Abstract: A detecting material to detect formaldehyde at low concentration in the atmosphere in a short time is prepared by impregnating a base material containing at least silica gel with a coloring liquid containing 4-amino-4-phenyl-3-ene-2-one and a buffer solution and volatilizing the solvent.

Abstract: A detecting material to detect formaldehyde at low concentration in the atmosphere in a short time is prepared by impregnating a base material containing at least silica gel with a coloring liquid containing 4-amino-4-phenyl-3-ene-2-one and a buffer solution and volatilizing the solvent.

Abstract: A vacuum switch apparatus has an electrically insulating vacuum enclosure which is evacuated to a vacuum degree of 2.times.10.sup.-2 Torr or less. One set of anode and cathode electrodes is arranged in the vacuum enclosure, having capacity which permits the flow of a discharge current of at least 1 KA therebetween and being operable to switch the discharge current at least 10.sup.6 shots. A high voltage power supply applies a high voltage of at least 20 KV across the anode and cathode electrodes. An electron beam irradiation unit irradiates an electron beam on the anode electrode through the cathode electrode. A control electrode is arranged between the beam irradiation unit and the cathode electrode, for controlling passage and interception of the electron beam. A control voltage power supply applies a control voltage to the control electrode.