302 Prof. Daniell on the Constant Voltaic Battery. 



As copper, from its comparative inactivity, its great con- 

 ducting power, and its commercial value, is the only metal 

 which is capable of being applied extensively for the construc- 

 tion of voltaic batteries upon a large scale, I constructed my 

 cells of that metal ; placing in contact with them a saturated 

 solution of sulphate of copper in dilute sulphuric acid (8 mea- 

 sures of water, 1 oil of vitriol), separating this portion of 

 the electrolytes from that which is in contact with the amal- 

 gamated zinc, and which is composed of the same diluted acid 

 without the salt of copper, by a diaphragm of membrane or 

 porous earthenware. Under this arrangement a part of the 

 current is conveyed by the electrolysis of the sulphate of cop- 

 per and a part by the dilute sulphuric acid : from the former 

 the copper is directly deposited in that compact form which 

 is now so well known from the formation of voltatypes, and by 

 the latter it is thrown down in a less coherent form by the se- 

 condary action of the hydrogen ; but both concur in the effects 

 which have been previously described. 



The only practical difficulty in this construction is the for- 

 mation of diaphragms, capable, at once, of allowing the elec- 

 trolytic action to proceed through them, and of perfectly pre- 

 venting the mixture of the liquids on their opposite sides ; the 

 latter action being, it will be remembered, one of the essential 

 principles of the batteries "pour les actions lentes " upon M. 

 Becquerel's construction. If a portion of the solution of cop- 

 per penetrates to the zinc side of the diaphragm it is decom- 

 posed, and the copper deposited upon the zinc producing 

 strong local action and loss of the generating metal ; for I have 

 not been fortunate enough to find, with M. Becquerel, that 

 the copper can be dissolved under such circumstances. 



Such are the principles which I have derived from experi- 

 ments, and which are capable of application to the construc- 

 tion of powerful constant batteries of different forms and ma- 

 terials. The form which I have preferred is that of hollow 

 cylinders of conducting metal, with central rods of generating 

 metal. This form is dependent upon another principle, which 

 I also worked out from experiments upon the diffusion of 

 the force of a small generating surface over a large conduct- 

 ing surface. These have also long since been published in 

 detail in the Philosophical Transactions, but they are not al- 

 luded to in M. E. Becquerel's ' Notice.' This cylindrical ar- 

 rangement is one of great capacity, and admits of the employ- 

 ment of large quantities of the electrolytes which are required 

 for energetic and long-continued action. 



I subjoin a sketch of the simple form in which the constant 

 battery is now generally constructed, which differs from that 



