The refining process above described is that which is most largely employed in this country, being a typical process for obtaining gasoline, kerosene, gas oil, lubricating oils and paraffine wax from the grade of crude petroleum produced from the central and central western states of the United States. The process is considerably varied, however, in dealing with crude petroleum of different characteristics. For example--there is produced in Mexico and imported into this country for refining in the plants located on the Atlantic Coast a very large amount of petroleum oil which is little more than thin asphalt. Oil of this character is not generally used for the production of lubricating oils or wax, but is instead merely refined for the production of gasoline, kerosene, and fuel oil, or for gasoline and fuel oil only. It will be understood that the term “fuel oil” merely indicates any heavy petroleum oil free from dirt and water, and fluid enough to be readily pumped through a pipe, and containing no constituents which would make it apt to give explosive mixtures with air. Fuel oil of this description is largely replacing coal as a fuel for steamships. The State of California produces a considerable quantity of this “asphalt base” crude petroleum, which, like the crude petroleum from Mexico, is subjected to refining processes very much simpler and yielding mainly gasoline, kerosene and fuel oil. It is usually also from crude petroleum of this character that the artificial asphalts which supplement the supply of natural asphalt for paving material are produced. These artificial asphalts in general represent the heavier constituents of crude petroleums, such as those of Mexico and California. The term artificial asphalt is perhaps a misnomer, for, although the properties of the asphalt are somewhat modified by the refining operation, the asphalt exists as such in the crude petroleum oil and the main purpose of the refining operation is merely to separate it from the fluid constituents of the oil in which it is dissolved.