Definition of ‘Area’ in Contact Catalysis

Abstract

IT is evident that the apparent area of an irregular surface will depend on the size of the object used for measuring it. This has been clearly expressed by Constable (NATURE, Sept. 15, p. 399), the ‘maximum’ area of a surface being defined as that of “the envelope of the monatomic film of hydrogen atoms closely packed, all in contact with each other and with the catalyst, and completely covering it”. This, as an arbitrary definition of area, is a useful one, though it is questionable whether it has any real physical significance, the work of Davisson and Germer on the diffraction of electrons indicating that the packing of gas atoms adsorbed on a metal surface follows that of the metal atoms in the crystal lattice.