118 MASS. EXPERIMENT STATION BULLETIN 166. 



Mean Molecular Weight. — The molecular weight (m) of the insoluble 



fatty acids can be calculated from the neutralization number (n) by means 



of the formula — 



„ 56108 



or directly from the acid equivalent (v) and weight (w) of insoluble fatty 

 acids taken: — 



2000 w 

 m = 



V 



Supplementary Notes. — Direct titration of the fatty acids in alcohol 

 with N/2 alkali in a manner similar to that of "Acid Number" is often 

 recommended, although the process tends to yield low neutrahzation 

 numbers, ^ probably due to the presence of lactones (inner anhydrides of 

 hydroxy acids) or of anhydrides of simple fatty acids, M^hich do not combine 

 with aqueous alkah in the cold, but readily hydrolyze on boiUng with alco- 

 holic potash. The lactones and anhydrides may result from drying under 

 unfavorable conditions. Marked differences between the two methods are 

 shown- in the references cited. In our hands, working with purified insol- 

 uble fatty acids, only slight differences were obtained except in the case of 

 oleic acid. The saturated acids were prepared Mnth special precautions 

 and dried at a low temperature, which precluded the possibihty of forming 

 anhydrides. Hydroxy acids, such as ricinoleic acid of castor oil, are par- 

 ticularly likely to dehydrate with the formation of inner anhydi'ides. 

 Lactones occur naturally or are readily formed from the fatty acids of 

 Sewarri fat and of wool wax. In the latter case they result to some extent 

 from heating at 100° C. The fatty acids of castor oil polymerize on long 

 standing even at ordinary temperature to polyricinoleic acid. Gamma 

 hydroxystearic acid on losing a molecule of water forms stearolactone, and 

 may serve as an example (Lewkowitsch) : — 



CH3 . (CH2)i3 . CH . (OH) . CH2 . CHa . COOH = 



CHa . (CH2)i3 . CH CH» . CH2 . CO -fHsO 

 i 1 



The neutrahzation numbers of the mixed insoluble acids of most vege- 

 table and animal oils and fats range from 185 to 215, averaging about 200, 

 with the exception of the vegetable fats of the myristica, coconut oil and 

 dika fat groups wliich range from about 252 to 271. 



The neutralization numbers of the mixed insoluble acids of some of the 

 more prominent oils and fats are linseed oil, 200; corn oil, 200; cottonseed 

 oil, 205; sesame oil, 200; rape oil, 185; peanut oil, 202; ohve oil, 201; 

 castor oil, 192; cod Uver oil, 205; palm oil, 207; cacao butter, 190; palm 

 nut oil, 261; coconut oil, 271; lard, 205; beef tallow, 208; and butter fat, 

 215 to 225. These figures are reasonably accurate in most instances. 



> Tortelli and Pergami, Chem. Rev. Fett u. Harz Indus., 9, pp. 182, 204 (1902); Lewkowitsch, 

 Analysis of Oils, Fats and Waxes, 1, pp. 518, 519 (1913). 



