358 THE ANALYSIS OF MILK AND MILK PRODUCTS. XV. 



of butter. Probably the best way is to melt a considerable 

 quantity of the butter at as low a temperature as possible in a 

 stoppered bottle and shake it continually until it stiffens. 



If the butter is to be tested for possible adulteration with 

 other animal fats, " oleomargarine," &c., the procedure is more 

 complicated. As already explained, butter fat differs from 

 other natural glycerides in containing considerable quantities 

 of fatty acid radicals of low molecular weight, e.g., butyric 

 acid. Butyric acid and its neighbouring homologues are 

 soluble in water and volatile in steam, while the higher fatty 

 acids are both insoluble and non- volatile. Upon these facts 

 most of the methods of analysis are based. 



The method adopted (though numerous modifications in 

 detail have been introduced) is essentially the decomposition 

 of a known weight (generally 5 grammes) of butter with excess 

 of caustic soda, whereby glycerol and soaps are produced. 

 The latter are then decomposed with a slight excess of dilute 

 sulphuric acid, thus liberating the fatty acids. The liquid is 

 then distilled until a certain proportion of it has passed over, 

 and the acidity of the distillate is then determined by means of 

 decinormal soda or baryta solution and phenolphthalein. 



Aqueous soda saponifies butter very slowly and is now 

 rarely or never used. An alcoholic solution works much more 

 rapidly and the alcohol is readily expelled by heat before the 

 soap is decomposed by sulphuric acid. A solution of caustic 

 soda in glycerol saponifies the butter very quickly, especially 

 as it can be raised to a high temperature, and the presence of 

 the glycerol does not interfere with subsequent operations. 

 This modification of the original Eeichert process, as it is 

 called, was introduced by Leffmann and Beam. The following 

 reagents are used : 



Soda solution. 20 grammes of pure caustic soda are dis- 

 solved in 20 c.c. of water; 20 c.c. of the clear solution are 

 then mixed with 180 c.c. of pure glycerol. 



Sulphuric acid. 1 volume of pure acid to 4 volumes of water. 



Barium hydrate. A decinormal solution. 



The sample is melted and filtered from casein, c. 

 5 grammes (about 5 '75 c.c.) of the melted fat are then run 

 into a 300 c.c. flask, previously thoroughly dried and weighed. 



