MIXTURES 217 



fire, b, placed underneath. Note that the coal itself is 

 not burned but only heated without air until it is 

 decomposed. 



255. Petroleum. Petroleum is an oily liquid found 

 in the earth in some places. Pennsylvania and Texas 

 have large oil fields. Petroleum contains many hydro- 

 carbons ( 218). Among the useful mixtures obtained 

 from it are kerosene, benzine, gasoline, naphtha, and 

 paraffin. Candles are commonly made from paraffin. 

 Note that each of these substances contains largely the 

 elements C and H. 



256. Coal Tar. In the process of making illuminat- 

 ing gas from coal, a thick black liquid called coal tar is 

 formed ( 254). This liquid has been found to contain 

 a great number of compounds, so that coal tar is now 

 the source of many common and important substances. 

 Among these we may mention phenol, or carbolic acid ; 

 saccharine, a substance that is far sweeter than sugar ; 

 aniline dyes of many shades ; and various essences and 

 perfumes. The compounds found in coal tar contain 

 chiefly the elements C, H, 0, and N. 



257. Explosives. Gunpowder and other explosives 

 are mixtures of such substances as may easily and 

 quickly act upon each other so as to produce a large 

 volume of gas. Explosives are generally either solids 

 or liquids. Under a slight impulse (a spark or a sudden 

 jarring) they quickly form into gases. These gases nat- 

 urally take up far more room than the solid or liquid 

 mass, and in expanding to their natural volume they 

 exert great force. 



