CONTRIBUTIONS FROM THE CHEMICAL LABORATORY 

 OF HARVARD COLLEGE. 



CONCERNING GAS-ANALYSIS BY MEASUREMENT 

 IN CONSTANT VOLUME UNDER CHANGING 



PRESSURE. 



By Theodore "William Richards. 



Received June 2, 1902. 



In Hempel's admirable book upon gas-analysis is described a method 

 of exact analysis which has not received the general attention that it de- 

 serves. Instead of measuring the changing volume under constant pres- 

 sure, he suggested measuring changing pressure in constant volume.* 



Possibly one reason for the neglect under which this excellent method 

 has suffered is the demand made by it for the use of a large quantity of 

 mercury. One object of this paper is therefore to point out that the same 

 principle may be applied conveniently in a simpler manner. 



In Hempel's apparatus the gas to be measured is confined in a bulb 

 immersed in a mercury-trough, and the absorption is effected in an Ett- 

 ling-Doyere gas-pipette. It is more convenient to measure the gas in a 

 bulb provided with a capillary outlet at the top, and to conduct the ab- 

 sorption in an ordinary Hempel pipette of small size, or in one of the 

 simpler forms of pipette recently used in this laboratory, f Tiiis manipu- 

 lation of course introduces the necessity of using rubber connections, 

 which Hempel desired to eliminate ; but if they are properly connected J 

 and securely wired, their introduction is not usually a serious defect. 



If not more than 25 per cent of the gas is to be absorbed in any one 

 process, a water column of 2.5 meters, easily obtainable in the labora- 

 tory, is enough to furnish the necessary change of pressure ; hence water 

 may be used as the liquid in the measuring vessel instead of mercury, pro- 



* Hempel's Gas-analysis, translated by Dennis, p. 76 (1002), p. 44 (1892) (Mac- 

 millan). 



t Richards, These Proceedings, 37, 273 (I'JOl). Zeitschr. anorg. Chein. 29, 

 359 (1002). 



} Richards, ('6/(/, papes 276 and 302, respectively. 



VOL. XXXVIII. — 18 



