Abstract: A gas detection apparatus with a gas detection element of which the electric resistance changes in accordance with a gas constituent, especially oxygen, in exhaust gas, wherein a fixed voltage is applied to a series circuit of the gas detection element and the reference resistor, and from the voltge at the voltage dividing point between the gas detection element and the reference resistor it is detected whether the gas constituent has exceeded a predetermined range or not. The gas detection apparatus includes a plurality of comparators each for comparing the voltage at the voltage dividing point with a corresponding one of the reference voltages to generate a comparison signal, and a logic circuit responsive to the rise or fall of the comparison signals showing that the gas constituent has exceeded a predetermined range.

Abstract: A self-hardening composition for making sand molds comprising a molding sand, a water glass as a binder and at least one salt of imidodisulfonic acid as a hardener.

Abstract: A catalyst for purifying exhaust gas from vehicles comprises a monolithic carrier having a plurality of exhaust gas passages penetrating through the carrier, a layer of active refractory metallic oxide such as .gamma.-alumina, containing 1 to 20% by weight of a catalytic metal such as platinum deposited as first layer on inside surfaces of said plurality of the passages, and a layer of exhaust gas-permeable refractory metallic oxide such as .gamma.-alumina free from a catalytic metal deposited as an outermost layer further upon the first layer.