GLASS-MAKING. i 59 



by dampers, so that the generator yields more or less gas accord- 

 ing to the requirements of the furnace. But the carbonic-acid 

 gas thus produced would be of no value as fuel, for it is totally 

 incombustible. Rising, however, through the mass of incandes- 

 cent fuel above it, the gas is speedily reduced to the condition of 

 carbonic oxide, that combustible gas whose blue flame plays over 



Fig. 2. An Interior View, showing the Brick-work which contains the Gas Generators 



and Melting Tank. 



the surface of an anthracite fire just after fresh fuel has been 

 thrown on. This mixes with the volatile hydrocarbons the coal- 

 gas given off when fresh coal is introduced into the generator 

 and the mixture passes at once to the chamber above the melting 

 tank. The air necessary for the burning of these generator gases 

 is first heated by passing through a number of chambers in the 

 lower part of the furnace. It is mixed with the gases to be burned 

 just before they reach the fire-clay bridge separating the gas gen- 

 erator from the melting tank. The main combustion takes place 

 right at this bridge, and produces an intense heat in the melting 

 chamber, for both the gas to be burned and the air to burn it are 

 highly heated before they are allowed to combine. The effect is 

 the same as would be produced on a small scale if one fed his 

 stove with the hot air from a register. This arrangement removes 

 in a simple and inexpensive way one of the chief objections to the 

 use of gas in glass-making. The fuel is so exceedingly convenient 

 that its use in the industry was proposed, and indeed attempted, 

 years ago, but a sufficiently intense heat could not be thus ob- 

 tained. 



The furnaces are in continuous operation for ten months in the 



