4 FATS, OILS, AND WAXES 



contained fat as a food reserve during the winter months. Even 

 the leaves of deciduous plants at the time of leaf-fall were 

 devoid of starch but contained fat. Whilst the power of form- 

 ing fat from starch is not uncommon in plants naturally ex- 

 posed to extreme winter cold, the ability to form starch on the 

 advent of warmer weather does not necessarily follow. Thus 

 many alpine Ericaceae and Salicaceae possess both starch and 

 fat during the vegetative season, and Gaultheria ovalifolia, a 

 lowland plant, has only fat. Wherefore the ability to form 

 starch is not entirely to be associated with the climatic con- 

 ditions resulting from high altitudes. These phenomena are 

 similar to those which will be mentioned in connection with 

 the conversion of starch into sugar under the influence of low 

 temperature (p. 176). 



The majority of vegetable fats are fluid at ordinary tem- 

 peratures ; a few, however, are solid, for instance, cacao butter 

 and the fat in the seeds of Myristica. 



CONSTITUTION OF FATS. 



The naturally occurring fats are mixtures of esters of 

 glycerol with fatty acids such as palmitic C15H31COOH or 

 stearic C17H35COOH acids, or with the unsaturated acid oleic 

 acid C17H33COOH. 



A wax, on the other hand, is an ester of a monohydric 

 alcohol as illustrated by the equation : — 



C15H31COOH + CaoHeiOH = C16H31COOC30K,, + H^O 

 Palmitic acid Myricyl Myricyl palmitate 

 alcohol 



myricyl palmitate being the chief constituent of beeswax. 



Lapworth and Pearson * have shown that the glycerol in 

 fats may be directly replaced by a higher polyhydric alcohol 

 such as mannitol. This replacement may be brought about 

 by distilling olein or stearin with mannitol under reduced 

 pressure in the presence of sodium ethoxide. By this treat- 

 ment much of the glycerol of the fat is expelled, the maximum 

 yield being reached when the proportion of fat to the mannitol 

 corresponds with two molecules of the former to three mole- 



* Lapworth and Pearson : " Biochem. Journ.." 1919. I3. 296. See 

 also Irvine and Gilchrist : " J. Chem. Soc," 1924, 125, 10. 



