183 



liquid-densities ^) and vapour-pressures *) published on former occasions 

 and finally of the values of the constant B '), it is now possible to 

 make a calculation of the critical density of hydrogen assuming the 

 diameter of Cailletet and Mathias to be a straight line for hydrogen ; 

 there is all the more reason for the latter supposition as according 

 to the figure the inclination of the diameter in the neighbourhood 

 of the critical point cannot deviate much from that at the lower 

 temperatures where the expansion of the liquid has been determined. 

 For this purpose, using the vapour-pressures and the value of B, 



by means of the relation ^) dji = 



P \ Ba ) 



-r- 1 ;r^ /) > the vapour densi- 



Aa { Aa' ) ^ 



ties are calculated at the same temperatures at which the density 



of the liquid has been measured. The constant Aa^ is taken equal 



to .99939. 



In this manner the ordinates of the diameter are obtained and 



by means of these the equation of the diameter. In the following 



table Qrvap and QrH'i denote the densities of the saturated vapour 



and the liquid respectively in gr. per cm^ and y the oi-dinate of the 



diameter. The two points through which the diameter is laid are 



indicated by an asterisk. 



Ï) H. Kamerlingh Onnes and C. A. Crommelin, Proc. XVI, 1, pg. 245, 

 Gomm. NO. 137a. 



2) H. Kamerlingh Onnes and W. H. Keesom, Proc. XVI, 1, pg. 440, Gomm. 

 N<J. 137d. 



■') H. Kamerlingh Onnes and W. J. de Haas, Proc. XV, 1, p. 405, Gomm. 

 NO. 127c. The values of B were smoothed in the manner as given in this paper. 



*) Ba v^ras found by graphical interpolation ; Ca does not come into account. 



