F 
J 
and ihe O;erations of the Blaft-Furnace. 12g 
always convex. In this ftate iron is too tich for melting 
without the addition of coarfe metal, and is unfit to be uifed 
in a cupola furnace for making fine caftings, where thinnefs 
and a good {kin are requifite. 
No. 4, or oxygenated crude iron, when iffuing from the 
blaft-furnace, throws off from all parts of the fluid furface a 
vaft number of metallic fparks: they arife from a different 
eaufe than that exerted in the former inftance. The extreme 
privation of carbon renders the metal fubject to the combina- 
tion-of oxygen fo foon as it comes into contac with atmo- 
fpheric air. This truth is evidently manifefied by the ejec- 
tion of fmail fpherules of iron from all parts of the furface: 
the deflagration does not, however, take place till the globule 
has been thrown two or three feet up in the air; it then in- 
flames and feparates, with a flight hiffing explofion, into a 
great many minute particles oF brilliant fire. When thefe 
are collected they prove to be a true oxyde of iron, but fo 
much faturated with oxygen as to poffefs no magnetic obe-= * 
dience. The furface of oxygenated iron, when running, is 
covered with waving flakes of an obfcure fmoky fine: ac- 
companied with a hiffing noife; forming a wonderful con- 
traft with the fine rich covering of plumbago in the other 
ftate of the metal, occafionally parting and exhibiting the 
iron in a flate of the greateit apparent purity, agitated in 
numberlefs minute fibres, from the abundance of the carbon 
united with the metal, 
When iron thus highly oxygenated comes to reft, {mall 
fpecks of oxyde begin to appear floating upon the furface: 
thefe increafe in fize; and when the metal has become folid, 
the upper furface is found entirely covered with a feale of 
blue oxyde of various thickneffes, dependent upon the ftage 
of oxygenation or extreme privation of carbon. This oxyde, 
in common, contains*about 15 per cent. of oxygen, and is 
very obedient to the magnet. In place of a dark blue f{mooth 
furface, convex and richly carbonated, the metal will exhibit 
a deep, rough, concave face, which, when the oxyde is re+ 
‘moved, prefents a great number of deep pits. This iron in 
fufion ftands lefs convex than carbonated iron, merely be- 
caufe it is lefs fufceptible of a ftate of extreme divifion ; and 
_ Vou. VY, S indeed 
