The electrical condition of hot surfaces during the adsorption of gases. Part III.—A platinum surface at temperatures up to 850° C

The experimental results on the electrical charging of gold, silver and nickel surfaces, as set fourth in Parts I and II of the present series, have led to the conclusion that there are at least five different types of adsorption of a gas on a hot metallic surface, each of which can be clearly defined in terms of the nature of the charge on, and the tenacity with which such charge is retained by, the surface. In three such cases the adsorbed gaseous molecules are in an active, electrically charged condition. Before the full significance of these observations in their bearing upon the nature and mechanism of heterogeneous catalysis can be properly appreciated it will be necessary to accumulate systematically further facts relating to the electrical condition of hot surfaces; and with this object the investigation is being extended to a variety of different surfaces. An account is given below of the experimental results obtained with a platinum surface at temperatures up to 850° C.Experimental . The apparatus used and the experimental procedure followed was as previously described. Platinum specially supplied by Messrs. Johnson and Matthey, and stated by them to contain over 99·5 per cent. Pt and to be free from non-platinum metals, in the form of a 22 S. W. G., 6 by 10 cm. sheet, to which was fused a 25 S. W. G. similar platinum wire, was employed and will be referred to in what follows for the sake of brevity as the surface. The charges were measured by means of a Lindemann quadrant electrometer.