394 SECTION MECHANICS. 



combustible gas, consisting chiefly of carbonic oxide and nitrogen, 

 mixed with hydrogen and hydrocarbon gases and vapours, distilled 

 from the fuel, some vapour of water, and more or less carbonic acid. 

 The gas is led, through flues or pipes, to the furnace, which may be 

 at any distance from the gas producers, and is there burned. Gas, 

 capable of producing, in such furnaces, the highest temperatures 

 ordinarily used in the arts, may be made from any description of 

 carbonaceous fuel, from anything in fact that will burn, however 

 much mineral matter it may contain, and whether it is wet or dry. 

 In Sweden, for instance, damp sawdust is used as the fuel to furnish 

 gas for welding and other high heat furnaces ; the large amount of 

 water that the gas from such a material contains being first removed 

 by cooling it, either by sprays of water or by passing it through a sur- 

 face condenser. 



The furnace consists essentially of a heating chamber, of any con- 

 venient shape, below which are placed four regenerator chambers, for 

 taking up the waste heat from the flame, on its way to the chimney, 

 and giving it out again to the entering air and gas. These chambers 

 are filled with loosely stacked fire bricks, and each of them is precisely 

 analogous in its action to a Cowper hot blast stove on a smaller scale. 

 The air and gas, entering the furnace, pass up through two of the 

 chambers, and are thus highly heated, before they are brought together, 

 and burn, at the entrance to the working chamber, or furnace proper, 

 in which the matters to be heated are placed ; and the spent flame, 

 from this, is at the same time drawn down to the chimney through the 

 other two chambers ; and, leaving the greater part of its available heat 

 in the brickwork filling these, escapes to the chimney nearly cool. At 

 intervals of half an hour to an hour the direction of the draught is re- 

 versed ; the air and gas being introduced, in the opposite direction, 

 through the two chambers that have been heated by the waste flame, 

 and the current passing to the chimney being turned through the first 

 pair of chambers, to reheat them in turn. 



As the heated gases are made to pass downwards, through the 

 regenerators, and the cool currents of air and combustible gas ascend, 

 the heating and cooling of the masses of brickwork take place very 

 uniformly ; the hot current descending always most freely through the 

 coolest channels, and the ascending current rising chiefly through the 



