EDIBLE FATS AND OILS. 137 



mix thoroughly, pour onto the crystal, and allow to cool. Introduce the watch 

 crystal into a wide-mouth 16-ounce bottle with ground-glass stopper. 



(5) Absorption of iodin in Hubl's method. Dissolve the fat or oil in the 

 bottle in 10 cc of chloroform. After complete solution has taken place add 

 30 cc of the iodin solution in the case of fats, or from 40 to 50 cc< in the case of 

 oils. Place the bottle in a dark place and allow to stand, with occasional 

 shaking, for three hours. & This time must be closely adhered to in order to get 

 good results. The excess of iodin should be at least as much as is absorbed. 



(4) Absorption of iodin in Hanus method. Add 25 cc of the iodin solution 

 to the chloroform solution of the fat. Allow to stand, with occasional shaking, 

 for thirty minutes. The excess of iodin should be at least 60 per cent of the 

 amount added. 



(5) Titration of the unabsorbed iodin. Add 10 cc of the potassium iodid 

 solution in the Hanus method, or 20 cc in the Hiibl method and shake thor- 

 oughly, then add 100 cc of distilled water to the contents of the bottle, washing 

 down any free iodin that may be noted on the stopper. Titrate the 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. 



(6) Standardizing the iodin solution by thiosulphate solution. At the time 

 of adding the iodin solution to the fat employ two bottles of the same size as 

 those used for the determination for conducting the operation described under 

 paragraphs (3), (4), and (5), but without the presence of any fat. In every 

 other respect the performance of the blank experiments should be just as de- 

 scribed. These blank experiments must be made each time the iodin solution Is 

 used. Great care must be taken that the temperature of the solution does not 

 change during the time of the operation, as acetic acid and alcohol have very 

 high coefficients of expansion, and a slight change of temperature makes an 

 appreciable difference in the strength of the solution. 



Per cent of iodin absorbed : 



Weight of fat taken gram__ 0. 250 



Quantity of iodin solution used cc__ 40.0 



Thiosulphate equivalent to iodin used cc 65.0 



Thiosulphate equivalent to remaining iodin cc__ 40.0 



Thiosulphate equivalent to iodin absorbed cc__ 25.0 



Per cent of iodin absorbed (25.0 x 0.012692 x 100) divided by 0.250 126.92 



7. Saponification Number or Koettstorfer Number. Official. 



(a) PREPARATION OF REAGENTS. 



(1) Standard sodium hydroxid solution. Use a tenth-normal solution of 

 sodium hydroxid. Each cubic centimeter contains 0.0040 gram of sodium 

 hydroxid and neutralizes 0.0088 gram of butyric acid. 



P. Ulzer (J. Soc. Chem. Ind., 1898, 17: 276) says iodin should be in excess, about 

 twice the amount that is absorbed. The solution loses strength with age, but can be used 

 as long as 35 cc of tenth-normal thiosulphate neutralize 25 cc of iodin solution. 



6 The time allowed does not give the complete iodin absorption power of an oil or fat 

 and can not be compared with determinations in which six to twelve hours have been 

 used. It gives very satisfactory comparative results, but the time factor must be very 

 closely observed. 



