224 THE SCIENTIFIC PAPERS OF 



prefer to group the producers together, leading the gas from all 

 into one main flue, from which the several furnaces draw their 

 supplies. The advantages of this are saving of labour and con- 

 venience of management, from the gas producers being all close 

 together, and greater regularity in working, as the furnaces are 

 seldom all shut off at once ; nor is it likely that all will require at 

 the same time an exceptional amount of gas. 



From the fact that the gas producers may be at any distance 

 from the furnaces that they supply, if they are only at a lower 

 level, it would be perfectly practicable to erect them in the very 

 coal mine itself, burning the slack and waste coal in situ (in place 

 of leaving it in the workings as is now often done), and distribut- 

 ing the gas by culverts to the works in the neighbourhood, instead 

 of carrying the coal to the different works and establishing special 

 gas producers at each. In rising to the mouth of the pit, the gas 

 would acquire sufficient pressure to send it through several miles 

 of culvert. 



In the regenerative furnace the gas and air employed are sepa- 

 rately heated by the waste heat of the flame, by means of what are 

 termed "regenerators," placed beneath the furnace. These are 

 four chambers, filled with fire-bricks, stacked loosely together, so 

 as to expose as much surface as possible ; the waste gases from the 

 flame are drawn down through two of the regenerators, and heat- 

 ing the upper rows of bricks to a temperature little short of that 

 in the furnace itself, pass successively over cooler and cooler sur- 

 faces and escape, at length, to the chimney flue nearly cold. The 

 current of hot gases is continued down through these two regene- 

 rators until a considerable depth of brickwork, near the top, is 

 uniformly heated to a temperature nearly equal to that of the 

 entering gas, the heat of the lower portion decreasing gradually 

 downwards, at a rate depending on the velocity of the current, 

 and the size and arrangement of the bricks. The direction of the 

 draught is then reversed ; the current of flame or hot waste gases 

 is employed to heat up the second pair of regenerators ; and the 

 gas and air entering the furnace are passed in the opposite direc- 

 tion through the first pair, and coming into contact, in the first 

 instance, with the cooler brickwork below, are gradually heated as 

 they ascend, until, at some distance from the top, they attain a 

 temperature nearly equal to the initial heat of the waste gases, 



