In the Callan's or May-nooth battery, a cast-iron vessel is used as the containing cell, and forms the negative element. A zinc plate, constituting the positive element, is placed in a porous cell within the iron cell. The excitant used in the iron cell is nitric acid, and that in the porous cell is dilute sulphuric acid (1 volume of vitriol to 7 of water). For experimenting, this battery is moderately cheap to construct, exposes a large negative surface, and evolves a powerful current; but it is costly in use from consuming so much nitric acid.
Mix together 15 parts powdered gas carbon, 3 of wood charcoal, and 10 of lump-sugar. Well shake down this powder, dry into paper moulds of the size and shape required, cylindrical being the most manageable. Bury the filled moulds in sand in a suitable iron or copper vessel, and gradually expose to a red heat. When cold, remove the burnt paper from the now solid cells, and soak them in a syrup made of equal parts lump-sugar and water. Well dry the cells, wrap them in paper, again bury in sand, and gradually expose them for some time to as strong a heat as practicable, but not less than a bright-red heat. For this purpose use may be made of an extempore furnace made of Fletcher's solid-flame burner, surmounted by a common unglazed earthenware drain-pipe, partially closed by an iron dome. The above described mixture, made with due care, does not crack as others do. (Symons, Sep. Brit. Assoc.)
Ross has an improvement in the ordinary combination of zinc and carbon, in which the carbon-rod is packed around with broken coke. In the zinc compartment, the exciting solution is a 1-Per cent. solution of sulphuric acid, or a 1 1/2-per cent. solution of hydrochloric acid; while in the carbon cell is a mixed liquid composed of 1 volume hyponitric acid, 3 of sulphuric (or 4 1/2 of hydrochloric) acid, and 4 of water. He also suggests nickel-plating, instead of amalgamating, the zincs.
Andre proposes carbon in the form of highly-burnt coke or wood charcoal, and in the shape of small pieces, separated from direct contact with the exciting liquid by an absorbent diaphragm. Salts of potassium, sodium, or ammonium, are used as the electrolyte. The zinc or iron electrodes are made in the form of tubes, and rest on wooden blocks surrounded by a tubular diaphragm, which allows the liquid to penetrate to the pieces of carbon in which the zinc or iron cells are imbedded. In another form, long strips of copper and zinc are coiled on a boss of wood, and separated by intervening pieces of indiarubber. The wheel or disc thus formed is revolved by an electro-motor, so that the exciting fluid does not cover more than half the disc at any one moment.