AttcMand Institute. 479 



the question brought by Mr. "Wbitaker before the notice of the members of 

 the Institute, it was certainly very remarkable, but he was not at all disposed 

 to doubt it ; but, taking it for granted that one water saved more gold than 

 the other, it could only arise from one of two causes — the one chemical and 

 the other mechanical. The two waters mentioned might be of different 

 specific gravities. This might be a possible explanation, but he did not 

 think it was sufficient to account for it. The water spoken of hj Mr. 

 Whitaker probably contained silica in solution. What action the silica 

 might have upon the gold was very obscure ; but still there was the fact as 

 stated by Mr. Whitaker, and there might be some unknown action between 

 silica, which was an acid, and gold, which might have some effect on the 

 gold, and make it less susceptible of amalgamating with the mercury than 

 if the water was quite clear. He 'only threw out these suggestions on the 

 spur of the moment, the question having come up during the last half -hour. 



2. " On the Greology of the Island of Pakihi," by Captain F. "W. Hutton, 

 F.G-.S. (Transactions, p. 113.) 



Captain Hutton said there were two or three things in connection with 

 the Island of Pakihi which gave it a particular interest, one of which was, 

 that it contained large quantities of manganese, by which they might ulti- 

 mately be able to extract gold from iron pyrites, without having to roast it. 



BEST METHOD OE SAVING aOLB AT THE THAMES. 



Dr. Purchas said he was aware that on that occasion he had promised 

 to give a viva voce description of the various processes employed in saving 

 gold. He had, however, no time to get up his subject as he should have 

 wished, but would, as there Avas so little business on the paper, say a few 

 words on the subject. The speaker then went on to describe the manner in 

 which gold was treated in South America, saying that far poorer ores than 

 those at the Thames were crushed and made payable. Speaking of the 

 space required for the working of some of the machinery in South America, 

 he said that on many claims a space as large as six men's ground at the 

 Thames was required for amalgamating ground. He then briefly explained 

 the process by which the amalgamation took place. The ore, speaking 

 more particularly of silver ore, was laid upon the ground mixed with 

 salt, and horses were kept going round, treading upon it, and so break- 

 ing it fine. It was also dressed three or four times with quicksilver, and, in 

 some seasons of the year, small quantities of lime were added. It was a 

 remarkable circumstance that in the winter the temperature was made 

 higher and in the summer was made lower by the process. If the ore was 

 poor in sulphur, then another ore having su^lphur was mixed with it, and 

 trodden down in it to make it work, and left on the ground, in summer 



