Engineering Wonders of the World
Volume I

336 ENGINEERING WONDERS OF THE WORLD. Wells that have ceased to flow of their own accord can sometimes be induced to do so by means of compressed air. This method of raising the oil is known as the The “A- i •#+ »» “ a*r lift” system, and con- /ill a sists of forcing air under con- siderable pressure through a column of 4-inch tubing to the bottom of the well. Inside this is another column of lesser diameter, up which the aerated oil rises to the surface. In effect the process is that of substituting compressed air for natural gas, but it can be applied to wells only where the level of the fluid stands high. DISTILLATION AND REFINING. Petroleum in its crude state is not often suitable for commercial purposes, although some heavy oils containing a small proportion of light products are used just as they come from the ground as fuel for steam-boilers ; while in certain parts of America some natural lubricating oils occur. The mineral product is a mixture of hydro- carbons, not infrequently containing traces of sulphur, oxygen, and nitrogen. The composi- tion, however, of the hydrocarbon constitu- ents is so complex that rarely will two oils from different fields yield a similar analysis. On the other hand, the very difference in the densities and boiling points of these renders it possible to separate petroleum into a series of mixtures with certain char- acteristics by distillation. To do this the oil is passed into a large still, from whose upper surface a pipe leads to a condenser. When heat is applied the more volatile constituents, such as benzine, gasoline, etc., pass off first as vapour, and are caught and condensed. As soon as these lighter con- stituents have all been given off, the heat is increased, so as to drive over the illuminating oils present. At this point distillation is often stopped unless lubricating oils are sought for. To obtain these more heat is required, and super- heated steam is admitted to ensure adequate circulation of the oil in the still. The steam serves the further purpose of preventing “ cracking,” or the decomposition of the heavy hydrocarbons into lighter varieties. There are, however, certain oils in whose treatment “ cracking ” is encouraged, since it reduces the density of the hydrocarbons and increases the quantity of the illuminants derived. Thus oils, having a specific gravity of from •860 to -880—such as those of the Eastern oil fields of the United States—are treated for the benzine and kerosene, both of which are in large proportions. On the other hand, the heavy oils of California, Texas, and Russia derive their main value from the heavy residuum, which is particularly suitable for liquid fuel. Benzine is often redistilled by steam heat, and divided into grades of spirit of specific gravities ranging from -680 to '740. These constitute the various kinds of spirit or “ petrol” that are generally used for motor cars. The distillates that are intended for use as lamp oils require chemiqal treatment or re- fining, in order that certain impurities may be removed. The effect of these, were they not eliminated, would be to cause the flame to smoke badly, and give off a disagreeable odour. The chemical process is too complex to be dealt with in this article. THE TRANSPORT OF PETROLEUM. Oil fields are often located a long distance from commercial centres and from points convenient for the establishment of refineries and for distribution. Originally railway tank cars were much used for the conveyance of the crude oil to refineries or consumers, but they have now given way largely to oil pipe lines. In America there exists a wonderful and complete