264 Mr. Thompson’s Experiments 
the greater part of the heat we find in them as foon as they 
come to be at reft, after having been difcharged from a gun. 
There is another circumftance that may poftibly be brought 
as an obje&ion to this opinion, and that is the running of the 
metal in brafs guns upon repeatedly firing them, by which 
means the vent is often fo far enlarged as to render the piece 
intirely ufelefs. But this, I think, proves nothing but that 
brafs is very eafily corroded, and deftroyed by the flame of 
gun-powder ; for it cannot be fuppofed, that in thefe cafes the 
metal is ever fairly melted. The vent of a mulket is very foon 
enlarged by firing, and after a long courfe of fervice it is found 
neceflary to ftop it up with a folid fcrew, through the center 
of which a new vent is made of the proper dimenfions. This 
operation is called bufhing, or rather bouching the piece ; but 
in all the better kind of fowling-pieces the vent is lined, or 
bouched, with gold, and they are found to ftand fire for any 
length of time without receiving the leaft injury. But every 
body knows that gold will run with a lefs heat than is required 
to melt iron : but gold is not corroded either by the fpirit of 
nitre, or the acid fpirit that is generated from fulphur, whereas 
iron is very eafily deftroyed by either ; and that 1 take to be 
the only reafon why a vent that is lined with gold is fo much 
more durable than one that is made in iron. But it feems, that 
iron is more durable than brafs ; and perhaps fteel, or fome 
other cheap metal, may be found that will fupply the place 
of gold, and by that means the great expence that attends 
bouching pieces with that precious metal may be fpared, and 
this improvement may be introduced into common ufe. 
This leads us to a very eafy and effe&ual remedy for that 
defeat fo long complained of in all kinds of brafs ordnance, 
the running of the vent ; for if thefe pieces were bouched with 
iron. 
