354 TENTH ANNUAL KEPORT OF 



Assuming as a mean for the insertion the deflection 26", for the 

 copper wirp 12*-*. 25, and the brass wire 5°. 5, the electro-motive force 

 of Smee's element is 212, which is scarcely greater than that of 

 Wollaston's, which we have seen is 208. With equal surfaces, the 

 resistances of the two elements are tolerably equal. From these 

 experiments, it does not appear that Smee's battery deserves any 

 preference over Wollaston's. It is yet to be determined whether 

 platinized platinum gives better results than platinized silver. 



§ Vj. The zinc and copjjer battery loitJi tivo liquids. — When the cop- 

 per of a zinc and copper battery is placed in a concentrated solution 

 of sulphate of copper, and this in dilute sulphuric acid, the two 

 liquids being separated by a porous partition, the injurious effects of 

 polarization are in a great measure removed ; the electro-motive force 

 becomes greater than in the ordinary zinc and copper battery, and the 

 strength of the current is constant. 



The electro-motive force of Daniell's battery is — 



E = 470. 



From Svanberg's experiments, {Fogg. Ann., LXXIIl, 290,) it ap- 

 pears that the electro-motive force of Daniell's battery changes but little 

 with the nature of the liquid. The copper being constantly immersed 

 in a concentrated solution of sulphate of copper, and the zinc im- 

 mersed in various liquids successively, the following values, expressed 

 in an arbitrary unit, were obtained for the electro-motive force : 



For concentrated solution of sulphate of zinc 15.6 



For the same, much diluted 15.9 



For concentrated solution of sulphate of copper 16,6 



For the same, much diluted 16,2 



For slightly acidified water 16.0 



For more strongly acidified water 16,7 



For a square decimetre of mean metallic surface, the resistance of 

 the element is 



R = 78 (acid =: 1 part SO3 -f 10 parts HO.) 

 By using an acid containing 1 part sulphuric acid to 5 of water, the 

 resistance for the unit of surface can be reduced to R =: 30. This re- 

 sistance is due to the earthen cells ; for Stuhrer's cells the resistance 

 would be about one-third ; therefore — 



R = 26 (1 SO3 + 10 HO,) 

 R = 10 (1 SO3 + 5 HO,) 



