FOODS 



93 



pink appears. Then add 12 c.c. of glycerol, when boric 

 acid is li berated and pink disappears. Titrate again ; 

 note number of c.c. used, and the difference x 0-0368- 

 gives amount of boric acid in 20 c.c. This X (100 -f- per- 

 centage of water in butter) -f- 20 = percentage. 



Saponification Equivalent of Koettstorfer for butter 

 fat varies from 242 to 253, and for margarine fat the mean 

 figure is about 284. The saponification of oils by alkalies 

 is a definite reaction, and may be represented by the 

 following general equation where F stands for the radicle 

 of the fatty acid : C 3 H 5 (OF) 3 + 3KOH = C 3 H 5 (OH) 3 

 + 3KOF. Therefore, if we know exactly the amount of 

 alkali necessary to saponify the oil under examination, 

 we can to some extent determine the nature of the glycerides 

 present. The amount of alkali required varies with the 

 composition of the fatty acids ; the lower the molecular 

 weight, the higher \\ill be the amount of soda or potash 

 needed to saponify. This amount may be stated in three 

 ways : (i) As a percentage, that is, the number of grammes 

 of alkali absorbed per 100 grm. of fat ; (2) The number 

 of milligrammes of alkali absorbed per i grm. of fat. This 

 is called the saponification value, and the figure for it is 

 ten times the percentage, since it is parts per thousand ; 

 and (3) As the number of grammes of fat which would be 

 saponified by i litre of normal alkali ; that is, in the case 

 of potash, by 56 grm. of alkali. This is called the 

 saponification equivalent, and may be got by dividing the 

 percentage of alkali absorbed into 5600, or if the exact 

 atomic weights are used, with oxygen = 16 as the basis, 

 into 5610. The following table from Moor & Partridge 

 summarizes these facts, in regard to the chief fats : 



