978 REPORT—1885. 
originaily combined with chlorine or iodine. This result gave a very strong support 
to the views from which it could be deduced, and proved conclusively the different 
velocities of different ions. 
Finally, Professor Schuster explained his views of the electric discharge of 
gases, which, in his opinion, presented many analogies to the electrolytic conduction, 
or rather that called by Helmholtz electric convection. The peculiar phenomena 
surrounding the negative electrode, as well as stratifications, do not appear in the 
discharge through mercury vapour, and were probably due to a splitting up of the 
two-atomed molecules at the negative pole. Phenomena of polarisation con- 
sequently appear at the kathode, but the ordinary methods of investigating these 
phenomena are not available in gases. Experiments which the author hoped to 
perform in the next few months will decide whether in the gaseous discharge 
each atom carries off, as in electrolysis, the same quantity of electricity. 
4, On the Determination of Chemical Affinity in terms of Electromotive 
Force. By C. R. Atper Wricat, D.Sc., F.R.S. 
During the last eight years, the author has carried out (partly by himself, and 
partly in conjunction with Dr. Rennie and with Mr. C. Thompson), a lengthy 
series of observations on various points connected with this problem, many of the 
results of which have been communicated from time to time to the Physical 
Society of London, and published in its proceedings and in the ‘ Philosophical 
Magazine, in a series of nine memoirs. Whilst these experiments have served to 
corroborate or correct various previously measured values, and to establish a 
number of new ones, they have as yet not sufficed to solve the entire problem, but 
on the contrary, rather tend to indicate that electrical measurements alone are 
unlikely to give any simple means of readily obtaining exact determinations of the 
amounts of force and energy involved in the occurrence of chemical changes, at 
least so far as the more deep-seated phases of these reactions are concerned. 
The fundamental idea involved in the conception of the possibility of such 
determinations being made is due to Sir William Thomson, having been put forth 
by him in a paper on the Mechanical Theory of Electrolysis! The reasoning 
involved may be simply stated as follows :— 
Faraday has shown (1) that when a compound is electrolysed, the weight of 
substance decomposed is proportionate to the quantity of electricity passing.’ 
In symbols, nq, where n is the number of grammes decomposed, and qg the 
quantity of electricity passed. (2) That the weight decomposed by a constant 
quantity of electricity is proportionate to the chemical equivalent of the substance ; 
ze. if a be the equivalent moa. Hence, on the whole, nwaq; and hence, 
n=ag x coustant, this constant, or ‘ Faraday coefficient,’ being a numerical value 
conveniently indicated by the symbol F, just as the Joule value J indicates the 
somewhat analogous constant relating to mechanical work and heat. Now, suppose 
the passage of the current to effect no work other than chemical decomposition, 
and let the lowering of potential (H.M.F.) occurring between the extremities of the 
mass through which the current passes causing decomposition be e; then eq repre- 
sents the work done: if frepresent the work done by the force of chemical affi- 
nity in synthesising a gramme of the compound decomposed from the products of 
decomposition, the work done is also nf= agi f; whence af = aE that is, the value 
of the chemical affinity per gramme equivalent of compound is measured by a value 
in E.M.F. 
1 Phil. Magq., 1851, vol. ii. p. 429, 
2 Various experimenters have been led to believe that under certain conditions, 
‘conduction without electrolysis ’ may take place, more especially when extremely 
feeble currents are passed through acidulated water. The author has shown in a 
rigorously conducted series of experiments that the non-appearance of products of 
decomposition in such cases is due to causes other than exceptionality to the law of 
Faraday (Phil. Mag., April 1881.) 
