occasioned by Differences of Concentration. 



355 



Hence it follows that the electromotive force of the cell is 

 positive if the liquid is more concentrated at the cathode and 

 consequently qk<q a and pk<p a , which is likewise confirmed 

 by a great number of observations by Dr. J. Moser. 



For inconsiderable concentrations, and correspondingly slight 

 diminutions of the pressure of vapour above the solution, for- 

 mulae (4 c) and (4d) give also the law of the increase of elec- 

 tromotive force with rising concentration of the solution, since 

 the value of (1 — n) is, according to Hittorf's investigations, 

 nearly constant for slight concentrations, but rises for greater 

 ones. 



The S of the following Tables is the quantity of water (pro- 

 portional to q) which is combined with the anhydrous salt in 

 the solution ; A is the electromotive force, according to the 

 observations of J. Moser, stated in thousandth parts of a 

 Daniell element (Cu, CuS0 4 , ZnS0 4 , Zn). The quantity 



1 , Sfr 



should, according to equation (4 c), be constant. 



For a cell with sulphate-of-copper solution and copper elec- 

 trodes the following values are found. 



Sulphate of Copper. 



Si. 



S«. 



A 



A 





Yalue of 1— n 



observed. 



calculated. 



n- 



according to Hittorf. 



128-5 



4-208 



27 



27 



0-0550 



0-724 for S= 6-35 



— 



6-352 



25 



23-75 



0-0552 





— 



8-496 



21 



21-45 



0-0562 





— 



1707 



16 



1594 



0-0548 





_ 



34-22 



10 



10-45 



0-0575 



0-644 for S>39-67 



As calculated values of A those are given which are obtained 

 when the value of q from the first observation is retained for 

 the others also. With sulphate and chloride of zinc, which 

 can be employed in more concentrated solutions, greater 

 deviations in these values occur* simultaneously with great 

 increase in the values of (1 — n). 



* Note added Jan. 1878. — More recent experiments by Dr. Moser show, 



dW 



indeed, that with zinc chloride the quantity =\ increases to half as 



dp 

 much again with greater concentrations, and can no longer be regarded as 

 approximately constant. 



2A2 



