356 On the Manufacture of Tin-plate. 
cumstance that appears to me to be deserv- 
ing of attention in the manufacture of a 
variety of other utensils employed in the 
arts.* 
These rollers are used without heat, but 
they are screwed down yery close one upon 
the other, only leaving bare room for the 
plates to pass, that the utmost attainable de- 
gree of pressure may be given to them. 
This last operation is called COLD ROLLING. 
When the plates have undergone this pro- 
cess, they are put one by one into troughs 
filled with a liquid preparation called the lies. 
This is merely water, in which bran has 
been steeped for nine or ten days, until it 
has acquired a sufficient acidity for the pur- 
pose. 'The design of putting the plates into 
the troughs singly, is, that there may be more 
certainty of the liquor getting between them, 
* The art of making good hard rolls appears to be 
very imperfectly understood, because the difficulty of 
producing them is very great.. Not one in three can be 
called thoroughly good. For if they are not sufficiently 
hardened on the surface, they will not wear, whereas if 
they are made hard throughout, or struck hard to the 
centre, as the workmen call it, they will generally crack 
across the middle and become useless. This fault is quite 
independent of air bubbles or flaws, which are always dis- 
coverable in turning by the lathe. 
