Electrolysis of Secondary Compomids. 249 



(Fe^ Og, 3SO3), was prepared with great care, and its solution 

 treated exactly in the same way as the last. It conducted 

 well, and 1 3 cubic inches of oxygen were collected from the 

 zincode in twenty-eight minutes. On neutralizing the liquid 

 of the platinode cell with ammonia, very slight traces of ses- 

 quioxide of iron appeared. The sesquioxide of iron had 

 therefore resisted the transfer as well as the sesquioxide of 

 aluminum. 



(y.) We next tried salts of the more ordinary constitution 

 of single equivalents of acid and base. The zincode and con- 

 necting cells were charged with solution of sulphate of copper 

 (CuO, SO3), and the platinode cell with dilute sulphuric acid. 

 The combination conducted well, 236 cubic inches of oxygen 

 were collected from the zincode, and an equivalent of hydro- 

 gen from the platinode; but the platinode plate was scarcely 

 covered with a very thin film of copper, the metal not having 

 been transferred in any considerable quantity. Upon neu- 

 tralizing the solutions on the two sides by carbonate of soda, 

 it was found that an equivalent of sulphuric acid had travelled 

 to the zincode. Upon reversing the arrangement, oxygen was 

 collected as before from the zincode, and an equivalent of 

 copper was thrown down upon the platinode, but no hydrogen 

 was evolved. 



{2.) The last experiments were varied by the substitution 

 of solution of sulphate of potassa for the dilute sulphuric acid 

 in combination with the sulphate of copper. When the copper 

 solution was placed at the zincode, none of the metal passed 

 over to the platinode, but a full equivalent of hydrogen was 

 collected with alkali and acid at their respective electrodes. 

 When the position of the two salts was reversed, the potassium 

 travelled into the platinode cell, and was at once indicated by 

 a precipitate of hydrated oxide of copper. The platinode 

 plate was also covered partly with coherent copper, and partly 

 with pulverulent metal, and only 3 cubic inches of hydrogen 

 were collected for 71 cubic inches of mixed gases in the inde- 

 pendent voltameter. None of the copper solution had pene- 

 trated to the zincode cell. 



Thus it appeared that copper refused to exchange places 

 with potassium in the circuit, as it had before refused to ex- 

 change with hydrogen, and so to pass from the zincode to the 

 platinode. 



(a. a.) Sulphate of s:inc (ZnO, SO3) was next subjected to 

 the same treatment, and the results were exactly similar; the 

 metal in all cases refusing like the copper to pass from the 

 zincode division of the diaphragm cell to the platinode in any 

 considerable quantity. 



