The ores of mercury which contain silver are as sayed in the same way, so as to ascertain the quan tity of mercury. The insoluble residue is then roast ed, to drive off the sulphur, after which it is mixed with twice its weight of pearl-ashes, and again ex posed to heat in a crucible. The product is then digested in muriatic acid, which dissolves the alkali, and leaves the silver in its metallic state.
A more easy way of assaying the mercurial ores is to reduce them to powder, and to mix them with one fourth part of lime, and as much iron filings, and then expose them to heat in an iron or earthenware retort, by which the mercury is expelled, and is collected in a receiver.
Itlangancse.
Manganese is not used in the arts in its metallic state. The black oxide, which is a native production, answers, without any' preparation, all the purposes for which the metal is employed.
Zinc.
The ores of zinc used in metallurgy, are calamine and blende. From these the metal is procured by a very simple process. The ore, after being hand•dress ed, to free it from foreign matter, is roasted, by which the sulphur of the former and the acid of the latter are expelled. The product is then washed, by which the lighter matter is separated, and the heavy part which remains is mixed with one-eighth of its weight of charcoal. The mixture is next reduced to powder in a mill, in which state it is put into the pots to be smelted. The pots in which the smelting is perform ed resemble oil jars in shape. Through the bottom of each there passes a tube, the upper end of which ter minates by an open mouth near the top of the pot, the lower end goes through the floor of the furnace into water. The pots are filled to the upper end of the tube with the mixture of ore and charcoal, and an in tense heat is applied to them, by means of a furnace. As the ore is reduced, the zinc is volatilized, and es capes through the tube into the water, where it is con densed in the form of globules. These are afterwards melted and cast into moulds.
Zinc, as thus procured, is not pure ; it almost al ways contains iron, manganese, arsenic, and copper.
To free it from these, it is again melted, and then well stirred along with sulphur and fat, the former of which combines with the foreign metals, and leaves the zinc nearly pure, while the latter prevents this metal from being oxidated.
Assay.—The assay of zinc ores may be performed in two different ways.
The simplest is, reducing the ore by charcoal. For this purpose, after being freed from impurities, it roasted, to drive off the sulphur. It is then mixed with one-half its weight of charcoal in powder, and exposed to a strong heat, for about an hour, in an earthen retort, the mouth of which terminates in water. The zinc condensed in the water and in the neck of the retort is collected and weighed.
The second method of assay is, to expose to a strong heat for about an hour the mixture of ore and char coal, in a covered crucible, with slips of copper, by which means the two metals unite. After the pro cess is finished, the product is washed, and the weight. which the copper has acquired indicates the quantity of zinc in the ore.
Bismuth.
Bismuth occurs native and mineralized by oxygen and sulp .ur, and is very easily obtained from its ores.
When native bismuth, and the oxide, are employed to yield the metal, they are merely exposed to heat, in contact with fuel, generally in shallow pits (lug in the earth. The metallic matter which collects at the bot tom is then mixed with an equal weight of black flux, and put into a crucible, and covered with common salt, to about the depth of half an inch. A strong heat is applied for a short time, by which the mixture fuses, and the bismuth collects at the bottom of the pot.
Instead of the above process, the ore is sometimes mixed with half its weight of borax and of pounded glass, and subjected to heat in a crucible lined with charcoal.
When the sulphuret of the metal is employed, it is first roasted by a gentle heat, to drive off as much of the sulphur as possible. After this, it is mixed with black flux, and subjected to heat, covered with com mon salt, as in the first process.
Bismuth obtained by these different processes con tains in general lead, silver, or cobalt, provided these were present in the ore ; it is sufficiently pure, however, for most purposes.