GASOLINE, a colorless, inflammable liquid, one of the lighter distillates of petroleum. In early use it was a general name for all the lighter oil ranking above kerosene, but as mineral oil came to be separated into a larger number of grades, of varying specific gravity, gasoline became the accepted name for distillate having a specific gravity between .629 and .667 (of 95° to }hurtle scale). The generally accepted European name for the same distillate is petrol. Gasoline has become of great com mercial importance as the most convenient source of vapor for internal-combustion engines of the types used in automobiles, motorcycles, aeroplanes, etc. The continued increased de mand forced u the price 70 per cent between J July 1914 and July 1916.
Crude petroleum, under ordinary methods of distillation, yields but a small percentage of gasoline, and the increased demand stimulated effort to increase the supply, and improved processes are now yielding a much enlarged production of this valued distillate.
Gasoline, like all other products of crude petroleum, was for a long time disposed of as waste in the effort to make kerosene ; it was there and had to come out. In the latter sixties it was exported to Europe in small quantities. Representing nearly the lightest portion of crude oil, gasoline is extracted by distillation, just as whisky is produced, and in 'much the same sort of apparatus. The stills or retorts may be of any shape and size; both are imma terial, and practice has differed. They may be cylinders placed horizontally and in banks, or cylindrical or conical, standing perpendicular and having curved domes. Rectification is ef fected by a copper coil, many feet in length in side the retort passing through the crude petroleum, carrying steam at a high pressure, assisted by a gentle direct fire varying from 122° to 257° F. Each retort has .an inlet pipe for the crude petroleum and an outlet pipe for the distillant. The outlet pipe passes over the side and down to a cooling coil or worm immersed in cold running water. This worm acts as a condenser that changes back to liquid form the vapors driven off the petroleum by the heat. A smaller pipe leads from the condenser to a re ceiver having glass sides through which the °still-man° can watch the flow of distilled oil. From the bottom of the receiver a number of pipes lead to different storage tanks, each pipe having a cut-off valve to regulate the flow of the varying gravities to their proper tanks, each cut-off being known as a °sweeping.° The first product from the retort is a gas formed by the mingling of the fumes of the petroleum with the small volume of air left in the reservoir; this is sometimes conveyed to the fire-box and used as fuel. When the first flow of the distil lant reaches the receiver, the still-man tests it with a Batumi hydrometer for its specific grav ity. Usually, this first flow is found to be about .90 specific gravity. It is of a highly volatile nature, so nearly a gas that when exposed to air it rises in an invisible vapor and will quickly evaporate. It cannot be confined for any length
of time in barrels, even if they have been sue cessively coated inside with wax and repeatedly painted outside to make them air-tight. Even in the coldest weather it will pass through the wood. For these reasons this gravity is not put out commercially, but is used to bring up the gravity of a mass made up of lower gravities; that is to say, if .88 is being tanked the still man lets all the .90, .89, .88 and enough of the .87 gravity oil flow into the receiver to make an average mixture of the density wanted. The oil is repeatedly tested with the hydrometer until the right gravity has been produced in the receiver, when it is let off to the proper storage tank. If .82 is the next grade wanted, all the gravities from .86 down to perhaps .78 are commingled in the receiver until a uniform fluid of the required gravity is obtained to let off into its tank. This process is called If rac tioning,° and is continued through the next dis tillant, down to about .42 specific gravity.
When the demand for more gasoline began to press upon the petroleum industry, it was at first met by the recovery of more °casing-head gas.° Natural gas and petroleum come from the same wells, usually on the first flow the gas being in the excess, for it is simply the vapor of petroleum. Much natural gas is lost from new wells, but it is possible to conserve a large part of the lighter product at the casing-head or mouth of the well, and much of the light oil, in a condition closely approaching gas, is now retained in the casing-head and drawn off for distillation into gasoline.
About 1913 the °cracking° process of pro ducing gasoline began to come into use, being first exploited as a secret process; but its prin ciple has gradually become known and it is now generally practised by oil refiners. Crude oil which has yielded its product of gasoline and other of the lighter distillates by the ordinary methods, is confined in a vessel and subjected to both heat and pressure, which breaks up the hydrocarbons or ucracks' the oil. One author ity gives 932° F. as the proper temperature and 50 to 75 pounds the proper pressure for crack ing oil to secure gasoline. In a preferred form of cracking apparatus the top and walls of the cylinder containing the oil are lined with steel balls, placed in layers. The oil is vaporized in passing out through the mass of hot balls, and released by a valve into an upper gasoline tank. Another type of cracker heats and compresses the oil in a coil or tube, which is so arranged that the production is continuous. It is a pe culiarity of the cracking process that it may be repeated many times, and more gasoline is formed every time. Even the heavy oil paraf fine can be cracked into crude oil, and the crude oil cracked into gasoline. The cost of crack ing is not prohibitive, and it appears to have settled the problem of gasoline supply.