1918.] The N.Z. Journal of Science and Technology. 43 
Applicability of Flotation. 
The success of the flotation process has been most marked in the treat¬ 
ment of copper, lead, and zinc sulphides, and it has been chiefly in the 
treatment of sulphides that the process has developed. There can be no 
doubt that success can be attained on other ores, but a large amount of’ 
experimental work yet remains to be done before hard-and-fast rules can 
be laid down as to the adaptability of the process. It is only a question of 
time before flotation will be applied to the concentration of gold-ores. As 
flotation is a concentration process, it is of value only when the valuable- 
constituents are in the mineral, or when it is desirous to remove a refractory 
mineral prior to cyanidation. It is of undoubted value in the treatment’ 
of cupriferous gold-ores. A small amount of copper renders the treatment 
of low-grade gold-ores unprofitable at the present time, not because copper 
prevents the dissolution of the gold, but because it consumes so much 
cyanide during the process. The flotation process will remove the bulk 
of the copper, while the remaining pulp will be in a fit state for ordinary 
cyanidation. This also applies to many of the high-grade silver-sulphide 
gold-ores, for I believe that it would be more profitable to remove the 
silver by a preliminary treatment than to submit the whole of the ore- 
contents to cyanidation. 
Experiments on the Smelting of New Zealand Ironsand. 
By J. E. L. Cull, Wellington. 
The events leading up to the experiments which I have to describe are 
as follows:— 
In the years 1899-1900 the author was in the employ of Messrs. Cutten 
Bros., consulting engineers, Dunedin, a great part of whose business was 
in alluvial gold-mining, chiefly by dredging. One of the great problems 
in dealing with the beaches on the west coast of the South Island was the 
great amount of black sand present. The fundamental property of the gold 
which is utilized in alluvial mining to assist in its separation from the sand 
is its high specific gravity, causing it to settle from a properly regulated 
stream of water and to be entangled in pockets, or in the texture of plush 
or matting. Black sand, with its high specific gravity and well-rounded 
grains, tends to be precipitated with the gold ; and if the gold be very fine 
or flaky it is extremely difficult to effect a separation of the two by gravity 
means, and resort must be had to amalgamation. Sometimes in con¬ 
centrates, where the amount of black sand with the gold is quite small, 
hand-magnets are used to get it out; and this suggested the use of a 
magnetic separating-machine where the amount of black sand was large 
in the sands before concentration. Mr. J. McPhee, of Dunedin, proposed 
a scheme of a belt passing over a magnetic pulley, which seemed very pro¬ 
mising ; and a machine was built, 8 in. diameter, 8 in. face, which worked 
well as a separator. On examining the sand-deposits on the Coast, how¬ 
ever, I soon found that by no means all of the heavy sand was magnetic, 
and concluded that the use of a magnetic separator was on this account 
not likely to pay in working the ordinary class of black-sand claims. 
Possessed now of a magnetic separator, I and several others decided to 
follow up the treatment of black sand from the point of view of its iron- 
content; and with that object in view Mr. S. H. Jenkinson afterwards 
went to the United States of America to get experience in the iron and 
