956 REPORT—1885. 
“molecular aggregates.’ Is this the fact? Before chemists can accept this con- 
clusion many difficulties must be removed which appear to surround the question. 
In the first place, it is in the highest degree remarkable that, with the one single 
exception of Liquefied ammonia, no known binary hydride is in the liquid state an 
electrolyte: liquid hydrogen chloride, bromide and iodide, for example, with- 
standing an E.M.F. of over 8,000 volts (8,040 De La Rue cells: Bleekrode). Water, 
again, according to Kohlrausch’s most recent determinations, has an almost infinite 
resistance. Yet a mixture of hydrogen chloride and water readily conducts, and is 
electrolysed ; an aqueous solution of sulphuric acid behaves similarly, although the 
acid itself has a very high resistance.! Very many similar examples might be 
quoted, but it is well known that aqueous solutions generally conduct more or less 
perfectly, and are electrolysed.” 
The current belief among physicists would appear to be that the dissolved 
electrolyte—the acid or the salt—is almost exclusively primarily decomposed 
(Wiedemann, ‘ Elektricitit, 1883, ii, 924). We are commonly told that sulphuric 
acid is added to water to make it conduct, but the chemist desires to know why 
the solution becomes conducting. It may be that in all cases the ‘ typical compound’ 
is the actual electrolyte—z.e. the body decomposed by the electric current—but the 
action only takes place when the typical compounds are conjoined and form the 
molecular aggregate, for it is an undoubted fact that HCl and H,SO, dissolve in 
water, forming ‘hydrates.’ This production of an ‘electrolytical system’ from 
dielectrics is, I venture to think, the important question for chemists to consider. 
I do not believe that we shall be able to state the exact conditions under which 
chemical change will take place until a satisfactory solution has been found. 
F. Kohlrausch (‘ Pogg. Ann.’ 1876, 159, 233) has shown that, on adding sul- 
phuric acid to water, the electric conductivity increases very rapidly until when 
about 30 per cent. of acid is present a maximum (6,914) is attained; conductivity 
then diminishes almost as rapidly, and a minimum (913) is reached when the con- 
centration corresponds with that of a monohydrate (H,SO,,0H,); from this point 
conductivity increases somewhat (to 1,031 at 9271 per cent. H,SO,), and then again 
falls, and is probably zero for the pure acid; on adding sulphuric anhydride to the 
acid conductivity again increases. Solutions of other acids and of a number of 
salts—chiefly deliquescent and very soluble salts—also exhibit maximum con- 
ductivity at particular degrees of concentration. In no other case has the existence 
of two maxima, such as are observed in solutions of sulphuric acid, been established ; 
but probably this is because the experiments either have not been, or cannot well 
be, carried out with pure substances or very concentrated solutions. Solutions of 
less soluble salts increase in conductivity as the amount of salt dissolved increases. 
Kohlrausch has suggested, as an explanation of the influence of the ‘ solvent’ on 
the conductivity of an ‘electrolyte,’ that in a solution the ions which are being 
transferred electrolytically come less frequently into collision than would be the case 
in the pure substance. There is therefore less opportunity for the formation of new 
molecules, and the ions are able to travel farther before entering into combination. 
Regarding the question from a chemist’s point of view, however, I cannot help 
thinking that this explanation is scarcely satisfactory or sufficient ; and I cannot 
It is more than probable that the most nearly pure sulphuric acid which can be 
obtained is not homogeneous, but is at least a mixture of H,SO,,H,S,0, and 
‘hydrated compounds’ in proportions depending on the temperature, and hence that 
{pure) sulphuric acid, H,SO,, like water, would behave as a dielectric. 
* On the other hand, it is remarkable that, whereas liquified ammonia may be 
electrolysed, an aqueous solution of ammonia is a most imperfect conductor (Faraday, 
F. Kohlrausch), although solutions of ammonium salts compare favourably in con- 
‘ductivity with corresponding sodium and potassium salts. This fact serves somewhat 
to allay the suspicion that Bleekrode did not take sufficient precautions to dry the 
ammonia; but his result cannot, I think, be accepted as final, on account of the 
relatively high E.M.F. required, and the repetition of the experiment with every 
precaution to ensure purity of the gas is most important. Faraday regarded the 
decomposition of ammonia on electrolysis of its solution as merely the result of 
secondary action. 
