20 FATS, OILS, AND WAXES 



then diluted with 50 c.c. of 50 per cent caustic potash. Finally, 

 the liquid is acidified with 60 c.c. of sulphuric acid (sp. gr. 1-3), 

 as described above. After the shaking with light petroleum 

 is completed, 50 c.c. of 94 per cent alcohol are added instead 

 of the salt solution ; this has the effect of accelerating the 

 separation of the petroleum layer which otherwise might take 

 a long time. 



Owing to the relatively small solubility of stearic acid in 

 light petroleum the method may give too low a result in the 

 case of substances very rich in stearin ; the result should, 

 therefore, be checked by a second estimation in which the 

 number of shakings with petroleum are increased two or three 

 fold. Leathes * has modified and considerably improved this 

 method. 



Kumagawa and Suto f have found that the following 

 method gives good results : Two to five grams of the dry sub- 

 stance J are heated on a water bath for two hours with 25 c.c. 

 of 5 N sodium hydroxide (20 grams in lOO c.c.) in a covered 

 beaker. The mixture is then transferred to a separating funnel 

 and acidified with 30 c.c. of 20 per cent hydrochloric acid. 

 The fatty acids set free are taken up with ether, and the 

 ethereal solution is filtered through asbestos and evaporated. 

 The residue, which contains colouring matter, lactic acid, and 

 other substances as well as fatty acids, is dried for some 

 hours at 50°, and then taken up with light petroleum, where- 

 upon the impurities separate out in resinous form. After 

 filtering through asbestos the petroleum is distilled off and 

 the residue, consisting of almost pure fatty acids, is dried at 

 50° to constant weight. 



QUANTITATIVE METHODS EMPLOYED FOR THE 

 CHARACTERIZATION OF FATS. 



The following estimations are in common use for the 

 characterization of fats : — 



* Leathes : " The Fats," London, 1926. 



t Kumagawa and Suto : " Biochem. Zeit.," 1908, 8, 212. 



I Yoshitaka Schimidzu ("Biochem. Zeit.," 1910, 28, 237) recommends 

 using undried material since drj'ing leads to a loss of fat, probably from 

 oxidation. 



