244 III. CHEMISTRY OF NEUTRAL FATS 



The iodine numbers of the so-called drying oils exceed 130. Although 

 the common figure for linseed oil approximates 180, extreme variations of 

 123 to 209 have been reported. "'^"'^^•^'^-'^^ The iodine values for many 

 edible oils such as corn, cottonseed, peanut, and soybean oils^"^ are in the 

 neighborhood of 100 (95-125). The latter fats are ordinarily not con- 

 sidered as drying oils, although soybean oil has found considerable applica- 

 tion in the paint industry in recent years. On the other hand, the iodine 

 number of coconut oil (8.4-8.8) approaches zero. 



The relationship of the iodine number to the index of refraction has al- 

 ready been mentioned. The change in this constant which occurs during 

 hydrogenation of cottonseed oil is given in Figure 6. 



(7) Thiocyanogen Number 



The thiocyanogen number is the amount of thiocyanogen, expressed as grams 

 of iodine, absorbed by one hundred grams of fat or oil. This determination of- 

 fers a useful adjunct in establishing the nature of the unsaturated fatty 

 acids in a fat or oil. Kaufmann^*"-^'*^ alone, and associated with Keller,'*^ 

 discovered that unsaturated fats react with thiocyanogen (CNS)2 in a 

 reproducible manner. However, instead of combining with all unsatu- 

 rated linkages as is the case with iodine, thiocyanogen reacts with only 1 of 

 the 2 unsaturated linkages in linoleic acid, and with 2 of the 3 double bonds 

 in linolenic acid. The reaction between thiocyanogen and oleic acid or 

 triolein is quantitative. ^'*^'^'*^ Riemenschneider, Swift, and Sando^** have 

 reported the thiocyanogen values of oleic acid, linoleic acid, and linolenic 

 acid as 89.4, 93.9, and 162.0, respectively, when a 0.1 A^ thiocyanogen solu- 

 tion is employed. The sensitivity of the reaction to the experimental 

 conditions which had been observed earlier^'*^-^*^ is shown by the fact that 

 the results on the 3 methyl esters tested were found to be 85.3, 92.7, and 

 159.6, respectively, when the thiocyanogen solution used had a concen- 

 trations^^ of 0.2 N. When u.sed in connection with the iodine value, the 

 thiocyanogen value can be used to estimate the quantity of each of the 



338 J. B. McNair, Botan. Rev., 11, 1-59 (1945). 



"» S. L. Ivanov, Biol. Generalis, 5, 579-586 (1929). 



3*« H. P. Kaufmann, Z. Unlersuch. Lebensm., 51, 15-27 (1926). 



3" H. P. Kaufmann, Analyst, 51, 264-265 (1926). 



'« H. P. Kaufmann and M. Keller, Analyst, 54, 304 (1929). 



'" D. H. Wlieeler, R. W. Riemenschneider, and C. E. Sando, /. Biol. Chem., 132, 

 687-699 (1940). 



"♦ L. Zeleny and C. H. Bailev, Ind. Eng. Chem., 24, 109-110 (1932). 



3« R. W. Riemenschneider, C. E. Swift, and C. E. Sando, Oil & Soap, 18, 203-206 

 (1941). 



"6 P. J. Gav, J. Soc. Chem. Ind., 51, 126-129T (1932). 



3" J. P. Kass, W. (). Lundherg, and O. O. Burr, Oil d: Soap, 17, 50-53 (1940). 



