QUANTITATIVE METHODS 



21 



(i) The Acid Number. 



This is the number of minigrams of potassium hydroxide re- 

 quired for the neutrahzation of the free acids in a sample of fat. 



This number is determined by dissolving i or 2 grams of 

 the sample in 15 or 20 c.c. of a mixture of I part of alcohol 

 with 2 parts of ether, and titrating the solution with N/io 

 alcoholic potash in the presence of phenolphthalein. 



(2) The Saponification Value. 



This is the number of milligrams of potassium hydroxide 

 required for saponifying I gram of the fat. 



From I to 2 grams of the sample are weighed out into a 

 250 c.c. conical flask ; 25 c.c. of approximately seminormal 

 alcoholic potash are then added, and the flask is attached to a 

 reflux condenser and heated over a water bath for about half 

 an hour ; the solution is then diluted with 25 c.c. of water and 

 cooled, then the excess of potash is titrated back by means 

 of N/2 hydrochloric acid. In order to determine the strength 

 of the alcoholic potash, 25 c.c. of it are heated at the same 

 time under exactly similar conditions in a second conical flask, 

 but without any fat ; in this way any error due to the effect 

 of the alkali on the glass vessel is eliminated. The difference 

 in the two titration readings gives the amount of acid equiva- 

 lent to the potash used up in saponifying the fat, from which 

 the number of milligrams of alkali required for I gram of fat 

 may be calculated. 



Since one molecule of any monobasic acid requires one 

 molecule of potash, the magnitude of the saponification value 

 is inversely proportional to the molecular weight of the acids 

 contained in the fat. 



* The oil contained in the kernel of the palm fruit, 

 t The oil contained in the pericarp of the fruit. 



