216 



III. — CHEMiaTRY. 



Art. XXXVI. — On the Absorption of Sulphur by Gold, and its Effects in 

 Retarding Amalgamation. By W. Skey, Analyst to the Geological 

 Survey of New Zealand. 



\^Read hefore the Wellington Philosophical Society, Septemher 17, 1870.] 



A PART of tlie duty assigned to me while recently on the Thames gold-field, 

 was to investigate into the causes of the loss of gold experienced by the pro- 

 prietors of the several batteries in that district, when working the auriferous 

 material. 



From an acquaintance with the various mechanical arrangements adopted 

 there for securing the gold, and from a knowledge of the nature and amount 

 of such loss, I was soon led to infer that much of it could scarcely be referred 

 to any of the causes severally supposed to be operative. 



The afiinity of gold and its richer alloys for mercury is so great, and their 

 negativeness, or u.naffectibility, to and by the various chemical substances 

 naturally having contact with them, so universally and so authoritatively 

 afiirmed, that it is generally supposed all we have to do in order to obtain an 

 amalgam of gold and mercury, is to present them to each other, with their 

 surfaces free from dust or stain, and to all appearance chemically clean. 



But, in experimenting upon a few samples of the Thames gold, I found 

 that though apparently quite free from any such stains, etc., they would not 

 uniformly amalgamate over their entire surfaces ; some, indeed, would not 

 amalgamate in the least, though to all appearance as bright, as clean, and as 

 chemically similar as those which did ; the action of boiling water upon these 

 did not in the least affect their negativeness to the mercury. This could not 

 therefore be owing to the intervention of air mechanically adherent to them. 



Observations taken since my return, show besides, that several of the 

 cleanest-looking samples of the Otago gold which have been deposited in the 

 Colonial Museum, manifest a similar negativeness to mercury — even to whole 

 samples of fine alluvial gold, and those surfaces of small nuggets so situated 

 that it was impossible they could have been hand-soiled. 



All these specimens were rendered readily amalgamable by cold solutions 

 of cyanide of potassium, nitric acid, chromic acid, or chloride of lime acidified, 

 and, with the exception of the moi'e cupreous of these, they were also rendered 

 amalgamable by roasting them in an open fire for a few minutes. 



