224 Transactions of the American Institute. 



varying, in specific gravity or density, from 0.820 to 0.782, or 40° 

 to 48° Beanme. It is chiefly a mixture of a great number of 

 hydrocarbons, compounds of carbon and hydrogen, the average pro- 

 portion of the two elements in the mixture being : 



Carbon 85 



Hydrogen 15 



100 



These hydrocarbons differ from each other in volatility. Some are 

 so volatile as to evaporate rapidly at ordinary temperature, making it 

 dangerous to approach an open tank of petroleum with a flame ; others 

 are much less volatile, some requiring a temperature of 700° to 800° 

 F. to vaporize them. 



The volatility of these component hydrocarbons is intimately 

 related to their specific gravity or weight, the lightest ones being the 

 most volatile, while the heavier oils possess the higher boiling points. 



The inflammability of the oils is also intimately connected with the 

 volatility and specific gravity. The light volatile oils ignite on the 

 approach of a burning match, no matter how cold they may be, while 

 the heavy, less volatile oils can only be ignited when they are heated 

 above the ordinary temperature of the air. 



The dark, offensive petroleum is subjected to a process of refining, in 

 order to separate, from the portion designed for burning in lamps, 



First. The lighter oils, which are very inflammable, and, owing to 

 their volatility, evolve vapors at ordinary temperatures which, when, 

 mixed with the proper proportions of air, constitute explosive mixtures. 



Second. The heavier oils, which do not burn well in lamps, but are 

 excellent lubricators. From these oils is obtained, by chilling and 

 pressing, the solid paraffin which is used for candles, for waterproofing 

 cloth, etc. 



Third. The tarry matter, which would crust the wicks of the lamps. 



Fourth. The coloring matter. 



Fifth. The compounds which cause the offensive odors of the crude 

 oil. 



Refining, as usually practiced, involves three successive operations : 



First. Fractional distillation. 



Second. Agitation with sulphuric acid. 



Third. Agitation with hydrate of soda or ammonia. 



For fractional distillation the apparatus employed consists of an 

 iron still, provided with a coil or worm of wrought iron pipe, which 



