CHAMBERS'S INFORMATION FOR THE PEOPLE. 



extent does, and therefore some caution is neces- 

 sary in using soft water which has been standing 

 any length of time in a lead cistern, for cooking 

 purposes. In certain alloys employed in the arts 

 lead is an indispensable metal ; thus, with antimony 

 it forms type-metal ; with tin, Britannia metal, 

 pewter, composition metal for pipes, and solder. 

 Much lead is converted into the carbonate (white- 

 lead) for the use of painters, while a lesser quantity 

 is made into red oxide, red-lead, or minium, as it 

 is variously called, and likewise used as a paint, 

 but also in the manufacture of flint-glass and glazes 

 for pottery. Besides these, other compounds of 

 lead are employed by dyers, calico-printers, and 

 druggists. 



In Great Britain, 69,037 tons of lead were 

 smelted in 1871, which maybe taken as nearly the 

 average for a considerable number of years. Its 

 value amounted to ,1,251,815, or rather more 

 than 18 per ton. In the same year, 65,167 tons, 

 valued at i, 393, 134, were imported, principally 

 from Spain and Greece ; while 44,787 tons, valued 

 at ^860,528 (some of it not being desilverised), 

 were exported. Both the imports and exports of 

 lead have increased of late. (In 1880, the total 

 produce of lead in Britain was 57,000 tons, 

 value ^954,000.) 



Zinc. 



Although in Europe the distinctive properties of 

 zinc were first described by Paracelsus, in the i6th 

 century, yet it had been known and used in the 

 East from an early period. The Romans were 

 acquainted with the art of making brass an alloy 

 of copper and zinc but this may have been ob- 

 tained from smelting an ore containing the two 

 metals, a practice not yet entirely abandoned. 

 The two principal ores of zinc are blende, or 

 sulphide of zinc called by the miners 'blackjack' 

 and calamine, or carbonate of zinc ; the former, 

 when pure, containing 67 per cent, and the latter, 

 52 per cent, of the metal ; but, like most ores, they 

 are rarely found pure. Blende is found in Wales, 

 Cornwall, and Derbyshire ; and calamine chiefly 

 in Cumberland. On the continent, there are well- 

 known localities for zinc ores, in Belgium, 

 Italy, Silesia, Carinthia, and Spain, in the north- 

 west of which large deposits of calamine were 

 discovered a few years ago. Three distinct kinds 

 of furnaces are in use for smelting zinc, namely, 

 the English, the Silesian, and the Belgian, in all of 

 which the metal is extracted by distillation, as it 

 goes off in vapour at a bright red-heat. The last 

 is now by preference used in England. It consists 

 of a wide, but comparatively shallow arched 

 chamber, with a fireplace along the bottom. The 

 chamber is divided by shelves and upright pieces, 

 into sixty or eighty pigeon-holes, each containing 

 a carefully made fire-clay retort, with a clay 

 condenser or nozzle, and a sheet-iron mouth- 

 piece. The size of the retort is about three feet six 

 inches long, and eight inches in diameter, and each 

 receives a charge of ground and roasted ore, mixed 

 with small-coal free from sulphur. The furnace 

 being in action, carbonic oxide gas soon forms, 

 and burns with its characteristic blue flame at the 

 mouth of the retorts, which after a time disappears, 

 and the white fumes of zinc then begin to appear. 

 The iron mouth-pieces are now put on, and the 

 furnace kept steadily going for about six hours, 

 when the melted zinc which has accumulated in 



412 



the condensers of the retorts is withdrawn by a 

 scraper, and cast into cakes or ingots. 



Zinc is of a bluish-gray colour, is comparatively 

 soft, though much harder than lead or tin, and 

 presents a crystalline fracture when broken. It 



Fig. 7. Zinc Retort, with Clay and Zinc Nozzles. 



is rather brittle at ordinary temperatures, but it 

 was discovered early in this century that, if heated 

 to between 200 and 300 F. its malleability and 

 ductility were so increased that it could be rolled 

 into thin sheets or drawn into fine wire. Since 

 then, zinc has been gradually applied to a great 

 many useful purposes, its use formerly being 

 chiefly confined to form brass with copper. In 

 moist air it takes on a superficial coating of oxide, 

 eventually converted into carbonate, which seems 

 to protect the body of the metal from further 

 oxidation. This property gives it a particular 

 value for roofing, spouting, skylight frames, and 

 the like, for which it is now much employed. The 

 so-called galvanised iron is merely iron dipped in 

 melted zinc to protect it from rusting. Plates for 

 engraving upon, light perforated screens, statuettes, 

 and other ornaments of zinc, have of late years 

 been extensively made. Oxide of zinc is used as 

 a white paint, for which purpose it keeps its colour 

 better, but has less body than white-lead. Some 

 of the salts of zinc are used in medicine and the 

 arts. 



From the zinc ores raised in the United King- 

 dom in 1880, 7162 tons of zinc were obtained, 

 the value of which was .123,544, and the mean 

 price per ton for the year about 17, 55. Our 

 great supply of zinc is obtained from Belgium and 

 the island of Sardinia, the former exporting it as 

 metallic zinc, the latter as ore. 



Aluminium. 



This interesting metal was first isolated as a 

 gray powder by Wohler in 1828; but it was little 

 known till the experiments of St Clair-Deville, in 

 1855, shewed that it could be prepared on a large 

 scale, and in a compact form, without much 

 difficulty. Clay and felspathic minerals are largely 

 composed of alumina, or the oxide of aluminium, 

 and therefore substances which might be used as 

 an ore of the metal are abundant. But aluminium 

 has of late been made chiefly from bauxite, a 

 mineral found in France, and consisting chiefly of 

 alumina and oxide of iron. From this, by cer- 

 tain processes, a double chloride of aluminium 

 and sodium is prepared, which is then heated in 

 a reverberatory furnace, with fluxes and metallic 

 sodium added. The sodium seizes the chlorine 

 in combination with the aluminium, and the latter 

 thus liberated falls to the bottom of the fused 

 mixture. 



Aluminium is a remarkably light metal, its 

 specific gravity being only 2-6, or about one-fourth 

 the density of silver. Its colour is white, with 

 more of a bluish tendency than silver ; and, so far 

 as is yet known, it is not in the least tarnished, 

 even by impure air. It is malleable and ductile, 



