CHEMISTRY. 213 



dence that discloses the fact, that the waste of coal in Great Brit- 

 ain at the mines and elsewhere exceeds 30,000,000 tons annually. 

 The waste in the United States sometimes exceeds 45 per cent., 

 and always 25 per cent., of the amount actually mined. This loss 

 falls most heavily upon the finer quality of coal, which, from its 

 mechanical constitution is more subject to comminution and 

 waste in handling and transportation, so that the higher the value 

 of the coal as a heat-producing agent, the greater is the percent- 

 age of loss. From the fact that the present method of combustion 

 requires the use of grate bars, open for a passage of air, an inci- 

 dental waste arises from the formation of slag or clinker, which 

 carries off into ash some portions of combustible matter, and by 

 impeding the draft causes all the losses from imperfect combustion, 

 which amount to 5, and in extreme cases to 25, per cent. 



" We have seen the results of a series of carefully conducted 

 trials, made by a board of engineers appointed by the Navy De- 

 partment to examine into the various methods of employing an- 

 thracite and bituminous coals as fuels. Competitive trials, of 48 

 hours each, between a given quantity of bituminous coal, se- 

 lected and employed in lumps of 4 inches cube, burned with a 

 forced blast under an ordinary tubular boiler, and an equal quan- 

 tity of the same sort of coal, one-third in lump and two-thirds 

 slack pulverized, and driven in above the fire by a similar forced 

 blast, were instituted, and the temperature of feed water, uptake, 

 engine, and fire-rooms carefully taken ; a uniform pressure of 40 

 pounds was maintained on the boiler, and an equal number of 

 strokes made by the engine in each experiment. The trials showed 

 that an evaporation of 8| pounds of water from a temperature of 

 140 F. could be effected with a pound of coal burned in lump at 

 the rate of 12 pounds to the square foot of grate surface, while 

 with one-third burned in lump and two-thirds pulverized, an ave- 

 rage evaporation of 9| pounds of water to the pound of coal was 

 reached. The conditions of the experiments were as nearly alike 

 as practicable in both cases. During the last part of the last ex- 

 periment the percentage in favor of pulverized fuel was raised to 

 20 per cent., and during 6 consecutive hours an evaporation of 

 upward of 11 pounds of water to the pound of coal was reached, 

 which would give more than 33 per cent. gain. This was owing 

 to the skill acquired by the firemen in the course of the experi- 

 ments. The result of the experiments seems to have decided 

 these points : 



"1. With ordinary care a complete rapid combustion can be 

 effected. The loss of combustible matter, either from the lump 

 coal alone or from the lump and pulverized together, was hardly 

 sufficient to discolor the ash, and the entire residuum of coke at the 

 end of 48 hours' constant burning at the rate of 66 pounds an hour 

 was not 12 pounds in either case, and the residuum ashes col- 

 lected and weighed was about 8 per cent, of the weight of coal 

 used, the lump coal giving a trifle the most. This indicates the 

 care with which the experiments were made. 



"2. The employment of two-thirds of the coal pulverized and 

 blown over the fire by an air-blast, gives an increased useful 



