Polarographs for classical d.c. polarography

The essential requirements for producing polarographic current-voltage curves are  

a means of applying a variable known d.c. voltage ranging from 0 to 2-3 

The apparatus depicted in Fig. 16.1 represents a manual polarograph which can be usefully employed to study the basic techniques of polarography. 

Commercial polarographs are also available in which the voltage scan is carried out automatically while a chart recorder plots the current-voltage curve. A counter-current control is incorporated which applies a small opposing current to the cell which can be adjusted to compensate for the residual current this leads to polarograms which are better defined. Most of these instruments also incorporate circuits which permit the performance of alternative, more sensitive types of polarography as discussed in Section 16.9 

A typical conventional polarogram for 0.003 M-cadmium sulphate in 1M potassium chloride in the presence of 0.001 per cent gelatin, and the corresponding derivative curve, are shown in Fig. 16.7 (/max is the maximum current recorded in the derivative mode). 

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