1 8 ELECTRO-CHEMISTRY. 



In the decomposition of the salt, the alkaline base 

 does not possess alkaline properties ; it has not yet 

 combined with negative electricity ; it therefore does 

 not change the colour of the turmeric in its passage 

 through I. When, however, it reaches the cup N, 

 it there combines with negative electricity, and has 

 its alkaline properties restored. If the contents of 

 the cup N be now decanted into I, the colour of the 

 turmeric will undergo the characteristic change. 



20. When the cup I is filled with a weak solution 

 of ammonia, the cup N with a solution of the sul- 

 phate of potash, and distilled water is put in the cup 

 P, the sulphate of potash is decomposed ; the acid 

 base of the salt being set free, is attracted by the posi- 

 tive wire to the cup P, but in its passage through I 

 it produces no chemical change upon the solution of 

 ammonia; a combination does not take place be- 

 tween the ammonia and the acid base which passes 

 through it. How is this ? 



The sulphate of potash in the cup N is decom- 

 posed, and the acid base of the salt set free is 

 attracted towards the cup P ; but in passing through 

 the intermediate cup, it does not combine with the 

 ammonia and form a neutral salt, because the alkali 

 in I requires to give off its negative electricity before 

 its ponderable constituent can combine with the 



