§§ 14, 15. CETYI^, CEROTYI^, MELYL- ALCOHOL. 13 



liquid It is optically inactive, and yields acrolein when heated with 

 acid sulphate of potassium. If the soap, after removal from the 

 liquid, is washed several times with solution of salt and the wash- 

 ings added to the liquid in the beaker, then the glycerine obtained 

 as described may be weighed. The estimation is not free from 

 error, but it permits of an approximately correct idea being formed 

 of the quantity of glycerine contained in the fat. (See § 128.) 



§ 14. Ceiylr, Ceroiylr, Melyl- Alcohol. — In solid fats, especially in 

 the so-called vegetable wax, cetyl, cerotyl, oi' raelyl may be present 

 as bases instead of glyceryl, in which case the fat is mucli more 

 difficult to- saponify than it, otherwise would have been and there 

 is formed, in addition to the soap, a kind of alcoholate of the fat- 

 alcohoL If to such a mixture of soap and alcoholate solution of 

 chloride of barium is added, a barium soap insoluble in alcohol 

 and ether is generally precipitated, whilst cetyl-, cerotyl-, or melyl- 

 alcohol is liberated arid may be extracted with ether. Or the 

 precipitation may be accomplished with acetate of lead (in the 

 absence of oleic acid), and the wax-alcohol extracted by ether from 

 the dried mass. (Cf. §§ 126, 129.) The melting-point (see 

 § 17) and the ultimate analysis will show which of these alcohols 

 has been isolated (§ 129). 



Vegetable wax frequently dissolves in boiling absolute alcohol, 

 but separates out again on the addition of a little water, as a rule 

 before the resins (§ 145). 



§ 16. Volatile Fat-Acids.-^ln prosecuting the examination of the 

 fat-acids the soap obtained in § 1 3 is warmed and again decomposed 

 with excess of hydrochloric acid, the mixture of fat-acids separated 

 from the aqueous liquid, and washed repeatedly with water. If 

 the odour of the mixture poiilts to the presence of a wlaiile acid, 

 this latter must be separated from the less volatile by distillation. 

 The distillate should be saturated with soda, evaporated, the 

 residue again decomposed with hydrochloric acid, and the fatty 

 acids separated from the aqueous liquid. The possible presence of 

 valerianic, caproic, caprylic, pelargonic, capric, and lauric (§ 130), 

 also angelic and methyl-crotonic acid must be borne in mind. 

 They may be identified by their boiling-points, saturating power 

 for bases, and composition. Of course the acid must be t-eated to 

 ascertain if it is a mixture or not of several volatile acids separable 

 by fractional distillation. (Cf. § 25.) 



