There is also a large amount of oil produced in the United States, mainly in Pennsylvania, which is of a character especially suited to the production of high grade lubricants by a simple refining method. With oil of this character the lubricating constituents do not require distillation to separate them from impurities. The crude petroleum may be directly reduced by distillation, taking off the three major fractions, that is, gasoline, kerosene and gas oil, and leaving behind in the still a very good grade of lubricating oil which, however, contains paraffine wax. To separate this wax from the lubricating oil, in which it is dissolved, an ingenious process called cold settling is resorted to. According to this process, the mixture of lubricating oil and wax is diluted with gasoline, enough gasoline being employed to make a very thin liquid, and the mixture is then chilled to a low temperature. From the chilled mixture the paraffine separates out in the form of a thick grease which settles to the bottom of the chilling tank. This grease is subsequently refined to produce the various grades of petroleum jelly. The lubricating oil diluted with naphtha and separated from the paraffine or grease as described is subjected to re-distillation for the separation of the naphtha and forms a base for the production of a wide variety of high grade lubricants. Returning to the analogy by which we compared crude petroleum oil to crude gravel mined from the hillsides, it will be noted as in the case of the gravel, the various crude petroleums differ in character considerably, according to their origin, and that the refining process must be modified to suit the character of the oil. The analogy may be pursued one step further to explain one of the most interesting developments of the modern petroleum industry, i. e., the manufacture of gasoline not naturally contained in crude petroleum. This process of _manufacturing gasoline_ is called “cracking.” Let us assume that we desire to obtain from crude gravel, mined from the ground, a maximum amount of fine gravel. We would first use all of the fine gravel which was naturally contained in the crude gravel and then we might pass the remainder of the gravel, which is too large for our use, through crushing rollers which would crush or crack it, thus producing an additional quantity of fine gravel. An analogous process has now been successfully developed for the treatment of petroleum oils. According to this process, a heavier constituent of the crude petroleum oil, for example, kerosene or gas oil, may be subjected to distillation at high temperatures, and under high pressure in special stills designed for this process, thus securing increased quantities of gasoline. In this operation a certain proportion of the heavier oil treated is caused to break down into gasoline. The U. S. Bureau of Mines estimates that in 1919 some 15% of the country’s total gasoline production was obtained by this process.