occasioned by Differences of Concentration. 357 



decomposes, according to R. Bunsen, 0*0092705 mgr. of water 



159*5 

 and times as much sulphate of copper — that is, 



0*082147 mgr. 



If, then, as in the numerical Tables, we denote by S the 

 amount of water contained with one part by weight of anhy- 

 drous salt in the solution, for the experiments with sulphate of 

 copper 



Sq: S = 0*0082147 sec, a / g ram : 1. 

 V centim. 



Now, if the diminution of the vapour-pressure by the salt- 

 solution employed is known, we obtain the constant b from 

 the equation 



& 



in which the pressure p is also to be reckoned in absolute 



P gram 



force-measure as j-. „• 



centim. sec/ 



Our equation (4 c) becomes 



2l = g(P,-PJ = (g6) .V(l-n) log (|). 



Consequently the value of the constant (£ need not be known 

 for the calculation of the Ws in electromagnetic measure. 



Since we have assumed for the vapour the validity of Ma- 

 riotte's law, the product 



e.(.v-f%M>».v, .<&=& 



The ratio — — - is, from Wiillner's experiments, in many salts 



nearly constant with changed temperature ; while the product 

 p .Y increases approximately in proportion to the absolute 

 temperature, which, within the limits of the temperature of 

 the apartment, is not of much consequence. In fact the ex- 

 periments do not show any considerable influence of the tem- 

 perature upon the electromotive force of the cells ; at least it 

 by no means varies in so great a proportion as the pressure of 

 the saturated vapour. 



For testing the accordance of the absolute value of the elec- 

 tromotive force of our series with that given by the formula, 

 sufficient data on the vapour-tension of the salt-solutions used 

 are still wanting. If we employ equation (4 c) in order to 

 calculate, from the electromotive force found by J. Moser for 



