676 DECOMPOSITION OF WATER. 



green, is poured out of the U-tube into a little dish and stirred, the 

 original blue colour is restored, because the soda and sulphuric acid 

 set free by the current combine again to form sodic sulphate. 



Blue vegetable colours are generally very evanescent, especially 

 when they are exposed to light. If it is desired to keep a stock 

 of the blue solution, it should be put in a bottle with one drop of 

 liquid carbolic acid well shaken, and then corked with a tight-fitting 

 sound cork. 



Water is resolved by the galvanic current into its 

 two constituents, hydrogen and oxygen. Both of these 

 bodies are gases, hence they are disengaged in the form 

 of bubbles when the electrodes are dipped in water. 

 Pure water is, however, a bad conductor of galvanic 

 electricity, and in order to increase its conductivity a 

 small quantity of sulphuric acid is added to it ; the 

 sulphuric acid remains unchanged if it is sufficiently 

 diluted with water. Both gases may be separately 

 received and examined by means of the apparatus 

 for decomposing water represented in fig. 343. The 

 short neck of a glass funnel is closed by an india- 

 rubber stopper ; two platinum wires pass through the 

 stopper, carrying platinum strips at the top, and be- 

 ing clamped to the brass pieces m m below by means 

 of the flat heads of the screws s. The wires from the 

 battery are similarly clamped by the screw heads pp. 

 The funnel is nearly filled with the dilute acid, and 

 two small tubes, g g, usually graduated into cubic centi- 

 metres, are quite filled with the same liquid, closed 

 with the finger, inverted, and dipped beneath the surface 

 of the liquid in the funnel : finally each tube is suspended 

 by the little glass ring at the end of it to one of the small 

 hooks fixed to the support t. As soon as the circuit is 

 closed decomposition begins, and gas bubbles rise from 



