of Aqueous and Alcoholic Solutions. 243 



and the solution itself with the other side, as in fig. 1. In this 

 vvay the constituent must necessarily be exhibited in the water, 

 either separately or in a state of combina- 

 tion with one or other of the elements of Fig. 1. 

 the water, which new combination would 

 in its turn suffer decomposition, whether [CZ^^^ 

 primary or secondary, if admitting it. 

 The readiest and simplest illustration of 

 the efficacy of this method, is to connect 

 the solution of any ordinary salt, such as 

 sulphate of soda, with two tubes contain- 

 ing distilled water, and one of the latter 

 with the positive and the other with the negative side of the 

 battery, as in fig. 2, where B contains the saline solution, and 

 A and C distilled water ; when by the passing of acid into 

 C and of alkali into A, the constituents will be exhibited in a 

 separate state. 



The first case hich shall be adverted to, is that of a simple 

 binary combination having neither acid nor alkaline qualities. 

 If an aqueous solution of bromide of iodine is mixed with a 

 solution of starch and acted 



Fig. 2. 



A 



on voltaically, iodine imme- 

 diately separates at the ne- 

 gative pole, forming the 

 usual blue combination with 

 starch. Apparently, there- 

 fore, the bromide is resolved 

 by the action of the current 

 into its constituents, iodine 

 going to the negative, and bromine to the positive. It is easy, 

 however, to show that this effect is entirely a secondary one: 

 the mixed solution of the bromide of iodine and of "^starch 

 was placed in the tube B, fig. 1, and the starcli solution in A, 

 the asbestus being moistened with the starch solution, B be- 

 ing made positive, and A negative by fifty pairs of two-inch 

 plates *=. Effervescence speedily ensued from both poles, but 

 after forty minutes' action not a" trace of any blue colour was 

 observed in either tube. The battery was then reversed, the 

 platinum foil in B being now connected with the negative 

 side, and that in A with the positive side. Within two mi- 

 nutes the blue combination appeared round the negative foil; 

 the effervescence ceasing at that pole, but continuing at the 

 positive. Had the bromide been directly decomposed, iodine 



• All the batteries employed in these experiments were on Ciuick- 

 •nank'6 connruction.* 



R2 



