Polarographs manual

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

The following experiments (Section 16.14-16.16), which can well be performed with a manual polarograph, serve to illustrate the general procedure to be followed in d.c. polarography it is advantageous to use a chart recorder to produce the polarogram. 

Now commence the voltage sweep using a scan rate of 5 mV per second, or with a manual polarograph, increase the voltage in steps of 0.05 V. The recorder plot will take the form shown in Fig. 16.4 if a manual instrument is used, then since the current oscillates as mercury drops grow and then fall away, the plot will have a saw-tooth appearance, and for measurement purposes a smooth curve must be drawn through the midpoint of the peaks of the plot. 

A simple polarograph can be constructed from a potentiometer and a sensitive current-measuring instrument according to the scheme in Figure 3.1. Manual recording of polarographic curves with such an apparatus is, however, very time consuming and cannot be recommended for practical analyses. 

The main advantage of manual instruments is that they are relatively inexpensive, and possess an educational value demonstrating clearly the principles of the polarographic method. The manual instruments can furthermore be advantageously applied to polarometric titrations. 

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