12 SUBSTANCES SOLUBLE LN PETROLEUM SPLRLT. 



olive oil. Any colouration produced by the first drops of sul- 

 phuric acid should be noted, and the experiment repeated with a 

 small quantity of the oil, adding a little syrupy phosphoric acid. 

 The behaviour of the oil to syrupy chloride of antimony, nitric 

 acid (from \ to 1 volume) of specific gravity 1 "3, alone or com- 

 bined Avith a little powdered sugar, may be tested. The action 

 of concentrated solution of bisulphide of calcium, borax, and 

 chloride of lime may also yield reactions characteristic of certain 

 oils. (See § 124.) It may finally be ascertained whether the oil 

 combines quickly with oxide of lead, and whether the plaster so 

 produced is soft or hard, soluble or insoluble in ether. 



If the fatty oil is solid at ordinary temperatures, a portion 

 may be melted, and the above tests with acids, etc., applied, The 

 solubility in ether should be tried, and note taken whether a 

 solution in two parts of warm ether deposit solid matter on 

 cooling. 



If the fixed oil from a vegetable substance j^artially solidifies 

 after standing several days, the liquid part may be separated from 

 the solid by filtration and expression, and each treated separately. 



§ 13. Composition ; Estimation of Glycerine. — It is well known 

 that natural fats are almost invariably mixtures of different 

 glycerides or ethereal salts. If the various constituents of which 

 a fixed oil is composed are to be ascertained, larger quantities 

 (250 to 500 or 1000 grams) must be saponified with a solution of 

 caustic soda of sjoecific gravity 1-25 to 1*3; and after complete 

 saponification, as shown by the soap dissolving in water warmed 

 on the steam bath without the separation of undecomposed oil, 

 the soap so formed may be thrown out by the addition of a con- 

 centrated solution of salt. The separation may be performed with 

 advantage in tall beakers, which should be placed on the water- 

 bath until the soap has assumed such a condition that on cooling 

 it can be removed as a solid cake. (See also § 15.) 



A measured jiortion of the aqueous liquid, after the removal of 

 the soap, may be concentrated on the water-bath, or preferably 

 at a temperature of 70° to 80°, and the residue treated with 

 absolute alcohol, or better with a mixture of about three volumes 

 of absolute alcohol to one to two of ether, which dissolves the 

 glycerine liberated hy tlic dccomi)osition of the oil. On evaporat- 

 ing this solution the glycerine remains behind as a sweet syrupy 



