EXAMINATION OF FATS. 1419 



TITRATION OF TITE UNABSOKBED IODIN. 



Add 20 cc of the potassium iodid solution and then 100 cc of dis- 

 tilled water to the contents of the bottle. Wash any iodin which 

 may be noticed upon the stopper of the bottle back into the bottle 

 with the potassium iodid solution. Titrate the excess of iodin with 

 the sodium thiosulphate solution, which is run in gradually, with con- 

 stant shaking, until the yellow color of the solution has almost disap- 

 peared. Add a few drops of starch paste, and continue the titration 

 until the blue color has entirely disappeared. Toward the end of the 

 reaction stopper the bottle and shake violently, so that any iodin 

 remaining in solution in the chloroform may be taken up by the potas- 

 sium iodid solution. The excess of sodium thiosulphate solution should 

 be sufficient to prevent a reappearance of any blue color in the flask 

 for live minutes. 



SETTING THE VALUE OF IODIN SOLUTION BY THIOSULPHATE SOLUTION. 



At the time of adding the iodin solution to the fat, two bottles of 

 the same size as those used for the determination should be employed 

 for conducting the operation described above, but without the pres- 

 ence of an} r fat. In every other respect the performance of the blank 

 experiments should be just as described. These blank experiments 

 must be made each time the iodin solution is used. 



Example blank determinations: Thirty cubic centimeters iodin solu- 

 tion required 46.55 cc of sodium thiosulphate solution. Thirty cubic 

 centimeters iodin solution required 46.65 cc of sodium thiosulphate 

 solution. Mean, 46.6 cc. 



Per cent of iodin absorbed: 



Weight of fat taken grams. . 1. 0479 



Quantity of iodin solution used cubic centimeters. . 40. 



Thiosulphate equivalent to iodin used do 62. 1 



Thiosulphate equivalent to remaining iodin do 30. 2 



Thiosulphate equivalent to iodin absorbed .do 31. 9 



Per cent of iodin absorbed, 31.9x0.0124x100-^1.0479=37.75. 



DETERMINATION OF SAPONIFICATION NUMBER AND SOLUBLE AND 

 INSOLUBLE ACIDS. a 



The saponification number, soluble and insoluble acids, were deter- 

 mined in one sample by the following method: 



PREPARATION OF REAGENTS. 



Standard sodium hydroxid solution. A decinormal solution of 

 sodium hydroxid is used. Each cubic centimeter contains 0.0040 



a U. S. Dept. Agr., Div. Chem. Bui. 46, revised, p. 47. 



