32 FATS, OILS, AND WAXES 



c.c, of gently warmed glacial acetic acid. The two solutions 

 are then united in a i litre graduated flask and made up to 

 the mark with more glacial acetic acid. 



This solution should be standardized on the following day 

 by mixing 20 c.c. of it with 10 c.c. of 10 per cent potassium 

 iodide solution and titrating the free iodine by means of the 

 standard thiosulphate. 



The actual determination of the iodine value is performed 

 as follows : — 



From o*2-0"4 gram of fat should be carefully weighed and 

 dissolved in 10 c.c. of pure carbon tetrachloride (which has 

 been shown by a blank test not to absorb iodine) ; 25 c.c. of 

 the iodine solution are then added and the flask is stoppered 

 and set aside in the dark for one or two hours. The liquid is 

 then transferred to a larger flask, the smaller flask being 

 washed out thoroughly by means of 10 c.c. of potassium 

 iodide solution and water until the total volume is about 300 

 c.c. The solution is then titrated with the thiosulphate. The 

 difference between this reading and the amount required by 

 25 c.c. of the iodine solution is a measure of the iodine absorbed 

 by the amount of fat. 



The values obtained by Wijs's method are, as a rule, rather 

 higher than those obtained by the Hlibl method. 



Appended is a list of iodine values of some important fats, 



(a) Drying Oils — 



Linseed oil 173-201 



Hemp-seed oil 148 



Sunflower oil 1 19-135 



Pine-seed oil 101-103 



(b) Semi-Drying Oils — 



Beech-nut oil 104-111 



Cotton-seed oil 108-110 



Sesame 103-108 



Rape oil (colza) 94-102 



(c) Non-Drying Oils — 



Almond oil 93-97 



Olive oil 79-88 



Grape-seed oil 96-142 



Castor oil 83 -go 



{d) Vegetable Fats — 



Cacao butter 32-41 



Palm-nut oil * 1317 



Coco-nut oil * . . . . . . 8-10 



* Though described as oils these substances are both solid at ordinary 

 temperatures, melting at about 25°. 



