ON ELECTROLYSIS AND ELECTRO-CHEMISTRY. 197 
in which the continuity of the numerical value of the conductivity of 
AgI and the mixture AgCl+AglI through their fusing points is very 
striking. The point of transition of AgI! from the amorphous to the 
crystalline state is also interesting, and is marked on the diagram. The 
conduction of these bodies below the fusing point is attended with 
chemical decomposition, but whether it is wholly or only partially of 
that nature is not demonstrated. The diagram also shows the results of 
Hittorf’s observations on Ag,S, which is decomposed by the current 
when solid; this body fuses at a red heat. Solid Cu,S was likewise shown 
by Hittorf? to conduct electrolytically. 
Plumbic chloride, bromide, iodide * also conduct, and glass‘ even at 
low temperature. Warburg and Tegetmeier® have shown that sodium 
penetrates quartz electrolytically. 
But all solid compound bodies do not. conduct electrolytically ; those 
in the following table conduct metallically :— 
Taste II.—Compound Bodies which conduct like Metals. 
Substance Observer 
Cuprous selenide, Cu,Se Hittorf 
Cupric sulphide, CuS 7 
Stannic sulphide, SnS, PS 
Argentic selenide, Ag,Se a 
Lead peroxide, PbO, 
Manganese dioxide, MnO, { 
Argentic oxide, Ag,O 
Magnetite S. P. Thompson 
Hematite FP 
There is also an increasing body of experimental evidence of electro- 
lytic action on the passage of electricity through gases, particularly in 
the neighbourhood of electric discharge. These phenomena will be con- 
sidered in Part V. 
There are, however, no liquids, other than pure metals and alloys, 
which conduct electricity with the same facility as fused or dissolved 
electrolytes without electrolytic conduction. Faraday ° considered that 
fused Hel,, HgCl,, and PbF, were liquids which were capable only of 
metallic conduction, but fused PbF’, has been shown to conduct electro- 
lytically by Beetz,’ and electrolytic action has been proved to exist also in 
the other two cases by J. W. Clark,® but it is not yet clear whether the 
conduction in these cases is entirely electrolytic. If it should prove to 
_ be so, conduction in liquids may prove to be, as J. J. Thomson ° suggests, 
of identical nature in metals and electrolytes. 
While, therefore, it would be unwise to say that whatever conduction 
there may be through liquids of very high resistance is not electrolytic, 
the difference in the condition and constitution of substances from which 
1 See also a paper by Lehmann, Wied. Ann. 38, p. 396. 
? Hittorf, Poge. Ann. 84, p. 5, 1851. 
® Helmholtz, Faraday Lecture. Gross, Monatsber. der Berl. Acad. 1877, p. 500. 
* Wiedemann, Jee. i. p. 558. 
® Nachr. v. d. K. Ges. d. Wiss. Gottingen, May 30, 1888. 
® Eup. Res. vol. 1, pp. 691, 692, 1340, and 1341. 
* Pogg. Ann. vol. 92, p. 452, 1854. 8 Phil. Mag. July 1885, p. 37. 
® Application of Dynamics to Physics, p. 297. 
