The use of a quartz crystal for measuring small mass changes (of the order of 10M9 g) is well established in vacuum or in a free atmosphere [l]. The principle of this quartz microbalance is based on the property of the resonance frequency of a quartz crystal to vary in a proportional way with small changes of the mass of a foreign substance deposited on one of its sides. Hence, by measuring the change of the frequency of an oscillator into which the quartz is inserted, the change of the mass can be detected and evaluated. It seems that Nomura and Iijima [2] were the first to apply this technique to an electrolytic medium for analytical purposes in 1981. A few years later, Bruckenstein and Shay [3] and practically at the same time Kanazawa and co-workers [4] used this technique for electrochemical kinetic stud- i