30 BULLETIN 867, U. S. DEPARTMENT OF AGRICULTURE. 
minimizing the labor of cleaning up the press. As 15 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 
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Fie. 15,—Sketch showing details of construction of the centrifugal separator shown in figure 14. 
second press In order to catch any fine ve 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 aad 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 
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