760 REPORT—1885. 
VI. AppENDA. 
Electrostatic calculation of E.M.F. needed to effect decomposition, (a) of an 
electrolyte, (b) of a dielectric. 
(a) I do not think the process is justified by anything Helmholtz has 
said, but I have allowed myself to reckon through what atomic distances 
mutual electrical attraction of two charged atoms might be overcome by 
means of an electrode differing in potential from a liquid by, say, a volt, 
z.e. by means of aslope of potential of 1 volt in 10-® centimetres. 
Let y be the effective distance between two oppositely charged atoms 
in a molecule, so that the force between them is q, and let this mole- 
cule come within range of the electrode, and so under the influence of the 
separating stress q 2 then decomposition will be effected when 
ae 
SE i.e. when y? = oe 
1 de ies Pe ae 
Taking therefore g = 1071, and WV — soo 1 10%, y comes out 
s d dx LOTS, coy Xt 4 
10-° or thereabouts—a very respectable atomic distance. This perhaps 
indicates that, within molecular range of either electrode, actual decom- 
position or tearing asunder of molecules may occur, but that through the 
rest of the liquid the action is propagated in some other way, e.g. by a 
divorced atom being projected so close to one of the constituents of a 
molecule as to combine with it in place of its former partner, and so on. 
In this way two postulates may be avoided—lst, the existence of con- 
tinuous dissociation in ordinary liquids unexposed to electrical influence, 
a hypothesis to which I understand chemists see some objections ; and 
2nd, the attraction of matter for electricity postulated by Helmholtz, so 
far as it is necessary to the explanation of polarisation. Polarisation 
would then really be the E.M.F. needed to tear asunder molecules of the 
given compound within molecular range of the electrode; and automatic 
interactions of the molecules must be trusted to carry the action forward 
throughout the whole mass. 
It appears that on this hypothesis an E.M.F. of one or two volts 
would be sufficient to decompose acid water, dr other similar compound, 
if atomic distance were something comparable with 10-®. But it may be 
considered that the magnitude of this distance points to something like 
at least incipient dissociation as necessary to electrolysis. Let us find its 
value more carefully. 
Put the problem thus: 
To find the relation between molecular distance, 2, and the least 
distance at which atomic electric attraction can be overcome by a slope 
of potential of 1 volt per z centimetres ; on the hypothesis that ordinary 
electrostatic laws are applicable. 
Wo. bow 
et YF 
But G= 1:5 x 1013 ’ 2°, 
and 3 x 10!°V = 108, 
