Electrical tests metal migration

A simple electrochemical cell can be made from two test tubes connected with a third tube (the crossbar of the H ), as shown in Figure 12-1. The hollow apparatus is filled by simultaneously pouring different solutions into the two test tubes, an aqueous solution (aq) of zinc sulfate into the left tube and a copper sulfate solution into the one on the right. Then a strip of zinc metal is dipped into the ZnS04 solution, a piece of copper is inserted into the CUSO4 solution, and the two ends of the metal strips are connected by wires to an voltmeter. The lateral connecting tube allows ionic migration necessary for a closed electrical circuit. The voltmeter will show the electrical potential of 1.10 volts, which leads to the movement of electrons in the wire from the zinc electrode toward the copper electrode. 

Spot test analysis makes frequent use of electrochemical separation methods. Especially in paper chromatography use is made of differential diffusion in which an electrical field serves to accomplish the desired separation. Of particular interest in spot test analysis is the employment of electrographic methods for examining metals, alloys and ores. The basic principle employed is the anodic solution of the metals. In practice, the specimen is made the anode and a piece of aluminum foil serves as cathode. Filter paper is moistened with the appropriate reagent solution and then placed between these two electrodes. The proper voltage is then applied. The movement of the metals then leads to an imprint on the paper and so reveals the exact position of the metals that have migrated from the surface of the test specimen. Hermance and Wadlow have published a comprehensive review of this procedure. 

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