EXPLOSIONS FROM COMBUSTIBLE DUST. 165 



Placing now the lamp in the box, some dust in the corner, and the box 

 over the spout, we are ready for another explosion. You observe, after 

 blowing vigorously for a second or two, the dust in the box takes fire ; 

 the box over the spout is shot off, and rises until the rope (about twelve 

 feet long) jerks it back ; it strikes the stage with great force, rebounds 

 and clears the foot-lights, and would strike the floor below were it not 

 for the rope. 



I have thrown a box similar to this in the open air twenty feet 

 high, while, as we shall see presently, less than an ounce of flour is 

 being consumed. 



I have fastened over the top of the spout five thicknesses of news- 

 paper ; upon igniting a boxful of dust as before, the paper is thrown 

 violently into the air, accompanied by a loud report as it bursts. 



For the last experiment I have a box of four cubic feet capacity 

 (Fig. 4) ; five sides are one and a half inch thick, the remaining side 

 one-quarter inch. Upon igniting the dust in this box, filled as in the 

 other cases, the quarter-inch side bursts, and a stream of fire shoots 

 out half-way across the stage. 



Fig. 4. 



One pound of carbon and two and two-thirds pounds of oxygen, 

 when they combine to produce carbonic acid, will evolve heat enough' 

 if it were applied through a perfect heat-engine, to raise 562 tons ten 

 feet high; if, therefore, forty per cent, of flour is carbon, it would 

 require two and a half pounds to accomplish this result, if an en^ne 

 from which there would be absolutely no radiation, conduction, orloss 

 of heat, in any way, were a practical possibility. Let us see how much 

 air would be required to supply oxygen enough. Under ordinary con- 

 ditions every 100 cubic inches of air contains 7.13 grains of oxygen, 

 from which we find that loli cubic feet of air would be required for 

 the 2f pounds of oxygen. Hence the 2^ pounds of flour must be equally 

 distributed as a dust through 151^ cubic feet of air, in order to produce 

 the most powerful result. 



If 41 ounces of flour requires 151 cubic feet of air for perfect com- 

 bustion, one cubic foot of air will supply oxygen enough for y^T of an 

 ounce of flour. Hence our box, which lifts the man so readily, burns 



