COPPER ORES. 303 



crucible, till all the arsenical fumes are dissipated. The residuum, be- 

 ing cooled and triturated, is to be exposed in a shallow earthen. dish, 

 made of refractory material, to a slow roasting heat, and stirred till the 

 sulphur and cLarcoalare burned away ; what remains being ground and 

 mixed with half its weight of calcined borax, or carbonate of soda, one- 

 twelfth its weight of lamp black, (finely pulverized charcoal will an- 

 swer,) and next, made into a dough with a few drops of oil, .is then to 

 be pressed down into a crucible, which is to be covered with a luted 

 lid, and subjected in a powerful air-furnace, first to a dull red heat, then 

 to vivid ignition forsevento twenty minutes. On cooling and breaking 

 the crucible, a button of metallic copper will be obtained, which may 

 be refined by melting again with borax in an open crucible. Its color 

 and malleability indicate pretty well the quality, as does its weight the 

 relative value, of the ore. It may be cupelled with lead to ascertain 

 if it contain silver or gold ; or it may be treated for the same purpose 

 with nitric acid. 



If the blowpipe trial show no arsenic, the first calcination may be 

 emitted ; and if neither sulphur nor arsenic are present, a portion of the 

 pulverized ore should be dried and treated directly with borax, lamp- 

 black, and oil. 



The ores of copper, (the sulphuret as well as the oxyds, carbonates, 

 &c.) may be reduced in the wet way, by solution in strong nitric acid. 

 The solution, if made from the sulphuret, will contain sulphuric acid 

 and free sulphur, as well as all the bases, (iron, nickel, cobalt, lead, sil- 

 ver, &c.) which may have been present in the original ore. If silver 

 is present it will be found as a heavy white curdy precipitate, at the 

 bottom, if the nitric acid employed contained any hydrochloric acid ; 

 and if the addition of this acid to the solution occasions no such pre- 

 cipitate, no silver is present. If the solution is free from lead, anti- 

 mony, arsenic, and other metals precipitable by sulphureted hydrogen, 

 the copper may be thrown down as sulphuret by means of a current of 

 this gas, the black precipitate, collected on a filter washed with water, 

 and redissolved in aqua regia, largely diluted, and finally precipitated by 

 caustic potash, which throws down the black oxyd of copper. This 

 dried and weighed will yield the true value of the ore in metallic cop- 

 per. If only iron and copper are present, (which may be previously de- 

 termined by the blowpipe,) they may be separated from their solutions 

 in nitric acid by ammonia, which throws down the iron as hydrated 

 peroxyd, but redissolves the copper precipitated by the first additions of 

 ammonia. The determination of the weight of the iron may then give 

 the amount of copper by the difference of weight, or the copper may 

 again be thrown down by potash as before directed. 



Reduction of Ores. Copper ores are reduced in England in a rever- 

 beratory furnace, and the process consists in alternate calcinations and 

 fusions. The volatile ingredients are carried off by the calcinations, 

 and any metals in combination with the copper are oxydized. The 

 usions serve to get rid of the various impurities, and finally bring out 

 he pure metal. 



The calcinations or roastings are performed either in a furnace, 01 

 j making piles in the open air. In this latter mode, which is in use 



What is the mode of assaying copper ores in the wet way ? How 

 4re copper ores reduced ? Describe the process of calcination ? 



