aoo Gun and Bell Metal. [Book VI. 



calicoes. Liver of fulphur and hepatic gas have a 

 ftrong action on copper ; the former diflblves the me- 

 tal by the dry, as well as by the humid way; the latter 

 ftrongly colours the furface, but its effect has not yet 

 been well examined into. Oils alib difiblve copper, 

 particularly thofe of an aromatic kind. 



There are few metals which will not form alloys with 

 copper. A metallic compound is made with copper 

 and arfenic in imitation of filver, but it fbon tarnifhes. 

 In treating of zinc, the procefs for making brafs has been 

 defcribed 1 . Pinchbeck is a kind of brafs made in imi- 

 tation of gold. Copper is the bafts of gun metal and 

 bell metal. Gun metal is faid to confift of copper, 

 with about one- tenth part of tin; bell metal, of copper 

 with about one-fifth of tin, It may in general be ob- 

 ferved, that a lefs proportion of tin is ufed for making 

 church bells than clock bells, and t^at a little zinc is 

 added for the 'bells of repeating watches, and other 

 fmall bells. 



Copper, in a ftate of fufion, is liable to aviolent ex- 

 plofion if touched with any humidity. In the calling 

 of bells and cannon they are particularly careful to 

 have the moulds dry; for if the leafl moifture finds 

 accefs, it is fuddenly converted into vapour, and by its 

 expansion throws the metal to a confiderable diftance, 

 to the great danger of the perfons prefent. 



The beft poffible proportions of copper and tin, for 

 the above purpofes, have never, I believe, been accu- 

 rately afcertained. The metallic compound ufed by 

 the Romans for their ftatues and plates for infcrip- 

 rions, is defcribed by Pliny the naturalift. They 

 firfl melted a quantity of copper ; into the melted 

 copper they put a third of its weight of old copper, 

 which had been long in ufe; to every hundred pounds 

 weight of this mixture they added twelve pounds and 



6 an 



