and Two New Types of Viscosity. 17 



and OH ions ionize H 2 to a large extent, whence the 

 apparently exceptional large ionic velocities hitherto assigned 

 to them. Hence we exclude these as two known marked 

 exceptions, and for the remaining 21 ions on Kohlrausch/s 

 list find an average value O0233 for a. Thus in (19) 



a - 7 = O0233-O0251= -0-0018, 



and the coefficient of 6 2 is almost 0. Thus we have the 

 simple average result 



A^o-isAo^ojl- 0-0018(^-18)} 

 implying 



^ ^ =i8\ isn {l-0-0018(£-18)}. . . (20) 



This shows that Ao^o departs from constancy over the range 

 of temperature from 0° to 36° only through the small tem- 

 perature coefficient whose average value for the ions is 0*0018. 

 This coefficient arises from the variation with temperature of 

 the sum of the two viscosity terms on the right-hand side of 

 (12). The average value of a—y just discussed is supple- 

 mented in the following table by its value for typical ions 

 obtained by subtracting KohlrausclYs a. from 0*0251. The 

 values of A are also given. 



R CI. Br. I. Li. Na. 



10 4 (y-«) 19 36 36 45 -10 6 



A 45-5 65-4 67*6 66-4 33-4 43-5 



K Rb. Cs. Mg. Sr. Ba. 



10 4 (y-a) 31 34 39 -4 20 12 



A 64-7 679 68-2 46 53 57 



It appears that y — a tends, on the whole, to increase with 

 increasing A. By the study of this coefficient it will yet be 

 possible to penetrate still farther into the mechanism of 

 molecular viscosity. We must now turn to the experiments 

 of Noyes and Coolidge, valuable on account of their wide 

 temperature range. 



For the viscosity of water above 100° the data of de Haas 

 reach to 160°. Beyond that point I must extrapolate to get 

 approximate viscosities of water at the higher temperatures 

 used by Noyes and Coolidge. The following is one formula 

 which gives the general trend of variation from 0° to 160°, 

 namely : 



l/ Vo = 56 + 3-25*. 



This gives a value at 100° which is 8 per cent, in error ; 

 nevertheless it gives the trend of change over 160° in a way 

 Phil Mag. S. 6. Vol. 14. No. 79. July 1907, C 



