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 



