PETROLEUM, OR ROCK OIL. 



CO 7 



Pa., and usually -wherever it is of the lighter or 

 less dense sorts, at once gives off considerable 

 quantities of vapors of its extreme rarer com- 

 ponents. Mixed with snch vapors are com- 

 monly, doubtless, portions of the firtt and 

 second members of the marsh-gas series, present 

 as gases : while it may be considered equally 

 certain that the vapors themselves are mainly 

 those of the third and fourth members, with 

 usually some part of the fifth also, of that 

 series. The regular ascent of the degrees of 

 temperature at which the more and more dense 

 oily and solid constituents of crude petroleum 

 bod, is availed of in the practice of distilling the 

 oiL in the way of separating the latter roughly 

 into certain portions such as are suitable for 

 different and special uses; the method being, 

 in fact, one of fractional distillation. 



In their general chemical character, the crude 

 rock oils are closely allied to the soft-solid and 

 solid bitumen*. The latter, as met with under 

 somewhat differing forms, or in different places, 

 have received a variety of other names, such as 

 natural or mineral tar, mineral pitch, Birla- 

 doe* tar, mineral ca men), 



and atphaltum, or asphalt. Of course the oils 

 are thus closely related also to the bitumen 

 which exists in solidified condition in the bitu- 

 minous, including the cannel, coals, and to that 

 which is infiltrated through, or collected with- 

 in small cavities in, certain forms of rock. The 

 name litumen. indeed, correctly includes not 

 only all the matters just indicated, but also the 

 rock oils, the latter being, in such case, dis- 

 tinguished as the " liquid bitumens." The 

 composite oils distilled from cannel coals, from 

 peat, from bituminous shales, and from native 

 bitumen or asphalt, or obtained by redistilling 

 from the coal tar which results during the 

 manufacture of coal gas, and in a less degree 

 that afforded by distillation of wood, are nearly 

 analogous to the crude rock oils, being like the 

 latter severally composed in the 'main of series 

 of hydrocarbons, liquid and solid; though to 

 what extent the components of the former 

 classes of oils are respectively identical with 

 those of the latter, appears to be not yet fully 

 determined. 



met with in different ofl-yieMing regions, 

 and often as obtained from springs or wells 

 near to each other in a given district, the 

 various native or mineral oils passing under the 

 name of petroleum, present a very great diver- 

 in color and general appearance, in con- 

 sistency, and even in odor. In density or spe- 

 cific gravity they exhibit a wide range of varia- 

 tion. 



To the very light and comparatively pure 

 rock oils found in some parts of the earth, as in 

 some of the springs in Georgia, near the Caspian 

 Sea, and which evidently consist chiefly of the 

 lower members of the hydrocarbon series, the 

 Greek name naphtha is, for distinction's sake, 

 still applied. It will be observed that native 

 naphtha is here spoken of. Almost any form 

 of petroleum, however, yields, when distilled, as 

 VOL. rr. 12 A 



do the oils artificially procured from coal, wood, 

 illed, and below a temperature 

 taken by different operators at from 1 ' 

 212' F., a mixture of lighter oils that, according 

 to their source, may be distinguished as coal 

 naphtha, wood naphtha, <tc. The light oil 

 thus separated from petroleum rarely takes any 

 distinguishing name, save when termed "spirits 

 of petroleum," being in commerce usually known 

 as " crude naphtha." From it native naphtha 

 would differ but little, and chiefly in the fact 

 of containing some small percentage of the 

 denser hydrocarbons. When the crude naphtha 

 illed and properly rectified, it affords, and 

 to the extent of a large portion of its entire 

 volume, the pure or " refined naphtha." This 

 is also known, though with less propriety, as 

 lenzolt, or lenzine. Of native naphtha the 

 specific gravity may vary between about .TOO 

 and .850, water being 1. Quotations of refined 

 naphtha in the Xew York market are for den- 

 sities ranging between 60 and 63 of Baume's 

 areometer, i. e., specific gravities of .745 to 



In the various forms of the areometer named, 

 ";ed for liquids lighter than water, the den- 

 sity of water, 1, is indicated by 10'% and the 

 ascending degrees of the scale from this point 

 show densities which are continually less; so 

 that, for example, 35 B. answers to sp. gr. 



and 60 B., as just seen, to sp. gr. 

 As a consequence of the general use of these 

 scales in testing densities of coal and rock 

 oils, &c., the expression "high gravity" has 

 come in describing such oils to signify their 

 rarity, i. e., in fact, low density or specific 

 gravity; and "low gravity," on the other hand, 

 to signify comparative heaviness, i. e., high den- 

 or specific gravity. 



The rock oils commonly met with in va- 

 rious parts of Xorth America, and in some 

 other parts of the earth, differ very obviously 

 from such as would take the name of naph- 

 tha (native), in being generally darker in color, 

 and always thicker and heavier. Their in- 

 creased density is, of course, due to the circum- 

 stance of their containing proportionally 1 

 the lighter component oils, and more of the 

 heavier, and of dissolved solid hydrocarbons. 

 But both the several oils and the solids which 

 enter into petroleum proper, when pure, are 

 quite devoid of color, the former as much so 

 as pure water, the hitter as pure spermaceti. 

 Hence, a yellow, reddish, brown, greenish, or 

 black color in petroleum always depends on 

 and indicates foreign intermixtures or impuri- 

 ties of some sort. The completely purified and 

 the purer native petroleum have the somewhat 

 resinous, aromatic and agreeable odor now fa- 

 miliarly known in good refined burning oil and 

 in benzine ; but certain impurities in the crude 

 oil, whether affecting its color or not, may 

 quite change its odor, and sometimes render the 

 oil highly offensive. Among the intermixed or 

 foreign substances which may impart color or 

 odor, or both, to crude petroleum, are, besides 



