The third form of apparatus contains both electrodes in the
same tube ; the transmission, therefore, of the electricity and
the consequent decomposition is far more rapid than in the
separate tubes. The resulting gas is the sum of the portions
evolved at the two electrodes, and the instrument is better
adapted than either of the former as a measurer of the quantity
of voltaic electricity transmitted in ordinary cases. It consists
of a straight tube (Fig. 5) closed at the upper extremity and

graduated, through the sides of which pass platina
wires (being fused into the glass), which are con-
nected with two plates within. The tube is fitted
by grinding into one mouth of a double-necked
bottle. If the latter be one-half or two-thirds
full of the dilute sulphuric acid, it will, upon
inclination of the whole, fiow into the tube and
fill it. When an electric current is passed through
the instrument, the gases
evolved against the plates
collect in the upper portion
of the tube, and are not
subject to the recombining
power of the platina.
