Skey.— On the Oxidation of Gold. 383 



it is (as I publicly asserted sixteen years ago) oxidized a,s 

 iron is in the presence of air and water ; for the only conceiv- 

 able 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 Eisner," 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 aeration 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 aerated, it may be assumed about 2gr. of oxygen 

 is present to the gallon. This is competent to oxidize ldwt. 

 of gold to the mono-oxide. We do not yet know really the 

 formula of the oxide formed, but I assume it does not con- 

 tain 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 ac- 

 curacy 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 lgr. of gold in nitro- muriatic acid, and dilute to 

 10 fluid-ounces. Immerse in this a piece of dry Swedish filter- 

 paper that has been just previously well washed in water. 

 Take the paper out and let it drain till no further dripping 



* Watt's Dictionary of Chemistry, vol. ii., p. 213. 



