COMPOSITION OF NATURAL FATS AND OILS 213 



oxidation of the unsaturated acid residues. Following this, the solution is 

 washed alternately with the bicarbonate solution and water. Violent shak- 

 ing should be avoided at first, but as the azelaoglycerides are removed, the 

 ether extract should be A'igorously agitated with the water. The combined 

 potassium bicarbonate and water extracts are treated with ether to remove 

 any neutral saturated triglyceride which may have been lost in the emul- 

 sion. The united ether extracts are dehydrated with anhydrous sodium 

 sulfate and the ether is distilled off. The residual crude product is dried 

 under a vacuum at 100 °C., weighed, and combined with the earlier product 

 which has been precipitated from the ether solution. 



The crude saturated triglycerides may require further purification. If 

 the quantity is too small for this step, the amount of free acid and the un- 

 saponifiable residue can be determined; the weight can be corrected by 

 this amount, assuming the acid product to be azelaopalmitostearin. If a 

 considerable amount of crude saturated triglyceride is available, the latter 

 should be tested for the presence of unsaturated triglycerides. This is 

 readily achieved by determination of the iodine number. If the iodine 

 number of the crude product exceeds one, the whole mass should be sub- 

 jected to the entire oxidation process for a second time. If the original 

 fat sample has an iodine number which exceeds 25 to 30, complete removal 

 of the unsaturated triglycerides can seldom be effected in a single opera- 

 tion. In some cases, the oxidation procedure must be carried out a third 

 time before piu'e saturated triglycerides can be isolated. A further 

 purification suggested by Hilditch,'^ which can be employed if a consider- 

 able quantity of the crude saturated triglyceride is present, i.e., 20 g. or 

 more, involves boiling of the product with water in an open dish to which is 

 added sufficient dilute potassium carbonate (K2CO3) to make the mixture 

 alkaline to phenolphthalein. The aqueous \2iyev is siphoned off and the 

 triglyceride is boiled with water several times until the washings are neu- 

 tral. By this procedure 80-90% of the triglycerides can be recovered in a 

 purified form with a negligible acid value. An additional amount of some- 

 what lower purity can be recovered by ether extraction of the aqueous and 

 potassium carbonate washings. The amount of free acidic compounds in 

 the ether-extracted portion can be corrected for by isolation of the free 

 acidic compounds from the extracted aqueous alkaline washings and by de- 

 termination of their acid values. 



Hilditch recommends the use of enough fat in the original sample to ob- 

 tain at lea.st 1 to 2 g. of saturated triglycerides. With fats of low saturated 

 acid content, 50 or even 100 g. is the minimum quantity to be used. WTiere 

 a determination of the proportion of the individual saturated fatty acids 

 present is also required, considerably larger amounts of the original fat 

 sample may be needed, as at least 20 g. of the saturated triglycerides are es- 

 sential for this latter analysis. AVhen it is necessary to work up such large 



