﻿Chemical Constants of some Diatomic Gases. 989 



According to Langen *, the value o£ G p may be split into a 

 translational term independent of T and equal to 5/2 . R for 

 a, diatomic gas, and a rotational term, C pr , dependent on T. 

 Equation (6) is then written 



l °geP = - ^ +| l0g c T + g j ^ j (Cpr- C) dT + i, 



logp(atm.) = -^+2-51ogT 



(6a) 



i r T //Tr T 



(6b) 



The constants i, C then supply the terms to (3), and 

 permit the integration of (1). The values of have been 

 calculated from a consideration of the experimental data by 

 Langen for several gases. Values of C had been calculated 

 by Nernstf by a somewhat arbitrary method, and although 

 his results provide a satisfactory approximation for particular 

 problems, they are not in accordance with modern theories 

 of specific heats, as was pointed out by the author in 1913 J. 



3. It will be noted that the equations so far given do not 

 provide a complete solution of the problem of predicting, 

 from purely thermal magnitudes (heats of formation and 

 specific heats) and universal constants, the behaviour of 

 materials when placed together under specified conditions in 

 the absence of passive resistances §. The final step was taken 

 in the case of monatomic substances by Sackur and by 

 Tetrode ||, who were able to calculate the value of i in terms 

 of universal constants. If the temperature is reduced to 

 such an extent that the atomic heat of the condensed phase 

 becomes negligible in comparison with unity, then (6) 



becomes 



lo g^=-^+2'51o g<! T + i, . . . (6c) 



since C pr is zero for a monatomic substance, and the value 



* A. Langen, Z. Elektrochem. xxv. p. 25 (19.19). 



t ' "Recent Applications of Thermodynamics to Chemistry/ 1907. 

 Theoretische Chemie, 8-10 Aufl., 1921, p. 799. 



X ' Thermodynamics; 1913, p. 496. 



§ It maybe that the influence of passive resistances could be included 

 by introducing a " heat of activation," in the sense understood by Perrin, 

 Trautz, W. C. M. Lewis, and others, in connexion with X, but this 

 problem is not considered in the present communication. 



|| Sackur, Ann. d. Physik, xl. p. 67 (1913). Tetrode, ibid, xxxviii. 

 p. 434, xxxix. p. 255 (1912). Stern, Z. Elektrochem. xxv. p. 66 (1919). 



