Abstract: A gas sensor has a gas-sensing component which changes color and/or conductivity on exposure to certain gases, which component comprises a (mono, di or tri) azatetrabenzoporphyrin. Certain (mono, di or tri) azatetrabenzoporphyrins containing a transition metal ion selected from chromium (III), vanadyl, manganese, cobalt or iron (III) are novel.

Abstract: A gas sensor has a gas-sensing component which changes color and/or conductivity on exposure to certain gases, which component comprises a (mono, di or tri) azatetrabenzoporphyrin. Certain (mono, di or tri) azatetrabenzoporphyrins containing a transition metal ion selected from chromium (III), vanadyl, manganese, cobalt or iron (III) are novel.

Abstract: A method and apparatus for welding together two metal workpieces, at least one of which has thereon a coating material which enters a fluid or visco-elastic phase at a temperature below the melting temperature of the workpieces, the method comprising the steps of subjecting the workpieces to a preliminary preparative treatment at a zone to be welded and thereafter applying (preferably be means of a high-energy beam such as a laser beam) sufficient heat to the workpieces at the weld zone to effect there the welding together thereof, wherein the preliminary preparative treatment comprises preheating the workpieces to the said lower temperature and pressing them together, at the zone to be welded with a force sufficiently great to expel coating material from between the workpieces at the weld zone. thereby to improve the quality of the subsequent weld.

Abstract: In electrical discharge apparatus, such as a gas laser, in which a glow discharge is to be produced in a gas between two electrodes, at least one pre-ionizing member is placed near the discharge space and extending between the electrodes so that current flows in the member which is made of intermediate resistivity material such as crystalline semiconductor material. As a result, the discharge space is pre-ionized which assists initiation of the main discharge. The pre-ionization may be due to the formation of numerous small arcs between the electrodes and the member and the resulting production of ultra-violet light.