Arizona republican., 1898-03-09
THE USE OF CYANIDE.
Experiments Made at the Colorado
 School of Mines Recently.

In a recent report issued under the auspices of the Colorado school of mines, the following reference is made to the use of cyanide:
 "The cyanide process, while gener- ally applicable to oXidized ore contain ing fine gold, is quite unsuitable to such ores if the gold occurs partly Tn a coarse state, unless the cyanide IS preceded or followed by amalgamat1on- It may also be broadly stated that cop per ores are unsuitable for cyanide treatment, even with dilute solutions. I am aware that the statement has been made that dilute solutions have no effect on copper sulphides. Prac- tical experience, however, does not confirm this statement. Copper invari- ably passes into solution and accumu- lates until it becomes of such strength as to be precipitated on the zinc in the boxes.
 1.-TWO experiences of MT. Skey of New Zealand in this direction are to the point. Chalcopyrite and copper glance were taken by MT. Skey, crush ed, thoroughly washed, and afterward placed in a 0.003 per cent cyanide so- lution for an hour. The solution be- ing tested a perceptible quantity of copper cyanide, traces of sulphur and oxidized sulphur compounds were . found in it. Sulphur of antimony is another objectionable mineral often stated to be quite unaffected by cya- hide solutions, although, as matter of fact, it is quite soluble. It is prob able that in the foregoing copper and antimonial minerals part of the sul- phur combined with the potassium, forming potassium sulphide that may possibly coat the gold with sulphide film, which protects it more or less from the solvent action of the cyanide.
 "In this connection an experiment by MT. Skey is suggestive. He found that a 1 per cent solution of pure cya- hide dissolved a given weight of gold in ten minutes, but on the addition of II, 100000 part of sulphur Gas sul- phide) to 1 per cent solution of cya- hide, it required two hours to dissolve the same weight in gold. While fully admitting the deleterious qualities of alkaline sulphides, I must state that I have not found such minute quanti- ties to be of serious moment in the practical application of the cyanide process. When the sulphur of a solu- ble mineral combines with the cyanO- gen it does not interfere with the solu- tiOn of the gold, and very probably for this reason, galena, though sOlu- ble, is usually quite amenable to cya- hide treatment. Zinc blends and pyr- ties are practically insoluble in cya- hide solutions.
 "In making extraction tests on ores it is important to note that an ab- normal consumption of cyanide is in variably associated with a low ex- traction of precious metals. This con- sumption may be due to free acid in the ore, acid or basic salts, or ores easily soluble in the solution The cause should at once be investigated, and the evil corrected, as far as pos sible, before proceeding with the test. Cyanide of potassium, though a most active chemical, is easily broken up by the acids, base metals and organic matter, forming numerous perplexing compounds, while in contact with the ore changes, and in passing through the precipitation boxeS It is doubtful if the complete chemistry of these changes is fully understood, even by those who have made it a careful study"