPLES. 



The residual analysis is started at about 10 minutes before the end 

 of each experimental period. Ten liters of air (apparent volume as 

 measured by the meter) are used for each determination. A dupli- 

 cate analysis follows, beginning at about three minutes before the end 

 of the experimental period. The rate of flow of air through the meter 

 is such that the second sample is about one-half taken at the end of 

 the experimental period, the remaining 5 liters of air being taken during 

 the beginning of the next period. It is assumed that the average com- 

 position of the sample will be that of the air at the moment of changing 

 from one period to another. The differences in results by the two 

 samples are usually insignificant, in which case the second series of 



