This name, meaning rock oil, is applied to certain bituminous fluids found in the earth. Solid bitumen, or asphalt, differs but little in chemical composition from petroleum, both being compounds of carbon and hydrogen
Many varieties of petroleum, and perhaps all, become thicker by exposure to the air, and finally solid, resembling asphaltum. Bitumen, and doubtless petroleum also, was known from the earliest ages, being the "pitch" which Noah used in building the Ark, and the "slime" used for mortar in the Tower of Babel, being dug from pits in the Valley of Sodom, precisely as is done in the same region at the present day, where the Arabs annually extract considerable quantities
The fluid petroleum has been collected in Burmah for at least 16 centuries. It is used by the inhabitants for light and fuel. The product obtained at the present time, from 520 wells, is said to be 420,000 hogsheads annually. In the United States, petroleum is not, as many suppose, a new discovery. Years ago springs of it were known at many localities, but its use was very limited. No method of purifying it was known, so that it was looked upon as valueless, and several wells bored for salt water were abandoned on account of the oil rendering the salt impure. In 1861 it was purified, and introduced extensively as an illuminating oil, to take the place of burning fluid (camphene and alcohol), the price of which was greatly enhanced, and which, by the explosive qualities of its vapor, was causing many severe accidents. The trade increased, new wells were bored, and some of them yielding several hundred barrels a day, and making their possessors at once wealthy, started what has been known as the oil fever. Lands sold for fabulous prices, sometimes for 500 times as much as 2 or 3 years before.
Petroleum has probably been formed by a slow decomposition of organic matter under the earth's surface. It is found in cavities and crevices, and through the substance of the rock. In mining for it a well 3 or 4 inches in diameter, and sometimes 700 or 800 feet deep, is bored by drills, generally by steam-power. When rock containing petroleum is being bored through, what is called "a show of oil" is found. The chips and water drawn up from the well show and smell of the oil, but, unless the drill strikes a cavity or crevice filled with oil, the well isn't productive. This uncertainty is the most unfortunate peculiarity of oilmining, and makes it, to a great extent, a lottery, for there are no surface indications by which these cavities can be discovered.
Petroleum is much lighter than water, of a dark green or black color, with a peculiar and, to most persons, unpleasant odor. It is commercially divided into two kinds, the heavy, or lubricating oil, and the light oil. The former is more dense, and sometimes of the consistence of thin molasses. It is used, without preparation, for lubricating machinery, for which it is admirably suited. The light oil, before it can be used, is submitted to several purifying processes, the most important of which is distillation.
For this purpose the crude oil is pumped into stills holding from 200 to 1000 galls. each, and submitted to a gradually increasing heat, the vapors being passed through a worm immersed in cold water. At first there comes over a very light, mobile, and volatile liquid exceedingly inflammable. This is benzine, largely used as a cheap substitute for turpentine in painting, and as a solvent for India-rubber. It differs from benzole (obtained by distillation from coal-gas tar), and the beautiful colors obtained from the latter cannot be made from the benzine of Petroleum. The terms benzine and benzole are often confounded, and even used as synonyms, but the name benzole is properly applied only to one of the many substances contained in coal-tar, and from which the aniline colors are obtained.
Next, there condenses a less volatile and inflammable liquid, of greater specific gravity. This is the burning oil, and is generally the most abundant and valuable product. When the heat rises to near 500 Fahr., the oil that comes over is no longer suitable for burning, but is an excellent lubricant for light machinery. Finally, a substance (paraffine) solid at common temperatures, distils over, and there remains in the retort, as the heat has been less or greater, a thick tarry matter, or a porous coke. When the lubricating oil, just mentioned, is exposed to cold, a considerable portion of paraffine separates from it, and can be collected upon filters, purified, and used for candles, and for other purposes.
All these products, and especially the burning oil, require further purification after the distillation. This usually consists in agitation, first with water, followed by strong sulphuric acid, caustic soda, and finished with water. The effect of this is to render the oil colorless, and to diminish the odor.
The relative amount of these several products varies very greatly in different regions, and indeed in the oil of different wells in the same region. Thus, the oil from Canada contains little or no benzine, much burning oil, and much paraffine, while that from Ohio and Western Virginia contains much benzine, about the same amount of burning oil as the former, and but little paraffine.
Petroleum is found in many localities on this continent. Among these may be mentioned as the most important, Canada West, Pennsylvania, Ohio, Western Virginia, California, Kentucky, and Tennessee. The first four yield more than nine-tenths of all now obtained, but it is probable that other regions will yield equally well when as thoroughly explored.
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