ZINC MANUFACTURE. The mode of obtaining zinc from the sulphuret and other ores is explained in the article ZINC. As brought to market, commonly under the name of speller, it is a bluish-white metal, having considerable hardness and toughness. The chief English supply is from Flintshire and the Isle of Man; but the market is mostly supplied from Upper Silieia, where the ore is smelted, and the spelter sent for shipment from Dantzic, Stettin, and Hamburg : shippers are willing to convey it freight-free to serve as ballast for the ships that bring German wool to Mr. Robert Hunt has given the following as an account of the British ores of zinc brought up to the surface in 1857 :— presenting an average of about 66s. per ton. The largest mass of zinc ever described was that which was displayed at the Great Exhibition in 1851, and which weighed 16,000 lbs. It was smelted from the ore by Messrs. Detmold, of New Jersey, in the United States. There is a vein of zinc-ore 9 feet thick, at a spot about 50 miles from New York, and easy of access, as it is not far beneath the surface. The ore is carried to Newark, iu New Jersey, where it is converted partly into metallic zinc, but mostly into zinc-white for house-painting. The metal is separated from the other ingredients of the ore by a process of vaporisation, as described in the article ZINO; but at Messrs. Detcnold's establishment some of the operations are conducted in a remarkable way. A vapour, containing nearly all the zinc, is sent by blast along pipes to a catching-house, where it passes into enormous bags of cotton 5 feet in diameter by 150 feet long ; the gases pass through the meshes of the bag, while an oxide of zinc cools down t" the state of a white powder, which is shaken out of the bag at intervals. This is the mode adopted, not in procuring metallic zinc, but as the preliminary stage in making zinc-white. The powder is either sold in a dry state, in barrels containing 200 lbs., or is ground up with linseed oil and sold in kegs.
In reference to the zinc-white above mentioned, it may be observed that the substance is recommended as a substitute for white lead in house-painting—not as being better suited in itself, but as being less injurious to the workmen. Some persons, moreover, attribute to it much greater permanency, and other qualities superior to those possessed by white lead. Linseed-oil and spirit of turpentine are mixed with the
zinc-white. Oil in good proportion gives it durability and efficacy of covering the surface of the work ; in excess, it has a softening and darkening effect. Turpentine in good proportion gives a ready fluidity for spreading; in excess, the paint becomes too transparent, and has a tendency to pulverise.
Metallic zinc is mostly used in the form of plates or sheets. When heated to a certain temperature it becomes malleable and ductile, and may then be rolled out to any convenient degree of thickness ; and although brittle before this heating, the brittleness never returns after the cooling. This is found to be a valuable property in zinc. In the form of sheets, zinc is largely used for baths, cisterns, tanks, spouts, pipes, chimney-pots, roofing, as also for plates for engraving, sheathing for ships, and as one element iu voltaic batteries. Being so much lighter than lead, zinc is found to be very useful for roofing. The joining of plates of zinc requires to be effected in a peculiar way. [SOLDERING.] In the making of zinc door-plates, a sheet of rolled zinc is cut to the proper size and shape, scraped to a clean surface, ham mered flat, planished with a broad and smooth-faced hammer, and polished. Plates for zincographic engraving require, not a smooth, but a fine granular surface ; they are rubbed first with ordinary sand, and then with fine sifted sand and water applied by means of a woollen rubber.
Many modes of coating iron and other metals with a thin layer of zinc have been described. Among these, one has been patented by Mr. Alexander Watt, editor of the' Chemist.' Steel or iron is pickled in a solution of sulpho-muriatic acid, and then exposed to galvanic action in a battery supplied with cyanide of potassium, liquid ammonia, metallic copper, metallic zinc, hydrochloric acid, and carbonate of potash. This subject is further treated under TINNING.
The chief use of zinc, perhaps, is as a compound in the formation of brass. [Biwa.] In 1860, metallic zinc, under the name of spelter, was imported from foreign countries to the extent of 21,000 tons.