308 



Prof. R. B. Clifton on the 



[June 14, 



shown by the copper terminals of a cell composed of amalgamated zinc 

 and copper in dilute sulphuric acid is mainly due to the contact of the 

 dilute sulphuric acid and the solution of copper sulphate in the Darnell's 

 cell. The contact between the copper and the copper-sulphate solution 

 appears to add but little, and the contact of the zinc and dilute acid 

 next to nothing, to the difference of potential ; at all events in the 

 case where the acid solution is weak. 



In such a Daniell's cell the distribution of potential appears to be that 

 indicated in fig. 6. 



Fig. 6. 



Copper. Amalgama- Dilute Sol. of Copper, 

 ted zinc, sulph. acid, cop.sulph. 



The very large difference of potential between copper and a solution 

 of potassium cyanide in contact, to which attention has been called at the 

 commencement of this paper, coupled with the fact that this difference 

 is of the opposite sign to that exhibited by copper and water, or copper 

 and a solution of copper sulphate in contact, shows that a voltaic cell of 

 considerable power may be constructed containing only one metal and 

 two liquids. Such cells have long been known ; for instance, Becquerel's 

 cell, composed of platinum in nitric acid, and platinum in a solution of 

 caustic potash ; but the only cell of this kind which I have seen described, 

 in which copper is the only metal present, is that devised by the late 

 Emperor Napoleon. 



A cell composed of copper in water and copper in a solution of potas- 

 sium cyanide (1 part by weight of cyanide to 5 parts by weight of dis- 

 tilled water) shows a difference of potential between its terminals equal 

 to 0-923 D, or 0*996 volt. 



This cell has, of course, a very large internal resistance ; but this re- 

 sistance may be greatly diminished by substituting a saturated solution 

 of copper sulphate for the water ; and although this substitution causes a 

 loss of potential at the junction of the copper and liquid, yet it is much 

 more than compensated by the gain at the junction of the two liquids. 



Thus a cell composed of copper in a saturated solution of copper sul- 

 phate, and copper in a solution of potassium cyanide (1 part by weight of 



