Abstract: An apparatus for enriching dissolved oxygen in water which comprises a plurality of dissolving devices, each of which comprises: (a) a pair of vertically arranged tubular bodies, the lower end of the first tubular body being provided with an inlet through which raw water is introduced and the lower end of the second tubular body being provided with an outlet for discharging oxygen enriched water; (b) a tube connecting the interior of both tubular bodies at the central portions thereof; (c) a bubbler disposed in the interior of the first tubular body for flowing an oxygen enriched gas into the raw water and for moving the raw water into the second tubular body through the connecting tube; (d) a pipe for connecting the top portions of the tubular bodies which form a chamber for the gas above the liquid level of the raw water in each of the tubular bodies; (e) a means for supplying an oxygen enriched gas into the chamber in the second tubular body; and (f) a means for supplying the gas in the chambers to the bub

Abstract: A reduction catalyst is disclosed. This catalyst comprises a naturally-occurring inorganic material which is a tuff consisting essentially of SiO.sub.2, Al.sub.2 O.sub.3 and H.sub.2 O containing 1-10% by weight of an alkali metal oxide and an alkaline earth metal oxide and has an X-ray diffraction pattern as shown in Table A or Table B. It is produced by depositing of the tuff metal ions selected from the group consisting of a metal belonging to Ib Group, IIb Group and VIII Group of Periodic Table, chromium, vanadium and manganese, followed by heat treatment, and repeating the same using different metal ions on each occasion. The catalyst is useful as a reduction catalyst for nitrogen oxides.

Abstract: The oxidation catalyst of this application is prepared by grinding and heat treating the tuff consisting essentially of SiO.sub.2, Al.sub.2 O.sub.3 and H.sub.2 O, and containing a total of 1 to 10% by weight of an alkaline metal oxide and alkaline earth metal oxide and having the X-ray diffraction pattern shown in the Table I or Table II. This catalyst eliminates NO in a dry exhaust gas which contains at least a small amount of oxygen.