382 Transactions. — Chemistry. 



may contain. Consequently the deposition of gold from solution being as we 

 know unaffected, or but slightly so (comparatively), by the condition of the 

 solvent, the great purity of gold deposited from these surface waters is 

 explained. 



The above explanation of the greater purity of our alluvial or drift gold 

 over gold found in the reef is, I think, much more plausible than that 

 which attributes this difference to the interaction of solutions of gold upon 

 the auriferous masses transported from the reef, whereby the silver of 

 these masses is replaced by gold and so removed, leaving the mass corres- 

 pondingly richer in gold. That this process can be continued until our 

 largest auriferous masses can be thus affected throughout appears to me 

 impossible when we consider the imperviousness of such metallic masses to 

 liquids, and how nearly the atomic volumes of gold and silver approximate. 

 That a superficial change, however, in this direction may occur is by no means 

 improbable, but such would escape detection unless it were especially sought 

 for. Thus the hypothesis advanced by Mr. Selwyn as to the manner in which 

 the nuggets of our drifts may have been formed receives support upon all 

 those points which appear of any importance. 



That nuggets of some size may, however, be in a few instances transported 

 bodily from these matrices into the drifts or water-courses is by no means 

 improbable, but in this case they would, I think, partake of the usual quality 

 of the reef gold of the country about, and so would be inferior in this respect 

 to gold formed in the manner above described. 



Whatever may be the origin, however, of any particular nugget, or of 

 nuggets generally, when we consider the auriferous nature of many mine 

 waters, also that of sea-water, together with the decomposing and aggregating 

 action of metallic sulphurets upon the gold of these waters, we cannot avoid 

 the conclusion that gold is now being deposited and aggTegated in many of 

 our drifts, and that such depositions have been going on from remotest times. 



In conclusion, the questions as to the source of the gold of our nuggets, 

 the nature of the agencies by which it is dissolved, and the precise chemical 

 state in which it exists in our auriferous waters, are subjects which it is not 

 incumbent upon me to discuss here. I will, however, take leave to make a 

 few observations upon them now. 



As regards their source I think this is rather in gold as disseminated in 

 certain of our slate, sandstone, or schist rocks, than in that of our reefs. 



In reference to the nature of the solvent I have shown* that sulphuretted 



hydrogen attacks gold at ordinary temperatures, forming a sulphide of the 



metal, and we know that all the sulphides of this metal we have to this time 



formed are soluble in alkaline sulphides ; therefore, as both these agents are 



* Trans. KZ. Inst., Vol. III., Art. XXX. 



