OILS AND FATS. 369 



Glycerin is soluble both in water and alcohol. It can 

 be obtained by boiling stearin and olein with a solution 

 of potassium hydrate. The fat (or stearin) is decomposed 

 by the substitution of potassium for glyceryl, and the re- 

 sulting products are potassium stearate and glyceryl hy- 

 drate or glycerin. We will explain this further in the 

 section on soaps. Glycerin has remarkable solvent powers, 

 dissolving readily the greatest variety of substances, min- 

 eral and organic. Nitrogtycerin is a powerfully explosive 

 oily liquid, made by the action of nitric acid on glycerin, 

 much as in the case of gun-cotton. It is very dangerous to 

 manufacture and to handle, and at the same time very use- 

 ful for blasting rocks. Mixed with porous silica and some 

 other substances it is called Dynamite. 



510. Candles made of Stearin and Stearic Acid. Stearin 

 may be obtained from lard and tallow by a simple process. 

 If the fat be melted, as it cools it hardens, forming a mass 

 from which the fluid olein can be pressed out, leaving the 

 stearin alone by itself. The stearin is used for making can- 

 dles, while the expressed olein is the well-known lard-oil. 

 But a better material for candles can be obtained by de- 

 composing the stearin with lime, thus forming a stearate of 

 lime, and then decomposing this with sulphuric acid. In 

 this way we obtain stearic acid, for the sulphuric acid takes 

 the lime away from the stearate of lime, and thus sets the 

 stearic acid free. This acid is a white, crystalline, translu- 

 cent substance with a brilliant lustre. It is a better ma- 

 terial for candles than stearin, because it is not so readily 

 softened by heat, its melting point being about ten degrees 

 higher than that of stearin. 



517. Soaps. In the preparation of glycerin, described 

 in 5 15, we did not tell you any thing about the potassium 

 stearate which was produced along with the glycerin ; this 

 substance is soap. Soap, then, as well as oils and fats, is a 



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