HANDBOOK FOR BIO-CHEMICAL LABOKATOEY. 7 



Fatty Acids, C n H 2n 2 . 



Preparation. Dissolve 20 grms. caustic potash in 100 c.c. 

 absolute alcohol, placing the vessel in cold water as consider- 

 able heat is generated. When all has dissolved that will, 

 decant the clear solution from the sediment. Now heat on 

 water-bath 50 grms. mutton tallow or leaf lard with 50 c.c. 

 alcohol in a flas~k connected with a return condenser. Continue 

 the application of heat until all the fat has melted; now add 

 the potash solution, and gently boil for one half to one hour. 

 "When the liquid in the flask does not give a cloudiness when 

 added to water, then all the fat has been converted into soap. 

 Filter through a cotton plug and dilute this liquid with 500 to 

 600 c.c. water* Boil over the naked flame until all the odor of 

 alcohol has disappeared, and add dilute sulphuric acid (1 to 4) 

 until the solution has a marked acid reaction. Allow this to 

 stand on the boiling water-bath until the separated fatty 

 acids have collected on the surface as an oily layer. Now 

 allow to cool, filter through a wet filter, wash the fatty acids 

 with cold water, and crystallize the same from hot 80$ alco- 

 hol. The oleic acid (C 18 H 34 2 ) remains nearly entirely in the 

 mother liquid, while the palmitic (C ]e H 32 OJ and stearic acid 

 (C 18 H 36 2 ) forms the crystals. Determine the melting point 

 of the mixture, then dissolve the same in cold alcohol, and 

 fractionally precipitate this solution with an alcoholic solu- 

 tion of sugar of lead (3 to 4 fractions are sufficient). Each 

 precipitate is shaken with ether and the fatty acid obtained 

 on the evaporation of the ether. Determine the melting- 

 point of each fraction, and a different melting-point will be 

 found for each, showing that the fatty acids obtained from 

 the fat consists of a mixture. The first lead precipitate con- 

 tains the stearic acid. 



Stearic acid melts at 69.2 C. 



Palmitic acid melts at 62 C. 



