The pipes go over hills and through swamps. They cross rivers sometimes by means of bridges, and sometimes they are anchored to the bed of the stream. If they have to go through a salt marsh, they are laid in concrete to preserve the iron. If these lines were suddenly destroyed and oil had to be carried in the old way, kerosene would become an expensive luxury.
Getting the oil out of the ground and carried to the refineries is not all of the business by any means. The early oils crusted on the lamp wicks, their smell was unendurable, and they were given to exploding. Evidently, if oil was to be used for lighting, it must be improved, and the first step was to distil it. To distil anything means to boil it and collect the vapor. If you hold a piece of cold earthenware in the steam of a teakettle, water will collect on it. This is distilled water, and is purer than that in the kettle. Petroleum was at first distilled in a rough way; but now it is done with the utmost care and exactness. The crude oil is pumped into boilers holding six hundred barrels or more. The fires are started, and the oil soon begins to turn into vapor. This vapor passes through coils of pipe or long, straight, parallel pipes. Cold water is pumped over these pipes, the vapor turns into a liquid again, and we have kerosene oil.
This is the outline of the process, but it is a small part of the actual work in all its details. Kerosene oil is only one of the many substances found in petroleum. Fortunately, some of these substances are light, like gasoline and benzine; some, like kerosene, are heavier; and paraffin and tar are heaviest of all. There are also gases, which pass off first and are saved to help keep the furnace going. Then come the others, one by one, according to their weight. The stillman keeps close watch, and when the color and appearance of the distillate changes, he turns it off into another tank. This process is called "fractional distillation," and the various products are called "fractions." No two kinds of petroleum and no two oil wells are just alike, and it needs a skillful man to manage either.
Even after all this distillation, the kerosene still chars the wick somewhat—which prevents the wick from drawing up the oil properly—and it still has a disagreeable smell. To fit it for burning in lamps, it must be treated with sulphuric acid, which carries away some of the impurities, and then with caustic soda, which carries away others. Before it can be put on the market, it is examined to see whether it is of the proper color. Then come three important tests. The first is to see that it is of the proper weight. If it is too heavy, it will not burn freely enough; if it is too light, then there is too much of the lighter oils in it for safety. The second test is the "flash test." The object of this is to see how hot the oil must be before it gives off a vapor which will burn. The third, the "burning test," is to discover how hot the oil must be before it will take fire and burn on the surface. Most civilized countries make definite laws forbidding the sale of kerosene oil that is not up to a standard of safety. Oil for use in lamps should have an open flash test of at least 100° F. and a burning point of not less than 125° F.
We say that we burn oil in our lamps, but what we really do is to heat the oil until it gives off gas, and then we burn the gas. To keep the flame regular and help on the burning, we use a chimney on the lamp. The hot air rises in the chimney and the cold air underneath rushes in to take its place and brings oxygen to the flame. In a close, stuffy room no lamp will give a good clear light, because there is not oxygen enough for its flame. Let in fresh air, and the light will be brighter. If you hold a cold plate in the flame before the chimney is put on, soot or carbon will be deposited. A lamp gives light because these particles of carbon become so hot that they glow. In lamps using a "mantle," there is the glow not only of these particles, but also of the mantle. In a wax candle, we light the wick, its heat melts the wax and carries it to the flame. When the wax is made hot enough, it becomes gas, and we burn the gas, not the wax. Wax alone will melt, but not take fire even if a burning match is held to it. The reason is that the match does not give heat enough to turn the wax into gas. But put a bit of wax upon a bed of burning coals, where there is a good supply of heat, and it will turn into gas and burn.
The products made from petroleum are as different in their character and uses as paraffin and naphtha. Some of them are used for oiling machinery; tar is used for dyes; naphtha dissolves resin to use in varnish; benzine is the great cleanser of clothes, printers' types, and almost everything else; gasoline runs automobiles, motors, and many sorts of engines; paraffin makes candles, seals jelly glasses, covers the heads of matches so that they are no longer spoiled by being wet, and makes the ever-useful "waxed paper"; printers' ink and waterproof roofing-paper both owe a debt to petroleum. Even in medicine, though a little petroleum is no longer looked upon as a cure-all, vaseline, one of its products, is of great value. It can be mixed with drugs without changing their character, and it does not become rancid. For these reasons, salves and other ointments can be mixed with it and preserved for years.