526 CONSIDERATION OF CARBON COMPOUNDS. 



Soaps are soluble in water and alcohol ; they contain rarely less 

 than 30 per cent., but sometimes as much as 70-80 per cent, of water. 



Potassium or soft soap is usually yellowish, but it is sometimes tinted green 

 artificially, and is then called "green soap." It contains, besides the potas- 

 sium salts of the fatty acids, the glycerin liberated in the saponification and 

 relatively much water. Hard or sodium soap is separated from the solution 

 after saponification by adding common salt to the boiling mixture to satura- 

 tion. The soap, being insoluble in the salt solution, separates as a molten 

 layer, which can be removed after cooling and solidifying. This method of 

 separating the soap is known as the "salting out" process. The soap is free 

 from glycerin, but contains some water. 



Ammonia liniment, Linimentum ammonice, and lime liniment, Lini- 

 mentum calcis, are obtained by mixing cottonseed oil with ammonia- 

 water and lime-water respectively. The oleate of ammonium or 

 calcium is formed, and remains mixed with the liberated glycerin. 



Lead plaster. Chiefly lead oleate, Pb(C 18 H 3 3O 2 ) 2 . Obtained by boiling lead 

 oxide with olive oil and water for several hours, until a homogeneous, pliable, 

 and tenacious mass is formed. Lead oleate differs from the oleate of the alkalies 

 by its complete insolubility in water. 



Experiment 62. Dissolve in a 500 c.c. flask 15 grammes of potassium hy- 

 droxide in 100 c.c. of alcohol. Melt 50 grammes of lard in an evaporating dish 

 and pour the liquefied fat into the flask. Heat over a water bath, and shake 

 cautiously when the alcohol begins to boil. Saponification takes place very 

 rapidly, and its completion is determined by pouring a few drops of the liquid 

 into a test-tube of water, when any unsaponified fat will float on the surface. 

 When saponification is complete the solution contains soap, glycerin, and any 

 excess of caustic potash. 



Pour the contents of the flask into 250 c.c. of hot 5 per cent, sulphuric acid ; 

 the fatty acids separate as an oily layer which solidifies on cooling. The solu- 

 tion contains potassium acid sulphate, sulphuric acid, and glycerin. When the 

 solution is neutralized, evaporated to crystallization, and extracted with alco- 

 hol, glycerin can be obtained by evaporation of the alcoholic extract. 



Reactions of fats and fatty acids. 



1. Boil 5 grammes of suet with 25 c.c. of alcohol and filter while 

 hot. Wash the residue with a little ether, squeeze as dry as possible 

 and then dry in the air. The resulting fibrous mass is the connective 

 tissue network of the adipose tissue and a little fat. Show the pres- 

 ence of protein in connective tissue by the xanthoproteic and Millon's 

 reactions. On evaporation of the alcoholic filtrate, fat is left. 



2. Rub a little fat on glazed white paper. Notice that this " grease- 

 spot" appears dark on a white background in reflected light, but 

 light (transparent) in transmitted light. The stain does not disappear 

 on heating. 



