SIX WILLIAM SIEMENS, F.R.S. 99 



into the furnace chamber. The products of combustion, instead of 

 passing directly to the chimney as in an ordinary furnace, are 

 directed downwards through the two other regenerators on their 

 way towards the chimney, where they part with their heat to the 

 checkerwork in such manner that the highest degree of heat is 

 imparted to the upper layers, and that the gaseous products reach 

 the chimney comparatively cool (about 300 Fahr.). After going 

 on in this way for half-an-hour, the currents are reversed by means 

 of suitable reversing valves, and the cold air and combustible gas 

 now enter the furnace chamber, after having taken up heat from 

 the regenerators in the reverse order in which it was deposited, 

 reaching the furnace therefore nearly at the temperature at which 

 the gases of combustion left the same. A great accumulation of 

 temperature within the regenerators is the result, one pair being 

 heated while the other pair is being cooled ; it is easy to conceive 

 that, in this way, heat may be produced within the furnace 

 chamber up to an apparently unlimited degree, and with a 

 minimum amount of chimney draught. 



Practically the limit is reached at the point where the mate- 

 rials composing the furnace chamber begin to melt ; whilst a 

 theoretical limit also exists in the fact that combustion ceases at a 

 point which has been laid down by St. Claire Deville at 4500 Fahr., 

 and which has been called by him the point of " dissociation." At 

 this point hydrogen might be mixed with oxygen and yet the two 

 would not combine, showing that combustion really only takes place 

 between the limits of temperature of about G00 and 4500 Fahr. 



To return to the regenerative gas-furnace. It is evident that 

 there must be economy where, within ordinary limits, any degree 

 of heat can be obtained, while the products of combustion pass into 

 the chimney only 300 hot. Practically a ton of steel is melted 

 in this furnace with 12 cwt. of small coal consumed in the gas- 

 producer, which latter may be placed at any reasonable distance 

 from the furnace, and consists of a brick chamber containing 

 several tons of fuel in a state of slow disintegration. In large 

 works, a considerable number of these gas-producers are connected 

 by tubes or flues with a number of furnaces. Collateral advan- 

 tages in this system of heating are, that no smoke is produced, 

 and that the works are not encumbered with solid fuel and ashes. 



Gas Producers at Bottom of Coal-pit. It is a favourite project 



H 2 



