62 SCIENCE OF THRESHING. 



every mesh in the chaffer properly, it will prevent any 

 chaff from passing through and will blow it into the 

 straw to be carried away with it. Besides, if the 

 chaffer is properly constructed and has the right 

 motion, as soon as the blast clears the forward 

 meshes of chaff, the grain will fall through at once, 

 and will then have the entire length of the sieve to 

 travel over before reaching the tailings spout, so that 

 there will be little chance of its being carried around 

 with the tailings. This is the crucial test of a 

 properly adjusted shoe, for if the blast does not pass 

 through the layer of grain and chaff until it has 

 passed half way along the sieve, or more, it is plain 

 that a part of the chaff has been sifting through the 

 sieve where there is no blast felt. The chaff will then 

 find its exit along the next loweY sieve to the tailings 

 spout. A portion of the grain cannot pass through 

 the chaffer at the front end, but is carried along with 

 the chaff to the point where the blast first affects it. 

 This may be so near the tailings spout as to cause the 

 grain to be carried over into the straw, or to go back 

 to the cylinder with the tailings, thus overloading the 

 elevator and unduly taxing the capacity of the sepa- 

 rating and cleaning devices, and this continued return 

 of the kernels to the cylinder is liable to crack or 

 crush them. As few sieves as possible should be used. 

 Oats usually require only one. In weedy wheat, in 

 some instances, a second sieve in the shoe will 

 improve the cleaning. Flax, if at all weedy, may be 

 run through two sieves below the chaffer. The mis- 

 take is often made of trying to run flax through a 



