520 Mr. W. Sutherland on the Viscosity 



that for the elements which have an unchanging virial con- 

 stant; thus we get the numbers 



25 17 19 



in agreement with the previous series of ratios. The fact 



that here CH 4 behaves as an element gas is noteworthy. 



Exact values of /3 are at present lacking for other gases, but 



sufficiently exact ones for the present comparison can be got 



by reducing the volume of a gramme of the gas when liquefied 



at its boiling-point under one atmo in the ratio *64, and thus 



we ffet: — 



Cl 2 . HC1. H 2 S. C 2 N 2 . 



(3 -48 -75 -70 -73 



M 70-8 36-4 34-0 520 



M/3 33-6 271 23-9 38-2 



(2a) 2 (relative) 259 224 206 282 



10 6 7? o 129 138 115 95 



C 410 256 395 461 



With these values we get : — 



Cl 2 . HC1. H 2 S. C 2 N 2 . 



M/3C/10 1377 695 944 1762 



M.H 5-8 7'9 10-5 17-7 



M(3C/10 2 M.H 24-0 8-8 9-0 100 



Here, again, the ratio for the element chlorine is about what 

 it ought to be, while for the compounds it is about half of 

 what it is for elements ; doubling its value for compounds we 

 get the values 24, 17, 20, which again harmonize with the 

 previous values, the complete series being 



31 20 21 24 17 25 25 17 19 24 17 18 20: Mean 21. 



Thus of the available data there is not one at variance with 

 the theory, while the distinction between the elements with 

 methane on the one hand and compounds on the other, which 

 was drawn in the study of characteristic equations, is borne 

 out here. In the paper on the " Laws of Molecular Force " 

 it was suggested that the difference in characteristic equa- 

 tions between compounds and elements is due to molecular 

 pairing in compounds, all the molecules being in pairs in the 

 liquid state, but in the gaseous state only a certain portion 

 of them depending on the volume occupied. Now in con- 

 sidering viscosity we seem to have taken no account of such 

 a -nbenomenon as that of pairing, but we have found that the 



