TRANSACTIONS OF SECTION B. 957 
resist the feeling that the production of electrolytically conducting solutions from 
dielectrics is in some manner dependent upon the occurrence of chemical change. 
If the composition of the solutions of maximum conductivity be calculated,’ it will 
be seen that they contain but a limited number of water molecules; thus the solu- 
tion of sulphuric acid of maximum conductivity (at 18°) contains 30°4 per cent. 
of acid, and therefore has the composition H,SO, : 12-4 H,O (approximately) ; for 
nitric acid the ratio is 1:8; for acetic acid it isabout 1:17. Now, it is highly 
remarkable that the solutions of maximum electric conductivity are also very 
nearly those in the formation of which nearly the maximum amount of heat is 
developed ; this will at once be obvious on comparison of the curves given by 
Thomsen (‘Thermochemische Untersuchungen’ vol. iii.), and by Kohlrausch. In 
the chemist’s experience, the point of maximum heat development is usually near 
to the point of maximum chemical change, and I think, therefore, that we are 
justified in concluding that, even if electrical conductivity be not a maximum at a 
particular concentration on account of the presence of a particular hydrate (belong- 
ing to the class of molecular aggregates) in maximum amount, at all events the 
‘structure’ of the system is especially favourable, and the ‘ chemical influence’ 
exerted by the one set of molecules upon the other is at a maximum at the point 
of maximum conductivity. The fact that the amount of sulphuric acid required 
to form a solution of maximum conductivity increases with temperature— 
Temp. SP Heyer) ayes vt Fomerpat grab os Her ol 609 «+ 708 
Percent. 30:2 309 317 325 335 341 345 35:4 
and also the fact that the maxima and minima of conductivity tend to become 
obliterated with rise of temperature (Kohlrausch), are both in accordance with the 
view that conductivity is in some way dependent upon chemical composition, as 
the effect of rise of temperature would be to cause the dissociation of hydrates 
such as I have referred to. The increase in conductivity of aqueous solutions with 
rise of temperature would appear to be against the view here put forward ; but it 
is probable that this may be largely due to diminution in viscosity and increase in 
the rate of diffusion. 
Our knowledge of the binary metallic compounds, which are generally admitted 
to be electrolytes per se, also affords evidence, I think, of an intimate relation 
between chemical constitution and ‘electrolysability.’ It has been pointed out 
(comp. L. Meyer, ‘ Theorien d. mod. Chemie,’ 4th ed. p. 554) that, whereas all the 
metallic chlorides and analogous compounds which cannot be electrolysed are easily- 
volatile bodies, the electrolysable metallic chlorides, &c., are fusible only at high 
temperatures. A careful discussion of the various known cases does not, however, 
justify the conclusion that decomposition takes place, or not, according as the tem- 
perature at which the body assumes the liquid state—and at which, therefore, there 
is full opportunity given for electrolysis to take place—is high or low, especially as 
recent observations show that electrolysis may take place prior to fusion. But it is 
especially noteworthy that many of the chlorides, &c. which are electrolytes un- 
doubtedly contain more than a single atom of metal in their molecules; indeed, 
after careful consideration of the evidence, I am inclined to go so far as to put for- 
ward the hypothesis that among metallic compounds only those are electrolytes 
which contain more than a single atom of metal in their molecules. No difficulty 
Percentage Composition in 
1 Formula Formula weight | in solution of |approximate mol.| Conductivity 
max. cond. ratios 
HNO, 63 29°7 deg as, 7330 
HO 36-4 18°3 eo 7174 
H,S0, 98 30°4 1: 124 6914 
H,PO, 98 46°8 26 1962 
C,H,0, 60 16°6 dL eolyy 152 
KOH 56 28-1 aL ats) 5995 
NaOH 40 15:2 dR pt 3276 
