ELECTRO-TELEGRAPHY 231 



gignals, on a delicate arrangement of the needle instrument the galvanometer, with 

 which we are now so familiar. 



The amount of electricity obtained by means of chemical action is increased to the 

 required extent by a judicious selection of the two metals forming the galvanic series 

 and of the liquid or liquids in which they are immersed. Zinc is invariably used as 

 one of the metals. Copper, silver, and platinum or graphite (gas carbon) is selected 

 for the other. When the two metals are immersed in the same liquid, a mixture of 

 sulphuric acid with salt-water, or fresh, is employed. When two liquids are used, they 

 are separated by a porous partition ; the zinc is usually placed in the sulphuric acid 

 solution, and the other metal in a solution varying with the nature of the arrange- 

 ments proposed. Zinc is naturally soluble in the acid solution in question; and 

 would therefore waste away and be consumed at the expense also of the acid, unless 

 precautions were taken to make it resist the ordinary action of the solvent. When 

 zinc is dissolved in mercury it is not attacked, under ordinary circumstances, by sul- 

 phuric acid solution. Hence the plate of zinc employed in all good Voltaic combina- 

 tions, as they are called after Volta, into which this acid, in a free state, enters, are 

 protected by being well amalgamated, that is, they are dipped in a strong acid mix- 

 ture and well washed ; and are then dipped into a mercury bath, and are placed aside 

 to drain. The operation is generally repeated a second time ; and, in the best arrange- 

 ments, the further precaution is taken of standing the zinc plate, while in the acid 

 water, in some loose mercury, placed either in the bottom of the containing vessel, or 

 in a gutta-percha cell : by the latter arrangement, mercury is economised. In single- 

 liquid arrangements, it is desirable to select a metal that is not attacked by the acid. 

 Copper has been extensively used, and is very valuable ; but it possesses the defect of 

 being slowly attackable. The waste, however, that it suffers in itself from this cause, 

 is of small moment compared with certain secondary results, which terminate in the 

 consumption of the acid and the zinc, and the destruction of the functions of the appa- 

 ratus. Gold or platinum are free from these defects, but are too costly. Silver is to 

 a great extent free from them, and has been much and successfully used, especially 

 when platinised, that is, having its surface covered with finely-divided powder of 

 platinum. The accumulated carbon from gas-retorts, cut into plates, and similarly 

 treated, forms, with amalgamated zinc, one of the cheapest and most effective combina- 

 tions. See GALVANISM OF PLATES. 



After the discovery of the electrical pile by Volta, and after Nicholson and Carlisle 

 had shown that water could be decomposed by the electric current produced by the 

 chemical action in the battery, Herr S. T. Sommering communicated a system of tele- 

 graphing, in 1808, to the Academy of Sciences at Munich. A series of twenty-four 

 wires were arranged to correspond with the letters of the alphabet, and ten to corre- 

 spond with numerals. One end of each wire being furnished with a gold point was 

 brought into a tube of water. When contact was made by the other end of one of the 

 wires with the pile or battery, a bubble of gas appears in the water of one of the glass 

 tubes. Thus, by a little careful arrangement, it was possible to convey intelligence 

 from one point to another by the decomposing power of the galvanic battery. 



A single pair of plates, no matter what their character, is unable to produce a force 

 that can overcome the resistance of a wire of any length, and produce an available 

 result at a distant station ; and hence a series of pairs of plates are employed in the 

 telegraphic arrrangements. E (fig. 804) represents a common mode of arranging a 

 f-eries of pairs of plates. It consists of a wooden trough made water-tight, and 

 divided into water-tight cells. The metals are connected in pairs by copper bands ; 

 each pair is placed astride over a partition, and all the zincs face one way. When the 

 plates (copper and zinc) are placed in, and the cells are filled up with pure white sand, 

 and the acid water poured in, we have the very portable battery that was originally 

 used by Mr. Cooke, and is still much employed. When batteries of a higher class are 

 employed, the cells are distinct pots or jars ; and great precautions are taken to pre- 

 vent any conducting communication existing between the neighbouring cells, save by 

 means of the copper band. In the trough form there is a leakage and loss of force 

 from cell to cell. The c, or copper, is the positive end of such a series, and the z, or 

 zinc, the negative ; and both are in a condition to discharge, either each to the other, 

 by means of a wire led from one to the other, or each to the earth, one by a wire lead- 

 ing to the earth at the place where the battery stands, and the other by a long wire 

 (say a telegraph wire), leading to the earth at a distant place. The resistance to be 

 overcome is, in the former case, less ; and the current of force in circulation is propor- 

 tionately greater. 



It is not practical or expedient in a work of this character to enter into any detailed 

 description of all the varieties of galvanic battery which have been employed. A few 

 only can be named. For use with the needle telegraph the sand battery is very com- 

 monly employed. This consists simply of amalgamated zinc and copper platee, the 



