APPENDIX. 
RECOMMENDATIONS FOR FUTURE INVESTIGATIONS. 
In. closing, the authors desire to offer the following recommenda- 
tions for future investigations : 
I. Laboratory experiments to determine the limits of inflamma- 
bility as affected by the following factors : 
1. Density of the dust cloud. 
2. Fineness of the dust particles. 
3. Chemical composition of the dust. 
4. Moisture content. 
5. Inert gases. 
6. Atmospheric humidity. 
7. Minimum temperature and amount of heat required for ignition. 
8. Sparks from metallic substances. 
9. Static electricity (not merely the voltage, but current measurements as 
well.) 
II. Field experiments on various types of machines handling dusty 
materials : 
1. Tests to prove that dust mixtures outside the limits of inflammability, as 
already determined, with reference to moisture content, inert gases, or 
atmospheric humidity, can not be ignited under the most severe condi- 
tions of ignition, such as those produced by an electric arc. 
2. Tests of various devices designed to prevent the propagation of explosions. 
RESUME OF SOME PAST EXPLOSIONS. 
The first large grain-dust explosion occurred in 1878 in the Wash- 
burn mill, at Minneapolis, Minn. At that time the "new process" 
system of milling, in which the grinding of wheat was done by mill- 
stones, was in vogue. It was assumed that, owing to a choking up 
of the feed spouts leading to the millstones above, one or more of 
the millstones became empty, and the running of the two stones 
against each other caused sparks, which ignited the dust in the 
conveyor boxes and dust rooms, causing an explosion in the dust 
room which destroyed the walls of the building. It is possible, and 
even probable, that the fire originated from open lights which were 
used at that time. 
Another very serious mill explosion occurred on June 24, 1913, 
when a feed-grinding plant in Buffalo, N. Y., was completely wrecked 
by an explosion, presumably of dust. None of the survivors of this 
explosion was able to give any information as to the cause of the 
initial fire, but it is stated that without a doubt the explosion was 
caused by the ignition of feed dust. 
49 
