IRON. 
earburet and the iron, which in the latter 
does not take place. If the carburet be 
merely sufficient to saturate all the iron at 
a moderate degree of ignition, the hard- 
ness will be considerable ; but the steel will 
be easily degraded to the state of iron by 
frequent ignition. Such steel in its hard 
state will be very uniform in its texture, 
not excessively hard in Us temper, but dis- 
posed to take a very fine firm edge, which 
will not easily be broken or injured by 
violence. These are accurately the proper- 
ties of the English cast steel, which is of so 
uniform a nature, as to be distinguished by 
its conchoidal or glassy fracture. When 
the dose of carbon in steel is greater, it will 
bear a greater heat without degradation, 
insomuch that it may be welded like iron. 
Its hardness will also be capable of a higher 
degree ; and if this degree produced by a 
stronger ignition be not given, the edge of 
the tool will never become fine and smooth ; 
and even at this higher degree, with all the 
advantage of subsequent tempering, it will 
be less smooth than that of the cast steel, 
and more disposed to break. Steel of this 
kind is better adapted for the construction 
of hammers, vices, hatchets, leather-cutters’ 
knives, and other instruments wherein the 
edge is either stout, or sudden blows unne- 
cessary, or the construction demands fre- 
quent heating and welding. 
By pursuing this train of reflection, it 
will follow, that, since crude iron dissects 
from steel only in the superabundance of 
carbon, it ought to be capable of extreme 
hardness, if ignited to that degree which 
is requisite to combine the greater part of 
this carbon with the iron, and then suddenly 
cooled. This is accordingly found to be 
the case. If the grey, crude iron, commonly 
distinguished by our founders by the name 
of soft metal, be heated to a white heat, 
and then plunged into water, it becomes 
very hard, much whiter, denser, and more 
metallic in its appearance ; and will bear a 
pretty good edge, fit for gravers, for the use 
of turners in iron or steel. In these tools 
the angle of the planes which form the 
edge is about 45°. The hardness of this 
kind of iron is not considerably diminished 
but by ignition continued for a length of 
time, which is a fact also conformable to 
what happens in steel. For the cast steel 
will be softened nearly as much by an- 
nealing to the straw colour, as the harder 
steels are by annealing to a purple or full 
blue. 
Some of our artists have taken advantage 
of this property of soft crude iron in the fa- 
brication of axles and collars for wheel- 
work ; for this material is easily filed and 
turned in its soft state, and may afterward 
be hardened so as to endure a much longer 
time of wear. 
The founders who cast wheels and other 
articles of mechanism are occasionally em- 
barrassed by this property. For, as the 
metal is poured into their moulds of moist- 
ened sand, the evaporation of the water 
carries oft' a great portion of the heat, and 
cools the iron so speedily, as to render it 
extremely hard, white, and ciose in its 
texture. This is most remarkable in such 
portions of the metal, as have the greatest 
distance to run from the git or aperture of 
reception. For these come in contact 
successively with a larger portion of the 
sand, and are therefore more suddenly 
cooled. We have seen the teeth of cog- 
wheels altogether in this state, while the 
rim and other parts of the wheel remained 
soft. The obvious remedy for this defect 
is to increase the number of gits, and to 
have the sand as dry as possible or con- 
venient. In o ther articles this property has 
been applied to advantage, particularly in 
the steel rollers for large laminating mills, 
which Messrs. Vandermonde, Monge, and 
Berthollet have supposed to be an over- 
cemented steel. They are made by casting 
the grey crude iron in moistened sand, the 
contact of which gives the hard steel tem- 
per to the outside surface, for the depth of 
more than half an inch. There is no doubt, 
but that the iron-masters pay considerable 
attention to the quality of the iron, and 
perhaps to the degree of heat and moisture 
of the sand in this operation, in order that 
the hardness may be such as to yield to 
the turning tool; and it is likewise under- 
stood, that a considerable number crack 
longitudinally in the cooling, a loss which 
in all probability arises from the difference 
of contraction between the hard and soft 
parts. 
A variety of facts concerning the harden- 
ing and softening of steel are collected by 
Guyton Morveau, the most interesting of 
which shall be here subjoined. According 
to Reaumur, that part of the steel which was 
hottest at the time of immersion in the wa- 
ter will be the hardest ; whence it has been 
thought a fair conclusion, that the hard- 
ness of steel is the greater, the stronger the 
ignition, and the more speedy the cooling. 
Nevertheless, the celebrated Rinman de- 
duces a very different consequence ; name- 
