16 BULLETIN 379, U. S. DEPARTMENT OF AGRICULTURE. 
It appears that the largest discharges of static electricity were 
obtained from the steel machines. Larger deflections were also ob- 
tained in threshing wheat than in threshing oats. The fires and 
explosions occur as a rule while fall wheat is being threshed and 
very rarely occur during the threshing of spring wheat. The dis- 
charge from the machines while smutty wheat is being threshed is 
more noticeable than when clean wheat is going through the ma- 
chine. Fall wheat as a rule contains much more smut than does 
spring wheat. The theory that the small particles of smut easily 
become electrified when the kernels are broken up by the cylinder 
teeth and that each particle becomes charged with static electricity 
has been advanced as a possible explanation of the fact that the 
largest discharges seem to occur when smutty wheat is being 
threshed. The theory is tentative and.can be proved only by ex- 
perimental work to determine in what manner the static electricity 
is generated. 
INFLAMMABILITY OF SMUT DUST. 
In addition to the experimental work carried on in the field dur- 
ing the progress of the investigations, a series of laboratory experi- 
ments to determine the inflammability of smut dust was conducted 
by J. C. Woodson, assistant agricultural engineer, at the University 
of Idaho. This work was done in the laboratories of the Depart- 
ment of Physics, and advice and assistance were obtained from 
Prof. Angell. 3 | 
The laboratory experiments were by no means conclusive and not 
so extensive as work already planned for the future, but were merely 
preliminary in nature. However, they were sufficient to indicate that 
smut dust is highly inflammable and can be ignited by an electro- 
static spark. 
FOREIGN MATERIAL ENTERING MACHINE. 
In many cases the investigations indicate that foreign material 
consisting of gravel, flint, metal, etc., entering the machines and the 
rubbing and friction of cylinder teeth produced sparks which may 
possibly have ignited the dust. In one case both cylinder and con- 
cave teeth were found bent forward after the explosion and showed 
signs of rubbing. 
In some cases the explosions occurred during the clean-up, which 
suggested to the owner the possibility of sparks being produced by 
foreign material entering the machine. This matter can be decided 
only by experimental work to establish clearly the relation between 
the suspended dust cloud and sparks produced in this manner. This 
‘rause has been assigned to dust explosions in grain mills and in- 
dustrial plants, and is at the present time receiving attention. 
