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It is then distilled at a red heat in a large earthenware The reduced metal rises in vapour. This vapour is condensed in a suitable apparatus. The metal generally contains small portions of arsenic.

The metal is of a bluish colour, and is much used instead of lead, in consequence of its cheapness. It is crystalline, and under ordinary circumstances brittle; but raised to a temperature of 270° it is malleable, and may be rolled out in sheets without fracture. By such treatment the metal retains its malleability. At a temperature of 400° it may be reduced to powder. At a red heat it boils and volatilises, and in the presence of air burns with a green light, giving rise to the protoxide of the metal, ZnO.

Zinc is readily dissolved by dilute acids. It is generally used in the preparation of hydrogen.

The only known oxide of this metal is the protoxide ZnO. It is a strong base and may be prepared by raising the carbonate to a red heat.

The neutral carbonate of zinc, ZnO,CO2, is found native; it is the chief ore of the metal and is called the calamine stone. It may be prepared by adding the carbonate of potash to a solution of the chloride of zinc, ZnCl + KO,CO2 = ZnO,CO2+ KCl.

The Sulphate of Zinc, ZnO,SO3+7HO, White Vitriol, resembles in appearance the sulphate of magnesia. This salt forms the chief part of the residue left when hydrogen is evolved by the action of dilute sulphuric acid on zinc. The sulphate of zinc is used in medicine as an emetic. It forms double salts with potash and ammonia, ZnO,SO, + KO,SO, + 7HO.

The Chloride of Zinc, ZnCl, is prepared by dissolving the oxide of zinc in hydrochloric acid, ZnO+ HCl = ZnCl+HO. It is very fusible and soluble in water and alcohol. The chloride of zinc com

bines with the chloride of ammonium to form a salt used in tinning and soft soldering the metals. The chloride of zinc is used as a disinfectant, and wood saturated with a solution of the chloride is not affected with dry rot. The salts of zinc are all soluble in hydrochloric acid, and most of them are soluble in water. In acid solutions hydrosulphuric acid produces no precipitate, but if an alkaline acetate be added, the white sulphide of zinc is thrown down. This precipitate is insoluble in potash.

Tests.

Sulphide of ammonium, precipitates the sulphide of zinc. Caustic alkalies give a white precipitate of the hydrate, soluble in excess.

The carbonates of the fixed alkalies precipitate the basic carbonate, insoluble in excess, but soluble in any salt of ammonia.

Carbonate of ammonia precipitates the carbonate, soluble in excess.

The carbonates of the alkaline earths; give no precipitate with zinc salts.

Zinc compounds when fused with carbonate of soda on charcoal in the inner flame of a blowpipe, give a white incrustation of the oxide of zinc. When moistened with cobalt and strongly heated, the colour becomes green.

CADMIUM.

Symbol, Cd; Equivalent, 56.

This metal is more volatile than zinc.

It is gene

rally associated with its ores. When the calamine stone is subjected to distillation with charcoal the

cadmium first comes off in vapour. It has a white tin colour, very malleable, burns when strongly heated. Hydrochloric and sulphuric acid have no effect on the metal at ordinary temperatures. It dissolves easily in nitric acid, and slightly oxidises in air. The Protoxide of Cadmium, CdO, may be prepared by igniting the carbonate in a crucible; it is infusible, dissolves in acids, and its salts are without colour.

The Sulphate of Cadmium, CdO,SO, + 4HO. – This salt is obtained by dissolving the oxide in dilute sulphuric acid, CdO + HO,SO,=HO,CdO, SO,. It is very soluble in water and forms double salts with ammonia and potash.

The Sulphide of Cadmium, CdS, is obtained by passing sulphuretted hydrogen gas through a solution of the chloride of cadmium, CdCl + HS CdS+CIH.

Tests.

Hydrosulphuric acid and the sulphide of ammonium precipitate the yellow sulphide of cadmium : insoluble in alkalies.

Ammonia precipitates a white hydrate, soluble in excess, from which the hydrosulphuric acid precipitates the sulphide.

The fixed caustic alkalies produce a precipitate of the white hydrate, insoluble in excess.

The alkaline carbonates precipitate the carbonate of cadmium: insoluble in excess.

Cadmium compounds, when exposed to the inner blowpipe flame with carbonate of soda or charcoal, give a yellow-brown incrustation of the oxide of cadmium.

TIN.

Symbol, Sn; Equivalent, 58.

Tin occurs in nature as the oxide and sulphide, but chiefly as the former. The chief sources of this metal are the mines of Cornwall, Saxony, Bohemia, and Malacca. It is also found as an alluvial deposit in the beds of small rivers. These two varieties are called mine tin and stream tin. The latter has a much higher commercial value.

Tin ore is reduced by first grinding it to powder, then roasting to get rid of the water, sulphur, and arsenic. It is then heated with coal, and the reduced metal is cast into large square blocks, a specimen of the metal is assayed, and the stamp of the Duchy of Cornwall placed on each block. Tin, when quite pure, is of a white colour, soft and malleable. It is not much affected at ordinary temperatures by exposure to water or air: when raised to its melting point it rapidly oxidises, passing into a white powder, a substance which is used in the arts for polishing, and known as putty powder. The metal is easily dissolved by hydrochloric and nitric acid.

The Protoxide of Tin, SnO, is prepared by adding a solution of carbonate of potash to a solution of the protochloride of tin:

SnCl,KO,CO, + HỌ = KCl + HO + CO, + SnO.

When the precipitated hydrate is dried and heated in an atmosphere of carbonic acid, it becomes a heavy black powder, unalterable in air, but burns like tinder in contact with a hot body, and changes into the binoxide. The protoxide has no basic properties.

Sn,O,.-If a solution of the protochloride of tin be

mixed with a solution of the hydrated sesquioxide of iron, a grey substance falls, which is the sesquioxide of tin.

The Binoxide of Tin, SnO2, has different properties according to the method by which it is prepared. If nitric acid be made to act on pure metallic tin, a white hydrate of the binoxide of tin is produced, insoluble in acids. If the bichloride of tin be precipitated by an alkali, a white precipitate is obtained of the hydrate of the binoxide, freely soluble in acids.

These precipitates have the same composition; and when heated lose their water and leave the pure binoxide of tin. They dissolve in caustic potash, and are precipitated unchanged by acids. The binoxide is a feeble base.

The Protochloride of Tin, SnCl, is obtained by dissolving metallic tin in hot hydrochloric acid. It is soluble in water and used as a deoxidising agent for the salts of mercury and silver.

The Bichloride of Tin, SnCl2, may be prepared by exposing metallic tin to the action of chlorine, or distilling 1 part of powdered tin with 5 parts of the protochloride of mercury. A solution of the bichloride of tin is much used as a mordant.

Protosulphide of Tin, SnS, is prepared by fusing metallic tin with an excess of sulphur, and strongly heating the residue. With hydrochloric acid gently heated it evolves hydrosulphuric acid.

Sesquisulphide of Tin, Sn,S,, may be prepared by gently heating the protosulphide with a third part of its weight of sulphur.

The Bisulphide of Tin, SnS2, Mosaic Gold, is prepared by raising to a low red heat in a glass flask 12 parts of tin, 6 of the chloride of ammonium, and 7 of flowers of sulphur. Two of these substances

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