146 PHYSIOLOGICAL AND PATHOLOGICAL CHEMISTRY. 



obtain the most even distribution of temperature possible: 

 the fat melts sooner than the corresponding fatty acid, i.e., 

 the melting-point of the first is lower. This is an invariable 

 rule. 



Separation of the Solid Fatty Acids from Oleic Acid. 



Heat the remainder of the fatty acids in a beaker on the 

 water-bath till melted, then add 100 cc. of 70 per cent, alcohol, 

 continue heating somewhat longer, filter while hot into a dish 

 or beaker, and let cool completely. A paste of crystallized 

 solid fatty acids forms, while the oleic acid, together with a 

 part of the solid fatty acids, remain in solution. Dilute the 

 pasty mass with 200 cc. of 70 per cent, alcohol, filter through 

 a dry filter, wash with some 70 per cent, alcohol, and pre- 

 serve the filtrate. Press the solid fatty acids dry between 

 filter-paper. The filtrate, when evaporated on the water- 

 bath, yields, when cold, a salve-like mass consisting of oleic 

 acid mixed with some solid fatty acids. 



The preparation of pure oleic acid as well as the separa- 

 tion of palmitic from stearic acid require somewhat more 

 detailed methods of procedure. 



Preparation of Oleic Acid. 



The semi-solid fatty acids are dissolved by heating with 

 sodium carbonate solution and a considerable quantity of 

 water (clear solution), and neutral lead acetate is added to 

 the solution as long as a precipitate forms. The mixture is 

 then faintly acidified with acetic acid. The lead salts sepa- 

 rate in viscous lumpy masses. Pour off the supernatant 

 fluid, knead the lead salts with warm water, decant and 

 remove the water adhering by heating on the water-bath. 

 When cold break up the lead plaster into small pieces, grind 

 it with about three times its volume of gypsum or caolin 

 (slightly burnt and ground clay) or sand, place the mixture 



