TINNING COPPEK, &C. 299 



Blocks of tin are often melted by the pewterers into small rods ; 

 I think the rods are not so pure as the grain tin ; at least, I found 

 that a cubic foot of the specimen I examined, weighed 7246 

 ounces: but even this sort exceeds in purity any of the kinds ex- 

 amined by the authors above mentioned. Chemistry affords cer- 

 tain methods of discovering the quantity of lead with which tin is 

 alloyed, but these methods are often troublesome in the applica- 

 tion ; an enlarged table, of the kind of which 1 hare here given a 

 specimen, will enable us to judge with sufficient precision of the 

 quantity of lead contained in any mixture of tin and lead, of which 

 we know the specific gravity. Pewterers, however, and other 

 dealers in tin, use not so accurate a method of judging of its pa. 

 rity, but one founded on the same principle ; for the specific gra- 

 vities of bodies being nothing but the weights of equal bulks of 

 them, they cast a bullet of pure tin, and another of the mixture of 

 tin and lead, which they want to examine, in the same mould ; and 

 the more the bullet of the mixture exceeds the bullet of pure tin 

 in weight, the more lead they conclude it contains. 



Pewter is a mixed metal ; it consists of tin united to small por- 

 tions of other metallic substances, such as lead, zinc, bismuth, and 

 the metallic part, commonly called regulus of antimony. We hare 

 three sorts of pewter in common use; they are distinguished by the 

 names of plate trifle ley. The plate pewter is used for plates 

 and dishes ; the trifle chiefly for pints and quarts ; and the ley. 

 metal for wine measures, &c. Our very best sort of pewter is 

 said to consist of 100 parts of tin, and of 17 of regulus of anti- 

 mony,* though others allow only 1O parts of regulus to 100 of 

 tint ; to this composition the French add a little copper. Crude 

 antimony, which consists of nearly equal portions of sulphur and 

 of a metallic substance, may be taken inwardly with great safety ; 

 but the metallic part, or regulus, when separated from the sulphur, 

 is held to be very poisonous. Yet plate pewter may be a very in. 

 nocent metal, the tin may lessen or annihilate the noxious qualities 

 of the metallic part of the antimony. We have an instance some, 

 what similar to this in standard silver, the use of which has never 



rcsscmble a des stalactites;" he say* also, that its exportation is> prohibited, but 

 that he does not see the reason for the prohibition, as it is not more pure than 

 Cornish tin: and in this observation he ii right, it is nothing but Cornish tin 

 in a particular form. Ch\m. par M. Baumc, vol. III. p. 422 



* Med. Trans, vol. I. p. 286. 



+ Petnb. Chem. p. 329. 



