362 Prof. Connel on the Voltaic Decomposition of Solutions. 



conducting power of water requires a little investigation. 

 Chlorine, bromine, and iodine are generall}' admitted to be 

 non-conductors themselves; and even if a little doubt may 

 exist as to iodine iu a slate of fusion, it is scarcel}' possible that 

 the minute quantity in an aqueous solution can operate in 

 that way. 



To ascertain whether such substances were capable of 

 transference in solution, an aqueous solution of bromine, with 

 a little undissolved bromine at the bottom, to maintain a state 

 of saturation, was placed in the tube B, the arrangement being 

 in all other respects the same as in the last-described experi- 

 ment with a solution of potash ; and after an hour's action of 

 seventy-two pairs of four-inch plates no discoloration from 

 transference of bromine could be observed in the water either 

 of A or of C ; and the latter had only a scarcely perceptible 

 smell of bromine, which I believe was due to the secondary 

 decomposition of a trace of hydrobromic acid drawn into C, 

 as both the liquids B and C showed some degree of acid re- 

 action. 



An aqueous solution of iodine was then substituted in B 

 for that of bromine, a little iodine being also left at the bottom, 

 and all other circumstances the same, and the battery re- 

 charged. After an hour's action there was no appearance 

 of iodine either in A or C. 



From these experiments, it is obvious that neither of these 

 substances are transferred in solution by voltaic agency. We 

 must therefore look for some other explanation of the in- 

 creased conducting power, and that which readily occurs is a 

 secondary action at the negative pole, by the union of hydro- 

 gen with the dissolved substance. To determine the accuracy 

 of this view, the current from fifty pairs of two-inch plates was 

 passed at the same time through a solution of bromine and 

 diluted sulphuric acid, and the hydrogen evolved from the 

 two negative poles collected, when after half an hour thirteen 

 cubic inches were collected from the sulphuric solution, and 

 only a bubble, the size of a pea, from the bromine solution : 

 the difference had evidently combined with bromine. 



When an aqueous solution of iodine, which had previously 

 been purified by sublimation, solution in alcohol and precipi- 

 tation by water, was substituted for that of bromine, the ac- 

 tion was much more feeble. In a quai'ter of an hour only 

 a small bubble of gas was collected from each negative pole, 

 and in two hours and a quarter -1 cubic inch from the sul- 

 phuric solution, and -077 from the iodic. 



It is thus evident, that both in the case of bromine and 

 iodine the action is increased by the combination of the dis- 

 solved substance with hydrogen of the decomposed water, but 



