DUST EXPLOSIONS IN GRAIN SEPARATORS. 11 
_the original theory and indicated the value of a grounding device 
of this kind. 
The possibility of static electricity as a source of cereal dust igni- 
tion was very clearly established by an explosion in the dextrine de- 
partment of a starch factory in one of the Eastern States (in Sep- 
tember, 1914). The origin of this explosion was traced to the genera- 
tion of static electricity by friction of particles of dextrine on an 
80-mesh brass gauze surrounding a revolving reel. This reel was 
revolving at the rate of only 16 revolutions per minute when the 
explosion occurred. 
At the time of the explosion this reel was grounded to an over- 
head sprinkling system. During the investigation which followed, 
however, it was found that the connection was made from the journal © 
box, and that a heavy film of fresh oil surrounded the shaft. This 
was thought to have served to insulate the shaft and allow the static 
electricity to accumulate within the reel until there was sufficient 
charge to ignite the dust. 
An English scientist has determined that if a cloud of dust is 
blown against an insulated conductor (a wire, for instance) the wire 
becomes charged with electricity, and under certain conditions may 
become so highly charged as to give off sparks.t 
EXPERIMENTAL FIELD AND LABORATORY WORK. 
METHODS OF GROUNDING MACHINES IN EXPERIMENTAL WORK. 
From results that had previously been obtained by grounding 
machines effectively in various branches of the milling industry and 
also by some machine operators in the Northwest, it was decided to 
conduct experimental work along this line with the grain separators, 
in an attempt to carry off any static electricity that might be gen- 
erated during the operation of the machine. 
The experimental work in developing a satisfactory grounding 
device was conducted along three distinct lines, as follows: 
1. Separately grounding each part, either directly or through its 
bearing. 7 
2. Connecting wires from all moving parts to one wire and ground- 
ing that wire. | 
3. Wiring all moving parts to some metallic portion of the sepa- 
rator of sufficient magnitude to act as a ground. 
DESCRIPTION OF VARIOUS METHODS. 
First method.—The first method was perhaps the most common 
among the thresher men who were inclined to accept the theory that 
1 Philosophical Magazine, London, 6 (1913), p. 481-494. ‘“ On the Electrification Asso- 
ciated with Dust Clouds,” by W. A. Douglass Rudge, Professor of Physics, University Col- 
lege, Bloemfontein. 
