By the arrangement described, the heads and necks of each retort are placed in a square recess or neck by itself; by walls built out between them, so that each may be perfectly closed in by a door from wall to wall. The doors are made of latticed wire work, for the purpose of holding clay when plastered over them, for the purpose of effectually confining the heat within the furnace ; each of these doors has a central eye-hole, provided also with a stopper, for watching the progress of the operation, and for enabling the workmen to determine the degree of heat to be applied, and other circumstances. By another arrangement the before-mentioned patentees propose to erect furnaces with several tiers of cylin drical retorts, placed one above another, with their necks or heads projecting beyond the front wall. The fire-place is covered by a low arch, to prevent the fire acting too violently upon the lowermost vessels ; but through the arch apertures are made for the circulation of the heated air among the vessels above.
The carbonate of zinc, which is employed as a white pigment, is manufactmed by pouring into a solution of zinc, in sulphuric acid, a solution of carbonate of ammonia, and afterwards washing and drying the 'pirate. The next im
portant use of zinc is in the fabrication of those fill and beautiful alloys with pe called brass, prince's metal, &c. See ALLOY, Correa, Baum, &c.
, is the native sul buret of zinc • the two substances are, however, difficult to combine artificially. The diluted sulphuric acid dissolves sine, giving out much heat to the solvent, while hydrogen escapes. An undissolved residue is left, which Proast says, is a mixture of arsenic, lead, and copper. The white vitriol, or white copperas, as it is usually termed, is crystallized rapidly, resem bling loaf sugar Sulphurous acid also dissolves zinc, sulphuretted hydrogen being evolved. Diluted nitric acid rapidly dissolves zinc, producing much heat, with the extrication of nitrous gas. Murratic acid operates violently upon zinc, disengaging much hydrogen. The phosphoric, fluorin, carbonic, acetic, suc cinic, benzoic, oxalic, tartaric, citric, and other acids, operate upon zinc, with various energy. The zinc is precipitated from its acid solutions, by means of the alkalies and soluble earths; the former redissolving the metal, if they be in excess. Most of the alloys or metallic combinations with zinc, have already been noticed under other heads.