148 PHYSIOLOGICAL AND PATHOLOGICAL CHEMISTRY. 



which crystallize, pressing out the mother-liquor between 

 filter-paper and, when dry, determining the melting-point : this 

 should be about 66. By evaporating the alcoholic mother- 

 liquor an acid having a melting-point of 56 will be obtained. 

 Both preparations are mixtures of palmitic and stearic acids. 

 In the first stearic acid is in excess, in the second palmitic acid, 



Separation of Glycerin, C 3 H 5 (OH) 3 . 



The aqueous solution obtained from the soap solution by 

 precipitating the fatty acids contains glycerin, besides potas- 

 sium sulphate and free sulphuric acid. Filter, nearly neutral- 

 ize with sodium hydroxide solution, and then completely neu- 

 tralize with sodium carbonate solution, evaporate, as nearly to 

 dry ness as possible, at first over a free flame, then on the water- 

 bath, and mix the residue with 50 cc. of 90 per cent, alcohol. 

 Filter the solution after it has stood for some time, evaporate 

 again on the water-bath as completely as possible, and dis- 

 solve the residue in absolute alcohol, so that the volume of 

 the mixture amounts to 25 cc. in all. Without filtering add 

 25 cc. of ether, shake thoroughly, and let stand for some time, 

 preferably till next day. The ether precipitates the greater 

 part of the remaining salts. Filter and evaporate the ethereal- 

 alcoholic filtrate cautiously by gently warming on a water- 

 bath. The glycerin is obtained in the form of a light yellow- 

 colored sirup having an intensely sweet taste. 



Reactions of Glycerin. 



1. Mix in a watch-glass a drop of glycerin with a little 

 borax and heat the mixture on a platinum wire in the Bunsen 

 flame. The flame is colored green for a short time (forma- 

 tion of the glycerin ester of boric acid). 1 



1 A better method of performing this experiment is to mix a little 

 borax and glycerin in a small porcelain dish or crucible, heat gently with 



