788 Mr. R. H. Fowler on the 



and S is given by Chapman's corrected formula * 



S = 0*1956 n(a)/L (Inverse 5th-power attractions.) (4) 



The numerical values deduced from Keesom's figures are 

 # = 000201 for 1 c.c. at normal pressure and temperature, 

 and S = 23"6. But the viscosity data for ordinary temper- 

 atures should be fairly comparable with the preceding "com- 

 pressibility" data, and should lead to the same values of 

 b, cr, II(cr), and S. When analysed, however, by Chapman's 

 formulae, they lead unmistakably to the values 6 = 0*00133, 

 S = 162. We may exhibit this significant discrepancy 

 thus : — 



Argon. 



no)xio 14 . s. bxio 3 . <rxio 8 . 



Compressibility data... 1'63 23'6 201 3'29 



Viscosity data 112 162 1-33 2'84 



The disagreement, particularly in the values of S and 

 II(c-), is striking; so far as I know at present similar dis- 

 crepancies occur for other gases besides argon, but the 

 available data are not generally so suitable for a direct 

 comparison. This disagreement is all the more interesting 

 in view of the close agreement between the two values of a 

 (or b) given by Chapman f himself. But the values of b 

 from the compressibility data there given appear to be 

 obtained from critical data, and must in my opinion give 

 way to values calculated from Kamerlingh Onnes' second 

 virial coefficient. 



The discrepancy which thus remains seems to arise from 

 the fact that whereas the theoretical formula for the second 

 virial coefficient B is exact, the formula used for the viscosity 

 is only correct so far as the first power of S/T. The agree- 

 ment of this approximate viscosity theory with experiment 

 is usually regarded as good, at least at ordinary temperatures,, 

 so that an exact formula including further powers of S/T 

 is not likely to improve this fit. It may well, however,, 

 bring the facts of compressibility and viscosity into reasonable 

 agreement — in particular at fairly high temperatures, and 

 so enable a reliable picture to be formed of the range and 

 intensity (under these conditions) of the intermolecular forces. 



* Chapman gives S = TI(cr)/37c in our notation for all power laws. 

 The correction affects only the numerical coefficient which becomes a 

 function of s the power law exponent (James, loc. cit.). 



t Phil. Trans. A, vol. 216. Table VIII. p. 347 (1916). 



