672 
Explosions from Combustible Dust. [October, 
dust, leaving the heavier material (purified middlings), which 
goes again to the stones to be ground into flour, 
Here is some of the dust from these “ middlings-machines 
you observe it burns as the other materials burned, quickly, 
and with intense heat. 
Here is some of the purified middlings ; each grain is 
comparatively large and heavy, making it difficult to blow it 
well into the air, but, as the blaze produced by each particle 
is quite large, a flash is produced which does not differ ma- 
terially from the others. 
Here is some of the general dust of the mill, — that is, 
dust swept up from the floors, walls, beams, &c. You will 
see it adts in all respedts like the other substances. 
And, finally, here is some of the flour taken this afternoon 
from the flour-sack at home ; it burns, you observe, if pos- 
sible with even more energy than the other kinds of dust. 
I have performed a few experiments, which I will now 
repeat, which will illustrate to you the immense power that 
these materials exert when burned in a confined space. 
This box (Fig. 2) has a capacity of 2 cubic feet ; the 
cover has a strip 3 inches deep nailed around it, so that it 
telescopes into the box : there is in this lower corner an 
opening for the nozzle of the bellows, in this an opening for 
the tube to the lamp. I place now a little flour in the 
corner, light the lamp, and my assistant places the cover 
upon the box and steps upon it. Take notice that upon 
blowing through the hole, and filling the box with a cloud 
of flour, the cover comes up suddenly, man and all, until 
the hot gas gets a vent, and a stream of fire shoots out in 
all directions. 
Here is a box (Fig. 3) of 3 cubic feet capacity, including 
this spout, g inches square and 15 inches long, coming from 
the top of it ; at the ends doors are arranged closed like 
steam-boiler man-holes ; openings for light and bellows are 
arranged as in the previous box. 
Here is a box, weighing 6 lbs., that will just slip over the 
spout ; it has a rope lest it should strike the wall after the 
explosion. 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 
12 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 20 feet 
