176 Natural Hiftory off in. [Book VI. 



>a white powder. The calx of tin refifts fufion more 

 than that of any other metal ; from which property it 

 is uieful to form an opake white enamel, when mixed 

 with pure glafs in. fufion. 



It is pbferved by miners, that though tin is the 

 lighteft of the metals, its ores are fome of the heavieft. 

 Tin is feldom or never found in the metallic or reguline 

 flate. The ores are often cryflallized, and of different 

 colours. Thofe which are of a reddifh colour gene- 

 rally contain a large proportion of iron. There alfo 

 is a fulphureous tin ore of a brilliant colour, fimilar 

 to that of zinc, or golden, like aurum x mufivum. The 

 more tranfparent ores of tin often contain "arfenic* 

 and this is feparated, almoft entirely, by repeated 

 roaftings. 



In order to reduce the ores of tin, they are firfl 

 cleanfed from foreign admixtures by forting, pounding, 

 and waffling. In the fmelting of the ore, care is taken 

 to add a larger quantity of fuel than is ufual in the 

 revival of other metals, and to avoid a greater heat 

 than is neceflkry to reduce the ore, in order that the 

 lofs by calcination may be as little as poffible. Almoft 

 all the tin ufed in Europe comes from Cornwall, which 

 has been famous for its tin mines from the remoteft 

 periods of hiftory. 



Tin is five times as dear as lead, and as a fmall 

 quantity of the latter mixed with a large quantity of 

 the former is with difficulty difcovered, the temptation 

 to adulterate tin is great, and the fear of detection fmall. 

 Bifiiop Watfon ftates, in his Chemical ErTays, that in 

 Cornwall the purity of tin is afcertained, before it is 

 expofed to fale, by what is called its coinage. The 

 tin, when fmeked from the ore, is poured into qua- 

 drangular moulds of flone, containing about three 

 hundred and twenty pounds of metal, which when 



hardened 



