Modern Magic: A Practical Treatise on the Art of Conjuring

Almost any kind of battery may be used to produce the necessary current, but for magical purposes one of the most convenient is the Bichromate Bottle Battery, depicted in Fig. 302. This consists of a plate of zinc and a plate of carbon (or sometimes two plates of carbon) immersed in an exciting fluid, consisting of two ounces and a half of bichromate of potash dissolved in a pint of water, with the addition of one-third of an ounce of sulphuric acid. The bottle is only filled to the top of the spherical portion, and the zinc is so arranged that it can be drawn up into the neck, and so out of the solution, when it is desired to suspend the action of the battery. The wires for conducting the current should be of copper covered with silk or cotton, and one of them must be connected with the zinc plate, and the other with the carbon plate of the battery, which has “binding screws” affixed for this purpose. For the purpose of instantly completing or disconnecting the electric circuit, the wires are affixed to the opposite sides of what is called a connecting stud (see Fig. 303), being a circular disc of wood or porcelain, with a moveable stud or button in the centre. On pressing this stud with the finger, the ends of the two wires are brought in contact, and the circuit is completed; but as soon as the pressure is removed, the stud rises by the action of a spring, and the circuit is again broken.