DUST EXPLOSIOlSrS IN GRAIN" SEPAEATORS. 17 



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 

 grain 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 OP 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 bum 

 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 



