LIPIDES (fats and RELATED SUBSTANCES) 



91 



Determination of fat 



The percentage of fat in a foodstuff is determined by extracting the 

 fat with etlier and weighing it. In tables of analyses this is generally 

 spoken of as fat, or more correctly, ether extract. ' It is not necessarily 

 all fat, since ether will dissolve many other substances such as waxes, 

 resins, fatty acids, and coloring matter, all of which may be contained 

 in natural fats. The ether extract of cereals is mainly fat, whereas a 

 large proportion of that obtained from vegetables consists of fatty acids, 

 phospholipides, nonsaponifiable matter, etc. The following table shows 

 how variable is the comi)osition of ether extract: 



Table 4-7 

 Composition of ether extract 



A special test for the determination of fat in certain dairy products, 

 particularly milk, was introduced in 1890 by Stephan Moulton Babcock. 

 The "Babcock test," as it is universally called, has been of decisive im- 

 portance to the growth of dairying in this country, since it made possible 

 a quick, practical means of judging the butter fat production of individual 

 cows, permitting selection of the best producers for breeding. The test 

 is made by treating a definite amount of milk with an equal volume of 

 90 per cent sulfuric acid and warming the mixture gently. On cen- 

 trifuging this mixture, the fat separates as a distinct layer, which is 

 measured in the neck of a special flask cahbrated to read directly the 

 percentage of butter fat. 



WAXES 



Definition 



"Waxes are classified as simple lipides, together with the true fats, 

 but unlike fats they contain higher monohydroxy (sometimes dihydroxy) 

 alcohols in place of glycerol. These alcohols exist in the- wax in com- 



