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 volatiHzes 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 

 porcelain. 



The imperfect reflection is caused by the impossibility of 

 bringing the sheet of glass, into perfect contact with the 

 stone, in consequence of air and dust getting between them. 

 As the ovens are now constructed, the utmost care will not 

 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 

 all 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 comfort- 

 able frame dwelling. In the state of New York there are at 

 this time, no less than eight cyhnder 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 

 years, two thirds. It now bears but about the same value as 

 the amount of the duty imposed upon its importation by 

 government ; of course it has entirely excluded the foreign 

 cylinder glass from our market. I believe there is at pres- 

 ent but one establishment in our country, for manufacturing 

 crown glass, and that is at or near Boston. This I under« 



