434 PETROLEUMS 



the world. They occur as gases, fluids, and solids, and many 

 are used in the arts and in medicine. The simplest of the 

 series is marsh gas, methane, fire-damp, or light carburetted 

 hydrogen (CH 4 ) the inflammable gas which causes coal- 

 pit explosions. 



When rock-oil is distilled, ethane and other gaseous 

 paraffins are first evolved, are collected, and in great part 

 liquefied by a condensing pump, and yield the liquid 

 cymogene, which, on account of the cold produced by its 

 rapid evaporation, is used in freezing machines. Proceed- 

 ing with the fractional distillation, the products which come 

 off below 170 Fahr., and consist chiefly of pentane and 

 hexane, are sold as petroleum spirit, or petroleum ether, 

 and used for making varnishes, for dissolving indiarubber, 

 and for singeing lamps. The next portion of the distillate, 

 coming off about 212 Fahr., is heptane, and is used for 

 illuminating purposes, under the names benzoline, paraffin 

 oil, and mineral sperm oil. For safe use this oil, when placed 

 in an open saucer at 100 Fahr., should not kindle when a 

 light is brought near its surface. At higher temperatures 

 there come off hexadecane and other paraffins, richer in 

 carbon, constituting such soft solids as vaseline and the 

 soft petroleums, while still higher temperatures produce 

 the hard paraffins, cereses, or paraffin waxes. These soft 

 and hard paraffins are also obtained by distillation from 

 shale, the liquid portions being separated by refrigeration, 

 and the solid products purified by melting and filtration. 

 They are frequently substituted for oils, lard, and wax in 

 the making of ointments and protectives. Liquid paraffin 

 is useful as a base for hypodermic and intratracheal injec- 

 tions of iodine. Mixed with sulphur and olive oil it is 

 employed for psoriasis and eczema, and with oxide of 

 zinc or iodoform as a protective for wounds. ' 



Rangoon petroleum, obtained from wells on the Caspian 

 shores, and the analogous Barbados or mineral tar, found 

 in the island of Barbados floating on the surface of springs 

 or pools, and in Trinidad forming extensive beds or lakes, 

 are of the consistence of treacle, of a dull green-brown 

 colour, with a petroleum odour and a bitter taste. 



ACTIONS AND USES. The petroleums belong physiologi- 





