354 On the Manufacture of Tin-plate. 
was the object in submitting them to that 
high temperature. 
When this is effected, the plates are taken 
to a floor, where they are suffered to cool— 
they are then straightened, and beaten smvoth 
upona cast-iron block. The workman knows 
by the appearance of the plates during this 
operation, whether they have been well scal- 
ed—for if they have, that is, if the rust or 
oxide which was attached to the iron, has 
been properly removed, they will appear 
mottled with blue and white, something like 
marbled paper. The operation we have been 
describing is called scaling. 
As it is impossible the plates can go through 
this process without being in some measure 
warped, or otherwise disfigured, they are 
now rolled a second time, between a pair of 
cast-iron rollers, properly hardened and finely 
polished. This operation makes both sides 
of the plates perfectly smooth, and imparts 
a sort of polish to their surfaces. These 
rollers are each about 17 inches long, and 
12 or 13 inches in diameter—but I am in- 
clined to think that if the diameter was 
greater,* they would set the plates flatter, 
and do the work better in every respect. 
' 
* Since the above was written, I have submitted the 
manuscript to a gentleman who is very largely engaged in 
