202 BUTTER 



In the case of most animal fats, however, it is seldom above i, 

 and adulteration of butter with margarine or other fats may thus 

 be readily detected in this manner. 



Saponification of Butter-fat. 



When butter-fat is boiled with caustic alkalies, saponification 

 takes place, with production of glycerol and the sodium salts of the 

 fatty acids (sodium soaps). A certain proportion of the caustic 

 alkali is thus neutralised, the amount undergoing neutralisation by 

 a given weight of butter depending upon the molecular weights of 

 the fatty acids. A certain weight of butter, which, as above 

 stated, contains a comparatively large proportion of acids of low 

 molecular weight, will lead to a neutralisation of a larger amount 

 of caustic potash than would be the case if an equal weight of 

 some other natural fat containing acids of higher molecular weight 

 were employed. 



Thus, in the case of butyric acid of molecular weight i88, 



C3H7.COO.CH2 



i 



C3H7.COO.CH + 3KOH = 3C3Hy.COOK-l-C3H6(OH)3 



C3H7.COO.CH2. 



in which 100 grams of the fat (glyceryl ester) will neutralise or 

 require for complete saponification 53-4 grams of caustic potash, 

 while with stearic acid of molecular weight 284, 



C17H35.COO.CH2 



I 

 Ci^H35.COO.CH + 3KOH = 3Ci7H36.COOK-F-C3H5(OH)3 



C17H35.COO.CH2. 



in which 100 grams of the fat will require i8-8 grams of caustic 

 potash. Use is made of this principle in a method proposed by 

 Koettstorfer for the quantitative examination of butter, it being 

 obvious from the above equations that adulteration of butter by 

 means of other natural fats (of higher average molecular weight) 

 leads to a smaller amount of caustic potash being required for 

 saponification per cent, of fat. The results are usually expressed 

 as the Koettstorfer number, this being the number of milligrams 

 of caustic potash required per i gram of butter-fat. In the case 

 of glyceryl-tributyrate the Koettstorfer number would be 534, while 

 with glyceryl-tristearate the value would be 188. For pure butter- 



