PETROLEUM, OR ROCK OIL. 



MARSH-GAS SERIES OF CONSTITUENTS OF PETROLEUM. 



Of the hydrocarbons given in the table, the 

 first is an extremely incondensible, or perma- 

 nent gas; the next two in order are either 

 permanent gases or possibly condensible by 

 cold and pressure ; and the fourth is, at ordi- 

 nary temperatures and when free to volatilize, 

 a vapor, liquefying at a little above the freezing 

 point of water. Then follow a long succession 

 of components that are liquid at common tem- 

 peratures, i. e., oils. Of these, it will be ob- 

 served, the boiling points stand successively 

 higher and higher ; and their densities, either 

 in the liquid or vaporous form (calculated, of 

 course, at a standard temperature), at the same 

 time progressively increase. Finally, at its 

 (chemically) higher extremity, the series termi- 

 nates in solids resembling spermaceti or wax, 

 and of which paraffine is the most important. 



The term paraffine, however, is frequently 

 used as a general designation for the total of 

 the solid hydrocarbons of petroleum. The 

 melting point of coal-tar paraffine is stated by 

 Regnault at 11 6. 6.; that of petroleum paraf- 

 fine, by Ure, at 140. Hydrocarbons belonging 

 to other than the marsh-gas series, have been 

 detected in some rock oils, in variable propor- 

 tions; and in less amount, and more rarely, 

 oxygenated oils also, which are more or less an- 

 alogous to creasote. So small, however, is the 

 entire proportion of oxygen in any rock oil, that 

 chemists agree in regarding pure crude petro- 



leum generally as consisting of two elements 

 only its approximate composition as a whole 

 being C 2 < H 24 . The rock oils generally contain 

 also more or less of pitch-like matter or bitu- 

 men, which is held in solution or suspension, 

 and to which in many cases their naturally 

 dark color is owing. In those oils which are 

 got by distillation from coal, peat, and wood, 

 the oxygenated component oils are present in 

 greater quantity. Of some of the oils in the 

 series above, from the fifth to the eighth inclu- 

 sive, M. Schorlemmer gives the boiling points 

 somewhat higher ranging from 102 to 248 F. 

 The question of the presence of the benzole 

 series of oils in petroleum will receive notice 

 in the section on Refining of Petroleum, &c. 



It is not to "be supposed that all the con- 

 stituents of petroleum now referred to are pres- 

 ent in every crude or native oil of the kind. 

 Some of them will be wanting from one rock 

 oil, others from another. From the lightest of 

 these oils especially, known as (native) naphtha, 

 the higher members generally of the marsh-gas 

 series will usually be nearly, if not altogether, 

 wanting. It will hereafter be more clearly 

 seen how close is the connection between 

 marsh-gas and petroleum such, indeed, that in 

 nature the oil almost invariably contains, and 

 in its various locations is almost invariably 

 accompanied with, the gas. Petroleum, as 

 freshly discharged from the wells of Oil Creek, 



