On the Movements of Liquid Metals in tke Voltaic Circuit. 163 



frequently with mercury into which some alkali-metal has been 

 deposited. 



46. The general phenomena of the movements may be briefly 

 redescribed thus : — A. When both the wires are in the electrolyte, 

 and the mercury between them, several cases occur : 1 . With a 

 strongly alkaline liquid, a positive flow of the solution from the 

 positive wire over the mercury to the negative wire occurs ; 2. With 

 a strongly acid liquid, a negative flow of the solution takes place ; 

 and 3. With a solution of a neutral or slightly alkaline salt, espe- 

 cially of a salt composed of a strong acid and a strong base, two 

 flows occur, a negative one from the negative wire towards the centre 

 of the mercury, and a positive one from the positive wire towards 

 the centre of the mercury, — the negative one being generally the 

 strongest. If in this 3rd case the mercury contains any impurity, 

 or if a substance be caused by any means to dissolve in the mercury, 

 the movements are notably affected : an electro-positive substance 

 (zinc, alkali-metal, &c.) increases the positive flow so as partly or 

 completely to overpower the negative movement ; and an electro- 

 negative substance increases the negative flow, in a few instances, so 

 as to overpower the positive movement. These influences are also 

 frequently detectable when liquids are used of alkaline or acid reac- 

 tion, as in cases 1 and 2. 



B. When the negative wire is in the mercury and the positive 

 one in the liquid, two cases occur : 1 . With pure mercury, the 

 motion is positive in nearly all liquids, whether acid, alkaline, or 

 neutral ; and 2. With mercury containing a small amount of an 

 electro-negative substance, imparted to it by reversing the connexions 

 of the wires for a short time, a temporary negative flow is produced 

 in certain liquids, chiefly nitrates, but not in certain other liquids. 



C. When the positive wire is in the mercury and the negative 

 one in the liquid, also two cases occur : 1 . With pure mercury, 

 the motion is negative in all liquids — acid, alkaline, or neutral; 

 and, 2. With mercury containing a small quantity of an electro- 

 positive substance imparted to it by reversing the connexions of the 

 wires for a few moments, a temporary and strong positive flow is 

 produced in certain liquids and not in certain others — and these 

 liquids are almost precisely the reverse of those named under B, 2. 



The general influence of electro-positive substances dissolved in 

 the globule is in all classes of cases to produce a positive flow, and 

 of electro-negative substances to produce a negative motion; and 

 the influence of electro-positive substances dissolved in the liquid 

 is, in cases of A only, to produce a positive flow, and of electro- 

 negative substances to produce a negative flow. 



47. The primary motions of the liquid and metal are, in all cases, 

 wholly at their surfaces of mutual contact ; whilst the movements 

 observed are only secondary effects, useful in enabling us to infer 

 the direction of the original motions : the masses of liquid and 

 metal serve merely as conductors of the electricity, and as stores of 

 material for supplying the acting surfaces. The movements obtained 

 are singularly symmetrical, probably in consequence of their essen- 

 tially dual or polar character. 



