Auckland Institute. 479 
the question brought by Mr. Whitaker 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 by 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 Geology 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 OF SAVING GOLD AT THE THAMES. 
Dr. Purchas said he was aware that on that occasion he had promised 
to give a vivá 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 was 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 itfine. 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 cireumstance 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 sulphur was mixed with it, and 
trodden down in it to make it work, and left on the ground, in summer 
