Addnl. data considered in abstracting and indexing are available from a source cited in the original document. The effect of varying the feed concn. as a periodic rectangular function was studied in the hydrogenation of C2H4 in a fixed bed of an Al2O3-Pt catalysts. The C2H4 conversion clearly depends on the frequency and passes through a max. of ?60% above that of steady operation. The absorbing equil. const. was not affected by the unsteady operation, but the effective rate constant was .apprx.50% higher, because of higher catalysts activity. The strong dependence of the conversion on the frequency is explained by the reaction kinetics and quant. fixed by the calcn. [on SciFinder (R)]