EQUATION AND TUE NATURE OF COHESION. 31 



gas L should be equal to PT Ln e (d] D). The correctional term will 

 be seen to include the cohesion in Log a and also the compressi- 

 bility of the molecules in the term Vjb c . A ' is of course a constant 

 of proportion. 



//. a as computed by van Laar. 



In order that the values computed by van Laar for a may 

 be readily compared with those found by these various methods 

 they are given in Column 9 of Table 2. To express his figures in 

 dynes for gram ,rool quantities, in place of the units he uses, I 

 have multiplied the square of the value of \ 'a given under the 

 heading „found" in his paper, by the factor 4.928 X 10 14 > this 

 being the square of the ratio of the number of molecules in a gram 

 mol to the number in 1 c. c. of gas under standard conditions, 

 multiplied by the factor for converting atmospheres to dynes per cm 2 . 



II. DETAILS OF CALCULATIONS. 



1 . Hydrogen . 



The determination of a for hydrogen is extremely important 

 from the theoretical point of view, for the valence of hydrogen is 

 always unity., {a). Determination from the formula: a = G.5 P c T r c 2 . 

 Critical data of II 2 according to Dewar are T c , 32 ; P c , 1 5 ; d v = 0.033. 

 According to Bulle T t . — 31.0 ; P c , 11. I 1 ,, is evidently lower than 

 15 atmospheres, since A', or Bl\jP c V c , with Dewar's figures would 

 be 2.88, au impossibly low figure, lower than helium, which has 

 less cohesion. With BulLe's figures combined with d r = 0.033 8 

 would be 3.001, an impossibly high figure, since this is higher 

 than S in very complex substances. S of hydrogen probably will be 

 found between Tie, or 3.12, and 2 , where S is 3.42. 1 have 

 accordingly taken as the most probable figure for P r the mean 

 between Dkwar's and Bulle's figures, or 13 atmospheres. This 

 would make S equal to 3.30. With P, = 13 and ^ = 0.033 

 a =0.319 X 10' 2 With P c taken as 11 atmospheres it would be 

 . 0.270 X 10 12 . 



(b). Determination from the surface tension of liquid hydrogen. 

 Either form of the formula may be used, namely : a = 3 MN ilB T c C/d ; 

 or a = 3 sF^N ifS MT; 2l3 /{d—D)(T c — r Tf i - Ck Eötvös constant;' 

 it is equal to 1.464 (Onnes). sV 2iZ at T (Abs) 14.83° is 25.137 

 ergs. d calculated from the density at 14.83° by the formula 

 d j{d — D) = {T r j \T I: - - 7')) 1 ' 3 is 0.00305. Solid B a at 13° Abs. 



