In order to discover what gases are obtained by the decomposition of water, the gases which separate at each electrode must be collected separately.
For this purpose a V-shaped tube is taken; one of its ends is open and the other fused up. A platinum wire, terminating inside the tube in a plate, is fused into the closed end; the closed end is entirely filled with water4 acidified with sulphuric acid, and another platinum wire, terminating in a plate, is immersed in the open end.
If a current from a galvanic battery be now passed through the wires an evolution of gases will be observed, and the gas which is obtained in the open branch passes into the air, while that in the closed branch accumulates above the water.
As this gas accumulates it displaces the water, which continues to descend in the closed and ascend into the open branch of the tubes.
When the water, in this way, reaches the top of the open end, the passage of the current is stopped, and the gas which was evolved from one of the electrodes only is obtained in the apparatus.
By this means it is easy to prove that a particular gas appears at each electrode.
If the closed end be connected with the negative pole—i.e. with that joined to the zinc—then the gas collected in the apparatus is capable of burning. This may be demonstrated by the following experiment:—The bent tube is taken off the stand, and its open end stopped up with the thumb and inclined in such a manner that the gas passes from the closed to the open end. It will then be found, on applying a lighted lamp or taper, that the gas burns. This combustible gas is hydrogen.