THE DETERMINATION OF ACETYL NUMBER. 77 



Acetyl Number of Insoluble Fatty Acids. 



The acetyl number of the insoluble fatty acids is determined by the 

 Massachusetts method in precisely the same way as that of the original 

 fat. The gravimetric process is not applicable on account of the forma- 

 tion of anhydrides of the fatty acids. The method for preparing the stock 

 of insoluble acids for analysis is the same as that for the determination of 

 "Insoluble Acids," with the elimination of such features as are necessary 

 only for quantitative work. 



In order to interpret the results satisfactorily it is necessaiy to know 

 the percentage of insoluble acids so that the acetyl number of the acids 

 may be considered in conjunction with the acetyl number of the fat. 



Results by Different Methods. 

 For convenience, the theoretical acetyl numbers of some hydroxy com- 

 pounds by the Benedikt and Ulzer, and Lewkowitsch methods are tabu- 

 lated to permit comparison with the acetyl numbers by the Massachu- 

 setts and gravimetric processes previously stated. When only one 

 hydroxj' compound of known composition is present in an oil or fat the 

 results can be readily converted from the basis of the original to that of 

 the acetylated product and vice versa. In other cases conversion is gen- 

 erally impracticable on account of the marked differences in assimilation 

 of acetyl by the several classes of hydroxj'' compounds. Formulas may 

 show the relation, however, that the results by different methods bear 

 to each other, (m) indicating the molecular weight of the hydroxy com- 

 pound, (d) the number of hydroxyls, and (i) the increase in weight on 

 acetylating: — 



Massachusetts Method. 



cm 



56108 d 



Gravimetric Method. 



im 

 42.016 d 



Benedikt and Ulzer, and Lewkowitsch Methods, 



c(m + 42.016 d) 

 56108 d 



