ZINC. A metal of a bluish-white colour; of considerable hardness, and sr malleable, when pure, as not to be broken with the hammer, though it eased be thus much extended. It is, however, easily rolled into sheets, by the fiatlit mill and in this state, it has recently been brought into very extensive me, in the manufacture of pipes, gutters, and a great variety of vessels and men& Its specific gravity is 7.0. In a temperature of from 210° to 300', it so much ductility, that it can be drawn into wire as well as laminated, = process, a patent was granted to Messrs. Hobson and Sylvester, of Sheffield.
Zinc melts at about 700° Fahr.; by continuing to wise the heat, it soon after becomes red hot, and burns with a dazzling white flame, and oxides with such rapidity, as to fly up in a floculent form, which is called the flowers of sine. When these are urged by a strong fire, they are converted into a clear yellow glass.
In the ordinary method of preparing the sulphate of zinc, or spelter, the ore is exposed to the heat of a furnace, in a melting-pot, from the bottom of which, a pipe descends into a vessel of water, for the purpose of receiving the metal, as they are melted, and for condensing such portion as pass off in the form of vapour. An improvement upon this mode was the subject of a patent, about fifteen years ago ; in which it was so arranged, that as the sine volatilized, the vapour should be received and condensed in a separate vessel, leaving the melted metal, each as lead, and other impurities, in the former. An improvement urn this mode of operating, was lately patented by Messrs. Benecke and Shears; their process consists, first, in a peculiar treatment of the ore, previous to its introduction into the furnace ; and secondly, in a peculiar arrangement of the retorts, and other appendages, by which a more convenient mode of chaiging the retorts is obtained, and a purer metal is the result.
The ores are first to be roasted in the ordinary way, by stratifying them with fuel, and setting fire to the pile. The ore is next spread out in the air, and lixiviated, to separate the sulphate of zinc ; it is next to be dried, pulverized, and roasted a second time, until the sulphur is extricated, when it should be powdered again, and mixed with an equal quantity of carbonaceous matters, such as powdered coal, charcoal, cinders, &c. ; in this state, it is to be saturated
with an alkaline ley, or a solution of common salt ; the solutions varying accord ing to the nature of the ore. Calamine, or other oxides of zinc, will require only to be pulverized and calcined.
With the ores prepared as before mentioned, the retorts are to be charged one of those is shown in perspective at a in the annexed figure ; they are made of fire-clay, or of such earth as will best stand the heat of the furnace. To the front end of these retorts are two apertures: the upper circular, for the reception of the neck of an earthen head-piece b; the lower, d, is square, for clearing out the residuum after working, which is closed during the distillation, by a stopper, and luted. The head-piece has likewise another tube fitted to it, and luted, merely for the purpose of lengthening it sufficiently to allow the vapour to cool as it descends, and to condense upon an iron plate beneath, as shown in the lowest figure in the diagram, which represents a cross or vertical section of a reverberatory furnace, in which a double row of such retorts may be supposed to be arranged, with a aperture between them, where the fire is situated, which rests upon a grating over an arched passage that communicates with the open air outside the building; this arched passage has a door, by the opening and shutting of which the heat of the furnace is regulated as may be required; and through one of the ends of this long passage an aperture is made for supplying the furnace with fuel. The earthen head-pieces b, it will be observed, have an aperture supplied with a stopper ; through these openings the ore and carbon, prepared as before mentioned, are introduced in sufficient quantity, by means of a ladle, into the body of the retort, when the apertures are closed and luted. The operation of distillation then commences ; the zinc, which rises in vapour, passes into the head-piece b, down the pipe c, and falls upon the iron plates beneath, in a condensed state.