36 COALFIELDS AND COLLIERIES OF AUSTRALIA. 



ccmcerned, yet some of the coals may not show to their best 

 advantage, simply because the boiler is not suitable for them. 

 To get the best effect out of coal, it must be burnt at a certain 

 rate per square foot of grate per hour. In order to burn some 

 coals to the best advantage the grate area would be so large 

 as to put it out of the question for certain purposes, such as 

 locomotive work. Two coals may have the same theoretical 

 heating value, and yet the useful effect for steaming purposes 

 may be different, according to the ratio of fixed carbon to 

 volatile hydrocarbons. Anthracite disintegrates slowly; semi- 

 aiithracite quicker, while with bituminous coal it is almost in- 

 stantaneous. 



Different coals should be compared under the conditions 

 they are to be used, so that they shall be subject to similar 

 losses; otherwise it is impossible to make suitable, allowances, 

 as in the case of locomotive tests for variations in grades, 

 curves, loads, number of vehicles, length of train, speed, stop- 

 pages, weather, quality of water, individuality of the engine- 

 driver, stoker, etc. 



Coals may sometimes be mutually improved by blending 

 them in proper proportions. For instance, with two coking 

 coals, one may not contain sufficient volatile matter to fuse 

 properly, while another may contain so much as to make the 

 coke too porous. For steaming purposes one available coal 

 may burn too fiercely and have too much volatile hydrocarbon, 

 while another may burn too sluggishly; it may be cheaper 

 to mix these than to obtain a coal more suitable in itself from 

 a distance. The gas from one coal may help to keep the other 

 alight, and the coking properties of another may prevent much 

 small coal from falling between the fire bars. 



To ascertain the calorific power of a coal when burnt under 

 a boiler, one must determine the quantity of water evaporated 

 in pounds by one pound of fuel. The number of calories lost 

 in the gases, by radiation and drawn with the ashes, must alsa 

 be known. The total quantity of heat developed by the com- 

 bustion oi' the fuel must be determined in order to be able to- 

 calculate the percentage of heat usefully employed. J. Holli- 

 day* says, draw all the fuel used to heat the water in the 

 boiler to 212 deg. F., and light up the fresh fuel with 201b. 

 dry wood; this kindling wood need not be taken into consider- 

 ation, as the heat developed by it is more than balanced by the 

 loss of heat from the boiler during the operation of drawing 

 the fire. Each charge of fuel is carefully weighed say 5001b. 

 of coal for each 25 sq. ft. of grate area carefully mix the fuel 

 beforehand to secure uniformity, and note how often the fur- 



*Boiler Experiments and Fuel Economy (Min. and Pro. 

 I.C.E., Vol. xcii., page 336, [1887-88.] ) 



