Experimental measurement of adsorption

3 For a recent theory of polymolecular adsorbed layers, with references to older theories, see Bradley, J.C.S. (1936), 1799. 

Freundlich,1 Rideal,2 and Hiickel3 have summarized the results of adsorption measurements on porous substances. Very roughly, it may be said that the ease of adsorption is proportional to the ease with which the gases can be liquefied, a fact which has been held to indicate that there is sometimes actual condensation of vapour in the smallest pores. Numerous empirical formulae, of which Freundlich s equation ( 9) is the best known, have been developed, but. none seem to fit the data with any accuracy over a considerable range of pressures. 

It is not too much to say that, at the present time, increased delicacy of measurement, with the use of simple surfaces, would be of far greater value than the multiplication of measurements on porous, highly adsorptive powders. 

Very careful outgassing of the glass is necessary in this w ork, since the adsorptive capacity of the glass vessels is usually far greater than that of the surfaces being studied. 

The weight of gas adsorbed is sometimes measured, and for this purpose various kinds of microbalance have been used. McBain s sorption balance consists of a delicate helical quartz spring,5 suspending the adsorbing solid the upper end of the spring is fixed, and the lower end observed with a cathetometer. Bradley6 has used a balance with a beam, supported in the centre by a fine horizontal quartz fibre and references to other types of balance are given by McBain.7 

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