renders this oxidized gold amalgamable may be explained in the same way; while the inability of sulphuric acid, or the iron-sulphate, to render gold amalgamable leads me to suppose that a basic sulphate of gold forms on the metal when these substances are used, and that this sulphate is not, or at least is not readily, decomposed by the mercury, so the amalgamation of the gold is much delayed or altogether impeded. This explanation of the anomaly referred to seems feasible to anyone who will compare this behaviour of gold with that of silver under much the same circumstances. This metal (silver) becomes rapidly non-amalgamable in distilled water, and, like gold that has been in the same water, becomes easily amalgamable by contact with hydrochloric acid or a chloride, and this solely, as we know, by a changing of the oxide or carbonate of silver that has formed in the distilled water into a chloride, which salt is rapidly decomposed by mercury, and so amalgamation readily proceeds.

This appears to me a satisfactory explanation of the anomaly described in my former paper, supposing that, as I allege, the refusal of gold that has had contact with air and water to amalgamate is really owing to its having been superficially oxidized therein; and that this is so I am now enabled, by the use of my gold-test papers, to demonstrate beyond all doubt.

Now, as every chemist and photographer knows, most of or all the compounds of gold with the other elements except sulphur and its congeners are soluble in hyposulphite of soda. This salt, therefore, in conjunction with air and water, should dissolve (metallic) gold—that is, it should (if the gold is oxidized under these circumstances) dissolve the oxide or carbonate of gold formed thereon, and so ultimately take up the whole of the gold present in my test-paper within a reasonable time.

Acting on this supposition I tried the experiment, and found that if only the “hypo.” is prevented from breaking up into sulphide compounds the gold is all quite removed from the paper in a few hours by the hypo. If we use the hyposulphite alone there is no certainty of result, as it is so easily decomposed to form a salt (sodic sulphide) that produces sulphide of gold, a compound not soluble in the hypo. By putting a little potash in the hypo. this decomposition is prevented and the gold is always completely removed. It was afterwards found that ammonia even has a solvent effect upon metallic gold, but its action is considerably slower than that of the hypo. Potash alone, it may be stated, did not show any solvent power upon gold.

That gold is, as shown above, soluble in hyposulphite of soda, also in aqueous ammonia, proves beyond all doubt that

it is (as I publicly asserted sixteen years ago) oxidized as iron is in the presence of air and water; for the only conceivable effect of either of these reagents (hypo. and ammonia) is to dissolve the auric compounds that can and do form upon the gold independently of their presence. As regards the solvent effect of potassic cyanide upon gold, this salt also only acts upon the gold that has been oxidized by air and water. This oxide or its carbonate it removes, and so exposes fresh gold-surfaces to be oxidized by air-water. It should be stated here, in justice to Elsner,^* that before my first paper on this subject was read here this chemist proved oxygen is necessary to the continued action of potassic cyanide upon gold; but he did not venture any statement as to the mode in which this gas acted in the process of solution.

These results have a practical value in relation to Cassell's cyanide process when applied to free gold, for in this state the metal has to be oxidized by the oxygen contained in the water before it can be taken up by the cyanide; hence we may properly conclude that stirring the solutions, free access to air, and even the aëration of the cyanide-solution would greatly assist the process of gold-extraction by the use of this salt. Any way, all depends very much on the free supply of oxygen in the solution; consequently, the nature of the water used has to be considered. In ordinary river-water, which is generally well aërated, it may be assumed about 2gr. of oxygen is present to the gallon. This is competent to oxidize 1dwt. of gold to the mono-oxide. We do not yet know really the formula of the oxide formed, but I assume it does not contain a greater proportion of oxygen than this compound does. This seems an ample supply of itself, leaving out the oxygen that enters the water as the process is going on; but much depends upon the rate at which this gas (oxygen) diffuses itself in water—a matter which I think chemists do not as yet know much about. Any way, a brisk circulation of the cyanide-solutions as applied upon free gold must prove beneficial, because it materially helps in bringing oxygen in contact with the gold that it is required to extract.

For the convenience of any one desirous of testing the accuracy of my statements regarding the solvent powers of hypo. and ammonia upon gold in contact with air and water, I give an easy method for preparing a delicate test-paper of regular composition.

Dissolve 1gr. of gold in nitr-muriatic acid, and dilute to 10 fluid-ounces. Immerse in this a piece of dry Swedish filterpaper that has been just previously well washed in water. Take the paper out and let it drain till no further dripping