Notes on Gold-Silver Alloys. 



149 



In the case of the -1 per cent, solution of chlorine the action 

 was so slow that in 304 hours only from 4-85 to 15-89 per cent, 

 of the metals was dissolved. 



Since it requires 130 parts of potassium cyanide and 106-5 

 of chlorine to dissolve gold and keep it in solution, then a -2 

 per cent, solution of chlorine should be almost equivalent to 

 •25 per cent, of potassium cyanide ; these proportions closely 

 approach the strength of solutions used in practice, e.^-., in 

 modifications of Munktell process, such as used at Maldon and 

 Cassilis, the amount of chlorine used being from 2 to 4 ozs. to 

 the cubic foot of water, while the ordinary practice in cyanide 

 operations is to use -1 to -4 per cent, solutions. 



On testing certain roasted ores by both processes, it was found 

 that by using a -25 per cent, solution of cyanide of potassium and 

 a -2 per cent, solution of chlorine, that almost an equal quantity 

 of gold was dissolved in 72 hours, the slight difference being in 

 favour of the chlorine. With badly roasted ores, such as have 

 been roasted at a low temperature, also those containing large 

 quantities of arseniates, it is not possible to dissolve a high 

 proportion of the gold present either with excess of a saturated 

 solution of chloi'ine or with potassium cyanide solutions, but 

 with ores which have been properly roasted, and in which the 

 gold is fine, it will be found that an ordinary solution of cyanide 

 will act as well as chlorine, and with the additional advantage 

 that the silver alloyed with the gold will be dissolved and may 

 be recovered also. 



Table showing the Solubility of Gold-Silver Alloys. 



Solvent — -25 per cent. Potassium Cyanide Solution — Circulating. 



