Copper y SI 
The power which the vitrified oxyd of lead has to sco- 
rify all metals, except gold, silver and platina, is amply 
shewn in the process of Assaying , and hence it must hap- 
pen that in refining, some of the copper becomes oxidated 
together with the lead ; but the same process of assaying 
shews that copper requires a large portion of lead for this 
purpose, and therefore the latter metal in so small a pro- 
portion as 6 to 8 per cent, is probably a most useful ad- 
dition where not too expensive. For of all the common 
imperfect metals, copper is that which scorifies and oxi- 
dates with most difficulty when in fusion, and therefore 
the same method, with some little variety, may be prac- 
tised to separate lead and tin (for example) from copper, 
as any or all of these metals from silver or gold, care be- 
ing taken in the former case not to carry the scorification 
beyond what is necessary to separate the more easily oxi- 
dable metals from the copper which then remains in the 
metallic state. This will be further noticed in the suc- 
ceeding article of Alloys of Copper, and the purification of 
bell-metaL After the greater part of the lead has been 
worked off as often as is judged necessary, the remaining 
copper must be kept for a while longer in fusion, to throw 
up the last portions of lead that may adhere. In assay- 
ing gold or silver the total expulsion of the lead is known 
by the fine metal becoming at once brilliant on the sur- 
face, but in refining copper this appearance can never 
take place, as the copper itself always forms a thin oxyd 
on its melted surface ; and therefore, to judge whether it 
is pure, the workman dips a polished iron rod in the melt 
ed mass, and draws out a portion of copper adhering to 
it, which, if pure, immediately falls off when the rod is 
dipped in water. The colour of the scoria is also another 
test. While the copper remains impure and alloyed with 
iron, sulphur, &c. the vitrified oxyd on the surface is black 
or of a dirty brown, but the scoria of pure copper is red, 
and also is readily separated from the iron w: hen. cold, 
leaving no stain behind. 
