MECHANICAL VALUE OF COAL. 85 



111 the careful tests of native coal, made for the English Govern- 

 ment by Sir H. de la Beche and Dr. (now Sir) Lyon Playfair, there 

 were eleven examples of soft coal that gave higher evapo]\\tive results 

 than the single good anthracite tested, although this particular hard 

 coal, in addition to having the highest per cent, of carbon, had also 

 3.46 per cent of hydrogen, being about three-fourths of the average 

 amount of hydrogen in the various soft coals tested. This was very 

 much in its favour, as the calorific value of hydrogen — by weight — 

 is more than four times that of carbon ; however, its specific gravity- 

 was 1.375, being heavier than any otlier coal, native or foreign, then 

 tested ; and, it is, we think, only in the fact that its particles were 

 so closely packed together, that the explanation of its comparatively 

 low power can be found. A general average, taken over a large 

 number of samples, shows American anthracites to weigh 400 lbs. per 

 cubic yard heavier than British anthracites. 



Outside of metallurgical oj^erations, hard coal for manufacturing 

 purposes has apparently nothing but its cleanliness to recommend 

 it ; and, presumably, it is for this benefit that the Toronto Water 

 Works pays with satisfaction fuel bills that are unduly heavy. 



Having thus narrowed our subject down to the consideration of 

 the exclusive use of bituminous coal, we will briefly review the four 

 different practices (which include the main modern theories) covering 

 its economical combustion, using the names of the several advocates : 

 Crami)ton, Mallett, Howden and Siemens, to identify their systems, 



1st. Champton. — For the easier understanding of this system, we 

 will j)i'enuse by stating that the known forms in which fuel exists 

 are three :^ — ^First, solid, either as lumps or dust; second, fluid, as oils, 

 either flowing or in the form of spray ; and, third, gaseous, either 

 simple or mixed, say with oxygen, so as to be more or less explosive. 



When fuel is in the himp form, oxygen can come into contact with 

 but a very limited portion, viz. : the outside, or surface of each piece. 

 This, when the lumps are large, results in slow combustion, and the 

 passage of a wasteful excess of cooling air through the furnace ; 

 hence, careful stokers (and careless ones, when in competition,) break 

 the pieces small before putting coal on the fire, and for the same 

 reason that we use chips in starting a fire, and choose small wood 

 when a quick fire is required for an eai-ly breakfast. But if (as in 

 the Cramj)ton method) the coal is reduced to dust, then steadily and 



