Chemical Affinity in terms of Electromotive Force. 369 



The values of e depend on the material of which the elec- 

 trodes are made. Other things being equal, carbon gives 

 higher values than platinum, and platinum than gold. 



In the case of acidulated water, rendering the solution 

 more dilute increases the value of e. 



From former observers' work it results that increasing the 

 temperature decreases e. 



(6) The above formula, in conjunction with experimental 

 determinations of the variations in the values of e under various 

 conditions, explains coherently and quantitatively the leading 

 facts connected with counter E.M.F., polarization, and the 

 E.M.F. of gas-batteries, and accounts for the possibility, under 

 certain conditions, of decomposing an electrolyte with a less 

 battery E.M.F. than corresponds to the work done in splitting 

 it up into the final products — and also indicates that the E.M.F. 

 of a Daniell cell is not constant, but is less the greater the 

 current it generates, to such an extent that with currents of 

 not very great magnitude a diminution in E.M.F. to the 

 extent of several per cent, is brought about, and that, in con- 

 sequence, certain of the methods in use for determining the 

 E.M.F. of cells and their internal resistance are, at any rate 

 for certain kinds of cells, incorrect, as they are based on the 

 assumption that the E.M.F. of the cell is constant. 



(7) By means of the above formula and the experimental 

 determinations of the causes which make e to vary, &c, infor- 

 mation can be deduced as to the amount of energy with 

 which gases are condensed upon the surface of solids, and in 

 particular as to the amount of energy requisite to break up 

 an electrolyte into " nascent" products solely. By conjoining 

 this determination with the determination of the methods for 

 finding the E.M.F. corresponding to the energy requisite to 

 break it up into the final products (described in Parts I. and 

 II.), information can be deduced concerning the affinity of 

 the constituents of the electrolyte, and the variations of that 

 affinity according as the constituents are " nascent " or in 

 their ordinary free state. For instance, the energy given out 

 in the transformation of nascent hydrogen and oxygen into 

 the ordinary free gases exceeds the energy that would be 

 developed by the union of these gases to form liquid water, 

 i. e. exceeds the energy equivalent to 34100 gramme -degrees 

 or to 1-50 volt. 



