226 THE CHEMISTRY OF THE FARM 



coagulates on boiling. In ordinary cows* milk the 

 albumin forms about 12 per cent, of the total albu- 

 minoids, but the proportion is somewhat variable. 



The fat of milk differs considerably in composition 

 from the fat of the animal body ; it consists of the 

 glycerides of at least nine fatty acids. Eight of these 

 form a perfect chemical series, in which each differs from 

 the preceding by the addition of C^^ to the molecule. 

 The lowest member of the series is butyric acid, C^HgOg; 

 the highest member is stearic acid, CigHggOg. The 

 average percentage composition of milk fat is about 

 as follows. — 



Butyrin 3.85 



Oaproin 3-60 



Caprylin .. .. .. '65 



Caprin 1-90 



Laurin 7*40 



Myristin .. .. .. 20-20 



Palmitin 25-70 



Stearin 1-80 



Olein 85 00 



100 00 



Olein and the lower members of the series are liquid 

 fats ; the fats become more solid as they rise in the 

 series, stearin being the hardest. About 7*0 per cent, 

 of the fatty acids, chiefly consisting of the three lower 

 members of the series, are soluble in water. The 

 soluble acids have also a lower boiling point, and can 

 be separated by distillation. These facts serve to 

 distinguish butter fat from animal fats (as margarine) 

 which contain no soluble and volatile fatty acids. The 

 proportion of the various fats changes somewhat with 

 the diet and condition of the animal ; the influence of 



