ELECTROPH′ORUS

A simple instrument for exciting electricity, generally used in the chemical laboratory for charging small Leyden jars when gases have to be exploded by the electric spark. To construct it, a plate of tinned iron is made into a circle of about 12 inches diameter; a raised border is then turned up for about half an inch, and the extreme edge is turned outwards over a wire to avoid a sharp border. A mixture of equal parts by weight of shell-lac, Venice turpentine, and resin, is made by gently heating them together with stirring until well fused and thoroughly incorporated. This composition is poured into the plate, to quite fill it, and kept melted until all bubbles have disappeared. Another portion of the instrument, serving the same purpose as the conductor of an electric machine, is a circle of wood, rather smaller than the resinous plate, rounded at the edge, and neatly covered with tin-foil. An insulating handle, formed of a piece of stout gla rod, is cemented into the centre of this wooden disc. Before using the instrument it must be carefully dried and slightly warmed. The resinous surface is excited by beating it obliquely with a folded piece of warm flannel. When this has been done for about a minute, the warm dry cover of the instrument is to be placed upon the resinous plate, and touched with the finger. If the cover is then raised a few inches, and the knuckle approached, a powerful spark of positive electricity will pa ; and if the cover be again replaced, touched, and raised, a second spark will pa . This may be repeated many times without again exciting the resinous plate. By receiving the sparks with the knobs of a Leyden jar, a charge strong enough to give a powerful shock, or explode a gaseous mixture, may be rapidly obtained. Other forms have been given to the instrument, but the e ential part of every one is a plate of some resinous substance.