Hittorf method electrodes used

A very simple type of apparatus used in the Hittorf method is shown in Figure 6.8. The solution to be electrolyzed is placed in the cell, and a small current is passed between the electrodes for a short period of time. The solution then is run out through the stopcocks and the samples analyzed for concentration changes. 

One important point to make is that the quantity accessed experimentally, in general, is the net transference number for a given species regardless of its exact speciation (6). Eor complex ions, if the Hittorf method (see below) is used to measure the transport of chloropalladate ions for example, by analysis of the amount of Pd accumulated on an electrode surface, one has no way of distinguishing between the transfer of [PdCy " and [PdClj] , both of which occur in solution. The existence of rapidly occurring equilibria, which will typically interconvert on time-scales much shorter than the measurement time-scale, means that the net transference of anionic palladium species of whatever form is... 

An illustration of the Hittorf method can be found in an early experimental report of the technique for barium chloride solutions, electrolysed using silver/silver chloride electrodes (8). The 18th run in this study reportedly passed 0.0194 F across the cell, which is schematically desalbed in Figure 20.5. 

The classical method of determining transference number is, apart from the e.m.f method described previously, long time electrolysis with electrodes reversible to only one of the conducting species. Subsequent chemical analysis of the electrolyte at the vicinity of the anode and cathode is then performed. The method was extensively used by Hittorf on liquid electrolytes and some solids and later on by Tubant in numerous studies of pure salts and mixtures of salts (Tubant (1914, 1920, 1921)1 - ). 

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