32 



COMPARISONS OF RESPIRATORY EXCHANGE. 



In the experiment the ether vessel, G, is weighed before and after the 

 period, and the amount of ether vaporized is thus accurately known. 

 At the end of the experiment the ether- vapor is shut off and the venti- 

 lating air-current is allowed to circulate for several minutes to sweep 

 out the carbon dioxide already formed and bring the whole apparatus 

 to room temperature. The oxygen supply is continued until the 

 apparatus has reached the same tension at the end as at the beginning. 

 The loss in weight of the oxygen cylinder, the increase in weight of the 

 carbon-dioxide absorbers, and the loss in weight of the ether container 

 give the necessary data for calculating the theoretical amounts of 

 carbon dioxide given off and oxygen consumed, and the amounts found 

 by actual experimenting. The results of a typical 15-minute test are 

 given in table 5a. 



Table 5a. — Results of an ether check test. 



Test for leaks in the apparatus. — Obviously, with this apparatus, 

 based as it is upon the closed-circuit principle, there must be absolutely 

 no leakage of air during experiments. In order to demonstrate this, 

 tests for leaks are frequently made. The general method used is to 

 admit oxygen or air into the apparatus until a slight tension is reached, 

 as shown by the petroleum manometer, then to ventilate the apparatus 

 for a moment or two in order to equalize the pressure throughout. 

 The tension equalizer diminishes in volume slightly, this being due to 

 air trapped between the acid-containers. The ventilation is stopped 

 and oxygen or air admitted to bring the tension to the desired point. 

 The apparatus is then again ventilated for 15 minutes and when the 

 ventilation is stopped the tension is noted. Change in pressure is evi- 

 dence of a leak, as otherwise the manometer would remain constant. 



Tests for completeness of carbon-dioxide absorption. — In order to be 

 sure that the soda-lime is absorbing the carbon dioxide completely 

 from the air-current, a portion of the circulating air is diverted through 

 the apparatus containing barium-hydroxide solution (see p. 28) for 

 about one minute. This test is usually made during the latter half of 

 the period. If carbon dioxide is present, a turbidity will be seen in 

 the solution. 



Test for completeness of water-vapor absorption. — Since the carbon- 

 dioxide excretion is determined by weight, the air entering the soda- 

 lime container must be dry; furthermore, the last water-absorber must 

 remove completely the water- vapor given off in the soda-lime container. 



