162 Mr. Connell's further Observations on the 



solution from that of the metallic salt by an animal membrane 

 only. 



When in these circumstances the alkaline solution was 

 made negative and the solution of sulphate of copper positive 

 by twenty couples of a large constant battery, and a very ener- 

 getic action was thus produced, the membrane was found in 

 ten minutes to be coated with metallic copper, mixed with 

 black oxide of copper and blue hydrated oxide. This expe- 

 riment I have found to be perfectly correct, and have obtained 

 the result with a power of thirty-six pairs of four-inch plates 

 on Cruickshank's construction. 



Shall we conclude then that the copper in such cases is a 

 product of the direct action of the current ? A little considera- 

 tion will, I think, show that this conclusion does not follow 

 so clearly or necessarily as may at first sight be supposed. 

 On this view the copper is travelling towards the negative pole 

 till it comes to the septum, in the pores of which it meets with 

 oxygen travelling in the opposite direction, and proceeding 

 from the other solution. A good deal of the copper combines 

 with this oxygen and forms the oxide we find on the membrane, 

 but a part of the metal does not succeed in effecting this union, 

 and is deposited in the metallic state, the equivalent oxygen 

 escaping. But can we not conceive, on the supposition that 

 water is undergoing direct decomposition on both sides of the 

 membrane, that the substance of that membrane may, in like 

 manner, present an obstacle to the union of the hydrogen and 

 oxygen travelling in opposite directions? and if any part of 

 the hydrogen fails in effecting this combination, it will of 

 course exercise a reducing action on the copper solution, just 

 as it would do at the pole itself. Thus then it may be doubted 

 whether the experiment affords any conclusive argument on 

 either side. If neither metal nor oxide appeared at the sep- 

 tum, this would indeed be decisive against direct electrolysis 

 of oxide or oxysulphion; but it may be doubted if the ob- 

 served appearances are conclusive as establishing such direct 

 decomposition. 



A method occurred to me by which it might be possible to 

 get some additional light on this subject. It soon became 

 evident that the substance of the membranes is not the only 

 obstacle to the combination, whether of copper or of hydrogen, 

 with oxygen. The oxide of copper deposited on the septum 

 plainly increases this obstacle, not only by penetrating into its 

 pores, but by forming a layer on its surface ; and on exami- 

 ning some of the membranes after experiment, I noticed that 

 the copper was chiefly deposited on the outer surface of such 

 a layer of oxide. It therefore appeared that the best way to 



