Clark cell

In 1893, the output of the Clark cell at 15 °C was defined by the International Electrical Congress as 1.434 volts, and this definition became law in the United States in 1894.

A platinum wire, fused into the glass tube, made contact with the mercury pool.

It was set up in an H-shaped glass vessel with zinc amalgam in one leg and pure mercury, surmounted by a layer of mercurous sulfate paste, in the other.

Electrical connections to the zinc amalgam and the mercury were made by platinum wires fused through the lower ends of the legs.

The design had two drawbacks—a rather large temperature coefficient of −1.15 mV/°C, and corrosion problems caused by the platinum wires alloying with the zinc amalgam connections where they enter the glass envelope.