For several decades clays have been used for decolorising mineral oils. Asimple method is percolation of the oil through a layer of clay. Some twentytimes the amount of oil is usually treated with such a layer. The first oilfiltered through the fresh clay is much more changed than the rest of theoil. It has a very light colour and its low refractive index indicates ahigh content of paraffinic and naphthenic hydrocarbons.

Most of the aromatic hydrocarbons are left behind in the clay. This suggestsadsorption analysis of oils using clay in the same large quantities thathave been successful with other adsorbents (Mair and White, 1935;Willingham, 1939; Allibone, 1941). Quantities of the order of 100 gm.alumina per gm. hydrocarbon were used by Winterstein and associates (1934)when separating a number of aromatic hydrocarbons.