﻿630 Dr. G. von Hevesy on the 



is connected with the series of potentials of ordinary metals 

 by a knowledge of the potential of radium, for this body can 

 obviously be investigated either as a radioactive body or as 

 a purely chemical substance. 



In this paper the influence of the electrode potential on 

 the electrolytic separation of the active deposits of radium, 

 thorium > and actinium is discussed* 



2. The Function of the Electrode Potential. 



Various electrode potentials can be obtained by dipping in 

 the solution under examination a pair of electrodes not acted 

 on by the liquid) and applying varying E.M.F.'s* By this 

 method, however, it is difficult to obtain definite EtM.F/s, on 

 account of the conductivity of the solution and its change 

 with polarization at the electrode. For this reason, another 

 method was used in which the electrolysis was carried out, 

 not by applying a difference of potential between the 

 electrodes, but simply by dipping the metal into a solution 

 of one of its salts containing the radioactive body under 

 investigation. 



For instance, the action of zinc on the active deposit of 

 radium was investigated by dipping a zinc plate into a 

 solution of zinc sulphate containing radium B and radium C. 

 This is analogous to producing the deposition of copper on an 

 iron plate by dipping it into a solution of FeS04 and O11SO4. 

 In the latter case, however, the potential difference Fe/FeSO-t 

 gradually falls to that ot Cu/CuSCh, owing to the increasing- 

 deposition of copper on the iron plate. On the other hand, 

 however, the deposition of about 10" 17 grin, of RaC cannot 

 influence the potential difference Zn/ZnSO*, the zinc acting 

 electrochemically throughout as pure zinc. 



The potential differences used are summarized in the table 

 that follows. Their values are taken from the latest work on 

 galvanic cells*. 



All electrolytes may be used in this work with the exception 

 of acids and of solutions of such bodies as the salts of zinc and 

 bismuth, which tend to become turbid. The former class are 

 not suitable for use, owing to their action on the matter 

 deposited on the electrode ; while in a turbid solution the 

 radioactive bodies are apt to be precipitated. 



The values of the single potential differences measured 

 against the normal calomel electrode are given in the 

 following table : — 



* " Messungen electron] otoiischer Krafte," Abhandlunyen der Bunscn 

 GeseUschaft, n.' 5 (1911). 



