14 FATS, OILS, AND WAXES 



alcoholic filtrates on careful evaporation yield a residue which 

 may be separately treated with ether to extract any fat con- 

 tained in them. It is obvious that the method cannot be 

 employed if the fat to be extracted is soluble in alcohol. 



The third method of drying, which involves the use of 

 anhydrous salts such as sodium sulphate, depends on the fact 

 that the anhydrous salt when ground up with the moist tissue 

 withdraws the water from it, forming the hydrated crystals. 

 In a few hours the substance is sufficiently dry to be powdered. 

 The chief objection to this process is the fact that a considerable 

 bulk of salt has to be employed and consequently the volume 

 of the material to be extracted is much increased. 



Whilst ether is one of the most commonly used solvents 

 for the extraction of fats, Leathes recommends a preliminary 

 extraction with alcohol, since this helps to dry the material 

 and frequently renders easier the subsequent extraction by 

 ether (see under Lipins, p. 51). 



In some cases a preliminary mild hydrolysis by boiling 

 with dilute hydrochloric acid is necessary to set free the fat 

 in a condition in which it can be readily extracted by the 

 appropriate solvent. 



CHARACTERIZATION OF FATS. 



The unequivocal establishment of the true fatty nature of 

 a given substance is not always easy, especially if only a small 

 amount of material is available. 



1. In the first instance, the solubilities of the substance 

 should be determined by placing it on a watch-glass and adding 

 a drop or two of the appropriate solvent. All fats dissolve 

 readily in the so-called fat solvents, namely, ether, petrol, 

 chloroform, benzene, acetone, and carbon disulphide ; they 

 are sparingly soluble in cold alcohol, but more soluble in hot 

 alcohol ; all are insoluble in water. These solvents will, how- 

 ever, also dissolve waxes, lipins, hydrocarbons, essential oils, 

 terpenes, resins, and chlorophyll, wherefore some further 

 method of characterization is essential. 



2. Fats leave a translucent mark on paper, and many of 

 the aforementioned substances will do the same ; but in the 



