impro\t:d methods for fat analysis. 129 



the filter paper extracted in a small beaker with three successive 20 cubic 

 centimeter portions of boiling alcohol, and poured into the flask; then 

 50 cubic centimeters of alcohoUc potash, accurately' measured with a 

 burette, and several glass beads are 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 cooUng to that. 

 temperature, titrated with N/2 hydrochloric acid, using 1 cubic centi- 

 meter of phenolphthalein or cotton blue as indicator. Cotton blue offers 

 certain advantages in the case of solutions that develop a reddish color 

 with caustic alkah. The alcoholic mixture is again brought to boil to 

 free any alkah occluded in the ceresine, and retitered if necessary. Sev- 

 eral blank determinations should be run with every series of tests, under 

 precisely similar conditions as to time and treatment except that the 

 ceresine may be omitted. However, every lot of ceresine must be tested. 

 It should be free from soluble matter and not assimilate any alkali on 

 saponification. The difference between the titration of the blank and that 

 of the excess alkali in the test is the acid equivalent of the fat after acetyl- 

 ation, which should be calculated to milligrams of potassium hydroxide 

 for 1 gram of fat. 



One cubic centimeter of N/2 acid is equivalent to 28.054 milligrams of 

 potassium hydroxide. 



The difference between the saponification number of the fat before and 

 after acetylation is the acetyl number. In case the original fat contains 

 free soluble acids their titer should be determined and proper correction 

 made for the same. 



Limit of error, 0.50 milligram. 



Synopsis of Reaction. — Acetylation of glycerides of monohydroxy and 

 dihydroxy acids, monoglycerides and diglycerides and free alcohols. (See 

 formulas.) 



Saponification of the acetylated product. (See formulas.) 



Saponification of the original or unacetylated product. 



Titration of excess alkah. 



Acetyl number by difference. 



