196 M. W. Beetz on the poxver of conducting Electricity 



when pieces of the same were thrown on paper saturated with 

 starch, the violet colour which the latter assumed was as intense 

 as that produced by pure iodine itself. Inasmuch as the devia- 

 tion of the galvanometer needle remained constant, the electro- 

 lysis cannot be ascribed to any impurity, or at most it may be 

 due to an impurity which continually forms itself anew in the 

 mass itself, t. e. to protiodide of mercui-y, as Faraday formerly 

 supposed. As, however, according to my experiments, free 

 iodine was liberated, all the protiodide which may have been 

 present in the vicinity of the positive wire must first have been 

 converted into periodide ; and if this had not itself conducted, 

 the current would have been interrupted. In the first experi- 

 ments, which were of short duration, this formation of periodide 

 was evidently not complete. Once complete, however, the libera- 

 tion of iodine proceeds rapidly, whilst protiodide is formed at 

 the negative pole ; hence periodide must, in fact, be an electro- 

 lyte. A quantitative determination of the separated iodine is 

 here quite impossible, but apparently it was less than 0*190 

 grm., which, according to the voltameter, must have been sepa- 

 rated ; on this account I conjecture that a part of this iodine 

 must have again combined with the protiodide which was con- 

 tained in mechanical mixture. Accordingly a very small tube 

 was filled witli 0*182 grm. of periodide of mercury. After ten 

 hours' action 0*098 grm. of silver were precipitated, according 

 to which 0*114 grm. of iodine should have been set free. But 

 the periodide only contained 0*101 grm. of iodine, and yet the 

 deviation of the galvanometer needle had been almost constant, 

 so that we are compelled to conclude that a recombination took 

 place. This recombination also showed itself externally, for the 

 limit of the black-coloured part lay far nearer to the positive pole 

 than in the former experiment, although the quantity of iodine 

 to be separated was not then double as great, and yet the breadth 

 of the tube was much greater. 



A second circumstance may also diminish the liberation of 

 iodine. It is well known that the protiodide, by heating, is de- 

 composed into mercury and periodide. When a galvanic current 

 was conducted through heated protiodide, mercury was separated 

 strongly at the negative pole ; but within the mass, also, particles 

 of mercury appeared, though certainly to a much less degree. 

 This must also be the case with the protiodide which arises from 

 the decomposition of the periodide, and is held by it in solution ; 

 branch currents may therefore be produced, for whose formation 

 the existence of a thread of mercury joining the poles is not at 

 all necessary. Only as much iodine will in every case be sepa- 

 rated at the positive pole as corresponds to the branch current 

 which passes immediately through the molten mass, and not 



