GEAIN-DUST EXPLOSIONS. 7 



ing down from the stock bin and elevator. The removable hopper 

 is partially withdrawn from under the mill platform. Above this 

 hopper is one of the steel carbon holders entering the wooden door 

 which has replaced the iron door of the lower part of the hood. 

 In this wooden door is located a peephole, covered with mica, for the 

 purpose of observing any sparks or flashes that may occur within 

 the hood. On the opposite side of the mill (PL II, fig, 2) is a similar 

 arrangement of peephole and carbon holder. The rheostat and 

 ammeter for regulating the carbon arc, located on the edge of the 

 hopper of the floor dump, are shown on the right. On the floor back 

 of these instruments can be seen the recently installed relief pipe (R), 

 leading from the hopper to the outside of the building, a distance of 

 8i feet. 



Plate III, flgure 1, shows the dust room, located at the end of the 

 conveyor, and the smaU door which gives access to the basement of 

 the mill building. A small box (E) was built over the open end of the 

 conveyor for the purpose of inclosing the carbon arc used in Series 4 

 (p. 14.) A rehef pipe extends from this box up through the roof, 

 and is capped by the hood (F). 



Figure 1 gives a sectional view of the 16-inch attrition miU 

 which was used for the tests described in this report. The grinding 



Fig. 1. — Sectional view of ball-bearing attrition mill. 



plates or disks (d^ and da) revolve in opposite directions at about 

 2,200 revolutions per minute. The upper part of the hood or casing 

 (c) inclosing the grinding disks can be readily removed. H is the 

 feeding hopper where the grain is introduced and fed by a "wabbler," 

 wliich is run by the friction pinion on the shaft (f ) . Horizontal slides 

 within the hopper regulate the amount of feed. The adjustment of 

 the fineness of grinding is accomplished by handwheels (1 an^ 2), 

 the latter serving as a locking device. The tension spring (ts) holds 



