the Converjion of cajl Into malleable Iron . 179 
procefs was remarkably fuccefsful and fhort, does not feem 
favourable to a late ingenious hypothefis, according to which 
water is the embodying principle of all elaftic fluids. I have 
never indeed confidered this as very probable, and, after the ob- 
fervations I have related, I fee no means of defending it. Will 
it be faid, that the pig iron, as being in fome fort a calx of 
iron, contains water ? 
In annealing crude iron, with or without charcoal, it is 
well known to increafe in all its dimenfions. I have feen bars 
originally ftraight bent like an S, when long expofed to heat in 
circumftances where they could not extend themfelves end* 
ways* I fuppofe this phenomenon may be owing to a very 
fmall beginning of this fermentative motion, which ads as an 
internal principle of expanfion. Caft iron bars, not in contad 
with charcoal, would, according to this fuppofition, by long 
annealing lofe of their weight ; or if the heat was too low for 
the elaftic fluid to be difcharged from their fubftance, they 
would probably blifter like fteel 1 an appearance undoubtedly 
owing to the generation of air. Mr* Horne, in his Eflay on 
Iron, fomewhere remarks, that on opening thefe blifters he 
has heard a whiftling noife as of air ruftiing out. 
During the whole of this procefs, frequent jets of white 
fparks, of a dazzling brightnefs, played from the furface of 
the metal. They would have afforded an extremely beautiful 
fpedacle but for the inconvenience of looking 011 fo hot a mafs. 
They arofe, no doubt, from the burning of fmall portions of 
iron. 
The effed of fo much ftirring as I have noted down does not 
require to be explained. 
The workman was clearly of opinion, that the fermenta- 
tion of hard or white crude iron is lefs than of grey in this 
B b 2 procefs ; 
