CMT measurements and electrochemical (EC) measurements of corrosion rate are generally in agreement, when only electrochemical dissolution of metals in acid takes place. However, dissolution of oxide layers and other acid-consuming reactions can cause CMT measurements to exceed EC measurements. It is shown that when aluminium dissolves in alkali, CMT measurements can also be applied, but in this case requiring titration with alkali. Titration with alkali is also required in a special situation, where corrosion of nickel in an acid solution and subsequent formation of a nickel complex results in liberation of an excess of acid. A non-electrochemical dissolution of nickel is evidenced in the latter case.