CONTRIBUTIONS FROM THE CHEMICAL LABORATORY 

 OF HARVARD COLLEGE. 



THERMAL EXPANSION OF HYDROGEN AND CARBON 

 DIOXIDE UNDER CONSTANT PRESSURE. 



By Theodore William Richards and Kenneth Lamartine Mark. 



Presented March 8, 1905. Received April 29, 1905. 



The Apparatus. 



In a former paper, a new apparatus is described for determining the 

 thermal coefficient of expansion of gases under constant pressure. This 

 yielded preliminary determinations of constancy sufficient to warrant 

 the belief that with greater care as to details the method might give 

 extremely accurate results.* The present paper describes further work 

 with this apparatus, proving that the hope was not a vain one. In this 

 new work it was endeavored not only to avoid all conceivable con- 

 stant errors, but also to introduce a number of technical improvements. 

 These objects were accomplished by improving the methods for the 

 determination of the constants of temperature, pressure, and of volume, 

 and by making the conditions of the experiments more uniform, thus 

 diminishing the number and magnitude of the corrections to be applied. 



Many possible sources of error, due to thermal expansion of standards, 

 were at once eliminated by maintaining the room at a constant tem- 

 perature. A perfectly firm, immovable foundation for the apparatus was 

 also found necessary, both to guard against the accidental moving of the 

 apparatus and to insure freedom from vibration on the part of the various 

 surfaces of mercury. 



A room about six meters square, with walls of masonry and floor 

 of concrete, situated in the basement of Boylston Hall, was therefore 

 chosen. The windows were provided with double layers of glass, and a 

 constant temperature of 200°. C. was maintained by means of a gas stove 

 provided with an automatic electrical gas regulator. The electric regu- 

 lating current was made and broken by a sealed hydrogen barometer, 



* These Proceedings, 38, 417 (1902). 



