Abstract
EVAPORATION of metals on to the walls of a glass tube at room temperature is known to yield films of high catalytic activity in many instances. In the case of tungsten a film of apparent area 140 cm.2 and estimated weight of order 1 mgm. was found1 by two methods to possess an area of 450 cm.2. It was concluded "that the film was probably not microcrystalline to any great extent", but this conclusion is now found to be invalid. These results, together with other data, are best explained by assuming that the film is microcrystalline, in accordance with the results of electron diffraction2. The crystallites of a sputtered platinum film have a side of â¼ 0·005µ by the latter method. Taking a simple model of equal spheres exposing all their surface to the reacting gas, we calculate for the above tungsten film a crystal diameter of 0·007µ. By itself, of course, the chemical evidence cannot decide whether the particles are crystalline or amorphous.
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