286 III. CHEMISTRY OF NEUTRAL FATS 



the above reaction, but in which different solvents are employed, or varia- 

 tions in the timing, temperature, or the use of inert gas are indicated. 



The procedures of Taffel and Revis^^* and of Lea*^^ were the earlier stand- 

 ard methods. The Lea technic gives reproducible results, but it involves 

 the heating of the chloroform-acetic acid solvent to boiling. Wheeler*^^ 

 proposed a simplified method with the same solvent in the cold, which was 

 accurately timed at one minute. Lowen et al.'^^'^ found that the peroxide 

 value varied as much as 50% when determined by the Wheeler method, as 

 the sample size was increased from 2 to 10 ml. Stansby*^^ reported that 

 the Lea as well as the Wheeler technics gave decreasing peroxide values 

 when an increasingly large sample was used. One of the methods which he 

 proposed which involved the use of sulfuric instead of acetic or hydro- 

 chloric acids was largely free from the above criticism. 



The recent procedure of Kokatnur and Jelling*^^ has numerous advan- 

 tages over the earlier methods in which chloroform or carbon tetrachloride 

 is employed as a solvent. Since the above method employs isopropanol as a 

 solvent, it provides a satisfactory solution for fat, and at the same time also 

 allows ready miscibility with water, thus avoiding a two-phase system 

 when the liberated iodine is titrated with thiosulfate. The Lingenfelter 

 modification^^" consists in the use of a microtitration apparatus and the use 

 of 0.1 N thiosulfate as a standard. Volz and Gortner*^^ have recently 

 demonstrated that the recovery of benzoyl peroxide was equally satis- 

 factory in the Lingenfelter method (99.1-101.1%), the Stansby method 

 (98.6-99.1%,), and the Lea procedure (100.6-102.2%) when 2.5 to 25.0 mg. 

 of the peroxide was used. Equally effective recoveries (98.9-100.3) were 

 shown when 1 g. of fat was added to the benzoyl peroxide and the latter 

 was determined by the Lingenfelter method. Moreover, the Lingenfelter 

 modification of the Kokatnur and Jelling procedure gave most consistent 

 results when samples of varying size were used, as indicated in Table 40. 



Lips et aU''^ compared the several procedures and favored a ferric thio- 

 cyanate method. Lea^^^ has recently suggested a simplification of his 

 earlier technic, while Paschke and Wheeler"^ have modified the earlier 

 Wheeler method by reducing the sample weight to 1 g. and increasing the 



«" A. Taffel and C. Revis, /. Soc. Chem. Ind., 50, 87-91T (1931). 

 *<» C. H. Lea, Proc. Roy. Soc. London, BIOS, 175-189 (1931). 

 «6 D. H. Wheeler, Oil & Soap, 9, 89-97 (1932). 



«' L. Lowen, L. Anderson, and R. W. Harrison, Ind. Eng. Chem., 29, 151-156 (1937). 

 «3 M. E. Stansby, Ind. Eng. Chem., Anal. Ed., 13, 627-631 (1941). 

 «9 V. R. Kokatnur and M. Jelling, J. Am. Chem. Soc, 63, 1432-1433 (1941). 

 «» J. F. Lingenfelter, Thesis, Cornell Univ., 1945. Cited by F. E. Volz and W. A. 

 Gortner, J. Am. Oil Chemists' Soc., U, 418 (1947). 



«i F. E. Volz and W. A. Gortner, J. Am. Oil Chemists' Soc, 24, 417-420 (1947). 



«" A. Lips, R. A. Chapman, and W. D. McFarlane, Oil & Soap, 20, 240-243 (1943). 



«" C. H. Lea, J. Soc Chem. Ind., 65, 286-290 (1946). 



"74 R. F. Paschke and D. H. Wheeler, Oil & Soap, 21, 52-57 (1944). 



