I02 PHYSIOGRAPHY. [chap. 



with a long upright tube C, which springs from the base of 

 the U. Each hmb of the U-tube has, at the top, an orifice, 

 closed by a stopcock. This tube, and part of the as- 

 cending tube, are filled with water, made slightly sour 

 by addition of a little oil of vitriol in order to render it a 

 better conductor of electricity ; but, it should be borne in 

 mind, that the acid does not otherwise affect the result of 

 the experiment. In each limb of the U-tube is a piece of 

 platinum, which communicates, by means of a wire, with one 

 end of the galvanic battery, AB. When the battery is in 

 action, a current of electricity passes in the direction indicated 

 by the arrows. Starting from one end A of the battery, it 

 passes through the wire to the tube O, where it enters the 

 water through the platinum plate. This plate forms one of 

 the electrodes ^ or entrances by which the electricity reaches 

 the liquid. The current is then conducted through the 

 acidulated water to the platinum electrode in the tube H, 

 and thence back to the battery at B, thus completing the 

 circuit. But, during this circuit, the current has wrought 

 a curious change in the water through which it has passed. 

 As soon indeed as the electric current traverses the liquid, 

 streams of little bubbles rise from the two platinum plates, 

 and the gases thus produced accumulate in the upper part 

 of the closed tubes, whilst the displaced liquid is forced 

 into the tube C, where the column consequently rises. 



These bubbles of gas result from the decomposition of 

 the water. The electricity, in fact, splits the water into two 

 distinct kinds of matter, both gaseous ; one gas appearing at 

 the pole where the current enters, and the other gas where 

 it leaves the water. Our apparatus enables us to collect 

 each constituent separately and to examine its properties. 

 On opening the stopcock at the top of the limb O, the 

 ^ Elcclivde, from o5(5r, hodos, a way ; otherwise called the pole. 



