On the Manufacture of Glass. 123 
sequence of an increased heat accelerating the operation, 
the workmen are tempted to employ it. It is probable this 
increased heat volatilizes the alkali from the immediate sur- 
face of the glass, and thus the silex deprived of its solvent, 
causes the dimness. The same effect is produced, as it is 
well known, by a long exposure of window glass to the 
weather, and is exhibited in a remarkable degree, upon frag- 
ments of glass which are left for months in the flattening 
ovens, which become perfectly opake, resembling pieces of 
wholly prevent it. The slight scratches are produced by 
shoving the sheet from one stone to the other. ‘These may 
be prevented in the following manner. A sheet of glass is 
made very thick, from one fourth to one third of an inch. 
This is placed upon the flattening stone, and the cylinder is 
brought upon it and flattened. Both sheets are then shoved 
down upon the other stone, the upper sheet is removed, and 
the thick one which is called a legger, returned to the flat- 
tening stone to receive another. All the glass which is cal- 
led imitation crown, is flattened in this manner ; and where 
| the above precautions are taken, it is nearly equal in quali- 
ty to crown glass, while it possesses the superior advantage of 
being thicker. . 
Imperfect as we commonly find cylinder glass, still its low 
price, (being but about one half that of crown,) insures for it 
an immense market, particularly in those parts of our country, 
where the inhabitants, having cleared their farms, are chang- 
ing their residence from the rude log cabin, to a more coinfort- 
able frame dwelling. In the state of New York there are at 
this time, no less than eight cylinder glass houses, which to- 
gether throw into the market from sixty to seventy thousand 
boxes annually. Indeed at the present moment the domestic 
competition is so great, that it has reduced the price in twelve 
ears, two thirds. It now bears but about the same value as 
ent but one establishment in our country, for manufacturing 
crown glass, and that is at or near Boston. This I under- 
