TINNING COPPER, &C. 997 



as lead ; and as a mixture consisting of a large portion of tin with 

 a small one of lead, cannot easily be distinguished from a mass of 

 pure tin ; the temptation to adulterate tin is r'at, and the fear of 

 detection small. In Cornwall, the purity of tin is ascertained, 

 before it is exposed to sale, by what is called its coil-age: the tin, 

 when smelted from the ore, is poured into quadrangular moulds of 

 stone, containing about 320 pounds weight of metal, which, when 

 hardened, is called a block of tin ; each block of tin is coined in the 

 following manner: " The officers appointed by the D>;ke of 

 Cornwall as"<a\ it, by taking off a piece of one of th uiuitr cor- 

 ners of the block, partly by cutting, and partly by breaking; and 

 if well purified, they stamp the face of the block with tie impression 

 of the seal of the Duchy . which stamp is a permission f'r the owner 

 to sell, and at the same time an assurance that the t-n so mark' d has 

 been purposely examined, and foun-J merchama'tlf *." This 

 rude mode of assay, is not wholly improper; for if the tin be 

 mixed with lead, UIP lead will by its superior weight sink to the 

 bottom, and thus he liable to be discovered, when the bottom cor- 

 ner of the block is < xamined. But though the seal of the Duchy may 

 be some security to the original purchasers of Muck tin, it can be 

 none at all to those foreigners who purchase our tin t'rom Holland ; 

 for, if we may believe an author of great note * in Holland every 

 tin founder has English stamps, and whatever hi- tin be, the in. 

 scription, block tin, makes it pass for Engli-h t." This foreign 

 adulteration of English tin may be the reason t> at Musschenbroeck, 

 who was many years professor of natural philosophy at Utrecht, 

 puts the specific gravity of what he calls pure tin equal to 73iO, 

 but that of English tin, and he has been followed by Wallerius, 

 equal to 7471 + ; for it will appear presently, that such sort of tin 

 must have contained near one.tenth of its weight of lead. 



Borlase'sNat Hist, of Cornw. p. 183. 



+ Newman's Chem. by Lewis, p. 89. 



J Mu>schen. Ess. de Phys. 1739. French Trans. Wallerii Min vol. I. p. 154. 

 There is a very good Table of Specific (.'r.i\it:.>, ;"ilj!i 3 hcd i. r, tn , ml vo- 

 lume i.f Mu-Mhenbroeck's Intruductio ail I'hiln- p.'im .V//H/- ;n, I7'";, in 

 which the author does more justice to J-inglish <m, ^ iiuti< tin weight of a 

 cubic foot of t!ie purest sort equal to 7295; avoir, oun. Um- spec 1 men cf the 

 purest sort of Milacca tin gave 7331, ;md another Gl> ounce* a cubic lV,or t 

 which-is the lightest of all the tins which he examined. 



