ACCURATE MEASUREMENT OF IONIC VELOCITIES, ETC. 



463 



10 th normal solutions at 18 and 25, but also in 50 th normal solutions at 18. In the 

 same way the mobilities of the chlorine ion in equimolecular solutions of different salts 

 have been gathered together in Table VI. In this case, also, the same mobility 



TABLE VI. Velocity of Cl ion in various Salt Solutions. 



occurs in solutions of potassium and sodium chlorides, and similarly for the hydrogen 

 mobilities which are given in Table VII. 



These results indicate that the direct measurement of the actual ionic mobility 

 gives us a means of comparing the degree of ionic dissociation of equimolecular 



TABLE VII. Velocity of H ion in various Acids. 



solutions of salts containing a common ion. If we assume that in dilute solutions v, 

 or the specific mobility of a given ion, is invariable in different salt solutions, then, 

 since U = av, a is proportional to U. Table VIII. contains a comparison on this 

 basis of the degrees of dissociation of all the salts containing one ion in common that 

 have been measured by us. The figures are given as the ratio of the degree of 

 dissociation of the salt to that of potassium chloride, which has been taken as 

 standard, and the same ratio has been calculated from the conductivity data, and the 

 results are given for comparison in the third and fifth columns of the table. 



From the very satisfactory agreement of the results obtained by the present 

 method with the corresponding numbers given by KOHLRAUSCH, it is evident that a 

 considerable degree of accuracy in the direct measurement of ionic velocities has been 

 attained. It is interesting to look over HITTORF'S early transport numbers, amongst 

 which deviations of 5 and 10 per cent, are frequently met with. 



The numbers subsequently obtained were much more concordant, but the method, 

 as already stated, is difficult and laborious, and only rarely can an experiment be 



