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Dry Cell

Sometimes it is necessary to use cells in such places where there is considerable jarring or motions for automobile or marine ignition. The ordinary cell is not well suited to this service on account of the liability of splitting of electrolyte.

Dry cell is modified form of Leclanche cell. Dry cell is not dry inside but it is pasty. It consists of a zinc weasel containing moist paste of Paris, flour,  zinc chloride, ammonium chloride and ware and a carbon, rod surrounded by second paste of ground carbon, manganese dioxide, ammonium chloride and water placed in muslin cloth. The top of the cell is covered with pitch in order to prevent leakage and evaporation. Zinc vessel itself calls as a negative electrode and carbon rod acts as a positive electrode. Local action is made almost negligible by using certain zinc alloys which are very homogenous. Polarization is prevented owing to use of manganese dioxide which combines with or absorbs the gases as fast as they are formed. Zinc chloride is used to prevent rotting or drying of the absorbing paste. The e.m.f. is produced as a result of chemicals used and is always the same regardless of the size of the dry cell. The e.m.f. of the new cell is 1.5 volts and decreases to 1.4 volts with the passing of time, even though the cell may remain idle. The internal resistance of dry cell is 0.1Ω and increases to 0.5 Ω with the passing of time. Such cells are useful for applications where small amounts of current are required for short period of time as for torches, transistors, tape recorders, door celled, gas ending ignition etc. In operation, the depolarizing agent gradually looses its effectiveness though absorption of hydrogen gas and the liquid materials eventually dry out. Both of these occurrences have the effect of increasing internal resistance of the cell and thus lowering its useful output. The process of deterioration is speeded up by heating. If the cell is required to supply a great deal of current, or is kept in use for long periods of time, the heat thus generated greatly shortens its life. These cells are small and compact n size, portable, clean and require little attention.

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