Manufacturing assays of copper

—The first thing is to make such a sample as will represent the whole ma to be valued; with which view, fragments must be taken from different spots, mixed, weighed, and ground together. A portion of this mixture being tried by the blow-pipe, will show, by the garlic or sulphurous smell of its fumes, whether arsenic, sulphur, or both, be the mineralizers. In the latter case, which often occurs, 100 gr. or 1000 gr. of the ore are to be mixed with one half its weight of saw-dust, then imbued with oil, and heated moderately in a crucible till all the arsenical fumes be di ipated. The residuum being cooled and triturated, is to be exposed in a shallow earthen cup to a slow roasting heat, till the sulphur and charcoal be burned away. What remains being ground and mixed with half its weight of calcined borax, one-twelfth its weight of lamp black, next made into a dough with a few drops of oil, is to be pre ed down into a crucible, which is to be covered with a luted lid, and to be subjected, in a powerful air furnace, first to a dull red heat, and then to vivid ignition for 20 minutes. On cooling and breaking the crucible, a button of metallic copper will be obtained. Its colour and malleability indicate pretty well the quality, as does its weight, the relative value of the ore. It should be cupelled with lead, to ascertain if it contains silver or gold. See A ay , and Silver . If the blow-pipe trial showed no arsenic, the first calcination may be omitted; and if neither sulphur nor arsenic, a portion of the ground ore should be dried, and treated directly with borax, lamp black and oil. It is very common to make a dry a ay of copper ores, by one roasting and one fusion along with 3 parts of black flux; from the weight of the metallic button the richne of the ore is inferred. The humid a ay is more exact, but it requires more skill and time. The sulphur and the silica are easily got rid of, by the acids which do not di olve them, but only the metallic oxides and the other earths. These oxides may then be thrown down by their appropriate reagents, the copper being precipitated in the state of either the black oxide, or pure metal. 105 parts of black oxide represent 100 of copper. Before entering upon the complete analysis of an ore, preliminary trials should be made, to ascertain what are its chief constituents. If it be sulphuret of copper, or copper pyrites, without silver or lead, 100 grains exactly of its average powder may be weighed out, treated in a matras with boiling muriatic acid for some time, gradually adding a few drops of nitric acid, till all action ceases, or till the ore be all di olved. The insoluble matter found floating in the liquid contains most of the sulphur; it may be separated upon a filter, washed, dried, and weighed; then verified by burning away. The incombustible residuum, treated by muriatic acid, may leave an insoluble deposit, which is to be added to the former. To the whole of the filtered solutions carbonate of potash is to be added; and the resulting precipitate, being washed, and digested repeatedly in water of ammonia, all its cupric oxide will have been di olved, whenever the ammonia is no longer rendered blue. Caustic potash, boiled with the ammoniacal solution, will separate the copper in the state of black oxide; which is to be thrown upon a filter, washed, dried, and weighed. The matter left undi olved by the ammonia, consists of oxide of iron, with probably a little alumina. The latter being separated by caustic potash, the iron oxide may be also washed, dried, and weighed. The powder which originally resisted the muriatic acid, is silica. A ay of copper ores, which contain iron, sulphur, silver, lead, and antimony. 100 grains of these ores, previously sampled, and pulverized, are to be boiled with nitric acid, adding fresh portions of it from time to time, till no more of the matter be di olved. The whole liquors which have been succe ively digested and decanted off, are to be filtered and treated with common salt, to precipitate the silver in the state of a chloride. The nitric acid, by its reaction upon the sulphur, having generated sulphuric acid, this will combine with the lead oxidized at the same time, constituting insoluble sulphate of lead, which will remain mixed with the gangue. Should a little nitrate of lead remain in the liquid, it may be thrown down by sulphate of soda, after the silver has been separated. The dilute liquid being concentrated by evaporation, is to be mixed with ammonia in such exce as to di olve all the cupric oxide, while it throws down all the oxide of iron and alumina; which two may be separated, as usual, by a little caustic potash. The portion of ore insoluble in the nitric acid, being digested in muriatic acid, every thing will be di olved except the sulphur and silica. These being collected upon a filter, and dried, the sulphur may be burned away, whereby the proportion of each is determined.