VOLTAIC ELECTRICITY. 



251 



dealers in chemical glassware as a U tube) put a solution of any 

 neutral salt, e. g., sodium sulphate. Color the 

 contents of the tube with the solution from purple 

 cabbage. In the arms of the tube place the plati- 

 num electrodes of a battery as shown in Fig. 197. 

 Close the circuit and presently the liquid at the 

 + electrode will be colored red and that at the 

 electrode, green. If, instead of coloring the solu- 

 tion, a strip of blue litmus paper be hung near 

 the + electrode it will be reddened, while a strip 

 of reddened litmus paper hung near the elec- 

 trode will be colored blue. Ttiese changes of color 

 are chemical tests; the appearance of the green or 

 blue denotes the presence of an alkali (caustic soda in this case), 

 while the appearance of the red denotes the presence of an acid. 



399. Electro-plating and Electro -gilding. 



From the -f- pole of a galvanic battery suspend a plate of 

 copper; from the pole, suspend a silver coin. Place 

 the copper and silver electrodes in a strong solution of 

 copper sulphate. When the circuit is closed, the salt of 

 copper is electrolyzed, the copper from the salt being 



FIG. 197. 



FIG. 198. 



deposited upon the silver coin, the sulphuric acid going to 

 the copper or + electrode as it did in the experiment 

 described in the last paragraph. The silver is thus copper- 

 plated. 

 (a.) If a solution of some silver salt be used and the direction of 



