Abstract:
Adsorption occurs when two heterogeneous phases are in contact, and when there is an increase of concentration of the molecules at the interface, caused by a condensation in the surface layer of the adsorbent. Freundlich (J.C.S. Abs ii 1907, p. 155) puts forward the view that adsorption is caused by an alteration in the surface tension between the solid and the liquid Substances which lower the surface tension will cause adsorption, and vice-versa.
The commercial uses of adsorption are very wide, and are of far reaching importance. The different types of gas masks used for protection against noxious gases depend upon adsorption by a suitable charcoal, usually animal charcoal. Adsorption is used in the decolorisation of raw sugar by animal charcoal, in the use of Fuller's earth for clarifying fats, and the use of bauxite for the removal of the last traces of sulphur from petroleum. The retention of organic and inorganic salts in the earth is largely due to adsorption caused by the colloidal nature of the soil. Langmuir (Far. Soc. Trans. 1922 (XVII) p. 3606) has investigated the phenomenon of heterogeneous catalysis and has shown that it is due to the adsorption of the reacting molecules on the surface of the catalyst. The first organised work on adsorption from solution was done by Freundlich (J.C.S. Abs ii 1907, p. 155). He investigated the adsorption of both organic and inorganic compounds from different solutions. Since this, a large amount of work has been done by various investigators on the conditions of equilibrium in adsorption from solutions. Also in recent years, a considerable amount of work has been done on the adsorption of vapours.
