﻿042 Dr. G. von Heresy on the 



There is still another explanation possible, and that is to 

 assume that in solution, in addition to the ions of B and of Q 

 which react Avith those of the immersed metal, there are also 

 free ions present, which are drawn in to the double layers at 

 the boundary of the metal and the solution. Free ions nre 

 such as can be separated from corresponding ions by diffu- 

 sion. They are always present in electrolytes, but only to a 

 very small extent ; they differ quantitatively from colloidal 

 particles only by their large value of ejm. This view 

 receives some support from the experiments carried out on 

 non-metals. If such bodies as glass, quartz, sulphur, &c, be 

 dipped in an active solution, a mixture of B and C, con- 

 taining chiefly C, is deposited on them though to a very 

 much smaller extent than on metals. 



That the smallest double layer which is always present at 

 the surface of separation of two different phases is sufficient 

 to produce deposition of a portion of the active matter on 

 the solid phases, is shown very well by the behaviour of 

 radium F ; for radium F is not only extraordinarily easily 

 deposited on a surface but is also extremely difficult to be 

 removed from it. 



To decide between these various explanations experiments 

 have been commenced on the migration and the diffusion of 

 the radioactive ions. When they are finished it is hoped 

 that results bearing on the valency and the sign of the ions 

 will be obtained. 



8. Determination of the Potential Difference between Metal and 

 Electrolyte from the Electrochemical action of the former 

 on radioactive substances. 



It has been shown that the ratio in which the B and C 

 products of radium, of thorium, or of actinium, are deposited 

 on metals immersed in solutions containing them, or on 

 platinum electrodes in the ordinary course of electrolysis, 

 is a function of the potential difference between metal and 

 electrolyte. Conversely, from a knowledge of this relation- 

 ship given by the results of figs. 4 and 5, the single potential 

 difference Metal/Electrolyte can be obtained from the ratio 

 of B to C in the active matter deposited on the metal. This 

 method is especially valuable when it is necessary to deter- 

 mine this potential difference as rapidly as possible. 



If actinium B and C be used as indicator, only a few 

 a-ray measurements of the activity of the plate need be 

 made, and after a few minutes an accurate value of the 

 potential difference under investigation is obtained. 



