Twenty-second Convention, 1905, Bui. 99, Cir. 26. 



The Hanus method (given in the Proceedings for 1903, Bui. 81, 

 p. 63) was adopted as an official method for the determination of the 

 iodin absorption of fats and oils. 



HANUS METHOD. 

 (A) Preparation of reagents. 



(1) Iodin solution. (a) Dissolve 13.2 grams iodin in 1,000 cc glacial acetic 99.5 

 per cent acid (showing no reduction with bichromate and H 2 SO 4 ); add enough bro- 

 min to double the halogen content determined by titration 3 cc of bromin is about 

 the proper amount. The iodin may be dissolved by the aid of heat, but the solu- 

 tion should be cold when bromin is added. 



(2) Dednormal sodium thiosulphate solution. Dissolve 24.8 grams of chemically pure 

 sodium thiosulphate, freshly pulverized as finely as possible and dried between filter 

 or blotting paper and dilute with water to 1 liter at the temperature at which the 

 titrations are to be made. 



(3) Starch paste. One gram of starch is boiled in 200 cc of distilled water for 10 

 minutes and cooled to room temperature. 



(4) Solution vf potassium iodid. One hundred and fifty grams of potassium iodid 

 are dissolved in water and made up to 1 liter. 



(5) Dednormal potassium bichromate. Dissolve 4.9066 grams of chemically pure 

 potassium bichromate in distilled water, and make the volume up to 1 liter at the 

 temperature at which the titrations are to be made. The bichromate solution should 

 be checked against pure iron. 



(B) Determination. 



(1) Standardizing the sodium thiosulphate solution. Place 20 cc of- the potassium 

 bichromate solution, to which has been added 10 ccof the solution of potassium iodid, 

 in a glass-stoppered flask. Add to this 5 cc of strong hydrochloric acid. Allow the 

 solution of sodium thiosulphate to flow slowly into the flask until the yellow color of 

 the liquid has almost disappeared. Add a few drops of the starch paste, and with 

 constant shaking continue to add the sodium thiosulphate solution until the blue 

 color just disappears. 



(2) Weighing the sample. Weigh about one-half gram of fat or 0.250 gram of oil 

 on a small watch crystal or by other suitable means. The fat is first melted, mixed 

 thoroughly, poured onto the crystal, and allowed to cool. Introduce the watch 

 crystal into a w r ide-mouth 16-ounce bottle with ground-glass stopper. 



a With drying oils which have a very high absorbent power, 0.100 to 0.200 gram should be 

 taken. 



(3) Absorption of iodin. The fat or oil in the bottle is dissolved in 10 cc of chloro- 

 form. After complete solution has taken place, 25 cc of the iodin solution are added. 

 Allow to stand, with occasional shaking, for 30 minutes. The excess of iodin should 

 be at least 60 per cent of the amount added. 



(4) Titration of the unabsorbed iodin. Add 10 ccof the potassium iodid solution 

 and shake thoroughly, then add 100 cc of distilled water to the contents of the bottle. 

 Titrate the excess of iodin with the sodium thiosulphate solution, which is added 

 gradually, with constant shaking, until the yellow color of the solution has almost 

 disappeared. 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 potassium iodid solution. 



