Nov. 2=. 1915 Improved Respiration Calorimeter 309 



has been passing for several hours the loss has no effect on the weight of 

 the absorber within the limits to which the weight is determined; yet if 

 the acid carried in this manner from the bottle mentioned in the pre- 

 ceding paragraph is allowed to escape into the air of the chamber, it has 

 a noticeable effect upon the respiration of the subject in a few minutes. 

 To avoid this effect, the air from the absorber passes through a trap which 

 removes the acid spray before it enters the pipe for air returning to the 

 chamber. For several years the trap consisted of sodium carbonate 

 between two layers of cotton wool inclosed in a metal cylinder about 

 15 cm. long and about twice the diameter of the air pipe. Later, a piece 

 of heavy glass tubing was substituted for the metal cylinder (Pi. XXXIV, 

 fig. i), and it was observed that the air was freed from acid apparently 

 by mechanical filtering rather than by chemical action between the acid 

 and the carbonate. The first layer of cotton arrested all the acid that 

 reached the trap during several months' use, and the carbonate appeared 

 to be unnecessary. In accordance with this suppositoin, the cotton and 

 carbonate in the trap were replaced by pumice stone in pieces very much 

 smaller than those in the stopper of the absorber, and this has prevented 

 the passage of the acid spray into the pipe for ingoing air. 



Supplying Oxygen to the; Air 



Oxygen to replace that used by the subject is admitted directly to the 

 chamber through a copper pipe of a bore of about 5 mm. passing through 

 an opening in one wall. The supply of oxygen is contained under pressure 

 in a steel cylinder, the outlet of which is closed with a pressure-regulating 

 valve by which the rate of admission of oxygen is governed. No attempt 

 is made to keep any definite proportion of oxygen in the air. The regu- 

 lator valve is usually set to admit oxygen at a rate that will keep the 

 volume of gas in the chamber fairly constant, as indicated by the rubber 

 diaphragm or the spirometer serving as an air-tension equalizer for the 

 chamber. The valve may be opened or closed by hand as regulation of 

 the volume is necessary; or by causing the diaphragm or spirometer 

 when nearly full to open and when nearly empty to close an electric circuit, 

 an auxiliary valve may be operated so that the admission of oxygen is 

 automatically regulated to keep the total volume of air in the chamber 

 within the desired limits. A simple auxiliary valve consists of a pinch- 

 cock actuated by an electromagnet so as to corfipress or release the rubber 

 tubing connecting the outlet of the regulating valve with the end of the 

 pipe taking oxygen to the chamber. 



The steel cylinder containing the oxygen is suspended from one arm of a 

 large sensitive balance, and from the other arm is suspended a similar 

 cylinder, empty, to serve as a counterpoise (PI. XXXIV, fig. i). The loss 

 in weight of the charged cylinder in a given period shows the amount of 

 gas admitted to the chamber during the period. Though each cylinder 



