SCIENCE OF THRESHING. 49 



the grain through the cylinder by the tailings elevator. 

 Each time a kernel receives a blow from a cylinder 

 tooth it is partially disintegrated, and many blows 

 crack or break it open. 



Only enough concave teeth should be used to 

 retard the passage of the straw through the concave 

 a sufficient length of time to allow all the kernels to 

 be loosened. More teeth than are required to do 

 this consume power unnecessarily as well as cut up 

 the straw to such an extent as to interfere with the 

 proper workings of the separating and cleaning 

 mechanisms. The machine will often do better 

 work with two or four rows of teeth than with 

 more. In handling oats, two rows of teeth are com- 

 monly enough, except when the kernel is small and 

 light and the oats, which may have been cut when 

 green, seem tough and cling to the heads; in this 

 case high speed in the cylinder and more rows of 

 teeth in the concave are required to loosen all of the 

 kernels from the straw. 



For use in sections of the country where flax is 

 grown the concave should be specially designed with 

 teeth set near together, as some conditions require 

 very close adjustment to -enable them to break open 

 the balls containing the seeds. Under some condi- 

 tions, the ball is often found to be saturated with an 

 oily, gummy substance which makes it very tough; 

 it is then liable to break off from the stalks and pass 

 whole through the machine. To meet such condi- 

 tions, use all the concave teeth possible and run the 

 cylinder at a high rate of speed, arranging the parts 



