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TO THE KDITOB. Sir,—Now that Dunedin ia to have an Exhibition, it almost becomes a national, if not governmental, duty to have the most complete gold-saving battery that is possible to be made exhibited therein for the benefit of the country. An extract from an expert at Pilgrim's Rest, Transvaal, South Africa, with the most modern appliances in quartz crushing, may prove of interest : •' With regard to mercurial processes. Taking a sample of rather high-grade ore, the most I ever obtained was 64 per cent. It was treated in the following way : Crushed in the battery, passed through screens of 1,000 holes to square inch, over eighty square feet of amalgamated copper plates and riffles, over sixty or seventy yards of blanketings, changed every ten minutes, over another set of amalgamated riffle plates into the 'buddies. The stuff from buddies was transferred to the Californian pan, the pulverisers running at sixty revolutions per minute. Here the stuff was ground for two hours; and at the end of that time a dried sample had the consistency of well-ground flour. Steam at a iiressure of 101b to the square inch was then et into the pans (in the Californian prooesßeß all grinding is wet), and at the same time a large quantity of mercury settlers were trimmed up, and agitators put to work. The grinding mullers on the pans were raised half an inch, so that grinding should cease, and to prevent flowing of mercury as much as possible. The whole mixture was very soon boiling, and the lifted matter mixing at the rate of sixty-seven revolutions per minute. This was kept up for two hours. Then, by the usual pan methods, amalgam was recovered as it settled in the well' known pan well of settler, etc During the whole of the time rigid sampling and assaying was going on, and at the clean up at the end of the month the figures showed aB follows; —From stamper boxes, 9 per cent.; from plates, 40 per cent.; from pans (including

treatment of blankets therein), 15 per cent.; slimes, which in cases assayed up to 22dwt per ton cased gold, 0; total, 64 per cent." To show further the loss of gold, I will state my experiences in connection with a crushing that my two mates and myself took out of the Crown and Cross reef, Carriek Range, in 1874. During a period of ninety-five days I took a pound weight of stone every dinner hour and roasted it in the blacksmith's fire, then crushed in a mortar, and the lowest return was ljgr per lb and the highest Bgr per lb. Now, taking the lowest result, it would give about 7oz per ton, and the crushing was 300 tons of blue stone, full of arsenic and sulphur; also about lewt per ton of arsenical pyrites, containing gold at the rate of 40oz per ton. The battery was the old-fashioned affairstamper boxes, 3 riffle of quicksilver, 3 copper plates, and 13ft of blanket tables. This constituted the whole of the goldsaving appliances I had, from which I received the following result: Cake of gold from boxes and copper tables, 1460z ; dirty gold, afterwards cleaned, 14oz; from blankets, about 40oz; total, 190oz.

Now, 300 toDs multiplied by 7oz per ton gives 2,1000z. I well knew what would be the result, and proposed to my mates that each of us had better have a common bellows rigged, and a mortar each, and we could easily crush out about 201b weight per day with a result of 4dwt each.

Hunting up figures as far back aa 1869 to the present time, I find that I have crushed and retorted about 21cwt of gold at different places, and, taking the above to represent 50 per cent, of the whole, which is the utmost according to the loss that I knew was going on from tests I always made, it would give a loss of about 140,0001b to the country, and all through imperfeot goldsaving appliances and imperfect knowledge. This subject demands attention, and the sooner the better.

The Vaughan and Newbury process is a grand one with chlorine gas, as used at Mount Morgan, but is expensive, costing about L2 per ton to extract the gold ; and it requires skill, there being a number of operations from the krom mill to the smelting furnace. I have it from good authority over there that the gold saved represents 99 per cent, of the whole. —I am, etc., W. Watson, Engineer, eto. Dunedin, May 28.

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