BULLETIX 681, U. S. DEPARTMENT OF AGRICULTURE. 
was discovered that the wooden platform and floor near the remov- 
able hopper of the attrition mill had been set on fire, evidently by 
some smoldering grain that had not been removed after the experi- 
ments of the preceding day. This result strongly suggests a greater 
use of sheet iron, or other noncombustible material, in milling 
plants. 
SERIES 13. 
Object. — The object of this experiment was to note the effect 
of a pressure-relief pipe. 
Conditions. — It had been suggested that a means for automatically 
relieving the pressure, due to an explosion, might aid materially 
in preventing the propagation of the flame to a dangerous part of 
the mill. Accordingly, a device (PI. II, fig. 2, and PL I, fig. 1) 
consisting of a pipe 5 inches in diameter and 8J feet long, with a 
rectangular end containing a light sheet-iron relief valve, which 
remained closed by its method of overhead suspension (fig. 3), was 
installed. This end of the relief pipe was inserted in the hopper 
(PL III, fig. 2), which had been lined with galvanized iron on account 
of the many fires that had occurred in the wooden hopper. 
Results. — 
1. In nearly all of the 14 explosions with the damper in service 
a flame and puff of smoke were observed at the end of the relief 
pipe (G), indicating that the relief valve opened properly. 
2. In four out of eight instances, however, flames were observed 
getting past the double damper, although never as far as the con- 
veyor end. 
SERIES 14 AND 15. 
Object. — The primary object of these last experiments was to 
determine whether certain grain products, such as oat hulls, con- 
taining considerable dust, barley malt sprouts, malt sprouts, brewers' 
dried grain, and ifc dried gram,"' ah of which had been recently re- 
ceived from various manufacturers, would give an explosion under 
severe conditions in an attrition mill. Incidentally, observations 
were made of the effects due to the relief pipe and double damper. 
Results. — 
1. By means of the electric arc, explosions were obtained with 
dusty oat hulls, malt sprouts, barley malt sprouts, brewers' dried 
grams, and various mixtures (Table 16). 
2. Out of 45 explosions with the damper in service, four flames 
passed the damper, one of them extending as far as the end of the screw 
conveyor. 
3. In all cases of explosions, puffs of smoke were observed at the 
end (G) of the relief pipe (PL I, fig. 1). 
