Cell, amalgam voltaic

Clark cell A type of voltaic cell consisting of an anode made of zinc amalgam and a cathode of mercury both immersed in a saturated solution of zinc sulphate. The Clark cell was formerly used as a standard of e.m.f. thee.m.tat IS C is 1.4345 volts. It is named after the British scientist Hosiah Clark (d. 1898). 

Daniell cell A type of primary voltaic cell with a copper positive electrode and a negative electrode of a zinc amalgam. The zinc-amalgam electrode is placed in an electrolyte of dilute sulphuric acid or zinc sulphate solution in a porous pot, which stands in a solution of copper sulphate in which the copper electrode is immersed. While the reaction takes place ions move through the porous pot, but when it is not in use the cell should be dismantled to prevent the diffusion of one electrolyte into the other. The e.m.f. of the cell is 1.08 volts with sulphmic acid and 1.10 volts with zinc sulphate. It was invented in 1836 by the British chemist John Daniell (1790-1845). 

Weston cell (cadmium cell) A type of primary voltaic cell, which is used as a standard it produces a constant e.m.f. of 1.0186 volts at 20°C. The cell is usually made in an H-shaped glass vessel with a mercury anode covert with a paste of cadmium sulphate and mercury(l) sulphate in one leg and a cadmium amalgam cathode covered with cadmium sulphate in the other leg. The electrolyte, which connects the two electrodes by means of the bar of the H, is a saturated solution of cadmium sulphate. In some cells sulphuric acid is added to prevent the hydrolysis of mercury sulphate. It is named after Edward Weston (1850-1936). 

Although Na(s) reacts violently with water to produce H2(g), at least for a short time, a sodium amalgam electrode does not react with water. This makes it possible to determine Eceii for the following voltaic cell. 

---