OBSERVATIONS. 59 
fefent, as they contain about eight parts 
of iron in a hundred. The very trifling 
mark of arfenic obferved in § i. de- 
ferves no notice. - ' 
Grey Copper Ore from 'Trefeaven. 
I only mention thefe experiments as 
a proof that the moifl: way of aflfaying 
ores is in fome cafes preferable to the 
common fmelting procefs. Copper-ores 
efpecially, afiayed in the dry way, do 
not give the exadt quantity of metal 
contained in them. This is partly owing 
to a tendency the calces of copper have 
to form in a llrong heat fcoriae, and 
partly to a diflblution of a portion of 
the copper by the alkaline fluxes which 
are ufually employed. 
The fluxes confifting of glafs, borax, 
and charcoal, recommended by Meflrs. 
Gellert, Tillet, de Morveau, and other 
metallurgifts, give, indeed, more regulus 
of 
t 
