134 MASS. EXPERIMENT STATION BULLETIN 166. 



repeatedly to be comparatively unstable. By the assimilation of oxj'gen 

 and water it may be converted into dihydroxystearic acid, a saturated 

 compound. 



CnHjsCOOH+HaO+O =Ci7H3.(OH)2COOH 



Whether the oxidation takes place in the glycerides or in the fatty acids 

 after hydrolysis is uncertain, although the latter appears the more probable 

 supposition. 



Monoglycerides and diglj^cerides result from the hydrolysis of triglyc- 

 erides, and free fattj'' acids condition their presence; the absence of free 

 fatty acids in a commercial product, however, does not necessarily pre- 

 clude the presence of monoglycerides and diglycerides. 



SoUd alcohols of the cyclic series (sterols) occur in oils and fats both in 

 combination as esters and as free alcohols. ^ The amount of sitosterol or 

 cholesterol is generally small, often inappreciable, and is indicated ap- 

 proximately by the unsaponifiable matter which it characterizes. Alco- 

 hols of the ethane and other series, free and in combination, compose a 

 considerable proportion of waxes. 



Oils and fats, therefore, may contain glycerides of monohydroxy and 

 dihydrox>' acids, possibly free hydroxy acids, monoglycerides and diglyc- 

 erides and free alcohols; and the insoluble acids, separated from the oils 

 and fats, may contain monohydrox}^ and dihydroxy acids and free alco- 

 hols. A portion, at least, of the free alcohols found in the insoluble acids 

 probably occurred in the fat as esters. With the exclusion of the natural 

 glycerides of hydroxy acids and a small amount of free alcohols the acetyl 

 number of many oils and fats may be deemed an index of quality, and when 

 considered in conjunction wdth the acid and iodine numbers may serve to 

 measure (more or less imperfectly, to be sure) the amount of hydrolysis 

 and of oxidation the product has undergone. To differentiate between 

 products of hydrolysis and of oxidation the percentage of insoluble acids 

 and their acetyl number should also be determined. 



Of the oils, fats and waxes wdth an appreciable content of hydroxy com- 

 pounds " might be mentioned candle nut oil, safflower oil, rape oil, peanut 

 oil, olive oil, elderberry oil, Japanese sardine oil, skate liver oil, shark 

 liver oil, seal oil, horses' foot oil, palm oil, bone fat and beeswax, having 

 acetyl numbers between 10 and 20; neat's-foot oil, Japan wax, carnauba 

 wax and wool wax, having acetyl numbers ranging from 25 to nearly 60; 

 and castor oil, having an acetyl number of about 170. 



Unsaponifiable IVIatter. 



The unsaponifiable matter indicates the percentage of all those compo- 

 nents of an oil, fat or wax which on boiling with potassium hydroxide do 

 not form water-soluble compounds. 



' See numerous references: Abderhalden, Physiol. Chem. (1908); Hammarsten, Physiol. Chem. 

 (1911); Leuthes, The Fats (1910). 

 2 Lewkowitsch, Analysis of Oils, Fats and Waxes, 1., pp. 434-435 (1913). 



