1914] 



on Surface Combustion 



55 



tion per square foot of heating surface nearly twice that of an express 

 locomotive boiler. The combustion of the gas was completed within 

 4 or 5 inches of the point where it entered the tube. Of the 

 total evaporation, no less than 70 per cent occurred over the first 

 linear foot of the tube, 22 per cent over the second foot, and only 

 8 per cent, over the last foot This points to a very effective 

 " radiation " transmission from the incandescent granular material in 

 the first third of the tube, where the zone of active combustion is 

 located, although it should be remarked that the loci of actual contact 

 between the incandescent material and the walls of the tube are so 



Fig. 10. 



rapidly cooled by the transmission of heat']to the water on the other 

 side that they never attain a temperature even approaching red heat. 

 The granular material in the remaining two-thirds of the tube serves 

 to bafiEe the hot products of combustion, and to make them repeatedly 

 impinge with high velocity against the walls of the tube, thus 

 materially accelerating their cooling, and either preventing or 

 minimising the formation of the feebly-conducting stationary film of 

 relatively cold gases which in ordinary boiler practice clings to the 

 tube walls, seriously impairing the heat transmission. 



Having thus satisfied ourselves of the efficiency of the funda- 



