156 FATS, OILS AND LIPINES. [CH. VI. 



that have been neutralised by the free or combined fatty 

 acids of i gram, of the fat is the value required. 



The saponification value of pure tristearin is 189. 

 (C 17 H 35 .COO) 3 C3H 5 + 3 KOH 



= 3 C 17 H 35 .COOK + C 3 H 5 (OH) 3 

 Mol. wt. 890 3 x 56 



i gram, requires 0-189 gram. KOH. 



The value for triolein is 190, and for tripalmitin 208. 



The saponification value is a measure of the mean 

 molecular weight of the fatty acids constituting the fat. 

 It is increased by a decrease in the molecular weight. It is 

 lowered by the presence of unsaponifiable substances, such 

 as cholesterol. 



3. The iodine value. Oleic acid is an unsaturated 

 acid, and can combine with two atoms of iodine. The 

 saturated acids and their glycerides do not absorb iodine. 

 The iodine value is the grams, of iodine absorbed by 100 

 grams, of the fatty material. Thus, triolein has a mole- 

 cular weight of 884, and can absorb 6 atoms of iodine per 

 molecule. So that 884 grams, absorb 6 x 127 = 762 grams, 

 of iodine, or 86-2 per cent. Since some fats contain 

 radicles with more than one double bond, it is clear that the 

 iodine value will not determine absolutely the character of a 

 fat. 



The emulsification of the fats. 



Fats can be emulsified, i.e. broken up into droplets, 

 either mechanically by agitation, or " spontaneously." 



" Spontaneous " emulsification takes place when a 

 melted oil or fat that contains a certain percentage of free 

 fatty acid is brought into contact with an alkali. The 

 fatty acid dissolves in the alkali to form a soluble soap, and 

 the diffusion currents thus set up break the globule of fat 

 into small particles, the process being maintained by the 

 continual exposure of fatty acid to the alkali. The 



