GEAIN-DUST EXPLOSIONS. 15 



SERIES 5. 



Ohject. — This test was run as a demonstration to Government 

 officials from the Bureau of Mines (G. A. Hulett and J. K. Clement) 

 and from the Bureau of Chemistry (D. J. Price, H. H. Brown, and W. 

 G. Goodenow). 



Conditions. — The arc was located near the disks, which were run at 

 their normal speed. Various kinds of grain products (except ele-^ 

 vator dust, the supply of which had been exhausted) were fed into 

 the attrition mill. 



Results. — Although explosions were readily obtained with flour and 

 wheat scourings, none was obtained with corn, as in Series 3. In 

 fact, the regularity and force of the explosions, none of which caused 

 the flame to extend as far as the end (E) (PI. Ill, fig. 1) of the conveyor, 

 were not nearly as great as in Series 3, in spite of the relatively low 

 humidity (49 per cent) of Series 5, as compared with other tests. 



SERIES 6 AND 7. 



Ohject. — These experiments were run to determme whether an 

 explosion would result from the discharge of static electricity. 



Conditions. — ^The conditions of testing were similar to those of 

 previous tests with the electric arc. The carbons were replaced by 

 f-inch brass balls screwed on the ends of long J-inch iron rods, which 

 replaced the f-inch iron carbon holders. These j-inch rods were in- 

 serted through porcelains in the wooden door of the hood, to insure 

 insulation from the metal frame of the machine, and were connected 

 by 15-foot leads to the poles of a small Wimshurst machine. 



Results. — ^Under normal conditions this machine was capable of 

 producing a good spark about 3 inches long, but under the condi- 

 tions of the test, with the long leads, and great leakage, it gave only 

 a very weak spark, hardly more than h inch long, between the brass 

 knobs near the disks of the miU. It was, therefore, decided to make 

 use of an induction coil instead of the static machine. By this 

 means a very hot and almost continuous spark 2 inches long could 

 be obtained between the brass knobs. On two different days a total 

 of 20 attempts was made to obtain explosions with various inflam- 

 mable dusts by means of the spark from an induction coil. The 

 spark gap was varied from J to If inches. No explosions occurred. 

 This negative result, of course, does not indicate that static electricity 

 can not cause an explosion in an attrition miH, but rather that un- 

 der the particular conditions of the test, the mixtures of air and dust 

 were not sufficiently inflammable to be ignited by the sparks from an 

 induction coil. In order to show that the electric arc, on accomit of 

 the greater amount and intensity of heat produced, could ignite 

 the same mixtures under the same conditions, the carbons were 

 quickly substituted for the brass knobs, and then within 10 minutes 



