MINING LECTURES THE THAMES. Professor Black on the Reduction of Silver Ore.

Te Aroha News, Volume III, Issue 133, 19 December 1885, Page 5

MINING LECTURES THE THAMES. Professor Black on the Reduction of Silver Ore.

All samples of lead contained more or less silver, and Dr Percy, of the London Sohbol of Mines, has said that there never was a sample* of galena analysed which did not contain silver.. Galena ia smelted until it assumes- the form of metallic lead, Until 25 years ago, no process was known for the separation of silver - from lead, unless the former was present at the rate; of 12 or 15 ounces to the ton. Now, however, a process has been patented by which the metal can be worked profitably if present in the proportion of 3 or sozs per tcjn, This is done by smelting the galena in a. series of large cast-iron pots, each containing from 7 to 12 tons of mofcber metal. Each pot is provided with a removable fireplace, so that the fire can be withdrawn when desired. In the central pot. the lead is melted until it fuses, and when the litharge or oxide of lead accumulates on the surface it is skimmed off. The fireplace is then removed, and the contents of the pot are allowed to solidity, being stirred as they cool, when crystals of lead containing a small proportion of silver, will form, and being heavier than the surrounding mass, sink to the bottom, whence the workman, with a perforated iron ladle, transfers them into the next pot in the row. The process is continued until the contents of the first pot are almost gone, and the residue is rich in silver, and and the crystal-forming process is kept up until the pure silver is found at one end of the row, and lead fit for the market—containing only from 10 to 15dwts of silver to the ton-at the other. The alloy of silver and lead is separated by cupellation. The cupel is practically a crucible made of calcined bone ash, thoroughly pulverised and moulded into the required shape, which the lecturer described very minutely. In the breast of the cupel there is a channel or slot, which allows the litharge to flow into a receptacle underneath the furnace, where it can be recovered. Part of the, litharge is absorbed by the bone-ash, which does not, however, absorb molten metals, because they cannot be oxidised. If any other metals are preeent—such as copper, zinc, or iron,—the lead has the property of imparting the oxygen to them until they are also thoroughly oxidised. The oxide of lead unites with oxide of copper, and the double oxide thus formed is fusible at l the temperature of the cupel, and is thus absorbed by the bone-ash. The pots containing silver and lead —the former to the extent of about 500 or 600ozs to the ton—are placed in a reverberating furnace, or in a furnace with tuyeres or blowers, such as can be seen at the La Monte works, and the lead is rapidly burned into oxide of lead, which flows away to the circumference of the cupel. A considerable quantity passes through to the slot and is collected, another part is absorbed by the bone-ash, and the silver gradually becomes purer and purer. In the English process, after the alloy ia reduced to the state of about 5,000 or 6,000 ounces of silver per ton, it is transferred to another crucible, where the same kind of treatment is continued, the last trace of lead disappears there is a beautiful display of prismatic colours known as Newton's rings, and a beautiful bath of metallic lead remains in the cupel The importance of the process to this district lies in the fact tbat there is abundance of lead in the ores. At the Tui creek he had seen galena which had been proved by a«say to contain 50 to 60 per cent, of lead, and about 12ozs silvor per ton. If this were pot in large enough quantities ifc would be found profitable to separa'e the two metals. In various processes grinding and roasting with table salt plays an important part in the extraction of silver from its ores, especially with sulphides such as those of Waihi. Professor Black mentioned that he had good authority for stating that telluride of silver was also found at Waihi, though he had not yet soen a specimen of it. Roasting with common salt reduced the silver to the same state as the white precipitate obtained from the mixture of muriatic acid with a solution of silver, which, again, is identical with the horn silver or chloride of silver found at Sunny Corner and elsewhere. This metal does not dissolve in nitric acid, but is soluble in a strong solution of brine, or in a solution of hyposulphide of soda. Upon these two facts are founded some of the most important processes for the extraction of silver. If the silver is in solution with lime, then, by adding mercury, an amalgam of mercury and silver will be formed, together with any gold, silver, or copper that may be present, which can be separated by retorting.

