204 THE CONSTITUENTS OF PLANTS. IX. 



with glycerine are kept moist both because of its non-volatility 

 and also because it absorbs water from the air. 



Glycerol is made from oils or fats by a process which shows 

 clearly the constitution of these substances. 



The oil or fat is boiled with caustic soda solution, when 

 decomposition occurs, the sodium of the alkali taking the 

 place of the glyceryl group, the latter uniting with the OH 

 of the sodium hydrate. A sodium salt of the fatty acid 

 and glycerol are thus produced, and being soluble, remain 

 mixed in solution. In order to separate them the sodium 

 salts are precipitated by the addition of common salt, in a 

 solution of which they are insoluble. The sodium salts rise to 

 the surface and on cooling form a solid cake, constituting soap. 



From the solution below, the glycerine can be recovered by 

 evaporation and distillation in vacuo. Taking olive oil, which 

 consists mainly of glyceryl oleate, C 8 H 5 (C 1H H 32 O 2 ) 3 , as example, 

 the reaction may be thus expressed : 



C 3 H 5 (C 1H H 3 A) 3 +3NaOH = 3NaC 18 H ii O f +C i H 6 (OH), 



Glyceryl oleate. Sodium hydrate. Sodium oleate. Glycerol. 



Glycerine is also prepared by the hydrolysis of fats by means 

 of superheated steam. Again taking olive oil as example, the 

 reaction would be 



C 3 H 5 (C lrt H,A) 3 + 3H 2 = 3HC 1H H,A + C 8 H 5 (OH) 8 



Glyceryl oleate. Water. Oleic acid. Glycerol. 



Although in the above example olive oil has been assumed 

 to be glyceryl oleate, it must be clearly understood that this is 

 not true and that all the oils are mixtures of the glyceryl salts 

 of several fatty acids Thus in linseed oil, glyceryl compounds 

 of linolenic and isolinolenic, linoleic, oleic, stearic, and palmitic 

 acids have been found. It is not definitely known whether in 

 the oils these substances are mixed or whether they are chemi- 

 cally combined, e.g., whether, say, the first three compounds 

 are present as such, i.e., as 



81 0,) 8 , and C 8 H 6 (C 1H H JW O a ) 8> 



/'C 1H H 2 A 

 or whether they may be present as C 3 H 5 ' C 1S H 81 (X 



[C 18 H., 8 2 



In plants, the oils are chiefly found in the seed or fruit, 

 though small quantities are contained in the straw and roots. 



