396 SECTION MECHANICS. 



good order, are very satisfactory. In this arrangement, the air only is 

 heated by the regenerator ; the gas producer being placed close to 

 the furnace, and the gas from it taken directly, without further 

 heating, to the point where it is burned. In the case of such a 

 furnace, there are several advantages in thus heating the air, only, by 

 the waste heat ; the tubes of the regenerator are not choked up by 

 deposits from the hot gas, nor is there the risk of loss of gas by 

 teakage ; and as the volume of burned gases is sufficient to heat 

 nearly twice as much air as is required for combustion in the furnace, a 

 moderate leakage of air, in the regenerator, into the current passing 

 to the chimney, does no harm ; since, if the regenerator exposes 

 sufficient surface, as much air, heated to nearly the full temperature of 

 the waste gases, may still be drawn into the working chamber as is 

 required there. The ordinary Siemens furnace, however, though 

 apparently more complicated, is probably a stronger and more 

 durable arrangement than any furnace working with continuous 

 tube regenerators can be made, and is better fitted to bear the 

 rough treatment that is generally the fate of such appliances in actual 

 work. 



A proposed modification of the Ponsard system of furnace, that 

 presents considerable theoretical advantages, is to supply the gas pro- 

 ducer, as well as the working chamber of the furnace, with highly 

 heated air from the regenerator ; the hot gas being taken, as in the 

 ordinary Ponsard furnace, direct, without further heating, from the gas 

 producer to the working chamber in which it is burned. The carrying 

 out of such an arrangement, in the case either of the Siemens furnace, or 

 of a furnace with tube regenerators, appears likely to present great prac- 

 tical difficulty, but if it can be successfully worked out, the increased 

 economy will be great ; as, in such a furnace, the whole of the heat 

 evolved from the fuel, except that still inevitably lost by external 

 cooling, and that carried off by the gases passing to the chimney, at 

 a temperature that need not exceed 100 or 150 C. would be avail- 

 able, in the working chamber, as heat of high temperature. 



In the Siemens furnace, in which the gas producer is supplied with cold 

 air, the sensible heat of the gases, as they leave the producer, does 

 not affect the temperature of the flame in the furnace ; for the amount 

 of heat contained in the products of combustion is sufficient to heat 