Valedictory Address to Professor Black at Thames, At the conclusion of the lecture on Friday evening Ilth insfc., the Chairman said that the Committeeof the School of Minos Associa tion had drawn up a short address for presentation t6 Professor Black. Professor Black had aroused amongst the miners a desire forscientific knowledge, and awakened an interest in chemistry, the study of which is essential to the School of Mines, and is in itself a highly interesting and pleasurable pursuit. It was now known in an authori tative manner that the Thames district contained many other minerals of a useful and valuable kind besides pilver aod gold, and ib was highly impirtant that Government should be impressed with this fact. Without such knowledge those in authority failed to recognise the importance of establishing Schools of Mines. These were some of the good results attending the visit of the Pro fessor, who had quite taken the Thames by storm, and could fairly adapt to his own circumstances the words of Csesar, and say that —"He came, he saw,andhe conquered." The Chairman thee called upon Mr Bruce to read the address, which was as follows :— To Professor Black. Dear Sir,-We, the Committee of the Thames School ot Mines, desire to thank you very cordially not only for the excellent instruction afforded by you in your lectures and by means of your practical classes through which a large amount of information has bean diffuesed, and a strong spirit of enthusiasm in favour of scientific knowledge evoked, but also for the kindly zeal with which you have entered upon the duties allocated to you by the Government, and put your time and, information 1 at the entire disposal of the public. No' better means than those adopted by you could have been taken for ensuring the success of the object which the people of, this town and district have at heart, v»z.\'tbe eftta^Yish'ing among them of a School of n^ Sj for by shewing the feasibility c| the'eoheme; ,-both to the Govern;^^ and the people, ]an accord between . nil concerned' bjas' been brouffM 'v ab.out' which ' promises .the' happt&'st' results. *In taking ,)<eaye of you, ejrywedo'so with regret, 1 wiehipg you %11 the'coiiaplimentst'of the f>season^-^hile; we' >cannot but 1 remSmbefthat/ybur 'connection with this district does not entirely cease with your presence here, because much yet

success of -wft f and^erMiy trust to your friendly care:fqrthe f cpmple-^ r ' ¥ tion oi.'in|Sy raaiterfl^ df.^tail, wbiofijoan^ only be met by the 4id of skill and%perj(|gk ence.— (Signed onbehalf of the Committee " Thames School, of Mines ), : %$ v - ; * James Kilqoub, Chairman, John t Watson, , IJon. Tretaurer.; / , T V; AiaBB^BBUOB/HoK.Seprete^i 1 , Professor Black said he was' 1 altogether taken by surprise by I' this ' handspTtie^testimonial, which was really much inpre^than . ; he deserved, for- he , had simply done his I duty in the quietest: possible manner. 'The • , • address would beJtreasured as long as he , lived, and. would be handed down to' his - children as an heirloom. , Cpming afl it ,- did from the promoters' of tHe Thames School of Mines, who had worked^ With ench- heartiness, he' valued it ■■morekfifian __ words could express,.; , He must^cjknjowledaje that during his ,viBit u to .the/rT^aniea he had,receiyeC mor ©- i n fo rm^°?nl'^ a . n * n any other goldfield where.He*h*ad^,lectur^d ; he had seen new minerals^and^oqkjojmations, and jcnany other unexpected', jthmgs, which he had often read' about,, but ? had not hitherto seen. With the utmost r confidence he >could say ( that . He\ knew «of no better field for a School of Mines jthan . jfbe Thames, in the first place because of ,, the extraordinary geological^formatipn of the peninsula, concerning 'which, geologists could not agree ; and next,, because of } the -- great variety of, minerals, existing . in t large quantities in a matrix which does not carry them in other parts of the, world. .For instance, near Tapu he had seen gold in a class of stone which, if it had been shqwn to him at Dunedin, apart from ,the gold itself, he would without hesitating have pronounced unlikely to be other that barren Dr. Hector had probably fallen into a similar mistake, and any other geologist would also have been, just as likely to j; do so. He trusted that Government would take. the proper view of the Thames School of Mines, and not only support the present unpretentious proposal, but also if they listened to his representations, establish a thoroughly efficient institution, for he was convinced that in the interest of the colony they could not be too liberal to the Thames in this respect. The miners must woik together unitedly and, they would then gain their object and obtain such a School of Mines as would satisfy the most ambitious of its promoters. In conclusion, be must express his extreme satisfaction with the result of his visit, and the kindness with which he had been overwhelmed by the Thames miners. (Prolonged applause).