40 THE CHEMISTRY OF CATTLE FEEDING 



the solid condition. They make a permanent translucent 

 stain on paper and are, therefore, easily distinguished from 

 volatile oils. The latter make a similar stain on paper, but 

 it disappears on gentle warming. 



The fats and oils are all insoluble in water ; and, with few 

 exceptions, they are also insoluble in alcohol. They are, 

 however, readily soluble in ether, chloroform, carbon bisulphide 

 and the lighter hydrocarbons, and they are freely miscible 

 with each other. 



Chemical Composition. The common fats and oils are 

 composed of the elements carbon, hydrogen and oxygen only, 

 and these elements are present in nearly but not exactly the 

 same proportions in all. 



They undergo saponification, i.e. when boiled with alkalis 

 they are converted into soaps and glycerine. By the action of 

 superheated steam, they yield fatty acids and glycerine. 

 Under certain conditions a similar decomposition is produced 

 by the action of ferments. It is evident, therefore, that the 

 natural fats are glycerides (glycerine esters) of the fatty acids. 

 This is further proved by the fact that when glycerine and fatty 

 acids in due proportion are heated together in sealed tubes to 

 temperatures between 200 and 300 C, they combine, forming 

 fats and water. If the acid radicles be designated for the 

 present by the symbol A, these changes can be represented by 

 simple equations as follows : 



C 3 H 5 A 3 + 3 KOH -> sKA 4- C 3 H 5 (OH) 3 



(Fat.) (Soap.) (Glycerine.) 



C 3 H 5 A 3 + 3 H 2 -> 3 HA + C 3 H 5 (OH) 3 



(Fatty acids.) 



As stated above, the last reaction is, under suitable conditions, 

 reversible. 



The alkali soaps are soluble in water ; the calcium, lead, 

 and other soaps are insoluble. They all react with sulphuric 

 acid, forming the corresponding sulphates and free fatty acids 

 according to the equation 



KA + H 2 SO 4 -> KHSO 4 + HA 



