Date of Award


Document Type

Union College Only

Degree Name

Bachelor of Science






In a constant current electrolysis, which is the unusual method of determining a substance quantitatively by electrodeposition, a single metal, in solution, is plated out on the cathode of the electrolysis cell. The current is maintained fairly constant by adjustment, little attention is paid to the potential applied to the cell. This method may be used if there is only one metal in solution, or it may actually be used to separate two metals if one lies above and the other below hydrogen in the electromotive series. In this case, hydrogen is evolved at the cathode after the deposition of the first metal, and hydrogen will continue to be liberated as long as the pH of the solution is not too high. A good example is the determination of copper in a sulfuric acid solution containing zinc. If, however, two metals lie close together in the electromotive series, their separation and determination using constant current electrolysis will prove impossible, since the two metals will come out together, or the second metal will start to plate out before the first is completely removed from the solution. This problem of separating metals by electrolysis may be solved by another method called “Graded Cathode Potential Electrodeposition.” In the case of the two metals, one above and the other below hydrogen in the electromotive series, the hydrogen being displaced acted as a control upon the cathode potential, keeping it at a certain value, which was the deposition potential of hydrogen. In graded cathode potential work, the same principle in used; a predetermined potential is chosen and the potential of the cathode is not allowed to fall below this value, preventing other metals from palting.