88 THE SCIENTIFIC PAPERS OF 



upon the other, inasmuch as the passage of air through the fire is 

 attended with the generation of heat, whereas the production of 

 the water gases, as well as the evolution of the hydro-carbons, is 

 carried on at the expense of heat. The generation of steam in 

 the water trough being dependent on the amount of heat in the 

 fire, regulates itself naturally to the requirements ; and the total 

 production of combustible gases varies with the admission of air. 

 And since the admission of air into the grate depends in its turn 

 upon the withdrawal of the gases evolved in the producer, the 

 production of the gases is entirely regulated by the demand for 

 them. The production of gas may even be arrested entirely for 

 12 hours without deranging the producer, which will begin work 

 again as soon as the gas valve of the furnace is reopened ; since 

 the mass of fuel and brickwork retain sufficient heat to keep up a 

 dull red heat in the producer during that interval. The gas is 

 however of a more uniform quality when there is a continuous 

 demand for it, and for this reason it is best to supply several 

 furnaces from one set of producers, so as to keep the producers 

 constantly at work. The opening H leading from each producer 

 into the main gas flue can be closed by inserting a damper from 

 above, as shown in Fig. 7, in case any one of the producers is 

 required to be stopped for repairs or because part of the furnaces 

 supplied are out of work. 



It is important that the main gas flue leading to the furnaces 

 should contain an excess of pressure however slight above the 

 atmosphere, in order to prevent any inward draughts of air 

 through crevices, which would produce a partial combustion of the 

 gas and diminish its heating power in the furnace, besides causing 

 a deposit of soot in the flues. It is therefore necessary to deliver 

 the gas into the furnace without depending upon a chimney 

 draught for that purpose. This could easily be accomplished if 

 the gas producers were placed at a lower level than the furnaces, 

 but as that is generally impossible, the following plan has been 

 adopted. The mixture of gases on leaving the producers has a 

 temperature ranging between 300 and 400 Fahr., which must 

 under all circumstances be sacrificed, since it makes no difference 

 to the result at what temperature the gas to be heated enters the 

 regenerators, the final temperature being in all cases very nearly 

 that of the heated chamber of the furnace or say 2500 Fahr. 



