FATS AND FIXED OILS 41 



The fatty acids so obtained are exactly similar to those pro- 

 duced from the same fats by direct saponification with steam. 

 They are for the most part non-volatile, and insoluble in water. 

 Their solubility in other reagents resembles that of the 

 original fats. 



The fatty acids obtained from the natural fats are not 

 single pure substances but mixtures of several. Stearic acid, 

 C 18 H 36 O 2 , palmitic acid, C 16 H 32 O 2 , and oleic acid, C 18 H 34 O 2 , 

 are of very common occurrence. One of them may pre- 

 dominate, but usually all three are present. Jointly, they form 

 over 90 per cent, of the fatty acid of all the common natural 

 fats, and the properties of the latter are determined to a 

 large extent by the relative proportions in which the three acids 

 referred to enter into their composition. The presence of 

 other fatty acids, even in small proportion, often imparts 

 peculiar properties to particular fats. 



The natural fats are often regarded as mixtures of the 

 glycerides of the several acids, e.g. tristearin, (C 18 H 3 5O 2 )3C 3 H5, 

 triolein, (C 18 H 33 O 2 ) 3 C 3 H 5 , tripalmitin, (C 16 H 31 O 2 ) 3 C 3 H 5 . It 

 is possible that such mixtures may exist to some extent, but 

 it is more probable that, so far as the main bulk of the fat 

 is concerned, the glycerine radicle is combined with two or 

 three different acids, thus 



Qi 8 H 33 O 2 ?C 3 H 5 

 CieHsiOg/ 



(Glycerine, stearate, oleate, palmitate.) 



The Fatty Acids. Oleic acid melts at T4C, stearic acid 

 at 69-2 C., and palmitic acid at 62 C. The melting points of 

 the glycerides, triolein, tristearin, and tripalmitin, are estimated 

 to be a little lower, viz. 2-4 C., 68' 2 C., and 69 C. respectively. 

 Olein does not solidify at temperatures above 5C. It is 

 evident, therefore, that the melting points of the natural fats 

 will vary according to the relative proportions in which these 

 three acids enter into their composition. The difference 

 between the melting points of stearic and palmitic acids is 

 comparatively small, but the melting point of oleic acid is 



