88 ADVENTURES IN RADIOISOTOPE RESEARCH 



Comment ok paper 6 



As shown by Nernst the electrode potential of a metal is proportional to the 

 logarithm of the concentration of its ions present in the suri'ounding solution. 

 The validity of this regularity was tested up to 0.0001 N ionic concentration. 

 The application of labelled bismuth and labelled lead permitted us to demonstrate 

 the validity of this regularity at much lower ionic concentrations than the above 

 mentioned one. When this investigation was carried out in 1913 the notion of 

 isotopes had just emerged, and it was thus of interest to demonstrate that the 

 voltage at which RaE, for example, is precipitated on the cathode, is influenced 

 by the addition of a bismuth salt to an extent to be expected on assuming the 

 practical chemical identity of bismuth and RaE. It is not, however, influenced 

 by adding salts of other metals. Below its decomposition voltage minute traces 

 of RaE aie deposited as well, this minute precipitation is also influenced by 

 addition of bismuth salts, but not by addition of salts of other metals. 



The large amount of radon available at the Vienna Institute made it possible 

 lo obtain a visible RaD layer on a platinum wire. The electrode potential of a 

 RtiDOj electrode was found, measured against a calomel electrode undistinguishable 

 from the potential of a lead peroxyde electrode. The experiments were carried 

 out with peroxide of lead instead of metallic lead, as the electrode potential of 

 metallic lead was found not to be sufficiently reproduceable. 



If it weie possible to measure these electrode potentials to an accuracy of 

 several decimals, we would piesumably measure some diffeience between the 

 electrode potential of lead peroxide and ladium D peroxide, as isotopes are not 

 strictly identical in their chemical properties. The very far-reaching practical 

 chemical identity of isotopes of an element is, however, conspicuously demon- 

 strated by the lesults of this paper. 



