Viscosity and Atomic Weight for the Inert Gases. 49 



The Critical Temperature of Neon. 



It is evident that, working backwards, this relation may 

 he used to estimate the critical temperature of neon, upon the 

 assumption that it applies for this gas. In that case the 

 value of 7j c for neon (shown by a cross in the diagram) would 

 be 0*887 x 10 -4 . This, according to Sutherland's equation, 

 would be the viscosity of neon at a temperature of 61°*1 

 absolute. That is to say, the critical temperature of neon is 

 61 0, 1 absolute. 



The author * has already made an estimate of this tempera- 

 ture based upon another relation, namely, that the critical 

 temperature is proportional to Sutherland's constant. This 

 is expressed by the equation 



T=H2C. 



Taking the value C = 56 obtained from the experiments, this 

 gives T c = 62°*7 absolute. The agreement between these two 

 figures 61*1 and 62*7 is remarkable, and constitutes weighty 

 evidence of the probable accuracy of the estimate. 



Application to Radium Emanation. 



It is generally accepted that the emanation from radium 

 belongs to the same group in the periodic table as the gase3 

 previously referred to. There is considerable justification, 

 therefore, for applying the two above-mentioned relations 

 to this case. The fact that the atomic weight and critical 

 temperature of the emanation are now known renders it 

 possible to estimate the viscosity, not only at the critical 

 point, but also at any other temperature, together with the 

 dependent molecular properties. 



The values of the atomic weight and critical temperature 

 used are those obtained by Ramsay and Gray f, viz. A = 222 

 and T c = 377° absolute. 



In the first place, using the relation 



T C =M2 G, 

 we obtain = 337. 



Further, using the second relation 



2- ?; 93 a 



ric ~ 10 10 * 



rj c is found to be 2*954 x 10" 4 . [This is shown by the cross 



marked Em on figure 2.] 



* Proc. Roy. Soc. A, vol. lxxxiv. p. 190. 



t Trans. Cheni. Soc. 1909, p. 1073. Brit. Assoc. Report, Sheffield, 

 1910. 



Phil. Mag. S. 6. Vol. 21. No. 121 Jan, 1911. E 



