576 



MR. F. E. SMITH, MR. T. MATHER, AND DR. T. M. LOWRY 



contact with the kathode surface there are columns of liquid of low concentration, and 

 in between these the electrolyte is of approximately normal concentration. The latter 

 has the higher conductivity, and since in addition there is an E.M.F. acting from the 

 columns of low concentration towards the main body of the electrolyte, the current 

 will pass into the kathode through the liquid in between the columns. Immediately 

 the concentration falls and possibly the resultant liquid of small density is pulled into 

 the columns of low concentration. If our assumptions are correct, an increase in the 

 current should result in the kathode film becoming thicker and more stable, and when 

 it is sufficiently stable to remain as a film a striated deposit should not be formed. 

 This was tested by experiment and found to be so. 



The following table indicates the results. All the solutions were pure, and the 

 same volume of electrolyte (350 cub. centims.) was taken in each case. 



It appears that for solutions of all concentrations striated deposits are obtained for 

 small current densities at the kathode, and matt deposits for very large current 

 densities. 



We may now compare the changes in the Rayleigh and Richards forms of 

 voltameter. In the latter case there is no descending anode liquid, and there will be, 

 therefore, less tendency for a star-like deposit to be formed on the base of the bowl. 

 In our own form of RICHARDS' voltameter the volume of kathode liquid was in general 

 about 250 cub. centims., and during electrolysis the mean concentration of the 

 solution must have diminished from 15 to 10'6 per cent. The mean concentration of 

 the electrolyte in the Rayleigh form remains constant and, in consequence, for the 

 same current density striae were produced in the Rayleigh form when they were 

 absent in the Richards form. This effect has also been observed by GUTHE* and by 

 VAN DlJKf. In the Richards form, as employed by the latter observer, the kathode 



* GUTHE, 'Phys. Rev.,' 19, p. 147, 1904. 



t VAX DIJK, 'Ann. der Phys.,' 19, p. 271, 1906. 



