In conveying oil through the pipe lines both gravity and pumping are used. The pumping station at the “tank farm” forces the crude into pipes through which it commences its long journey to the refinery. This pumping equipment is in itself a wonderful mechanism and drives the oil over heights where gravity cannot assist. The pipe at the field lines where the journey starts varies in diameter from 2 to 8 inches and the joints are screw threaded. The main trunk lines are from 6 to 12 inches in diameter and pumping stations to continue the driving process are located at necessary intervals along the route. In some fields the oil is heavier than in others and then the stations have to be located nearer to each other, while in the case of certain very heavy crudes, heat is applied to promote the flow before it enters the pipe-line. By this system the amount of oil that flows under the soil of the United States to distant points exceeds half a million barrels daily. Concealed and unobtrusive, these lines do their work so well that millions of people whom they serve are unaware of their existence. Everyone knows of the freight train that links up the small town factory with the central distributing point, and of the grain car which carries the farmer’s wheat to the seaboard; but little attention is paid to this great but inconspicuous transportation adjunct of American industry, the petroleum pipe-line. As the system has grown, handling in tank cars of anything but refined product has become more and more nearly obsolete, for economic reasons. Once installed, the pipe-line system is cheap and easily maintained. It would, indeed, be quite impossible to conduct the American oil industry of to-day by the use of railroads, even though they were greatly multiplied. The crude oil which flows daily, east of the Rocky Mountains, through pipe-lines would fill over 2,500 tank cars. Since, on the average, a barrel of crude travels 1,000 miles before it reaches its destination, it would require approximately 75,000 tank cars to do the daily work of transportation effected by the pipe-lines, not to mention approximately 900 engines which it is estimated would be required to move them. Leaving out all the possibilities of congestion in stormy weather, it will be seen that such a task is one that railroads could not hope to carry out. In its present dimensions the oil industry, therefore, owes as much to the pipe-line as to the actual existence of oil deposits themselves. The work they perform is infinitely more even and uninterrupted than that of any system of railroad or water transportation. The pipe-lines run to full capacity, winter and summer, day and night, the year round, making possible the existence of great central refining plants where the crude can be treated in bulk at the lowest possible cost, and where distribution can be effected at the lightest impost on the ultimate consumer. CHAPTER IX