10 
BULLETIN" 681, IT. S. DEPARTMENT OF AGRICULTURE. 
Plate I shows the puffs of smoke, dust, and charred particles that 
followed a flame issuing from the end (G) of the relief pipe when an 
explosion occurred in the attrition mill (Series 13). 
MATERIALS USED IN THE INVESTIGATION. 
DESCRIPTION. 
Fine oat hulls 
Elevator dust 
Oat hulls 
Flour direct from 
store. 
Flour (oven dried) 
Graham flour 
Wheat scoiirings ...... 
Corn 
Wheat shorts 
Coarse floor sweeping: 
Fine floor sweepings. . 
Conveyor mixture 
No. 2 feed dust 
No. 1 feed dust 
Fine oat hull dust.. . . . 
No. 3 elevator dust . . 
Barley malt sprouts. . . 
Malt sprouts 
Brewers' dried grain. . 
Dried grain 
Oat hulls, finely ground in an attrition mill, millstone, or other grinding 
mill. 
Dust that has settled on machines, beams, etc., in a grain elevator. It is 
a highly inflammable dust of a very light and fine texture, and com- 
posed of floating carbonaceous material of grain, outer skins, together 
with foreign dust. 
The hulls stripped from oats, as in the preparation of oatmeal. 
The interior or endosperm of any grain reduced to a very fine powdery 
state and free from the branny covering. It is composed rnostlj' of 
starch, and is highly inflammable when in suspension. 
Flour dried in an oven at about 150° F. 
This is wheat which is ground but not bolted. It contains all of the 
flour, bran, and germy parts. 
A fluffy and inflammable dust taken from dust collectors which are con- 
nected to the scouring or brush machines. It consists of foreign mate- 
rials, such as dirt, smut, and portions of the light, thin, and loose outer 
skins of the bran. 
Shelled corn. 
Composed of the finer portions of bran, germ, and some floury material, 
separated from flour, in the process of milling. 
A coarser mill dust, settling on floor in immediate vicinity of mill. 
The lighter and finer mill dust which settles in the room and outside the 
immediate vicinity of the attrition mill. 
A mixture of various materials as obtained from the end of the screw con- 
veyor. 
Consists of very fine particles of bran, fuzz, smut dust, and dirt, taken 
from the dust collector which draws air from the first scourer. 
A material taken from the dust collector drawing the air through the 
second scourer. It consists almost entirely of the outer layers of the 
bran which have been removed by the scouring action of beaters. 
This material is very finely ground oat hulls, brought out by the con- 
veyor in the form of dust. 
Floating dust gathered by hand from the beams and. machinery in the 
elevator. 
Consists of barley malt sprouts that have been used as mash material and 
then dried. 
Consists of the radicles grown on the barley during the germinating proc- 
ess, and later broken off and dried. 
This is the residue from a mash tub in a brewery or distillery, and con- 
sists of malt, corn, rice, hops, etc., which have been boiled and then 
dried. 
This corresponds to "brewers' dried grain,'' except that the original 
mash consists of corn, barley, malt, and the radicles grown on barley 
during the germinating process, which are later broken off and dried. 
EXPERIMENTAL WORK. 
The results of the investigation are reported, first, by describing 
and summarizing briefly each one of the experiments performed, and, 
second, by discussing each one of the factors mentioned in the scope 
of the work (p. 12). 
PRELIMINARY TESTS. 
The experimental mill building at The Pennsylvania State College 
was completed in the spring of 1915, and the attrition mill, elevators, 
and conveyor were installed during the early part of the summer. 
During August several preliminary experiments were made for the 
primary purpose of ascertaining if explosions would result from the 
sparks emitted by foreign materials (nails, flint, matches, etc.) when 
passing between the grinding disks along with the grain. 
