FARM MACHINERY 



283 



there are certain physical differences between the grains to 

 be separated. It is reasonable to think that no machine can 

 separate two grains whose difference lies wholly in the name 

 or color. The modern fanning mill is arranged to utilize 

 several of the physical differences which may exist between 

 grains. These differences may be, (1) difference in weight, 

 (2) difference in size, (3) difference in shape. 



In addition, the roughness of the hull and the location of 

 the heavy part of the seed may be used to some extent in 

 making certain selec- 

 tions or separations. A 

 separation based upon 

 a variance in weight is 

 made by the use of a 

 strong current of air. 

 Some grain graders use 

 1 his method almost 

 entirely at the present 

 time, and formerly all 

 machines depended 

 principally upon "fan- 

 ning" to do the sepa- 

 rating, hence the name 

 fanning mill. No doubt, the heavier grains are the most 

 desirable for seed, and therefore fanning is the most im- 

 portant feature of the modern fanning mill. 



Sieves, screens or riddles are used to grade the grain 

 according to size. The grain first passes through a coarse 

 screen, which takes out all the large particles, then over a 

 finer sieve, or a combination of finer sieves, which lets the 

 small grains and weed seeds through and which retains the 

 larger seeds in one or more grades. 



A section of a fanning- mill in 

 which the blast does not strike the grain 

 until after it has passed through the sieves. 



