TINNING COPPER, &C. 



contained the mo>l of it, to more than one grain in an 

 ounce ; that is, it did not constitute more than one five.hu;ulre*ith 

 and seventy sixth part of the weight of the tin, tin-re being 576 

 giains in a J-'rtnch ounce. This proportion of arsenic is so wholly 

 incon-iilerable, that it is very properly concluded, that the internal 

 use of such small portions of tin, as can mix themselves with our 

 food, from being prepared in tinned vessels, can be in no sensible 

 degree dangerous on account of the arsenic which the tin may con- 

 tain. But though tin may not be noxious, on account of the 

 arsenic which it holds, it still remains) tu be deti.tetl, \v In (her it may 

 not b<- poisonous of itself; as lead is universally allowed to be, 

 win n taken into the stomach. The large quantities of tin, which 

 are someiin es given in medicine with much safety, and the con. 

 stant use which our ancestors made of it in plates and dishes, before 

 the ii.tru tiction of china or other earthen ware, without experi. 

 pacing any mischief, render all other proof of the innocent nature 

 of pure tin superfluous. And hence it may be proper to add a few 

 observations concerning the purity of tin. 



The ores of metallic substances often contain more substances 

 than that particular one from which they receive their denomina- 

 tion. M. Kller, of Berlin, had in his collection an ore, -which con. 

 tained gold and silver, and iron and quicksilver, closely united 

 tog< ther in the same mass. Lead ore, it has been remarked, so 

 often contains silver, that it is seldom found without it ; it is often 

 also mixed with a sulphureous pyrites, which is a sort of iron ore, 

 and with blackjack, which is an ore of zinc ; so that lead, and 

 silver, and iron, and zinc, are commonly enough to be met with in 

 the same lump of lead ore. Tin ore, in like manner, though it is 

 sometimes unmixed, is often otherwise; it frequently contains 

 botli tin, and iron, and copper. The lire with which tin ore is 

 smelted, is sufficiently strong to smelt the ores of the metals which 

 are mixed with it ; and hence the reader may understand, that, 

 without any fraudulent proceeding in the tin smelter, there may be 

 a variety in the purity of tin, which is exposed to sale in the same 

 country; and this variety is still more likely to take place, in spe- 

 cimen- of tin from different countries, as from the East Indies, 

 from England, and from Germany. This natural variety in the 

 purity of tin, though sufficiently discernible, is far less than that 

 which is fraudulently introduced. Tin is above five times as dear 



