Maclaukin. — Action of Potassiuvi-Gyanidc upon Gold. 695 



Art. LXXIII. — On the Action of Potassium-Cyanide Solution 



upon Gold. 



Bv J. S. Maclaukin, B.Sc. 



[Read before the Aucldand Institute, 34th February, 1896.] 



In the Journal of the Chemical Society (Trans., 1893, pp. 

 724-738, and Trans., 1895, pp. 199-212) two papers on the 

 action of cyanide upon gold have been published. These 

 papers contain an explanation of the peculiar action of dilute 

 solutions of potassium cyanide, and a record of a number of 

 experiments which, I think, prove conclusively that this 

 explanation is correct and sufficient. So far as I am aware, 

 the statements contained in these papers have passed un- 

 challenged in Europe. In New Zealand, however, Mr. Skey 

 has published" some experiments from which he concluded 

 that no satisfactory explanation had been given of the action 

 of cyanide on gold. As such a statement is likely to mislead 

 those who have not had an opportunity of reading the original 

 papers on the subject, I shall briefly outline my work already 

 referred to, and shall then consider Mr. Skey's views. 



The knowledge of the subject when I began my researches 

 was as follows : Gold was known to be soluble in potassium- 

 cyanide solutions, but the nature of the action was disputed. 

 Most of the text-books referred back to Eisner (J. Pr. Chem., 

 37, 333) and credited hmi with the explanation embodied in 

 the following equation : — 



4Au + 8KCN + O, + 20H., - 4AuCNKCN + 4K0H. 



On the other hand, Macarthur (patentee of the cyanide pro- 

 cess), in a paper read before the Society of Chemical Industry, 

 (Journal, 1890, p. 270), called in question the necessity of 

 oxygen. 



In the extraction of gold from its ores it was known that 

 dilute solutions of potassium cyanide acted more satisfactorily 

 than concentrated ones. Moreover, L. Janin had noticed that 

 silver is more soluble in dilute than in concentrated solutions. 

 No satisfactory explanation w^as, however, given. 



It seemed, therefore, that an answer was required to the 

 following questions : — 



1. Is oxygen necessary for the solution of gold in potassium- 

 cyanide solutions? 



* Mines Report, 1895, pp. 186-189. 



