﻿Electrochemistry of Radioactive Bodies. 633 



is of great value in the investigation of a very short-lived 

 body such as radium A, for electrolysis may be begun as soon 

 as the sodium commences to dissolve. 



The volume of liquid used in the experiments to be 

 described was always 8 c.cm. The surface of the electrode 

 was 2*5 sq. cm., and one side was coated with enamel. The 

 electrode was always rotated evenly in the liquid for a definite 

 interval. The time of immersion was four minutes in the 

 experiments on the radium and thorium active deposits, and 

 two minutes for those on the actinium deposit. When this 

 time had expired, the electrode was immediately washed with 

 distilled water, dried with filter-paper and inserted in the 

 a-ray electroscope, and its change of activity measured for a 

 considerable time. In all the experiments activity was mea- 

 sured by a-rays only. The absolute amount of RaC in the 

 solutions used varied between 



8 . 10~ 16 and I . 10 ~ 16 gr. per c.cm. of solution, and of ThC, 



1 . 10~ 16 and 05 . 10~ 16 gr. per c.cm. of solution. 



These figures are obtained by calibrating the electroscope 

 with a U3OS film emitting a known number of a particles* 

 For the film I am indebted to Dr* H. Geiger. The calcu- 

 lations involve the known periods of thorium, radium, 

 radium C, and thorium C, the number of a particles emitted 

 by these elements (Rutherford and Geiger), and the ranges 

 of the cc particles of uranium, radium C, and of thorium C* 

 If, in addition, the branching in the thorium series be taken 

 into account, the concentration of thorium C becomes three 

 times less. (Cf. paragraph 10*) 



3. The Ratio of the amount of B product to C in the Radium, 

 the Thorium, and the Actinium Series, as Functions of the 

 Electrode Potential. 



With a positive potential like that of silver the deposit 

 on the electrode is practically pure C« If we proceed from 

 silver to zinc, the potentials becoming less and less positive, 

 the ratio of the amount of C to that of B separated out 

 diminishes continuously, until when negative potentials are 

 reached B is deposited in excess of C. This is shown by the 

 curves obtained. As the potentials become less positive, 

 the curves which at first are decay- curves of gradually 

 become less steep, until a potential is reached at which B 

 and C separate out in equilibrium amount. With more 

 negative potentials the curves become rise-curves, owing to 

 the excess of B over C. 



