THE DETERMINATION OF ACETYL NUMBER. 



75 



Acetyl Number on Original Product {Massachusetts Method) — Con. 



Diglyccrides. 



Name. 



Formula. 



Molecular 

 Weight. 



Saponifi- 

 cation 

 Number. 



Theoret- 

 ical 

 AcetV'l 

 Number. 



Recip- 

 rocal. 



Dipalmitin, 

 Distearin, 

 Diolein, . 



(Ci5H,,iCOO)2C.!H5(OH), 

 (Ci-H3.^COO)2C3Hr,(OH), 

 (Ci7H33COO)2C,.H5(OH), 



98.687 

 89.829 

 90.413 



.0101330 

 .0111323 

 .0110604 



Gravimetric Process. ^ 



After acetylating, a gravimetric process for acetyl number may be 

 conducted in a manner similar to that for the quantitative determination 

 of insoluble fatty acids, observing all the precautions therein noted as to 

 ceresine, washing, drying, w^eighing, etc. 



This mocUfication is apparently rather more difficult, tedious and sub- 

 ject to error than the saponification or volumetric process (Massachusetts 

 method). A certain amount of loss arises from the dehydration of free 

 fatty acids by acetic anhydride during acetylation, and is difficult to 

 prevent, although of little consequence where the amount of free acids is 

 relatively small. 



The acetyl number (a) is calculated from the increase in weight (i) by 

 the foUoW'ing formula: — 



56108 i 

 42.016 



or 1335.39604 i 



In case only one hj'droxj^ compound of known molecular weight (m) 

 and number of hydroxyls (d) is present, its amount can be calculated 

 from the increase in weight (i) of the oil, fat or wax on acetj^lating. The 

 theoretical increase for a hydroxy compound is — 



42.016 d 



* This process has not received sufficient study in this laboratory to warrant positive state- 

 ments, but is similar to the methods described by Lewkowitsch (loco citato), 1, pp. 358-363, 

 466, 467. 



