THE DAIRY 



183 



Dihydroxystearic acid, H.CigH33(OH)20a 



Oleic acid, H.CjsHgsOa . 



Stearic acid, H-CigH^jOo 



Palmitic acid, H.C16H33O2 



Myristic acid, H.C,4H2702 



Laurie acid, H.C12H23O2 



Capric acid, H.CmHigOa 



Caprylic acid, H.CgHiaOa 



Caproio acid, H-CgHiiOa 



Butyric acid, H.O4H7O2 



Grammes. 



0-38 



44-42 



3-40 



14-83 



16-43 



5-01 



1-19 



M6 



1-64 



4-27 



92-73 



The proportions, however, are variable, but the important 

 fact to notice is the occurrence in milk fat of the last three or 

 four acids in the above list, mere traces of which are present 

 in other fats. These acids differ from those of higher mole- 

 cular weight in being volatile in steam. The proportion of 

 volatile acids from butter fat varies from 7 "5 to 9*7 per cent* 

 of the fat, while in suet, for example, there is usually about 

 0*4 per cent, of volatile acids. 



Butter fat alsoi contains traces of a substance, cholestei'ol, 

 C^qH^jOH, present largely in wool fat, and of lecithin, 

 03H,(C,8H3,0,)2[HPO,.N(CH3)3C2H,OH], present in certain 

 seeds, especially peas and beans, and of. a colouring substance 

 of unknown composition known as " lacto-chrome." Milk fat 

 melts at about 30° to 33° C, and has a specific gravity of "930 



37*8° 39*5° 



at 15° C, at g^Tyo (molten) = -9118, at g^;^ = '9113. Con- 

 traction occurs at the moment of solidification ; hence solid 

 milk fat is heavier, volume for volume, than the liquid fat at 

 the same temperature. Milk fat, however, varies considerably 

 both in composition and physical properties, being affected by 

 the food, period of lactation, and other circumstances under 

 which the cows are kept. It exists in milk in the form of 

 minute globules varying in diameter from 0016 to "010 mm. 

 In the milk of Jersey and Guernsey cows the average size of the 

 globules is considerably larger than in the milk of Ayrshire, also 

 in lecently calved cows than in those far advanced in lactation. 



