bo 
Or 
ON SOME IMPORTANT REACTIONS OF DOUBLE 
CYANIDES BEARING UPON THE CYANIDE 
PROCESS FOR THE EXTRACTION OF GOLD. 
By G. A. GoyDEr. 
[Read December 3, 1894. 
While endeavoring to find an accurate process for the quanti- 
tative determination of simple cyanide of potassium in solutions 
containing also double cyanides, such as the sump liquors obtain- 
ing in the McArthur-Forrest process for extracting gold, I found 
that cyanide of potassium was alkaline to phenol phthalein, and 
that the quantity of alkaline cyanide present could be accurately 
determined, in the absence of caustic alkalies and alkaline car- 
bonates, by titrating with acid, using phenol phthalein as 
indicator. The presence of bicarbonates makes the end reaction 
more uncertain, but by adopting special precautions accurate 
results may still be obtained. The double salt zinc potassium 
cyanide is quite neutral to phenol phthalein. I am further 
investigating this reaction with the object mentioned above. 
It appears to be generally believed that such double salts as 
zinc potassium cyanide in aqueous solution have no solvent action 
on gold. JI have, however, found by experiment that this double 
cyanide readily dissolves gold, although the action is slower than 
that of the simple alkaline cyanides. When a solution of zinc 
potassium cyanide is shaken with gold-leaf in the presence of 
oxygen, or air, the gold is dissolved, forming gold potassium 
cyanide, while zinc is deposited as oxide. A secondary reaction 
also takes place, involving the formation of the auricyanides of 
zine and of potassium, the former of which appears to be in- 
soluble, and of zincate of potash. Copper potassium cyanide 
also dissolves gold, although the action is still slower than that 
of the zine double salt. It is hardly necessary to point out that 
the above reactions may be of considerable importance in the 
McArthur-Forrest process. 
In order to determine the total cyanogen in sump liquors I 
have devised the following modification of Rose & Finkener’s 
process :—A measured quantity of the liquor is heated on the 
water bath, or gently boiled, for 20 minutes with excess of oxide 
of mercury with occasional agitation, filtered and washed. To 
the filtrate about one gram. of caustic soda is added and excess 
