( 32 ) 

 estimated by means of the formula of Helmholtz ') 



2ü„ V 



f/+ V 



I — 



Here po means the osmotic pressure for a concentration of 1 gram-ion 

 per cM^., « the charge of a gram-ion in electromagnetic units. 



We take a definite case for this estimation, namely a solution of 

 sulphate of copper with the concentration r^ =z 3.10—5 , the lowest 

 value we find among the numbers of Kohlrausch ") for this salt. 

 We shall suppose that, in this case, applies the formula for com- 

 pletely dissociated solutions. 



t/= 218.10-1+ r=373.10-w 



so — (C/-F)= 155.10-1*. Taking E^=l volt or IQSC. G.S., 

 H=10\ we find £. = 0,78. 



This is the difference in C. G. S. units between two points on the 

 axis of Z, 1 cM. apart. 



The difference of concentration is determined by 



Comparing our for/uula for the velocity of diffusion with that of 



Po 



J 



Nernst"'), it appears that A=z—-^ where — ^. force required to 



J U u 



move a gram-ion, with migration-velocity it, with the velocity of 



1 cM. per second through the solution. 



Co / dc^\ dc-, 



l± — l[\J^ -1)^-1— . . . . 



We retain only the first term, so 



Co U-\- V 



2A 



') Wied. Ann. 3. p. 201, 1878. In this form the forinulii, is given by Nernst, Zeitschr. 

 f. ph. Chem. 4, p. 129, 1889. 

 2) Wied. Ann. 50, p. 404. 1893. 

 ^) Zeitschr. f. ph. Chem. 2, p. 619, 1888. 



