Leclanché cell

The Leclanché cell is a battery invented and patented by the French scientist Georges Leclanché in 1866. The battery contained a conducting solution (electrolyte) of ammonium chloride, a cathode (positive terminal) of carbon, a depolarizer of manganese dioxide, and an anode (negative terminal) of zinc. The chemistry of this cell was later successfully adapted to manufacture a dry cell.

In 1866, Georges Leclanché invented a battery that consisted of a zinc anode and a manganese dioxide cathode wrapped in a porous material, dipped in a jar of ammonium chloride solution. The manganese dioxide cathode had a little carbon mixed into it as well, which improved conductivity and absorption. It provided a voltage of 1.4 volts. This cell achieved very quick success in telegraphy, signalling and electric bell work.

The dry cell form was used to power early telephones—usually from an adjacent wooden box affixed to the wall—before telephones could draw power from the telephone line itself. The Leclanché cell could not provide a sustained current for very long. In lengthy conversations, the battery would run down, rendering the conversation inaudible. This was because certain chemical reactions in the cell increased the internal resistance and, thus, lowered the voltage. These reactions reversed themselves when the battery was left idle, so it was good only for intermittent use.

The original form of the cell used a porous pot. This gave it a relatively high internal resistance and various modifications were made to reduce it. These included the "Agglomerate block cell" and the "Sack cell".

The chemical process which produces electricity in a Leclanché cell begins when zinc atoms on the surface of the anode oxidize, i.e. they give up both their valence electrons to become positively charged ions. As the zinc ions move away from the anode, leaving their electrons on its surface, the anode becomes more negatively charged than the cathode. When the cell is connected in an external electrical circuit, the excess electrons on the zinc anode flow through the circuit to the carbon rod, the movement of electrons forming an electric current.

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