SCIENCE OF THRESHING. 6l 



the fan side, and will tend to make the blast uniform 

 for the entire width of the sieve. 



As before stated there are a great variety of sieves, 

 the woven wire ones having the preference in former 

 years. They admit the blast very freely and the 

 straws run through the meshes and fill them up, so 

 they are in some disfavor now. The present ten- 

 dency is toward sheet metal sieves having either a 

 plain perforated surface or irregular lips and corru- 

 gations and lips. Chaffers are frequently made of 

 wooden slats set at an angle, or with plain wood, 

 perforated at an angle to the surface. 



The angle of the blast as it passes through the 

 sieve should be upward rather than backward. The 

 reason is that a kernel will fall through a perpendic- 

 ular blast better than through an angularly directed 

 one, and a perpendicular blast also lifts the chaff 

 from the sieve better. 



The correct direction is given the blast by proper 

 adjustment of the lip or slat forming the sieve meshes, 

 the blast taking its direction from the lip. 



The holes or meshes should be only large enough 

 to allow the grain to pass through freely. When the 

 sieve is properly constructed and the blast properly 

 adjusted, there need be no waste and the grain will be 

 well cleaned. When the shoe is working properly, 

 there will be a very small quantity of tailings to 

 return to the cylinder. (Tailings, so-called, are the 

 grain and chaff which did not go through the sieves, 

 but are passed over the chaffer.) That this is so will 

 be seen if it is remembered that when the blast strikes 



