As already stated, those ions in a solution of electrolytes will first be discharged which have the lowest deposition potentials, and so long as these ions are present around the electrode in considerable concentration they, almost alone, are discharged, but, as their concentration diminishes, other ions whose deposition potentials are higher but still within that of the current applied, will also begin to separate.  For example, from a nitric acid solution of copper nitrate, the copper ions will first be discharged at the cathode, but as they diminish in concentration hydrogen ions from the acid (or water) will be also discharged.  Since the hydrogen thus liberated is a reducing agent, the nitric acid in the solution is slowly reduced to ammonia, and it may happen that if the current is passed through for a long time, such a solution will become alkaline.  Oxygen is liberated at the anode, but, since there is no oxidizable substance present around that electrode, it escapes as oxygen gas.  It should be noted that, in general, the changes occurring at the cathode are reductions, while those at the anode are oxidations.

For analytical purposes, solutions of nitrates or sulphates of the metals are preferable to those of the chlorides, since liberated chlorine attacks the electrodes.  In some cases, as for example, that of silver, solution of salts forming complex ions, like that of the double cyanide of silver and potassium, yield better metallic deposits.

Most metals are deposited as such upon the cathode; a few, notably lead and manganese, separate in the form of dioxides upon the anode.  It is evidently important that the deposited material should be so firmly adherent that it can be washed, dried, and weighed without loss in handling.  To secure these conditions it is essential that the current density (that is, the amount of current per unit of area of the electrodes) shall not be too high.  In prescribing analytical conditions it is customary to state the current strength in “normal densities” expressed in amperes per 100 sq. cm. of electrode surface, as, for example, “N.D_{100} = 2 amps.”

If deposition occurs too rapidly, the deposit is likely to be spongy or loosely adherent and falls off on subsequent treatment.  This places a practical limit to the current density to be employed, for a given electrode surface.  The cause of the unsatisfactory character of the deposit is apparently sometimes to be found in the coincident liberation of considerable hydrogen and sometimes in the failure of the rapidly deposited material to form a continuous adherent surface.  The effect of rotating electrodes upon the character of the deposit is referred to below.

The negative ions of an electrolyte are attracted to the anode and are discharged on contact with it.  Anions such as the chloride ion yield chlorine atoms, from which gaseous chlorine molecules are formed and escape.  The radicals which compose such ions as no_{3}^{-} or so_{4}^{—­} are not capable of independent existence after discharge, and break down into oxygen and N_{2}O_{5} and so_{3} respectively.  The oxygen escapes and the anhydrides, reacting with water, re-form nitric and sulphuric acids.