1914] '^. W' Thomas 211 



The supernatant alkaline extract is decanted and (2)^ about 

 three-fourths of this dark colored extract is acidulated with nitric 

 acid, taking care to add not more than a slight excess of acid (see 

 page 216). The nitric acid must be fresh and free from lower 

 Oxides of nitrogen. This acidification precipitates the "humic 

 acids " in flakes that soon settle imder a clear yellow sol. 



(3) The precipitate is collected on a filter paper and washed 

 until free from acid, and, while still moist, is extracted with boihng 

 alcohol until a color is no longer imparted to the alcohol. The ex- 

 tracted precipitate of humns and silicic acid is now discarded and 

 (4) the alcohol Solution is evaporated, maintaining the original 

 volume by additions of water. After the alcohol is completely 

 removed, the aqueous sol. is filtered and the filtrate discarded. 



The residue (5) insoluble in water, which may contain resin 

 acids, resin esters, fatty glycerides, paraffinic acid, lignoceric acid, 

 a-mono-hydroxy stearic acid, hentriacontane, agrosterol, phytosterol 

 and other substances not yet identified, is dried, powdered, and 

 extracted with petroleuni ether until all soluble matter has been 

 removed. The residue insoluble in petroleum ether contains the 

 resin acids and resin esters. 



(6) After evaporation of the petroleum ether, the residue is 

 taken up in hot alcohol and the alcohol sol. allowed to cool; the 

 portion insoluble in cold alcohol containing hentriacontane, agro- 

 sterol, phytosterol, ct-mono-hydroxy stearic acid and lignoceric acid 

 (7) is saponified with alcoholic potassium hydroxide sol., evapo- 

 rated to dryness and extracted with petroleum ether, which takes 

 up hentriacontane,^ agrosteroP and phytosterol.''' The petroleum 

 ether sol. is filtered and evaporated. The three above-mentioned 

 substances in the residue may be separated and identified by virtue 

 of the difference in their chemical and physical properties (9). 



Hentriacontane: C31H64; m.p., 68° C. ; sp.g. at melting point, 



4 The numerals in parenthesis refer to the sections in the summary at 

 page 218. 



^ Schreiner and Shorey : Paraffin hydrocarbons in soils, Journ. Anier. Chem. 

 Soc, 191 1, xxxiii, p. 81. 



ß Schreiner and Shorey : The presence of a cholesterol substance in soils, 

 ibid., 1909, xxxi, p. Ii6. 



^Schreiner and Shorey: Cholesterol bodies in soils, Journ. Biol. Chem., 

 191 1, ix, p. 9. 



