DESPITE the great amount of experimental work in the past twenty years on the physical adsorption of gases by solids, the effect of a chemisorbed film on the subsequent physical adsorption of other gases has never, to our knowledge, been thoroughly investigated. However, occasional observations have been noted, particularly in connexion with the Brunauer–Emmett–Teller surf ace-area measurements1; and the general conclusion has been that the presence of a chemisorbed film does not affect such measurements, provided that there is no blocking of capillaries, as might occur on a porous solid2. The following observations may therefore be of interest.