COMPOSITION OF FEEDING-STUFFS n 



solid fat, similar to tallow, is the result. If, on the 

 other hand, oleic acid is the chief acid present, then 

 the fat at ordinary temperatures has a more or less 

 fluid form, and is generally called an oil. In this 

 book the word fat will be used to denote all sub- 

 stances of this class, whether solid or liquid. Many 

 oils, e.g. linseed, hemp, sunflower seed, take up 

 oxygen when exposed to the air, and when spread 

 in a thin layer become solid. They are called on 

 this account drying oils. In most fats free fatty 

 acids are found in addition to the compounds 

 formed from fatty acids and glycerine. Fats 

 freshly extracted from the animal body, or from 

 new ripe seeds, contain only small amounts of these 

 free fatty acids. Where, however, oily seeds are 

 not fully ripe, or where, owing to bad weather at 

 the time of harvesting, they have sprouted, large 

 quantities of free fatty acids are to be found. 



When feeding-stuffs rich in fats are stored it is 

 also found that the percentage of free fatty acids 

 rises, particularly if there is much moisture present. 

 Such food-stuffs soon acquire a sour taste and smell, 

 and in time become quite rancid, owing to the 

 further decomposition of the free fatty acids. 



In order to determine the quantity of fat in a 

 feeding-stuff a finely ground sample is extracted 

 with some solvent that will dissolve the fat. Ether 

 is generally used for the extraction, and the residue 

 left after distilling off the ether is dried and weighed. 



