Urea of Mercury.—These present less variety than those of many other metals ; and on account of the peculiar properties of the metal, the management of its ores, whether for the purposes of analysis or reduction, is less complicated and difficult. In order to analyse the ore of native mercury, or native amalgam, it may be dissolved in nitric acid. The gold, if any is present, remains in the state of powder, and may be estimated by its weight. The affusion of water precipitates the bismuth, if the solution happens to contain any. Common salt precipitates the silver, and also part of the mercury, but the latter may be redis solved by a sufficient quantity of water, or, which is far better, of oxymuriatic acid, while the muriate of silver remains insoluble; lastly, the mercury may be precipitated by sulphate of iron, and estimated. Native einnaoar may be treated with a mixture of three parts muriatic, and one part nitric acid, which dissolves the mercury, and leaves the sulphur. Muriate of mercury may be digested in muriatic acid, till the whole is Muriate of barytes precipitates the sulphuric acid, 100 parts of which are equivalent to 186 of sulphate of mercury, sa the proportion of this salt being known, we have that of the muriate. A very simple process is followed for reducing the ores of mercury ; the best and most amend& method is that ed at the mines of Dean: Ponta and Poria. The ore, as it is brought out of ffie mine, is carefully sorted by the band, and those parts which seem destitute of metal are rejected. It is next reduced to powder, and accurately mixed with one fifth of quicklime, which has fallen to powder by exposing it to the air, the quantity of quicklime being regulated by the pro portions of cinnabar contained in the ore. The mixture being thus prepared, is introduced into iron retorts, which are capable of holding about sixty pounds weight. The retorts, to the number of forty or fifty, are fixed in a long furnace, and a glass receiver is attached to each, but it is not luted. A moderate heat is then for the purpose of driving off the whole of the moisture, and when this is done, the jomuigs of the vessels must be closely stopped with tem and a full red heat is to be applied, and continued for seven or eight at the end of which time the whole of the mercury will be volatilized, and condensed in the receiver. By this process, it is found that from six to ten ounces of metal are produced from one hundred pounds of the ore.
Ores of Copper.—This metal is found native in the state of oxide, in the state of snlphuret, and in that of salt, combined with carbonic, muriatic, phosphoric, and arsenic acids. Native copper sometimes contains gold, sillier, or iron. It be dissolved in nitric acid : the gold remains in the state of a blackish or violet-coloured powder; the liver may be separated by a polished plate of copper (or it may be precipitated from a separate portion of the solution by common salt); the iron may be separated by boiling the solution to dryness, and treating the residuum with water. By this process, the nitrate of iron is decomposed ' • the oxide of iron remains, while the water dissolves the nitrate of copper; this last salt maybe decomposed by boiling it with potash; the precipi tate dried in a red heat is black oxide of copper; one hundred parts of it denote eighty of the metallic copper. Sulphuret of copper may be dissolved in dilutic nitric acid; part of the sulphur remains unaltered, and may be estimated by weighing it, and burning it off; part is acidified, and may be precipitated by nitrate of barytes, 100 parts of the dried precipitate indicating 14.5 of sulphur. By evaporation to dryness, and solution in water, the iron is separated, and the copper may be estimated as in the last paragraph, or =Tiede acid may be used instead of nitric acid, but in that case it is more difficult to obtain a complete solution. The usual process employed in our Cornish mining districts, for reducing copper ores to the state, are described under the article Correa, (which see.)
Ores of Iron.—Notwithstanding the great variety of iron ores, they may be all, se far as analysis is concerned, arranged under three heads ; namely, sulphurete, oxides, and salts. The first are distinguished by their general. bronze colour, but more particularly by the suffocating smell of sulphureous acid gas, which they afford by being heated to redness in the open air. The second consist of iron united with oxygen, and are by far the most common of all. Nearly the whole of the iron ores in use are of this kind, containing also different propor tions of earthy matter in their composition. The third division comprehends such as consist of the oxide of iron combined with some acid, and hence are called salts ; the principal varieties of these are the phosphates, sulphates, arseniates, and carbonates. The various processes employed at our great iron works for the reduction of the different species of iron ore, are given under the article Icon.
Ores of Tin.—Tin-stone, or vein tin, as it is called in Corn wail, contains a Imp proportion of stony matters ; it therefore requires considerable care in its preparation, previously to its being reduced. It is first broken by hammers into places about the size of a hen's egg, when it is ready for the operation of stamp ing, which is performed in the way already described for the ores of gold, excepting that there are only three stompers. A tin plate of about a foot square, and pierced with holes, to admit a moderate sized knitting needle, is inserted in front of the trough, and that surface of the plate with the rough extremities of the holes is on the inside, by which the holes are prevented from being plugged up with the ore. As the ore is reduced to the proper fineness, it passes with the water through the holes into the labyrinth where it is collected, and after being washed on a wooden table, it is ready for roasting. In this state it has a considerableproportion of copper and iron pyrites, and is called black tin ; after being calcined, at a low red heat, for several hours in a large rever beratory furnace, the ore comes out of a bright ochrey red colour, owing to the decomposition and oxidation of some of the metallic substances; but the oxide of tin, when the operation is properly conducted, remains unaltered. The are is washed a second time, to separate the remaining impurities, and the water, which is impregnated with sulphate of copper, is retained, and dem:unposed by means of old iron. The reduction of the ore is the next step in the process; seven cwt. of roasted ore, with one fifth of he bulk of small coal, are introduced into a reverberatory furnace, which is about seven feet long, and three and a half wide—no lime, or, indeed, flux of any kind, is required. A brisk beat is kept up for about six hours, the tin sinking down as it is reduced, and covered with black scoriae. The furnace is now tapped, and the metal flows into a shallow pit ; when the whole of the metal has run out, the scoriae are removed from the furnace, and a fresh charge is made. The metal in the ph throws up a slag, rich in metal, which is immediately returned into the furnace, and after the melted tin has cooled a little, it is taken out with ladles, and poured into granite moulds ; each charge affords on an average from four to five cwt. of metal, but as the first 'corks are not entirely free from metal, they are again stamped and washed, and mixed with a new parcel of roasted ore. The pigs of tin are next put into a small reverberatory furnace, where, without any addition, they are subjected to a very gentle•heat; the purest part of the tin melts first, and is drawn off, forming what is called common grained tin ; the other part con tains some copper, arsenic, and iron, which is brought to a state of fusion, and cast into pip, forming common tin.