DECOMPOSITION OF COPPER SULPHATE. 681 



is made the anode, and vice versa. The copper is now deposited 

 upon the new cathode, while the sulphuric acid, now disengaged at 

 the new anode, dissolves the previously deposited copper ; this 

 copper, therefore, gradually disappears again. 



A solution of 3 grammes cupric sulphate in about 30 CC water, the 

 same as made previously (page 215), is available also for the 

 galvanic decomposition. The current from two Grove or Bunsen 

 elements has the most suitable strength for this experiment ; if the 

 current is weaker it takes too long a time before a copper deposit 

 appears ; and again, if the current is considerably stronger the 

 copper is deposited upon the platinum as a dark red and even black 

 powder instead of as a uniform brilliant coating. 



The electrode which is covered with copper after the experiment 

 should be dipped into a test-tube anda little nitric acid poured over it ; 

 the copper is very soon dissolved, and afterwards the platinum 

 should be washed with a little water. 



These decompositions, of solution of sodic and cupric 

 sulphate and of acidulated water, prove that when a 

 compound in the liquid state forms part of a closed gal- 

 vanic circuit, chemical changes are produced in the 

 liquid by the action of the current, and we may conclude 

 that in the liquids of the elements themselves similar 

 decompositions must be effected by the current. The 

 diagram, fig. 346, represents a battery of three copper 

 and zinc elements, the liquid being acidulated water. 

 KU KZ, -/T 3 , are the three copper plates, Z^ Z^ Z^ the 

 three zinc plates ; K^ is the positive pole of the battery, 

 Z% the negative pole, and from the poles wires pass to 

 the electrodes, p 1 and p 2 , which are immersed in acidu- 

 lated water. The (positive) current flows from K to p^ 

 through the water to p 2 , and thence to Z% ; it therefore 

 enters the water through p^ and leaves it through p 2 

 and />!, which is connected with the copper, is the anode, 

 while p 2 , which is connected with the zinc, is the 

 cathode. Thus at p l oxygen is disengaged, arid at p 2 

 hydrogen. 



