On the Manufacture of Tin-plate. 353 
flame could play only on one side of each 
plate, whereas, by being bent in the form 
already described, the flame can operate 
equally on both sides. It may here be re- 
marked that the form of all tin-plates, one 
sort excepted, is that of a parallelogram, 
and that if a piece of stiff paper, or paste- 
board, 132 inches long, and 10 inches wide, 
be bent in the centre at an angle of about 
sixty degrees, and then put to stand on the 
two ends, we shall have the form of a plate 
No. 1. properly bent for the scaling oven. 
The operation of cleansing, as it is called, 
and which is preparatory to the process of 
scaling, is commenced by steeping the plates 
for the space of four or five minutes, in a 
mixture of muriatic acid and water, in the 
proportion of four pounds of acid to three 
gallons of water. This quantity of the di- 
luted acid will generally be sufficient for 
eighteen hundred plates, or eight boxes of 
225 plates each. 
When the plates have been steeped for the 
time prescribed, they are taken out of the 
liquor, and placed upon the floor, three in a 
row, and then by means of an iron rod put 
under them, they are conveyed to a furnace 
heated red-hot, where they remain until the 
heat takes off the scale, the removal of which 
VOL, III. yy 
