The relative weights of gold and silver dissolved by potassium cyanide solutions from alloys of these metals.

By J. S. Maclaurin, B.Sc., University College, Auckland, New Zealand.

In the extraction, by means of potassium cyanide solutions, of gold and silver from ores containing them, it is found that the percentage of gold recovered is almost always larger than the percentage of silver. This fact must be due to one or both of two causes; 1st, in an alloy of gold and silver the gold is more readily dissolved than the silver, or, 2nd, gold generally exists in the metallic state, whilst silver is often combined with sulphur, tellurium, &c., forming compounds which are only slowly dissolved by the cyanide. In order to test the first of these hypotheses, alloys of gold and silver of varying composition were prepared, and, after being rolled into sheets, circular plates were stamped out of them. These plates were then exposed, fa Nessler test-glasses, to the action of a 0.5 per cent, solution of potassium cyanide for two hours. The cyanide solutions were evaporated to dryness, and the bullion and gold determined by ordinaryassay methods.

The results are contained in the following table.

These results show that, practically, gold and silver are [unclear: dissolvel] from an alloy of these metals in the proportions (by weight) in [unclear: which] they exist in the alloy. At first sight this appears to be in direct opposition to my results on the rate of solution of the two [unclear: metals] when separate (Trans., 1895, 67,199), as it was then shown that "the ratio of the amount of gold dissolved by any given cyanide [unclear: solution] to that of the silver dissolved by the same solution is nearly in this ratio of their atomic weights," or, in other words, for every 197 part of gold dissolved only 108 of silver pass into solution. In an alloy [unclear: of] the two metals, let A represent the weight of gold, and B the [unclear: weight] of silver, then the relative areas of the metals exposed to the [unclear: cyanide] will be gold = A/sp. gr. of Au = A/19.3, silver = B/sp. gr. of [unclear: Ag]= B/10.45^*