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 newspaper; 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 engine from which there would be absolutely no radiation, conduction, or loss of heat, in any way, were a practical possibility. Let us see how much air would be required to supply oxygen enough. Under ordinary conditions every 100 cubic inches of air contains 7.13 grains of oxygen, from which we find that 15112 cubic feet of air would be required for the 223 pounds of oxygen. Hence the 212 pounds of flour must be equally distributed as a dust through 15112 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 combustion, one cubic foot of air will supply oxygen enough for 40151 of an ounce of flour. Hence our box, which lifts the man so readily, burns
