164- Mr. Connell on the Voltaic Decomposition of Solutions. 



A solution of iodate of magnesia, obtained by saturating so- 

 lution of iodic acid with calcined magnesia with the aid of 

 heat, was mixed with starch solution and placed on the blad- 

 der-side of the septum, and a starch solution on the other side 

 of it; and the former made positive and the latter negative by 

 thirty- six pairs of four-inch plates. In three or four minutes 

 blue matter was observed beginning to be formed and soon 

 increasing considerably, being deposited on the positive side 

 of the diaphragm, and thence spreading into the liquid. None 

 whatever appeared on the negative side. When examined 

 after twenty minutes' action, the blue matter was found to be 

 mixed with magnesia. I conclude, therefore, that the whole of 

 the hydrogen arising from directly decomposed water did not 

 succeed in uniting with the oxygen coming in the opposite di- 

 rection from the other side of the diaphragm, and that the 

 obstacle to this union gradually increased as magnesia con- 

 tinued to be drawn towai'ds the diaphragm and to be depo- 

 sited in its pores, and ultimately on its surface. This hydro- 

 gen so escaping combination united in its nascent state with 

 the oxygen of iodic acid, and set the iodine free, producing 

 the usual blue compound with starch. 



The nature of the action was still further illustrated when 

 solution of iodate of potash or of iodic acid was substituted for 

 that of iodate of magnesia, all other circumstances being the 

 same. With the first of these substances a mere trace of blue 

 matter appeared on the positive side of the diaphragm in a 

 quarter of an hour, and more on the other side ; and with the 

 second of them no blue was visible on either side in that time. 

 The explanation seems to be that a trifling obstacle is afforded 

 by the accumulation of a concentrated solution of potash in 

 the pores of the diaphragm on its positive side, to the union 

 of the hydrogen and oxygen passing in opposite directions, 

 where iodate of potash is acted on; whilst where iodic acid is 

 employed no substance is drawn towards the diaphragm, its 

 pores suffer no obstruction ; and no sufficient obstacle is af- 

 forded to the combination of hydrogen and oxygen so as to 

 produce any secondary action. 



Some observations which were made in a different quarter* 

 on the experiments formerly detailed, will not occupy much 

 time in noticing them. 



I argued that such substances as iodic acid and bromide of 

 iodine in solution were not directly decomposed, because when 

 positively electrified in connexion with negatively electrified 

 solution of starch, iodine did not pass towards the negative 



* See observations of M. Poggendorffin the supplementary volume of 

 his Annalen, p. 590. 



