VOLATILE FATTY ACIDS IN BUTTER. 359 



After cooling, the flask and fat are weighed. 20 c.c. of the 

 glycerol solution of soda are then run in and the flask heated 

 directly over the lamp. After the water (in the soda solution) 

 has boiled off, the contents of the flask will become quite clear 

 in a few minutes. The flask, now containing glycerol and 

 soap, is allowed to cool and 135 c.c. of water added. When 

 the soap is dissolved, 5 c.c. of the sulphuric acid and a piece of 

 pumice are added, the flask connected to a glass condenser 

 fitted with a bulb arrangement to prevent spirting, and 110 c.c. 

 are distilled over in half an hour. The distillate, which must 

 be filtered if not clear, is then titrated, with the alkali after 

 addition of a few drops of phenolphthalein. 5 grammes of 

 butter treated in this way require from 24 to 34 c.c. of deci- 

 normal alkali, while 5 grammes of most animal fats require 

 less than 1 c.c. 



Commercial "margarine," which consists of animal fats 

 churned with milk so as to acquire a flavour of butter, usually 

 requires from 1 to 2 c.c. of decinormal alkali. 



Another method of distinguishing butter fat from other fats 

 is by determining the amount of alkali necessary for saponi- 

 fication of a fixed quantity of the fat, or what is practically its 

 reciprocal, the " saponification equivalent," i.e., the weight 

 of fat equivalent to the gramme equivalent of the alkali. 

 The saponification equivalent of butter, in consequence of the 

 acids of low molecular weight which it contains, is much 

 smaller than that of most other fats, the actual values found 

 being about 247 for genuine butter and about 288 for most 

 other fats. For other methods the reader must refer to some . 

 manual of analysis. 



Butter Colouring. The natural colouring matter of milk is 

 apparently contained in the fat and is subject to considerable 

 variation. The amount is usually least in winter, and at that 

 season butter is often white in colour. It is a common prac- 

 tice to add some colouring substance to the cream in the 

 churn, so that the colour of the butter may be deeper. The 

 usual addition is annatto, a colouring matter obtained from the 

 seeds of Bixa orellana. 



The colouring substance is soluble in alkaline solutions and 



