128 MASS. EXPERIMENT STATION BULLETIN 166. 



. Acetyl Number. 



The acetyl number indicates the number of milligrams of potassium 

 hydroxide required to combine with the acetyl ^ absorbed by 1 gram of an 

 oil, fat or wax on acetylation. ^ 



Reagents. — Acetic anhydride : Kahlbaum's. 



Ceresine: pure white, filtered. 



Alcohol: redistilled, free from acids and aldehydes. 



Alcoholic potash: 50 cubic centimeters of a saturated solution of potas- 

 sium hydroxide, free from carbonate, to 1,000 cubic centimeters of alcohol. 

 The solution should be allowed to stand at least twenty-four hours and 

 filtered immediately before use. 



N/2 hydrochloric acid. 



Phenolphthalein solution: 1 gram to 100 cubic centimeters of alcohol, 

 neutralized. 



Cotton blue 6B solution: 2 grams to 100 cubic centimeters of alcohol. 

 The indicator should be boiled in a flask under a reflux condenser for two 

 hours and then filtered. 



Method. — Into a 300 cubic centimeter Erlenmeyer flask are brought 5 

 grams of fat, together with 10 cubic centimeters of acetic anhydride. The 

 flask is connected with a spiral or other form of reflux condenser and heated 

 in a boiling water bath (immersed in the water) for from one to one and 

 one-half hours. Longer heating yields higher results, but is accompanied 

 by partial decomposition of the fat with formation of aldehydes or other 

 bodies that give a reddish color with caustic alkaU. After acetylating, the 

 spiral is removed from the flask and sufficient ceresine added to form a 

 solid disk with the fat when chilled in cold water. The amount of ceresine 

 required will vary with the consistency of the product under examination. 

 For butter fat 0.5 gram is ample; for softer fats and oils, rather more; 

 and for harder fats, less. With the flask still in the water bath, 150 cubic 

 centimeters of boiling water are added with as little disturbance of the 

 fat layer as possible. ■ The flask is then removed and the contents rotated 

 vigorously to dissolve occluded acetic acid. The flask is immersed in 

 cold water to soUdify the ceresine fat, after which the solution is decanted 

 through a dense, 12.5 centimeter filter, care being taken not to break the 

 insoluble cake. Another 150 cubic centimeters of boiling water is added, 

 thoroughly agitated, heated a few minutes on the bath, cooled and de- 

 canted, the process being repeated until the final filtrate gives a decided 

 color with two or three drops of N/10 alkali, using phenolphthalein as 

 indicator (about six times). Prolonged washing is likely to cause some 

 hydrolysis of the acetylated product. 



The filter and inverted flask containing the cake of ceresine fat are 

 allowed to drain in a cool place until practically diy. The smaU particles 

 adhering to the filter are then scraped into the flask, the inner portion of 



» On saponification the acetyl hydrolyzes to acetic acid and combines with the alkali. 

 ' Benedikt and Ulzer, and Lewkowitsch report on the basis of the acetylated product. 



