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sumed and the resulting- flame may be directed on the body to 

 be heated. He found that the apertures between the coals could not 

 admit enough of air to burn the smoke completely, and he in- 

 troduced an additional portion immediately below the grate. I 

 am not acquainted with the practical value of this invention, in 

 fact 1 know it only from Watt's paper in the Repertory, and a 

 drawing of one attached to a Scotch still in the 6th volume of 

 Tilloch's Magazine ; I have hovrever mentioned it as it seems 

 to be forgotten, it will probably be valuable in small stoves, 

 but in large furnaces the slag would I think soon choak 

 the grate and we cannot remove it without interrupting the 

 draught by opening the ash-pit. Mr. Roberton of Glasgow at- 

 tempted to produce the same effect by a much simpler contrivance. 

 He feeds the fire through a door which is constantly filled with 

 coal, and thus no large aperture is left through which a stream of 

 cold air may rush to lower the temperature, the fuel which is in- 

 trodviced gives off its elastic products which are mixed with air, ad- 

 mitted through a slit over the door, and are burned in passing over 

 the coke which occupies the posterior part of the furnace ; as 

 soon as flame ceases to be formed, fresh coal must be introduced 

 which pushes forward the former portion now completely coked : and 

 with attention to supply it in small quantities and at short intervals 

 of time, not an atom of smoke will escape from the chimney, at 

 least in the reverberatory furnace : the apparatus does not succeed 

 so well, when applied to heat a boiler. It will readily appear that 

 the mixture of air and coal gas cannot be much heated while it is 

 in contact with a metallic surface whose temperature is not far 

 above 212, it must therefore escape unconsumed into the chimney 



