On the Manufacture of Glass. 117 



thrusting this down by means of an iron rod. In this way, 

 with the black oxid of manganese, I have usually succeeded, 

 perfectly. The effect of the lime, (which enters into all the 

 mixtures,) is thought to be, to aid in the fusion of the mate- 

 rial ; and it certainly produces one other effect, that is, it 

 renders the glass a better conductor of caloric, so that in 

 tempering, and in the other operations which it undergoes, 

 there is less liability of loss by breaking, particularly, when 

 under the action of the diamond. 



The wood used in the furnace for melting and blowing, is 

 from three to three and a half feet in length, split so fine that 

 no stick will measure more than two inches in diameter, and 

 all of it requires to be kiln dried. Six ovens built in the center 

 of the manufactory, each containing a half a cord of wood, 

 are used for this purpose. The furnace when in operation 

 consumes six cords of this wood in twenty four hours. 



The Furnace itself is constructed either of artificial stone, 

 made of the same clay as the pots, or of some natural 

 sandstone, that is nearly or completely infusible, when ex- 

 posed to the elevated temperature requisite in the fusion 

 of glass. 



The kind generally preferred is that obtained from Hav- 

 erstraw on the North River. 



The pots of which there are ten, are placed five on each 

 side of the furnace, upon benches extending the length of 

 it, raised about twenty inches from the bottom of the tone, 

 which term is applied to the space in the middle of the fur- 

 nace between the pots — opposite each pot, is a ring stone, 

 through which a space is left denominated the ring, of about 

 seven and a half inches in diameter. Through this the ma- 

 terials are put into the pots, and the glass taken from them 

 for blowing. They also constitute the only draught to the 

 furnace, which is regulated by small clay stones called cook- 

 ies. At each end of the furnace, is a fire place of sufficient 

 size to admit the passage of the pots into the tone, with 

 which it directly communicates. The fire places after the 

 pots have been put into the furnace are closed, by means of 

 a claystone door, eight inches thick, through which is an 

 opening near its center four inches in diameter, to admit 

 the wood — a space is also left at the bottom of the door for 

 the admission of air, and the lock stone which forms the 

 bottom of the fire place is also perforated for the same pur- 

 pose. 



