194 M. W. Beetz on the power of conducting Electricity 



light on the compound insulators, which by fusion become con- 

 ductors ; to a great extent they form but a higher class in the 

 series of bodies which conduct at ordinary temperatures, and 

 which at lower temperatures, on solidification, become non-con- 

 ductors. Of these, water is an example. Franklin* and Achardf 

 have shown that in its solid state, as ice, it insulates frictional 

 electricity ; and since then, Faraday J found that its insulating 

 action is still more decided towards galvanic electricity. Faraday, 

 however, found some exceptions to the general rule, that the 

 compound bodies, which by fusing have become conductors, still 

 follow the law of fixed electrolytic action. In the several series 

 of his Researches he has expressed several views of the deport- 

 ment of these exceptional bodies, the most important of which 

 are sulphuret of silver §, periodide of mercury ||, and fluoride of 

 lead^ ; bodies which, on increasing their temperature, become 

 conductors, but which show no traces of decomposition. Hit- 

 torff's** experiments on the first of these substances are so 

 complete, that it is not necessary for me to enter on the same. 

 Sulphuret of silver deports itself as an actual electrolyte, but 

 at increased temperatures the separated particles of silver com- 

 bine and form a metallic thread or covering, which connects 

 both ends, and causes the whole conductor to become a metallic 

 one. When the body cools, conduction ceases, owing to the 

 rupture of this thread. To sulphuret of silver Hittorfi* adds 

 another substance, sulphuret of copper, whose apparent metallic 

 conduction he also reduces to an electrolytic one. 



When publishing his Experimental Researches, Faraday, in a 

 note to paragraph 448, concerning periodide of mercury, remarks, 

 *' It is just possible that this case may, by more delicate experi- 

 ment, hereafter disappear." In paragraph 691 the case is, in 

 fact, more carefully considered. '' The case is an exception, 

 and I think the only one, to the statement, that all bodies 

 subject to the law of liquido-conduction are decomposable. I 

 incline, however, to believe that a portion of protiodide of mer- 

 cury is retained dissolved in the periodide, and that to its slow 

 decomposition the feeble conducting power is due. Periodide 

 would be formed, as a secondary result, at the anode ; and the 

 mercury at the cathode would also forai, as a secondary result, 

 protiodide. Both these bodies would mingle with the fluid mass, 

 and thus no final separation appear, notwithstanding the con- 



* Experiments and Observations, p. 36. 



t Chemisch physische Schriften. Berl. 1 780, p. 11 . 



X Experimental Researches, par. 384. 



§ Ibid. pars. 433, 437, 438, 1340. 



II Ibid. pars. 414, 448, 691, 1341. 



% Ibid. par. 1340. 



** Pogg. Ann, vol. hixxiv. p. 1. 



