Batteries will furnish electricity when the circuit is closed, that is to say, when the conducting wires starting, one from the carbon, and the other from the zinc, are put into communication, whether by direct contact or through the medium of a conducting liquid. It sometimes happens that batteries, which appear to be in good order, do not work. This is generally due to some foreign substance preventing the conductivity at the points of contact, or to the copper band of one zinc resting upon another zinc. Before using a battery, try if the current escapes well from both extremities. For this purpose present the point of the negative wire to the carbon of the other end, and a spark should immediately ensue. The same experiment being made with the positive wire, against the last zinc, another spark should be produced; or it is still more easy to have the two ends of the wires made to rest at a short distance from each other upon a piece of carbon, or upon a file, and then rubbing with one wire while the other remains in contact. Numerous sparks will immediately appear.
When one element of a battery is wrongly put up, discover the defect by successively presenting the end of one of the wires to the carbon of each element, and that which does not produce any spark belongs to the defective element. Too much porosity in the cells is another cause of stoppage in the current, because the solution of zinc which penetrates deposits upon the carbon a whitish coat preventing further action. Change the cell and scrape off the coat entirely from the carbon. This generally takes place when the battery has been working several days without the addition of fresh liquor, or when there is too much acid. The battery will also cease working from too great an accumulation of zinc sulphate, which, not having sufficient water to remain in solution, crystallises upon the zinc, and prevents any further action*. Remove the acid solution, substitute a fresh one, and clean the zinc. Laminated zinc is preferable to that cast in a mould, because the latter is not so homogeneous, and is more rapidly corroded, and even perforated.
Every 24 hours, or oftener, the losses of batteries must be made good by adding, without taking the elements apart, about two teaspoonfuls of amalgamating salt, and as much of sulphuric acid, to the liquor of the zinc plates, and stirring with a glass rod. Nitric acid, to replace that evaporated, is put into the porous cell. This manner of operating may be sufficient for 5 or 6 days; but after this lapse of time, all the old liquors must be removed, and fresh ones added. Although amalgamated zinc is scarcely corroded, even in a very acid solution, when the two poles are not in connection by direct contact, or through a conducting liquid, it is preferable to take the batteries apart every evening, in the following manner: - All the binding screws are let loose, and cleaned; the cylinders of carbon are removed, and, without washing, deposited in a vessel especially for their use; the porous cells are removed, and their acid is poured into a special vessel. The cells are not washed; the zincs are removed from the acid liquor, and placed in an inclined position upon the edges of the stoneware pots; the batteries are made ready to work by a converse manipulation.
Batteries must be kept in a place where the temperature does not greatly vary. A frost arrests their action, and great heat increases it too much. A good place for them is a box, and they are put at such a height that they may easily be manipulated. This box should have means of ventilation, in such a way that the air coming in at the lower part will, escape at the top through a flue, and carry away with it the acid fumes constantly disengaged. It is best to keep the batteries in a room different from that where the baths and the metals are to be operated upon, as these are easily injured by acid vapours. The galvanic current may be conducted into the workroom by wires passing through holes in the wall, and covered with guttapercha.
An intense current, for brass and hard deposits will be obtained by joining alternately the zinc of one element to the copper or carbon of the next. For silver plating, a smooth and not too hard deposit is desired, the current should be feeble in intensity, but considerable in quantity, and may be obtained by connecting together all the zincs on the one side, and all the coppers or carbons on the other.
The porous cells are absolutely necessary in batteries working with two exciting solutions. But the trouble arising from the clogging of the pores of the cell, and from the difficulty of preventing the diffusion between the two liquids of the porous cell and of the jar, the specific gravity of which is constantly varying, makes it desirable that the cell should be dispensed with in batteries worked with but one exciting fluid.
Each element is composed of a glass vessel which is half, filled With nitric acid at 36°-40° B., and which receives a hollow cylinder of pulverised coke, moulded and cemented at a high temperature, by sugar, gum, or tar. At the upper part of this cylinder, where it does not dip into the acid, a copper collar is fixed, which may be tightened at will by means of a screw. A copper band or ribbon is fixed to the collar, and may be connected with the zinc of another element. A porous porcelain cell is placed inside the coke cylinder, and contains a diluted solution of sulphuric acid, 1 part acid and 9 water, into which is put a bar or cylinder of zinc strongly amalgamated, or covered with mercury. When a battery of several elements is to be formed, the coke of the first element is connected with the zinc of the second, and so on, and the apparatus is completed, at one end, by coke communicating with the anode, and at the other, by a zinc connected with the cathode, or object to be electroplated.