Electrochemical properties which determine metal distribution over a cathode of a given shape are cathode polarization, solution conductivity, and cathode efficiency. A steep slope of the cathode potential current density curve, a small or negative slope of the cathode current efficiency current density curve, and a low specific resistivity of the electrolyte favor more uniform metal distribution or higher throwing power. How these characteristics of Watt bath are affected by changes in the plating variables indicate their probably effect on throwing power.
The specific resistivity of the Watt bath is about 11 ohm-cm at 60oC and it decreases in the usual way with increase in termperature. It also decreases with increasing total concentration and increasing chloride on concentration. It is but little affected by pH within the range 2.0 to 5.5.
Like the cathode efficiency of all plating bath, that of the Watt bath rises with increase in current density until the limiting current density is reached. It also rises with increase in temperature and with total concentration. Increase in chloride ion concentration has a more markedly beneficial effect, but the effect of pH is the most pronounced.
The throwing power of the