CHARACTERIZATION OF FATS 



29 



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 mole- 

 cule of potash, the magnitude of the saponification value is 

 inversely proportional to the molecular weight of the acids 

 contained in the fat. 



Butyrin , 

 Palmitin . 

 Stearin . 

 Olein 



Coco-nut oil 

 Palm-kernel oi 

 Palm oil . 

 Olive oil . 



(3) Iodine Value. 



It was first observed by Hiibl that an alcoholic solution 

 of iodine containing mercuric chloride reacted at ordinary 

 temperatures both with the free unsaturated acids and with 



