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and lead were found in some, but in such small proper* 
tion as to appear only an accidental impurity,. 
Copper with 7?«.— The alloys of copper and tin are ex-* 
tremely important in the arts, and curious as chemical 
mixtures* They form in different proportions mixtures 
which have a distinct and appropriate use* Tin added 
to copper makes it more fusible, much less liable to rust 
or coiTosion by common substances, harder, denser, and 
more sonorous,, In these respects the alloy has a real ad- 
vantage over unmixed copper, but this is in many cases 
more than counterbalanced by the extreme brittleness^, 
which even a moderate portion of tin imparts, and which 
is a singular circumstance considering how very mallea- 
ble both metals are before mixture, and the remarkable 
softness and ductility of tin* 
The sensible qualities of the different mixtures are the 
following. Copper alloyed with from 1 to about 5 per 
cent* of tin is much harder than before, the colour yellow 
with a cast of red, and the fracture granular. It is still 
considerably malleable* This appears to be the usual 
composition of many of the very ancient copper tools and 
weapons before the common use of iron ; whence it ap- 
pears that the ancients did not (as has often been sup- 
posed) possess any peculiar art of hardening pure copper, 
otherwise than by mixture* It is certain that the quench- 
ing of red hot copper in water will not at all make it hard- 
er, or have any such effect as it has upon iron* An alloy 
in which the tin is from one-tenth to one-eighth of the 
whole is hard, brittle, but still a little malleable, close- 
grained, and yellowish- white* Where the tin is as much 
as one-sixth of the mass, it is now entirely brittle, and 
continues so in every higher proportion* The yellowness 
is not entirely lost till the tin is above 7- 23ds of the whole,. 
Copper, or sometimes copper with a little zinc, alloyed 
with as much tin as will make from about one-tenth to 
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