CONSTANTS FOR IDENTIFICATION OF FATS AND OILS 247 



oil. Tlii.s constant is an index of the proportion of hydroxy! groups in a fat. 

 When the fat under investigation is treated with acetic anhydride, an 

 acetjd group is introduced wherever a free hydroxyl is present. After 

 washing out of the excess acetic anhydride and the acetic acid Hberated dur- 

 ing the reaction from the acetylated fat, the latter can be dried and the ace- 

 tic acid in combination set free from a weighed amount. ^^^ As noted above, 

 the weight of potassium hydroxide necessary to neutrahze the acetic acid 

 from one gram of acetylated fat is the unit in which this constant is ex- 

 pressed. 



Although this constant is employed mainly to determine the amount of 

 ricinoleic acid present in fats such as castor oil, it has some imiJortance in the 

 biological field, in view of the reputed nutritional value of some of the 

 hydroxvstearic acids. It is also of considerable value in assessing the 

 amount of mono- and diglycerides in a mixture of fats. Any free hydroxyl 

 groups of glycerol become acetylated in the same way as those on the fatty 

 acid residue. By comparing the degree of acetylation of the unhydro- 

 lyzed fat with that of its component fatty acids, one obtains an index of the 

 proportion of the glycerol combined with only one or two fatty acid residues. 

 The acetyl value of castor oil is usually approximately 150, while that for 

 most other fats varies from 28 to 13, with the exception of carnauba wax,^^* 

 for which the ^'alue is 55. 



(11) Unsaponifiahle Matter 



The unsaponifiable fraction (also referred to as non-saponifiable residue 

 or fraction, abbreviated as N.S.F.) makes up that part of the fat which 

 cannot be changed to water-soluble products by the process of saponifica- 

 tion. It can readily be separated by ether extraction from the soap solu- 

 tion resulting from saponification of the fat. More precise methods for its 

 determination are outlined by the Fat Analysis Committee of the American 

 Chemical Society.^'*-'" 



The products which are found in this fraction consist of the higher alco- 

 hols, including the sterols, the fat-soluble vitamins, A, D, and E, such pro- 

 vitamins as the carotenoids, and any hydrocarbons which are present, such 

 as paraffin or mineral oil. Resinous substances may also be included if the 

 oil has been prepared by ether or petroleum ether extraction of food prod- 

 ucts. Another interesting hydrocarbon found to the extent of 0.41 to 

 0.54% in olive oil is squalene,^*-^*^ which has the empirical formula, 



«« E. G. Mahin, Quantitative Analysis, 3rd ed., McGraw-Hill, New York, 1924, pp. 

 382, 390-391. 



'" Anonymous, Official and Tentative Methods of Analysis of the Association of Official 

 and Agricultural Chemists, 4th ed., XXXI, "Oils, P"'atR and Waxes," ])afi;es 420-421, 

 l«):}o. 



«* T. Thorhjarnarsoii and J. C. Druniniond, Analyst, 60, 23-29 (1935). 



«' J. Grossfeld and H. Tinim, Z. Unlersuch. Lebensw., 77, 249-253 (1939). 



