Wherever and however nature carries on its mysterious process of producing the various grades of petroleum found all over the globe, the lighter and the heavier grades, the brighter and the darker colored ones, all are found in shallow places, above ground or near the surface, or deep down in the bowels of the earth, those found lowest being generally of lighter consistency than those found on or nearer to the surface. They are all hydrocarbon compounds of like characteristics, differing only in their specific gravity, in their color, odor or in purity. The deposits found above ground or near the surface, which are almost solid or are liquids of heavy specific gravity, appear to be the result of evaporation of their lighter constituents or of a gigantic filtering process, by which the liquid constituents have percolated to a lower stratum, leaving the heaviest ones retained where they are found in an upper stratum or on the surface, as Ozokerite wax.

The petroleum oils of Pennsylvania, in Venango, Clarion and Butler counties, in Warren and McKean counties, vary in color from light amber-yellow to dark black, and vary in specific gravity from 30° to 55° Baume; from thick lubricating oils to nearly pure benzine. Franklin county oils are celebrated for their fine bright, dark ruby color, their fine lubricating quality and excellent cold test, which makes them valuable as lubricants on refrigerator machinery.

The Ohio crude oils containing sulphur and having an unpleasant sulphurous odor, are desulphurized during the process of distillation by placing a desulphurizing chamber between the retort and the cooler. This chamber is separately heated and is filled with iron oxide, copper sulphate, porous lime coke, or other desulphurizing agents, and hot air can be driven through the oil. When a temperature of 130° F. is attained in the desulphurizing chamber, the still is fired and the heating of the chamber is increased to prevent the passing vapors of the oil from condensing in the chamber before passing through the cooler. Introducing nascent hydrogen into the still or the desulphurizing chamber, and its vapors mingling with those of the distilling oil, improves the color and odor of the distillate and changes the product into one of lighter gravity and purer odor.

Aluminium chloride also is used to desulphurize Ohio petroleum. One hundred parts of the oil are heated and while agitated, 0.8 part of aluminium chloride is gradually added, whereby a little muriatic acid and much sulphureted hydrogen are evolved. When no more gas is eliminated, the oil is allowed to cool and is drawn off from over the aluminium residuum and washed with water and soda lye, and is distilled with the addition of a little lime.

In order to enhance the value of the various forms of petroleum and to make them adapted and available for their manifold uses in the market, they are either purified, condensed or distilled. Some require only straining or settling and exposure to the atmosphere, for a period of time, to vaporize all traces of inflammable, light hydrocarbon compounds and to settle all gritty matter and impurities, to make them serviceable for lubricating purposes. Others are condensed and the lighter vapors driven off and settling of gritty impurities is effected by application of steam heat. The greater bulk, however, is subjected to distillation, in order to separate the different grades of hydrocarbon compounds from each other and thus obtain various useful products.