CONTRIBUTIONS FROM THE CHEMICAL LABORATORY 

 OF HARVARD COLLEGE. 



AN APPARATUS FOR THE MEASUREMENT OF THE 

 EXPANSION OF GASES BY HEAT UNDER 

 CONSTANT PRESSURE. 



By Theodore William Richards and Kenneth Lamartine Mark. 



Presented November 12, 1902. Received October 22, 1902. 



Most of the work which has been done upon the relation to the law 

 of Gay-Lussac or Dalton * has involved the measurement of changing 

 tension in constant volume. The results are neither numerous nor com- 

 prehensive enough to justify their use in connection with the scanty data 

 concerning Boyle's law, for the construction of the isobars or isopiestic 

 lines representing the temperature-volume relation. 



Since in some respects this temperature-volume curve is less difficult 

 to interpret than the temperature-pressure curve, and since our knowl- 

 edge of the fundamental tendencies underlying the slight but weighty 

 irregularities of aeriform material cannot be complete without it, the 

 present investigation was undertaken with the object of directly measur- 

 ing the expansion of gases under constant pressure. 



It is needless to point out that the results when complete may throw 

 important light on the new theory of compressible atoms; indeed this 

 hope really caused the beginning of the research. 



In planning an investigation of this kind it is highly important to 

 study the degree of definition required by the various experimental 

 observations. The coefficient of expansion of hydrogen is not far from 

 0.00366 at 0° ; and if the next decimal place of this value is to be 

 determined accurately, the temperature, when the range is between 0° 

 and 100° C., must be known to within 0.03° C, the pressure under 

 which the gas is measured to within 0.02 mm. of mercury, and the 

 volume to within one part in four thousand. 



* Or Charles. See Klassiker der exakt. Wiss., 44, 14 (1894). 

 vol xxxviii. — 27 



