untreated catalyst. The resistance of zeolites to attack by (or dissolution in) aqueous acids follows the same order.At lower temperatures (<210°C) the activity of NaY for the decomposition of the secondary ester remained constant. Constant activities were observed for silica-aluminas with the normal ester at 190°C (Sanyal and Weller, 1971), but our sample of silica-alumina aged at 190°C in the decomposition of the secondary ester. The activity of AgY increased slowly with time in the decomposition of the secondary ester at 140-170°C. Apparently, the silver ion is reduced to metallic silver by the reactant or products, and the zeolite is transformed to the hydrogen form.