86 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



uniformly fed into the furnace, by blast, with the air supply limited 

 to little more than that absolutely required for chemical combination 

 — say 13 lbs. of air per pound of solid fuel — perfect and smokeless 

 combustion and an intense heat are attained, with the additional 

 advantage that a refuse fuel of low price can be utilized, with corres- 

 ponding economy. 



Even with this form of fuel, the oxygen has but surface contact 

 with the dust, as with the lumps ; but the surface, per unit weight, 

 is increased so enormously that the speed of burning closely 

 approaches that of explosion. 



An increased evaporation of 22 per cent, has been obtained by the 

 use of pulverized coal ; in part due to the very small excess of air 

 requiring to be warmed, and in part to the higher temperatures 

 attained. Not only for the evaporation of water is high temperature 

 an advantage, but, as the speed of heat ti'ansmission through metal 

 plates increases (approximately) as the difference between the squares 

 of the different temperatures on the fire and water sides of the 

 plates, the speedier the ti'ansfer, the less is the amount of absorbent 

 surface to be provided. Therefore, the dust-fuel system permits the 

 construction of a smaller boiler to develop the same horse-power, but 

 it has the disadvantage of requiring mechanical stoking and mecha- 

 nical disintegration of fuel. Mr. T. Crampton very early took a long 

 step in advance of current ideas and methods in the use of soft coal, 

 and the limited adoption of his patent in daily pj-actice is probably 

 due to the little time so busy and successful an engineer could devote 

 to its advocacy ; and also to the fact that the working plant 

 required was somewhat elaborate for small horse-powers, and for 

 large establishments, a further step in advance of his practice was 

 soon afterwards taken by Dr. W. Siemens, who converted coal waste, 

 shales of low quality, and other low priced fuels at once into the 

 gaseous form (carbonic oxide), using this gas — which, although not 

 luminous, possesses large calorific powei' — as fuel for all industrial pur- 

 poses. The gaseous form of fuel infinitely increases the possible 

 surface and closeness of mechanical contact between fuel and oxygen 

 before combustion, and readily peimits the absolute control of the 

 amount of air supplied. 



2nd. Mallett. — Before more fully describing the recent " Siemens" 

 developments, E. J. Mallett's theories and arguments deserve consid- 



