=Refining Crude Oil.=--The crude oil is purchased by refiners and treated to produce “yellow oil.” In this process it is put into a tank (it is generally considered profitable to refine cotton seed oil only in large quantities) supplied with a revolving agitator. Into the tank is put a solution of eighteen to twenty per cent caustic soda. The quantity and strength of the solution necessary is determined by treating a small sample. To a small sample of oil add the soda solution, stirring continuously, having it heated to a temperature of 160° to 180° F. When sufficient soda lye has been added a floculent precipitation will be noticed. This indicates a “breaking” of the oil. By calculation of the relative amount the comparative quantities can be arrived at. An excessive amount of lye will saponify its equivalent in good oil, therefore care must be exercised to see that only the proper amount is used. In a practical way the soda is introduced in the crude oil solution and agitation is started to insure the thorough mixing of the caustic soda and the oil. The floculent substance appearing, the agitation is stopped and the oil allowed to settle, the sediment and substance other than oil collecting at the bottom of the tank. A small quantity (about one-quarter of one per cent by weight) of fullers earth is added and the oil removed by pumping through a filter press producing what is known to the trade as “yellow oil.” The sediment, known as “foots” is collected in kettles and treated with additional lye, boiled and settled with salt; water added, settled and drawn. This treatment is duplicated as many times as necessary, until the soap stock will separate from impurities. When thoroughly settled draw the soap stock into packages for the soap trade. The finished “foots” contains about 33 to 40 per cent of moisture and a small percentage of lye. =Deodorizing Cotton Seed Oil.=--The “yellow oil” of trade has a decided flavor which it is desirable to remove, and this process is accomplished by deodorizing. (See Fig. 155.) _Treating Tank._--This tank is equipped for heating the oil to a very high temperature by the introduction of a large coil surface, preferably rings, one within the other and arranged so that each ring is accessible. The kettle coils, etc., should be made extra heavy. The top of the kettle must also be hooded and as the oil boils violently the steam must be given free opportunity to escape. The escape pipe should be at least sixteen to twenty inches in diameter in a tank six feet in diameter, and should be provided with a goose neck, so that the steam rising which condenses, does not drip back into the tank. Fig. 155 show the construction of an oil treating tank.