The materials having been reduced to fine powder, and the proportion of water stated having been added, are intimately mixed together by hand or mechanically. The moist mixture is moulded at the ordinary temperature, either by a simple compressing press, or by a press in which two pistons moving towards each other compress the block on two opposite faces; or the mixture may be compressed by drawing, as in the manufacture of electric light carbon. After compression, the products are sufficiently solid to be manipulated. They are then put in a stove, or oven, the temperature of which is gradually raised to about 350° C. (about 662° Fahr.); a temperature which is insufficient to decompose the depolarising substance (manganese dioxide), but sufficient to drive out first the volatile parts of the agglomerating material, and then to transform its fixed parts in a body unattackable by the ammonia of the cell. During the gradual heating, or baking, which lasts about two hours, what remains of the water in the agglomerate is driven off; then come the more volatile oils contained in the pitch, and finally the sulphur. The sulphur is added to the mixture, not as an agglomerative, but as a chemical re-agent (and this is a characteristic feature in the invention), acting on what remains of the pitch, as it acts on all carbo-hydrides at a high temperature, transforming it partially into volatile sulphuretted compounds, which are expelled by the heat, and partially into a fixed and unattackable body, somewhat similar to vulcanite. The action of the sulphur on the pitch can very well be likened to its
action on caoutchouc (which is likewise a hydro-carbon) during the process of vulcanisation.
Fig. 9.
These agglomerate blocks, however prepared, are placed in glass or porcelain containing vessels, as shown in [Fig. 9], with a rod of zinc, separated from actual contact with the carbon by means of a couple of crossed indiarubber bands, which serve at the same time to hold the zinc rods upright. The exciting solution, as in the case of the ordinary Leclanché consists in a solution of ammonium chloride.
Among the various advantages claimed for the agglomerate form of Leclanché over the ordinary type, may be mentioned the following:—
1st.—The depolarising power of the manganese oxide is used to the best advantage, and that, owing to this, the electro-motive force of the battery is kept at the same point.
2nd.—That, owing to the absence of the porous cell, there is less internal resistance in the battery and therefore more available current.
3rd.—That the resistance of the battery remains pretty constant, whatever work be put upon it.