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LII. The Electrochemistry of Radioactive Bodies. 

 By Georg von Hevesy, Ph.D.* 



1. Introduction. 



IT is well known that all metals when immersed in a liquid 

 possess a tendency to go into solution. Each has a 

 certain definite solution-tension, just as each liquid possesses 

 a certain vapour-pressure. On these two conceptions Nernst 

 has founded his theory of the origin of the electric current in 

 a galvanic cell. Only in special cases, namely, with the very 

 positive metals, is it possible to demonstrate experimentally 

 the solution of a metal in water, because the excessively small 

 amount of ions which the less positive metals produce in 

 solution soon produces a sufficiently great osmotic pressure 

 to prevent further solution of the metal. 



The amount of some radioactive bodies necessary for 

 detection is extraordinarily small compared with that of an 

 ordinary chemical substance, and it is therefore to be expected 

 that when a radioactive element is immersed in water, or in 

 an aqueous solution, the ions thereby produced are capable of 

 detection by these activities. Electrolytic decomposition of 

 salt solutions, and the solution of the metals causing it, always 

 accompanying each other, the smallest E.M.F. between two 

 electrodes suffices to produce some decomposition of the salt, 

 yet, as a rule, the solution-tension of the infinitely small 

 amount of metal deposited on the electrode is sufficient to 

 hinder further decomposition. 



Continuous decomposition of a salt solution takes place 

 only after a certain E.M.F. has been attained, viz. the 

 decomposition voltage. This is the fundamental idea of 

 Le Blanc's theory of decomposition. With solutions of radio- 

 active bodies, however, it is to be expected that electrolytic 

 dissociation is capable of being detected when the E.M.F. is 

 less than the decomposition voltage. 



The electrochemistry of radioactive bodies is thus not 

 confined, as the electrochemistry of non-radioactive bodies is, 

 to E.M.F/s exceeding the decomposition voltage, but may 

 deal with quantities of substances which are separated out by 

 residual currents. 



On the other hand, it must not be concluded in the case of 

 radioactive bodies that because detectable amounts have been 

 deposited by electrolysis on the electrode, therefore the 



* Communicated bv Prof. E. Rutherford, F.R.S. 



