250 



VOLTAIC ELECTRICITY. 



alphabet that they understand a message from the mere clicks of 

 the lever, and do not use any recording apparatus. 



397. Chemical Effects of the Voltaic Cur- 

 rent. Many chemical compounds in solution may be 



FIG. 196. 



decomposed by forcing the current to traverse the solution. 

 Substances which are thus decomposed are called electro- 

 lytes ; the process is called electrolysis; the compound is 

 said to be elect roly zed. The electrolysis of water is easily 

 accomplished, affording a satisfactory qualitative and quan- 

 titative analysis of the liquid. 



(a.) The apparatus consists of a vessel (Fig. 196) containing water 

 (to which a little acid has been added to increase its conductivity) 

 in which are immersed two platinum strips which constitute the 

 two electrodes of a battery. When the circuit is closed, bubbles of 

 oxygen escape from the positive electrode and bubbles of hydrogen 

 from the negative. The gases may be collected separately by 

 inverting over the electrodes tubes filled with water as shown in 

 the figure. The volume of hydrogen thus collected will be twice 

 as great as that of the oxygen. 



398. Electrolysis of Salts. Into a bent tube (known to 



