These facts prove, I think, that gold is chemically acted upon when in contact with water or neutral saline solutions charged with oxygen and nitrogen gases, and that this action is facilitated by the presence of alkaline substances and especially when these are used hot in place of being used cold. It seems to me there can be little doubt entertained, but that gold thus acted upon has been oxidized, and this either to a sub-oxide, or to the purple oxide of gold.

The gold used in these experiments was prepared as pure as possible. Some I twice precipitated by oxalic acid, from very dilute solutions of its chloride.

Other gold I electro-deposited on platinum from its cyanide. Both samples gave similar results, but that obtained by deposition, yielded them quicker, owing perhaps, to the fact of its being coupled with platinum.

There are two circumstances connected with this subject I should relate, which puzzled me a great deal, as they hardly seem to tally with certain reactions of this metal as now known. They are—first, that proto-sulphate of iron in contact with gold which has been acted upon by alkaline solutions or both does not render it amalgamable; secondly, that sunlight, even direct, does not appear to exercise any influence in the reaction I have described. Possibly, though, the purple oxide of gold may prove on examination to be invulnerable in these respects.

I may further relate that gold in either argentic-nitrate or mercuric-chloride rapidly becomes non-amalgamable, but it is recovered to its former condition by acetic acid, I question whether either of these salts are decomposed here. I further find that pure gold, fused with borax and bisulphate of potash, though very bright, will not amalgamate; the solution of flux was acid. In weak sulphuric acid also, gold passes to this nonamalgamable condition.

These results, however, and the question they raise demand investigation

and I hope soon to be able to accomplish this to an extent which will enable me to throw a clear light upon the subject under consideration. Whatever may be the precise nature, however, of the film thus induced upon gold, and of the reactions which result in the removal or alteration of this film as here described, it is certain that films of this kind must cover the surfaces of a portion of our native gold, and thus retard to a more or less extent, its complete amalgamation when milled.

Thus what with the tendency of this metal to enfilm in presence of common water or alkaline solutions in the manner described, and its tendency to become sulphuretted when in contact with soluble sulphides, there can be but little doubt entertained that most of the natural surfaces of native gold are varnished as it were, with auriferous compounds, and these have to be decomposed by mercury ere amalgamation can proceed, except we use in conjunction with this metal a substance capable of decomposing such films, or else remove them mechanically, as is at present largely accomplished in the stamper boxes.

With reference to mercury, the results I have as yet been able to get, do not point so distinctly to its oxidation by oxygen in presence of water, as those described above do to that of gold. Its mobility at the temperature I have to operate under, stands in the way of my observing indications of any superficial change I may have induced upon it in my experiments. Theoretically it would on first thought appear, that if gold or silver does oxidize, as I affirm, under the above circumstances, mercury should also oxidize under them, as it is certainly positive to both these metals in acid generally. It must be considered, however, in connection with this matter, that gold and silver at their fusing points are in a condition unfavourable to their oxidation, and so mercury (a metal which naturally classes with these), being used in my experiments at a temperature far above its fusing point, may for this reason be less readily oxidizable under the circumstances stated than either of the above metals in their solid state. It appears to me that we should take into consideration here, not only the temperature we are operating under, but the different physical conditions of mercury as compared with that of the above metals at this temperature.

The only results I have yet obtained as to the oxidation of mercury, or otherwise under these circumstances seems to show that it is so oxidized. Thus I find that electric currents of some strength are generated by it in water containing a little sodic chloride; also in aqueous solution of caustic or carbonated alkali; as the only conceivable effect of the salts named is to conduct the electricity thus generated and so render it detectable, I conclude that the action upon mercury which these currents indicate is not originated by such salts, but by the oxidation of this metal.