GALVANIC ELECTRICITY. 117 



were introduced, the negative electrode would appro- 

 priate all the oxygen to itself, thereby becoming grad- 

 ually converted into oxide of copper, and nothing but 

 hydrogen gas would be obtained. 



281. DECOMPOSITION OF A SALT. The 

 Describe the decomposition effected by the galvanic 



decomposition * 



of a salt. current, may be more strikingly illustrated 

 by introducing the electrodes into a dilute 

 solution of sal-ammoniac, previously 

 colored by litmus, or red cabbage. 

 Chlorine is liberated at the positive 

 pole, and bleaches the solution in its 

 vicinity, while ammonia is evolved 

 with hydrogen, at the negative pole, 

 and changes the color of the solution from blue to red. 

 That of the cabbage is changed by the same means, 

 from red to green. By employing a glass box with two 

 compartments, such as is represented in the figure, the 

 two portions of the liquid may be kept distinct. It is 

 essential, for reasons that will be understood from the 

 preceding paragraph, that there be an unbroken chain 

 of molecules of the electrolyte, or substance to be de- 

 composed, between the electrodes. This is effected by 

 making the partition quite loose, and keeping it in its 

 place by strips of paper, placed along the edge. All the 

 communication that is essential, then takes place through 

 the pores of the paper, while the partition at the same 

 time prevents the mixing of the contents of the sepa- 

 rate cells. The same object may be accomplished by 

 the employment of two tea-cups, holding the liquids, 

 and connected by moistened lamp-wick ; a larger pile, 



