cases petroleum flows to the surface without previous drilling, the boring of wells to various depths, up to 4,500 feet, is the method now adopted. The depth, of course, is not always the same, on account of the different locations of the oil deposits. Some wells flow to the top of the ground, while, in others, the oil must be pumped to the surface. In all cases a derrick is first erected over the spot selected for the well, and the drilling is done by means of a bar of steel, shaped like a chisel, which is alternately lifted and dropped on the rock, the broken rock, etc. being pumped out every little while with the aid of water.
37. Transportation.— In the early days of the oil industry, the transportation of both crude and refined oil was accomplished by means of barrels loaded on carts or railroad cars. Later tank wagons and tank cars, built of sheet iron, took their places, and are still employed to a great extent. But pipe lines, similar to the gas and water mains that underlie all our cities and towns, are now in general use. These pipes are made of wrought iron, with screwed joints. They are laid a few feet underground, and connect the oil-producing regions with various points on the coast and with many of the principal cities of the eastern portion of the United States. Through these numerous pipe lines the oil is forced by powerful steam pumps placed at various places along the lines. It is usually crude oil that is transported in this manner, to be refined where fuel is cheap and railroads or steamship lines are convenient.
DISTILATION AND REFINING
38. Distillation is the name given to the process of separating the various compounds of the crude oil through vaporization by means of heat, and afterwards cooling or condensing the vapors. It will be shown in Table VII that the boiling points of the various hydrocarbons, given under the heads of Liquids and Solids, vary from 86° to 699°. By carefully regulating the heat of the distilling apparatus,
