PAItT II.

Materia Mibica.

385

The purest and best tin of Cornwall is procured from thetin stone, which is found beneath the beds of streams, particu-larly at Carn near Perran. The ore is found under a stratumof clay about fifty feet thick, and a layer of rounded stones;occurring loose in lumps and grains of various sizes. It isfirst washed, then bruised and passed through wire sieves con-taining 16 meshes in the square inch; and next smelted withcharcoal, in a common blast furnace, through a hole in thebottom of which the reduced metallic tin flows into a pit below;to purify it, the tin in the fused state is ladled from thepit into an iron boiler placed over a fire; and pieces ofcharcoal plunged, by means of an iron instrument, to its bot-tom, which occasions an ebullition, and causes any slag it con-tains to rise to the surface, whence it is skimmed off. Thetin is lastly cast into bars or pigs, weighing from 2 to 3 cwt,each. 1

Qualities. — Tin has a very slight, somewhat disagreeable,taste, and emits a peculiar odour when rubbed. Jt has thecolour and the brilliancy of silver; is very malleable; but haslittle ductility and tenacity; is easily cut with a knife; and isflexible, producing a peculiar crackling noise when bent back-wards and forwards. Its specific gravity, after fusion, is 7 "291;and after being hammered, 7'299.' It melts at 442 Fahr.,but is not volatilized, and on cooling crystallizes in rhombs.Tin exposed to the air soon loses its lustre, and when meltedit is oxidized, a gray oxide being formed on its surface, whichbecomes yellow if the heat be continued; and if raised to afull red heat takes fire, and acquires a pure white colour. Itis also oxidized by many acids; and combines readily withsulphur.Officinal. Stanntjm : Stanni limatura. Lond. Edin. Dub. The

filings and powder of tin.

Tin melted and agitated briskly in a heated mortar with awarm pestle till it cools, or shaken in a wooden box, is re-duced to a kind of powder, consisting of small rounded par-ticles, with very little lustre; but still in the metallic state.This is the powder of the pharmacopceias.

Medical properties and uses. — Tin is anthelmintic. It wasformerly used in hysteria and hypochondriasis; but its efficacyin these complaints cannot extend beyond its power of dis-lcdgings worms. It is generally supposed to operate mechani-cally only; but it has been suggested, that " it is not impro-bable, it may act by generating hydrogen gas in the intestinalcanal, which proves noxious to the animal; and its efficacyhas been said to be increased by combination with sulphur,

Jikin'i Dictionary of Chemistry.

Br i'son.

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