102 TECHNOLOGY. 
The crucible is first heated before the alloyed metal is put in, that any 
cracks may become apparent; and the metal is covered with a layer of 
charcoal, to prevent oxidation by exposure to the air. After it is thoroughly 
melted a specimen is taken out, the alloy tested, and, if necessary, rectified. 
If the proof is satisfactory, the metal is cast into zngots, in moulds of cast 
or wrought iron. Silver is taken out of the crucible with an iron ladle 
coated with clay ; gold is manipulated with a black-lead crucible held by 
tongs. In England and the United States the cast-iron crucible is raised. 
from the furnace by the aid of a crane, and set into a peculiar pouring 
machine, which is gradually tilted by a curved rack and pinion, to allow 
the contents to flow into the iron forms. 7.20, figs. 1 and 2, exhibit such 
a machine. As the crucible is tilted, the carriage upon which the moulds 
are placed is moved along directly under its nose. : 
2. Rottine. The ingots having been cast and cooled are next passed 
through the rolling mill (fig.3). Its construction differs slightly from that 
of the common rolling mill. mis a cog-wheel, which receives motion from 
the driving power of the machine; upon the same shaft are wheels, x and 0, 
gearing into wheels, p and x, upon the axis of the rollers; gg (fig.3") are the 
set screws which serve to adjust the distance between the rollers ; and jig. 4 
shows the manner in which these screws are moved together by the screws, H, 
turning the wheels, r. The rollers are of steel or iron, case-hardened, and 
are usually from four to twelve inches in length. When the requisite 
thickness is thought to be attained, a few blanks are struck and tested in 
the scales; if they are too thick, the rolling is continued ; if too thin, the 
bars must be melted over again. In some cases a flattening mill is made 
use of to prepare the bars for the rolling mill; pl. 20, jig. 7, is an end, and 
jig. 8 a front view of the machine. It is, in fact, a rolling mill, but less 
substantially built than the one already described, and serves to remove the 
chief inequalities of the bars, and to extend them slightly. su is the driving 
pulley upon the shaft of the pinion, c, which engages with the cog-wheel, r, 
upon the lower roller, 6, upon the other end of which is a wheel which 
engages with a similar wheel upon the upper roller. A central wheel upon 
the top of the machine engages with the wheels, e, upon the top of the 
screws which adjust the distance of the rollers, and turns them equally. 
The bars then pass to the drawing machine, of which jig. 10 exhibits a 
top, and jig. 11 a side view; jig. 12 shows the pincers and a section of the 
drawing plate ; fig. 13 is a top-view of the vice; jig. 14, a front view of the 
drawing plate. 
From the driving-pulley L, motion is communicated to the wheel e, on 
the shaft of which are two polygonal disks, ¥, which carry the endless chain 
7, upon which the pincer-carriage travels (jig. 12). The bars are secured 
by screws into the jaws of the pincers, and are drawn through the drawing 
plate. To diminish the ends of the bars that they may pass through the 
dies to the pincers, they are introduced between the rollers of a machine, 
seen in pl. 20, jig. 9, arranged something like the rollers of a rolling- 
mill. The upper roller is cylindrical, but the lower is formed with three 
flat sides. The end of a slip of metal is presented between the rollers while 
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