168 COMPOSITION OF THE BODY 



(c) They burn with a luminous and smoky flame. 



(a) They are not volatile. 



(e) They are readily soluble in chloroform, ether and benzene. 

 They are also soluble in boiling alcohol, from which they separate 

 on cooling, often in crystalline form. 



(/") They are insoluble in water. 



Or) With soap they form a fine emulsion. 



(h) On being decomposed by heat they give rise to irritating 

 acrolein vapors. 



(z) When boiled with caustic alkali, alkali salts of the fatty 

 acids are formed and glycerine is set free. This process is called 

 saponification. 



Fats form a large part of the reserve food substances of plants. 

 They occur in largest quantities as storage material in seeds, many 

 of which, as the seeds of Ricinus or Cocos, are especially rich in 

 these substances. 



The translocation and assimilation of fats is preceded by their 

 division into fatty acids and glycerine. Free fatty acids may or 

 may not be present with fats in a resting condition, but where 

 translocation is going on there is to be found the maximum quan- 

 tity of free fatty acid. Even at this time very little free glycer- 

 ine can be detected ; it is probably immediately assimilated. 

 Fatty acids, or neutral fats in the presence of fatty acids, readily 

 form an emulsion with sodium phosphate and other reagents and 

 this no doubt facilitates the transformation of the fat. 



236. Extraction of Fats. The separation of the fats from the tis- 

 sues in which they occur is accomplished by grinding up the tissue 

 as finely as possible, and covering it with about twice its volume of 

 a solvent, preferably ethyl or petroleum ether. Petroleum ether 

 is probably best, as it extracts less of other substances. The ex- 

 traction should be continued until all the fat is removed if the 

 work is of a quantitative nature. 



The fat is then separated from the solution by evaporation of the 

 solvent. This should be done over the steam-bath and away from 

 the flame. The odor of petroleum in the fat thus obtained is un- 



