Oil refining of the day—and into the first years of the 20th century—relied on a relatively simple distillation process that separated crude oil into portions, called fractions, of different hydrocarbon compounds (molecules consisting of varying arrangements of carbon and hydrogen atoms) with different boiling points. Distillation process of chemicals. The process of distillation starts when a liquid is heated to boiling point. The liquid starts to evaporate, by appearing in a vapor form. Distillation is expended to detach liquids from nonvolatile solids, as in the separation of alcoholic liquors from fermented materials, or in the separation of two or more liquids with distinct boiling points, as in the separation of gasoline, kerosene, and lubricating oil from crude oil.