36 SCIENCE OF THRESHING. 



The blast should be sufficiently strong to insure its 

 continual flow under all circumstances and conditions, 

 but not fast enough to blow any of the grain over 

 with the chaff. 



There is a difference between a blast of strong 

 pressure and a blast of high speed. A current of air 

 may be traveling slowly, and still go with force and 

 be difficult to stop, as is that produced from a slow 

 moving air-pump ; or it may be moving quite rapidly 

 but with no particular force more than the momentum 

 produced by its own weight, like the zephyr of a 

 summer day or the breeze from a lady's fan. The 

 least obstruction would stop or turn such a blast. 

 THE KERNELS OF GRAIN WILL FALL THROUGH A 

 BLAST OF ANY PRESSURE OR STRENGTH, BUT WILL 

 NOT FALL THROUGH A VERY RAPIDLY TRAVELING 

 BLAST. 



The chaff is easily lifted on account of its light 

 weight. To do good work then, it requires a mild 

 or slow blast delivered with strength or force. This 

 blast should be spread under the entire surface of the 

 sieve and be made to flow through every mesh. It 

 should be strongest and of greatest quantity at the 

 front end of the sieve, which receives the grain and 

 chaff, for it is here that the greatest work is to be 

 done in lifting the sheet of chaff intermingled with 

 grain. It should decrease in quantity and pressure 

 toward the rear end where the least work is required. 

 Thus if a light kernel has been lifted with the chaff 

 at the front end, it will have a chance to fall before 

 reaching the rear end of the sieve. If the blast is 



