204 ELEMENTARY GENERAL SCIENCE CHAP. 



the passage of the electric current, but, as we have seen, this 

 immediately reacts with the water present and oxygen appears at 

 the anode. In the next illustration of the chemical action of the 

 electric current we have two secondary products formed. 



Electrolysis of Sodium Sulphate. Expt. 197. Make a 

 strong solution of sodium sulphate (Glauber's salt), Na 2 SO 4 , in 

 water. Place a porous pot out of a Bunsen's cell into a large 

 beaker. Pour some of the sodium sulphate solution into the 

 porous vessel and also fill the beaker to the same height with 

 the solution. Colour these portions of the solution with litmus, 

 and then redden the solution in the porous vessel by the addition 

 of a drop or two of acid. Plunge platinum electrodes into the 

 solution ; one in the porous vessel and the other in the beaker. 

 Connect that in the former with the zinc or - pole of the battery 

 and that in the beaker with the carbon or + pole. After a 

 time it will be noticed that the solution in the porous vessel 

 becomes blue, while that in the beaker turns red. It will also 

 be noticed that gases are given off at each electrode ; that from 

 the one in the porous vessel will, if collected and examined, be 

 found to be hydrogen, that from the other electrode oxygen. 



Explanation of Electrolysis of Sodium Sulphate. The 



experiment really consists of three chemical reactions. First 

 the sodium sulphate is decomposed, as the following equation 

 shows : 



But at the moment of their liberation the two groups, Na 2 and 

 SO 4 , are acted upon by the water in which the salt is dissolved. 

 As the student will learn, sodium acts upon water, forming sodium 

 hydrate and liberating hydrogen, a change which is most simply 

 expressed by an equation : 



sodium 

 hydrate. 



It is this hydrogen, which is the result of a secondary reaction, 

 which is liberated at the kathode. The sodium hydrate, being 

 alkaline, has the power of turning reddened litmus blue again, a 

 phenomenon which was observed in performing the last experi- 

 ment. 



The third reaction which takes place is the action of water 

 upon the liberated group, S0 4 , which has been described in the 



