Y OF INDUSTRIAL SUBSTANCES lf>0 



Class 



of Compounds Composition Use 



Fats Salts of certain organic acids To make soaps, 



called fatty acids. lubricants. 



Oils Liquid fats 



Soaps When fats are boiled with Washing pur- 



sodium hydroxide or al- poses. Gly- 



kali, a soap and glycerin cerin used 



are formed. to in a k c 



smokeless 

 powder. 



178. Gunpowder. Ordinary gunpowder is a mixture of 

 charcoal, sulphur, and potassium nitrate. The efficiency 

 of gunpowder depends upon the formation of a large volume 

 of hot gases in a closed space. The pressure exerted by these 

 gases propels the bullets, breaks the stones, etc. If gun- 

 powder is wet, the potassium nitrate dissolves and the 

 powder loses its effectiveness. 



179. Sand. Sand is composed of silicon dioxide (sym- 

 bol SiO 2 ). On account of their hardness, some varieties 

 of sand and mixtures are used for grindstones. 



180. Glass. When sand and several other substances 

 are mixed and heated, the fused mixture forms glass. The 

 coloring of glass is caused by the introduction of oxides of 

 metals into the heated mass. 



181. Clay. Clay is an impure form of aluminum silicate. 

 Clay is formed by the slow "breaking up" or decomposi- 

 tion of certain parts of rocks called the feldspars (silicates of 

 aluminum, sodium, or potassium). The decomposition 



