Fixed capacity electrical condensers

748,560. Capacitors. NAPIER & SON, Ltd., D. June 1, 1954 [June 5, 1953], No. 15619/53. Class 37. A capacitor of the type employing concentric cylindrical electrodes comprises a casing having a cylindrical insulating side wall 3 and metallic end walls 1, 2 to which the cylindrical electrodes 5, 6 are bolted, the end walls being secured to the side wall solely by means of a thermosetting resinous adhesive compound whereby the end walls may be adjusted during manufacture to achieve the desired radial spacing between the electrodes. The capacitor is either gas-filled or evacuated and gas-tight joints are provided by the adhesive which may comprise a sealing compound of the type sold under the Registered Trade Mark " Araldite " as Araldite No. 1. The end walls which. serve as the terminals for the capacitor preferably consist of a low-expansion steel such as that sold under the Registered Trade Mark " Invar," and the side wall 3 preferably consists of fused silica such as is sold under the Registered Trade Mark " Vitreosil." The plates 5, 6 may be machined from a solid piece of aluminium and are provided with peripheral slots 9, 10 which permit slight expansion of the aluminium electrodes with respect to the end walls 1, 2. Each end wall is provided with three holes through which locating members in the form of hard steel rods are inserted during the curing of the thermosetting adhesive to ensure the correct location of the electrodes. The rods pass through corresponding holes in the bases of the electrodes 5, 6 so that their ends lie between the plates of the electrodes. After curing, the steel rods are withdrawn and all except one or two of the holes are sealed, the remaining holes being used for evacuating the capacitor or filling it with a suitable gas such as sulphur hexafluoride under a pressure of 30 to 40 lb. per sq. inch, after which the remaining hole or holes is or are then sealed. The external surface of the capacitor may be coated with a synthetic resilient insulating material as described in Specification 746,171.