EXAMINATION OF ADIPOSE TISSUE. 147 



in a dry flask, pour on two to three times the volume of ether, 

 and let stand, shaking repeatedly, till next day. Precipitate 

 the lead completely from the filtered ethereal solution by 

 means of hydrochloric acid, place the ethereal solution in a 

 separating-funnel, and shake repeatedly with water. The 

 -solution, when separated and filtered through a dry filter, 

 yields oleic acid on distillation or evaporation of the ether. 

 The purification of the oleic acid depends upon the solubility 

 of the lead oleate in ether and the insolubility of the lead 

 palmitate and stearate. Some of the lead palmitate and 

 stearate always dissolves, however, and some of the oleate 

 remains undissolved in the residue. 



Separation of Palmitic from Stearic Acid. 

 Dissolve the solid fatty acids in 95 per cent, alcohol (to 

 <each gram 20 cc. of alcohol), then take a tenth of the solution 

 and determine how much of an alcoholic solution of neutral 

 lead acetate is necessary for complete precipitation. Measure 

 off nine times as much of the same lead acetate solution and 

 divide it into five equal parts. Add the first fifth to the 

 alcoholic solution of the fatty acids, filter, then precipitate 

 with the second fifth, etc. (fractional precipitation). Each 

 precipitate is washed with cold alcohol, pressed between 

 filter-paper, decomposed with hydrochloric acid, and extracted 

 with ether. The ether extract is washed with water, the ether 

 evaporated, and the melting-point * of the residue determined. 

 A complete separation of palmitic from stearic acid is only to 

 be attained by repeating the fractional precipitation several 

 times. That the solid fatty acids form a mixture of different 

 acids may also be shown in a very simple way by allowing a 

 hot solution of 5 g. of the fatty acids in 100 cc. of 95 per cent, 

 alcohol to stand till next day, filtering off the fatty acids 



1 Sheep-fat gives more solid fatty acids, especially stearic acid, than 

 jhog-fat. 



