122 EXPERIMENT STATION. [Jan. 



brought 5 grams of fat together with 50 cubic centimeters of 

 alcoholic potash, accurately measured with a burette, and 50 

 dTibic centimeters of alcohol. The flask is connected with a 

 condensing tube and heated on asbestos board at low ebullition 

 until saponification is complete, about thirty minutes. When 

 cool, the solution is titrated with N/2 hydrochloric acid, using 

 a few drops of phenolphthalein as indicator. The tempera- 

 ture of the solution during titration should be adequate to 

 maintain the soap in solution but not to greatly exceed that 

 requirement. Absorption of carbonic acid from the air should 

 be carefully guarded against at all times, especially during the 

 process of cooling. Several blank determinations should be 

 conducted with every series of tests. The difference between 

 the acid titration of the blank and of the test gives the alkali 

 required by the fat. 



One cubic centimeter of N/2 acid is equivalent to 28.079 

 milligrams of potassium hydrate. 



Limit of error, .50 saponification number. 



Syiiopsis of Reaction. 



C3H5(R02)3 + 3 KOH = 3 RO JC + C3H,(OH)3 



fat alkiili salt glycerol. 



Titration of excess alkali. 



R in the graphic formula of the fatty acids represents and 

 H in different amounts, according to the acid, but usually in the 

 proportion of CnH2n-i, except in the case of unsaturated acids. 



Supplementary Notes. — The term " saponification or sat- 

 uration equivalent," as employed by Allen and others, indicates 

 the grams of fat that are saponifiable with one equivalent of 

 potassium hydrate in grams (50.158). Tn other words, the 

 grams of fat saponifiable with 1 liter of N/1 potassium hydrate. 



.^ . . , , , 56158 mg. of fat 



baponihcation equivalent (sj) = or m /i u- r 



s cc i^ / A ctiK.aii 



56158 

 Saponification number (s) = ^ 



The lower the molecular weight of the fatty acids for esters) 

 the more alkali will be required to satisfy 1 gram, and the 



