30 BULLETIN 867, U. S. DEPARTMENT OE AGRICULTURE. 



minimizing the labor of cleaning up the press. As 13 usual in such 

 operations, the oil must be pumped through the filter press and back 

 into the original mixing tank for half an hour or so in order to coat 

 the leaves with a layer of earth, owing to the fact that the first run- 

 nings of oil are cloudy and clear up only when the plates are well 

 covered. The stream of clear oil should then be pumped through a 



Fig. 1.1.— Sketch showing details of construction of the centrifugal separator shown in figure 14. 



second press in order to catch any fine specks which may escape the 

 first filtration. 



Such treatment should produce a very light oil, no darker than a 

 fine straw color. However, low-quality beans and faulty factory 

 practice may result in greater color and unreasonable acidity. Fac- 

 tors contributing to high acidity are moisture and heat, particularly 

 the former, while those affecting color are largely heat, particularly 

 when the oil is heated in contact with seed coats or hulls. A clear 

 bleached oil heated for a little over half an hour at 195° F. materially 

 darkens, but samples of oil heated for one hour at 400° F. suffered 

 practically no change in acidity. This refers to both No. 1 oil and 

 refined No. 3 oil. The acidity of the oil does not materially increase 

 during the several days which elapse between manufacture and 

 finishing. Under common practice the oil from the first day's run 

 is collected at the end of the day for weighing. It is then dried over 



