DUST EXPLOSIONS IN GRAIN SEPARATORS. Iz 
EXPERIMENTS WITH MATCHES AND ACIDS. 
Experiments also were conducted to determine the resulting action 
of various acids on matches. A current opinion existed that many 
erain fires in the fields were caused in this manner. Matches were 
tied about the neck of a small vial containing sulphuric acid and also 
one containing nitric acid. A cork about one-eighth of an inch thick 
was placed in the mouth, and the bottles were inverted, allowing the 
acids to eat through the corks and come in contact with the match 
heads. These acids were tried with eight different varieties of 
matches, but failed to ignite the matches in a single case. The acids 
experienced no difficulty in eating out the corks, the nitric acid doing 
so in 40 to 60 minutes and the sulphuric acid requiring 6 to 10 hours. 
NATURE OF DUST EXPLOSIONS. 
THEORY OF DUST EXPLOSIONS. 
The theory of dust explosions, although not entirely new, has not 
been understood clearly by a number of people, who are, therefore, 
at a loss to know in what manner these explosions originate and the 
circumstances necessary for their occurrence. That dust itself can 
be made to explode without the presence of inflammable gases has 
seemed incredible. | 
Experimental work has shown that the dust produced during the 
handling of grain can be ignited under certain conditions, and will 
propagate a flame with explosive violence. It must not be concluded 
that grain dusts will ignite spontaneously. On the contrary there 
-must be some outside source of heat. This source may be very small, 
as a heated coil of wire or an electric spark as used in the experi- 
mental work, or it may be larger, as a flame which may have a lower 
temperature but a larger heating surface. 
The following illustration may simplify the explanation of the 
nature of dust explosions. We might try for some time to burn 
a block of wood with a lighted match. If we take a knife and chip 
the block the shavings will ignite more quickly. We might make 
excelsior and find it would ignite still more rapidly, and then con- 
tinue by gradual reduction to a degree of fineness until dust is pro- | 
duced, when it is found that the mass will burn rapidly when in. 
suspension and diffused in the air. The rate of burning is so rapid 
that a violent explosion may result. 
Many theories have been advanced as to the conditions under which 
dust explosions are produced and the amount of dust in suspension 
necessary to propagate the explosion, The predominating factors 
which determine the inflammability of a dust and the action of a 
dust explosion have not been definitely determined. It is generally 
