4th.—That, owing to the fact that the liquid comes into contact with both elements immediately, the battery is ready for use directly on being charged.
5th.—That the renewal or recharging is exceedingly easy, since the elements can be removed together, fresh solution added, or new depolarising blocks substituted.
But when this battery came to be put to the test of practical work, it was found the block form could not be credited with all these advantages, and that their chief superiority over the old cell consisted rather in their lower internal resistance than in anything else. Even this is not an advantage in the case of bell work, except when several bells are arranged in parallel, so that a large current is required. The blocks certainly polarise more quickly than the old form, and it does not appear that they depolarise any more rapidly. Probably the enormous pressure to which the blocks are subjected, in the first two processes, renders the composition almost impermeable to the passage of the fluid, so that depolarisation cannot take place very rapidly. Another and serious objection to these blocks is that, after a little work, pieces break away from the blocks and settle on the zinc. This sets up a "short circuit," and the zincs are consumed whether the battery is in action or not.
The author has had no opportunity for making any practical tests with the blocks prepared by process No. 3, but he is under the impression that the blocks would be even more friable than those prepared under greater pressure.
Fig. 10.
§ 30. A third form of Leclanché, and one which has given considerable satisfaction, is the one known as "Judson's Patent." This consists, as shown at [Fig. 10], in a cylinder of corrugated carbon encased in an outer coating of an insulating composition. Inside the cell are two or more thin carbon sheets, cemented to the sides of the cell by Prout's elastic glue, or some similar
compound, so as to leave spaces, which are filled in with granular carbon and manganese. The surface of the plates is perforated, so as to allow ready access to the exciting fluid. The zinc rod, which is affixed to the cover, stands in the centre of the cell, touching it at no part. Owing to the very large surface presented by the corrugations in the carbon, and by the perforated carbon plates, the internal resistance of this form of battery is very low; hence the current, if employed against a small outer resistance, is large. But this, except in the case of bells arranged in parallel, is of no great advantage.