674 Explosions from Combustible Dust. October, 
were applied through a perfect heat-engine, to raise 562 tons 
10 feet high ; if, therefore, 40 per cent of flour is carbon, it 
would require 2J lbs. to accomplish this result, if an engine 
from which there would be absolutely no radiation, conduc- 
tion, 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 15 1 j cubic feet of air would be required for the 2§ lbs. 
of oxygen. Hence the lbs. of flour must be equally dis- 
tributed as a dust through 15 ij cubic feet of air, in order to 
produce the most powerful result. 
If 41 ounces of flour require 151 cubic feet of air for per- 
fect combustion, 1 cubic foot of air will supply oxygen 
enough for iW of an ounce of flour. Hence our box, which 
lifts the man so readily, burns ounce of flour or less ; and 
the other, which throws the box into the air, f of an ounce, 
unless, as I think quite probable, an additional amount of 
air is drawn in through the cracks as soon as the vent is 
opened at the top of the box. In fact these experiments 
work better if a few small holes are made near the bottom 
of the boxes. 
It may be worthy of mention here, as a point of interest 
to insurance companies, that in all dust-explosions a fire 
precedes the explosion in every case. The dust must burn 
before the heat that produces the immense expansive force 
is generated. 
Too great precaution cannot be taken in all kinds of manu- 
factories, where combustible dust is produced, against fire, 
especially in those establishments where it is conveyed in 
thick clouds by air-draughts through spouts and rooms. — 
Popular Science Monthly. 
