32 
alumina, either tog'ether or separate, are infusible in the heat 
of a furnace) and these together become a liquid scoria: 
while at the same instant, the oxygen of the ironstone, separ- 
ating from the metal or iron part, combines with the other 
part of carbon of the cokes, and the metal thus set free, by 
its superior specific gravity, falls through the scoria into the 
bottom of the furnace. The nitrogen of the air seems 
capable of no action in combustion, but that of taking off 
caloric sufficient to raise its temperature to an equilibrium 
with its surrounding matters. 
Carbon then unites with two portions of oxygen, that of 
the air, and that of the iron-stone : and when it is found in 
such abundance as to saturate both, and to spare, the surplus 
partly unites with the metal, and constitutes a grey, kishy, 
or carbonated iron ; but when oxygen is most abundant, the 
metal is found inclining to whiteness, imperfect, and by a 
covering of its oxide or honey-comb when cast, is known to 
be oxygenated or forge iron, and this in a greater or less 
degree, as the principle of carbon is more or less deficient in 
the furnace. 
It is worthy of remark, that when carbonated iron is made 
it leaves the furnace at a temperature below that of oxy- 
genated iron ; yet the fusion of the former is said to be 
more perfect than that of the latter. 
This seeming paradox we thus explain — It is known that 
the capacity for heat, of all the gases and liquids is much 
greater than that of any of the metals or solids ; hence so 
long as there is carbon sufficient in the furnace, to take up 
all the oxygen, the formation of carbonic acid gas, or oxide, 
prevents the furnace from exceeding a certain point of tem- 
perature ; and the metal having lost all its inherent oxygen, 
(that combined with it as iron-stone or an oxide) by its 
union with carbon, is rendered very fluid and perfectly re- 
duced. On the. other hand, when the proportion of carbon 
is too small, the excess of the oxygen of the air becomes 
