8 BULLETIN 1010, tr. 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 (b) of materially darker 



so- 



zso c 



JOO< 



/OO" /SO" 200° 



rertP£RATV/?E (CE/V7:J 



Fig. 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 samples for colorimetric readings were withdrawn and the heating 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 



