196 SCIENCE OF SUCCESSFUL THRESHING 



"sun-cracked," the percentage may be somewhat larger. 

 The condition of the grain will determine the number and 

 position of the concave teeth, two, four or six rows being 

 used as required. 



Besides requiring a special spacing of the cylinder and 

 concave teeth, the cylinder speed must be lower for rice 

 than for ordinary grain. The twelve-bar cylinder-speed 

 for rice should be 900 revolutions per minute and in order 

 to give the proper speed to the other parts of the separator, 

 it is necessary to have special pulleys on the cylinder shaft. 

 These are larger than the regular pulleys and allow the 

 cylinder to run at the desired low speed, while maintaining 

 normal speed of the other parts of the separator. In the 

 same manner, the twenty-bar cylinder speed for rice should 

 be from 575 to 600 revolutions, and to obtain this, a corre- 

 sponding change in all the pulleys on the cylinder shaft 

 must be made. More rice is apt to be cracked the first few 

 days a new separator runs, than will be afterwards, when 

 the cylinder teeth have become worn smooth. 



Of the two principal varieties of rice the Japan and 

 the Honduras the former is much harder to knock out of 

 the head, but is not as easily cracked as is the latter. The 

 Golden rice of the Atlantic Coast States, however, is much 

 more easily cracked than either of the above varieties, so 

 that more care is required in threshing, and a special 

 feeder is often used. 



For rice the adjustable chaffer and shoe-sieve should be 

 set in the same position and with about the same opening 



