SCIENTIFIC AGRICULTURE 



October 



A New Seed Cleaning Process 



By EDGAR D. EDDY 



President. Eddy Seed Cleaners, Limited, 



Toronto, Canada. 



Accurate separation of seeds on the 

 basis of comparative specific gravity has 

 long been recognized as highly desirable 

 and many attempts by various means 

 have been made to effect it. The separa- 

 tions by air currents as employed in 

 standard seed cleaning machinery are far 

 from accurate, as anyone realizes who 

 has tried to make a eompletie separation 

 by ordinary mills, of seeds which are 

 nearly the same specific gravity. Some 

 success has been achieved with small lots 

 of beans, peas and cereals by introducing 

 the grains into a brine, stirring the whole 

 mass and allowing the heavier kernels to 

 sink and the lighter ones to float. For 

 various reasons this method has been 

 found impracticable and has been em- 

 ployed only in a limited way for prepar- 

 ing special samples for experimental or 

 other purposes. 



Experiments With Liquid. 



While attempting to determine the 

 comparative specific gravity of clover 

 seed and certain w^ed seeds, the writer 

 observed that when a mixture of seeds 

 was introduced into and agitated with a 

 liquid of specific gravity intermediate 

 between that of the light and lieavy seeds, 

 the desired separation was not effected 

 because of air envelopes adhering to the 

 heavy seeds causing them to float, and 

 surface tension causing light and heavy 

 seeds to cling together in clusters, many 

 of Which would nemain suspended in the 

 liquid instead of sinking or floating. To 

 overcome this condition, a test tube con- 

 taining a seed mixture in liquid was sub- 

 jected to pressure in a milk-testing centri- 

 fuge, thus (expelling all the air from the 

 liquid and from around the seeds. A per- 

 fect separation then resulted, as each in- 

 dividual seed was free to sink or float 

 according to its specific gravity in com- 

 parison with that of the liquid. Further 

 experimients with a re-built small cream 

 separator bowl clearly demonstrated the 

 practicability of separating seeds by cen- 

 trifugal action in a liquid of proper den- 

 sity, and the valuie of the separations 



effected. The problem then was how to 

 provide for continuous separation and 

 at the same time maintain continuous dis- 

 charge of both the heavy and light por- 

 tions of the seed mixture. This has been 

 accomplished by a method entirely new 

 in centrifugal separator construction. The 

 machine operates continuously and at 

 large capacity. 



Centrifug-al Action and Liquid. 



As now developed and applied on a 

 commercial scale, the process does for 

 seed cleaning what the cream separator 

 did for the dairy industry. It utilizes 

 centrifugal force to separate completely 

 and instantaneously particles of different 

 specific gravity. As the separation of 

 butter fat from the other constituents of 

 milk by gravity is slow and incomplete, 

 so the separation of sieeds which are 

 slightly different in specific gravity is 

 very imperfectly done by gravity and air 

 currents. And, as centrifugal action 

 makes a perfect and immediate separa- 

 tion of butter fat from the other consti- 

 tuents of mjlk, so it makes a perfect and 

 immediate separation of seeds or other 

 solid particles of only very slightly dif- 

 ferent specific gravity when the nedes- 

 sary medium is provided. 



In order that centrifugal action may 

 be effective with seeds or other solid 

 particles it is necessary- that a liquid car- 

 rier be provided, the specific gravity of 

 which should be at a point intermediate 

 between the specific gravities of the 

 materials which it is desired to separate. 

 When the seeds and liquid are introduced 

 togiether into a rapidly revolving bowl 

 the seeds which are lighter than the liquid 

 are forced to the centre, while those which 

 are as heavy as or heavier than the liquid 

 are thrown to the circumference. By regu- 

 lating the density of the liquid, the propor- 

 tions of the seeds going into the li^ht and 

 heavy separations are under perfect con- 

 trol. The liquid used for cleaning clover 

 seed usually requires a density of 

 about 1.2. 



