668 Explosions from Combustible Dust. [Odtober, 
when blown into the air by means of a pair of ordinary 
hand-bellows. 
I have here two boards, about 12 by 18 inches, nailed to- 
gether, forming a V {see Fig. 1). Just outside of the V an 
ordinary Bunsen gas-burner is placed, and within is a small 
handful of dust taken from a sash and blind fadtory. Upon 
blowing it smartly with the bellows a cloud is formed about 
15 feet high, — extending, in fadt, to the ceiling, — which 
ignites from the lamp and produces a flash, very quick and 
exceedingly hot , resembling very much a gunpowder flash. 
You will notice that a large amount of dust falls from all 
around the edge of the flame without burning ; that is be- 
cause it is not thick enough. Two things are necessary : 
first, that each grain of dust be surrounded with air, so that 
it can get the oxygen required instantly ; and, secondly, that 
each grain shall be so near its neighbour that the flame will 
bridge over the space and pass the fire from particle to 
particle. 
I think, after seeing the immense flame produced by such 
a small amount of fine saw- and sandpaper-dust, you will 
no longer wonder at the rapid spread of flames in furniture 
and similar fadtories. You know it is pradtically impossible 
to put out a fire after any headway is attained in these 
establishments ; the draught produced will blow all the dust 
from walls and rafters into the air, and the building in an 
