THE SMITHSONIAN INSTITUTION. 337 



The value 21 of the resistance of the Daniell element for one squaro 

 deciraetre of mean surface, refers to the case in which the zinc cylin- 

 der is immersed in a mixture of one part sulphuric acid to ten parts 

 water. 



The numbers given for the Stohrer clement refer to the same li- 

 quid, and the number opposite b to Leipsic cells ; that opposite c to 

 red clay cells. The resistance of Daniell's battery holds good for the 

 same strength of sulphuric acid, and for red cells. 



With equal surface and like liquid, the resistance of the DeleuJl 

 •element a is to the Stohrer element as 21 : 12 ; thus the discrepancy 

 is purely in the dissimilarity of the clay cells. 



By using red clay cells (c) instead of white, (&,) the resistance to 

 conduction is increased in the ratio of 12 : 43, or 3. G times greater. 

 Thus it may be expected, that, by using Leipsic clay cells, the resistance 

 of the zinc and copper battery will be 3.6 times less than by using 

 earthen cells, or for one square decimetre of mean surface, 78 c)^ q 



Yg ' ■ 



The WoUaston element was immersed in a liquid composed of one 

 part sulphuric acid to twenty parts water. When one square deci- 

 metre of zinc was used, the mean resistance w^as 6.8. But since 

 ■each surftice of the zinc is effective, 6.8 is the resistance for an effect- 

 ive zinc surface of two square decimetres ; thus, for one square de- 

 cimetre the resistance is 13.6 ; for stronger acids the resistance would 

 naturally decrease considerably. 



§ 10. Elcclro-motive force. — By means of the two equations, (1) 

 and (2), the resistance R of the element, as well as the electro-mo- 

 tive force E, can be computed. From the measurements already given 

 above, we get the values of the electro-motive force of the zinc and 

 carbon batteries of Stohrer and Deleuil, and of the zinc and copper 

 batteries, as they are presented in the tables under E, namely; 



For the zmc and carbon battery of Peleuil — 



883 

 880 

 847 



Mean = 855 



For the zinc and carbon battery of Stohrer — 



783 



7T2 



Mean 77T 



For the zinc and copper battery — 



48G. 

 454 



Mean 470 



22 



