CONSTANTS FOll 1DENT1FK:AT10N OF FATS AND OILS 



243 



The Hanus reagent is also more stable. BulF^' states that, while the 

 Wijs reagent lasts only one month, the Hanus solution remains satisfactory 

 for at least one year. 



Both the Hanus and the Wijs methods are in current use in the United 

 States, but the latter procedure is employed much more in Great Britain 

 and Europe. The results are 2 to 4% lower with the Hanus procedure 

 than with the Wijs technic; Lewkowitsch^^* states that the higher results 

 are the correct ones. The discrepancies between the two procedures are 

 especially marked where the oils have high iodine values. This is especially 

 true with drying oils such as tung oil. Possibly the Wijs reagent brings 



40 60 



IODINE NUMBER 



Fig. 6. The relationship between the melting point and the iodine 

 number of cottonseed oil during hydrogenation."^ 



about a better addition of iodine to the conjugated double bonds present 

 in the elaeostearic acid glycerides of tung oil. However, sterols will 

 cause the results to be abnormally high when the Wijs procedure is 

 used. 



The Association of Official Agricultural Chemists has adopted the Hanus 

 method as the official one. On the other hand, the Committee on Analysis 

 of Commercial Fats and Oils of the Division of Industrial Chemists and 

 Chemical Engineers of the American Chemical Societ}^ has accepted the 

 Wijs procedure as the standard. '^^ A comparison of results obtained bj^ 

 the Hiibl, Wijs, and Hanus methods has l)een reported ])y Hunt,*^® as well 

 as by Tolman and Miuisou.^-'^ 



"3 H. B. Bull, The Biochemistry of the Lipids, Buigess, Minneapolis, 1936, p. 87. 



^^* J. I. Lewkowitsch, Chemical Technology and Analysis of Oils, Fats, and Waxes, 

 6th ed., Vol. Ill, Macmillan, London, 1938 (reprint, original ed., 1921-1923). 



^^ "Standard Methods for the Sampling and Analysis of Commercial Fats and Oils,' 

 Iml. Eng. Chem., 11, 1161-1168 (1919). 



»3« F. W. Hunt, J. Soc. Chem. Ind., 21, 454-4.56 (1902). 



3" L. M. Tolman and L. S. Munson, J. Am. Chem. Soc, 25, 244-251 (1903). 



