Chap. 32.] Antique Statues and Medals* 201 



an half of a mixture compofed of equal parts of lead 

 and tin. Tin melted with copper forms the compound 

 called bronze. Of this compound the fpecific gra- 

 vity is always greater than would be deduced by com- 

 putation from the quantities and fpecific gravities of 

 its component parts. There feems to be a happy re- 

 lation'between thefe metals, which fits them for form- 

 ing, in conjunction, compounds of great firmnefs, den- 

 fity, and clofenefs. From thefe properties they admit 

 of an excellent polim, and Pliny accordingly informs 

 us, that the beft looking-glaiFes of his time were made 

 of a compofition of copper and tin. But the attention 

 of philofophers is more particularly directed to the 

 mixture of copper and tin, on account of its being the 

 fubftance of which the fpeculums of reflecting ttle- 

 fcopes are made. Mr. Mudge found, after a number 

 of trials, that fourteen ounces and an half of grain tin, 

 with two pounds of copper, made the beft compofition 

 for this purpofe ; an addition of half an ounce more 

 of the tin rendered the compofition too hard to be 

 properly polifhed. 



Pot metal is made of copper and lead, the latter 

 being one-fourth or one-fifth of the weight of the for- 

 mer. Lead, however, does not feem to have any re- 

 markable attraction for copper, and does not promote 

 its fufion, unlefs the lead is heated to a high degree ; 

 the copper then diiTolves with fome degree of efferve- 

 fcence. On allowing the compound to cool, the cop- 

 per feparates again, and forms litde grains in the mais, 

 through which the lead remains difperfed. It is eafy 

 to feparate the' lead again from the copper, if the mals 

 is expofed in a furnace , for the lead melts firft and 

 leaves the copper; the lead, however, which runs of? 

 at firft, contains fome of the copper, which may be 

 afily feparated by melting the lead and taking off the 



fcum, 



