126 MR CONNELL ON THE ACTION OF VOLTAIC ELECTRICITY 



with alkali at tlie negative, and effervescence at both poles ; but in that time no 

 discoloration of any of the liquids was visible. In twenty-five minutes the water 

 in C had acquired a imiform although slight browTi tint ; and in forty minutes 

 this bro'mi colom- had become much more decided. The liquid in B had been 

 acid for some time, and was quite colourless, with the exception of the slightest 

 possible yellow tint which its upper layer had acquu'ed, and which was not only 

 confined entirely to the upper part, but was far less deep than the brown colour 

 which the whole of C had acquired. The liquid in A was not at aU dis- 

 coloured. 



This experiment was repeated with the same arrangement and same power, 

 the only difference being, that the thi'ee tubes were aU of the size of 1^ dram. 

 In fifteen minutes a slight l)rowning commenced near the positive pole in C, with 

 acid on both sides of the liquid in B, and on the asbestus between B and C. In 

 forty minutes C was brown throughout, and neither A nor B at all discoloured ; 

 and when in fifty minutes the process was stopped, the liquid in C smelt like a 

 strong solution of iodine, whilst that in A and B was stiU without the least change 

 of tint. 



It seems clear, that in these two experiments iodine appeared in the posi- 

 tive tube C, only in virtue of hydriodic acid having been drawn through the water 

 in B into that in C, and there decomposed by nascent oxygen. The very trivial 

 discoloration of the hydriodic liquid in the upper layer of B in the former of 

 these experiments, was, I conceive, merely accidental, and arose from some sub- 

 ordinate secondary action, caused probably by the evolution of a few bubbles of 

 oxygen, at some of the intermediate points on the asbestus. Some similar instan- 

 ces will afterwards occur, and in these experiments we ought always to bear in 

 mind how extremely susceptible of decomposition hydriodic acid is. The main 

 secondaiy action was plainly that in C. This was made still clearer by an exa- 

 mination of the aqueous Mquids in B and C, after the close of the experiments. 

 When the liquid in B was examined, both before and after concentration by heat, 

 it was found to be a weak solution of hydriodic acid. On the other hand, when 

 the liquid in C was concentrated by heat till the free iodine had been aU expelled, 

 it was found to be a weak solution of iodic acid ; in other words, the hydriodic 

 acid passing from B to C, as shown by the acid reaction on the asbestus between 

 them, had not only been decomposed, and its iodine set free, but a part of that 

 iodine had been oxidated by the excess of oxygen at the positive pole. If any 

 doubt remained as to the existence of a secondai-y action, these facts, I think, 

 would suJBBce to remove them. 



I have mentioned, that in these experiments iodine appeared sooner on the 

 positive side than with aqueous solutions. This cu'cumstance arises from acid 

 appearing sooner on the positive side of the asbestus in the former case than in 



