8 
BULLETIN 1010, I T . S. DEPARTMENT OF AGRICULTURE. 
obtained, while at temperatures considerably above 100° C. a less 
pronounced bleaching is effected. Since the oil must be dehydrated 
at a temperature somewhat above 100° C, treatment with fuller's 
earth at temperatures below that point, even if effective, would not 
be practicable, since time would be lost in waiting for the oil to cool. 
In this connection, some tests were made to determine the bleach- 
ing effect of heating without the fuller's earth. Two '300-gram 
samples of oil, (a) of average color, and (2>) of materially darker 
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Fiq. 3.— The extent of bleaching effected in two samples of corn oil when heated to various temperatures 
up to 300° C 
color, previously treated with caustic, were heated slowly, with con- 
stant stirring, to 250° C. At 100°, 150° and 200° C, respectively, 
the temperatures were maintained constant for five minutes; then 
samples for colorimetric readings were withdrawn and the heating 
continued. Figure 3 shows the extent to which the heating bleached 
these oils. A decided bleach seems to be effected at a temperature 
of 200° to 250° C. Above that temperature the oil apparently turns 
darker. Both samples of oil bleached slightly up to 100° C, then 
darkened somewhat until 150° C. was reached, and then bleached 
again as the temperature rose to 250° C. It is generally recognized 
