=The Leclanche Cell.=--This cell was invented by Leclanche, a French electrician, and was the first cell in which sal-ammoniac was used. This form of cell, as shown in fig. 45, is in general use for electric bells, its great recommendation being that, once charged, it retains its power without attention for considerable time. Two jars are employed in its construction; the outer one is of glass, contains a zinc rod, and is charged with a solution of ammonium chloride, called sal-ammoniac. The inner jar is of porous earthenware, containing a carbon plate, and is filled with a mixture of manganese peroxide and broken gas carbon. When the carbon plate and the zinc rod are connected, a steady current of electricity is set up, the chemical action which takes place being as follows: _the zinc becomes oxidized by the oxygen from the manganese peroxide, and is subsequently converted into zinc chloride by the action of the sal-ammoniac_. After the battery has been in continuous use for some hours, the manganese becomes exhausted of oxygen, and the force of the electrical current is greatly diminished; but if the battery be allowed to rest for a short time, the manganese obtains a fresh supply of oxygen from the atmosphere, and is again fit for use. After about 18 months work, the glass cell will probably require recharging with sal-ammoniac, and the zinc rod may also need renewing; but should the porous cell get out of order, it is better to get a new one than to attempt to recharge it. The directions for setting up a Leclanche cell are as follows: 1. Place in the glass jar six ounces of sal-ammoniac, and pour in water until the jar is one-third full, then stir thoroughly. 2. Place the porous cup in the solution, and if necessary add water until it rises to within 1-1/2 inches of the top of the porous cup. 3. Put the zinc rod in place and set the cell away (not connected up), for about 12 hours, so as to allow the liquid to thoroughly soak into the porous cup. This will lower the level of the liquid to about one-third the height of the jar. The cell will then be ready for use. As the level of the liquid is lowered by evaporation, it should be maintained at the stated height by adding water. The Leclanche cell is adapted to open circuit work, being extensively used for ringing electric bells. The objections to the Leclanche cell are: 1. Rapid polarization; 2. High internal resistance due to porous pot; 3. Restricted space for electrolyte causing rapid lowering of level of liquid by evaporation; 4. Eating away of the zinc rod at the surface of the liquid, rendering the rod useless before the lower part is consumed. =Fuller Bichromate Cell.=--In the bichromate cells or the chromic acid cells, bichromate of soda, or bichromate of potassium, is used for the depolarizer, water and sulphuric acid being added for attacking the zinc.