assumed hy Insulators at High Tempe7'atures, 193 



somewhat less^ probably because the wires became covered with 

 a stratum of solidifying iodine* Conduction^ therefore,, although 

 very little, certainly took place. In order to ascertain whether 

 this conduction was metallic or electrolytic, the wires were so 

 arranged as to be in connexion with the battery in one position, 

 and with the galvanometer in another. After the current had 

 passed for some time from one wire through the iodine to the 

 other, the two were connected with the galvanometer, when a 

 deviation of the needle, amounting to between 1 and 4 degrees, 

 ensued, and always in the same direction as must have occurred 

 in any ordinary galvanic decomposition. The conduction, there- 

 fore, was electrolytic, or at any rate partly so, and could not on 

 that account be peculiar to the iodine itself. In order to ascer- 

 tain whether a rapid solution of platinum in iodine furnished 

 the small quantity of electrolyte which was here decomposed, the 

 platinum wires were replaced by pieces of graphite, a substance 

 employed by Faraday* as electrodes in the electrolysis of chlo- 

 rides and iodides, because it was not acted upon by these bodies ; 

 conduction, however, still took place, which must have been 

 caused by the slight impurity of the iodine. After twice subli- 

 ming about an ounce of this substance at a gentle heat, so 

 that each time only about half the quantity used was sublimated, 

 the experiments were repeated with the thus purified iodine. 

 The needle still deviated, but at most to 5 degrees, when the 

 fused iodine was introduced into the circuit which contained the 

 galvanometer, and still the electrodes became charged. At 

 length I sought to destroy the impurity in an electrolytic man- 

 ner by introducing the iodine into a glass tube into which two 

 platinum wires were led, and which was afterwards completely 

 sealed up ; the deviation decreased a little, but afterwards re- 

 mained pretty constant, although a zinc and iron battery of six 

 elements acted on it for three hours. The platinum wires re- 

 mained polarized, but the conduction electfolytic to the last. 

 On opening the glass and testing the iodine by evaporation, a 

 small residue was obtained. Hence I think we may with cer- 

 tainty conclude, that the very small conducting power of purified 

 iodine is due to the admixture of a small quantity of some vola- 

 tile electrolyte (hydriodic acid ?) ; but that during the continued 

 action of the current the electrodes begin to be acted upon, and 

 thus new, though very small, quantities of an electrolyte become 

 mixed with the iodine, whilst this substance itself is a non-con- 

 ductor. Hence there remains no elementary body which, when 

 converted into the liquid state, becomes a better conductor. 

 Faraday'sf beautiful experiments have already thrown much 



* Experimental Researches, par. 794. f Ibid. Ser. V. and VII. p 



Phil Mag. S . 4. Vol. 8. No. 51. BepU 1854. O 



