A few years ago, a Californian chemist invented an improvement of the principles of maximum heating and evaporating surfaces. His name was Trumble, and the process is known as the Trumble process. The crude oil is heated to the desired temperature in pipes or retorts set in a primary furnace, the hot gases of combustion from which are utilized to heat the distillation chamber proper. Entering the vertical cylinder at the top, the oil is spread over and through perforated plates falling on a cone-shaped plate to divert the continuous stream of oil to the sides of the still, down which it flows in a thin film. Other conical plates, arranged at intervals underneath, maintain the flow in the desired channel until it reaches the outlet at the bottom. When 60 or 70 per cent. (comprising the motor spirit series, the kerosenes, and perhaps the intermediate fractions) are to be removed, it is common practice to distil the crude oil in a series of stills, cylindrical in shape, connected continuously. The best-known system is that patented 35 years ago by Mr. Henderson, of the Broxburn Oil Company, Ltd., for the distillation of shale oil, and since adopted by many refiners of petroleum. In this system, the crude oil flows from a charging tank by gravity through a pre-heater, heated by the passage, from the second or other still, of distillates of suitable temperature, and thence into the first still. Here it is raised to distillation temperature, and the specific gravity of the distillate therefrom fixed. The feed of the crude oil is constant, the residue formed in the still passing through a connection at the bottom into the second still in the series, at the top, and led from back to front so that the inlet and outlet shall be as far apart as possible. It is here raised to a higher temperature, yielding a distillate of higher specific gravity, the residue passing on to the next still, and so on through the series of stills until it reaches the point where all the motor spirit (or benzine, as it is called), kerosene, and the intermediate distillates are removed. The distillates obtained from the refining of the crude are usually purified by treatment successively with sulphuric acid and solution of caustic soda, this process of chemical treatment being necessary before the products are fit for the market.