286 AGRICULTURAL ENGINEERING 



be made of selected material and well put together, and the 

 wire cloth should be firm and not easily distorted. Perfo- 

 rated sieves are the best when made of zinc. They are 

 the most accurate, as the perforations are quite sure to be of 

 the same size. Their capacity, however, is less, and they 

 prevent the passage of a blast of air through them. 



Sieves should be well cared for. A punctured or sagged 

 sieve has its efficiency very much reduced. It would be well 

 to provide a rack for storing the sieves while not in use. 

 The practice of piling them one upon the other is not at all 

 to be commended. 



QUESTIONS 



1. Why is the fanning mill necessary in the grading of small-grain 

 seed? 



2. What are the three functions of a fanning mill? 



3. Upon what three physical differences in seed does separation 

 depend? 



4. What devices are used to separate by differences in weight? In 

 size? In shape? 



5. Describe two types of fanning mills. 



6. What points of construction should be observed in making a 

 selection of a fanning mill? 



7. Describe the adjustments of the blast and sieves in a fanning 

 mill. 



8. Of what materials are the sieves made, and what is the ad- 

 vantage of each? 



9. How should the sieves be cared for? 



