ON ELECTROLYSIS AND ELECTRO-CHEMISTRY. 193 
would be of great interest, for it would probably indicate an important 
change in the nature of the conduction. From what has been said about 
Faraday’s law we have concluded that the conduction in an electrolyte is 
of the same nature for different electromotive forces, and therefore no 
_ deviation from Ohm’s law is likely to be detected. Butif the nature of 
_ the ions changed with increase of current we should expect the fact might 
be indicated by a deviation from Ohm’s law; and, conversely, if it be pos- 
sible to increase the current to such a limit that Ohm’s law no longer 
holds, some change in the nature of the conduction should be looked for. 
Besides gases there are some bodies which do not follow Ohm’s law. I 
am under the impression that a lead-pencil mark on ground glass does not. 
According to Braun,! psilomelane, iron pyrites, and copper pyrites do not, 
. and, according to Quincke,? some of the liquids of high resistance—ether, 
% OS,, turpentine oil, rock oil, and benzene—are disobedient for electromotive 
g forces of, say, 30,000 volts and upwards. When the divergence shows itself 
_ there are indications of electrolytic decomposition. Quincke also refers to 
__ observations on departure from Ohm’s law in thin layers of gutta-percha, 
_ sulphur, paraffin, and shellac for small electromotive forces by Schulze- 
Berge,’ and to anomalous conduction observed by himself. 
f The direct verification of Ohm’slaw for copper sulphate has been pushed 
by Fitzgerald and Trouton® to the extent of determining, by Chrystal’s 
_ method, that, for this salt, h (in the formula p. 192) is less than 3 x 10~°. 
- The maximum current employed was 10 ampéres per square centimetre. 
The previous verifications are by Beetz® for zinc vitriol solution, by 
F. Kohlrausch’ for dilute H,SO,, for E.M.F.s from 54, to $ Grove cell 
for zine vitriol solution, by Reinold® and Riicker for thin liquid films, 
and by HE. Cohn® for H,SO, and CuSO, solution (in reply to a paper by 
_ Overbeck !°), using currents with periods of alternation between 100 and 
25000 per second. 
Some additional evidence in favour of the application of Ohm’s law 
_ to conduction in electrolytes is derived from the very numerous measure- 
_ ments of the resistance of electrolytes. Jam not aware that any of the 
_ many observers in this or other departments have suggested a variation 
of resistance with current, as an explanation of differences in the numerical 
_ yalues obtained for the specific resistance of the same solution, with the 
exception of Kopp '! in some experiments on Joule’s law. 
The one point that remains to be settled is whether any experimental 
_ evidence can be found for the deduction from Maxwell’s ‘Theory of 
Light’ that electrolytes, being transparent, should behave as dielectrics 
for rapidly alternating electromotive forces. There are two ways of 
approaching the question: (1) to find the length of the light-wave for 
which electrolytes are opaque; (2) to find the rapidity of electrical 
vibration for which the electrolytes cease to conduct. Nothing seems to 
have been done in No. (1); as to No. (2) Prof. J. J. Thomson !” has found 
' Poge. Ann. 153, 1874, p. 556; Wied. Ann. 1, 1877, p. 95; 19, 1883, p. 340. 
* Wied. Ann. 28, 1886, p. 542. 
* Verhandl. der Phys. Ges. zu Berlin, 14, 1, 1886, p. 90. 
* Wied. Ann. 10, 1880, p. 551. 
§ B.A. Rep. 1888, p. 341; 1886, p. 312; 1887, p. 345. 
® Pogg. Ann. 125, 1865, p. 126; 117, 1867, prlot 
d The detection of any deviation from Ohm’s law in an electrolyte 
4 Thid. 138, 1869, pp. 280, 370. 8 Proc. Roy. Soc. 31, 1881, p. 524. 
4 Wied. Ann. 21, 1884, p. 646. 10 Wied. Ann. 6, 1879, p, 210. 
_ " Beibl. 10, 1886, p. 714. % Proc. Roy. Soc. 45, p. 288. 
1890, 0) 
