The swelling of charcoal. Part II.—Some factors controlling the expansion caused by water, benzene and pyridine vapours

Abstract

The experiments described in Part I of this series led to the conclusion that the expansion which charcoal undergoes in contact with water vapour, carbon dioxide, ammonia, and sulphur dioxide is connected with the existence in the adsorbed phase of a pressure due to the free movement of the molecules in directions parallel to the interface. In a later paper it was pointed out that if the relation between the percentage linear expansion ( x ) and the surface pressure (F) be assumed to take the form x = λ F, (1) where λ is a constant, then the equation found empirically to relate the ad­sorption and expansion in the case of these gases reduces to an expression of the Schofield-Rideal equation of state: F (A – B) = i RT. (2) Here A stands for the area per (gram) molecule, and is equal to M∑/ s if s is the weight in grams of an adsorbate (of molecular weight M) taken up by 1 gram of charcoal the effective surface area of which is ∑; B is the “incom­pressible” cross-sectional area per gram molecule; and i is a constant determined by the mutual cohesion of molecules and is equal to unity when such cohesion is absent.