416 
Cast Steel. 
the more usual characters of hot-short Iron are owing, 
with perhaps a little sulphur. 
Physical properties of Iron and Steel. 
Iron whether in the states of cast or bar Iron, or steel, 
is attractable by the magnet, and capable of acquiring po- 
larity, this last property however is more durable and pow- 
erful in steel than in any of the other forms of this metal. 
j 
Supercarbonized cast iron is of a dark grey almost 
black colour, has a granular fracture, is very brittle, is 
more fusible than the other kinds of cast iron, and yields 
without difficulty to the file. White cast iron is of a tin- 
white colour, and a coarse grained fracture ; it is brittle 
but very hard, and less fusible than the preceding variety. 
The grey and the mottled varieties approach nearer to the 
one or the other in proportion to their colour. The spe- 
cific gravity of cast iron has not been ascertained with 
great e actness, and no doubt is subject to some varia- 
tions : that which is most highly carbonized has the least 
specific gravity, nor does it probably ever much exceed 
7.01. Cast iron takes impressions from moulds with 
much more sharpness and precision than any other metal : 
and when in fusion if pieces of cast iron are thrown in, 
they will be observed to float on the surface till they melt 
and mix indistinguishably with the rest ; hence it has 
been generally acquiesced in that melted cast iron is of 
greater specific gravity than when solid ; contrary to 
what takes place in all the other metals. This however 
seems to be founded on a mere fallacy, for if it were true^ 
the iron when poured into a mould and beginning to so- 
lidify, ought to spirt out part of the melted metal, as wa- 
ter does under similar circumstances when converting 
into ice : whereas on the contrary, a considerable contrac- 
tion happens which obliges the workmen who are employed 
in casting large pieces, to fill the runners or channels into 
the mould with melted metal 3 lest any cavities should be 
