Powder electrodes of the first kind

Two types of powder electrodes can be distinguished and they have quite different characteristics. Electrodes belonging to one type are called powder electrodes of the first kind and electrodes belonging to the other types are called compound powder electrodes. 

Powder electrodes of the first kind fulfill the following conditions the powder in the electrode is a pure metal by which the platinum leading-out electrode is covered the solution contains ions of that metal. Thus under such conditions both the leading-out electrode and the powder correspond to reversible electrodes of the first kind differing only in the dispersion of the metallic component. Powder electrodes not having this structure are compound powder electrodes. 

We will give two examples of powder electrodes of the first kind to which this section is devoted ... 

In our laboratory we have examined silver, nickel, and copper powder electrodes of the first kind, and the latter two especially have been examined in detail. As a rule, powder electrodes of the first kind correspond, as far as their properties are concerned, to ordinary electrodes of the first kind apart from some characteristics resulting from the dispersion of the metal. We have found experimentally the following properties. There is a marked, but not too big, influence of the metallic powder s preparation on the value of powder-electrode potential and on the value of its normal potential. These potentials are almost equal to the values for corresponding ordinary electrodes of the first kind but they are produced far better. The discrepancy of the measured values does not exceed 0.5 to 1 mv the presence of oxygen has no influence and the size of the powder s grain is of no importance either. 

Powder electrodes of the first kind as we have said, are a particular case of homogenous, compact electrodes of the first kind. They have some specific and valuable characteristics, are reversible to the positive ion of the electrode material, but are not very useful in apparatus for testing the surface of a powder. 

Cells containing powders had already been constructed at the end of the last century. They were mainly modifications of electrodes of the first kind, the metal being introduced as a powder instead of in its homogeneous solid state to obtain better establishing and better reproduction of its potential in the solution of its own ions. By means of such electrodes the normal potentials of some metals were also determined. These electrodes were reversible to the cations present in the solution. In more recent times Huttig and Herrman sought some relation between catalytic properties of copper powders and the electromotive force of a ceU containing such a half-cell, and they applied a half-ceU made of a copper... 

Powders of metals were prepared in various chemical ways, by means of electrolysis, and by means of Raney s method with a different procedure in the process (different initial alloys, different temperatures of leeching, etc.). The amount by which the leading-out electrode is dipped in the powder has no influence on the measured potential value. The temperature coefficient of potential is almost equal to the values for ordinary electrodes of the first kind, in the examined temperatures from 15°C to 35°C. As for copper and nickel we have found too that powders prepared in various ways and differing in their catal3rtic properties change the potential values of powder electrodes which have the same-solutions. Such powders also differ in the values of their counted out normal potentials. 

The formation of an adsorption layer on the metal powder, introduced later into the powder electrode, has little or no influence on the obtained potential value, or, in some cases, it has only a considerably insignificant influence. The facts can be easily explained when it is pointed out that, as far as the first kind of powder electrode is concerned, its potential in relation to... 

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