32 A RESPIRATION CALORIMETER. 



TESTING THE WATER AND CARBON-DIOXIDE ABSORBER SYSTEM. 



In a closed-circuit apparatus every precaution must be taken to guard 

 against leakage of air ; hence the absorber system is frequently subjected 

 to the most rigid tests for tightness. 



Each water-absorber is tested, immediately after being weighed, in the 

 following manner : A one-holed rubber stopper fitted with a Y tube is 

 inserted in the coupling of the water-absorber at the end through which 

 the air leaves the can. One arm of the Y is connected with a water 

 manometer capable of indicating pressures up to 4 feet of water, and the 

 other arm is connected by means of a length of rubber tubing to a 

 bicycle pump for obtaining an increased air-pressure. A solid-rubber 

 stopper is used to insure a tight closure of the other coupling on the 

 absorber. By means of the bicycle pump the desired pressure is put 

 on the absorber, and the screw piuchcock on the rubber tube between 

 the pump and the manometer is then tightly closed. After a prelim- 

 inary fluctuation in pressure, which lasts for a moment or two, a piece 

 of paper is slipped between the glass arm of the manometer and the 

 wooden support at such a point that its lower edge just coincides with 

 the bottom of the meniscus. A leakage of air from the absorber is 

 accompanied by a fall of water in the manometer. No leakage should 

 be apparent at the end of from three to five minutes. At the conclusion 

 of the test the manometer is disconnected and the pressure released. 



An extended experience shows that after the removable ends of the 

 carbon-dioxide absorbers are well screwed on a leak rarely occurs at 

 this point ; consequently it is not necessary to test each individual 

 absorber after weighing. 



The water- absorbers are then coupled with the three carbon-dioxide 

 absorbers as in use and the system as a whole is tested to prove not only 

 the tightness of the individual absorbers themselves, but also of all the 

 couplings. In this test a solid-rubber stopper is used to close the coup- 

 lings on the exit end of the last water-absorber, and the Y tube of the 

 manometer is connected with the side tube G, figure 10, attached just 

 beyond the mercury valve. Pressure is then put on the system by 

 means of the bicycle pump and the tightness of closure tested, as for the 

 separate cans. By the use of this method of testing, leaks in this por- 

 tion of the apparatus have been practically eliminated. 



MAINTENANCE OF THE SUPPLY OP OXYGEN. 



To replace the oxygen consumed by the subject, as well as to main- 

 tain a constant volume inside the system, supplies of oxygen are ad- 

 mitted from time to time. The oxygen used for the purpose is a com- 

 mercial product, the so-called ' ' commercial oxygen ' ' manufactured by 



