(3) The Varied Uses of Petroleum.—Much the greatest uses of petroleum are for power and light. In some cases it is burned in its crude form. For instance, in the southwestern United States and southeastern Russia oil-burning locomotives are used, not only because the railroads are near the oil-fields of Oklahoma, Texas, California, or Baku, but because oil can be employed more easily than coal, since it does not need a stoker. Many warships are oil burners because of the ease and speed with which this kind of fuel can be put aboard. Even in mid-ocean during a storm or a battle a warship can renew its supply of petroleum by pumping the liquid from a tender through a hose. As a source of light petroleum is used all over the world. City people often fail to realize this, but among farmers and in backward countries kerosene is the main source of light.
In its use for power petroleum possesses a great advantage because it can not only be burned, but exploded, thus giving power without the intervention of a boiler and steam. Everyone is familiar with its use in this way in automobiles, where the refined petroleum product known as gasoline is employed, but crude oil can also be used in the same way in the Diesel engine.
As a lubricant the• effect of petroleum upon the development of power is fast coming to be almost as important as its effect as a fuel. Modern methods of utilizing many kinds of power demand high, speed machinery like dynamos, motors, automobile and airplane engines, and many machines in factories. Such machinery must be lubricated with high-grade oils, and petroleum is the only good source of such oils. Hence without petroleum many of our present uses of power would be impossible.
(4) Why Petroleum Should be Used Sparingly.—$y its very nature petroleum tends to rapid exhaustion. At first, when a source of oil is tapped, the gushers often waste a great deal, later they merely flow gently, next they cease to flow naturally, and must be pumped, and finally the wells that are pumped give a smaller and smaller out put. A well that lasts a generation is rare. In spite of the drilling of new wells, the yield of the Pennsylvania field has fallen from 33,000, 000 barrels in 1891 to only 7,000,000 in 1917. Pennsylvania, which in 1890 ranked as the world's greatest producer, was in 1917 exceeded by Oklahoma, California, Texas, Illinois, Louisiana, Kansas, West Virginia and Ohio among the American States, as well as by foreign regions such as the Tampico and Baku fields. The way in which production changes is well illustrated in the table on page 197.
The demand for petroleum, especially for automobiles and for lubricants, is increasing enormously. If the present conditions con tinue it will be only a few decades before the supply will be largely exhausted. So far as fuel is concerned this will not be serious, for
wood alcohol made from the abundant vegetation of the torrid zone can take the place of gasoline, and coal can do all that is done by the cruder forms of petroleum. For lubricants so essential to power, however, we know of no good substitute. If they should become scarce and high priced it would cause great inconvenience and ex pense. It is a serious question whether the country ought not to take steps to prevent the consumption of oil where other substitutes are available, such as coal on warships, hydro-electric power on rail ways, and alcohol in automobiles.
A somewhat hopeful feature of the situation is that vast beds of shale in Colorado, Scotland and many other regions are impregnated with oil. This can be extracted by heating the shale, but the proc ess is costly. Hence Scotland is the only country where there has thus far been large production, and the oil shales will probably be available long after the liquid petroleum is largely exhausted.
How Petroleum Influences Human Activity.—In its effect , on man the geographical distribution of petroleum is much less impor tant than the distribution of coal. If its value for fuel had been known earlier it might have caused manufacturing cities to grow up where it occurs, but now this rarely happens. This is partly because petroleum is so easily transported, and partly because towns in oil producing regions are generally disagreeable. Even the better resi dential portions usually smell of oil, while the parts where most of the people must work are very dirty and greasy. Slimy, oil-covered pools are scattered among black, forbidding derricks. Another reason why manufacturing centers do not grow up around oil wells is that such places are not permanent. Like " boom " mining towns, they usually grow for a few decades and then decay as the oil gives out.
The most important effect of petroleum upon man is the way in which it has led to two great improvements in machinery: (1) It has made all sources of power much more effective by making it possible to use high-speed machinery, requiring cheap, heavy lubri cants. (2) It has led to the invention of the light engines which are necessary for the automobile and especially the airplane. If there had been no such thing as cheap, easily combustible kerosene and gasoline it is doubtful whether we should have had these means of transportation for generations. When the world's petroleum is practically exhausted and its place taken by alcohol and other sub stances still to be invented, future generations will still owe to petro leum one of the most important advances in transportation.