CHARACTERISTICS OF THE NATURAL FATS 109 



THE CHARACTERISTICS OF THE NATURAL FATS. 



The various animal fats and vegetable oils differ from one another 

 very strikingly in their physical characteristics and chemical behavior. 

 These differences are in the main determined by the relative propor- 

 tions in which the glycerides of the three fatty acids above mentioned 

 occur in the fat. The glycerides of oleic acid have the lowest melting- 

 point, those of stearic acid the highest, and hence olive' oil, which con- 

 sists very largely of glycerol trioleate is fluid at ordinary tempera- 

 tures, while mutton-fat, which contains a high proportion of glycerol 

 tristearate, is solid or semi-solid at ordinary temperatures. The 

 melting-points of the pure fats are as follow: 



Triolein. . . . . . -. ; . t. . .- . y .... -6.0C. 



Tripalmitin 65.0,C. 



Tristearin ............'.'....'. 71. 5 C. 



a small admixture of triolein, however, reduces the melting-point of a 

 fat to a very considerable degree. 



The chemical reactivity of the fats is also strongly influenced by 

 their content of oleates. The unsaturated bond in oleic acid renders 

 it capable, under appropriate conditions, of directly absorbing hydrogen, 

 being thereby converted into the corresponding saturated acid. The 

 artificial hydrogenation of vegetable oil is now being very largely 

 practised and results in the production of a solid fat, utilizable for a 

 variety of household purposes for which the fluid oil would be unsuited. 

 The significance of the process, however, goes far beyond this. The 

 addition of two atoms of hydrogen to the oleic acid molecule adds 

 considerably to its calorific value, since the heat of combustion of the 

 hydrogen to water is thus rendered available for nutritive purposes. 

 In the aggregate the hydrogenation of vegetable oils adds to the 

 nutritive value of these fats an amount 1 which would otherwise 

 require a very great deal of space and labor to produce. From 

 an economic point of view therefore, and as a means of food con- 

 servation, the hydrogenation of vegetable oils is a very desirable 

 thing to encourage. It is true that the vegetable oils fail in important 

 respects to furnish the nutritive equivalent of animal fats, for, as we 

 shall see in later chapters, the animal fats contain accessory foodstuffs 

 which are essential for growth, and even for the maintenance of health, 

 while the vegetable oils are lacking in these. To the extent, however, 

 to which fats are employed in the diet for their mere fuel-value, the 

 vegetable oils are fully equivalent substitutes for the animal fats, and 

 only a small proportion of the total fat-consumption, at any rate in 

 adults, is requisite to furnish the accessory foodstuffs which we acquire 

 from the animal fats. It is probable that there would be no danger of 

 shortage of the accessory foods being caused by the utilization of vege- 



1 Roughly 7 per cent. 



