118 MR CONNELL ON THE ACTION OF VOLTAIC ELECTRICITY 



twenty minutes the battery was reverse'd as before described ; instantly the posi- 

 tive foil was covered with red matter, without any evolution of gas from that 

 pole, and dense red liquid continued to fall from it, a brisk effervescence going on 

 at the same time at the negative pole. 



In these experiments it is CAadent that the appearance of chlorine or iodine 

 at the positive pole before reversal, is dependent on acid passing over into the 

 positive water ; and the appearance is sooner observed and much more marked 

 in the case of iodine than in that of chlorine, because hydriodic acid is a much 

 weaker and more easily reduceable combination than muriatic acid, although the 

 reaction of the latter acid on the positive side is much more marked than that of 

 the former. On reversal, chlorine or iodine alone appears at the positive pole, and 

 that instantly, the oxygen being entirely employed in reducing the corresponding 

 acid. In the experiments formerly detailed, when weaker powers were employed, 

 the chlorine or iodine was much longer of appeai-ing pi-evious to reversal, just be- 

 cause acid was longer of being carried over in sufficient quantity to make its secon- 

 dary decomposition visible under the less energetic oxidating agency. In this point 

 of view moderate powers are perhaps best calculated for such experiments, be- 

 cause the apparent contrast between the results at the positive pole before and 

 after reversal is more striking, although the appearances with more powerful bat- 

 teries are, on a very slight reflection, equally indicative of a secondary action. 



The experiment with hydriodic acid was varied by connecting two glass-cups, 

 of the capacity of a quarter of an ounce containing water, with the tube A of 1 J 

 dram measure containing the acid, the acid being made negative by a battery of 

 72 pau's of 4 inch plates, and one of the water-glasses C positive ; the other B, 

 being intennediate, and aU the three vessels being connected by asbestus, as in 

 Fig. 2. Slight effervescence was observed at both poles, in one or two minutes. 

 During the first fifty minutes not the least discoloration of any of the liquids was 

 observed. A few minutes afterwards the positive liquid in C began to acquire a 

 very slight bro^vn tint, with slight acid reaction at the positive pole ; and in ten 

 minutes more the brown tint throughout the liquid in C was quite decided, with- 

 out the slightest discoloration of that of B or A ; and acid was also observed on 

 the asbestus between B and C. The battery was then reversed, when the usual 

 instant discoloration ensued at the positive pole without effervescence, whUe gas 

 arose from the negative. Here, again, the iodine which appeared in the positive 

 liquid before reversal, evidently owed its origin to a secondary action on the acid, 

 which had travelled to the positive pole thi-ough the liquid in B. 



A moderately strong solution of chloride of potassium was now placed in A, 

 fig. 1, connected with the negative side of seventy-two pau-s of 4-inch plates, and 

 distilled water in B, connected with the positive side, asbestus being interposed as 

 usual. In two or three minutes acid appeared at the positive pole, and near the 



