For several decades clays have been used for decolorising mineral oils. A
simple method is percolation of the oil through a layer of clay. Some twenty
times the amount of oil is usually treated with such a layer. The first oil
filtered through the fresh clay is much more changed than the rest of the
oil. It has a very light colour and its low refractive index indicates a
high content of paraffinic and naphthenic hydrocarbons.
Most of the aromatic hydrocarbons are left behind in the clay. This suggests
adsorption analysis of oils using clay in the same large quantities that
have 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.