234 III. CHEMISTRY OF NEUTRAL FATS 



complished either by using the oxides of nitrogen or sulfur, '^^"•^'^^"'"^ or by 

 the action of selenium. '"^''''^ The elaidoglycerides so formed have dif- 

 ferent solubilities in acetone, and may be resolved from the other triglyc- 

 erides. Thus, by determinations of saturated, elaidic, and combined 

 oleic and linoleic acids, it is possible to calculate the proportions of the dif- 

 ferent unsaturated acids in the fats. The accuracy is of a lower order than 

 is possible for the solid fats having a larger proportion of saturated acids. 



Hilditch''' has suggested the distribution of unsaturated fatty acids as 

 indicated in Table 23 for several vegetable fats. Such values are purely 

 tentative and are based on the total Cis unsaturated acids divided accord- 

 ing to the "rule of even distribution," which has been shown to hold for 

 liquid fats. 



Table 23 

 Calculated Proportion (Mole per Cent) of Triglycerides in Some Liquid Fats" 



" Adapted from T. P. Hilditch, The Chemical Constitution of the Natural Fats, 2nd ed., 

 Wiley, New York, 1947, p. 219. 



* Stearic, arachidic, behenic, or lignoceric acid may be present Ln place of some of the 

 palmitic acids. 



Although much progress has been made in our knowledge of the com- 

 position of fat, little has as yet been accomplished insofar as the under- 

 standing of their specific configuration is concerned. As described earlier, 

 a number of mixed triglj^cerides have been isolated from natural fats ; how- 

 ever, these have given us only qualitative data rather than quantitative 

 values. Moreoever, by the technics available, only the least soluble have 

 been separated. It is suggested by Longenecker^" that the production of 

 such a selective configuration may mean the operation of a specific biological 

 process. 



5. Constants Used for Identification of Fats and Oils 



A number of physical and chemical constants are commonly employed 

 to facilitate the identification of fats, as well as to establish their purity. 

 Some of these values may be ([uite specific for the appraisal of the purity 



301 H. N. Griffiths and T. P. Hilditch, J. Chem. Soc, 1932, 2315-2324. 

 a>2 H. N. Griffiths and T. P. Hilditch, Analyst, 59, 312-318 (1934). 



303 T. P. Hilditch and H. N. Griffiths, J. Soc. Chem. Ind., 53, 75-81T (1934). 



304 S. H. Bertram, Chem. Weekhlad, 33, 3-5 (1936); Ole, Fette, WacJise, Seife, Kosmetik, 

 1938, No. 7, 1-4; Chem. Abst., 32, 7755 (1938). 



306 B. G. Gunde and T. P. Hilditch, /. Soc. Chem. Ind., 59, 47-53T (1940). 



