The Leclanche.
This battery consists of a carbon rod surrounded by granular peroxide of manganese forming the positive pole and a piece of zinc for the negative pole, both elements being immersed in a solution of sal ammoniac (chloride of ammonia). If a wire be run outside the solution and connecting the carbon and zinc, a current of electricity flows along it. The chemical action taking place is as follows: The zinc combines with the chlorine of the solution, liberating free hydrogen and ammonia. The hydrogen appears at the carbon, where it is acted upon by the oxygen of the peroxide of manganese. If too much current is taken from the cell, that is, if the wire or circuit be of too low resistance, the oxidizing action of the peroxide is not rapid enough, and a film of hydrogen, which is a poor conductor, forms over the carbon and increases the resistance of the battery—also setting up what is termed “local action” (actually, a battery opposing a battery).
After a rest, the hydrogen is absorbed, but a cell rarely regains its pristine activity after too severe demands upon it. The original Leclanche batteries were imported from France, the home of the inventor, but of recent years they are made in the United States, England and Germany. The most important point to be considered in a galvanic cell is the purity of its active parts. The zincs should be as near chemically pure as can be obtained; the peroxide of manganese of the best quality and perfectly free from foreign substances, and the sal ammoniac the purest that can be manufactured. The actual difference in work between a battery so constructed, and the average cheap cell sold at a price to catch the unwise, is tremendous. And this difference is indicated, not only in work, but when the battery is at rest. Local action in a cheap battery will exhaust it even when it is not in circuit, whereas a battery cell of good material will remain in good order for months without more attention than the addition of water or sal ammoniac. It has been often remarked that the batteries made to-day are inferior to those made years ago, but it is only true of the cheap-priced cells; if a good price is paid and attention given to securing a well made cell, the output will be as satisfactory.
Fig. 52.
To set up a Leclanche cell, proceed as follows: Put six ounces of sal ammoniac into the glass jar; fill the jar one-third full of clear water and stir. Put in the porous cup and fill the jar with water up to its neck, pouring a few teaspoonfuls of water into the hole in porous cup. When the cell is in working condition, the level of the solution will be found to have receded, owing to absorption by the porous cup. To prevent the creeping of sal ammoniac up the neck of jar and on to the terminals of the cell, a layer of paraffin is applied to neck of jar and porous cup. Should this need renewing, vaseline can be used, or any heavy grease, care being taken that it does not get on electrodes or where the wires are to be fastened. When the cell refuses to work, throw out old solution, wash porous cup, jar and zinc in warm water, and replace with new solution. There is a limit, when a new porous cup must be used, but this can be done when cell does not work after being treated as above. The electromotive force of the Leclanche cell is about 1.45, and current on short circuit of nearly one ampere, depending of course on thickness and porosity of porous cup, size of zinc, and a few other points.