80 MILK 



Of these compounds, butyrin, caproin, caprylin, caprin, and 

 laurin are glycerids of volatile acids, while myristicin, palmitin, 

 stearin, and olein are glycerids of non- volatile acids. Butyrin is 

 present in larger amount than the glycerids and other volatile 

 acids. It decomposes readily and forms butyric acid, which ren- 

 ders the fat rancid. 



^ The volatile acids are largely responsible for the odor and flavor 

 of milk and butter. They are present in milk-fat throughout the 

 year in nearly the same quantity. The amount is somewhat 

 greater in spring and summer, when cows feed on fresh fodder, 

 than during the balance of the year, when the animals receive 

 chiefly dry food. Volatile acids diminish during the progress of 

 the lactation period. 



The glycerids of non-volatile acids are chiefly oleic, palmitic, 

 stearic, and myristic acids. The consistency of butter-fat de- 

 pends largely upon the relative quantities of non-volatile acids. 

 The melting-point of palmitin is 61 C.; of olein, 5 C.; of myris- 

 ticin, 54 C.; and of stearin, 65.5 C. The largest amount of these 

 is represented by olein, and consequently the variability of this 

 compound has the greatest influence upon the consistency of milk- 

 fat. During the spring and early summer more olein is taken up 

 from the green fodder than from the food consumed during the 

 winter months, and consequently the fat is harder in winter than 

 in spring and summer. 



The chemical composition of large and small fat globules has 

 been investigated by Klusemann, Gutzeit, and Lemus. The 

 results of these authors are not in harmony, perhaps because it is 

 difficult to separate globules of different sizes. Shaw and Eckles 

 separated cream with a predominance of large globules from 

 cream with a predominance of small ones by means of a hand sepa- 

 rator, and further eliminated small globules from the first cream 

 by allowing the fat to rise in a narrow, tall vessel. Chemical 

 examination of the globules obtained showed differences so slight 

 that they easily ranged within experimental error. Therefore it 

 seems justifiable to assume that the composition of fat in globules 

 is uniform, no matter what their size. 



^ The melting-point of butter-fat is given by various authorities 

 within the limits of 29.5 and 36 C. Butter-fat is liquid while 

 the milk is in the cow's udder, therefore, since the body tempera- 

 ture of the cow is 38.5 to 39 C. While emulsified in milk, butter- 

 fat begins to solidify at about 25 C.; sometimes it is liquid at 

 even lower temperature, depending upon its composition. 



Milk-fat is insoluble in water, but it dissolves 0.2 per cent, 

 water by heating to 100 C. Milk-fat is soluble in ether, carbon 

 disulphid, nitrobenzene, and acetone. It is slightly soluble in 



