Maclaurin. — Action of Potassinvi- Cyanide upon Gold. 697 



Table I. 



These results show that the rate of solution of gold in 

 potassium-cyanide solutions gradually increases as the con- 

 centration of the solution decreases, reaches a maximum at 

 0-25-per-cent. solution, and then decreases continuously. Pre- 

 cisely similar results were obtained with silver. In seeking 

 for an explanation of this remarkable variation in the solu- 

 bility of gold in potassium-cyanide solutions I was led to 

 investigate the solubility of oxygen in such solutions, and 

 obtained the following results : — 



These results show that the solubility of oxygen in cyanide 

 solutions decreases rapidly as the concentration increases, a 

 50-per-cent. solution dissolving little more than one-tenth of 

 the amount of oxygen absorbed by pure water. It will be 

 seen from the table already given that the amount of gold 

 dissolved by a 50-per-cent. solution is about one-thirteenth of 

 that dissolved by a solution containmg 0-25 per cent. It is 

 therefore evident that the rate of solution of gold in these two 

 solutions is almost proportional to the amount of oxygen con- 

 tained in each. In Table IV. the relations of the gold to the 

 oxygen are shown under the heading Au/0 (found). On con- 

 sidering these it is evident that the solubility of the gold is 

 dependent upon that of oxygen, but that something else inter- 

 feres with the action. For, if the amount of gold dissolved 

 depended solely on the amount of oxygen in solution, the 

 values for Au/0 should be constant ; but in the results found 



