72 MASS. EXPERIMENT STATION BULLETIN 151. 



acids. The saponification number of the acetylated fat is detennined by 

 the same process as that of the original fat, and the difference measures 

 the amount of acetyl that has been assimilated. The process may be 

 appropriately described as a method by analogy. 



The reagents employed in the determination are summarized so that 

 their appHcation may be clearly understood : — 



Af-etic anhydride, Kahlbaum's. 



Ccrcsine, pure white, filtered. 



Alcohol, redistUlod, free from acids and aldehydes. 



Alcoholic potash, 50 c.c. of a saturated solution of potassium hydroxide, free frona 



carbonate, to 1,000 c.c. of alcohol. The solution should be allowed to stand 



at least twenty-four hours and filtered immediately before use. 

 N/2 hydrochloric acid. 

 Alkali blue (6B), 1 gram to 100 c.c. of alcohol. The indicator should be digested 



in a stoppered bottle for several days at room temperature, with occasional 



shaking, and then filtered. 

 Phenolphthalein, 1 gram to 100 c.c. of alcohol, neutralized. 



After what has been said, the details of the method should be so evident 

 as to require no further explanation. 



Into a 300 c.c. Erlenmeyer flask are brought 5 grams of fat, together with 10 c.c. 

 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 accom- 

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

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

 is removed from the bath and sufficient ceresine added to form, with the fat, a 

 solid disc when chilled in cold water. The amount of ceresine required will vary 

 with the consistency of the product under examination. For butter fat .4 to .5 

 grams is ample; for softer fats and oils rather more; and for harder fats, less. The 

 flask is heated on the water bath and the contents rotated until the ceresine and 

 acetylated fat form a homogeneous mixture. One hundred and fifty c.c. of boil- 

 ing water are then poured carefully into the flask with as little disturbance of the 

 fat layer as possible, and the solution heated on the bath with occasional agitation 

 to remove occluded acetic acid. The flask is immersed in cold water to solidify 

 the ceresine-fat, after which the solution is decanted through a dense, ether-ex- 

 tracted filter, care being taken not to break the insoluble cake. Another 150 c.c. 

 of boiling water are added, thoroughly agitated, heated as above, cooled and 

 decanted, the process being repeated until the final filtrate gives a decided color 

 with two or three drops of NAo alkali, using phenolphthalein as indicator (about 

 six times). Prolonged washing is likely to cause slight dissociation 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 dry. The small particles adhering to the 

 filter are then scraped into the flask, and 50 c.c. of alcoholic potash, accurately 

 measured with a burette, 50 c.c. of alcohol and several glass beads added. The 

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

 boiled on a water bath until saponification is complete, — about sixty minutes. 

 The flask is placed in a water bath at 60° C. and the solution, after cooling to that 

 temperature, titrated with N/2 hydrochloric acid, using 1 c.c. of alkali blue as 

 indicator. Phenolphthalein may be employed, though less satisfactory for colored 

 solutions. The alcoholic mixture is again brought to boil to free any alkali occluded 

 in the ceresine, and retitered if necessary. Several blank determinations should 



