On the Manufacture of Tin-plate. 355 
The technical name of this apparatus is 
rolls, not rollers. All the rolls which are 
employed in rolling plates, either hot or cold, 
in this manufactory, are hard rolls—and there 
is as much difference between a pair of hard 
cast iron rolls, and a pair of soft rolls, al- 
though they may both be run out of the 
same pot of metal, as there is between iron 
and steel. The workmen inform me that 
the difference is entirely occasioned by the 
manner of casting them—the soft rolls being 
cast in sand, whereas the hard rolls are form- 
_ed by pouring the metal into a thick cast iron 
box—and that the metal, by coming in con- 
tact with the cold box is sufficiently chilled 
to render the whole face of the roll entirely 
hard. ‘The difference in the temper of these 
two kinds of rolls isso great, that when they 
are put into the lathe to be turned perfectly 
true, the turnings from the one will be th of 
an inch in thickness, whilst the turnings 
which come from the other are not larger 
than very fine needles. The temper of cast 
iron thus varying according to the nature of 
the mould into which it is poured, is a cir- 
the manufacture of tin-plates, and he tells me that the 
cold rolls which are employed in his work, are 30 inches in 
diameter. 
