THE DETERMINATION OF ACETYL NUMBER. 71 



number will continue the hydrolysis, although a portion is likely to re- 

 main unchanged, thereby yielding too low an acid number, due to the 

 inabilitj' of the anh3'drides to combine with alkali. As complete hy- 

 drolysis occurs on saponification, the acetyl (ether) number would be 

 too high and even appear when none exists. 



Lewkowitsch^ proposed the acetylation of the natural product. In 

 conformity thereto the acetyl number indicates the milligrams of potas- 

 sium hydroxide required for the neutralization of the acetic acid obtained 

 on saponifying one gram of an acetylated oil, fat or wax. This method 

 requires the saponification of the acetylated fat and the determination of 

 the resulting acetic acid bj^ either a filtration or distillation process. The 

 former process is an adaptation of the regular method for the direct deter- 

 mination of soluble acids, and the latter process is a modified Reichert- 

 INIeissl test, Mith repeated distillation of the aqueous solution until the 

 distillate is free from acids. The presence of natural soluble or volatile 

 acids necessitates a similar treatment of the unacetylated fat in order to 

 determine the amount of alkali assimilated by those acids for which 

 proper corrections must be made to obtain the true acetyl number. The 

 occurrence of the lower acids makes the determination a long and tedious 

 operation. 



Proposed Method. 



Analytical methods for the examination of oils and fats is a subject 

 that has been given considerable study by the writer in connection with 

 feeding experiments and other investigations made at the Massachusetts 

 Agricultural Experiment Station. During the past few years the deter- 

 mination of acetyl number has received particular attention with a view 

 to evohdng a process that might be free from the objections cited for the 

 Benedikt and Ulzer, and Lewkowitsch methods. Believing that this end 

 has been attained in some measure, a report of progress is now offered 

 in the hope that it may lead to further improvement. 



The custom of reporting acetyl number on the basis of the acetylated 

 product appears unwarranted. It is contrary to general practice in 

 analj-tical work and is the exception in fat analysis. The definition- 

 here adopted places the acetyl number on a par with other tests, and is 

 as follows: the acetyl number indicates the milligrams of potassium 

 hydro.xide required for the saponification of the acetyl assimilated by 

 one gram of an oil, fat or wax on acetylation. 



Method in Detail. 

 The development of the method extended over a period of several 

 years, and finally resolved into an adaptation of several well-known proc- 

 esses. For instance, ceresine is used to solidify the acetylated fat so 

 that it may be washed by decantation as in the determination of insoluble 



1 Loco citato, 1, pp. 337, 338 (1909). 



2 The hydroxyl value of Twitchell is reported in a similar manner. Jour. Amer. Chem. Society, 

 29, pp. 506-571 (1907). 



