42 THE CHEMISTRY OF CATTLE FEEDING 



much lower. Oleic acid predominates in the so-called oils, 

 e.g. olive oil, and in the solid fats of lower melting point. 

 Stearic and palmitic acids enter more largely into the com- 

 position of the harder fats, e.g. tallow, suet, etc. 



It is important to notice that the melting points of the 

 natural fats are not absolutely constant, but they vary only 

 within comparatively narrow limits. For instance, butter fat 

 usually melts at about 33 C., but some butters are a little 

 harder or softer than others, and the difference is attributed 

 to slight variations in the relative proportions of oleic to 

 stearic and palmitic acids. 



Stearic and palmitic acids are saturated compounds of the 

 same homologous series as acetic acid. The constitutional 

 formulae of these substances are given as follows : 



CH 3 .(CH 2 ) 16 .COOH CH 3 .(CH 2 ) 14 .COOH 



(Stearic acid.) (Palmitic acid.) 



Oleic acid is an unsaturated compound. It contains two 

 atoms of hydrogen less than stearic acid. There are, there- 

 fore, blanks on two of the carbon atoms which are united by 

 an olefine union commonly represented by a double bond as 

 follows : 



CH 3 .(CH 2 ) 7 .CH:=CH.(CH 2 ) 7 .CO.OH 



(Oleic acid.) 



Like all such compounds it can form addition products 

 with halogens, e.g. Ci 8 H 34 O 2 Br 2 dibromo-stearic acid. Mild 

 oxidising agents convert it into dihydroxy-stearic acid. By 

 the action of nitric acid and other powerful oxidising agents 

 the molecule is split up into compounds of lower molecular 

 weight. Nitrous acid converts oleic acid into an isomeric 

 form called elaidic acid, which is solid at ordinary temperatures, 

 and melts at about 45 C. 



The following are the more important acids which enter 

 into the composition of various natural fats : 



