For demonstration of the decomposition of water, determination of chemical composition by electrolysis and with applications in the evaluation of the electro chemical equivalent of hydrogen. For the electrolysis of water, platinum electrodes are used and for the electrolysis of ammonia or hydrochloric acid carbon electrodes are used. The electrodes, available separately, are mounted in rubber stopper for insertion into the open ends of the voltameter limbs. This method, in addition to being convenient, obviates the use of fragile connections, such as platinum wire loops fused through the limbs. The glass unit has two connected limbs, each of approximately 50 ml. capacity, integral with reservoir tube and funnel shaped bulb, with a stopcock at the top of each limb for use on 12V D.C. supply.