16 BULLETIN 370, U. S. DEPARTMENT OF AGRICULTTJEE. 



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 cjdinder 

 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 Avheat 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 Uni^ ersity 

 of Idaho. This work was done in the laboratories of the Depart- 

 ment of Physics, and advice and assistance were obtained from 

 Prof. Angell. 



The laboratory experiments were hj 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 igTiited by an electro- 

 static spark. 



FOREIGN MATERIAL ENTERING MACHINE. 



In manj^ 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 

 sigTis 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 

 cause has been assigned to dust explosions in grain mills and in- 

 dustrial plants, and is at the present time receiving attention. 



