﻿644 Dr. G. von Hevesy on the 



solution. This process is demonstrated very clearly by the 

 methods described in this paper, and some results will be 

 given here, though a complete account is reserved for a 

 subsequent communication. If a copper plate be dipped in 

 water containing radium B and radium C in equilibrium for 

 0*2 sec, the mixture of B and C obtained on it contains more 

 than 85 per cent, of B, and corresponds, therefore, to an 

 E.M.F. of 2 volts measured against the calomel electrode. The 

 electronegative metals, therefore, really commence to decom- 

 pose water immediately after being dipped in it. If measure- 

 ments of this process be observed for periods longer than a 

 few seconds, the results are less concordant than those 

 obtained with short exposures, and depend somewhat on the 

 gases surrounding the plate (air, hydrogen, &c). Here, 

 also, oxidation of the copper, and solution of the oxide 

 formed, play no inconsiderable part, processes which in the 

 case of mercury have been investigated thoroughly by 

 Warburg. However, the production of positive ions in the 

 water seems always to take place much more rapidly than 

 the second process of oxidation and solution of the oxide, 

 and by working rapidly this second process may be entirely 

 obviated. 



10. The Electrochemical behaviour of Thorium C and the 

 branching in the Thorium Series. 



A consideration of the curves of figs. 4 and 5 shows at 

 once that radium can be separated in a much purer form 

 by the method * described in this paper than either thorium C 

 or actinium C. This can be explained as being due to small 

 differences in the electrochemical properties of the three C's, 

 or may be explained as follows :■- — 



When radium B and C are present in equilibrium amounts, 

 it follows from their periods that for every radium C mole- 

 cule present there are 1*4 molecules of radium B. In the 

 case of thorium B and C, this ratio is 10 - 6, and consequently 

 the probability that some B will separate out with the C is 

 much greater. In the case of actinium B and C, however, 

 although the ratio of B molecules to C molecules is higher 



* The method used by v. Lerch proves this also, for Fajans {Phys. 

 Zeit. xii. p. 370 (1911)) using this method was able to obtain radium C 

 containing- less than O05 per cent, of radium B. From v. Lerch's work 

 on thorium C ( Wien. Ber. cxvi. p. 6 (1907), however, it is found that the 

 period of thorium C prepared by deposition on nickel is about 0'75 min. 

 too high, on account of the presence of a little thorium B. This amount 

 can be readily calculated from the data supplied, and is 1 per cent, of 

 the equilibrium quantity of thorium B. 



