W. Skey. — Desilverinrj of Argentiferous Gold. 47 



destroyed. tSimilar disasters occurred at Waitangi, aud great loss was 

 occasioned. 



Aet. V. — On a iieio Mode for the direct Desilvering of Argentiferous Gold. 



By "William Sket, Analytical Chemist to the G-eological Survey of 



New Zealand. 



[JRead "before the Wellington FMlosopMcal Society^ 2^t7i August, 1868.] 

 The tedious nature of the method at present employed to desilver argenti- 

 ferous gold, Avas particularly forced upon my attention a few weeks ago, on 

 reading an account of a new patent process by which the silver is rem-oved 

 from the alloy by chlorine ejected into the mass while in a molten state, 

 dependence being placed on borax as a preventative to the volatilization of 

 the chloride of silver thus formed. Having doubts as to the complete 

 prevention of this volatilization by borax, doubts which grew into positive 

 disbelief before the results of experiments made in this direction, and 

 thinking that there must be a want felt for a shorter method than that now 

 in use, I sought for one which should, as in this patent process instanced, 

 also effect a direct desilvering, but without producing a silver compound so 

 volatile as to necessitate similar precautionary measures. 



The most promising course apparent was in some way to take advantage 

 of the poAverful basic properties of oxide of silver as compared to those of 

 oxide of gold. Silver is, however, I believe, still considered to be quite un- 

 oxidizable in the dry way, its oxide, indeed, and its salts, with volatile acid, 

 suffering complete decomposition at elevated temperatures ; but it occurred 

 to me if, together with nascent or feebly-combined oxygen, a free or loosely- 

 combined fixed acid were presented to the molten alloy, that the oxidation of 

 the silver would be then effected. 



The well-known fact of the absorption of oxygen by molten silver, and 

 its liberation as the metal cools, was assuring ; for though the quantity thus 

 absorbed is so small as to forbid the idea of this absorption being a chemical 

 one (27 equivalents of silver only absorbing 1 of oxygen), still I was con- 

 vinced from this that any oxygen I might liberate in contact with the silver 

 would to a certain extent be retained by it, and in a condensed form, con- 

 sequently in a manner most favourable for subsequent chemical combination 

 therewith. 



Acting on these suggestions, after several preliminary trials I selected 

 bichromate of potash as being able singly to supply both these desiderata, 

 namely, nascent oxygen and a loosely-combined acid of some fixity ; this 

 salt being slowly decomposed at a white heat, with liberation of oxygen^ 

 sesquioxide of chromium, and chromate of potash. 



