Hoffman's voltameter

In chemistry, an apparatus for collecting gases produced by the electrolysis of a liquid.

It consists of a vertical E-shaped glass tube with the three limbs pointing upwards. There are taps at the upper ends of the outer limbs and a reservoir at the top of the central limb. Platinum electrodes fused into the lower ends of the outer limbs are connected to a source of direct current. At the beginning of an experiment, the outer limbs are completely filled with electrolyte by opening the taps. The taps are then closed and the current switched on. Gases evolved at the electrodes bubble up the outer limbs and collect at the top, where they can be measured.