Cast Steel. 
409 
pressure of the superincumbent scoriae are taken into con- 
sideration, we shall cease to be surprised at the apparent 
« anomaly. The existence of oxygen in cast iron, is ma- 
nifest from the phenomena that accompany the operation 
of puddling as already described in a preceding section. 
The crude iron being subjected to a high temperature* 
under a pressure no greater than that of the atmosphere, 
the oxygen and carbon that it contains react upon each 
, other and produce carbonic acid and gaseous oxyd of car- 
bon, which having escaped, the metal is found reduced 
to a state of malleability. The same effects take place in 
close vessels, as Dr. Beddoes has well shown. If crude 
cast iron is put into a retort, as soon as the vessel and its 
contents have acquired a low red heat, an inflammable 
gas, mixed with carbonic acid, is given out with consider- 
able rapidity (this inflammable gas must, from the cir- 
cumstances, be the oxyd of carbon) when the production 
of gas ceases, the iron upon examination will be found 
to have lost somewhat of its weight, and to be nearly in 
the state of bar iron. But though this combination of the 
oxygen and carbon of the crude metal, and the conse- 
quent generation of air takes place with great ease when 
the beak of the retort is but just dipped under water, yet 
if the pressure amounts to five inches of water, in addi- 
tion to the atmosphere, the disengagement of air proceeds 
very slowly, and entirely ceases if instead of the w T ater, a 
single half inch of mercury is employed ; although upon 
removing this obstacle the bubbles of air pass through as 
before. 
Bv the treatment that cast iron undergoes during its con- 
version into malleable bar iron, the greater part of the ox- 
ygen and carbon is got rid of ; still, however, a small 
quantity of oxygen, the smaller in proportion to the good- 
ness of the iron, remains. This is inferred with much 
probability from the blistered appearance that the bars of 
