104 II. CHEMISTRY OF FATTY ACIDS AND GLYCEROL 



Longenecker.'^^ Few determinations are available on the unsaturated 

 acids. Wood et al.^^^ have reported the following values (at 50°C.): 

 oleic acid, 1.4487; elaidic acid, 1.4468; linoleic acid, 1.4588; and linolenic 

 acid, 1.4678. Wan and Chen^^^ have found a considerably higher value 

 for a-elaeostearic acid, namely, 1.5112 at 50°C., while /3-elaeostearic acid 

 has a refractive index of 1.5022 at 75°C. Results on ethyl linoleate and 

 ethyl linolenate over a wide range of temperatures are reported by Mc- 

 Cutcheon.''^'^"'' 



Table 36 



Refractive Indices of Saturated Fatty Acids as Influenced by Temperature 

 AND Molecular Refractivity at 80 °C." 



« A. Dorinson, M. R. McCorkle, and A. W. Ralston, ./. Am. Chem. Soc, 64, 2739-2741 



(1942). 



The refractive index is a straight-line function of temperature between 

 40° and 80°C., although the slope changes^^^ ^^^i^^y 40°^ rj.^^^ refractive 

 index varies with the polymorphic form^^^; it becomes progressively greater 

 with extension of chain length. 



(a) Molecular Refractivity. The molecular refractivity is a value which 

 relates refractive index to molecular weight and density. It is readily 

 calculated from the Lorentz-Lorenz formula :^*^'^^^ 



359 K. F. Mattil and H. E. Longenecker, Oil & Soap, 21, 16-19 (1944). 

 '^° T. R. Wood, F. L. Jackson, A. R. Baldwin, and H. E. Longenecker, J. Am. Chem. 

 Soc, 66, 287-289 (1944). 



3" S. W. Wan and M. C. Chen, /. Am. Chem. Soc, 61, 2283-2284 (1939). 



3«2 J. W. McCutcheon, Can. J. Research, B18, 231-239 (1940). 



3" J. Thihaud and F. Dupre la Tour, Compt. rend., 190, 945-947 (1930). 



3" H. A. Lorentz, Ann. physitc. Chem., 9, 641-665 (1880). 



365 L. Lorenz, Ann. physilc. Chem., 11, 70-103 (1880). 



