TIN. . 59<J 



ORDER V. 



OTHER METALS PROPER HAVING ISOMORPHOUS RELATIONS WITH 

 THE MAGNESIAN FAMILY. 



SECTION I. 



TIN. 

 Eq. 735.3 or 58.<)2 ; Sn (stannum). 



Tin does not occur native, but its common ore is reduced 

 by a simple process, and mankind appear to have been in pos- 

 session of this metal from the earliest ages. The most produc- 

 tive mines of tin are those of Cornwall, from which the ancients 

 appear to have derived their principal supply of this metal, 

 and those of the peninsula of Malacca and island of Banca in 

 India. 



The only important ore of tin is the peroxide, which is found 

 in Cornwall, both in veins traversing the primary rocks, and in 

 alluvial deposits in their neighbourhood. In the latter case the 

 ore presents itself in rounded grains of greater or less size, 

 which form together a bed covered by clay and gravel. The ore 

 has evidently been removed from its original situation, and the 

 grains rounded by the action of water, which has at the same 

 time divested it of the other metallic ores with which it is ac- 

 companied in the vein; these being softer are more easily re- 

 duced to powder, and have been carried away by the stream. 

 This ore, called stream tin, is easily reduced by coal, and gives 

 the purest tin. The metal from the ore of the veins, is conta- 

 minated with iron, copper, arsenic and antimony, from which a 

 portion of it is partially purified by liquation. Bars of the im- 

 pure metal are exposed to a moderate heat, by which the pure 

 tin is first melted, and separates from a less fusible alloy, con- 

 taining the foreign metals. The purer portion is called grain 

 tin, and the other ordinary tin or block tin. The mass of grain 

 tin is heated till it becomes brittle, and then let fall from a 

 height. By this it splits into irregular prisms, somewhat re- 

 sembling basaltic columns. This splitting is a mark of the 

 purity of the tin, for it does not happen when the tin is im- 

 pure. 



