Loose or dirty connections are the cause of probably eight out of every ten troubles affecting bells and batteries.
When the fluid in a Leclanche cell becomes milky, more sal ammoniac must be added. Or, better still, throw out the old solution, wash the porous jar thoroughly in clean water, scrape the zinc bright, and half fill the cell with fresh solution.
The zinc wearing away rapidly or becoming covered with crystals, and a strong smell of ammonia, show generally that the cell is being worked too hard, or that the current is leaking where it should not.
A zinc rod in a cell working the average door bell should last for six months, the porous jar for a year.
The Dry Cell.
The Leclanche cell being a cell with much free liquid is liable to dry up if not watched. The dry cell ([Fig. 3]) is a modern form of the Leclanche where the liquid is held by an absorbent material, such as blotting paper, or plaster.
Fig. 3
A typical dry cell[A]is shown in the figure. An outside case of zinc is lined with blotting paper dampened with chloride of zinc and sal ammoniac. A carbon rod is then inserted in the centre and packed around with carbon dust and peroxide of manganese. The latter mixture is also somewhat dampened.
[A] For full description of this class of battery see No. 3 Book on “Dry Batteries.”