Polarization curves of the hydrogen evolution reaction are presented for rhenium and niobium electrodes in dilute hydrochloric acid solutions as a function of temperature. The Tafet reaction is the rate-determining step in the hydrogen evolution reaction on rhenium. The behavior of niobium electrodes is much more complicated. The presence of the passive oxide layer on niobium produces an ohmic contribution to the total overvoltage. The corrected activation-overvoltage curves for niobium show a change of Tafel slope which is consistent with a Volmer-Tafel mechanism if certain assumptions are made about the distribution of potential at the interface. Activation energies of the hydrogen reaction are computed for both rhenium and niobium electrodes.Comparatively few studies on the electrochemical behavior of rhenium and niobium electrodes have been reported. Pecherskaya and Stender (1) measured hydrogen overvoltage on rhenium. Hydrogen overvoltage on niobium was studied by Bockris (2), by Kononchuk and Barmashenko (3), and by Rotinyan and 1Present address: ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 139.80.123.38 Downloaded on 2015-03-15 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 139.80.123.38 Downloaded on 2015-03-15 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 139.80.123.38 Downloaded on 2015-03-15 to IP

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PROPERTIES OF SUPPORTED METALLIC CATALYSTS 2783 4. .The solubility curves of magnesium sulfate hexa-, penta-and tetrahydrate have been studied a t 85,95 and 100'.The preparation of the hexa-, penta-, tetra-, di-, five-fourths and monohydrates of magnesium sulfate has been discussed, together with their identification with the aid of the petrographic microscope, and new optical data for the hexa-, penta-, tetra-, di-and five-fourths hydrates have been given.It has been suggested that there is a relation between the degree of crystallographic perfection exhibited by a salt and the rate a t which it comes to equilibrium with its aqueous solution, 6.