Page:The American Cyclopædia (1879) Volume XIII.djvu/383

Rh these substances. On the contrary, springs of it issue in different parts of the world from all the stratified rocks, and from the volcanic and metamorphic formations. In Ohio and West Virginia it is found in the coal measures, and the wells are in some instances sunk through these into the sandstones and slates before they become productive. In N. W. Pennsylvania or in New York the wells are entirely outside of the coal field, and so remote from it that we cannot well imagine any connection between the oil and the coal beds. The strata in which the oil is found dip S. and pass below the coal measures at least 500 or 600 ft., the nearest coal bed to the more northern springs occurring in the tops of the highest hills, perhaps 30 m. distant. The conglomerate which underlies the coal formation caps some of the hills in the oil region, and attains a thickness of from 100 to 300 ft. The shales and sandstones that succeed below this rock belong to the Chemung and Portage groups of the New York geologists, and extend over a large portion of southern New York, west of Binghamton, and of northwestern Pennsylvania. The oil wells are bored in this group through alternating layers of shales and sandstones, and an occasional stratum of a bluish sandy limestone. The next group below is that known as the Hamilton shales in New York, and in Ohio as the black slate. Prof. Newberry considers this the source which affords the petroleum. It contains much carbonaceous matter, and is supposed by him to be amply sufficient for generating the supplies that are forced upward from it by the water that finds its way beneath the oil, and by the pressure of the carburetted hydrogen gas also furnished from the same source. It is from these slates that the oil springs of Ontario issue, and these are far distant from the coal formation. In southern California the oil issues from shales interstratified with coarse sandstones of enormous thickness, and nowhere containing coal. In the northern part of that state it issues from serpentine and other metamorphic rocks of cretaceous age. Around volcanoes petroleum is often seen floating upon the surface of the water, as around the volcanic isles of Cape Verd; and to the south of Vesuvius a spring of it rises up through the sea. Springs also issue beneath the sea upon the coast of Venezuela, and in the Santa Barbara channel off the coast of southern California. Wells sunk near together vary in their yield, in the depth at which they become productive, and even sometimes, as in the Kanawha region of Virginia, in the quality of the oil they afford.—Petroleum from different localities varies considerably in character. The substance is ordinarily of a greenish hue by reflected light, and brown by transmitted light, more or less deep and opaque; but some varieties of light clear oils are reddish. The oils of northern Italy are of the latter class. At Baku it is observed that the oil from the central portion of the tract is clear and pure as if distilled,

and by its faint yellow tint resembles Sauterne wine. That obtained nearer the sides of the tract is darker, gradually changing to a yellowish green, then reddish brown, and finally to asphalt. Those of southern California are leek-green when taken fresh from the rock; but they soon become brown and black, changing to maltha and asphalt. The Canadian oils are black, but those of Pennsylvania, Ohio, West Virginia, Rangoon, and many other localities, are for the most part of the ordinary color. All have a disagreable, pungent odor. In the province of Ontario oil has been obtained remarkable for its garlicky odor. The quality of petroleums is indicated by their specific gravity, and this is taken by Baumé's hydrometer, the higher degrees of which mark the lighter oils, such as are most esteemed. The best are some of those of Oil creek, of 46° B. Others of the same district increase in density to 38°. At Tidioute oils are obtained of 43°. At Franklin they rate from 33° to 36°, and on French creek also they are heavy. At Mecca, Pa., they are dark, thick, and heavy, so that when cold they refuse to flow. Their density is 26° or 27°, corresponding to a specific gravity of about 0.90. The oil from Cuba, N. Y., resembles that of Franklin, marking 32°. Rangoon petroleum is described as of semi-fluid consistence, like goose grease. As it occurs in nature it is of no definite composition, but consists of various oily hydrocarbons, which hold in solution paraffine and other substances, some of which contain nitrogen. When of the greatest fluidity they resemble naphtha, and have been called by this name, and also oil of naphtha. As the proportion of carbon increases, the mixture becomes thicker and darker, resembling tar in appearance; and at length, by further diminution of the fluid ingredients, it passes into asphalt. There are two classes of petroleums which are quite distinct. The first may be termed paraffine oils, as they invariably yield paraffine by distillation; the second never yield paraffine. The first are exceedingly stable compounds, changing but little if at all on exposure to the atmosphere; these form the greater portion of the petroleums of commerce. The second are very unstable, and change rapidly on exposure to the atmosphere to maltha and asphalt. While they are found in some localities in large quantities, they have as yet proved of limited value for commercial purposes when compared with the other variety. The oils of California and Trinidad are of this class.—Comparatively little is known of the chemical composition of petroleum. Warren and Storer in this country and Pelouze and Cahours in France have investigated the more volatile portion of the Pennsylvania and Rangoon oils, but whether the substances they obtained are educts or products is uncertain. These two petroleums were found to be similar. Two groups of hydrocarbons were isolated, having the constitution of the hydrides of