MILK. 289 



CHEMISTRY OF THE MILK COMPONENTS. 



Fats. In the older literature milk fat was given a com- 

 paratively simple composition. It was assumed to consist of 

 stearin, palmitin, olein and butyrin essentially, the last named 

 volatile fat imparting the flavor to the separated butter. At 

 the present time we must admit that our knowledge is far from 

 exact on the subject, but we know that the composition of milk 

 fat is by no means as simple as once assumed. In the chapter 

 on the fats an analysis is given which conforms better to our 

 modern notions. We find then besides butyrin several gly- 

 cerol esters of the same series of comparatively volatile acids. 

 Among the heavier fatty acids myristic acid seems to have 

 some importance, as disclosed by a number of analyses. A 

 small amount of lecithin appears to be also present. 



Although produced from a variety of materials in feeding 

 experiments, milk fat, as butter, maintains a rather constant 

 composition as disclosed by both chemical and physical tests. 

 The melting point of the fat is usually between 31 and 32.5 

 C. and its specific gravity at 38 is about 0.912. Butter fat 

 is easily saponified and from the saponified mass the fatty 

 acids which are non-volatile and practically insoluble in hot 

 water may be separated. These insoluble acids amount in the 

 mean to about 87.5 per cent of the weight of the original but- 

 ter fat. That is 10 grams of average butter fat should yield 

 8.75 gm. of insoluble acids, the difference representing the 

 lighter soluble fatty acids and glycerol. In the fat from very 

 rich milk the insoluble acids may be somewhat lower than this, 

 while in poor milk they would be higher. These facts are 

 important in distinguishing between butter and its substitutes. 



Fat Globules. In milk the fat exists in the form of minute 

 globules of different sizes. The diameters of these globules 

 vary between about 0.0016 mm. and o.oi mm. A cubic centi- 

 meter of normal milk containing 3.5 per cent of fat contains 

 100 millions or more of these globules. In the milk they are 

 described as existing in the form of an emulsion, but of the 



