GLASS MICROCAPILLARY ELECTRODES 



Additional electrodes have to be spaced by reference to the first but it is 

 often difficult to see very fine tips. During this process some electrodes 

 may become displaced, and eventually the relative positions must be 

 determined. A device shown in Figure 35.17 can be used. 



Silver 



Length of perspex 

 tube filled with very 

 weak salt solution 



Figure 35.17 Fluid potentiometer for the determination of electrode spacing 



A silver plate is placed at each end of a short tube, filled with a very 

 dilute salt solution and 2 V applied between them. The electrode is intro- 

 duced through a hole in the upper plate and the potential gradient is measured 

 over a short distance which is determined with an accurate micrometer. 

 The potential difference between neighbouring tips is used to find their 

 spacing. 



At the upper end of the electrode, electrical leakage presents difficulty. 

 Electrode shanks of increasing length can be used to reduce this, and the 



Figure 35.18 A method of holding a group of electrodes 



orifices placed some distance apart. In addition the electrodes may be 

 separated a little by interposing pieces of impregnated paper, and the 

 glass coated with wax. 



Such an assembly is cemented to a holder with wax {Figure 35.18), and 

 thin silver wire introduced to estabhsh connection with each. The electrodes 

 can be filled with electrolyte solution in the usual manner. 



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