Professor Black on the Extraction of of Gold from Rocky Ores by the Process of Fusion.

Lake Wakatip Mail, Issue 1579, 4 March 1887, Page 5

Professor Black on the Extraction of of Gold from Rocky Ores by the Process of Fusion.

(SPICIALLY.REPORTED.)]

On Saturday evening, 19th February ult., Prof. Black addressed a large meeting of miners and others on abovenamed subject in tne Borough Hall, Arrowtown. Mr John A. Miller, a well-known authority on mining, expressed the pleasure it gave the miners of this district to have the Professor address them on a subject so intimately connected with the prosperity of the country. Professor Black, on rising, apologised for the manner in which he was placed in lecturing that evening, owing to a pressure of engagements in other goldfields of the country, and iu a few well chosen remarks, which brought the audience thoroughly into sympathy with himself, began by exhibiting and describing minutely the few chemical instruments and appliances necessary for the assay of gold as they lay on the table. First in order, because of its importance in all chemical enquiries where weight is concerned, he showed the construction, and explained the working of a small chemical balance which stood before him, protected by its glass case. " That balance," (he said) is capable of weighing accurately to the hundredth part of a grain, and may be purchased in the colony at a cost of about £3 10s." Then exhibiting the other instruments of the assayer (crucibles, muffle, cupels, ingot mould and tongs, describing their U9es, and mentioning, by the way, that those and the few chemical substances, such as litharge, borax, carbonate of soda and wood-char-coal needed in this process, might be procured at a trifling cost) he seemed all at once to strike the reef supposed to contain the precious ore. The easy manner in which, by a little skilful and amusing mimicry, he took out about two tons of stone from the body of the reef, and prepared to describe the method of assay, was evidently greatly relished by the miners. the stone a rough crushing with a sledge, he gathered it into a heap, which he carefully divided into four equal parts

with the shovel. Taking one of these parts aside he broke it up into small pieces, which he afterwards collected into a heap, dividing it also into four equal parts. Afterwards taking one part of this latter heap and subjecting a portion of it to a more careful crushing, he set aside a small quantity, say about an ounce, as thoroughly representative of the reef, and that portion fie ground to an impalpable powder in an agate mortar. After weighing very carefully 200 grains of the fine powder, 200 grains of borax, 200 grains of anhydrous carbonate of soda, 400 grains of litharge and 7 grains of wood charcoal, and mixing them intimately in a mortar, he transferred them cautiously into a crucible. " Now," he said, "the mixture is ready to be fused." The crucible and its contents he then carefully placed in the fire, adjusting it so that the heat might be gradually raised by the use of the smith's bellows. Here, he observed, a smithy is a convenient place for such an operation as has been already described, as well as for what follows. In seven or eight minutes he had the crucible raised to a dull red heat, aud its contents being thoroughly fused (which may be known from the dark glassy appearance and homogenous movement of the mass), and having previously heated the tongs on the hearth to be in readiness, he lifted the crucible from the fire and poured its contents into the ingot mould, where it remained till quite cooled. Then tipping the mould to loosen its contents, he produced a conical-shaped mass consisting of

' giass and metallic lead, the glass being but ; a mere slag; the lead containing all the gold I and silver in the stone, and from which, by a very simple process, the value of the stone may be I accurately determined. Holding up a button of ' lead obtained in the manner already described, he said, " Let us suppose this button to weiyh one hundred grains. Now since we know that twelve grains of wood charcoal will liberate two hundred i grains of lead in cupellation, let us place the button ; of lead aud twelve grains of charcoal in this boneash cupel. Now plate the muffle in the fire with the fuel heaped well over and around it; then carefully place the cupel containing the lecd anil charcoal within the muftle, and raise the heat gradually up to a cherry-red. Lookiug into the muffle, you ■ will see gn*y fumes Wgin to rise, anil as some of the ; lead j.'oes off in the fumes and the rest is absorbed , by the cupel, leaving a brownish streak around ; ! you will then see in the bottom of the cupel a small

brilliant speck of molten gold. Allotting this to cool, the experienced miner will he able to judge its purity from its colur. If it shows a bright yellow, he will judge it to be pure gold, if paler than yellow, a good deal of silver is present. But to ascertain accurately the value of the stone or reef from which this was taken, proceed as follows Suppose the button of metal containing gold and silver to weigh one grain, add to it two and a-half grains of pure metallic silver, aud flatten both metals together on an anvil. Now the button weighs three and a-half grains Place this in a dish containing strong nitric acid ; apply heat | gently, and in a few minutes the silter will have been dissolved by the acid, while all the gold in the button remains Itehiud in the form cf pure metallic gold. Now pouring off the silver solution, and washing and drying the gold very carefully, and then weighing it, from its weight the value of the stone may be easily calculated. This having concluded the lecture, the chairman rose to propose a vote of thanks to Prof. Black, who had so kindly and fully instructed them that evening in the method of separating gold from its ores by fusion. He hoped in a short time the miners would have the assayer at work in all the goldmining centres of this colony, telling thein the value of the stone discovered, that public companies would l>e formed for the purchasing the stone taken out by the miners, and placed on the market at its known value, so that the industrious miner should himself directly reap the fruit of his own labour, and then the whole mining industry of the country would rest on an honest and firm foundation.

The Professor returned thanks for the hearty manner in which he was complimented, and for the close attention given to a lecture of this kind, unaccompanied by experiments; adding that he was always happy to meet with the miners of this neighborhood, among whom he had many friends. He also Btated that he expected shortly large sums of money would be employed in developing the mineral wealth of the Wakatipu region, the whole of which from Macetown to Mount Aurum, and Skippers to Mount Earnslaw—would before many years become the most important goldfield in the Southern hemisphere.