o\ gold: its fokmation in our reefs. 167 



5. — That it becomes non-anialganiable when allowed contact 



with weak sulphuric acid ; also when fused beneath 



bisulphate of potash and borax. 



These facts prove that gold is chemically acted upon when in 



contact with water or neutral saline solutions charged with air, 



and that this action is facilitated by the presence of alkaline 



substances, and especially when these are used hot instead of cold. 



It seems to me, therefore, there can be little doubt but that gold 



thus acted upon has been oxidized, and has afterwards combined 



with carbonic acid to form a carbonate of gold, which, having a 



yellow colour, would thus remain invisible. 



THE AGENCIES WHICH HAVE BROUGHT THE GOLD INTO THE REEFS. 



Having shown in the preceeding pages the reduction of gold 

 from its acid or alkaline solutions by metallic sulphides, and its 

 sulphurization and oxidation by ordinary agencies of air and 

 water, we may now speak of the nature of those substances which 

 are likely to have brought auriferous compounds into solution, and 

 thus to put them in a condition favourable for their translation 

 from the country rock into the reefs. 



In regard to the sulphide of gold, Bischof has long since proved 

 it to be soluble in alkaline sulphides ; and since then Professor 

 Eglinton has indirectly pi'oved this for the sodic sulphide, by 

 showing, as already stated, that even the metal itself is soluble in 

 this salt. 



The carbonate and oxide of gold are, I find, readily soluble in 

 bicarbonates of the alkalies. 



In testing I use thinly electro-gilded platinum or pyrites, 

 according as to whether I wish for a minute quantity of gold^ 

 fixed or detached. By this means I can detect a disappearance 

 of gold in sealed vessels, at common temperatures, containing 

 carbonate of soda and free carbonic acid. The disappearance is, 

 however, very slow, occupying about two years. 



By this means, I found that hot solutions of cai'bonate of soda 

 show^ed a marked solvent power on gold in twenty-four hours. 



Sea-water, aqueous solutions of caustic potash, and strong 

 solutions of sodic chloride, even after digesting gold for many 

 hours, do not appear to have any effect upon it, nor does the 

 addition of hydrochlorine acid to the salt alter the result. 



Thus it is probable, that, in the alkaline sulphides, carbonate 

 of soda, and carbonic acid, all very common in our rocks, we have 

 the agencies necessary to dissolve the gold they contain, so that it 

 can be transported to the reefs by those aqueous currents which 

 are ever setting in that direction. 



CONCLUSION. 



In the foregoing pages I have set forth and discussed my own 

 theory relating to the formation of gold in reefs, comparing it 

 with the other popular theories on this subject. 



