12 Testing Uilk and Its Products. 



milk, while the lowland breeds, the Ayrshire, and other 

 breeds have uniformly smaller globules. The diameter 

 of average sized fat globules in fresh milkers is about 

 .004 millimeter, or one six-thousandth of an inch; that 

 is, it takes about six thousand such globules placed side 

 by side to cover one inch in length. The globules of 

 any sample of milk vary greatly in size; the largest 

 globules are recovered in the cream when the milk is 

 set or run through a cream separator, and the smallest 

 ones remain in the skim milk; thoroughly skimmed sep- 

 arator skim milk contains only a small number of very 

 minute fat globules. 



Milk fat is composed of so-called glycerides of the 

 fatty acids, i. e., compounds of the latter with glycerin; 

 some of the fatty acids are insoluble in water, viz., 

 palmitic, stearic, and oleic acids, while others are solu- 

 ble and volatile, the chief ones among the latter being 

 butyric, eaprylic, and eapronic acids. The glycerides 

 of the insoluble fatty acids make up about 92 per cent, 

 of the pure milk fat; about 8 per cent, of the glycer- 

 ides of volatile fatty acids are therefore found in nat- 

 ural milk- (and butter-) fat. The distinction between 

 natural and artificial butter lies mainly in this point, 

 since artificial butter (butterine, oleomargarine) as well 

 as other solid animal fats contain only a very small 

 quantity of volatile fatty acids. The glycerides of the 

 volatile fatty acids are unstable compounds, and are 

 easily decomposed through the action of bacteria or 

 light; the volatile fatty acids thus set free, principally 

 butyric acid, are the cause of the unpleasant odor met 

 with in rancid butter. 



