ON FURNACES. 395 



hottest. The position of the regenerators, below the level of the work- 

 ing chamber, gives also the advantage of an absence of indraughts of 

 cold air into this ; as owing to the ascending draught of the hot pas- 

 sages, through which the gas and air are introduced, a balance of 

 pressure, or even an outward pressure, may be maintained in it, while 

 the furnace is in full work. 



The saving of fuel in the regenerative gas furnace amounts in 

 average practice, when the furnaces are well managed, to fully fifty 

 per cent, on the quantity used in an ordinary furnace doing the same 

 work. The saving is greater, the higher the heat that is required in 

 the working chamber ; and where the most intense heats are needed, 

 as in making or melting mild steel on the open hearth of a rever- 

 beratory furnace, no other than a regenerative furnace can be used ; 

 in no other is a sufficiently steady and intense heat maintained, 

 without cutting draughts. 



Other advantages of the system are the freedom of the flame from 

 dust ; its diminished oxidizing or cutting action, (the waste on iron 

 piles, heated in a well-designed and well-managed gas furnace, being 

 only one-half or one-third as great as in an ordinary coal furnace) ; 

 and thirdly, the facility with which, whatever fuel is used, a uniform, 

 living flame, of any required length, may be obtained, by making the 

 mixture of the gas and air more or less rapid and intimate ; from two 

 or three feet only, as in the furnaces for melting steel in crucibles, to 

 thirty or forty feet, in large plate-glass furnaces ; the hottest part of 

 the flanie, in the latter case, being not where the gas and air meet, 

 but some five-and-twenty feet away, where they begin to be thoroughly 

 mixed. 



Since the Siemens furnace has been in use, several other gas fur- 

 naces, with continuous tube regenerators, have been brought forward. 

 Furnaces, that is, in which the air, and in some also the gas, are 

 heated, not by being introduced through masses of brickwork, pre- 

 viously raised to a high temperature, but by being passed, in con- 

 tinuous currents, without reversing, through fireclay tubes or hollow 

 bricks, round which the burned gases are drawn away to the chimney. 

 The Ponsard furnace, which has been recently brought into use, to 

 some extent, in France and Belgium, appears to be the best designed 

 of these modifications ; and the quoted results of its working, when in 



