358 Prof. Connel 07i the Voltaic Decomposition of Solutions. 



secondary action is excluded. Next let us suppose that both 

 substances are decomposed, and that either the elements 

 going to the same pole unite on their journey, or by an in- 

 terchange of elements the oxygen of water unites with the 

 metal of the haloid, and the hydrogen of water with the electro- 

 negative constituent of the haloid. The former of these al- 

 ternations is contradicted by the fact, that the acid formed is 

 a hydracid; and the latter, although it might account for the 

 formation of acid and alkali, would not account for the li- 

 beration of the electro- negative constituent of the haloid at 

 the positive pole, and of hydrogen in fixed and definite pro- 

 portion at the negative, whatever be the strength of the so- 

 lution. It appears to me then sufficient, in order to prove the 

 aqueous solution of a haloid as a hydracid salt, to show the 

 separation of the hydracid by voltaic action, under circum- 

 stances which exclude secondary action. 



To exhibit this result the solution was placed in the tube B, 

 fig. 2, (p. 24'3) and distilled water in A and C, A being made 

 negative and B positive. When solutions of the chlorides of 

 potassium and of calcium, and of the iodide of potassium were 

 treated in this way by fifty pairs of two-inch plates, acid and al- 

 kali were speedily detected at their proper poles in C and A, 

 and on the corresponding sides of the vessel B, and continued 

 to inci'ease whilst the action lasted. The acid collected in C 

 was found in the case of the chlorides to be the muriatic. 

 In the case of the iodide the nature of the acid was somewhat 

 ambiguous with the above power, but when seventy pairs of 

 four- inch plates were employed it was decidedly the iodic. 

 There appeared, however, little doubt that this latter acid 

 had originated in an oxidating action at the positive pole on 

 reduced hydriodic acid ; and this view was confirmed by con- 

 necting the tube B, containing a solution of iodide of potas- 

 sium, with two other vessels, C and D, containing distilled 

 water on the positive sides, as in fig, 4, and acting with seventy 

 pairs of four-inch plates : — 



Fiff. 4. 



when the acid produced in C was found to be the hydri- 

 odic, and that in D the iodic; in other words, the acid separated 

 from B was the hydriodic, but on passing to the poles it was 



