12 BULLETIN 681, U. S. DEPARTMENT OF AGRICULTUEE. 



just witliiii the space previously occupied by the hopper. A very 

 thick cloud of dust wms blown into the room. Immediately an 

 explosion, or rather a large flame, occurred, followed by a second and 

 more extensive one, covering nearly all the floor area of the dusty 

 side of the building and extending almost to the roof. The door and 

 windows were open. Otherwise, some damage might have resulted. 

 As it was, the arms of the man who handled the torch were burned. 

 The results of these preliminary experiments (observed by J. K. 

 Clement, B. W. Dedrick, M. P. Helman, J. Weaver, and F. Kline), 

 may be summarized as follows: 



1. More than 40 attempts with a total of from 3 to 5 pounds of 

 foreign materials, such as nails, small pieces of stone and flint, and 

 matches, fed along with various kinds of explosive grain products, 

 failed to produce a single explosion. 



2. Two attempts with a naked flame were successful in producing 

 explosions. 



EXPERIMENTS FROM APRIL 6, 1916, TO OCTOBER 3, 1917. 



SERIES 1. 



Ohject.-=— The object of the test was to determine whether explosions 

 could be obtained by foreign materials capable of emitting sparks 

 when ground, or by an electric arc located near the disks of the 

 attrition mill. 



Conditions. — The two removable hon doors of the miH were replaced 

 by wooden doors, provided with peepholes covered with several 

 layers of mica, and drilled for the insertion of iron carbon holders for 

 the electric arc. The position of the arc could be shifted between the 

 shaft and periphery of the disks, but it was soon found that its location 

 did not seem to have any effect on the regularity of the explosions. 

 As a rule, in this and succeeding tests, the arc was located nearer the 

 shaft than the periphery. A rheostat and ammeter were provided for 

 regulating the current (usually 15 to 20 amperes) through the arc. 

 The hopper underneath the grinding disks was put in place, and its 

 hand hole was left open so that the flash due to an explosion could be 

 seen. 



'Results. — 



1. Sparks from foreign materials did not cause an explosion. 



2. The electric arc caused four explosions out of six attempts when 

 large handfuls of feed were used. 



3. Lovr rates of feeding did not produce an explosion with the 

 electric arc. 



4. Oat hulls, gi'ound or unground, did not ignite, except when 

 mixed with the higlily inflammable elevator dust. 



5. With elevator dust, when fed by the handful, either alone or 

 with oat hulls, four explosions out of four attempts were obtained. 



