TIN. 271 



constituents are, tin 34, copper 36, sulphur 25, iron 2. Klaproth. 

 It has been found only in Cornwall. 



The purest and best metal, known in commerce by the name of 

 grain tin, is smelted from stream tin, whilst the article called block 

 tin is extracted from the ore dug out of veins. After the ore is 

 obtained from the mines, it is reduced to powder in a stamping- 

 mill ; it is then washed carefully, and the oxide being mixed with 

 one-fifth of its weight of coke, is roasted in a reverberatory furnace, 

 through a hole in the bottom of which the metallic tin flows into a 

 vessel below. It is afterwards fused in an iron boiler, where it is 

 freed from the scoria which covers it, and finally purified by the 

 addition of charcoal. The metal is usually cast into small bars, or 

 ingots for exportation. 



Tin has a silvery-white colour, which, by exposure to the air, ac- 

 quires a slight superficial tarnish. It feels greasy, and emits a pecu- 

 liar and rather fetid odour when rubbed. It is very soft and mallea- 

 ble, but has little ductility and tenacity. When bent backwards and 

 forwards, it occasions a peculiar crackling noise. Its specific gra- 

 vity is 7*3 ; it melts at 442 ; and if it be then stirred rapidly while 

 it gradually cools, it is obtained in the form of a fine granular pow- 

 der, which is the Pulvis Stanni of the pharmacopoeias. There are 

 two oxides of tin. When tin is exposed to heat in an open vessel, 

 it absorbs oxygen, and is converted into a grey powder. The pro- 

 toxide may also be obtained by pouring diluted muriatic acid upon 

 tin filings, and leaving them in contact forty-eight hours. It may 

 then be separated from the acid by decomposing it by the action of 

 an alkali. The peroxide may be obtained either by heating the 

 protoxide, as we have just stated, or by the action of nitric acid, 

 slightly diluted, upon the metal. A white powder is produced, 

 which is a hydrate of the peroxide, from which the water may be 

 expelled by a red heat. The peroxide of tin is of a straw-yellow 

 colour : it is commonly known under the name of patty powder, 

 and is used for staining glass and polishing silver-plate. Both of 

 the oxides of tin form salts by uniting with acids. Tin combines 

 with chlorine in two proportions. The protochloride may be 

 obtained by boiling tin in a state of minute division, in muriatic 

 acid ; the perchloride may be obtained by exposing tin to the 



