| into foundry pigs. 
CASTING. 
‘iron for casting, or fowndry cron as it is called, 
, becomes good and soft in proportion as it receives 
a higher charge of carbon, consequently, a com- 
pletely opposite process must be used to obtain 
this iron and bar-iron; the one having :to be 
charged with carbon, while the other has to be 
deprived of it. Accordingly, instead of remelt- 
ing the forge-iron in a furnace where it is ex- 
posed to air and heat only, without contact with 
the fuel, as is done to make bar-iron,—it must 
be remelted for making foundry iron in close mix- 
| ture with the fuel, and with as little exposure to 
air as possible; and it accordingly undergoes this 
melting, in which it absorbs an additional quan- 
tity of carbon, after which it is tapped and cast 
The name of pig-vron is very 
generally applied in all countries to those straight 
bars, of about four feet in length, in which iron 
for casting is sold. The iron, when it first runs 
from the furnace, is received into a round-bot- 
tomed trough or gutter made in sand, from one 
side of which a number of similar troughs are 
formed at right angles to the first, and three or 
four inches apart, the whole being truly level, 
and open to common communication, so that 
when the first or principal gutter fills with fluid 
iron, all the others will fill also, and the quantity 
of iron when so cast and taken up, resembles an 
immense comb with coarse teeth. These teeth 
are knocked off close to their junction with the 
transverse piece, and then become pigs of iron; 
while the cross piece, which is always larger and 
|| more irregular than the others, is called the sow. 
Pig and sow iron are always sold together; but 
the sow often contains impurities on the furnace, 
| and is not so much esteemed as the pigs. 
CASTING. Iron, as well as brass, and other 
metals which melt at temperatures above igni- 
tion, is cast in moulds made of sand. The kind 
of sand most employed is loam, which possesses 
a sufficient portion of argillaceous matter to ren- 
der it moderately cohesive when damp. The 
mould is formed by burying in the sand a wooden 
pattern, having exactly the shape of the article 
to be cast. Thesand is most commonly enclosed 
in flasks, which are square wooden frames, re- 
sembling boxes, open at top and bottom. If the 
pattern be of such form that it can be lifted out 
of the sand without deranging the form of the 
mould, it is only necessary to make an impres- 
sion of the pattern in one flask; and articles of 
this kind are sometimes cast in the open sand 
upon the floor of the foundry. But, when the 
shape is such that the pattern could not be ex- 
tracted without breaking the mould, two flasks 
are necessary, having half the mould formed in 
each. The first flask is filled with sand, by ram- 
ming it close, and is smoothed off at the top. 
The pattern is separated into halves, one-half be- 
ing imbedded in this flask. A quantity of white 
sand, or burned sand, is sprinkled over the sur- 
face, to prevent the two flasks from cohering. 
GASTING IN PLASTER. 725 
the first, having pins to guide it; the other half 
of the pattern is put in its place, and the flask is 
filled with sand, which, of course, receives the 
impression of the remaining half of the pattern 
on its under side. After one or more holes are 
made in the top, to permit the metal to be poured 
in, and the steam and air to escape, the flasks are 
separated, and the pattern withdrawn. When 
the flasks are again united, a perfect cavity, or 
mould, is formed, into which the melted metal is 
poured. The arrangement of the mould is, of 
course, varied for different articles. When the 
form of the article is complex and difficult, as in 
some hollow vessels, crooked pipes, &c., the pat- 
tern is made in three or more pieces, which are 
put together to form the mould, and afterwards 
taken apart to extract them. In some other 
irregular articles, as andirons, one part is cast 
first, and afterwards inserted in the flask which 
is to form the other part. The metal for small 
articles is usually dipped up with iron ladles, 
coated with clay, and poured into the moulds. 
In large articles, such as cannon, the mould is 
formed in a pit dug in the earth near the 
furnace, and the melted metal is conveyed to 
it in a continued stream, through a channel 
communicating with the bottom of the furnace. 
Cannon - balls are sometimes cast in moulds 
made of iron, and, to prevent the melted metal 
from adhering, the inside of the mould is cov- 
ered with powder of black lead. Rollers for 
flattening iron are also cast in iron cases. This 
method is called chill casting, and has for its ob- 
ject the hardening of the surface of the metal, 
by the sudden reduction of temperature, which 
takes place in consequence of the superior con- 
ducting power of the iron mould. These rollers 
are afterwards turned smooth in a powerful lathe, 
which has a slow motion, that the cutting tool 
may not become heated by the friction. 
CASTING IN PLASTER. Copies are most 
frequently taken, both from new models, and 
from old statues, by casting them in plaster. For 
this purpose, a mould in plaster is first made from 
the surface of the statue or figure itself ; and this 
mould is afterwards used to reproduce the figure 
by casting. Plaster is prepared for use by pul- 
verizing common gypsum, and exposing it to the 
heat of a fire until its moisture is wholly expelled. 
While in this dry state, if it be mixed with water, 
to the consistence of cream or paste, it has the 
property of hardening in a few minutes, and | 
takes a very sharp impression. The hardness 
afterwards increases by keeping, till it approaches 
the character of stone. Moulds are formed in the 
following manner :—The statue, or figure to be 
copied, is first oiled, to prevent it from cohering 
with the gypsum. A quantity of liquid plaster 
sufficient for the mould is then poured on, imme- 
diately after being mixed, and suffered to harden. 
If the subject be a bass-relief, or any figure which 
can be withdrawn without injury, the mould may 
be considered as finished, requiring only to be 
| The second flask is then placed upon the top of 
OCS ee 
