LESSONS IN CHEMISTRY. 179 







When glycerin is poured slowly into a mixture of sulphuric 

 and nitric acids a yellowish oil, called nitroglycerin, is formed. 

 It is insoluble in water, but very explosive. For use it is mixed 

 with some inert matter, as finely divided silica, when it is known 

 as dynamite. 



One of the oldest industries involving chemical principles is 

 soap-making from natural fats and oils. Hard soap is made as 

 follows: A solution of carbonate of soda is boiled with lime, 

 forming an insoluble calcium carbonate and a soluble sodium 

 hydrate, called soda lye. Tallow is then boiled with a weak 

 lye, and as the process continues, stronger lyes are added until all 

 of the tallow has disappeared. In order to separate the soap 

 from the solution, a quantity of salt is thrown into the liquid, 

 when the soap rises to the surface, and is transferred to molds. 

 As tallow contains both stearin and olein the soap formed con- 

 sists of a mixture of sodium stearate and oleate, while glycerin 

 remains in solution. When a lye of potassium hydrate is used, 

 soft soap is formed. A great variety of soaps are made, but in 

 every case the essentials of the process are the same. Soaps con- 

 tain from 30 to 80 per cent, of water, which evaporates slowly, 

 so that in general soap that has been well dried is more econom- 

 ical than that which is freshly made. 



Tallow is extensively used in the manufacture of stearine 

 candles. For this purpose the tallow is first converted into lime 

 soap, which is decomposed by sulphuric acid, causing the fatty 

 matters to separate from the other parts of the solution. They 

 are then strongly compressed to squeeze out tha olein, leaving 

 the solid elements for manufacture into candles. 



Palm oil, cocoanut oil, olive oil, castor oil are common and 

 useful oils. Linseed oil has a tendency to become solid when ex- 

 posed to the air, and is called a drying oil. This tendency is 

 increased by heating the oil with litharge or the bin oxide of man- 

 ganese, when it is called boiled linseed oil. This oil is extensively 

 used by painters everywhere. 



Several interesting acids of vegetable origin are used exten- 

 sively in the arts. Of these, perhaps the most interesting is 



