102 
Brass « 
general purposes, and particularly for the coinage. A 
number of very ingenious experiments were then made on 
the best method of freeing the metal of church bells from 
their tin and other alloy, and obtaining thence a good 
malleable copper with the least possible expence or loss. 
The circumstances in which it is worth while to melt 
down great bells for the sake of the pure copper do not 
€)ften occur, but the various processes may be here short- 
ly noticed as important to the history of the chemical 
properties of copper alloys, and as a very happy example 
of the application of theoretic chemistry to the purposes 
of manufacture. Pelletier and Fourcroy seem to have 
chiefly distinguished themselves in this research, and each 
chemist appears to have followed nearly the same track, 
but with an acknowledged priority in the former. 
The great principle on which all the modes of purify- 
ing bell-metal depend, is the much more ready oxydabi* 
lity of tin by the united action of heat and oxygen, than 
copper. Hence even when bell-metal is simply kept melt- 
ed in an open vessel, a degree of separation of the two me- 
tals begins instantly, the tin oxydating much faster and 
sooner than the copper, and of course the proportion of 
copper being therefore constantly increasing in the fluid 
metal below. 
Another equally important circumstance also depend- 
ing on the much stronger affinity of tin for oxygen, is, that 
when oxyd of copper is mixed with tin at its lowest state 
of oxygenation, the tin still retains its superior affini- 
ty for oxygen, and deprives the oxyd of copper of this 
principle, and the products are, tin highly oxygenated and 
in a pasty semi-fluid mass, and copper in the reguline 
state, partly collected at the bottom of the vessel and part* 
ly in small globules entangled in the oxyd of tin. 
The direct experiments of Fourcroy on this point are 
valuable'- 
